Browse Prior Art Database

Clear Kerf Region for Mlm Stud Lift-Off

IP.com Disclosure Number: IPCOM000040268D
Original Publication Date: 1987-Oct-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Lurowist, J: AUTHOR

Abstract

This method eliminates damage caused during lift-off (L/O) of the stencil structure used to form studs on semiconductor devices. A redesign of the mask provides a clear kerf around chips, avoiding L/O structure removal in one piece with attendant problems. A previous processing sequence stud L/O step involved a one-piece lift-off stencil. Unwanted metal and photoresist (PR) came off in one large circular disc-shaped piece. This could crumple and be trapped between wafers. Abrasion damage to the studs on the wafer surface resulted in losses and a reduction in product reliability. Even when the stencil is not trapped, its mass can result in stud damage and metal land damage as it moves.

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Clear Kerf Region for Mlm Stud Lift-Off

This method eliminates damage caused during lift-off (L/O) of the stencil structure used to form studs on semiconductor devices. A redesign of the mask provides a clear kerf around chips, avoiding L/O structure removal in one piece with attendant problems. A previous processing sequence stud L/O step involved a one-piece lift-off stencil. Unwanted metal and photoresist (PR) came off in one large circular disc-shaped piece. This could crumple and be trapped between wafers. Abrasion damage to the studs on the wafer surface resulted in losses and a reduction in product reliability. Even when the stencil is not trapped, its mass can result in stud damage and metal land damage as it moves. In the initial design of the L/O structure there was a blanket layer of PR broken only by the holes through which the evaporated metal deposited onto the underlying wafer surface to form the desired studs. After metal deposition, these small openings and the periphery of the wafer were the only points of entry for the softening attack of the PR by the L/O solvent. In this method, a clear ring is located around each chip. This provides more places over the wafer surface for the solvent to attack the PR. This results in breaking the L/O stencil into chip size pieces vs. a circular piece that may be 5 inches in diameter. This new method shortens L/O time and allows smaller discrete chip-size pieces to be loosened and safely floated away from the...