In vacuo investigations on the nucleation of TaCN by plasma enhanced atomic layer deposition

The nucleation of TaCN films during plasma enhanced atomic layer deposition (PEALD) using pentakis-(dimethylamino)tantalum (PDMAT) in combination with H2/Ar plasma was investigated on several substrate surfaces by X-ray photoelectron spectroscopy (XPS) without vacuum break. A cluster tool combining a process reactor with a surface analysis unit under high vacuum conditions ensures a direct qualification and quantification of the chemical surface composition by XPS starting from the very first precursor pulse. Due to the high sensitivity of in vacuo XPS measurements, tantalum can be detected at the substrate surface already after the very first precursor pulse of the PEALD process. The amount of adsorbed tantalum precursor molecules on the silicon oxide surface is much higher compared to the H-terminated Si and low-k surfaces. The early cycles are characterized by the onset of TaO bonds. A TaO interface layer grows on the substrate surface until all the reactive OH-groups are consumed. This is followed by the emergence of TaC and TaN bonds when the homogenous growth mode begins. The PEALD nucleation of TaCN was also investigated on low-k substrates (SiCOH). The homogeneous film body on all substrates consist of Ta- carbide -nitride, and -oxide compounds. In summary, we obtained precise information about the initital tantalum precursor adsorption on several substrate materials and explored the capability to enhance the initial growth on low-k substrates. These examples demonstrate as well that in-vacuo XPS measurements are ideally suited for studying film growth nucleation.