Effect of Humidity on Photoresist Performance

This paper discusses the effect of varied humidity on lithographic performance during photoresist exposure. In the presence of water, exposure causes the sensitizer to be converted into acid; without water, a less soluble ester forms. The effect of humidity on the resist chemistry was measured using infrared spectroscopy. To completely convert the sensitizer to acid, humidities exceeding 40% were needed. At lower humidities, significant amounts of ester, rather than acid, were formed. The effect of humidity during exposure was also measured using lithographic techniques. As humidity decreased from 40 to 20%, the dissolution rate decreased by up to 65%, dose-to-clear (E-0) increased by up to 25%, the dose-to-print increased by up to 15%, and contrast decreased by up to 10%. The magnitude of these effects was resist-dependent. The time of equilibration of water into and out of the resist film was less than 30 s.