In situ investigation of the passivation of Si and Ge by electron cyclotron resonance plasma enhanced chemical vapor deposition of SiO2

Abstract

In situ real time single wavelength ellipsometry and spectroscopic ellipsometry were used to monitor electron cyclotron resonance plasma enhanced chemical vapor deposition of SiO2 on Si and Ge at substrate temperatures from floating temperature (<50 °C) to 400 °C. Dielectric layers were evaluated by capacitance–voltage measurements. Single wavelength ellipsometry and x-ray photoelectron spectroscopy results show that oxidation occurred along with SiO2 deposition at the initial stage of plasma enhanced chemical vapor deposition. The real time oxidation analysis shows that the subcutaneous oxidation follows parabolic growth kinetics during SiO2 deposition. The parabolic rate coefficient is proportional to the voltage drop across the subcutaneous oxide layer, and yields temperature activated transport. The subcutaneous oxidation of Ge yields a Ge rich oxide that degrades the electrical properties of metal–oxide capacitors. A thin Si layer deposited at room temperature before SiO2 deposition protects the Ge surface from undesirable oxidation during SiO2 deposition. The required thickness of Si layer is predicted. Electron cyclotron resonance plasma oxidation at 400 °C after SiO2 deposition reduces the slow trap states. An Al/SiO2/Si/Ge structure shows improved electrical properties of metal–oxide Ge capacitors. For c-Si substrates, a rapid thermal anneal of the deposited SiO2 in high vacuum can effectively eliminate the OH group incorporation, and thus reduces both interface trapped charge and slow trap states.

Band Gap-Engineered Group-IV Optoelectronic Semiconductors, Photodiodes and Prototype Photovoltaic Devices

“…The deposition of SiO 2 on Ge surfaces is known to lead to subcutaneous oxidation of Ge. 19 The subcutaneous layer consists of amorphous Ge and GeO 2 , which is hygroscopic. Fortunately, straightforward solutions to this problem are available, either in the form of a-Si 20 or III-V passivating layers.…”

Ambient stability of wet chemically passivated germanium wafer for crystalline solar cells

“…Since germanium oxide is water soluble and has poor thermal and electrical properties [1,2], it is not suitable for surface passivation. Posthumaa et al [3] used hydrogenated amorphous silicon films to passivate Ge surfaces and obtained 17 cm/s for the value of S while Nagashima et al [4] and Wang et al [5] attempted the passivation of Ge surfaces by SiN and SiO 2 layers. However, these processes require a high vacuum system and time-consuming thin film deposition, and therefore, are not suitable for routine measurements of t. On the other hand, wet chemical processes are fairly simple and can be performed at room temperature.…”