Fine-tuning of the interface in high-quality epitaxial silicon films deposited by plasma-enhanced chemical vapor deposit

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Fine-tuning of the interface in high-quality epitaxial silicon films deposited by plasma-enhanced chemical vapor deposition at 200 °C Mario Morenoa) National Institute for Astrophysics, Optics and Electronics, Electronics Department, INAOE, 72840 Puebla, Mexico

Gilles Patriarche Laboratoire de Photonique et de Nanostructures LPN-CNRS, Route de Nozay, 91460 Marcoussis, France

Pere Roca i Cabarrocasb) Laboratoire de Physique des Interfaces et des Couches Minces, Ecole Polytechnique, CNRS, LPICM, 91128 Palaiseau, France (Received 15 November 2012; accepted 1 February 2013)

High-quality epitaxial silicon thin films have been deposited by plasma-enhanced chemical vapor deposition (PECVD) at 200 °C in a standard radiofrequency (RF) PECVD reactor. We optimized a silicon tetrafluoride (SiF4) plasma to clean the surface of ,100. crystalline silicon wafers and without breaking vacuum, an epitaxial silicon film was grown from SiF4, hydrogen (H2), and argon (Ar) gas mixtures. We demonstrate that the H2/SiF4 flow rate ratio is a key parameter to grow high-quality epitaxial silicon films. Moreover, by changing this ratio, we can fine-tune the composition of the interface between the crystalline silicon (c-Si) wafer and the epitaxial film. In this way, at low values of the H2/SiF4 flow rate ratio, an abrupt interface is achieved. On the contrary, by increasing this ratio we can obtain a porous and fragile interface layer, composed of hydrogen-rich microcavities, which allows the transfer of the epitaxial film to foreign substrates. I. INTRODUCTION

Address all correspondence to these authors. a) e-mail: [email protected] b) e-mail: [email protected] DOI: 10.1557/jmr.2013.52

PECVD has become the standard semiconductor deposition system of choice for large substrate areas (.1 m2) in microelectronics and photovoltaic industries. Even tough high-quality epi-Si films have been produced by PECVD technique using SiH4-H2 mixtures,9–11 there is no information related to this kind of films produced by SiF4-H2 mixtures. Moreover, the c-Si/epitaxial interface has not been studied systematically. In previous works,12–15 we studied fluorine-based microcrystalline silicon films (lc-Si:H:F), and demonstrated that lc-Si:H:F can be deposited with a higher crystalline fraction (and larger grains size) than lc-Si:H films produced from SiH4-H2 gas mixtures. Taking advantage of the above, we have studied a process to produce epi-Si films on (100) crystalline silicon (c-Si) substrates, using optimized lc-Si: H:F deposition conditions. A dry process has been developed to etch the native oxide from a c-Si wafer using a SiF4 plasma in a standard PECVD reactor,16 and immediately without breaking the vacuum, an epi-Si film is grown at low temperature (200 °C) from a H2, SiF4, and Ar gas mixture. We have performed a systematic study on the effect of H2/SiF4 flow rate ratio on the quality of the epi-Si films and as well on the quality of the interface with the c-Si wafer. We found that by optimizing the H2/SiF4 ratio it is possible not only to produce films with ve