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Handbook of Silicon Based MEMS Materials and Technologies by Teruaki Motooka, Ari Lehto, Markku Tilli, Veikko Lindroos

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22.2.2. Resist Application

22.2.2.1. Spin Coating

Spin coating dominates standard resist applications, but spray coating has advantages in coating highly 3D profiles. Wet etched 54.7° angles can be better coated by spray; but, usually, resist thickness uniformity with spray is inferior to spin coating. In spin coating optimized processes can have 0.1% uniformity for thin resists planar wafers, and a few percent can be achieved for tens of micrometers thick resists.

Photoresists are typically comprised of three major components (PMMA is an exceptional one-component resist):

  • base resin, e.g., novolak, bisazide, or epoxy
  • photoactive compound, e.g., DNQ (diazonaphtoquinone) or hexafluoroantimonite salts
  • solvent, e.g., MEK (methyl-ethyl ketone), ...

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