Orientation-Dependence of Low Temperature Epitaxial Silicon Growth
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Orientation-Dependence of Low Temperature Epitaxial Silicon Growth Thomas A. Wagner1, Lars Oberbeck1, Melanie Nerding2, Horst P. Strunk2, and Ralf B. Bergmann1 1 Institute of Physical Electronics, University of Stuttgart, Pfaffenwaldring 47, 70569 Stuttgart, Germany 2 Institute of Microcharacterisation, University of Erlangen, Cauerstr. 6, 91508 Erlangen, Germany
ABSTRACT Electronic properties of thin epitaxial silicon films deposited at temperatures below 650°C by means of ion-assisted deposition strongly depend on substrate orientation as well as on deposition temperature: In (100)-oriented epitaxial films we find a low density of structural defects, and the minority carrier diffusion length is only limited by the presence of point defects or point defect complexes. These investigations also show an improvement of the electronic quality with increasing deposition temperature. Epitaxy on non-(100)-oriented substrates results in a significantly higher density of structural defects. The electronic properties of films deposited on stable flat surfaces, such as (111)- and (113)-oriented substrates are inferior as compared to (100)-oriented films, but are still superior to those of films deposited on faceted surfaces, as shown by light beam induced current and electron back-scattering diffraction measurements of polycrystalline thin films.
INTRODUCTION Silicon homoepitaxy at high deposition temperatures Tdep = 1000…1100°C is widely used in semiconductor industry and provides high quality silicon films for microelectronic devices. However, many applications such as the formation of abrupt homojunctions or the need to use foreign substrates require a low thermal budget during processing, thus limiting the deposition temperature to a much lower regime. In principle, the growth of epitaxial silicon films is possible even at room–temperature [1]. However, at very low deposition temperatures the epitaxial thickness of the deposited films is limited [2]. At deposition temperatures Tdep ≥ 435°C the growth of several µm-thick films is possible [3]. We have shown before that silicon epitaxy on monocrystalline (100)-oriented substrates using ion-assisted deposition (IAD) allows us to deposit high quality thin films with majority carrier properties comparable to bulk silicon [4] and a minority carrier diffusion length L > 20 µm even at a low deposition temperature such as 550°C and a very high deposition rate rdep = 0.8 µm/min [5]. In this paper, we investigate the crystalline quality of thin epitaxial films deposited by IAD at Tdep ≤ 650°C as a function of the substrate orientation and correlate structural with electronic properties of the films. Furthermore, we demonstrate the influence of deposition temperature and deposition rate on the formation of extended structural and point defects.
A22.3.1
ION-ASSISTED DEPOSITION FOR THIN FILM GROWTH Ion-assisted deposition is an advanced physical vapor beam technique which uses a small fraction of ionized silicon atoms within the Si beam. These Si+ ions are accelerated towards the s
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