Sidewall Passivation Mechanism of CF4 Added Polysilicon Gate Etch Process

http://www.ece.ogi.edu/passsschedule

The introduction of fluorine via CF4 to a typical HBr/Cl2/O2 polysilicon etch process suppresses the formation of SiOxBry or SiOxCly via formation of volatile SiF4.

O2を加えたプラズマにさらにCF4を添加してSiOxBry or SiOxCly層の形成を防ぐ→何のためか？
O. Joubert Microelectronic Engineering 69 (2003) 350もおそらく同様のテーマ

Joubert らのNotched gate process はラジカルによるoveretchを利用（基板温度のコントロールはあるのか？）

In this work, the notch generated is not an ion-induced asymmetric notch [4], but on the other hand, a well controlled symmetric notch. The notch is designed thanks to the absence of passivation layer at the bottom of the gate allowing the radicals of the plasma to induce a lateral etch rate.

J. Foucher, G. Cunge, L. Vallier, O. Joubert, Microelectronic Engineering 61.62 (2002) 849-857

1996, Bell et al.

Ions and neutrals may be adsorbed on the sidewalls of the features and form a passivation layer which can slow down or completely stop the lateral etching [5-8,11].

（酸素に限っていない）

Guinn and co-workers [26,27] have recently shown in the important case of polysilicon trench etching that the addition of oxygen to a Cl2 discharge leads to a SiOxCly layer on the sidewalls of the photoresist.

26: V. Guinn and V. M. Donnelly, J. Appl. Phys. 75, 2227 (1994)
27: V. Guinn, C. C. Cheng, and V. M. Donnelly, J. Vac. Sci. Technol. B 13, 214 (1995).