In-Situ Aluminum-Induced Crystallization of Si Thin-Films on Glass Substrates above the Eutectic Temperature using HW-CV
- PDF / 325,444 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 19 Downloads / 169 Views
A4.24.1
In-Situ Aluminum-Induced Crystallization of Si Thin-Films on Glass Substrates above the Eutectic Temperature using HW-CVD Ozgenc Ebil, Roger Aparicio and Robert Birkmire Institute of Energy Conversion, University of Delaware Newark, DE 19716 U.S.A.
ABSTRACT The growth of poly-Si films on glass substrates using an in-situ aluminum-induced crystallization (AIC) process above the Si-Al eutectic temperature of 577 oC is discussed. Silicon films were deposited by Hot-Wire Chemical Vapor Deposition (HW-CVD) onto Al coated Corning 7059 glass substrates. The back surface coverage and the average grain size of the films were compared as a function of growth rate and the Si/Al thickness ratio. SEM and EDS analysis of samples with a Si/Al ratio of 1 revealed two domains in the films which varied in morphology and composition; rougher areas containing a mixture of Si and Al with Al content up to 35%, and relatively smoother areas composed of almost entirely Si. This non-uniform morphology seems to be the result of the absence of a native oxide layer when a liquid phase is formed during the deposition. Si grains as large as 50 µm in diameter and back surface coverage up to 90% were obtained for both the Si/Al ratios of 1 and 5. However, no continuous Si films were obtained. The sample with a Si/Al ratio of 1 had columnar grains reaching to the film surface, whereas on the Si/Al ratio of 5 large Si grains did not extend to the film surface.
INTRODUCTION Thin-film polycrystalline silicon (poly-Si) has attracted interest for semiconductor applications such as thin-film transistors (TFT) and sensors [1]. In addition, poly-Si is a potential substitute for crystalline silicon (c-Si) and amorphous silicon (a-Si) in photovoltaic applications since it may combine the benefits of c-Si performance with thin-film a-Si large area manufacturability. The key requirements to obtain poly-Si films adequate for solar cells are a low temperature process which allows the use of low cost substrates and poly-Si films with grain sizes comparable to the film thickness [2]. Hot-Wire Chemical Vapor Deposition (HW-CVD) has attracted both academic and industrial interest because of its ability to reach high deposition rates at low and moderate temperatures. However, poly-Si films deposited by HW-CVD on bare glass or other substrates typically have an average grain size of 10-50 nm. Such a grain structure presents a potential problem for device performance since it introduces an excessive number of grain boundaries which, if left unpassivated, lead to poor solar cell properties. Furthermore, passivation of such a large network of surface defects is an impractical matter. Therefore, increasing the grain size of HW-CVD films remains a critical issue. Parallel to this, it has been extensively reported that a-Si in contact with certain metals like Al, Au, Ni, Pb crystallizes at temperatures as low as 150 oC [3-5]. Crystallization by this process also leads to micrometer size grains. The Si-Al system has been one of the most studied because Al forms a
Data Loading...
