Patent ID: 8470499

Claim:
A system for fabricating an alternating phase shift mask, the system comprising: one or more circuitry enabled to irradiate at least a portion of a prepared transparent substrate, wherein the at least a portion of the prepared transparent substrate has formed in it an etch stop layer; one or more circuitry enabled to be positioned in an area substantially under the etch stop layer to detect transmittance intensity due to the irradiation; and one or more circuitry enabled to determine completion of etch process of a substrate substantially similar to the prepared transparent substrate based on the detected transmittance intensity, wherein the one or more circuitry enabled to determine completion of etch process determines completion of the etch process based on a rate of change of the measured transmittance intensity being greater than a threshold transmittance intensity rate of change value, and wherein the etch stop layer is formed in a low transmittance region having a lower transmittance than that of the transparent substrate.