Etching for Micromachining Processing

Kirt R. Williams and Richard S. Muller

Berkeley Sensor & Actuator Center 
University of California at Berkeley
497 Cory Hall
Berkeley, CA 94720-1770

Electronics Research Laboratory Memorandum No. UCB/ERL M96/37
29 July 1996


Abstract

The etch rates for 317 combinations of
16 materials 
(single-crystal silicon, doped and undoped polysilicon,
several types of silicon oxide, 
stoichiometric and silicon-rich silicon nitride,
aluminum, tungsten, titanium, Ti/W alloy, 
and two brands of positive photoresist)
used in the fabrication of microelectromechanical
systems and integrated circuits
in 28 wet, plasma, and plasmaless-gas-phase etches 
(several HF solutions, H3PO4, HNO3+H2O+NH4F,
KOH, Type A aluminum etchant, H2O+H2O2+HF, H2O2, piranha, acetone, 
HF vapor, XeF2, 
and various combinations of SF6, CF4, CHF3, 
Cl2, O2, N2, and He in plasmas)
were measured and are tabulated.
Etch preparation, use, 
and chemical reactions (from the technical literature) are given.
Sample preparation and MEMS applications 
are described for the materials.

Because etch rates vary with a number of conditions,
we also report in the tables the observed range of etch rates by
the authors and others in our laboratory.
To help explain this variation,
we discuss at the length the chemical and physical steps 
in wet and dry etching, leading up to discussions of 
15 sources of wet-etch-rate variation and 
14 sources of plasma-etch-rate variation.

Tips on determining when an etch is complete are given.



Contents

I. Introduction
II. Wet-Etch Processes and Etch-Rate Variation
	A. Overview of Wet Etches
	B. Wet-Etch Processes
        C. Wet-Etch-Rate Variation
III. Plasma-Etch Processes and Etch-Rate Variation
        A. Overview of Plasma Etches
        B. Plasma-Etch Processes
        C. Plasma-Etch-Rate Variation
IV. The Wet Etches
        A. Comparison of Wet and Plasma Etches
        B. Wet-Etch Chemicals
        C. Information about Individual Wet Etches
V. The Plasma and Plasmaless-Gas-Phase Etches
        A. Purposes of the Etch Gases
        B. Information about Individual Plasma and Plasmaless-Gas-Phase Etches
VI. Sample Preparation / MEMS Applications
VII. Etch-Rate Measurement Techniques
VIII. Etch-Rate Results
        A. Etch-Rate Tables
        B. Discussion of Etch-Rate Data
IX. End-of-Etch Detection
Acknowledgments
References


List of Figures

Figure 1: Chemical and Physical Steps in the Wet-Etch Process
Figure 2: Parallel-Plate Reactor--Physical and Chemical Steps in the Plasma-Etch Process
Figure 3: Chemical-Plasma versus Ion-Enhanced-Plasma Etching


List of Tables\fR

Table 1: User-Controllable Parameters in Wet-Etch-Rate Variation
Table 2: User-Controllable Parameters in Plasma-Etch-Rate Variation
Table 3: Wet-Etch Rates 
Table 4: Plasma- and Plasmaless-Gas-Phase-Etch Rates 
Etch Rates (version containing all data): at end of paper