Characterization
and Control of Galvanic Corrosion During GaAs Wafer Photoresist Processing
J. Moore, H.
Hendriks*, and A. Morales*
General Chemical -
Electronic Materials,
*M/A-COM: Tyco,
Keywords: galvanic
corrosion, noble metal, photoresist stripper, gallium arsenide (GaAs), and metal
lift-off
Abstract:
The occurrence of galvanic
corrosion on compound semiconductor substrates with exposed metal has been
observed as deleterious device effects.1-7 Noble metals, e.g. gold, platinum,
etc., in contact with exposed GaAs can induce undesired galvanic etching during
wet process steps and result in surface irregularities that adversely affect
yield. This phenomenon can occur when stripping photoresist using an aggressive
wet chemistry. Rinsing steps that use de-ionized (DI) water can make matters
worse.1-3,5-7 Control and minimization of compound semiconductor and metal
corrosion has received much attention in wafer fabrication. Some facilities
have used electrical measurements or SEM (scanning electron microscopy)
observations to characterize and alleviate corrosion issues. For photoresist
mask strip steps, some facilities avoid problems by choosing a corrosion-safe
chemistry, which may not necessarily provide optimum performance.
Unfortunately, challenges in removing tenacious organic residues exist,
especially from deep ultraviolet (DUV) and hard-baked exposures. Although
residue removal typically involves more aggressive chemistries, substrate
protection and cleaning efficacy can be achieved. Using novel chemistry
formulations and process techniques, galvanic corrosion can be controlled. This
paper characterizes GaAs based corrosion near ohmic and gate metal layer
features and shows how it varies with the choice of chemistry and the addition
of water due to absorption or rinsing.