A study on the material design for the reduction of LWR
2007
It is generally believed that the chemically amplified reaction between photo-generated acid catalyst and acid labile
group of polymer during post-exposure bake (PEB) process plays a critical role for the reduction of line width roughness
(LWR) in ArF lithography. In this work, we revealed experimentally how large the chemically amplified reaction affects
LWR, and developed a new resist system with low LWR. Aerial image contrast dependence on LWR revealed that the
innate LWR in a conventional ArF photoresist, which is independent of the aerial image contrast, was 5 nm. Surface
roughness of a non-patterned resist film at half-exposed area, which was well correlated with LWR, was measured by
AFM. The surface roughness increased from 1.7 nm to 10.8 nm during PEB process. The half-exposed area was baked
and again dissolved into organic solution, and spin-coated on Si wafer, and then developed with 2.38 % TMAH solution.
The recoated half-exposed resist film caused a 60 % reduction on the surface roughness. It revealed that uniform
distribution of deblocked polymer was important factor for roughness reduction. HPLC analysis indicated that
distribution of acidic group formulation in the polymer was gradually extended with increasing exposure dose. A Resist
system that suppresses the chemically amplified reaction successfully reduced LWR from 6.5 nm to 4.8 nm.
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