Electrolytic Shaping of Germanium and Silicon

Mechanical shaping techniques, such as abrasive cutting, leave the surface of a semiconductor in a damaged condition which adversely affects the electrical properties of p-n junctions in or near the damaged material. Such damaged material may ye removed by electrolytic etching. Alternatively, all of the shaping m a y be done electrolytically, so t h a t no damaged material is produced. Electrolytic shaping is particularly well suited to making devices with small"dimensions. A discussion of electrolytic etching can conveniently be divided into t w o topics -- the choice of electrolyte and the method of localizing the etching action to produce a desired shape. It is usually possible to find an electrolyte in which the rate at which material is removed is accurately proportional to the current. For semiconductors, just as for metals, the choice of electrolyte is a specific problem for each material; satisfactory electrolytes for germanium and silicon will be described. T h e principle** of localization arc the «amo, whatever the electrolyte used. Electrolytic etching takes place where current flows from the semiconductor to the electrolyte. C u r r e n t flow m a y l>e concentrated at certain areas of the semiconductor-electrolyte interface by controlling the flow of current in the electiolyte or in the semiconductor. LOCALIZATION IN E L E C T R O L Y T E