The low temperature atomic layer deposition of ruthenium and the effect of oxygen exposure

Abstract

We have studied the atomic layer deposition (ALD) of ruthenium using bis(2,4-dimethylpentadienyl) ruthenium and oxygen. We show that the process is achievable at a low operating temperature of 185 °C. Variation in the exposure time and pressure of the oxygen counterreactant has significant effects on the nucleation, growth rate and composition of the deposited ruthenium films. High oxygen pressure helps to promote the nucleation of ruthenium on a silicon dioxide substrate. Although saturation conditions are achieved with the Ru precursor, saturation of the ruthenium growth rate with oxygen exposure is observed only for a small range of oxygen exposure. Increasing the oxygen exposure further results in the incorporation of oxygen in the deposited film to form ruthenium oxide, a process which is enhanced at higher deposition temperature. We propose that the slow diffusion of oxygen to the subsurface region is a rate-limiting step in this process. We demonstrate that the composition of the deposited films from metallic ruthenium to ruthenium oxide, as well as the average grain size, may be regulated by tuning the pressure and exposure time of the oxygen counterreactant. Hence, this low temperature ALD process provides a flexible route to the deposition of Ru-based films.