EFFECT OF OVERCOATS IN CHEMICALLY AMPLIFIED RESISTS AGAINST WATER ANDORGANIC-BASES

We have evaluated poly-(acrylic acid) (PAA) and poly-(alpha-methyl-sty rene) (PMST) as overcoats used to stabilize the lithographic performan ce of chemically amplified resist during the delay (FED) between expos ure and post-exposure baking. We used water. aniline and NMP as model compounds of airborne contaminants. Both films are shown to improve th e stability of resist performance during FED. PMST is more effective i n preventing atmospheric water penetration than PAA, as evidenced by t he finding that che sensitivity of PAA-coated resist is dependent on t he relative humidity of ambient air. Conversely, the PAA-coated resist is more stable against high vapor concentration of aniline and NMP, w hen exposed for several hours. This is probably because the negative c harge of the carboxyl groups in PAA electrically traps aniline and NMP , preventing their penetration to the resist films.