Origin of contaminants in metal films photochemically deposited from the metal hexacarbonyls.

Research directed toward understanding the source of contaminants in photochemically grown films is reported. Cr, Mo, and W films have been deposited onto silicon substrates by photolysis of their corresponding hexacarbonyls with CW 257-nm light over a range of 1-5000 W/cm2 in a chamber with a base pressure of 10-8 Torr. Films from all three metals exhibit ripples (1000-3000-angstrom-wide), indicating the predominance of surface photochemistry. Samples were also prepared in rough vacuum (10-4 Torr) and transported in air for comparison. Air-exposed Cr films are 30-35% Cr and 60-70% O; carbon is not detected. Those not exposed to air show appreciable amounts of C and reduced amounts of O, indicating that the presence of air alters the composition of the films. Similar variations are found for Mo and W. Film growth due to gas-phase photolysis is compared with that from surface photolysis. Quantitative differences in composition indicate that photoreactions taking place at the surface are distinctive.