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The difficulty in etching soda lime glass stems from impurities in its varied
chemical composition. Because of this, soda lime glass in not usually used as a
substrate in reactive ion etching. Instead, fused silica or quartz substrates are
used. Etching of these substrates is more common because of the wealth of
information on etching silicon available from the semiconductor industry. 51
Samples were hence prepared on silicon substrates to repeat the etching
experiments. Due to difficulties which arose with the etcher, however, etching
experiments using the silicon substrates were not able to be performed.
4.6 Binary Photoresist Gratings
Without the ability to etch, the realization of four level lenses was not
possible. However, using the surface relief profile of the photoresist, the
formation of binary lenses in photoresist was possible. The thickness of the
photoresist necessary to produce a binary element with the proper phase
Set 1 Set 2
CHF3 30 seem 30 seem
Ar 4.5 seem 4.5 seem
pressure 60 mToor 60 mToor
power 350 W 600 W
time 40 min 41 min
Table 4-2 Etching parameters.