Determination of residual casting solvent concentration gradients in resist films by a "halt development" technique

The resolution of the microlithography process used to manufacture semicond uctor devices is a function of many variables. One interesting and importan t contributor to resolution is the "surface induction" phenomenon that occu rs during development of many photoresist materials. This phenomenon is man ifested by a change in dissolution rate as a function of thickness. The top or surface regions of these films dissolve more slowly than the bulk of th e film for reasons that are not understood. One popular theory for surface induction is that the variation in rate is caused by a gradient in the conc entration of residual casting solvent. However, no study has been performed that directly measured the concentration gradient in residual casting solv ent and related that gradient to the extent of surface induction. A ''halt development" procedure has been developed that allows isolation and analysi s of thin layers (slices) from resist films. The analysis for concentration of residual casting solvent was accomplished by radiolabeling the solvent and analyzing the layers by scintillation counting. The dissolution rate da ta was acquired by a multiwavelength interferometry technique. Two resists systems were studied, one with a large extent of surface inhibition and one with a nearly constant dissolution rate. Neither formulation has a signifi cant concentration gradient of residual casting solvent over a range of bak e temperatures (70-110 degreesC). Therefore, it can be concluded that conce ntration gradients in the residual casting solvent alone cannot account for the surface induction observed in this particular resist system. (C) 2001 American Vacuum Society.