High-speed imaging of photoresist stripping phenomena induced by laser irradiation without causing the laser damage

For the semiconductor and liquid crystal display manufacturing process, resist removal by using laser irradiation has been investigated instead of conventional processes such as oxygen plasma and chemical method. An advanced laser resist stripping method for the positive-tone diazonaphthoquinone (DNQ) / novolak resist was successfully developed without causing the laser damage to the Si wafer. The pulsed laser irradiation in water can improve the resist stripping effect when compared with that of conventional atmosphere irradiation, however, the mechanism has yet to be clarified. In this study, we investigated the analysis of resist stripping phenomenon by using a high-speed laser imaging system. A pulsed laser at 640 nm (pulse duration: 40 ns) was used as an illumination laser and a CCD camera detected the reflectance image on the sample. Time resolution of this system depended on the pulse duration of illumination laser. Time-resolved images were acquired based on the “1-on-1” method. Time-resolved images were acquired from 40 ns to 10 us after the laser irradiation. At the laser irradiated spot, changes of the resist were observed after 40 ns from the laser irradiation. The resist was completely stripped from the Si wafer surface after 10 us. The duration of resist removal phenomenon in the water condition was longer than that in the normal atmosphere condition. A resist stripping mechanism could be elucidated by combining experimental high-speed laser imaging and a finite element (FE) analysis. The mechanism of the resist stripping in the water condition will be presented.