Growth kinetics and initial stage growth during plasma-enhanced Ti atomic layer deposition

We have investigated the growth kinetics of plasma-enhanced Ti atomic layer deposition (ALD) using a quartz crystal microbalance. Ti ALD films were grown at temperatures from 20 to 200 °C using TiCl4 as a source gas and rf plasma-produced atomic H as the reducing agent. Postdeposition ex situ chemical analyses of thin films showed that the main impurity is oxygen, mostly incorporated during the air exposure prior to analysis. The thickness per cycle, corresponding to the growth rate, was measured by quartz crystal microbalance as a function of various key growth parameters, including TiCl4 and H exposure time, rf plasma power, and sample temperature. The growth rates were independent of TiCl4 exposure above 1×103 L, indicating typical ALD mode growth. The key kinetic parameters for Cl extraction reaction and TiCl4 adsorption kinetics were obtained and the growth kinetics were modeled to predict the growth rates based upon these results. Also, the dependency of growth kinetics on different substrate materials was investigated during the early stages of deposition with various thin films predeposited on the crystal rate monitor surface by sputtering or evaporation. The initial growth rates on Pt, Al, Au, and Cu are higher due to the higher Cl extraction rates, while those on Si and amorphous C are smaller due to etching of substrate materials by atomic H.