Abrasive material

Abstract

The present invention provides an abrasive material capable of polishing difficult-to-polish silicon carbide at a high degree of surface precision. The present invention relates to an abrasive material including manganese dioxide particles having a non-needle-like shape possessing a ratio of the longitudinal axis to the transverse axis of the particles observed with a scanning electron microscope of 3.0 or less. The abrasive material is preferable if the average particle size D.sub.SEM of the longitudinal axis of the observed particles is 1.0 m or less, and if the particle size D.sub.50 of the volume-based cumulative fraction of 50% in laser diffraction/scattering particle size distribution measurement is 2.0 m or less.

Claims

1. A method of polishing a substrate, comprising: (a) providing an abrasive material comprising manganese dioxide particles having a non-needle-like shape having a longitudinal axis and a transverse axis, wherein a ratio of the longitudinal axis to the transverse axis of the particles is 3.0 or less; and (b) polishing a substrate with said abrasive material; wherein the substrate is polished to a surface roughness of 0.17 nm or less.

2. The method according to claim 1, wherein the average particle size D.sub.SEM of the longitudinal axis of the manganese dioxide particles is 1.0 m or less.

3. The method according to claim 1, wherein the particle size D.sub.50 of the volume-based cumulative fraction of 50% in laser diffraction/scattering particle size distribution measurement is 2.0 m or less.

4. The method according to claim 1, wherein specific surface area of the abrasive material is 20 m.sup.2/g or more.

5. The method according to claim 1, wherein the crystal structure of manganese dioxide is of the -type.

6. The method according to claim 1, wherein the crystal structure of manganese dioxide is of the -type.

7. The method according to claim 5, wherein the manganese dioxide particles have been formed by a dry pulverization step of dry pulverizing -type manganese dioxide deposited on an anode by electrolysis.

8. The method according to claim 6, wherein the manganese dioxide particles have been formed by a heating step of heating -type manganese dioxide deposited on an anode by electrolysis in a hot atmosphere set at 200 C. to 600 C.; and a dry pulverization step of dry pulverizing the heated manganese dioxide.

9. The method according to claim 1, wherein a ratio of the longitudinal axis to the transverse axis of the particles is 1.00 to 1.67.

10. The method according to claim 1, wherein the abrasive material is in the form of a slurry.

11. The method according to claim 1, wherein the substrate comprises silicon carbide.

12. The method according to claim 1, wherein step (b) comprises polishing the substrate at a polishing rate of 0.07 m/hr or more.

13. A method of polishing a substrate, comprising: (a) providing an abrasive material comprising manganese dioxide particles having a non-needle-like shape having a longitudinal axis and a transverse axis, wherein a ratio of the longitudinal axis to the transverse axis of the particles is 3.0 or less, wherein the average particle size D.sub.SEM of the longitudinal axis of the particles is 1.0 m or less, and wherein the particle size D.sub.50 of the volume-based cumulative fraction of 50% in laser diffraction/scattering particle size distribution measurement is 2.0 m or less; and (b) polishing a substrate with said abrasive material; wherein the manganese dioxide particles have been formed by a heating step of heating -type manganese dioxide deposited on an anode by electrolysis in a hot atmosphere set at 200 C. to 600 C.; and a dry pulverization step of dry pulverizing the heated manganese dioxide.

14. The method according to claim 13, wherein the abrasive material is in the form of a slurry.

15. The method according to claim 13, wherein the substrate comprises silicon carbide.

16. The method according to claim 13, wherein the specific surface area of the abrasive material is 20 m.sup.2/g or more.

17. The method according to claim 13, wherein a ratio of the longitudinal axis to the transverse axis of the particles is 1.00 to 1.67.

18. A method of polishing a substrate, comprising: (a) providing an abrasive material comprising manganese dioxide particles having a non-needle-like shape having a longitudinal axis and a transverse axis, wherein a ratio of the longitudinal axis to the transverse axis of the particles is 3.0 or less; and (b) polishing a substrate with said abrasive material; wherein the crystal structure of manganese dioxide is of the -type; wherein the manganese dioxide particles have been formed by a heating step of heating -type manganese dioxide deposited on an anode by electrolysis in a hot atmosphere set at 200 C. to 600 C.; and a dry pulverization step of dry pulverizing the heated manganese dioxide.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 is a scanning electron micrograph of Example 1 (magnification: 100,000).

EMBODIMENTS FOR CARRYING OUT THE INVENTION

(2) The best mode for carrying out the present invention is described with reference to Examples and Comparative Examples.

Example 1

(3) In Example 1, manganese dioxide was deposited on an anode by electrolysis of an aqueous solution of manganese sulfate, and the thus deposited manganese dioxide was used. The manganese dioxide obtained by electrolysis was disintegrated with a disintegrator (Atomizer, manufactured by Powrex Corp.), then pulverized with a jet mill (PJM-200SP, manufactured by Nippon Pneumatic Mfg. Co., Ltd.) (pulverization condition: pulverization object was pulverized at a rate of 4 kg/hour, by jetting compressed air at 0.05 MPa), and thus, an abrasive material in which the particle size D.sub.50 of the volume-based cumulative fraction of 50% in laser diffraction/scattering particle size distribution measurement was 0.45 m was produced. The crystal structure of the obtained manganese dioxide was found to be of the -type by examination with X-ray diffraction.

(4) The particle shape of the abrasive material of Example 1 was examined with a scanning electron microscope (FE-SEM, S-4800, manufactured by Hitachi Ltd.). FIG. 1 shows the observed microgram. The particles in the observed microgram were found to be non-needle-like and nearly spherical. The lengths of the long axis and the lengths of the short axis perpendicular to the long axis were measured for 100 particles observed to be primary particles, with the aid of the observed microgram at a magnification of 100,000 based on the FE-SEM; thus, the average length of the long axis and the average length of the short axis were observed to be 0.16 m and 0.11 m, respectively; and the ratio of the long axis length to the short axis length of each of the particles was calculated to be 1.00 to 1.25. The specific surface area of the abrasive material of Example 1 was measured and observed to be 40 m.sup.2/g on the basis of the BET method (according to 6.2 Flow Method, (3.5) One Point Method of JIS R 1626-1996 (a specific surface area measurement method of fine ceramic powder based on the gas adsorption BET method); in this measurement, a mixed gas was used which was composed of helium as carrier gas and nitrogen as adsorbate gas).

(5) Next, the results obtained by polishing a silicon carbide single crystal plate with the abrasive material of Example 1 are described. The silicon carbide single crystal plate as the polishing object was a 6HSiC single crystal of 2 inches in diameter and 250 mm in thickness, and the polishing surface was the on-axis plane (parallel to the wafer surface cut perpendicular to the crystal axis). Before polishing, the surface roughness Ra of the to-be-polished surface of the substrate was measured with an AFM (atomic force microscope, Nanoscope IIIa, manufactured by Veeco Instruments, Inc.) and was observed to be 2.46 nm.

(6) The polishing conditions were as follows: an abrasive material slurry containing 10 wt % of manganese dioxide was used; the abrasive load was set at 190 g/cm.sup.2; and the single crystal substrate was placed on an abrasive pad (IC-1000, manufactured by Nitta Haas Inc.) and polished for 180 minutes. After polishing, the polished surface was washed with water to remove the attached slurry and was dried. The surface roughness was measured with an AFM for randomly selected five points on the dried polished surface, and the average Ra was observed to be 0.10 nm. The polishing rate was calculated by measuring the substrate weights before and after polishing, and was observed to be 0.12 m/hr.

Example 2

(7) Manganese dioxide deposited on an anode under the same electrolysis conditions as in Example 1 was calcined at 450 C. for 1 hour, and the thus obtained manganese dioxide was used in Example 2. The calcined manganese dioxide was disintegrated in the same manner as in Example 1, then pulverized with a jet mill, and thus an abrasive material in which the particle size D.sub.50 of the volume-based cumulative fraction of 50% in laser diffraction/scattering particle size distribution measurement was 0.58 m was produced. The crystal structure of the obtained manganese dioxide was found to be of the -type by examination with X-ray diffraction.

(8) The particle shape of the abrasive material of Example 2 was examined with an FE-SEM in the same manner as in Example 1, and it was revealed that the observed particles were each non-needle-like and nearly spherical, like the particles shown in FIG. 1. The lengths of the long axis and the lengths of the short axis perpendicular to the long axis were measured for 100 particles observed to be primary particles, with the aid of the observed microgram at a magnification of 100,000 based on the FE-SEM; thus, the average length of the long axis and the average length of the short axis were observed to be 0.16 m and 0.13 m, respectively; and the ratio of the long axis length to the short axis length of each of the particles was calculated to be 1.00 to 1.67. The specific surface area of the abrasive material of Example 2 was measured and observed to be 40 m.sup.2/g on the basis of the BET method.

(9) By using the abrasive material of Example 2, a silicon carbide single crystal plate was polished under the same conditions as in Example 1, and consequently the obtained surface roughness Ra of the polished surface was observed to be 0.17 nm. The polishing rate in Example 2 was observed to be 0.07 m/hr.

Example 3

(10) In Example 3, manganese dioxide deposited on an anode under the same electrolysis conditions as in Example 1 was used, and the obtained manganese dioxide was twice pulverized with an impact pulverizer composed of a rotating blade and a screen (Beater Mill, manufactured by Retsch Co., Ltd.), to produce an abrasive material. It was an abrasive material that includes manganese dioxide in which the particle size D.sub.50 of the volume-based cumulative fraction of 50% in laser diffraction/scattering particle size distribution measurement was 0.77 m. The crystal structure of the obtained manganese dioxide was found to be of the -type by examination with X-ray diffraction.

(11) The particle shape of the abrasive material of Example 3 was examined with an FE-SEM in the same manner as in Example 1, and it was revealed that the observed particles were each non-needle-like and nearly spherical, like the particles shown in FIG. 1. The lengths of the long axis and the lengths of the short axis perpendicular to the long axis were measured for 100 particles observed to be primary particles, with the aid of the observed microgram at a magnification of 100,000 based on the FE-SEM; thus, the average length of the long axis and the average length of the short axis were observed to be 0.23 m and 0.19 m, respectively; and the ratio of the long axis length to the short axis length of each of the particles was calculated to be 1.00 to 1.52. The specific surface area of the abrasive material of Example 3 was measured and observed to be 41 m.sup.2/g on the basis of the BET method.

(12) By using the abrasive material of Example 3, a silicon carbide single crystal plate was polished under the same conditions as in Example 1, and consequently the obtained surface roughness Ra of the polished surface was observed to be 0.10 nm. The polishing rate in Example 3 was observed to be 0.10 m/hr.

Comparative Example 1

(13) In Comparative example 1, manganese dioxide obtained by electrolysis under the same conditions as in Example 1 was wet pulverized with a pulverizer (Dynomill, pulverizing medium: 0.8 mm zirconia beads, manufactured by Willey A. Bachofen AG Maschinenfabrik) to produce an abrasive material. In the abrasive material of Comparative Example 1, the particle size D.sub.50 of the volume-based cumulative fraction of 50% in laser diffraction/scattering particle size distribution measurement was observed to be 0.38. The crystal structure of the obtained manganese dioxide was found to be of the -type by examination with X-ray diffraction.

(14) The particle shape of the abrasive material of Comparative Example 1 was examined with an FE-SEM in the same manner as in Example 1, and it was verified that the observed particles included a large number of needle-shaped particles. The lengths of the long axis and the lengths of the short axis perpendicular to the long axis were measured for 100 particles observed to be primary particles, with the aid of the observed microgram at a magnification of 100,000 based on the FE-SEM; thus, the average length of the long axis and the average length of the short axis were observed to be 1.45 m and 0.14 m, respectively; and the ratio of the long axis length to the short axis length of each of the particles was calculated to be 3.60 to 10.50. The specific surface area of the abrasive material of Comparative Example 1 was measured and observed to be 18 m.sup.2/g on the basis of the BET method.

(15) By using the abrasive material of Comparative Example 1, a silicon carbide single crystal plate was polished under the same conditions as in Example 1, and consequently the obtained surface roughness Ra of the polished surface was observed to be 0.56 nm. The polishing rate in Comparative Example 1 was observed to be 0.03 m/hr.

Comparative Example 2

(16) In Comparative Example 2, a commercially available colloidal silica (Compol 80, manufactured by Fujimi Inc.) was used as an abrasive material. In the abrasive material of Comparative Example 2, the particle size D.sub.50 of the volume-based cumulative fraction of 50% in laser diffraction/scattering particle size distribution measurement was observed to be 0.10 m. The particle shape of the abrasive material of Comparative Example 2 was examined with an FE-SEM in the same manner as in Example 1, and it was verified that the observed particles were each nearly spherical. The lengths of the long axis and the lengths of the short axis perpendicular to the long axis were measured for 100 particles observed to be primary particles were measured with aid of the observed microgram at a magnification of 50,000 based on the FE-SEM; thus, the average length of the long axis and the average length of the short axis were observed to be 0.08 m and 0.08 m, respectively; and the ratio of the long axis length to the short axis length of each of the particles was calculated to be 1.00 to 1.05.

(17) By using the abrasive material of Comparative Example 2, an abrasive material slurry containing 10 wt % of the abrasive material was prepared. By using the abrasive slurry, an abrasive treatment was performed under the same conditions as in Example 1. Consequently, the obtained surface roughness Ra of the polished surface was observed to be 2.53 nm, and the surface roughness showed little change between before and after polishing. The polishing rate in Comparative Example 2 was observed to be 0.01 m/hr.

Comparative Example 3

(18) Manganese dioxide obtained under the same electrolysis conditions as in Example 1 was calcined at 850 C. (1 hour), and the thus obtained manganese dioxide was used in Comparative Example 3. The crystal structure of the manganese dioxide having been calcined was identified by X-ray diffraction to be dimanganese trioxide (Mn.sub.2O.sub.3). After the calcination, the obtained manganese dioxide was pulverized until the average particle size reached 0.4 m. The particle shape of the abrasive material of Comparative Example 3 was examined with an FE-SEM in the same manner as in Example 1, and it was verified that the particles were each nearly spherical. The lengths of the long axis and the lengths of the short axis perpendicular to the long axis were measured for 100 particles observed to be primary particles, with the aid of the observed microgram at a magnification of 100,000 based on the FE-SEM; thus, the average length of the long axis and the average length of the short axis were observed to be 0.31 m and 0.27 m, respectively; and the ratio of the long axis length to the short axis length of each of the particles was calculated to be 1.00 to 1.47.

(19) The dimanganese trioxide powder having been pulverized was dispersed in purified water so as for the slurry concentration to be 10 wt % to prepare a dimanganese trioxide slurry. By using the slurry, a polishing test was performed under the same conditions as in Example 1. Consequently, the obtained surface roughness Ra of the polished surface was observed to be 2.33 nm, and the surface roughness showed little change between before and after polishing. The polishing rate in Comparative Example 3 was observed to be 0.02 m/hr.

Comparative Example 4

(20) In Comparative Example 4, oxides of rare earths (trade name: M601; CeO.sub.2: 63 wt %, La.sub.2O.sub.3: 31 wt %, Pr.sub.6O.sub.11: 6 wt %, manufactured by Mitsui Mining & Smelting Co., Ltd.) were used as an abrasive material. In the abrasive material of Comparative Example 4, the particle size D.sub.50 of the volume-based cumulative fraction of 50% in laser diffraction/scattering particle size distribution measurement was observed to be 0.55 m. The particle shape of the abrasive material of Comparative Example 3 was examined with an FE-SEM in the same manner as in Example 1, and it was verified that the particles were each nearly spherical. The lengths of the long axis and the lengths of the short axis perpendicular to the long axis were measured for 100 particles observed to be primary particles with aid of the observed microgram at a magnification of 50,000 based on the FE-SEM; thus, the average length of the long axis and the average length of the short axis were observed to be 0.31 m and 0.23 m, respectively; the ratio of the length of the long axis to the length of the short axis of each of the particles was calculated to be 1.00 to 1.71.

(21) By using the abrasive material of Comparative Example 4, an abrasive material slurry containing 10 wt % of the abrasive material was prepared. By using the abrasive slurry, a polishing was performed under the same conditions as in Example 1. Consequently, the obtained surface roughness Ra of the polished surface was observed to be 2.50 nm, and the surface roughness showed little change between before and after polishing. The polishing rate in Comparative Example 4 was observed to be 0.01 m/hr.

INDUSTRIAL APPLICABILITY

(22) According to the present invention, it is possible to polish silicon carbide, which is difficult to polish, extremely rapidly at a high degree of surface precision.