Characterization of photoacid generation in chemically amplified photoresists usingpH-sensitive fluorescence imaging

Chemically amplified resists (CARs) are widely used throughout the semiconductor industry due to the necessity for high throughput in the lithography process. In this class of resists image transfer is achieved by generation of catalyst concentration gradients. The catalyst is typically a strong acid which is generated by the photolytic decomposition of a photoacid generator compound (PAG) during exposure to the lithographic radiation. The photoacid is activated by a postexposure bake (PEB) to locally diffuse and catalytically generate reactions in the resist matrix. The purpose of these reactions (linking reactions in a negative-tone resist or deprotection reactions in a positive-tone resist) is to alter the solubility of the resist in response to the subsequent development step. The creation of the differential dissolution rate between the exposed and unexposed resist areas is the fundamental step required for patterning the resist. The chemical amplification occurs during PEB with the multiple recycling of the photoacid to promote many chemical reactions.; This dissertation describes novel, quantitative, non-destructive techniques for characterizing acid generation in CARs, specifically measurements of the efficiency or quantum yield of PAGs and imaging of latent microlithographic features. The techniques involve doping the resists with fluorescent molecules whose spectroscopic properties are functions of the local acid concentration. Spectroscopic imaging of the exposed resist films therefore provides a means to spatially map the quantity and distribution of photoacid on wafer. An understanding of acid generation is of paramount importance for resist design and the process control of the image formation of almost all the lithographic techniques used in the semiconductor industry today, as well as those expected for the long-term future. Hence, industrial relevance is in fact a significant goal for the research described herein.