Jung-Woo Choi

Initial Stage Modification for 6H-SiC Single Crystal Grown by the Physical Vapor Transport (PVT) Method

Two SiC single crystal ingots were prepared using sublimation PVT techniques through the different process procedure and then their crystal quality was systematically compared, because the present research was focused to improve the quality of SiC crystal by modifying the initial stage of the PVT growth. Before the main growth step for growing SiC bulk crystal, initial stage period where growth rate was kept to relatively low rate of <10μm/h was introduced to conventional process procedure. N-type 2”-SiC single crystals exhibiting the polytype of 6H-SiC was successfully fabricated. As compared to the characteristics of SiC crystal grown using the conventional schedule, the quality of SiC crystal grown with modifying the initial stage was significantly improved, exhibiting decrease of defect formation such as micropipe and polytype formation.

Resistivity Increase in 6H-SiC Crystal Grown with Simple Modification in PVT Process

6H-SiC single crystal was grown with simple modification in PVT process to investigate the aspect of resistivity change in crystal. The modified process consisted of a new initial step to get rid of impurities in the growth cell before the main growth of SiC crystal. The new step in the modified process was designed to consist of higher temperature than the growth temperature for sublimation of impurities. SiC crystal grown with using 2 times of impurities sublimation process (ISP) step exhibited lower variation of resistivity value on whole wafer than SiC grown using with 1 time. With implementation of new modified step in growth process, SiC single crystal with resistivity value above 103Ωcm could be obtained by simple PVT process and conventional low-purity SiC source material.

Quality improvement of 4″ 4H-SiC crystal by using modified seed adhesion method

The method to attach seed to crucible lid as well as seed quality is very important for obtaining high quality crystals. Therefore, modified seeding method was developed for improving adhesive layer between seed and graphite crucible lid. SiC single crystal grown with modified seeding method definitely exhibited lower micropipe density (MPD) and lower full width at half maximum (FWHM) values comparing with values from conventional seeding method. Etch pit density of SiC crystal was successfully decreased with using the modified seeding method.

The Quality Investigation of 6H-SiC Crystals Grown by a Conventional PVT Method with Various SiC Powders

In this paper, we investigate the quality difference of SiC crystals grown by a conventional physical vapor transport method using various SiC powders. While the growth rate was revealed to be dependent upon the particle size of the SiC powder, the growth rate of SiC bulk crystals grown using SiC powder with a smaller particle size (20 nm) was definitely higher than those using lager particle sizes with and , respectively. All grown 2 inch SiC single crystals were proven to be the polytype of 6H-SiC and the carrier concentration levels of about were determined from Hall measurements. It was revealed that the particle size and process method of SiC powder played an important role in obtaining a good quality, high growth rate, and to reduce growth temperature.

Non-Polar SiC Crystal Growth with m-Plane(1-100) and a-Plane(11-20) by PVT Method

The present research was focused to produce 2 inch wafers from small rectangular seeds and to investigate the quality of non-polar SiC substrates grown by a conventional PVT method. The non-polar SiC seeds were prepared by cutting along <0001> direction of 6H-SiC crystal grown on (0001) basal plane. As SiC ingot grows, many defects in connected region were gradually diminished. While the full width at half maximum (FWHM) values of m-plane SiC substrate measured along a-direction and c-direction were 60 arcsec and 70 arcsec, respectively, and the FWHM values of a-plane SiC substrate measured along m-direction and c-direction were 27 arcsec and 31 arcsec respectively. The stacking faults lying in the basal plane can be detected by molten KOH etching as linear etch pits extending along <0001> on the (11-20) surface and the carrier concentration was observed by Raman spectrum.

The Effect of Slurry Composition and Flatness on Sub-Surface Damage and Removal in Chemical Mechanical Polishing of 6H-SiC

The effect of slurry composition and wafer flatness on a material removal rate (MRR) and resulting surface roughness which are evaluation parameters to determine the CMP characteristics of the on-axis 6H-SiC substrate were systematically investigated. 10 x 10 mm2 6H-SiC substrates and 2-inch SiC wafers fabricated from the ingot grown by a conventional physical vapor transport (PVT) method are used for this study. The SiC substrate after the CMP process using slurry added oxidizers into slurry consisted of KOH-based colloidal silica and nano-size diamond particle exhibited the significant MRR value and a fine surface without any surface damages. SiC wafers having high bow value after the CMP process exhibited large variation in surface roughness value compared to wafer with low bow value. The CMP-processed SiC wafer having a low bow value of 10m was observed to result in the MRR value of 0.15 m/h and the mean height (Ra) value of 0.772Ǻ.

Characterization of Non-polar 6H-SiC Substrates for Optoelectronic Device Applications

The present research was focused to investigate the quality of non-polar SiC substrates grown by a conventional PVT method for optoelectronic applications. The half part of the PVT-grown 6H-SiC crystal boules was sliced along a-direction and m-direction to extensively analyze non-polar planes and then remaining part of that was sliced along the basal plane to produce wafers. The non-polar SiC m-plane and a-plane exhibited apparent peaks around 2 theta

The Micro Bubble Effect in the Seed Adhesion on the Crystal Quality of 6H-SiC grown by a Physical Vapor Transport (PVT) Process

With different seed adhesion methods, we obtained two different aspects with or without micro-bubble in the interface between a seed and a dense graphite seed holder. To improve the quality of SiC wafer, we introduced a sucrose caramelizing step at the seed adhesion using the sucrose, The n-type 2 inch single crystal exhibiting the polytype of 6H-SiC were successfully fabricated and carrier concentration levels of about was determined from Hall measurements, As compared to the characteristics of SiC crystal grown with micro-bubble in the interface between the seed and the dense graphite seed holder, the SiC crystal grown without micro-bubble definitely exhibited lower resistivity, lower micropipe density and higher mobility relatively.

The Diameter Expansion of 6H-SiC Single Crystals by the Modification of Inner Guide Tube

A sublimation method using the SiC seed crystal and SiC powder as the source material is commonly adopted to grow SiC bulk single crystal. However, it has proved to be difficult to achieve the high quality crystal and the process reliability because SiC single crystal should be grown at very high temperature in closed system. The present research was focused to improve SiC crystal quality grown by PVT method through using the new inner guide tube. The new inner guide tube was designed to prevent the enlargement of polycrystalline region into single crystalline region and to enlarge the diameter of SiC single crystal. The 6H-SiC crystals were grown by conventional PVT process. The seed adhered on seed holder and the high purity SiC source materials are placed on opposite side in sealed graphite crucible surrounded by graphite insulation. The SiC bulk growth was conducted around 2300 of growth temperature and 50 mbar in an argon atmosphere of growth pressure. The axial thermal gradient across the SiC crystal during the growth was estimated in the range of 1520 /cm.