1.0 INTRODUCTION

The goal of this chapter is to develop a fundamental understanding of the mechanisms by which the processes of chemical vapor deposition and dry etching proceed, with emphasis on the physics occurring at the length scale of the evolving feature. It is useful, at the very outset, to discuss the issue of scales and the need to divide the modeling section of this book into reactor scale and feature scale portions.

It can be safely asserted that most etch and deposition systems operate much below atmospheric pressure. At the same time, the size of the patterns that are being transferred on the wafer are getting smaller. This combination of low pressure and submicron features implies that gas phase transport, at the length scale of the trench being filled or the contact being etched, occurs in the free molecular flow regime. In other words, particles are traveling in straight line trajectories, and thus the continuum transport equations are no longer valid at that small length scale. On the other hand, depending primarily upon pressure, this may not be true at the length scale of the reactor itself, where the continuum equations might hold. Thus, there are two very disparate length scales in an etch or deposition system, and this leads to different descriptions of the physics occurring at the two scales.

If the reader is convinced that the physical phenomena that occur during deposition and etching proceed along two separate length scales, let us now address the...