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We have tried to fabricated nano and micro structures together by using MR-I-8000 resist. However, we havent obtained any good patterns. After that, when we extracted microstrucutes from our design, nearly good resolution patterns were fabricated. In that time, thermal resist was not seen in some of the substrate. Therefore, ı need to some suggestion about thermal and UV Nil.
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Thank you for your help:)
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Hi,
I'm doing a process that uses a thin layer of SU-8 as an insulator. I was getting short circuits so I made a simple metal-SU8-metal structure (Figure 1 ). My SU-8 tests included SU8-2000.5, 2001, and 2002 with thickness varying from 0.7 um to 4.5 um. I also tested two different e-beam evaporated thin films, gold and chromium, around 100 nm for each layer.
All of them seemed to be shorted. I have attached some pictures showing the layers under the microscope (Figure 2-5). I spotted some potential pinholes or bubbles ONLY in SU-8 layers on top of the bottom electrode. The SU-8 layer alone on Si and Au/Cr layers alone seem rather clean. I wonder why this is happening and if you have any suggestions?
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I agree with the points raised by Xuhua Wang and Robb Engle It might be that 'high' substrate temperatures during Au/Cr coating might exacerbating H20 contamination effects. Perhaps a very simple way to reduce substrate heating would be to increase your deposition time with a moveable shutter, depositing your film in a series of short bursts with periods of substrate cooling in between.
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Hi! I am creating the recipes for our spin coater and also monitoring the thickness of the resist over 1 year already. Target thickness is 4.7um and the control window is +/-50nm. This resist is always drifting: I am adjusting the spinning speed to lower rpm to keep the thickness back in limits and then wait another month until it drops by 100nm. I talked to the tool vendor and they claim that the problem might be in the bowl exhaust, although some recipes have the exhaust step and some don't and the thickness behavior is similar. The resist manufacturer claims that it is only a factor of 2 parameters: spinning speed (its uniformity) and the exhaust of the solvent from the bowl. However the monitor is done in exact same conditions every week, there should not be any clear drift of thickness (if the exhaust is bad for example, then the thickness would have value x and it would stay there).
Do you have a deeper experience about it?
Many thanks in advance!
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1) Usually resist coats wafer non-uniformly, the film is thinner in the center. So, if you have similar wafers, but measuare in different points, you'll get different thicknesses. E.g. non-uniformity of ~25-30 nm for 4.7 um film is typical for such thick resist. Also, it depends on wafer size.
2) How do you measure thickness? Ellipsometry results depend on refractive index of your film - something could happen and index will be changed, e.g. new bottle of resist, or substrate were not cleaned well and some sublayer left, etc.
AFM/profilometry can make scratches on resist, so the real thickness is large than measured. For this measurements openings in resist are needed, it means you have to make lithography and develop. Unexposed areas (where thickness is measured) are developed very slow, too. This "dark erosion" depend on your coating parameters and developer characteristics, so remaining thickness could be varied.
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Why a cleanroom service corridor often must be designed slightly positive or neutral pressure (beside the cross-contamination possibilities) ? Is it possible that we designed a negative pressure cleanroom in Pharmaceutical Industry ? And why we should design a negative pressure cleanroom ?
Regards
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In a hospital setting, for instance, we have a positive pressure cleanroom for mixing sterile preparations of medications... intravenous admixtures.
The NEGATIVE pressure cleanroom is for chemotherapy agents... where you do not want the medication to go anywhere. This keeps the cytotoxic chemical IN.
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Do you use any software to simulate semiconductor processes (e.g. lithography, PVD, ALD, ...) to explore different geometries of your device?
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Image reversal with positive and negative photoresists is relatively straightforward. However, with e-beam resists such as PMMA, is it possible, if so is the process straightforward and what process conditions are modified from a normal e-beam exposure (dose, post-bake etc.) in order to achieve this? 
Thank you.
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Hi,
 Yes you can make PMMA negative by using a very high dose to crosslink it. See our paper: http://dx.doi.org/10.1088/0268-1242/11/8/021 (“Crosslinked PMMA as a high-resolution negative resist for electron beam lithography and applications for low-dimensional structures” Zailer I., Frost J. E. F., Chabasseur-Molyneux V., Ford C. J. B., Pepper M., Ritchie D. A. and Jones G. A. C., 1996, Semicond. Sci. Tech., 11, 1235–1238). We've since used it a lot for patterning contacts to antidots.
 I hope that helps.
  Chris.
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Not really an academic question...I need to buy CZ and FZ wafers (small batches) for the fabrication of heterojunction solar cells. I'd like to know who are considered really good and reliable suppliers in Europe. I am aware of some, but I don't know if it makes a difference to buy from one or the other if the given wafer characteristics are the same.
Thanks
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You may get your silicon wafers from siltronic having the web: http://www.siltronic.com/int/en/home/index.jsp  We used its wafers for diverse device manufacturing including solar cells.
wish you ssuccess
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I want to use sodium hydroxide to make nanochannels in glass, I have tried to make it using 7M NaOH for 24h,but it did not work.  
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Hi Feng,
I may be mistaken, but I don't think you can use NaOH to etch glass. It certainly can be used to etch Si and that process is usually hindered by the presence of oxides which may be the problem. Typically the only way I can think of with NaOH is to have it molten, which is probably something you'd want to avoid anyway. HF is actually your best bet in this case I'd say.
Hope that helps!
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Hi,
I am trying to do a liftoff processing with AZ5214E (positive) after HfOx ALD deposition at 110ºC for 40nm thickness.
I have experienced two main problems:
1. When the sample is put in the ALD system just few time after development It turns out that when the ALD process is finished I observe that the resist is shown to be "exploded" in bubbles shapes during the processing. 
2. The liftoff is quite hard to get done properly on small patterned regions (8x8um squares), even after sonication in acetone for 30min at 60ºC.
I guess that the solution for problem 1 is to do some hardbake before putting the sample into the ALD chamber. I have tried that (90ºC for 2min in a hotplate) and it has'nt worked out. I guess that so should go to higher temperatures (120ºC for 3 min?). Also i could try to leave the sample in vacuum for 24h to do some PR outgassing.
I would really appreciate some help/advise to solve these issues.
Thanks in advance.
Best,
Raúl. 
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Regarding #2 lift-off, you might a hard time to achieve lift-off using ALD, since the deposition is normally very conformal and hence, the photoresist sidewall will also be covered during the deposition. For a good lift-off, you should prefer evaporation, although I have no experience with evaporation of HfOx. I would actually be curious to hear about that. 
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Our evaporated gates (in vacuum chamber @ 1E-6 mbar) consist of two different materials with different thermal expansion coefficients. After cooling down the sample to 0.3K, they act like a bi-metall, which produces stress to our substrate. In order to evaluate that stress, I do COMSOL simulations. The strength of the stress is dependent to the ratio of the thermal expansion coefficients and to the difference between the temperature of deposition and the temperature to which the sample will be cooled down in order to measure it.
The challenge now is to estimate the temperature of deposition, which is the one for zero thermal expansion. For sure there is a big difference in taking the temperature of the cooled substrate during evaporation and in taking the ones of the melting points of the materials.
Any ideas? Are there any publications about the build-up temperatures of metal crystals while vacuum evaporation/deposition processes?
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Here is a paper where they evaporated a thermocouple on the surface of the substrate, measured surface temperature rise during deposition and compared to theoretical calculations.. The theory was not far off...