Nucleation Studies of HfO2 Thin Films Produced by Atomic Layer Deposition

A hot wall Atomic Layer Deposition (ALD) flow reactor equipped with a Quartz Crystal Microbalance (QCM) has been used for the deposition of HfO2 thin films with tetrakis (dimethylamino) hafnium (TDMAH) and H2O as precursors. HfO2 films were deposited on Hterminated Si and SC1 chemical oxide starting surfaces. Spectroscopic ellipsometry (SE) and QCM measurements confirm linear growth of the films at a substrate temperature of 275°C. FTIR spectra indicate the films are amorphous as-deposited. Two distinct growth regimes are observed: from 1-50 cycles, both surfaces display similar growth rates of about 1.0 Å/cycle; from 50-200 cycles, HfO2 growth is decreased by about 15% to ~0.87 Å/cycle on both surfaces. Nucleation and initial growth behavior of the films on Si-H were examined using X-ray photoelectron spectroscopy (XPS). Angle-resolved XPS, at take-off angles of θ=0, 15, 30, 45 and 60° measured from the normal to the sample surface, is used to probe the interfacial region of thin films (4, 7, 10, 15 and 25 cycles) on H-terminated samples. Initially, an interfacial layer comprised of a SiOx/HfSiOx mixture is grown between 1-10 ALD cycles. We observe that the Si/HfO2 interface is unstable, and oxidation continues up to the 25 th ALD cycle, reaching a thickness of ~18Å. INTRODUCTION As the use of Si based gate oxides are reaching their scaling limitations, hafnium-based oxide materials are the leading candidates to replace them as the insulating layer in transistor gate stacks. Among the desirable properties of the Hf containing insulating materials is a high dielectric constant (k~25), suitable band gaps and offsets, good electrical properties and good resistance to reaction with atmospheric moisture. Atomic layer deposition (ALD) is an excellent technique for depositing such high-k oxides since the low process temperatures and characteristic self-limiting surface reactions provide precise, monolayer growth control and excellent conformal films. The deposition of HfO2 thin films has been studied on various starting Si surfaces, including different chemical oxides and hydrogen-terminated Si (Si-H). However, a serious problem which plagues most gate oxide processes on Si-H is the formation of an interfacial SiOx layer during deposition , which increases the equivalent oxide thickness (EOT) and degrades the electrical characteristics of the device. In order to maximize the potential of high-k dielectric materials for this application, a stable interface is required between the dielectric and the Si substrate. Metal-organic precursors are popular for HfO2 deposition due to low toxicity, ease to handle, low deposition temperature and impurity content in the film. In Mater. Res. Soc. Symp. Proc. Vol. 996 © 2007 Materials Research Society 0996-H03-09