Photoresist
Coating a light-sensitive film.
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At a glance
Inputs
- Wafer (often freshly deposited/oxidized)
- Liquid photoresist
- Adhesion promoter
Outputs
- Wafer with a uniform, light-sensitive resist film
What is it?
Applying a light-sensitive polymer (photoresist) to the wafer so that a pattern can be optically transferred in the lithography step.
Why is it needed?
Photoresist is the recording medium of chipmaking: it captures the mask pattern as a physical stencil that guides etching or implantation. Its resolution and sensitivity gate the whole patterning process.
How does it work?
Liquid resist is dispensed onto the wafer, which is spun at high speed to produce a thin, uniform film, then soft-baked to drive off solvent.
Positive resist becomes soluble where exposed to light; negative resist becomes insoluble. The choice determines whether exposed regions are removed or retained after development.
Critical parameters
- Resist thickness
- Uniformity
- Soft-bake temperature
- Adhesion
Typical defects
- Thickness variation
- Comets/striations from particles
- Poor adhesion / lifting
- Bubbles
Equipment involved
- Spin coater / track system
- Hot plates
Materials involved
- Photoresist polymer
- Solvents
- Adhesion promoter (e.g. HMDS)
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