Cleanrooms and equipment

In exposure areas using chemically amplified resists, why are basic molecular contaminants such as ammonia and amines controlled especially strictly?

  1. ABecause the resist changes color
  2. BBecause the exposure tool's lenses dissolve
  3. CBecause acid generated by exposure is neutralized, causing defects such as the top of the pattern overhanging like an eave (T-top)
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Answer: C. Because acid generated by exposure is neutralized, causing defects such as the top of the pattern overhanging like an eave (T-top)

In chemically amplified resists, a tiny amount of acid generated by exposure acts as a catalyst and changes solubility during the post-exposure bake (PEB). When basic substances in the air enter the resist surface, the acid is neutralized and the reaction fails to proceed near the surface, so the top of the pattern overhangs in a T-top shape. Chemical filters are therefore used on exposure tools and coater/developers.

  • A. Color change is not the problem.
  • B. The lenses do not dissolve.
  • C. Correct. Pattern defects from acid neutralization are the problem.
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