azu_td_1349475_sip1_... - Arizona Campus Repository

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where n is the index of the substrate and d is its thickness. Setting this equal to
(2tc/2 m ), the phase height of a step for the M 111 mask, and solving for the
thickness d M gives
dM = —r^
2
(n* 1 ). 3.23
This is the etch depth required after exposing mask number M. After etching the
substrate to this required depth, the remaining photoresist is removed. This
process is then repeated M times for an N level element (since each mask
produces 2 phase levels).