High-Temperature Gas Source Method Research Articles

(Invited) Progress in Fast 4H-SiC Crystal Growth and Defect Reduction By High-Temperature Gas-Source Method

Practical applications of 4H-SiC Schottky barrier diodes (SBDs) and metal-oxide-semiconductor field-effect transistors (MOSFETs) have started in various fields. Ongoing efforts to improve the productivity and quality of 4H-SiC wafers are crucial to further expand the production volume of the SiC power devices. The sublimation method is a standard growth process to produce SiC bulk crystals. In the method, powder source is sublimated at a temperature of ~2200ºC and recrystallized on a seed crystal. Although the growth techniques to obtain large diameter (150-200 mm) SiC substrates have developed using the sublimation method, the growth rates remain in about 0.3-0.5 mm/h. We have attempted to realize much higher growth rates in SiC crystal growth by the high-temperature gas-source method (high-temperature chemical vapor deposition) using SiH4 and C3H8 as the source gases and obtained ~3 mm/h or more at a high growth temperature at 2500-2550ºC and high input partial pressure of the source gases (>10 kPa for SiH4) [1]. Another topic in the high-temperature gas-source method can be realizing dislocation densities lower than those of the seed crystals. In the proper conditions, we observe no significant increase in the dislocation densities in the early stage of the growth and gradual reduction of the dislocation densities along the growth direction. In this paper, we introduce the key techniques in obtaining a high growth rate and high material quality in SiC bulk crystal growth by the high-temperature gas-source method.[1] H. Tsuchida and T. Kanda, Materials Science in Semiconductor Processing 176 (2024) 108315.

Advances in fast 4H–SiC crystal growth and defect reduction by high-temperature gas-source method

Advances in fast 4H–SiC crystal growth and defect reduction by high-temperature gas-source method

Investigation of propagation and coalescence of threading screw and mixed dislocations in 4H-SiC crystals grown by the high-temperature gas source method

• 4H-SiC crystals grown by the high-temperature gas source method were investigated. • Cross-sectional sample was observed by synchrotron X-ray section topography. • Coalescence of TSD and TMD was confirmed by topography images. Propagation of threading screw dislocations (TSDs) and mixed dislocations (TMDs) in 4H-SiC crystals grown by the high-temperature gas source method were investigated. Cross-sectional samples cut in the growth direction were prepared and X-ray transmission topography with a diffraction vector g = 000 4 ¯ was performed to reveal the dislocation lines. The topography image revealed that some pairs of TSDs/TMDs extending in the growth direction approached each other and merged in the middle of the grown crystal. Direct observations by synchrotron X-ray section topography confirmed that a pair of TSD and TMD with opposing c -component Burgers vectors had merged and the c -components of the dislocations were annihilated during crystal growth. Some pairs of TSDs/TMDs, however, showed no coalescence, although they could be annihilated topologically. The mechanism behind the success and failure of TSD/TMD coalescence was also discussed.

Reduction in dislocation densities in 4H-SiC bulk crystal grown at high growth rate by high-temperature gas-source method

We performed fast growth of a 4H-SiC crystal using the gas-source method and investigated the crystal to reveal changes in dislocation densities along the growth direction. The remarkable reduction in densities of threading and basal plane dislocations to be less than 1/10 and 1/20, respectively, was confirmed in the crystal grown at ∼3 mm h−1. The change in radial distribution of threading dislocations indicates enhanced reduction in dislocation densities within an area containing high density dislocations. We discussed possible mechanisms which could explain declining densities of threading dislocations according to the results obtained by classifying threading dislocations into each Burgers vector.

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

The process conditions for fast growth of 4 in. 4H-polytype SiC (4H-SiC) single crystals were studied for high-temperature gas source method. Prior to experiments, crystal growth simulations were conducted to investigate the influence of vertical gas-flow velocity on the radial distribution of the growth rate. Crystal growth experiments were performed using the crucibles designed for 4 in. crystal growth following the simulation studies. By investigating growth rate as functions of the input partial pressure of source gases and temperatures of growing surfaces, expressions for the growth rate of 4-in. crystals were derived. We also clarified the optimal conditions for single-crystal growth. Finally, fast growth of 4 in. 4H-SiC crystals with uniform shape was demonstrated.

X-Ray Topography Analysis of 4H-SiC Crystals Grown by the High-Temperature Gas Source Method

Synchrotron X-ray topography was carried out for 4H-SiC crystals grown by high-temperature gas source method, and transmission topography analysis with g= or 0004 was carried out for the cross-sectional samples. Dislocation contrasts extended in the growth direction were observed and the propagation behavior of threading screw dislocations (TSDs), threading edge dislocations (TEDs), basal plane dislocations (BPDs) and stacking faults (SFs) in the facet and step-flow regions were discussed. The propagation of dislocations in the fast grown crystal with a growth rate of 3.1mm/h was also evaluated by cross-sectional topography.

Fast growth of n-type 4H-SiC bulk crystal by gas-source method

Abstract Fast growth of n-type 4H-SiC crystals was attempted using a high-temperature gas-source method. High growth rates exceeding 9 mm/h were archived at a seed temperature of 2550 °C, although the formation of macro-step bunching caused doping fluctuation and voids in the grown crystal. We investigated a trade-off between growth-rate enhancement and macro-step formation and how to improve the trade-off. By controlling the growth conditions, the growth of highly nitrogen-doped 4H-SiC crystals without the doping fluctuation and void formation were accomplished under a high growth rate exceeding 3 mm/h, maintaining the density of threading screw dislocations in the same level with the seed crystal. The influence of growth parameters on nitrogen incorporations into grown crystals was also surveyed.

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.

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.

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.

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.

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.

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.

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.

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.