A New Positive Resist for KrF Excimer Laser Lithography

Abstract

Photolithography using KrF excimer laser (248 nm) is the most exciting technology which has the capability of resolution below 0.5 pm. However good profiles of resist patterns are not obtained by the KrF excimer laser lithography because of strong absorption of conventional deep UV resist such as naphtoquinonediazide-novolac resin type. In order to resolve this problem, a new positive resist (STAR-P) for KrF excimer laser lithography has been developed. This resist is composed of 2-diazo-1,3-dicarbonyl compounds for a sensitizer, which is an alkaline dissolution inhibitor for base polymer, poly (stylene-co-maleic acid half ester) as a base polymer, and diethylene glycol dimethyl ester as a coating solvent. 2-diazo-1,3-dicarbonyl compounds have a strong absorption peak at around 248nm, and are effectively bleached by KrF excimer laser exposure. Moreover, the transmittance of base polymer at 1.0pm thickness is 70% at 248nm. In this study, the photobleachability, thermal stability and inhibition of these sensitizers were evaluated on several 2-diazo-1,3-dicarbonyl compounds which had different substuents. The resolution of these resists were evaluated by a KrF excimer laser stepper system (NA:0.36). The new resist with 1,7-bis(3-chlorosulfony1-4-methyl phenyl)-4-diazo-3,5-heptanedione as sensitizer (STAR-P2) shows the best results. Strong photobleaching occurred at around. 248 nm by KrF excimer laser exposure. The loss of resist thickness at unexposed regions after developing was hardly observed. It was found that chlorosulfonyl groups have a superior capacity for alkaline inhibition. Gamma (γ) value was 2.71, and it was much higher than that of conventional positive resist of naphtoquinonediazide-novolac resin type (1.05). High aspect ratio sub-micron patterns were obtained in spite of the 1.Oμm resist thickness. In conclusion, a new positive resist for KrF excimer laser lithography has been developed. As STAR-P2 has excellent photobleachability for the KrF excimer laser exposure, high aspect ratio patterns can be attained at 1pm thickness. A new single-layer-resist system for KrF excimer laser lithography is realized by using this new resist (STAR-P2).