JP6677558B2 - Composition for polishing magnetic disk substrate, method for manufacturing magnetic disk substrate and polishing method - Google Patents

Description

  The present invention relates to a magnetic disk substrate polishing composition, a method for manufacturing a magnetic disk substrate using the polishing composition, and a polishing method.

  In the manufacture of a magnetic disk substrate, pre-polishing (primary polishing) is generally performed prior to a final polishing step (final polishing) performed to finish the surface of a final product with a high degree of polishing efficiency. For example, by performing at least preliminary polishing and final polishing on a disk substrate (hereinafter, also referred to as “Ni-P substrate”) on which nickel phosphorus plating has been performed, a highly accurate surface can be efficiently realized. In such a polishing process, even in the polishing performed before the final polishing step as in the above-mentioned preliminary polishing, it is desirable to realize a good surface state because it contributes to the improvement of the surface accuracy in the final polishing step.

  One of the factors that affect the surface accuracy of the object to be polished is the material and properties of the abrasive grains contained in the polishing liquid. For example, according to the polishing liquid using silica as abrasive grains, the surface quality (for example, defects due to surface smoothness and piercing of abrasive grains) of the surface to be polished is improved as compared with the polishing liquid using abrasive grains such as alumina having higher hardness. Tend to. Patent Literatures 1 to 3 are given as technical literature on polishing techniques using silica as abrasive grains.

JP 2004-204155 A JP 2012-054281 A JP 2014-116057 A

  However, polishing liquids using silica abrasive grains generally tend to have poor polishing efficiency (typically, polishing rate), and are used in polishing requiring a high polishing rate, such as primary polishing of a Ni-P substrate. In such a case, there is a possibility that such a request cannot be sufficiently satisfied.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a composition for polishing a magnetic disk substrate that can achieve both a high polishing rate and a reduction in waviness by using silica abrasive grains. Another related object is to provide a method for manufacturing a magnetic disk substrate and a polishing method using the above polishing composition.

  According to the present invention, there is provided a composition for polishing a magnetic disk substrate, comprising abrasive grains containing silica particles and water. The ratio (A75 / A50) of the cumulative 75% aspect ratio (A75) to the cumulative 50% aspect ratio (A50) in the volume-based aspect ratio distribution of the abrasive grains is 1.05 or more. Further, the number average aspect ratio of the abrasive grains is preferably 1.3 or less. According to the polishing composition containing abrasive grains satisfying the above-mentioned characteristics, a high polishing rate and a reduction in undulation can be achieved at a high level in polishing a magnetic disk substrate.

  The polishing composition disclosed herein preferably has a pH of 5 or less. When the abrasive grains satisfying the above A75 / A50 are used in a polishing composition having such a pH, the effects of the present invention can be more suitably exerted.

  The polishing composition disclosed herein is suitable as a polishing composition used in a step before the finish polishing step. For example, the polishing composition is suitably used for primary polishing of a magnetic disk substrate. Since the polishing composition disclosed herein can exhibit a high polishing rate, it is useful to be used in a polishing process requiring high polishing efficiency such as the primary polishing.

  Further, according to the present invention, a method for manufacturing a magnetic disk substrate is provided. The manufacturing method includes a step (1) of polishing a magnetic disk substrate (substrate to be polished) using any of the magnetic disk substrate polishing compositions disclosed herein. According to such a manufacturing method, a magnetic disk substrate having a high-quality surface can be manufactured with high productivity. In a preferred aspect, the method for manufacturing a magnetic disk substrate further includes, after the step (1), a step (2) of polishing the magnetic disk substrate (substrate to be polished) using a finish polishing composition. The finish polishing composition preferably contains colloidal silica. By performing the above step (2) after the above step (1), a magnetic disk substrate having a higher quality surface can be manufactured with high productivity.

  As another aspect of the magnetic disk substrate manufacturing method disclosed herein, a magnetic disk substrate manufactured by the method is provided. Such a magnetic disk substrate is preferable because it has a high-quality surface and can be advantageous in terms of production cost.

  According to the present invention, a method for polishing a magnetic disk substrate is provided. The polishing method is characterized in that one of the compositions for polishing a magnetic disk substrate disclosed herein is supplied to a magnetic disk substrate (substrate to be polished) to polish the magnetic disk substrate. According to such a polishing method, the surface quality of the magnetic disk substrate can be efficiently improved. In a preferred aspect, in the method of polishing a magnetic disk substrate, after the step (1), a finish polishing composition is supplied to the magnetic disk substrate (substrate to be polished) to polish the substrate to be polished ( 2). The finish polishing composition preferably contains colloidal silica. By performing the step (2) after the step (1), a higher quality magnetic disk substrate surface can be obtained.

  Hereinafter, preferred embodiments of the present invention will be described. It should be noted that matters other than matters specifically mentioned in the present specification and necessary for carrying out the present invention can be grasped as design matters of those skilled in the art based on conventional techniques in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and common technical knowledge in the field.

<Abrasives>
(Aspect ratio distribution)
The polishing composition disclosed herein contains abrasive grains. The ratio (A75 / A50) of the cumulative 75% aspect ratio (A75) to the cumulative 50% aspect ratio (A50) in the volume-based aspect ratio distribution of the abrasive grains is 1.05 or more. Here, the “cumulative 75% aspect ratio” means that the cumulative volume distribution of the abrasive grains from the side having the smaller aspect ratio is 75% in the cumulative volume distribution curve in which the total volume of the aspect ratio distribution of the abrasive grains obtained on a volume basis is 100%. % Means the aspect ratio of the point. The “cumulative 50% aspect ratio” is defined as a cumulative volume distribution curve in which the total volume of the aspect ratio distribution of the abrasive grains obtained on a volume basis is 100%. % Means the aspect ratio of the point. The cumulative volume distribution curve is typically represented by a graph in which the horizontal axis represents the aspect ratio and the vertical axis represents the cumulative volume (%). Abrasive grains having the ratio (A75 / A50) of 1.05 or more contribute to compatibility between a high polishing rate and reduction of undulation in polishing of a magnetic disk substrate.

  The reason why the above-described effects can be obtained is not particularly limited, but is considered as follows, for example. That is, when the value of the ratio (A75 / A50) is large, the degree of non-sphericity (the degree of distortion from a sphere) of the particles located on the high aspect ratio side is higher than the aspect ratio located on the median volume basis. Means that. Further, it means that particles having a medium to low aspect ratio on a volume basis have a high sphericity. By using abrasive grains having a high ratio (A75 / A50), particles having a high aspect ratio contribute to improvement of the polishing rate, and particles having a low aspect ratio contribute to reduction of waviness. As a result, it is considered that both a high polishing rate and a reduction in undulation can be achieved at a high level.

  From the above viewpoint, the ratio (A75 / A50) is preferably 1.10 or more, more preferably 1.15 or more, and particularly preferably 1.20 or more (typically 1.25 or more). . From the viewpoint of the availability of abrasive grains, the ratio (A75 / A50) is suitably about 1.50 or less (eg, 1.35 or less).

  The cumulative 75% aspect ratio (A75) in the volume-based aspect ratio distribution of the abrasive grains is not particularly limited as long as the above ratio (A75 / A50) is satisfied. In a preferred embodiment, A75 is 1.05 or more, more preferably 1.10 or more, further preferably 1.20 or more, particularly preferably 1.30 or more (for example, 1.40 or more) from the viewpoint of the polishing rate or the like. ). In addition, from the viewpoint of surface quality and the like, the above-mentioned A75 is usually appropriately 1.70 or less, preferably 1.60 or less, more preferably 1.50 or less, further preferably 1.45 or less, particularly preferably 1.45 or less. Preferably it is 1.40 or less (for example, 1.35 or less).

  The cumulative 50% aspect ratio (A50) in the volume-based aspect ratio distribution of the abrasive grains is not particularly limited as long as the above ratio (A75 / A50) is satisfied. In one preferred embodiment, A50 is 1.25 or less. By using such abrasive grains, undulation can be favorably reduced. The reason is not particularly limited, but is considered as follows, for example. In other words, it can be said that an abrasive having A50 equal to or less than a predetermined value is an abrasive containing particles having an aspect ratio (low aspect ratio) equal to or lower than a predetermined value in a volume ratio equal to or higher than a predetermined value. Abrasive grains containing particles having a high sphericity represented by A50 equal to or less than a predetermined value have rolling properties, so that processing is stable during polishing and surface quality is improved (typically undulation). Reduction). The A50 is more preferably 1.20 or less, further preferably 1.15 or less, particularly preferably 1.10 or less, and most preferably 1.05 or less, from the viewpoint of reducing undulations and the like. The cumulative 50% aspect ratio of the abrasive grains is 1.00 or more in principle, and may be 1.05 or more (for example, 1.10 or more).

  Further, the cumulative 90% aspect ratio (A90) in the volume-based aspect ratio distribution of the abrasive grains disclosed herein is not particularly limited. Here, the “cumulative 90% aspect ratio” means that the cumulative volume of the abrasive grains from the side having the smaller aspect ratio is 90% in the cumulative volume distribution curve in which the total volume of the aspect ratio distribution of the abrasive grains obtained on a volume basis is 100%. % Means the aspect ratio of the point. Abrasive grains according to a preferred embodiment have A90 of 1.25 or more. By using such abrasive grains, a high polishing rate is realized. The A90 is more preferably 1.30 or more, further preferably 1.40 or more, particularly preferably 1.50 or more, and most preferably 1.60 or more, from the viewpoint of the polishing rate or the like. In addition, the cumulative 90% aspect ratio of the abrasive grains is usually preferably 3.0 or less from the viewpoints of durability (for example, resistance to collapse due to stress) of the abrasive grains and stability of polishing. Yes, preferably 2.5 or less, more preferably 2.0 or less (for example, less than 2.0). For example, for polishing containing abrasive grains having a cumulative 90% aspect ratio of greater than 1.25 and less than 3.00 (more preferably 1.31 or more and 2.20 or less, more preferably 1.52 or more and 1.96 or less). Compositions are preferred.

  In addition, the value of the ratio of the cumulative 90% aspect ratio (A90) to the cumulative 75% aspect ratio (A75) (A90 / A75) is preferably 1.05 or more, more preferably 1. It is 10 or more, more preferably 1.20 or more. The value of the above ratio (A90 / A75) is preferably 1.6 or less, more preferably 1.5 or less, from the viewpoint of obtaining a higher quality surface.

  The volume-based aspect ratio distribution of the abrasive grains can be adjusted by selecting abrasive grains to be used or a combination thereof. For example, A50, A75 and A90 in the above-described aspect ratio distribution are adjusted to the appropriate ranges disclosed herein by using large-diameter particles having a large aspect ratio mixed with smaller-diameter particles at an appropriate weight ratio. can do.

  In the present specification, the cumulative volume aspect ratio as a reference for A50, A75 and A90 means a cumulative volume aspect ratio grasped as an overall property of abrasive grains contained in the polishing composition. Therefore, when the abrasive particles contained in the polishing composition are, for example, a mixture of two types of abrasive particles X, Y, the cumulative volume aspect ratio is determined by the abrasive particles (that is, a mixture of the abrasive particles X, Y). Can be determined by measuring the aspect ratio and the volume of a plurality of abrasive grains contained in the abrasive grains as a measurement sample.

As a specific procedure, using a scanning electron microscope (SEM), abrasive grains to be measured (one kind of abrasive grains may be used, and a mixture of two or more kinds of abrasive grains may be used. Or more) may be observed in a SEM image containing 100 or more particles in one visual field. The observation magnification is 50,000 times. Then, for the smallest rectangle circumscribing each particle image, the value obtained by dividing the length of the long side (the value of the long axis) by the length of the short side (the value of the short axis) is the ratio of the long diameter / short diameter of each particle ( (Aspect ratio). Moreover, to calculate the value obtained by 4πr ^3/3 from the radius r of the ideal yen (perfect circle) having an area equal to the projected area of each particle image as the volume of each particle. Here, the above aspect ratio and volume are calculated by counting particles independently dispersed in the polishing composition as one particle, regardless of whether they are primary particles or secondary particles. And Then, by deriving the cumulative volume distribution curve of the aspect ratio distribution from the aspect ratio and the volume of the predetermined number of particles, each of the above-described cumulative volume aspect ratios can be obtained. Such a cumulative volume aspect ratio can be determined using general image analysis software. The same applies to the embodiments described later.

  As the abrasive grains disclosed herein, those having a number average aspect ratio of 1.3 or less are preferably used. A small number average aspect ratio suggests a high sphericity of small diameter particles, which tends to be dominant in the number measured. In such abrasive grains having a low number average aspect ratio, small-diameter particles contributing to the improvement of surface quality tend to impart rolling properties. Due to the rolling properties of the small-diameter particles, processing is stabilized, and undulation is preferably reduced. The number average aspect ratio of the abrasive grains is more preferably 1.25 or less, and still more preferably 1.10 or less (eg, 1.05 or less, typically 1.02 or less). Further, the number average aspect ratio of the abrasive grains is at least 1.00 in principle, and is preferably at least 1.01 from the viewpoint of the polishing rate. The number average aspect ratio may be 1.10 or more.

  The number average aspect ratio of the abrasive grains is measured, for example, by the following method. Specifically, using an SEM, 1000 or more abrasive grains contained in the abrasive grains to be measured (one kind of abrasive grains or a mixture of two or more kinds of abrasive grains) may be used. Are observed in an SEM image containing 100 or more particles in one visual field. The observation magnification is 50,000 times. For the abrasive grains in the observation image, a minimum rectangle circumscribing each particle image is drawn. Then, for the rectangle drawn for each particle image, the value obtained by dividing the length of the long side (the value of the long axis) by the length of the short side (the value of the short axis) is the long diameter / short diameter ratio (aspect ratio). ). The number average aspect ratio can be determined by arithmetically averaging the aspect ratios of the predetermined number of particles. The number aspect ratio can be obtained by using general image analysis software. The same applies to the embodiments described later.

(Average primary particle diameter)
The average primary particle size (D1) of the abrasive grains disclosed herein is not particularly limited. Usually, abrasive grains having an average primary particle diameter of 150 nm or less are used. The average primary particle diameter is suitably 100 nm or less (for example, 80 nm or less, typically less than 70 nm). In a preferred embodiment, the abrasive has an average primary particle size of less than 60 nm. Abrasive grains having an average primary particle size of not more than a predetermined value contain small-sized particles in a ratio of not less than a predetermined value. By using such abrasive grains, waviness can be preferably reduced by the action of small-diameter particles (specifically, finer processing points on the substrate surface) while obtaining a high polishing rate. The average primary particle diameter of the abrasive grains is more preferably 55 nm or less, and still more preferably 50 nm or less. The average primary particle diameter of the abrasive grains is suitably about 10 nm or more, preferably 20 nm or more, more preferably 30 nm or more, and still more preferably 35 nm or more (for example, 40 nm or more, and more preferably 45 nm or more). . Higher polishing rates can be achieved by increasing the average primary particle size.

  In the technology disclosed herein, the average primary particle diameter of the abrasive grains refers to an average particle diameter (specific surface area-converted particle diameter) determined based on the BET method. The specific surface area can be measured using, for example, a surface area measuring device manufactured by Micromeritex Co., Ltd., trade name “Flow Sorb II 2300”. The same applies to the embodiments described later.

(Silica particles)
The polishing composition disclosed herein contains silica particles as abrasive grains. The silica particles contained in the abrasive grains may be various types of silica particles containing silica as a main component. Here, the silica particles containing silica as a main component are particles in which 90% by weight or more (normally 95% by weight or more, typically 98% by weight or more) of the particles is silica. Examples of the silica particles that can be used include, but are not particularly limited to, colloidal silica, precipitated silica, sodium silicate silica, alkoxide silica, fumed silica, dried silica, explosive silica, and the like. Examples of usable silica particles further include silica obtained using the above silica particles (ie, precipitated silica, sodium silicate method silica, alkoxide method silica, fumed silica, dried silica, explosion method silica, etc.) as a raw material. Particles. Examples of such silica particles include the above-mentioned raw material silica particles (hereinafter also referred to as “raw silica”), heat treatment such as heating, drying and baking, pressure treatment such as autoclave treatment, crushing and pulverization ( Silica particles obtained by applying one or more treatments selected from mechanical treatments such as crushing) and surface modification (for example, introduction of functional groups, chemical modification such as metal modification). obtain. The abrasive in the technology disclosed herein may include one kind of such silica particles alone or in combination of two or more kinds.

  As the silica particles, for example, silica particles obtained by subjecting raw material silica to heat treatment (hereinafter also referred to as “heat-treated silica”), specifically, heated silica particles, dried silica particles, Silica particles and the like can be preferably used. Here, the heated silica particles are typically obtained through a process of maintaining the silica particles in an environment of 60 ° C. or more and less than 110 ° C. for a certain time or more (for example, 15 minutes or more, typically 30 minutes or more). Silica particles. The dried silica particles are typically used in an environment of 110 ° C. or more and less than 500 ° C. (preferably 300 ° C. or more and less than 500 ° C.) for a given time or more (eg, 15 minutes or more, typically 30 minutes). Above) refers to silica particles obtained through a holding process. The calcined silica particles (hereinafter also referred to as “calcined silica”) are typically 500 ° C. or more, preferably 700 ° C. or more, and more preferably 900 ° C. or more for a certain period of time (for example, 15 ° C. or more). (Typically 30 minutes or more). The silica particles obtained through the process of heat-treating any of the above-mentioned raw material silicas (precipitated silica, sodium silicate silica, alkoxide silica, fumed silica, dried silica, explosive silica, etc.) It is a typical example included in the concept of silica.

  Another preferred example of silica particles that can be used as a component of silica abrasive grains in the technology disclosed herein is colloidal silica. Among them, it is preferable to use colloidal silica synthesized through particle growth in an aqueous phase, such as sodium silicate silica and alkoxide silica. According to the silica abrasive grains containing this type of colloidal silica, a high polishing rate and good surface accuracy can be suitably achieved. When the silica abrasive grains disclosed herein contain colloidal silica, the colloidal silica contained in the silica abrasive grains may be one type, or may be two or more types having different production conditions and / or physical properties. . Further, the silica abrasive may be composed of one or more kinds of colloidal silica, and may be composed of a combination of colloidal silica and other silica particles (that is, silica particles other than colloidal silica). There may be.

  The particle shape of the colloidal silica is not particularly limited, and may be, for example, spherical or non-spherical. Specific examples of the non-spherical shape include a peanut shape (that is, a shape of a peanut shell), a cocoon shape, a shape with projections (for example, a confetti shape), a rugby ball shape, and the like. Although not particularly limited, the average value (number average aspect ratio) of the major axis / minor axis ratio of colloidal silica is preferably 1.01 or more, and more preferably 1.05 or more (for example, 1.1 or more). . A higher polishing rate can be achieved by increasing the number average aspect ratio. The number average aspect ratio of colloidal silica can be measured by the same method as the above-mentioned number average aspect ratio of abrasive grains.

  The technique disclosed herein can be preferably implemented in a mode in which the abrasive grains contained in the polishing composition include heat-treated silica alone or a combination of heat-treated silica and other silica particles. In an embodiment including a combination of heat-treated silica and other silica particles, the particle size and aspect ratio of the heat-treated silica used are not particularly limited.

  For example, in the technology disclosed herein, the heat-treated silica used in combination with another silica has an average primary particle diameter of about 10 nm or more (more preferably 20 nm or more, further preferably 30 nm or more, particularly preferably 40 nm or more, Heat-treated silica (typically 50 nm or more) can be preferably used. The average primary particle diameter of the heat-treated silica is usually about 150 nm or less (preferably 100 nm or less, more preferably 80 nm or less, and typically less than 70 nm). By using the heat-treated silica having the above average primary particle diameter, it is possible to suitably obtain abrasive grains whose abrasive grain characteristics such as A75 / A50 are adjusted to a desired range. The average primary particle diameter of the heat-treated silica can be measured in the same manner as the above-mentioned average primary particle diameter of the abrasive grains.

  In the technology disclosed herein, the number-average aspect ratio of the heat-treated silica used in combination with another silica is usually appropriately 1.10 or more, preferably 1.20 or more, more preferably Is 1.30 or more, more preferably 1.35 or more. Even if the heat-treated silica has a high number average aspect ratio, chipping of particles hardly occurs during processing, and it can be an abrasive grain that imparts good workability. The heat-treated silica preferably has a number average aspect ratio of usually 3.0 or less, preferably 2.5 or less, more preferably 2.0 or less (eg, 1.7 or less). By using the heat-treated silica having the above number average aspect ratio, it is possible to suitably obtain abrasive grains whose abrasive grain properties such as A75 / A50 are adjusted to a desired range. The number average aspect ratio of the heat-treated silica can be measured by the same method as the above-mentioned number average aspect ratio of the abrasive grains.

  The type of other silica particles used in combination with the heat-treated silica is not particularly limited, and the above-mentioned silica particles (colloidal silica, precipitated silica, sodium silicate method silica, alkoxide method silica, fumed silica, dried silica, One or two or more kinds of explosive silica) can be used. Among them, colloidal silica is preferred. Therefore, the technology disclosed herein can be preferably implemented in a mode in which the silica abrasive grains contained in the polishing composition include a combination of heat-treated silica and colloidal silica. By using colloidal silica in addition to heat-treated silica, higher surface accuracy can be realized.

  The particle size and aspect ratio of the other silica (preferably colloidal silica) are not particularly limited. For example, in the abrasive grains disclosed herein, the other silica used in combination with the heat-treated silica has an average primary particle diameter of about 100 nm or less (more preferably 80 nm or less, still more preferably less than 60 nm, and typically 40 nm or less. ) Can be preferably used. The average primary particle diameter of the other silica is usually about 10 nm or more (preferably 20 nm or more, more preferably 30 nm or more). By using silica having the above average primary particle diameter, it is possible to suitably obtain abrasive grains whose abrasive properties such as A75 / A50 are adjusted to a desired range. The average primary particle diameter of the other silica can be measured in the same manner as the above-mentioned average primary particle diameter of the abrasive grains.

  In the abrasive grains disclosed herein, the number average aspect ratio of the other silica used in combination with the heat-treated silica is usually 1.25 or less (preferably 1.10 or less, more preferably 1.05 or less, More preferably, it is 1.02 or less, typically 1.01 or less. The number average aspect ratio of the other silica is 1.00 or more in principle, and may be 1.01 or more. The number average aspect ratio of the other silica can be measured in the same manner as the above-described number average aspect ratio of the abrasive grains.

  As described above, in the embodiment in which the abrasive grains contain at least the heat-treated silica, the content of the heat-treated silica in the abrasive grains is not particularly limited. From the viewpoint of the polishing rate, the content of the above-mentioned heat-treated silica is preferably 10% by weight or more of the abrasive grains, more preferably 20% by weight or more (for example, 25% by weight or more), and further preferably 30% by weight or more. is there. The upper limit of the content of the heat-treated silica in the abrasive grains is not particularly limited, and may be substantially 100% by weight (typically 99% by weight or more). From the viewpoint of balancing various performances (eg, polishing rate, undulation of the surface to be polished, etc.), the content of the heat-treated silica in the abrasive grains is preferably 90% by weight or less, more preferably 80% by weight or less (for example, 75% by weight or less), and more preferably 60% by weight or less.

Further, in an aspect in which the abrasive grains contained in the polishing composition include a combination of the heat-treated silica and other silica particles, the weight (W _A ) of the heat-treated silica (silica particles A) contained in the silica abrasive grains is different from that of the other abrasive grains. silica ratio of the weight of _{(W B)} (silica particles B, preferably colloidal silica) _(W a / W _B) is not particularly limited. In light of the polishing rate, the ratio (W _A / W _B ) is preferably equal to or greater than 0.20, more preferably equal to or greater than 0.30, still more preferably equal to or greater than 0.50, and particularly preferably equal to or greater than 1.0. (For example, 1.5 or more). From the viewpoint of obtaining a higher polishing _rate, the W A / _{W B} can be 10 or more, may be 30 or more. Various performance balance from the point of view to take in (for example polishing rate, the surface accuracy of the polished surface after polishing), the W A _/ W _B, 50 or less (e.g., 15 or less, typically 5.0 or less) and Advantageously, in another aspect it can be 3.0 or less, even 2.0 or less (eg 1.5 or less).

(Particles other than silica particles)
The polishing composition disclosed herein can contain particles other than silica particles. As particles other than silica particles, any of inorganic particles, organic particles, and organic-inorganic composite particles can be used. Specific examples of the inorganic particles include oxide particles such as alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, and red iron oxide particles; silicon nitride particles. And nitride particles such as boron nitride particles; carbide particles such as silicon carbide particles and boron carbide particles; diamond particles; carbonates such as calcium carbonate and barium carbonate; Examples of the alumina particles include α-alumina, intermediate alumina other than α-alumina, and composites thereof. Intermediate alumina is a general term for alumina particles other than α-alumina, and specific examples include γ-alumina, δ-alumina, θ-alumina, η-alumina, κ-alumina, and composites thereof. Specific examples of the organic particles include polymethyl methacrylate (PMMA) particles and poly (meth) acrylic acid particles (here, (meth) acrylic acid means acrylic acid and methacrylic acid comprehensively). And polyacrylonitrile particles. These particles other than silica particles can be used alone or in combination of two or more.

  In the polishing composition disclosed herein, the content of the silica particles in the solid content of the polishing composition is not particularly limited. The content of the silica particles is preferably 40% by weight or more, more preferably 50% by weight or more, even more preferably 60% by weight or more of the entire solid content from the viewpoint of easily exhibiting the effect of the present invention. And still more preferably 80% by weight or more, particularly preferably 90% by weight or more (for example, 99% by weight or more). In the present specification, the solid content contained in the polishing composition refers to a residue (non-volatile content) after evaporating water from the polishing composition at a temperature at which bound water is not removed (for example, 60 ° C.). Say.

  The polishing composition disclosed herein can be preferably implemented in a mode substantially free of alumina abrasive grains (for example, α-alumina abrasive grains). According to such a polishing composition, deterioration in quality (for example, generation of scratches and dents, residual alumina, piercing defects of abrasive grains, and the like) due to use of alumina abrasive grains is prevented. In the present specification, the phrase "substantially does not contain predetermined abrasive grains (for example, alumina abrasive grains)" means that the proportion of the abrasive grains is 1% by weight or less (more than the total amount of solids contained in the polishing composition). Preferably 0.5% by weight or less, typically 0.1% by weight or less). A polishing composition in which the proportion of alumina abrasive grains is 0% by weight, that is, a polishing composition containing no alumina abrasive grains, is particularly preferred. In addition, the polishing composition disclosed herein can be preferably implemented in a mode substantially free of α-alumina abrasive grains.

  The polishing composition disclosed herein can also be preferably practiced in a mode substantially free of particles (non-silica particles) other than silica particles. Here, the phrase "substantially free of non-silica particles" means that the proportion of non-silica particles is 1% by weight or less (more preferably 0.5% by weight or less, typically 0.1% by weight or less). In such an embodiment, the application effects of the technology disclosed herein can be suitably exhibited.

<Polishing composition>
(water)
The polishing composition disclosed herein typically contains, in addition to the abrasive grains described above, water for dispersing the abrasive grains. As the water, ion-exchanged water (deionized water), pure water, ultrapure water, distilled water and the like can be preferably used.

  The polishing composition (typically a slurry-like composition) disclosed herein can be preferably implemented, for example, in a form having a solid content of 5 g / L to 300 g / L. The form in which the solid content is 10 g / L to 200 g / L is more preferable.

(acid)
The polishing composition disclosed herein can be preferably practiced in a mode containing an acid as a polishing accelerator. Examples of acids that can be suitably used include inorganic acids and organic acids (for example, organic carboxylic acids having 1 to 10 carbon atoms, organic phosphonic acids, organic sulfonic acids, amino acids and the like). Not limited. The acids can be used alone or in combination of two or more.

  Specific examples of the inorganic acid include phosphoric acid, nitric acid, sulfuric acid, hydrochloric acid, hypophosphorous acid, phosphonic acid, boric acid, and sulfamic acid.

  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, valine, leucine, a Leucine, serine, threonine, cysteine, methionine, phenylalanine, tryptophan, tyrosine, proline, cystine, glutamine, asparagine, lysine, arginine, nicotinic acid, picolinic acid, 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, Tan-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 (methylene phosphonic acid), methanesulfonic acid, ethanesulfonic acid, aminoethanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, and 2-naphthalenesulfonic acid.

  Preferred acids from the viewpoint of polishing efficiency include phosphoric acid, nitric acid, sulfuric acid, sulfamic acid, phytic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, methanesulfonic acid and the like. Of these, nitric acid, sulfuric acid, phosphoric acid, sulfamic acid and methanesulfonic acid are preferred.

  When the polishing composition contains an acid, its content is not particularly limited. Usually, the content of the acid is appropriately 1 g / L or more, preferably 3 g / L or more, more preferably 5 g / L or more (for example, 10 g / L or more). When the content of the acid is too small, the polishing rate tends to be insufficient, which may not be practically preferable. Usually, the content of the acid is suitably 200 g / L or less, preferably 100 g / L or less, and more preferably 50 g / L or less (for example, 30 g / L or less). If the content of the acid is too large, the surface accuracy of the object to be polished tends to decrease, which may not be practically preferable.

The acid may be used in the form of a salt of the acid. Examples of the salt include a metal salt (for example, an alkali metal salt such as a lithium salt, a sodium salt, and a potassium salt) and an ammonium salt (for example, a tetramethylammonium salt, a tetraethylammonium salt, and the like) of the above-described inorganic acids and organic acids. Quaternary ammonium salts), alkanolamine salts (for example, monoethanolamine salts, diethanolamine salts, and triethanolamine salts).
Specific examples of the salt include alkali metal phosphates and alkali metal phosphates such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. Hydrogen phosphate; alkali metal salts of the organic acids exemplified above; other alkali metal salts of glutamic acid diacetate, alkali metal salts of diethylenetriaminepentaacetic acid, alkali metal salts of hydroxyethylethylenediaminetriacetic acid, and 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 included in the polishing composition disclosed herein, a salt of an inorganic acid (for example, an alkali metal salt or an ammonium salt) can be preferably used. For example, potassium chloride, sodium chloride, ammonium chloride, potassium nitrate, sodium nitrate, ammonium nitrate, potassium phosphate and the like can be preferably used.

  The acids and salts thereof can be used alone or in combination of two or more. In a preferred embodiment of the polishing composition disclosed herein, an acid (preferably an inorganic acid) and a salt of an acid different from the acid (preferably a salt of an inorganic acid) can be used in combination.

(Oxidant)
The polishing composition disclosed herein can contain an oxidizing agent as needed. Examples of the oxidizing agent include peroxide, nitric acid or a salt thereof, periodic acid or a salt thereof, peroxo acid or a salt thereof, permanganic acid or a salt thereof, chromic acid or a salt thereof, oxyacid or a salt thereof, and metal salts. , Sulfuric acids and the like, but are not limited thereto. The oxidizing agents can be used alone or in combination of two or more. Specific examples of the oxidizing agent include hydrogen peroxide, sodium peroxide, barium peroxide, nitric acid, iron nitrate, aluminum nitrate, ammonium nitrate, peroxomonosulfuric acid, ammonium peroxomonosulfate, metal salts of peroxomonosulfate, peroxodisulfuric acid, and peroxodisulfide. Ammonium sulfate, metal peroxodisulfate, peroxophosphoric acid, peroxosulfuric acid, sodium peroxoborate, formic acid, peracetic acid, perbenzoic acid, perphthalic acid, hypobromite, hypoiodic acid, chloric acid, bromate, Iodic acid, periodic acid, perchloric acid, hypochlorous acid, sodium hypochlorite, calcium hypochlorite, potassium permanganate, metal chromate, metal dichromate, iron chloride, iron sulfate, Examples include iron citrate and iron ammonium sulfate. Preferred oxidizing agents include hydrogen peroxide, iron nitrate, periodic acid, peroxomonosulfuric acid, 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, its content is preferably at least 1 g / L, more preferably at least 3 g / L, even more preferably at least 4 g / L, based on the amount of the active ingredient. 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 decreases, which may not be practically preferable. When the polishing composition contains an oxidizing agent, its content is preferably 30 g / L or less, more preferably 15 g / L or less, based on the amount of the active ingredient. If the content of the oxidizing agent is too large, the surface accuracy of the object to be polished is likely to decrease, which may not be practically preferable.

(Basic compound)
The polishing composition may contain a basic compound as necessary. Here, the basic compound refers to a compound having a function of increasing the pH of the polishing composition when added to the polishing composition. Examples of the basic compound include alkali metal hydroxides, carbonates and bicarbonates, quaternary ammonium or its salts, ammonia, amines, phosphates and hydrogen phosphates, and organic acid salts. The basic compounds can be used alone or in combination of two or more.

Specific examples of the alkali metal hydroxide include potassium hydroxide, sodium hydroxide and the like.
Specific examples of carbonates and hydrogen carbonates include ammonium hydrogen carbonate, ammonium carbonate, potassium hydrogen carbonate, potassium carbonate, sodium hydrogen carbonate, sodium carbonate, and the like.
Specific examples of the quaternary ammonium or a salt thereof include quaternary ammonium hydroxides such as tetramethylammonium hydroxide, tetraethylammonium hydroxide and tetrabutylammonium hydroxide; alkali metals of such quaternary ammonium hydroxides Salts (eg, sodium salts and potassium salts);
Specific examples of the amine include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, ethylenediamine, monoethanolamine, N- (β-aminoethyl) ethanolamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, and 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 alkali salts such as tripotassium phosphate, dipotassium hydrogen phosphate, potassium dihydrogen phosphate, trisodium phosphate, disodium hydrogen phosphate, and sodium dihydrogen phosphate. Metal salts.
Specific examples of the organic acid salt include potassium citrate, potassium oxalate, potassium tartrate, potassium sodium tartrate, ammonium tartrate and the like.

(Other components)
The polishing composition disclosed herein is a polishing composition such as a surfactant, a water-soluble polymer, a dispersant, a chelating agent, a preservative, and a fungicide, as long as the effects of the present invention are not significantly impaired. If necessary, a known additive that can be used for a product (for example, a polishing composition for a magnetic disk substrate such as a Ni-P substrate) may be further contained.

The surfactant is not particularly limited, and any of anionic surfactants, nonionic surfactants, cationic surfactants, and amphoteric surfactants can be used. Use of a surfactant (typically, a water-soluble organic compound having a molecular weight of less than 1 × 10 ⁴ ) can improve the dispersion stability of the polishing composition. One type of surfactant can be used alone, or two or more types can be used in combination.
Specific examples of the anionic surfactant include polyoxyethylene alkyl ether acetic acid, polyoxyethylene alkyl sulfate, alkyl sulfate, polyoxyethylene alkyl sulfate, alkyl sulfate, alkylbenzene sulfonic acid, alkyl phosphate, polyoxyethylene. Alkyl phosphate ester, polyoxyethylene sulfosuccinic acid, alkyl sulfosuccinic acid, alkyl naphthalene sulfonic acid, alkyl diphenyl ether disulfonic acid, polyacrylic acid, sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium polyoxyethylene alkyl ether sulfate, Ammonium polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene alkyl phenyl ether sulfate Sodium, and salts thereof.
Other specific examples of anionic surfactants include polyalkylaryl sulfonic acid compounds such as naphthalene sulfonic acid formaldehyde condensate, methyl naphthalene sulfonic acid formaldehyde condensate, anthracene sulfonic acid formaldehyde condensate, and benzene sulfonic acid formaldehyde condensate Melamine formalin resin sulfonic acid compounds such as melamine sulfonic acid formaldehyde condensate; lignin sulfonic acid compounds such as lignin sulfonic acid and modified lignin sulfonic acid; aromatic amino sulfonic acids such as aminoaryl sulfonic acid-phenol-formaldehyde condensate Polyisoprenesulfonic acid, polyvinylsulfonic acid, polyallylsulfonic acid, polyisoamylenesulfonic acid, polystyrenesulfonic acid; and the like. Etc. The. As the salt, an alkali metal salt such as a sodium salt and a potassium salt is preferable.
Specific examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, sorbitan fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, and alkyl alkanolamide. .
Specific examples of the cationic surfactant include an alkyltrimethylammonium salt, an alkyldimethylammonium salt, an alkylbenzyldimethylammonium salt, and an alkylamine salt.
Specific examples of the amphoteric surfactant include alkyl betaine and alkylamine oxide.

  In a polishing composition containing a 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. From the viewpoint of the 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.

  The polishing composition disclosed herein may contain a water-soluble polymer. By including a water-soluble polymer, surface accuracy after polishing can be improved. Examples of the water-soluble polymer include polyalkylarylsulfonic acid compounds such as naphthalenesulfonic acid formaldehyde condensate, methylnaphthalenesulfonic acid formaldehyde condensate and anthracenesulfonic acid formaldehyde; melamine formalin resin sulfone such as melaminesulfonic acid formaldehyde condensate Acid compounds; Lignin sulfonic acid compounds such as lignin sulfonic acid and modified lignin sulfonic acid; Aromatic amino sulfonic acid compounds such as aminoaryl sulfonic acid-phenol-formaldehyde condensate; others, polyisoprene sulfonic acid and polyvinyl sulfonic acid , Polyallylsulfonic acid, polyisoamylenesulfonic acid, polystyrenesulfonic acid salt, polyacrylate, polyvinyl acetate, polymaleic acid, polyitaconic acid, polyvinyl Alcohol, polyglycerin, polyvinylpyrrolidone, copolymer of isoprenesulfonic acid and acrylic acid, polyvinylpyrrolidone polyacrylic acid copolymer, polyvinylpyrrolidone vinyl acetate copolymer, diallylamine hydrochloride sulfur dioxide copolymer, carboxymethylcellulose, carboxymethylcellulose , Hydroxyethylcellulose, hydroxypropylcellulose, pullulan, chitosan, chitosan salts and the like. The water-soluble polymers can be used alone or in combination of two or more.

  In the polishing composition of the embodiment containing the water-soluble polymer, the content of the water-soluble polymer in the polishing liquid (in the embodiment containing a plurality of water-soluble polymers, the total content thereof) is, for example, 0.01 g. / L or more is appropriate. The content is preferably 0.05 g / L or more, more preferably 0.08 g / L or more, and further preferably 0.1 g / L or more, from the viewpoint of the surface smoothness of the object to be polished (for example, a magnetic disk substrate) after polishing. It is 1 g / L or more. From the viewpoint of the polishing rate and the like, the content is suitably 10 g / L or less, and preferably 5 g / L or less, for example, 1 g / L or less. The technology disclosed herein can be preferably implemented even in a mode in which the polishing composition does not substantially contain a water-soluble polymer.

  Examples of dispersants include polycarboxylic acid-based dispersants such as sodium polycarboxylate and ammonium polycarboxylate; naphthalenesulfonic acid-based dispersants such as sodium naphthalenesulfonic acid and ammonium naphthalenesulfonic acid; alkylsulfonic acid Dispersants; polyphosphoric acid dispersants; polyalkylene polyamine dispersants; quaternary ammonium dispersants; alkyl polyamine dispersants; alkylene oxide dispersants; polyhydric alcohol ester dispersants;

  Examples of the chelating agent include an aminocarboxylic acid-based chelating agent and an organic phosphonic acid-based chelating agent. Examples of aminocarboxylic acid-based chelating agents include ethylenediaminetetraacetic acid, sodium ethylenediaminetetraacetate, nitrilotriacetic acid, sodium nitrilotriacetate, ammonium nitrilotriacetate, hydroxyethylethylenediaminetriacetic acid, sodium hydroxyethylethylenediaminetriacetate, and diethylenetriaminepentaacetic acid. , Sodium diethylene triamine pentaacetate, triethylene tetramine hexaacetic acid and sodium triethylene tetramine hexaacetate. Examples of the organic phosphonic acid chelating agent include 2-aminoethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, aminotri (methylenephosphonic acid), ethylenediaminetetrakis (methylenephosphonic acid), and diethylenetriaminepenta (methylenephosphonic acid). 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-methylphosphonic acid Includes nosuccinic acid. Of these, organic phosphonic acid-based chelating agents are more preferred, and particularly preferred are ethylenediaminetetrakis (methylenephosphonic acid) and diethylenetriaminepenta (methylenephosphonic acid). Particularly preferred chelating agents include ethylenediaminetetrakis (methylenephosphonic acid).

  Examples of preservatives and fungicides include isothiazoline preservatives such as 2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, and paraoxybenzoates. Phenoxyethanol and the like.

(Polishing liquid)
The polishing composition disclosed herein is typically supplied to a polishing target (magnetic disk substrate) in the form of a polishing liquid containing the polishing composition, and used for polishing the polishing target. The polishing liquid may be, for example, one prepared by diluting (typically, diluting with water) the polishing composition. Alternatively, the polishing composition may be used as it is as a polishing liquid. That is, the concept of the polishing composition in the technology disclosed herein includes a polishing liquid (working slurry) supplied to an object to be polished and used for polishing the object to be polished, and used as a polishing liquid after dilution. Both concentrates are included. Such a polishing composition in the form of a concentrated solution is advantageous from the viewpoints of convenience, cost reduction, and the like during production, distribution, storage, and the like. The concentration ratio can be, for example, about 1.5 to 50 times. From the viewpoint of the storage stability of the concentrate, a concentration ratio of about 2 to 20 times (typically, 2 to 10 times) is appropriate.

  The content of the abrasive grains in the polishing liquid (when a plurality of types of abrasive grains are included, the total content thereof) is not particularly limited, but is typically 5 g / L or more and 10 g / L or more. , And more preferably 20 g / L or more. Increasing the abrasive content tends to achieve higher polishing rates. From the viewpoint of the surface smoothness of the substrate after polishing and the stability of polishing, the content is usually suitably 250 g / L or less, preferably 200 g / L or less, more preferably 150 g / L or less, and still more preferably. Is 100 g / L or less.

(PH)
The pH of the polishing composition disclosed herein is not particularly limited. The pH of the polishing composition can be, for example, 12.0 or less (typically 0.5 to 12.0), and 10.0 or less (typically 0.5 to 10.0). It may be. From the viewpoints of a polishing rate, surface accuracy, and the like, the pH of the polishing composition can be set to 7.0 or less (for example, 0.5 to 7.0), and 5.0 or less (typically 1.0 to 1.0). To 5.0), more preferably 4.0 or less (for example, 1.0 to 4.0). The pH of the polishing composition is, for example, 3.0 or less (typically 1.0 to 3.0, preferably 1.0 to 2.0, more preferably 1.0 to 1.8). Can be. If necessary, a pH adjuster such as an organic acid, an inorganic acid, or a basic compound can be contained so that the above-mentioned pH is realized in the polishing liquid. The above pH can be preferably applied, for example, to a polishing composition for polishing (particularly for primary polishing) a magnetic disk substrate such as a Ni-P substrate.

(Multi-component polishing composition)
Note that the polishing composition disclosed herein may be a single-pack type or a multi-pack type including a two-pack type. For example, a solution A containing a part of components (typically components other than water) of the constituents of the polishing composition and a solution B containing the remaining components are mixed to polish the object to be polished. May be configured to be used. A multi-part polishing composition according to a preferred embodiment includes a liquid A containing abrasive grains (typically, an abrasive dispersion liquid that may contain a dispersant) and a component other than the abrasive grains (eg, acid, aqueous solution). B) containing a reactive polymer and other additives. Usually, these are stored separately before use, and can be mixed at the time of use (at the time of polishing the substrate to be polished). At the time of mixing, an oxidizing agent such as hydrogen peroxide may be further mixed. For example, when the oxidizing agent (for example, hydrogen peroxide) is supplied in the form of an aqueous solution (for example, aqueous hydrogen peroxide), the aqueous solution can be a liquid C constituting the multi-component polishing composition.

  The polishing composition disclosed herein can be preferably applied to, for example, polishing of a Ni-P substrate. The base disk may be made of, for example, aluminum alloy, glass, glassy carbon, or the like. A disk substrate provided with a metal layer or a metal compound layer other than the nickel phosphorus plating layer on the surface of such a base disk may be used. Among them, it is suitable as a polishing composition for a Ni-P substrate having a nickel phosphorus plating layer on a base disk made of an aluminum alloy. In such an application, it is particularly significant to apply the technology disclosed herein.

  The polishing composition disclosed herein is used in applications requiring high polishing efficiency, such as a pre-polishing step in a manufacturing process of a polished object (magnetic disk substrate) that requires a high-precision surface after the final polishing step. Can be used in a particularly meaningful way. When a plurality of pre-polishing steps are provided as a pre-step of the final polishing step, the pre-polishing step can be used, and the same or different polishing compositions can be used in these pre-polishing steps. The polishing composition disclosed herein is suitable, for example, as a polishing composition used in a primary polishing step (first polishing step) of an object to be polished. Above all, it can be preferably used in the first polishing step (primary polishing step) after nickel phosphorus plating in the manufacturing process of the Ni-P substrate.

  According to the polishing composition disclosed herein, the arithmetic mean waviness (Wa) of the surface of a magnetic disk substrate (typically, a Ni-P substrate) after polishing can be adjusted to preferably less than 5 °. Further, the above-described waviness reduction can be realized at a high polishing rate of about 0.25 μm / min or more (for example, 0.30 μm / min or more, typically 0.40 μm / min or more). Therefore, according to the technology disclosed herein, there is provided a method of polishing a magnetic disk substrate suitable for efficiently reducing undulation (also referred to as undulation reduction method). The arithmetic mean waviness (Wa) and the polishing rate are measured by the methods described in Examples described later.

  The polishing composition disclosed herein has, for example, a surface roughness (arithmetic average roughness (Ra)) of 20 ° measured by a laser scanning surface roughness meter “TMS-3000WRC” manufactured by Schmitt Measurement System Inc. It is suitable for use in polishing a magnetic disk substrate of about 300 ° (typically primary polishing) to adjust the surface roughness (arithmetic average roughness (Ra)) of the magnetic disk substrate to 10 ° or less. In such an application, it is particularly significant to apply the technology disclosed herein.

<Polishing process>
The polishing composition disclosed herein can be suitably used for polishing an object to be polished (here, a magnetic disk substrate), for example, in a mode including the following operation. Hereinafter, a preferred embodiment of a method for polishing an object to be polished (also referred to as a substrate to be polished) using the polishing composition disclosed herein will be described.
That is, a polishing liquid (working slurry) containing any of the polishing compositions disclosed herein is prepared. Preparing the polishing liquid may include preparing a polishing liquid by adding operations such as concentration adjustment (for example, dilution) and pH adjustment to the polishing composition. Alternatively, the polishing composition may be used as it is as a polishing liquid.

  Next, the polishing liquid is supplied to the object to be polished and polished by a conventional method. For example, an object to be polished is set in a general polishing apparatus, and 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, while continuously supplying the polishing liquid, a polishing pad is pressed against the surface of the object to be polished, and the two are relatively moved (for example, rotationally moved). Through such a polishing step, polishing of the object to be polished is completed.

  The polishing step as described above can be a part of a manufacturing process of a magnetic disk substrate (for example, a Ni-P substrate). Therefore, according to this specification, a method for manufacturing a magnetic disk substrate and a polishing method including the above-mentioned polishing step are provided.

  The polishing composition disclosed herein can be preferably used in a pre-polishing step (for example, a primary polishing step) of an object to be polished. According to this specification, there is provided a method of manufacturing a polished object (substrate) and a method of polishing, including a step of performing preliminary polishing using any of the polishing compositions (preliminary polishing compositions) described above. The method includes a step (1) of polishing the object by supplying the polishing composition disclosed herein to the object to be polished. The method may include a finish polishing step after the preliminary polishing step. The polishing composition (final polishing composition) used in the final polishing step is not particularly limited. Accordingly, the matters disclosed in this specification include a step (1) of polishing an object to be polished with the polishing composition containing abrasive grains disclosed herein, and a polishing composition used in the step (1). And a polishing method for a magnetic disk substrate, which includes, in this order, a step (2) of polishing an object to be polished with a polishing composition different from the above. According to this manufacturing method, a magnetic disk substrate can be manufactured efficiently.

  The abrasive used in the step (2) is not particularly limited, and typically, for the purpose of distinguishing from the abrasive used in the step (1) (the abrasive A2 used in the step (2), Various types of abrasive grains exemplified as “abrasive grains A1”) and different types of abrasive grains A2 from the abrasive grains A1 are used. In the step (2), it is preferable to use a finish polishing composition including the abrasive grains A2 having a smaller number average aspect ratio than the abrasive grains A1 used in the step (1). As the number average aspect ratio (average value of the major axis / minor axis ratio) of the abrasive grains A2, the ratio (Aspect2 / Aspect1) between the number average aspect ratio Aspect1 of the abrasive grains A1 and the number average aspect ratio Aspect2 of the abrasive grains A2 is 1. Those having less than (more preferably 0.9 or less, further preferably 0.8 or less) are preferably used. More specifically, the number average aspect ratio of the abrasive grains A2 is 1.00 or more, and preferably 1.01 or more (for example, 1.05 or more). A higher polishing rate can be achieved by increasing the number average aspect ratio. In addition, the number average aspect ratio is preferably less than 1.5, more preferably less than 1.3, and further preferably less than 1.25, from the viewpoint of reducing surface roughness. Moreover, it is preferable that A90 of the abrasive grain A2 is less than 1.25 (for example, less than 1.2, and further less than 1.1) from the viewpoint of surface quality. In addition, the number average aspect ratio and A90 of the abrasive grains A2 can be measured by the same methods as those for the number average aspect ratio and A90 of the above abrasive grains A1.

  Preferable examples of the abrasive grains A2 include colloidal silica. By using colloidal silica, a polished object with high surface accuracy can be efficiently manufactured. The particle shape of the colloidal silica used as the abrasive grains A2 is not particularly limited. For example, the particle shape may be spherical or non-spherical, but spherical colloidal silica is preferably used.

  In the finish polishing composition containing the abrasive grains A2 (for example, silica abrasive grains, typically colloidal silica), the average primary particle diameter (D1) of the abrasive grains A2 contained in the finish polishing composition is not particularly limited. From the viewpoint of surface accuracy after the final polishing, the average primary particle diameter of the abrasive grains A2 contained in the final polishing composition may be smaller than the average primary particle diameter of the abrasive grains A1 included in the preliminary polishing composition. preferable. The average primary particle diameter of the abrasive grains A2 contained in the finish polishing composition can be, for example, 70 nm or less (typically 5 nm or more and less than 70 nm), and 65 nm or less (typically 5 nm to 65 nm, for example, 10 nm). To 50 nm). In a preferred embodiment, the average primary particle diameter of the abrasive grains A2 contained in the finish polishing composition can be, for example, less than 40 nm (typically 5 nm or more and less than 40 nm), and 35 nm or less (typically 5 nm). To 35 nm, for example, 10 nm to 30 nm). In addition, the average primary particle diameter of the abrasive grains A2 can be measured by the same method as the above-described average primary particle diameter of the abrasive grains A1.

  In the finish polishing composition containing the abrasive grains A2 (for example, silica abrasive grains, typically colloidal silica), the content of the abrasive grains A2 is not particularly limited. The content of the abrasive grains A2 is preferably 40% by weight or more, more preferably 50% by weight or more, even more preferably 60% by weight or more (for example, 80% by weight) of the total solid content contained in the finish polishing composition. %).

  The finish polishing composition typically contains water in addition to the abrasive grains A2. In addition, the same component (acid, oxidizing agent, basic compound, various additives, etc.) as the above-mentioned polishing composition can be contained in the final polishing composition as necessary. Although not particularly limited, the pH of the finish polishing composition can be, for example, 12.0 or less (typically 0.5 to 12.0), and preferably 7.0 or less (for example, 0 or less). 0.5 to 7.0), more preferably 5.0 or less (typically 1.0 to 5.0), and still more preferably 4.0 or less (eg, 1.0 to 4.0). In a preferred embodiment, the pH of the finish polishing composition is 3.0 or less (typically 1.0 to 3.0, preferably 1.0 to 3.5, more preferably 1.0 to 3.0. ).

  Hereinafter, some examples of the present invention will be described, but the present invention is not intended to be limited to those shown in the examples.

<Examples 1 to 7>
[Preparation of polishing composition]
A plurality of types of silica particles (heat-treated silica, colloidal silicas A to D) having different aspect ratios and average particle diameters were prepared. Abrasive grains containing these silica particles alone or in combination, phosphoric acid, 31% hydrogen peroxide solution, and deionized water are mixed to obtain 45 g / L abrasive grains and 12.5 g / phosphoric acid. L, Polishing compositions of Examples 1 to 7 containing 31% aqueous hydrogen peroxide at a rate of 40 g / L were prepared. The pH of the polishing composition according to each example was 1.5. Table 1 shows the types and physical properties of the abrasive grains used in each example.

[Disk polishing]
The polishing composition according to each example was directly used as a polishing liquid, and the object to be polished was polished under the following conditions. As an object to be polished, an aluminum substrate for a hard disk having an electroless nickel phosphorus plating layer on the surface was used. The object to be polished (substrate to be polished) has a diameter of 3.5 inches (a donut type having an outer diameter of about 95 mm and an inner diameter of about 25 mm), a thickness of 1.75 mm, and a surface roughness Ra before polishing (Schmitt Measurement System). The arithmetic average roughness of the nickel-phosphorous plating layer measured by a laser scan type surface roughness meter “TMS-3000WRC” manufactured by Inc.) was 130 °.

(Polishing conditions)
Polishing device: Double-sided polishing machine manufactured by System Seiko, model "9.5B-5P"
Polishing pad: polyurethane pad manufactured by FILWEL, trade name "CR200"
Number of substrates to be polished: 15 (3 substrates / carrier x 5 carriers)
Polishing liquid supply rate: 135 mL / min Polishing load: 120 g / cm ²
Upper platen rotation speed: 27 rpm
Lower platen rotation speed: 36 rpm
Sun gear (sun gear) rotation speed: 8 rpm
Polishing amount: Thickness of about 2.2 μm in total on both sides of each substrate

[Polishing rate]
The polishing rate when the substrate to be polished was polished under the above polishing conditions using the polishing composition according to each example was calculated. The polishing rate was determined based on the following formula.
Polishing rate [μm / min] = Amount of weight loss of substrate by polishing [g] / (substrate area [cm ² ] × density of nickel phosphorus plating [g / cm ³ ] × polishing time [min]) × 10 ⁴
The obtained value was converted to a relative value when the polishing rate of Example 3 was set to 1, and is shown in the column of “polishing rate” in Table 1.

[Long wavelength swell]
Using KLA Tencor (U.S.A.) "Optiflat III", the value of the arithmetic mean waviness (Wa) measured under the condition of a cutoff value of 5 mm in a range of a radius of 20 mm to 44 mm from the center of the polished substrate was measured. did. Then, the obtained measurement value was evaluated as “○” when the measured value was less than 5 °, and “△” when the measured value was 5 ° or more. The results are shown in the column of "Waviness" in Table 1.

  As shown in Table 1, the number average aspect ratio is 1.3 or less, and the ratio of the cumulative 75% aspect ratio (A75) to the cumulative 50% aspect ratio (A50) in the volume-based aspect ratio distribution (A75 / In Examples 1 to 4 using abrasive grains having A50) of 1.05 or more, both a high polishing rate and a reduction in swell could be achieved at a high level. On the other hand, in Examples 5 to 7 in which the number average aspect ratio exceeds 1.3 or the ratio (A75 / A50) is less than 1.05, it is not possible to achieve both the polishing rate and the undulation reduction. Was. From these results, it is understood that according to the technology disclosed herein, a high polishing rate and a reduction in waviness can be achieved at a high level.

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

Claims (6)

Abrasive grains containing silica particles, and water, a magnetic disk substrate polishing composition comprising:
The number average aspect ratio of the abrasive grains is 1.3 or less,
A magnetic disk, wherein the ratio (A75 / A50) of the cumulative 75% aspect ratio (A75) to the cumulative 50% aspect ratio (A50) in the volume-based aspect ratio distribution of the abrasive grains is 1.05 or more and 1.50 or less. Substrate polishing composition.   The polishing composition according to claim 1, wherein the pH is 5 or less.   The polishing composition according to claim 1, which is used in a step before the finish polishing step. A method for manufacturing a magnetic disk substrate, comprising:
A manufacturing method comprising a step (1) of polishing a substrate to be polished using the polishing composition according to claim 1. After the step (1), the method further includes a step (2) of polishing the substrate to be polished using the finish polishing composition,
The production method according to claim 4, wherein the finish polishing composition contains colloidal silica. A method for polishing a magnetic disk substrate, comprising: supplying the polishing composition according to claim 1 to a substrate to be polished, and polishing the substrate to be polished.