A method for improving the in-plane resistivity uniformity of an epitaxial wafer

Abstract

The present invention discloses a method for improving the in-plane resistivity uniformity of an epitaxial wafer. The substrate to be made into the epitaxial wafer is heat-treated. The heat treatment includes the following five steps: S1. Keep the temperature at 480 - 500 °C for 20 - 40 min; S2. Raise the temperature to 780 - 800 °C at a rate of 4 - 6 °C / min; S3. Keep the temperature at 780 - 800 °C for 10 - 20 min; S4. Lower the temperature to 480 - 500 °C at a rate of 3 - 4 °C / min; S5. Keep the temperature at 480 - 500 °C for 20 - 40 min. Steps S1 - S5 are carried out in an inert atmosphere. By heat-treating the heavily doped red phosphorus substrate of the SRP radially non-uniform epitaxial wafer, the present application effectively improves the radial SRP distribution of the epitaxial wafer and solves the problem of abnormal chip BVdss distribution caused by the non-uniformity of the radial SRP of the epitaxial wafer.

Description

Technical Field

[0001] The present invention belongs to the technical field of substrate processing, and particularly relates to a method for improving the in-plane resistivity uniformity of an epitaxial wafer. Background Art

[0002] At present, more than 90% of the chips and devices globally use silicon as the substrate material. For a single-crystalline silicon substrate, the manufacturing steps of chips in the prior art generally include the following processes:

[0003] 1. Obtaining high-purity silicon (ordinary grade, photovoltaic grade or semiconductor grade) through smelting; 2. Obtaining a single-crystalline silicon ingot by pulling the high-purity silicon; 3. Obtaining a silicon wafer with a standard crystal orientation and flatness through cutting, grinding, polishing, etc., which is also called a substrate, a wafer, etc.; 4. Epitaxially growing an epitaxial wafer on the substrate; 5. Obtaining a wafer through deposition, trenches, etching, etc. on the epitaxial wafer, and then obtaining a chip after installing electrodes, scribing, and cutting.

[0004] Currently, with the strong market demand for power devices in the integrated circuit industry, the demand for heavily doped substrates has gradually increased, and low-resistivity heavily doped substrates need to be used in combination with an epitaxial process. The radial distribution of the SRP (Spreading Resistance Profile) of the epitaxial layer of an epitaxial wafer is a key parameter of the epitaxial layer, directly affecting the yield of chip devices. The resistivity SRP of the epitaxial layer shows a gradient distribution, and the radial distribution of SRP is affected by the radial oxygen precipitation of the substrate. Especially when the substrate is a heavily doped red phosphorus substrate (resistivity ≤ 0.0015 Ω·cm), since phosphorus atoms are easily extruded and diffused by the oxygen precipitates in the substrate, affecting the epitaxial layer. For the substrate made from the head (0 m to 200 mm position) of a heavily doped red phosphorus single-crystalline silicon ingot, the oxygen content and oxygen precipitation concentration are high and uneven, and the in-plane radial distribution of the oxygen content and oxygen precipitation concentration is high in the center and low at the edge. Therefore, the phosphorus atoms in the substrate made from the head (0 m to 200 mm position) of a heavily doped red phosphorus single-crystalline silicon ingot are more likely to diffuse into the epitaxial layer, showing severe diffusion in the center and slight diffusion at the edge. As a result, the radial distribution of SRP after epitaxy shows a large difference between the center and the edge, ultimately leading to the uneven distribution of the BVdss (Breakdown Voltage) of chip devices (low BV in the center and high BV at the edge). Summary of the Invention

[0005] The purpose of the present invention is to provide a method for improving the in-plane resistivity uniformity of an epitaxial wafer to solve the deficiencies of the prior art. The substrate processed by this method can produce an epitaxial wafer with a uniform radial SRP distribution, effectively improving the uneven distribution of the BVdss of chip devices.

[0006] The purpose of the present invention is achieved by the following technical solutions:

[0007] A method for improving the in-plane resistivity uniformity of an epitaxial wafer, comprising heat-treating a substrate to be made into the epitaxial wafer; the heat treatment includes the following five steps:

[0008] S1. Hold at 480 - 500 °C for 20 - 40 min;

[0009] S2. Heat up to 780 - 800 °C at a rate of 4 - 6 °C / min;

[0010] S3. Hold at 780 - 800 °C for 10 - 20 min;

[0011] S4. Cool down to 480 - 500 °C at a rate of 3 - 4 °C / min;

[0012] S5. Hold at 480 - 500 °C for 20 - 40 min;

[0013] Steps S1 - S5 are carried out in an inert atmosphere.

[0014] Preferably, the substrate comes from the head position of a heavily doped red phosphorus crystal bar, i.e., the position of 0 - 200 mm of the crystal bar.

[0015] Preferably, the substrate is N-type, with a thickness of 755 - 795 um and a resistivity range of 0.001 - 0.0015 Ω·cm.

[0016] Preferably, the epitaxial layer of the epitaxial wafer is N-type, with a thickness of 2 - 8 um and a resistivity SRP range of 0.001 - 1 Ω·cm.

[0017] Preferably, the heat treatment is carried out at normal pressure.

[0018] Preferably, the inert atmosphere used is Ar.

[0019] Preferably, the Ar gas flow rate in steps S1 - S5 is 8 - 12 L / min.

[0020] Preferably, after the holding in step S5 ends, the substrate is cooled to room temperature in an inert atmosphere at a cooling rate of 50 - 70 °C / s.

[0021] Preferably, the inert atmosphere is Ar.

[0022] This application effectively improves the radial SRP distribution of the epitaxial wafer by heat-treating the heavily doped red phosphorus substrate of the epitaxial wafer with non-uniform SRP radial distribution, and solves the problem of abnormal BVdss distribution of the chip caused by non-uniform radial SRP of the epitaxial wafer. Description of the Drawings

[0023] Figure 1It is an SRP diagram of an epitaxial wafer made of a substrate at the head of a heavily phosphorus-doped crystal bar in the prior art;

[0024] Figure 2 It is an epitaxial wafer made of a substrate at the head of a heavily phosphorus-doped crystal bar in the prior art, and a BVdss diagram of a chip further fabricated from this epitaxial wafer;

[0025] Figure 3 It is an SRP diagram of an epitaxial wafer made of a substrate in the middle of a heavily phosphorus-doped crystal bar in the prior art;

[0026] Figure 4 It is an SRP diagram of an epitaxial wafer made of a substrate at the head of a heavily phosphorus-doped crystal bar after heat treatment;

[0027] Figure 5 It is an epitaxial wafer made of a substrate at the head of a heavily phosphorus-doped crystal bar after heat treatment, and a BVdss diagram of a chip further fabricated from this epitaxial wafer. Detailed implementation manners

[0028] The present invention provides a method for improving the in-plane resistivity uniformity of an epitaxial wafer, which lies in performing heat treatment on a substrate to be made into an epitaxial wafer; wherein the heat treatment includes the following five steps:

[0029] S1. Keep the temperature at 480 - 500 °C for 20 - 40 min; during this stage, a small amount of oxygen precipitates in the substrate to form, which is the incubation period of oxygen precipitates;

[0030] S2. Raise the temperature to 780 - 800 °C at a rate of 4 - 6 °C / min; during this stage, the oxygen precipitation increases rapidly, which is the rapid growth period of oxygen precipitation;

[0031] S3. Keep the temperature at 780 - 800 °C for 10 - 20 min; during this stage, the oxygen precipitation increases slowly, and the overall in-plane oxygen precipitation approaches saturation;

[0032] S4. Lower the temperature to 480 - 500 °C at a rate of 3 - 4 °C / min; during this stage, the oxygen precipitates tend to be stable;

[0033] S5. Keep the temperature at 480 - 500 °C for 20 - 40 min; during this stage, the oxygen precipitates remain stable.

[0034] Steps S1 - S5 are carried out in an inert atmosphere to avoid the reaction of oxygen and moisture in the atmosphere on the substrate surface.

[0035] In this application, high-temperature heat treatment is performed on a heavily doped red phosphorus substrate with an SRP radially non-uniform epitaxial layer, and by optimizing the heat treatment process, the heat treatment is divided into five distinct stages. First, heat preservation is carried out at a low temperature of 480 - 500 °C to incubate oxygen precipitates in the substrate. Then, it is heated to 780 - 800 °C at a certain rate. During the heating process, the oxygen precipitates increase rapidly, and heat preservation is carried out at 780 - 800 °C for a certain period of time to maximize the precipitation of oxygen precipitates. Then, it is cooled to 480 - 500 °C at a certain rate and heat-preserved to make the oxygen precipitates tend to a stable state at low temperature. If the heat preservation temperature is too high and the time is too long, non-uniform oxygen precipitation is likely to form; conversely, if the heat preservation temperature is too low and the time is too short, oxygen precipitation is not likely to form.

[0036] After the above treatment, the oxygen content and oxygen precipitation concentration in the substrate plane reach saturation as a whole, and the in-plane oxygen precipitation reaches uniform distribution. When epitaxial growth occurs, even if phosphorus atoms in the substrate are extruded by oxygen precipitates and diffuse to affect the epitaxial layer, the phosphorus atoms can still be evenly distributed and do not affect the SRP result of the epitaxial layer. After comparative testing, the SRP after epitaxy is basically the same, and the BVdss test result is significantly improved.

[0037] Therefore, by performing heat treatment on the heavily doped red phosphorus substrate of the SRP radially non-uniform epitaxial wafer in this application, the radial SRP distribution of the epitaxial wafer is effectively improved, and the problem of abnormal BVdss distribution of the chip caused by non-uniform radial SRP of the epitaxial wafer is solved.

[0038] Preferably, the substrate is N-type, with a thickness of 755 - 795 um, a resistivity range of 0.001 - 0.0015 Ω·cm. The substrate comes from the head position of the heavily doped red phosphorus crystal bar, that is, the 0 - 200 mm position of the crystal bar. The method of this application is particularly applicable to the above substrate. Of course, the method of this application can also be applicable to other substrates with non-uniform oxygen precipitation.

[0039] An epitaxial wafer with a uniform SRP radial distribution can be obtained by using a conventional epitaxial method for the substrate processed by this application. This application provides a typical epitaxial method, which is as follows: On the substrate, a process of growing a single crystal film by chemical vapor deposition (CVD, Chemical vapor deposition) in the arrangement and extension of the substrate crystal orientation, the chemical vapor deposition temperature is 700 - 1200 °C, the epitaxial layer is N-type, with a thickness of 2 - 8 um, and the resistivity SRP range is 0.001 - 1 Ω·cm.

[0040] The heat treatment in this application can be carried out under normal pressure.

[0041] Preferably, the inert gas in steps S1 - S5 is argon (Ar). More preferably, the Ar gas flow rate is 8 - 12 L / min.

[0042] Preferably, after the heat preservation in step S5, the substrate is placed in a cooling chamber and cooled to room temperature at a cooling rate of 50-70 °C / s and then taken out. The cooling chamber is protected by an inert atmosphere, and the inert atmosphere is preferably Ar; if the cooling rate is too fast, it is easy to cause the lattice arrangement to be disordered and form dislocation defects; if the cooling rate is too slow, other unstable oxygen precipitates are easily formed, which also affects the resistivity of the substrate.

[0043] Example 1

[0044] A substrate (with a thickness of 775 μm and a resistivity of 0.001-0.0015 Ω·cm) made of the head of a heavily doped red phosphorus crystal rod (the total length of the crystal rod is 1400 mm, and the head position of the crystal rod is 0-200 mm) in the prior art. Due to the large difference in radial oxygen precipitation at the head of the crystal rod and the small difference in radial oxygen precipitates in the middle of the crystal rod, the SRP radial distribution of the epitaxial layer is poor after epitaxy of the substrate made of the head of the crystal rod, resulting in abnormal BVdss distribution of the chips made therefrom: the BVdss at the edge is high and the BVdss at the center is low. The test results of the SRP of the epitaxial layer of the epitaxial wafer after epitaxy of this substrate and the BVdss of the chips made from this epitaxial wafer are as Figure 1 and 2 shown. At the same time, the SRP of the epitaxial layer of the epitaxial wafer obtained from the substrate in the middle of the crystal rod was measured, and the results are as Figure 3 shown.

[0045] To solve the above problems, this example provides a method for heat-treating a substrate made of the head of a crystal rod, so as to improve the in-plane resistivity of the epitaxial wafer; the method is as follows:

[0046] Place the substrate in a heating furnace and perform heat treatment on it under normal pressure. The specific steps are as follows:

[0047] S1. Keep warm at 490 °C for 30 min;

[0048] S2. Heat up to 790 °C at a rate of 5 °C / min;

[0049] S3. Keep warm at 790 °C for 15 min;

[0050] S4. Cool down to 490 °C at a rate of 3.5 °C / min;

[0051] S5. Keep warm at 490 °C for 30 min;

[0052] S6. Place the substrate in a cooling chamber and cool it to room temperature at a cooling rate of 60 °C / s;

[0053] Steps S1-S6 are carried out in an argon atmosphere with an argon flow rate of 10 L / min.

[0054] After the heat preservation is completed, the substrate is cooled to room temperature in the cooling chamber at a cooling rate of 60 °C / s and then taken out. The atmosphere in the cooling chamber is Ar. An epitaxial wafer is made from this substrate, and the SRP of its epitaxial layer is measured. The results are as Figure 4 shown. The above epitaxial wafer is made into a chip, and its BVdss is tested. The results are as Figure 5 shown.

[0055] It can be seen from Figures 1 to 5 that there are obvious differences in the SRP of the epitaxial layer between the epitaxial wafer made from the substrate at the head of the crystal bar without heat treatment and the epitaxial layer SRP of the epitaxial wafer made from the substrate in the middle of the crystal bar. The radial distribution is poor, resulting in abnormal distribution of the chip BVdss. After heat treatment, the SRP radial distribution is uniform and basically the same as the SRP of the epitaxial layer of the epitaxial wafer made from the substrate in the middle of the crystal bar. As a result, the BVdss test results of the chips from the substrate at the head of the heat-treated crystal bar have also been significantly improved.

[0056] Example 2

[0057] The substrate made from the head of the heavily phosphorus-doped crystal bar is placed in a heating furnace and heat-treated under normal pressure. The specific steps are as follows:

[0058] S1. Keep the temperature at 500 °C for 30 min;

[0059] S2. Heat up to 800 °C at a rate of 5 °C / min;

[0060] S3. Keep the temperature at 800 °C for 10 min;

[0061] S4. Cool down to 480 °C at a rate of 4 °C / min;

[0062] S5. Keep the temperature at 480 °C for 40 min;

[0063] S6. Place the substrate in the cooling chamber and cool it to room temperature at a cooling rate of 70 °C / s;

[0064] Steps S1 to S6 are carried out in an argon atmosphere with an argon flow rate of 10 L / min.

[0065] Example 3

[0066] The substrate made from the head of the heavily phosphorus-doped crystal bar is placed in a heating furnace and heat-treated under normal pressure. The specific steps are as follows:

[0067] S1. Keep the temperature at 480 °C for 40 min;

[0068] S2. Heat up to 795 °C at a rate of 6 °C / min;

[0069] S3. Keep the temperature at 795 °C for 12 min;

[0070] S4. Cool down to 490 °C at a rate of 3.5 °C / min;

[0071] S5. Hold at 490 °C for 30 min;

[0072] S6. Place the substrate in the cooling chamber and cool it to room temperature at a cooling rate of 60 °C / s;

[0073] Steps S1 to S6 are carried out in an argon atmosphere with an argon flow rate of 11 L / min.

[0074] Example 4

[0075] Place the substrate made of the head of a heavily phosphorus-doped crystal rod in a heating furnace and perform heat treatment on it under normal pressure. The specific steps are as follows:

[0076] S1. Hold at 490 °C for 30 min;

[0077] S2. Heat up to 785 °C at a rate of 5 °C / min;

[0078] S3. Hold at 785 °C for 15 min;

[0079] S4. Cool down to 490 °C at a rate of 3.5 °C / min;

[0080] S5. Hold at 490 °C for 30 min;

[0081] S6. Place the substrate in the cooling chamber and cool it to room temperature at a cooling rate of 60 °C / s;

[0082] Steps S1 to S6 are carried out in an argon atmosphere with an argon flow rate of 12 L / min.

[0083] Example 5

[0084] Place the substrate made of the head of a heavily phosphorus-doped crystal rod in a heating furnace and perform heat treatment on it under normal pressure. The specific steps are as follows:

[0085] S1. Hold at 490 °C for 35 min;

[0086] S2. Heat up to 780 °C at a rate of 4 °C / min;

[0087] S3. Hold at 780 °C for 20 min;

[0088] S4. Cool down to 500 °C at a rate of 3 °C / min;

[0089] S5. Hold at 500 °C for 20 min;

[0090] S6. Place the substrate in a cooling chamber and cool it to room temperature at a cooling rate of 50 °C / s;

[0091] Steps S1 to S6 are carried out under an argon atmosphere with an argon flow rate of 10 L / min.

[0092] Although the preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be construed as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention. Obviously, those skilled in the art can make various changes and variations to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. A method for improving the in-plane resistivity uniformity of an epitaxial wafer, characterized by The substrate to be made into the epitaxial wafer is heat-treated; the substrate is from the head position of a heavily phosphorus-doped crystal bar, that is, the position of 0 - 200 mm of the crystal bar; The heat treatment includes the following five steps: S1. Keep the temperature at 480 - 500 °C for 20 - 40 min; S2. Increase the temperature to 780 - 800 °C at a rate of 4 - 6 °C / min; S3. Keep the temperature at 780 - 800 °C for 10 - 20 min; S4. Decrease the temperature to 480 - 500 °C at a rate of 3 - 4 °C / min; S5. Keep the temperature at 480 - 500 °C for 20 - 40 min; Steps S1 - S5 are carried out in an inert atmosphere; The epitaxial wafer is obtained by using a conventional epitaxial method on the heat-treated substrate.

2. The method for improving the in-plane resistivity uniformity of the epitaxial wafer as described in claim 1, wherein, The substrate is N-type, with a thickness of 755 - 795 um and a resistivity range of 0.001 - 0.0015 Ω·cm.

3. The method for improving the in-plane resistivity uniformity of the epitaxial wafer as described in claim 1, wherein, The epitaxial layer of the epitaxial wafer is N-type, with a thickness of 2 - 8 um and a resistivity SRP range of 0.001 - 1 Ω·cm.

4. The method for improving the in-plane resistivity uniformity of the epitaxial wafer as described in claim 1, wherein, The heat treatment is carried out under normal pressure.

5. The method for improving the in-plane resistivity uniformity of the epitaxial wafer as described in claim 1, wherein, The inert atmosphere used is Ar.

6. The method for improving the in-plane resistivity uniformity of the epitaxial wafer as described in claim 5, wherein, The Ar gas flow rate in steps S1 - S5 is 8 - 12 L / min.

7. The method for improving the in-plane resistivity uniformity of the epitaxial wafer as described in claim 1, wherein, After the insulation in step S5 ends, the substrate is cooled to room temperature in an inert atmosphere at a cooling rate of 50 - 70 °C / s.

8. The method for improving the in-plane resistivity uniformity of the epitaxial wafer as described in claim 7, wherein, The inert atmosphere is Ar.

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