Silicon wafer BMD auxiliary positioning device and silicon wafer BMD measurement method

Abstract

A silicon wafer BMD auxiliary positioning device and a silicon wafer BMD measurement method, comprising a fixing fixture and a positioning plate, wherein the fixing fixture comprises a clamping assembly and a frame, wherein one end of the clamping assembly is slidably connected to one side of the frame, and the other end of the clamping assembly contacts the other side of the frame, and the frame can slide along the positioning plate. The present invention uses a silicon wafer BMD auxiliary positioning device to align the cleavage surface of the silicon wafer with the positioning plate, then clamps the silicon wafer with the clamping assembly, flips the frame 180 degrees, and then removes the positioning plate to align the cleavage surface of the silicon wafer with a microscope, so that when the microscope is counting, because the silicon wafer always remains horizontal, when the microscope observes the BMD number, the microscope only needs to be adjusted once to make the area observed by the microscope clear, and then at the same depth, the BMD counting is more accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of a device and method for detecting BMD in a single-crystal silicon body, and in particular to a silicon wafer BMD auxiliary positioning device and a silicon wafer BMD measurement method. Background Art

[0002] One of the main uses of monocrystalline silicon materials is in the semiconductor field. For some application fields, semiconductor monocrystalline silicon has strict purity requirements. Impurity elements, especially metal impurity elements, have a negative impact on semiconductor monocrystalline silicon wafers that cannot be ignored. Therefore, in addition to strict control of impurity elements during production and processing, the inner getter (IG) principle is also used to further remove the influence of impurity elements. Bulk micro defects (BMDs) are the main body of the inner getter, and their density has a slight correlation with the ability of silicon wafer IG. For some applications with corresponding needs, the number of BMDs needs to be controlled to achieve the desired effect.

[0003] For the evaluation of BMD of semiconductor silicon wafers, the silicon wafers must first be subjected to multiple heat treatments so that the intrinsic vacancy defects inside the wafer can combine with interstitial oxygen to form oxygen precipitation and diffuse and grow at high temperature; BMD is a body defect and needs to be observed away from the surface because the surface is in contact with the outside world and its situation is significantly different from that in the body. Therefore, the complete silicon wafer after heat treatment needs to be split along the center line so that the cross section can be observed through a microscope and the BMD can be counted. In the prior art, since the silicon wafer needs to be placed upright on the stage for observation, the silicon wafer is usually fixed on the stage for observation by a clip. However, when observing the BMD number of the silicon wafer at a depth of 0μm-100μm under a microscope, if the cleavage surface of the silicon wafer is not placed horizontally, some areas are clear and some areas are blurred when the microscope observes the BMD number. The lens needs to be re-adjusted to make the blurred area gradually clear, but when the camera is adjusted, it is easy to cause the depth of the silicon wafer to change, resulting in inaccurate number when counting BMD. Summary of the invention

[0004] In view of this, in order to address the above-mentioned deficiencies, it is necessary to propose a silicon wafer BMD auxiliary positioning device that can accurately count BMD when observing a silicon wafer at a depth of 0 μm-100 μm.

[0005] It is also necessary to propose a method for measuring BMD of silicon wafers.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A silicon wafer BMD auxiliary positioning device includes a fixing fixture and a positioning plate. The fixing fixture includes a clamping assembly and a frame. One end of the clamping assembly is slidably connected to one side of the frame, and the other end of the clamping assembly contacts the other side of the frame. The frame can slide along the positioning plate.

[0008] Preferably, the clamping assembly includes a top block, a connecting rod, a moving block, and a spring. A long hole is opened on one side of the frame along the length direction. The top block is connected to one end of the connecting rod. The connecting rod passes through the long hole and is connected to the moving block. The spring is wrapped around the connecting rod. One end of the spring is connected to the top block, and the other end of the spring is slidably connected to one side of the frame.

[0009] Preferably, there are at least two clamping assemblies.

[0010] Preferably, the positioning plate is provided with a slide rail along the length direction, one end of the frame is open, and the frame slides along the slide rail.

[0011] Preferably, a support block is provided along the length direction of the side of the frame body opposite to the long hole, one side of the support block is connected to one side of the frame body, the other side of the support block contacts the top block, and the bottom of the support block contacts the slide rail on the same side.

[0012] A method for measuring silicon wafer BMD, comprising the silicon wafer BMD auxiliary positioning device as described above, and the specific steps are as follows:

[0013] Step 1: Cleaning the heat-treated silicon wafer with a chemical agent to obtain a cleaned silicon wafer;

[0014] Step 2: Cleavage the cleaned silicon wafer to obtain a sample;

[0015] Step 3: Perform horizontal preferential etching on the sample to obtain the sample to be tested;

[0016] Step 4: inserting the sample to be tested into the fixing fixture, the cleavage surface of the sample to be tested contacts the positioning plate, the clamping assembly fixes the silicon wafer in the frame, and then the positioning plate is removed to expose the cleavage surface of the sample to be tested;

[0017] Step 5: Turn the fixing fixture over and place it on the stage to expose the cleavage surface of the sample to be tested, and observe the number of BMDs of the sample to be tested through a microscope.

[0018] Preferably, in step 1, the chemical agent is HF or HNO3.

[0019] Preferably, in step 2, when the cleaned silicon wafer is cleaved, a soft pad needs to be placed under the cleaned silicon wafer.

[0020] Preferably, in step three, the horizontal selective etching is specifically as follows: placing the sample horizontally in a corrosion tray for etching, pouring in a selective etching liquid for etching, then cleaning the cleaned silicon wafer after etching with the selective etching liquid with deionized water, and then soaking it with alkaline solution to obtain a sample to be tested.

[0021] Preferably, the preferential etching solution is HF or HNO3 or Cu(NO3)2 or AgNO3.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention uses a silicon wafer BMD auxiliary positioning device to align the cleavage surface of the silicon wafer with a positioning plate, then clamps the silicon wafer through a clamping assembly, flips the fixing fixture 180 degrees, and then removes the positioning plate to align the cleavage surface of the silicon wafer with the microscope, so that when the microscope is counting, because the silicon wafer always remains horizontal, when the microscope observes the BMD number, the microscope only needs to be adjusted once to make the area observed by the microscope clear, and then at the same depth, the BMD counting is more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic diagram of the structure of the silicon wafer BMD auxiliary positioning device.

[0025] Figure 2 A schematic diagram of the structure of the fixing fixture.

[0026] Figure 3 It is a structural schematic diagram of the positioning plate.

[0027] Figure 4 This is an electron microscope image of the BMD density at a depth of 400 μm-500 μm in the center of the silicon wafer in Example 1.

[0028] Figure 5 This is an electron microscope image of the BMD density at a depth of 300 μm-200 μm in the center of the silicon wafer in Example 1.

[0029] Figure 6 This is an electron microscope image of the BMD density distribution of the silicon wafer 0μm-200μm in the comparative example.

[0030] In the figure: a silicon wafer BMD auxiliary positioning device 10, a fixing fixture 100, a clamping assembly 110, a top block 111, a connecting rod 112, a moving block 113, a spring 114, a frame 120, a long hole 121, a support block 122, a positioning plate 200, and a slide rail 210. DETAILED DESCRIPTION

[0031] 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.

[0032] Please see Figures 1 to 3 A silicon wafer BMD auxiliary positioning device 10 includes a fixing fixture 100 and a positioning plate 200. The fixing fixture 100 includes a clamping assembly 110 and a frame 120. The frame 120 is U-shaped. One end of the clamping assembly 110 is slidably connected to one side of the frame 120, and the other end of the clamping assembly 110 contacts the other side of the frame 120. The frame 120 can slide along the positioning plate 200.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention uses a silicon wafer BMD auxiliary positioning device to align the cleavage surface of the silicon wafer with the positioning plate 200, then clamps the silicon wafer through the clamping assembly 110 to prevent the sample from moving, flips the frame 120 180 degrees, and then removes the positioning plate 200 to align the cleavage surface of the silicon wafer with the microscope. When the microscope is counting, because the silicon wafer always remains horizontal, when the microscope observes the BMD number, the microscope only needs to be adjusted once to make the area observed by the microscope clear, and then at the same depth, the BMD counting is more accurate.

[0035] Furthermore, the clamping assembly 110 includes a top block 111, a connecting rod 112, a moving block 113, and a spring 114. A long hole 121 is opened on one side of the frame 120 along the length direction. The top block 111 is connected to one end of the connecting rod 112. The connecting rod 112 passes through the long hole 121 and is connected to the moving block 113. The spring 114 is wrapped around the connecting rod 112. One end of the spring 114 is connected to the top block 111, and the other end of the spring 114 is slidably connected to one side of the frame 120. The diameter of the spring is larger than the diameter of the long hole.

[0036] Furthermore, there are at least two clamping assemblies 110 .

[0037] Furthermore, the positioning plate 200 is provided with a slide rail 210 along the length direction, one end of the frame 120 is open, and the frame 120 slides along the slide rail 210 .

[0038] Furthermore, a support block 122 is provided along the length direction of the side of the frame 120 opposite to the long hole 121, one side of the support block 122 is connected to one side of the frame 120, the other side of the support block 122 is in contact with the top block 111, the bottom of the support block 122 is in contact with the slide rail 210 on the same side, and the lower edge of the support block 122 is lower than the lower edge of the side wall of the frame 120, so that it is convenient to clean the cleavage surface of the silicon wafer during observation and to remove the silicon wafer from the silicon wafer BMD auxiliary positioning device.

[0039] A method for measuring silicon wafer BMD, comprising the silicon wafer BMD auxiliary positioning device as described above, and the specific steps are as follows:

[0040] Step 1: Cleaning the heat-treated silicon wafer with a chemical agent to obtain a cleaned silicon wafer;

[0041] Step 2: Cleavage the cleaned silicon wafer to obtain a sample;

[0042] Step 3: Perform horizontal preferential etching on the sample to obtain the sample to be tested;

[0043] Step 4: insert the sample to be tested into the fixing fixture 100, the cleavage surface of the sample to be tested contacts the positioning plate 200, the clamping assembly 110 fixes the silicon wafer in the frame 120, and then the positioning plate 200 is removed to expose the cleavage surface of the sample to be tested;

[0044] Step 5: Place the fixing fixture 100 on the stage to expose the cleavage surface of the sample to be tested, and observe the number of BMDs of the sample to be tested through a microscope.

[0045] Furthermore, in step one, the chemical agent is HF or HNO3, and in step one, either chemical cleaning or mechanical polishing can be used to remove the oxide film.

[0046] Specifically, in step 1, after the silicon wafer is heat treated, a dense oxide film is formed on the surface of the silicon wafer, which is removed by chemical agents to avoid the influence of the oxide film when observing through a microscope.

[0047] Furthermore, in step 2, when the cleaned silicon wafer is cleaved, a soft pad is placed under the cleaned silicon wafer.

[0048] Specifically, during cleavage, a small cut is first made on the edge of the cleaned silicon wafer with a diamond pen; the cleaned silicon wafer is placed on a soft pad, and the diamond pen is used to press the edge of the small cut to extend the area near the cut. <110> direction, self-cleavage cracks appear, set a soft pad under the cleaned silicon wafer, so that the silicon wafer is slightly stressed near the damaged mouth, and then regular cracks are made along the cleavage surface, so that the cleavage sample has high integrity, and the cleavage surface of the silicon wafer will not have a lightning-shaped cleavage surface; then use a diamond pen to extend the self-dissociation crack and press gently to continuously extend the self-cleavage crack; when the length of the self-cleavage crack is close to the radius, use the diamond pen to gently tap near the notch, and the silicon wafer will be thrown away along the self-cleavage crack; use the same steps to remove the long strip sample from the silicon wafer, the width of the sample is controlled at 10mm-15mm, and the length is as close to the diameter of the silicon wafer as possible; the sample removed by this method ensures to the greatest extent that the two cross-sections are parallel to each other, the surface integrity is high, and there is no damage to cause detection interference.

[0049] Furthermore, in step three, the horizontal selective etching is specifically as follows: placing the sample horizontally in a corrosion tray for etching, pouring in a selective etching solution for etching, and then cleaning the cleaned silicon wafer after etching with the selective etching solution with deionized water, and then soaking it with an alkaline solution to obtain a sample to be tested; compared with the vertical selective method, the horizontal selective method etches the sample, so that the entire sample is corroded more evenly, and when using the same solution, the horizontal selective method uses a new etching solution each time, so that the etching effects of samples from different batches are the same. If the etching effects of samples from different batches are different, sometimes the BMD in the silicon wafer is not corroded and exposed, resulting in a deviation in the BMD count.

[0050] Specifically, a long strip of sample is placed in a corrosion tray, a sufficient amount of selective corrosion liquid is poured into it, and the corrosion tray is gently shaken at an appropriate time to allow the liquid to fully contact and react with the sample for 2 minutes to 10 minutes to reveal the BMD. The sample after selective corrosion is washed with deionized water overflow for 30 minutes to 60 minutes to remove the residual selective corrosion liquid in the sample, and then immersed in an alkaline solution below 80°C for 2 minutes to 30 minutes to remove the residual acid or weak acid salt on the surface of the sample. After soaking, the surface of the sample is washed again with hot water and deionized overflow water to remove the alkaline solution and avoid interference during observation.

[0051] Furthermore, the preferred etching solution is HF or HNO3 or Cu(NO3)2 or AgNO3.

[0052] Specifically, in step four, the sample to be tested is inserted into the fixing fixture 100, the cleavage surface of the sample to be tested is in contact with the positioning plate 200, and is fixed using the clamping assembly 110. The two clamping assemblies 110 are respectively clamped at 10 mm from the edge of the sample to be tested and at the center of the sample to be tested to mark the counting positions of the edge and the center.

[0053] Specifically, in step 5, the fixed sample to be tested is placed under a microscope together with the fixing fixture 100, and a magnification of 500 is used. The position of the fixing fixture is adjusted to ensure that the cleavage surface of the sample to be tested is parallel to the edge of the field of view and the distance is less than 30 μm. From the edge of the cleavage surface to 100 μm, a region with >40 BMDs is selected (the region is ≤100*200 μm), and the BMD count is performed in the selected region, and the area of ​​the region is calculated, and the result is converted into a universal density, i.e., ea / cm 2 .

[0054] Specifically, if it is necessary to observe that the number of BMDs of the entire silicon wafer is uniform, a pretreatment step is performed before the heat treatment of the original silicon wafer, and the pretreatment step is specifically: heating the original silicon wafer to a first predetermined temperature at a first predetermined heating rate, introducing a first predetermined gas, reacting for a first predetermined time, and performing pretreatment to obtain an original silicon wafer with a dense film to isolate the path for oxygen elements, vacancies and interstitial silicon inside the original silicon wafer to diffuse outward;

[0055] Then, the second predetermined gas is introduced into the original silicon wafer with a dense film and maintained for a second predetermined time to allow the vacancies, interstitial silicon and interstitial oxygen inside the original silicon wafer to diffuse evenly to obtain an intermediate silicon wafer. The intermediate silicon wafer is then heat-treated and the heat-treated intermediate silicon wafer is inspected under a microscope to obtain the number of BMDs in the silicon wafer.

[0056] Before the heat treatment procedure, the original silicon wafer is heated to a first predetermined temperature at a first predetermined heating rate, a first predetermined gas is introduced, the reaction is carried out for a first predetermined time, and pretreatment is performed to obtain an original silicon wafer with a dense film. Then, a second predetermined gas is introduced into the original silicon wafer with a dense film and maintained for a second predetermined time to make the vacancies and interstitial oxygen inside the original silicon wafer diffuse evenly to obtain an intermediate silicon wafer; by pretreating the silicon wafer, the interstitial oxygen elements and vacancies inside the silicon wafer are prevented from diffusing outward, and the vacancies and interstitial oxygen inside the silicon wafer diffuse evenly, and then uniform BMD is generated inside the silicon wafer during heat treatment. Because the BMD inside the silicon wafer is evenly distributed, there will be no error in the BMD counting of the silicon wafer under a microscope due to the selection of the density area, so that the detection quantity of BMD is more accurate.

[0057] Furthermore, the method for detecting BMD in the single crystal silicon body also includes a heat treatment step, and the heat treatment step is specifically: cooling the intermediate silicon wafer to a third predetermined temperature at a predetermined cooling rate, reacting for a third predetermined time, so that the vacancies and interstitial oxygen form BMD, and after the intermediate silicon wafer reacts for the third predetermined time, heating it to a fourth predetermined temperature at a second predetermined heating rate, maintaining it for a fourth predetermined time, to obtain a processed silicon wafer.

[0058] Furthermore, in the pretreatment step, the first predetermined heating rate is 50°C / s-100°C / s, the first predetermined temperature is 1000°C-1200°C, the first predetermined gas is nitrogen or oxygen, the pressure of the nitrogen or oxygen is 10bar-100bar, the first predetermined time is 1min-30min, the second predetermined gas is argon, the pressure of the argon is 10bar-100bar, and the second predetermined time is 5min-30min; in the pretreatment step, the heating rate needs to be strictly controlled. If the heating rate is too slow or the temperature stays in the low temperature area for too long, it is easy to generate BMD nuclei inside the silicon wafer, thereby affecting the generation of BMD during subsequent heat treatment. After oxygen or nitrogen reacts on the surface of the silicon wafer for 1min-30min, the introduction of oxygen or nitrogen is immediately stopped and switched to argon to avoid excessive thickness of the oxide film or nitride film formed on the surface of the original silicon wafer, and the introduction of argon is maintained for a certain time so that the vacancies, interstitial silicon, and interstitial oxygen inside the original silicon wafer are evenly diffused inside the silicon wafer.

[0059] Specifically, both nitrogen and oxygen can generate dense nitride films. However, in the process of generating oxide films, oxygen will still diffuse outward to a certain extent, which can reduce the defect density near the film to a certain extent. The formed nitride film can maintain the defect density near the film and even increase the number of defects, making the defect distribution in the silicon body more uniform.

[0060] Furthermore, in the heat treatment step, the predetermined cooling rate is 10°C / min-40°C / min, the third predetermined temperature is 700°C-900°C, the third predetermined time is 2h-10h, the second predetermined heating rate is 5°C / min-10°C / min, the fourth predetermined temperature is 1000°C-1100°C, and the fourth predetermined time is 10h-35h; in the heat treatment step, the predetermined cooling rate needs to be strictly controlled to avoid silicon wafer breakage caused by too fast cooling.

[0061] Then carry out the above step 1 and the subsequent specific steps for detection.

[0062] The invention is specifically described by the following examples and comparative examples.

[0063] Example: Cut a single crystal silicon into a silicon wafer with a thickness of 1 mm, quickly heat the silicon wafer to 1100° C. at 80° C. / s, introduce 50 bar nitrogen, and react for 20 min. After reacting for 20 min, introduce 60 bar argon and keep for 10 min, then cool to 800° C. at a rate of 20° C. / min, react for 4 h, and then heat to 1000° C. at a rate of 7° C. / min after reacting for 4 h to obtain a processed silicon wafer, and then mechanically polish the processed silicon wafer to remove 30 μm of thickness on the front and back sides of the silicon wafer to be processed, and then split the silicon wafer in half and inspect under a microscope. The distribution of BMD at different depths inside the silicon wafer is shown in the specific example. Figure 4 , 5 shown.

[0064] Comparative Example: Single crystal silicon was cut into silicon wafers with a thickness of 1 mm, and the silicon wafers were heated to 800°C and reacted for 4 hours. After reacting for 4 hours, the temperature was then raised to 1000°C at a rate of 7°C / min to obtain a silicon wafer to be processed. The silicon wafer was then mechanically polished to remove 30 μm of thickness on the front and back sides of the silicon wafer to be processed, and then the silicon wafer was split in half and examined under a microscope. The distribution of BMD inside the silicon wafer of the specific comparative example is shown in FIG. Figure 6 shown.

[0065] In summary, by performing pretreatment before heat treatment, a nitride film is first formed on the surface of the silicon wafer under high temperature conditions to isolate the oxygen elements, vacancies and interstitial silicon inside the silicon wafer from diffusing outward, and then argon gas is introduced into the silicon wafer with a dense film and maintained for a certain period of time to allow the vacancies, interstitial silicon and interstitial oxygen inside the silicon wafer to diffuse evenly. Then, in the subsequent heat treatment process, a uniform BMD is generated in the body of the silicon wafer, so that the detection result is more accurate during detection.

[0066] 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 measuring BMD of a silicon wafer, characterized in that: Including silicon wafer BMD auxiliary positioning device, The silicon wafer BMD auxiliary positioning device comprises a fixing fixture and a positioning plate, wherein the fixing fixture comprises a clamping assembly and a frame, wherein one end of the clamping assembly is slidably connected to one side of the frame, and the other end of the clamping assembly contacts the other side of the frame, and the frame can slide along the positioning plate; the specific steps are as follows: Step 1: Cleaning the heat-treated silicon wafer with a chemical agent to obtain a cleaned silicon wafer to remove the oxide film; Step 2: Cleavage the cleaned silicon wafer to obtain a sample; Step 3: Perform horizontal preferential etching on the sample to obtain the sample to be tested; Step 4: inserting the sample to be tested into the fixing fixture, the cleavage surface of the sample to be tested contacts the positioning plate, the clamping assembly fixes the silicon wafer in the frame, and then the positioning plate is removed to expose the cleavage surface of the sample to be tested, so that the cleavage surface of the sample to be tested always remains horizontal; Step 5: Turn the fixing fixture over and place it on the stage to expose the cleavage surface of the sample to be tested, and observe the number of BMDs of the sample to be tested through a microscope.

2. The method for measuring silicon wafer BMD according to claim 1, characterized in that: The clamping assembly includes a top block, a connecting rod, a moving block, and a spring. A long hole is opened on one side of the frame along the length direction. The diameter of the spring is larger than the diameter of the long hole. The top block is connected to one end of the connecting rod, and the connecting rod passes through the long hole and is connected to the moving block. The spring is wrapped around the connecting rod, one end of the spring is connected to the top block, and the other end of the spring is slidably connected to one side of the frame.

3. The method for measuring silicon wafer BMD according to claim 1, characterized in that: There are at least two clamping assemblies.

4. The method for measuring silicon wafer BMD according to claim 2, characterized in that: The positioning plate is provided with a slide rail along the length direction, one end of the frame is open, and the frame slides along the slide rail.

5. The method for measuring silicon wafer BMD according to claim 4, characterized in that: A support block is arranged along the length direction on the side of the frame body opposite to the long hole, one side of the support block is connected to one side of the frame body, the other side of the support block contacts the top block, and the bottom of the support block contacts the slide rail on the same side.

6. The method for measuring silicon wafer BMD according to claim 1, characterized in that: In step 1, the chemical agent is HF or HNO3.

7. The method for measuring silicon wafer BMD according to claim 1, characterized in that: In step 2, when the cleaned silicon wafer is cleaved, a soft pad is placed under the cleaned silicon wafer.

8. The method for measuring silicon wafer BMD according to claim 1, characterized in that: In step three, the horizontal selective etching is specifically as follows: placing the sample horizontally in a corrosion tray for etching, pouring in the selective etching liquid for etching, then cleaning the cleaned silicon wafer after etching with the selective etching liquid with deionized water, and then soaking it with alkaline solution to obtain a sample to be tested.

9. The method for measuring silicon wafer BMD according to claim 8, characterized in that: The preferred etching solution is HF or HNO3 or Cu(NO3)2 or AgNO3.

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