Principal Research Results

Establishment of the Base Technology of Large-Capacitance
SiC Semiconductor−Development of High Growth Rate and Large-Diameter Epitaxy Technique−Background
Since the power electronics devices applying SiC semiconductor can realize high efficiency compared to devices using thepresent Si semiconductor, the SiC devices are expected as high-voltage and low-loss devices. We have been developing SiC epitaxy
technique ＊ 1 aiming to adopt SiC devices to the electric power industry. The development of the 4H-SiC ＊ 2 epitaxy technique achieving high-quality, high growth rate and large-diameter is essential to realize the SiC semiconductor devices for electric power industry
as well as public use.

Objectives
This study aims to develop the epitaxy technique for the growth of high-quality 4H-SiC epilayers achieving large-diameter
uniformity and high growth rate.

Principal Results
1. Development of high growth rate and large-diameter epitaxy reactor (CVD ＊ 3 reactor)
The inside design of the CVD reactor was examined. The vertical position of the susceptor and induction coil can be
modified to adjust the temperature gradient in the CVD reactor. To obtain large-diameter uniformity, we modified the diameter andhorizontal/vertical position of the gas inlet as well as the rotation system of the susceptor (Fig. 1).
2. Performance of the developed CVD reactor
Growth rate increases with the increase in source gas concentration. A maximum growth rate of up to 250μm/h is achieved.
This growth rate is the highest in recently reported high speed 4H-SiC epitaxy (Fig. 2).
The modification of the CVD reactor for the large-diameter uniformity makes it possible to obtain simultaneously highgrowth rate and large-diameter uniformity in the level capable for practical use (Fig. 3). This is the first report that achieves a highgrowth rate more than 20μm/h in a large-area over 4-in. diameter.
3. Quality of the as-grown epilayer
The quality of epilayers is investigated using low-temperature photoluminescence (PL) (Fig. 4(a)), atomic force microscopy(AFM) (Fig. 4(b)), and PL decay time measurement (Fig. 4(c)). In each measurement, the results indicate the as-grown epilayers havehigh purity and a high quality.
From the above-mentioned results, we developed high growth rate and large-diameter 4H-SiC epitaxy technique with thequality that was enough for the practical use of the SiC devices and demonstrated it. This result won a research encouragement prize in
16th Meeting on SiC and Related Wide Bandgap Semiconductors, the Japan Society of Applied Physics, in 2007.

Future Developments
It is planned to practically develop the high growth rate and large-diameter epitaxy technique and apply it to high-voltage
devices.
Main Researcher: Masahiko Ito, Ph. D.,
Visiting Researcher, Advanced Functional Materials Sector, Materials Science Research Laboratory
Reference
M. Ito et al, “Development of 4H-SiC epitaxial growth technique achieving high growth rate and large-area uniformity”: Applied
Physics Express 1 (2008) 015001＊1：Technique for depositing high-quality SiC single crystal film on the substrates.
＊2：One of the polytypes of SiC single crystal. It has suitable physical properties as power devices.
＊3：Abbreviation of “Chemical Vapor Deposition”. The chemical process to produce thin films from the source gases.

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4. Power Delivery

Fig.1 Cross-sectional schematic drawing of theCVD reactor

Fig.2 Growth rate as a function of source gasconcentration. The insert shows aInduction heating is applied mainly to the hot wall, andthe susceptor is heated by radiation from the hot wall.
To optimize the growth condition, the diameter andposition of the gas inlet as well as the vertical positionof the induction coil and the susceptor can bemodified.

Nomarski microscope image of anepilayer surface grown at a 250μm/h.
The growth rate of 250μm/h is more than 10 times
higher than the typical growth rate in recent multiwafer reactors.

4Fig.3 Radial direction distribution of thegrowth rate (red) and intentional n-type
doping concentration (blue) on thesusceptor
The mean growth rate of 79μm/h, and both thegrowth rate uniformity and the n-type doping
concentration uniformity for practical use are achievedin a 5-in. diameter area.

Fig.4(a) Low-temperature PL spectra taken
fr o m a n epi l a ye r gr o w n a t a 75μm/h. (b) AFM surface image, and(c) typical decay curve obtained for a
280-μm-thick epilayer

Uniformity of the growth rate σ/mean= 1.1%,
Mean growth rate 79μm/h,Uniformity of the n-type doping concentration
σ/mean= 6.7%,
Mean n-type doping concentration 9.3 ×1013 cm-3

The PL of free-exiton (I77), which suggests highquality of the crystal, is notably predominant. The
surface of thick epilayer has good morphology(RMS=0.20 nm), and the epilayer has long carrier
lifetime (1.0μs on average). These results indicate
high quality of the crystals on the level sufficient forpractical use.

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