Mechanism for QBD failure in poly gates

Judith B. Barker; Robert Wu; Richard G. Cosway; Julie Stephens; Rich Cote

doi:10.1117/12.324333

3 September 1998 Mechanism for QBD failure in poly gates

Judith B. Barker, Robert Wu, Richard G. Cosway, Julie Stephens, Rich Cote

Proceedings Volume 3507, Process, Equipment, and Materials Control in Integrated Circuit Manufacturing IV; (1998) https://doi.org/10.1117/12.324333
Event: Microelectronic Manufacturing, 1998, Santa Clara, CA, United States

Abstract

One of the most widespread uses of polysilicon in MOS devices is as the gate electrode for transistors. The gates described here are processed via a two stage poly deposition. The first stage is a thin gate poly deposition used as an implant screen for threshold adjust implants followed by a thick gate poly deposition. Soon after on- product measurement was introduce at a thin gate polysilicon deposition, QBD failures became the most frequent failure mode. A cross-functional team discovered the wafers failing for QBD were used as on-product measurement wafers at polysilicon deposition. Process mapping revealed the wafer failures for QBD were always loaded directly next to poly dummy wafers during deposition. TEM of nucleation sites disclosed there is a competing reaction between the poly dummy wafer directly above the product wafer and the product wafer. The silane prefers to react on the dummy wafer, leading to less area coverage on the product wafers, which leads to rougher, larger grains. The preclean process for the thick gate poly deposition uses a HF dip. It was proposed that HF was penetrating more easily into the rougher poly grains during the HF dip, damaging the gate oxide, and subsequently causing shorts.

Citation Download Citation

Judith B. Barker, Robert Wu, Richard G. Cosway, Julie Stephens, and Rich Cote "Mechanism for QBD failure in poly gates", Proc. SPIE 3507, Process, Equipment, and Materials Control in Integrated Circuit Manufacturing IV, (3 September 1998); https://doi.org/10.1117/12.324333

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