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0989-A04-02

Effects of Nitrogen Addition on the Properties of a-SiCN:H Films Using Hexamethyldisilazane Amornrat Limmanee1, Michio Otsubo1, Tsutomu Sugiura1, Takehiko Sato2, Shinsuke Miyajima1, Akira Yamada3, and Makoto Konagai1 1

Department of Physical Electronics, Tokyo Institute of Technology, 2-12-1-S9-9 O-okayama, Meguro-ku, Tokyo, 152-8552, Japan 2

Material&Processing Technology, Mitsubishi Electric Corporation, 1-1-57, Miyashimo,Sagamihara, Kanagawa, 229-1195, Japan 3

Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1-S9-9 O-okayama, Meguro-ku, Tokyo, 152-8552, Japan ABSTRACT We deposited a –SiCN:H films by HWCVD using a gas mixture of hexamethyldisilazane (HMDS), H2 and N2, and fabricated cast polycrystalline silicon (poly c-Si) solar cells with the a-SiCN:H passivation and anti-reflection layer. N2 addition led to the reduction of the refractive index (n) of the a-SiCN:H films due to the increase in nitrogen concentration of the films. This improved performance of the antireflection layer. The advantage of adding N2 to the process was demonstrated by the improvement in short circuit current (JSC) and efficiency (η) of cast poly c-Si silicon solar cells. INTRODUCTION Hydrogenated amorphous silicon carbon nitride (a-SiCN:H) films deposited by hot-wire chemical vapor deposition (HWCVD) using HMDS has been reported as a new passivation layer of silicon solar cells [1-2]. Using HMDS which is a non-explosive and low cost material enables the process to become safer and more economical. The surface recombination velocity of 1~10 Ω cm n-type c-Si with the a-SiCN:H film is lower than 50 cm/s. The η of cast poly c-Si solar cell with these a-SiCN:H films as a passivation layer reached 13.75% (2cm x 2cm) [3]. The effective reflectivity of cell surface was found to be high, indicating that optimization of the anti-reflection layer is still required. Reducing the n of the a-SiCN:H films is thought to be an effective way to lower surface reflectivity that will lead to improvements of JSC and η of the cells. Using only HMDS and H2 is found to be hard to adjust chemical composition and optical properties of a-SiCN:H films. Therefore, in this work we introduce N2 to our process for the

purpose of providing more variation of the optical properties of the films. The effects of N2 addition on the structural, electrical, optical and interface properties of a-SiCN:H films were examined. We especially focused on the changes in the optical properties and passivation quality of the films. Optimum deposition condition was deduced from experiment results and was practically used in the fabrication of cast poly c-Si solar cells. The improvements in JSC and η were achieved due to the reduction of optical losses at the surface. The benefit of adding N2 to the process was verified by the flexibility of the n EXPERIMENTAL DETAILS The a-SiCN:H films were deposited on n-type CZ (001) silicon wafer (380 µm thickness) with various deposition conditions as shown in Table I. The N2 flow rate was varied from 0 to