Study of 193nm photoresist degradation during short time fluorocarbon plasma exposures. II. Plasma parameter trends for photoresist degradation

<jats:p>The mechanisms of modified layer formation and the effect of surface condition on the roughness formation of 193nm photoresist (PR) materials during short time fluorocarbon plasma exposures were investigated. The authors employed a shutter approach to minimize the plasma transient effects on processing of PR surfaces. Photoresist etching behavior and surface roughness formation during the initial etch period depend strongly on ion energy, pressure, and stage temperature, and reflect the degree of surface fluorination for these process conditions. The authors found that a high etch rate for low fluorination conditions leads to rougher surfaces as compared to etching of highly fluorinated PRs. The comparison of x-ray photoelectron spectroscopy and atomic force and scanning electron microscopy data for PR materials processed using different plasma operating conditions showed that smooth surfaces resulted when during the initial period of plasma-polymer interaction the fluorine content of the PR surface was large relative to the oxygen content of the unexposed polymer. One interpretation of this observation is that a larger amount of fluorine on the PR surface relative to the bulk oxygen content of the PR material reduces the microscopic etch nonuniformity, e.g., due to selective etching of ester groups. The grain size distribution of PR roughness was determined through Fourier transformation of the atomic force microscopy data. The results indicate that a process dependent grain size distribution is introduced initially (approximately several seconds) and subsequently only grows in amplitude as the root mean square roughness increases. The authors interpret this observation as surface roughness being formed at the beginning of the etch process and that subsequently the height of the grains grows by the roughness transfer into the underlying polymer material.</jats:p>