Abrasive material ane method for manufacturing the same

Abstract

To provide an abrasive material capable of releasing internal stress remaining inside and exhibiting appropriate frangibility without requiring much energy and time and without changing a surface state depending on a temperature or an atmosphere.SOLUTION: This method for manufacturing the abrasive material acquires, in a first step, an abrasive material yet to be processed, which contains an abrasive 1 made of a first material having a first linear thermal expansion coefficient and a coat layer 3 which is made of a second material having a second linear thermal expansion coefficient larger than the first linear thermal expansion coefficient within a specific temperature range and which covers the abrasive. In a second step, the abrasive material yet to be processed is cooled to a cooling temperature of -50°C or lower to be a cooling abrasive material. The specific temperature range is from the cooling temperature to +20K.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an abrasive material and a method for making the abrasive material. [Background technology]

[0002] As disclosed in Patent Document 1, diamond abrasive grains, which are superabrasive grains, are used to process semiconductor wafers such as SiC, which are highly hard and difficult to grind and polish. Also, Non-Patent Document 1 shows that the crushing behavior of diamond abrasive grains changes depending on internal stress, and heat treatment is known as a method for controlling internal stress. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-80847 [Non-patent literature]

[0004] [Non-Patent Document 1] "Internal strain distribution and microfracture behavior of various single crystal diamonds for cutting tools," by Hitoshi Kadotani et al., Proceedings of the 2019 Japan Society for Precision Engineering Spring Meeting Academic Lectures, pp. 644-645 Summary of the Invention [Problem to be solved by the invention]

[0005] However, even diamond abrasive grains suffer from problems such as reduced machining efficiency due to wear and loss of cutting edge. For this reason, abrasive grains with adequate friability are required. Furthermore, heat treatment of abrasive grains requires a large amount of energy and time, and the surface condition of the abrasive grains may change depending on the temperature and atmosphere. Furthermore, while it is easy to introduce internal stress into abrasive grains by heat treatment, it is difficult to release the internal stress remaining within the abrasive grains.

[0006] The present invention has been made in consideration of the above-mentioned conventional situation, and aims to solve the problem of obtaining an abrasive material that does not require a large amount of energy or time, does not change the surface state due to temperature or atmosphere, is capable of releasing internal stress remaining inside, and ultimately has appropriate friability. [Means for solving the problem]

[0007] The manufacturing method of the abrasive material of the first teaching includes a first step of obtaining a raw abrasive material comprising abrasive grains made of a first material having a first linear thermal expansion coefficient and a coating layer that is made of a second material having a second linear thermal expansion coefficient greater than the first linear thermal expansion coefficient in a specific temperature range and that coats the abrasive grains; a second step of cooling the untreated abrasive to a cooling temperature of −50° C. or less to obtain a cooled abrasive; The specific temperature range is from the cooling temperature to +20K.

[0008] In the manufacturing method of the abrasive material of the first teaching, the raw abrasive material is cooled, causing the coating layer to thermally shrink, and the abrasive grains are given compressive stress due to the difference in linear thermal expansion coefficients. The cooling process requires less energy and time than the heating process. Furthermore, because the raw abrasive material consists of abrasive grains and a coating layer, the surface condition of the cooled abrasive material obtained in the second step is less likely to change due to temperature or atmosphere. Since the abrasive grains in the obtained abrasive material have compressive stress imparted to them, even if tensile stress remains inside the abrasive grains of the raw abrasive material, that tensile stress can be released. In this way, the abrasive material with compressive stress imparted to the inside of the abrasive grains exhibits appropriate crushability.

[0009] Thus, this manufacturing method can produce an abrasive material consisting of abrasive grains and a coating layer. This abrasive material is not the abrasive grain itself, but is included in a grinding wheel or the like, similar to the abrasive grains, and is used to process semiconductor wafers such as SiC wafers.

[0010] The abrasive material of the second teaching comprises abrasive grains made of a first material having a first linear thermal expansion coefficient, and a coating layer made of a second material having a second linear thermal expansion coefficient greater than the first linear thermal expansion coefficient in a specific temperature range, the coating layer covering the abrasive grains; The coating layer is cooled to a cooling temperature of -50°C or less, and then maintained at room temperature, whereby compressive stress is imparted to the abrasive grains due to thermal contraction during cooling of the coating layer.

[0011] The abrasive material of the second teaching is manufactured by the manufacturing method of the first teaching. [Effects of the Invention]

[0012] According to the manufacturing method of the first teaching, it is possible to obtain an abrasive material with appropriate friability without requiring a large amount of energy or time, without changing the surface condition due to temperature or atmosphere, and without releasing internal stress remaining inside. The abrasive material of the second teaching is manufactured without requiring a large amount of energy or time, and without changing the surface condition significantly due to temperature or atmosphere. And the abrasive material of the third teaching also releases internal stress remaining inside, thereby exhibiting appropriate friability. [Brief explanation of the drawings]

[0013] [Figure 1] 2 is a schematic cross-sectional view of an abrasive material before treatment and an abrasive material according to an embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] The abrasive consists of abrasive grains and a coating layer. The first material of the abrasive grains is not particularly limited, but examples include diamond, CBN, silicon carbide, alumina, zirconia, ceria, chromium oxide, iron oxide, silica, titania, etc., as well as mixtures thereof. In particular, when used to polish semiconductor wafers, diamond or CBN superabrasive grains are preferred. These are abrasive grains used to process difficult-to-process materials, so the effect of internal stress control is optimally exerted.

[0015] When the first material of the abrasive grains is diamond, the diamond preferably contains a metal. In this case, there is a tendency for the diamond to be highly micro-fracturable, and tools such as grinding wheels can exhibit high processing durability. The metal contained in the diamond is not particularly limited, but it is preferable that it has a thermal expansion greater than that of the diamond crystal, such as transition metals, particularly Fe, Ni, Co, Mn, etc. Furthermore, the metal may be derived from the diamond manufacturing process or may be intentionally introduced. The metal contained in the diamond may exist as metal particles in the diamond crystal, may react with the diamond crystal to form a chemical bond, or may be diffused into the diamond crystal lattice.

[0016] The content of metal contained in diamond is not particularly limited, but for the high friability of abrasive grain, it is preferably 0.1 mass% or more, more preferably 0.2 mass% or more, even more preferably 0.3 mass% or more, particularly preferably 0.5 mass% or more.On the other hand, if the content of metal contained in diamond is too large, the hardness and strength of abrasive grain will decrease, so it is preferably 10 mass% or less, more preferably 5 mass% or less, even more preferably 3 mass% or less, particularly preferably 1 mass% or less.

[0017] The second material of the coating layer is not particularly limited and can be metal, ceramic, or the like, but is preferably metal because it applies compressive stress to the abrasive grains through thermal contraction. A metallic coating layer can easily and effectively coat the abrasive grains using a gas-phase process such as wet plating, molten salt plating, or sputtering. Furthermore, the ductility of metal makes the coating layer less likely to break even when stress is applied to it during the cooling process.

[0018] Specifically, the second material of the coating layer can be Ni, Cu, Sn, Ag, Ti, Pt, etc., or an alloy containing at least one of these as a main component. Here, the main component is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and particularly preferably 98% by mass or more. By using these materials, it is possible to effectively control the internal stress of the abrasive grains. Furthermore, since these materials are generally used as coating layers for covering abrasive grains, they can be used directly in tool manufacturing without the need to remove the coating layer after controlling the internal stress of the abrasive grains.

[0019] The coating layer may cover the entire abrasive grains or may cover only part of the abrasive grains, but it is preferable that the coating layer cover the entire abrasive grains, since it is preferable to apply compressive stress to the entire abrasive grains.

[0020] The coating layer preferably accounts for 5% by mass or more of the total abrasive, more preferably 10% by mass or more, even more preferably 20% by mass or more, even more preferably 30% by mass or more, more preferably 40% by mass or more, and particularly preferably 50% by mass or more, because the coating layer adequately covers the abrasive grains.

[0021] According to the inventors' understanding, the cooling temperature is preferably -50°C or lower. The cooling temperature is more preferably -100°C or lower, even more preferably -150°C or lower, even more preferably -170°C or lower, and particularly preferably -190°C or lower. This allows the contraction force of the coating layer to be applied to the abrasive grains, changing the internal stress.

[0022] The cooling method is not particularly limited, but examples include cooling with liquid nitrogen, a freezer, liquid argon, liquid oxygen, and the like.

[0023] The second linear thermal expansion coefficient does not need to be greater than the first linear thermal expansion coefficient over the entire temperature range from the cooling temperature to room temperature. It is sufficient for the second linear thermal expansion coefficient to be greater than the first linear thermal expansion coefficient at least in a specific temperature range that is narrower than the temperature range from the cooling temperature to room temperature. If there is a difference in the thermal expansion coefficients over the specific temperature range, compressive stress can be applied to the abrasive grains.

[0024] According to the inventors' understanding, the specific temperature range is sufficient if it is from the cooling temperature to +20 K. If the coating layer thermally shrinks within this specific temperature range, compressive stress can be applied to the abrasive grains. The specific temperature range is more preferably from the cooling temperature to +50 K, even more preferably from the cooling temperature to +100 K, even more preferably from the cooling temperature to +150 K, more preferably from the cooling temperature to +170 K, and particularly preferably from the cooling temperature to +190 K. A temperature range of from the cooling temperature to 20°C is particularly preferred.

[0025] According to the inventors' understanding, the first linear thermal expansion coefficient is preferably 1.5 times or more, more preferably 2 times or more, even more preferably 4 times or more, even more preferably 10 times or more, more preferably 20 times or more, and particularly preferably 50 times or more, the second linear thermal expansion coefficient. In this case, the contraction force of the coating layer is suitably applied to the abrasive grains, thereby changing the internal stress.

[0026] The Raman peak position of the abrasive is preferably shifted to the higher wavenumber side compared to the abrasive before treatment. This increases the crushability of the abrasive. For example, when the abrasive grains are made of diamond, the average value of the Raman peak position of the abrasive grains in the abrasive before treatment is preferably 1331.0 / cm or less, more preferably 1330.5 / cm or less, even more preferably 1330.0 / cm or less, and particularly preferably 1329.5 / cm or less. In these cases, the internal stress of the abrasive grains changes favorably.

[0027] The average rate at which each cooled abrasive is heated to room temperature is preferably 1°C / min to 30°C / min. If the rate is less than 1°C / min, the production time will be long and the efficiency will be low. If the rate is more than 30°C / min, the abrasive grains are likely to be adversely affected, such as cracks occurring in the abrasive grains.

[0028] The control of the internal stress of the abrasive grains by cooling may be the relaxation of tensile stress. In this case, this is effectively achieved by the contraction of the coating layer. In addition, in this case, if the abrasive grains are diamond, the average value of the Raman peak positions of the abrasive grains in the untreated abrasive material should be 1331.0 / cm or less.

[0029] The coating layer may be removed after cooling. The removal method is not particularly limited, and in the case of metal, removal by dissolution with acid can be adopted. [Example]

[0030] In the first step, multiple coated diamonds ("FRM N56 40-60" manufactured by Global Diamond Co., Ltd.) were prepared as raw abrasives. As shown in Figure 1, the raw abrasives consisted of abrasive grains 1 and a coating layer 3 that completely covered the abrasive grains 1. The abrasive grains 1 were primarily composed of diamond as the first material, and contained 0.18% by mass of Ni and 0.39% by mass of Mn as impurities. The coating layer 3 was made of Ni as the second material. The ratio of the coating layer 3 to the total of the abrasive grains 1 and the coating layer 3 was 56% by mass.

[0031] In the specific temperature range (77K to 97K) from the planned cooling temperature to +20K, the first linear thermal expansion coefficient of diamond is 5 to 7 × 10 -6 / K, and the second linear thermal expansion coefficient of Ni is approximately 0.05 × 10 -6 / K. Therefore, the second linear thermal expansion coefficient of Ni in this specific temperature range is about 100 to 140 times the first linear thermal expansion coefficient of diamond.

[0032] In addition, the first linear thermal expansion coefficient of diamond is 5 to 13 × 10 in the temperature range from the planned cooling temperature to 20 °C (77 K to 293 K). -6 / K, and the second linear thermal expansion coefficient of Ni is approximately 0.05×10 -6 / K. Therefore, the second linear thermal expansion coefficient of Ni in this temperature range is about 100 to 260 times the first linear thermal expansion coefficient of diamond.

[0033] In the second step, each untreated abrasive was placed in a glass container and cooled to -196°C in liquid nitrogen for 3 hours.

[0034] Thereafter, each cooled abrasive was taken out and allowed to stand at room temperature to gradually increase the temperature to room temperature, thereby obtaining each abrasive.

[0035] In the first step, a plurality of diamonds ("FRM 40-60" manufactured by Global Diamond Co., Ltd.) without a coating layer, which differs from the coated diamonds of the examples, were prepared as untreated abrasives.

[0036] In the second step, each untreated abrasive was placed in a glass container and kept in liquid nitrogen for 3 hours to obtain each cooled abrasive, and then each cooled abrasive was taken out and left to stand at room temperature to gradually increase the temperature to obtain each abrasive.

[0037] The following evaluations were carried out for each abrasive material of the Examples and each abrasive material of the Comparative Examples, except that for each abrasive material of the Examples, the coating layer 3 was mostly dissolved and removed in advance by stirring the abrasive material in 20% nitric acid.

[0038] Using a microscopic laser Raman spectrometer ("LabRAM HR Evolution" by Horiba, Ltd.), Raman spectra were obtained at five measurement points within each of 100 abrasives from the Examples and Comparative Examples under the following conditions, and the average of the peak positions was calculated. The equivalent circle diameters of all the analyzed abrasives were within the range of 25 to 75 μm.

[0039] Measurement room temperature: 24°C Calibration sample: Si Excitation wavelength: 532 nm Grating: 1800gr / mm Exposure time: 8 seconds Number of times accumulated: 2 times

[0040] The obtained Raman spectrum was subjected to baseline correction, peak search, and fitting using software (Horiba, Ltd. "Labspec6"). The results are shown in Table 1.

[0041] [Table 1]

[0042] As can be seen from Table 1, the Raman peak position of diamond is normally around 1333 / cm, but the average value of the Raman peak position of the untreated abrasive is smaller than this value in both the examples and the comparative examples, which shows that tensile stress exists within the diamond abrasive grains of the untreated abrasive.

[0043] However, the Raman peak position of the abrasive of the Example, which was once cooled and returned to room temperature, shifted to the higher wavenumber side. In contrast, the Raman peak position of the abrasive of the Comparative Example did not change even after being once cooled and returned to room temperature. This shows that the tensile stress of the abrasive of the Example was relaxed. This is thought to be due to the compressive stress applied to the abrasive of the Example due to the thermal contraction of the coating layer.

[0044] Furthermore, cooling treatment can reduce energy and time compared to heating treatment. Furthermore, since the abrasive material of the embodiment is composed of abrasive grains 1 and a coating layer 3 before treatment, the surface condition of the cooled abrasive material obtained in the second step or the abrasive material returned to room temperature is less likely to change due to temperature or atmosphere. The abrasive material of the embodiment is not the abrasive grains 1 themselves, but like the abrasive grains 1, it is included in grinding wheels and used to process semiconductor wafers such as SiC. This abrasive material exhibits moderate crushability because compressive stress is applied inside the abrasive grains 1. [Industrial Applicability]

[0045] The present invention can be used in a method for manufacturing a grinding wheel or the like. [Explanation of symbols]

[0046] 1...Abrasive grain 3...Coat layer

Claims

1. a first step of obtaining a raw abrasive material comprising abrasive grains made of a first material having a first linear thermal expansion coefficient and a coating layer made of a second material having a second linear thermal expansion coefficient greater than the first linear thermal expansion coefficient in a specific temperature range, the coating layer covering the abrasive grains; a second step of cooling the untreated abrasive to a cooling temperature of −50° C. or less to obtain a cooled abrasive; The method for producing an abrasive material, wherein the specific temperature range is from the cooling temperature to +20K.

2. 2. The method for producing an abrasive material according to claim 1, wherein the cooling temperature is −100° C. or lower.

3. 3. The method for producing an abrasive material according to claim 2, wherein the cooling temperature is −150° C. or lower.

4. 4. The method for producing an abrasive material according to claim 3, wherein the cooling temperature is the temperature of liquid nitrogen.

5. 2. The method for producing an abrasive material according to claim 1, wherein the specific temperature range is from the cooling temperature to +100K.

6. The method for producing an abrasive material according to claim 5, wherein the specific temperature range is from the cooling temperature to +150K.

7. 2. The method for producing an abrasive material according to claim 1, wherein the first linear thermal expansion coefficient is 1.5 times or more the second linear thermal expansion coefficient.

8. The method for producing an abrasive material according to claim 7, wherein the first linear thermal expansion coefficient is at least 10 times the second linear thermal expansion coefficient.

9. 2. The method for producing an abrasive material according to claim 1, wherein the first linear thermal expansion coefficient is 50 times or more the second linear thermal expansion coefficient.

10. 2. The method for producing an abrasive according to 1, wherein the abrasive has a Raman peak position shifted to a higher wave number side than that of the untreated abrasive.

11. the first material is diamond; The method for producing an abrasive according to claim 10, wherein the average value of the Raman peak positions of the untreated abrasive is 1331.0 / cm or less.

12. a coating layer that is made of a second material having a second linear thermal expansion coefficient that is greater than the first linear thermal expansion coefficient within a specific temperature range and that covers the abrasive grains; An abrasive material characterized in that after being cooled to a cooling temperature of -50°C or less, it is maintained at room temperature, and compressive stress is imparted to the abrasive grains by thermal contraction of the coating layer during cooling.

13. the first material is cubic boron nitride or diamond; 13. The abrasive of claim 12, wherein the second material is a metal.

14. the first material is diamond; 13. The abrasive of claim 12, wherein the second material is a metal.

15. 15. The abrasive according to claim 13 or 14, wherein the second material is Ni.

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