Method for pulling a single crystal substrate silicon wafer with uniform in-plane oxygen content distribution

Abstract

The present invention provides a method for pulling a single crystal substrate silicon wafer with uniform in-plane oxygen content distribution, which relates to the technical field of single crystal silicon preparation methods. In the process of vertically pulling a single crystal, a CUSP magnetic field is applied to both sides of a quartz crucible. Under a predetermined magnetic field strength, the CUSP magnetic field rises synchronously with the quartz crucible, which can more effectively suppress the convection of the melt and increase the thickness of the boundary diffusion layer. Under the action of the CUSP magnetic field, the axial distribution uniformity and radial distribution uniformity of oxygen are improved, and the radial distribution uniformity of impurities is also improved, so that the oxygen content of the pulled crystal rod is uniformly distributed in the plane.

Description

Technical Field

[0001] The present invention belongs to the technical field of single crystal silicon preparation methods, and in particular relates to a method for pulling a single crystal substrate silicon wafer with an oxygen content uniformly distributed in a plane. Background Art

[0002] Low-oxygen single-crystal silicon substrates used in insulated gate bipolar transistor (IGBT) products are an important semiconductor material. Low-oxygen single-crystal silicon substrates have higher carrier mobility and lower defect density, which can improve the performance and reliability of IGBT products. When manufacturing low-oxygen single-crystal silicon substrates, it is necessary to control the oxygen content and distribution to obtain the best crystal quality and electrical properties.

[0003] At present, the substrate silicon wafers of IGBT mainly come from silicon wafers less than 200mm cut from single crystal silicon grown by the zone melting method. In order to reduce the manufacturing cost of IGBT, the large-size silicon wafer is the main development direction, but it is extremely difficult to grow silicon wafers with a diameter of 200mm by the zone melting method. The biggest difficulty lies in the high-frequency heating equipment capacity and crystallization process conditions. Due to technical blockade, the process conditions for the development and production of large-diameter zone melting silicon single crystals need to be explored, especially the heating coil structure and crystal pulling parameters. Even if large-diameter silicon wafers can be manufactured by the zone melting method, it is difficult to provide a stable supply at a low price.

[0004] Although the Czochralski method can stably produce large silicon wafers with a diameter of 200mm or more at low cost, the oxygen content of single crystal silicon grown by the Czochralski method is usually 8~18ppma. Even if the substrate produced has an oxygen content of less than 5ppma, the in-plane distribution of the oxygen content is extremely unstable. Excessively high in-plane oxygen content will produce oxygen donors during the sintering process of the IGBT manufacturing step, causing a change in the resistivity of the silicon wafer before and after heat treatment. In addition, when the silicon wafer is used at the device end after epitaxy or substrate growth, the forward voltage drop VF fluctuates greatly, causing device failure. Summary of the invention

[0005] In view of this, the present invention provides a method for pulling a single crystal substrate silicon wafer having a uniform in-plane distribution of oxygen content.

[0006] A method for pulling a single crystal substrate silicon wafer with an in-plane uniform distribution of oxygen content. During the process of pulling a single crystal, a CUSP magnetic field is applied to both sides of a quartz crucible. Under a predetermined magnetic field strength, the CUSP magnetic field rises synchronously with the quartz crucible to pull a crystal rod with an in-plane uniform distribution of oxygen content.

[0007] Preferably, the steps include:

[0008] S1: Set up CUSP magnetic field on both sides of the quartz crucible, and then perform material processing;

[0009] S2: After the material is oxidized, during the entire crystal pulling stage, the heater is adjusted to rise by a first predetermined distance so that the heating zone of the heater is located above the liquid surface of the silicon solution, thereby reducing the oxygen content in the early stage of crystal pulling;

[0010] S3: during the process of the heater rising, applying the CUSP magnetic field, and adjusting the CUSP magnetic field to drop to a second predetermined distance so that the center of the magnetic field is located below the liquid surface;

[0011] S4: In the equal diameter step, the CUSP magnetic field and the quartz crucible rise synchronously to pull the crystal and obtain a crystal rod.

[0012] Preferably, in step S2, the first predetermined distance that the heater rises is: NCP+80mm~+130mm.

[0013] Preferably, in step S3, the second predetermined distance by which the CUSP magnetic field drops is MCP~260mm~~140mm.

[0014] Preferably, in step S4: the intensity of the CUSP magnetic field is 4000 Gs-4500 Gs.

[0015] Preferably, in the step S2, during the entire crystal pulling stage, the rotation speed of the quartz crucible is 0.1 mm / min to 1 mm / min.

[0016] Preferably, in the step S4, the rising rate of the quartz crucible is 0.12-0.15 mm / min.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention is a method for pulling a single crystal substrate silicon wafer with uniform in-plane oxygen content distribution. In the process of pulling a single crystal, a CUSP magnetic field is applied to both sides of a quartz crucible. Under a predetermined magnetic field strength, the CUSP magnetic field rises synchronously with the quartz crucible, which can more effectively suppress the convection of the melt and increase the thickness of the boundary diffusion layer. Under the action of the CUSP magnetic field, the axial distribution uniformity and radial distribution uniformity of oxygen are improved, and the radial distribution uniformity of impurities is also improved, so that the oxygen content of the pulled crystal rod is uniformly distributed in the plane. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is the oxygen content distribution of the product prepared for the first time in Example 1.

[0020] Figure 2 This is the oxygen content distribution of the product prepared for the second time in Example 1.

[0021] Figure 3This is the oxygen content distribution of the product prepared for the third time in Example 1.

[0022] Figure 4 This is the oxygen content distribution of the product prepared in Comparative Example 7.

[0023] Figure 5 This is the oxygen content distribution of the product prepared in Comparative Example 14.

[0024] Figure 6 This is the oxygen content distribution of the product prepared in Comparative Example 25. DETAILED DESCRIPTION

[0025] The technical solutions and technical effects of the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings of the present invention.

[0026] A method for pulling a single crystal substrate silicon wafer with an in-plane uniform distribution of oxygen content. During the process of pulling a single crystal, a CUSP magnetic field is applied to both sides of a quartz crucible. Under a predetermined magnetic field strength, the CUSP magnetic field rises synchronously with the quartz crucible to pull a crystal rod with an in-plane uniform distribution of oxygen content.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] The present invention is a method for pulling a single crystal substrate silicon wafer with uniform in-plane oxygen content distribution. In the process of pulling a single crystal, a CUSP magnetic field is applied to both sides of a quartz crucible. Under a predetermined magnetic field strength, the CUSP magnetic field rises synchronously with the quartz crucible, which can more effectively suppress the convection of the melt and increase the thickness of the boundary diffusion layer. Under the action of the CUSP magnetic field, the axial distribution uniformity and radial distribution uniformity of oxygen are improved, and the radial distribution uniformity of impurities is also improved, so that the oxygen content of the pulled crystal rod is uniformly distributed in the plane.

[0029] Further, the following steps are included:

[0030] S1: Set up CUSP magnetic field on both sides of the quartz crucible, and then perform material processing;

[0031] S2: After the material is oxidized, during the entire crystal pulling stage, the heater is adjusted to rise by a first predetermined distance so that the heating zone of the heater is located above the liquid surface of the silicon solution, thereby reducing the oxygen content in the early stage of crystal pulling;

[0032] S3: During the rising process of the heater, a CUSP magnetic field is applied, and the CUSP magnetic field is adjusted to drop to a second predetermined distance so that the center of the magnetic field is located below the liquid surface; the CUSP magnetic field has only a pure horizontal magnetic field component at the crystal-melt interface and the free surface. The horizontal magnetic field component diverges from the crucible axis to the outer diameter, and its value is basically proportional to the crucible radius. There are strong orthogonal magnetic field components on the side walls and bottom of the crucible. The CUSP magnetic field can more effectively suppress the convection of the melt, increase the thickness of the boundary diffusion layer, and make the oxygen content evenly distributed in the surface.

[0033] Specifically, the center of the magnetic field: refers to the center that is not affected by magnetic lines of force;

[0034] S4: In the equal diameter step, the CUSP magnetic field and the quartz crucible rise synchronously to pull the crystal to obtain a crystal rod. Maintaining the relative position of the magnetic field and the silicon liquid remains unchanged can more effectively suppress the convection of the melt and increase the thickness of the boundary diffusion layer.

[0035] Furthermore, in the step S2: the first predetermined distance that the heater rises is: NCP+80mm~+130mm, so as to move the heating zone of the heater upward and adjust the reaction temperature of the quartz crucible to reduce the oxygen content, and the heater cannot be directly raised to the first predetermined distance, and it is necessary to ensure that the silicon material in the quartz crucible is completely melted.

[0036] Specifically, the heater is lifted up by a transmission motor.

[0037] Further, the rising speed of the heater is consistent with the rising speed of the quartz crucible.

[0038] Furthermore, in step S3: the second predetermined distance that the CUSP magnetic field drops is: MCP~260mm~~140mm, and the magnetic field is raised and lowered by a motor.

[0039] Furthermore, in step S4: the intensity of the CUSP magnetic field is 4000Gs~4500Gs, the CUSP magnetic field coil distribution is symmetrical about the central axis and the central plane of the coil, and has a divergent magnetic field with radial and longitudinal components, which can effectively suppress thermal convection and forced convection caused by relative rotation of the single crystal rod and the crucible in three dimensions.

[0040] Furthermore, in the step S2, during the entire crystal pulling stage, the rotation speed of the quartz crucible is 0.1 mm / min to 1 mm / min, which slows down the reaction and dissolution rate of the silicon liquid and the quartz crucible and reduces the generation of oxygen content.

[0041] Furthermore, in the step S4, the rising rate of the quartz crucible is 0.12-0.15 mm / min.

[0042] For ease of understanding, the present invention is further illustrated by the following examples and comparative examples:

[0043] Embodiment 1~2:

[0044] When pulling a crystal rod with a diameter of 200mm, the argon flow rate is 50~150slm, the pulling speed is 0.4~1.1mm / min, the crystal rotation is 2~8mm / min, and a CUSP magnetic field is set on both sides of the quartz crucible, and then the material is chemically processed. When the chemical is completed, the rotation speed of the quartz crucible is 0.1~1mm / min. During the entire crystal pulling stage, the heater is adjusted to rise NCP+130mm, and the rising speed of the heater is consistent with the rising speed of the quartz crucible. During the rising process of the heater, a 4000GsCUSP magnetic field is applied, and the CUSP magnetic field is adjusted to drop MCP~200mm. In the equal diameter step, the CUSP magnetic field rises synchronously with the quartz crucible, and the rising rate of the quartz crucible is 0.12~0.15mm / min. Crystal pulling is carried out to obtain a crystal rod with a diameter of 200mm.

[0045] The above method was implemented three times to obtain the results of the central point oxygen content shown in Table 1, and the conditions not mentioned were the same;

[0046] Table 1

[0047]

[0048] The crystal rod pulled in Example 1 is cut into samples by a cutting machine, and the oxygen uniformity of the samples is tested by an FTIR machine. By testing 81 points in the plane, an oxygen uniformity picture is obtained based on the test results of the 81 points. The oxygen uniformity picture is as shown in FIG. Figures 1 to 3 shown.

[0049] By the above Figures 1 to 3 It can be seen that by applying the CUSP magnetic field and adjusting the position and strength of the magnetic field, the axial distribution uniformity of oxygen, the radial distribution uniformity of oxygen, and the radial distribution uniformity of impurities are all good. As can be seen from Table 1, the oxygen content is less than 3ppma, and a low-oxygen single crystal silicon substrate with an oxygen content of less than 3ppma can be used. It has a higher carrier mobility and a lower defect density, which can improve the performance and reliability of IGBT products.

[0050] Comparative Examples 1-6, MCP is 0 mm, oxygen content distribution under different crucible rotations;

[0051] Comparative Examples 7-12, MCP is 100 mm, oxygen content distribution under different crucible rotations;

[0052] Comparative Examples 13-18, MCP is -100 mm, oxygen content distribution under different crucible rotations;

[0053] Comparative Examples 19-24, MCP is 200 mm, oxygen content distribution under different crucible rotations;

[0054] Comparative Examples 25-29, MCP is -200 mm, oxygen content distribution under different crucible rotations;

[0055] In the above comparative example, except for the above scalars, the unmentioned conditions are the same as those in Example 1, and the variables and results are shown in Table 2.

[0056] Table 2

[0057]

[0058] When the crucible speed of comparative example 7 was changed to 0.1-1 mm / min and MCP was 100 mm, when the crucible speed of comparative example 14 was changed to 1-2 mm / min and MCP was -100 mm, when the crucible speed of comparative example 25 was changed to 1-2 mm / min and MCP was -200 mm, the crystal rods pulled by each were cut into samples by a cutting machine, and the oxygen uniformity of the samples was tested by an FTIR machine. By testing 81 points in the surface, an oxygen uniformity picture was obtained according to the test results of the 81 points. The oxygen uniformity picture is shown in FIG. Figures 4 to 6 shown.

[0059] Therefore, it can be concluded that setting up the CUSP magnetic field does not necessarily lead to uniform distribution of oxygen content in the plane and lower oxygen content. Through the in-plane distribution detection of oxygen content, although the oxygen content at some center points is reduced to below 3ppma (Comparative Example 25), the oxygen content in the in-plane distribution detection of oxygen content is still over 3ppma. Therefore, only when the rotation speed of the quartz crucible is matched with the position of the CUSP magnetic field, can the axial and radial distribution of oxygen be uniform and the oxygen content be lower than oxygen content <3ppma.

[0060] What is disclosed above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. A person skilled in the art can understand that all or part of the processes of the above embodiments and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A method for pulling a single crystal substrate silicon wafer with a uniform in-plane oxygen content distribution, characterized in that: In the process of pulling a single crystal, a CUSP magnetic field is applied on both sides of the quartz crucible. Under a predetermined magnetic field strength, the CUSP magnetic field and the quartz crucible rise synchronously to pull a crystal rod with a uniform distribution of oxygen content in the surface; The following steps are included: S1: Set up CUSP magnetic field on both sides of the quartz crucible and then perform material processing; S2: After the material is oxidized, during the entire crystal pulling stage, the heater is adjusted to rise by a first predetermined distance so that the heating zone of the heater is located above the liquid surface of the silicon solution, thereby reducing the oxygen content in the early stage of crystal pulling; The rising speed of the heater is consistent with the rising speed of the quartz crucible; S3: during the process of the heater rising, applying the CUSP magnetic field, and adjusting the CUSP magnetic field to drop to a second predetermined distance so that the center of the magnetic field is located below the liquid surface; S4: In the equal diameter step, the CUSP magnetic field and the quartz crucible rise synchronously to pull the crystal, so that the oxygen content of the pulled crystal rod is evenly distributed in the surface, and the crystal rod is obtained; the rising rate of the quartz crucible is 0.12-0.15mm / min; In step S2: the first predetermined distance that the heater rises is: NCP+80mm~+130mm; In the step S2, during the entire crystal pulling stage, the rotation speed of the quartz crucible is 0.1-1 mm / min; In the step S3: the second predetermined distance of the CUSP magnetic field drop is: MCP-260mm~-200mm, so that the rotation speed of the quartz crucible is adapted to the position of the CUSP magnetic field; In the step S4: the intensity of the CUSP magnetic field is 4000Gs~4500Gs.

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