Author:  Bijian ZHENG     2014-06-19

Currently, the most widely used photoresists in optical lithography are organic-based resists. The major limitations of such resists include the photon accumulation severely affects the quality of photolithography patterns and the size of the pattern is constrained by the diffraction limit. Phase-change lithography, which uses semiconductor-based resists such as chalcogenide Ge2Sb2Te5 films, was developed to overcome these limitations. Phase-change lithography is based on the etching-rate (solubility) difference between the amorphous (as-deposited) and crystalline (annealed) states of phase-change materials in acid/alkaline solution. Because the Gaussian profile of the laser beam intensity confines the "phase-change" process well within the localised laser-heated area, it would efficiently fabricate sub-diffraction structures.

Recently, PhD candidate student Zeng BiJian supervised by Prof. Miao XiangShui, proposed a metallic resist, instead of chalcogenide semiconductor-based resist, for Phase-change lithography. They successfully used Mg58Cu29Y13 metallic glass films as a new kind of resist in phase-change lithography. The paper entitled “Metallic resist for phase-change lithography” was published by Scientific Reports(4, 5300, DOI:doi:10.1038/srep05300) on June 16, 2014.

The metallic resist composed of Mg58Cu29Y13 films, which exhibits a considerable difference in etching rate between amorphous and crystalline states in nitric acid/ethanol solution(Fig.1). Furthermore, the heat distribution in Mg58Cu29Y13 thin film is better and can be more easily controlled than that in Ge2Sb2Te5 during exposure. They succeeded in fabricating both continuous lines(Fig.2) and discrete dots patterns (Fig.3) on Mg58Cu29Y13 thin films via laser irradiation and wet etching. The results demonstrate that a metallic resist of Mg58Cu29Y13 is suitable for phase change lithography, and this type of resist has potential due to its outstanding characteristics.