Laser Produced Plasma (LPP) EUV source technology has advanced towards the specifications needed for actual chip production.
Diffractive optical elements improve imaging by optimizing the illumination for critical mask patterns without excessive loss of light.
In the last edition of this column [1], I began the difficult process of trying to understand the fundamental mechanisms behind the formation of line edge roughness (LER). The approach I’ve taken is called stochastic modeling, and involves the use of random variables and probability density functions to describe the statistical fluctuations that are expected. We began with photon shot noise, which follows Poisson statistics, then looked at the initial distribution of photoacid generator (PAG) in the resist, which also follows Poisson statistics. The exposure reaction itself is probabilistic, with the probability that any particular PAG will be exposed given by the solution to the continuum kinetic equation of exposure. The results so far are summarized in the following table:
