Selective wet etching of Ge2Sb2Te5 phase-change thin films in thermal lithography with tetramethylammonium

In this paper, we study Ge 2 Sb 2 Te 5 phase-change film as a promising inorganic photoresist using organic alkaline: tetramethylammonium hydroxide (TMAH) solution, instead of inorganic alkali or acid as etchant. The basic etching properties are investigated by prior and posterior annealing Ge 2 Sb 2 Te 5 films. Selectivity is found to be dependent on concentration of TMAH. There is a good selectivity in the 25% TMAH solution, in which the amorphous state is etched away, whereas the crystalline state remains. The etching rate decreases when the concentration of TMAH is diluted; and an opposite selectivity, compared with 25% TMAH solution, is observed in the 0.125% TMAH solution. Selective etching with laser crystallization in different power levels is also studied, and an excellent wet selectivity in the 25% TMAH solution is obtained. The remaining crystalline lines are observed by atomic force microscopy. The surface roughness after etching is at a good level. The selective wet-etching mechanism is also discussed.