Preparation method of ultra-high-purity germanium single crystal

Abstract

The preparation method of the ultra-high-purity germanium single crystal comprises the following steps: S1, putting corroded 12N high-purity germanium polycrystals into a crucible; s2, vacuumizing, introducing nitrogen for purging, and maintaining the pressure; s3, high-purity hydrogen is introduced, exhaust is maintained, and flowing type vacuum is maintained; s4, under flowing type vacuum, heating to 950-1000 DEG C, and melting the materials; s5, descending the seed crystal to the liquid level of the melt in the crucible, and preheating the seed crystal; s6, starting crucible rotation and crystal rotation in opposite rotation directions, inserting the seed crystal below the liquid level of the melt to form an aperture, and pulling to grow a crystal bar; s7, the pulling furnace is cooled, and the crystal bar is annealed; s8, descending the crystal bar into the crucible; s9, raising the temperature of the lifting furnace, completely melting the crystal bar again, and lifting the seed crystal away from the crucible; s10, repeating the steps S6 to S9 for specified times; s11, after the step S10 is repeated for the specified number of times, the step S6 and the step S7 are repeated, and the crystal bar is a product crystal bar; and S12, cooling, stopping crystal rotation and crucible rotation, opening the lifting furnace, and cutting off the product crystal bar.

Description

Technical Field

[0001] The present disclosure relates to the field of crystal growth, and more specifically to a method for preparing an ultra-high purity germanium single crystal. Background Art

[0002] The purity and defects of germanium crystals affect downstream performance. Under the same raw materials, the higher the purity and the fewer defects the crystals obtained by the pulling method, the better. Especially for the application of detectors, further development and research is needed. Summary of the invention

[0003] In view of the problems existing in the background technology, an object of the present disclosure is to provide a method for preparing detector-grade high-purity germanium single crystal, which can improve the purity and reduce defects.

[0004] Thus, a method for preparing ultra-high purity germanium single crystals includes the following steps: S1, loading the corroded 12N high purity germanium polycrystals into the crucible of a pulling furnace; S2, evacuating and blowing high purity nitrogen, then stopping evacuating and blowing nitrogen, and maintaining pressure; S3, switching to passing high purity hydrogen, and maintaining exhaust, so as to maintain a flowing vacuum in the pulling furnace; S4, under the flowing vacuum, heating the pulling furnace to 950-1000°C, and melting the 12N high purity germanium polycrystals in the crucible into a melt; S5, after the melting is completed, lowering the seed crystal to 10-20mm from the liquid surface of the melt in the crucible, and preheating the seed crystal for 30min; S6, turning on the crucible rotor that rotates the crucible and the crystal rotor that rotates the seed crystal in opposite directions, inserting the seed crystal 10-20mm below the liquid surface of the melt, causing an aperture to appear, and performing seeding, necking, neck thinning, shoulder release, equal diameter, and tailing, and pulling the raw material. When a crystal rod grows out and there is no or only a small amount of residual material in the crucible, the crucible rotation and crystal rotation are stopped; S7, the pulling furnace is cooled to 400-600°C and maintained for 30-60 minutes to anneal the crystal rod; S8, the crystal rod is lowered into the crucible and separated from the bottom of the crucible; S9, the pulling furnace is heated to 950-1000°C, the crystal rod is completely melted into the crucible again to form a melt, and the seed crystal is lifted out of the crucible; S10, steps S6 to S9 are repeated for a specified number of times; S11, after step S10 is repeated for a specified number of times, steps S6 and S7 are repeated, and the crystal rod is the product crystal rod; S12, after step S11 is completed, the temperature is lowered, the crystal rotation and crucible rotation are turned off, the hydrogen is stopped, the nitrogen is switched to be filled and the exhaust is maintained, so that the pressure in the pulling furnace reaches normal pressure, and then the nitrogen is stopped and the exhaust is stopped, the pulling furnace is opened, and the product crystal rod is cut off.

[0005] The beneficial effects of the present disclosure are as follows: in the preparation method of ultra-high purity germanium single crystal according to the present disclosure, whether it is the pulling of step S6 in the repeated steps S6 to S9 or the repeated step S6 in step S11 for finally forming the product crystal rod, during the pulling process, each layer of the melt can contact the hydrogen forming a flowing vacuum, and the remelting of step S9 in the repeated steps S6 to S9 further increases the contact area between the germanium melt and the hydrogen, thereby taking away impurities in the germanium melt and purifying the crystal raw material. Each time the remelting growth is performed, the crystal raw material is purified once, and the crystal purity is improved once; whether it is the repeated step S7 in the repeated steps S6 to S9 or the repeated step S7 in step S11 for finally forming the product crystal rod, crystal defects can be reduced (especially for detector applications, disc pits, coefficient structures, and mosaic structures are to be avoided as much as possible). After the crystal is remelted, raw material defects are reduced, and each time the annealing is performed, the crystal defects are reduced once. In other words, by repeating the remelting and annealing in steps S6 to S9 and repeating the annealing in step S7 in step S11 , the purity is improved and the defects are reduced, thereby being able to meet the requirements of detector applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a nine-point test chart.

[0007] Figure 2 This is a photograph of the dislocation density of Example 1 under a metallographic microscope.

[0008] Figure 3 This is a defect photograph of the disc-shaped pit of Comparative Example 1.

[0009] Figure 4 This is a defect photograph of the coefficient structure of comparative example 1.

[0010] Figure 5 This is a defect photo of the mosaic of Comparative Example 1. DETAILED DESCRIPTION

[0011] It will be understood that the disclosed embodiments are merely examples of the present disclosure, which may be implemented in various forms, and therefore, the specific details disclosed herein should not be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to implement the present disclosure in various ways.

[0012] [Method for preparing ultra-high purity germanium single crystal]

[0013] The method for preparing an ultra-high purity germanium single crystal according to the present disclosure comprises the following steps:

[0014] S1, loading the corroded 12N high purity germanium polycrystal into the crucible of the pulling furnace;

[0015] S2, evacuate and purge with high-purity nitrogen, then stop evacuating and purge with nitrogen, and maintain pressure;

[0016] S3, switch to introduce high-purity hydrogen and maintain exhaust to maintain a flowing vacuum in the pulling furnace;

[0017] S4, under a flowing vacuum, the pulling furnace is heated to 950-1000°C to polycrystallize the 12N high-purity germanium in the crucible into a melt;

[0018] S5, after the melting is completed, the seed crystal is lowered to 10-20 mm from the liquid surface of the melt in the crucible, and the seed crystal is preheated for 30 minutes;

[0019] S6, start the crucible rotation and the seed crystal rotation in opposite directions, insert the seed crystal 10-20 mm below the liquid surface of the melt, and an aperture appears. Then, seeding, necking, neck thinning, shoulder release, equal diameter, and tailing are performed, and a crystal rod is grown by pulling. When there is no residual material or only a small amount of residual material in the crucible, stop the crucible rotation and the crystal crystal rotation.

[0020] S7, the pulling furnace is cooled to 400-600°C and maintained for 30-60 minutes to anneal the crystal rod;

[0021] S8, lowering the crystal rod into the crucible and separating it from the bottom of the crucible;

[0022] S9, the pulling furnace is heated to 950-1000°C, the crystal rod is completely melted into the crucible again to form a melt, and the seed crystal is lifted out of the crucible;

[0023] S10, repeating steps S6 to S9 for a specified number of times;

[0024] S11, after step S10 is repeated for a specified number of times, steps S6 and S7 are repeated, and the crystal ingot is a product crystal ingot;

[0025] S12, after step S11 is completed, cool down, turn off the crystal turner and the crucible turner, stop passing hydrogen, switch to nitrogen filling and maintain exhaust, so that the pulling furnace reaches normal pressure, then stop filling nitrogen and stop exhausting, open the pulling furnace, and cut the product crystal rod.

[0026] In the preparation method of ultra-high purity germanium single crystal according to the present disclosure, whether it is the pulling of step S6 in the repeated steps S6 to S9 or the repeated step S6 in step S11 for finally forming the product crystal rod, during the pulling process, each layer of the melt can contact the hydrogen forming a flowing vacuum, and the remelting of step S9 in the repeated steps S6 to S9 increases the contact area between the germanium melt and the hydrogen, thereby taking away impurities in the germanium melt and purifying the crystal raw material. Each time the remelting growth is performed, the crystal raw material is purified once, and the crystal purity is improved once; whether it is the repeated step S7 in the repeated steps S6 to S9 or the repeated step S7 in step S11 for finally forming the product crystal rod, crystal defects can be reduced (especially for detector applications, disc-shaped pits, coefficient structures, and mosaic structures are to be avoided as much as possible). After the crystal is remelted, raw material defects are reduced, and each time the crystal is annealed, the crystal defects are reduced once. In other words, by repeating the remelting and annealing in steps S6 to S9 and repeating the annealing in step S7 in step S11 , the purity is improved and the defects are reduced, thereby being able to meet the requirements of detector applications.

[0027] In step S1, for example, a mixed solution of 68% HNO3:49% HF in a volume ratio of 1:4 is used for etching.

[0028] In step S2, for example, vacuum is first drawn, and then high-purity nitrogen is introduced. The pulling furnace is purged by vacuuming and nitrogen filling for multiple times. After the purging is completed, vacuuming and nitrogen filling are stopped, and then the pressure is maintained. Specifically, in step S2, vacuuming and nitrogen filling are performed 3-5 times, and each time the vacuum is drawn to below 1Pa, the purity of the high-purity nitrogen is 7N, the pressure is maintained for 2h, and the pressure of the pressure maintenance is 1×10 -4 Below Pa.

[0029] In step S3, for example, the pressure of the flowing vacuum is 0.095-0.105 MPa.

[0030] In step S5, the net impurity carrier concentration of the seed crystal is less than 2E11cm -3 .

[0031] In step S6, for example, the rotation speeds of the crucible rotation and the crystal rotation are 1-5 rpm, and the pulling speed is 20-24 mm / h.

[0032] In one example, in step S10, the prescribed number of times is 5-15 times.

[0033] In one example, in step S3, the purity of hydrogen is 9N; in step S12, the purity of nitrogen is 7N.

[0034] [test]

[0035] Example 1

[0036] The method for preparing the ultra-high purity germanium single crystal of Example 1 adopts the following steps:

[0037] S1, loading the etched 12N high purity germanium polycrystal into the crucible of the pulling furnace, and etching with a mixed solution of 68% HNO3:49% HF in a volume ratio of 1:4;

[0038] S2, first evacuate the vacuum, then pass high-purity nitrogen, the purity of high-purity nitrogen is 7N, evacuate and fill with nitrogen 4 times, evacuate to 1Pa each time, and purge the pulling furnace. After the purge, stop evacuating and passing high-purity nitrogen, and then maintain the pressure for 2h. The pressure of the pressure is 1×10 -4 Pa;

[0039] S3, switch to introduce 9N high-purity hydrogen and maintain exhaust to maintain a flowing vacuum in the pulling furnace, and the pressure of the flowing vacuum is 0.1MPa;

[0040] S4, under a flowing vacuum, the pulling furnace is heated to 980° C. to polycrystallize the 12N high-purity germanium in the crucible into a melt;

[0041] S5, after the material is melted, the seed crystal is lowered to 15 mm from the liquid surface of the melt in the crucible, and the seed crystal is preheated for 30 min, wherein the net impurity carrier concentration of the seed crystal is 5E10cm -3 ;

[0042] S6, start the crucible rotation and the crystal rotation in opposite directions, insert the seed crystal 15mm below the liquid surface of the melt, and the aperture appears. Then, seeding, necking, neck thinning, shoulder release, equal diameter, and tailing are performed, and the crystal rod is grown by pulling. Only a small amount of residual material is left in the crucible, and the crucible rotation and the crystal rotation are stopped. The rotation speed of the crucible rotation and the crystal rotation is 4rpm, and the pulling speed is 22mm / h.

[0043] S7, the pulling furnace is cooled to 500°C and maintained for 45 minutes to anneal the crystal rod;

[0044] S8, lowering the crystal rod into the crucible and separating it from the bottom of the crucible;

[0045] S9, the pulling furnace is heated to 980°C, the crystal rod is completely melted into the crucible again to form a melt, and the seed crystal is lifted out of the crucible;

[0046] S10, repeating steps S6 to S9 for a specified number of times, the specified number of times being 10 times;

[0047] S11, after step S10 is repeated for a specified number of times, steps S6 and S7 are repeated, and the crystal ingot is a product crystal ingot;

[0048] S12, after step S11 is completed, cool down, turn off the crystal turner and crucible turner, stop passing hydrogen, switch to filling nitrogen with a purity of 7N and maintain exhaust, so that the pulling furnace reaches normal pressure, then stop filling nitrogen and stop exhausting, open the pulling furnace, and cut the product crystal rod.

[0049] Comparative Example 1

[0050] Except that steps S7 to S11 are not performed and "after step S11 is finished" in step S12 is "after step S6 is finished", the rest is the same as Example 1. That is, in Comparative Example 1, only the cooling process of step S12 is directly performed after step S6. In other words, Comparative Example 1 is a conventional pulling process without annealing.

[0051] A whole disc with a thickness of 1 mm was taken from the tail of the equal-diameter section of the product crystal rod prepared by Example 1 and Comparative Example 1, and then a square piece of 10 mm×10 mm was taken from the center and edge of the disc, and two square pieces were used to test the carrier concentration (the average of the two square pieces was taken). The carrier concentration (i.e., the corresponding purity) was tested by HL9900 produced by Toho Technology, USA.

[0052] The carrier concentration of Example 1 is 6.02E9cm -3 , the carrier concentration of comparative example 1 is 9.47E9cm -3 .

[0053] The tails of the equal-diameter sections of the product crystal rods of Example 1 and Comparative Example 1 were used to make wafers according to the test process of CN114088707A.

[0054] according to Figure 1 Observe 9 points under a metallographic microscope. If there are no disc-shaped pits, coefficient structures and mosaic defects, only the dislocations at the 9 points can be counted. If disc-shaped pits, coefficient structures and mosaic defects appear, mark the defects at the corresponding points.

[0055] In Example 1, the entire wafer has no disc-shaped pits, coefficient structures and mosaic defects. Figure 2 This is a photograph of the dislocation density of Example 1 under a metallographic microscope.

[0056] Comparative Example 1 had disc-shaped pits, coefficient structures, and mosaic defects. Figure 3 This is a defect photograph of the disc-shaped pit of Comparative Example 1. Figure 4 This is a defect photograph of the coefficient structure of comparative example 1. Figure 5 This is a defect photo of the mosaic of Comparative Example 1. Figure 2 see, Figure 2 There is no Figures 3 to 5 That is, disc pits, coefficient structures and mosaic defects are eliminated.

[0057] The above detailed description is used to describe multiple exemplary embodiments, but this document is not intended to be limited to the explicitly disclosed combinations. Therefore, unless otherwise stated, the various features disclosed herein can be combined together to form multiple additional combinations that are not shown for the sake of simplicity.

Claims

1. A method for preparing an ultra-high purity germanium single crystal, characterized in that: Includes steps: S1, loading the corroded 12N high purity germanium polycrystal into the crucible of the pulling furnace; S2, evacuate and purge with high-purity nitrogen, then stop evacuating and purge with nitrogen, and maintain pressure; S3, switch to introduce high-purity hydrogen and maintain exhaust to maintain a flowing vacuum in the pulling furnace; S4, under a flowing vacuum, the pulling furnace is heated to 950-1000°C to polycrystallize the 12N high-purity germanium in the crucible into a melt; S5, after the melting is completed, the seed crystal is lowered to 10-20 mm from the liquid surface of the melt in the crucible, and the seed crystal is preheated for 30 minutes; S6, start the crucible rotation and the seed crystal rotation in opposite directions, insert the seed crystal 10-20 mm below the liquid surface of the melt, and an aperture appears. Then, seeding, necking, neck thinning, shoulder release, equal diameter, and tailing are performed, and a crystal rod is grown by pulling. When there is no residual material or only a small amount of residual material in the crucible, stop the crucible rotation and the crystal crystal rotation. S7, the pulling furnace is cooled to 400-600°C and maintained for 30-60 minutes to anneal the crystal rod; S8, lowering the crystal rod into the crucible and separating it from the bottom of the crucible; S9, the pulling furnace is heated to 950-1000°C, the crystal rod is completely melted into the crucible again to form a melt, and the seed crystal is lifted out of the crucible; S10, repeating steps S6 to S9 for a specified number of times; S11, after step S10 is repeated for a specified number of times, steps S6 and S7 are repeated, and the crystal ingot is a product crystal ingot; S12, after step S11 is completed, cool down, turn off the crystal turner and the crucible turner, stop passing hydrogen, switch to nitrogen filling and maintain exhaust, so that the pulling furnace reaches normal pressure, then stop filling nitrogen and stop exhausting, open the pulling furnace, and cut the product crystal rod.

2. The method for preparing detector-grade high-purity germanium single crystal according to claim 1, characterized in that: In step S1, a mixed solution of 68% HNO3:49% HF in a volume ratio of 1:4 is used for etching.

3. The method for preparing an ultra-high purity germanium single crystal according to claim 1, characterized in that: In step S2, vacuum is first drawn, and then high-purity nitrogen is introduced. The pulling furnace is purged by vacuuming and filling with nitrogen multiple times. After the purging is completed, the vacuuming and the introduction of high-purity nitrogen are stopped, and then the pressure is maintained.

4. The method for preparing an ultra-high purity germanium single crystal according to claim 3, characterized in that: In step S2, vacuum-fill with nitrogen 3-5 times, vacuuming to below 1Pa each time, the purity of high-purity nitrogen is 7N, the pressure is maintained for 2h, and the pressure of the pressure is 1×10 -4 Below Pa.

5. The method for preparing an ultra-high purity germanium single crystal according to claim 1, characterized in that: In step S3, the pressure of the flowing vacuum is 0.095-0.105 MPa.

6. The method for preparing an ultra-high purity germanium single crystal according to claim 1, characterized in that: In step S5, the net impurity carrier concentration of the seed crystal is less than 2E11cm -3 .

7. The method for preparing an ultra-high purity germanium single crystal according to claim 1, characterized in that: In step S6, The speed of crucible rotation and crystal rotation is 1-5rpm. The pulling speed is 20-24 mm / h.

8. The method for preparing an ultra-high purity germanium single crystal according to claim 1, characterized in that: In step S10, the prescribed number of times is 5-15 times.

9. The method for preparing an ultra-high purity germanium single crystal according to claim 1, characterized in that: In step S3, the purity of hydrogen is 9N; In step S12, the purity of nitrogen is 7N.

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