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“The EUV resist challenges resists can be summed up succinctly,” Brainard said. “They are the three basic properties — resolution, line-edge roughness and sensitivity. My colleagues and I call it the RLS trade-off. You need all three properties for EUV [and EUV resists] to be successful, and when you improve one, you make another one worse.” According to Brainard, one can take a simple resist and measure its line-edge roughness (LER) and sensitivity, and then perhaps add more base to it. However, when this is done, the resist slows down. “These are chemically amplified resists, so the light generates acid. If you add more base, it kills the acid and then you require more light,” Brainard said. The result is, however, that by adding the base, LER is reduced, resulting in smoother lines. Conversely, if the base is reduced, the resist is more sensitive, but LER worsens.
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