Yuichiro Tokuda

Fast 4H-SiC Crystal Growth by High-Temperature Gas Source Method

Possibilities of very fast 4H-SiC crystal growth using a high-temperature gas source method are surveyed by computational simulation and experimental studies. The temperature range suitable to obtain high growth rates are investigated by simulating temperature dependences of growth rates for H2+SiH4+C3H8 and H2 +SiH4+C3H8+HCl gas systems. Simulation and experimental results demonstrate that an increase in source gas flow rates as well as gas-flow velocities enhance growth rates. High growth rates exceeding 1 mm/h are experimentally obtained using both gas systems. Single crystal growth on a 3-inch diameter seed crystal is also demonstrated.

High-speed, high-quality crystal growth of 4H-SiC by high-temperature gas source method

By employing computational simulations and experiments, we explore the potential for fast, high-quality 4H-SiC crystal growth using a high-temperature gas source method. Appropriate temperature ranges for obtaining high growth rates in H2 + SiH4 + C3H8 + HCl and H2 + SiH4 + C3H8 gas systems are examined computationally. Experimental results show that an increase in the gas flow velocity enhances the crystal growth rate, and high growth rates of >1 and >2 mm/h are obtained using the H2 + SiH4 + C3H8 + HCl and H2 + SiH4 + C3H8 gas systems, respectively. Single crystal growth that retains the low threading screw dislocation density of the seed crystal is accomplished, even at very high growth rates of >2 mm/h.

Structural analysis of double-layer Shockley stacking faults formed in heavily-nitrogen-doped 4H-SiC during annealing

We investigated the structures and expansion behavior of double-Shockley stacking faults (DSFs) formed in heavily nitrogen-doped 4H-SiC during annealing. Heavily doped epilayers prepared as specimens were successively annealed. Various types of DSFs showing different shapes and dislocation contrasts were found in photoluminescence and synchrotron X-ray topography images. Taking account of every possible stacking sequence forming DSFs, the structures of various types of DSFs were determined from observations by plan-view transmission electron microscopy (TEM) and cross-sectional high-angle annular dark-field scanning TEM. We found that a bounding dislocation enclosing a DSF splits into two partial dislocations (PDs), and their Burgers vectors are identical, while the distance of the two PDs depended on their core structures (30° Si-, 30° C- or 90° C-core). We also discussed the contrast rule for the dislocation consisting of two PDs in the synchrotron X-ray topography images and the mobile PDs for the DSF ...

Evolution of Fast 4H-SiC CVD Growth and Defect Reduction Techniques

This paper introduces our recent challenges in fast 4H-SiC CVD growth and defect reduction. Enhanced growth rates in 4H-SiC epitaxial growth by high-speed wafer rotation and in a high-temperature gas source method promoting SiC bulk growth by increasing the gas flow velocity are demonstrated. Trials and results of deflecting threading dislocations by patterned C-face 4H-SiC epitaxial growth are also shown.

4H-SiC Bulk Growth Using High-Temperature Gas Source Method

Our latest results of SiC bulk growth by High-Temperature Gas Source Method　are given in this paper. Based on Mullins-Sekerka instability, optimal growth conditions to preclude dendrite crystals, which are one of the pending issues for high-speed bulk growth, was studied. First, the simulation studies showed that high temperature gradient in a growing crystal is required for high-speed bulk growth without dendrite crystals. Second, high-speed bulk growth was demonstrated under high temperature gradient.

Doping Fluctuation and Defect Formation in Fast 4H-SiC Crystal Growth Using a High-Temperature Gas Source Method

This paper investigates the quality of 4H-SiC crystals grown at a very fast growth rate (> 2.5 mm/h) using a high-temperature gas source method. Differences in nitrogen doping efficiency were clarified in facet and step-flow regions. In case for growth in the macro-step bunching mode, doping fluctuation and void formation were observed in the macro-step bunching region. Propagation of threading screw dislocations (TSDs) in the grown crystal was also investigated by synchrotron X-ray topography.

Developing Technologies of SiC Gas Source Growth Method

In order to diffuse the use of SiC, mass-production technologies of SiC wafers are needed. It is easy to be understood that high-speed and long-sized growth technologies are connected directly with mass-production technologies. The gas source growth method such as HT-CVD has the possibilities and the potential of the high-speed and long-sized growth. In this article, it was clarified that the high growth rate were achieved by the control of the source gas partial pressures and by the gas boundary layers. The average growth rate was 1mm/h on the f4 inch-diameter crystal, and the maximum growth rate reached 3.6 mm/h on the 12.5x25 mm tetragon by the above gas control. The crystal qualities of the gas source methods were also evaluated the equivalent level in comparison with the sublimation method. Concerning the 1mm/h-growth f3 inch crystal, the densities of TSDs were kept in the 102 cm-2 levels from the seed to the upper-side of the ingot. Moreover, the ingot size increased year by year and a f4 inch x 43 mm sized ingot has been developed.

High-Speed and Long-Length SiC Growth Using High-Temperature Gas Source Method

This article gives the results of crystal growth by a High-Temperature Gas Source Method such as HTCVD. It was reported that clusters were formed and were an important factor of the growth in HTCVDs, and some influences of them were investigated. The difference between the model with and without clustering was compared. The experimental growth rates corresponded to the cluster model, and this indicated that clusters affect the crystal growth. Relations between the experimental growth rate and the growth temperature as a function of gas flow ratio were investigated. The gas flow ratio was defined: (SiH4+C3H8) / (SiH4+C3H8+H2). Maximum growth rate was 2.3mm/h under high source gas ratio. At present, a Φ75mm×54mm sized ingot has been developed.

Dislocation Analysis of 4H-SiC Crystals Obtained at Fast Growth Rate by the High-Temperature Gas Source Method

This paper reports on evidence of high-quality and very fast 4H-SiC crystal growth achieved using a high-temperature gas source method. The formation of threading screw dislocations (TSDs) during crystal growth was examined by comparing synchrotron X-ray topography images taken for a seed and grown crystals, while the generation of a high density of new TSDs is observed under improper growth condition. High-quality crystal growth retaining the TSD density of the seed crystal was accomplished under an improved condition, even for a very high growth rate of 2.1 mm/h.

Limitations in Very Fast Growth of 4H-SiC Crystals by High-Temperature Gas Source Method

Limitations in the very fast growth of 4H-SiC crystals are surveyed for a high-temperature gas source method. The evolution of macro-step bunching and void formation in crystal growth is investigated by changing the partial pressures of the source gases and crystal rotation speeds. The variation in macro-step formation depending on radial positions, where step-flow or spiral growth governs, of a grown crystal is also revealed. Based on the relation between growth conditions and macro-step bunching, a trade-off between growth rate enhancement and crystal quality and a method to improve such trade-off are discussed. Nitrogen at a high concentration under very high growth rates in the high-temperature gas source method is also investigated.