Hi Tom,

the mask must hold somewhere. Most maskaligner hold the mask with vacuum,
either from top or bottom. If the mask is hold from bottom (chrome side) the
maximum wafer size depends on the opening of the mask holder. If the mask is
hold from the top the wafer size can be the same as the mask. However, the
exposure area is limited by the opening of the mask holder.

Moreover, in case of vacuum contact exposure mode, the edge of 1/2" on the
mask is necessary to seal the vacuum chamber.

Therefore a 1" larger mask is recommended usually. If existing masks should
be used with wafers of the same size, the manufacturer of your maskaligner
may find a solution for that. However, this will not be a standard solution.

        Michael.


        Dr. Michael Hornung
        Application Engineer
        ----------------------------------------------------------------
        SUSS MicroTec
        Berliner Str. 48 / D-35614 Asslar
        Phone:  +49-(0)6441-984152
        FAX:            +49-(0)6441-98418852
        e-mail: [email protected]
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-----Ursprüngliche Nachricht-----
Von: Tom Fan [mailto:[email protected]]
Gesendet: Mittwoch, 16. Juli 2003 07:27
An: [email protected]
Betreff: [mems-talk] Mask size



Hi all,

Whats the typical correlation between the sizes of photomasks and wafers in
MEMS fabrication? If I were to fabricate microdevices on 4" wafers, do I
need
4" or 5" photomasks? I learned from an Internet site that the masks should
be
1" larger than the wafers to be used. Is this customary or masks of the same

size as wafers can also be used? Anybody can clarify this issue for me?

Thanks,
Tom Fan


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