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Nonstaining Silicon Nitride Etch

IP.com Disclosure Number: IPCOM000082395D
Original Publication Date: 1974-Nov-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Ormond, DW: AUTHOR

Abstract

Standard phosphoric acid etch solutions which are used to etch silicon-nitride films in metal-oxide semiconductor field-effect transistor (MOS-FET) processing, can contain metal impurities. These metal impurities form metal deposits on the bare silicon surface during the nitride etch step, by an electrochemical displacement plating reaction. As a direct consequence of the silicon staining, the subsequent devices that are formed on the contaminated silicon surface (MOS capacitors and FET's) exhibit poor electrical characteristics, i.e., poor minority carrier generation times and low-dielectric breakdown voltages.

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Nonstaining Silicon Nitride Etch

Standard phosphoric acid etch solutions which are used to etch silicon- nitride films in metal-oxide semiconductor field-effect transistor (MOS-FET) processing, can contain metal impurities. These metal impurities form metal deposits on the bare silicon surface during the nitride etch step, by an electrochemical displacement plating reaction. As a direct consequence of the silicon staining, the subsequent devices that are formed on the contaminated silicon surface (MOS capacitors and FET's) exhibit poor electrical characteristics,
i.e., poor minority carrier generation times and low-dielectric breakdown voltages.

The present method solves this metal contamination problem by formulating a chelating agent in the phosphoric acid etch solution, thus preventing metal ions from electrochemically plating out on the silicon.

The standard method for silicon nitride etching is to use concentrated phosphoric acid (85% by wt.) and deionized water in such proportions that the ensuing mixture boils at 180 Degrees C. Apparently the etch solution is a large reservoir for metal impurities, and it is these impurities which deposit on bare silicon surfaces by electrochemical displacement plating. Some of the more blatant contaminants have been shown to be antimony and copper.

The present method formulates the phosphoric etch solution in such a manner as to inhibit the silicon staining problem by the use of a chelating agent, such as hydrochloric acid. The hydrochloric acid, when added directly to the etch formulation, chemically reacts with any...