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

摘要

Polycrystalline Ge thin films have been grown by MOCVD in an atmospheric laminar flow reactor using GeEt_4 as precursor. Hydrogen is required to remove the carbon contamination of the films which is observed under inert atmosphere. The decomposition mechanism of GeEt_4 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 film with formation of H_2 and C_2H_4 as gaseous by-products, likely by the β-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 C_2H_6, likely by the hydrogenation of C_2H_4, 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.