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 Sb 33 Te 67 is necessary in order to obtain a stoichiometric Sb 2 Te 3 film. Moreover, the growth temperature is also a key factor in obtaining a highly-oriented film, namely the ideal growth temperature for an Sb 2 Te 3 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 Al 2 O 3 or Si(111) substrates even though there are some misoriented grains as well as twins present. Finally, we demonstrate the growth of highly-oriented Sb 2 Te 3 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.

Differences in Sb ₂Te ₃ Growth by Pulsed Laser and Sputter Deposition

“…Therefore 600 K is the highest practical growth temperature for Sb 2 Te 3 using quasi-equilibrium deposition methods, such as MBE. This low sticking coefficient may also explain some of the non-stoichiometric films reported recently in the literature [32,33] and the lower growth rates at temperatures above 533 K [35]. Figure 6(b) depicts the case where the substrate temperature is too high, and there is no seed layer.…”

“…Recently, a number of publications have reported PVD growth of Sb 2 Te 3 . Magnetron sputtering is commonly used to deposit phase change superlattice materials [12,28,32,33], and Sb 2 Te 3 -based alloys have been realised in industrial fabrication lines. However, it is hard to control the uniformity and accurate atomistic stacking of crystals.…”

“…Moreover, understanding these dependencies might help to explain why different research groups seem to grow different crystals despite their growth temperatures being similar. For example, there are some reports that the sputter grown Sb 2 Te 3 is actually Te deficient [32,33], whilst other groups do not see this effect, and there are even reports that high quality Sb 2 Te 3 can be grown at temperatures as low as 140 • C while other reports show that temperatures as high as 300 • C are necessary [13,35]. Boschker and Calarco discussed the differences between sputtering, PLD and MBE for Ge 2 Sb 2 Te 5 fabrication, but the origin of these differences is unclear [41].…”

Dielectric relaxation in amorphous and crystalline Sb2Te3 thin films

“…Thin antimony telluride films, 80 nanometers thick, were obtained by RF magnetron sputtering on a silicon substrate at room temperature [16]. The dielectric spectra were measured with a wide-band dielectric spectrometer "Concept-81" (Novocontrol Technologies).…”

Chalcogenide Materials Engineering for Phase‐Change Memory and Future Electronics Applications: From Sb–Te to Bi–Te

“…[14,15] Sample Characterization: XRD was conducted to analyze the crystal structures of the grown films. [15] TEM was performed for microstructure observations. [14] Hall effect measurements were used to investigate electrical transport properties.…”