Method for preparing ultra-high-purity germanium single crystal by VB method

Abstract

The invention discloses a method for preparing an ultra-high-purity germanium single crystal by a VB method. The method comprises the following steps: step 1, cleaning; step 2, mounting; step 3, charging; step 4, melting materials; step 5, seeding and inoculating; step 6, single crystal growth; step 7, cooling and annealing; and step 8, discharging and demolding. The ultra-pure single crystal grown by the method is equal in diameter, and the diameter of the single crystal is controlled according to requirements. The heating mode of the VB method is a high-frequency induction heating mode which is different from a resistance heating mode of a traditional VB method.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-high purity germanium single crystal preparation, and in particular relates to a method for preparing ultra-high purity germanium single crystal by a VB method. Background Art

[0002] Ultra-high-purity germanium single crystals are a key material for high-purity germanium detectors. Due to germanium's narrow bandgap and large atomic number, ultra-high-purity germanium detectors offer superior energy resolution, a wide energy measurement range, and high detection efficiency. Therefore, ultra-high-purity germanium detectors have broad application prospects in fields such as dark matter, nuclear power, materials science, trace element analysis, security inspection, and national defense. In recent years, a number of domestic companies, including Lincang Xinyuan Germanium Industry, Anhui Guangzhi, and Guangdong Xiandao, have reported successfully producing ultra-high-purity germanium single crystals using the Czochralski method, marking a breakthrough in my country's deep-energy-level ultra-high-purity germanium production technology.

[0003] Currently, the two methods for producing detector-grade ultra-high-purity germanium single crystals are the horizontal method and the Czochralski method. Due to the specific process conditions, the horizontal method has a low yield rate for grown germanium single crystals. Furthermore, the crystal shape makes subsequent processing difficult, making it unable to meet the demands of modern high-end industrial production. The Czochralski method, however, is also affected by temperature control, making it difficult to control the diameter of the grown crystals. Consequently, the diameter of the grown crystals is inconsistent, resulting in significant waste in subsequent processing. Summary of the Invention

[0004] To solve the above problems, the present invention provides a method for preparing ultra-high purity germanium single crystals by the VB method, comprising the following steps: Step 1, cleaning: using chemical solution to clean the quartz tube, quartz crucible, quartz support, high-purity germanium ingot and seed crystal; Step 2, Installation: First, install the high-frequency induction device with an insulation layer and connect it to the high-frequency induction control cabinet, then embed the cylindrical silicon carbide into the inner wall of the high-frequency induction coil, and finally install the quartz support insulation component to the lifting platform; Step 3, loading: The seed crystal and germanium ingot are placed into a specially treated quartz crucible, which is then placed into a quartz tube. The quartz tube is then passed from top to bottom through the high-frequency induction coil and placed on a quartz support and insulation fixture. The sealing cover is then installed, and the inlet and outlet pipes are connected. High-purity nitrogen is introduced for purging, followed by high-purity hydrogen. Step 4, melting the material: Turn on the high-frequency control cabinet and slowly increase the high-frequency power. The heat generated by the high-frequency induction cylindrical silicon carbide is transferred to the germanium polycrystalline material to completely melt it. Step 5, seeding: slowly raise the lifting platform to the designated position to fuse the seed crystal with the germanium solution; Step 6, single crystal growth: slowly lower the lifting platform, keep the high-frequency induction coil heating to maintain the melt temperature constant; the carrier is lowered to cause the melt to reach the solidification temperature and crystallize; thus starting the directional growth of the single crystal from bottom to top; stop lowering after the germanium single crystal is fully grown; Step 7, cooling annealing: slowly reduce the high-frequency induction power to release the thermal stress inside the crystal; Step 8: Remove from the oven and demold: After the crystal has completely cooled, turn off the hydrogen inlet and open the nitrogen inlet. After the purge is complete, open the seal, remove the quartz crucible containing the germanium single crystal, and place it in an ultrasonic vibrator filled with ultrapure water for ultrasonic vibration. After the germanium single crystal and the quartz crucible are separated, remove the single crystal and invert it. The entire process is carried out in an ultra-clean working environment.

[0005] Furthermore, the trace impurity content of the quartz tube and the quartz crucible is less than 0.01 PPM.

[0006] Furthermore, the chemicals are nitric acid and hydrofluoric acid in a ratio of 3:1, both of which are MOS grade.

[0007] Furthermore, the purity of hydrogen and nitrogen is 6N or above.

[0008] Furthermore, the resistivity of deionized water is greater than 18 MΩ•cm.

[0009] The above-mentioned technical solution of the present invention has the following beneficial technical effects: the ultra-high-purity single crystals grown by the present invention are of uniform diameter, and the single crystal diameter is controlled and grown as required. Furthermore, the heating method of the VB method of the present invention is high-frequency induction heating, which differs from the resistance heating method of the traditional VB method. This heating method is cleaner, and the heater and accessories used are less polluting and easier to control within the clean room. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is a flow chart of a method for preparing ultra-high purity germanium single crystals using the VB method; Figure 2 This is a schematic diagram of the device structure for preparing ultra-high purity germanium single crystals by the VB method; Figure 3 is a schematic diagram of the silicon carbide ring structure; Figure 4 This is the shape of the single crystal grown by the CZ method; Figure 5 This is the shape of the single crystal grown by the VB method.

[0011] Reference numerals: 1: Drive motor; 2: Air inlet; 3: Air inlet valve; 4: Sealing cover; 5: High-purity quartz tube; 6: Specially treated high-purity quartz crucible; 7: High-frequency induction coil; 8: Germanium crystal; 9: Seed crystal cavity; 10: Insulation support; 11: Lifting platform; 12: Air outlet; 13: Lifting guide rail; 14: High-frequency induction heating control cabinet. DETAILED DESCRIPTION

[0012] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0013] Example 1: Method for preparing ultra-high purity germanium single crystal by VB method.

[0014] The basic process is as follows Figure 1 The process includes: 1. Cleaning materials; 2. Charging the furnace; 3. Loading materials; 4. Vacuuming and inflating; 5. Melting the material and seed; 6. Growing single crystal; 7. Cooling and annealing; 8. Unloading from the furnace and demoulding.

[0015] like Figure 2 The device for preparing ultra-high purity germanium single crystal by the VB method shown in the figure specifically includes the following steps: Step 1: Use 3:1 nitric acid and hydrofluoric acid to clean the quartz tube 5 and 4-inch quartz crucible 6, then rinse the residual chemical solution with deionized water, and then dehydrate and dry with methanol. Use 3:1 nitric acid and hydrofluoric acid to clean 5kg high-purity germanium ingot and high-purity germanium single crystal seed crystal, then rinse the residual chemical solution with deionized water, and then place them in a 1:1:5 solution of hydrochloric acid, hydrogen peroxide and deionized pure water for etching for 10 minutes. Then take them out and rinse them with deionized water, dehydrate and dry them with methanol, and then place them in a Class 100 drying cabinet for drying. Step 2: Install the high-frequency induction coil 7 and connect it to the high-frequency induction heating control cabinet 14. Figure 3 As shown, the silicon carbide ring is inserted into the inner wall of the high-frequency induction coil 7, and then the heat-insulating support member 10 is fixed on the lifting platform and lifted to the designated position; Step 3: Load the high-purity germanium single crystal seed crystal into the quartz crucible seed crystal cavity 9, then load the germanium ingot into the specially treated quartz crucible 6, and then load it into the high-purity quartz tube 5; pass the loaded quartz tube from top to bottom through the silicon carbide ring, and make the quartz tube outlet 12 pass through the insulation support 10 and the lifting platform 11; Step 4: Install the sealing cover 4 on the quartz tube and connect the air inlet 2 and the air outlet 12 to the vacuum pumping system, and start vacuuming; after the vacuuming is completed, close the air outlet, open the air inlet, fill the quartz tube with high-purity nitrogen until the pressure is 0, and keep purging for half an hour, then switch to high-purity hydrogen purging and purge for another half an hour, always keeping hydrogen inlet; Step 5: Turn on the high-frequency induction heating control cabinet 14 and slowly increase the high-frequency power to heat the germanium ingot to slowly melt it. After the germanium material is completely melted into liquid, keep the high-frequency induction heating power unchanged, adjust the rising platform 11, so that the seed crystal in the seed crystal cavity is melted with the germanium solution, and keep it for 2 hours; Step 6: Turn on the descending function, so that the heat-insulating support fixture and the quartz tube slowly descend with the lifting platform, causing the temperature of the lower part of the germanium melt to slowly drop to the crystallization point and start to grow single crystals from bottom to top. After the lifting platform slowly descends to the specified position, all the crystal growth of the germanium liquid is completed, and the descending function is turned off; Step 7: Slowly reduce the high-frequency power to slowly reduce the high-frequency induction heating temperature until it drops to 0. When the temperature drops to room temperature, turn off the hydrogen and switch to nitrogen purge for half an hour; Step 8: Disconnect the air inlet and outlet connectors, open the quartz tube sealing cover, lift out the entire quartz tube, then take out the quartz crucible containing the high-purity germanium single crystal, place it in an ultrasonic oscillator filled with pure water, take it out after 2 hours, and stand it upside down to obtain an ultra-high-purity germanium single crystal.

[0016] The germanium single crystal obtained in this example was sliced ​​and sampled, and a low-temperature (77K) Hall test was performed to obtain the crystal carrier concentration and mobility, as shown in Table 1: Table 1 Currently, there are two preparation methods: the horizontal method and the Czochralski method. The horizontal method involves installing a seed crystal at one end of a quartz boat, fusing the seed crystal, and solidifying the solution from one end to the other to obtain a single crystal. The Czochralski method involves melting the seed crystal and then pulling it upward to obtain a single crystal. This method, on the other hand, involves melting the seed crystal and then transferring the solid-liquid solution from the bottom up to obtain a single crystal. The main differences are listed in Table 2 below.

[0017] Table 2 As shown in Table 2, due to the characteristics of the process conditions, the qualified rate of germanium single crystals grown by the horizontal method is low, and the subsequent processing is difficult due to the characteristics of the crystal shape, which can no longer meet the needs of modern high-end industrial production. The application of the CZ method in the growth of ultra-high purity germanium single crystals is affected by temperature control, making it difficult to control the crystal growth diameter. Figure 4 As shown, the diameters of the grown crystals are inconsistent, and subsequent processing will result in a lot of waste. However, the ultra-high purity single crystals grown by the present invention are of equal diameter, such as Figure 5As shown, the single crystal diameter is controlled and grown as required. The heating method of the VB method of the present invention is high-frequency induction heating, which is different from the resistance heating method of the traditional VB method. The main differences are shown in Table 3: Process Heating method Heating materials This method High-frequency induction Silicon carbide Traditional VB method Current resistance heating furnace Table 3 It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

Claims

1. A method for preparing ultra-high purity germanium single crystals by VB method, characterized in that: The following steps are involved: Step 1, cleaning: using chemical solution to clean the quartz tube, quartz crucible, quartz support, high-purity germanium ingot and seed crystal; Step 2, Installation: First, install the high-frequency induction device with an insulation layer and connect it to the high-frequency induction control cabinet, then embed the cylindrical silicon carbide into the inner wall of the high-frequency induction coil, and finally install the quartz support insulation component to the lifting platform; Step 3, loading: The seed crystal and germanium ingot are placed into a specially treated quartz crucible, which is then placed into a quartz tube. The quartz tube is then passed from top to bottom through the high-frequency induction coil and placed on a quartz support and insulation fixture. The sealing cover is then installed, and the inlet and outlet pipes are connected. High-purity nitrogen is introduced for purging, followed by high-purity hydrogen. Step 4, melting the material: Turn on the high-frequency control cabinet and slowly increase the high-frequency power. The heat generated by the high-frequency induction cylindrical silicon carbide is transferred to the germanium polycrystalline material to completely melt it. Step 5, seeding: slowly raise the lifting platform to the designated position to fuse the seed crystal with the germanium solution; Step 6, single crystal growth: slowly lower the lifting platform, keep the high-frequency induction coil heating to maintain the melt temperature constant; the carrier is lowered to cause the melt to reach the solidification temperature and crystallize; thus starting the directional growth of the single crystal from bottom to top; stop lowering after the germanium single crystal is fully grown; Step 7, cooling annealing: slowly reduce the high-frequency induction power to release the thermal stress inside the crystal; Step 8, demoulding: After the crystal is completely cooled, turn off the hydrogen gas inlet, open the nitrogen gas inlet and purge it. Then, open the seal, take out the quartz crucible containing the germanium single crystal, and put it into an ultrasonic oscillator filled with ultrapure water for ultrasonic oscillation. After the germanium single crystal and the quartz crucible are separated, take out the single crystal and stand it upside down.

2. The method for preparing ultra-high purity germanium single crystal by the VB method according to claim 1, characterized in that: The trace impurity content of the quartz tube and the quartz crucible is less than 0.01 PPM.

3. The method for preparing ultra-high purity germanium single crystal by the VB method according to claim 1, characterized in that: The chemicals are nitric acid and hydrofluoric acid in a ratio of 3:1, both of which are MOS grade.

4. The method for preparing ultra-high purity germanium single crystal by the VB method according to claim 1, characterized in that: The purity of the hydrogen and nitrogen is 6N.

5. The method for preparing ultra-high purity germanium single crystal by VB method according to claim 1, characterized in that: The resistivity of the deionized water is greater than 18 MΩ·cm.

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