Interfacial reaction induced strain relaxation in Hf-silicate film on strained Si_0.7Ge_0.3(001) as a function of annealing temperature

Abstract

Hf-based dielectrics were prepared using atomic layer deposition in order to investigate the effect of Si incorporation on the interfacial reaction and thermal stability in HfO 2 films on SiGe substrates. Two concentrations [100% HfO 2 and 50% HfO 2 50% SiO 2 (HfSiO)] were used on strained Si 0.7 Ge 0.3 substrates; a partially-crystalline phase was observed in the asgrown HfO 2 film, and was not observed in the as-grown HfSiO film. Phase separation between the SiO x and HfO x in HfSiO film did occur, however, when the annealing temperature was increased to over 900 8C, leading to the out-diffusion of Si from the Si 0.7 Ge 0.3 substrate and the formation of a Ge-rich layer at the interface between HfSiO and Si 0.7 Ge 0.3 . Finally, the strain in the Si 0.7 Ge 0.3 substrate was relaxed, and interfacial states greatly increased in HfSiO/Si 0.7 Ge 0.3 with the 900 8C anneal.ß 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1 Introduction As the size of Si-based metal-oxidesemiconductor (MOS) devices decrease and higher speeds are required for operation, advanced MOS structure research has focused on new potential materials for high performance applications. Among high mobility semiconductor materials, strained Si 1Àx Ge x has attracted both industry and academic research due to a higher hole mobility value (1050 cm 2 /V s at Si 0.2 Ge 0.8 ) than that of Si (505 cm 2 /V s) [1,2]. HfO 2 is an attractive material for the replacement of conventional SiO 2 ; a high dielectric constant (K ¼ 15-20) leads to increased thickness, which can reduce current leakage across the gate oxide through direct tunneling. Specifically, SiO 2 -incorporated HfO 2 films (Hf-silicate) show good thermal stability and an acceptable band offset value when in contact with Si [3,4]. However, Hf-silicate films can separate readily into SiO 2 and HfO 2 , depending on the film composition and annealing temperature [5,6]. In our previous reports, phase separation of HfSiO film on a Si substrate was observed after rapid thermal annealing (RTA) at 900 8C, leading to a downgrading of electrical properties [7]. We noted that the