Advances in the deposition of microcrystalline silicon at high rate by distributed electron cyclotron resonance P. Roca i Cabarrocas a, ⁎ , P. Bulkin a , D. Daineka a , T.H. Dao a , P. Leempoel b , P. Descamps b , T. Kervyn de Meerendré b , J. Charliac b a Laboratoire de Physique des Interfaces et des Couches Minces, Ecole Polytechnique, CNRS, 91128 Palaiseau, France b Dow Corning ATVB Energy – Europe, Rue Jules Bordet, Parc Industriel Zone C, B-7180 Seneffe, Belgium Available online 15 December 2007 Abstract We report on the growth of microcrystalline silicon films at high rates (14 Å/s) in a MDECR plasma reactor. Our studies show that the growth process can be described by the same mechanisms as in RF deposition. However, the higher deposition rate achieved in MDECR leads to a higher substrate temperature requirement (225–250 °C) in order to allow hydrogen to diffuse within the film and induce its crystallization. Moreover we also found that microcrystalline silicon growth requires high microwave power (depletion mode) to produce enough atomic hydrogen and low sheath potential to limit ion bombardment. Combining these conditions we could achieve deposition rates up to 28 Å/s (limited by the silane flow rate) in films with a crystalline fraction of the order of 65% which is well adapted for solar cell applications. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Historically, the first report on microcrystalline silicon plasma deposition was published in 1968 by Veprek et al. [1]. However, until now the growth mechanism of this material is still an open question. In 1993, the Swiss team IMT (Neuchâtel) presented that microcrystalline silicon (μc-Si:H) can be used as the active layer (intrinsic layer) of p-i-n solar cells [2]. Since then, photovoltaic research of this material increased consider- ably. In addition, μc-Si:H is also a potential candidate to replace amorphous silicon (a-Si:H) as active layer in thin film transistors (TFTs) [3] due to its higher electron mobility. The crucial advantage of μc-Si:H in comparison with a-Si:H is its stability under light exposure [4,5]. The stability of μc-Si depends on crystalline fraction of the film and according to [5], from 60% of crystalline fraction and up, optic and electronic properties of the films are stable. However, because of its low absorption coefficient, a thickness in the range of 1–4 μm is necessary if one wants to use μc-Si:H as the active layer in p-i-n (or n-i-p) solar cells. As a consequence, the deposition rate of μc-Si:H becomes a critical parameter to reduce production costs. Matrix distributed electron cyclotron resonance (MDECR) plasma offers the possibility to deposit films at very high rate due to its very high electron density due to the confinement of hot electrons by a multipolar magnetic field [6]. Besides, this plasma technique appears well adapted to be scaled up to large area substrates, since it consists of units, easily expandable in two dimensions [6–8]. Another key feature of MDECR plasma is the possibility of depositing μc-Si:H from pure silane, which allows to reduce production costs (no hydrogen is required) and makes MDECR a technique of high industrial interest. In this paper we show that the growth process in MDECR reactors can be described by the same growth mechanisms as in RF (Radio Frequency) plasma deposition [9]. Moreover, we have studied a large process window scanning the deposition parameters such as silane flow rate, substrate temperature, and RF bias. From the study of the films properties we conclude that the higher deposition rate achieved in MDECR leads to a higher substrate temperature requirement in order to allow for hydrogen to diffuse into the film and to induce its crystal- lization. Also, we have found that microcrystalline silicon growth requires low sheath potential to limit ion bombardment. Available online at www.sciencedirect.com Thin Solid Films 516 (2008) 6834 – 6838 www.elsevier.com/locate/tsf ⁎ Corresponding author. E-mail address: pere.roca@polytechnique.edu (P. Roca i Cabarrocas). 0040-6090/$ - see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.12.067