Low Silicon and SiGe Loss in High Dose Implant Resist Strip

摘要

The loss of both silicon and silicon germanium in resist strip process has attracted much attention for generic device development. Such loss mainly stems from the substrate re-oxidation during strip. In this paper, we focus on the high-dose implant resist strip to investigate the re-oxidation of substrate Si and SiGe without compromising the removal capabilities of photoresist (PR) and residue. Besides, the impact of ashing gas ratio on SiN offset spacer critical dimension (CD) is also addressed. Specifically, we studied the substrate re-oxidation performance under various ash process parameters such as pressure, gas ratio, pin position, process time in crust and over-ash (OA) steps. Aside from the re-oxidation effect, we also compared the defect removal capabilities with the above ashing conditions and the dependence of SiN offset spacer CD on ash gas ratio. Results indicate A) The high pressure in preheat step coupled with the low pressure in main-step can effectively preclude Si/SiGe loss. B) For SiGe substrate, the lower ratio of O2/forming gas (FG) exhibits the different impacts between N-MOS and P-MOS implant condition. C) Less OA time brings to better performance for residue removal. D) Continuous offset spacer CD shrink is noticed in each step of lightly doped drain (LDD) loop. The optimized strip scheme delivers not only a residue-free process with the minimum substrate loss but also the improved device performance on both N-MOS and P-MOS.