High-quality sputter-grown layered chalcogenide films for phase change memory applications and beyond

Abstract

This paper summarizes recent progress on thin film growth of chalcogenides by sputtering. The materials discussed include Sb–Te, Bi–Te, Ge–Te, and their superlattices, materials that are technologically important particularly for non-volatile phase change memory. In this work, the sputter-growth behavior of high-quality layered chalcogenide films is discussed. Sputtering is one of the most commonly used thin-film growth techniques in the semiconductor industry, however, the complex interrelationship between growth parameters can lead to difficulty in fabricating high-quality films although the deposition method itself is relatively simple. Here, we successfully demonstrate the fabrication of highly-oriented layered chalcogenide materials by sputtering. The selection of the appropriate sputtering target is important. In particular, it was found that a Te-rich Sb–Te alloy target such as Sb33Te67 is necessary in order to obtain a stoichiometric Sb2Te3 film. Moreover, the growth temperature is also a key factor in obtaining a highly-oriented film, namely the ideal growth temperature for an Sb2Te3 film is between 230 °C and 250 °C after the growth of an amorphous seed layer at room temperature. Furthermore, it was found that this technique is also useful to grow films epitaxially on Al2O3 or Si(111) substrates even though there are some misoriented grains as well as twins present. Finally, we demonstrate the growth of highly-oriented Sb2Te3 films on a flexible substrate. The versatility of sputtering will become technologically more and more important for the various applications represented by phase change memory.