XPS study on the selective wet etching mechanism of GeSbTe phase change thin films with tetramethylammonium hydroxide

Abstract

Phase change lithography has pretty potential applications for high density optical data storage mastering and micro/nano structure patterning because it is not restricted by optical diffraction limitation and at relatively low cost. GeSbTe, as an initially investigated material for phase change lithography, its mechanism of selective etching in inorganic or organic alkaline aqueous solutions, such as NaOH and tetramethylammonium hydroxide (TMAH), is still unknown. In this paper, XPS measurement is used to study the selective wet etching mechanism of GeSbTe phase change thin films with TMAH solution, and the results show that oxidization played an important role in the etching process. Ge, Sb and Te are oxidized into GeO₂, Sb₂O₅ and TeO₂, respectively, and then as the corresponding salts dissolved into the etchant solution. Ge-X (X is Ge, Sb or Te) bonds are first broken in the etching, then Sb-X bonds, and finally Te-Te bonds. To confirm the effect of oxidization in the etching, H₂O2 as an oxidant is added into the TMAH solution, and the etching rates are increased greatly for both amorphous and crystalline states. The selective etching mechanism of Ge₂Sb₂Te₅ phase change films is discussed by the difference of bonds breakage between the amorphous and crystalline states.