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Rixecker, and F. Young-Wook, A. One hour after immersion of the substrate 6, cooling was started at a rate of 0. Subsequently, the holding jig 5 was moved upwards to draw up and recover the substrate 6 from the melt 1, and the crucible was then allowed to cool to room temperature.
The micropipe defects were evaluated in the following manner:. A bulk silicon carbide single crystal was grown on a seed substrate 6 by the cooling method in the same manner as in Example I except that the graphite crucible 3 was charged with raw alloy materials having a composition of Si 0. This example illustrates the production of a bulk silicon carbide single crystal by the temperature gradient method using a crystal growth apparatus as shown in Figure 3.
The crystal growth apparatus shown in Figure 3 comprises a graphite crucible 3 containing an alloy melt 1, and the crucible 2 is placed in a reactor tube 10 made of quartz glass. The reactor tube is surrounded by a high-frequency induction heating coil 2b to heat the graphite crucible 3 by induction heating.
Also in the apparatus shown in Figure 3 , the temperature of the side wall of the crucible 3 is directly measured by a plurality of optical pyrometers 4. The high-frequency induction heating is controlled by the measured values of temperature of the side wall of the crucible 3. A temperature difference is formed along the height of the crucible 3 depending on the positional relationship between the crucible 3 and the high-frequency induction heating coil 2b.
The temperature gradient which is formed can be adjusted by varying the number of turns of the coil 2b and distance of adjacent turns thereof. In order to obtain an increased temperature gradient, it is effective to apply forced cooling to the lower temperature region of the crucible 3 using a water cooling jig. In this example, the upper part of the graphite crucible 3 formed the lower temperature region. The temperature of the melt 1 in the vicinity of a seed substrate 6 which was immersed in the lower temperature region was determined by measuring the temperature of the side wall of the crucible 3 by a pyrometer 4 located at the level where the substrate was positioned.
The temperature gradient was calculated from the difference in the temperature of the side wall of the crucible between the level where the substrate 6 was positioned and the level where the temperature was highest and from the distance between these two levels. The alloy melt formed in the graphite crucible 3 was heated for 5 hours while the above-described temperature gradient was maintained so that carbon was dissolved from the inner wall of the crucible into the melt to reach its saturation level and form a molten solution.
The graphite crucible 3 and the holding jig 5 which held the seed single crystal were both rotated in reverse directions to each other. In addition, the bulk silicon carbide single crystal was evaluated with respect to micropipe defects in the same manner as in Example 1. A bulk silicon carbide single crystal was grown on a seed substrate 6 by the temperature gradient method in the same manner as in Example 4 except the graphite crucible 3 was charged with raw alloy materials having a composition of Si 0.
A bulk silicon carbide single crystal was grown on a seed substrate 6 by the cooling method in the same manner as in Example 1 except that the graphite crucible 3 was charged with raw alloy materials having a composition of Si 0. A bulk silicon carbide single crystal was grown on a seed substrate 6 by the cooling method in the same manner as in Example 2 except that the graphite crucible 3 was charged with raw alloy materials having a composition of Si 0.
A bulk silicon carbide single crystal was grown on a seed substrate 6 by the temperature gradient method in the same manner as in Example 4 except that the graphite crucible 3 was charged with raw alloy materials having a composition of Si 0. The conditions of production and the results of measurements of the single crystals grown on a substrate for the foregoing examples and comparative examples are shown in Table 1.
Table 1 Composition of alloy charged atomic ratio Temp. As the cooling rate or the temperature gradient increases, the growth rate of a silicon carbide single crystal increases. It is considered from this result that diffusion of carbon dissolved in the alloy melt to reach the surface of the substrate would be the rate-determining stage for crystal growth of silicon carbide.
In Examples 1 - 3 by the cooling method , since the crystal growth step by cooling was performed just once, the resulting crystals had a thickness which was smaller than that obtained in Examples 4 - 6 by the temperature gradient method in which the duration of crystal growth was longer.
It should be understood that even in Examples 1 - 3, the crystals can be made to have an increased thickness by repeating the heating and cooling steps. All the silicon carbide single crystals obtained in Examples 1 - 6 and Comparative Example 1 - 4 had the crystal form of 6H-SiC which was the same as that of the substrate when examined by Raman spectroscopy and electron diffraction.
A method of producing a silicon carbide single crystal comprising the steps of: immersing a seed substrate of silicon carbide in a melt of an alloy comprising Si, C, and M wherein M is either Mn or Ti and allowing a silicon carbide single crystal to grow on the seed substrate by supercooling of the alloy melt as a molten solution at least in the vicinity of the seed substrate so as to create a state which is supersaturated with SiC, characterised in that the melt has an atomic ratio between Si and M in which the value of x, when expressed as Si 1-x M x , is 0.
A method as claimed in claim 1 wherein the supercooling of the alloy melt is achieved by cooling the alloy melt. A method as claimed in claim 2 wherein the growth of the silicon carbide single crystal on the substrate is continued by terminating the cooling of the alloy melt at a temperature which is higher than the solidus temperature of the alloy and subsequently performing supercooling repeatedly by repeated heating and cooling of the melt.
A method as claimed in claim 1 wherein the supercooling of the alloy melt is achieved by forming a temperature gradient in the alloy melt.
Composition of alloy charged atomic ratio. EPB1 en. DED1 en. WOA1 en. JPB2 en. Material for raising single crystal sic and method of preparing single crystal sic. EPA1 en. EPA4 en. USB2 en. KRB1 en.
TWIB en. Powder preparation Silicon carbide SiC is a compound of silicon and carbon with a chemical formula of SiC. Kneading The fine grain sub-micron powder is then homogeneously mixed with non-oxide sintering aids a binder to form a paste. Shape forming The resulting pasty mixture may be compacted and shaped either by extrusion or by cold isostatic pressing. Extrusion consists in forcing the pasty mixture through a die with an opening. Silicon carbide tubes are produced through extrusion.
The properties in the extrusion direction differ from the properties in other directions. Cold isostatic pressing is the powder compaction method conducted at room temperature, and it involves applying pressure from multiple directions through a liquid medium surrounding the compacted part. A flexible mold immersed in a pressurized liquid medium is used. Materials with a uniform anisotropic structure are prepared using an isostatic pressing method.
The materials used to produce silicon carbide plates and blocks are manufactured by cold isostatic pressing. Computer Numerical Control CNC Machining CNC machining is used to machine the surface of the plates or drill the holes on process and services sides in the cylindrical blocks.
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