Itsuo Nishiyama

Novolak Resist Removal by Laser Irradiation (532 nm) and Adhesion between Resist and Substrate

A diazonaphthoquinone/novolak resist on a 42-alloy substrate was irradiated by the second harmonic wave (532 nm) of a pulsed Nd3+YAG laser. The resist was removed, despite the existence of hexamethyldisilane (HMDS). There was no apparent damage to the substrate. In contrast, the resist on a Si wafer could not perfectly be removed. In some cases, there was damage to the substrate. The peeling strength of the resist with HMDS was about three times than that without HMDS. The width of the resist removed by laser irradiation without HMDS was 1.02–1.03 times larger than that with HMDS. The use of this process will benefit the environment, since expensive and toxic chemicals are not used.

Parametric Study on the Physical Action of Steam--Water Mixture Jet: Removal of Photoresist Film from Silicon Wafer Surfaces

We performed experiments to elucidate the physical action of a steam–water mixture jet, which we have proposed as a promising, environmentally friendly tool for cleaning surfaces. Photoresist-coated silicon wafers were adopted as the target and the jet performance of resist removal was evaluated, with several parameters being varied. We found that the resist-removal performance improves as the thickness or the mechanical strength of the resist film decreases, resist–wafer adhesivity decreases, or jet duration increases. The results imply that the essential part of the resist removal by the jet is a physical process including peel-off, in contrast to the established techniques such as the batch cleaning method utilizing chemical reactions. The results also indicate that the physical impact of the jet can be controlled, which will be a significant advantage in applying the jet as a cleaning technique.

Measurement of Adhesion Force of Resist to Wafer by Using SAICAS: Characteristics of Lift-Off of Resist by Steam-Water Mixed Spray

We performed two experiments on resist-coated wafers. In the measurement of the resist-wafer adhesivity, we confirmed that it is significantly increased by an HMDS layer in between. In the resist-removal experiment using steam-water mixed spray, we found that the area of resist removal is limited within the area of spray application if HMDS is used, otherwise the former can be larger than the latter. These results suggest that the resist removal from a wafer surface by steam-water mixed spray is essentially a peel-off process.