Ans

Remove Si surface particles, metal Ion, organic, micro-roughness and native
Oxide. 

Use 22220A, where SPM (CR) 1min to remove light organic, 100:1 HF 3min to remove any native oxide, and APM 7min to enhance particle remove and Si surface metal ion stripping capability, HPM 3min to remove heavy metal ions.

APM dip time concerns: 除去Si表面的缺陷, 使Si/SiO2的介面較好, remove particle. 半导体技术天地[Semiconductor Technology  : 造成Si表面的侵蝕, 增加表面的roughness, 影響GOI, 且影響表面雜質 濃 度而影響

long dip time is recommend for better megasonic particle removal capability, use of low concentration, or low temperature and improve the process window. too short : particle remain, resulting more abundant Vt adjust implant dosage remained in Si body and results to HNLP device Vt shift.