Initial HfO₂ Growth on Si(100) and GaAs(100) Substrates using TEMAH+H₂O and TDMAH+H₂O ALD Processes

Abstract

Atomic layer deposition (ALD) is a cyclic growth process that is distinguished by a self-limiting, two-step surface reaction that results in precise growth control and high quality, conformal thin films. Due to the continuous downscaling of MOSFET devices, a large interest has recently developed in the ALD of high-kappa dielectric materials as gate oxide layers on Si and III-V substrates. The ALD of HfO₂ is an established process; however, there is still controversy over the initial growth mechanisms on differently prepared Si surfaces. This motivated a comparison of the nucleation stage of HfO₂ films grown on OH- (Si-OH) and H-terminated (Si-H) Si(100) surfaces. Two different ALD chemistries are investigated, including tetrakis[ethylmethylamino]hafnium (Hf[N(CH₃)(C₂H₅)]₄), abbreviated as TEMAH, and tetrakis[dimethylamino]hafnium (Hf[N(CH₃)₂]₄, abbreviated as TDMAH. H₂O is used as the oxidizing precursor. Deposition temperatures of 250-275°C result in a linear growth per cycle of 1 A/cycle. Techniques including Rutherford backscattering spectrometry (RBS), X-ray photoelectron spectroscopy (XPS), spectroscopic ellipsometry (SE), and transmission electron microscopy are used to examine the film interface and initial film growth. HfO₂ films are also subjected to post-deposition anneals, and the film morphology is examined with X-ray diffraction, Fourier transform infrared spectroscopy and atomic force microscopy.

GaAs MOSFET devices have long proven elusive due to the lack of a stable native oxide. Recent research into high-kappa dielectric materials for use in Si-based devices has presented many new options for insulating layers on GaAs. HfO₂ growth on GaAs(100) from a TDMAH+H₂O ALD process is studied here. Three different GaAs surface treatments are examined, including buffered oxide etch (BOE), NH₄OH, and a simple acetone/methanol wash (to retain the native oxide surface). Initial HfO₂ growth on these surfaces is characterized with RBS and SE. The interfacial composition is examined with XPS both before and after HfO₂ deposition. Also, an interesting native oxide 'consumption' mechanism is investigated, which involves the dissolution of the GaAs native oxide during the ALD process. This project presents the first detailed study of HfO₂ growth on GaAs with the TDMAH/H₂O ALD chemistry, providing XPS, RBS and SE characterization of early film growth.