Extrusion spin coating: an efficient and deterministic photoresist coating method in microlithography

Extrusion spin coating was developed to reduce photoresist waste and to improve coating uniformity in microlithography. This new method uses an efficient extrusion coating technique to apply a thin film of resist to a wafer prior to spinning. This initial layer of photoresist eliminates the spreading phase, the most inefficient step in conventional spin coating. The initial layer also provides existing spin coating models with preset initial conditions, allowing the prediction of coating thickness and uniformity a priori. This paper compares the experimental results with Emslie et al.´s predictive models of spin coating. A solvent concentration of 80% or higher in the coating chamber environment was found to be necessary to attain a predictable coating thickness with 5-Å uniformity. With optimized process variables, the mean coating thickness matched theoretical predictions within a variation of 0.01 μm. Defect-free coating results were achieved with coating efficiencies as high as 40%.