Chemical Etching - Chemical Etching of Silicon 1 IV....

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Chemical Etching of Silicon 1 IV. Etching Technology B. Schwartz* Bell Laboratories, Murray Hill, New Jersey 07974 and H. Robbins* Galamar Industries, Palo Alto, California 94304 ABSTRACT The etching of silicon in HNO3-HF based systems proceeds by a sequen- tial oxidation-followed-by-dissolution process. In those composition regions where the solution is very low in HNO3 and rich in HF, the rate-limiting process is the oxidation step. Consequently, electron concentration, surface orientation, crystal defects, and catalysis by lower oxides of nitrogen play an important role. In those compositions where HF is in limited supply, dis- solution of the formed oxide is the rate-controlling step and diffusion of the complexing fluoride species is the important factor. Therefore, crystal ori- entation and conductivity type independence as well as hydrodynamic control are the consequences. In order to meaningfully select an etching composition to solve a specific processing problem, it is necessary to understand this com- position-mechanism interaction. Corollary with the mechanism understanding, sample geometry effects have been followed as a function of solution com- position. The HF-HNO3-H20 solution composition plane has been characterized into various regions where the two basic mechanisms interact and specific procesing utilization is shown. Similar results are shown for the system HF- HNO3-HC2HsO2. In addition, a number of particular etching problems are posed, and solutions offered, that make use of these composition characteriza- tions, and show how one can use their information to solve other practical processing problems. Most of the data on silicon etching that one can find in the literature involve studies of the mechanisms and kinetics of the dissolution process (1-4). There are a few examples of practical applications, but they deal primarily with crystallographic aspects of the etching, e.g., defect delineation (5) or anisotropic crystal plane etching (6). Because of the sophistication of present-day silicon technology, it appears to be desirable to be able to control the geometrical aspects of a silicon slice, e.g., from sharp, possibly peaked corners and edges to smooth and rounded edges and corners, merely by controlling the chemical etching environments. It would, therefore, seem appropriate to present some data on the geometrical effects ob- served on the etching of silicon rectangular parallel- epipeds in solutions of HNOs, HF, and HeO with and without HC2H302. These observations were made at the same time as the previously published kinetics data were being obtained (1,2), but it is only recently that many requests for geometric information have made us aware of the usefulness of disseminating these configurational data. In order to make the picture more complete, some of the original iso-etch-rate figures will also be in- cluded, for comparison purposes.
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This note was uploaded on 09/17/2009 for the course EEL 5225 taught by Professor Arnold during the Fall '08 term at University of Florida.

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Chemical Etching - Chemical Etching of Silicon 1 IV....

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