Effect of Hydrogen Radical on Properties of Hydrogen in Hydrogenated Microcrystalline Silicon

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EFFECT OF HYDROGEN RADICAL ON PROPERTIES OF HYDROGEN IN HYDROGENATED MICROCRYSTALLINE SILICON

Takashi Itoh*, Noriyuki Yamana*, Hiroki Inouchi**, Norimitsu Yoshida**, Hidekuni Harada**, Hiroaki Kondo*, Kanta Yamamoto*, Shuichi Nonomura** and Shoji Nitta* *Department of Electrical Engineering, Gifu University, 1-1 Yanaido, Gifu 501-1193, Japan **Environment and Renewable Energy Systems, Graduate School of Engineering, Gifu University, 1-1 Yanaido, Gifu 501-1193, Japan ABSTRACT Hydrogenated microcrystalline silicon (µc-Si:H) films are prepared by hot-wire assisted plasma enhanced chemical vapor deposition, which controls the hydrogen radical density by filament temperatures, T f, without changing other conditions. The effect of hydrogen radical on the properties of incorporated hydrogen into µc-Si:H films is studied using infrared absorption and gas effusion spectroscopies. The hydrogen concentration decreases with increasing T f. The crystalline volume fraction, Xc, increases with T f and shows a peak at T f of 1850 °C. Integrated intensities of the modes near 2000 and 2100 cm-1 decrease with increasing T f. Integrated intensity of the mode near 880 cm -1 shows almost same tendency of X c. The effect of hydrogen radical on the properties of incorporated hydrogen into µc-Si:H films is discussed.

INTRODUCTION Hydrogenated microcrystalline silicon (µc-Si:H) films can be prepared by plasma enhanced chemical vapor deposition (PECVD) using high dilution of SiH 4 in H2. Hydrogen radical density is one of the key deposition parameters on the growth of µc-Si:H. The effects of the hydrogen radical on the properties of incorporated hydrogen and the growth of µc-Si:H, however, are not yet understood. Recently we demonstrated hot-wire assisted PECVD as a new preparation method for µc-Si:H [1]. The hot-wire assisted PECVD consists of conventional PECVD for deposition and hot-wire for exiting hydrogen. The advantage of this method is that the hydrogen radical density is controlled by filament temperature, T f, without changing the other preparation conditions. In this report, µc-Si:H films were prepared at T f from room temperature to 2000 °C by hot-wire assisted PECVD. The effect of the hydrogen radicals on the incorporated hydrogen into µc-Si:H has been studied using infrared (IR) absorption and gas effusion spectroscopies. From these results, the properties of incorporated hydrogen into µc-Si:H films are discussed. Based on these results, the growth of µc-Si:H is also discussed.

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EXPERIMENT The samples were prepared on sapphire and crystalline silicon (c-Si) substrates by hotwire assisted PECVD using SiH4 and H2 . The total gas pressure was 6 Torr with the ratio R=H2/SiH4 of ~60. The substrate temperature, Ts, was ~250 °C and the rf-power (13.56 MHz) was 40 W. The filament temperature, Tf, was varied from room temperature (~20 °C) to ~2000 °C. The film thickness was from 0.7 to 0.9 µm. The Tf was measured by a radiation thermometer. Detail of hot-wire assisted PECVD apparatus was described elsewhere [1, 2]. The crystal

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