JP2014140937A - Abrasive and polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abrasive which does not use an abrasive grain including a rare earth element like a cerium oxide abrasive grain and secures polishing performance (polishing rate and surface roughness) which is equivalent to a case where the cerium oxide abrasive grain is used.SOLUTION: The abrasive includes: an abrasive grain of which main constituent is zirconium oxide (ZrO); and a polishing assistant composed of metallic salt. A content percentage of the assistant (Ma/Mg) that is a mass ratio of the polishing assistant content (Ma) to the abrasive grain content (Mg), is preferably 0.1-2. Polishing performance is improved by the presence of a suitable amount of the metallic salt in the abrasive grain. A reason for this is that ionic concentration in the slurry is raised by the salting-out effect of the metallic salt, charge balance on the surface of the abrasive grain is lost, so that particles are loosely aggregated with each other, and the abrasive grain consisting of zirconium oxide is easily retained in the abrasive pad.

Description

  The present invention relates to an abrasive and a polishing method suitable for polishing precision parts such as glass (particularly optical glass).

  Precision parts such as optical lenses, glass for plasma or liquid crystal display panels, glass for color filters for liquid crystal TVs, glass for LSI photomasks, etc. have strict requirements for flatness and surface roughness, and high precision surface polishing. It is manufactured through.

  For such surface polishing, abrasive grains (fine particles) made of cerium oxide, which is said to exhibit a chemical mechanical polishing action, are used in addition to abrasive grains made of silicon dioxide, aluminum oxide, zirconium oxide and the like. When abrasive grains made of cerium oxide are used for surface polishing, not only good surface roughness but also a high polishing rate can be obtained, and the polishing performance can be improved.

  Most recently, it has been required to reduce the amount of rare elements such as rare earth elements, and new abrasives and polishing methods that do not contain rare earth elements have been actively studied. There is a description related to this in Patent Document 1 below.

JP 2012-74736 A

  Patent Document 1 discloses a chemical composition comprising an abrasive (0.01 to 1% by mass) such as ceria or zirconia, a halide salt (0.05 to 5 mM), and water as an abrasive suitable for a substrate such as a semiconductor wafer. -A mechanical polishing composition is proposed.

  In Patent Document 1, the action or influence of the halide salt on polishing is not clarified, and ceria or alumina is the only abrasive that has a substantial influence on the polishability by the addition of the halide salt. . Conversely, when the abrasive is zirconia, in Patent Document 1, a halide salt (specifically, potassium iodide: KI) does not act effectively.

  The reason for this may be that the amount of halide salt added is too small with respect to the abrasive made of zirconia. When the example ([0027]) described in Patent Document 1 is actually observed, KI is about 0.5 mM with respect to 1% by mass of zirconia (see the description of [0031] because there is no specific description). It is. If considered in terms of 1 L of polishing composition (since there is no specific description of the total amount necessary for specifying the KI amount, a general total amount is assumed), the ratio of KI to zirconia is 0.0083. It turns out that it is a very small amount.

  The present invention has been made in view of such circumstances, and while using abrasive grains mainly composed of zirconium oxide, excellent polishing performance equivalent to that obtained when abrasive grains made of cerium oxide are used at low cost. It aims at providing the abrasive | polishing material and polishing method which are obtained by this.

  As a result of intensive studies and trial and error to solve this problem, the present inventor used a polishing slurry in which abrasive grains made of zirconium oxide and metal salts were appropriately dispersed until the abrasive grains made of cerium oxide were used. In addition, it has been newly found that the surface roughness and polishing rate equivalent to the case of using the same can be obtained, and the polishing performance can be greatly improved. By developing this discovery, a series of the present invention described below has been completed.

《Abrasive material》
(1) The abrasive of the present invention is an abrasive comprising an abrasive mainly composed of zirconium oxide (ZrO ₂ ) and a polishing aid comprising a metal salt, and the content of the abrasive (Mg ) The auxiliary agent content (Ma / Mg), which is a mass ratio of the content (Ma) of the polishing auxiliary to), is 0.1 to 2.

(2) With the abrasive of the present invention, it is possible to ensure good polishing properties without using abrasive grains made of rare cerium oxide or the like.

  By the way, the mechanism by which the abrasive of the present invention exhibits excellent abrasiveness is not necessarily clear, but at present, it is considered as follows. By adding a metal salt to a slurry containing abrasive grains made of zirconium oxide, the ion concentration in the slurry increases due to the salting out effect, and the charge balance on the abrasive grain surface is lost. As a result, since the particles loosely aggregated, the abrasive grains made of zirconium oxide are likely to stay on the polishing pad, and the polishing rate is considered to be improved.

  Further, since the metal salt according to the present invention can exhibit reducibility, for example, oxygen in zirconium oxide constituting the abrasive grains is reduced, and the abrasive grains in an oxygen deficient state or an oxygen deficient state are abradable. It is thought that it improves.

  As described above, the polishing material of the present invention may cause not only mechanical polishing but also chemical polishing, and may develop a so-called chemical polishing action. However, the mechanism is under intensive study, and the details are clear at present. Not a reason. In any case, when polishing is performed using abrasive grains made of zirconium oxide, it is certain that an appropriate amount of metal salt improves the polishing properties.

<Polishing method>
The present invention can be grasped not only as the above-described abrasive but also as a polishing method using the same. That is, the present invention provides a polishing method comprising: a preparation step of preparing a polishing slurry in which abrasive grains mainly composed of zirconium oxide are dispersed in a dispersion medium; and a polishing step of polishing a material to be polished using the polishing slurry. The polishing slurry further includes a polishing aid made of a metal salt, and the auxiliary agent content is a mass ratio of the content (Ma) of the polishing aid to the content (Mg) of the abrasive grains. A polishing method characterized in that (Ma / Mg) is 0.1 to 2.

<Others>
(1) The aforementioned auxiliary agent content is 0.1 to 2, 0.12 to 1.8, 0.15 to 1.7, 0.2 to 1.5, or 0.3 to 1.2. Preferably there is. When the content of the auxiliary agent is too small, the polishing effect of the polishing auxiliary made of a metal salt is poor. On the other hand, in the case of the present invention, the upper limit value of the auxiliary agent content is not necessarily essential, and even if the auxiliary agent content is large, the polishing property (particularly the polishing rate) can be improved. However, since it is uneconomical if the auxiliary content is excessive, the upper limit of the auxiliary content as described above is provided for convenience in the present invention.

(2) The abrasive grains according to the present invention are composed of zirconium oxide, but may contain other elements and compounds (particularly oxides). For example, hafnium (Hf) having characteristics similar to Zr may be included. In addition, the abrasive according to the present invention may appropriately contain impurities that are difficult to separate or remove and modified elements that are effective for improving characteristics. Although no limitation on the content thereof, the whole grains is taken as 100 mass%, ZrO ₂ is 50 mass% or more, 70 wt% or more, 80 mass% or more and even more may be at least 90 mass%. Thus the herein abrasive ZrO ₂ is contained more than 50 wt% of "abrasive grains mainly composed of ZrO _2."

(3) The state and form of the abrasive of the present invention are not limited. For example, a powder composition before being dispersed in a dispersion medium such as water or a polishing composition (abrasive slurry) in which abrasive grains are dispersed in a dispersion medium may be used. That is, the abrasive of the present invention may be a mixed powder obtained by mixing abrasive powder and metal salt powder, or a polishing slurry in which abrasive grains and metal salt are dispersed in a dispersion medium. In the present invention, the state of the metal salt is not limited. That is, the metal salt may be a crystallized solid or may be dissolved in a dispersion medium and ionized. In this specification, including both cases, it is referred to as a metal salt.

(4) There is no limitation on the pH when the metal salt according to the present invention is dissolved in water. As an example, the metal salt according to the present invention is preferably an aqueous solution having a pH of 3 to 10, more preferably 4 to 9, when dissolved in water.

(5) Unless otherwise specified, “x to y” in this specification includes a lower limit value x and an upper limit value y. Any numerical value included in the specific numerical values or numerical ranges described in the present specification can be arbitrarily set as a new lower limit value or upper limit value such as “ab”.

  The present invention will be described in more detail with reference to embodiments of the invention. One or more configurations selected from the present specification can be arbitrarily added to the configuration of the present invention described above. The contents described in this specification are appropriately applied to the abrasive and the polishing method according to the present invention. Which embodiment is the best depends on the target, required performance, and the like.

《Abrasive material》
(1) Abrasive Grains As described above, the abrasive grains according to the present invention need only contain zirconium oxide (ZrO ₂ ) as a main component, and may contain modifying elements, inevitable impurities, and the like. The abrasive grains according to the present invention may be mixed abrasive grains including other kinds of abrasive grains having a composition other than ZrO ₂ .

The shape, size, production method and the like of the abrasive grains are not limited, but for example, the average particle diameter is preferably 0.1 to 3 μm, 0.3 to 2 μm, and more preferably 0.5 to 1 μm. If the average particle size is too small, the polishing rate is small, and if the average particle size is too large, the surface roughness of the polished surface increases. Incidentally, the average particle diameter is "volume average particle diameter", for samples (abrasive powder) to be measured, for each particle diameter (particle diameter: d _i) the volume occupancy of the respective particles (weight: v _i / V ₀ ) is the total sum (Σd _i · v _i / V ₀ ) (V ₀ is the volume of the entire sample). Specifically, the particle size is measured according to JIS Z8825-1 using a laser diffraction / scattering particle size distribution meter (LA750 manufactured by Horiba, Ltd.).

(2) Polishing aid The polishing aid according to the present invention is sufficient if it contains a metal salt. Such metal salts include alkali metal salts, chlorides or sulfates. Specific examples include sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, lithium chloride, magnesium chloride, zinc chloride, manganese chloride, cobalt chloride, nickel chloride, iron chloride, and iron sulfate. In particular, the metal salt is sodium, potassium or iron hydrochloride or sulfate, and it is preferable that the metal salt further consists only of the hydrochloride and / or sulfate.

<Polishing method>
The type of the dispersion medium used for the preparation of the polishing slurry is not limited, but usually ion exchange water or the like is used. Further, the ratio of the dispersion medium is not limited. For example, when the entire polishing slurry is 100% by mass, the dispersion medium may be 80 to 99% by mass, and further 90 to 98% by mass. If the amount of the dispersion medium is excessive, an improvement in the polishing rate cannot be expected. If the amount of the dispersion medium is too small, the abrasive grains are excessive, which is uneconomical.

  In the preparation step of preparing the polishing slurry, the mixed powder of the abrasive grains and the polishing aid may be dispersed in the dispersion medium, or the abrasive grains may be dispersed in the dispersion medium to which the polishing aid is added. A polishing aid may be added to the dispersion medium in which is dispersed.

<Polishing target>
The object to be polished (the material to be polished) by the abrasive of the present invention is not limited, and examples thereof include various glasses, semiconductor substrates, metal substrates, and the like. In particular, the polishing material of the present invention is used for polishing precision glass such as optical lenses, plasma or liquid crystal display panel glass, liquid crystal TV color filter glass, LSI photomask glass, etc. that require high precision polishing. Is preferred.

<Production of sample>
(1) Abrasive grains Zirconium oxide powder (ZC3000 manufactured by Admatechs Co., Ltd.) was prepared as abrasive grains. The average particle size of this powder was 0.8 μm. In addition, a commercially available cerium oxide powder (SHOROX A-10 manufactured by Showa Denko KK / average particle size 1 μm) was also prepared (see Sample C5). In addition, each average particle diameter is calculated | required with the laser diffraction scattering type particle size distribution analyzer.

(2) Polishing aids As polishing aids, powders of sodium chloride, potassium chloride, sodium sulfate, lithium chloride, zinc chloride, iron (II) chloride, iron (II) sulfate, magnesium chloride, ammonium chloride and sodium phosphate ( A commercially available reagent) was prepared.

(3) Preparation Step Each abrasive grain and each polishing aid described above and ion-exchanged water (dispersion medium) were mixed at a ratio shown in Table 1, and stirred with a homomixer to prepare various polishing slurries. However, Sample C5 and Sample C6 were only abrasive grains and a dispersion medium.

《Polishing process》
Using each polishing slurry shown in Table 1, soda glass (diameter 50 mm, thickness 2 mm) as a material to be polished was polished. In addition, the surface of the soda glass was previously roughened into a glass shape with sandpaper (# 400) before polishing.

  For polishing, a single-side polishing apparatus (manufactured by MTT Co., Ltd., BC-15) was used. At this time, each polishing slurry was polished while being dropped on a polishing pad made of urethane resin (KSP66A, manufactured by Kuju Electric Co., Ltd.) at a rate of 25 cc / min.

The surface pressure between the polishing pad containing the polishing slurry and the soda glass as the material to be polished was about 200 g / cm ² , and the rotation speed of the polishing pad sliding on the soda glass was 60 rpm. This polishing was performed for 30 minutes.

<Measurement>
(1) Polishing rate The mass of the material to be polished (soda glass) was measured before and after polishing. The change in mass before and after polishing was divided by the cross-sectional area of soda glass, and the polishing rate (μm / min) was determined in terms of the reduction in the thickness of the material to be polished. The results are also shown in Table 1.

(2) Surface roughness The surface of soda glass after polishing was measured with a non-contact surface shape measuring instrument (NewView 7200, manufactured by Canon Inc.), and arithmetic average roughness Ra in the range of 0.70 mm x 0.53 mm (JIS) Asked. The results are also shown in Table 1. Incidentally, the surface roughness Ra of the soda glass before polishing was about 0.1 to 0.2 μm.

<Evaluation>
From the results shown in Table 1, the following can be understood. As is clear when Samples 1 to 11 and Sample C4 are compared, it is understood that the polishing rate is greatly improved by using a polishing slurry to which a metal salt (polishing aid) is added (blended). In other words, it was confirmed that an abrasive combined with a zirconium oxide abrasive and a polishing aid made of a metal salt could be an alternative to an abrasive made of cerium oxide abrasive.

  Further, as apparent from comparison between Samples 1 to 11 and Samples C2 to C3, the polishing aid is effective only if it is a metal element hydrochloride or sulfate, and other salts (especially ammonium salts and phosphoric acid). It was found that the polishing rate in the case of using (salt) was lower than that of sample C4 (in the case where the abrasive was composed only of zirconium oxide).

  Further, as apparent from comparison between Samples 1 to 4 and Sample C1, the polishing aid (for example, sodium chloride) is too small (auxiliary content is less than 0.1) with respect to the abrasive grains (zirconium oxide). It was found that the polishing rate was not improved. In addition, as can be seen by comparing samples 1 to 4, the polishing rate is improved by increasing the auxiliary agent content, but when the auxiliary agent content is 0.4 or more, the polishing rate does not increase so much and becomes saturated. I understand.

  Thus, it can be seen that an appropriate amount of metal salt contained in the polishing slurry effectively acts to improve the polishing properties. The reason for this is that the ion concentration in the slurry increases due to the salting out effect of the metal salt, the charge balance of the abrasive grain surface is disrupted, and the grains are loosely aggregated, so that the abrasive grains made of zirconium oxide tend to stay in the polishing pad. This is thought to be part of the reason. In addition, it is considered that the reduction of the metal salt causes a mechanochemical reaction between the abrasive grains and the material to be polished to improve the polishing performance.

  In any case, sample no. By using the abrasive (polishing slurry) according to the present invention as in 1 to 11, good and efficient polishing can be performed without using abrasive grains (cerium oxide particles) made of rare rare earth elements. Became clear.

Claims (8)

Abrasive grains mainly composed of zirconium oxide (ZrO ₂ );
A polishing aid comprising a metal salt;
An abrasive containing
An abrasive content, which is a mass ratio of the content (Ma) of the polishing aid to the content (Mg) of the abrasive grains, is 0.1 to 2. .   2. The abrasive according to claim 1, wherein the metal salt is any one of a metal element hydrochloride, sulfate, nitrate, oxalate, or a mixed salt obtained by mixing one or more thereof.   The abrasive according to claim 2, wherein the metal salt is a hydrochloride or sulfate of sodium, potassium or iron.   The abrasive according to any one of claims 1 to 3, wherein the abrasive has an average particle size of 0.1 to 5 µm.   The abrasive according to any one of claims 1 to 4, comprising a mixed powder obtained by mixing the abrasive powder and the metal salt powder.   The abrasive according to claim 1, comprising an abrasive slurry in which the abrasive grains and the metal salt are dispersed in a dispersion medium.   The abrasive according to claim 6, wherein the polishing slurry has a pH of 3 to 10. A preparation step of preparing a polishing slurry in which abrasive grains mainly composed of zirconium oxide (ZrO ₂ ) are dispersed in a dispersion medium;
A polishing step of polishing a material to be polished using the polishing slurry;
A polishing method comprising:
The polishing slurry further includes a polishing aid made of a metal salt, and an auxiliary agent content (Ma / Mg) which is a mass ratio of the content (Ma) of the polishing auxiliary to the content (Mg) of the abrasive grains. Is a polishing method characterized by 0.1-2.