JP6362395B2 - Polishing composition and method for manufacturing magnetic disk substrate - Google Patents

Description

  The present invention relates to a polishing composition for use in polishing a magnetic disk substrate and a method for producing a magnetic disk substrate using the polishing composition.

  A magnetic disk substrate is required to have a highly accurate surface for high capacity. For this reason, the manufacturing process of the magnetic disk substrate generally includes a step of polishing the surface to be polished of the magnetic disk substrate. Such a polishing process is usually performed by supplying a polishing composition (polishing slurry) containing abrasive grains to the object to be polished. The polishing step typically includes a polishing (primary polishing) step that places importance on polishing efficiency, and a final polishing step that is performed to finish the surface accuracy of the final product. Patent Documents 1 to 3 are listed as technical documents related to polishing of a magnetic disk substrate. Patent Document 4 is a technical document mainly relating to polishing of a silicon substrate.

Japanese Patent No. 3997154 Japanese Patent No. 4255976 Japanese Patent No. 4251516 Japanese Patent No. 3926293

  By the way, when a polishing object such as a substrate is polished with a polishing composition, a polishing pad is usually used together with the polishing composition. In such a polishing pad, as its use time (that is, polishing time) increases, the polishing surface is worn or deteriorated due to the influence of components contained in the polishing composition, friction with the object to be polished, or the like. Deterioration of the polishing pad may adversely affect the polishing process performed using the polishing pad, and specifically contributes to a decrease in the polishing rate (amount for removing the surface of the object to be polished per unit time). It may become. In order to prevent such adverse effects, the polishing process is continued by replacing the polishing pad that has been used after a certain polishing time with a new one, or by regenerating its polishing surface. Therefore, if the reduction of the polishing rate when the polishing pad is used for a long time can be effectively suppressed, it not only has an advantage in cost, but also improves the quality stability of the polishing object and improves the polishing efficiency. This is preferable in terms of (typically shortening the polishing time).

  The present invention has been made in view of such circumstances, and is a polishing composition used for polishing a magnetic disk substrate, which can suppress a decrease in polishing rate due to long-time use of a polishing pad. An object is to provide a composition. Another object of the present invention is to provide a method for producing a magnetic disk substrate using such a polishing composition.

According to this specification, a polishing composition for use in polishing a magnetic disk substrate is provided. The polishing composition contains silica abrasive grains having an average minor axis Ds and inorganic particles having an average particle diameter Db of less than 50% of the average minor axis Ds. According to such a polishing composition, it is possible to suppress a decrease in polishing rate due to long-time use of the polishing pad.
In the present specification, “long-term use of the polishing pad” means that the polishing pad is used for polishing a polishing object for a time corresponding to a substantial life of the so-called polishing pad. From the viewpoint of cost, it is preferable that the polishing pad be used for a longer time. The polishing composition disclosed herein is preferable for polishing in a mode in which, for example, one polishing pad is used for 20 hours or longer (preferably 40 hours or longer, more preferably 100 hours or longer, more preferably 200 hours or longer). Can be applied.

  In a preferred embodiment of the polishing composition disclosed herein, the polishing composition contains 3 to 50 parts by weight of the inorganic particles with respect to 100 parts by weight of the silica abrasive grains. According to such a polishing composition, it is possible to suitably suppress a decrease in the polishing rate due to the use of the polishing pad for a long time.

  The polishing composition disclosed herein preferably has an electric conductivity of 10 mS / cm or more. According to such a polishing composition, it is possible to effectively suppress a decrease in the polishing rate due to long-time use of the polishing pad.

  As the silica abrasive grains, those having an average minor axis Ds of 25 nm or more and 300 nm or less are preferable. According to the polishing composition containing such silica abrasive grains, a practical polishing rate can be maintained for a long time. Moreover, according to the polishing composition containing such silica abrasive grains, the occurrence of defects on the polishing target surface of the magnetic disk substrate that is the polishing target tends to be reduced.

  According to a preferred embodiment of the technology disclosed herein, the polishing composition is used in polishing with a polishing pad having a polishing surface made of polyurethane foam. In polishing using such a polishing pad, it is particularly meaningful to use the polishing composition disclosed herein.

According to this specification, it is also a polishing composition for use in polishing a magnetic disk substrate, comprising silica abrasive grains having an average minor axis Ds, and an average particle diameter Db smaller than the average minor axis Ds. Polishing composition containing the inorganic particle which has is provided. The polishing composition is configured so that the polishing rate does not become higher in polishing with a polishing pad at the beginning of use than the control polishing composition in which the inorganic particles are replaced with the same weight of the silica abrasive. Has been. According to such a polishing composition, a decrease in the polishing rate due to long-time use of the polishing pad can be suppressed as compared with the control polishing composition. As a result, the average polishing rate over the entire period of use of the polishing pad (for example, about 200 hours) can be higher for the polishing composition than for the reference polishing composition.
In this specification, the “polishing pad at the beginning of use” refers to polishing immediately after starting use for the first time in the polishing step (typically within 30 minutes) after dressing a new polishing pad by a general method. Refers to the pad.

  According to this specification, a method of manufacturing a magnetic disk substrate is provided. In the manufacturing method, a polishing object is set in a polishing apparatus including a polishing pad having a polishing surface made of polyurethane foam, and any of the polishing disclosed herein is provided between the polishing object and the polishing pad. And supplying the composition for polishing, and polishing the polishing object by moving the polishing pad relative to the polishing object. According to such a manufacturing method, since a decrease in the polishing rate due to long-time use of the polishing pad can be suppressed, a magnetic disk substrate having a high quality surface can be stably manufactured.

4 is a graph showing the results of a polishing rate evaluation test using polishing compositions according to Example 1 and Comparative Example 1. FIG.

  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.

<Abrasive>
The polishing composition disclosed herein contains abrasive grains. The abrasive is a component that plays a role of realizing a high polishing effect when an object to be polished is polished using a polishing composition containing the abrasive. In the polishing composition disclosed herein, the abrasive grains preferably include silica abrasive grains. The silica abrasive grains are not particularly limited as long as they are composed of silica. Specifically, examples of the silica abrasive include colloidal silica abrasive, fumed silica abrasive, and precipitated silica abrasive. As the silica abrasive grains disclosed herein, colloidal silica abrasive grains can be preferably used.

  In a preferred embodiment of the abrasive grains disclosed herein, the average projected area equivalent circle diameter Da (hereinafter referred to as “average particle diameter Da”) of the abrasive grains is preferably 20 nm or more, more preferably 30 nm or more. More preferably, it is 50 nm or more. By increasing the average particle diameter Da of the abrasive grains, higher polishing efficiency (typically a polishing rate) can be realized. Further, from the viewpoint of easily obtaining a surface with higher smoothness, the average particle diameter Da is preferably 900 nm or less, more preferably 500 nm or less, and further preferably 300 nm or less (for example, 100 nm or less). In the technique disclosed herein, the average particle diameter Da of the abrasive grains can be determined by, for example, photographic observation using an electron microscope. Specifically, a predetermined number (for example, 500) of abrasive grains is observed using a scanning electron microscope (SEM), and the diameter of a circle having the same area as the projected area of each particle image is calculated. By calculating the average value by the number average, the average particle diameter Da of the abrasive grains can be obtained.

  The shape (outer shape) of the abrasive grains may be spherical or non-spherical. Specific examples of non-spherical abrasive grains include peanut shapes (ie, peanut shell shapes), bowl-shaped shapes, rugby ball shapes, rosary ball shapes, chain shapes, branched chain shapes, and other elongated shapes. Is mentioned. Other specific examples of non-spherical abrasive grains include confetti-shaped abrasive grains.

  It is appropriate that the average minor axis Ds of the abrasive grains is usually 15 nm or more. From the viewpoint of improving the polishing rate, the average minor axis Ds of the abrasive grains is preferably 25 nm or more, more preferably 45 nm or more, and further preferably 50 nm or more. Further, the average minor axis Ds of the abrasive grains is suitably 900 nm or less, for example, from the viewpoint of obtaining a highly smooth surface, preferably 500 nm or less, more preferably 300 nm or less (typically 100 nm). Hereinafter, for example, 80 nm or less is appropriate.

  The average minor axis Ds of the abrasive grains and the major axis / minor axis ratio (aspect ratio) of the abrasive grains to be described later can be determined by, for example, photographic observation using an electron microscope. Specifically, a scanning electron microscope (SEM) is used to observe a predetermined number (for example, 500) of abrasive grains and draw a rectangle that circumscribes each particle image and has a minimum area. About the rectangle drawn with respect to each particle | grain image, the length of the short side is measured, and the average short diameter Ds of an abrasive grain can be calculated | required by calculating the average value by number average. In addition, a value obtained by dividing the long side length (major axis value) by the short side length (minor axis value) of the rectangle is calculated as a major axis / minor axis ratio (aspect ratio). An average aspect ratio can be obtained by arithmetically averaging the aspect ratios of the predetermined number of particles. The shape (outer shape) of the abrasive grains can also be grasped by photographic observation using an electron microscope.

  Although not particularly limited, the average value (average aspect ratio) of the major axis / minor axis ratio of the abrasive grains is preferably 1.05 or more, and more preferably 1.1 or more. Higher polishing rates can be achieved by increasing the average aspect ratio of the abrasive grains. The average aspect ratio of the abrasive grains is preferably 3.0 or less, more preferably 2.0 or less, and still more preferably 1.5 or less, from the viewpoint of reducing scratches.

  The content of abrasive grains in the polishing composition (that is, the abrasive grain concentration of the polishing composition) is not particularly limited. The abrasive concentration can be, for example, 300 g / L or less, and is usually preferably 200 g / L or less, more preferably 150 g / L or less, and even more preferably 100 g / L or less. The abrasive concentration is preferably 10 g / L or more, and more preferably 30 g / L or more. It is preferable that the abrasive concentration is equal to or higher than the lower limit value described above because the polishing rate tends to be improved. It is practically preferable in terms of cost that the abrasive concentration is not more than the upper limit described above.

<Inorganic particles>
The polishing composition disclosed herein contains inorganic particles. The inorganic particles enable the mechanical polishing force of the silica abrasive grains to act more effectively on the object to be polished, regardless of deterioration due to long-term use of the polishing pad, thereby reducing the polishing rate. It is a component that plays a role to suppress.

  The material of the inorganic particles is not particularly limited, and can be appropriately selected according to the purpose of use or usage of the polishing composition. Specific examples of the inorganic particles include silica particles, alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, oxide particles such as bengara particles; Examples thereof include 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 inorganic particle can be used individually by 1 type or in combination of 2 or more types.

  A suitable example of the inorganic particles is silica particles. Examples of the silica particles include colloidal silica particles, fumed silica particles, particles made of precipitated siliceous particles, and the like. As a preferred example of the inorganic particles disclosed herein, colloidal silica particles are exemplified.

  Alternatively, in another preferred embodiment of the inorganic particles disclosed herein, particles other than silica particles can be employed. For example, particles harder than silica (such as alumina particles) may be used as the inorganic particles. Alternatively, particles softer than silica (for example, magnesium oxide particles) may be used as the inorganic particles.

  The shape (outer shape) of the inorganic particles may be spherical or non-spherical. Specific examples of non-spherical inorganic particles include peanut shape (ie, peanut shell shape), bowl shape, rugby ball shape, rosary ball shape, chain shape, branched chain shape, and other long and narrow inorganic particles. Is mentioned. Other specific examples of non-spherical inorganic particles include confetti-shaped inorganic particles.

  In the polishing composition disclosed herein, the average projected area equivalent circle diameter Db (hereinafter referred to as “average particle diameter Db”) of the inorganic particles is usually smaller than the average minor axis Ds of the abrasive grains (that is, , Ds / Db> 1) is suitable, and Db is preferably less than 50% of Ds (ie, Ds / Db> 2). By containing inorganic particles having such an average particle diameter Db, the inorganic particles function as anti-slip, and even when the polishing pad has deteriorated due to long-term use or the like, the polishing pad is prevented from slipping (slipping). Tend to be. For this reason, according to the polishing composition containing this inorganic particle, the fall of the polishing rate by long-time use of a polishing pad can be suppressed. From the viewpoint of better suppressing a decrease in the polishing rate due to long-time use of the polishing pad, Ds / Db is preferably larger than 3, more preferably 5 or more, still more preferably 8 or more, for example 10 or more. The upper limit of Ds / Db is not particularly limited, but is usually suitably 100 or less, preferably 50 or less, more preferably 30 or less, and even more preferably 20 or less.

In a preferred embodiment of the polishing composition disclosed herein, the average particle diameter Db of the inorganic particles is preferably 1 nm or more, more preferably 3 nm or more, further preferably 5 nm or more, for example, 8 nm or more. . The average particle diameter Db of the inorganic particles is preferably 100 nm or less, more preferably 50 nm or less, and still more preferably less than 30 nm.
Here, the average particle diameter Db of the inorganic particles can be determined, for example, by photographic observation using an electron microscope. Specifically, a predetermined number (for example, 500) of inorganic particles is observed using a scanning electron microscope (SEM), and the diameter of a circle having the same area as the projected area of each particle image is calculated. By calculating the average value by the number average, the average particle diameter Db of the inorganic particles can be obtained.

  The content of the inorganic particles in the polishing composition (that is, the concentration of inorganic particles in the polishing composition) is not particularly limited. The concentration of the inorganic particles in the polishing composition can be, for example, 100 g / L or less, usually 50 g / L or less, more preferably 20 g / L or less. Moreover, it is preferable that the inorganic particle density | concentration of polishing composition is 1 g / L or more, More preferably, it is 3 g / L or more. When the inorganic particle concentration is equal to or higher than the lower limit value described above, a decrease in the polishing rate due to long-time use of the polishing pad can be effectively suppressed. When the inorganic particle concentration is equal to or lower than the above-described upper limit value, the content of abrasive grains can be ensured, so that the polishing rate can be improved.

  The content of the inorganic particles in the polishing composition is such that the inorganic particles are 1 part by weight or more and 60 parts by weight or less (more preferably 3 parts by weight or more and 50 parts by weight or less, more preferably 100 parts by weight of the abrasive grains. Is preferably 5 parts by weight or more and 30 parts by weight or less. When the content of the inorganic particles is in the above-described range, the improvement of the polishing rate and the suppression of the decrease in the polishing rate due to the long use of the polishing pad can be balanced.

  The total concentration of the abrasive grains and the inorganic particles in the polishing composition is not particularly limited. The total concentration is usually suitably 350 g / L or less, preferably 200 g / L or less, more preferably 150 g / L or less, still more preferably 120 g / L or less, for example 100 g / L or less. Moreover, it is preferable that the said total concentration is larger than 10 g / L, More preferably, it is 30 g / L or more, More preferably, it is 50 g / L or more. When the total concentration of the abrasive grains and the inorganic particles is within the above-described range, an improvement in the polishing rate and a suppression of a decrease in the polishing rate due to the long-time use of the polishing pad can be balanced.

  As described above, the inorganic particles disclosed herein are mainly used for the purpose of suppressing a decrease in the polishing rate, and need not exhibit a practical level of polishing power alone as abrasive grains. . For this reason, the polishing composition disclosed herein is in the initial stage of use compared to the control polishing composition having a composition in which the inorganic particles contained in the polishing composition are replaced with the same weight of the silica abrasive grains. In the polishing with the polishing pad, the polishing rate can be lowered. On the other hand, such a polishing composition contains the inorganic particles, so that the polishing time is, for example, 20 hours or longer (preferably 40 hours or longer, more preferably 100 hours or longer, more preferably 200 hours or longer). A decrease in the polishing rate can be suppressed as compared with the target polishing composition. As a result, the average polishing rate over the entire period of use of the polishing pad (for example, about 200 hours) can be higher for the polishing composition than for the reference polishing composition. The inorganic particles do not need to exhibit a practical level of polishing power alone as described above, but this does not exclude that the inorganic particles exhibit a certain level of polishing power. .

<Electrical conductivity>
The electrical conductivity of the polishing composition disclosed herein is preferably 10 mS / cm or more. When the electrical conductivity increases, a decrease in the polishing rate due to long-time use of the polishing pad tends to be more appropriately suppressed. The reason is not necessarily clear, but, for example, the electrostatic repulsion between the components contained in the polishing composition is reduced due to an increase in electrical conductivity, and the polishing pad and the object to be polished are polished during polishing. It can be considered that an increase in the amount of inorganic particles or abrasive grains present in the sphere has an advantageous effect. From this viewpoint, the electric conductivity is more preferably 20 mS / cm or more, and further preferably 30 mS / cm or more (typically 40 mS / cm or more, for example, 50 mS / cm or more).
The upper limit value of the electrical conductivity of the polishing composition is not particularly limited, but is usually suitably 500 mS / cm or less, and preferably 200 mS / cm or less from the viewpoint of suppressing excessive association of abrasive grains. More preferably, it is 150 mS / cm or less (for example, 120 mS / cm or less).
In this specification, the electrical conductivity of the polishing composition is determined under the condition that the total concentration of the abrasive grains and the inorganic particles in the polishing composition is 77.5 g / L (however, the abrasive grains and the inorganic particles The weight ratio is the same as that of the polishing composition).
The electrical conductivity of the polishing composition can be measured by a conventional method. As the measuring device, for example, a conductivity meter (model “DS-12”, working electrode “3552-10D”) manufactured by Horiba, Ltd. can be used. As a measurement sample used for measuring electrical conductivity, for example, the polishing composition is diluted with water so that the total concentration of abrasive grains and inorganic particles in the polishing composition is 77.5 g / L. Alternatively, a concentrated product can be used. As water, ion exchange water, distilled water, pure water, or the like can be used.

  The method for adjusting the electrical conductivity of the polishing composition is not particularly limited. For example, with respect to some or all of the constituents of the polishing composition, an appropriate amount of electrolyte (salt, acid, alkali, etc.) is blended in the polishing composition, the polishing composition is diluted or concentrated The electric conductivity can be adjusted by a method such as ion exchange treatment. The method for adjusting electrical conductivity may be used individually by 1 type, and may use 2 or more types together.

<Salt>
The polishing composition disclosed herein may contain a salt in addition to the above-described abrasive grains and inorganic particles. The salt is ionized in the polishing composition, and at least a part of the salt is present as a cation or an anion, thereby contributing to adjustment of electric conductivity. The salt may be an inorganic salt or an organic salt. The salt may be an acidic salt, a basic salt, or a normal salt. The polishing composition disclosed herein may contain one kind of salt alone, or may contain two or more kinds of salts in combination.

  Examples of salts include inorganic or organic acid metal salts such as lithium salts, sodium salts and potassium salts, such as alkali metal salts; ammonium salts such as quaternary ammonium salts such as tetramethylammonium salts and tetraethylammonium salts. Alkanolamine salts such as monoethanolamine salt, diethanolamine salt and triethanolamine salt; Specific examples of the salt include tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate and the like alkali metal phosphates and alkali metals Hydrogen phosphate salt; alkali metal salt of organic acid exemplified above; other alkali metal salt of glutamic acid diacetic acid, alkali metal salt of diethylenetriaminepentaacetic acid, alkali metal salt of hydroxyethylethylenediaminetriacetic acid, triethylenetetramine hexaacetic acid Alkali metal salts; and the like. The alkali metal in these alkali metal salts can be, for example, lithium, sodium, potassium, and the like. As a salt that can be contained in the polishing composition disclosed herein, for example, a salt of an inorganic acid is preferably employed. Typically, an alkali metal salt or an ammonium salt of an inorganic acid can be preferably used. For example, potassium chloride, sodium chloride, ammonium chloride, potassium phosphate and the like can be preferably used.

  When salt is contained in the polishing composition, the content is not particularly limited, and can be set so that, for example, the electric conductivity of the polishing composition falls within an appropriate range. The content of the salt in the polishing composition is usually appropriately 0.01 mol / L or more, preferably 0.03 mol / L or more, more preferably 0.05 mol / L or more, and still more preferably. Is 0.1 mol / L or more (typically 0.15 mol / L or more, for example, 0.18 mol / L or more). When the salt content is equal to or higher than the lower limit value described above, a decrease in the polishing rate due to long-term use of the polishing pad can be effectively suppressed. The upper limit value of the salt content in the polishing composition is not particularly limited. The salt content is usually suitably 3 mol / L or less, preferably 1 mol / L or less, more preferably 0.5 mol / L or less, and even more preferably 0.25 mol / L or less. Excessive association or aggregation of abrasive grains and / or inorganic particles can be suppressed when the salt content is not more than the upper limit described above.

<Acid>
The polishing composition preferably contains an acid as a polishing accelerator. Examples of acids that can be suitably used include, but are not limited to, inorganic acids and organic acids (for example, organic carboxylic acids, organic phosphonic acids, organic sulfonic acids, etc. having about 1 to 10 carbon atoms). . An acid can be used individually by 1 type or in combination of 2 or more types.
Specific examples of the inorganic acid include nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, hypophosphorous acid, phosphonic acid, boric acid and the like.
Specific examples of organic acids include citric acid, maleic acid, malic acid, glycolic acid, succinic acid, itaconic acid, malonic acid, iminodiacetic acid, gluconic acid, lactic acid, mandelic acid, tartaric acid, crotonic acid, nicotinic acid, acetic acid , Adipic acid, formic acid, oxalic acid, propionic acid, valeric acid, caproic acid, caprylic acid, capric acid, cyclohexanecarboxylic acid, phenylacetic acid, benzoic acid, crotonic acid, methacrylic acid, glutaric acid, fumaric acid, phthalic acid, isophthalic acid Acid, terephthalic acid, glycolic acid, tartronic acid, glyceric acid, hydroxybutyric acid, hydroxyacetic acid, hydroxybenzoic acid, salicylic acid, isocitric acid, methylene succinic acid, gallic acid, ascorbic acid, nitroacetic acid, oxaloacetic acid, glycine, alanine, glutamic acid , Aspartic acid, nicotinic acid, picoline , Methyl acid phosphate, ethyl acid phosphate, ethyl glycol acid phosphate, isopropyl acid phosphate, phytic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetra (methylenephosphonic acid), diethylenetriaminepenta (Methylenephosphonic acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethanehydroxy-1,1,2-triphosphonic acid Ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid, α-methylphosphono Examples include succinic acid, aminopoly (methylenephosphonic acid), methanesulfonic acid, ethanesulfonic acid, aminoethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and 2-naphthalenesulfonic acid.

When an acid is contained in the polishing composition, the content is preferably 1 g / L or more, more preferably 5 g / L or more. If the acid content is too small, the polishing rate is lowered, which may be undesirable in practice.
Moreover, when an acid is contained in polishing composition, it is preferable that the content is 100 g / L or less, More preferably, it is 50 g / L or less. When there is too much content of an acid, the surface precision of a grinding | polishing target object will worsen, and it may be unpreferable practically.

<Oxidizing agent>
The polishing composition disclosed herein can contain an oxidizing agent as a polishing accelerator, if necessary.

  Examples of the oxidizing agent include peroxide, nitric acid or a salt thereof, peroxo acid or a salt thereof, permanganic acid or a salt thereof, chromic acid or a salt thereof, oxygen acid or a salt thereof, metal salt, sulfuric acid, and the like. However, it is not limited to these. An oxidizing agent can be used individually by 1 type or in combination of 2 or more types. Specific examples of the oxidizing agent include hydrogen peroxide, sodium peroxide, barium peroxide, nitric acid, iron nitrate, aluminum nitrate, ammonium nitrate, peroxodisulfuric acid, ammonium peroxodisulfate, peroxodisulfate metal salt, peroxophosphoric acid, peroxosulfuric acid. , Sodium peroxoborate, performic acid, peracetic acid, perbenzoic acid, perphthalic acid, hypobromous acid, hypoiodous acid, chloric acid, bromic acid, iodic acid, periodic acid, perchloric acid, hypochlorous acid Examples thereof include acid, sodium hypochlorite, calcium hypochlorite, potassium permanganate, metal chromate, metal dichromate, iron chloride, iron sulfate, iron citrate, and iron iron sulfate. Preferable oxidizing agents include hydrogen peroxide, iron nitrate, peroxodisulfuric acid and nitric acid. It preferably contains at least hydrogen peroxide, and more preferably consists of hydrogen peroxide.

When the polishing composition contains an oxidizing agent, the content is preferably 1 g / L or more, more preferably 3 g / L or more, and further preferably 4 g / L or more. If the content of the oxidizing agent is too small, the rate of oxidizing the object to be polished becomes slow and the polishing rate is lowered, which may be undesirable in practice.
Moreover, when an oxidizing agent is included in polishing composition, it is preferable that the content is 30 g / L or less, More preferably, it is 15 g / L or less. When there is too much content of an oxidizing agent, the surface precision of a grinding | polishing target object will deteriorate, and it may be unpreferable practically.

<Basic compound>
The polishing composition can contain a basic compound. Here, the basic compound refers to a compound having a function of increasing the pH of the composition when added to the polishing composition. Examples thereof include alkali metal hydroxides, carbonates and hydrogencarbonates, quaternary ammonium or salts thereof, ammonia, amines, phosphates and hydrogenphosphates, and organic acid salts. A basic compound can be used individually by 1 type or in combination of 2 or more types.

Specific examples of the alkali metal hydroxide include potassium hydroxide and sodium hydroxide.
Specific examples of the carbonate or bicarbonate include ammonium bicarbonate, ammonium carbonate, potassium bicarbonate, potassium carbonate, sodium bicarbonate, sodium carbonate and the like.
Specific examples of the quaternary ammonium or a salt thereof include quaternary ammonium hydroxide such as tetramethylammonium hydroxide, tetraethylammonium hydroxide, and tetrabutylammonium hydroxide.
Specific examples of amines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N- (β-aminoethyl) ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, anhydrous piperazine , Piperazine hexahydrate, 1- (2-aminoethyl) piperazine, N-methylpiperazine, guanidine, azoles such as imidazole and triazole, and the like.
Specific examples of phosphates and hydrogen phosphates include alkalis such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. Metal salts are mentioned.

<Surfactant>
The polishing composition may contain a surfactant for the purpose of improving dispersion stability. As the surfactant, an anionic one can be preferably used. For example, a sulfonic acid anionic surfactant can be preferably used. The concept of the sulfonic acid anionic surfactant here includes a sulfonic acid compound and a salt thereof. Examples of the sulfonate compound include polyalkylaryl sulfonic acid compounds such as naphthalene sulfonic acid formaldehyde condensate, methyl naphthalene sulfonic acid formaldehyde condensate, anthracene sulfonic acid formaldehyde condensate, benzene sulfonic acid formaldehyde condensate; melamine sulfonic acid Melamine formalin sulfonic acid compounds such as formaldehyde condensates; lignin sulfonic acid compounds such as lignin sulfonic acid and modified lignin sulfonic acid; Aromatic amino sulfonic acid compounds such as aminoarylsulfonic acid-phenol-formaldehyde condensates; , Polyisoprene sulfonic acid, polyvinyl sulfonic acid, polyallyl sulfonic acid, polyisoamylene sulfonic acid, polystyrene sulfonic acid and the like. As a salt of such a sulfonic acid compound, an alkali metal salt such as a sodium salt or a potassium salt is preferable. A preferred example of the sulfonic acid compound salt is naphthalenesulfonic acid formaldehyde condensate sodium salt.
Among the sulfonic acid anionic surfactants, naphthalene sulfonic acid formaldehyde condensates such as naphthalene sulfonic acid formaldehyde condensate and methyl naphthalene sulfonic acid formaldehyde condensate and salts thereof are preferable.

Other examples of the anionic surfactant include polyacrylic acid anionic surfactants such as polyacrylic acid and salts thereof (for example, alkali metal salts such as sodium salt).
Other examples of anionic surfactants include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium polyoxyethylene alkyl ether sulfate, ammonium polyoxyethylene alkyl phenyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate, etc. Is mentioned.

  In the polishing composition containing the surfactant, it is appropriate that the content of the surfactant is, for example, 0.005 g / L or more. The content is preferably 0.01 g / L or more, more preferably 0.1 g / L or more, from the viewpoint of the smoothness of the surface after polishing. Further, from the viewpoint of polishing rate and the like, the content is suitably 100 g / L or less, preferably 50 g / L or less, for example 10 g / L or less.

<Other ingredients>
The polishing composition is used for polishing a polishing composition (typically, a magnetic disk substrate such as a Ni-P substrate) such as a chelating agent or a preservative as long as the effects of the present invention are not significantly hindered. You may further contain the well-known additive which may be used for the polishing composition used as needed.

  Examples of chelating agents include aminocarboxylic acid chelating agents and organic phosphonic acid chelating agents. Examples of aminocarboxylic acid chelating agents include ethylenediaminetetraacetic acid, ethylenediaminetetraacetic acid sodium, nitrilotriacetic acid, nitrilotriacetic acid sodium, nitrilotriacetic acid ammonium, hydroxyethylethylenediaminetriacetic acid, hydroxyethylethylenediamine sodium triacetate, diethylenetriaminepentaacetic acid Diethylenetriamine sodium pentaacetate, triethylenetetramine hexaacetic acid and sodium triethylenetetramine hexaacetate. Examples of organic phosphonic acid chelating agents include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetrakis (methylenephosphonic acid), diethylenetriaminepenta (methylenephosphonic). Acid), ethane-1,1-diphosphonic acid, ethane-1,1,2-triphosphonic acid, ethane-1-hydroxy-1,1-diphosphonic acid, ethane-1-hydroxy-1,1,2-triphosphonic acid Ethane-1,2-dicarboxy-1,2-diphosphonic acid, methanehydroxyphosphonic acid, 2-phosphonobutane-1,2-dicarboxylic acid, 1-phosphonobutane-2,3,4-tricarboxylic acid and α-methylphospho Nosuccinic acid is included. Of these, organic phosphonic acid-based chelating agents are more preferable, and ethylenediaminetetrakis (methylenephosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid) are particularly preferable. A particularly preferred chelating agent is ethylenediaminetetrakis (methylenephosphonic acid).

<Polishing composition>
The pH of the polishing composition is not particularly limited. For example, from the viewpoint of polishing rate, surface smoothness, etc., pH 4 or less is preferable, and pH 3 or less is more preferable. If necessary, a pH adjusting agent such as an organic acid or an inorganic acid can be contained so that the above pH is realized in the polishing liquid. The pH can be preferably applied to, for example, a polishing liquid used for polishing Ni—P.

  The polishing composition as described above is typically supplied to a polishing object (magnetic disk substrate) 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 a polishing composition. Or you may use polishing composition as polishing liquid as it is. That is, the concept of the polishing composition in the technology disclosed herein includes both the polishing liquid (working slurry) supplied to the object to be polished and the concentrated liquid diluted and used as the polishing liquid. .

The polishing composition may be in a concentrated form (concentrated liquid form) before being supplied to the object to be polished. Such a polishing composition in the form of a concentrated solution is advantageous from the viewpoints of convenience, cost reduction, etc. during production, distribution, storage and the like. The concentration factor can be set to about 1.5 to 50 times, for example. From the viewpoint of the storage stability of the concentrate, a concentration factor of about 2 to 20 times (typically 2 to 10 times) is usually appropriate.
Thus, the polishing composition in the form of a concentrated liquid can be suitably used in a mode in which a polishing liquid is prepared by diluting at a desired timing and the polishing liquid is supplied to a polishing object.

<Polishing pad>
The polishing pad used in the method disclosed herein is not particularly limited. As a preferred example, a polishing pad having foamed polyurethane at least on the polishing surface can be mentioned. The polishing pad may be, for example, a polishing pad composed entirely of foamed polyurethane, a polishing pad in which a layer of foamed polyurethane is supported on a pad base material such as a nonwoven fabric, and the like. As the polyurethane foam constituting the polished surface, a polyurethane resin foam formed by a wet film forming method is typically used.

<Application>
The polishing composition disclosed herein can be used for polishing various magnetic disk substrates. As a preferable application object, a magnetic disk substrate (Ni-P substrate) having a nickel phosphorus plating layer on the surface of a base disk is exemplified. The base disk can be made of, for example, aluminum alloy, glass, glassy carbon, or the like. A disk substrate provided with a metal layer or metal compound layer other than the nickel phosphorus plating layer on the surface of such a base disk may be used. Among them, a preferable application target is a Ni-P substrate having a nickel phosphorus plating layer on a base disk made of aluminum alloy.

The polishing composition disclosed herein can be used, for example, as follows. That is, a magnetic disk substrate as a polishing object is set in a polishing apparatus equipped with a polishing pad, and any of the polishing compositions disclosed herein is supplied between the polishing object and the polishing pad. . Typically, a polishing liquid is supplied to the surface of the object to be polished (surface to be polished) through a polishing pad of the polishing apparatus. Typically, the polishing liquid is continuously supplied while the polishing pad is pressed against the surface of the object to be polished, and the two are relatively moved (for example, rotated). The polishing of the object to be polished is completed through this polishing step.
The polishing process as described above may be a part of a manufacturing process of a magnetic disk substrate (for example, a magnetic disk substrate such as a Ni-P substrate). Therefore, according to this specification, the manufacturing method of the board | substrate including the said grinding | polishing process is provided. As the polishing pad, a polishing pad having a polishing surface made of polyurethane foam is particularly preferable.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples. In the following description, “parts” and “%” are based on weight unless otherwise specified.

<Example 1>
Abrasive grains 68.7 g / L, inorganic particles 8.9 g / L (12.9 parts relative to 100 parts of abrasive grains), nitric acid (HNO ₃ ) 20 g / L, potassium chloride (KCl) 14.9 g / L, excess A polishing composition was prepared so that hydrogen oxide (H ₂ O ₂ ) was 6.2 g / L, and the balance was ion-exchanged water. The polishing composition had a pH of 0.6.
As the abrasive grains, colloidal silica having an average particle diameter Da of 68.9 nm and an average minor diameter Ds of 63.9 nm was used. The average particle diameter Da is calculated by observing 500 abrasive grains using a scanning electron microscope (SEM), calculating the diameter of a circle having the same area as the projected area of each particle image, and calculating the average value thereof. Was determined by Similarly, the average short diameter Ds is determined by observing 500 abrasive grains using SEM, measuring the length of the short side of the rectangle drawn for each particle image, and calculating the average value. Obtained by calculating.
As the inorganic particles, colloidal silica having an average particle diameter Db of 19 nm was used. The average particle diameter Db was determined by observing 500 abrasive grains using an SEM, calculating the diameter of a circle having the same area as the projected area of each particle image, and calculating the average value.
The total concentration of abrasive grains and inorganic particles in the polishing composition is 77.5 g / L (7.5%). It was 110 mS / cm when the electrical conductivity of the said polishing composition was measured. The electrical conductivity was measured using a conductivity meter (model “DS-12”, used electrode “3552-10D”) manufactured by HORIBA, Ltd. (the same applies in the following examples).

<Example 2>
A polishing composition was prepared by the same method as that for preparing the polishing composition according to Example 1 described above, except that the concentration of nitric acid was 8 g / L. The polishing composition had a pH of 1.1. The total concentration of abrasive grains and inorganic particles in the polishing composition is 77.5 g / L. The electric conductivity of the polishing composition was measured and found to be 57 mS / cm.

<Example 3>
Abrasive grains 73.0 g / L, inorganic particles 4.5 g / L (6.2 parts with respect to 100 parts of abrasive grains), nitric acid 8 g / L, potassium chloride 14.9 g / L, hydrogen peroxide 6.2 g / L A polishing composition was prepared so that the balance was ion exchange water. The polishing composition had a pH of 1.1. The total concentration of abrasive grains and inorganic particles in the polishing composition is 77.5 g / L. The electric conductivity of the polishing composition was measured and found to be 57 mS / cm.

<Example 4>
A polishing composition was prepared by the same method as that for preparing the polishing composition according to Example 3 described above, except that the concentration of potassium chloride was 7.9 g / L. The polishing composition had a pH of 1.1. The total concentration of abrasive grains and inorganic particles in the polishing composition is 77.5 g / L. The electrical conductivity of the polishing composition was measured and found to be 49 mS / cm.

<Comparative Example 1>
A polishing composition was prepared so that the abrasive grains were 77.5 g / L, nitric acid 20 g / L, hydrogen peroxide 6.1 g / L, and the balance being ion-exchanged water. The polishing composition had a pH of 0.6.
As the abrasive grains, colloidal silica similar to that used in Example 1 was used. The abrasive grain concentration in the polishing composition is 7.5%. The electrical conductivity of the polishing composition was measured and found to be 95 mS / cm.

<Comparative example 2>
A polishing composition was prepared by the same method as that for preparing the polishing composition according to Comparative Example 1 described above, except that the concentration of nitric acid was 8 g / L. The polishing composition had a pH of 1.1. The electric conductivity of the polishing composition was measured and found to be 39 mS / cm.

<Comparative Example 3>
A polishing composition was prepared so that abrasive grains were 77.5 g / L, nitric acid 8 g / L, potassium chloride 14.9 g / L, hydrogen peroxide water 6.1 g / L, and the balance being ion-exchanged water. The polishing composition had a pH of 1.1. As the abrasive grains, colloidal silica similar to that used in Example 1 was used. It was 110 mS / cm when the electrical conductivity of the said polishing composition was measured.

<Comparative example 4>
A polishing composition was prepared by the same method as that of the polishing composition according to Comparative Example 1 described above except that the concentration of nitric acid was 1.5 g / L. The polishing composition had a pH of 1.6. The electric conductivity of the polishing composition was measured and found to be 9.8 mS / cm.

<Polishing pad>
A polishing pad (manufactured by FILWEL, trade name “NP-378”) having a foamed polyurethane produced by a wet film formation method on a polishing surface was prepared.

<Polishing rate evaluation>
The polishing composition according to Example 1 and Comparative Example 1 was directly used as a polishing liquid, and the polishing rate when a magnetic disk substrate was polished under the polishing conditions described later was measured. Further, the relationship between the polishing rate and the polishing time was examined. As the substrate to be polished, a hard disk aluminum substrate having a diameter of 3.5 inches (about 95 mm) and a thickness of 1.27 mm and having an electroless nickel phosphorus plating layer on the surface thereof was used. Schmitt Measurement System Inc. The surface roughness (arithmetic mean roughness (Ra)) of the nickel phosphorus plating layer measured by a laser scan type surface roughness meter “TMS-3000WRC” manufactured by the company was 130 mm before polishing. The polishing time is up to 40 hours, and the weight of the magnetic disk substrate, which is the object to be polished, is measured each time a predetermined time has elapsed from the start of polishing, and converted to the thickness of the magnetic disk substrate removed by polishing. Thus, the polishing rate was calculated.

The polishing conditions in the polishing rate evaluation test were as follows.
Polishing device: Double-side polishing device ("9.5B-5P" manufactured by System Seiko Co., Ltd.)
Polishing load: 120 g / cm ²
Number of substrates loaded: 3 / carrier x 5 carriers (15 total)
Upper platen rotation speed: 27rpm
Lower platen rotation speed: 36rpm
Sun gear rotation speed: 8rpm
Polishing liquid supply rate: 135 mL / min Polishing liquid temperature: 25 ° C.
Rinse: ion-exchanged water (1 to 1.5 L / min)

  The relationship between the polishing rate and the polishing time when the polishing composition according to Example 1 and Comparative Example 1 were polished under the above-described polishing conditions is shown in FIG. The vertical axis in FIG. 1 indicates the polishing rate (unit: μm / min), and the horizontal axis indicates the polishing time (unit: time).

  As is clear from the results shown in FIG. 1, when the magnetic disk substrate was polished using the polishing composition according to Example 1, a good polishing rate was maintained even when polished for 30 hours. It was confirmed that On the other hand, when the magnetic disk substrate was polished using the polishing composition according to Comparative Example 1, although the polishing rate at the beginning of polishing was higher than that in Example 1, the polishing rate was subsequently lowered. When 30 hours passed, the polishing rate was clearly lower than that of the polishing composition according to Example 1. The polishing rate after 40 hours using the polishing composition according to Comparative Example 1 was 60% or less of the initial polishing rate at the start of polishing.

  Next, the polishing compositions according to Examples 1 to 4 and Comparative Examples 1 to 4 were directly used as a polishing liquid, and the polishing rate when polishing for 40 hours (that is, the polishing rate when using a deteriorated polishing pad) and The motor torque was measured. Specifically, the weight of the substrate when 40 hours passed from the start of polishing and the weight of the substrate when polished again for 10 minutes were measured, and the polishing rate was calculated from the difference between them. The motor torque was determined by recording the torque applied to the motor of the lower surface plate when 40 hours had elapsed from the start of polishing. The results are shown in Table 1.

  As can be seen from the comparison between Examples 1 to 4 and Comparative Examples 1 to 4 in Table 1, in any case where the nitric acid concentration is 20 g / L and 8 g / L, the post-degradation polishing rate (ie, The polishing rate with the polishing pad deteriorated by polishing for 40 hours) and the motor torque were clearly improved. From the comparison of Examples 1 to 4, it can be seen that the effect of improving the post-deterioration polishing rate and motor torque tends to increase as the electrical conductivity increases. Further, as can be seen from the comparison between Comparative Examples 2 and 3, the post-degradation polishing rate tended to slightly improve even when potassium chloride was added, but the improvement effect was small in the system containing no inorganic particles. Further, when the motor torque was compared between the case where potassium chloride was not used and the case where inorganic particles were included and the case where inorganic particles were not included, the motor torque was higher when inorganic particles were included even after 40 hours. It was confirmed that it was maintained. In Comparative Example 4 where the electrical conductivity was 9.8 mS / cm, the post-degradation polishing rate was even lower than that in Comparative 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 (7)

A polishing composition for use in polishing a magnetic disk substrate,
Silica abrasive grains having an average minor axis Ds;
Inorganic particles having an average particle diameter Db of less than 50% of the average short diameter Ds;
Only including,
Polishing composition whose average aspect-ratio of the said silica abrasive grain is 1.05 or more, and ratio (Ds / Db) of the said average short diameter Ds and the said average particle diameter Db is larger than three .   The polishing composition according to claim 1, comprising 3 to 50 parts by weight of the inorganic particles with respect to 100 parts by weight of the silica abrasive grains.   Polishing composition of Claim 1 or 2 whose electrical conductivity is 10 mS / cm or more.   The polishing composition according to any one of claims 1 to 3, wherein the average minor axis Ds is 25 nm or more and 300 nm or less.   The polishing composition according to any one of claims 1 to 4, which is used in polishing with a polishing pad having a polishing surface made of polyurethane foam. A polishing composition for use in polishing a magnetic disk substrate,
Silica abrasive grains having an average minor axis Ds;
Inorganic particles having an average particle diameter Db smaller than the average minor axis Ds;
Including
The average aspect ratio of the silica abrasive grains is 1.05 or more, and the ratio of the average minor diameter Ds to the average particle diameter Db (Ds / Db) is greater than 3.
A polishing composition configured so that the polishing rate does not increase in comparison with a control polishing composition having a composition in which the inorganic particles are replaced with the same weight of the silica abrasive grains in polishing using a polishing pad at the beginning of use. . A method of manufacturing a magnetic disk substrate comprising:
Setting an object to be polished in a polishing apparatus having a polishing pad having a polishing surface made of polyurethane foam;
Supplying the polishing composition according to any one of claims 1 to 6 between the polishing object and the polishing pad; and moving the polishing pad relative to the polishing object. Polishing the object to be polished;
A method of manufacturing a magnetic disk substrate.