Etch is a process that removes materials from a wafer surface to achieve the
requirements of IC design. There are two types of etch processes: pattern and
blanket. Pattern etch selectively removes materials from designated areas and
transfers the patterns of the photoresist or hard mask on the wafer surface to films
underneath. Blanket etch removes all or part of the film on the surface to achieve
the desired processing results. This chapter covers both etch processes, with an
emphasis on pattern etch. First in the MOSFET gate patterning process, a photolithography process with gate mask defines the photoresist pattern on the polysilicon film on the wafer surface. A pattern etch
process transfers the pattern of the photoresist to polysilicon film underneath.
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