Use of Failure Modes and Effects Analysis (FMEA) Methodology in Evaluation of Process Transfer of Ohmic Liftoff from Low-Pressure-Solvent to High-Pressure-NMP Liftoff

J.W.Crites and S.W.Kittinger

Cobham DES, Roanoke, 5310 Valley Park Drive, Roanoke, VA 24019 Phone: (540) 563-8600, E-mail: james.crites@cobhamdes.com

KEYWORDS: FMEA, ohmic, metal, spray, liftoff
ABSTRACT

Liftoff metallization processes are widely used in the processing of GaAs and other III-V compound-semiconductor integrated circuits and FET products. The primary application is following electron-beam evaporation of an interconnect-metal film where the liftoff is usually accomplished by one or more solvent, tape, or high-pressure spray methods. This paper demonstrates the use of the Failure Modes and Effects Analysis (FMEA) method for assessing the requirements and risks associated with a process change. In this particular example, the original process method in use for comparison as the baseline was a low-pressure acetone liftoff of a multilayer ohmic contact film. Yield difficulties corresponding to incomplete liftoff had been experienced when using the baseline low-pressure method and the objective was to transfer the process to a high pressure spray tool so that thorough and efficient liftoff could be sustained.

The use of an FMEA approach wherein the modes of potential failure are carefully evaluated and subjected to experimentation and control was highly beneficial in organizing the improvement effort. Details of failure modes and solutions are presented.

 

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