Magnetic disc substrate polishing method

Abstract

To provide a magnetic disc substrate polishing method that enables halation reduction by achieving adjustment of a carrier circumferential speed of a carrier at time of polishing and a polishing agent composition used for the polishing.SOLUTION: A polishing method 1 for polishing a magnetic disc substrate using a polishing agent composition and a polishing machine includes: a polishing agent composition preparation process S1 of preparing a polishing agent composition; and a polishing process S2 including a pad surface contact process of bringing a pad surface into contact with a substrate surface, a polishing agent composition supply process of supplying the polishing agent composition, a rotation process of rotating a flat plate and a polishing pad, and a planetary motion process of causing a carrier 5 fitted to the magnetic disc substrate to perform planetary motion. The polishing agent composition used for the polishing contains at least colloidal silica, acids, and oxidizing agents, a value of pH (25°C) is in a range between 1.3 or more and 4.0 or less, and a content of sulfuric acid in acid composing the polishing agent composition is 0% by mass or more and 1.0% by mass or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for polishing a magnetic disk substrate, and more particularly to a method for polishing a magnetic disk substrate such as a glass magnetic disk substrate or an aluminum magnetic disk substrate used as a magnetic recording medium, and more particularly to a method for polishing a magnetic disk substrate for finish polishing an aluminum disk substrate for a magnetic recording medium, which is made of an aluminum alloy and has an electroless nickel-phosphorus plating film formed on the surface thereof. [Background technology]

[0002] Conventionally, in order to polish various magnetic disk substrates such as the above-mentioned glass magnetic disk substrates and aluminum magnetic disk substrates, a polishing step has been carried out in which an abrasive composition for magnetic disk substrates (hereinafter simply referred to as "abrasive composition") is supplied to a polishing machine and the substrate surface of the magnetic disk substrate to be polished is polished.

[0003] During the polishing process, small scratches, or "scratches," that occur on the substrate surface can cause errors during magnetic recording and reading. Furthermore, so-called "burrs" formed around the scratches can cause problems such as collisions with the magnetic head during writing and reading. Furthermore, "waviness," which occurs when the substrate surface of the magnetic disk substrate warps or bulges, can also cause problems such as collisions with the magnetic head. These problems can hinder improvements in the magnetic recording density of magnetic disk substrates, so there is a need to suppress the occurrence of the above-mentioned scratches and other problems during polishing in order to improve magnetic recording density.

[0004] In addition to the defects such as scratches, burrs, and waviness mentioned above, "halation" that occurs on the substrate surface of a magnetic disk substrate after polishing is known to be a factor that inhibits improvement in magnetic recording density. Here, halation is a fine defect that can be detected on the substrate surface under specific measurement conditions using a substrate full-surface defect inspection machine, and the number of detected defects can be quantitatively measured and evaluated as a "halation count" (for details of the inspection machine and measurement conditions, see the Examples below).

[0005] Explaining in more detail, halation is presumed to be a phenomenon resulting from the widespread presence of shallow polishing scratches extending in a specific direction on the substrate surface, and its occurrence is thought to be influenced by, for example, inconsistencies resulting from the combination of the polishing machine used in the polishing process, the polishing conditions of the polishing machine, the specifications and types of the carrier and polishing pad of the polishing machine, the characteristics of the magnetic disk substrate itself, and the composition of the abrasive composition used in polishing.

[0006] As described above, halation is a factor that inhibits further improvement of magnetic recording density, and therefore, there is a need to reduce the occurrence of this halation. For example, it has been proposed to suppress the occurrence of halation by adjusting the particle size of the abrasive grains contained in the polishing compound composition within a predetermined range (see Patent Document 2). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent Document 1 Patent No. 7085323 [Patent Document 2] Patent Document 2: JP 2019-8846 A Summary of the Invention [Problem to be solved by the invention]

[0008] By using a polishing compound in which the grain size of the abrasive grains is adjusted to a predetermined range, it has been possible to suppress the halation occurring on the substrate surface to some extent. However, as mentioned above, it has been thought that the occurrence of halation is caused not only by the polishing compound but also by various other factors such as the polishing machine and the influence of a disharmony caused by a combination of these factors.

[0009] In view of the above circumstances, the present invention focuses on the relationship between the abrasive composition used in the polishing process and the polishing conditions of the polishing machine, and aims to provide a method for polishing a magnetic disk substrate that can reduce the occurrence of halation by adjusting both of these factors. [Means for solving the problem]

[0010] In order to solve the above problems, the inventors of the present application conducted extensive research into the relationship between the abrasive composition used in the polishing process and the polishing conditions of the polishing machine, and as a result, discovered a method for polishing a magnetic disk substrate that can solve the above problems by adjusting the relationship between the peripheral speed of a carrier that is mounted with a magnetic disk substrate and performs planetary motion in a planetary polishing region and the properties of the abrasive composition, in particular the pH (25°C) value of the abrasive composition and the content of sulfuric acid among the acids contained in the abrasive composition.

[0011] [1] A method for polishing a magnetic disk substrate using an abrasive composition for magnetic disk substrates, a disk-shaped carrier, a polishing pad, a surface plate, and a polishing machine having a planetary motion mechanism that causes the carrier to perform planetary motion consisting of a combination of rotational motion and revolutional motion in a planetary polishing region, the method comprising the steps of: preparing the abrasive composition for magnetic disk substrates to be used in polishing the magnetic disk substrates; a pad surface abutting step of abutting the pad surface of the polishing pad against the substrate surface of the magnetic disk substrate to be polished, which is attached to the carrier; an abrasive composition supplying step of supplying the prepared abrasive composition for magnetic disk substrates between the abutted substrate surface and the pad surface; a rotating step of rotating the platen and the polishing pad while the abrasive composition for magnetic disk substrates is being supplied; and a polishing step including a planetary motion step of setting the circumferential speed of the carrier to which the magnetic disk substrate is attached to 20 mm / s or more by the planetary motion mechanism and causing the carrier to perform planetary motion in the planetary polishing region, wherein the abrasive composition for magnetic disk substrates contains at least colloidal silica, an acid, and an oxidizing agent, has a pH (25°C) value in the range of 1.3 to 4.0, and the content of sulfuric acid in the acid constituting the abrasive composition for magnetic disk substrates is 0 to 1.0 mass%.

[0012] [2] The method for polishing a magnetic disk substrate according to [1], wherein the acid includes at least an inorganic acid and an organic acid.

[0013] [3] The method for polishing a magnetic disk substrate according to [1], wherein the content of the sulfuric acid in the acid is 0% by mass or more and 0.8% by mass or less.

[0014] [4] The method for polishing a magnetic disk substrate according to [1], wherein the acid contains at least an organic phosphonic acid.

[0015] [5] The method for polishing a magnetic disk substrate according to any one of [1] to [4], wherein the magnetic disk substrate is a nickel-phosphorus plated aluminum alloy substrate, and the polishing step is a finish polishing step for performing finish polishing on the surface of the aluminum alloy substrate. [Effects of the Invention]

[0016] The method for polishing a magnetic disk substrate of the present invention reduces the occurrence of conventional defects such as scratches, burrs, and undulations that occur on the surface of a magnetic disk substrate after polishing, and also has the effect of reducing the occurrence of halation. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a flowchart showing the flow of a method for polishing a magnetic disk substrate according to an embodiment of the present invention. [Figure 2] 1 is an explanatory diagram showing a schematic configuration of a polishing machine used in a method for polishing a magnetic disk substrate according to an embodiment of the present invention; [Figure 3] FIG. 2 is a top view illustrating a schematic configuration of a carrier, a sun gear, an internal gear, and a planetary motion mechanism of the grinding machine. [Figure 4] FIG. 2 is a top view illustrating a schematic configuration of a carrier. [Figure 5] FIG. 2 is a partial cross-sectional side view showing a schematic configuration of a magnetic disk substrate and a polishing machine during a polishing process. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following describes embodiments of the present invention, but it should be understood that the present invention is not limited to the following embodiments, and that appropriate modifications and improvements to the following embodiments based on the ordinary knowledge of those skilled in the art, as long as they do not deviate from the spirit of the present invention, also fall within the scope of the present invention.

[0019] A method 1 for polishing a magnetic disk substrate according to one embodiment of the present invention (hereinafter simply referred to as "polishing method 1") and a polishing machine 3 used in the polishing method 1 will be described below with reference to Figs. 1 to 5. Fig. 1 is a flowchart showing the flow of the method 1 for polishing a magnetic disk substrate according to this embodiment, Fig. 2 is an explanatory diagram showing a schematic configuration of the polishing machine 3 used in the method 1 for polishing a magnetic disk substrate according to this embodiment, Fig. 3 is an explanatory diagram viewed from above showing the schematic configuration of the carrier 5, sun gear 9, internal gear 10, and planetary motion mechanism 8 of the polishing machine 3, Fig. 4 is an explanatory diagram viewed from above showing the schematic configuration of the carrier 5, and Fig. 5 is a partial cross-sectional side view showing the schematic configuration of the magnetic disk substrate 4 and the polishing machine 3 during the polishing step S2.

[0020] 1.Method for polishing magnetic disk substrates The polishing method 1 of this embodiment uses an abrasive composition (corresponding to the abrasive composition for magnetic disk substrates in the present invention) and a polishing machine 3 to polish a magnetic disk substrate 4 to be polished while moving it in planetary motion in a planetary polishing region A, and is mainly comprised of an abrasive composition preparation step S1 in which the abrasive composition to be used in the polishing process is prepared in advance, and a polishing step S2 in which the prepared abrasive composition is supplied and the magnetic disk substrate 4 is polished (see Figure 1).

[0021] The polishing process S2 includes a pad surface abutment process S2a in which the pad surfaces 6a, 6b of the polishing pad 6 are abutted against the substrate surfaces 4a, 4b of the magnetic disk substrate 4 mounted on the carrier 5; an abrasive composition supply process S2b in which a prepared abrasive composition is supplied between the abutted substrate surfaces 4a, 4b and the pad surfaces 6a, 6b; a rotation process S2c in which the upper and lower surface plates 7a, 7b (corresponding to the surface plates in this invention) and the polishing pad 6 are rotated, respectively, while the abrasive composition is supplied; and a planetary motion process S2d in which the carrier 5 mounted with the magnetic disk substrate 4 is subjected to planetary motion in the planetary polishing region A by the planetary motion mechanism unit 8.

[0022] Here, the polishing step S2 includes the polishing compound supply step S2b, the rotation step S2c, and the planetary motion step S2d, which are all performed at the same time after the pad surface contact step S2a. After a predetermined polishing time has elapsed, a polishing termination step S3 is performed to terminate the polishing process.

[0023] More specifically, the polishing method 1 of this embodiment involves polishing a magnetic disk substrate 4 mounted on a carrier 5 using an abrasive composition and a polishing machine 3 having an upper surface plate 7a and a lower surface plate 7b to which a plurality of (five in this embodiment) disc-shaped carriers 5 are attached, with polishing pads 6 attached, each of which is arranged to sandwich the carrier 5 from above and below, as shown in Figures 2 to 5, and a planetary motion mechanism 8 that causes the carrier 5 to perform planetary motion consisting of a combination of rotational motion and revolutional motion in the planetary polishing region A.

[0024] In the polishing method 1 of this embodiment, the magnetic disk substrate 4 to be polished can be, for example, a disk-shaped glass substrate or an aluminum alloy substrate that can be used as a magnetic recording medium. These magnetic disk substrates 4 can be processed to a predetermined substrate thickness by a grinding process or the like before the polishing method 1 of this embodiment, and then, if necessary, the entire magnetic disk substrate 4, including the substrate surfaces 4a and 4b, can be plated or the like. Furthermore, the magnetic disk substrate 4 can be subjected to a rough polishing process by a well-known polishing method before the polishing method 1 of this embodiment is carried out. In particular, the polishing method of this embodiment is suitable for use with a nickel-phosphorus-plated aluminum alloy substrate as the magnetic disk substrate 4, which is subjected to the polishing step S2 as a finish polishing process after the rough polishing process.

[0025] 1.1 Polishing machine The polishing machine 3 used in the polishing method 1 of this embodiment can suitably be a double-sided polishing machine that can simultaneously polish both the front and back substrate surfaces 4a, 4b of the magnetic disk substrate 4 to be polished. Note that the use of such a double-sided polishing machine is not limited, and the polishing method 1 of this embodiment can also be applied to the case where a single-sided polishing machine that polishes one substrate surface 4a (or the other substrate surface 4b) of the magnetic disk substrate 4 is used.

[0026] As shown in Figure 2, the polishing machine 3 is basically configured to mainly comprise a sun gear 9 that is rotatably driven along a central axis C (see the dotted line in Figure 2), an annular (ring-shaped) internal gear 10 that is arranged a predetermined distance away from the sun gear 9 so as to surround the sun gear 9, one or more disk-shaped carriers 5 that are inserted and arranged in a planetary polishing area A formed between the sun gear 9 and the internal gear 10 with at least a portion of the carrier 5 abutting the sun gear 9 and the internal gear 10, a planetary motion mechanism 8 that causes the carrier 5 to perform planetary motion in the planetary polishing area A based on the respective gear ratios of the sun gear 9, the internal gear 10, and the carrier 5, and an upper surface plate 7a and a lower surface plate 7b to which polishing pads 6 are attached, each of which is installed so as to sandwich the carrier 5 from above and below.

[0027] Here, the sun gear 9 is formed to be rotatable about a central axis C, and further has a gear portion 9a with a plurality of gear teeth formed along its outer circumferential surface. Meanwhile, the annular internal gear 10 has a gear portion 10a with a plurality of gear teeth formed along its inner circumferential surface. Furthermore, the disc-shaped carrier 5 has a gear portion 5a with a plurality of gear teeth formed along its outer circumferential surface that can mesh with the gear portion 9a of the sun gear 9 and the gear portion 10a of the internal gear 10.

[0028] As a result, by rotating the sun gear 9 about the central axis C using the planetary motion mechanism 8 formed by meshing the gear portions 5a, 9a, and 10a between the sun gear 9 and the internal gear 10, the rotation is transmitted to the gear portion 5a of the carrier 5 via the gear portion 9a of the sun gear 9, causing the carrier 5 to rotate on its axis. Furthermore, because the carrier 5 is disposed between the sun gear 9 and the internal gear 10 so that it can mesh with them, the carrier 5 can perform orbital motion around the sun gear 9 in addition to rotating on its axis. That is, in the planetary polishing region A, the carrier 5 performs planetary motion.

[0029] Here, the grinding machine 3 has a sun gear rotation drive unit that generates a driving force for rotating the sun gear 9 about the central axis C, and an internal gear rotation drive unit that generates a driving force for rotating the internal gear 10 about the central axis C (neither is shown). These components have a well-known drive motor and a rotation transmission mechanism that converts the generated driving force into rotational force and transmits it to the sun gear 9, etc.

[0030] In the polishing method 1 of this embodiment, the rotation speeds of the sun gear 9 and the internal gear 10 are controlled to adjust the carrier circumferential speed of the carrier 5 (details of which will be described later) within a predetermined range, i.e., to a carrier circumferential speed of at least 20 mm / s or more. Note that, in this adjustment, the rotation of either the sun gear 9 or the internal gear 10 may be stopped to adjust the carrier circumferential speed. For example, only the sun gear 9 may be rotated and the internal gear 10 may be stopped, or the sun gear 9 may be stopped and only the internal gear 10 may be rotated.

[0031] As shown in Fig. 4, the carrier 5 on which the magnetic disk substrate 4 to be polished is mounted further has a substrate holder 12 having a plurality of (two in Figs. 3 and 4) circular holding holes 11 bored out with the same diameter and passing through, in order to hold the magnetic disk substrate 4. The carrier 5 of the polisher 3 used in the polishing method 1 of this embodiment has a pair of circular holding holes 11 formed at positions symmetrical with respect to the center of the disk-shaped carrier 5.

[0032] The magnetic disk substrate 4 to be polished is machined into a disk shape with approximately the same diameter as the circular holding hole 11 so that it can be attached to the circular holding hole 11 of the carrier 5. This allows the disk-shaped magnetic disk substrate 4 to be fitted into the circular holding hole 11 and fixed in place, thereby holding the magnetic disk substrate 4 on the carrier 5. Polishing can be carried out in this state.

[0033] In the polishing method 1 of this embodiment, as shown in FIG. 3, five carriers 5 are arranged around the sun gear 9 (or the central axis C) at approximately equal intervals.

[0034] 5, the magnetic disk substrate 4 held by the carrier 5 disposed between the sun gear 9 and the internal gear 10 is set so that the substrate surfaces 4a, 4b respectively protrude slightly upward and downward from the carrier surfaces 5b, 5c of the carrier 5. An upper surface plate 7a and a lower surface plate 7b, to which polishing pads 6 are attached, are disposed facing the substrate surfaces 4a, 4b, respectively, so as to sandwich the carrier 5 and the magnetic disk substrate 4 from above and below.

[0035] In the polishing method 1 of this embodiment, the upper surface plate 7a and the lower surface plate 7b of the polishing machine 3 are controlled to rotate in opposite directions. That is, when the upper surface plate 7a rotates in the forward direction (clockwise direction CW), the lower surface plate 7b rotates in the reverse direction (counterclockwise direction CCW) (see FIG. 2). The rotational directions of the upper surface plate 7a and the lower surface plate 7b are configured to be switchable as appropriate.

[0036] 1.1.1 Career To explain the carrier 5, which is one component of the polishing machine 3, in more detail, conventionally known metal carriers and resin carriers can be used. Examples of metal carriers include stainless steel carriers, steel carriers, and titanium carriers, while examples of resin carriers include aramid carriers, APA carriers, and epoxy glass carriers.

[0037] Here, the aramid carrier is a carrier using an aramid laminate plate made by impregnating aramid nonwoven fabric with epoxy resin. It has a low content of metal elements, so there is almost no metal effect on the workpiece. As a result, it has the characteristics of a low scratch rate, excellent wear resistance, and suitable for long-term continuous use. On the other hand, the APA carrier is a carrier using a material in which a polyester base material is sandwiched between aramid prepregs. It exhibits high polishing quality comparable to the aramid carrier, and is characterized by excellent tear strength and continuous use.

[0038] Furthermore, the epoxy glass carrier is a carrier made of a laminated plate of glass woven fabric impregnated with epoxy resin, and is characterized by high bending strength and elastic modulus, making it suitable for use with high torque. In addition to the resin carriers described above, carriers 5 made of other general engineering plastic materials, such as polyvinyl chloride resin and fluororesin, can also be used. In the polishing method 1 of this embodiment, the shape of the carrier 5, particularly the carrier thickness, may be any thickness that is thinner than the substrate thickness of the magnetic disk substrate 4 to be polished. That is, the carrier 5 may be thick enough to be held in the circular holding hole 11 of the carrier 5, so that the substrate surfaces 4a and 4b of the magnetic disk substrate 4 can protrude upward or downward from the carrier surfaces 5b and 5c of the carrier 5, respectively, without interfering with polishing by the polishing pad 6.

[0039] In recent years, with the trend toward thinner magnetic disk substrates 4 themselves, there has been a demand for thinner carriers 5 as well. As a result, the use of metal carriers has been reconsidered from the perspective of the strength of carrier 5. In this case, if the material constituting the metal carrier is more rigid than the magnetic disk substrate 4, such as an aluminum alloy, the metal carrier may be coated with a resin on its surface to protect it from wear due to contact with the metal carrier.

[0040] 1.1.2 Carrier peripheral speed In the polishing method 1 of this embodiment, the carrier 5 has a circumferential velocity of at least 20 mm / s or more, and more preferably 30 mm / s or more. If the carrier circumferential velocity is less than 20 mm / s, halation on the polished substrate surfaces 4a and 4b may worsen. Although there is no particular upper limit to the carrier circumferential velocity, if the carrier circumferential velocity exceeds 100 mm / s, the polishing rate may decrease depending on other polishing conditions. Therefore, it is preferable to set the carrier circumferential velocity to 20 mm / s or more and 100 mm / s or less.

[0041] In the polishing method 1 of this embodiment, the "carrier peripheral speed" is a numerical value that represents the moving distance per unit time of the outermost position of the carrier 5 in the rotational motion of the carrier 5, in relation to the planetary motion of the carrier 5 caused by the rotation of the sun gear 9 and / or the internal gear 10. In other words, it corresponds to the distance traveled per unit time by the outermost position of the carrier 5, where the gear portion 5a of the carrier 5 is provided, during the planetary motion.

[0042] Here, the carrier circumferential speed is adjusted by adjusting the rotation speed of the sun gear 9 and / or the internal gear 10 so as to obtain the carrier rotation speed determined by the carrier circumferential speed and the diameter of the carrier 5. At this time, the rotation of the upper surface plate 7a and the lower surface plate 7b, which are arranged so as to sandwich the carrier 5 from above and below, causes the rotation of the carrier 5 to act in a direction that offsets the relative movement of the magnetic disk substrate 4 mounted on the carrier 5, and therefore, it is known that if the carrier circumferential speed is increased, the polishing speed of the magnetic disk substrate 4 tends to decrease, as described above.

[0043] The effect of reducing halation by increasing the carrier peripheral speed is presumed to be due to the fact that the direction in which the magnetic disk substrate 4 is rubbed by the polishing pad 6 and the abrasive grains in the abrasive composition during polishing changes in a shorter time as the carrier peripheral speed increases, and therefore the time spent rubbing from all directions becomes longer, resulting in more uniformity. As will be described later, it is a prerequisite that the etching power due to the pH (25°C) value of the abrasive composition is within an appropriate range, and the polishing method of the present invention achieves the effect of reducing halation by the relationship between the pH (25°C) value of the abrasive composition and the carrier peripheral speed.

[0044] 1.1.3 Polishing pads The polishing pad 6 used in the polishing method 1 of this embodiment is not particularly limited, but examples include a porous pad made by hardening and foaming a urethane composition, a nonwoven pad made by impregnating a felt-like fibrous sheet with a polymer mainly made of thermoplastic polyurethane resin, and a suede pad having a microporous surface layer made of a polymer material mainly made of polyurethane on a base layer such as a nonwoven fabric or film-like sheet. In particular, a suede pad can be preferably used.

[0045] 2. Abrasive composition The polishing compound used in the polishing method 1 of this embodiment is characterized by containing at least colloidal silica as abrasive grains, an acid, and an oxidizing agent, and having a pH (25°C) in the range of 1.3 to 4.0. The polishing compound may contain a water-soluble polymer compound as an optional component.

[0046] 2.1 Colloidal silica (abrasive grains) The colloidal silica used as abrasive grains in the polishing compound composition used in polishing method 1 of this embodiment preferably has an average particle diameter of 5 to 50 nm. An average particle diameter of 5 nm or more can prevent a decrease in the polishing rate. An average particle diameter of 50 nm or less can prevent deterioration of surface roughness and scratches. The average particle diameter of colloidal silica is measured as the Heywood diameter (diameter equivalent to a circle with a projected area) by analyzing the results of photographs taken with a transmission electron microscope, and the average particle diameter (D50) is the particle diameter at which the cumulative particle size distribution (accumulated volume basis) from the small particle size side becomes 50%.

[0047] Furthermore, the concentration of colloidal silica in the polishing compound can be in the range of 1 to 50% by mass. By setting the concentration of colloidal silica to 1% by mass or more, it is possible to suppress a decrease in the polishing rate. Furthermore, by setting the concentration of colloidal silica to 50% by mass or less, it is possible to reduce the cost of preparing the polishing compound.

[0048] Colloidal silica is known to have various shapes, such as spherical, confetti-shaped (particulate with protrusions on the surface), and irregular shapes, and the primary particles are monodispersed in water to form a colloid. The colloidal silica used in the polishing method of the present invention is preferably spherical or nearly spherical.

[0049] Colloidal silica can be produced by a water glass method using sodium silicate or potassium silicate as a raw material, an alkoxysilane method in which colloidal silica is obtained by hydrolyzing an alkoxysilane such as tetraethoxysilane with an acid or alkali, or a method in which metallic silicon is reacted with water in the presence of an alkali catalyst to generate hydrogen gas.

[0050] 2.2 Acid In the polishing method 1 of this embodiment, from the viewpoint of the effect of reducing halation and waviness, the content of sulfuric acid in the acids constituting the polishing compound composition is 0 mass % or more and 1.0 mass % or less, more preferably 0 mass % or more and 0.8 mass % or less.

[0051] Here, sulfuric acid is a type of inorganic acid commonly used when polishing a nickel-phosphorus-plated aluminum alloy substrate as the magnetic disk substrate 4. Its strong etching power allows it to be used to improve the polishing rate. However, as already explained, the polishing method of the present invention aims to solve the main problem of reducing halation and waviness, and it is particularly necessary to appropriately control the etching power. Therefore, as described above, the content of sulfuric acid in the acids constituting the polishing compound composition is specified to be within the above range. More preferably, the content of sulfuric acid can be set to 0% by mass or more and 0.5% by mass or less.

[0052] The acid used in the polishing compound composition preferably includes an inorganic acid and / or an organic acid. For example, the inorganic acid is preferably a phosphorus-containing inorganic acid. Specific examples of phosphorus-containing inorganic acids include phosphoric acid, phosphonic acid, phosphinic acid, pyrophosphoric acid, and tripolyphosphoric acid. Phosphoric acid is particularly preferred.

[0053] On the other hand, organic phosphonic acids are preferred as organic acids. Specific examples of organic phosphonic acids include 2-aminoethylphosphonic 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-1,1,2-triphosphonic acid, ethane-1,2-dicarboxy-1,2-diphosphonic acid, and methanehydroxyphosphonic acid. 1-hydroxyethylidene-1,1-diphosphonic acid is particularly preferred.

[0054] These compounds composed of inorganic acids and organic acids can be used in combination of two or more kinds. For example, two or more kinds of phosphorus-containing inorganic acids, which are inorganic acids, can be combined, or two or more kinds of organic phosphonic acids, which are organic acids, can be combined. Furthermore, one or more kinds of phosphorus-containing inorganic acids, which are inorganic acids, and one or more kinds of organic phosphonic acids, which are organic acids, can be combined. A specific example is a combination of phosphoric acid and 1-hydroxyethylidene-1,1-diphosphonic acid.

[0055] Furthermore, the concentration of the acid in the polishing compound is preferably 0.1 to 20 mass %, more preferably 0.2 to 10 mass %. The concentration of the acid in the polishing compound can be determined appropriately depending on the pH (25°C) of the polishing compound.

[0056] 2.3 Oxidizing agents Examples of oxidizing agents used in the polishing compound include peroxides, permanganic acid or its salts, chromic acid or its salts, peroxoacids or their salts, halogenated oxoacids or their salts, oxygenated acids or their salts, and mixtures of two or more of these oxidizing agents. More specifically, examples include hydrogen peroxide, sodium peroxide, barium peroxide, potassium permanganate, metal chromate salts, persulfuric acid, sodium persulfate, potassium persulfate, ammonium persulfate, peroxophosphoric acid, sodium peroxoborate, performic acid, peracetic acid, hypochlorous acid, sodium hypochlorite, and calcium hypochlorite. Hydrogen peroxide, persulfuric acid and its salts, and hypochlorous acid and its salts are preferred, with hydrogen peroxide being particularly preferred. The content of the oxidizing agent in the polishing compound is preferably 0.01 to 10.0% by mass, more preferably 0.05 to 5.0% by mass.

[0057] 2.4 Optional ingredients (water-soluble polymer compound) Examples of water-soluble polymeric compounds that can be contained as optional components in the polishing compound composition include anionic water-soluble polymeric compounds, cationic water-soluble polymeric compounds, and nonionic water-soluble polymeric compounds. Preferably, anionic water-soluble polymeric compounds can be used. In particular, copolymers containing structural units derived from a monomer having a carboxylic acid group, structural units derived from a monomer having an amide group, and structural units derived from a monomer having a sulfonic acid group can be preferably used. That is, water-soluble polymeric compounds copolymerized from a monomer having a carboxylic acid group and / or its salt, a monomer having an amide group, and a monomer having a sulfonic acid group can be preferably used.

[0058] 2.4.1 Monomers with carboxylic acid groups Examples of the monomer having a carboxylic acid group and / or its salt include acrylic acid, methacrylic acid, maleic acid, itaconic acid, and salts thereof. At least a portion of the structural units derived from the monomer having a carboxylic acid group may be contained in the water-soluble polymer compound as a carboxylic acid salt. Examples of the carboxylic acid salt include sodium salt, potassium salt, magnesium salt, ammonium salt, amine salt, and alkylammonium salt.

[0059] In order to incorporate a structural unit derived from a monomer having a carboxylic acid group into a water-soluble polymer compound as a carboxylic acid, the monomer having a carboxylic acid group may be polymerized, or a salt of a monomer having a carboxylic acid group may be polymerized and then converted into a carboxylic acid by cation exchange. In addition, in order to incorporate a structural unit derived from a monomer having a carboxylic acid group into a water-soluble polymer compound as a carboxylic acid salt, the salt of a monomer having a carboxylic acid group may be polymerized, or a monomer having a carboxylic acid group may be polymerized and then neutralized with a base to form a carboxylic acid salt.

[0060] The pH value of a water-soluble polymer compound can be used to evaluate the ratio of structural units contained as carboxylic acids to structural units contained as carboxylic acid salts in a water-soluble polymer compound. When the pH value of a water-soluble polymer compound is low, it can be evaluated that the ratio of structural units contained as carboxylic acids is high. On the other hand, when the pH value of a water-soluble polymer compound is high, it can be evaluated that the ratio of structural units contained as carboxylic acid salts is high. In the present invention, for example, a water-soluble polymer compound whose pH (25°C) in a 10% by mass aqueous solution of the water-soluble polymer compound is in the range of 1 to 13 can be used.

[0061] 2.4.2 Monomers with amide groups As the monomer having an amide group, it is preferable to use an α,β-ethylenically unsaturated amide. More specific examples include α,β-ethylenically unsaturated carboxylic acid amides such as acrylamide, methacrylamide, N-alkylacrylamide, and N-alkylmethacrylamide. More preferred examples include N-alkylacrylamide and N-alkylmethacrylamide. Specific examples of preferred N-alkylacrylamides and N-alkylmethacrylamides include N-methylacrylamide, N-ethylacrylamide, Nn-propylacrylamide, N-isopropylacrylamide, Nn-butylacrylamide, N-isobutylacrylamide, N-sec-butylacrylamide, N-tert-butylacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide, Nn-propylmethacrylamide, N-isopropylmethacrylamide, Nn-butylmethacrylamide, N-isobutylmethacrylamide, N-sec-butylmethacrylamide, and N-tert-butylmethacrylamide.

[0062] In particular, Nn-butylacrylamide, N-iso-butylacrylamide, N-sec-butylacrylamide, N-tert-butylacrylamide, Nn-butylmethacrylamide, N-iso-butylmethacrylamide, N-sec-butylmethacrylamide, N-tert-butylmethacrylamide, and the like are particularly preferred.

[0063] 2.4.3 Monomers with sulfonic acid groups Specific examples of the monomer having a sulfonic acid group include isoprene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, styrenesulfonic acid, vinylsulfonic acid, allylsulfonic acid, isoamylenesulfonic acid, etc. Preferred examples include 2-acrylamido-2-methylpropanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, etc.

[0064] 2.4.4 Copolymers The water-soluble polymer compound used in the polishing compound composition is preferably a copolymer obtained by combining and polymerizing these monomer components. Preferred copolymer combinations include a combination of acrylic acid and / or its salt with N-alkylacrylamide, a combination of acrylic acid and / or its salt with N-alkylmethacrylamide, a combination of methacrylic acid and / or its salt with N-alkylacrylamide, a combination of methacrylic acid and / or its salt with N-alkylacrylamide, a combination of methacrylic acid and / or its salt with N-alkylmethacrylamide, a combination of acrylic acid and / or its salt with N-alkylacrylamide and a monomer having a sulfonic acid group, a combination of acrylic acid and / or its salt with N-alkylmethacrylamide and a monomer having a sulfonic acid group, a combination of methacrylic acid and / or its salt with N-alkyl ... and a combination of methacrylic acid and / or its salt with N-alkylmethacrylamide and a monomer having a sulfonic acid group.

[0065] In particular, N-alkylacrylamides or N-alkylmethacrylamides in which the alkyl group is at least one selected from the group consisting of an n-butyl group, an iso-butyl group, a sec-butyl group, and a tert-butyl group are particularly preferably used.

[0066] The ratio of the structural units derived from the monomer having a carboxylic acid group to the structural units derived from the monomer having an amide group in the water-soluble polymer compound is preferably in the range of 95:5 to 5:95 in molar ratio, and more preferably in the range of 90:10 to 10:90 in molar ratio, and the proportion of the structural units derived from the monomer having a sulfonic acid group in the copolymer is preferably in the range of 0.01 to 10 mol%.

[0067] 2.4.5 Manufacturing method of water-soluble polymer compounds Although the method for producing a water-soluble polymer compound is not particularly limited, aqueous solution polymerization is preferred. According to the aqueous solution polymerization method, a water-soluble polymer compound can be obtained as a uniform solution. The polymerization solvent for the aqueous solution polymerization method is preferably an aqueous solvent, and water is particularly preferred. Furthermore, to improve the solubility of the monomer components in the solvent, an organic solvent may be added as appropriate within a range that does not adversely affect the polymerization of each monomer. Examples of the organic solvent include alcohols such as isopropyl alcohol and ketones such as acetone. These can be used alone or in combination of two or more.

[0068] A method for producing a water-soluble polymer compound using the aqueous solvent is described below. While known polymerization initiators can be used in the polymerization reaction, radical polymerization initiators are particularly preferred. Examples of radical polymerization initiators include persulfates such as sodium persulfate, potassium persulfate, and ammonium persulfate; hydroperoxides such as t-butyl hydroperoxide; water-soluble peroxides such as hydrogen peroxide; ketone peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide; oil-soluble peroxides such as dialkyl peroxides such as di-t-butyl peroxide and t-butylcumyl peroxide; and azo compounds such as azobisisobutyronitrile and 2,2-azobis(2-methylpropionamidine) dihydrochloride. These peroxide-based radical polymerization initiators may be used alone or in combination. Among the peroxide-based radical polymerization initiators described above, persulfates and azo compounds are preferred because they allow for easy control of the molecular weight of the resulting water-soluble polymer compound, with azobisisobutyronitrile being particularly preferred.

[0069] 3. Physical properties (pH (25℃)) The pH (25°C) of the polishing compound is 1.3 or more and 4.0 or less, preferably 1.4 or more and 4.0 or less. If the pH (25°C) of the polishing compound is less than 1.3, there is a concern that halation may worsen. If the pH (25°C) of the polishing compound is more than 4.0, there is a concern that the removal rate may decrease.

[0070] As explained in the section on carrier circumferential speed above, the reason why halation worsens when the pH (25°C) of the abrasive composition is less than 1.3 is that the direction in which the magnetic disk substrate 4 is rubbed by the polishing pad 6 and the abrasive grains in the abrasive composition changes in a shorter time as the carrier circumferential speed increases. Therefore, even if the time spent rubbing from all directions is made more uniform, for example, the nickel-phosphorus plating film on the surface of an aluminum alloy substrate used as the magnetic disk substrate 4 is strongly etched, which is thought to result in worsening halation.

[0071] The above-mentioned various components are mixed together to prepare an abrasive composition in advance so as to have desired physical properties (pH (25° C.)) (abrasive composition preparation step S1).

[0072] 4. Magnetic disk substrate The magnetic disk substrate 4 to be polished by the polishing method 1 of this embodiment is not particularly limited, but is preferably a glass substrate or an aluminum alloy substrate for a magnetic disk, and more preferably, as already explained, a nickel-phosphorus plated aluminum alloy substrate can be used.

[0073] 5.Polishing method To carry out the polishing method 1 of this embodiment, polishing pads 6 are attached to the upper and lower plates 7a and 7b of the polishing machine 3 (see FIG. 2 or 5), respectively. Then, the carrier 5, with the magnetic disk substrate 4 mounted in the circular holding hole 11, is set in the polishing machine 3. At this time, the gear portion 5a of the carrier 5 is set in a state in which it is meshed with the gear portion 9a of the sun gear 9 and the gear portion 10a of the internal gear 10 of the polishing machine 3, respectively. Then, the pad surfaces 6a and 6b of the polishing pads 6 attached to the upper and lower plates 7a and 7b are brought into contact with the front and back substrate surfaces 4a and 4b of the magnetic disk substrate 4, respectively (pad surface contacting step S2a). Then, the polishing agent composition prepared in the polishing agent composition preparing step S1 is supplied between the pad surfaces 6a and 6b and the substrate surfaces 4a and 4b (polishing agent composition supplying step S2b).

[0074] Furthermore, at the same timing as the supply of the abrasive composition, the polishing machine 3 is operated to rotate the upper and lower surface plates 7a, 7b and the polishing pad 6 (rotation step S2c), while the carrier 5 is caused to perform planetary motion in the planetary polishing region A (planetary motion step S2d). At this time, the upper and lower surface plates 7a and 7b rotate in opposite directions about the central axis C. As a result, polishing is performed with the magnetic disk substrate 4 sandwiched between the upper and lower surface plates 7a and 7b (polishing step S2). [Example]

[0075] The present invention will be specifically described below based on examples, but it goes without saying that the present invention is not limited to these examples and can be implemented in various forms as long as it falls within the technical scope of the present invention.

[0076] In the following examples, it is assumed that an electroless nickel-phosphorus plated aluminum alloy substrate, the surface of which has been roughly polished under predetermined conditions, is used as the magnetic disk substrate, and the surface of the magnetic disk substrate is then finish-polished.

[0077] (1) Method for preparing abrasive composition The polishing compound compositions used in Examples 1 to 9 and Comparative Examples 1 to 5 were prepared using the materials shown in Table 1 below, in the amounts shown in Table 1. Table 2 shows the evaluation results of polishing using the polishing compound compositions of Examples 1 to 4 and Comparative Example 1, and Table 3 shows the evaluation results of polishing using the polishing compound compositions of Examples 1, 5 to 9 and Comparative Examples 2 to 5.

[0078] [Table 1]

[0079] (2) Average particle size (D50) of colloidal silica observed with a transmission electron microscope The particle size (Heywood diameter) of colloidal silica was measured as the Heywood diameter (diameter equivalent to a circle with a projected area) by taking a photograph of the field of view at 100,000 times magnification using a transmission electron microscope (TEM) (JEOL Ltd., JEM2000FX (200 kV) transmission electron microscope). This photograph was then analyzed using analysis software (Mountec Co., Ltd., Mac-View Ver. 4.0) to measure the Heywood diameter. The average particle size of colloidal silica was determined by analyzing the particle sizes of approximately 2,000 colloidal silica particles using the method described above, and calculating the particle size at which the cumulative particle size distribution (cumulative volume basis) from the smallest particle size side constitutes 50% using the same analysis software (Mountec Co., Ltd., Mac-View Ver. 4.0). This average particle size (D50) was calculated.

[0080] (3) Polishing conditions The polishing was carried out on a roughly polished aluminum alloy substrate (hereinafter referred to as "aluminum disk") having an outer diameter of 97 mm and plated with electroless nickel-phosphorus. Polishing machine: Speedfam Co., Ltd., 9B double-sided polishing machine Polishing pad: FILWEL Co., Ltd. P2 pad Carrier: Aramid carrier Internal gear: Stops rotation Sun gear: 2.1 to 12.6 rpm Carrier peripheral speed: 17~104mm / s Number of substrates to be polished: 10 (2 substrates / carrier x 5 carriers) Rotation speed of upper surface plate: -12 to -20 rpm Lower surface plate 20rpm Abrasive composition supply rate: 100 ml / min Polishing time: 300s Processing pressure: 13kPa

[0081] (4) Other preparations and settings A polishing compound prepared with the ingredients and amounts shown in Table 1 was passed through a filter with a mesh size of 0.45 μm, and then supplied to a polishing machine for polishing. The polishing conditions were set by calculating the rotation speed of the 9-inch diameter carrier used in the polishing machine so as to achieve the specified carrier peripheral speed, and determining the rotation speed of the sun gear of the polishing machine when the internal gear was stopped (rotation speed = 0 rpm).

[0082] Table 2 below shows the results of polishing performed by varying the carrier circumferential speed in Examples 1 to 4 and Comparative Example 1, and lists the sun gear rotation speed, lower platen rotation speed, and upper platen rotation speed corresponding to each carrier circumferential speed. The carrier circumferential speed can be changed by varying the sun gear rotation speed.

[0083] Here, the reason why the rotational speed of the upper platen is set low in conjunction with the setting of the carrier peripheral speed high is as follows.

[0084] That is, in the polishing machine, the upper platen is set to rotate in the opposite direction (clockwise) to the revolution direction of the carrier, while the lower platen is set to rotate in the opposite direction (counterclockwise) to the upper platen. As a result, if the circumferential speed of the carrier is set high and the rotation speed of the upper platen is kept constant, it is expected that the upper disk surface (corresponding to the substrate surface in this invention) of the aluminum disk, which is the magnetic disk substrate to be polished, will be excessively polished relative to the lower disk surface of the aluminum disk, resulting in over-grinding. To avoid such a problem, the rotation speed of the upper platen is set low.

[0085] [Table 2]

[0086] [Table 3]

[0087] (5) Evaluation results (5-1) Polishing speed The polishing rate was calculated based on the following formula (1) by measuring the mass of the aluminum disk lost after polishing. <Calculation formula for polishing speed> Polishing speed (μm / min) = mass loss of aluminum disc (g) / polishing time (min) / area of ​​one side of aluminum disc (cm 2 ) / density of electroless nickel-phosphorus plating film (g / cm 3 ) / 2×10 4 ...Equation (1) (However, in the above formula (1), the area of ​​one side of the aluminum disc is 69 cm 2 , the density of the electroless nickel-phosphorus plating film is 8.0 g / cm 3 (calculated as

[0088] (5-2) Polishing speed ratio The polishing rate ratios are shown in Tables 2 and 3 as relative values ​​for Examples 2 to 9 and Comparative Examples 1 to 5, where the polishing rate for Example 1 calculated using the above formula (1) is set to 1 (reference).

[0089] (5-3) Method for evaluating halation on the substrate surface after polishing Halation was measured using a substrate full surface defect inspection machine (NS2000H, manufactured by Hitachi High-Tech Fine Systems Corporation). The measurement conditions are as follows. <Measurement conditions> PMT / APD Power Control:Voltage :Hi-Light1 OFF :Hi-Light2 900V Scan Pitch: 3 μm Inner / Outer Radius:15.5000-48.0000mm Positive Level: 59mV H2 White Spot Level: 80.0mV

[0090] Under the above measurement conditions, halation can be detected as a minute defect on the substrate surface, and as already explained, can be quantitatively evaluated as a halation count.

[0091] (5-4) Halation ratio The halation ratios are shown in Tables 2 and 3, respectively, as relative values ​​for Examples 2 to 9 and Comparative Examples 1 to 5, where the halation count of Example 1, which was quantitatively determined using the above-mentioned measuring equipment and conditions, is set to 1 (reference). The smaller the halation ratio value, the better the polishing characteristics.

[0092] (5-5) Evaluation method for short wavelength waviness of substrate surface after polishing The waviness of the substrate surface was measured using a three-dimensional optical profiler New View 8300 (manufactured by Ametec Co., Ltd.). The measurement conditions for the substrate surface are as follows. Lens: 10x Mirau ZOOM:1.0x Measurement Type: Surface Measure Mode: CSI Scan Length: 5 μm Camera Mode: 1024×1024 Filter: Band Pass Cut Off: Short 20,000μm :Long 100.000μm Measurement points Radius:30.00mm Angle: 36 points every 10°

[0093] (5-6) Swell ratio The waviness ratios of Examples 2 to 9 and Comparative Examples 1 to 5 are shown in Tables 2 and 3 as relative values, with the waviness of Example 1 quantitatively determined using the above-mentioned measuring equipment and conditions taken as 1 (reference). The smaller the waviness ratio value, the better the polishing characteristics.

[0094] (6) Discussion of evaluation results In Examples 1 to 4, halation and short wavelength waviness are improved compared to Comparative Example 1, in which the carrier peripheral speed is less than 20 mm / s. In addition, in Examples 2 to 4, the carrier peripheral speed is increased compared to Example 1, and it is recognized that halation and short wavelength waviness are further improved compared to Example 1.

[0095] It is observed that in Examples 5 to 9, halation is improved compared to Comparative Examples 2 and 3, in which the pH (25°C) value of the polishing compound composition is less than 1.3. Furthermore, in Examples 5 to 9, the pH (25°C) value of the polishing compound composition is higher than in Example 1, and it is observed that halation is improved more than in Example 1.

[0096] The pH (25°C) of the polishing compound composition of Example 6 is the same as that of Example 7 (1.7), but the polishing compound composition of Example 6 does not contain sulfuric acid, whereas the polishing compound composition of Example 7 contains sulfuric acid. As a result, it is recognized that the halation and short wavelength waviness of Example 6 are improved compared to those of Example 7.

[0097] A similar trend was observed in Example 8 compared to Example 9, in that the pH (25°C) of the polishing compound composition was the same (2.0), but the polishing compound composition of Example 8 did not contain sulfuric acid, whereas the polishing compound composition of Example 9 contained sulfuric acid. As a result, it was found that Example 8 had improved halation and short wavelength waviness compared to Example 9.

[0098] Furthermore, the pH (25°C) of the polishing compound of Comparative Example 3 is the same as that of Comparative Example 2 (1.2), but the polishing compound of Comparative Example 3 contains sulfuric acid, whereas the polishing compound of Comparative Example 2 does not. As a result, it is observed that the halation of Comparative Example 3 is further deteriorated compared to Comparative Example 2.

[0099] In Comparative Example 4, the pH (25°C) of the polishing compound composition is the same as that of Example 5 (1.4), but the content of sulfuric acid in the polishing compound composition of Comparative Example 4 exceeds 1.0 mass %. As a result, in Comparative Example 4, halation is further deteriorated compared to Example 5, and deterioration of short wavelength waviness is also observed.

[0100] The pH (25°C) of the polishing compound composition of Comparative Example 5 is the same as that of Example 6 (1.7), but the sulfuric acid content of the polishing compound composition of Comparative Example 5 exceeds 1.0 mass. As a result, the halation of Comparative Example 5 is further worsened compared to Example 6, and the short wavelength waviness is also worsened.

[0101] From the above considerations, it is clear that the polishing method of the present invention has the excellent effect of reducing halation and waviness on the polished substrate surface. [Industrial Applicability]

[0102] The polishing method of the present invention can be applied to polishing electronic components such as semiconductors and magnetic recording media such as hard disks. In particular, it can be applied to surface polishing of substrates for magnetic recording media such as glass magnetic disk substrates and aluminum magnetic disk substrates. Furthermore, it can be applied to finish polishing of aluminum magnetic disk substrates for magnetic recording media, which have an electroless nickel-phosphorus plating film formed on the surface of an aluminum alloy substrate. [Explanation of symbols]

[0103] 1: Polishing method (polishing method for magnetic disk substrate), 3: Polishing machine, 4: Magnetic disk substrate, 4a, 4b: Substrate surface, 5: Carrier, 5a, 9a, 10a: Gear portion, 5b, 5c: Carrier surface, 6: Polishing pad, 6a: Pad surface, 7a: Upper surface plate, 7b: Lower surface plate, 8: Planetary motion mechanism portion, 9: Sun gear, 10: Internal gear, 11: Circular retaining hole, 12: Substrate retaining portion, A: Planetary polishing area, C: Central axis, S1: Abrasive composition preparation step, S2: Polishing step, S2a: Pad surface contact step (polishing step), S2b: Abrasive composition supply step (polishing step), S2c: Rotation step (polishing step), S2d: Planetary motion step (polishing step), S3: Polishing completion step, CW: Clockwise direction, CCW: Counterclockwise direction.

Claims

1. A method for polishing a magnetic disk substrate using an abrasive composition for magnetic disk substrates, and a polishing machine having a disk-shaped carrier, a polishing pad, a surface plate, and a planetary motion mechanism that causes the carrier to perform planetary motion consisting of a combination of rotational motion and revolutional motion in a planetary polishing region, comprising: an abrasive composition preparation step of preparing the abrasive composition for magnetic disk substrates to be used for polishing the magnetic disk substrates; a polishing process including a pad surface contacting step of contacting the pad surface of the polishing pad with the substrate surface of the magnetic disk substrate to be polished which is mounted on the carrier; an abrasive composition supplying step of supplying the prepared abrasive composition for magnetic disk substrates between the contacted substrate surface and the pad surface; a rotation step of rotating the platen and the polishing pad while the abrasive composition for magnetic disk substrates is being supplied; and a planetary motion step of setting the carrier peripheral speed of the carrier mounted with the magnetic disk substrate to 20 mm / s or more by the planetary motion mechanism and causing the carrier to perform planetary motion in the planetary polishing region. Equipped with The abrasive composition for magnetic disk substrates comprises: Contains at least colloidal silica, an acid, and an oxidizing agent, The pH (25°C) value is in the range of 1.3 or more and 4.0 or less, The method for polishing a magnetic disk substrate, wherein the content of sulfuric acid in the acid constituting the abrasive composition for a magnetic disk substrate is 0% by mass or more and 1.0% by mass or less.

2. The acid is 2. The method for polishing a magnetic disk substrate according to claim 1, wherein the polishing agent contains at least an inorganic acid and an organic acid.

3. 2. The method for polishing a magnetic disk substrate according to claim 1, wherein the content of the sulfuric acid in the acid is 0% by mass or more and 0.8% by mass or less.

4. The acid is 2. The method for polishing a magnetic disk substrate according to claim 1, wherein the polishing agent contains at least an organic phosphonic acid.

5. The magnetic disk substrate is a nickel-phosphorus plated aluminum alloy substrate; and The polishing step includes:

5. The method for polishing a magnetic disk substrate according to claim 1, further comprising a finish polishing step of polishing the surface of the aluminum alloy substrate.

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