Abrasive stone for compound semiconductor wafer

Abstract

Provided is an abrasive stone for a compound semiconductor wafer, the abrasive stone comprising a super abrasive grain layer with pores, the layer comprising: diamond abrasive grains with an average particle diameter of 0.10-20.00 μm; and a vitrified bond. The pores in the super abrasive grain layer contain voids with a diameter of 40.00 μm or less as measured by mercury intrusion porosimetry. The D50 of the voids is greater than the average particle diameter of the diamond abrasive grains.

Description

Compound semiconductor wafer grinding wheels

[0001] The present disclosure relates to a grinding wheel for compound semiconductor wafers. This application claims priority to Japanese Patent Application No. 2024-128809, filed on August 5, 2024. The entire contents of said Japanese Patent Application are incorporated herein by reference.

[0002] Conventionally, grinding wheels for compound semiconductor wafers and vitrified bond grinding wheels are disclosed in, for example, Japanese Patent Laid-Open No. 2012-200831 (Patent Document 1), Japanese Patent Laid-Open No. 8-57768 (Patent Document 2), and Japanese Patent Laid-Open No. 2003-136410 (Patent Document 3).

[0003] JP 2012-200831 A JP 8-57768 A JP 2003-136410 A

[0004] The grinding wheel for compound semiconductor wafers disclosed herein comprises diamond abrasive grains having an average grain size of 0.10 μm or more and 20.00 μm or less, and a vitrified bond, and has a superabrasive grain layer in which pores are formed, the superabrasive grain layer containing pores with a pore size of 40.00 μm or less as measured by mercury intrusion porosimetry, and the diameter D50 of the pores is larger than the average grain size of the diamond abrasive grains.

[0005] Fig. 1 is a perspective view of a grinding wheel 20 for compound semiconductor wafers having a superabrasive layer 6 fixed to a base metal 120. Fig. 2 is a bottom view of the grinding wheel 20 for compound semiconductor wafers shown in Fig. 1. Fig. 3 is a diagram of the superabrasive layer 6 having a vitrified bond 2 and diamond abrasive grains 3, and having pores 8 formed therein. Fig. 4 is a diagram of the superabrasive layer 6 having a vitrified bond 2, diamond abrasive grains 3, and filler 4, and having pores 8 formed therein. Fig. 5 is a perspective view showing the grinding surface 61 of the superabrasive layer 6 provided on the base metal 120 in the grinding wheel 20 for compound semiconductor wafers. Fig. 6 is a schematic diagram showing large pores 80 formed on the grinding surface 61 of the superabrasive layer 6.

[0006] [Problem to be Solved by the Present Disclosure] Conventional grinding stones for compound semiconductor wafers have had the problem of being prone to clogging.

[0007] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described.

[0008] Patent Document 1 discloses the pore structure of a grinding tool for semiconductor wafers, and discloses a technique for improving grinding load and sharpness.

[0009] Conventional grinding wheels cannot meet the required grinding performance (sharpness, low grinding load, low wear). The reason for this is that in recent years, the crystallinity of compound semiconductors has improved and wafers have become larger in diameter, making them more difficult to grind. Furthermore, the grinding load and processing temperature have increased, making it impossible for conventional grinding wheels to meet these requirements.

[0010] The compound semiconductor wafer grinding wheel 20 according to the present disclosure includes diamond abrasive grains having an average grain size of 0.10 μm to 20.00 μm, a vitrified bond, and a pore-formed superabrasive layer. The superabrasive layer contains pores having a diameter of 40.00 μm or less as measured by mercury intrusion porosimetry, and the diameter D50 of the pores is larger than the average grain size of the diamond abrasive grains.

[0011] In a compound semiconductor wafer grinding wheel constructed in this way, the pores have a diameter equal to or larger than the diamond abrasive grain size, allowing contaminants (chips, detached abrasive grains, and aggregates of glass binder) to be expelled into the wheel through these pores, enabling stable processing to continue without clogging the grinding surface.Finner pores would clog, making it impossible to continue processing.

[0012] Preferably, the superabrasive layer further comprises a filler, and the diameter D50 of the pores is larger than the average particle size of the diamond abrasive grains and the average particle size of the filler, thereby further preventing clogging of the grinding surface during processing.

[0013] Preferably, the average particle size of the filler is 0.5 to 1.5 times the average particle size of the diamond abrasive grains. This range is the preferred average particle size range of the filler. If the average particle size of the filler is within this range, the diameters of the diamond abrasive grains, the filler, and the pores are well balanced, and the grinding performance is further improved.

[0014] Preferably, the ratio of the diameter D50 of the pores to the diameter D1, which is the larger of the average diameter of the diamond abrasive grains or the average diameter of the filler, is greater than 1.0 and not more than 2.5. This range is preferable in order to maintain high contaminant discharge performance and high strength of the superabrasive grain layer.

[0015] Preferably, in the superabrasive layer, the volume of the pores measured by mercury intrusion porosimetry is 45% by volume or more and 70% by volume or less with respect to the apparent volume of the superabrasive layer. ３ / g) / apparent volume of superabrasive layer (cm ３ It is preferable that the pore content, expressed as ρ / g), is 45% by volume or more and 70% by volume or less. This range is preferable in order to maintain high contaminant removal performance and high strength of the superabrasive layer. More preferably, the pore content is 50% by volume or more and 60% by volume or less. This prevents clogging of the grinding surface during processing, while providing the superabrasive layer with appropriate strength and improving wear resistance.

[0016] Preferably, the large pores having an opening diameter of 50 μm or more are formed on the grinding surface of the superabrasive layer. By forming the large pores, it becomes possible to further improve the contaminant discharge performance. There may be one or more large pores.

[0017] Preferably, the total opening area of ​​the large pores in the grinding surface is 5% to 20%. Within this range, both the contaminant removal performance and the high strength of the superabrasive layer can be achieved at a high level.

[0018] Preferably, the softening point of the vitrified bond is 500° C. to 900° C. If the softening point is within the above range, thermal damage to the diamond abrasive grains during the grinding wheel manufacturing process can be suppressed.

[0019] Preferably, hBN, MoS in the superabrasive layer ２ The total content of graphite and graphite is less than 0.2% by volume. When compound semiconductor wafers are ground, the above substances can become impurities, so it is preferable that the content is low.

[0020] The present disclosure will be described below. Fig. 1 is a perspective view of a grinding wheel 20 for compound semiconductor wafers having a superabrasive layer 6 fixed to a base metal 120. Fig. 2 is a bottom view of the grinding wheel 20 for compound semiconductor wafers shown in Fig. 1. As shown in Figs. 1 and 2, the grinding wheel 20 for compound semiconductor wafers of the present disclosure comprises a ring-shaped base metal 120 and a superabrasive layer 6 attached to the base metal 120. In this example, a so-called segment-type superabrasive layer 6 is provided on the base metal 120. Holes 122 are formed in the base metal 120.

[0021] 3 is a diagram of a superabrasive layer 6 having a vitrified bond 2 and diamond abrasive grains 3 and having pores 8. As shown in FIG. 3, the superabrasive layer 6 includes at least diamond abrasive grains 3, a vitrified bond 2 as a glass binder, and pores 8.

[0022] 4 is a diagram of a superabrasive layer 6 having a vitrified bond 2, diamond abrasive grains 3, and filler 4, and having pores 8. Furthermore, as shown in FIG. 4, the superabrasive layer 6 can also contain filler 4.

[0023] In the present disclosure, the volume ratios of the diamond abrasive grains 3, filler 4, vitrified bond 2, and pores 8 are not particularly limited and can be changed as appropriate to suit the needs of those skilled in the art. For example, the diamond abrasive grains 3 can be 30 volume%, the vitrified bond 2 can be 10 volume%, and the pores 8 can be 60 volume%. In addition, in the case of an embodiment including the filler 4, the diamond abrasive grains 3 can be 15 volume%, the filler 4 can be 15 volume%, the vitrified bond 2 can be 10 volume%, and the pores 8 can be 60 volume%. The ranges of possible volume ratios are 2.5 to 30 volume% of diamond abrasive grains, 0 to 27.5 volume% of filler, 5 to 20 volume% of vitrified bond, and 30 to 80 volume% of pores.

[0024] The type of diamond abrasive grains 3 is not particularly limited, but a preferred average particle size range is 0.10 μm or more and 20.00 μm or less. If the average particle size exceeds 20.00 μm, the surface roughness of the ground compound semiconductor wafer will deteriorate. More preferably, it is 0.10 μm or more and 2.00 μm or less. By using diamond abrasive grains 3 in this range, the compound semiconductor wafer can be ground even more smoothly when ground using the compound semiconductor wafer grinding wheel 20.

[0025] This disclosure does not particularly limit the method for measuring the average particle size of the diamond abrasive grains 3 and the filler 4 described below. For example, in an abrasive grain layer that does not contain the filler 4 described below, diamond abrasive grains 3 can be collected from the superabrasive grain layer 6 using a mixed acid by a diamond powder dissolution extraction method, and then measured using a laser diffraction or centrifugal particle size distribution analyzer. Furthermore, in an abrasive grain layer that contains filler 4, the cross section of the superabrasive grain layer 6 can be sampled using ion beam processing, and the Ferret diameter can be measured for the color gamut corresponding to the diamond abrasive grains or filler from the cross-sectional image observed using an electron microscope. The observation magnification is not particularly limited, but a magnification that is too low compared to the particle size is undesirable because it naturally makes it difficult to distinguish the particles. For example, for particles with a particle diameter of 2.00 μm, it is recommended to select an appropriate range from 3,000 to 10,000 times. It is desirable to use at least 50 samples or more to calculate the average particle size. In any case, methods easy for those skilled in the art can be used.

[0026] The vitrified bond 2 preferably has a softening point in a temperature range that does not excessively burn the diamond abrasive grains 3 in the manufacturing process described below. That is, the vitrified bond 2 preferably has a softening point of 500°C or higher and 900°C or lower. The preferred composition of the vitrified bond 2 is not particularly limited, but an example is SiO ２ :30 to 50% by mass, Al ２ O ３ :2 to 10% by mass, B ２ O ３ : 40-60% by mass, RO: 1-10% by mass, R ２O: 2 to 5 mass % (wherein RO represents alkaline earth metal oxide and RO represents alkali metal oxide) can be contained, which can suppress deterioration of grinding performance due to burnout of diamond abrasive grains.

[0027] The pores 8 are formed for various reasons during the manufacturing process described below. They are formed from unfilled voids during powder compaction, traces of binder leaching during firing, and pore-forming materials (volatile resins, hollow particles, etc.) having a desired diameter. In this disclosure, the pores 8 include pores with a pore diameter of 40.00 μm or less. More specifically, among the pore diameters and pore volumes measured by mercury porosimetry (JIS R1655:2003), the diameters and volumes of pores 8 with a pore diameter of 40.00 μm or less are considered to be the pore diameter and pore volume, and pores 8 with a pore diameter of more than 40.00 μm are considered to be normal pores 8 and are distinguished from pores.

[0028] The present disclosure does not particularly limit the type of filler 4. Generally available hexagonal boron nitride, alumina, silica, SiC, soft minerals, etc. can be applied within the scope of obvious application to those skilled in the art.

[0029] FIG. 5 is a perspective view showing the grinding surface 61 of the superabrasive layer 6 provided on the base metal 120 of the grinding wheel 20 for compound semiconductor wafers. FIG. 6 is a schematic diagram showing large pores 80 provided on the grinding surface 61 of the superabrasive layer 6. The pores 8 can include large pores 80 with an opening diameter of 50 μm or more on the grinding surface 61 of the superabrasive layer 6. The grinding surface 61 is imaged with an optical microscope, and the circle-equivalent diameter of each large pore 80 is taken as the opening diameter of the large pore 80. Pores 8 with an opening diameter of less than 50 μm are not included in the large pores 80. Forming large pores 80 can enhance the contamination removal ability of the superabrasive layer 6. A superabrasive layer 6 that does not include the above-mentioned small pores would result in unstable processing and would not achieve the effects of the present disclosure.

[0030] The present disclosure does not limit the method for forming large pores, and any method suitable for grinding wheel manufacturing methods used by those skilled in the art can be employed. Examples include adding a foaming agent during raw material mixing and foaming during firing to form large pores, or adding phenolic resin beads and decomposing the resin during firing to form large pores. The size of the large pores is controlled by the diameter of the foaming agent or resin beads added. Even with the same pore diameter, the opening area varies depending on the position where the pores are exposed (the area and radius of the cut surface vary depending on the cutting position of the sphere). Therefore, to obtain a stable opening area, it is desirable to use a pore diameter that matches the area of ​​the working surface of the abrasive layer and the volume fraction of the large pores. For example, when forming a small number of large pores in a small-area abrasive layer, applying an excessively large pore diameter is undesirable because it results in large variations in the opening area of ​​the working surface of the abrasive layer. A suitable example is a pore diameter of 100 cm2. ２ When the volume fraction of large pores is 5% by volume, the diameter of the beads to be applied should be 250 μm or less.

[0031] The compound semiconductor wafer grinding wheel 20 of the present disclosure was created to grind compound semiconductor wafers, such as SiC and GaN, to a smooth surface, ensuring stable, long-term grinding even for recent wafers that have improved crystallinity and larger diameters. Compound semiconductor wafers are known to be harder and more difficult to cut than conventional silicon semiconductors. High-hardness grinding wheels are often used to process these wafers. While grinding wheels with dense structures are often used, the increasing difficulty of grinding wafers in recent years has led to new challenges, such as unstable grinding processes.

[0032] The grinding surface 61 (Figure 5) of the grinding wheel after unstable processing was analyzed in detail. As a result, it was discovered that a large amount of contaminants (agglomerates consisting of diamond abrasive grains 3 detached from the superabrasive layer 6, vitrified bond 2, filler 4, and wafer chips) adhered, resulting in significant clogging. With wafers that are difficult to cut, the processing temperature and load increase, causing the low-softening vitrified bond 2 to become entrapped and forming strong contaminants. On the other hand, with densified grinding wheels, the contaminant evacuation path is narrow, so processing instability due to clogging becomes increasingly pronounced. Based on these analyses, the inventors came up with the following technical idea to ensure a contaminant evacuation path.

[0033] That is, in the present disclosure, in a superabrasive layer 6 including at least diamond abrasive grains 3, a vitrified bond 2, and pores 8, pores having a pore diameter of 40.00 μm or less as measured by mercury porosimetry (JIS R1655:2003) are contained, and the volume-based median of the pore diameter (pore diameter D50) is larger than the average particle diameter of the diamond abrasive grains 3. In another embodiment of the present disclosure, in a superabrasive layer 6 further including a filler 4, the pore diameter D50 is larger than the average particle diameter of the diamond abrasive grains 3 and the average particle diameter of the filler 4. By making the pore diameter D50 a predetermined size or larger, a contaminant discharge path is secured, and stable grinding can be continued without clogging.

[0034] If the pore diameter D50 becomes too large relative to the average particle diameters of the diamond abrasive grains 3 and the filler 4, the hardness and strength of the compound semiconductor wafer grinding wheel 20 will decrease, undesirably deteriorating the wear resistance. A suitable pore diameter D50 is a ratio of the larger of the average particle diameter of the diamond abrasive grains 3 and the average particle diameter of the filler 4 that is greater than 1.0 and not greater than 2.5. More preferably, the ratio is 1.5 or greater and not greater than 2.5.

[0035] Furthermore, the pore content of the superabrasive layer 6 according to the present disclosure is preferably in the range of 45% by volume or more and 70% by volume or less relative to the apparent volume of the superabrasive layer 6. If it is less than 45% by volume, contaminant discharge is insufficient, making the grinding process unstable. If it exceeds 70% by volume, the strength of the superabrasive layer 6 is insufficient, making it prone to reduced wear resistance. A more desirable pore content is 50% by volume or more and 60% by volume or less.

[0036] The pore content and pore diameter D50 can be adjusted in the grindstone manufacturing process described next.

[0037] The grinding wheel manufacturing process consists of raw material mixing, dry granulation, powder compaction, air firing, and adjustment processing. In raw material mixing, the necessary raw materials are procured and mixed uniformly using known methods to obtain a mixed powder. The raw materials include diamond powder, glass frit powder, and optionally filler powder, resin beads as pore-forming materials, and wax as a molding aid. Glass frit powder is glass powder made by crushing glass to an appropriate size.

[0038] These raw materials are mixed, for example, in a wet ball mill, and the mixed slurry is recovered. Here, by changing the particle size and amount of the glass frit powder and pore-forming material, the pore diameter D50 and the amount of pores in the subsequent superabrasive layer can be adjusted. That is, by increasing the average particle size of the glass frit powder and pore-forming material, the pore diameter D50 can be enlarged, and by increasing the amount of these added, the amount of pores can be increased. Furthermore, multiple glass frit powders adjusted to different average particle sizes can be prepared in advance and mixed to control the particle size distribution of the glass frit powder. For example, when using diamond abrasive grains 3 with an average particle size of 0.80 μm, glass frit powders with median particle sizes of 1.6 μm and 4.0 μm can be prepared and mixed in a 3:1 ratio. In addition, commercially available glass frit is often in the form of coarse flakes of about several hundred μm. In such cases, it is preferable to pre-pulverize the glass frit to a size equivalent to that of diamond. The pulverization method is not particularly limited, but as an example, glass frit with an average particle size of 150 μm can be pulverized to an average particle size of 4 μm by using a wet ball mill with zirconia balls with a ball diameter of 3 mm as pulverization media for 72 hours.

[0039] In addition, in the compound semiconductor wafer grinding wheel 20 that uses diamond abrasive grains 3 (or filler 4) with relatively coarse grains (grain size exceeding 20.00 μm), the pore size can be controlled only by the pore-forming material. On the other hand, in the compound semiconductor wafer grinding wheel 20 that uses fine diamond abrasive grains 3 (or filler 4), the particle size required for the pore-forming material also becomes fine, and it tends to be difficult to control the pore size due to aggregation, etc., so the pore size can be controlled by the particle size of the glass frit powder. The particle size of the fine diamond abrasive grains 3 is, for example, 20.00 μm or less, and may be 10.00 μm or less, 6.00 μm or less, 2.00 μm or less, or 0.60 μm or less.

[0040] In dry granulation, the mixed slurry is dried and granulated to obtain granules having a diameter of approximately several tens to several hundreds of micrometers. Known drying and granulation techniques can be used here as well. For example, freeze-drying or spray granulation can be used. When manufacturing a superabrasive layer 6 containing large pores 80, large-diameter beads for forming the large pores 80 can be mixed into the granules. If large-diameter beads are mixed in a stage prior to the granulation, they are likely to be deformed and crushed by the energy generated during mixing, or to separate from the other raw material powders. However, by mixing large-diameter beads into the granules, the size of the large pores 8 can be reliably controlled.

[0041] In powder compaction, granules are filled into a mold having a desired shape and compacted under a predetermined pressure to obtain a green compact. Cold pressing and hot pressing can be used as the compaction method. Depending on the circumstances of the skilled artisan, a procedure may be adopted in which a highly viscous slurry is extruded to form a wet green compact, which is then dried to obtain the green compact.

[0042] In air sintering, the compact is placed in a known heating furnace and solidified under an atmospheric temperature regime using a predetermined heating program to obtain a sintered body. During sintering, the pore-forming material volatilizes and disappears, turning into pores, and the glass frit powder seeps into the spaces between the diamond abrasive grains 3 and the filler 4 to form glass bridges. The gaps where the glass has dissolved also form as pores 8. At this time, the pore diameter D50 can be controlled by controlling the sintering atmosphere. Specifically, by setting the sintering conditions to a low temperature and a short time, excessive wetting and spreading of the glass can be suppressed, increasing the pore diameter D50 and pore volume.

[0043] In the conditioning process, the sintered surface of the sintered body is removed, and the sintered body is attached to a predetermined position on a separately prepared base metal. The inner and outer peripheral surfaces and the surface of the sintered body (the surface that forms the grinding surface in FIG. 5) are then finished with a truing stone of a predetermined grain size, thereby producing the superabrasive grain layer and grinding stone according to the present disclosure.

[0044] [Details of the embodiment of the present disclosure] The grinding performance of the grinding wheel of the present disclosure was evaluated by the following procedure.

[0045]

[0046]

[0047]

[0048]

[0049]

[0050] The "diameter ratio" in Table 5 is the value of "average particle diameter of filler / average particle diameter of diamond abrasive grains."

[0051]

[0052]

[0053]

[0054]

[0055] First, diamond abrasive grains and fillers having the average particle sizes listed in Tables 1 to 9 were prepared. Alumina was used as the filler. Resin beads with an average diameter of 1.00 to 5.00 μm were prepared as pore-forming materials. As the glass frit constituting the vitrified bond, glass frit with a softening temperature of 850°C was prepared for grinding wheels with diamond abrasive grain diameters of 6.00 μm or more, and glass frit with a softening temperature of 700°C was prepared for grinding wheels with diamond abrasive grain diameters of 2.00 μm or less. The glass frit had a particle size of approximately 150 μm. The glass frit was pre-pulverized into a fine powder using a ball mill and a bead mill to obtain an average particle size similar to that of each diamond grain and filler grain.

[0056] These raw material powders and wax as a molding aid were placed in a pot and mixed for 72 hours in a wet ball mill using zirconia balls. For sample numbers 1-1 to 1-10, 2-1 to 2-22, and 7-1 to 7-10, the volume ratio of glass frit to diamond abrasive grains was 5 (diamond abrasive grains): 1 (glass frit). For sample numbers 3-1 to 3-6, 4-1 to 4-10, 5-1 to 5-10, and 6-1 to 6-10, which contained filler, the ratio was 3 (diamond abrasive grains): 2 (filler): 1 (frit). After mixing the diamond abrasive grains and glass frit powder and filler, the slurry composed of these mixtures (diamond, frit, filler, 1.0 to 5.0 μm pore-forming material, molding aid, solvent used for mixing (ethanol, etc.)) was collected and dried in a hot water bath to obtain a dried product, which was then sized and sieved using a sieve with a predetermined opening to obtain granules. Furthermore, in the samples 7-1 to 7-10 in which large pores 80 were formed, resin beads for large pores (average particle size 150 μm) were added to the granules, and the mixture was simply mixed using a shaker.

[0057] The granules were filled into a mold and subjected to a temperature of 150°C and a surface pressure of 0.2 ton / cm. ２ The mixture was subjected to warm compression molding (hot pressing) at 100°C to obtain a green compact.

[0058] The green compact was placed in an atmospheric furnace and held at a maximum temperature of 650 to 950°C for 2 hours, after which the furnace was cooled to obtain a sintered body.

[0059] The sintered body was attached to an aluminum base metal with a wheel diameter of 200 mm, and the inner, outer periphery, and surface were machined with a WA grindstone with a grit size of #240. In this way, grindstones 20 for compound semiconductor wafers having superabrasive grain layers 6 corresponding to sample numbers 1-1 to 7-10 in the table were produced.

[0060] The pore size and pore content of the superabrasive grain layers of these sample numbers were measured by mercury intrusion porosimetry. It was confirmed that the pore content was in the range of 45 to 50% for all samples except for sample numbers 6-1 to 6-10, in which the pore content was varied.

[0061] The grinding wheels in Tables 1 to 9 were subjected to grinding under the following conditions. The grinding machine was a Tokyo Seimitsu HRG300, and the workpiece was a commonly available 6-inch single crystal SiC wafer (dummy grade 4H-N). The processing conditions were: for grinding wheels with a diamond abrasive grain size of 6.00 μm or more, the spindle rotation speed was 1750 rpm, the table rotation speed was 300 rpm, the wheel feed rate was 0.6 μm / s, and the processing thickness was 25 μm. For grinding wheels with a diamond grain size of 2.00 μm or less, the spindle rotation speed was 1750 rpm, the table rotation speed was 300 rpm, the wheel feed rate was 0.3 μm / s, and the processing thickness was 10 μm.

[0062] In the evaluation, the wear rate (change in height of the superabrasive layer 6 before and after wear / change in thickness of the ground portion of the workpiece (wafer) before and after grinding) was measured on both the Si and C faces of the SiC wafer, i.e., the amount of thickness retreat of the superabrasive layer relative to the amount of wafer thickness processed, the maximum current value (spindle current value), and the grinding load (spindle load), and the average values ​​were calculated. Depending on the grinding wheel and processing conditions, the spindle current value was overloaded, making processing impossible, and there were also results in which only the spindle Z position dropped even though the wafer thickness did not decrease (i.e., only the grinding wheel side was worn). In each table, results are listed as "OVER" for current overload and "ABORT" for wear only on the grinding wheel side.

[0063] In the "clogging" column, "A" indicates that no clogging occurred on the grinding surface 61 of the superabrasive layer 6 from the start to the end of processing. "B" indicates that clogging occurred in a portion of the grinding surface 61 of the superabrasive layer 6. "C" indicates that clogging occurred in most of the grinding surface 61 of the superabrasive layer 6.

[0064] It was confirmed that samples in which the pore diameter D50 was smaller than the particle diameter of the diamond abrasive grains were rated B or C in terms of clogging.

[0065] The following can be seen from each table regarding vitrified bond superabrasive wheels used as grinding wheels for compound semiconductor wafers. In Tables 2 and 3, sample numbers 2-1, 2-2, 2-12, and 2-13, in which the average particle size of the diamond abrasive grains exceeds 20.00 μm, do not experience clogging problems due to the large average particle size of the diamond abrasive grains. In contrast, for sample numbers 2-3 to 2-11 and sample numbers 2-14 to 2-22, in which the average particle size of the diamond abrasive grains is 20.00 μm or less, the clogging evaluation is worse for sample numbers 2-14 to 2-22, in which the pore diameter is smaller than the average particle size of the diamond abrasive grains, compared to sample numbers 2-3 to 2-11, in which the pore diameter is larger than the average particle size of the diamond abrasive grains. Even if the average particle size of the diamond abrasive grains is 20.00 μm or less, clogging can be prevented if the pore diameter is larger than the diamond particle size, as shown in sample numbers 2-3 to 2-11. In Samples 2-1 and 2-2, the average particle size of the diamond abrasive grains was large, so the roughness of the ground surface after grinding deteriorated.

[0066] From Table 4, it can be seen that the grinding stone for compound semiconductor wafers may contain a filler.

[0067] From Table 5, it can be seen that more favorable results can be obtained in the evaluation of the wear rate and grinding load when the value of the average particle diameter of the filler / the average particle diameter of the diamond abrasive grains is 0.5 times or more and 1.5 times or less. More specifically, it can be seen that favorable results are obtained in terms of achieving both the wear rate and the grinding load in sample numbers 4-2 to 4-4 and 4-7 to 4-8, where the diameter ratio, which is the value of the average particle diameter of the filler / the average particle diameter of the diamond abrasive grains, is 0.5 times or more and 1.5 times or less.

[0068] Table 6 shows that the balance between the wear rate and the grinding load is improved in sample numbers 5-5 (pore diameter D50 / filler average particle diameter = 0.99 / 0.57 = 1.7) to 5-10 (pore diameter D50 / filler average particle diameter = 1.81 / 0.57 = 3.2). In other words, when a filler is included, more preferable results are obtained when the value of pore diameter D50 / filler average particle diameter is 1.7 or more and 3.2 or less.

[0069] The "apparent volume of the superabrasive layer" in Table 7 is a value expressed as the volume / mass of the superabrasive layer. A predetermined rectangular parallelepiped is cut out from the superabrasive layer, and the product of its length, width, and height is calculated. The "apparent volume of the superabrasive layer" is calculated by dividing this product by the mass of the rectangular parallelepiped. Tables 7 and 8 show that sample numbers 6-3 to 6-9, which have a pore content (pore volume / apparent volume of the superabrasive layer) of 45% by volume or more and 70% by volume or less, provide more favorable results in the evaluation of the wear rate and grinding load. More preferably, sample numbers 6-5 to 6-7, which have a pore content of 55% by volume or more and 60% by volume or less, are superior in that they can achieve both a good wear rate and a good grinding load.

[0070] The "large pore area ratio" in Table 9 is expressed as (total opening area of ​​large pores / area of ​​grinding surface). Regarding the measurement of large pores with an opening diameter of 50 μm or more on the grinding surface, the grinding surface is observed, and those with a maximum opening diameter of 50 μm or more are recognized as large pores. The sum of the areas of all large pores in a field of view containing 10 or more large pores is defined as the total opening area. In a field of view containing 10 or more large pores, the ratio of the total opening area to the area of ​​the grinding surface in that field is the "large pore area ratio." It can be seen that a large pore area ratio of 5% or more and 20% or less provides more favorable results in the evaluation of the wear rate and grinding load.

[0071] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0072] 2 Vitrified bond, 3 Diamond abrasive grains, 4 Filler, 6 Superabrasive grain layer, 8 Pores, 20 Compound semiconductor wafer grinding wheel, 61 Grinding surface, 80 Large pores, 120 Base metal, 122 Pores.

Claims

1. A grinding wheel for compound semiconductor wafers, comprising diamond abrasive grains having an average grain size of 0.10 μm or more and 20.00 μm or less, a vitrified bond, and a superabrasive grain layer having pores formed therein, the pores in the superabrasive grain layer containing pores with a pore size of 40.00 μm or less as measured by mercury intrusion porosimetry, and the diameter D50 of the pores being larger than the average grain size of the diamond abrasive grains.

2. The grindstone for compound semiconductor wafers according to claim 1, wherein the superabrasive layer further comprises a filler, and the diameter D50 of the pores is larger than the average particle diameter of the diamond abrasive grains and the average particle diameter of the filler.

3. The grindstone for compound semiconductor wafers according to claim 2, wherein the average particle size of said filler is 0.5 to 1.5 times the average particle size of said diamond abrasive grains.

4. A grinding wheel for compound semiconductor wafers according to claim 2 or 3, wherein the ratio of diameter D50 of the pores to diameter D1, which is the larger of the average diameter of the diamond abrasive grains or the average diameter of the filler, is greater than 1.0 and not more than 2.

5.

5. A grinding wheel for compound semiconductor wafers according to claim 1 or 2, wherein the volume of the pores in the superabrasive layer measured by mercury intrusion porosimetry is 45% by volume or more and 70% by volume or less of the apparent volume of the superabrasive layer.

6. The grindstone for compound semiconductor wafers according to claim 1, wherein said pores include large pores, and said large pores have an opening diameter of 50 μm or more formed on the grinding surface of said superabrasive layer.

7. The grindstone for compound semiconductor wafers according to claim 6, wherein the total open area of ​​the large pores in the grinding surface is 5% or more and 20% or less.

8. The grindstone for compound semiconductor wafers according to claim 1, wherein the softening point of said vitrified bond is 500°C or higher and 900°C or lower.

9. hBN and MoS in the superabrasive layer ２ 2. The grinding wheel for compound semiconductor wafers according to claim 1, wherein the total content of graphite and graphite is less than 0.2% by volume.

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