In-Situ Post Etch Fluorocarbon Byproduct Removal for HDP Void Reduction

DRAM Recessed Access Device (RAD) module is impacted by Cap oxide voids that causes yield impact through broken wordline. The Cap oxide is the high-density plasma (HDP) oxide that caps the metal wordline. This failure is correlated to queue time at RAD Cap Oxide Dep (HDP) from the incoming clean step, with higher wait time (queue time or qtime) causing fails. The fails are also heavily impacting slot 25 in the FOUP with a unique wafer shading while remaining wafer slots have an edge of the wafer shading. The interaction of the FOUP with the wafers was analyzed through Airborne molecular contamination (AMC) measurements. High Acids and HF AMC were observed post Etch and Strip. Oxide etch uses C4F6/Ar/O2 plasma for selective Oxide etch. This selective etch relies on high fluorocarbon deposition for selectivity. An insitu post etch treatment (PET) with Oxygen plasma is presented in this paper to remove the fluorocarbons in the etch chamber itself to minimize byproduct outgassing into the FOUP inner walls which prevents further interaction of byproduct from the FOUP downstream causing the voids.