Fourier transform infrared (FUR) spectroscopy was used to study the effects of various resist process variables on the photospeed. Resist components which are responsible for photospeed changes were identified. The doublet peak around 2100 cm-1 , which corresponds to the diazo group of photoactime compound (PAC), was used for a quantitative measurement of PAC content. The peak at 1700 cm-1, which corresponds to the acetyl group of the solvent used in the resist, was used to measure the solvent content. The PAC is stable at low temperatures, but begins to decompose at 120°C. This temperature is called critical temperature. It was found that below the critical temperature, the solvent content and the resist-thickness-induced changes in reflectivity are the main factors affecting the photospeed. Above the critical temperature, PAC content is the main factor that affects photospeed. The above described technique was also used to study the kinetics of photochemical reactions during resist exposure, and the effect of fluorescent light on resist in a typical manufacturing area. The effects were found to be negligible for wafers in a black cassette and oriented parallel to the light rays, even when exposed for several hours.