The Effect of In-Situ STI Liner Oxide on Threshold Voltage and Its Application to Enhance Yield Stability

摘要

Because of possessing many promising properties, shallow trench isolation (STI) using HDP (High Density Plasma) CVD oxide as trench-filling material has been widely adopted by existent ULSI technology. We have found recently that threshold voltage of MOSFET would be intensively influenced by D/S (Deposition/Sputtering) ratio of HDP tool and it will consequently lead to unstable yield performance. In light of this, we have proposed an approach to compensate the effect by in-situ depositing a thin liner oxide layer before main HDP process proceeds. Through this technique, trench corner clipping phenomenon can be modulated by changing the liner oxide thickness and stable threshold voltage and yield performance are achieved. In addition, trench-filling capability still maintains with liner oxide existence, which is vindicated by SEM micrograph with void-free filling. Most importantly, this technique is fully compatible with incumbent ULSI technology.