Photo resist spectral matching technique

A high pressure mercury arc lamp such as the light source in a projection aligner is utilized in a photo resist calibrating process. The light source is utilized with narrow band interference filters centered on the mercury emission lines to isolate exposures to one narrow band of wave length at a time. The assumption is made (incorrectly) that the energy in each band of wave lengths from the high pressure mercury arc lamp is equal. Exposure to a narrow strip of photo resist-preferably in the form of a bar graph-on a semi-conductor wafer is made. A single wave length band is exposed for each bar of the graph. As each bar of the graph is scanned, exposure is varied in known ways (eg. linearly variable neutral density filters, changing apertures size, and/or varying exposure from changing wafer motion). The wafer is then developed and examined to determine the ratio of sensitivity for each wave length. A light meter is then placed in and exposed to the same high pressure mercury arc lamp. The meter is tailored to the same ratio of selectivity that was measured on the photo resist coated wafer. A surprising result is present in that the unknown energy distribution of the lamp results in the light meter being set to a measured spectral sensitivity for the photo resist. The meter accurately matches the photo resist and thereafter may be used with any number of spectrally variable light sources to accurately calibrate the same photo resist.