Method and device for electrochemical mechanical polishing of third-generation semiconductor wafer based on fixed abrasive

Abstract

The electrochemical mechanical polishing method and device are characterized in that a workpiece clamping device is adjusted according to the size of the semiconductor wafer and is adsorbed on a pressurizing device, and the semiconductor wafer is connected to a positive electrode of a power supply through a conducting ring to serve as an anode of an electrolysis system; the fixed abrasive pad is fixed on the polishing disc through a conductive adhesive and is connected to a power supply cathode through a conductive ring to serve as a cathode of the electrolysis system; during polishing, a polishing solution is connected with a conductive adhesive for fixing the polishing pad through a through hole in the fixed abrasive pad to form an electrolytic tank path, chemical oxidation and anodic oxidation are carried out on the surface of the third-generation semiconductor wafer during polishing to form a passivation oxide layer with low hardness, and valleys of the passivation oxide layer are passivated and protected. And the peak is quickly removed by the fixed abrasive, so that a polishing mode of anodizing and online removing the surface of the third-generation semiconductor wafer is realized. The method has the advantages of high abrasive utilization rate, high material removal rate, good surface quality, recycling of the polishing solution and the like.

Description

Technical Field

[0001] The present invention relates to a method and a device for electrochemical mechanical polishing of third-generation semiconductor wafers based on a fixed abrasive, specifically to an electrochemical mechanical polishing method and a device using a fixed abrasive pad as a polishing pad, which is mainly used for polishing third-generation semiconductor materials such as silicon carbide and gallium nitride that are chemically inert and brittle. Background Art

[0002] The third-generation semiconductor materials have the advantages of wide bandgap, wide bandgap, high critical breakdown electric field, high thermal conductivity, high carrier saturation migration velocity, low relative dielectric constant and high temperature resistance. They are considered to be ideal materials for high-temperature and high-frequency optoelectronic devices and are widely used in various fields such as aerospace, photovoltaics, electric vehicles and 5G communications. They mainly include silicon carbide, gallium nitride, diamond, etc. The surface quality of the third-generation semiconductor materials has a crucial impact on the performance of their devices. Therefore, in applications, there are strict requirements for their surface quality after processing. At present, the third-generation semiconductor materials require the wafer surface to be ultra-smooth, defect-free, and damage-free, with a surface roughness below the nanometer level. However, the ultra-hard and brittle material characteristics of the third-generation semiconductor substrate (represented by single-crystal silicon carbide) lead to low processing efficiency and serious surface damage, which seriously restricts the application of the third-generation semiconductor.

[0003] Chemical mechanical polishing of silicon carbide substrates with electrochemical assistance is a feasible process technology route. Chinese patent CN114654380A discloses a method for electrochemical mechanical polishing of silicon carbide wafers. During polishing, the graphite disk, polishing pad and silicon carbide are immersed in an electrolyte (polishing liquid), and the silicon carbide wafer is bonded to a copper polishing head through a conductive adhesive. During polishing, the diamond abrasive and the aluminum oxide abrasive in the polishing liquid are mixed and added to the polishing area in the form of free abrasives; Chinese patent CN111515852A discloses an electrochemical mechanical polishing machine, which is mainly used for ultra-precision polishing of interconnected metals in integrated circuit manufacturing. It mainly immerses the workpiece and the rotating polishing head in the polishing liquid to form a current loop for polishing, thereby generating an electrolytic reaction, causing electrochemical reaction on the workpiece surface, and performing electrochemical mechanical polishing under the action of pressure and rotation speed; Kazuya Osaka University, Japan The Yamamura team built an electrochemical mechanical polishing test platform, with the positive pole of the power supply connected to a copper plate, and a single crystal SiC workpiece attached to the copper plate as the anode of the electrolytic cell. The polishing head was connected to the negative pole of the power supply as the cathode of the electrolytic cell. The device was used to study the oxidation mechanism of single crystal SiC anodization, and electrochemical mechanical polishing was performed to obtain a good polishing effect. Chinese patent CN115415857A discloses a photoelectrochemical mechanical polishing device and a material efficient removal adjustment method, which mainly targets the designed mechanical structure, ultraviolet light radiates the wafer through the polishing pad through hole to promote oxidation, and the current feedback of the electrochemical workstation adjusts the polishing pressure to improve the polishing efficiency. In the method of electrochemical mechanical polishing proposed by the researchers in the patent and the paper, the feasibility of using the electrochemical mechanical polishing method to process single crystal SiC wafer semiconductor wafers was verified. Electrochemical mechanical polishing uses the workpiece as the anode, and can quickly form an oxide layer on the workpiece surface under the joint drive of the electric field force and the abrasive, and achieve material removal through the mechanical action of the abrasive. However, semiconductor wafers have poor electrical conductivity and the speed of anodization is difficult to control, which introduces pitting pits, cavities, microcracks, over-oxidation and other defects on the wafer surface. During polishing, the workpiece, polishing head, polishing pad, polishing disc, etc. need to be immersed in the polishing liquid containing electrolyte. According to the anodization sequence, it is necessary to ensure that the workpiece to be polished is the anode of the electrolytic cell system. The centrifugal effect generated by the high-speed rotation of the polishing pad and the workpiece has the characteristic of unstable conductive circuit formed between the polishing liquid and the workpiece.

[0004] In general, the current electrochemical mechanical polishing of silicon carbide substrates has problems such as difficult control of electrode anodization sequence and oxidation rate, low processing efficiency, and poor surface quality, which cannot meet the high-efficiency and low-cost processing requirements of third-generation semiconductors. Summary of the invention

[0005] The present invention is mainly aimed at the problems that the electrode anodization sequence and oxidation speed are difficult to control, the processing efficiency is low, the surface quality is poor, etc. when electrochemical mechanical polishing is used due to the high hardness and brittleness and chemical inertness of the third-generation semiconductors, and the material removal rate is low during the polishing process. A new method and device for electrochemical mechanical polishing of third-generation semiconductor wafers based on fixed abrasives are invented. In view of the polishing characteristics and processing requirements of the third-generation semiconductor materials, the wafer is used as the anode of the electrolytic cell, and a certain concentration of oxidant is added to the polishing liquid. Under the combined action of electric field anodization and polishing liquid chemical oxidation, an oxide layer with a passivating effect is generated on the surface of the wafer. The peaks of the passivating oxide layer are preferentially mechanically removed by the fixed abrasive pad, while the valleys of the passivating oxide layer are protected. The peaks and valleys of the passivating oxide layer are completely removed in a reciprocating cycle, thereby effectively improving the material removal efficiency and reducing the surface roughness of the workpiece, and achieving the polishing processing goal of online real-time anodization and efficient material removal.

[0006] One of the technical solutions of the present invention is:

[0007] A method for electrochemical mechanical polishing of a third-generation semiconductor wafer based on a fixed abrasive is characterized in that: first, the wafer is used as the anode of an electrolytic cell, one or both of an electrolyte or an oxidant are added to a polishing liquid, and an oxide layer with a passivation effect is generated on the surface of the wafer under the combined action of electric field anodization and polishing liquid chemical oxidation, and the peaks of the passivation oxide layer are mechanically removed by a fixed abrasive pad, while the valleys of the passivation oxide layer are protected, and the peaks and valleys of the passivation oxide layer are completely removed by a reciprocating cycle, thereby effectively improving the material removal efficiency and reducing the surface roughness of the wafer, thereby achieving the polishing processing goal of online real-time anodization and efficient material removal; secondly, a fixed abrasive pad is used to polish the semiconductor wafer, the abrasive motion trajectory is determined, and the fixed abrasive utilization rate is high; during the polishing process, the polishing liquid is continuously sprayed only on the surface of the fixed abrasive pad, and the wafer, the polishing head, the polishing disc and the fixed abrasive pad do not need to be immersed in the polishing liquid during polishing, so that the oxidation sequence during anodization is easy to control.

[0008] The DC power supply for anodized wafers has two working modes: constant voltage and constant current. During polishing, the voltage range is 0.001~20V, and the current range is 0.001~2A, which is continuously adjustable.

[0009] The electrolyte added to the polishing liquid is one or more combinations of NaCl, NaNO3, and Na2SO4 to improve the conductivity of the polishing liquid during electrochemical anodizing of the wafer, and the mass concentration is 0.1 to 30%.

[0010] The oxidant added to the polishing liquid is one or more combinations of Na2S2O7, NaClO3, KMnO4, and H2O2, with a mass concentration of 0.01 to 15%. The combined effects of chemical oxidation and electrochemical oxidation of the polishing liquid jointly promote the oxidation film formation rate of the wafer.

[0011] The second technical solution of the present invention is:

[0012] A novel electrochemical mechanical polishing device for third-generation semiconductor wafers based on fixed abrasives is characterized in that: a fixed abrasive pad 12 is fixed on a polishing disc 14 by a conductive adhesive 13, the polishing disc 14 and a driving disc 20 are circumferentially positioned, and an insulating gasket 15 is used in the middle to insulate, the fixed abrasive pad 12 on the polishing disc 14 is driven by a driving shaft 22 to perform a circular rotational motion, a semiconductor wafer 11 is adsorbed on a pressing block 8 by a conductive rubber 9, and the polished semiconductor wafer 11 on a workpiece clamping fixture 10 is driven by a driving shaft 6 to perform a circular rotational motion with the fixed abrasive pad 12 under a set pressure to achieve polishing; the positive electrode of a power supply device 5 is connected to the semiconductor wafer 11 through a conductive ring 7 to form an anode of anodized anode, the negative electrode is connected to the polishing base disc under the fixed abrasive pad 12 through a conductive ring 16 to form a cathode, a through hole 37 is processed on the polishing pad, and a conductive circuit is formed by relying on the electrolyte in the polishing liquid.

[0013] The surface of the fixed abrasive pad is provided with grooves, and through holes 37 are evenly distributed in the grooves. The shape of the through holes is one of round, diamond and square. The size of the through holes ranges from 0.1 to 5 mm. The through holes are arranged in the grooves of the fixed abrasive pad in a concentric circle or rectangular array.

[0014] The outer ring 34 and the inner ring 36 of the conductive ring are connected via an elastic contact sheet 35 , and the outer ring and the inner ring of the conductive ring can rotate and ensure the stability of conduction.

[0015] The polishing liquid 19 is delivered to the polishing pad through a constant temperature circulation device, and a filtering device 27 is used to filter out particulate impurities in the polishing liquid during the circulation process.

[0016] The beneficial effects of the present invention are:

[0017] The present invention has the advantages of high material removal rate, good flattening effect, good processing stability, and recycling of polishing liquid, and can be applied to the efficient and low-damage polishing of third-generation semiconductor materials that are chemically inert, stable, hard and brittle. The present invention uses a fixed abrasive pad to polish semiconductor wafers, the abrasive motion trajectory is determined, the fixed abrasive utilization rate is high, the fixed abrasive wear belongs to two-body wear, and the sub-surface damage to the semiconductor wafer is low; during the polishing process, the semiconductor wafer, the polishing head, the polishing disc and the pressurizing device do not need to be immersed in the polishing liquid during polishing, and the oxidation sequence is easy to control during anodizing; chemical oxidation and anodizing occur on the surface of the third-generation semiconductor wafer to form a passivation oxide layer with lower hardness, the valley of the passivation oxide layer is passivated and protected, and the peak is quickly removed by the fixed abrasive, which improves the material removal rate and surface quality of the wafer; the polishing liquid can be recycled, which greatly reduces the processing cost of polishing waste liquid during traditional chemical mechanical polishing of third-generation semiconductor wafers.

[0018] The present invention adjusts the workpiece clamping device according to the size of the semiconductor wafer and adsorbs it on the pressurizing device. The semiconductor wafer is connected to the positive electrode of the power supply through a conductive ring to serve as the anode of the electrolytic system; the fixed abrasive pad is fixed on the polishing disk through a conductive glue, and is connected to the negative electrode of the power supply through a conductive ring to serve as the cathode of the electrolytic system; during polishing, the polishing liquid is connected to the conductive glue of the fixed polishing pad through the through hole on the fixed abrasive pad to form an electrolytic cell passage, and during polishing, chemical oxidation and anodic oxidation occur on the surface of the third-generation semiconductor wafer to form a passivation oxide layer with lower hardness, the valleys of the passivation oxide layer are passivated and protected, and the peaks are quickly removed by the fixed abrasive, thereby realizing a polishing mode of anodizing and online removal of the surface of the third-generation semiconductor wafer. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of the electrochemical polishing device of the present invention.

[0020] Figure 2 It is a schematic structural diagram of the workpiece clamping device of the present invention.

[0021] Figure 3 It is a schematic structural diagram of the conductive ring of the present invention.

[0022] Figure 4 Schematic diagram of the fixed abrasive pad and the conductive through holes thereon of the present invention.

[0023] In the figure: 1. Ammeter, 2. Anode wire of electrolytic cell, 3. Cathode wire of electrolytic cell, 4. Voltmeter, 5. DC power supply, 6. Polishing head drive shaft, 7. Conductive ring, 8. Press block, 9. Conductive rubber, 10. Workpiece clamping device, 11. Semiconductor workpiece, 12. Fixed abrasive pad, 13. Conductive rubber, 14. Polishing disc, 15. Insulating gasket, 16. Conductive ring, 17. Fixed conductive ring support rod, 18. Polishing liquid nozzle, 19. Polishing liquid, 20. Drive disc, 21. Polishing liquid, 22. Polishing disc drive shaft, 23. Polishing liquid supply peristaltic pump, 24. Polishing frame, 25. Polishing liquid recovery peristaltic pump, 26. Polishing liquid supply pipeline, 27. Filter device, 28. Polishing liquid container, 29. Water bath, 30. Water, 31. Polishing liquid, 32. Stirring bar, 33. Constant temperature magnetic stirrer, 34. Conductive ring outer ring, 35. Conductive ring elastic contact piece, 36. Conductive ring inner ring, 37. Fixed abrasive pad conductive through hole, 38. Fixed abrasive pad protrusion. DETAILED DESCRIPTION

[0024] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0025] Example 1.

[0026] like Figure 1-4 shown.

[0027] A new type of electrochemical mechanical polishing device for third-generation semiconductor wafers based on fixed abrasives. Under the action of an external electric field, the chemical oxidant in the polishing liquid and the anodic oxidation work together to form a low-hardness oxide layer on the surface of the workpiece. The oxide layer is quickly removed by the mechanical action of the fixed abrasive pad to achieve high-efficiency and low-damage processing of third-generation semiconductors. The electrochemical mechanical polishing device includes a polishing disc and drive, a fixed abrasive pad, a conductive ring, a power supply device, and a polishing liquid supply device (such as Figure 1 ); the workpiece clamping device (such as Figure 2 ), can be designed according to the size of the workpiece, and adsorbed on the pressurizing device through conductive rubber; the conductive ring (such as Figure 3 ) are respectively fixed on the support rods of the pressure device and the polishing disk, and the inner ring of the conductive ring can rotate with the rotation center; the fixed abrasive pad is fixed on the polishing disk with a conductive adhesive, and the fixed abrasive polishing pad can rotate with the rotation of the polishing disk. Under the action of the polishing liquid, the semiconductor wafer and the base disk under the fixed abrasive pad form a conductive circuit through the through hole (such as Figure 4 ), the semiconductor wafer is connected to the positive pole of the power supply.

[0028] like Figure 1 As shown, the fixed abrasive pad 12 is fixed on the polishing disc 14 by the conductive glue 13, the polishing disc 14 and the driving disc 20 are positioned circumferentially, and the middle is insulated by the insulating gasket 15. The fixed abrasive pad 12 on the polishing disc 14 is driven by the driving shaft 22 to make a circular rotation motion, the semiconductor wafer 11 is adsorbed on the pressing block 8 by the conductive rubber 9, and the polished semiconductor wafer 11 on the workpiece clamping fixture 10 is driven by the driving shaft 6 to make a circular rotation motion with the fixed abrasive pad 12 under a set pressure to achieve polishing; the positive electrode of the power supply device 5 is connected to the semiconductor wafer 11 through the conductive ring 7 to form an anode of anodization, and the negative electrode is connected to the polishing disc 14 under the fixed abrasive pad 12 through the conductive ring 16 to form a cathode, and the conductive glue 13 is added between the fixed abrasive pad 12 and the polishing disc 14, and the polishing abrasive pad 12 is processed with a through hole 37 (such as Figure 4 ), relying on the electrolyte in the polishing liquid to form a conductive circuit. The surface of the fixed abrasive pad is provided with grooves (such as Figure 4 ), the groove is uniformly distributed with through holes 37, the shape of the through holes is one of round, diamond, and square, the size of the through holes ranges from 0.1 to 5 mm, and the arrangement of the through holes in the groove of the fixed abrasive pad is a concentric circle or rectangular array. The outer ring 34 of the conductive ring 7 (or 14) is connected to the inner ring 36 through an elastic contact sheet 35, such as Figure 3 The outer ring 34 and the inner ring 36 of the conductive ring can rotate and ensure the stability of the conductive. The polishing liquid 19 is passed through a constant temperature circulation device (such as Figure 1The polishing liquid 19 is transported to the polishing pad (shown in the middle right part), and the filtering device 27 is used to filter out the particulate impurities in the polishing liquid during the circulation process. The polishing liquid supply peristaltic pump 23 continuously transports the polishing liquid 19 from the polishing liquid container 28 to the polishing liquid nozzle 18 through the polishing liquid supply pipeline 26. The polishing liquid nozzle 18 and the polishing drive device are both installed in the polishing machine frame 24. After passing through the fixed abrasive pad 12, the polishing liquid 19 finally flows into the polishing machine frame 24 and is filtered by the polishing liquid recovery peristaltic pump 25 and the filtering device 27 and then flows back to the polishing liquid container 28. The polishing liquid container 28 is placed in the water 30 of the water bath 29. A stirring rod 32 is installed in the polishing liquid container 28, and the water bath 29 is placed on a constant temperature magnetic stirrer 33. The constant temperature magnetic stirrer 33 magnetically stirs the water 30 of the water bath 29 and the polishing liquid 31 in the polishing liquid container 28 to make the temperature of the water 30 uniform, and the temperature of the polishing liquid 31 is uniform and no precipitation occurs. The DC power supply of the anodized wafer of the present invention can adopt two working modes: constant voltage and constant current. During polishing, the voltage range is 0.001-20V, and the current range is 0.001-2A, which are continuously adjustable. The positive electrode of the power supply device is connected to the semiconductor wafer through a conductive ring to form the anode of the electrolysis system, and the negative electrode is connected to the polishing base plate under the fixed abrasive pad through a conductive ring to form the cathode. Through holes are processed on the polishing pad, and a conductive loop is formed by the electrolyte in the polishing liquid. The fixed abrasive pad is fixed on the polishing disc through conductive glue, and the polishing disc and the driving disc are circumferentially positioned, and the middle is insulated by an insulating gasket. The fixed abrasive pad on the polishing disc is driven by the driving shaft to perform a circular rotation motion, and the semiconductor wafer is adsorbed on the pressing block through the conductive rubber. The polished semiconductor wafer on the workpiece clamping fixture is driven by the driving shaft to perform a circular rotation motion with the fixed abrasive pad under a set pressure to achieve polishing.

[0029] Example 2.

[0030] like Figure 1 shown.

[0031] A novel electrochemical mechanical polishing device for third-generation semiconductor wafers based on fixed abrasives ( Figure 1A polishing method (shown in the figure) is used to polish a 4-inch single-crystalline SiC semiconductor wafer. According to the size of the 4-inch SiC wafer, the clamping device for fixing the SiC wafer is adjusted and fixed to the pressure device through conductive rubber adsorption. In order to facilitate direct contact between the single-crystalline SiC and the fixed abrasive pad, the single-crystalline SiC after adsorption is required to be 0.2 mm higher than the clamping device; the workpiece (third-generation semiconductor crystal, the same below) is connected to the positive electrode of the DC power supply, and the negative electrode is connected to the conductive rubber for fixing the fixed abrasive pad. The polishing liquid is composed of 10% NaCl by mass, 7% H2O2 by mass and the remainder of water. The polishing liquid temperature is room temperature and the flow rate is set to 30m L / min, the power supply voltage is set to 2V constant voltage mode, the speed of the fixed abrasive polishing pad is 85r / min, the SiC wafer rotates at a speed of 80r / min under a pressure of 3.0psi, and the polishing liquid diffuses to the polishing area of ​​the single crystal SiC using centrifugal force. The material removal rate of traditional chemical mechanical polishing is generally less than 1μm / h. After 20min of electrochemical mechanical polishing, the surface roughness Sa of the SiC wafer drops from 163.33nm to 5.45nm, and the material removal rate MRR reaches 26.352μm / h. The surface quality of the SiC wafer is significantly improved, and the material removal rate is also improved.

[0032] Example 3.

[0033] The NaCl in Example 2 is replaced by NaNO3 or NaSO4, and H2O2 is replaced by one of Na2S2O7, NaClO3 or KMnO4, and their mass percentages are adjusted to meet the ratio requirements that the mass percentage of NaNO3 or NaSO4 is 0.1-30%, and the mass percentage of Na2S2O7, NaClO3 or KMnO4 is 0.01-15%. When the constant voltage working mode is adopted, the power supply voltage is adjusted within the constant voltage range of 0.001-20V. When the constant current working mode is adopted, the current range is between 0.001-2A. The remaining parameters are the same or similar to those in Example 2. Experiments have shown that the material removal rate and the surface roughness Sa of the wafer are similar to those in Example 2, proving that the method of the present invention is reliable and stable.

[0034] Comparative example 1.

[0035] This comparative example uses ordinary polishing liquid and immersion processing, the material removal rate is generally less than 2 μm / h, and the surface roughness Sa of the SiC wafer is about 165 nm.

[0036] Example 4.

[0037] A method for electrochemical mechanical polishing of a third-generation semiconductor wafer based on a fixed abrasive, polishing a 6-inch single-crystal SiC wafer, adjusting a clamping device according to the size of the 6-inch single-crystal SiC wafer, and fixing the wafer with conductive rubber so that the wafer is not thrown off during polishing on a pressurizing device. After polishing, the wafer workpiece can be easily replaced. The fixed single-crystal SiC wafer can directly contact the fixed abrasive pad during polishing. The electrolyte in the polishing liquid is composed of 20% by mass NaNO3, 10% NaCl, 5% NaSO4 and the remainder water. The oxidant is composed of 5% by mass Na2S2O7, 2% NaClO3, 1% KMnO4, 15% H2O2 and the remainder water. The power supply is set to 1 In the 0mA constant current mode, the polishing liquid flows to the conductive adhesive through the through holes on the fixed abrasive pad. The current flows from the single-crystal SiC wafer through the polishing liquid to the conductive adhesive, and then through the conductive ring to the negative electrode of the power supply to form a conductive loop. The polishing disk speed is 100r / min, the single-crystal SiC wafer speed is 95r / min, the polishing pressure is 5psi, the polishing liquid is kept at a constant temperature of 60℃, and the flow rate is 45mL / min. After 60min of electrochemical mechanical polishing, the surface roughness Sa of the SiC wafer drops from 157.62nm to 16.83nm, and the material removal rate increases from the traditional 0.834μm / h to 35.236μm / h. The surface quality of the SiC wafer is significantly improved, and the material removal rate is significantly improved.

[0038] Example 5.

[0039] The invention discloses an electrochemical mechanical polishing method for a third-generation semiconductor wafer based on a fixed abrasive, wherein a 2-inch single-crystal GaN wafer is polished, a clamping device is adjusted according to the size of the 2-inch single-crystal GaN wafer, and a conductive rubber can be used to adsorb the wafer on a polishing pressure device during polishing. The polishing liquid is composed of 3% Na2SO4, 30% NaCl and the remainder water in mass percentage, and the oxidant is composed of 3% H2O2, 10% KMnO4 and the remainder water in mass percentage. The flow rate is 80mL / min, the power supply is set to a constant voltage mode of 15V, the polishing disc speed is 60r / min, the single crystal GaN wafer speed is set to 55r / min, the polishing pressure is set to 1.5psi, and the current is conducted to the conductive ring of the negative pole of the power supply through the through hole of the fixed abrasive pad under the action of the polishing liquid. The used polishing liquid is recycled again through a peristaltic pump, and the polishing liquid is kept in a constant temperature state by stirring, thereby realizing the recycling of the polishing liquid. After polishing the single crystal GaN wafer for 30 minutes, the surface roughness Ra of the GaN wafer dropped from 83.14nm to 4.37nm, and the material removal rate increased from the traditional 1.132μm / h to 18.249μm / h. The surface quality of the 2-inch single crystal GaN wafer is significantly improved, and the material removal rate is significantly improved.

[0040] Example 6.

[0041] The invention discloses an electrochemical mechanical polishing method for a third-generation semiconductor wafer based on a fixed abrasive. The method comprises polishing a 3-inch single-crystal GaN wafer, adjusting a clamping device according to the size of the 3-inch single-crystal GaN wafer, fixing the wafer on a polishing pressure device during polishing, and facilitating replacement of a workpiece. The polishing liquid comprises 10% by mass of NaNO3 and the remainder of water, and the oxidant comprises 15% by mass of KMnO4, 1% of Na2S2O7 and the remainder of water. The polishing liquid is at room temperature, the flow rate is 70 mL / min, the power supply is set to a constant pressure mode of 30 V, the rotation speed of the polishing disc is 120 r / min, the rotation speed of the single-crystal GaN wafer is set to 115 r / min, the polishing pressure is 2 psi, and the surface roughness Sa of the GaN wafer is reduced from 137.22 nm to 2.85 nm after polishing for 50 min, and the material removal rate is increased from the traditional 0.936 μm / h to 27.831 μm / h. The surface quality of the 3-inch single-crystal GaN wafer is significantly improved, and the material removal rate is significantly improved.

[0042] Example 7.

[0043] The components and mass percentages of the polishing liquid and the oxidant in Examples 3-5 are adjusted to meet the requirements that the electrolyte is a combination of two or more of NaCl, NaNO3, and Na2SO4, and the mass concentration of the electrolyte is 0.1-30%. The oxidant is a combination of two or more of Na2S2O7, NaClO3, KMnO4, and H2O2, and the mass concentration is 0.01-15%. At the same time, the voltage range is 0.001-20V, and the current range is 0.001-2A, which are continuously adjustable. The other parameters are the same or similar. The final experimental results are the same or similar to those of Examples 3-5.

[0044] The above descriptions are merely embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent changes made using the contents of the specification and drawings of the present invention will not depart from the scope of the present invention.

[0045] The present invention does not involve parts that are the same as the prior art or can be implemented by using the prior art.

Claims

1. An electrochemical mechanical polishing method for a third generation semiconductor wafer based on a fixed abrasive, characterized in that: First, the wafer is used as the anode of the electrolytic cell, and one or both of electrolytes or oxidants are added to the polishing liquid. Under the combined action of electric field anodization and polishing liquid chemical oxidation, an oxide layer with a passivating effect is generated on the wafer surface. The peaks of the passivating oxide layer are mechanically removed by a fixed abrasive pad, while the valleys of the passivating oxide layer are protected. The peaks and valleys of the passivating oxide layer are completely removed by repeated cycles, thereby effectively improving the material removal efficiency and reducing the wafer surface roughness, achieving the polishing processing goal of online real-time anodization and efficient material removal. Secondly, the fixed abrasive pad is used to polish the semiconductor wafer, the abrasive movement trajectory is determined, and the fixed abrasive utilization rate is high; During the polishing process, the polishing liquid is continuously sprayed only on the surface of the fixed abrasive pad. The wafer, polishing head, polishing disc and fixed abrasive pad do not need to be immersed in the polishing liquid during polishing, so that the oxidation sequence during anodizing is easy to control.

2. The method according to claim 1, characterized in that: The DC power supply for anodized wafers has two working modes: constant voltage and constant current. During polishing, the voltage range is 0.001~20V, and the current range is 0.001~2A, which is continuously adjustable.

3. The method according to claim 1, characterized in that: The electrolyte added to the polishing liquid is one or more combinations of NaCl, NaNO3, and Na2SO4 to improve the conductivity of the polishing liquid during electrochemical anodization of the wafer, and the mass concentration is 0.1 to 30%.

4. The method according to claim 1, characterized in that: The oxidant added to the polishing liquid is one or more combinations of Na2S2O7, NaClO3, KMnO4, and H2O2, with a mass concentration of 0.01 to 15%. The combined effects of chemical oxidation and electrochemical oxidation of the polishing liquid jointly promote the oxidation film formation rate of the wafer.

5. A novel electrochemical mechanical polishing device for third-generation semiconductor wafers based on fixed abrasives, characterized in that: The fixed abrasive pad (12) is fixed on the polishing disc (14) through the conductive rubber (13). The polishing disc (14) and the driving disc (20) are positioned in the circumferential direction and insulated by an insulating gasket (15) in the middle. The fixed abrasive pad (12) on the polishing disc (14) is driven by the driving shaft (22) to perform a circular rotational motion. The semiconductor wafer (11) is adsorbed on the pressing block (8) through the conductive rubber (9). The semiconductor wafer (11) to be polished on the workpiece clamping and fixing device (10) is driven by the driving shaft (6) to perform a circular rotational motion with the fixed abrasive pad (12) under a set pressure to achieve polishing. The positive electrode of the power supply device (5) is connected to the semiconductor wafer (11) through the conductive ring (7) to form an anode of anodized anode, and the negative electrode is connected to the polishing base disc under the fixed abrasive pad (12) through the conductive ring (16) to form a cathode. A through hole (37) is processed on the polishing pad to form a conductive circuit by relying on the electrolyte in the polishing liquid.

6. The device according to claim 5, characterized in that: The surface of the fixed abrasive pad is provided with grooves, and through holes (37) are evenly distributed in the grooves. The shape of the through holes is one of circular, diamond and square. The size of the through holes ranges from 0.1 to 5 mm. The through holes are arranged in the grooves of the fixed abrasive pad in a concentric circle or rectangular array.

7. The device according to claim 1, characterized in that: The outer ring (34) and the inner ring (36) of the conductive ring are connected via an elastic contact sheet (35), and the outer ring and the inner ring of the conductive ring can rotate and ensure the stability of conduction.

8. The device according to claim 1, characterized in that: The polishing liquid (19) is transported to the polishing pad through a constant temperature circulation device, and a filtering device (27) is used to filter out particulate impurities in the polishing liquid during the circulation process.

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