Microfabrication - Science topic

Alkali metaller, toprak alkali metaller, geçiş metaller iyon pil üretimi için kullanılabilir. Hidrojen ve soygazlar sıvılaştırılarak iyon pil üretimi için kullanılabilir. Diğer gaz halinde bulunan elementler de birtakım yöntemler uygulanarak iyon pil üretiminde kullanılabilir. Bu durum pilde kutupsuzluk ve kutup ortamını ortadan kaldırmakla başlar. Anotun ortadan kaldırmak için katotuda ortadan kaldırmak gerekir. Anot kendi arasında hem homojen hem de kutuplu,katot kendi arasında hem homojen hem de kutuplu olmalı. Bu durumda Anot ve katotta kutupsuzluk sağlanmalıdır. Periyodik cetvelde bunda en çok s,p,d,f orbitallerinde rastlanır. Lityum elementinin son orbitalindeki elektron sıvılaştırılarak ayrıştırılır ve kutupsuz hale getirilir.2s orbitaline karşılık gelen 1s orbitali tam doludur. 1s orbitali de kendi arasında yüksüz hale getirilerek nötr hale getirilir. Bağlanma enerjileri eşit hale getirilerek nötr hale getirilir. Bağlanma enerjisi ile anot katot aynı hizaya getirilerek kendi arasında kutupsuzluk sağlanır. Bu durumda yük elektroskopun yük akışına benzeyecek şekilde nötrlenir. Bu durumu en iyi sağlayacak olan toprak metalleridir. 2A ve 3A elementleri kullanılabilir.

High-k dielectric materials play a crucial role in semiconductor devices, especially dynamic random-access memory (DRAM) capacitors. Let’s explore some deposition methods for high-k dielectrics, including those that allow for thicker films:

Hence, while ALD remains the gold standard for precise, thin high-k films, CVD and other methods allow for thicker films. Researchers continue to explore new materials and deposition techniques to enhance DRAM capacitor properties and meet scaling requirements.

Rassoul Tabassian Have you tried silanization of the mold before doing the PDMS process? A drop of Trichloro(1H,1H,2H,2H-perfluorooctyl)silane (from Sigma Aldrich) on the mold and then heating up the mold at 200 degrees on a hot plate for 1 hour with a lid on top (a glass petri dish would do)will help.

I do not know of any suitable water soluble photoresists, but an alternate would be to use water soluble 3D printed molds like this paper:

3D printed water-soluble scafolds for rapid production of PDMS micro-fuidic fow chambers

Teymour Seymour Talha-Dean is it possible to deposit the metal as a blanket, pattern it and then do a wet chemical etch? perhaps if the metal is uniformly coated as opposed to having side wall coated PR as is the case in liftoff the metal would have higher integrity to the substrate.

Best of luck.

Omnicoat could help

I have no direct experience with magnesium deposition and I got that you do not want a metallic adhesion layer, but can you consider to coat the glass beforehand with some other oxide? Al2O3 or TiO2 are excellent adhesion layers.

The other thing, glass substrates are not as clean as silicon ones. Try plasma and piranha cleaning and also if possible remove water from the surface by heating the substrate in vacuum prior of the deposition if the chamber allows for it.

a few seconds dip in buffered HF or diluted HF removes the oxide without affecting the SiN

Thanks Shelender Kumar and . Aluminum will oxidize as soon as it is in contact with the outside environment so I imagine that the Al etchant will have to etch the native oxide first, which is just a few nanometers. Based on Thomas I could simply use the Al etchant to etch alumina as well?

I'm planning on using photoresist as my mask.

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.

Thanks Qiyou Chen

Well we don't have a fast camera as well. What we do is just measure when from collection pool

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

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!

i I suggest using this genetic algorithm for optimization.

I think u r curious about PR deposition behavior but this depend upon quantity and RPM...

Anyday.

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.

Paul - thats great

My email is Jonathan.Sellars@agas.com if you need anything else

Regards

Jon

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.

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

Seemingly of some possible interest:

thank you, much appreciated.

Good question

Less aggressive cleaning can be done using aceton and IPA solvents.

Yiou Liu please see this article :

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

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.

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

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.

Imadeddine AZZOUZ Yes. I need to remove the handle layer of the SOI wafer. The thickness is 375 um.

you can read this book

"Nano Plating - Microstructure Formation Theory of Plated Films and a Database of Plated Films, by: T Watanabe."

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

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

You can try Anisotropic Crystalline Etch Simulation (ACES) developed by Micro Actuators, Sensors and Systems Group (MASS) at UIUC

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.

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

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.

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.

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

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

Hi Ramiz Raza

Your question is sound simple, but actually it becomes problematic for even experienced researchers, I met it several times even I knew it well ( neglected or forgot the issue during the process development). To answer your question clearly and sufficiently:

1. The first mask must have a proper alignment masks. Asking your experienced colleagues for proper design that suitable for your process, especially for multiple steps process or process involving the use of really thin-films;

2. And this alignment mask will be formed/etched on the wafer after the processing steps like etching or metalization ;

3. In the second resist coating; the resit will cover the previously formed alignment masks on the wafer, and you can focus the optic there to see well the resist coated alignment masks for correct alignment of the second layer.

However, problem appeared if the thickness of the second coated resist is too thick to the etched depth of the previous alignment mask- or the etch depth of the alignment mask is too shallow ( happened often when process ultrathin layer); Sometimes, we must do an extra step of etching just for sufficient deep imprinting the first alignment masks into the wafer.

4. After processed, the first processed alignment mask can be wider or narrower than its original design; while the second mask can be transparency or dark ones. To see and align well, then these both factors must be given sufficient attention for proper design of the second alignment masks. For instance, after the first mask, following with the etching; a dried etching do not widening the alignment mask too much, but if followed by a wet etching, especially if the under etching is happened, then the alignment masks will be created with much larger than its designed ( and expected ) dimension . Therefore, this things must be known in advance for proper design of alignment mask in the second mask.

Generally, mask relates inherently to the process development of the device, which is never perfect. Therefore you really need to have deep advice/cross-check from a really experienced process engineer to obtain a good design; and even that should do a double check before officially mask order ( not only the finance issue, it takes months to re-order the masks).

Hope it helps

Cheers

Hien D Tong

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.

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.

Michael G. Weller It depends on the pressure you are working on. Plastic syringe cannot withstand higher pressure values.

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!

Hi Somanna Kollimada,

I obtained the issues of how to remove the exposed - SU8 resists , may I ask if you have any suggestion?

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！

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

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.

No oolite at all, but calcispheres (= calciodinoflagellate cysts) -@ Som Nath Kundal -

Try using a silicone based oil or vacuum grease. Best of luck.

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.

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

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

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

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.

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.

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.

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

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.

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.

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.

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

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

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.

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

I also don't recommend to do so, since a-Si is easily removed by HF acid

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.

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. 

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

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.

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.

@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.

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.