Defect analysis in 157-nm photolithography process

Reducing defects in the semiconductor photolithography process has become increasingly critical. Many kinds of defects can occur during photolithography, such as missing contact holes or pattern collapses that occur during developing. As the pattern size becomes finer, the exposure wavelength has been shortened from 248-nm to 193-nm, and then to 157-nm. In addition, the resin structure and the chemical characteristics of the resist material have changed greatly. Changing the resist material from I-line to 248-nm created the problem of satellite defects peculiar to chemically amplified resist. Previous studies have suggested that a satellite defect is a complex salt of PAG, quencher, and TMAH, and is soluble in water.1) Because the resist material for 157-nm lithography is highly hydrophobic and is used for making ultra-thin films, defect evaluations of it are necessary. This paper evaluates the defects arising with various kinds of 157-nm lithography resist. Just as with 248-nm resist, a deposition defect peculiar to CAR occurs with 157-nm resist, but it occurs more frequently than with 248-nm resist. Unique defects appear with 157-nm resist, but their appearance and frequency seem to depend on the resist structure. The number of missing contact holes increases when the contact angle to ultra-pure water on the 157-nm resist film raise. It is necessary to elucidate on the mechanism that the unique defect occur in 157-nm resist.