Surface species during ALD of platinum observed with in situ reflection IR spectroscopy

Abstract

Thermal atomic layer deposition (ALD) and plasma-enhanced ALD (PE-ALD) of Pt, using MeCpPtMe₃ as the precursor and O₂ gas or O₂ plasma as the reactant, are studied with in situ reflection Fourier transform infrared spectroscopy (FTIR) at different substrate temperatures. This is done to identify the functional groups present during Pt ALD and investigate the origin of the temperature dependent growth rate of the thermal process. Evidence is given that CH and CC containing species are present on the surface after precursor exposure at low substrate temperatures (<150 °C), poisoning the surface during thermal ALD. Both species are removed by O₂ plasma enabling PE-ALD below 150 °C through combustion reactions. Above 150 °C, no CH stretching modes were detected and the CC vibration diminished, indicating dehydrogenation reactions and ligand restructuring. In addition, the PE-ALD FTIR spectra revealed the presence of combustion reaction products on the surface after precursor exposure. These were removed during the reactant exposure and during this exposure the formation of surface OH groups was found for both high and low substrate temperatures. We conclude that the decrease in the growth rate for the thermal process is caused by the inability of the surface to properly dehydrogenate and restructure the poisoning precursor ligands.