Fusao Hirose

High-Quality SiC Bulk Single Crystal Growth Based on Simulation and Experiment

The numerical simulation and in-situ X-ray topography were applied to observe the phenomena inside a crucible. Numerical simulation pointed out that macroscopic grown crystal quality such as grown crystal shape strongly depends on the temperature distribution inside a crucible. In-situ X-ray topography revealed that when the defects were generated, and how the defects were propagated. Most of defects were generated at the initial growth stage. It is important to control the initial stage in order to obtain a high quality SiC single crystal. Numerical simulation also suggested that it is important reduce the residual stress in a grown crystal in order to avoid the dislocation occurrence. From these results based on numerical simulation and experiment, SiC sublimation growth was controlled actively, and the large and high quality SiC single crystal have been grown. Introduction Silicon carbide single crystal is usually grown by sublimation (modified Lely method). Since the first report of modified Lely method [1], more than 20 years has passed. However, there is a lot of remaining issues that should be solved. The main reason of this situation is that sublimation process is a black box process inside a closed carbon crucible above 2000 K. It is so difficult to know what going on inside a crucible, that it is much difficult to control the sublimation process actively. In order to overcome this point, the authors have applied the numerical simulation to see the phenomena inside a furnace [2,3,4,5]. The authors also developed the in-situ X-ray topography system to observe the crystal growth features inside a closed carbon crucible [6,7]. By using these observation tools, the SiC sublimation growth could be understand more detail [7,8,9,10], and could be controlled actively [3,11,12]. In this paper, the observation results and the example active control of SiC sublimation growth are described. Simulation The configuration of numerical modeling was based on the conventional RF induction-heating furnace that we used in experiments. Electromagnetic and thermal fields were analyzed by the commercial software, Flux-Expert [13,14], and CFD-ACE+[15]. Since convective heat transfer could be neglected in our experiments, the equation for momentum transfer was not analyzed. From the thermal fields, the concentration distribution of sublimated species was analyzed according to the LTCE model [13]. The residual stress in a grown crystal was also analyzed. Materials Science Forum Online: 2004-06-15 ISSN: 1662-9752, Vols. 457-460, pp 29-34 doi:10.4028/www.scientific.net/MSF.457-460.29

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.

Reducing Stacking Faults in Highly Doped N-Type 4H-SiC Crystal

We investigated a way of reducing the stacking fault (SF) density on a highly nitrogen (N) doped 4H-SiC crystal. SFs were generated at highly N doped crystal exceeding 4 x 1019 cm-3 and the density was increased with increasing N concentration. We found that Al co-doping had the potential to suppress this SF generation and was effective up to an N concentration of about 1 x 1021cm-3. This effect depended strongly on the Al concentration. We discussed the reason for the SF suppression effect of Al co-doping.

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.

Stress Analysis of SiC Bulk Single Crystal Growth by Sublimation Method

In order to grow a high quality SiC bulk single crystal, it is i mportant to moderate the residual stress in the grown crystal. The residual stress is affected by not only the temperature distribution, but also by the boundary conditions. In this study, firstly, the effect of the polycrystal and of the crucible walls on the stress distribution was numerically analyzed. The effect of the grown crystal shape on the residual stress was also analyzed and compar ed to the growth experiment. It is pointed out that in order to moderate the residual stress, it is nece sary to take care not only of the temperature distribution but also of the boundary conditions.

Mechanism of nitrogen incorporation in sublimation growth of SiC

Abstract 6H-SiC crystals have been grown on the Si-face and the C-face of 6H-SiC seed crystals by sublimation growth, respectively, and their deep photoluminescence (PL) have been investigated in detail. The deep PL spectrum of undoped 6H-SiC crystal grown on the C-face consisted of multiple broad emissions. On the other hand, undoped 6H-SiC crystal grown on the Si-face showed a single weak emission peak. In the case of the nitrogen-doped 6H-SiC crystals grown on the C-face, the emissions decreased with increasing nitrogen doping concentration and that of the nitrogen-doped 4H-SiC crystals grown on the C-face also showed the same behavior. As a C-vacancy is easy to form during the sublimation growth on the C-face, we think that nitrogen occupies the C-vacancy during the doping growth and leads to a decrease in the C-vacancy concentration as reflected by the PL analysis. We speculated that the difference in the doping concentration of nitrogen in the C-face and the Si-face-grown SiC crystal is related to the presence of the C-vacancy during crystal growth.

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.

Characteristics of an amorphous magnetic alloy layer prepared by laser quenching, and its application to a torque sensor

Abstract To fabricate an amorphous magnetic alloy layer, an Fe78B13Si9 crystalline layer firmly fixed on a stainless steel substrate by silver brazing was melt quenched by laser irradiation. The laser-quenched layer consisted mainly of the amorphous single phase with an orderly striped pattern, divided by the heat-affected zones. The vibrating sample magnetometry measurements indicated that the laser-quenched layer had the magnetic easy direction along the direction of the laser scan. Taking into account the magnetic anisotropy, the laser-quenched layer was utilized to construct a non-contact-type static torque sensor. It was found that the sensitivity and the linearity were very good when the laser beam was scanned parallel to the direction of maximum stress induced on the shaft surface by the applied torque.

Inclination of a threading dislocation in an epilayer of 4H-SiC

Threading dislocations (TDs) are inclined from the [0001] c-axis in 4H-SiC epilayers which are produced by the step-controlled technique. The reason for this inclination is discussed in the framework of isotropic elastic theory of dislocation. The elastic strain energy of a TD in an epilayer is calculated as a function of its orientation, and the minimum energy orientation is used to predict the inclination angle. The results of the calculations are as follows. For a cut-off angle (α) of 4°, a threading edge dislocation (TED) and a threading pure screw dislocation (TpSD) are inclined from the c-axis by 12 and 2°, respectively: Threading near screw dislocations (TnSDs) and threading mixed dislocations (TMDs) are inclined by angles ranging from 8 to 15° from the c-axis, depending on their actual Burgers vectors. Similarly for α of 8°, a TED and a TpSD are inclined from the c-axis by 21 and 4°, respectively: TnSDs and TMDs are inclined from the c-axis by angles ranging from 7 to 17°. These predictions are in good agreement with experiment.

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.