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YAG Laser Removal of Debris Lying on Excimer-Etched Polyimide Surfaces

IP.com Disclosure Number: IPCOM000105706D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 44K

Publishing Venue

IBM

Related People

Dreyfus, RW: AUTHOR [+3]

Abstract

Excimer UV laser drilling of via holes in polyimide (Thermid) leaves a surface coating of carbonaceous particles, i.e., debris, around the hole. This debris must be removed because it interferes with further processing. Ashing is often used, but has several disadvantages, among them: cracking of the polyimide, slowness as ashing is optimum for removing small thickness of contamination, and ashing requires large, expensive etching tools.

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YAG Laser Removal of Debris Lying on Excimer-Etched Polyimide Surfaces

      Excimer UV laser drilling of via holes in polyimide (Thermid)
leaves a surface coating of carbonaceous particles, i.e., debris,
around the hole.  This debris must be removed because it interferes
with further processing.  Ashing is often used, but has several
disadvantages, among them: cracking of the polyimide, slowness as
ashing is optimum for removing small thickness of contamination, and
ashing requires large, expensive etching tools.

      The present disclosure involves using a second specialized
laser to remove the bulk of the debris without damaging the
polyimide.  It is herein proposed to use a longer ( > UV wavelength)
to remove the debris without interacting with the polyimide, as the
latter is transparent at longer wavelengths.  Specifically, it is
suggested that a YAG (Nd) laser at 1.06&mu.m will remove the debris
from a contaminated polyimide surface.  Polyimide is known to be
transparent at 1.06&mu.m, and hence is not normally affected at power
levels which remove debris.  The specific means of interaction of the
YAG laser with particulates is that it raises their temperature into
the thousands of degree range, as the particulates do not have good
thermal conductivity into the bulk polyimide due to limited surface
contact area, besides their higher optical absorption [1].  The range
in YAG laser fluence which will remove debris from polyimide is 0.3
to 0.6 J/cm [2] us...