Hello Yilmaz

I try some answers to your question:

1. it is impossible to introduce a resist into the SOI-material instead of the
BOX-oxide since this is a high temperature process far above the temperatures
resist can withstand

2. the thermal expansion coefficient od ALL the organic materials is by far
(more than a factor of 100 !!!) higher than the expansion coefficient of
Silicon-Oxide. Silicon is inbetween both - so with the oxide after cooling down
(delta T roughly 1000°C) you get the comprssive stress in the BOX-oxide, in case
of resists the temperature difference is lower (roughly 100°C) but the expansion
coefficient difference much higher and hence you end up with a high tensile
stress in the resist.

Regards
Arno



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[email protected]] Im Auftrag von
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Gesendet: Dienstag, 18. Januar 2011 06:10
An: [email protected]
Betreff: [mems-talk] stress state of photoresists

Hello mems-talk community,

I have a question about the stress state of resists after they are
developed, and ready for masking purposes.

To give an example related to my question:

I am working with SOI wafers, and the BOX oxide is in compressive
state of stress. Hence, once you remove some parts of the silicon
layers from certain places of your wafer (espacially if the silicon is
removed from same location of both sides of the BOX layer) you will
see that the BOX layer oxide will tend to have wrinkles, which
indicates that the BOX oxide is in compressive state, and once it is
free to move it will buckle up and down to change its stress state.

Now, my questions is:

What would be the case if we were using resist as BOX instead of
thermal oxide as BOX? Would it be in compressive stress, and buckle up
and down, or would it be in tensile state of stress and keep staying
in completely flat (no wrinkles at all) state?

The result may depend on the resist we are using, but I would be glad
if someone can tell me if there is a resist with tensile state of
stress?

I am looking forward to your replies, and
Thanks in advance,

Mehmet Yilmaz
Mechanical Engineer