I am trying to fabricate a ring structure using deep UV. But the problem is I couldn't resolve the ring as I have some photoresist left between the straight and ring waveguide after development. I tried to use short time plasma cleaning but it did not help. As I have limitation I could not use e-beam lithography.
I have attached a picture of my structure.
Thank you.
Can you give us an estimate on the size of the device? (For example: how wide are those lines in your photo and what is the thickness of the photoresist layer?)
If your process can withstand it, I would recommend submerging the sample in room temperature acetone and using ultrasonication. Then IPA, then deionized water. The precise duration of ultrasonication would need some tuning though.
Thank you, Eugene, for your reply. The width of the line is 1.5micron and the photoresist thickness is 500nm.
I think the feature size is small and I need to use the photoresist as hard mask for etching so ultrasonication might not be suitable.
dear Ahmed, from your picture I see a problem with photoresist patterning, and it could be due to the resolution limitation of your exposure tool (stepper or maskaligner?), as this geometry requires a much higher resolution than the mere thickness of your guide (1.5um). We fabricate such devices using an i-line stepper tool with 350nm resolution. You can try changing the exposure parameters: for example with a positive tone photoresist you might want to increase the exposure time, and possibly increase the developement time as well.
regards
Alvise
Thank you a lot Mr. Bagolini. Actually, I have the limitation in term of the mask aligner. So, I am trying to optimize dose and photoresist thickness to develop the structure. I am using a thin negative resist to get the required resolution. I have tried both near UV and deep UV and observed the same problem. Moreover, by adjusting dose I have observed either over or under-expose so my feature shrinks/swell and did not achieve the required gap between the waveguide.
I am not getting any significant change for higher development time. Could you explain the significance of the development time for negative resist? As I understand the longer development time will cause some sort of erosion/undercutting of the sample.
Thank you.
Naim
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