The use of sulfuric acid to strip photoresist from silicon wafers is a
widely employed technique in the semiconductor manufacturing community. In
most cases, the acid is combined with hydrogen peroxide to oxidize stripped
photoresist material, though the use of sparged ozone in sulfuric solution
is also used to remove resist residues on wafers following the ashing
process. Although they have been used for many years, sulfuric acid
processes also have proven to be costly. This is due to the need for
frequent bath change-outs and the use of high temperature which impose
safety and environmental concerns. As a result of these and other
considerations, the use of mixtures of ozone and de-ionized water for
photoresist stripping has been investigated. Results show that the technique
effectively removes hard-baked resist (ashed and un-ashed) from bare silicon
and patterned wafers and produces cleaner surfaces (i.e. particles and
metals), compared to outcomes from SPM processes.
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