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Multiple Metal Film Structures for Wiring VLSI Circuit Chips

IP.com Disclosure Number: IPCOM000100756D
Original Publication Date: 1990-Jun-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 2 page(s) / 65K

Publishing Venue

IBM

Related People

Chang, HC: AUTHOR [+4]

Abstract

The topography of VLSI chips includes steps with nearly vertical slopes. Covering such sharp steps with thin metal films is a well- known problem in semiconductor fabrication processes. The established procedure today is to evaporate aluminum (or Al-copper alloys) and to build up film thickness that exceed the step height by typically 50%. The resulting metal films have reduced cross sections at the step, but they are still continuous.

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Multiple Metal Film Structures for Wiring VLSI Circuit Chips

       The topography of VLSI chips includes steps with nearly
vertical slopes.  Covering such sharp steps with thin metal films is
a well- known problem in semiconductor fabrication processes.  The
established procedure today is to evaporate aluminum (or Al-copper
alloys) and to build up film thickness that exceed the step height by
typically 50%.  The resulting metal films have reduced cross sections
at the step, but they are still continuous.

      An additional problem arises if the silicon wafer temperature
during the aluminum evaporation is below 150oC. Given a vacuum of
about 10-6 Torr, which is typical for evaporation processes, the
already reduced cross section at the step is further reduced by a
thin film of aluminum oxide referred to as a "seam".  A schematic
cross section of such a situation is shown in Fig. 1.  These seams
form during the growth of the upper Al films because their lateral
surfaces over the steps are exposed to residual gas molecules -
mostly water vapor - arriving at rates comparable to the impingement
rate of Al atoms.  The aluminum reacts with the residual gases to
form a separate phase of Al2O3 .

      The Al2O3 at the seam does not form a continuous film, but
allows current to flow between the upper and lower parts of the Al
films.  However, the cohesion at the phase boundary between the oxide
film and the lower Al film is apparently weak.  During thermal
cy...