(685e) Kinetics of Ald Ruthenium Nucleation and Growth Studied Using on-Line Auger Electron Spectroscopy

Ruthenium is of interest in advanced silicon device technology because it can act as a seed layer for advanced interconnects, and it is a candidate PMOS metal gate electrode with a relatively high work function, good thermal stability, and good adhesion. Cyclopentadienyl-based precursors and oxygen reactants are widely studied, and the resulting Ru films have been well characterized. However, better control of nucleation is needed because in many applications, the metal/substrate interface plays a significant role in device performance. For this study, we investigated the kinetics of ALD Ru nucleation and growth using a unique ALD reactor system equipped with Auger electron spectroscopy. Reactants were bis-(cyclopentadienyl) ruthenium and oxygen, and deposition was studied on various substrates including SiH, SiO2, and HfO2. XPS and AES data show that oxidation of the Si-H surface is required before Ru chemisorption. A kinetic model based on the extent of Si-H oxidation versus oxygen exposure was developed, and the rate of substrate oxidation is found to limit the metal nucleation rate. This leads to a substrate dependent growth incubation period, with a slowly increasing growth rate per ALD cycle. It is interesting to note that for Ru ALD on HfO2, AES shows that the Hf/O ratio increases with the number of cycles, indicating HfO2 is reduced at the metal/dielectric interface during Ru deposition. HfO2 reduction can result in oxygen vacancy formation which tends to lower the effective work function of the Ru. Electrical characterization of ALD Ru will also be discussed. These results give fundamental insight into mechanisms of ALD metal nucleation, which can be used to modify and control nucleation for advanced ALD applications.