Large-diameter infrared silicon single crystal and annealing method and application thereof

Abstract

The invention relates to the technical field of preparation of infrared optical materials, and particularly discloses a large-diameter infrared silicon single crystal as well as an annealing method and application thereof. The annealing method of the large-diameter infrared silicon single crystal is provided by controlling parameters such as temperature, heating rate and cooling rate of different annealing stages under the protective gas atmosphere, and the annealing method can be used for uniformly heating a silicon single crystal rod without increasing the concentration of oxygen donors, so that the quality of the large-diameter infrared silicon single crystal is improved. And the internal stress and lattice defects of the silicon single crystal rod can be effectively reduced. The prepared infrared silicon single crystal has excellent optical transmittance and optical uniformity, the average infrared transmittance within the range of 2-6 microns is larger than or equal to 52.4%, and the optical uniformity is smaller than or equal to 7.5 * 10 <-5 >. The large-diameter infrared silicon single crystal prepared by the method can be applied to preparation of a large-diameter infrared remote sensing detection lens or an infrared optical window and related fields of the large-diameter infrared remote sensing detection lens or the infrared optical window.

Description

Technical Field

[0001] The invention relates to the technical field of infrared optical material preparation, and in particular to a large-diameter infrared silicon single crystal and an annealing method and application thereof. Background Art

[0002] High-resolution infrared optical detection systems are widely used in many fields such as space detection, ground detection, remote control and telemetry, industrial temperature measurement, fire rescue, intelligent driving, medical treatment, environmental protection and consumer electronics. Infrared optical materials are not only the foundation of the infrared technology industry, but also the core of high-resolution infrared optical detection systems. As a major type of infrared optical material, silicon single crystal is the preferred material for 2~6μm short and medium-wave infrared spectrum detection systems due to its advantages such as good infrared transmittance, high refractive index, easy processing into lenses, corrosion resistance, low dispersion, no deliquescence, high mechanical strength and good chemical stability. With the continuous development of science and technology, the infrared lens, the core component of the infrared detection system, has put forward higher requirements on the size and quality of single crystal silicon. The diameter of the infrared silicon single crystal lens required for the space detection system is usually required to reach more than 300mm, and the required optical performance is also getting higher and higher. However, in the process of pulling large-diameter infrared silicon single crystals with a diameter of more than 300mm, due to the limitations of process conditions, more serious internal stress, lattice defects, oxygen donor effect and other problems often occur, which seriously affect the optical properties of infrared silicon single crystals.

[0003] At present, the annealing methods of silicon single crystals mainly improve their electrical properties, but do not specifically solve the problems that affect the optical properties caused by the large-diameter infrared silicon single crystal pulling process. In addition, for the annealing of large-size silicon single crystals, the maximum annealing temperature is too high (such as more than 1000°C), which will cause uneven heating and easily cause new stress problems. There are few reports in the prior art on the annealing methods of large-diameter infrared silicon single crystals that can eliminate the oxygen donor effect while solving problems such as stress, internal defects, and substandard optical properties. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a simple, efficient, and engineering-applicable large-diameter infrared silicon single crystal annealing method, which can reduce the internal stress, lattice defects, and oxygen donor effect of the large-diameter infrared silicon single crystal, and the obtained product has excellent optical properties such as transmittance and optical uniformity. The infrared silicon single crystal obtained by the present invention can be applied to related fields such as the preparation of large-aperture infrared remote sensing detection lenses or infrared optical windows.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: In a first aspect, the present invention provides a method for annealing a large-diameter infrared silicon single crystal, the method comprising the following steps: In a protective gas atmosphere, heating a large diameter single crystal silicon rod to T1 at a first preset rate and keeping the temperature for a first preset time, then cooling to T2 at a second preset rate, cooling to T3 at a third preset rate, and finally cooling to T4 at a fourth preset rate, and cooling to obtain a large diameter infrared silicon single crystal; Wherein, the T1 is 660°C to 700°C; The temperature T2 is 500°C to 520°C; The T3 is 390°C to 410°C; The T4 is 160°C to 200°C; The first preset rate is 6°C / min~12°C / min; The second preset rate is 3°C / min~6°C / min; The third preset rate is 8°C / min~10°C / min; The fourth preset rate is 1°C / min to 2°C / min.

[0006] The temperature-time relationship curve in the annealing method of large-diameter infrared silicon single crystal provided by the present invention is as follows: Figure 1 As shown, under a protective gas atmosphere, by controlling parameters such as temperature, heating rate and cooling rate in different annealing stages, the single crystal silicon rod can be heated evenly without increasing the oxygen donor concentration, and the internal stress and lattice defects of the single crystal silicon rod can be effectively eliminated. Among them, cooling to the T2 stage (i.e., the first stage of cooling) and cooling to the T4 stage (i.e., the third stage of cooling) using a lower cooling rate can effectively eliminate the internal stress and lattice defects of the single crystal silicon rod; cooling to the T3 stage (i.e., the second stage of cooling) using a higher cooling rate can effectively eliminate the oxygen donor effect of the single crystal silicon rod. The large-diameter infrared silicon single crystal annealing process provided by the present invention can not only reduce the internal stress, lattice defects, and oxygen donor effect of the large-diameter infrared silicon single crystal, but also effectively improve the optical transmittance and optical uniformity of the infrared silicon single crystal, with an average transmittance of ≥52.4% in the range of 2μm~6μm, and an optical uniformity of ≤7.5×10 -5 In addition, the annealing method of the large-diameter infrared silicon single crystal provided by the present invention is simple and efficient, does not involve special processes, and has strong engineering applicability and prospects for wide promotion and application.

[0007] Preferably, the large-diameter single crystal silicon rod comprises a single crystal silicon rod with a diameter of 300 mm to 500 mm; the purity of the protective gas is ≥99.999%; and the protective gas comprises argon or nitrogen.

[0008] The present invention is described by taking annealing under the protection of high-purity argon as an example.

[0009] The present invention provides that the large diameter single crystal silicon rod is placed in a protective gas atmosphere, specifically including placing the large diameter single crystal silicon rod in a high temperature control precision annealing furnace, evacuating the annealing furnace to 1-5 Pa, and filling it with high purity protective gas.

[0010] Preferably, the first preset time is 120 min to 240 min.

[0011] Preferably, the first preset rate is 9°C / min-10°C / min.

[0012] Preferably, the second preset rate is 3°C / min-5°C / min.

[0013] Preferably, the third preset rate is 9°C / min-10°C / min.

[0014] Preferably, when the temperature drops to T2, the air cooling device is turned on, the temperature is lowered to T3 at a third preset rate, and the air cooling device is turned off; wherein the wind speed of the air cooling device is 8m / s~15m / s.

[0015] Preferably, the fourth preset rate is 1.5°C / min to 2°C / min.

[0016] In a second aspect, the present invention provides a large-diameter infrared silicon single crystal, which is prepared by the annealing method of the large-diameter infrared silicon single crystal provided in the first aspect.

[0017] The infrared silicon single crystal provided by the present invention has excellent optical transmittance and optical uniformity. The average transmittance in the range of 2μm~6μm is ≥52.4%, and the optical uniformity is ≤7.5×10 -5 , meeting the requirements of high-quality infrared optical systems.

[0018] Thirdly, in view of the fact that the large-diameter infrared silicon single crystal provided by the present invention has excellent optical properties, it can be used in the fields of preparing large-aperture infrared remote sensing detection lenses and infrared optical windows. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A curve diagram showing the relationship between temperature and time in the annealing method for a large-diameter infrared silicon single crystal provided by the present invention; Figure 2 This is an optical uniformity detection diagram of infrared silicon single crystal Ⅰ in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] According to "GJB2919A-2015 National Military Standard of the People's Republic of China Specification for Germanium for Infrared Optics", an infrared spectrometer is used to measure the average transmittance of the obtained infrared silicon single crystal in the 2μm~6μm band; according to this specification, an interferometer is used to measure the optical uniformity of the obtained infrared silicon single crystal at a wavelength of 3.39μm.

[0023] Example 1 This embodiment provides an annealing method for a large-diameter infrared silicon single crystal, and the annealing method includes the following steps: S1. Place the cut single crystal silicon rod with a diameter of 450mm and a thickness of 100mm in a high temperature control precision annealing furnace, evacuate the annealing furnace to 5Pa, fill it with high-purity argon gas with a purity of 99.9995% to normal pressure, raise the temperature of the annealing furnace to 670°C at a heating rate of 8°C / min, keep the temperature constant for 210min, and then turn off the heating; Start the cooling program. The first stage of cooling is to 510°C at a cooling rate of 3.5°C / min. The wind speed of the blowing device is turned on to reach 13m / s. The second stage of cooling is to 410°C at a cooling rate of 10°C / min. The blowing device is turned off. The third stage of cooling is to 190°C at a cooling rate of 1.5°C / min. S2. Take out the above-mentioned single crystal silicon rod from the annealing furnace and cool it naturally to room temperature, thereby obtaining the large-diameter single crystal silicon after annealing, which is recorded as infrared silicon single crystal I.

[0024] The average infrared transmittance of infrared silicon single crystal I in the range of 2μm~6μm is 53.2%, and the optical uniformity at a wavelength of 3.39μm is 4.2×10 -5 Among them, the optical uniformity detection diagram of infrared silicon single crystal I is as follows: Figure 2 shown.

[0025] Example 2 This embodiment provides an annealing method for a large-diameter infrared silicon single crystal, and the annealing method includes the following steps: S1. Place the cut single crystal silicon rod with a diameter of 500 mm and a thickness of 20 mm in a high temperature control precision annealing furnace, evacuate the annealing furnace to 4 Pa, fill it with high-purity argon gas with a purity of 99.9995% to normal pressure, raise the temperature of the annealing furnace to 700°C at a heating rate of 12°C / min, keep the temperature constant for 240 minutes, and then turn off the heating; Start the cooling program. The first stage of cooling is to 520°C at a cooling rate of 3°C / min. The blowing device is turned on with a wind speed of 15m / s. The second stage of cooling is to 390°C at a cooling rate of 10°C / min. The blowing device is turned off. The third stage of cooling is to 160°C at a cooling rate of 2°C / min. S2. Take out the above-mentioned single crystal silicon rod from the annealing furnace and cool it naturally to room temperature, thereby obtaining the large-diameter single crystal silicon after annealing, which is recorded as infrared silicon single crystal II.

[0026] The average infrared transmittance of infrared silicon single crystal II in the range of 2μm~6μm is 52.4%, and the optical uniformity at a wavelength of 3.39μm is 7.5×10 -5 .

[0027] Example 3 This embodiment provides an annealing method for a large-diameter infrared silicon single crystal, and the annealing method includes the following steps: S1. Place the cut single crystal silicon rod with a diameter of 400 mm and a thickness of 200 mm in a high temperature control precision annealing furnace, evacuate the annealing furnace to 2 Pa, fill it with high-purity argon gas with a purity of 99.9995% to normal pressure, raise the temperature of the annealing furnace to 680°C at a heating rate of 10°C / min, keep the temperature constant for 180 minutes, and then turn off the heating; Start the cooling program. The first stage of cooling is to cool down to 510°C at a cooling rate of 4°C / min. The blowing device is turned on with a wind speed of 10m / s. The second stage of cooling is to cool down to 400°C at a cooling rate of 9°C / min. The blowing device is turned off. The third stage of cooling is to cool down to 180°C at a cooling rate of 1.5°C / min. S2. Take out the above-mentioned single crystal silicon rod from the annealing furnace and cool it naturally to room temperature, thereby obtaining the large-diameter single crystal silicon after annealing, which is recorded as infrared silicon single crystal III.

[0028] The average infrared transmittance of infrared silicon single crystal III in the range of 2μm~6μm is 53.1%, and the optical uniformity at a wavelength of 3.39μm is 2.6×10 -5 .

[0029] Example 4 This embodiment provides an annealing method for a large-diameter infrared silicon single crystal, and the annealing method includes the following steps: S1. Place the cut single crystal silicon rod with a diameter of 350 mm and a thickness of 400 mm in a high temperature control precision annealing furnace, evacuate the annealing furnace to 1 Pa, fill it with high-purity argon gas with a purity of 99.9999% to normal pressure, raise the temperature of the annealing furnace to 690°C at a heating rate of 9°C / min, keep the temperature constant for 150 minutes, and then turn off the heating; Start the cooling program. The first stage of cooling is to 500°C at a cooling rate of 4°C / min. The blowing device is turned on with a wind speed of 12m / s. The second stage of cooling is to 400°C at a cooling rate of 9°C / min. The blowing device is turned off. The third stage of cooling is to 170°C at a cooling rate of 1.5°C / min. S2. Take out the above-mentioned single crystal silicon rod from the annealing furnace and cool it naturally to room temperature, thereby obtaining the annealed large-diameter single crystal silicon, which is recorded as infrared silicon single crystal IV.

[0030] The average infrared transmittance of infrared silicon single crystal IV in the range of 2μm~6μm is 53.5%, and the optical uniformity at a wavelength of 3.39μm is 2.1×10 -5 .

[0031] Example 5 This embodiment provides an annealing method for a large-diameter infrared silicon single crystal, and the annealing method includes the following steps: S1. Place the cut single crystal silicon rod with a diameter of 300 mm and a thickness of 500 mm in a high temperature control precision annealing furnace, evacuate the annealing furnace to 3 Pa, fill it with high-purity argon gas with a purity of 99.999% to normal pressure, raise the temperature of the annealing furnace to 660°C at a heating rate of 6°C / min, keep the temperature constant for 120 minutes, and then turn off the heating; Start the cooling program. The first stage of cooling is to 520°C at a cooling rate of 3°C / min. The wind speed of the blowing device is turned on to reach 8m / s. The second stage of cooling is to 410°C at a cooling rate of 8°C / min. The blowing device is turned off. The third stage of cooling is to 200°C at a cooling rate of 1°C / min. S2. Take out the above-mentioned single crystal silicon rod from the annealing furnace and cool it naturally to room temperature, thereby obtaining a large-diameter single crystal silicon after annealing, which is recorded as infrared silicon single crystal V.

[0032] The average infrared transmittance of infrared silicon single crystal V in the range of 2μm~6μm is 52.5%, and the optical uniformity at a wavelength of 3.39μm is 6.5×10 -5 .

[0033] Comparative Example 1 This comparative example provides an annealing method for a large-diameter infrared silicon single crystal, which is basically the same as that in Example 4, the only difference is that "raising the annealing furnace temperature to 690°C at a heating rate of 9°C / min" in step S1 is changed to "raising the annealing furnace temperature to 650°C at a heating rate of 9°C / min", and the remaining parameters are the same as those in Example 4. Finally, a large-diameter single crystal silicon is obtained after annealing, which is recorded as infrared silicon single crystal pair I.

[0034] The average infrared transmittance of infrared silicon single crystal to I in the range of 2μm~6μm is 51.4%, and the optical uniformity at 3.39μm is 1.5×10 -4 .

[0035] Compared with the infrared silicon single crystal IV prepared in Example 4, the optical properties of the infrared silicon single crystal I prepared in this comparative example are significantly reduced. The reason may be that when T1 is reduced from 690°C to 650°C, the internal stress of the single crystal cannot be completely released due to the reduction of the maximum annealing temperature, which is not conducive to repairing lattice defects, thereby affecting the ability of the single crystal to plastically deform, and further significantly weakening the optical properties of the obtained product, such as the average infrared transmittance in the range of 2μm to 6μm and the optical uniformity at 3.39μm.

[0036] Comparative Example 2 This comparative example provides an annealing method for a large-diameter infrared silicon single crystal, which is basically the same as that in Example 4, the only difference is that "raising the annealing furnace temperature to 690°C at a heating rate of 9°C / min" in step S1 is changed to "raising the annealing furnace temperature to 720°C at a heating rate of 9°C / min", and the remaining parameters are the same as those in Example 4. Finally, a large-diameter single crystal silicon is obtained after annealing, which is recorded as infrared silicon single crystal pair II.

[0037] The average infrared transmittance of infrared silicon single crystal pair II in the range of 2μm~6μm is 51.2%, and the optical uniformity at 3.39μm is 2.6×10 -4 .

[0038] Compared with the infrared silicon single crystal IV prepared in Example 4, the optical properties of the infrared silicon single crystal II prepared in this comparative example are significantly reduced. The reason may be that when T1 is increased from 690°C to 720°C, the concentration of oxygen donors in the single crystal increases due to the increase in the maximum annealing temperature, resulting in an increase in the single crystal carrier absorption, further significantly weakening the optical properties of the obtained product, such as the average infrared transmittance in the range of 2μm to 6μm and the optical uniformity at 3.39μm.

[0039] Comparative Example 3 This comparative example provides an annealing method for a large-diameter infrared silicon single crystal, which is basically the same as that in Example 4, the only difference is that "the first stage of cooling is reduced to 500°C at a cooling rate of 4°C / min" in step S1 is changed to "the first stage of cooling is reduced to 500°C at a cooling rate of 7°C / min", and the remaining parameters are the same as those in Example 4. Finally, a large-diameter single crystal silicon is obtained after annealing, which is recorded as infrared silicon single crystal pair III.

[0040] The average infrared transmittance of infrared silicon single crystal to III in the range of 2μm~6μm is 51.6%, and the optical uniformity at 3.39μm is 1.6×10-4 .

[0041] Compared with the infrared silicon single crystal IV prepared in Example 4, the optical properties of the infrared silicon single crystal III prepared in this comparative example are significantly reduced. The reason may be that the cooling rate of the first stage of cooling is significantly increased, which makes the center temperature and edge temperature of the large-size single crystal silicon uneven during the cooling process, and the lattice defect repair and stress release effects are not good, resulting in a significant reduction in the optical properties of the product.

[0042] Comparative Example 4 This comparative example provides an annealing method for a large-diameter infrared silicon single crystal, which is basically the same as that in Example 4, with the only difference being that "the second stage of cooling is reduced to 400°C at a cooling rate of 9°C / min" in step S1 is changed to "the second stage of cooling is reduced to 380°C at a cooling rate of 11°C / min", and the remaining parameters are the same as those in Example 4. Finally, a large-diameter single crystal silicon is obtained after annealing, which is recorded as infrared silicon single crystal pair IV.

[0043] The average infrared transmittance of infrared silicon single crystal to IV in the range of 2μm~6μm is 51.8%, and the optical uniformity at 3.39μm is 1.4×10 -4 .

[0044] Compared with the infrared silicon single crystal IV prepared in Example 4, the optical performance of the infrared silicon single crystal IV prepared in this comparative example is significantly reduced. The reason may be that increasing the cooling rate of the second stage cooling within the scope of protection of the present invention while slightly increasing T3 will make the center temperature and edge temperature of the large-size single crystal silicon uneven during the cooling process, and the rapid cooling temperature interval is too long, which will lead to poor stress release effect, resulting in the product's average infrared transmittance in the range of 2μm~6μm and the optical uniformity at a wavelength of 3.39μm. The optical performance is significantly weakened.

[0045] Comparative Example 5 This comparative example provides an annealing method for a large-diameter infrared silicon single crystal, which is basically the same as that in Example 4, the only difference is that "the second stage of cooling is reduced to 400°C at a cooling rate of 9°C / min" in step S1 is changed to "the second stage of cooling is reduced to 400°C at a cooling rate of 5°C / min", and the remaining parameters are the same as those in Example 4. Finally, a large-diameter single crystal silicon is obtained after annealing, which is recorded as infrared silicon single crystal pair V.

[0046] The average infrared transmittance of infrared silicon single crystal to V in the range of 2μm~6μm is 50.8%, and the optical uniformity at 3.39μm is 1.2×10 -4 .

[0047] Compared with the infrared silicon single crystal IV prepared in Example 4, the optical properties of the infrared silicon single crystal V prepared in this comparative example are significantly reduced. The reason may be that reducing the cooling rate of the second stage of cooling within the scope of protection of the present invention will cause the intermittent oxygen in the large-sized single crystal silicon to form oxygen donors in this temperature range, increase the single crystal carrier absorption, and cause the optical properties of the product to be significantly weakened.

[0048] In summary, the large-diameter infrared silicon single crystal obtained by the annealing method provided in Examples 1 to 5 can have an average infrared transmittance of more than 52% and an optical uniformity of less than 1×10 -5 , meeting the use requirements of infrared silicon single crystals in large-aperture infrared optical systems. In addition, the annealing method of large-diameter infrared silicon single crystals provided by the present invention is simple and efficient, does not involve special processes, and has strong engineering applicability.

[0049] Compared with Example 4, the optical properties of the products obtained in Comparative Examples 1 to 5, such as the average infrared transmittance in the range of 2μm to 6μm and the optical uniformity at 3.39μm, are significantly weakened. The reason is that the T1, T2, T3 and T4 temperature settings provided by the present invention are an organic whole with parameters such as the heating rate or cooling rate at different stages. Within the parameter range provided by the present invention, the single crystal silicon rod can be heated evenly without increasing the oxygen donor concentration, and the internal stress and lattice defects of the single crystal silicon rod can be effectively eliminated. The infrared silicon single crystal obtained by the present invention has excellent optical transmittance and optical uniformity, with an average infrared transmittance of ≥52.4% in the range of 2μm to 6μm and an optical uniformity of ≤7.5×10 -5 In view of the excellent optical properties of the large-diameter infrared silicon single crystal prepared by the present invention, it can be used in related fields such as the preparation of large-aperture infrared remote sensing detection lenses and infrared optical windows.

[0050] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for annealing a large diameter infrared silicon single crystal, characterized in that: The annealing method comprises the following steps: Under a protective gas atmosphere, the large diameter single crystal silicon rod is heated to T1 at a first preset rate and kept at the temperature for a first preset time, then cooled to T2 at a second preset rate, cooled to T3 at a third preset rate, and finally cooled to T4 at a fourth preset rate, and cooled to obtain a large diameter infrared silicon single crystal; Wherein, the T1 is 660°C to 700°C; The temperature T2 is 500°C to 520°C; The T3 is 390°C to 410°C; The T4 is 160°C to 200°C; The first preset rate is 6°C / min~12°C / min; The second preset rate is 3°C / min~6°C / min; The third preset rate is 8°C / min~10°C / min; The fourth preset rate is 1°C / min to 2°C / min.

2. The annealing method of large-diameter infrared silicon single crystal according to claim 1, characterized in that: The large-diameter single crystal silicon rod comprises a single crystal silicon rod with a diameter of 300 mm to 500 mm; and / or The purity of the protective gas is ≥ 99.999%; and / or The protective gas includes argon or nitrogen.

3. The annealing method of large-diameter infrared silicon single crystal according to claim 1, characterized in that: The first preset time is 120min~240min.

4. The annealing method of large-diameter infrared silicon single crystal according to claim 1, characterized in that: The first preset rate is 9°C / min-10°C / min.

5. The annealing method of large-diameter infrared silicon single crystal according to claim 1, characterized in that: The second preset rate is 3°C / min~5°C / min.

6. The annealing method of large-diameter infrared silicon single crystal according to claim 1, characterized in that: The third preset rate is 9°C / min-10°C / min.

7. The annealing method of large-diameter infrared silicon single crystal according to claim 1, characterized in that: When the temperature drops to T2, the air cooling device is turned on, the temperature is lowered to T3 at a third preset rate, and the air cooling device is turned off; wherein the wind speed of the air cooling device is 8m / s~15m / s.

8. The annealing method of large-diameter infrared silicon single crystal according to claim 1, characterized in that: The fourth preset rate is 1.5°C / min~2°C / min.

9. A large diameter infrared silicon single crystal, characterized in that: The large-diameter infrared silicon single crystal is prepared by the annealing method of any one of claims 1 to 8.

10. Use of the large-diameter infrared silicon single crystal according to claim 9 in a large-aperture infrared remote sensing detection lens or an infrared optical window.

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