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Improved Lift-Off Process for Fabricating Metal Studs (On Semiconductor Substrates)

IP.com Disclosure Number: IPCOM000037246D
Original Publication Date: 1989-Dec-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 3 page(s) / 99K

Publishing Venue

IBM

Related People

Greco, NA: AUTHOR [+2]

Abstract

An improvement in existing processes for lift-off of fine structures, such as metal studs, is described in this article. The disclosed procedure employs the inverted lift-off technique to lift off metal but avoids problems related to long ashing of the underlaying material by use of a second solvent to effect its removal.

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Improved Lift-Off Process for Fabricating Metal Studs (On Semiconductor Substrates)

An improvement in existing processes for lift-off of fine structures, such as metal studs, is described in this article. The disclosed procedure employs the inverted lift-off technique to lift off metal but avoids problems related to long ashing of the underlaying material by use of a second solvent to effect its removal.

Present lift-off techniques used in advanced transistor production to fabricate metal studs begin with a planarizing layer of resist spun down and hard baked to render it insoluble. A release layer (such as polysulfone) is then spun down and baked followed by an imaging layer of photoresist and another bake. After imaging and silylating the photoresist, transferring the image by oxygen RIE, and depositing the metal, lift-off is accomplished and the polysulfone dissolves releasing the metal. The hard baked (cross-linked) planarizing layer remains intact throughout the lift-off process, protecting the metal studs from being "ripped-off" from the substrate or otherwise damaged by the metal stencil as it is peeling off during lift-off. After lift-off, the underlayer must then be oxygen ashed away. It is this ashing procedure, i.e., the long ashing time required to remove the thick underlayer (3.8 microns) that has been found to contribute to "collars" seen around the metal images, as shown in Fig. 1.

(Image Omitted)

The disclosed procedure avoids the damaging long ash step by employing two soluble layers, i.e., a two-solvent procedure. Lift-off is accomplished by dissolving the thin release layer (polysulfone) in a first solvent. Then the remaining thick underlayer is removed by dissolving it in a second solvent. This requires, of course, that the underlayer be insoluble to the fi...