An in-situ investigation of the surface oxidation of ultra-thin films ofNi and Hf

摘要

Single wavelength (670 nm laser diode) optical monitoring of reflectance at 1 second intervals was used to observe the surface oxidation of Ni and Hafnium metal films in-situ in a low pressure oxygen atmosphere and also in a microwave plasma oxygen environment. After depositing thin metal films by sputtering in an oxygen-free environment, the observed reflectance quickly decreased when low pressure oxygen gas was introduced into the vacuum chamber and reached a stable value within a few seconds, after formation of a thin oxide layer. An additional rapid fall in reflectance and increase in oxide thickness was observed when a microwave plasma generator was used to produce an oxygen plasma containing atomic oxygen. Based on pre-determined optical properties of the metal and metal oxide films, the optical monitoring data was fitted to obtain the thickness of the metal oxide as a function of time. The fitting results showed that the exposure to low pressure oxygen forms an equilibrium thickness of less than 0.5 nm of NiO_x and 0.78 nm of HfO_x, while the oxygen microwave plasma treatment produces an equilibrium thickness of 1.5 nm for both NiO_x and HfO_x.