Utilizing near edge X-ray absorption fine structure to probe interfacial issues in photolithography

Control of the shape, critical dimension (CD), and roughness is critical for the fabrication of sub 100 nm features, where the CD and roughness budget are approaching the molecular dimension of the resist polymers. Here we utilize near edge Xray absorption fine structure (NEXAFS) to provide detailed chemical insight into two interfacial problems facing sub 100 run patterning. First, chemically amplified photo-resists are sensitive to surface phenomenon, which causes deviations in the pattern profile near the interface. Striking examples include T-topping, closure, footing, and undercutting. NEXAFS was used to illustrate that the surface extent of deprotection in a model resist film can be different than the bulk deprotection. Second, line edge roughness becomes increasingly critical with shrinking patterns, and may be intimately related to the line edge deprotection profile. A NEXAFS technique to surface depth profile for compositional gradients is described with the potential to provide chemical information about the resist line edge.