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Browse Prior Art Database

Selective Etchant for N Type Silicon

IP.com Disclosure Number: IPCOM000074097D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Pugacz-Muraszkiewicz, IJ: AUTHOR

Abstract

The use of an aqueous metal hydroxide solution, such as sodium or potassium hydroxide, as an etchant for silicon at elevated temperatures is known. While such an etchant etches n-type silicon preferentially at room temperature at very low rates, it loses the selective etching property at temperatures and concentrations sufficiently high to give practical etching rates.

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Selective Etchant for N Type Silicon

The use of an aqueous metal hydroxide solution, such as sodium or potassium hydroxide, as an etchant for silicon at elevated temperatures is known. While such an etchant etches n-type silicon preferentially at room temperature at very low rates, it loses the selective etching property at temperatures and concentrations sufficiently high to give practical etching rates.

Selective etching may be attained with practical etching rates if an alkali metal halide salt is added to the alkali metal hydroxide etchant. Such a selective etchant preferably consists of an aqueous solution of 15 to 25 weight per cent each of the alkali metal hydroxide and the alkali metal halide salt. Any of the alkali metal hydroxides, such as lithium hydroxide, sodium hydroxide, or potassium hydroxide, may be used with any of the alkali metal halide salts, such as lithium fluoride, sodium chloride, potassium bromide, or sodium iodide. Best results are obtained by using the same alkali metal in both the hydroxide and the halogen salt. Such a solution etches n-type silicon at a rate three orders of magnitude greater than p-type silicon.

The selective etchant may be used for quality control inspection of integrated circuit devices for extraneous diffusions produced as a result of defects in masking layers or to check the depth and shape of desired diffusions. For example, extraneous p-type diffusions or a p-type isolation diffusion in n-type silicon can be sh...