JP6622991B2 - Polishing composition - Google Patents

Description

  The present invention relates to a polishing composition. Specifically, the present invention relates to a polishing composition used for polishing a high hardness material such as a silicon carbide single crystal.

  Polishing (wrapping) of flat surfaces of high-hardness materials such as diamond, sapphire (aluminum oxide), silicon carbide, boron carbide, tungsten carbide, silicon nitride, and titanium nitride by supplying diamond abrasive grains to a polishing surface plate. It is realized by. However, in lapping using diamond abrasive grains, there is a limit to the improvement of surface flatness due to generation and remaining of scratches. Therefore, polishing (polishing) performed by supplying a polishing slurry between the polishing pad and an object to be polished using a polishing pad after lapping using diamond abrasive grains or instead of lapping has been studied. Yes. Patent documents 1-4 are mentioned as literature which discloses this kind of conventional technology.

JP 2011-121153 A Japanese Patent Application Laid-Open No. 2012-2448569 JP 2014-24154 A Japanese Patent No. 5592276

  In the above-mentioned prior art documents, the polishing rate (amount for removing the surface of the object to be polished per unit time) by devising the components (abrasive grains, oxidizing agent, etc.) of the slurry (polishing composition) used for polishing. Improvement of surface flatness after polishing has been proposed. However, even such a technique is insufficient to satisfy the practical requirement level regarding the polishing rate and the surface flatness, and there is still room for improvement.

  The present invention has been made in view of the above circumstances, and its main object is a polishing composition that can be realized at a high level of both a polishing rate and surface flatness with respect to the surface of a high hardness material. Is to provide.

According to the present invention, a polishing composition for polishing a material having a Vickers hardness of 1500 Hv or more is provided. The polishing composition includes a first alumina abrasive grain having an average secondary particle diameter D2 _f and a second alumina abrasive grain having an average secondary particle diameter D2 _s smaller than the first alumina abrasive grain. As described above, by using a combination of alumina abrasive grains having different average secondary particle diameters, it is possible to achieve a high level of both the polishing rate and the surface flatness with respect to the surface of the high hardness material.

  In a preferred embodiment of the polishing composition disclosed herein, α-alumina is included as the first alumina abrasive grains. Such first alumina abrasive grains can effectively contribute to the improvement of the polishing rate. The second alumina abrasive grains include at least one selected from the group consisting of alumina sol (also referred to as colloidal alumina) and intermediate alumina. Such second alumina abrasive grains can effectively contribute to improvement of surface flatness. Therefore, by using the first alumina abrasive grains and the second alumina abrasive grains in combination so as to satisfy the above average secondary particle diameter, it is possible to more effectively realize both the polishing rate and the surface flatness. Can be done.

In a preferred embodiment of the polishing composition disclosed herein, the relationship between the average secondary particle diameter D2 _f of the first alumina abrasive grains and the average secondary particle diameter D2 _{s of} the second alumina abrasive grains is represented by the following formula: : 1 <(D2 _f / D2 _s ) <20; By using a combination of the first alumina abrasive grains and the second alumina abrasive grains so as to have the specific average secondary particle diameter ratio, both the polishing rate and the surface flatness can be realized at a higher level.

In a preferred embodiment of the polishing composition disclosed herein, the average secondary particle diameter D2 _{f of} the first alumina abrasive grains is 350 nm or more and 1000 nm or less. The average secondary particle diameter D2 _s of the second alumina abrasive grains is 20nm or more 300nm or less. When the average secondary particle diameter D2 _f of the first alumina abrasive grains and the average secondary particle diameter D2 _{s of} the second alumina abrasive grains are within the above ranges, both the polishing rate and the surface flatness are suitably realized. Can be done.

  In a preferred aspect of the polishing composition disclosed herein, the content ratio of the first alumina abrasive grains and the second alumina abrasive grains (first alumina abrasive grains: second alumina abrasive grains) is based on weight. It is in the range of 95: 5 to 5:95. When the content ratio of the first alumina abrasive grains and the second alumina abrasive grains is within this range, the polishing rate improvement effect and the planarization effect can be more suitably exhibited.

  In a preferred embodiment of the polishing composition disclosed herein, the pH is in the range of 8-11. In the polishing composition having a pH within the above range, the application effect of the present invention can be suitably exhibited.

  Hereinafter, preferred embodiments of the present invention will be described. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

<Polishing object>
The polishing composition disclosed herein is used for polishing a material having a Vickers hardness of 1500 Hv or higher (high hardness material). The Vickers hardness of the high hardness material is preferably 1800 Hv or higher (for example, 2000 Hv or higher, typically 2200 Hv or higher). The upper limit of Vickers hardness is not particularly limited, but may be about 7000 Hv or less (for example, 5000 Hv or less, typically 3000 Hv or less). In the present specification, the Vickers hardness can be measured based on JIS R 1610: 2003. An international standard corresponding to the JIS standard is ISO 14705: 2000.

  Examples of the material having a Vickers hardness of 1500 Hv or more include diamond, sapphire (aluminum oxide), silicon carbide, boron carbide, tungsten carbide, silicon nitride, and titanium nitride. The polishing method disclosed herein can be preferably applied to a single crystal surface of the above material that is mechanically and chemically stable. Especially, it is preferable that the grinding | polishing target object surface is comprised from the silicon carbide. Silicon carbide is expected as a semiconductor substrate material with low power loss and excellent heat resistance, and the practical advantage of improving its surface properties is particularly great. The polishing composition disclosed herein is particularly preferably applied to a silicon carbide single crystal surface.

<Polishing composition>
(Abrasive grains)
The polishing composition disclosed herein includes a first alumina abrasive grain having an average secondary particle diameter D2 _f, and a second alumina abrasive grain having an average secondary particle diameter D2 _s smaller than the first alumina abrasive grain. Containing. As described above, by using a combination of alumina abrasive grains having different average secondary particle diameters, it is possible to achieve a high level of both the polishing rate and the surface flatness with respect to the surface of the high hardness material.

The average secondary particle diameter of the first alumina abrasive grains (hereinafter sometimes simply referred to as “D2 _f ”) is the average secondary particle diameter of the second alumina abrasive grains (hereinafter simply referred to as “D2 _s ”). (That is, D2 _f > D2 _s is sufficient) and is not particularly limited. D2 _f is suitably, for example, 100 nm or more, usually 150 nm or more, typically 200 nm or more. From the viewpoint of polishing efficiency, the D2 _f, preferably 300nm or more, more preferably 350nm or more, more preferably 400nm or more. From the viewpoint of achieving both a polishing rate and surface flatness, first alumina abrasive grains having a D2 _f of 200 nm to 3000 nm are preferred, first alumina abrasive grains having a diameter of 300 nm to 2000 nm are preferred, and 350 nm to 1000 nm (for example, 800 nm or less). ) Is particularly preferred.

On the other hand, the second alumina abrasive grains are not particularly limited as long as the average secondary particle diameter D2 _s is smaller than D2 _f . From the viewpoint of flattening effect, the second alumina abrasive grains can D2 _s is preferably adopted as the 500nm or less. For example, from the viewpoint of achieving both polishing efficiency and surface flatness, second alumina abrasive grains having a D2 _s of 20 nm to 450 nm are preferable, second alumina abrasive grains having a diameter of 50 nm to 400 nm are preferable, and those having a diameter of 75 nm to 300 nm are preferable. Particularly preferred. For example, the second alumina abrasive grains may have D2 _f of 75 nm or more and 150 nm or less (for example, 100 nm or less).

The relationship between D2 _f and D2 _s satisfies 1 <(D2 _f / D2 _s ) <20 from the viewpoint of better exhibiting the effect of using the first alumina abrasive grains and the second alumina abrasive grains together. preferable. By using the first alumina abrasive grains and the second alumina abrasive grains in combination so as to have a specific average secondary particle diameter ratio, both the polishing rate and the surface flatness can be realized at a higher level. In the technology disclosed herein, for example, the relationship between D2 _f and D2 _s is 1.2 ≦ (D2 _f / D2 _s ) ≦ 15, more preferably 1.5 ≦ (D2 _f / D2 _s ) ≦ 10. More preferably, 1.8 ≦ (D2 _f / D2 _s ) ≦ 8, particularly preferably 2 ≦ (D2 _f / D2 _s ) ≦ 6.

D2 _f is preferably 100 nm or more larger than D2 _{s, and} more preferably 200 nm or more. The value obtained by subtracting D2 _s from D2 _{f (i.e.,} D2 f -D2 _s) is preferably not 1000nm or less, more preferably 800nm or less, more preferably 500nm or less. For example, D2 _f -D2 _s may be 250 nm or less.

  The average secondary particle diameter of the abrasive grains is less than 500 nm, for example, by a dynamic light scattering method using a model “UPA-UT151” manufactured by Nikkiso Co., Ltd. The average diameter can be measured as Mv). Moreover, about 500 nm or more particle | grains, it can measure as a volume average particle diameter by the pore electrical resistance method etc. using the model "Multisizer 3" by a BECKMAN COULTER company.

  The ratio (weight basis) between the content of the first alumina abrasive grains and the content of the second alumina abrasive grains is not particularly limited. The weight ratio of the first alumina abrasive grains to the second alumina abrasive grains is 95: 5 to 5:95 from the viewpoint of better exhibiting the effect of using the first alumina abrasive grains and the second alumina abrasive grains together. It is appropriate that it is 95: 5 to 20:80, more preferably 95: 5 to 40:60. From the standpoint of polishing efficiency and the like, it is effective to set the content of the first alumina abrasive grains to be equal to or more than the content of the second alumina abrasive grains. The technique disclosed here can be preferably implemented, for example, in a mode in which the weight ratio of the first alumina abrasive grains to the second alumina abrasive grains is 95: 5 to 70:30.

  Each of the first alumina abrasive grains and the second alumina abrasive grains can be used by appropriately selecting those having an appropriate average secondary particle diameter from various known alumina particles. Examples of such known alumina particles include α-alumina and intermediate alumina. Here, intermediate alumina is a generic term for alumina particles other than α-alumina, and specific examples include γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, χ-alumina, and the like. Is done. Further, alumina called fumed alumina (typically alumina fine particles produced when high-temperature firing of an alumina salt) may be used based on classification according to the production method. Further, alumina (referred to as alumina hydrate such as boehmite) called colloidal alumina or alumina sol is also included in the examples of the known alumina particles.

  Specific examples of the alumina particles that can be preferably used as the first alumina abrasive grains include α-alumina. Such first alumina abrasive grains can effectively contribute to the improvement of the polishing rate. As the second alumina abrasive grains, α-alumina having an average secondary particle diameter smaller than that of the first alumina abrasive grains may be used, or alumina particles other than α-alumina may be used.

  In a preferred embodiment, the first alumina abrasive grains and the second alumina abrasive grains can be selected such that the hardness of the second alumina abrasive grains is lower than the hardness of the first alumina abrasive grains. By this, the polishing rate improvement effect by the 1st alumina abrasive grain and the surface flatness improvement effect by the 2nd alumina abrasive grain can each be exhibited efficiently, and both coexistence with a polishing rate and surface flatness is higher. Can be realized at a level. For example, when α-alumina is used as the first alumina abrasive grains, various intermediate aluminas can be preferably employed as the second alumina abrasive grains. The intermediate alumina may be fumed alumina. Alumina sol (colloidal alumina) can also be preferably used as the second alumina abrasive grains.

  The polishing composition disclosed herein contains alumina abrasive grains other than the first alumina abrasive grains and the second alumina abrasive grains (that is, third and subsequent alumina abrasive grains) as long as the effects of the present invention are not impaired. May be. When the third and subsequent alumina abrasive grains are contained, the total weight of the first alumina abrasive grains and the second alumina abrasive grains in the total weight of the alumina abrasive grains contained in the polishing composition may be 70% by weight. It is suitable, preferably 80% by weight or more, more preferably 90% by weight or more. Among these, a polishing composition in which 100% by weight of the alumina abrasive grains contained in the polishing composition is a first alumina abrasive grain and a second alumina abrasive grain is preferable.

  The polishing composition disclosed herein may contain abrasive grains made of a material other than alumina (hereinafter also referred to as non-alumina abrasive grains) as long as the effects of the present invention are not impaired. Examples of such non-alumina abrasive particles include oxide particles such as silica particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, and iron oxide particles. Nitride particles such as silicon nitride particles and boron nitride particles; carbide particles such as silicon carbide particles and boron carbide particles; diamond particles; carbonates such as calcium carbonate and barium carbonate; An abrasive is mentioned.

The content of the non-alumina abrasive is suitably, for example, 30% by weight or less, preferably 20% by weight or less, more preferably 10% by weight, based on the total weight of the abrasive grains contained in the polishing composition. % Or less.
The technique disclosed here can be preferably implemented in a mode in which the total proportion of alumina abrasive grains is greater than 90% by weight of the total weight of abrasive grains contained in the polishing composition. The ratio of the alumina abrasive grains is more preferably 95% by weight or more, further preferably 98% by weight or more, and particularly preferably 99% by weight or more. Among these, a polishing composition in which 100% by weight of the abrasive grains contained in the polishing composition is alumina abrasive grains is preferable.

  Moreover, it is preferable that the polishing composition disclosed here does not contain a diamond particle substantially as an abrasive grain. Diamond particles can be a limiting factor for improving smoothness due to their high hardness. Further, since diamond particles are generally expensive, they cannot be said to be an advantageous material in terms of cost performance. From a practical aspect, it is desirable that the degree of dependence on high-priced materials such as diamond particles is low.

(Polishing aid)
The polishing composition disclosed herein preferably contains a polishing aid. The polishing aid is a component that enhances the effect of polishing, and typically a water-soluble one is used. The polishing aid is not particularly limited, but exhibits an action of modifying the surface of the object to be polished (typically oxidative deterioration) in polishing, thereby causing weakening of the surface of the object to be polished. It is thought that it contributes to polishing with abrasive grains.

  Polishing aids include peroxides such as hydrogen peroxide; nitric acid, its salts iron nitrate, silver nitrate, aluminum nitrate, and nitrates such as its complex cerium ammonium nitrate; peroxomonosulfuric acid, peroxodisulfuric acid, etc. Persulfuric acid, persulfuric acid compounds such as ammonium persulfate and potassium persulfate; chloric acid and salts thereof, perchloric acid and perchloric acid such as potassium perchlorate; chlorine compounds; bromic acid and bromine which is a salt thereof Bromine compounds such as potassium acid; iodine compounds such as iodic acid, its salt ammonium iodate, periodic acid, its salt sodium periodate, potassium periodate, etc .; iron acid, its salt iron ferrate Iron acids such as permanganic acid, permanganates such as sodium permanganate and potassium permanganate; chromic acid and salts thereof chromic acid Chromic acids such as potassium and potassium dichromate; vanadic acid and its salts vanadate such as ammonium vanadate, sodium vanadate and potassium vanadate; ruthenium acids such as perruthenic acid and its salts; molybdic acid and its salts And molybdic acids such as ammonium molybdate and disodium molybdate; rhenic acids such as perrhenic acid and its salts; tungstic acids such as tungstic acid and its salt, disodium tungstate. These may be used alone or in combination of two or more. Among these, from the viewpoint of polishing efficiency and the like, permanganic acid or a salt thereof, chromic acid or a salt thereof, iron acid or a salt thereof is preferable, and sodium permanganate or potassium permanganate is particularly preferable.

  In a preferred embodiment, the polishing composition contains a composite metal oxide as a polishing aid. Examples of the composite metal oxide include nitrate metal salts, iron acids, permanganic acids, chromic acids, vanadic acids, ruthenium acids, molybdic acids, rhenic acids, and tungstic acids. Among these, iron acids, permanganic acids, and chromic acids are more preferable, and permanganic acids are more preferable.

  In a more preferable embodiment, the composite metal oxide includes a monovalent or divalent metal element (excluding transition metal elements) and a fourth periodic transition metal element in the periodic table. CMO is used. Preferred examples of the monovalent or divalent metal element (excluding transition metal elements) include Na, K, Mg, and Ca. Of these, Na and K are more preferable. Preferable examples of the fourth periodic transition metal element in the periodic table include Fe, Mn, Cr, V, and Ti. Among these, Fe, Mn, and Cr are more preferable, and Mn is more preferable.

  When the polishing composition disclosed herein contains a composite metal oxide (preferably a composite metal oxide CMO) as a polishing aid, it may or may not contain a polishing aid other than the composite metal oxide. Also good. The technique disclosed herein can also be preferably implemented in an embodiment that does not substantially contain a polishing aid (for example, hydrogen peroxide) other than a composite metal oxide (preferably a composite metal oxide CMO) as a polishing aid.

(Other ingredients)
The polishing composition disclosed herein is a chelating agent, a thickener, a dispersant, a pH adjuster, a surfactant, an organic acid, an organic acid salt, an inorganic acid, an inorganic material, as long as the effects of the present invention are not impaired. Known additives that can be used in polishing compositions (typically high-hardness material polishing compositions such as silicon carbide substrate polishing compositions), such as acid salts, rust inhibitors, antiseptics, and fungicides May be further contained as necessary. The content of the additive may be set as appropriate according to the purpose of the addition, and does not characterize the present invention, so a detailed description is omitted.

(solvent)
The solvent used in the polishing composition is not particularly limited as long as it can disperse the abrasive grains. As the solvent, ion exchange water (deionized water), pure water, ultrapure water, distilled water and the like can be preferably used. The polishing composition disclosed herein may further contain an organic solvent (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water, if necessary. Usually, it is preferable that 90 volume% or more of the solvent contained in polishing composition is water, and it is more preferable that 95 volume% or more (typically 99-100 volume%) is water.

<Polishing liquid>
The polishing composition disclosed herein is typically supplied to a polishing object in the form of a polishing liquid containing the polishing composition, and used for polishing the polishing object. The polishing liquid may be prepared, for example, by diluting (typically diluting with water) any of the polishing compositions disclosed herein. Or you may use this polishing composition as polishing liquid as it is. That is, the concept of the polishing composition in the technology disclosed herein is used as a polishing liquid diluted with a polishing liquid (working slurry) that is supplied to a polishing object and used for polishing the polishing object. Both concentrated liquid (polishing liquid stock solution) are included. Another example of the polishing liquid containing the polishing composition disclosed herein is a polishing liquid obtained by adjusting the pH of the composition.

  The abrasive content (total content of a plurality of abrasive grains) in the polishing liquid disclosed herein is not particularly limited, but is typically 0.1% by weight or more from the viewpoint of polishing efficiency. It is preferably 5% by weight or more, more preferably 1% by weight or more, further preferably 3% by weight or more, and particularly preferably 5% by weight or more. Higher polishing rates can be achieved by increasing the abrasive content. In addition, from the viewpoint of dispersion stability of the polishing composition, the content is usually suitably 30% by weight or less, preferably 20% by weight or less, more preferably 15% by weight or less, and still more preferably. 10% by weight or less. In a preferred embodiment, the content of the first alumina abrasive grains in the polishing liquid is greater than the content of the second alumina abrasive grains. The value obtained by subtracting the content of the second alumina abrasive grains from the content of the first alumina abrasive grains is preferably 1% by weight or more, more preferably 2% by weight or more, and further preferably 3% by weight from the viewpoint of polishing efficiency and the like. % Or more.

  The content of the polishing aid in the polishing liquid (in the case where a plurality of polishing aids are included, the total content thereof) is not particularly limited, but it is usually suitably 0.1% by weight or more. From the viewpoint of polishing rate and the like, the content is preferably 0.5% by weight or more, and more preferably 1% by weight or more. On the other hand, if the content of the polishing aid is too large, the polishing rate improvement effect tends to slow down, and the stability of the composition may decrease. From the viewpoint of the stability of the polishing composition, the content of the polishing aid is usually suitably 10% by weight or less, preferably 8% by weight or less, and 5% by weight or less. More preferably.

  The pH of the polishing liquid is preferably 2 or more (for example, 3 or more), more preferably 6 or more, still more preferably 8 or more, and particularly preferably 8.5 or more. The upper limit of the pH of the polishing liquid is not particularly limited, but is preferably 12 or less (for example, 11 or less), and more preferably 10 or less (for example, 9.5 or less). As a result, the object to be polished can be more evenly polished.

<Concentrate>
The polishing composition disclosed herein may be in a concentrated form (that is, in the form of a polishing liquid concentrate) before being supplied to the object to be polished. The polishing composition in such a concentrated form is advantageous from the viewpoints of convenience, cost reduction, etc. during production, distribution, storage and the like. The concentration factor can be, for example, about 2 to 5 times in terms of volume.

  Thus, the polishing composition in the form of a concentrated liquid can be used in such a manner that a polishing liquid is prepared by diluting at a desired timing and the polishing liquid is supplied to a polishing object. The dilution can be typically performed by adding the aforementioned solvent to the concentrated solution and mixing. Moreover, when the said solvent is a mixed solvent, you may add and dilute only some components among the structural components of this solvent, and add the mixed solvent which contains those structural components in a different ratio from the said solvent. May be diluted. In addition, as will be described later, in a multi-component polishing composition, a part of them may be diluted and then mixed with another agent to prepare a polishing liquid, or a plurality of agents may be mixed. Later, the mixture may be diluted to prepare a polishing liquid.

  The content of abrasive grains in the concentrated liquid can be, for example, 40% by weight or less. From the viewpoint of the stability of the polishing composition (for example, dispersion stability of abrasive grains) and filterability, the content is usually 30% by weight or less, and 20% by weight or less (for example, 15% by weight or less). ). Further, from the viewpoints of convenience, cost reduction, etc. during production, distribution, storage, etc., the content of the abrasive grains can be, for example, 0.2% by weight or more, preferably 1% by weight or more, and more preferably Is 3% by weight or more (for example, 4% by weight or more).

  The polishing composition disclosed herein may be a one-part type or a multi-part type including a two-part type. For example, the liquid A containing a part of the constituent components (typically components other than the solvent) of the polishing composition and the liquid B containing the remaining components are mixed to polish the polishing object. It may be configured to be used.

<Preparation of polishing composition>
The manufacturing method of polishing composition disclosed here is not specifically limited. For example, each component contained in the polishing composition may be mixed using a well-known mixing device such as a blade-type stirrer, an ultrasonic disperser, or a homomixer. The aspect which mixes these components is not specifically limited, For example, all the components may be mixed at once and may be mixed in the order set suitably.

<Polishing method>
According to this specification, a polishing method for polishing a material to be polished having a Vickers hardness of 1500 Hv or more is provided. The above polishing method is characterized by including a step of polishing an object to be polished using the polishing composition disclosed herein. A polishing method according to a preferred embodiment includes a step of performing preliminary polishing (preliminary polishing step) and a step of performing final polishing (finishing polishing step). Here, the preliminary polishing step is a step of performing preliminary polishing on a polishing object made of a material having at least a surface (surface to be polished) having a Vickers hardness of 1500 Hv or more. In a typical embodiment, the preliminary polishing process is a polishing process that is arranged immediately before the finishing polishing process. The preliminary polishing process may be a single-stage polishing process or a multi-stage polishing process of two or more stages. Further, the finish polishing step referred to here is a step of performing finish polishing on the polishing target that has been subjected to preliminary polishing, and is the last of the polishing steps performed using a polishing slurry containing abrasive grains ( That is, it means a polishing step arranged on the most downstream side. Thus, in the polishing method including the preliminary polishing step and the final polishing step, the polishing composition disclosed herein may be used in the preliminary polishing step, may be used in the final polishing step, or preliminary polishing. It may be used in both the process and the finish polishing process.

  In a preferred embodiment, the polishing step using the polishing composition is a preliminary polishing step. In the preliminary polishing process, a required polishing rate is larger than that in the finishing polishing process. Therefore, the polishing composition disclosed herein is suitable as a polishing composition (preliminary polishing composition) used in a preliminary polishing step on the surface of a high hardness material. When the preliminary polishing step includes two or more stages of multiple polishing steps, the polishing composition disclosed herein can be preferably applied to the preliminary (upstream) preliminary polishing. Especially, it can be preferably used in the first preliminary polishing step (typically the primary polishing step) that has passed through the lapping step described later.

  The preliminary polishing and the finishing polishing can be applied to both polishing by a single-side polishing apparatus and polishing by a double-side polishing apparatus. In a single-side polishing machine, a polishing object is affixed to a ceramic plate with wax, or a polishing object is held using a holder called a carrier, and a polishing pad is pressed against one side of the polishing object while supplying a polishing composition. Then, one side of the object to be polished is polished by relatively moving both of them (for example, rotational movement). In a double-side polishing apparatus, a polishing object is held by using a holder called a carrier, and a polishing pad is pressed against the opposite surface of the polishing object while supplying a polishing composition from above, and these are rotated in a relative direction. Thus, both surfaces of the object to be polished are polished simultaneously.

  The polishing pad used in each polishing step disclosed herein is not particularly limited. For example, any of a non-woven fabric type, a suede type, a rigid foamed polyurethane type, a product containing abrasive grains, a product containing no abrasive grains, and the like may be used.

  The abrasive polished by the method disclosed herein is typically cleaned after polishing. This washing can be performed using an appropriate washing solution. The cleaning liquid to be used is not particularly limited, and a known and commonly used cleaning liquid can be appropriately selected and used.

  Note that the polishing method disclosed herein may include any other process in addition to the preliminary polishing process and the finishing polishing process. An example of such a process is a lapping process performed before the preliminary polishing process. The lapping step is a step of polishing the polishing object by pressing the surface of the polishing surface plate (for example, cast iron surface plate) against the polishing object. Therefore, no polishing pad is used in the lapping process. The lapping process is typically performed by supplying abrasive grains (typically diamond abrasive grains) between the polishing surface plate and the object to be polished. Further, the polishing method disclosed herein may include an additional process (a cleaning process or a polishing process) before the preliminary polishing process or between the preliminary polishing process and the finishing polishing process.

  Hereinafter, some examples relating to the present invention will be described. However, the present invention is not intended to be limited to the examples. In the following description, “%” is based on weight unless otherwise specified.

<Preparation of polishing composition>
(Example 1)
Α-alumina (average secondary particle diameter 500 nm) as the first alumina abrasive grains, alumina sol (average secondary particle diameter 90 nm) as the second alumina abrasive grains, and potassium permanganate (KMnO ₄ ) as the polishing aid ) And deionized water were mixed to prepare a polishing composition. The content of α-alumina in the polishing composition was 6%, the content of alumina sol was 2%, and the content of KMnO ₄ was 1.2%. The pH of the polishing composition was adjusted to 9.0 using potassium hydroxide (KOH).

(Example 2)
Example 1 except that hydrogen peroxide (H ₂ O ₂ ) was used instead of KMnO ₄ and the content of H ₂ O ₂ in the polishing composition was 1.2%. A polishing composition was prepared.

Example 3
For polishing in the same manner as in Example 1 except that fumed alumina (average secondary particle size 250 nm) was used instead of alumina sol and the content of fumed alumina in the polishing composition was 2%. A composition was prepared.

(Comparative Example 1)
A polishing composition was prepared in the same manner as in Example 1 except that alumina sol as the second alumina abrasive grains was not used.

(Comparative Example 2)
A polishing composition was prepared in the same manner as in Example 1 except that α-alumina as the first alumina abrasive grains was not used and the content of the alumina sol was 6%.

(Comparative Example 3)
A polishing composition was prepared in the same manner as in Example 3 except that α-alumina as the first alumina abrasive grains was not used and the content of fumed alumina was 6%.

<Evaluation of polishing rate>
The prepared polishing composition was directly used as a polishing liquid, and polishing was performed on the surface of an SiC wafer that had been lapped in advance using diamond abrasive grains having an average particle diameter of 5 μm under the following conditions. And the polishing rate was computed according to the following formulas (1) and (2). The results are shown in the corresponding column of Table 1.
(1) Polishing allowance [cm] = SiC wafer weight difference before and after polishing [g] / SiC density [g / cm ³ ] (= 3.21 g / cm ³ ) / Polishing target area [cm ² ] ( = 19.62 cm ² )
(2) Polishing rate [nm / hour] = polishing allowance [cm] × 10 ⁷ / polishing time (= 1 hour)
[Policing condition]
Polishing device: Single-side polishing device manufactured by Nippon Engis Co., Ltd. Model “EJ-380IN”
Polishing pad: “SUBA800” manufactured by Nitta Haas
Polishing pressure: 300 g / cm ²
Surface plate rotation speed: 80 rotations / minute Polishing time: 1 hour Head rotation speed: 40 rotations / minute Polishing liquid supply rate: 20 mL / minute (flowing)
Polishing liquid temperature: 25 ° C
Polishing object: SiC wafer (conduction type: n-type, crystal type 4H 4 ° off) 2 inches

<Flatness>
Using a non-contact surface shape measuring instrument (trade name “NewView 5032”, manufactured by Zygo), the surface roughness Ra is measured under the conditions of a magnification of 10 times and a measurement area of 700 μm × 500 μm. (Nm) was measured. The results are shown in Table 1.

  As shown in Table 1, the polishing composition of Example 1 using a combination of α-alumina and alumina sol having a smaller average secondary particle diameter than the first alumina abrasive grains and the second alumina abrasive grains, While maintaining a polishing rate comparable to that of the polishing composition of Comparative Example 1 in which the α-alumina alone was used, the surface roughness was suppressed to a smaller level. The polishing composition of Example 2 using a combination of the same α-alumina and alumina sol as in Example 1 has an improved polishing rate compared to the polishing composition of Comparative Example 2 using the above-mentioned alumina sol alone, In addition, the surface roughness was kept small. The polishing composition of Example 3 using a combination of the first alumina abrasive grains and fumed alumina having a smaller average secondary particle size than that of the first alumina abrasive grains was used for polishing of Comparative Example 3 using the fumed alumina alone. Compared with the composition, the polishing rate was improved, and the surface roughness was also kept small. From these results, it was confirmed that by using a combination of alumina abrasive grains having different average secondary particle diameters, both the polishing rate and the surface flatness can be achieved at a high level. In the polishing composition of Example 1, a higher polishing rate was realized as compared with Example 2.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

Claims (5)

A polishing composition for polishing a material having a Vickers hardness of 1500 Hv or more, wherein the material having a Vickers hardness of 1500 Hv or more is silicon carbide,
A first alumina abrasive grain having an average secondary particle diameter D2 _f ;
A second alumina abrasive grain having an average secondary particle diameter D2 _s smaller than the first alumina abrasive grain,
The average secondary particle diameter D2 _{f of} the first alumina abrasive grains is 350 nm or more and 1000 nm or less,
The average secondary particle diameter D2 _s second alumina abrasive grains is 20nm or more 300nm or less, the polishing composition. The polishing composition according to claim 1, wherein the first alumina abrasive grains include α-alumina, and the second alumina abrasive grains include at least one selected from the group consisting of alumina sol and intermediate alumina. The relationship between the average secondary particle diameter D2 _f of the first alumina abrasive grains and the average secondary particle diameter D2 _{s of} the second alumina abrasive grains satisfies the following formula: 1 <(D2 _f / D2 _s ) <20; The polishing composition according to claim 1 or 2. The ratio of the content of the first alumina abrasive grains and the second alumina abrasive grains (first alumina abrasive grains: second alumina abrasive grains) is in the range of 95: 5 to 5:95 on a weight basis. 4. The polishing composition according to any one of items 1 to 3 . The polishing composition according to any one of claims 1 to 4 , wherein the pH is in the range of 8 to 11.