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Neutral Periodate Etchant for Tungsten

IP.com Disclosure Number: IPCOM000073676D
Original Publication Date: 1971-Jan-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Prabhu, RS: AUTHOR

Abstract

Metallic tungsten is highly resistant to many etching solutions. The well known etchants for tungsten are (1) strongly alkaline potassium ferricyanide solution and (2) strongly acidic mixture of hydrofluoric and nitric acids. The photoresists used in semiconductor processing are not resistant to these strongly acidic and alkaline mediums.

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Neutral Periodate Etchant for Tungsten

Metallic tungsten is highly resistant to many etching solutions. The well known etchants for tungsten are (1) strongly alkaline potassium ferricyanide solution and (2) strongly acidic mixture of hydrofluoric and nitric acids. The photoresists used in semiconductor processing are not resistant to these strongly acidic and alkaline mediums.

The neutral periodate solution etches tungsten at a reasonably fast rate, and yet is very safe for any photoresist.

A typical solution may contain:

100 ml water (deionized)

11.5 g lithium periodate

1.0 g sulfuric acid (96%). to this solution add sufficient lithium hydroxide to bring the pH to 7.

This solution etches both tungsten and molybdenum, at a rate of 1500 angstroms/min at 40 degrees C. The etch rate is maximum between pH = 6 to 7 and increases with increase in temperature. The concentration and temperature can be varied to change the rate of etching. Sodium or potassium salts can be used instead of lithium salts. The periodate etchant can be used to etch other refractory metals such as Ta, Nb, V and Cr.

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