Probing surface and bulk chemistry in resist films using near edge X-ray absorption fine structure

The performance of chemically amplified photoresists is extremely sensitive to interfacial and surface phenomena, which cause deviations in the pattern profile near an interface. Striking examples include T-topping or closure near the air/resist interface and footing or undercutting near the resist/substrate interface. One focus of our research is to identify mechanisms that cause lithographic patterns to deviate near interfaces. Near edge x-ray absorption fine structure (NEXAFS) is a powerful tool that can be developed and adapted to probe for detailed chemical information near lithographically relevant interfaces. NEXAFS showed that our model resist films exhibited significant surface segregation of the photo acid generator (PAG) at the air interface. The PAG surface mole fraction was 20-70 times greater than the bulk mole fraction and the amount of surface segregation was dependent on the polarity of the polymer. NEXAFS also revealed that the PAG surface fraction was reduced after a postexposure bake. In the absence of delay times between processing steps, the PAG surface enhancement led to a faster deprotection reaction rate near the air, interface relative to the bulk. However, when significant postexposure delay times were incorporated into the processing, NEXAFS showed that the surface deprotection reaction was incomplete after postexposure baking. Comparison of carbon K-edge, and oxygen K-edge NEXAFS spectra showed that the incomplete surface reaction was localized at the air interface. While delay effects have previously been linked to deterioration of resist performance, NEXAFS proved to be a valuable tool for providing detailed chemical specificity about the resist surface composition and deprotection kinetics. (C) 2002 American Vacuum Society.