(562c) Deposition Of Conformal Metal Oxide Films In Supercritical Carbon Dioxide

Metal oxide films have wide applications in the areas of microelectronics, catalysts, photovoltaics and optical devices due to their interesting chemical, electrical and optical properties. In microelectronics, the scaling of devices creates a need for conformal thin films of metal oxides within high aspect ratio features. Conventional methods for depositing metal oxide films include chemical vapor deposition (CVD) and atomic layer deposition (ALD), although both have limitations. CVD is subject to precursor volatility constraints that often give rise to low vapor phase concentrations and non-conformal depositions. ALD provides excellent step coverage, however, requires longer process times. Supercritical fluid deposition (SFD) is a novel technique which overcomes these limitations in order to successfully deposit conformal metal oxide and metal films. This is enabled by SFD because of higher precursor concentration and reduced mass transfer limitation.

Here, we demonstrate the surface-selective, cold wall, SFD process to obtain conformal and pure metal oxide films. Oxides of Ce, Hf, Ti, Nb, Ta, Zr, Bi and other metals are deposited from organometallic compounds in supercritical CO₂ via hydrolysis. The precursor reacts with water, which is present in CO₂ as an impurity in the system, or can be added in controlled amounts. Film thickness is dependent on both water and precursor concentration. It was found that drying CO₂, to remove trace amount of water, resulted in thinner films. The deposited films ranged in thickness from 20 nm - 260 nm depending on precursor type, water concentration and reaction conditions. Deposited films characterized by means of XPS, SEM, AFM, XRD and profilometry concluded that as-deposited or annealed films were highly pure and conformal. An in depth kinetic study of hafnium oxide film growth is underway.