GB2401610A

GB2401610A - Polishing composition

Info

Publication number: GB2401610A
Application number: GB0410214A
Authority: GB
Inventors: Takanori Uno; Hiroyasu Sugiyama; Toshiki Owaki
Original assignee: Fujimi Inc
Current assignee: Fujimi Inc
Priority date: 2003-05-09
Filing date: 2004-05-07
Publication date: 2004-11-17
Anticipated expiration: 2024-05-07
Also published as: CN1550532A; MY144061A; JP2004331886A; GB2401610B; CN100392035C; GB0410214D0; JP4202183B2

Abstract

A polishing composition comprises an alumina grain which contains a -alumina as the main component; fumed alumina; a polishing accelerator which contains at least one component selected from the group consisting of organic acids, inorganic acids, and salts thereof; and water. Examples of the polishing accelerator include succinic acid, citric acid, aluminium nitrate and iron nitrate. The polishing composition may further comprise alumina sol. Also shown is a method for polishing a substrate for a magnetic disk using the polishing composition.

Description

At:: À :e it-

POLISHING COMPOSITION

BACKGROUND OF THE INVENTION

The present invention relates to a polishing composition to be used for polishing a substrate for a magnetic disk and the like.

With respect to a magnetic disk for use as a hard disk serving as a memory device for a computer, there have been strong demands for high recording density. Therefore, a substrate for a magnetic disk is required to have superior surface characteristics.

Japanese Laid-Open Patent Publication No. 7-216345 and Japanese National Phase Laid-Open Patent Publication No. 11 511394 disclose polishing compositions improved so as to satisfy such a requirement for a substrate. The polishing composition in Japanese Laid- Open Patent Publication No. 7 216345 contains water, an alumina abrasive, and a polishing accelerator consisting of molybdate and an organic acid. The polishing composition in Japanese National Phase Laid-Open Patent Publication No. 11-511394 contains a-alumina particles serving as an abrasive, solid materials serving as a polishing accelerator such as aluminum hydrate, and water. The content of a-alumina particles in the polishing composition is set at 1 to 50% by weight of all solid materials.

However, the former polishing composition has a low polishing rate for a substrate. The latter polishing composition has a relatively high polishing rate for a substrate, but the surface roughness of the polished substrate shows only a small improvement.

SUMMARY OE THE INVENTION

:e ac.e..' A: Accordingly, it is an objective of the present invention to provide a polishing composition more suitable for use in polishing a substrate for a magnetic disk.

To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a polishing composition is provided. The polishing composition contains an alumina grain which contains aalumina as a main component, fumed alumina, a polishing accelerator which contains at least one component selected from the group consisting of organic acids, inorganic acids, and salts of these acids, and water.

The present invention also provides a method for polishing an object. The method includes preparing the above polishing composition, and polishing the surface of the object by using the polishing composition.

Other aspects and advantages of the invention will become apparent from the following description, illustrating by way of example the principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One embodiment of the present invention will now be described.

A polishing composition according to this embodiment contains (a) an alumina grain which contains a-alumina as a main component, (b) fumed alumina, (c) a polishing accelerator which contains at least one component selected from the group consisting of organic acids, inorganic acids, and salts of these acids, and (d) water.

:e c.' ce:.

The polishing composition is used for polishing, for example, a substrate for a magnetic disk. This substrate may be a substrate formed by providing an electroless plating layer composed of nickel-phosphorus on a blank member composed of an aluminum alloy, or a substrate containing nickel-iron, boron carbide, or carbon.

The alumina grain is an abrasive and plays a role in mechanically polishing an object. "To contain -alumina as a main component" means that the -conversion ratio is no less than 50% in the crystal form which composes the alumina grain.

The term 'a-conversion ratio" used here is obtained from the integrated intensity ratio of a (113) plane diffraction line by X-ray diffraction measurement. The alumina grain may contain 5-alumina, O-alumina, or K-alumina together with a- alumina or may contain a-alumina having different u-conversion ratios. When the a-conversion ratio is less than 50%, the alumina grain might have low mechanical polishing ability. As for abrasives other than the alumina grain, known abrasives are silicon dioxide, titanium oxide, and the like. However, these have low mechanical polishing ability.

Average particle size of the alumina grain determined by the laser diffraction and scattering method is preferably no more than 2.0 um, more preferably from 0.05 to 1.0 Bum inclusive. The average particle size of the alumina grain may be measured using a laser diffraction and scattering type grain size measuring machine (LS-230 made by Coulter). If the average particle size is less than 0.05 m, the alumina grain might have low mechanical polishing ability. If the average particle size exceeds 2.0 am, the surface roughness of the polished object might worsen and scratches might occur on the surface of the polished object.

The content of the alumina grain in the polishing Ail crate; ce composition is preferably from 0.01 to 40% by weight inclusive, more preferably from 2 to 25% by weight inclusive. If the content is less than O.01% by weight, the polishing rate of the polishing rate might be reduced. If the content exceeds 40% by weight, the alumina grain might be agglomerated in the polishing composition, and as a result, stability of the polishing composition might be deteriorated.

The fumed alumina is an abrasive and plays a role in mechanically polishing an object. The fumed alumina also plays a role in reducing the microwaviness of the surface of the polished object to improve the surface roughness of the polished object. It might be thought that this is because the fumed alumina acts on the surface of the alumina grain, thereby improving the dispersibility of the alumina grain in the polishing composition. The term "microwaviness" used here means micro irregularities measured by use of a surface roughness measuring device with a given measuring wavelength, which are expressed by height (A). If the polishing composition contains fumed silica in place of the fumed alumina, the polishing composition has a low polishing rate because fumed silica has low polishing ability, with the result that it is impossible to reduce the surface roughness of the polished object. As shown in the following reaction formula 1, the fumed alumina is synthesized in the acid- hydrogen reaction of aluminum chloride, contains 6-alumina and has a - converision ratio of less than 50.

Reaction Formula 1 41Cl3 + 6H2 3O2 2Al203 + 12HCl Average primary particle size of the fumed alumina determined from a specific surface area measured by a BET method is preferably from 0.005 to 0.5,um inclusive, more preferably from 0.01 to 0.1 Am inclusive. Maximum secondary ie, particle size of the fumed alumina determined by the laser diffraction and scattering method is preferably 1.5 Am or so.

In the polishing composition, the particles of the fumed alumina associate to form aggregates. If the average primary particle size of the fumed alumina is less than 0.005 um, the polishing composition might have a low polishing rate because the degree of improving the dispersibility of the alumina grain is small. If the average primary particle size exceeds O.S Em or the maximum secondary particle size exceeds 1.5 m, the stability of the polishing composition might be deteriorated because the aggregates of the fumed alumina are large, with the result that precipitation might occur in the polishing composition.

The content of the fumed alumina in the polishing composition is preferably no more than 50% by weight of the; alumina grain, more preferably from 0.005 to 20% by weight inclusive, and most preferably from 1 to 12.5% by weight inclusive. If the content of the fumed alumina is less than 0.005% by weight of the alumina grain, it might be impossible to sufficiently improve the dispersibility of the alumina grain, with the result that the polishing composition might have a low polishing rate. If the content of the fumed alumina exceeds 50% by weight of the alumina grain, mechanical polishing ability of the alumina grain might be impaired because the amount of the fumed alumina acting on the surface of the alumina grain becomes excessive, with the result that the polishing composition might have a low polishing rate.

The polishing accelerator plays a role in accelerating the mechanical polishing by the alumina grain and the fumed alumina. The polishing accelerator preferably contains at least one acid selected from the group consisting of organic acids and inorganic acids because of its strong chemical polishing ability. The polishing accelerator more preferably . :e e. À À :e contains at least one component selected from the group consisting of citric acid, maleic acid, maleic anhydride, malic acid, glycolic acid, succinic acid, itaconic acid, malonic acid, iminondiacetic acid, gluconic acid, latic acid, mandelic acid, tartaric acid, crotonic acid, nicotinic acid, acetic acid, thiomalic acid, formic acid, oxalic acid, carboxyethyl thiosuccinic acid, aluminum nitrate, and iron nitrate, and most preferably contains at least one acid selected from the group consisting of citric acid, malic acid, glycolic acid, succinic acid, itaconic acid, iminondiacetic acid, and carboxyethyl thiosuccinic acid.

The content of the polishing accelerator in the polishing composition is preferably from 0.01 to 10% by weight inclusive, more preferably from 0. 05 to 5% by weight inclusive, and most preferably from 0.1 to 3% by weight inclusive. If the content of the polishing accelerator is less than 0.01% by weight, the polishing composition might have a low polishing rate. If the content of the polishing accelerator exceeds 10% by weight, the polishing rate of the polishing composition might be becoming saturated and hence this is uneconomical.

The water plays a role as a medium for dissolving and dispersing components other than water in the polishing composition. It is preferred that the water contains as little impurities as possible. More specifically, purified water, ultrapure water, or distilled water is preferable.

polishing composition according to this embodiment is prepared by mixing an alumina grain, fumed alumina, a polishing accelerator, and water. During the mixing, the order of in which each component is added may be in any order, or all the components may be added at the same time.

When the surface of a substrate for a magnetic disk is ' À se À.: c.e.' .e t' tee. .

polished using a polishing composition according to this embodiment, for example, the surface of the substrate is rubbed with a polishing pad while supplying the polishing composition to the surface of the substrate. is

A polishing composition according to this embodiment is preferably used in the first polishing step in a plurality of polishing steps commonly carried out during the manufacturing processes for a substrate. The first polishing step is generally performed to remove the waviness and surface defects such as large scratches and irregularities on the substrate which might not be capable of being removed in the following polishing step. On the other hand, the final polishing step is generally performed to make an adjustment to a desired surface roughness of the substrate and to remove surface defects which occurred in the previous polishing step and surface defects which could not be removed in the previous polishing step.

The present embodiment provides the following advantages.

A polishing composition according to this embodiment contains an alumina grain and fumed alumina for mechanically polishing an object and a polishing accelerator for accelerating the mechanical polishing by the alumina grain and the fumed alumina. Therefore, the polishing composition has an ability to polish an object, in particular, to polish a substrate for a magnetic disk at a high speed. In other words, the polishing composition according to the embodiment has a high polishing rate for a substrate.

Fumed alumina in a polishing composition according to this embodiment has an ability to reduce the microwaviness of the surface of the polished object. Therefore, the polished object has reduced surface roughness.

e Joe ce À It should be apparent to those skilled in the art that the present invention may be embodied in many other specific forms without departing from the spirit of scope of the invention. Particularly, it should be understood that the invention may be embodied in the following forms.

The polishing composition may further contain alumina sol.

The alumina sol plays a role in suppressing surface defects, such as microprotrusions and micropits, on the polished object and in reducing the surface roughness of the polished object by reducing microwaviness of the surface of the polished object. It might be thought that this is because the alumina sol adheres to the surface of the alumina grain, thereby promoting mechanical polishing ability of the alumina grain.

Furthermore, because the alumina sol disperses in the polishing composition in a colloidal state, the alumina sol prevents the precipitation of the alumina grain by improving the dispersibility of the alumina grain and causes the alumina grain to be easily held by a polishing pad during the polishing an object.

The alumina sol may contain at least one component selected from the group consisting of alumina hydrates and aluminum hydroxide dispersed in a colloidal state in an acid aqueous solution. The alumina hydrates may be boehmite, pseudobohmite, diaspore, gibbsite, or bayerite. The acid aqueous solution is prepared by adjusting the pH of water to the acid side by use of organic acids, inorganic acids, or salts of these acids. The alumina sol may contain two or more kinds of alumina hydrates. Preferable alumina hydrate is boehmite or pseudobohmite because boehmite and pseudobohmite have relatively high abilities to suppress surface defects and to reduce the surface roughness of the polished object.

The content of the alumina sol in the polishing :e ac.e cee ele. eerie te.

composition is preferably from 0.01 to 201 by weight inclusive, more preferably from 0.05 to 15% by weight inclusive, and most preferably from 0.1 to 10% by weight inclusive in terms of the weight of solid content in the alumina sol. If the content is less than 0.01% by weight, the effect of promoting mechanical polishing ability of the alumina grain might be small because the amount of the alumina sol adhering to the surface of the alumina grain becomes insufficient, with the result that it might be impossible to sufficiently reduce the surface roughness of the polished object. If the content of the alumina sol exceeds 20% by weight, the effect of suppressing surface defects and the effect of reducing the surface roughness of the polished object might be becoming saturated and hence this is uneconomical.

The polishing composition may further contain a surfactant, a rust inhibitor, a sedimentation inhibitor, etc. The surfactant improves the dispersibility of the alumina grain in the polishing composition. The surfactant may be a nonionic surfactant or anionic surfactant. The nonionic surfactant is preferably polyoxyethylene polyoxypropylene alkylether represented by the following general formula 2, a polyoxyethylene polyoxypropylene copolymer represented by the following general formulae 3 or 4, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbit fatty acid ester, or urethane associated surfactant represented by the following general formula 5. The anionic surfactant is preferably polycarboxylates such as sodium polyacrylate, or polymers, such as a copolymer of lsoprene sulfonic acid and acrylic acid, including a monomer unit derived from isoprene sulfonic acid or its salt. When the polishing composition containing the above listed nonionic surfactant or the above listed anionic surfactant is used for polishing the surface of a substrate for a magnetic disk, the flatness of the surface of the substrate is improved because the surface droop of an outer .e It: À as: : peripheral portion of the substrate is suppressed.

General Formula 2 fH3 R-O - (CH2CHO)I(CH2CH2O)H In the general formula 2, R denotes an alkyl group, and 1 and m each denote an integer.

General Formula 3 IH3 I-lo(CH2Cll2o)n(CHCH20)o(CH2 CH2O)pH In the general formula 3, n, o and p each denote an integer.

General Formula 4 fH3 fH3 Ho(cHcH2o)q(cH2cH2o)r(ccH2o)sH In the general formula 4, q, r and s each denote an integer.

General Formula 5

O O 11 11

X-(C-NH-Y-NH-C-(OC CH2)uZ)t In the general formula 5, X denotes a residue of polyether polyol which is derived from a compound having an active oxygen atom and alkylene oxide (however, the polyether chain contains 20 to 90% by weight of oxyethylene group), t denotes an integer between 2 to 8 inclusive (= the number of hydroxy] groups in one molecule of the abovedescribed polyether polyol), Y denotes a divalent hydrocarbon group, Z denotes a residue of a monovalent compound having an active oxygen atom, and u denotes an integer of 3 or more.

:' . Ale e:; e:. ,.e The polishing composition may be prepared by diluting a stock solution with water immediately before use.

The polishing of a substrate for a magnetic disk may be performed in a single polishing step In such a case, the polishing composition may be used in the single polishing step.

The polishing composition may be used in the polishing step other than the first polishing step. For example, the polishing composition may be used in the final polishing step.

The polishing composition may be used in polishing an object other than a substrate for a magnetic disk. The object other than a substrate for a magnetic disk may be an object containing tungsten, copper, silicon, glass, or ceramic. More specifically, the object may be a semiconductor wafer or an optical lens.

The present invention will now be described in more detail by referring to Examples and Comparative Examples.

In Examples 1 to 30, stock solutions were prepared by mixing an alumina grain, fumed alumina, a polishing accelerator, and water, and alumian sol as necessary. In Comparative Examples 1 to 44, stock solutions containing at least two components selected from the group consisting of an alumina grain, fumed alumina, and a polishing accelerator.

Detailed compositions of respective stock solutions are shown

in Table 1.

In Example 3, Example 24 and Comparative Example 7, the alumina grain in the stock solution is alumina particles with an Reconversion ratio of 97%. In Examples 22 to 26 and Comparative Examples 2, 3, 22, 23, 27, and 28, the alumina sol in the stock solution is prepared by adding 10% by weight boehmite to an acid aqueous solution (pH 3) and then! dispersing the solution in a colloidal state by use of a homomixer.

Polishing compositions were prepared by diluting each stock solution with three times volume of water. Using each of the polishing composition, the surface of a substrate for a magnetic disk was polished under the following polishing conditions.

<Polishing conditions> ; Substrate to be polished: An electroless Ni-P substrate 3.5 inches in diameter; Polishing machine: One-side polishing machine (made by Udagawa Optical Machine Co., Ltd., fixed base diameter 300 mm) Polishing pad: Polyurethane pad (CR200, made by Kanebo LTD.) Polishing load: 100 g/cm2 Rotational number of bottom fixed base: 100 rpm Supply amount of polishing composition: 8 ml/minute Polishing time: Time long enough to be able to remove a finishing allowance of 1 um (determined beforehand by a preliminary experiment) ; With respect to polishing processes carried out under the above-mentioned conditions, the polishing rate was calculated based on the following equation. And by dividing a calculated polishing rate by the polishing rate in Comparative Example 6, the ratio of the polishing rate to that of Comparative Example 6 was found. The column entitled "polishing rate" in Table 1 indicates the ratio of the polishing rate to that of Comparative Example 6.

<Equation> Polishing rate [um/minute] = reduced amount of substrate [g] I. .: . . due to polishing / (area [cm2] of substrate surface to be polished x density [g/cm3] of Ni-P plated layer x polishing time [minute!) x lO4.

The size of microwaviness was measured on the substrate surface after polishing by use of a noncontact surface roughness measuring device (Micro XAM made by PhaseShift, objective lens: lox, filter: Gaussian Bandpass), Ra values being measured at 80 to 450 m. The measurements were made in two places each on the front and back surfaces of one substrate, and an average Ra value of the four measurement values was regarded as the size of microwaviness. By dividing the size of microwaviness thus measured by the size of i microwaviness of Comparative Example 6, the ratio of the, microwaviness to that of Comparative Example 6 was found. The; column entitled "microwaviness" in Table 1 indicates the ratio of the microwaviness to that of Comparative Example 6. A hyphen in the column entitled "microwaviness" means that the size of microwaviness cannot be measured because of surface defects.

À À e À l ú 0 a r N r _ _ _ _ 0 0 r _-r N N rl {} clP cap c4 cop c dP c# cap CP rap cP c I P clP c CP CiP C cap ciP cap Cot c cap to cop rut r 0 Or 0 al up o '- ol 0 0 o 0 o Cal -1 o r 0 0 À | o 1-----1 -------- 1 N _ O : PD-_ _ _ -- i_ v v v v v v 4ualuo:) 0 0 0 0 0 0 0 0 0 0 0 r I 0 0 0 0 0 0 r 0 0 0 0 0 I: 11:fi 3i; :l ua44uM r r r u' r <3, m | r r r r | r r r r r r 3ZIS o o o o o o c 31oF4ed 1 o o o olo ol o o ol ol o o olo o o o ol o o c 0 0 0 0 0 0 O O 0 0 0 0 0 0 0 0 r pUI | ó ó l | ó | | N N N | N N C N N N 1 f1f!1:| quauo - | 1 ' (D<D (D kD \9 1 - ,1 {D :', l2Sed 0 0 o | o lo | 0 0 0 0 0 o lo 0 w o lo 0 0 0 l a 0 0 O 1 | | ó O O t1 O O ii r O O ó O r O R l x w $ x x w x x r N N N N X N À e ece e ce e U 1 N N r c N N O O O OO O O 0 = O C N N V V V r ON N 0 N| r 0| l O jUG UOD _ _ N O _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ F.PL 1, V U U O. o o o o. 0 0 0 0 0 O 0 0 0 0 0 _ l UT I 1 1 1 DU I U I I 0 ll, r.:: a, Ia 0 0 0 0 l | -| a a a a a a a a _ _ _ _ _ _ 1, C 4 ((96 4M' ) I tD 1 N I W | 9 to | ; v C ala)F4Sed I kL)o O OO OO O O O O O W O O O O OI O O O O O 0 3 0 0 0 0 0 r 0 0 0 r O _ O N ó O O ó O O O O 1 0 I N.1 N rI 1 u, X () [1 X O ú1 N X o, U __ # # # #.

# , , # a _ a r r dP d 0- _ r _ _ 1-dF _ _ _ _ _ r ' N a u _ 0 _ _ O 0 0 _ 0 l 1 a a l l a I dP O U. O O 0 O a o a, r 0 r o m _ _ O _ c 1a a uo _ _ 0 _ _ _ 0 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Iz. :11: 1 1 v 3,ua 4u c 0 0 o 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 U l O O U O U V O O O U U U U U U U Àd V Àd U O U Q 1: I _. 1:4'IZ<: a|uoo 115 r| | | | ; oT41ea 1 | I | N ' n| I? UTH i4 1;0: -0. u a 4u 0 l D D | D D D 1 I D D D W D D J,l I a\ 1 4 S e a I I MD LD I I I I I D D O D D D D D UD D D O I | W D O pu 12| o o 0 O O O O O O r __ 5141 S a S S S S S S SINS S| N | N N|N|N N r N0 l,1 N 0 D r 0 o NIN P Q L I x x X <1< b1' W. W, W, c i1 r' te etle te À Incidentally, in Table 1, the particle size of the alumina grain shows the average particle size, which is determined by using a laser diffraction and scattering type grain size measuring machine (LS-230 made by Coulter) and the particle size of the fumed alumina shows the average primary particle size, which is determined from the specific surface area measured by the BET method.

As shown in Table 1, Examples 1 to 30 are good in any of results of polishing rate and microwaviness. Moreover, Examples 22 to 26 are particularly good in result of microwaviness because of the presence of alumina sol. In contrast, Comparative Examples 1 to 44 are not good in at least any one of results of polishing rate and microwaviness.

The present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims. a' 4

Claims

À . . . . CLAIMS: 1. A polishing composition characterized by: an alumina

grain which contains -alumina as a main -component; fumed alumina; a polishing accelerator which contains at least one component selected from the group consisting of organic acids, inorganic acids, and salts of these acids; and water.
2. The polishing composition according to claim 1, characterized in that average particle size of the alumina grain is no more than 2.0 m. r
3. The polishing composition according to claim 1 or 2, characterized in that the content of the alumina grain in the polishing composition is from 0.01 to 40% by weight inclusive.
4. The polishing composition according to any one of claims 1 to 3, characterized in that the -conversion ratio is no less than 50% in the crystal form which composes the alumina grain.
5. The polishing composition according to any one of claims 1 to 4, characterized in that average primary particle size of the fumed alumina is from 0.005 to 0.5 Em inclusive.
6. The polishing composition according to any one of claims 1 to 5, characterized in that the content of the fumed alumina in the polishing composition is no more than 50% by weight.
7. The polishing composition according to any one of claims 1 to 6, characterized in that the polishing accelerator contains at least one component selected from the group A. .. e. .. ., .e e.e ede.

consisting of citric acid, maleic acid, maleic anLydride, malic acid, glycolic acid, succinic acid, itaconic acid, malonic acid, iminondiacetic acid, gluconic acid, latic acid, mandelic acid, tartaric acid, crotonic acid, nicotinic acid, acetic acid, thiomalic acid, formic acid, oxalic acid, carboxyethyl thiosuccinic acid, aluminum nitrate, and iron nitrate.
8. The polishing composition according to any one of claims 1 to 7, characterized in that the polishing accelerator contains at least one component selected from the group consisting of citric acid, malic acid, glycolic acid, succinic acid, itaconic acid, iminondiacetic acid, and carboxyethyl thiosuccinic acid.
9. The polishing composition according to any one of claims 1 to 8, characterized in that the content of the polishing accelerator in the polishing composition is from 0.01 to 10% by weight inclusive.
10. The polishing composition according to any one of claims 1 to 9, characterized by alumina sol.
11. The polishing composition according to claim 10, characterized in that the alumina sol contains at least one component selected from the group consisting of alumina hydrates and aluminum hydroxide dispersed in a colloidal state in an acid aqueous solution.
12. The polishing composition according to claim 11, characterized in that the alumina hydrates are boehmite or pseudobohmite.
13. The polishing composition according lo any one of claims 1 to 12, characterized in that the polishing composition is , r used for polishing a substrate for a magnetic disk.
14. A method for polishing a substrate for a magnetic disk, the method characterized by: preparing the polishing composition according to any one of claims 1 to 12; polishing the surface of the substrate by using the polishing composition.
15. A polishing composition substantially as hereinbefore described with reference to

the examples.
16. A method for polishing a substrate substantially hereinbefore described with reference to the examples.