Growth of thick 4H-SiC epilayers in a vertical radiant-heating reactor
- PDF / 918,175 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 59 Downloads / 181 Views
Growth of thick 4H-SiC epilayers in a vertical radiant-heating reactor H. Tsuchida, I. Kamata, T. Jikimoto, and K. Izumi Central Research Institute of Electric Power Industry, 2-6-1 Nagasaka, Yokosuka, Kanagawa 240-0196, Japan ABSTRACT Growth of very thick 4H-SiC epilayers up to 215 µm has been demonstrated in a vertical radiant-heating reactor. Surface roughness is maintained as small as ~0.2 nm even for epilayers over 150 µm in thickness, and a regular step structure without macro step bunching is observed from the very thick epilayers indicating a stable step-flow growth. Photoluminescence and secondary ion mass spectroscopy (SIMS) were performed for a 150 µm-thick epilayer. The Photoluminescence showed strong free excitons and comparatively small nitrogen bound excitons, while aluminum-, boron- and titanium-related lines were almost negligible. The SIMS analysis found no impurities exceeding 1 [ 1014 cm-3. The influence of growth parameters on thickness uniformity will also be shown. INTRODUCTION Low-loss frequency converters and solid state circuit breakers are expected to enable flexible and efficient electric power transmission in current and future electric power systems. In such high-power applications, further increases in voltage levels of power semiconductor devices are desirable to reduce the number of devices connected in series, and a consequent reduction in the scale and cost of electric power equipment. Silicon carbide is a promising material for high-voltage power semiconductor devices [1]. From the material parameters of SiC, we may expect even over 20 kV devices with low forward voltage drop. A 12.3 kV PiN diode has been reported recently in use of thick SiC epilayers [2]. In order to fabricate SiC devices in higher voltage levels, it is need to acquire techniques in SiC epitaxy to achieve very thick epilayers over 100 µm or even a few hundred microns with a low carrier density around the 1014 cm-3 level. Growth of 150 µm-thick epilayers in a horizontal hot-wall reactor has been reported to achieve a low carrier density and good morphology [3]. For high-voltage SiC bipolar devices, impurity levels and defect densities may be expected to be very low to obtain sufficient minority carrier lifetime. Surface morphology should also be maintained through thick epitaxial growth within the level allowable for device fabrication. Increasing growth rate while maintaining high crystal quality and good uniformity with sufficient wafer capacity is a challenge for current SiC epitaxy. In a vertical hot-wall reactor, high growth rates up to 30 µm/h have been achieved with a specular surface [4]. In this paper, we report on growth of very thick epilayers in a vertical radiant-heating reactor. EXPERIMENT The CVD reactor used in this experiment has been described in detail elsewhere [5]. The reactor consists of a vertical hot-wall and an inner susceptor as shown in Fig. 1. We used a V-shaped susceptor with capacity for 2 [ 2-inch wafers. In this reactor, induction current flows only in the hot-wall, so that the sus
Data Loading...
