TABLE OF CONTENTS There are five important characteristics to consider in selecting any dry etch process. These are rate, feature profiles, compositional selectivity, damage and uniformity across the wafer. In general, the balance between chemical and physical contributions to the etching for each type of process will largely determine these characteristics. Chemical contributions generally produce rapid rates, compositional selectivity and lower damage. However, they also can decrease anisotropy (ratio of vertical to horizontal etch rates) and can even produce either isotropic etching or etch rates that depend on the relative reactivity of different crystallographic facets, as observed in wet etching. Physical sputtering contributions generally increase anisotropy, but they also damage the surface, degrading device performance that depends on near-surface crystal quality. Consequently, the simultaneous goals of an etch process that is both highly anisotropic and damage free are frequently in conflict and an acceptable compromise between the two will drive the process selection for GaAs device fabrication. In this chapter, the many practical issues that must be considered to successfully dry etch GaAs will be discussed.
It is possible to etch device structures using either liquid-phase "wet" etch processes or gas-phase "dry" processes. Both approaches have their own advantages and disadvantages and the best choice depends on the specifics of the application. (For advantages and disadvantages of dry etching, see side note in page 149.)
Wet etch processes, in general, produce better surface electronic properties than many dry etch processes because they don't...
