Atomic Layer Deposition of Materials for Phase-Change Memories

Germanium antimony telluride (GST) materials and precursors for gas-phase thin film deposition are briefly reviewed. In the experimental part we show that alkylsilyls of tellurium can be used as tellurium precursors in plasma-free atomic layer deposition (ALD). Compounds with a general formula (R3Si)(2)Te react with various metal halides producing metal telluride thin films. Sb2Te3, GeTe and GST films can be deposited by ALD at temperatures below 100 degrees C using (Et3Si)(2)Te, SbCl3 and GeCl2 center dot C4H8O2 as precursors. All three precursors exhibit a typical saturative ALD growth behaviour in binary telluride processes. When processing ternary materials some non-ideal behaviour exist but by adjusting the exposure times and ratio of the binary cycles Ge-Te and Sb-Te, the GST composition could be controlled. The ternary films are amorphous as-deposited and crystallize at 130 degrees C in the cubic structure, and at around 250-300 degrees C the stable hexagonal phase is formed. Phase change behavior of the ALD GST films was studied using a static laser tester and found to be similar to sputter deposited films.