Semiconductor Principle Animation:Chip Lithography and Etch Lab

At 2000 rpm a 20 µm puddle is flung down to about 5 µm in the first second; after that solvent evaporation takes over and the film sets in about twenty seconds. EUV resist is only 35 nm thick, DUV resist 90 nm.

The finer the pitch, the less diffracted light the lens can collect and the blurrier the image. R = k1·λ/NA: going from 193 nm to 13.5 nm turns a 36 nm pitch from a uniform blur into crisp light and dark lines.

More dose widens the exposed spaces and thins the lines; too little and the spaces never clear. The dose range that keeps the linewidth within ±10% is the process window. The rough line edges in the SEM image come from random photon counts.

A bias on the wafer drives ions almost straight down, so the trench walls stay vertical. The resist is consumed too, at a 4:1 selectivity; narrow trenches etch slower, and the last seconds of over-etch let them reach the bottom.

Near 20 nm, electrons scatter off surfaces and grain boundaries and copper’s resistivity doubles; the barrier takes another slice of the cross-section, so resistance rises faster than the area shrinks. That is why advanced nodes are trying metals such as ruthenium and molybdenum.