Electrolytic Shaping of Germanium 

 , and Silicon 



^ By A. UHLIR, JR. 



i (Manuscript received November 9, 1955) 



Properties of electrolyte-semiconductor barriers are described, with em- 

 phasis on germanium. The use of these barriers in localizing electrolytic 

 ! etching is discussed. Other localization techniques are mentioned. Electro- 

 lytes for etching germanium and silicon are given. 



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INTRODUCTION 



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I 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 

 j material. Such damaged material may be removed by electrolytic etch- 

 ing. Alternatively, all of the shaping may be done electrolytically, so 

 that no damaged material is produced. Electrolytic shaping is particu- 

 [ larly well suited to making devices with small dimensions. 

 I A discussion of electrolytic etching can conveniently be divided into 

 [■ two topics — the choice of electrolyte and the method of localizing the 

 ji etching action to produce a desired shape. It is usually possible to find 

 1 an electrolyte in which the rate at which material is removed is accurately 

 proportional to the current. For semiconductors, just as for metals, the 

 I choice of electrolyte is a specific problem for each material ; satisfactory 

 j electrolytes for germanium and silicon will be described. 



The principles of localization are the same, whatever the electrolyte 



used. Electrolytic etching takes place where current flows from the 



semiconductor to the electrolyte. Current flow may be concentrated at 



I certain areas of the semiconductor-electrolyte interface by controlling 



the flow of current in the electrolyte or in the semiconductor. 



LOCALIZATION IN ELECTROLYTE 



Localization techniques involving the electrolytic current are appli- 

 cable to both metals and semiconductors. In some of these techniques, 



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