Influence of material on process focus budget and process window of 80 nm DRAM devices

摘要

A new type of focus monitoring mask, multiple phase-phase shift mask (MP-PSM), has been designed, and the focus budget of a lithography process was investigated. MP-PSM was used to identity focus controllability of several scanners and was able to detect focus change smaller then 20 nm. We also investigated the difference in focus variation across a wafer between double side polished wafers and single side polished wafers. A comparative study of focus controllability of a scanner using 80 nm node DRAM pattern showed that the focus controllability of a scanner was directly affected by wafer type. Using double side polished wafers increased the process window.