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Microfabrication - Science topic

Microfabrication is the term that describes processes of fabrication of miniature structures, of micrometre sizes and smaller.
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Facing trouble (bonding-leakage) while using hand-pressure to pass liquid through my microfluidics device. I used UVO-cleaning instead of plasma-bonding (PB not available).
The way I cleaned the glass slide before UVO step: H2SO4 (70%) Overnight> dH2O > Soak with Methanol (~100%) > IPA (~100) > also add Acetone (~100) sometimes > UVO-treatment.
Microfluidics Channel precision = 20 um
PDMS (10:1)
Glass slide = Microscope cover slip 25*45mm
Please let me know if you need more clarification.
Thank you for your suggestion.
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I have not tried UVO cleaning. I found that typical microscope slides are problematic. We use Corning Incorporated micro slides (2947-75x50) at my lab. We clean the slides before hand with 2% dawn detergent (spray bottle), rinse thoroughly with tap water, then deionized water and finally with isopropanol. The slides are then dry under nitrogen and not touched with bare hands. We functionalize the PDMS and slide surfaces in a Harrick plasma generator for 30-90 seconds.
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Hi!
I want to manufature a chip for drop-seq. From previous studies 80-100 um depth has been used. The dripping crossing width is 94um. The drop size is required to be both 100 and 125. The inlet has some viscosity coming from cell lysate (CA-630) and Iodixanol (for cell suspension). Which depth is better and can easily realise both drop size?
Thanks!
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Thanks Qiyou Chen
Well we don't have a fast camera as well. What we do is just measure when from collection pool
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I tried to find options to remove the buried oxide layer (1um) with 22-um thick patterned silicon (SOI) wafer after bonding with glass wafer.
Initially, I plan to immerse my bonded wafer to HF, but that could affect the glass wafer....
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Dear researcher!
You can use Apiezon wax to cover all the areas which you do not to etch. Meaning you can cover the whole wafers except the holes.
This wax is very nice to work with as an etching mask.
Best wishes
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Hi,
I tried to use SU-8 2150 to fabricate some micro structures (with a thickness of about 500um) with Mask Aligner. But I saw some white residue on top surface of the structure (see picture attached) after development. I used PGMEA to develop, followed by rinse with IPA. But no matter how long I developed, the white stuff was still there.
Does anyone have similar experience? What are the possible reasons for this?
Thanks!
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I think that the problem could be an overexposure, 200 second is to much if the doses that arrive to the wafer is 20mw/cm2, the time need to be around 20 s. May be you can try to adjust the expose parameters. Regards!
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Hi everyone,
I am working with SU8 2075 and I found some issues with the edge reflow.
This is the experimental protocol:
- 3'' Si wafers were used as substrates. Wafers are cleaned using ACE (10 min), IPA (10 min) Piranha (H2SO4:H2O2 3:1) (30 min), dehydration (30 min@ 250 °C).
- A quantity of SU-8 2075 was casted on the middle of the wafer. I started trying 3.6 g (that is about 1.2 g x inch, as suggeste by the manual 1 mL x inch). I tryed also to reduce the quantity to 2.5 g or 2 g of resist. I tryed to cast the resist on the middle, or span the resist over the substrate using a syringe needle or tilting the wafer.
- Wafer was moved in the spin coater and different rotation speeds were tested for the coating. First step: 500 RPM @ 100 RPM/s for 15s
Second step: desidered RPM @ 300 RPM/s for 30 s
I tryied 1000, 1500, 2000, 2500, 3000 RPM for the second step.
- The bottom side of the wafer was cleaned from photoresist excess
- Wafer was positioned over a bubble-levelled hotplate. I tryed ramp the temperature from RT to 65 °C, wait the desidered time, the ramp to 65 °C to 95 °C, wait the disedered time, with ramp rate of 5°C/min. I also tryed to put the wafer directly on hot hotplate at 65 or 95 °C.
I found the following issues:
- If the resist was casted on the middle without span it over the surface, a sort of signature of the position of the resist after the drop casting step remain after the spin coating. Probably it is related to a sort of drying of the dropped resist surface I think...
- After the spin coating step, on the edge of the wafer there is an amount of resist: the edge beads. This edge is about 2-3 mm extension on the wafer. But, when the wafer was placed over the hotplate, the edge became larger and larger and increase with the temperature and time. This is the so-called reflow process.
When I use low spin coating speed (1000 RPM), the reflow allows the edge to reach the wafer center and planarize the wafer thickness all over the substrate.
On the other hand, when I use high spin coating speed (3000 RPM), the reflow is limited and the resist thickness is due to the photoresist spin and not from the edge reflow.
At middle spin coating speed (1500 - 2500 RPM), the reflow does not allow the edge to reach the wafer center and planarize the wafer thickness all over the substrate. As consequence, I obtain large edge (about 2 cm) and small working area on the center.
I am not sure, but I would to understand if the reflow is something wanted or unwanted using SU-8. If yes, how I can have it anytimes, also with middle spin coating speed. If not, how I can avoid it?
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Hi Alessandro,
I think your first issue can be avoided by spinning right away after pouring the photoresist. Don't let it sit too long before spinning.
To prevent edge beads from forming (or at least make them smaller) you could apply very high accelerations at the beginning and the end of the spinning process. You could also clean the edge beads using acetone or PGMEA solvent before baking. hope this helps!
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I am trying to fabricate 150 um depth microneedles with 45% KOH solution at 90 degree. What are the best methods available to optimize and predict this procedure ? Are there any optimizations available ?
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i I suggest using this genetic algorithm for optimization.
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Hello all,
iam searching for literature similar to the book "Photolithography Basic of Microstructuring" from MicroChemicals or literature in general for lithography in microfabrication. It should explain the process steps and its meaning and influence to the results.
Maybe someone have a tip for me, I would really appreciate it.
best regards
RE
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What is the average height (max) of a structure that can be easily fabricated using Nanoscribe?
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Haha Anuj Singhal , nothing! At the beginning I was imagining id be printing big structures but I am mostly printing small ones now. Well, we do have some surface roughness or stitching related problems printing micro-optics. The output light pattern is not homogeneous.
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We are having trouble sourcing a reliable supply of HSQ. Can anyone recommend a supplier in Europe?
I know the issue is probably a fundamental one with the Dow Corning supply chain & production priorities, and not with our local Ellsworth office.
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Paul - thats great
My email is Jonathan.Sellars@agas.com if you need anything else
Regards
Jon
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Hi everyone,
I'm using SU-8 as an adhesive bonder (Kapton on silicon), but once I hardbake the SU-8 layer at 150C, the remaining solvents in the SU-8 evaporate and make bubbles, and essentially deteriorate the adhesion quality. I tried soft-bake or PEB the SU-8 at higher temperatures or hardbake with slow ramps but they weren't helpful.
Any suggestions would be appreciated,
Thank you!
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Prebaking at 65 °C and 95 °C is recommended for most of the SU-8 series photoresists.
Before processing the SU-8 make sure your substrate is dehydrated (keep the substrate on hot plate or in oven) after rinsing in nitrogen.
Coat the sample and make sure that there is no bubble is present before spin coating (air bubbles generates during pouring of PR). For this you may wait for few sec/minutes.
Once coating is done prebake the substrate at 65 °C and 95 °C as suggested in the SU-8 data sheet.
Higher baking temperature increases the evaporation rate of the solvent, which sometimes causes the bubble formtation in the resist film.
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Hello all,
I am interested in fabricating a particular design for a microfluidic chip used for particle sorting. Would you please kindly let me know where I can find a lab that offers a microfabrication service for a customized design in Germany, and what the expected costs are, and how much time it takes for delivery.
Kind regards.
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Hi Abdulkarem Odhah I don't think that Bartels does and for Microfluidic shop (I don't know) you can write a request and they'll tell you.
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The premise is such that we have two independently fabricated su8 fluidic structures, we want to integrate them by bonding them together to make them functional. Any insights, standard protocols, or even brief thoughts on better ways to achieve SU-8 to SU-8 bonding by using any methods, chemical, physical, etc will be highly appreciated?.
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Dear Bhushan Kharbikar,
I did once during my post doc year in James Watt Nano Fabrication Centre, University of Glasgow.
1. Clean the surface that you want to attach / integrate - perhaps with ultrasonic desiccator.
2. Expose the desired surface with O2 plasma in vacuum chamber, in my case approximately 30 sec - I never exposed longer than that as I remembered.
3. Using the tweezer, attach / integrate the exposure surface.
4. Let's the clock ticking for around 30 - 45 min, then it's now ready to utilize.
I hope this helps. All the best & Cheerio
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I was wondering if anyone had advice on removing a nickel hard mask - which seems to have become resistant to my standard Nickel etch. The sample is GaN with a hard Nickel mask, which has undergone AR-Cl ICP etching. Normally I would remove the nickel using a dilute (5-10%) Nitric acid etch, however it seems like it has become resistant to this etch.
I have also tried dilute Aqua Regia, a dilute Nitric + Acetic + Sulphuric acid mix, and eventually a concentrated Aqua Regia* (* NOT A GOOD IDEA - I got excited when it changed colour and started bubbling, but on inspection it etched everything EXCEPT the residue!)
My current theory is that during the ICP etch the Nickel has reacted possibly with the chlorine to produce NiCl. I have read that this can happen around 200C - which is a little above what the ICP set temperature is at 150C - however presumably the sample can heat up above this.
I was wondering if anyone has had similar issues - and/or if there were any wet etches I could try which would etch NiCl (should this be it).
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What techniques are used to make anisotropic SiO2, HfO2, and TiN thin films? (If possible)
The SiO2, HfO2, and TiN are used for the gate stack in certain MOSFETs. There are many studies were isotropic layers were created.
In the particular process that I am studying making anisotropic layers of SiO2, HfO2, and TiN , of only few nanometers each, will make the process a lot easier. However, I am not sure of its feasibility and repeatability.
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Muhammad Hamza El-Saba
thank you, much appreciated.
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Removal of SU-8 structure is a difficult task. Who is willing to share the latest developments?
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Try Pirani solution, incase SU-8 is the only layer on the substrate. A 5um thick Su-8 3005 is removed within 20 seconds of agitated cleaning.
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Is any way or method to seal agarose pad or channels fabricated agarose gel pad to glass slides as like we do plasma bonding with PDMS to glass slides?.
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Good question
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I need perfect cleanliness for further processes but I am not sure which cleaning method would be sufficient yet letting the layers intact.
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Less aggressive cleaning can be done using aceton and IPA solvents.
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I am looking to fabricate PDMS pillars which are 0.5um or 1um in diameter, and up to 10um tall. Pattern definition and etch on a silicon substrate to create the mould, using E-beam and RIE etching doesn't present too much of a problem.
When I come to mould my PDMS against this, does anyone have any advice on getting decent demoulding without too much breakage/stretching/deformation? Will this even present a problem?
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Hi, I'm looking for a dicing tape that can withstand later cleaning and processing steps on the sample (including acetone, IPA, and MF24A immersion). Do you have any experience with such tape?
Thanks
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Lei, Wei-Sheng, Brad Eaton, and Ajay Kumar. "Dicing tape protection for wafer dicing using laser scribe process." U.S. Patent 9,159,621, issued October 13, 2015.
Harvard
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Hello,
I am working on a project that requires connecting the top side of a SI polished-polished wafer with its bottom side. I have been using p-type Silicon since I do anodic bonding at the end of the microfabrication and it works at a lower temp than n-type silicon. I was wondering if anybody with experience in RIE-ICP could tell me if using p-type or n-type silicon affects the etching rate and the etching quality significantly?
Thanks
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Reactive ion etching of silicon may depend on the conduction type of the etched materials. It may also depend on the its conductivity. This relies on the nature of the chemical reactions and their need to either electrons of holes.
For more information you can follow the thesis:https://thesis.library.caltech.edu/5846/2/MDH-Thesis-Rev1.pdf
Best wishes
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Hi there,
I am specifically looking for commercial and/or lab-made wet etchants options for etching specifically glass substrate and/or SiO2 with the underneath Si substrate. In my device, I have metal electrodes that are separated by micron gaps on top of the glass or SiO2/Si substrate. I would like to etch the underneath substrate wherever the micron gap exists and leaving the metal electrodes intact.Is there any suggestions, I appreciate your valuable suggestions in advance.
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Giuseppe Curro and John Reye Thank you both, the reference document you provided is useful, I am also reading many papers and figured it out that I would better go for Dry etching.
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Hi
Im currently trying to simulate adhesive single lap joints with a square wave geometry on the micrometre scale. I was wondering if anyone had any suggestions on how to get the elements to fail at a reasonable stress based on my cohesive law (damage initiation was set at 2MPa), they also fail unpredictably with some failing and others remaining present for the entire simulation.
The mesh has been refined whilsts keeping the layer one element thick.
Ive looked at most of the conventional things such as ensuring element deletion is switched on etc. Im not sure if theres any other consideration needed for such a complex geometry in which the adhesive consists of both vertical and horizontal components.
Ive tried running the simulation in Abaqus Explicit and using mass scaling to try and get a usable result, however it seems to be tricky finding suitable values for time increment, mass scaling factor
The image attached represents a section of the joint near the end with the undeformed and deformed images given. (from Abaqus Standard). Any help/ suggestions would be gretaly appreciated!
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I'll take a step back. Maybe Abaqus is indeed right, given the model that you built... What I mean by this is...
-- Are you sure failure should occur at every point of the interface? Do you have experimental data (from yourself or the literature) to expect that the interface should fail everywhere?
-- You should look at stresses at the interface without cohesive elements, i.e. a simple elastic analysis. Look at normal tensile stress and shear stress, as proxies for respectively Mode I and Mode II failure. What are the effect of the contractions due to Poisson's effect? Given the geometry, they may be important. Looking at these features should help you understand the problem.
-- Looking at your model and thinking about single-lap joint geometry, it seems that the vertical side of each teeth is subjected to a state of local tension at the interface and cohesive elements fail. On the horizontal face of the teeth, shear likely dominates and cohesive elements do not fail. Thus, to get complete detachment, you have to weaken Mode II behavior of cohesive elements. In particular, it seems that cohesive elements on horizontal faces are indeed activated, thus the problem is probably not about initiation but about propagation. You need to decrease the value of Energy Release Rate in Mode II (or, conversely, decrease the value of the crack shear displacement at failure).
-- Not all the vertical faces however fail. Why? It's an unloading mechanism. In the picture you show, you have pair of teeths still bonded along the shared vertical face, but with the other vertical faces failed. The bonded vertical interface is there because the tensile load is not sufficient to break it, and that is due to the fact that the load in those two teeth is decreased by the failure of the other two vertical faces (I hope it's clear, look at your picture to understand what I'm saying).
In summary, I suspect Abaqus may be right this time. You need to understand the physics behind the results you're getting.
Happy to discuss it further if you want.
Regards,
Luca
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I want to apply a coating to a metallic surface with micro-grates. I want the coating to be applied only on the top of the grates and not intrude into the ridges. Can anyone please tell me how can I do this with a facile and cost effective method like spraying or deep coating?
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You may want to check PDMS stamp for this kind of applications.
1- Prepare the PDMS Stamp
2- Dip into the solution to be coated
3- Stamp on the surface using a guide to get a better alignment. You can do this under a microscope. You will need to prepare a thin PDMS stamp to be able to use it under the microscope.
Alternatively, you will need to go for basic photo-lithography using photo-resist to protect the areas you want to keep clean. If you will decide for this path. Send me a message, I will guide you.
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Hello,
Does anyone have any experience with the wet etching of <111> Si?
I need to etch the handle layer of an SOI wafer completely.
Thank you.
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Imadeddine AZZOUZ Yes. I need to remove the handle layer of the SOI wafer. The thickness is 375 um.
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I use a homemade Sn electrolyte to fabricate the Cu-Sn pillars with the diameter of 20-40 micrometers. But the surface morphology of Sn pillars is totally different with the Sn electrodeposit from other references. Could anyone help me with the formation mechanisms about the structures? Any evaluation is appreciated. 
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you can read this book
"Nano Plating - Microstructure Formation Theory of Plated Films and a Database of Plated Films, by: T Watanabe."
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5" substrate clamped between two surface with orings providing a seal for the electrolyte. Does the e-field vary with localized thickness (dist from substrate to plate)?
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Dear James,
The electrolyte can be considered a conducting medium with high ionic conductivity. The electrolyte has an electric conductivity sigma.
So, it has a resistance R= L/sigma A, Since there is a dielectric between the two electrolytic electrodes will drop only a very small voltage on them compared to the those dropped on the electrolyte. This is only the case in charging and discharging phase while a current passing in the capacitor. In case of electrostatic the voltage drop on the electrolyte will be zero and all the voltage will be dropped on insulator. As the thickness of the electrolyte increases its resistance increases.
Best wishes
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I've created a simple cantilever MEMS structure with very thin aluminum contact pads. Through the release process of the MEMS structure, the contact pads have become damaged and therefore do not bond with wirebonds. Are there any options i have to re-deposit more metal (increase the thickness) on the metal contact pads, without affecting the rest of the structure?
i have few chips that have already been released and few chips that havent been released yet.
help is appreciated! thank you.
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Dear Kissan,
What are the size of the pads? If the pads are relatively large you can support the them by silver epoxy where you can supply them by a silver spot by a fine injector.
You can cover the whole device by adhesive tape except the pads and then support by electroplating silver on it.
Best wishes
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I'm trying to build a mask for etching metal, but I need simulation tool to get an idea of how to build one.
Is there any suitable open source software I can use to do this?
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You can try Anisotropic Crystalline Etch Simulation (ACES) developed by Micro Actuators, Sensors and Systems Group (MASS) at UIUC
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We wish to know if it is possible to create a commercial measuring product with nanoliter precision. We are creating a microfluidic device in PMMA. We wish to measure 100 ul volume of a solution with nanoliter precision. The same would have graduated markings to track the nanoliter volume change. Is it possible to create such a device with current mass fabrication tools?
We are in design phase of our project and it will help us understand if we should go ahead with it or not.
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Hello Rohan,
yes, it is possible. There are different nanofabrication techniques that you can use to control small volumes (even smaller than nl). I guess that one of your challenges is to have a non- deformable material when you are 'pumping' your fluid through the micro/nanochannel as any compliance int eh material would lead to inaccuracies in the fluid control and measurement. You could, for instance, use RIE to create a Si microfluidic or nanofluidic channel. You could also use other etching techniques to fabricate the device in glass. PMMA, as you mention is an option too as it is less deformable that the commonly used PDMS in microfluidics.
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We are making microchannels by machining in Plexiglas (PMMA). We want to cover the same with Pressure sensitive adhesive tape (PSA tape) to close the channels to improve turnaround time of our prototyping stage.
The PSA tapes are usually acrylate adhesive on a backing of some other polymer. We would then conduct some surface reaction utilizing the surface chemistry of PMMA.
We are not sure that if we use PSA tape, if we could perform reaction on the tape side of the channel or not.
Please let me know if anyone has done so?
P.S. we are using microparticles, and are not sure if they would stick to the tape due to the adhesive or the chemistry.
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Hello Rohan,
You should cut the PSA to match the channels in the PMMA. it is going to be different, specially if you used a solvent to clean your channel.
Regards,
Ahmed
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hello,
i am currently dealing with su-8 2100 photoresist.
Hemispherical grooves expose the back of the quartz substrate to create a needle-shaped cured SU-8. and now, after developing, SU-8 is separated into two layers.
the first two layers are divided into the shape of the needle i wated, but the second layer comes from the shape of the rod that i did not wanted.
Since this is my first time dealing with SU-8 photoresist, it is not easy to solve problem.
Do you know anyone who solve this problem??
thanks.
My protocol was attached below:
1. spin coating : 1000/10s, 3000rpm/ 60s
2. prebake : 65 ℃ 5min, 95℃ 20min
3. uv exposure : 4~6s
4. PEB : 65℃ 5min, 95 ℃ 10min
5. development : 10~15min(microchem developer)
-sincerely-
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Hi Joonghoon,
I have read your answer and also I have checked the MicroChem (MC) application note for SU-8 2100, and it clearly matches your process. I was also looking for protocols for such a dense distribution of needles. I have found a protocol from the Vandervilt Uni, where they use a much larger soft bake or prebake (2h 5min at 95ºC), they clearly stated that it is a longer time that the company recomends, but they don´t explain the reason for such long prebake.
Here is the link:
The prebake or softbake is just to eliminate the solvent. Someone comented here in RG that solvent could act as a polimerization inhibitor... but it doesn´t look like the case, because you used the MC protocol and you get more polymerization that you want. So the prebake shouldn´t be the problem.
I also try to make a ray-tracing simulation, but I cannot measure properly the heith of your lenslets, and also I get a larger focal distance for the beam... but it doesn´t match with your images, where your cones are 33.4 and 46.1 um tall. It is true that as the polymerization progress the index and absortion of the SU-8 can change a bit, but not so much.
The exposure stage should be studied, your times are ok with MC protocol, but for a 100um thick layer of SU8, and you want just 33um so probably you are using 2/3 more energy that you need, and that can cause the formation of the rods. So you are starting the formation of photoacid in a bigger volume, that then, during the PEB start to polymerize.
I think this could be the main problem.
Another one, could be the fact that you have a very dense distribution of needles, so developing could be difficult and uncomplete with the MC protocol you used. So if some un-crosslinked SU8 remained there after the 10-15min develop, it would poymerize during the hardbake. You could avoid this with an ultrasound bath.
I would try reduce the exposure dose to 1/3 of the time (2s instead of 6s).
(Sometimes the lamps provide different amounts of energy and therefore the manufacturers recommend to make your own calibrations)
May be you could also use a thinner layer of SU-8, just the size you want for your needles.
In your second image I read the title: Axicons, so I wonder if you are doing axicons, because they would be fine to focus light in a linear spot.
I hope it helps.
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I am trying to dice a 4" wafer made from Gorilla glass ( McMaster Carr 8410T3) using a Disco DAD3220 wafer dicing machine. I am having trouble getting a clean cut.
When I set the blade to cut the entire thickness of the wafer, the wafer cracks.
When I try to cut only part way throughput the wafer, the cutting is executed well but when I try to tap the wafer along the scored edge, it shatters.
Do you have any suggestions on how to work around these issues or experience with dicing Gorilla glass and could share your experiences?
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I tried to cut gorilla glass on the Disco DAD saw. Glass was cracking, producig a net of cracks.
I think that Gorilla glass may be impossible to cut. According to Wiki
"During its manufacture, the glass is toughened by ion exchange. The material is immersed in a molten alkaline potassium salt at a temperature of approximately 400 °C wherein smaller sodium ions in the glass are replaced by larger potassium ions from the salt bath. The larger ions occupy more volume and thereby create a surface layer of high residual compressive stress, giving the glass surface increased strength"
My understanding is that when you cut gorilla glass you release the stress introduced by the process. I think that this whole process is designed to precut the glass and then dip it in the molten salt.
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Lithography
Photoresist
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I have found that SU-8 is typically very robust; especially if you perform a true hard bake at the end of processing. This is one reason SU-8 has been so popular.
However, if you start working with much thinner films (I have successfully achieved reproducible 50 nm thick films by dilution with cyclopentane) you will find that you may start to encounter problems with harsh chemicals or environments.
Can you give any more dteilas on the film thickness and the end application of your structure?
Jules
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Are there any important points to take into account when moving from commercially available disk electrodes (e.g., 3 mm diameter platinum disk electrodes) to a commercially available screen-printed or microfabricated electrodes?
Firstly, can anybody explain how the typical commercial disk electrodes are fabricated? Is the metal produced by an additive (sputtering) or subtractive method (or combination of both)?
I would also be interested in suggestions such as robustness (limiting number of scans, potential window, etc.), surface orientation (e.g., Au <111>), differences in surface immobilisation techniques, etc.
Thank you in advance.
Best regards,
Marie B.
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Some SPE electrodes are inks which means that they are made at 150 deg C and are full of organic binders, whilst other are made from pastes at 800 deg C so the gold is much purer as all the organic material is burnt away, this is illustrated in this paper - https://www.zimmerpeacock.com/2019/09/06/zp-published-in-ieee/
The honest answer is you have to try and it is important to ask yourself the question 'am I going to SPE because I want perfect results, or because I would like to say my research can become a manufactured product', if you want perfect results use a disk electrode if you truly want to work towards a product then I recommend A-AC-G-AC-203-N - https://www.zimmerpeacocktech.com/products/electrochemical-sensors/value-screen-printed-electrodes/
Best
Martin
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If photoresist is coated over first alignment marks then how will I do 2nd alignment through MJB4 mask aligner?
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Yes, in most cases if the alignment marks are suitable, you should easily be able to pattern multilayers.
What stack (material and thickness) do you have, and how large or small are the alignment marks?
Jules
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Hi everyone!
I am trying to dive into the droplets microfluidic world using a low-cost microfabrication approach. However I am experiencing some issues.
Th configuration I am employing for droplet formation is a conventional flow focusing device. The oil phase is composed of hexadecane + 0'5% (v/v) Span and the aqueous phase is simply MiliQ water. However, the liquid leaks over the surface of the bottom layer. I am afraid this is because the pressure that appears in the junction is so high that the bonding that I employed to seal the device is not enough.
Apart from that, do you think that it is important to use an oil with a lower viscosity than hexadecane (as HFE) to reduce this effect?
Another point, at what extend does Aquapel help in droplet formation?
Thank you in advance for your answers
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Hi Juan,
As Ali Kalantarifard mentioned might need a bit more info to help.
One thing to be careful of is that hexadecane can swell PDMS and can potentially cause leaking (atleast from my experience). As Ali said don't think the viscosity is an issue, people commonly use much more viscous oils (e.g. mineral oil).
If your device material is not naturally hydrophobic you will need to do surface treatment. For PDMS devices our lab typically uses aquapel for fluorocarbon based oils, and RainX to treat for hydrocarbon oils, mineral oil, etc.
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I am working with lift off technique with a negative photoresist (AZ nLOF2020) which is a cresol novolak based one.
The baking and post-exposure baking are done at 100ºC for 60s and the exposure is under 60 mJ/cm². I believe that is more than enough to avoid the excess of cross-linking. During the deposition of the film, the wafer temperature does not exceed 60ºC.
The manufacturer recommends to do the strip with DMSO (dimethylsulfoxide) or NMP (N-methyl-pyrrolidone) at 80ºC. However I am not able to completely remove the photoresist and I observe a strong adhesion between it and the wafer (SiO2 coated). Some parts are easily removed while another are strongly adhered.
Some remarks:
  • I tried: DMSO, NMP, PGMEA, and Acetone at different temperatures and times
  • The film I work with is a glassy semiconductor and it is sensitive to basic media (including DMSO).
  • Ultrasound bath helps to remove the photoresist but also removes the film
Does anyone experience something similar with negative photoresist? Could I try another solvent?
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Hello,
I have tried Remover PG from micro-chem, it is an NMP based solution. It worked really well with AZnLof when heated up to 80 C. Make sure not to use Acetone, it makes it harder to remove the resist.
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Hey !
I'm a grad student trying to develop an alternative for syringe pumps, requesting users to share information on
  • Advantages and Disadvantages of Syringe Pumps
  • Bottlenecks faced in particular applications
  • What are the preferred alternatives?
  • How many experiments are performed annually on average?
  • What is the price range you are looking at?
  • Any other desirable you would want in the Syringe Pump?
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Michael G. Weller It depends on the pressure you are working on. Plastic syringe cannot withstand higher pressure values.
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Hi all,
Like many of you, I was coating my Si wafer molds with a silanization agent (TFOCS) using vapor deposition technique to facilitate easy removal of PDMS.
However, the last time, I unfortunately added to much of TFOCS and coated my wafers with a really thick TFOCS layer which messed up the entire geometry.
Do you have any idea how can I remove TFOCS without damaging the wafer? I have poured PDMS and remove it multiple times but it seems like TFOCS layer remains intact. I tried to clean the wafer with IPA but it did not work either.
I appreciate any suggestions,
Thank you!
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Hi,
It happened a lot to me. You can try washing the wafer with isopropanol or acetone for a few minutes following by DI water rinsing. If you can put the wafer with acetone or isopropanol in an ultrasonic bath for 5 minutes, you can remove the most unbounded silane molecules.
I hope this works for you as well!
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    I have horizontal Su8 beams (width 5um, height 5 um) fabricated on glass coverslips. The beams are attached to large Su8 pads around 500 um* 500 um.
    A layer of Omnicoat was spun prior to Su8 deposition to facilitate release of the beams using MF26. By dipping the coverslip in MF26 for a short duration (3-5 sec) after development of Su8 I was hoping to release only the beams and have the pads still attached.
Unfortunately, I am getting either complete release (beams + pads) or the whole thing is stuck. Even after I release the beams manually using a micro-pipette attached to an XYZ positioner, within a day, the beams stick to the surface.
    I have tried storing the coverslip in dry air and under water. In both cases, the beams re attach after release.
    Can anyone suggest how to prevent this? It would be a great help. If any more details are required, please let me know.
Thanks.
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Hi Somanna Kollimada,
I obtained the issues of how to remove the exposed - SU8 resists , may I ask if you have any suggestion?
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Hi
I was wondering if anyone had experience with exposing SU8 from the backside of a transparent substrate and could give me an estimate for the relative exposure dose compared to a front side exposure.
The backside exposure is to prevent the overhanging profile if I exposed from the front, as positively sloped features are required.
Im trying to create 50um features which correlates to an exposure dose of 150-250mJ/cm^2. When I used the same protocol as I would for a topside exposure on silicon (produces good results) the features werent even close to being the correct height; as if they hadnt even been exposed really.
Would it be a fair estimate to try an exposure dose around 600-900mJ/cm^2, or could there be any other issue
Thanks
Alex
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I met the problem of dose for SU8 for backside too,I used more does than SI
and got excellent result, but just one time!
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Can I fabricate same height of main channel(h=5um) and narrow channels(5um) which is joint between two main channel(5um) through multlayer lithography?.kindly give valuable suggestions.thanks
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As said by Max, go for one layer, it should not be a problem at all. If you are planning to use mask photolithography, you might want to use a high resolution mask (like chromium).
Good luck
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In our microfabrication lab, we get messages to work with photoresists and e-beam resists (generally PMMA) in different work stations, because 'they can contaminate each other'. What is the reason for this, if it is indeed problematic?
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They are known to interact chemically. For example, in case you spin coat PMMA in a spin coater that was not cleaned after the previous use with photoresist (or vice versa), the resulting deposition onto the coater walls becomes hardly soluble in aceton. This layer then may generate excessive particles during subsequent removal.
In case both PMMA and photoresist intrude into the vacuum part of the system, there is an increased risk of blocking it. Also there might be other associated problems.
To sum up, it's definetely better to avoid using these two substances together on the same work station. In case only one station is available, always thoroughly clean it before switching from photo- to ebeam-resist and vice versa.
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These microfacies belang to Cretaceous plagic limeston in the Azerbaijan (NW Iran). I cant identify plancton microfossils.
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No oolite at all, but calcispheres (= calciodinoflagellate cysts) -@ Som Nath Kundal -
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Cheers everyone
I'm currently working with a microfabricated device composed by a thin PDMS sheet assembled onto a glycerol-coated glass slide. I need the PDMS to glide over the glass, hence I'm using the glycerol on the glass slide. The goal is to stretch the cells on the PDMS. However, if I want to grow cells in this device for more than 5 days in the incubator, the PDMS layer becomes stuck to the glass and I cannot stretch it. I don't know if this is due to adsorption of glycerol by PDMS or just a consequence of glycerol evaporation. Anyone has any ideas? And, in that line, anyone can suggest a compound which will also allow the PDMS to glide over the glass while not being adsorbed/evaporated? Thanks in advance!
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Try using a silicone based oil or vacuum grease. Best of luck.
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I am trying to measure a step height of the iron. I have tried HCl with a 1:100 ratio with water, but the solution etched the alumina under the Fe as well, making my AFM data unreliable. I also tried ferric chloride, but that did not etch the iron. I believe the alumina to be alpha-alumina; it was deposited by e-beam evaporation. The alumina layer is 50 nm thick.
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Try to etch with an aqueous solution of carbonate or iron sulphide. The acids that are released are weaker and the medium is neutral. It will turn out to be an unpleasantly smelling hydrogen sulfate. Try the solution, and then salt on the salt powder, and then drip with water.
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We are designing a MEMS pressure sensor for long-term use, hopefully years, underwater. Possibly saltwater as well. The device has metal traces and uses a typical method to measure pressure.
We need a passivation layer to protect the electronics from water and the external environment. Research papers in this topic each have very different opinions as to what layers, in what order and thickness to use. Some recommend SiNx, or SiO2, or SiON, or combinations of these layers in varying thicknesses.
Is there a good way to pick the passivation stack besides picking a few different layers and thicknesses? What are the pros/cons of using SiNx/SiO2/SiON? Can you recommend a particular stack for my application?
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Yes, SU-8 could be used as a protection coating for MEMS structures. Another possible material is parylene-C. Usually SU-8 should be spin coated on the device, whereas parylene-C can be evaporated onto the sample in a low-vacuum chamber. It is a standard polymer material used for many of the MEMS sealing applications.
Jose
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I'm using su-8 2025 on glass and want it to be part of my final fluidic device, but I'm having a lot of detaching problems even before entering water. How could I improve it, and what kind of promotors can I use?
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I would suggest you to expose your sample to oxygen plasma to activate the surface before spin coating SU-8. All the baking steps are important in the processing of SU-8. Most importantly, do a long hard baking step at temperature close to 140 degree. Also cool down the sample slowly after hard-baking (you may just turn off the hot plate and let the sample cool down with the hot plate). Stress is an important reason behind the delamination of SU-8 from glass surface. Controlled hard-baking will help you in managing the stress effects.
Jose
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We are developing a MEMS sensor that has a platinum resistance thermometer (PRT) and need to make pads for electrical contact to this device. We want to be able to make electrical contact by soldering the pads to a PCB and (alternatively) do gold wirebonding.
If we make the pads out of platinum:
Is it possible to solder to platinum pads? If so, what is a the recommended platinum thickness for soldering?
Is it possible to wirebond gold wires to platinum pads? If so, what is the recommended platinum thickness for wirebonding?
Would you recommend adding other metals on top of the platinum pads to improve solderability and wirebonding?
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Hi,
Depositing 1 micron Pt sounds to be practically difficult for wire bonding. I had successfully wire-bonded on metal pads of thickness just above 300 nm. All you need to do is to play with the wire-bonding conditions. Gold wire can be used on Pt pads.
Thanks,
Jose
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I want to pattern a 1000nm thermal oxide layer with features down to 10 microns. We have successfully used dry etching, but the etch rate is very slow (30nm/min). I believe wet etching with HF could be the solution, but last time we tried we had problems with HF undercutting the photoresist.
Can you recommend a recipe to accurately wet etch a thick layer of SiO2? For instance, photoresist thickness/baking and what formulation of HF to use, ideally with a reference.
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Hi. I have the experience of working with wet etching of ITO-glass wafers and used to have undercutting. The best solution I found was to bake the wafer (i baked at 120 degree c for minimum 30min) before spin coating of photoresist. The reason was that photoresist may adhere to water molecules (moist) on surface. Water molecules may evaoporate later or dissolve away and cause a weak bonding between photoresist and wafer in the respective region.
BTW, I let the wafer to cool down for a short while before I spin coat photoresist.
I also baked photoresist after developing (an additional baking step) to make structure of the edges of photoresist patterns firm.
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Recently, I try to realize a anodic bonding between Si wafer and Pyrex7740 glass, with two intermediate layers-a 2um thickness SiO2 and a 400nm thickness Si3N4.
Can anyone give me some suggestions about the success of this anodic bonding?
There are papers reported about the successful anodic bonding between Si-SiN-SiO, but with the increase of the intermediate layers, especially SiN, will degrade the possibility of successful anodic bonding.
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We have done anodic bonding to Si covered with a thin layer of SiO2 (no nitride). You may be able to get this to work - it seems you will just have to try it.
I would test anodic bonding at 400C with -1500V, or as high a voltage as you can apply before seeing sparks.
Good luck.
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I'm trying to deposit an amorphous carbon layer at 300 ˚C using PECVD with methane and helium as my primary carrier gasses. I've been using a Plasmatherm RF chamber (13.56 MHz) with great success at depositing amorphous silicon, silicon dioxide, and silicon carbide (hydrogenated), but attempts to deposit just carbon (hydrogenated) have all failed at 300 ˚C. However, I can deposit carbon at lower temperatures of 100 ˚C with ease. I'm assuming that the residence time of the carbon ions is either too low in the chamber or the temperature causes any ionized particles that land on the substrate to desorb before they can effectively bond onto the surface. I've tried varying deposition parameters to alleviate these concerns with no success.
Can anyone point me in a good direction to go with depositing at 300 ˚C? Does anyone have experience with this?
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Thanks for your response. Unfortunately the tool I'm working with is not plumbed with H2 so I have to rely on CH4 as the only source of hydrogen. As to the deposition temperature, I'd like to use the carbon layer as a transition zone between a-SiC and a polymer. The a-SiC layer's properties are ideal for my application if deposited at +300 ˚C but deteriorate if deposited at 100 ˚C. Its a catch 22 for me.
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physics
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Concentrated sulphuric acid (98%) also etches the cured PDMS very quickly (except chemically modified, e.g. irradiated, parts -> this makes possible to use PDMS as a negative resist material in lithography). Dilute sulphuric acid does not etch PDMS away. If concentrated sulfuric acid does not damage your polymer, you can use this method to remove your cured PDMS layer selectively.
KOH and NaOH solutions etch only the chemically modified (irradiated) parts of PDMS -> positive resist material in lithograpy
30 wt% KOH + 20 wt% IPA+50 wt% DI water solution at 70 °C temperature etches away the cured PDMS (even if PDMS is chemically modified/degraded by e.g. radiation).
More detailed info (etch rates, etc.) in my two latest papers:
S.Z. Szilasi, C. Cserháti, Selective etching of PDMS: Etching technique for application as a positive tone resist, Applied Surface Science 457 (2018) 662–669
S.Z. Szilasi, L. Juhasz, Selective etching of PDMS: Etching as a negative tone resist, Applied Surface Science 447 (2018) 697–703
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I am wondering if it is possible to use pillar array columns for separations other than in the reversed-phase mode? I have found a paper explaining the difficulty of coating the pillar surface with C18 being the small interpillar spaces, and because of the adsorbed water that may cause polymerization (and thus clogging). However, I don't quite understand how this would translate in modifying the pillar surface to suit normal phase, or other modes. As far as my knowledge goes, the silicon forms silicon dioxide spontaneously, and the surface should, therefore, be modified just as easily as silica-based packed columns.
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Thank you for answering.
What exactly do you mean with HILIC? For that mode, you need a polar stationary phase, and the pillar array format is only available in RP mode. Pharmafluidics only sells C18 end capped coated pillars. This is exactly why I started to wonder about the other separation modes. I understand that when the interpillar distance is too small, it would clog. However, if C18 modifications are possible (which is a very long chain, longer than others), then this made me think that other coatings should be possible as well... but somewhere here in the thinking process I must be making a mistake because I have not found any paper discussing this, or other modes with pillar array columns.
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Hi
Im using SU8 3050 on stainless steel to create periodic rectangular features. My main issue is that following the development, the widths of the features are larger than in the intended design. My mask is dark field with rectangles of 5mmx 300um wide for the exposure. Under the microscope instead of being 300um, the features appear noticeably larger, around 350um-400um.
To minimize mask contamination Ive been using proximity lithography with a gap of 20um, would this cause such a substantial increase in substrate exposure leading to the larger features?
My fabrication procedure is:
1) 4 minute solvent clean in ultrasonic bath with acetone, methanol, IPA and then RO water, dehydration bake of at least 2 hours
2)Spin SU8-3050 at 2000rpm for 30 s
3)Pre-exposure bake for 30 mins at 115oC
4)Exposure for 50s
5)Post exposure bake gradually increasing from 65oC to 95oC
6)Develop in EC solvent for 8 minutes, wash in IPA
7)Hardening bake for an hour
I was contemplating whether it is possible to overdevelop SU8, but I doubt this is the cause.
My main query, is whether the issue is merely light diffraction due to the use of proximity lithography?
Any suggestions as to why the lines are thicker than intended would be great!
Alex
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300 microns feature is a relatively massive structure to fabricate and should not broaden by 30%, even though the resist thickness is some 70 microns or so. There can be several reasons for this result.
1) You do not specify the size of your metal plate, but in general the smaller the substrate the more pronounced will be the edge bead effect (resist agglomeration at the edges making a thicker rim compared to the resist thickness in the centre of the sample). Thick edge bead will make sure that you actual gap is considerable larger than 20 microns you set. It will be 20 microns from the mask to the surface of the edge bead, but a lot more from the mask to the resist surface at the centre.
2) 50 s exposure is a meaningless parameter. The resist supplier suggests 150-250 mJ/cm^2 exposure dose and you might want to run an exposure series with varying dose to optimise your process. It may very well be, that the actual exposure dose delivered within those 50 s is way too high causing overexposure and subsequently features broadening.
3) Post-bake time should be minimised to prevent the photoagent diffusion and feature broadening (slow ramping to 95C and no more than 5 min at 95). Although not directly related to the question, the pre-bake temperature of 115 deg C feels excessive. I'd recommend to not have it higher than 95 deg C.
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I'm working on patterning hydrogels micro-structures on wafers using UV exposure. It is referred by many papers that by silanizing the wafer, adhesion between the hydrogel and the wafer can be improved. Problem is that wafers become very hydrophobic and are very difficult to wet with hydrogel precursors.
I tried to spin coat PEG-DA (MW 575) and HEMA-DMAEMA on wafers modified with Silane A174. Both compounds quickly evaporated or flowed off wafers....
Any input is appreciated. Thank you!
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what spin coating solvents have you tried? spin coating solvents should have higher boiling point than toluene and wet your substrate with a low contact angle. Try spin coating with no PEG polymer dissolved and just see if the liquid coats your silanized wafers nicely and you can watch the interference colors spin past as the solution spins off. Off the top of my head I'd recommend you try amyl acetate.
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We are looking for highly accurate and stable low pressure sensor for a new sensor design. We need to have very low temperature effects and high linearity.
Regards Bern Mark
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Hello, Bernd.Mark Markd !
For your application, I advise you to purchase this type of sensor https://www.amphenol-sensors.com/en/products/pressure-mems/mems-elements-devices/3260-p2701
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I am looking to outsource production of copper features with micron resolution on polymer substrates. I currently do this myself, but am looking for potential larger scale production.
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Jerome,
My company may be able to help depending upon your exact needs. See our website (www.scitechprecision.com) and send your detailed specification using the enquiries link
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Hi , my project needs good isolation between copper and graphene, who's thickness should be less than 200nm. As my wafers is gone through many process so its not acceptable  in those  machines which deposit Sio2 . so is there any alternative material or oxide layer I can use as insulating layer between graphene  and copper layer  ?
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Anyone cannot chose any materials on the merits of experimental facilities, instead, it should be chosen on the basis of anyone's requirement. Like for electronic applications, you cannot use any conducting material like h-BN. If you need isolation, you've to add some insulator, like polymers. Among polymers or insulation materials, you can choose as per your convenience.
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Hi,
I'm working on an electrochemical biosensor integrated into a microfluidic system. The working and counter electrodes are gold, and the reference electrode is Ag/AgCl.
I'm planning to either immobilize thiolized nucleic acids on the bare gold WE surface, or use 11-mercaptoundecanoic acid SAM method to functionalize the WE surface for EDC-NHS coupling to proteins.
Due to the way the microfluidic device is fabricated, I may need to immobilize the biorecognition probes within closed channels (post-bonding). I also want to functionalize only the WE, while keeping the CE/RE uncoated.
Can anyone guide me on how this can be done?
Thank you,
Afiq
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Hi Afiq,
You can make electrochemical desorption of 11-mercaptoundecanoic from the CE. The electrochemical desorption can be done by sweeping the potential between 0 to -1.4V in 0.1M KOH solution. You should optimize the potential window.
Good luck
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Hydrofluoric acid etch for microfluidic fabrication.
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I also don't recommend to do so, since a-Si is easily removed by HF acid
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I am trying to achieve a 2mm thickness of SU8-100. I am applying 3-4 layers (200-250 microns each layer) to achieve this thickness, however, the SiO2 wafer is bowing after baking. After I spin on the SU8, I insert the wafer into an oven set at 65C for 30 minutes and then set the oven to 95C and bake the wafer/SU8 for another 90 minutes.The end result is that the SU8 thickness varies across the wafer, and the last layer is causing the wafer to bow.
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I make thick layers with volumetric dispensing instead of spinning. When baking, you need to ramp down the temperature slowly. The film stress created by the variation in coefficients of thermal expansion between the SU-8 and the wafer will be greatest when the temperature falls across the glass transition temperature too fast. This needs to be done on a carefully leveled plate since the viscosity will get low enough for reflow during the bake. I also use a hot plate instead of an oven. The advantage of using a hot plate is the way the heat gradient is created in the SU-8 with the SU-8 in contact with the wafer is always hotter than the SU-8 on the top surface.
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I tried making a composite of 10wt% particle loading, mixed and exposed by photolithography but the features though i can view the pattern after post bake but, upon developing everything washes off/ or no sign  of it.
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Right around 10 microns is where you will begin to see the effects of optical attenuation through your mask (at relevant wavelengths). It is often difficult to balance the exposure of SU-8 when you have features much larger than 10 microns mixed with features that are smaller than 10 microns (@ 1 micron, optical attenuation can be around 90%, depending on a number of factors). You typically end up with some cracking in the larger features because of over exposure when you get the small features to develop well. These crack can often be "healed" by a hard bake though.
Doing a longer soft bake can improve your results by insuring that all of the solvent is baked out of the SU-8. The solvent can act as a photo-inhibitor and cause the optimal exposure range to be narrower. There is no cross-linking happening during this bake and you really can't over bake SU-8 during the soft bake.
Having said all that, it is possible to loose adhesion with overexposure as well. After doing a long soft bake, I find that the best exposure is about 70% of the lowest exposure suggested by the data sheet.
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Hello
When it comes to thin-film which one is more desirable? (Particularly, where the thin film is used as the first layer of a multi-layer thin films fabrication)
1- a film with a higher internal tress and higher Tensile
Strength?
or
2-a film with a lower internal tress and lower Tensile
Strength?
Thank you for your time and help.
Best Regards
Ali
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As far as I know, desirable is practically always compression since the surface - coated layer or generated zone of the same material - is produced to protect the surface, i.e. it should not form cracks which causes corrosion or other failures. If possible it should repair itself, cf. our teeth. This means that the layer below is under tension since everything has to be in equilibrium. For a multi-layer system this might have a complex stress-strain construct especially since some layers are less strength than other. Too high stress can also damage the entire system (spalling observed in coated materials but also in quenched and tempered surfaces like railroad tracks) so that the investigation of stress is essential in practically all technical fields. 
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I have fabricating su8 chips using su8 100 on the glass substrate. I have tried few times by changing the exposed time, spin coating speed, and even the prebake temperature, but for most chips there always remained some material in tiny patterns which cannot be perfectly removed by developing. I found the development will be stopped after 2hr immersing in su8 developer solution.
Please let me know whether you encountered the same situation and why this happened? Thanks.
My protocol was attached below:
1, preparation the substrate:      wash,  120℃ for 10min
2, coating:  500rpms 7s, 1400rpm for 30s
3, prebake: 65℃ 30min, 95℃ 60min
 4, UV exposure: 6-8s
 5, postbake: 65℃ 15min, 95℃ 20min
6, development, immersing for 2-3hr(MicroChem Developer)
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Dear Guo,
not at all. I have doubt that some light may leak to the dark area during the light exposure and cause this insoluble residual of the photoresist.  In order to exclude this hypothesis you can make a trial with all steps carried out except the light exposure. If the resist could be completely developed without any residuals, this means that there is light scattering to the dark areas which render the resist partly insoluble during development. 
Best wishes
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I am trying to fabricate free standing PMMA micro structures on Silicon substrate, which requires isotropic, selective silicon etching leaving large undercut. I've tried wet etching with KOH, however the selectivity was poor. Reactive ion etching with SF6+C4H8 yields better results, but longer etching time towards desired undercut (~20um) partially destroys PMMA. 
Could someone please suggest different recipe with RIE or an alternate approach? (XeF2 would have been promising option, unfortunately we don't have it)
Thank you very much. 
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I propose you to add a protective layering on PMMA wich will be etched away when the required silicon undercut is reached. "SOG" Spin on Glass should be easily applied on PMMA and removed by wet etching in BHF after finishing undercut process.
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We have a Faraday cup in the beam line. This cup can be moved back and forth in a single axis. We measure diameter and uniformity of He ion beam by measuring the current induced in the faraday cup at different positions. The He ion beam itself can be moved with the help of deflectors.
When the faraday cup is at -72V bias:
The cup gives us normal reading (which is about -0.8 to -1.2 nA current) in first half of the beamline but when it reaches approximately the middle of the beamline, the current value drops and switches polarity (it shows about +0.1 nA current), which remains the case thoughout the second half of the beamline. When we move the cup back to the first half of the beamline, it switches back to normal values. 
When the cup is at +72V bias or is grounded:
In this case, the problem is exactly reversed. The cup gives normal but slightly lower and positive reading (which is about +0.4 to +1 nA) in second half of the beam, but gives Zero reading in the first half of the beam.
At negative bias of the cup: When we move the whole ion beam with help of deflectors to the first half of the beamline, we have a normal reading. Which means the problem is with the position and not the beam. We have also changed Ammeter, which gives us the same result. Also, we know from resist exposure experiments that there is no blockage of the beam.
The beamline is under vacuum for the experiments. The wire connections to the faraday cup are covered with copper tape so that the plastic covering of wires doesn't accumulate charge. This copper tape is touching the faraday cup body and is grounded. The wires seem to hang a little and might touch the beamline chamber when the cup is moved to the center of the beam line, but since the wires are covered with copper tape (which is grounded) we are not sure if that is the problem.
Kindly help us out. If possible, also suggest some experiments to find out more about the problem.
Edit: The beam is continues and has Gaussian profile
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The problem was solved after about 3 weeks of posting this question. The trouble was being caused due to an open hole on side of the cup (it's usually covered by a tiny screw, but somehow the screw came off). Electrons were entering the cup from this hole and causing the ammeter to give a wrong value. The problem was resolved after this hole was covered by the copper tape.
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We have developed a torsional micro-gyroscope using UV-LIGA process. The device has been tested for resonator characteristics using LDV. However, at present, we do not have rate table characterization facility (both the equipment and sensing circuit) with us. Can someone help us to get this characterization done?
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@Nadeem Qaiser: The gyroscope can be characterize for resonant frequency and Q factor using Polytec MSA-500 Micro System Analyzer. It has LDV for measuring out-of-plane frequency response and stroboscopy for extracting in-plane frequency response. To find the sensitivity, you will need a capacitive ROIC like MS3110 hybrid integrated to the gyroscope. You will require a rate-table to apply the angular-rate. Please feel free to ask if you have any query.
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Hi! Im using a contact lithography machine to process negative type dryfilm. I would like to ask if there are any existing methods for changing the slope of the resist similar to that of a positive resist without using a new resist entirely.
So far I have tried with changing exposure gaps and increasing exposure doses, but the best I seem to get is a an angle nearing 90 degrees with some undercuts.
Thank you in advance for your help!
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Dear John Rico,
I have fabricated these kind of structures in the negative photoresist SU8. By over exposing this resist, it will result in a positive tapered sidewall. The best way is to do sector exposure to find the proper exposure dose. Antoher way, that others used, is exposure from the backside so through the (glass) substrate.    
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SU8 2005 of height 6micron is coated over the electrodes and DI water is placed above it. Drop is actuated at 500V, 50kHz. 
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K. Actually I need to know about the amount of degradation or the charge transfer between the drop and the dielectric. If you come across some idea or literature please share..
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We are conducting our experiment with 20 um width channels. We are using a punch for making inlet/outlet holes in our PDMS channels. However, there are always some fiber/dusts like residuals blocking our channels. We think that they are PDMS residuals remained in the channels after punching. Is there any way to clean those residuals or avoid making them?
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Dear Morteza,
What we usually do is the following: Put a piece of scotch tape on the PDMS side which has the channels. Then, from the other side, punch the acces holes with a sharp hollow needle all the way trhough. Retract the needle with PDMS residue and remove the scotch tape. This should ersult in a clean PDMS channel surface.Flushing with IPA and blowdry with N2 can be performed if necessary. 
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Which are the main companies for screen printed electrode machine, which we are planing to procure to fabricate our own screen printed electrodes. Please suggest
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Do you want to do your own screen printing using your own inks? You can make your own screens by purchasing the raw materials. We have done this in the past by purchasing the screen supplies from a local art store. For conductive inks, you will probably need to bake out the organic carrier at a high temperature. This is something that most standard screen printers are not doing so you will need to add that to the standard screen printing equipment list (the typical ink dryer will not work). Most screen printing "machines" are designed to print t-shirts. I'm not sure how well that would work for you. You will need to be able to "register" your screens if you are printing multiple layers which can be done either by careful placement of your art while burning your screens or by having an adjustable screen or substrate holder.
I'd need to know more specifics about your application to make more detailed recommendations.
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I want to deposit an interdigitated pattern of electrodes on a Silicon substrate. The technical details of which are :
a.) Substrate                           :   Silicon , square shaped , 0.5 inch side length 
b.) First layer (base layer)   :  Titanium (as an adhesive between Platinum                                                                        and Silicon) , thickness : 20 nm
c.) Second layer (top layer) :  Platinum (conducting electrode),                                                                                            thickness:180 nm       
The techniques should allow the user a fair amount of parameter control like film  thickness etc.
An example of the electrode pattern is attached as an image file.
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Dear Afraz, instead of sputtering you can use metal evaporation (thermal or e-beam), as Peter Knapen allready mentioned. The thickness is usually controlled In-Situ by a quartz crystal. About the process; you can first deposit the metal and photolithographically pattern the metal layer and etch it. Or you can pattern the substrate first, deposit the metal and lift off the photoresist. Both ways do have their pros and cons.