Page 62 - Semiconductor Manufacturing Handbook

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Source: SEMICONDUCTOR MANUFACTURING HANDBOOK

CHAPTER 6

PLASMA PROCESS CONTROL

David J. Coumou
MKS Instruments, Inc.
Rochester, New York

6.1 INTRODUCTION

Plasma processing is an intricate and integral part of the manufacturing of semiconductor devices.
Plasma chambers are used in the manufacturing of semiconductor devices to etch or deposit thin
films of material on a substrate. For etch, the objective is to create a high-density plasma that gen-
erates ions that travel from the plasma discharge and strike a target to remove atoms of material. For
deposition, the process is similar to etch with the exception that the objective is to coat the target
with material. The control of the plasma process is analogous to other manufacturing processes and
respective control systems. It is a process where physics that is described by mathematics meets a
form of control methodology. In the case of high-density plasma chambers, the plant model is a con-
sortium of chemistry and physics. The pursuit of an optimal control scheme for this manufacturing
process faces endless and daunting degrees of challenge. As the size of features, often referred to as
critical dimensions or CD, decreases and the surface area of targets increases, a higher level of inte-
gration on semiconductor devices is produced. Increasing the process rate is highly advantageous
because the cost of semiconductor manufacturing is directly proportional to the time required for
fabrication. These are just some of the vexing issues that challenge the control of the manufacturing
process of this industry. It is paramount that the control methodology is repeatable and targeted man-
ufacturing yields are maintained.
This chapter serves to present the basis of plasma physics and a survey of control schemes and
metrology. The chapter will not focus on vacuum or flow control and chemistry. To meet this objec-
tive, this chapter presents a survey of a great body of work in these areas. For this reason, an
acknowledgment is warranted to a number of exceptional contributors to this field. The attempt at
the provision of precise references and direction to additional information has been a rigorous task.
It is hoped that none of the work of the great contributors to this field has been omitted.

6.2 FUNDAMENTALS OF PLASMA GENERATION
AND PROCESS CONTROL

In this section the development of a physical model of high-density plasma reactors is described.
The first model will be developed for an inductively coupled source. This is then followed by a
capacitive-coupled parallel plate. In each subsection, models, theories, and practices will be
explored.

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