Chapter 9 - ETCHING AND THE FORMATION OF ETCH PITS

Abstract

This chapter provides an overview of etching and the formation of etch pits. As both Ge and Si crystals are fairly inert to the attack of nonoxidizing chemicals, an etching solution to be effective should contain an oxidizing agent together with a complexing agent or solvent for the oxide formed. To be effective, these active agents must be adsorbed on the surface and react chemically with it and, in addition, the products of the reaction must be desorbed and move away from the surface for the reaction to continue at a reasonable rate. A wide variety of etchants has been developed, primarily from an empirical approach, that have these qualities in varying degrees. Nitric acid and hydrogen peroxide are among the more commonly used oxidizing agents, while an anion such as F− or the hydroxyl ion (OH−) are generally used to form water-soluble complexes with the semiconductor. Either water or acetic acid is added as moderating agents, and, in their role of diluents, they are able to provide some control over the reaction rate of the etchant.