Study of HfO2 films deposited on strained Si1−xGex layers by atomic layer deposition

Abstract

This paper focuses on the growth of HfO2 by atomic layer deposition (ALD) at 350°C on pseudomorphic Si1−xGex thin films (x=15% and 25%). Two different Si1−xGex surface preparations (chemical oxidation and HF “last” treatment) have been investigated to obtain the highest HfO2 film quality with the thinnest interfacial layer possible. The initial stages of the ALD growth on these different surfaces (i.e., hafnium adsorption and chlorine contamination) analyzed by total x-ray fluorescence show that HF last treated Si1−xGex surfaces are more convenient than chemically oxidized ones to grow high quality HfO2 layers. This result is confirmed by x-ray photoelectron spectroscopy investigations of the interfacial layer structure as a function of the surface treatment. As-deposited and annealed thin HfO2 layers (2.5, 3.5, 5, and 8nm) grown on HF last treated Si0.75Ge0.25 strained layers were analyzed by mercury probe. An equivalent oxide thickness as low as 0.7nm was obtained for a 2.5nm as-deposited HfO2 film. Mobility results show that a 22% mobility enhancement is obtained in the entire effective field range with HfO2∕SiGe compared to the HfO2∕Si reference.