Thermal decomposition mechanisms of tetraethylgermane in metal-organic chemical vapor deposition

Polycrystalline Ge thin films have been grown by MOCVD in an atmospheric laminar flow reactor using GeEt4 as precursor. Hydrogen is required to remove the carbon contamination of the films which is observed under inert atmosphere. The decomposition mechanism of GeEt4 in the CVD reactor has been investigated from analyses of the gaseous by-products in a variety of chemical environments. The overall reaction is the growth of Ge thin him with formation of H-2 and C2H4 as gaseous by-products, likely by the beta-hydrogen elimination mechanism rather than radical pathways. The decomposition process under inert atmosphere is predominantly homogeneous with likely formation of intermediates as nutrient species for the film. Secondary heterogeneous processes including polymerization reactions or incomplete removal of the ligands and subsequent dehydrogenation lead to carbon contamination of the layers. In ambient H-2, the formation of C2H6, likely by the hydrogenation of C2H4, prevents the polymerization of the olefin and accounts for the beneficial influence of H-2 in this low temperature deposition process of pure Ge thin films. (C) 1998 Elsevier Science B.V.