The authors have developed an atomic-force-microscopy-based technique to measure intrinsic material roughness after base development. This method involves performing an interrupted development of the resist film and measuring the resulting film roughness after a certain fixed film loss. Employing this technique, the authors previously established that the photoacid generator ͑PAG͒ is a major material contributor of film roughness and that PAG segregation in the resist is likely responsible for nanoscale dissolution inhomogeneities. The additional roughness imparted on a test polymer by incorporation of a series of iodonium, sulfonium, diazo, and imido PAGs was measured. The roughness was then correlated to the inhibition properties of the various PAGs. This was accomplished both through a NMR technique that measures interaction of the PAG with the polymer and by evaluating the dissolution inhibition properties of the PAG through a percolation model. Several PAGs that result in significantly lower material roughness and thus the potential for significantly reduced linewidth roughness in resist imaging have been identified.
We have developed an improved AFM-based technique to measure intrinsic material roughness (IMR) after base development. We have investigated the contribution of different polymeric PAGs to IMR. These polymeric PAGs include copolymers of several styrenic PAGs with hydroxystyrene. The IMR of these polymer-bound PAGs is reduced relative to that of their nonpolymeric counterparts with DUV exposure. Theses results represent further evidence for PAG segregation during the bake steps as being responsible for increased IMR in exposed resists, presumably by increasing the dissolution rate inhomogeneity on a nano-scale level. The work also shows that the effects of PAG segregation can be mitigated by employing polymer-bound PAGs.
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