A method and system for investigating the effect of abrasive particle concentration in a polishing liquid on the degree of contact

Abstract

The application discloses a method for researching the influence of abrasive concentration in polishing liquid on contact degree, which comprises the following steps: fixing the position of a light-transmitting substrate, which is made of the same material as a wafer; distributing abrasive particles with a certain set distribution density on a polishing pad, wherein the distribution state comprises the number of abrasive particles per unit area and the uniformity of abrasive particle distribution; connecting the polishing pad to a pressure applying device and controlling the pressure applying device to set the pressure so that the polishing pad is pressed against the light-transmitting substrate; obtaining an image of the contact surface of the light-transmitting substrate and the polishing pad from the side of the light-transmitting substrate opposite to the polishing pad, which is recorded as a contact image; and obtaining the contact area of the light-transmitting substrate and the polishing pad according to the contact image. The method can narrow the gap between the grinding effect control mechanism and the actual situation.

Description

Technical Field

[0001] This application generally relates to the field of wafer polishing technology, and more particularly to a method and system for studying the effect of abrasive concentration in polishing slurry on the degree of contact. Background Technology

[0002] With the rise of cutting-edge technologies such as 5G and artificial intelligence, the performance requirements for semiconductor wafers are gradually increasing. Wafers used in different application scenarios need to achieve corresponding levels of surface smoothness. Therefore, it is necessary to study the factors that affect the surface smoothness of wafers during the polishing process. The polishing process generally involves placing the wafer in a polishing slurry containing abrasive particles (hereinafter referred to as abrasive grains), with the surface to be polished facing upwards, and then polishing it using a polishing pad. The contact area between the polishing pad and the wafer surface has a significant impact on the polishing effect. Besides the externally applied pressure, the most significant factor affecting the contact area is the distribution density of the abrasive grains between the two surfaces, which is directly determined by the concentration of abrasive grains in the polishing slurry. Therefore, studying the effect of abrasive grain concentration on wafer smoothness ultimately translates to studying the effect of abrasive grain distribution density on the contact area. Obtaining the relationship between abrasive grain distribution density and contact area can guide actual wafer polishing work. The existing technology employs the following method: infrared light is incident into the transparent substrate used to replace the wafer at a set angle from one side, and then the emitted infrared light is captured from the other side. The contact area between the polishing pad and the transparent substrate is estimated based on the attenuation of the emitted and emitted infrared light. Specifically, as follows... Figure 3 As shown in the figure. However, this method can only obtain the numerical value of the contact area, but not an image of the contact surface. Therefore, the accuracy of this contact area value cannot be confirmed. When used to guide the actual grinding of wafer surfaces, the smoothness of the wafer surface often fails to meet the required standards. Therefore, how to improve the method of measuring the contact area between the grinding parties to obtain a more accurate relationship between abrasive concentration and the smoothness of the wafer surface after grinding has become an urgent problem to be solved in this field. Summary of the Invention

[0003] In view of the above-mentioned defects or deficiencies in the prior art, it is desirable to provide a method and system for studying the influence of abrasive concentration in polishing fluid on the degree of contact that can narrow the gap between the grinding effect control mechanism and the actual situation.

[0004] The specific technical solution is as follows:

[0005] First aspect

[0006] This application provides a method for studying the effect of abrasive concentration in polishing slurry on the degree of contact, comprising the following steps:

[0007] The position of the light-transmitting substrate is fixed, and the material of the light-transmitting substrate is the same as that of the wafer in terms of the contact surface with the polishing pad;

[0008] Abrasive grains with a certain set distribution density are distributed onto a polishing pad, wherein a certain distribution density value corresponds to the concentration value of abrasive grains in another corresponding polishing fluid;

[0009] The polishing pad is connected to a pressure application device, and the pressure application device is controlled to set a pressure to press the polishing pad against the light-transmitting substrate;

[0010] An image of the contact surface between the polishing pad and the light-transmitting substrate is obtained from the side of the light-transmitting substrate facing away from the polishing pad, and is recorded as the contact image;

[0011] The corresponding contact area value is obtained based on the contact image;

[0012] The distribution density is changed, and the corresponding contact area is obtained respectively, thereby obtaining the correspondence between the distribution density of the abrasive particles and the contact area;

[0013] Based on the relationship between the distribution density of abrasive particles and the contact area, the relationship between abrasive particle concentration and the contact area is obtained.

[0014] As a further limitation of this application, the step of distributing abrasive grains with a certain predetermined density onto the polishing pad specifically includes the following steps:

[0015] Abrasive particles are added to a solvent to obtain a suspension with a set concentration of abrasive particles;

[0016] The polishing pad is placed in the suspension, soaked at a set temperature, and then removed.

[0017] The removed polishing pad is dried to obtain a polishing pad with a set density of abrasive grains on the surface.

[0018] As a further limitation of this application, the step of obtaining the corresponding contact area value based on the contact image specifically includes the following steps:

[0019] Acquire a reference image, which is an image captured when the polishing pad and the light-transmitting substrate are not in contact, and are stacked in the same way as when they are in contact.

[0020] The contact image is compared with the control image, and the contact pixels are obtained. The contact pixels are the pixels in the contact image whose gray level is greater than the corresponding pixel gray level in the control image.

[0021] The contact area value is obtained based on the proportion of the contact pixels in the contact image and the actual area captured when the polishing pad and the light-transmitting substrate are stacked, corresponding to the contact image.

[0022] As a further limitation of this application, the step of placing the polishing pad in the suspension, soaking it at a set temperature and then taking it out further includes the following step: performing magnetic stirring on the suspension for a continuous set time.

[0023] As a further limitation of this application, the solvent is anhydrous ethanol.

[0024] Second aspect

[0025] This application provides a system for measuring the contact area between a polishing pad and a wafer, comprising:

[0026] A light-transmitting substrate holder, which is used to fix the position of the light-transmitting substrate;

[0027] A pressure application device is used to press a polishing pad with abrasive particles distributed in a predetermined pattern on the surface against the light-transmitting substrate at a predetermined pressure.

[0028] An image capturing device is used to acquire a contact image of the contact surfaces of the light-transmitting substrate and the polishing pad from the side of the substrate facing away from the polishing pad.

[0029] An image processing device is used to obtain the contact area between the two objects based on the contact image.

[0030] The beneficial effects of this application are:

[0031] To address the problem of not being able to accurately obtain the contact area between the polishing pad and the transparent substrate in existing technologies, the solution provided in this application involves, on the one hand, using a transparent substrate made of the same material as the wafer in the contact surface with the polishing pad instead of the actual wafer; on the other hand, using a polishing pad with a surface abrasive grains of a predetermined distribution density instead of immersing the polishing pad in a polishing slurry containing abrasive grains. Both methods allow for the acquisition of images of the contact surface between the polishing pad and the substrate from the side of the transparent substrate away from the polishing pad using an image capturing device. The contact area data can then be directly measured based on the acquired images. The contact area data obtained in this way under different conditions is more accurate, and the surface smoothness of the wafer obtained to guide actual polishing work will be closer to the predetermined standard. Attached Figure Description

[0032] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0033] Figure 1 A flowchart illustrating the steps of a method for studying the effect of abrasive concentration in polishing slurry on the degree of contact, provided in an embodiment of this application.

[0034] Figure 2 A schematic diagram of a system for measuring the contact area between a polishing pad and a wafer, provided in an embodiment of this application;

[0035] Figure 3 This is a schematic diagram of a system for measuring the contact area between a polishing pad and a wafer in the prior art;

[0036] The diagram is labeled as follows: 10, light-transmitting substrate holder; 1, light-transmitting substrate; 20, pressure application device; 21, abrasive grain; 2, polishing pad; 3, image capturing device. Detailed Implementation

[0037] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0038] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0039] Please refer to Figure 1 The following is a flowchart illustrating the steps of a method for studying the effect of abrasive concentration in polishing slurry on the degree of contact, as provided in this embodiment:

[0040] S1: Fix the position of the light-transmitting substrate, wherein the material of the light-transmitting substrate is the same as that of the wafer in terms of the contact surface with the polishing pad;

[0041] S2: Abrasive particles with a certain set distribution density are distributed onto a polishing pad, wherein a certain distribution density value corresponds to the concentration value of abrasive particles in another corresponding polishing liquid;

[0042] S3: Connect the polishing pad to the pressure application device, and control the pressure application device to set the pressure to press the polishing pad against the light-transmitting substrate;

[0043] S4: Obtain an image of the contact surface between the polishing pad and the light-transmitting substrate from the side of the light-transmitting substrate facing away from the polishing pad, and record it as a contact image;

[0044] S5: Obtain the corresponding contact area value based on the contact image;

[0045] S6: Change the value of the distribution density and obtain the corresponding contact area value respectively, thereby obtaining the correspondence between the distribution density of the abrasive particles and the contact area;

[0046] S7: Based on the correspondence between the distribution density of abrasive particles and the contact area, obtain the correspondence between the abrasive particle concentration and the contact area.

[0047] Figure 2 This is a schematic diagram of a system for measuring the contact area between a polishing pad and a wafer, provided in an embodiment of this application. Figure 2 At the top is the image capturing device 3 of the measurement system. Since the light-transmitting substrate 1 used to simulate the wafer is made of light-transmitting material, a contact image of the contact surface between the light-transmitting substrate 1 and the polishing pad 2 can be captured through the light-transmitting substrate 1. The contact image needs to be processed to determine the exact contact area within the overlapping region of the two.

[0048] The processing method involves comparing the contact image with an image of the light-transmitting substrate 1 and the polishing pad 2 when they are not in contact. Under the same image acquisition conditions, the pixels whose grayscale values ​​change compared to the grayscale values ​​of the pixels in the contact image are identified as the contact pixels. Once the contact pixels are obtained, the actual contact area between the two within the overlapping area can be calculated based on the proportion of the contact pixels in the contact image and the overlapping area of ​​the light-transmitting substrate 1 and the polishing pad 2 corresponding to the contact image.

[0049] It is conceivable that, in the contact image, since there are abrasive grains distributed in a predetermined pattern between the light-transmitting substrate 1 and the polishing pad 2, the contact area between them will inevitably be affected by the pressure applied to the polishing pad 2 by the pressure application device 20, and will also be affected by the distribution of the abrasive grains. Therefore, by continuously adjusting the pressure and the distribution of the abrasive grains 21, the value of the actual contact area between the light-transmitting substrate 1 and the polishing pad 2 under the corresponding conditions can be obtained.

[0050] Specifically, this scheme simulates placing the wafer and the polishing pad into a polishing slurry containing the abrasive grains 21. Therefore, it is necessary to simulate the final distribution of the abrasive grains between the two before the polishing pad 2 is placed against the light-transmitting substrate 1. The method proposed in this scheme is to first place the abrasive grains 21 in anhydrous ethanol to form a suspension, and then magnetically stir the suspension to ensure that the abrasive grains 21 are evenly distributed. Since temperature affects the distribution of the abrasive grains 21 on the surface of the polishing pad 2, that is, at different temperatures, although the number of abrasive grains 21 distributed per unit area is the same, their uniformity of distribution is different, and the uniformity also affects the value of the contact area. Therefore, temperature needs to be used as another independent variable to study the influencing factors of the contact area.

[0051] Specifically, the following steps are included:

[0052] Clean the surface of the light-transmitting substrate 1 to be contacted;

[0053] Adjust the distance between the objective lens of the pressure application device 20 and the light-transmitting substrate 1 so that the objective lens is focused on the lower surface of the light-transmitting substrate 1 to ensure that the image is clear and confirm that the light-transmitting substrate 1 is clean.

[0054] The surface to be tested of the polishing pad 2 is fixed to the stage of the pressure application device 20 so that it can be uniformly loaded and the contact surface formed after loading can be captured by the image capturing device 3.

[0055] The pressure application device 20 is used to apply a stepped load to the surface of the polishing pad 2 to form a contact surface with the light-transmitting substrate 1, and the pressure and actual contact area image of each loading are recorded.

[0056] Unload the pressure output by the pressure application device 20 and let the surface of the polishing pad 2 be tested stand for more than 5 minutes to ensure that the deformation of the surface is restored.

[0057] Clean the light-transmitting substrate 1.

[0058] Clean the surface to be tested of the polishing pad 2.

[0059] The measurement of the actual contact area of ​​the abrasive-free surface has been completed.

[0060] The main steps involved in creating an abrasive surface containing polishing fluid are as follows:

[0061] Add silica abrasive particles 21 to anhydrous ethanol and stir magnetically for 20 minutes.

[0062] The surface to be tested is completely immersed in anhydrous ethanol containing silica abrasive particles and magnetically stirred for 10 minutes to disperse the abrasive particles in the anhydrous ethanol and make them contact the surface to be tested of the polishing pad 2.

[0063] The surface to be tested of the polishing pad 2 is removed horizontally and dried.

[0064] The surface of the polishing pad 2 containing polishing fluid abrasive particles is now complete.

[0065] Measuring the actual contact area of ​​the surface of the polishing pad 2 with abrasive particles under different pressures mainly includes the following steps:

[0066] Adjust the distance between the objective lens of the image capturing device 3 and the light-transmitting substrate so that the objective lens is focused on the lower surface of the light-transmitting substrate 1 to ensure that the image is clear and confirm that the light-transmitting substrate 1 is clean.

[0067] The dried polishing pad 2 is placed on the stage of the pressure application device 20 so that it can be uniformly loaded and the resulting contact surface can be captured by the image capturing device 3.

[0068] The pressure application device 20 is used to apply a stepped load to the surface of the polishing pad 2 to form a contact surface with the light-transmitting substrate 1, and the pressure and actual contact area image of each loading are recorded.

[0069] Unload the pressure output by the pressure application device 20 and let the surface of the polishing pad 2 be tested stand for 5 minutes to ensure that the deformation of the surface of the polishing pad 2 is restored.

[0070] Clean the light-transmitting substrate 1.

[0071] Clean the surface of the polishing pad 2 to be tested.

[0072] Repeat the above steps until all samples have been measured, and record the concentration of the silica turbidity corresponding to each group of contact images.

[0073] The measurement of the actual contact area of ​​the abrasive surface has been completed.

[0074] The extraction and comparative analysis of the actual contact area mainly includes the following steps:

[0075] The measured contact images are imported into MATLAB software, and the contact images are quantified to obtain the image matrix (each pixel).

[0076] Subtract the unloaded control image matrix from the loaded contact image matrix.

[0077] The resulting image after subtraction is binarized.

[0078] Let the processed contact image matrix be a×b matrix, and c be the number of matrix points with data of 1 (increased gray level), the proportion of which is c / (a×b).

[0079] The pressure-actual contact area curves of the tested surface of the polishing pad 2 with different concentrations of abrasive particles were plotted using the obtained data.

[0080] By comparing the pressure-actual contact area curves of different abrasive concentrations, the difference between the actual contact area of ​​the surface with different concentrations of abrasive particles and the surface without abrasive particles under each pressure was calculated. Experimental data showed that as the concentration of silica abrasive particles in the turbid liquid increases, the actual contact area between the tested surface of the polishing pad 2 and the light-transmitting substrate 1 under the same pressure will gradually decrease.

[0081] The extraction and comparative analysis of the actual contact area have been completed.

[0082] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for studying the effect of abrasive concentration in polishing slurry on the degree of contact, characterized in that, Includes the following steps: The position of the light-transmitting substrate is fixed. The material of the light-transmitting substrate is the same as that of the wafer in the aspect where it forms a contact surface with the polishing pad. The light-transmitting substrate is a light-transmitting material. An image of the contact surface between the light-transmitting substrate and the polishing pad can be captured from the side of the light-transmitting substrate that is away from the polishing pad. Abrasive grains with a certain set distribution density are distributed onto a polishing pad, wherein a certain distribution density value corresponds to the concentration value of abrasive grains in another corresponding polishing fluid; The method of distributing abrasive particles with a certain set distribution density onto a polishing pad includes: adding abrasive particles to a solvent to obtain a suspension with a set concentration of abrasive particles; placing the polishing pad in the suspension; soaking it at a set temperature and then removing it; and drying the removed polishing pad to obtain a polishing pad with a set density of abrasive particles on the surface. The polishing pad is connected to a pressure application device, and the pressure application device is controlled to set a pressure to press the polishing pad against the light-transmitting substrate; An image of the contact surface between the polishing pad and the light-transmitting substrate is obtained from the side of the light-transmitting substrate facing away from the polishing pad, and is recorded as the contact image; The corresponding contact area value is obtained based on the contact image; The step of obtaining the corresponding contact area value based on the contact image includes: obtaining a reference image, which is an image collected when the polishing pad and the light-transmitting substrate are not in contact, and are stacked in the same way as after they are in contact; comparing the contact image with the reference image; and obtaining contact pixels, which are pixels in the contact image with a gray level greater than the corresponding pixel gray level in the reference image; and obtaining the contact area value based on the proportion of the contact pixels in the contact image and the actual area collected when the polishing pad and the light-transmitting substrate are stacked corresponding to the contact image. The distribution density is changed, and the corresponding contact area is obtained respectively, thereby obtaining the correspondence between the distribution density of the abrasive particles and the contact area; Based on the relationship between the distribution density of abrasive particles and the contact area, the relationship between abrasive particle concentration and the contact area is obtained.

2. The method for studying the effect of abrasive concentration in polishing slurry on the degree of contact according to claim 1, characterized in that, The step of placing the polishing pad in the suspension, soaking it at a set temperature, and then removing it further includes the following step: continuously stirring the suspension with magnetic force for a set time.

3. The method for studying the effect of abrasive concentration in polishing slurry on the degree of contact according to claim 1 or 2, characterized in that, The solvent is anhydrous ethanol.

4. A system for measuring the contact area between a polishing pad and a wafer, characterized in that, The measurement system, applicable to the method of any one of claims 1-3, comprises: A light-transmitting substrate holder (10) is used to fix the position of the light-transmitting substrate (1); A pressure application device (20) is used to press the polishing pad (2) with abrasive grains (21) on the surface in a set distribution against the light-transmitting substrate (1) at a set pressure. Image capturing device (3), the image capturing device (3) is used to acquire a contact image of the contact surface of the light-transmitting substrate (1) from the side opposite to the polishing pad (2); An image processing device is used to obtain a contact area value between the polishing pad and the light-transmitting substrate based on the contact image. Specifically, it is used to obtain a reference image, which is an image captured when the polishing pad and the light-transmitting substrate are not in contact, and are stacked in the same way as after they are in contact. The contact image is compared with the reference image, and contact pixels are obtained. The contact pixels are pixels in the contact image with a gray level greater than the corresponding pixel gray level in the reference image. The contact area value is obtained based on the proportion of the contact pixels in the contact image and the actual area captured when the polishing pad and the light-transmitting substrate are stacked, corresponding to the contact image.

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