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Etching Silicon Nitride With Buffered Hydrofluoric Acid

IP.com Disclosure Number: IPCOM000078716D
Original Publication Date: 1973-Feb-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 41K

Publishing Venue

IBM

Related People

Bratter, RL: AUTHOR

Abstract

The present method provides a technique for etching silicon nitride which eliminates the need for hot etchants, such as hot hydrophosphoric acid or NH(4)H(2)PO(4).

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Etching Silicon Nitride With Buffered Hydrofluoric Acid

The present method provides a technique for etching silicon nitride which eliminates the need for hot etchants, such as hot hydrophosphoric acid or NH(4)H(2)PO(4).

Because of the relative inertness of silicon nitride film, it requires such hot etchants. While it was known that silicon nitride films were etchable by concentrated hydrofluoric acid (49%), this etchant had not been used because it appeared to attack the photoresist usually utilized for masks during etching.

The following procedure avoids the above problems by the utilization of buffered hydrofluoric acid as the etchant.

With reference to Fig. 1, silicon nitride film 10 covers substrate 11. Heavily doped phosphosilicate glass film 12 covers the silicon nitride film. Then, Fig. 2, a thin layer of pyrolytic silicon dioxide is deposited on the phosphosilicate glass. Then, utilizing standard photo-resist 13 and etchants for silicon dioxide and phosphosilicate glass, the pattern shown in Fig. 2 is formed. This is the negative of the pattern which is to be etched in the silicon nitride.

The wafer is then heated to a temperature of about 1200 degrees C. At this temperature, the following reaction takes place in the shaded area 14 beneath the silicon nitride in Fig. 3: 3Si(3)N(4) + 2P(2)O(5) 4SiP + 5SiO(2) + 6N(2).

The wafer is then dip etched in buffered hydrofluoric acid, during which the remaining silicon dioxide, phosphosilicate glass, and the conver...