Analysis of the effects of reflectance and refraction generated by wafers made from fused silica, ALOxNy and TiSixNy under different light sources on pattern length and best focus

In semi-conductor photo-lithography processing, line-width is constantly shrinking. That is why process window requirements are becoming stricter. Under these strict conditions, the influences of focus and pattern length are more important. This investigation tries to explore the deviation of best focus and the variation in pattern length resulting from the reflectance and refraction of fused silica, ALOxNy and TiSixNy wafers are coated with the same thickness of SEPR 432 PR (Photo Resist). Experimental results indicate that after excluding the influence of photo resist impacts, the refraction generated by the auto focus light source(halogens lamp) causes deviation of the best focus, and the extent of deviation has a directly proportion relationship with refraction, and no direct relationship exists between exposure light source (laser) and the deviation of best focus. The reflectance generated by exposure light source only changes the measures of pattern length, and an inverse relationship exists between reflectance and pattern length; that is, received pattern length reduces with increasing wafer reflectance.