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Subtractive Etching of Metals

IP.com Disclosure Number: IPCOM000090172D
Original Publication Date: 1969-Feb-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Collins, RH: AUTHOR [+5]

Abstract

Conventional subtractive etching of Al or other metals, used as conductor stripes for semiconductor contacts, is not completely satisfactory. Local galvanic couple effects on the metal lead to irregular bubble formation with consequent uneven etching. Bridging between the lands is the result. Prolongation of the etching to remove bridging between the lands unfortunately produces either undercuts or open lands or both. Etching at lower temperatures does not solve the problem, although the size of the bubbles is reduced.

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Subtractive Etching of Metals

Conventional subtractive etching of Al or other metals, used as conductor stripes for semiconductor contacts, is not completely satisfactory. Local galvanic couple effects on the metal lead to irregular bubble formation with consequent uneven etching. Bridging between the lands is the result. Prolongation of the etching to remove bridging between the lands unfortunately produces either undercuts or open lands or both. Etching at lower temperatures does not solve the problem, although the size of the bubbles is reduced.

Local coupling effects can be eliminated by introducing a more noble metal,
i.e., a metal more electropositive, into the system. For instance, a suitable electrode can be dipped into the solution with or without an applied potential. In another system, a 4 x 4 memory, sub etch photoresist pattern is put on an aluminized oxide wafer. A spiral of gold wire is held in tight contact to the back of the wafer. On immersion in phosphoric acid/nitric acid etching solution at 70 degrees C, hydrogen bubbles form only on the gold. No bridging or opens are visible at the end. Without the gold, the mentioned defects appear. A variant is plating the gold on the back of the wafer by evaporation or other methods The results here are also good. A third method is introduction of ions of the more electropositive metal into the etching solution via soluble salts. The speed of etching increases by one order of magnitude.

Al, Mo, Ag, and Cr...