A device and method for judging the level of seed crystal contact liquid

Abstract

The present invention discloses a device and method for judging the horizontality of seed crystal contact with liquid, wherein the device part includes a graphite crucible, a graphite seed crystal holder, a graphite seed crystal rod and a silicon carbide seed crystal, a single positive graphite electrode and two or more negative graphite electrodes on the graphite seed crystal holder are placed on the edge of the seed crystal holder and arranged in a rotationally symmetrical manner so that the multiple electrodes are in the same horizontal plane, the seed crystal is lowered to the liquid surface, and the electrodes on the seed crystal holder form a closed loop current with the solution, and the horizontality of the seed crystal when in contact with the solution is judged by the deflection of the external ammeter pointer, so as to ensure the stability of the flow at the growth interface and the high-quality growth of the crystal, and provide a basis for the subsequent crystal quality analysis. After the liquid contact process is completed, the wire is separated from the graphite electrode and pulled to the middle and upper part of the growth chamber to avoid electromagnetic interference to the crystal growth process. In addition, the graphite electrode and the wire can be used multiple times, which effectively saves the process cost.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing silicon carbide by liquid phase method, and particularly relates to a device and method for judging the liquid contact level of a seed crystal. Background Art

[0002] Silicon carbide is a group IV-IV compound and wide-bandgap semiconductor used in high-power, high-frequency, and high-temperature fields, showing excellent inherent properties in the high-end device market. The liquid phase epitaxy method is driven by the supersaturation of carbon dissolved in a silicon solvent, and it can grow silicon carbide single crystal ingots with ultra-low dislocation density under conditions that better satisfy thermodynamic equilibrium. In addition, solution growth can achieve high-concentration P-type doping by adding aluminum elements.

[0003] In the solution method, a graphite crucible is the container for the reaction and provides a carbon source for the crystal growth process. Solid silicon is transformed into a melt at high temperature, and the molten silicon contacts the graphite crucible wall to dissolve carbon in the melt. During the crystal growth process, the seed crystal area belongs to the low-temperature zone, and the crucible bottom belongs to the high-temperature zone. The solubility of carbon at high temperature is higher than that at low temperature. The carbon at the bottom of the crucible dissolves in the melt and flows to the liquid surface position under the drive of the temperature gradient. The melt supersaturation drives the seed crystal to grow into a silicon carbide single crystal ingot.

[0004] In the liquid phase method for preparing SiC single crystals, the seed crystal needs to be lowered during the crystal growth stage to make the seed crystal contact the liquid surface. The lifting part of the seed crystal axis is usually divided into two sections: the part connected to the graphite seed crystal holder is the graphite seed crystal rod, and the top of the graphite seed crystal rod is connected to the stainless steel seed crystal rod. However, the matching of the two connection parts requires extremely high processing accuracy, which is difficult to achieve by the current processing technology, so the deviation of the horizontal degree at the connection is likely to occur. Once the bottom surface of the seed crystal graphite holder is tilted, along with the rotation of the seed crystal during the crystal growth process, it will ultimately lead to flow disorder and rough growth surface at the seed crystal, and defects such as polytypes, microtubes, solvent inclusions, and threading dislocations will be generated, which greatly harms the crystal quality. Summary of the Invention

[0005] The purpose of the present invention is to provide a device and method for judging the liquid contact level of a seed crystal to solve the problems existing in the above-mentioned prior art, and to ensure a high-level liquid contact between the seed crystal and the solution, so as to ensure the stability of the flow at the growth interface and the high-quality growth of the crystal.

[0006] To achieve the above purpose, the present invention provides the following solution: The present invention provides a device for judging the liquid contact level of a seed crystal, including

[0007] a graphite crucible filled with a melt for the growth of silicon carbide single crystals;

[0008] A graphite seed rod, the top of the graphite seed rod is connected to a stainless-steel seed rod, the bottom end of the graphite seed rod is located in the growth cavity of the graphite crucible, and the graphite seed rod can move up and down along the growth cavity of the graphite crucible;

[0009] A graphite seed holder, the bottom of the graphite seed rod is connected with the graphite seed holder, and a plurality of graphite electrodes are arranged on the graphite seed holder; the plurality of graphite electrodes include a single positive graphite electrode and two or more negative graphite electrodes, and the plurality of graphite electrodes are placed at the edge of the graphite seed holder and are rotationally symmetrically arranged around the center point of the graphite seed holder; an ammeter is arranged on the circuit where each graphite electrode is connected to the power supply;

[0010] A silicon carbide seed crystal, the silicon carbide seed crystal is bonded to the bottom of the graphite seed holder.

[0011] In one embodiment, the outer layer of the graphite crucible is wrapped with a heat-insulating material.

[0012] In one embodiment, the stainless-steel seed rod is connected to the graphite seed rod through upper and lower flange clamps, and the stainless-steel seed rod is used to drive the graphite seed rod to move up and down along the growth cavity of the graphite crucible.

[0013] In one embodiment, a lifting servo motor is equipped on the stainless-steel seed rod, the lifting servo motor is used to drive the stainless-steel seed rod and the graphite seed rod to move up and down, and a displacement sensor is used to detect the displacement amount of the up and down movement of the graphite seed rod.

[0014] In one embodiment, the bottom of the graphite seed rod is connected with the graphite seed holder by a thread.

[0015] In one embodiment, the bottom surface of the graphite electrode is flush with the bottom surface of the graphite seed holder; there is a silicon carbide electrical insulation coating between the graphite electrode and the graphite seed holder.

[0016] In one embodiment, the wire connecting the graphite electrode can be drawn out and separated from the graphite electrode.

[0017] In one embodiment, a bottom rotary lifting mechanism is further included, and the graphite crucible is placed on the bottom rotary lifting mechanism.

[0018] The present invention also provides a method for judging the liquid contact level of the seed crystal, which is applied to the device for judging the liquid contact level of the seed crystal as described above, and includes the following steps:

[0019] Bond the silicon carbide seed crystal to the bottom of the graphite seed crystal holder. Insert three or more graphite electrodes with rotational symmetry into the graphite seed crystal holder, and maintain a safe distance between the graphite electrodes and the silicon carbide seed crystal. The bottom ends of the graphite electrodes are flush with the bottom end of the graphite seed crystal holder. One of the graphite electrodes is connected to the positive pole, and the rest are connected to the negative pole. Each electrode is connected to the outside of the growth chamber of the graphite crucible through a wire, and an ammeter is connected in series on the branch of each electrode connected to the power supply.

[0020] After heating the silicon carbide seed crystal to complete melting by electromagnetic induction of the coil, start the lifting servo motor of the graphite seed crystal rod to lower the silicon carbide seed crystal to contact the liquid surface of the molten liquid.

[0021] If the silicon carbide seed crystal contacts the liquid surface horizontally, the pointers of multiple ammeters deflect simultaneously. The accurate liquid surface height can be obtained by reading the data of the displacement sensor on the panel. If the silicon carbide seed crystal deviates from the horizontal position, the pointers of multiple ammeters do not deflect simultaneously, that is, at this time, the silicon carbide seed crystal and the liquid surface of the molten liquid are not in the same plane, and the levelness of the silicon carbide seed crystal needs to be readjusted.

[0022] The present invention has achieved the following beneficial technical effects compared with the prior art:

[0023] The device and method for judging the liquid contact levelness of the seed crystal in the present invention. The device part includes a graphite crucible, a graphite seed crystal holder, a graphite seed crystal rod and a silicon carbide seed crystal. Place the single positive graphite electrode and two or more negative graphite electrodes on the graphite seed crystal holder at the edge of the seed crystal holder and arrange them in rotational symmetry, so that multiple electrodes are in the same horizontal plane. Lower the seed crystal to the liquid surface. The electrodes on the seed crystal holder form a closed-loop current with the solution, and judge the levelness when the seed crystal contacts the solution through the deflection of the external ammeter pointer, so as to ensure the stability of the flow at the growth interface and the high-quality growth of the crystal, and provide a basis for the subsequent crystal quality analysis. After the liquid contact process is over, the wire is separated from the graphite electrode and lifted to the upper middle part of the growth chamber to avoid electromagnetic interference during the crystal growth process. In addition, the graphite electrode and the wire can be reused multiple times, effectively saving the process cost. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0025] Figure 1 It is the overall structural schematic diagram of the device for judging the liquid contact levelness of the seed crystal in the embodiment of the present invention;

[0026] Figure 2 It is a top view of the distribution position of graphite electrodes on the graphite seed crystal holder;

[0027] Figure 3 It is a circuit diagram for judging the liquid contact levelness of the seed crystal. Among them, in the circuit, the molten liquid acts as a resistor. A separate ammeter is connected in series on each negative graphite electrode, and the positive and negative graphite electrodes are connected to the positive and negative poles of the power supply through wires;

[0028] Among them, 1 is a graphite seed crystal rod, 2 is a graphite electrode, 3 is a heat insulation material, 4 is a graphite crucible, 5 is a graphite seed crystal holder, 6 is a silicon carbide seed crystal, 7 is a molten liquid, 8 is a bottom rotation and lifting mechanism, and 9 is an ammeter. Specific implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0030] The purpose of the present invention is to provide a device and method for judging the liquid contact levelness of the seed crystal to solve the problems existing in the above-mentioned prior art. A plurality of graphite electrodes and wires are used to form a closed circuit when the graphite seed crystal holder contacts the solution. An ammeter is connected in series in each branch, and the high-level liquid contact of the seed crystal is judged by the deflection of the ammeter pointer.

[0031] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0032] As Figures 1 - 3 shown, this embodiment provides a device for judging the liquid contact levelness of the seed crystal, including a graphite crucible 4, and a molten liquid 7 for the growth of silicon carbide single crystals is contained in the graphite crucible 4;

[0033] A graphite seed crystal rod 1, the top of the graphite seed crystal rod 1 is connected to a stainless steel seed crystal rod, the bottom end of the graphite seed crystal rod 1 is located in the growth cavity of the graphite crucible 4, and the graphite seed crystal rod 1 can move up and down along the growth cavity of the graphite crucible 4;

[0034] A graphite seed crystal holder 5, the bottom of the graphite seed crystal rod 1 is connected with a graphite seed crystal holder 5, and a plurality of graphite electrodes 2 are arranged on the graphite seed crystal holder 5; the plurality of graphite electrodes 2 include a single positive graphite electrode and two or more negative graphite electrodes, and the plurality of graphite electrodes 2 are placed on the edge of the graphite seed crystal holder 5 and are rotationally symmetrically arranged around the center point of the graphite seed crystal holder 5; an ammeter 9 is arranged on the circuit where each graphite electrode 2 is connected to the power supply;

[0035] The silicon carbide seed crystal 6 is adhesively bonded to the bottom of the graphite seed crystal holder 5.

[0036] In one embodiment, the outer layer of the graphite crucible 4 is wrapped with a heat-insulating material.

[0037] In one embodiment, the stainless-steel seed crystal rod is connected to the graphite seed crystal rod 1 through upper and lower flange clamps, and the stainless-steel seed crystal rod is used to drive the graphite seed crystal rod 1 to move up and down along the growth cavity of the graphite crucible 4.

[0038] In one embodiment, the stainless-steel seed crystal rod is equipped with a lifting servo motor, which is used to drive the stainless-steel seed crystal rod and the graphite seed crystal rod 1 to move up and down, and a displacement sensor is used to detect the displacement of the up and down movement of the graphite seed crystal rod 1.

[0039] In one embodiment, the bottom of the graphite seed crystal rod 1 is threadedly connected to the graphite seed crystal holder 5.

[0040] In one embodiment, the bottom surface of the graphite electrode 2 is flush with the bottom surface of the graphite seed crystal holder 5; there is a silicon carbide electrical insulation coating between the graphite electrode 2 and the graphite seed crystal holder 5.

[0041] In one embodiment, the wire connecting the graphite electrode 2 can be drawn out and separated from the graphite electrode 2.

[0042] In one embodiment, it further includes a bottom rotary lifting mechanism 8, and the graphite crucible 4 is placed on the bottom rotary lifting mechanism 8.

[0043] The present invention also provides a method for judging the liquid contact level of the seed crystal, which is applied to the device for judging the liquid contact level of the seed crystal as described above, and includes the following steps:

[0044] Adhesively bond the silicon carbide seed crystal 6 to the bottom of the graphite seed crystal holder 5, insert three or more graphite electrodes 2 with rotational symmetry into the graphite seed crystal holder 5, and keep a safe distance between the graphite electrodes 2 and the silicon carbide seed crystal 6; the bottom ends of the graphite electrodes 2 are flush with the bottom end of the graphite seed crystal holder 5, one of the graphite electrodes 2 is connected to the positive electrode, and the rest are connected to the negative electrode. Each electrode is connected to the outside of the growth cavity of the graphite crucible 4 through a wire, and an ammeter 9 is connected in series on the branch of each electrode connected to the power supply;

[0045] After heating the silicon carbide seed crystal 6 to complete melting by coil electromagnetic induction, start the lifting servo motor of the graphite seed crystal rod 1 to make the silicon carbide seed crystal 6 move down to contact the liquid surface of the molten liquid 7;

[0046] If the silicon carbide seed crystal 6 is in horizontal contact with the liquid surface, the pointers of multiple ammeters 9 will deflect simultaneously, and the precise liquid surface height can be obtained by reading the data of the displacement sensor on the panel; if the silicon carbide seed crystal 6 deviates from the horizontal position, the pointers of multiple ammeters 9 will not deflect simultaneously, that is, at this time, the silicon carbide seed crystal 6 and the liquid surface of the molten liquid 7 are not in the same plane, and the levelness of the silicon carbide seed crystal 6 needs to be readjusted.

[0047] The wires and the graphite electrode 2 in the present invention can be reused multiple times. After the liquid contact process is completed, the wires can be withdrawn from the growth chamber and continue to be used in subsequent processes. Preferably, using thin wires or ultra-thin wires can reduce the induced current generated by the wires in the alternating magnetic field, avoid the floating of the pointer of the ammeter 9, and at the same time minimize the electromagnetic interference to the internal magnetic field of the growth chamber; the bottom end of the graphite electrode 2 is flush with the bottom end of the graphite seed crystal holder 5 to avoid affecting the flow of the solution around the seed crystal. At the same time, the graphite electrode 2 should be long enough to prevent the wire from extending too far into the high-temperature area and melting. After the crystal growth process is completed, the graphite electrode 2 is withdrawn from the graphite seed crystal holder 5, and the damaged or contaminated part of the electrode tail is removed by machining methods to facilitate multiple uses in subsequent processes.

[0048] It should be noted that for those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention, and any reference signs in the claims should not be regarded as limiting the claims involved.

[0049] Specific examples are used in the present invention to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A device for judging the level of a seed crystal in contact with liquid, characterized in that: include A graphite crucible containing a molten liquid for growing a silicon carbide single crystal; A graphite seed crystal rod, the top of which is connected to a stainless steel seed crystal rod, the bottom of which is located in the growth chamber of the graphite crucible, and the graphite seed crystal rod can move up and down along the growth chamber of the graphite crucible; A graphite seed crystal holder, the bottom of the graphite seed crystal rod is connected to the graphite seed crystal holder, and a plurality of graphite electrodes are arranged on the graphite seed crystal holder; the plurality of graphite electrodes include a positive graphite electrode and two or more negative graphite electrodes, and the plurality of graphite electrodes are placed on the edge of the graphite seed crystal holder and arranged rotationally symmetrically about the center point of the graphite seed crystal holder; an ammeter is provided on the circuit connecting each graphite electrode to a power source; A silicon carbide seed crystal, the bottom of the graphite seed crystal holder is bonded with the silicon carbide seed crystal; The outer layer of the graphite crucible is wrapped with a heat-insulating material; the stainless steel seed crystal rod is connected to the graphite seed crystal rod through upper and lower flange clamps, and the stainless steel seed crystal rod is used to drive the graphite seed crystal rod to move up and down along the growth cavity of the graphite crucible.

2. The device for judging the level of seed crystal contact with liquid according to claim 1, characterized in that: The stainless steel seed crystal rod is equipped with a lifting servo motor, which is used to drive the stainless steel seed crystal rod and the graphite seed crystal rod to move up and down, and the displacement sensor is used to detect the displacement of the graphite seed crystal rod when it moves up and down.

3. The device for judging the level of seed crystal contact with liquid according to claim 1, characterized in that: The bottom of the graphite seed crystal rod is connected to the graphite seed crystal holder through threads.

4. The device for judging the level of seed crystal contact with liquid according to claim 1, characterized in that: The bottom surface of the graphite electrode is flush with the bottom surface of the graphite seed crystal holder; and a silicon carbide electrical insulation coating is provided between the graphite electrode and the graphite seed crystal holder.

5. The device for judging the level of seed crystal contact with liquid according to claim 1, characterized in that: The wires connected to the graphite electrodes can be pulled out and separated from the graphite electrodes.

6. The device for judging the level of seed crystal contact with liquid according to claim 1, characterized in that: It also includes a bottom rotating lifting mechanism, and the graphite crucible is placed on the bottom rotating lifting mechanism.

7. A method for judging the level of a seed crystal in contact with liquid, applied to the device for judging the level of a seed crystal in contact with liquid as claimed in any one of claims 1 to 6, characterized in that: The following steps are involved: The silicon carbide seed crystal is bonded to the bottom of the graphite seed crystal holder, and three or more rotationally symmetrical graphite electrodes are inserted into the graphite seed crystal holder, and a safe distance is maintained between the graphite electrode and the silicon carbide seed crystal; the bottom end of the graphite electrode is flush with the bottom end of the graphite seed crystal holder, one of the graphite electrodes is connected to the positive electrode, and the other electrodes are connected to the negative electrode, each electrode is connected to the outside of the growth chamber of the graphite crucible through a wire, and an ammeter is connected in series to the branch connecting each electrode to the power supply; After the silicon carbide seed crystal is heated to be completely melted by electromagnetic induction of the coil, the graphite seed crystal rod lifting servo motor is started to move the silicon carbide seed crystal downward to contact the liquid surface of the molten liquid; If the silicon carbide seed crystal is in horizontal contact with the liquid surface, multiple ammeter pointers will deflect at the same time, and the precise liquid level height can be obtained by reading the data of the displacement sensor on the panel; if the silicon carbide seed crystal deviates from the horizontal position, the pointers of multiple ammeters will not deflect at the same time, that is, the silicon carbide seed crystal and the liquid surface of the molten liquid are not on the same plane at this time, and the levelness of the silicon carbide seed crystal needs to be readjusted.

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