A large-size high-resistance infrared silicon single crystal and its preparation method

Abstract

The present invention relates to the field of infrared optical materials technology, and specifically discloses a large-scale high-resistance infrared silicon single crystal and a preparation method thereof. The cobalt oxide doping concentration in the large-scale high-resistance infrared silicon single crystal is 10ppm to 100ppm, and the atomic concentration of phosphorus in the large-scale high-resistance infrared silicon single crystal is 2×10 13 / cm 3 ~6×10 13 / cm 3 The present invention dopes the infrared silicon single crystal with oxides of the transition metal cobalt and phosphorus impurities. The carriers of cobalt and phosphorus react with the carriers of impurities such as boron and oxygen to form a complex, thereby reducing the concentration of free carriers in the silicon single crystal. The absorption coefficient of the doped silicon single crystal is small, which can significantly increase the infrared transmittance of the silicon single crystal in the medium-wave band. The resistivity can reach above 600Ω·cm, which can meet the requirements for the use of infrared silicon single crystals in high-performance infrared optical systems.

Description

Technical Field

[0001] The present invention relates to the technical field of infrared optical materials, and in particular to a large-size high-resistance infrared silicon single crystal and a preparation method thereof. Background Art

[0002] Silicon is a common semiconductor material. Silicon single crystals have a diamond structure composed of covalent bonds and possess excellent electrical and mechanical properties. They are primarily used as substrates for integrated circuit chips and solar cells. Silicon single crystals exhibit excellent infrared optical properties. With a band gap of 1.12 eV, silicon is opaque in the visible light range. However, when infrared light enters silicon, its energy is insufficient to excite electrons within the silicon from the valence band to the conduction band, and therefore is not absorbed. The ideal transmission band for silicon single crystals is 2 μm to 6 μm, with a theoretical transmittance of 53.8% in this band. Combined with their high mechanical strength, low dispersion, and corrosion resistance, they are ideal short- and medium-wave infrared optical materials.

[0003] Currently, the main methods for producing silicon single crystals include the Czochralski (CZ) method and the floating zone melting (FZ) method. The advantages of the CZ method include low crystal stress, easy crystallization, good single crystal integrity, large diameter and length, and high growth rate. However, due to the contact of the melt with the quartz crucible, it is difficult to produce single crystals with high purity and high resistivity. The advantage of the floating zone melting method is that it does not come into contact with any other substances, such as quartz, and can produce high-purity, oxygen-free, high-resistance silicon. However, its disadvantages are that the maximum silicon rod diameter is limited to 8 inches, the growth rate is slow, and the production cost is high.

[0004] High-performance infrared optical systems used for long-range detection in aerospace and other applications place higher demands on the size, optical transmittance, and absorption coefficient of silicon single crystals. Typically, large-aperture detection systems require infrared silicon lenses larger than 200 mm, with transmittance ≥52% and an absorption coefficient ≤0.05 in the 2μm-6μm band. To meet these requirements, the silicon single crystal resistivity must exceed 500Ω·cm. However, while silicon single crystals grown using the floating zone melting method can achieve resistivity exceeding 500Ω·cm, diameters cannot exceed 200 mm, and production efficiency is low and costs are high. Existing methods for producing high-resistance silicon single crystals using the Czochralski method, whether for P-type or N-type single crystals, are only capable of producing silicon single crystals with resistivity below 300Ω·cm (resistivity cannot reach 500Ω·cm). These methods are complex, requiring multiple batches of doping and crystal pulling, and fail to specifically address carrier absorption in infrared silicon single crystals, thus failing to meet the high-resistance infrared silicon single crystal requirements for high-performance optical lenses. Summary of the Invention

[0005] In response to the above problems, the present invention provides a large-size high-resistance infrared silicon single crystal and a preparation method thereof. By controlling the doping material and its doping amount, the carriers of impurities such as boron and oxygen are compensated and recombine, thereby reducing the concentration of free carriers in the silicon single crystal, thereby improving the infrared optical performance of the silicon single crystal and greatly reducing the manufacturing cost.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0007] In a first aspect, the present invention provides a large-sized high-resistance infrared silicon single crystal, wherein the doping concentration of cobalt oxide in the large-sized high-resistance infrared silicon single crystal is 10ppm~100ppm, and the atomic concentration of phosphorus in the large-sized high-resistance infrared silicon single crystal is 2×10 13 / cm 3 ~6×10 13 / cm 3 .

[0008] Compared to existing technologies, the large-scale, high-resistance infrared silicon single crystals provided by the present invention incorporate transition metal cobalt oxide and phosphorus impurities into the infrared silicon single crystals. The cobalt and phosphorus carriers recombine with carriers from impurities such as boron and oxygen, thereby reducing the concentration of free carriers in the silicon single crystal. The doped silicon single crystals have a low absorption coefficient, significantly increasing their infrared transmittance in the medium-wavelength band. Experimental results demonstrate that the large-scale, high-resistance infrared silicon single crystals provided by the present invention can achieve a resistivity exceeding 800Ω·cm, an average infrared transmittance of ≥52% in the 2μm to 6μm range, an absorption coefficient of ≤0.01 at 3μm, and a diameter of ≥200mm, meeting the requirements for use in high-performance infrared optical systems.

[0009] Preferably, the doping concentration of cobalt oxide in the large-size high-resistance infrared silicon single crystal is 10 ppm to 80 ppm, and more preferably 20 ppm to 50 ppm.

[0010] Preferably, the large-size high-resistance infrared silicon single crystal is produced by a Czochralski single crystal manufacturing method.

[0011] In a second aspect, the present invention provides a method for preparing the large-size high-resistance infrared silicon single crystal, comprising the following steps:

[0012] The raw materials are weighed according to the designed ratio, and polycrystalline silicon, cobalt oxide and silicon-phosphorus alloy are placed in a crucible. After the seed crystal is melted under an inert atmosphere, the seed crystal is pulled to grow in equal diameter to obtain a large-sized high-resistance infrared silicon single crystal.

[0013] The method for preparing large-size high-resistance infrared silicon single crystals provided by the present invention has a simple, efficient, low-cost process and does not involve any special processes. It is suitable for the preparation of large-diameter infrared silicon single crystals. It can not only improve the resistivity of the silicon single crystals, but also enhance the infrared optical transmittance of the silicon single crystals. It has strong engineering applicability and is suitable for large-scale production.

[0014] Preferably, the atomic concentration of phosphorus in the silicon-phosphorus alloy is ≥10 18 / cm 3 , more preferably 5×10 18 / cm 3 ~5×10 19 / cm 3 .

[0015] Preferably, the purity of the cobalt oxide is ≥99.9995%, and the purity of the polysilicon is ≥10N.

[0016] Preferably, the crucible is a quartz crucible with a purity of ≥99.99%.

[0017] Preferably, the inert atmosphere includes an argon atmosphere with a purity of ≥99.9999%, and the flow rate of the argon is 100 L / min~130 L / min.

[0018] The present invention selects raw materials such as high-purity cobalt oxide, polysilicon, quartz crucible and argon gas, further reducing the generation of impurities during the preparation process and ensuring the stability of the preparation process of large-size high-resistance infrared silicon single crystals.

[0019] Preferably, the temperature of the fusion-bonding seed crystal is 1430° C. to 1450° C., and the pressure is 1 kPa to 2 kPa (more preferably 1 kPa to 1.5 kPa).

[0020] It should be noted that the welding of seed crystals of the present invention includes first melting the raw materials in the crucible into a melt, and then immersing one end of the seed crystal into the melt for subsequent isodiametric growth to form a single crystal.

[0021] By limiting parameters such as temperature, pressure, and argon flow rate of the fusion seed crystal, the present invention can further reduce the oxygen content and free carrier concentration in the silicon single crystal, thereby increasing both the resistivity and infrared optical transmittance of the infrared silicon single crystal.

[0022] For example, the pulling of the seed crystal includes necking, shouldering, equal diameter growth and tailing in sequence.

[0023] Preferably, during the isodiametric growth process, the rotation speed of the crucible is 4 r / min to 6 r / min, and the rotation speed of the seed crystal is 6 r / min to 9 r / min.

[0024] By limiting the conditions for isodiameter growth, the present invention can ensure the stability of the solid-liquid interface during the single crystal growth process, thereby ensuring the quality of the finished infrared silicon single crystal. The present invention does not limit the necking and shouldering processes, and conventional operations in the field can be used.

[0025] For example, the finishing includes the following steps: after the equal-diameter growth is completed, the diameter and crucible heel ratio control programs are turned off, the temperature is raised to 1435℃~1460℃, and the pulling speed is manually adjusted to 1mm / min~5mm / min to gradually reduce the diameter of the single crystal until the single crystal is separated from the liquid surface, thereby obtaining a large-size high-resistance infrared silicon single crystal. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a graph showing the infrared transmittance of the large-sized high-resistance infrared silicon single crystal in Example 2 of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0028] In the present invention, materials not otherwise specified are all commercially available products.

[0029] Example 1

[0030] This embodiment provides a large-sized high-resistance infrared silicon single crystal. The doping concentration of cobalt oxide in the large-sized high-resistance infrared silicon single crystal is 10 ppm, and the atomic concentration of phosphorus in the large-sized high-resistance infrared silicon single crystal is 2×10 13 / cm 3 .

[0031] The method for preparing the large-size high-resistance infrared silicon single crystal comprises the following steps:

[0032] Weigh the raw materials according to the designed ratio, and mix 100 kg of 10N pure polysilicon, 1 g of 99.9999% pure cobalt oxide and 0.1 g of silicon-phosphorus alloy (the atomic concentration of phosphorus in the silicon-phosphorus alloy is 2×10 19 / cm 3 ) is placed in a quartz crucible with a purity of 99.99%, and then placed in a vertical single crystal furnace; high-purity argon with a purity of 99.9999% is introduced into the furnace at a flow rate of 100L / min, the temperature is raised to 1430℃, the furnace pressure is 1kPa, and after the seed crystal is fused, the seed crystal is pulled in sequence for necking, shouldering, equal diameter growth (the rotation speed of the quartz crucible is 4r / min, the rotation speed of the seed crystal is 6r / min) and tailing to obtain a large-size high-resistance infrared silicon single crystal.

[0033] Example 2

[0034] This embodiment provides a large-sized high-resistance infrared silicon single crystal. The doping concentration of cobalt oxide in the large-sized high-resistance infrared silicon single crystal is 26.7ppm, and the atomic concentration of phosphorus in the large-sized high-resistance infrared silicon single crystal is 4×10 13 / cm 3 .

[0035] The method for preparing the large-size high-resistance infrared silicon single crystal comprises the following steps:

[0036] Weigh the raw materials according to the designed ratio, and mix 150kg of 11N pure polysilicon, 4g of 99.9999% pure cobalt oxide and 0.3g of silicon-phosphorus alloy (the atomic concentration of phosphorus in the silicon-phosphorus alloy is 4×10 19 / cm 3 ) is placed in a quartz crucible with a purity of 99.995%, and then placed in a vertical single crystal furnace; high-purity argon with a purity of 99.99995% is introduced into the furnace at a flow rate of 120L / min, the temperature is raised to 1440℃, the furnace pressure is 1.25kPa, and after the seed crystal is fused, the seed crystal is pulled in sequence for necking, shouldering, equal diameter growth (the rotation speed of the quartz crucible is 5r / min, and the rotation speed of the seed crystal is 7r / min) and finishing to obtain a large-size high-resistance infrared silicon single crystal.

[0037] Example 3

[0038] This embodiment provides a large-sized high-resistance infrared silicon single crystal. The doping concentration of cobalt oxide in the large-sized high-resistance infrared silicon single crystal is 90ppm, and the atomic concentration of phosphorus in the large-sized high-resistance infrared silicon single crystal is 6×10 13 / cm 3 .

[0039] The method for preparing the large-size high-resistance infrared silicon single crystal comprises the following steps:

[0040] Weigh the raw materials according to the designed ratio, and mix 200 kg of 10N pure polysilicon, 18 g of 99.9995% pure cobalt oxide and 0.3 g of silicon-phosphorus alloy (the atomic concentration of phosphorus in the silicon-phosphorus alloy is 4×10 19 / cm 3 ) is placed in a quartz crucible with a purity of 99.99%, and then placed in a vertical single crystal furnace; high-purity argon gas with a purity of 99.9999% is introduced into the furnace at a flow rate of 130L / min, the temperature is raised to 1450℃, the furnace pressure is 1.3kPa, and after the seed crystal is fused, the seed crystal is pulled in sequence for necking, shouldering, equal diameter growth (the rotation speed of the quartz crucible is 6r / min, and the rotation speed of the seed crystal is 9r / min) and finishing to obtain a large-size high-resistance infrared silicon single crystal.

[0041] Example 4

[0042] This embodiment provides a large-sized high-resistance infrared silicon single crystal. The doping concentration of cobalt oxide in the large-sized high-resistance infrared silicon single crystal is 50ppm, and the atomic concentration of phosphorus in the large-sized high-resistance infrared silicon single crystal is 2×10 13 / cm 3 ~6×10 13 / cm 3 .

[0043] The method for preparing the large-size high-resistance infrared silicon single crystal comprises the following steps:

[0044] Weigh the raw materials according to the designed ratio, and mix 100 kg of 11N pure polysilicon, 5 g of 99.9999% pure cobalt oxide and 0.12 g of silicon-phosphorus alloy (the atomic concentration of phosphorus in the silicon-phosphorus alloy is 4×10 19 / cm 3 ) is placed in a quartz crucible with a purity of 99.995%, and then placed in a vertical single crystal furnace; high-purity argon gas with a purity of 99.99995% is introduced into the furnace at a flow rate of 110L / min, the temperature is raised to 1445℃, the furnace pressure is 1.9kPa, and after the seed crystal is fused, the seed crystal is pulled in sequence for necking, shouldering, equal diameter growth (the rotation speed of the quartz crucible is 5r / min, the rotation speed of the seed crystal is 8r / min) and finishing to obtain a large-size high-resistance infrared silicon single crystal.

[0045] Comparative Example 1

[0046] This comparative example provides an infrared silicon single crystal (not doped with cobalt oxide), the atomic concentration of phosphorus in the infrared silicon single crystal is 4×10 13 / cm 3 .

[0047] The above-mentioned method for preparing infrared silicon single crystal is similar to that of Example 2, except that the addition of cobalt oxide to the raw materials is omitted. The remaining conditions are the same as those of Example 2 and will not be repeated here.

[0048] Comparative Example 2

[0049] This comparative example provides an infrared silicon single crystal (not doped with phosphorus), and the doping concentration of cobalt oxide in the infrared silicon single crystal is 26.7 ppm.

[0050] The above-mentioned method for preparing infrared silicon single crystal is similar to that of Example 2, except that the silicon-phosphorus alloy is omitted from the raw materials. The remaining conditions are the same as those of Example 2 and will not be described in detail.

[0051] Comparative Example 3

[0052] This comparative example provides an infrared silicon single crystal, wherein the doping concentration of cobalt oxide in the infrared silicon single crystal is 150ppm, and the atomic concentration of phosphorus in the infrared silicon single crystal is 4×10 13 / cm 3 .

[0053] The preparation method for the infrared silicon single crystal described above is similar to that of Example 2, differing only in that the raw materials are 150 kg of 11N-purity polycrystalline silicon, 22.5 g of 99.9999% pure cobalt oxide, and 0.3 g of a silicon-phosphorus alloy. Aside from the different amount of cobalt oxide added, all other conditions are the same as in Example 2 and are not further described.

[0054] Comparative Example 4

[0055] This comparative example provides an infrared silicon single crystal. The doping concentration of cobalt oxide in the large-size high-resistance infrared silicon single crystal is 26.7ppm, and the atomic concentration of phosphorus in the infrared silicon single crystal is 2×10 14 / cm 3 .

[0056] The above-mentioned infrared silicon single crystal preparation method is similar to that of Example 2, differing only in that the raw materials are 150 kg of 11N-purity polycrystalline silicon, 4 g of 99.9999%-purity cobalt oxide, and 1.5 g of a silicon-phosphorus alloy. Aside from the different amount of silicon-phosphorus alloy added, all other conditions are the same as those of Example 2 and are not further described.

[0057] Verification test

[0058] Infrared optical performance tests were performed on the infrared silicon single crystals provided in Examples 1 to 4 and Comparative Examples 1 to 4, respectively. The test results are shown in Table 1. The resistivity was measured using a Hall effect tester in accordance with the GB / T 4326 standard; the infrared transmittance was measured in the 2μm-6μm band using an infrared spectrometer in accordance with the GJB2919A standard; and the absorption coefficient was measured in the 3μm wavelength band using an infrared spectrometer in accordance with the GJB2919A standard. The absorption coefficient was calculated according to Formula 1:

[0059] Formula 1

[0060] Where ɑ represents the absorption coefficient, cm -1 ; d represents the sample thickness, cm; R represents the reflectance; T λ Indicates transmittance.

[0061] The reflectance R is calculated by formula 2:

[0062] Formula 2

[0063] Where R represents reflectance and n represents refractive index. At a wavelength of 3 μm (@3 μm), n = 3.4320, and the sample thickness for the transmittance test is 2 cm.

[0064] Table 1 Performance test results of infrared silicon single crystals of the embodiment and comparative example

[0065]

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A large-size high-resistance infrared silicon single crystal, characterized in that: The doping concentration of cobalt oxide in the large-scale high-resistance infrared silicon single crystal is 10ppm~100ppm, and the atomic concentration of phosphorus in the large-scale high-resistance infrared silicon single crystal is 2×10 13 / cm 3 ~6×10 13 / cm 3 .

2. The large-size high-resistance infrared silicon single crystal according to claim 1, characterized in that: The doping concentration of cobalt oxide in the large-size high-resistance infrared silicon single crystal is 10ppm-80ppm.

3. The large-size high-resistance infrared silicon single crystal according to claim 1, characterized in that: The large-size high-resistance infrared silicon single crystal is manufactured by adopting a Czochralski single crystal manufacturing method.

4. The method for preparing a large-size high-resistance infrared silicon single crystal according to any one of claims 1 to 3, characterized in that: The following steps are involved: The raw materials are weighed according to the designed ratio, and polycrystalline silicon, cobalt oxide and silicon-phosphorus alloy are placed in a crucible. After the seed crystal is melted under an inert atmosphere, the seed crystal is pulled to grow in equal diameter to obtain a large-sized high-resistance infrared silicon single crystal.

5. The method for preparing a large-size high-resistance infrared silicon single crystal according to claim 4, characterized in that: The atomic concentration of phosphorus in the silicon-phosphorus alloy is ≥10 18 / cm 3 .

6. The method for preparing a large-size high-resistance infrared silicon single crystal according to claim 4, characterized in that: The purity of the cobalt oxide is ≥99.9995%, the purity of the polysilicon is ≥10N, and the crucible is a quartz crucible with a purity of ≥99.99%.

7. The method for preparing a large-size high-resistance infrared silicon single crystal according to claim 4, characterized in that: The inert atmosphere includes an argon atmosphere with a purity of ≥99.9999%, and the flow rate of the argon is 100 L / min~130 L / min.

8. The method for preparing a large-size high-resistance infrared silicon single crystal according to claim 4, characterized in that: The temperature of the fusion seed crystal is 1430° C. to 1450° C., and the pressure is 1 kPa to 2 kPa.

9. The method for preparing a large-size high-resistance infrared silicon single crystal according to claim 4, wherein: The step of pulling the seed crystal to perform isodiametric growth specifically includes: pulling the seed crystal to perform necking, shoulder release, isodiametric growth and tailing in sequence.

10. The method for preparing a large-size high-resistance infrared silicon single crystal according to claim 4 or 9, characterized in that: During the isodiametric growth process, the rotation speed of the crucible is 4 r / min to 6 r / min, and the rotation speed of the seed crystal is 6 r / min to 9 r / min.

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