Plasma Etch Mechanisms

Plasma etching is a complex process involving several elementary processes or mechanisms. Some of these processes are illustrated on slide 1:
- chemical etching
- ion induced or enhanced etching
- physical etching / ion bombardment
- trenching
- sidewall passivation
- mask erosion

Anisotropic plasma etching has two major components (slide 2), chemical etching (neutrals and radicals of the plasma) and physical bombardment (ion assisted etching reactions). VLSI plasma etch processes are characterized by a varying significance of the chemical and physical components. Aluminum etching is a very chemical etch while SiO2 etching has a very strong physical component. Silicon etching has a strong chemical and physical components. To understand plasma etching mechanisms and improve processes, it is essential to describe these two components and the synergy existing between these two components.

The synergy between the chemical and physical components in plasma etching was first shown in an experiment by Coburn and Winters. In this classical experiment, the silicon etch rate increased by one order of magnitude when XeF2 was present at the surface and the argon ion beam was turned on (slide 3).

More plasma etch fundamentals …