THERMAL-DECOMPOSITION MECHANISMS OF TETRAETHYLGERMANE IN METAL-ORGANIC CHEMICAL-VAPOR-DEPOSITION

Polycrystalline Ge thin films have been grown by MOCVD in an atmospher ic laminar flow reactor using GeEt4 as precursor. Hydrogen is required to remove the carbon contamination of the films which is observed und er inert atmosphere. The decomposition mechanism of GeEt4 in the CVD r eactor has been investigated from analyses of the gaseous by-products in a variety of chemical environments. The overall reaction is the gro wth of Ge thin him with formation of H-2 and C2H4 as gaseous by-produc ts, likely by the beta-hydrogen elimination mechanism rather than radi cal pathways. The decomposition process under inert atmosphere is pred ominantly homogeneous with likely formation of intermediates as nutrie nt species for the film. Secondary heterogeneous processes including p olymerization reactions or incomplete removal of the ligands and subse quent dehydrogenation lead to carbon contamination of the layers. In a mbient H-2, the formation of C2H6, likely by the hydrogenation of C2H4 , prevents the polymerization of the olefin and accounts for the benef icial influence of H-2 in this low temperature deposition process of p ure Ge thin films. (C) 1998 Elsevier Science B.V.