Ultra-thin crystalline silicon films produced by plasma assisted epitaxial growth on silicon wafers and their transfer to foreign substrates^*

Laboratoire de Physique des Interfaces et des Couches Minces, École Polytechnique, CNRS, Palaiseau, France

^a Address for correspondence: National Institute for Astrophysics, Optics and Electronics, INAOE, Puebla, Mexico; e-mail: mmoreno@inaoep.mx

Received: 22 April 2010
Accepted: 28 July 2010
Published online: 5 October 2010

Abstract

We have developed a new process to produce ultra-thin crystalline silicon films with thicknesses in the range of 0.1 − 1 μm on flexible substrates. A crystalline silicon wafer was cleaned by SiF₄ plasma exposure and without breaking vacuum, an epitaxial film was grown from SiF₄, H₂ and Ar gas mixtures at low substrate temperature (T_sub ≈ 200 °C) in a standard RF PECVD reactor. We found that H₂ dilution is a key parameter for the growth of high quality epitaxial films and modification of the structural composition of the interface with the c-Si wafer, allowing one to switch from a smooth interface at low hydrogen flow rates to a fragile one, composed of hydrogen-rich micro-cavities, at high hydrogen flow rates. This feature can be advantageously used to separate the epitaxial film from the crystalline Si wafer. As a example demonstration, we show that by depositing a metal film followed by a spin-coated polyimide layer and applying a moderate thermal treatment to the stack, the fragile interface breaks down and allows one to obtain an ultrathin crystalline wafer on the flexible polyimide support.