Invited Paper TF2-MoM1
ALD of Metal Chalcogenide Thin Films

Monday, November 9, 2009, 8:20 am, Room B4

ALD of metal sulphide thin films has been known since the discovery of the technology in early 70s whereas ALD of metal selenide and telluride films has been limited because of a lack of precursors that would at the same time be safe and exhibit high reactivity as required in ALD. In this presentation we show that alkylsilanes of tellurium and selenium can be used as tellurium and selenium precursors in thermal ALD. Compounds with a general formula (R₃Si)₂Te and (R₃Si)₂Se react with various metal halides producing metal telluride and selenide thin films. Sb₂Te₃, GeTe and Ge₂Sb₂Te₅ films can be deposited by ALD at 90 °C using (Et₃Si)₂Te, SbCl₃ and GeCl₂·C₄H₈O₂ as precursors. All three precursors exhibit a typical saturative ALD growth behaviour. The Ge₂Sb₂Te₅ films show excellent conformality on a high aspect-ratio trench structure. Many other selenide and telluride films can be deposited by ALD using alkylsilanes of tellurium and selenium as precursors. Those deposited in this work include ZnTe, Bi₂Te₃, ZnSe, Bi₂Se₃, In₂Se₃ and Cu_xSe_y. The growth temperature has in some cases been 400 ^oC showing the thermal stability of these new Se and Te precursors. Growth rates of these binary chalcogenide films are typically between 0.5 and 1 Å/cycle. Other metal precursors than chlorides are also possible in the selenide and telluride depositions, as exemplified by the use of GeBr₂ and Sb(OEt)₃.