A simple method to evaluate photoresist sensitivity and development/exposure latitude was developed to compare 2 linewidths in positive photoresist under equivalent processing conditions. This method was based on image size measurement by a Nanoline measurement system as a function of exposure and development. In addition, the system was complicated by a variety of materials and a corresponding wide variation in optical parameters, complex refractive indices and thicknesses used in manufacture of integrated circuits. If processing proceeds with controlled oxide thickness, photoresist material, and processing conditions, the linewidth measurements would slightly be affected by the optical variations. It was necessary to calibrate Nanoline measurement system prior to evaluating photoresist performance. The calibration was done by establishing a correlation between the measurements of line/space pair of patterned oxide wafer using Nanoline and scanning electron microscopy (SEM). The calibration yielded a small difference of 0.05 urn. between Nanoline and SEM. Also, the Nanoline system was used to measure a mask which was the third order traceable to National Bureau Standard (NBS) to set up the fourth order NBS standard for MT measurement system. The characterization of positive photoresist and processing by changing exposure and development time were calculated and plotted to obtain a slope of delta linewidth versus wafer processing, which was known as relative process latitude (RPL).
"Calibration and Characterization of a Resist Process through Linewidth Measurement on Wafers,"
Journal of the Microelectronic Engineering Conference: Vol. 4
, Article 35.
Available at: http://scholarworks.rit.edu/ritamec/vol4/iss1/35