Method for growing gallium oxide single crystal by casting and semiconductor device containing gallium oxide single crystal

Abstract

The disclosure provides a method for growing a gallium oxide single crystal by casting and a semiconductor device containing the gallium oxide single crystal. The method includes: 1) heating a solid gallium oxide to complete melting, cooling to a melting point of the gallium oxide, and maintaining a melt state for at least 30 min; and 2) conducting gradient cooling on a gallium oxide melt obtained in step 1) until a solid gallium oxide single crystal is obtained. The gradient cooling is to cool the gallium oxide melt obtained in step 1) to a first temperature according to a first gradient, and then continue cooling to a room temperature according to a second gradient to obtain the gallium oxide single crystal. In step 1), since the solid gallium oxide is heated to the first temperature, oxygen with a volume fraction of at least 2% is present in a growth atmosphere.

Claims

1. A method for growing a gallium oxide single crystal by casting, comprising the following steps: 1) Heating a solid gallium oxide to complete melting, cooling to a melting point of the gallium oxide, and maintaining a melt state for at least 30 min; and 2) conducting gradient cooling on a gallium oxide melt obtained in step 1) until a solid gallium oxide single crystal is obtained, wherein the gradient cooling is to cool the gallium oxide melt obtained in step 1) to a first temperature according to a first gradient, and then continue cooling to a room temperature according to a second gradient to obtain the gallium oxide single crystal, and in step 1), since the solid gallium oxide is heated to the first temperature, oxygen with a volume fraction of 2-10% is present in a growth atmosphere; and the growth atmosphere comprises an inert gas; wherein: a cooling rate of the first gradient is 10-20 C./h; a cooling rate of the second gradient is 30-60 C./h; the first temperature is 1,500-1,700 C.; and the method does not use a single crystal seed.

2. The method according to claim 1, wherein in step 1), before or when heating to the first temperature, the oxygen is introduced so that the volume fraction of the oxygen in the growth atmosphere reaches 2-10%.

3. The method according to claim 1, wherein in step 2), when the cooling is continued to the first temperature according to the first gradient, the oxygen in the growth atmosphere is replaced with an inert gas.

4. The method according to claim 1, wherein the inert gas is one or more selected from the group consisting of argon, nitrogen, and carbon dioxide.

5. The method according to claim 1, wherein the gallium oxide single crystal has a diameter of 2-4 inches.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of gallium oxide single crystal materials of different dimensions;

(2) FIG. 2 shows an image of a gallium oxide single crystal prepared by a CZ method;

(3) FIG. 3 shows an image of a gallium oxide single crystal prepared by an EFG method;

(4) FIG. 4 is a growth flow chart of the CZ method;

(5) FIG. 5 is a growth flow chart of a casting method provided by the present disclosure;

(6) FIG. 6 is a high-resolution X-ray rocking curve graph measured by a gallium oxide single crystal substrate obtained in Example 1; and

(7) FIG. 7 is a high-resolution X-ray rocking curve graph measured by a gallium oxide single crystal substrate obtained in Example 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(8) The present disclosure will be further described below with reference to specific examples. In the following examples, a method for growing a gallium oxide single crystal by casting provided by the present disclosure is adopted. The solid gallium oxide raw material is put into a metal crucible and heated by intermediate frequency induction to a fully melted melt. Without using a single crystal seed, and by controlling a first temperature, a melting point holding time, a growth atmosphere, and gradient cooling conditions, the melt is gradually solidified. The gallium oxide single crystal grown by casting has a diameter of at least 2 inches and a thickness of at least 10 mm.

(9) The following examples are only a preferred specific implementation method of the present disclosure, and should not be construed as a limitation on the protection scope of the present disclosure. Replacement or non-essential improvements made by those skilled in the art according to the solution of the present disclosure within the technical scope disclosed by the present disclosure all belong to the protection scope of the present disclosure.

(10) Compared with the CZ method and the EFG method, the present disclosure effectively simplifies the growth process of the gallium oxide crystal (see FIG. 4 and FIG. 5 for the process flow). On the one hand, there is no need to use the single crystal seed which is difficult in production to induce crystal growth. On the other hand, the growth steps such as seeding, necking, shouldering, cylindrical growth, and tailing, which require a lot of adjustment of process parameters are not required, which saves the growth time. Compared with the conventional casting method, there is no need to lay the single crystal seed at the bottom, such that the single crystal nucleates and grows spontaneously, avoiding the bottom with more impurities and defects, so as to improve the crystal quality.

(11) Detection of melting point of gallium oxide: the melting point of the gallium oxide can be tested by an infrared thermometer. Generally, the stage where the temperature is maintained is the melting point range of the gallium oxide. The actual measured melting point of the gallium oxide in the present disclosure is about 1,800 C.

(12) Detection of volume fraction of oxygen: the volume fraction of the oxygen in the growth atmosphere can be detected in real time by an oxygen sensor.

(13) Detection of single crystal quality: the peak shape and FWHM of the crystal are tested by a high-resolution X-ray rocking curve. A more symmetrical and sharper peak shape of the rocking curve indicates a smaller FWHM, and a smaller FWHM indicates higher single crystal quality.

Example 1

(14) A method for growing a gallium oxide single crystal included the following specific steps.

(15) (1) The commercially available gallium oxide powder with a purity of 99.999% was pressed into a round disk with a pressure of 20 MPa, and sintered at 1,200 C. for 10 h. The sintered disk was put into a 100 mm100 mm container (such as an iridium crucible). The container containing the disk was put into the crystal growth furnace containing thermal insulation materials. The crystal growth furnace was sealed, vacuumized to be less than or equal to 1 Pa by a mechanical pump, and then filled with argon to make the pressure in the furnace equal to one atmosphere. A circulating cooling water device was opened.

(16) The solid gallium oxide could be prepared by the above method, which could improve the filling efficiency. The purchased solid gallium oxide could also be directly used. The raw material for preparing the solid gallium oxide by the above method: the gallium oxide powder had a purity of preferably 99.999%. Using the gallium oxide with a purity of 99.999% as the raw material could reduce the introduction of impurities during the growth of the gallium oxide crystals and improve the quality of the obtained gallium oxide crystals. Pressing the gallium oxide powder into a disk could effectively reduce the volume of raw materials in the crucible, and avoid multiple filling and melting. Vacuumizing the crystal growth furnace and introducing the inert gas could reduce the oxygen in the furnace and avoid oxidation damage to the iridium crucible caused by high oxygen components in the air. The zirconia fiber bricks were used as the insulation materials to form a suitable temperature gradient, which directly affected the growth of the gallium oxide single crystal. The following examples and comparative examples are all applicable.

(17) The size of the container is not affected by the crystal size, and other sizes can be selected.

(18) (2) An intermediate frequency induction heating device was turned on to heat at a rate of 100-200 C./h to melt the raw materials in the crucible, and an infrared thermometer was used to monitor the temperature of the crucible and the disk. When the temperature of the disk reached the first temperature of 1,500 C., 2% volume fraction of oxygen was introduced at one time. The power was continuously increased to heat, and the disk was completely melted, such that the melt temperature was 5-10 C. larger than the melting point of the gallium oxide for 0.5-2 h. The heating power was decreased to cool the melt to the melting point of the gallium oxide for 30 min.

(19) (3) The intermediate frequency induction power was decreased to slowly cool at the first gradient of 10 C./h, such that the melt on the surface of the crucible gradually solidified and grew into a gallium oxide crystal. During crystal growth, the argon and oxygen atmosphere in the crystal growth furnace were maintained, the micro-positive pressure state in the furnace was maintained, and the gas in the furnace was replaced with the argon when the temperature of the crystal in the crucible dropped to 1,500 C. through measurement with an infrared thermometer.

(20) (4) The cooling rate was increased to a second gradient of 50 C./h to gradually cool the crystal. When the temperature in the furnace was completely cooled to the room temperature, the gallium oxide single crystal was obtained.

(21) For the gallium oxide single crystal obtained in Example 1, it could be observed that the single crystal was transparent without obvious cracks and bubbles, and the size of the single crystal part reached 100 mm50 mm. After cutting, grinding and polishing, a 4-inch single crystal substrate could be obtained.

(22) A high-resolution X-ray rocking curve of the (100) plane gallium oxide single crystal substrate obtained in the present example was tested. As shown in FIG. 6, the rocking curve is relatively symmetrical, and the FWHM is 150 arcsec, indicating that the single crystal quality is high.

Example 2

(23) A method for growing a large-size bulk gallium oxide single crystal included the following specific steps.

(24) (1) The gallium oxide powder with a purity of 99.999% was pressed into round disk with a pressure of 30 MPa, and sintered at 1,200 C. for 12 h. The sintered disk was put into a 50 mm50 mm iridium crucible. The iridium crucible containing the disk was put into the crystal growth furnace containing thermal insulation materials of zirconia fiber bricks. The crystal growth furnace was sealed, vacuumized to be less than or equal to 1 Pa by a mechanical pump, and then filled with argon to make the pressure in the furnace equal to one atmosphere. A circulating cooling water device was opened.

(25) (2) An intermediate frequency induction heating device was turned on to heat at a rate of 100-200 C./h to melt the raw materials in the crucible. When the temperature of the disk reached the first temperature of 1,600 C., 5% volume fraction of oxygen was introduced. The power was continuously increased to heat, and the disk was completely melted, such that the melt temperature was 60 C. larger than the melting point of the gallium oxide for 2 h. The heating power was decreased to cool the melt to the melting point of the gallium oxide for 30 min.

(26) (3) The intermediate frequency induction power was decreased to slowly cool at the first gradient of 20 C./h, such that the melt on the surface of the crucible gradually solidified and grew into a gallium oxide crystal. The micro-positive pressure state in the furnace was maintained, and the gas in the furnace was replaced with the argon when the temperature of the crystal in the crucible dropped to 1,600 C.

(27) (4) The cooling rate was increased to a second gradient of 30 C./h to gradually cool the crystal. When the temperature in the furnace was completely cooled to the room temperature, the gallium oxide single crystal was obtained.

(28) For the gallium oxide single crystal obtained in Example 2, it could be observed that the single crystal was transparent without obvious cracks and bubbles, and the size of the single crystal part reached 50 mm20 mm. After cutting, grinding and polishing, a 2-inch single crystal substrate could be obtained.

(29) A high-resolution X-ray rocking curve of the (100) plane gallium oxide single crystal substrate obtained in the present example was tested. As shown in FIG. 7, the rocking curve is in bilateral symmetry, and the FWHM is 47.5 arcsec, indicating that the gallium oxide single crystal quality is high.

Example 3

(30) A method for growing a large-size bulk gallium oxide single crystal included the following specific steps.

(31) (1) The gallium oxide powder with a purity of 99.999% was pressed into round disk with a pressure of 30 MPa, and sintered at 1,200 C. for 12 h. The sintered disk was put into a 80 mm80 mm iridium crucible. The iridium crucible containing the disk was put into the crystal growth furnace containing thermal insulation materials of zirconia fiber bricks. The crystal growth furnace was sealed, vacuumized to be less than or equal to 1 Pa by a mechanical pump, and then filled with argon to make the pressure in the furnace equal to one atmosphere. A circulating cooling water device was opened.

(32) (2) An intermediate frequency induction heating device was turned on to heat at a rate of 100-200 C./h to melt the raw materials in the crucible. When the temperature of the disk reached the first temperature of 1,700 C., 10% volume fraction of oxygen was introduced. The power was continuously increased to heat, and the disk was completely melted, such that the melt temperature was 100 C. larger than the melting point of the gallium oxide for 2 h. The heating power was decreased to cool the melt to the melting point of the gallium oxide for 50 min.

(33) (3) The intermediate frequency induction power was decreased to slowly cool at the first gradient of 15 C./h, such that the melt on the surface of the crucible gradually solidified and grew into a gallium oxide crystal. The gas in the furnace was replaced with the argon when the temperature of the crystal in the crucible dropped to 1,700 C.

(34) (4) The cooling rate was increased to a second gradient of 40 C./h to gradually cool the crystal. When the temperature in the furnace was completely cooled to the room temperature, the gallium oxide single crystal was obtained.

(35) For the gallium oxide single crystal obtained in Example 3, it could be observed that the single crystal was transparent without obvious cracks and bubbles, and the size of the single crystal part reached 80 mm40 mm. After cutting, grinding and polishing, a 3-inch single crystal substrate could be obtained.

Examples 4 to 13

(36) Examples 4 to 13 adopted the preparation method as in Example 1 to prepare a gallium oxide single crystal, and changed some experimental parameters: the first temperature, the melting point holding time, the volume fraction of the oxygen, the first gradient, the replaced inert gas, and the second gradient, etc. As shown in Table 1 below, a large-size bulk gallium oxide single crystal without obvious cracks can be finally obtained. The (100), (010) and (001) plane gallium oxide single crystal substrates obtained by processing had no problems of cracking, twinning and bubbles. After high-resolution X-ray rocking curve testing, the FWHM was less than 150 arcsec, indicating that the single crystal quality was high.

(37) TABLE-US-00001 TABLE 1 First Melt Volume Replaced Second Example temperature holding fraction of First gradient inert gradient SN ( C.) time (min) oxygen (%) ( C./h) gas ( C./h) Example 4 1500 30 2 10 Ar 20 Example 5 1500 40 5 20 Ar 30 Example 6 1500 40 5 30 Ar 50 Example 7 1500 50 10 40 N.sub.2 60 Example 8 1600 30 2 10 Ar 20 Example 9 1600 50 3 15 Ar 100 Example 10 1600 50 5 20 N.sub.2 40 Example 11 1700 30 5 20 Ar 30 Example 12 1700 40 8 90 Ar 50 Example 13 1700 50 10 40 N.sub.2 60

Comparative Example 1

(38) The same growth method and equipment as in Example 1 were used, except that the first gradient was directly cooled to the room temperature at a rate of 100 C./h (without the second gradient), such that the melt on the surface of the crucible was gradually solidified and grown into a gallium oxide crystal. When the temperature in the furnace was completely cooled to the room temperature, the crystal growth furnace was opened and the crucible was taken out. After detection, the crystal in the crucible was a polycrystal and could not be used.

(39) Compared with Example 1, Comparative Example 1 did not undergo gradient cooling, and the cooling rate was too high, which was the main reason for the failure to form a single crystal.

Comparative Example 2

(40) The same growth method and equipment as in Example 1 were used, except that the first gradient was directly cooled to the room temperature at a rate of 200 C./h (without the second gradient), such that the melt on the surface of the crucible was gradually solidified and grown into a gallium oxide crystal. When the temperature in the furnace was completely cooled to the room temperature, the crystal growth furnace was opened and the crucible was taken out. After detection, the crystal in the crucible was a polycrystal and could not be used.

(41) Compared with Example 1, Comparative Example 2 did not undergo gradient cooling, and the cooling rate was too high, which was the main reason for the failure to form a single crystal.

Comparative Example 3

(42) The same growth method and equipment as in Example 1 were used, except that oxygen was not introduced when the temperature rose to the first temperature, such that the melt on the surface of the crucible was gradually solidified and grown into a gallium oxide crystal. When the temperature in the furnace was completely cooled to the room temperature, the crucible was taken out for detection. There were large crystalline impurities in the center of the crystal, leading to the formation of the polycrystal.

(43) Compared with Example 1, Comparative Example 3 did not introduce the oxygen during the growth of the single crystal, and a large amount of gallium oxide was volatilized and decomposed, and reacted with the crucible material to form floating objects that accumulated in the center of the crucible, unable to form a single crystal.

Comparative Example 4

(44) The same growth method and equipment as in Example 1 were used, except that only 1% oxygen was introduced when the temperature rose to the first temperature, such that the melt on the surface of the crucible was gradually solidified and grown into a gallium oxide crystal. When the temperature in the furnace was completely cooled to the room temperature, the crucible was taken out for detection. There were large crystalline impurities in the center of the crystal, leading to the formation of the polycrystal.

(45) Compared with Example 1, Comparative Example 4 did not introduce enough oxygen during the growth of the single crystal, and the gallium oxide was still volatilized and decomposed, and reacted with the crucible material to form floating objects that accumulated in the center of the crucible, unable to form a single crystal.

Comparative Example 5

(46) The same growth method and equipment as in Example 1 were used, except that the gallium oxide was directly cooled after melting, and there was no maintenance procedure, such that the melt on the surface of the crucible was gradually solidified and grown into a gallium oxide crystal. When the temperature in the furnace was completely cooled to the room temperature, the crucible was taken out and a polycrystal was detected.

(47) Compared with Example 1, Comparative Example 5 did not maintain the melting point of gallium oxide for 30 min, resulting in the presence of gallium oxide solid particles in the melt, and multi-point nucleation could not form a single crystal during cooling.

(48) It can be seen from the above examples and comparative examples that the heat preservation procedure of the gallium oxide melt, reasonable gradient cooling and a suitable volume fraction of the oxygen are the necessary conditions for obtaining a large-size bulk gallium oxide single crystal by casting. The present disclosure is not limited to the above-mentioned examples, and any solution after improvement or transformation of the present disclosure shall fall within the protection scope of the appended claims of the present disclosure.