Synthesis and use of precursors for ALD of tellurium and selenium thin films

A process for forming a Te and/or Se containing thin film on a substrate in a reaction chamber comprising a plurality of deposition cycles, each cycle comprising in order:

• contacting the substrate with a first vapor phase reactant comprising a metal halide, wherein the metal in the metal halide is selected from the group consisting of Sb, Ge, Bi, Zn, Cu, In, Ag, Au, Pb, Cd, and Hg;
• removing excess first reactant with the aid of a purge gas;
• contacting the substrate with a second vapor phase reactant, wherein the second reactant comprises Te(SiR1R2R3)2 or Se(SiR1R2R3), wherein R1, R2, and R3 are alkyl groups with one or more carbon atoms;
• and
• removing excess second reactant with the aid of a purge gas.