Hello Malar, What is the feature size you are trying to create on the bottom of the trench? Which type of mask aligner are you using? If the features are not too small (<20 um) and you are hands-on person, you might try to do the following: In the lamp house of the most mask aligners, there is element to make the light more uniform, usually fly-eye or similar kind of the lenses, which is located in the focal point of the front lens. Now this element is quite large - several cm and that is for several reasons - to reduce the heat on fly-eye, make the light distribution more uniform and sometimes to create so called "off-axis" illumination which reduces the diffraction and improves the resolution in close proximities. This is exactly what you do not want when you are exposing in large proximity (260 um) because all off-axis light will blur the image too much. So you have to reduce the size of the fly-eye by making an aperture there. How big the aperture needs to be you can find out experimentally or by simulation if you have access to such software. I was once involved in the project where similar thing was required, and that time I have used the aluminum foil to make the aperture - I cut out the aperture with my wedding ring :) as it was close to the dimension predicted by simulation and there was no better tool in the clean room available to do it. Stack it to the fly-eye by folding and edges of the foil and voila - the machine was ready. I do not recall exactly what the resolution and depth of the was (20 um L/S in 250 um depth or 10 um L/S in 250 um depth) but we were able to achieve it, both in simulation and also physically. I used the software called Layout LAB from GenISys to predict the size of the aperture ~ 1.5 cm or something like that. Do not expect sharp profile of the resist or anything like that. Be careful when sticking the aperture - the fly-eye and the holder can get quite hot. And try to position the aperture as close as possible into the center of the fly-eye as this is the whole point to use only the on-axis light. And of course, you will have to increase the exposure time a lot to keep the same energy. Now if this would not be enough, you can always try to do more funny thing like etch the recesses into the photo mask so you can physically get your mask closer to the bottom of the trenches. That could be a nice experiment to do and maybe even to publish, so if you would need help with that let me know. With best regards, Daniel Daniel Figura smartfabgroupT Company process consulting . data processing . fab software Phone: +421 944 45 26 86 E-mail: daniel.figura@smartfabgroup.com, Web: www.smartfabgroup.com Disclaimer notice: The information contained in this message and any attachments is intended only for the personal and confidential use of the designated recipient(s) named above. If you are not the intended recipient of this message you are hereby notified that any review, disseminitation, distribution or copying of this message is strictly prohibited. If you have received this message by error, please notify the sender immediately. -----Original Message----- From: mems-talk-bounces+daniel.figura=smartfabgroup.com@memsnet.org [mailto:mems-talk-bounces+daniel.figura=smartfabgroup.com@memsnet.org] On Behalf Of Malar C Sent: Friday, May 09, 2014 12:49 To: General MEMS discussion Subject: Re: [mems-talk] Comb Structure Lithography Thank you for the reply I am using contact lithography with minimum feature size of 5 um. I won't be able to use focus offset to focus at the bottom of the pit. Malar _______________________________________________ Hosted by the MEMS and Nanotechnology Exchange, the country's leading provider of MEMS and Nanotechnology design and fabrication services. Visit us at http://www.mems-exchange.org Want to advertise to this community? See http://www.memsnet.org To unsubscribe: http://mail.mems-exchange.org/mailman/listinfo/mems-talk _______________________________________________ Hosted by the MEMS and Nanotechnology Exchange, the country's leading provider of MEMS and Nanotechnology design and fabrication services. Visit us at http://www.mems-exchange.org Want to advertise to this community? See http://www.memsnet.org To unsubscribe: http://mail.mems-exchange.org/mailman/listinfo/mems-talk