Electrical and structural properties of poly-Si films grown by furnace and rapid thermal annealing of amorphous Si

Abstract

In the present work, the effect of rapid thermal annealing (RTA) on the electrical and structural properties of poly-Si thin films, grown by the crystallization of a-Si films deposited by rapid thermal low-pressure chemical vapor deposition, has been studied. Structural and electrical results were obtained using atomic force microscopy, transmission electron microscopy, electron spin resonance, electrical resistivity, and Hall mobility techniques. The effects of the grain size, grain boundaries, and surface roughness on the electrical characteristics of poly-Si films have been investigated. Amorphous Si (a-Si) films crystallized by RTA at 850 °C for 45 s result in the formation of poly-Si with small grains, an electron spin density Ns=5.2×1016 cm−3, and a Hall mobility μH=30 cm2 V−1 s−1. A two-stage annealing, involving low-temperature annealing at 600 °C for 6 h, followed by RTA at 850 °C in five steps of 30 s each, results in the formation of poly-Si films with large grains free of in-grain defects, low surface roughness, and higher Hall mobility μH=43 cm2 V−1 s−1, characteristics rendering such poly-Si films suitable for the fabrication of good performance thin film transistors.

The effect of rapid thermal annealed seed layer on the epitaxial poly-Si thin film solar cell׳s structure quality and performance

“…As it was reported, trap densities can be reduced by increasing the temperature and time of the thermal annealing due to the extinction of crystal defects [10]. Additionally, it was found that RTA treatment of the SPC poly-Si films can decrease the electron spin density from 2.3 Â 10 17 cm À 3 to 2.9 À3.2 Â 10 16 cm À 3 [11]. In poly-Si, the electron spin resonance signal arises mainly from Si dangling bonds from grain boundaries [12].…”

“…In poly-Si, the electron spin resonance signal arises mainly from Si dangling bonds from grain boundaries [12]. Thus, RTA treatment can decrease the dangling bonds density at the grain boundaries in SPC poly-Si [11]. Based on the reasons above, RTA treatment can improve the electronic properties of the SPC seed layer.…”

Crystallization of amorphous silicon films by rapid thermal annealing for heterojunction photovoltaic solar cells

“…The electron spin resonance technique has been used to measure the spin density, which is correlated to the density of dangling bonds at grain boundaries, and defects within the grain. It has been shown that high temperature RTA reduces the spin density and (or) dangling bond density (compared to infrared furnace) resulting in poly-Si films of good electrical quality (as confirmed by Hall mobility measurements) [11]. Thus, RTA has the capability of greatly improving c-Si film characteristics by reducing the density of dangling bonds and in-grain microtwins.…”

“…Microtwins may terminate inside a grain and act as scattering centres. Microtwin defects are unstable, and it has been shown that their density can be drastically reduced with RTA annealing temperatures above 750°C [11]. The electron spin resonance technique has been used to measure the spin density, which is correlated to the density of dangling bonds at grain boundaries, and defects within the grain.…”

Thermal Stress Effects on the Electrical Properties of p-Channel Polycrystalline-Silicon Thin-Film Transistors Fabricated via Metal-Induced Lateral Crystallization

“…Poly-Si TFTs are generally made by depositing a-Si:H thinfilm onto a glass sheet using chemical vapor deposition (CVD) and subsequently exposing the deposited glass to high temperatures for a sufficient period of time to crystallized the a-Si:H into poly-Si, which has been named "solid-phase crystallized (SPC) poly-Si" [13], [14]. This crystallization step is typically performed at 600 • C for several tens of hours, or alternatively, rapid thermal annealing [15] or laser excimer annealing [16] can be employed, wherein a laser or, some other source of a sharp temperature gradient, can be used to minimize the heating of the glass substrate [17]. In either case, however, the substrate still experiences a temperature of 400 to 600 • C.…”