Yasushi Urakami

Defect-less trench filling of epitaxial Si growth by H/sub 2/ annealing

A new trench filling epitaxial Si growth process is proposed for the high aspect ratio doped region. Pre-H/sub 2/-annealing treatment before filling epitaxial growth realizes the prevention of the crystal defects in the filling epitaxial layer. After filling epitaxial growth, the sequential processes, i.e., HCl etching, refilling epitaxial growth and post-H/sub 2/-annealing, make a trench filling. The fabricated doped region has a high aspect shape (width: 3.0 /spl mu/m, depth: 32 /spl mu/m, aspect ratio: 10.7), which has been investigated by the cross-sectional SCM observation.

Fabrication of high aspect ratio doping region by using trench filling of epitaxial Si growth

A new trench filling epitaxial Si growth process has been proposed for the high aspect ratio doping region. This epitaxial process realizes the reducing void size in the trench compared with a conventional epitaxial process. The influence of the micro-void on multi-RESURF effect has been estimated by using numerical simulation. The decrease of breakdown voltage of simulated structures with micro-void that reflect experimental results is below 2.5% compared with ideal non-void structure.

TSD Reduction by RAF (Repeated a-Face) Growth Method

A reduction in threading screw dislocation (TSD) density in 4H-SiC (silicon carbide) crystal is required for SiC power devices. In this study, TSD’s transformation by the RAF (repeated a-face) growth method [1] is observed by transmission X-ray topography (g=0004) of the cross-section of the crystal. Increasing the number of repetitions of a-face growth and offsetting c-face growth to an angle of several degrees reduce TSDs. TSD density is reduced to 1.3 TSD/cm2. The RAF growth method is very effective towards growing high quality SiC crystals.

Breakthrough of on-resistance Si limit by Super 3D MOSFET under 100V breakdown voltage

Under 100V breakdown voltage, a new device structure is required for the purpose of reducing on-resistance and for high reliability. In this study, it was demonstrated that the Si limit of on-resistance was broken by Super 3D MOSFET structure in an actual prototype fabrication. This Super 3D MOSFET has a wide current path in the depth direction without enlarging its surface area. Its on-resistance was 16.4 m¿·mm2 at the breakdown voltage of 58V. This on-resistance was below the Si limit and the lowest result ever reported. Moreover, it was clarified that the UIS (unclamped inductive switching) endurance of this device was 3.08 J/cm2 with 3 mm × 3 mm size chip and this result was 1.5 times stronger than that of conventional structure. This Super 3D structure was fabricated by simplified trench filling epitaxial process and high aspect ratio trench etching process. The Super 3D MOSFET is very attractive for automotive motor drive use.

Development of RAF Quality 150mm 4H-SiC Wafer

We have developed RAF (Repeated a-face) growth method which is high quality bulk crystal growth technology [1, 2]. A block crystal more than 150 mm square size was produced by the RAF growth method. Since c-face growth crystal was produced on the seed obtained from the block crystal, high quality 150mm 4H-SiC wafer was achieved. This paper reports the results of the quality evaluation.

Growth of Low Resistivity n-Type 4H-SiC Bulk Crystals by Sublimation Method Using Co-Doping Technique

The nitrogen (N) and aluminum (Al) co-doped growth of n-type 4H-SiC bulk crystals were performed by sublimation method. In the co-doping growth, we achieved the lowest resistivity of 6.9mWcm, and we also confirmed phenomenon of stacking faults suppression in spite of high N concentration more than 8 x 1019cm-3.

Growth Study of p-Type 4H-SiC with Using Aluminum and Nitrogen Co-Doping by 2-Zone Heating Sublimation Method

p-type SiC crystals doped with aluminum and nitrogen were grown by the sublimation method. We found that Al and N co-doping is effective for stabilized growth of p-type 4H-SiC polytype. We studied the relationship of polytype of grown crystals and the condition of Al and N feeding during the crystal growth. p-type 4H-SiC with p~1 x 1018 cm-3 are stably-obtained with this method.

Characterization of Vacant Broken Line Defects in A-Face Grown Crystals of Silicon Carbide

A new type of defects, vacant broken line defects, was found to occur in a-face grown crystals of 4H-Silicon Carbide. We characterized the vacant broken line defects by high voltage transmission electron microscope (HV-TEM). The HV-TEM image revealed that the edges of broken line defects were connected by a bundle of dislocations, which elongated to the growth direction on the basal plane. The analysis by gb method for determining Burgers vector indicated that the dislocations were not pure screw dislocations, but complex of screw and edge dislocations. The vacant broken line defect was considered to be a quasi-stable state of a bundle of basal plane dislocations in a-face growth, similar to a micropipe defect in c-face growth.

Fourier Transform Analysis of Basal Plane Dislocation Structure in Repeated A-Face Grown Crystals

Morphological features, such as the orientation and linearity of basal plane dislocations (BPDs) in SiC crystals, were analyzed by applying a two-dimensional fast Fourier transform (2D-FFT) to X-ray topographic images of the BPDs. An SiC crystal fabricated by an improved repeated a-face (RAF) method and an SiC crystal fabricated by an conventional RAF method discussed in a previous study were evaluated. In the 2D-FFT images of the improved crystal, streaks along the directions were observed, indicating that the BPDs were highly oriented along the directions. The degree of orientation of the BPDs, which may reflect their linearity, was calculated, and the improved RAF crystal had a much higher degree of orientation than the conventional RAF crystal.