A method for preparing a high-purity germanium single crystal vacancy-free group

Abstract

This invention discloses a method for preparing high-purity germanium single crystals without vacancy groups, relating to the field of defect control technology for high-purity semiconductor single crystals. The steps include: S1 Furnace pretreatment: The Czochralski furnace is evacuated to ≤1×10⁻⁶. ‑3 Pa: High-purity hydrogen gas (9N purity) is introduced, pressurized to 0.12–0.15 MPa, and baked at 900℃ for 2–4 hours. S2: High-purity germanium polycrystalline raw material is charged into the pretreated Czochralski furnace, maintaining a hydrogen pressure of 0.12–0.15 MPa, heated to 945–950℃ and melted at a constant temperature for 40–60 minutes to form a supersaturated hydrogen melt. This invention utilizes a moderately supersaturated hydrogen partial pressure to increase the hydrogen concentration in the melt and lattice, allowing hydrogen atoms to fill lattice vacancies in situ and suppressing vacancy cluster formation. Combined with in-situ pressure-holding annealing after growth, vacancy clusters are further dissociated. This invention can control the vacancy cluster concentration to 1×10⁻⁶. 9 cm ‑3 The following steps reduce the V2H deep-level defect concentration.

Description

Technical Field

[0001] This invention relates to the field of defect control technology for high-purity single crystal semiconductors, specifically a method for preparing high-purity germanium single crystals free of vacancy groups. Background Technology

[0002] High-purity germanium single crystals are core materials for high-end equipment such as high-purity nuclear radiation detectors, dark matter detectors, and gamma-ray imaging. Vacancy clusters are the most significant deep-level defects in high-purity germanium single crystals. As precursors for V2H generation, they directly generate V2H traps in the hydrogen atmosphere through the interstitial hydrogen between double-vacancy V2 traps. The more vacancy clusters there are, the higher the V2H concentration, leading to increased carrier trapping losses. Simultaneously, small and medium-sized vacancy clusters can trap electrons and holes, reducing charge collection efficiency and causing spectral tailing and deterioration of energy resolution. Vacancy clusters also disrupt lattice periodicity, increasing thermally excited carriers in the bulk, resulting in increased reverse leakage current and noise in the device.

[0003] Current methods for growing high-purity germanium single crystals using atmospheric pressure hydrogen gas cannot effectively fill lattice vacancies. During crystal cooling, free vacancies aggregate to form vacancy clusters, with concentrations often exceeding 1 × 10⁻⁶. 9 cm -3 While increasing hydrogen pressure can enhance hydrogen's ability to fill lattice vacancies, it also significantly increases the solubility and lattice penetration of trace impurities in hydrogen in germanium melt. At the same time, it exacerbates the high-temperature corrosion and element volatilization of quartz crucibles, graphite, and metal components, introducing electrically active impurities such as Si, O, C, and heavy metals. In addition, high pressure can also disrupt the stability of the temperature field inside the furnace, inducing impurity segregation and defect proliferation. It is impossible to simultaneously meet the detector-level performance requirements of ultra-high purity 13N and low dislocation and low vacancy clusters. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high-purity germanium single crystals without vacancy groups, so as to overcome the shortcomings of the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing high-purity germanium single crystals without vacancy clusters, comprising furnace pretreatment, charging and melting, crystal pulling and necking, shoulder formation, constant diameter growth, and annealing and cooling processes, characterized in that the specific steps are as follows:

[0006] S1 Furnace Body Pretreatment: Vacuuming the Czochralski furnace to ≤1×10 -3 Pa, introduce high-purity hydrogen gas with a purity of 9N, pressurize to 0.12–0.15 MPa, and bake at a constant temperature of 900℃ for 2–4 hours;

[0007] S2 Charging and Melting: High-purity germanium polycrystalline raw material is charged into the pretreated Czochralski furnace, the hydrogen pressure is maintained at 0.12–0.15 MPa, the temperature is raised to 945–950℃ and kept at a constant temperature for 40–60 min to form a supersaturated hydrogen melt.

[0008] S3 crystal deriving and necking: A 13N dislocation-free seed crystal with the

[100] crystal orientation is used for crystal deriving, and the necking diameter is controlled to be 2–3 mm and the length to be 15–20 mm.

[0009] S4 Slow Shoulder Release: Maintain hydrogen pressure at 0.12–0.15 MPa, release the shoulder at a cooling rate of 10–15 °C / h, and control the shoulder release angle at 45–60°.

[0010] S5 hydrogen supersaturated constant diameter growth: maintain hydrogen pressure at 0.12–0.15 MPa throughout the process, control temperature gradient at 5–8℃ / cm, pulling speed at 0.8–1.2 mm / h, and crystal rotation speed at 5–10 rpm;

[0011] S6 In-situ Annealing: After growth, maintain hydrogen pressure at 0.12–0.15 MPa, cool to 600℃ at a rate of 3℃ / min and hold at that temperature for 2 hours, then allow the furnace to cool naturally to room temperature. The furnace is then removed to obtain 13N high-purity germanium single crystals without vacancies.

[0012] Preferably, in step S1, the Czochralski furnace is evacuated to 1×10⁻⁶. -3 Pa.

[0013] Preferably, in step S2, the high-purity germanium polycrystalline raw material is 13N high-purity germanium polycrystalline.

[0014] Preferably, in step S3, the crystal orientation deviation of the seed crystal is <0.5°.

[0015] Preferably, in step S4, the cooling rate is 12℃ / h and the shoulder angle is 50°.

[0016] Preferably, in step S5, the temperature gradient is 6℃ / cm, the pulling speed is 1.0mm / h, and the crystal rotation speed is 8rpm.

[0017] Preferably, the hydrogen pressure is maintained at 0.13 MPa throughout steps S1 to S6.

[0018] In the above technical solution, the present invention provides a method for preparing high-purity germanium single crystals without vacancies: using a moderately supersaturated hydrogen partial pressure of 0.12–0.15 MPa, compared with a normal pressure hydrogen environment, can effectively increase the hydrogen concentration in the melt and solid phase. During crystal growth, hydrogen atoms can fill single and double vacancies in the crystal lattice in situ, suppressing the enrichment of supersaturated vacancies, and controlling the vacancy concentration in the crystal at 1×10⁻⁶. 9 cm-3 The following approach reduces the precursors of V2H deep-level defects at the source, thereby significantly lowering the concentration of V2H deep traps;

[0019] After crystal growth is completed, the present invention performs step-by-step in-situ annealing without opening the furnace to release pressure, while maintaining pressure. The residual supersaturated hydrogen atoms can continuously fill vacancies and dissociate small vacancy clusters, avoiding vacancy agglomeration and rebound caused by contact with the outside air after the furnace is cooled.

[0020] The hydrogen pressure range defined by this invention avoids the problem of insufficient hydrogen atom supply under low pressure, and also avoids the defects of high-pressure hydrogen corrosion of the furnace body, introduction of impurities, and disruption of the temperature field. The final 13N high-purity germanium single crystal can meet the requirements of detector-level applications. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0022] Figure 1 This is a process flow diagram of the method for preparing high-purity germanium single crystals without vacancy groups according to the present invention;

[0023] Figure 2 The DLTS spectra measured in Example 1 and Comparative Examples 1-4 of this invention are shown. Detailed Implementation

[0024] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0025] Please see Figure 1-2 All hydrogen pressure comparison experiments provided in this invention embodiment follow the single variable principle to ensure the comparability of experimental results:

[0026] Example 1 is the optimal parameter set:

[0027] This embodiment provides a method for preparing high-purity germanium single crystals without vacancy groups, the specific steps of which are as follows:

[0028] S1 Furnace Body Pretreatment: Vacuuming the Czochralski furnace to 1×10 -3 Pa, high-purity hydrogen gas with a purity of 9N is introduced, the pressure is slowly increased to 0.13MPa, and the mixture is baked at a constant temperature of 900℃ for 2 hours to establish a hydrogen supersaturated clean environment.

[0029] S2 Charging and Melting: 13N high-purity germanium polycrystalline raw material is charged into the pretreated Czochralski furnace, the hydrogen pressure is maintained at 0.13MPa, the temperature is raised to 948℃ at a rate of 10℃ / min, and the temperature is kept constant for 40min to allow the hydrogen to fully dissolve in the germanium melt and form a supersaturated hydrogen melt.

[0030] S3 seed crystal necking: The seed crystal is slowly lowered to the surface of the melt. After the seed crystal and the melt are fully fused, necking is performed at a pulling speed of 1.0 mm / h, controlling the necking diameter to be 2.5 mm and the length to be 18 mm, to eliminate dislocations introduced by the seed crystal.

[0031] S4 Slow Shoulder Formation: Maintain hydrogen pressure at 0.13MPa, perform shoulder formation at a cooling rate of 12℃ / h, control the shoulder formation angle at 50°, and slowly form to the target diameter of 100mm.

[0032] S5 hydrogen supersaturated constant diameter growth: maintain hydrogen pressure at 0.13MPa throughout the process, control the solid-liquid interface temperature gradient at 6℃ / cm, pull-out speed at 1.0mm / h, crystal rotation speed at 8rpm, and keep the solid-liquid interface flat.

[0033] S6 In-situ Annealing: After growth is completed, pull-up and rotation are stopped immediately. The hydrogen pressure is maintained at 0.13 MPa without opening the furnace. The temperature is reduced to 600℃ at a rate of 3℃ / min and kept at a constant temperature for 2 hours to promote hydrogen atom diffusion. Then, the furnace is naturally cooled to room temperature, and the finished single crystal is obtained.

[0034] Comparative Example 1

[0035] Traditional atmospheric pressure process, atmospheric pressure, pressure ≈ 0.1MPa, other aspects are the same as in Example 1.

[0036] Comparative Example 2

[0037] Low-pressure boundary group, 0.11MPa (<0.12MPa), other conditions are the same as in Example 1.

[0038] Comparative Example 3

[0039] The in-situ pressure holding annealing was cancelled, and the furnace was opened directly for cooling after growth. The rest was the same as in Example 1.

[0040] Comparative Example 4

[0041] High-pressure boundary group, 0.17MPa (>0.15MPa), other conditions are the same as in Example 1.

[0042] Experimental test results

[0043] The V2H concentration detection data for each group of samples are shown in the table below:

[0044] Group <![CDATA[V2H concentration / cm -3 > Example 1 4.56e8 Comparative Example 1 1.58e9 Comparative Example 2 1.25e9 Comparative Example 3 3.275e9 Comparative Example 4 2.75e9

[0045] Results analysis:

[0046] Example 1 demonstrates the best overall performance, with vacancy cluster concentration stably controlled at 1×10⁻⁶. 9 cm -3 The following has the best overall performance.

[0047] In Comparative Examples 1-2, when the hydrogen pressure is <0.12MPa, the hydrogen supply to the interstitial lattice is insufficient, and the single vacancies generated during solidification cannot be fully filled. A large number of free vacancies diffuse and agglomerate during the cooling stage to form high-concentration vacancy clusters.

[0048] Comparative Example 3: The in-situ pressure holding annealing process was eliminated. After the growth was completed, the hydrogen partial pressure in the furnace dropped rapidly, and the supersaturated hydrogen atoms were lost. The vacancies could not be continuously filled and the vacancy groups could not be dissociated, and the vacancy group concentration eventually increased significantly.

[0049] In Comparative Example 4, when the hydrogen pressure is >0.15MPa, the high-pressure hydrogen gas exacerbates the corrosion of the furnace components, introduces impurities such as Si, O, and C, and causes distortion of the temperature field inside the furnace, increases the concentration of vacancy clusters, and makes the purity and defect index of the single crystal unable to meet the requirements for detector-level use.

[0050] In this document, N represents the material purity grade; 9N and 13N respectively refer to high-purity materials of the corresponding purity grades; cm -3 rpm is the unit of concentration; rpm is the unit of rotational speed.

[0051] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for preparing high-purity germanium single crystals without vacancy clusters, comprising furnace pretreatment, charging and melting, crystal pulling and necking, shoulder formation, constant-diameter growth, and annealing and cooling processes, characterized in that, The specific steps are as follows: S1 Furnace Body Pretreatment: Vacuuming the Czochralski furnace to ≤1×10 -3 Pa, introduce high-purity hydrogen gas with a purity of 9N, pressurize to 0.12–0.15 MPa, and bake at a constant temperature of 900℃ for 2–4 hours; S2 Charging and Melting: High-purity germanium polycrystalline raw material is charged into the pretreated Czochralski furnace, the hydrogen pressure is maintained at 0.12–0.15 MPa, the temperature is raised to 945–950℃ and kept at a constant temperature for 40–60 min to form a supersaturated hydrogen melt. S3 crystal deriving and necking: A 13N dislocation-free seed crystal with the [100] crystal orientation is used for crystal deriving, and the necking diameter is controlled to be 2–3 mm and the length to be 15–20 mm. S4 shoulder release: Maintain hydrogen pressure at 0.12–0.15 MPa, release the shoulder at a cooling rate of 10–15 °C / h, and control the shoulder release angle at 45–60°. S5 constant diameter growth: maintain hydrogen pressure at 0.12–0.15 MPa throughout the process, control temperature gradient at 5–8℃ / cm, pulling speed at 0.8–1.2 mm / h, and crystal rotation speed at 5–10 rpm; S6 Annealing and Cooling: After growth, maintain the hydrogen pressure at 0.12–0.15 MPa, cool down to 600℃ at a rate of 3℃ / min and hold at that temperature for 2 hours, then allow the furnace to cool naturally to room temperature. The furnace will then produce 13N high-purity germanium single crystals without vacancies.

2. The method for preparing high-purity germanium single crystals without vacancy groups according to claim 1, characterized in that, In step S1, the Czochralski furnace is evacuated to 1×10⁻⁶ oz. -3 Pa.

3. The method for preparing high-purity germanium single crystals without vacancy groups according to claim 1, characterized in that, In step S2, the high-purity germanium polycrystalline raw material is 13N high-purity germanium polycrystalline.

4. The method for preparing high-purity germanium single crystals without vacancy groups according to claim 1, characterized in that, In step S3, the crystal orientation deviation of the seed crystal is <0.5°.

5. The method for preparing high-purity germanium single crystals without vacancy groups according to claim 1, characterized in that, In step S4, the cooling rate is 12℃ / h and the shoulder angle is 50°.

6. The method for preparing high-purity germanium single crystals without vacancy groups according to claim 1, characterized in that, In step S5, the temperature gradient is 6℃ / cm, the pulling speed is 1.0mm / h, and the crystal rotation speed is 8rpm.

7. The method for preparing high-purity germanium single crystals without vacancies according to claim 1, characterized in that, The hydrogen pressure is maintained at 0.13 MPa throughout steps S1 to S6.

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