Device and method for accelerating SiC electrochemical mechanical polishing rate by water bath heating

Abstract

The present invention discloses a device for accelerating the SiC electrochemical mechanical polishing rate by water bath heating, belonging to the technical field of ultra-precision processing equipment for semiconductor hard and brittle materials, including: an electrolyte tank filled with electrolyte, and an electrochemical workstation. Two first copper polishing heads are rotatably installed on the bottom wall of the electrolyte tank. A heating mechanism is arranged in the electrolyte tank. The top wall of the first copper polishing head is bonded with a SiC wafer through conductive glue. The first copper polishing head is connected to the anode of the electrochemical workstation through a first conductive slip ring and a wire. The cathode of the electrochemical workstation is connected to a second copper polishing head through a wire and a second conductive slip ring. A polishing pad is installed on the side of the second copper polishing head close to the SiC wafer. A plurality of through holes are circumferentially arranged on the second copper polishing head with the axis direction of the second copper polishing head as the center. By arranging a heating mechanism to heat the electrolyte, the present invention can improve the charge utilization efficiency, anodic oxidation rate and polishing rate of the SiC wafer electrochemical mechanical polishing.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultra-precision processing equipment for semiconductor hard and brittle materials, and particularly relates to a device and method for accelerating the electrochemical mechanical polishing rate of SiC by water bath heating. Background Art

[0002] As a typical hard and brittle material difficult to process, the existing mature technology for SiC is to use chemical mechanical polishing method for ultra-precision processing of wafers. Through the reaction of the oxidant in the polishing liquid with the wafer surface to generate a soft oxide layer, and then the soft oxide layer is removed through mechanical removal to achieve the purpose of polishing. However, the polishing removal rate of this method is very low, the time consumption is long, the resource consumption is large, and the processing cost is very high. Chinese Patent CN104742009A discloses a chemical mechanical polishing method for SiC materials, which promotes the oxidation of the SiC layer surface by the oxidant by adding a high-temperature and high-pressure environment in the chemical mechanical polishing, and at the same time realizes the control of the oxidation process. However, the method used in this scheme is the chemical mechanical polishing method, which does not involve the field of electrochemical mechanical polishing. The electrochemical oxidation of SiC is not carried out by applying an external electric field, but the oxidation of SiC is carried out by using chemical reagents. High temperature promotes the oxidation efficiency of chemical reagents for SiC, but does not involve the research direction of increasing the charge utilization efficiency and anodic oxidation rate of electrochemistry by increasing the temperature.

[0003] The recently proposed electrochemical mechanical polishing method makes the SiC wafer surface undergo an oxidation reaction by applying an external electric field. Some existing technologies are used to enhance the anodic oxidation rate in the electrochemical mechanical polishing process of SiC. For example, Patent CN 109465739 A uses ultraviolet light to directly irradiate the SiC wafer surface to modify the SiC surface, generate electron-hole pairs, and then oxidize the SiC surface by holes through the application of an external electric field to achieve the purpose of oxidizing SiC to produce a softened layer; there is also Patent CN 110587387 A, which uses ultrasonic vibration assistance to generate instant high temperature, high stress and enhance friction on the SiC surface, enhancing the anodic oxidation rate and oxide layer removal rate of SiC. However, the current anodic oxidation rate and polishing rate are still relatively low, and the charge utilization efficiency also needs to be improved.

[0004] Therefore, it is necessary to propose a device and method for accelerating the electrochemical mechanical polishing rate of SiC by water bath heating to solve the above problems. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a device and method for accelerating the electrochemical mechanical polishing rate of SiC by water bath heating, which are used to solve the problems of relatively low anodic oxidation rate and polishing rate and low charge utilization efficiency in the prior art.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a device for accelerating the SiC electrochemical mechanical polishing rate by water bath heating, comprising: an electrolyte tank filled with electrolyte, and an electrochemical workstation. Two first copper polishing heads are rotatably installed on the bottom wall of the electrolyte tank. A heating mechanism is arranged in the electrolyte tank. A SiC wafer is adhesively bonded to the top wall of the first copper polishing head through an electrically conductive adhesive. A first electrically conductive slip ring is installed on the first copper polishing head. The first electrically conductive slip ring is connected to the anode of the electrochemical workstation through a wire. The first electrically conductive slip ring is hermetically connected to the electrolyte tank. The cathode of the electrochemical workstation is connected to a second electrically conductive slip ring through a wire. A second copper polishing head is installed on the second electrically conductive slip ring. A polishing pad is installed on the side of the second copper polishing head close to the SiC wafer. A plurality of through holes are circumferentially arranged on the second copper polishing head with the axis direction of the second copper polishing head as the center.

[0008] Further, the through holes include a first through hole group and a second through hole group circumferentially arranged with the axis direction of the second copper polishing head as the center. The first through hole group includes four first through holes arranged side by side in the radial direction of the second copper polishing head. The second through hole group includes five second through holes arranged side by side in the radial direction of the second copper polishing head. The first through holes and the second through holes are arranged in a staggered manner.

[0009] Further, a support plate is installed in the electrolyte tank. An inner hole through which the second copper polishing head can pass and an annular groove communicated with the inner hole are provided on the support plate. An annular pressing plate capable of sliding along the axis direction of the annular groove is installed in the annular groove. An elastic member is connected between the annular pressing plate and the inner wall of the annular groove. The cross section of the annular pressing plate is L-shaped. The first inner wall of the annular pressing plate abuts against the top wall of the second copper polishing head. The second inner wall of the annular pressing plate abuts against the side wall of the second copper polishing head.

[0010] Further, a threaded groove is provided on the support plate. An annular threaded plate is threadedly connected in the threaded groove. The annular threaded plate and the support plate form the annular groove after being connected. The elastic member is connected between the annular threaded plate and the annular pressing plate. A limiting hole is provided on one of the annular threaded plate and the annular pressing plate. A sliding rod matched with the limiting hole is installed on the other of the annular threaded plate and the annular pressing plate. The sliding rod is limited and slidably connected in the limiting hole.

[0011] Further, balls are installed on both the first inner wall and the second inner wall of the annular pressing plate.

[0012] Further, a thrust bearing is connected between the first copper polishing head and the bottom wall of the electrolyte tank.

[0013] An implementation method of a device for accelerating the SiC electrochemical mechanical polishing rate by water bath heating comprises the following steps:

[0014] S1: Preparation of SiC wafer: Before polishing, the SiC wafer is successively cleaned with acetone and deionized water. After cleaning, the SiC wafer is placed in an oven and dried at a temperature of 100°C for 1 h, and the mass M1 is measured.

[0015] S2: Preparation for polishing: The SiC wafer is mounted on the first copper polishing head, and 5% NaNO3 electrolyte is poured into the electrolyte tank until the electrolyte submerges the SiC wafer and exceeds it by 1 cm.

[0016] S3: Polishing process: Adjust the polishing pressure to 100 KPa, raise the temperature of the electrolyte to a constant temperature T through the temperature-raising mechanism, start the driving mechanism to make the first copper polishing head and the second copper polishing head rotate in opposite directions, and polish the SiC wafer with the polishing pad. Among them, the rotation speed of the first copper polishing head is 30 r / min, the rotation speed of the second copper polishing head is 150 r / min, and the polishing pad uses a cerium oxide polishing pad.

[0017] S4: After polishing for 30 min, the SiC wafer is successively cleaned with acetone and deionized water, then placed in an oven and dried at a temperature of 100°C for 1 h, and the mass M2 is measured, and the removal rate is calculated. The formula for calculating the removal rate is: where P is the density of the SiC wafer, S is the polishing area of the SiC wafer, and t is the polishing time of the SiC wafer.

[0018] The beneficial effects of the present invention are as follows:

[0019] In the present invention, by immersing a part of the second copper polishing head with multiple through holes in the electrolyte, the contact between the surface of the SiC wafer and the electrolyte is maintained during the polishing process, avoiding dry friction on the surface of the SiC wafer and ensuring the oxidation rate of the surface of the SiC wafer; by setting a temperature-raising mechanism to heat the electrolyte, the charge utilization efficiency, anodic oxidation rate and polishing rate of the electrochemical mechanical polishing of the SiC wafer can be improved. By symmetrically designing the number of polishing stations, the resource loss during the electrochemical mechanical polishing of the SiC wafer is reduced, the polishing cost is saved, the polishing difficulty is reduced, and the polishing efficiency is improved.

[0020] Other advantages, objectives and features of the present invention will be described in the subsequent specification, and to some extent, they are obvious to those skilled in the art, or those skilled in the art can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to make the objectives, technical solutions and beneficial effects of the present invention clearer, the present invention provides the following drawings for illustration:

[0022] Figure 1Schematic diagram of the working process of the embodiment of the present invention;

[0023] Figure 2 Cross-sectional view of the overall structure of the embodiment of the present invention;

[0024] Figure 3 For the embodiment of the present invention Figure 2 Enlarged view of local area A;

[0025] Figure 4 Top view of the second copper polishing head of the embodiment of the present invention.

[0026] The reference signs in the drawings are as follows: 1, electrolyte tank; 2, first copper polishing head; 201, first conductive slip ring; 202, thrust bearing; 3, heating mechanism; 4, SiC wafer; 5, electrochemical workstation; 6, second copper polishing head; 601, through hole; 602, first through hole; 603, second through hole; 604, second conductive slip ring; 7, polishing pad; 8, support plate; 801, annular groove; 802, annular pressing plate; 803, elastic member; 804, threaded groove; 805, annular threaded plate; 806, limiting hole; 807, slide bar; 808, ball. Detailed implementation manners

[0027] As Figures 1 to 4 shown, the present invention provides a device for accelerating the SiC electrochemical mechanical polishing rate by water bath heating, including: an electrolyte tank 1 filled with electrolyte, and an electrochemical workstation 5. Two first copper polishing heads 2 are rotatably installed on the bottom wall of the electrolyte tank 1. A heating mechanism 3 is arranged in the electrolyte tank 1. A SiC wafer 4 is adhesively bonded to the top wall of the first copper polishing head 2 through conductive glue. A first conductive slip ring 201 is installed on the first copper polishing head 2. The first conductive slip ring 201 is connected to the anode of the electrochemical workstation 5 through a wire. The first conductive slip ring 201 is hermetically connected to the electrolyte tank 1. The cathode of the electrochemical workstation 5 is connected to a second conductive slip ring 604 through a wire. A second copper polishing head 6 is installed on the second conductive slip ring 604. A polishing pad 7 is installed on the side of the second copper polishing head 6 close to the SiC wafer 4. A plurality of through holes 601 are circumferentially arranged on the second copper polishing head 6 with the axis direction of the second copper polishing head 6 as the center.

[0028] In this solution, as Figure 1, the SiC wafer 4 and the second copper polishing head 6 are electrically connected through the electrolyte to form a closed circuit, so that the surface of the SiC wafer 4 is oxidized; the electrolyte tank 1 contains an electrolyte with a height exceeding the SiC wafer 4 and lower than the top surface of the second copper polishing head 6, submerging the SiC wafer 4 and part of the second copper polishing head 6 in the electrolyte. The electrolyte is heated by the heating mechanism 3 and the temperature of the electrolyte is kept constant at T. The first copper polishing head 2 and the second copper polishing head 6 are respectively connected with a driving mechanism, and the first copper polishing head 2 and the second copper polishing head 6 are driven to rotate by the driving mechanism, and the rotation directions of the first copper polishing head 2 and the second copper polishing head 6 are opposite, so that the polishing pad 7 on the second copper polishing head 6 polishes the SiC wafer 4.

[0029] In this solution, by submerging a part of the second copper polishing head 6 with multiple through holes 601 in the electrolyte, the contact between the surface of the SiC wafer 4 and the electrolyte is maintained during the polishing process, avoiding dry friction on the surface of the SiC wafer 4 and ensuring the oxidation rate of the surface of the SiC wafer 4; by setting the heating mechanism 3 to heat the electrolyte, the charge utilization efficiency, anodic oxidation rate and polishing rate of the electrochemical mechanical polishing of the SiC wafer 4 can be improved. By symmetrically designing the number of polishing stations, the resource loss during the electrochemical mechanical polishing of the SiC wafer 4 is reduced, the polishing cost is saved, the polishing difficulty is reduced, and the polishing efficiency is improved; by setting the first conductive slip ring 201, the sealing performance of the connection between the first copper polishing head 2 and the electrolyte tank 1 is ensured.

[0030] In an embodiment of the present invention, the through hole 601 includes a first through hole 602 group and a second through hole 603 group circumferentially arranged with the axis direction of the second copper polishing head 6 as the center. The first through hole 602 group includes 4 first through holes 602 arranged side by side in the radial direction of the second copper polishing head 6. The second through hole 603 group includes 5 second through holes 603 arranged side by side in the radial direction of the second copper polishing head 6. The first through hole 602 and the second through hole 603 are arranged in a staggered manner.

[0031] In this solution, by setting 4 first through holes 602 and 5 second through holes 603 arranged in a staggered manner with the first through holes 602, the contact area between the electrolyte and the SiC wafer 4 during the polishing process is ensured, thereby avoiding dry friction on the surface of the SiC wafer 4 and ensuring the oxidation rate of the surface of the SiC wafer 4.

[0032] In an embodiment of the present invention, a support plate 8 is installed in the electrolyte tank 1. The support plate 8 is provided with an inner hole through which the second copper polishing head 6 can pass and an annular groove 801 communicated with the inner hole. The opening direction of the annular groove 801 is downward. An annular pressing plate 802 capable of sliding along the axial direction of the annular groove 801 is installed in the annular groove 801. An elastic member 803 is connected between the annular pressing plate 802 and the inner wall of the annular groove 801. The cross section of the annular pressing plate 802 is L-shaped. The first inner wall of the annular pressing plate 802 abuts against the top wall of the second copper polishing head 6, and the second inner wall of the annular pressing plate 802 abuts against the side wall of the second copper polishing head 6.

[0033] In this solution, after the second copper polishing head 6 is placed on the SiC wafer 4, the support plate 8 is installed in the electrolyte tank 1 so that the support plate 8 covers the second copper polishing head 6, preventing the electrolyte from splashing out of the electrolyte tank 1 due to the rotation of the second copper polishing head 6 during the polishing process, which may reduce the electrolyte and lower the oxidation rate of the surface of the SiC wafer 4. Moreover, the cavity formed inside the annular pressing plate 802 cooperates with the second copper polishing head 6, causing the first inner wall of the annular pressing plate 802 to abut against the top wall of the second copper polishing head 6, the second inner wall of the annular pressing plate 802 to abut against the side wall of the second copper polishing head 6, and the elastic member 803 to be in a compressed state. During the polishing process, under the action of the elastic member 803, the polishing pad 7 on the second copper polishing head 6 always remains in contact with the top wall of the SiC wafer 4, ensuring the polishing effect and preventing the thickness of the SiC wafer 4 from decreasing during the polishing process, resulting in a gap between the second copper polishing head 6 and the top wall of the SiC wafer 4 and affecting the polishing. In addition, the annular pressing plate 802 limits the rotation of the second copper polishing head 6, ensuring the stability of the rotation of the second copper polishing head 6.

[0034] In an embodiment of the present invention, the support plate 8 is provided with a threaded groove 804. An annular threaded plate 805 is threadedly connected in the threaded groove 804. After the annular threaded plate 805 is connected to the support plate 8, the annular groove 801 is formed. The elastic member 803 is connected between the annular threaded plate 805 and the annular pressing plate 802. One of the annular threaded plate 805 and the annular pressing plate 802 is provided with a limiting hole 806, and a sliding rod 807 cooperating with the limiting hole 806 is installed on the other of the annular threaded plate 805 and the annular pressing plate 802. The sliding rod 807 is connected in the limiting hole 806 in a limited sliding manner.

[0035] In this solution, by setting the sliding rod 807 to cooperate with the limit hole 806, the annular threaded plate 805 and the annular pressing plate 802 are connected as a whole. Thus, when the annular threaded plate 805 is rotated, the annular pressing plate 803 can be driven to rotate synchronously with the annular threaded plate 805. By setting the annular threaded plate 805, rotating the annular threaded plate 805 can make the annular threaded plate 805 move along the axial direction of the thread groove 804 to adjust the height of the annular pressing plate 803, so that the annular pressing plate 803 can adapt to the second cylindrical polishing head 6 of different heights; and the compression degree of the elastic member 803 can be adjusted, thereby adjusting the pressure of the annular pressing plate 803 on the second cylindrical polishing head 6, avoiding damage to the second copper polishing head 6 caused by excessive pressure; and the second copper polishing head 6 can be taken out by screwing the annular threaded plate 805 out of the thread groove 804, which is convenient for the installation and disassembly of the second copper polishing head 6.

[0036] In an embodiment of the present invention, balls 808 are installed on both the first inner wall and the second inner wall of the annular pressing plate 802.

[0037] In this solution, by setting the balls 808, when the second copper polishing head 6 rotates, the friction between the second copper polishing head 6 and the annular pressing plate 802 is reduced.

[0038] In an embodiment of the present invention, a thrust bearing 202 is connected between the first copper polishing head 2 and the bottom wall of the electrolyte tank 1.

[0039] In this solution, by setting the thrust bearing 202 as the bearing component for the pressure received by the first copper polishing head 2, it is avoided that the first copper polishing head 2 is damaged due to pressure, resulting in damage to the electrolyte tank 1 and the first conductive slip ring 201.

[0040] An implementation method of a device for accelerating the SiC electrochemical mechanical polishing rate by water bath heating includes the following steps:

[0041] S1: Preparation of SiC wafer 4: Before polishing, the SiC wafer 4 is cleaned successively with acetone and deionized water. After cleaning, the SiC wafer 4 is placed in an oven and dried at a temperature of 100 °C for 1 h, and the mass M1 is measured.

[0042] S2: Polishing preparation: The SiC wafer 4 is installed on the first copper polishing head 2, and 5% NaNO3 electrolyte is poured into the electrolyte tank 1 until the electrolyte submerges the SiC wafer 4 and exceeds it by 1 cm;

[0043] S3: Polishing process: Adjust the polishing pressure to 100 KPa, raise the temperature of the electrolyte to a constant temperature T through the heating mechanism 3, start the driving mechanism to rotate the first copper polishing head 2 and the second copper polishing head 6 in opposite directions, and polish the SiC wafer 4 with the polishing pad 7. Among them, the rotation speed of the first copper polishing head 2 is 30 r / min, the rotation speed of the second copper polishing head 6 is 150 r / min, and the polishing pad 7 is a cerium oxide polishing pad;

[0044] S4: After polishing for 30 min, wash the SiC wafer 4 with acetone and deionized water in sequence, then put the SiC wafer 4 into an oven and dry it at a temperature of 100 °C for 1 h, weigh the mass M2, and calculate the removal rate. The formula for calculating the removal rate is: where P is the density of the SiC wafer 4, S is the polishing area of the SiC wafer 4, and t is the polishing time of the SiC wafer 4.

[0045] In this solution, as shown in the following table, in three experiments, the relationship between the electrolyte temperature and the current density and the removal rate. By comparing the removal rates under different temperature conditions, it is obtained that an increase in temperature will increase the removal rate, and an increase in the current density will also increase the removal rate.

[0046]

[0047] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. An apparatus for accelerating the SiC electrochemical mechanical polishing rate by water bath heating, characterized in that, Including: An electrolyte tank filled with electrolyte, and an electrochemical workstation. Two first copper polishing heads are rotatably installed on the bottom wall of the electrolyte tank. A heating mechanism is arranged in the electrolyte tank. An SiC wafer is adhesively bonded to the top wall of the first copper polishing head through conductive glue. A first conductive slip ring is installed on the first copper polishing head. The first conductive slip ring is connected to the anode of the electrochemical workstation through a wire. The first conductive slip ring is hermetically connected to the electrolyte tank. The cathode of the electrochemical workstation is connected to a second conductive slip ring through a wire. A second copper polishing head is installed on the second conductive slip ring. A polishing pad is installed on the side of the second copper polishing head close to the SiC wafer. A plurality of through holes are circumferentially arranged on the second copper polishing head with the axis direction of the second copper polishing head as the center. The through holes include a first through hole group and a second through hole group circumferentially arranged with the axis direction of the second copper polishing head as the center. The first through hole group includes four first through holes arranged side by side in the radial direction of the second copper polishing head. The second through hole group includes five second through holes arranged side by side in the radial direction of the second copper polishing head. The first through holes and the second through holes are arranged in a staggered manner. A support plate is installed in the electrolyte tank. The support plate is provided with an inner hole through which the second copper polishing head can pass and an annular groove communicated with the inner hole. An annular pressing plate capable of sliding along the axis direction of the annular groove is installed in the annular groove. An elastic member is connected between the annular pressing plate and the inner wall of the annular groove. The cross section of the annular pressing plate is L-shaped. The first inner wall of the annular pressing plate abuts against the top wall of the second copper polishing head. The second inner wall of the annular pressing plate abuts against the side wall of the second copper polishing head. The support plate is provided with a threaded groove. An annular threaded plate is threadedly connected in the threaded groove. The annular threaded plate and the support plate form the annular groove after being connected. The elastic member is connected between the annular threaded plate and the annular pressing plate. One of the annular threaded plate and the annular pressing plate is provided with a limiting hole. A sliding rod matched with the limiting hole is installed on the other of the annular threaded plate and the annular pressing plate. The sliding rod is limited and slidably connected in the limiting hole.

2. The device for accelerating the SiC electrochemical mechanical polishing rate by water bath heating according to claim 1, wherein: Ball bearings are installed on both the first inner wall and the second inner wall of the annular pressing plate.

3. The device for accelerating the SiC electrochemical mechanical polishing rate by water bath heating according to claim 2, wherein: A thrust bearing is connected between the first copper polishing head and the bottom wall of the electrolyte tank.

4. The implementation method of the device for accelerating the SiC electrochemical mechanical polishing rate by water bath heating according to any one of claims 1-3, characterized in that, Including the following steps: S1: Preparation of SiC wafer: Before polishing, the SiC wafer is washed with acetone and deionized water in sequence. After washing, the SiC wafer is placed in an oven and dried at a temperature of 100°C for 1 h, and the mass M1 is weighed. S2: Polishing preparation: The SiC wafer is installed on the first copper polishing head. 5% NaNO3 electrolyte is poured into the electrolyte tank until the electrolyte submerges the SiC wafer and exceeds 1 cm. S3: Polishing process: Adjust the polishing pressure to 100 KPa, raise the temperature of the electrolyte to a constant temperature T through the heating mechanism, start the driving mechanism to make the first copper polishing head and the second copper polishing head rotate in opposite directions, and polish the SiC wafer through the polishing pad. Among them, the rotation speed of the first copper polishing head is 30 r / min, the rotation speed of the second copper polishing head is 150 r / min, and the polishing pad uses a cerium oxide polishing pad; S4: After polishing for 30 min, clean the SiC wafer successively with acetone and deionized water, then put the SiC wafer into an oven and dry it at a temperature of 100 °C for 1 h, weigh the mass M2, and calculate the removal rate. The formula for calculating the removal rate is: , where P is the density of the SiC wafer, S is the polished area of the SiC wafer, and t is the polishing time of the SiC wafer.

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