Polycrystalline silicon deposited on glass by subatmospheric-pressure chemical vapour deposition at a high rate

Abstract

A bstractAmorphous silicon ®lms have been deposited on glass by subatmosphericpressure chemical vapour deposition and then crystallized by solid-phase crystallization. The structural and electrical properties of these polycrystalline silicon ®lms are presented in this work. Good crystalline quality at a deposition pressure of about 400 mbar has been achieved as well as values of the mobility± lifetime product above 10 ¡ 5 cm 2 V ¡ 1 and an ambipolar di usion length near 200 nm. Depending upon the deposition temperature and pressure, growth rates of up to 20 mm h ¡ 1 can be obtained. In-situ doping with arsenic and boron has been studied using Hall e ect measurements. High mobilities around 45 cm 2 V ¡ 1 s ¡ 1 have been attained for highly n-type doped samples and mobilities in the range from 20 to 30 cm 2 V ¡ 1 s ¡ 1 for boron-doped samples.} 1. I ntroduction Polycrystalline silicon (polysilicon) has received attention as a material for thin-®lm transistors (Mimura et al. 1989), photovoltaic conversion of solar energy (Matsuyama et al. 1993), integrated circuit applications and microelectromechanica l systems (Tada et al. 2000). Although the technology of amorphous silicon (a-Si) is well established, the carrier mobilities are too small and instabilities arise with applied bias, an increase in temperature and on light exposure. Polysilicon does not have these limitations but grain boundaries degrade the electrical and optical properties.The possibility of depositing polysilicon material with device-quality electronic properties at moderate temperatures (below 600°C) compatible with the use of glass substrates is interesting for industrial applications. It is known that silicon ®lms deposited by thermal chemical vapour deposition (CVD) in an amorphous state

Doped Polycrystalline Silicon Thin Films Deposited on Glass from Trichlorosilane**

“…As can be seen, mobility increases with p from a low value (0.07 cm 2 V −1 s −1 ) for the less‐doped sample to ∼15 cm 2 V −1 s −1 for the sample with the highest boron content. A similar trend is seen in the work of Münster et al, where the authors report mobilities in the range of 6 to 30 cm 2 V −1 s −1 . The behavior in Figure can also be explained by the presence of a high density of trap states in the grain boundaries.…”

Controlling Stress in Large-Grained Solid Phase Crystallized n-Type Poly-Si Thin Films To Improve Crystal Quality

“…Thus, there is a need to control the stress in the poly-Si films. The stress level in poly-Si films can be conveniently determined from the wavenumber shift using the following equation: 26,31,37…”

“…Thus, there is a need to control the stress in the poly-Si films. The stress level in poly-Si films can be conveniently determined from the wavenumber shift using the following equation: ,, σ = prefix− ( 250 MPa cm ) × normalΔ ω where σ is the stress and Δω is the shift (wavenumber) in the Raman peak position of the poly-Si film compared to that of unstressed single-crystal Si.…”