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Metal Liftoff Process for CMOS Integrated Circuits

IP.com Disclosure Number: IPCOM000103364D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 1 page(s) / 41K

Publishing Venue

IBM

Related People

Gut, GM: AUTHOR [+2]

Abstract

A metal liftoff process requires the formation of a photoresist profile on a semiconductor wafer which is wider on the top than on the bottom. Evaporation of metal from a point source results in a normal incidence of metal particles on the wafers and the liftoff image. The undercut profile of the resist permits a discontinuity to form in the metal at the resist edges. A solvent strip of the resist then removes the resist and the unwanted metal. The process leaves metal lines where the resist was originally developed out.

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Metal Liftoff Process for CMOS Integrated Circuits

      A metal liftoff process requires the formation of a photoresist
profile on a semiconductor wafer which is wider on the top than on
the bottom.  Evaporation of metal from a point source results in a
normal incidence of metal particles on the wafers and the liftoff
image.  The undercut profile of the resist permits a discontinuity to
form in the metal at the resist edges.  A solvent strip of the resist
then removes the resist and the unwanted metal.  The process leaves
metal lines where the resist was originally developed out.

      The liftoff profile formation process, which is the subject of
this disclosure, uses a commercially available photoresist, AZ 5214
photoresist.  This resist exhibits the property of tone reversal when
it is baked and subjected to blanket exposure after initial pattern
exposure.

      The process is performed as follows:
   1.  Spin coat a layer of AZ 5214 photoresist on the semiconductor
wafer to a thickness greater than the evaporated metal thickness.
Prebake at 95 Celsius for 60 seconds.
   2.  Expose a negative tone image of the desired metal lines using
photo-lithography equipment.
   3.  Bake the wafers after exposure at 125 Celsius on a hotplate
for 40 seconds.
   4.  Blanket expose the wafers on a flood expose tool to render the
previously unexposed resist soluble in developer.
   5.  Develop in sodium metal silicate solution to achieve the
desired un...