TSI process performance in a transformer coupled plasma dry develop tool

We investigated dry development of resist in the Lam Research TCP 9400SE plasma etcher to meet process specifications for the 180 nn lithography generation. A full-wafer imaging interferometer was integrated onto the tool, and used to measure etch rates, uniformities and stability of same in-situ. Etch rates of > 5000 A/min and selectivities of > 15:1 of silylated to unsilylated resist can be obtained in oxygen plasmas in the TCP in the electrode temperature range studied. However, lateral etching (undercut) underneath patterned oxide islands was measured to be similar to 30 nm/min for a typical oxygen process and could not be eliminated in pure oxygen plasmas. To control the lateral etching, we investigated the use of SO2 addition to the oxygen discharge. SO2 addition was found to eliminate the lateral etching component of the resist etch and reduce the etch lag effect, while having a minimal reduction in the overall resist etch rate. We have used the SO2 process to minimize the effect of over-etch on developed resist profiles.