SiC wafer wrapping method

Abstract

This invention provides a lapping method for SiC wafers that makes it easier to maintain the sharpness of the fixed abrasive grains, as the holding portion is prone to retraction and changeover during lapping. [Solution] The lapping method of the present invention involves lapping a SiC wafer W with the polishing layer 10 of a polishing tool 15 in the presence of a lapping liquid 19a. The polishing layer 10 consists of fixed abrasive grains 1 made of diamond and a holding part 3 that holds the fixed abrasive grains 1. The holding part 3 consists of at least one of metal and resin. The lapping liquid 19a consists of free abrasive grains made of Al2O3.

Description

[Technical Field]

[0001] The present invention relates to a lapping method for SiC wafers. [Background Art]

[0002] A conventional lapping method is disclosed in Patent Document 1. This lapping method uses a lapping machine provided with a surface plate and a carrier. The surface plate has a fixing surface extending in a direction orthogonal to a first axis, and is rotated around the first axis. A lap plate is attached to the fixing surface of the surface plate. The lap plate is composed of a plate body and a polishing layer fixed to the upper surface of the plate. The polishing layer of Patent Document 1 is composed of fixed abrasive grains and a holding portion that holds the fixed abrasive grains. The fixed abrasive grains are composed of hard abrasive grains such as diamond, and soft abrasive grains such as cerium oxide. The holding portion is vitreous (vitrified bond). As the holding portion, those made of resin (resin bond), those made of metal (metal bond), those in which countless metal particles or the like are dispersed in resin, and the like are also known (for example, Patent Documents 2 to 4).

[0003] A SiC wafer having a surface to be polished is fixed to the carrier, and the carrier rotates the surface to be polished around a second axis parallel to the first axis. This lapping machine performs lapping processing on the SiC wafer with the polishing layer of the lap plate in the presence of a predetermined surface pressure and a lapping liquid. [Prior Art Documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Unexamined Patent Application Publication No. 2019-141974 [Patent Document 2] Japanese Patent No. 3050379 [Patent Document 3] Japanese Patent No. 6326737 [Patent Document 4] Japanese Unexamined Patent Application Publication No. 2018-126813 [Summary of the Invention] [Problems that the invention aims to solve]

[0005] However, conventional lapping methods have the problem that the fixed abrasive grains do not easily recede or change in shape, which is necessary to maintain their sharpness.

[0006] In particular, with lapping machines, the low load per unit area and slow peripheral speed result in lower processing efficiency compared to other polishing methods, making them prone to the aforementioned problems. Furthermore, when the fixed abrasive grains are superabrasive grains such as diamond, due to the hardness and high cost of the fixed abrasive grains, the holding part is made of high strength and density to firmly hold the fixed abrasive grains in order to make the most of them, and the holding part is less likely to retract or change in grain.

[0007] The present invention has been made in view of the above-mentioned conventional circumstances, and aims to solve the problem of providing a lapping method that makes it easier to maintain the sharpness of the fixed abrasive grains when lapping a SiC wafer, as the holding portion is prone to retraction and change in grain. [Means for solving the problem]

[0008] The present invention relates to a lapping method for a SiC wafer, in which a SiC wafer is lapped by the polishing layer of a polishing tool in the presence of a lapping solution. The abrasive layer consists of fixed abrasive grains and a holding portion that holds the fixed abrasive grains. The holding portion is made of at least one of metal and resin. The lapping liquid is characterized in that the free abrasive particles consist of Al2O3.

[0009] In the lapping method of the present invention, the holding part that holds the fixed abrasive grains is made of at least one of metal and resin, and the lapping liquid used consists of Al2O3 as the free abrasive grains. According to the inventor's test results, in this case, the replacement of the polishing layer is promoted, enabling high-precision continuous processing.

[0010] Furthermore, this lapping method places minimal stress on the fixed abrasive grains, making them less prone to cracking or other damage. As a result, the grinding tool can achieve sufficient machining efficiency. [Effects of the Invention]

[0011] The lapping method of the present invention, when lapping a SiC wafer, exhibits sufficient processing efficiency by having sufficient holding force for the fixed abrasive grains, while the holding portion is prone to retraction and change in grain, making it easier to maintain the sharpness of the fixed abrasive grains. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a 2000x micrograph of the dendritic powder made of Cu used in Experiment 1. [Figure 2] Figure 2 is a schematic cross-sectional view of the polished layers of the reference example and Examples 1-6 used in Test 1. [Figure 3] Figure 3 is a schematic cross-sectional view of the single-sided lapping machine used in Test 1. [Figure 4] Figure 4 is a schematic cross-sectional view of the polished layer of Example 7 used in Test 2. [Modes for carrying out the invention]

[0013] In the lapping method of the present invention, the holding part consists of at least one of metal and resin, and does not contain vitrified material. According to the inventor's test results, when the free abrasive particles of the lapping liquid are Al2O3, the surface roughness of the workpiece is large if the holding part is vitrified.

[0014] Preferably, the holding portion has countless aggregates made of metal. It is preferable that the aggregates are not bonded to each other, that is, they do not form metallic bonds like those formed when the aggregates solidify after melting. Further, it is preferable that the aggregates are not joined to each other, that is, the aggregates are not subjected to sintering or firing. It is preferable that the aggregates of the holding portion are entangled with each other while forming pores therebetween. Such aggregates can be obtained by pressurizing a molded body to caulk the aggregates to each other without sintering or firing the aggregates.

[0015] In this case, since the holding portion has lower strength and is coarser than conventional holding portions, it is prone to recession and dressing of the abrasive grains. In addition, in this case, the low strength and coarseness of the holding portion are not achieved by a lubricant such as carbon, but by the entanglement of the aggregates, so the holding portion has sufficient holding force for fixed abrasive grains. Further, in this lapping method, since the load on the fixed abrasive grains is small, cracks and the like are less likely to occur in the fixed abrasive grains. For these reasons, the polishing tool exhibits sufficient processing efficiency.

[0016] Preferably, each aggregate contains at least one of copper and tin as a main component. This is because copper and tin have excellent ductility, and the aggregates are likely to be entangled with each other while forming pores therebetween by caulking.

[0017] The aggregates may be spherical or granular produced by gas atomization or water atomization, but preferably are at least one of dendritic and flaky shapes. When the aggregates are at least one of dendritic and flaky shapes, the specific surface area of each aggregate is increased, and the aggregates are easily deformed to become entangled with each other.

[0018] The aggregate has a specific surface area of 350 cm 2 / g or more is preferable. In this case, it is easy to form a holding portion that is entangled with each other while forming pores between the aggregates without bonding or joining them to each other. Such dendritic aggregates can be produced by electrolyzing a solution containing metal ions. Flaky aggregates can be produced by a mechanical crushing method in which raw material powder is flattened by a stamp mill.

[0019] Each pore may be impregnated with resin. The resin used to impregnate each pore should be a low-viscosity liquid in order to penetrate into the fine particles, and epoxy, phenol, vinyl acetate, melamine, urea, etc., can be used. All pores may be impregnated with resin, or only some pores may be impregnated with resin, leaving pores without resin in the holding area. As a result, the abrasive layer can exhibit appropriate holding force, retraction, and surface changeability of the fixed abrasive grains due to the elastic deformation of the holding area.

[0020] (Test 1) Examples 1 to 3, comparative examples 1 to 4, and reference examples embodying the present invention will be described below with reference to the drawings.

[0021] <Preparation process> First, we prepared the following: countless fixed abrasive grains, countless metallic aggregates, resin, spherical metal powder, glass frit, and free abrasive grains. Fixed abrasive grain: Diamond (SD5000 (D50: 5μm)) Aggregate: Dendritic powder made of Cu (Specific surface area: 450-5000 cm²) 2 Spherical powder consisting of ( / g), Sn (specific surface area: 350-1000 cm²) 2 / g) Resin: Epoxy or phenolic Metal powders: Spherical powders made of Cu, Spherical powders made of Sn Glass frit: A composition consisting of silica, alumina, calcium oxide, soda oxide, and potassium oxide. Free abrasive particles: Al2O3 (average particle size: 0.5, 2, 3, 5, 10 μm)

[0022] Figure 1 shows a 2000x magnification micrograph of a dendritic powder made of Cu.

[0023] [Table 1]

[0024] (Example 1) As shown in Table 1, 66% by mass of resin and 34% by mass of spherical powder made of Cu are placed in a container, and fixed abrasive grains are added and mixed so that the concentration of the polishing layer is 75 (fixed abrasive grain content is 18.75% by volume), and then molded at a unit pressure of 200 kg / cm². 2 The material was cured at 180°C to form the polishing layer 10 of Example 1. The polishing layer 10 was then fixed to the upper surface of the plate body 15a to form the lapping plate 15.

[0025] (Example 2) As shown in Table 1, 70% by mass of spherical powder made of Cu and 30% by mass of spherical powder made of Sn were placed in a container, and fixed abrasive grains were added and mixed so that the concentration in the abrasive layer was 75 (fixed abrasive grain content was 18.75% by volume). The mixture was then sintered in a mold at 500°C and 200 kg / cm². 2 Sintering was performed to form the polishing layer 10 of Example 2. The polishing layer 10 was then fixed to the upper surface of the plate body 15a to form the lapping plate 15.

[0026] (Example 3 and Reference Example) <Mixed molding process> As shown in Table 1, 70% by mass of dendritic powder made of Cu and 30% by mass of spherical powder made of Sn were placed in a container, and fixed abrasive grains were added and mixed to achieve a concentration of 75 in the polishing layer. A molded body of a predetermined shape was then formed in a mold.

[0027] <Crimping process> Place the molded body into the crimping mold and apply a unit pressure of 2 tons / cm². 2 The aggregates were then pressed and crimped together. In this way, the polishing layer 10 of Example 3 and the Reference Example was formed. The polishing layer 10 was then fixed to the upper surface of the plate body 15a to form the lap plate 15.

[0028] (Comparative Example 1) As shown in Table 1, 66% by mass of resin and 34% by mass of spherical powder made of Cu were placed in a container, and fixed abrasive grains were added and mixed to achieve a concentration of 75 in the polishing layer. The polishing layer 10 of Comparative Example 1 was formed in the same manner as in Example 1. The polishing layer 10 was then fixed to the upper surface of the plate body 15a to form a lapping plate 15.

[0029] (Comparative Example 2) As shown in Table 1, 70% by mass of spherical powder made of Cu and 30% by mass of spherical powder made of Sn were placed in a container, and fixed abrasive grains were added and mixed to achieve a concentration of 75 in the polishing layer. The polishing layer 10 of Comparative Example 2 was formed in the same manner as in Example 2. The polishing layer 10 was then fixed to the upper surface of the plate body 15a to form a lapping plate 15.

[0030] (Comparative Examples 3 and 4) As shown in Table 1, 100% by mass of glass frit was placed in a container, and fixed abrasive grains were added and mixed to achieve a concentration of 75 in the polishing layer. A molded body was then formed in a mold. After pre-baking the molded body, it was fired at 900°C to form the polishing layers 10 of Comparative Examples 3 and 4. These polishing layers 10 were then fixed to the upper surface of the plate body 15a to form a lapping plate 15.

[0031] Although not shown in the figures, the polishing layer 10 of Example 1 and Comparative Example 1 consists of countless fixed abrasive grains 1 and a resin-made holder 3 that holds each fixed abrasive grain 1. The holder 3 holds each fixed abrasive grain 1. In addition, the polishing layer 10 of Example 2 and Comparative Example 2 has a holder 3 made of high-strength sintered metal. Furthermore, the polishing layer 10 of Comparative Examples 3 and 4 has a holder 3 made of porous glass (vitrified). The surface of each polishing layer 10 is ground to expose the fixed abrasive grains 1, forming a polished surface 10a.

[0032] As shown in Figure 2, the polishing layer 10 of Example 3 and the Reference Example consists of countless aggregates 5 whose holding parts 3 are made of metal. Each aggregate 5 is intertwined with one another, forming pores 7 between them without being bonded or joined together. The surface of the polishing layer 10 of Example 3 and the Reference Example is also ground to expose the fixed abrasive grains 1, thereby forming a polished surface 10a.

[0033] A single-sided lapping machine was prepared. As shown in Figure 3, this single-sided lapping machine comprises a base plate 11 and a carrier 13. The base plate 11 has a fixed surface 11a extending in a direction perpendicular to the first axis O1, and is rotated around the first axis O1 by a drive device 11b. A lapping plate 15, which serves as a polishing tool, is attached to the fixed surface 11a of the base plate 11. The lapping plate 15 consists of a plate body 15a and a polishing layer 10 fixed to the upper surface of the plate body 15a. The surface of the polishing layer 10 is the polishing surface 10a.

[0034] A workpiece W, whose lower surface is the surface to be polished Wa, is fixed to the carrier 13. The carrier 13 is designed to rotate the surface to be polished Wa around a second axis O2 parallel to the first axis O1 as the surface plate 11 rotates. The carrier 13 is also designed to apply pressure to the polishing surface 10a of the polishing layer 10 by a pressurizing device 17. A lapping liquid supply device 19 is provided between the polishing surface 10a and the surface to be polished Wa to supply lapping liquid 19a.

[0035] The back surfaces of the lap plates 15 having the polishing layer 10 of Examples 1-3, Comparative Examples 1-4, and Reference Example were attached to the fixed surface 11a of the surface plate 11.

[0036] Furthermore, in Examples 1-3 and Comparative Example 4, as shown in Table 1, lapping solution 19a was used which contained free abrasive particles made of Al2O3 with an average particle size of 3 μm (60% of the average particle size of the fixed abrasive particles) in a water-soluble solution.

[0037] Then, a processing test was conducted under the following conditions to evaluate the amount of material removed from the workpiece W (μm) and the surface roughness Ra (μm) of the workpiece W. The results are shown in Table 2.

[0038] <Processing conditions> Wrap plate dimensions: Outer diameter 240 x Width 20 (mm) Workpiece: SiC wafer (20 x 20 mm) Processing conditions: Rotation speed 200 rpm, unit pressure 200 gr / cm 2 Workpiece rotation conditions: accompanying rotation Lapping liquid: 100cc / min Processing time: 60 minutes

[0039] [Table 2]

[0040] In the lapping methods of Examples 1 to 3, the holding part 3 that holds the fixed diamond abrasive grains 1 is made of metal or resin, and the lapping liquid 19a consisting of Al2O3 free abrasive grains is used. As a result, the replacement of the polishing layer 10 is accelerated, enabling high-precision continuous machining.

[0041] Furthermore, these lapping methods result in a low surface roughness of the workpiece W. In addition, these lapping methods place a low load on the fixed abrasive grains 1, making it less likely for cracks or other damage to occur in the fixed abrasive grains 1. As a result, the lapping plate 15 exhibits sufficient processing efficiency.

[0042] Upon closer examination, the results from Comparative Example 1 and Example 1, and from Comparative Example 2 and Example 2, show that the amount of workpiece W removed by a matrix-type retaining part 3, such as resin or metal, is significantly improved by 1.5 times with the addition of Al2O3, which is a free abrasive particle. This is thought to be because the Al2O3 free abrasive particle effectively retracts the retaining part 3 through a lapping action, promoting surface replacement and thus improving and maintaining cutting performance.

[0043] Furthermore, the results from Comparative Examples 3 and 4 show that when the holding part 3 is vitrified, the surface roughness of the workpiece W is greater compared to matrix-type holding parts 3 made of metal or resin. In particular, as in Comparative Example 4, when free abrasive grains of Al2O3 are added, the surface roughness is even greater than in Comparative Example 3. This is thought to be because when the holding part 3 is vitrified, the protrusion of the fixed abrasive grains 1 tends to be higher, and because the bridges are thin, the Al2O3 breaks the bridges, causing the fixed abrasive grains 1 to fall off and making them more likely to attack the polished surface Wa of the workpiece W.

[0044] Furthermore, the results from Example 3 show that when the holding part 3 is crimped, the amount of workpiece W removed is significantly larger, and the processing efficiency is improved.

[0045] (Exam 2) In the SiC wafer lapping method of Example 3, a resin (epoxy-based) was prepared, and after the crimping process, an impregnation process was performed in which the resin was impregnated into each pore 7. As shown in Figure 4, the polishing layer 20 obtained in Example 4 had resin impregnated into all pores 7. In these polishing layers 20, the holding portion 3 underwent elastic deformation, exhibiting appropriate holding force, retractability, and surface changeability of the fixed abrasive grains 1.

[0046] Although the present invention has been described above in reference to Examples 1 to 4, it goes without saying that the present invention is not limited to Examples 1 to 4, and can be applied with appropriate modifications without departing from its spirit.

[0047] For example, in the above embodiments 1 to 4, the polishing layers 10 and 20 were attached to the base plate 11 of a single-sided lapping machine to polish the mating material, but the present invention is also applicable when attached to the base plate of a double-sided lapping machine to polish the mating material.

[0048] Furthermore, although dendritic aggregate was used as aggregate 5 in the above-mentioned Examples 3 and 4, it is possible to obtain the same effects as dendritic aggregate by using spherical, flake, or linear aggregate. [Industrial applicability]

[0049] This invention can be used in a lapping machine. [Explanation of Symbols]

[0050] 10, 20... Polishing layer, lapping plate (polishing tool) 1… Fixed abrasive grains 3...Holding part 5…Aggregates 7… Stomata 19a... Lapping liquid 9… Resin

Claims

1. In a method for lapping a SiC wafer, in which the SiC wafer is lapped by the polishing layer of a polishing tool in the presence of a lapping solution, The abrasive layer consists of fixed abrasive grains and a holding portion that holds the fixed abrasive grains. The holding portion is made of at least one of metal and resin. The lapping liquid contains free abrasive particles, which are Al 2 O 3 A method for wrapping a SiC wafer, characterized by comprising the following.

2. The aforementioned holding part has countless metal aggregates, The method for wrapping a SiC wafer according to claim 1, wherein each of the aggregates is intertwined with each other while forming pores between them without being bonded or joined together, by pressurizing the molded body and crimping each of the aggregates together without sintering or firing each of the aggregates.

3. The method for wrapping a SiC wafer according to claim 2, wherein the resin is impregnated into each of the pores.

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