Optimization of fabrication process for dual-trench-type alternating PSM

We have optimized a fabrication process of an alternating phase shift mask (alt-PSM) with dual trench structure. In quartz etching process using a RIE system, one of the key issues is to obtain a precise controllability of phase mean to target. In order to improve a phase controllability, re- etching process using an etching depth monitoring method with atomic force microscopy is applied in actual fabrication process. With regard to phase uniformity and resist selectivity for quartz, etching conditions such as RF power, pressure, and gas concentration are optimized by orthogonal design method. To improve a sidewall profile of quartz, the effect of inert gas is also examined. Under the practical etching process, phase man to target within +/- 5 degree(s) is obtained. Phase uniformity is improved within 1.0 degree(s). Sidewall profile is improve within 87 degree(s). Optical intensity balance between shallow and deep trench apertures is obtained completely equal from AIMS evaluation result.

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