Hello Karthi,
with this question I cannot help. SU8 absorbs i-line so the thicker layer
requires higher dose, but how much I do not know. You can use SU8 data sheet for
starting point, which calls for 150 – 260 mJ/cm2 for that thickness range on Si.
But simple half a day experimentation would give you all that data for your
particular process and substrate.
Daniel
From: KarthiKeyan K [mailto:karthimems@gmail.com]
Sent: Wednesday, July 01, 2015 7:01 AM
To: General MEMS discussion; daniel.figura@smartfabgroup.com
Subject: Re: [mems-talk] SU8 2075 Pattern - Reg:
Dear Sir,
Please suggest how to calculate the UV exposure time for different thickness of
SU8 2075 negative photoresist layer.
I have used different SU8 layer thickness such as 60,80,100,120,140,160 micro
meter thickness.
Looking forward to your reply.
Best Regards,
Karthikeyan K
On Tue, Jun 30, 2015 at 12:21 PM, Daniel Figura > wrote:
Hello Karthi,
I would expect that reason is heavy overexposure. Try to make an exposure matrix
to see where your process is. The easiest way to do it is to take the coated
wafer, load it into your exposure system, cover the part of the mask and expose
the substrate, than uncover different part and expose with different dose and so
forth. Make e.g. 6 sectors with 50, 100, 200, 500, 1000, 2000 mJ/ cm2, PEB,
develop and inspect. You should see that at some low dose, you lose all the
structures, while at higher they remain and only get wider and wider. Try to
find optimum and repeated with finer steps in exposure dose.
In case that would not lead to the conclusion, check whether your exposure light
is all ok, that it is collimated, that you have right exposure gap or in contact
(not sitting on the edge bead), you do not have scattered light from substrate
or chuck, etc. If your structures are so much wider than on the mask, which
means that some parts of resist which you did not intend to expose get exposed
as well.
What dose do you use now? What is the thickness of your layer?
Keep in mind that the optimum process might not give you 0 litho bias (1:1 size)
- there might be other consideration you need to take into the account, e.g.
whether you structures does not get distorted during PEB, have enough adhesion
to the substrates during development etc. Once you get a reliable process, you
can fix the remaining bias on the mask.
Daniel
-----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 KarthiKeyan K
Sent: Thursday, June 25, 2015 5:05 AM
To: General MEMS discussion
Subject: [mems-talk] SU8 2075 Pattern - Reg:
Dear Friends,
Actually i am working in SU8 2075 negative photoresist and am facing to achieve
exact size of mask pattern on my SU8 photoresist for the example my mask pattern
size is 50 micro meter means i have achieved 60 micro meter.
So Please suggest how to get exact size of the mask pattern on my SU8
Photoresist layer??? any parameter to get exact size of the mask pattern on my
SU8 Photoresist.??
Looking forward to your suggestions.
Thanking you,
Best Regards,
Karthi
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--
Thanks & Best Regards,
KarthiKeyan K,
Research Associate,
Centre for MEMS & Microfluidics,
Department of Electronics & Communication Engineering,
Rajalakshmi Engineering College (REC),
Chennai - 602105
Mobile No: +91-9944477213
Email ID: karthimems@gmail.com
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