WO2024248130A1 - Method for polishing object to be polished, and polishing pad - Google Patents

Abstract

This method for polishing an object to be polished includes a step for polishing the object to be polished by sliding a polishing pad having a polishing layer containing a composition including a hydrolyzable resin and abrasive grains relative to the object to be polished. The step for polishing the object to be polished includes: a first step for polishing the object to be polished while supplying a first polishing liquid containing a hydrolysis promoter for promoting hydrolysis onto the surface of the polishing layer; and a second step, after the first step, for polishing the object to be polished while supplying a second polishing liquid having a lower concentration of the hydrolysis promoter than the first polishing liquid onto the surface of the polishing layer.

Description

Method for polishing object and polishing pad

The present invention relates to a method for polishing an object and a polishing pad.

In the manufacturing process of substrates used in semiconductor devices, etc., a cylindrical single crystal (ingot) is sliced into disks to form wafers, and then rough polishing (lapping, primary polishing) is carried out to ensure that both sides of the wafer are parallel and to achieve the specified thickness. The roughly polished wafers are then chemically etched and precision mechanically polished (secondary polishing, mechanical polishing) to create a highly flat mirror surface. Finally, a finishing polishing process (chemical mechanical polishing, CMP) is carried out, which also involves chemical action, to achieve atomic-level flatness.

In this type of polishing, a polishing method using a polishing pad is used. A known polishing pad has an abrasive layer containing a binder resin and abrasive grains fixed thereto (see, for example, Patent Document 1). As the binder resin, a curable resin such as a phenol resin, epoxy resin, or acrylic phenol resin is usually used.

In addition, in polishing processes, in order to smooth the surface of the workpiece, it is common to use multiple polishing pads with different abrasive grain sizes depending on the degree of polishing, from rough polishing to precision mechanical polishing. For example, after rough polishing is performed using a polishing pad with a large abrasive grain size, precision mechanical polishing is performed using a polishing pad with a small abrasive grain size.

JP 2018-51733 A

However, when using multiple polishing pads with different abrasive grain sizes, it was necessary to use multiple devices for each polishing pad, or to replace the polishing pads. This required additional capital investment and involved time-consuming processing, resulting in poor work efficiency. For this reason, it is desirable to be able to change the degree of polishing with a single polishing pad.

The present invention was made in consideration of the above circumstances, and aims to provide a polishing method and polishing pad for an object to be polished that can change the polishing speed and surface roughness of the object to be polished with a single polishing pad, thereby improving work efficiency.

[1] A method for polishing an object to be polished, comprising the steps of polishing the object to be polished by sliding the object to be polished against a polishing pad having a polishing layer containing a composition including a hydrolyzable resin and an abrasive grain relative to one another, the step of polishing the object to be polished comprising: a first step of polishing the object to be polished while supplying a first polishing liquid containing a hydrolysis promoter that promotes hydrolysis to a surface of the polishing layer; and a second step of polishing the object to be polished while supplying, after the first step, a second polishing liquid having a lower concentration of hydrolysis promoter than the first polishing liquid to the surface of the polishing layer.
[2] A method for polishing an object to be polished according to the item [1], wherein in the first step, the object to be polished is polished in a state in which the height of protruding abrasive grains on the surface of the polishing layer is adjusted to H1 by supplying the first polishing liquid, and in the second step, the object to be polished is polished in a state in which the height of protruding abrasive grains on the surface of the polishing layer is adjusted to H2, which is lower than H1, by supplying the second polishing liquid.
[3] The method for polishing an object to be polished according to [1] or [2], wherein the hydrolysis accelerator is an alkaline substance.
[4] The method for polishing an object to be polished according to any one of [1] to [3], wherein the hydrolyzable resin is mainly composed of a glycolic acid polymer.
[5] The method for polishing a workpiece according to any one of [1] to [4], wherein the pH of the first polishing liquid is higher than 12, and the pH of the second polishing liquid is 12 or less.
[6] A polishing pad comprising a polishing layer containing a composition including a hydrolyzable resin and an abrasive grain, wherein when the height of protruding abrasive grains from the surface of the polishing layer when polished with a polishing liquid having a pH of 13 is H1', and the height of protruding abrasive grains from the surface of the polishing layer when polished with a polishing liquid having a pH of 12 is H2', H2'/H1' is 0.79 or less.
[7] The polishing pad according to [6], wherein the abrasive grains have a median diameter of 2 μm or more and 50 μm or less.
[8] The polishing pad according to [6] or [7], wherein the rate of thickness reduction when a molded body of the composition excluding the abrasive grains is immersed in water at 60°C is 12 µm/h or more.
[9] The polishing pad according to any one of [6] to [8], wherein a molded body made of the composition excluding the abrasive grains has a tensile strength of 55 MPa or more.

The present invention provides a method for polishing an object that can change the polishing speed and the surface roughness of the object to be polished with a single polishing pad, thereby improving processing efficiency.

FIG. 1A is a schematic cross-sectional view showing the state of abrasive grains near the surface of the polishing layer, and FIG. 1B is a graph showing an example of the relationship between the pH of the polishing liquid and the protruding height of the abrasive grains in the polishing layer. FIG. 2A is a schematic plan view of a polishing pad according to one embodiment of the present invention, and FIG. 2B is a schematic cross-sectional view of the polishing pad of FIG. 2A taken along line 2B-2B. FIG. 3 is a schematic cross-sectional view showing a method for polishing an object according to an embodiment of the present invention. 4A to 4C are schematic cross-sectional views showing the molding process in the example. 5A and 5B are graphs showing the pH dependence of the protruding height of abrasive grains of polishing pads of Examples and Comparative Examples.

The inventors have investigated various binder resins for fixing abrasive grains in polishing pads and have found that hydrolyzable resins such as glycolic acid polymers and lactic acid polymers exhibit appropriate disintegration properties through hydrolysis. They have found that by using such hydrolyzable resins as the binder resin, it is possible to easily expose the abrasive grains buried in the binder resin to the surface of the polishing layer.

Furthermore, after further investigations, the inventors discovered that by adjusting the pH of the polishing liquid that is brought into contact with the polishing layer containing a hydrolyzable resin and abrasive grains, it is possible to change the height at which the abrasive grains protrude from the surface of the polishing layer, thereby changing the polishing speed and the surface roughness (degree of polishing) of the workpiece.

FIG. 1A is a schematic cross-sectional view showing the state of the abrasive grains 112 near the surface of the polishing layer, and FIG. 1B is a graph showing an example of the relationship between the pH of the polishing liquid and the protruding height of the abrasive grains in the polishing layer. In FIG. 1A, (a) shows the state immediately after preparation, (b) shows the state after contact with a relatively weakly alkaline polishing liquid, and (c) shows the state after contact with a relatively strongly alkaline polishing liquid.

Immediately after preparation, the abrasive grains 112 are embedded in the hydrolyzable resin 111 and are not exposed on the surface of the abrasive layer (see FIG. 1A (a)). On the other hand, when the abrasive layer is brought into contact with an alkaline abrasive liquid, the hydrolyzable resin 111 is hydrolyzed and disintegrates, and part of the tip of the abrasive grain 112 is exposed on the surface of the abrasive layer (see FIG. 1A (b)). When the abrasive layer is brought into contact with an even stronger alkaline abrasive liquid, the hydrolysis of the hydrolyzable resin 111 proceeds further, and the protruding height of the tip of the abrasive grain 112 becomes even greater (see FIG. 1A (c)).

In this way, as the pH of the polishing liquid is increased, the proportion of abrasive grains 112 that protrude higher from the surface of the polishing layer increases (see Figure 1A). As a result, as the pH of the polishing liquid is increased, the protruding height of the abrasive grains in the polishing layer increases, and the polishing speed also increases (see Figure 1B). In other words, simply by changing the pH of the polishing liquid, and thus the concentration of the alkaline substance acting as a hydrolysis promoter, the polishing speed and the surface roughness of the workpiece can be adjusted, so that a single polishing pad can be used for everything from rough polishing to precision mechanical polishing.

In other words, the method for polishing an object to be polished according to one embodiment of the present invention includes a step of polishing the object to be polished by supplying a polishing liquid containing water to the surface of a polishing pad having an abrasive layer containing a hydrolyzable resin and abrasive grains, while sliding the polishing pad and the object to be polished relative to each other. In this step, the concentration of the hydrolysis promoter in the polishing liquid is reduced to gradually reduce the protruding height of the abrasive grains while performing the polishing process.

　Below, we will explain the polishing pad used in the method for polishing the object to be polished, and then we will explain the method for polishing the object to be polished.

1. Polishing Pad Figure 2A is a schematic plan view of a polishing pad 100 according to one embodiment of the present invention, and Figure 2B is a schematic cross-sectional view of the polishing pad 100 of Figure 2A taken along line 2B-2B.

The polishing pad 100 according to this embodiment includes a polishing layer 110 that includes a hydrolyzable resin and abrasive grains (see FIG. 2B). The polishing layer 110 includes a hydrolyzable resin 111 and abrasive grains 112 fixed by the hydrolyzable resin 111. In this embodiment, grooves 110A are arranged on the surface of the polishing layer 110, and an uneven pattern is formed. Note that FIG. 2 shows an example of the polishing pad 100 that is made of the polishing layer 110, but this is not limited to this, and the polishing pad 100 may further include other layers.

1-1. Abrasive Layer The abrasive layer contains a composition that includes a hydrolyzable resin and abrasive grains.

1-1-1. Hydrolyzable resin The hydrolyzable resin is not particularly limited as long as it is a resin that exhibits hydrolysis. The hydrolyzable resin includes not only resins that are decomposed by microorganisms, but also resins that are decomposed by hydrolysis not involving microorganisms.

Hydrolyzable resins include polyesters having ester bonds in the main chain, polycarbonates having carbonate bonds in the main chain, etc. Examples of hydrolyzable resins include lactic acid polymers, glycolic acid polymers, hydroxybutyric acid polymers, hydroxyvaleric acid polymers, caprolactone polymers, ethylene succinate polymers, butylene succinate polymers (including, for example, polybutylene succinate, polybutylene succinate adipate, polybutylene succinate terephthalate, polyethylene succinate, polybutylene succinate carbonate, etc.), dioxanone polymers, trimethylene carbonate polymers, etc. Among these, lactic acid polymers and glycolic acid polymers are preferred, and glycolic acid polymers are preferred from the viewpoint of having higher strength and hydrolysis rate, and being easier to adjust the protruding height of the abrasive grains in the polishing layer. In other words, it is preferable that the hydrolyzable resin contains glycolic acid polymer as the main component. "Containing glycolic acid polymer as the main component" means that the content of glycolic acid polymer relative to the total amount of hydrolyzable resin is 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

The glycolic acid polymer is a polymer containing a structural unit (-(-O-CH ₂ -CO-)-) derived from glycolic acid, and is a polymer mainly composed of structural units derived from glycolic acid. The glycolic acid polymer may be a homopolymer of glycolic acid or a copolymer of glycolic acid and a monomer copolymerizable therewith.

Examples of copolymerizable monomers include:
Glycols such as ethylene glycol, propylene glycol, butanediol, heptanediol, hexanediol, octanediol, nonanediol, decanediol, 1,4-cyclohexanedimethanol, neopentyl glycol, bisphenol A, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol;
Dicarboxylic acids such as oxalic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, malonic acid, glutaric acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, bis(p-carboxyphenyl)methane, anthracenedicarboxylic acid, 4,4'-diphenyl ether dicarboxylic acid, 5-sodium sulfoisophthalic acid, and 5-tetrabutylphosphonium isophthalic acid;
Hydroxycarboxylic acids such as lactic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, and hydroxybenzoic acid;
Lactides;
Lactones such as caprolactone, valerolactone, propiolactone, undecalactone, and 1,5-oxepan-2-one;
Carbonates such as trimethylene carbonate are included.

The term "mainly composed of structural units derived from glycolic acid" means that the content of structural units derived from glycolic acid is 50% by mass or more relative to the total amount of structural units constituting the glycolic acid polymer. The content of structural units derived from glycolic acid is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. When the content of structural units constituting the glycolic acid polymer is 50% by mass or more, the strength of the glycolic acid polymer can be increased, so that sufficient strength can be obtained when used in a polishing pad. Furthermore, when the content of structural units constituting the glycolic acid polymer is 70% by mass or more, hydrolysis is more likely to proceed, making it easier to adjust the protruding height of the abrasive grains in the polishing layer.

In particular, from the viewpoint of having higher strength and hydrolysis rate, it is preferable that the glycolic acid polymer is a homopolymer of glycolic acid.

The weight-average molecular weight of the hydrolyzable resin is not particularly limited, but is preferably 70,000 to 500,000. When the weight-average molecular weight of the hydrolyzable resin is 70,000 or more, the strength of the hydrolyzable resin is higher, so that the retention and durability of the abrasive grains can be improved. In addition, sufficient strength is obtained for handling, such as when removing the polishing pad from the mold during molding or when attaching the polishing pad to the platen of the polishing device. When the weight-average molecular weight of the hydrolyzable resin is 500,000 or less, not only can moldability be further maintained, but the time until disintegration due to hydrolysis can be shortened. From the same viewpoint, the weight-average molecular weight of the hydrolyzable resin is more preferably 90,000 to 400,000, even more preferably 100,000 to 350,000, and particularly preferably 110,000 to 300,000.

The weight average molecular weight of the hydrolyzable resin can be measured by gel permeation chromatography (GPC) under the following measurement conditions.
(Measurement conditions)
Apparatus: Showa Denko "Shodex-104"
Column: Two HFIP-606M columns connected in series with one HFIP-G column as a precolumn Column temperature: 40°C
Eluent: HFIP solution containing 5 mM sodium trifluoroacetate Flow rate: 0.6 mL/min
Detector: RI (differential refractive index) detector Molecular weight calibration: Five types of standard polymethyl methacrylate with different molecular weights

The content of the hydrolyzable resin is preferably 20% by mass or more and 90% by mass or less, more preferably 30% by mass or more and 80% by mass or less, even more preferably 40% by mass or more and 70% by mass or less, and particularly preferably 43% by mass or more and 52% by mass or less, relative to the total amount of the polishing layer (or the total amount of the above composition). If the content of the hydrolyzable resin is less than 20% by mass, the strength of the polishing layer containing the abrasive grains will be weakened, which is not preferred. If the content of the hydrolyzable resin is more than 90% by mass, the proportion of the abrasive grains will decrease and the polishing speed will be slow, which is not preferred. If the hydrolyzable resin has the above content, the proportion of the hydrolyzable resin that collapses due to hydrolysis will be greater than a specified amount, making it easier to adjust the protruding height of the abrasive grains in the polishing layer while suppressing excessive collapse of the polishing layer.

1-1-2. Abrasive grains The material of the abrasive grains is not particularly limited, and examples thereof include diamond, silicon carbide, boron carbide, boron nitride, silicon nitride, cerium oxide, aluminum oxide, zirconium oxide, silicon oxide, iron oxide, manganese oxide, magnesium oxide, calcium oxide, barium oxide, zinc oxide, titanium oxide, chromium oxide, barium carbonate, and calcium carbonate. Among these, diamond, boron carbide, and boron nitride are preferred from the viewpoint of increasing the polishing speed, and diamond is more preferred from the viewpoint of facilitating processing of a substrate with high hardness such as a SiC substrate.

The median diameter of the abrasive grains depends on the desired degree of polishing, but for example, the median diameter is preferably 2 μm or more and 50 μm or less, more preferably 3 μm or more and 40 μm or less, even more preferably 5 μm or more and 20 μm or less, and particularly preferably 6 μm or more and 15 μm or less.

The median diameter of the abrasive grains can be determined from the particle size distribution measured in accordance with Particle Size Analysis - Laser Diffraction and Scattering Method (ISO 13320:2020). Specifically, it can be measured using a laser diffraction particle sizer (e.g. Malvern's Mastersizer 3000) at a measurement temperature of 21°C, with ion-exchanged water as the dispersion medium and a refractive index of 1.330 for the dispersion medium, under the conditions of the Mie theory for the light scattering model.

The average particle size of the abrasive grains may be, for example, 1 nm or more and 1 mm or less. The average particle size of the abrasive grains can be measured in the same manner as described above.

The content of the abrasive grains is not particularly limited, but is preferably 10% by mass or more and 80% by mass or less with respect to the polishing layer (or the total amount of the composition). When the content of the abrasive grains is 10% by mass or more, the polishing speed can be further increased. When the content of the abrasive grains is 80% by mass or less, the moldability or processability into a polishing pad can be further increased. From the same viewpoint, the content of the abrasive grains is more preferably 20% by mass or more and 70% by mass or less with respect to the polishing layer (or the total amount of the composition), even more preferably 30% by mass or more and 60% by mass or less, and particularly preferably 48% by mass or more and 57% by mass or less.

The abrasive grain content can be measured by thermogravimetric analysis (TGA).
Specifically, on the surface of the polishing layer of an unused polishing pad, an arbitrary straight line passing through the center O of the polishing layer is called a straight line L, and a straight line passing through the center O of the polishing layer perpendicular to the straight line L is called a straight line M. The center O of the polishing layer, the midpoints between the center O of the polishing layer and the end of the polishing layer on the straight line L are called a1 and a2, and the midpoints between the center O of the polishing layer and the end of the polishing layer on the straight line M are called b1 and b2. From the range including each of the measurement points of O, a1, a2, b1, and b2, 100 mg or more of measurement samples are taken from the polishing layer, appropriately crushed, and used as the measurement samples from each measurement point. 20±2 mg of the measurement sample is placed in a platinum pan, heated from room temperature to 800°C at a rate of 10°C/min under an air atmosphere, and held at 800°C for 30 minutes, components other than abrasive grains are burned off, and the remaining sample weight is divided by the mass of the measurement material to obtain the content of abrasive grains in the polishing layer at each measurement point. In the present application, the arithmetic mean value of the abrasive grain content at each of the five points was taken as the representative value of the abrasive grain content of the polishing layer.

1-1-3. Other components The composition may further contain other components other than the hydrolyzable resin and the abrasive grains. Examples of other components include resins other than the hydrolyzable resin and hydrolysis accelerators. In particular, from the viewpoint of further increasing the polishing rate, it is preferable that the composition further contains a hydrolysis accelerator. The hydrolysis accelerator may be used alone or in combination of two or more kinds.

The hydrolysis accelerator is a compound that accelerates the hydrolysis reaction of the hydrolyzable resin. For example, a compound that dissolves in the polishing solution to promote the penetration of the solution into the glycolic acid polymer is preferred, and a compound that generates an acid or alkali in the presence of water is even more preferred. Examples of such decomposition accelerators include carboxylic acid anhydrides, phosphorus compounds, cyclic esters, and basic metal oxides.

Examples of carboxylic acid anhydrides include hexanoic anhydride, octanoic anhydride, decanoic anhydride, lauric anhydride, myristic anhydride, palmitic anhydride, stearic anhydride, benzoic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, trimellitic anhydride, tetrahydrophthalic anhydride, butane tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, diphenylsulfone tetracarboxylic dianhydride, biphenyl tetracarboxylic dianhydride, ethylene glycol bisanhydrotrimellitate, and glycerin bisanhydrotrimellitate monoacetate. Among these, phthalic anhydride, trimellitic anhydride, benzoic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and benzene-1,2,4,5-tetracarboxylic anhydride (pyromellitic anhydride) are preferred.

As phosphorus compounds, organic phosphorus compounds such as phosphate esters and phosphites are preferred, and organic phosphorus compounds having at least one selected from the group consisting of a long-chain alkyl group having 8 to 24 carbon atoms, an aromatic ring, and a pentaerythritol skeleton are more preferred.

Examples of the phosphate ester having a long-chain alkyl group having 8 to 24 carbon atoms include mono- or di-stearyl acid phosphate or a mixture thereof, and di-2-ethylhexyl acid phosphate.
Examples of the phosphite having an aromatic ring include tris(nonylphenyl)phosphite and the like.
Examples of the phosphite having a pentaerythritol skeleton include cyclic neopentanetetraylbis(2,6-di-tert-butyl-4-methylphenyl)phosphite, cyclic neopentanetetraylbis(2,4-di-tert-butylphenyl)phosphite, and cyclic neopentanetetraylbis(octadecyl)phosphite.

Examples of cyclic esters include glycolide, lactide, ε-caprolactone, γ-valerolactone, δ-valerolactone, diglycolic anhydride, and glutaric anhydride.

Examples of basic metal oxides include magnesium oxide, zinc oxide, calcium oxide, sodium oxide, and copper oxide.

Among these, cyclic esters are preferred, and glycolide is more preferred, from the viewpoint of being relatively stable during molding and further promoting hydrolysis of the hydrolyzable resin within the polishing layer in which water has penetrated.

The content of the hydrolysis promoter is preferably 0.5% by mass or more and 50% by mass or less with respect to the total amount of the hydrolyzable resin. When the content of the hydrolysis promoter is 0.5% by mass or more, the hydrolysis of the hydrolyzable resin can be further promoted, and the decrease in the polishing rate can be further reduced. When the content of the hydrolysis promoter is 50% by mass or less, not only can the bleed-out of the hydrolysis promoter be more unlikely to occur, but excessive collapse due to excessive hydrolysis can be further suppressed. From the same viewpoint, the content of the hydrolysis promoter is more preferably 1% by mass or more and 30% by mass or less, and even more preferably 10% by mass or more and 25% by mass or less.

The thickness of the polishing layer is not particularly limited, but when used, for example, for processing substrates for semiconductor devices, it is preferably 0.1 mm to 50 mm, more preferably 0.3 mm to 30 mm, even more preferably 0.4 mm to 10 mm, and particularly preferably 0.5 mm to 5 mm. A polishing layer thickness of 0.1 mm or more is preferable from the viewpoint that the polishing layer can adequately retain abrasive grains.

1-1-4. Physical properties (protruding height of abrasive grains)
The polishing degree of the polishing layer can be adjusted by the height of the protruding abrasive grains on the surface of the polishing layer.As mentioned above, the height of the protruding abrasive grains can be adjusted by the concentration of the hydrolysis promoter in the polishing liquid, preferably by pH.From the viewpoint of adjusting the polishing degree in a wider range, it is preferable that the change in the height of the protruding abrasive grains of the polishing layer is large with respect to the change in the pH of the polishing liquid.

For example, if the height of protruding abrasive grains on the surface of the polishing layer when polished with a polishing liquid having a pH of 13 is H1', and the height of protruding abrasive grains on the surface of the polishing layer when polished with a polishing liquid having a pH of 12 is H2', it is preferable that H2'/H1' is 0.79 or less, and more preferably 0.44 or less. The polishing conditions can be the same as those in the examples described below.

The height of protruding abrasive grains on the surface of the polishing layer can be obtained using a laser microscope (for example, Keyence VK-X260). The center of the polishing pad is O, the distance from the center O to the edge of the polishing pad (polishing layer) is 1, a circle with a radius of 0.6 is drawn from the center O, and the circumference of the circle is divided into 6 equal parts, and each of the 6 points on the circumference is used as the measurement point. The arithmetic mean of the measurement points is used as the representative value of the protruding height of the abrasive grains on the surface of the polishing layer. The protruding height of the abrasive grains at each of the measurement points is observed by observing the field of view including each measurement point with a laser microscope with an objective lens N.A. = 0.95 at a magnification of 50 times, and the protruding height of the abrasive grains observed in the same field of view is Ha, and the protruding height of the nth abrasive grain in order of height is Ha (n). Next, when the height display is set based on the apex of the protruding portion of the abrasive grain, and the height of the flat area (height of the binder resin) observed due to the difference in contrast closest to Ha(n) is taken as Hb(n), the protruding height H(n) of the abrasive grain can be obtained by subtracting Hb(n) from Ha(n).
The height H of the abrasive grains in this application is the arithmetic mean value of the heights of the abrasive grains for n=1 to 5, and can be calculated by Equation 1.

H2'/H1' can be adjusted by the composition of the polishing layer, specifically the type and amount of hydrolyzable resin and the type and amount of hydrolysis promoter contained in the polishing layer. For example, if the content of hydrolyzable resin, preferably glycolic acid polymer, is increased, the amount of change in the height of the protruding abrasive grains on the polishing layer surface when the pH is reduced from 13 to 12 is large, and H2'/H1' tends to become smaller.

(Thickness reduction rate)
The thickness reduction rate when the molded body of the above composition (base material) excluding the abrasive grains is immersed in water at 60°C is preferably 12 μm/h or more. The polishing layer containing the composition having such a thickness reduction rate can easily adjust the protruding height of the abrasive grains by changing the concentration of the hydrolysis promoter in the polishing liquid. There is no particular limit to the upper limit of the thickness reduction rate, but from the viewpoint of extending the life of the polishing pad, it is preferably 2 mm/h or less, more preferably 1 mm/h or less, even more preferably 500 μm/h or less, and particularly preferably 100 μm/h or less.

The rate of thickness reduction can be measured by the following procedure.
1) The above composition that does not contain abrasive grains is injection molded to obtain a prism of 10 mm x 10 mm x 120 mm, and a cubic test piece (molded body) with a side length of 10 mm is obtained from the prism. The above composition that does not contain abrasive grains can also be molded by heating and melting a molded body of a composition that contains abrasive grains, i.e., an abrasive layer. The abrasive layer is heated and melted, and the resulting melt is passed through a filter to separate the composition that contains abrasive grains and the other hydrolyzable resins, i.e., the composition that does not contain abrasive grains, and the composition that does not contain abrasive grains is molded to produce a molded body, which can be used as a test piece.
2) Next, the test specimen was placed in a 1 L autoclave, the autoclave was filled with water (deionized water) at 60° C., and the test specimen was completely immersed at normal pressure. The above procedure was repeated to prepare immersion test specimens with different immersion times.
Each immersion test piece is cut to expose the cross section. After drying, the thickness of the core (hard part) of the test piece is measured. The reduction in thickness is calculated from the difference between the thickness (10 mm) before immersion and the thickness of the core (hard part) before drying.
3) The time change in the thickness reduction of the test piece is calculated based on the measured values of the thickness reduction of the test piece measured at different immersion times, and the thickness reduction rate of the 10 mm test piece is calculated (unit: mm/h) from the time change in the thickness reduction of the test piece in the range where the time change in the thickness reduction of the test piece is linear.

The rate at which the thickness is reduced can be adjusted, for example, by the type of binder resin and the type and content of the hydrolysis promoter. For example, when the binder resin is a glycolic acid polymer, the rate at which the thickness is reduced tends to be large. Also, when the content of the hydrolysis promoter is high, the rate at which the thickness is reduced tends to be large.

(Tensile strength)
The tensile strength of the composition excluding the abrasive grains at 25°C is preferably 55 MPa or more. If the tensile strength is 55 MPa or more, the retention of the abrasive grains can be further increased. From the same viewpoint, the tensile strength is more preferably 60 MPa or more. The upper limit of the tensile strength is not particularly limited, but can be, for example, 1000 MPa or less. The tensile strength can be measured according to ISO527.

(Tensile Modulus)
The tensile modulus of the composition excluding the abrasive grains at 25°C is preferably 1 GPa or more. If the tensile modulus is 1 GPa or more, when the polishing pad is brought into contact with the polished object and a load is applied, the abrasive grains protruding from the surface are less likely to be pushed back into the base material. This makes it possible to reduce the decrease in polishing speed. In addition, it is possible to reduce the edge sagging of the polished object after polishing (the phenomenon in which the edge is intensively scraped off and the dimensional accuracy is reduced). From the same viewpoint, the tensile modulus is more preferably 3 GPa or more, and even more preferably 5 GPa or more. The upper limit of the tensile modulus is not particularly limited, but can be, for example, 50 GPa or less. The tensile modulus can be measured in accordance with ISO527.

The tensile strength and tensile modulus of the composition excluding the abrasive grains can be adjusted by the type and molecular weight of the binder resin contained in the composition, and the type and content of the hydrolysis promoter. For example, if a glycolic acid polymer is used as the binder resin, the tensile strength tends to be large. Also, if the content of the hydrolysis promoter is low, the tensile strength tends to be large.

1-1-5. Shape In this embodiment, as described above, the surface of the polishing layer 110 may be formed with grooves 110A as necessary (see FIGS. 1A and 1B). This makes it easier for the polishing liquid containing water to spread over the entire surface of the polishing layer 110 via the grooves 110A, and also makes it easier for shavings generated by hydrolysis of the hydrolyzable resin to be discharged to the outside through the grooves 110A.

1-2. Other Layers As described above, the polishing pad 100 may further include other layers as necessary. Examples of the other layers include a base layer and an adhesive layer. The base layer may be, for example, a resin film. The adhesive layer may be an adhesive layer for attaching the polishing pad 100 to a polishing plate (platen 210 described later).

1-3. Manufacturing method The polishing pad according to the present embodiment can be manufactured by any method. For example, the polishing pad can be manufactured through a step of 1) obtaining a composition containing a hydrolyzable resin and an abrasive grain, and a step of 2) molding the obtained composition.

In step 1), for example, the hydrolyzable resin and the abrasive grains are kneaded to obtain the above composition. As the kneading machine, for example, a roll, a kneader, a Banbury mixer, an extruder (single-shaft, multi-shaft), etc. can be used. From the viewpoint of improving processability, it is preferable to perform the kneading under heating.

In step 2), the obtained composition is molded into a desired shape. The molding method is not particularly limited, and may be, for example, any of injection molding, melt extrusion molding, solidification extrusion molding, and compression molding.

In this embodiment, grooves may be formed on the surface of the polishing layer obtained by molding. The grooves may be formed by cutting the surface of the molded body of the composition, or by molding the composition using a metal mold or die on which a pattern corresponding to the grooves is formed.

2. Method for polishing an object to be polished Hereinafter, a method for polishing an object to be polished according to one embodiment of the present invention will be described with reference to the drawings.

FIG. 3 is a schematic diagram showing a polishing apparatus 200 using the polishing pad 100 according to the present embodiment. Note that detailed illustration of the polishing pad 100 is omitted in FIG. 3.

As shown in FIG. 3, the polishing apparatus 200 includes a polishing pad 100, a disk-shaped base plate 210 that supports the polishing pad 100, a disk-shaped polishing head 230 that holds the workpiece 220, a weight 240, and a supply nozzle 250 that supplies the polishing liquid W. The base plate 210 is rotatable by a rotating shaft (not shown), and the polishing head 230 is rotatable by a rotating shaft 230A.

In this embodiment, the polishing pad 100 and the workpiece 220 are slid relative to each other while the polishing liquid W is supplied to the surface of the polishing layer of the polishing pad 100, thereby polishing the workpiece 220.

Specifically, first, the polishing pad 100 is attached to the platen 210. Next, the workpiece 220 held by the polishing head 230 is pressed against the polishing surface of the polishing pad 100, and the platen 210 and/or the polishing head 230 are rotated while the polishing liquid W is supplied from the supply nozzle 250. This causes the polishing pad 100 and the workpiece 220 to slide relative to each other, polishing the processed surface (polished surface) of the workpiece 220.

The type of the object to be polished 220 is not particularly limited, and examples include materials for semiconductor devices and electronic components, particularly Si substrates, SiC substrates, GaAs substrates, glass, substrates for hard disks and LCDs (liquid crystal displays), etc. Among these, semiconductor wafers are preferred, and SiC substrates, sapphire substrates, or GaN substrates used in power devices are more preferred.

In this embodiment, the polishing liquid W contains at least water and a hydrolysis promoter. The hydrolysis promoter may be the same as that described above. In particular, from the viewpoint of further increasing the hydrolysis rate of the hydrolyzable resin, it is preferable that the polishing liquid W contains an alkaline substance or an acidic substance as a hydrolysis promoter, and an alkaline substance is more preferable. In an aqueous solution containing an alkaline substance, the carboxylic acid terminal generated by hydrolysis remains as a carboxylate ion, and the oligomer of the polymer generated by hydrolysis is likely to dissolve into the liquid. Therefore, compared to an acidic substance, an alkaline substance can promote hydrolysis more with a small amount of addition. Examples of alkaline substances include alkali metal hydroxides such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) and organic alkalis such as tetramethylammonium hydroxide.

In this embodiment, from the viewpoint of performing rough polishing to precision mechanical polishing, the concentration of the hydrolysis promoter in the polishing liquid is gradually lowered, and the protruding height of the abrasive grains in the polishing layer is gradually reduced while polishing the workpiece 220 (see FIG. 1A).

That is, in the step of polishing the workpiece 220, a first step of polishing the workpiece 220 while supplying a first polishing liquid (polishing liquid W) containing a hydrolysis promoter to the surface of the polishing layer, and a second step of polishing the workpiece 220 while supplying a second polishing liquid (polishing liquid W) having a lower concentration of the hydrolysis promoter than the first polishing liquid are performed in this order. The difference in concentration of the hydrolysis promoter between the first polishing liquid and the second polishing liquid depends on the type of hydrolysis promoter, but for example, the first polishing liquid can be 1.5 to 1,000,000 times the substance amount concentration in the solution as compared to the second polishing liquid.
As described above, since the hydrolysis promoter is preferably an alkaline substance, for example, in the first step, it is preferable to polish the object to be polished 220 while supplying a first polishing liquid having a relatively high pH, and in the second step, to polish the object to be polished 220 while supplying a second polishing liquid having a lower pH than the first polishing liquid.

In the first step, the workpiece 220 is polished in a state where the height of the abrasive grains protruding from the polishing layer surface is adjusted to H1 by supplying a first polishing liquid. In the second step, the workpiece 220 is polished in a state where the height of the abrasive grains protruding from the polishing layer surface is adjusted to H2, which is lower than H1, by supplying a second polishing liquid having a lower pH than the first polishing liquid. The heights H1 and H2 of the abrasive grains protruding from the polishing layer surface can be measured by the method described above.

The pH of the first polishing liquid and the second polishing liquid may be set so as to achieve the desired height of abrasive grain protrusion on the surface of the polishing layer, and although this depends on the type of hydrolyzable resin, it is usually within the range of 1 to 14, preferably 7 to 14.

For example, glycolic acid polymers exhibit a high hydrolysis rate when the polishing liquid W has a pH of 9 or more, preferably a pH of 12 or more, and more preferably a pH of 13 or more. Therefore, in the first step, it is preferable to polish the object to be polished 220 while supplying a first polishing liquid having a pH higher than 12, and then in the second step, polish the object to be polished 220 while supplying a second polishing liquid having a pH of 12 or less.

The pH of the polishing solution W is a value measured by a pH meter at 20°C. The pH of the polishing solution W can be adjusted by the concentration (content) of the alkaline substance.

The temperature of the polishing liquid W is not particularly limited, but can be from 1°C to 60°C.

(Action)
In the above embodiment, as described above, a first polishing liquid having a relatively high concentration of hydrolysis promoter is supplied to polish the workpiece 220 with the protruding height of the polishing layer relatively increased, and then a second polishing liquid having a relatively low concentration of hydrolysis promoter is supplied to polish the workpiece 220 with the protruding height of the polishing layer relatively decreased. This allows a single polishing pad to perform processes from rough polishing to precision mechanical polishing, simply by changing the pH of the polishing liquid.

3. Modifications In the above embodiment, a polishing pad having grooves on the surface of the polishing layer is used, but the present invention is not limited to this, and a polishing pad having no grooves on the surface of the polishing layer may be used.

In addition, in the above embodiment, a polishing pad made of an abrasive layer is used, but this is not limited to the above, and a polishing pad having a base layer and an abrasive layer may be used. In this case, the abrasive layer may be disposed uniformly over the entire base layer, or may be disposed in a pattern.

In the above embodiment, an example was shown in which the process of polishing the workpiece 220 includes at least the first and second steps, but if necessary, a further process of polishing the workpiece 220 may be performed while supplying a polishing liquid having a lower pH than the second polishing liquid.

The present disclosure will be described below with reference to examples. The scope of the present disclosure should not be construed as being limited by the examples.

1. Materials 1-1. Binder resin - PGA-1 (homopolymer of glycolic acid, weight average molecular weight 298,000)
・PGA-2 (homopolymer of glycolic acid, weight average molecular weight 115,000)
・PPS (polyphenylene sulfide, weight average molecular weight 60400)

The weight average molecular weight of each resin was measured by gel permeation chromatography (GPC).

(Weight average molecular weight of PGA)
Apparatus: "Shodex-104" manufactured by Showa Denko Co., Ltd.
Column: Two HFIP-606M columns connected in series with one HFIP-G column as a precolumn Column temperature: 40°C
Eluent: HFIP solution containing 5 mM sodium trifluoroacetate Flow rate: 0.6 mL/min
Detector: RI (differential refractive index) detector Molecular weight calibration: Five types of standard polymethyl methacrylate with different molecular weights

(Weight average molecular weight of PPS)
Equipment: Senshu Scientific High Temperature GPC SSC-7000
Column temperature: 210 ° C.
Eluent: 1-chloronaphthalene Flow rate: 0.7 mL/min
Detector: UV detector (360 nm)
Molecular weight calibration: 5 types of standard polystyrene with different molecular weights

1-2. Abrasive grain: #800 GC fine grain abrasive (silicon carbide abrasive, manufactured by Naniwa Kenma Kogyo Co., Ltd.)

1-3. Hydrolysis accelerator Glycolide: Pyromellitic anhydride = 14:5 (weight ratio)

2. Preparation and Evaluation of Polishing Pads 2-1. Preparation of Polishing Pads (Examples 1 to 3, Comparative Example 1)
(1) Kneading step The binder resin shown in Table 1 was weighed to be 67% by volume (Examples 1 to 3: 50% by mass, Comparative Example 1: 46% by mass), and #800 GC fine abrasive (manufactured by Naniwa Kenma Kogyo Co., Ltd.) was weighed to be 33% by volume (Examples 1 to 3: 50% by mass, Comparative Example 1: 54% by mass), and kneaded using a Labo Plastomill (manufactured by Toyo Seiki Seisakusho Co., Ltd.) to obtain a composition. Kneading was performed at a predetermined heater temperature, with a preheating time of 1 minute, a kneading time of 5 minutes, and a rotation speed of 50 rpm. The heater temperature was set to 250°C for PGA and 320°C for PPS.

4A to 4C are schematic cross-sectional views showing the molding process in the embodiment. In the drawings, reference numeral 301 denotes a ferroelectric plate, and 302 denotes an aluminum foil.

As shown in FIG. 4, an aluminum punched sheet 303 having a thickness of 0.3 mm and through holes with a diameter of 3 mm arranged at intervals of 5 mm was prepared.
On this aluminum punching sheet 303, a 0.5 mm thick SUS mold 304 with a hole of 150 mm diameter was placed as shown in Fig. 4, and the above kneaded composition 305 was set in the SUS mold 304 and press molded to obtain a polishing pad 100 consisting of a polishing layer of 0.8 mm thickness and having grooves on the surface, as shown in Fig. 1A and Fig. 1B. The temperature of the press was set to the same temperature as the heater temperature of the above Labo Plastomill.

2-2. Evaluation Immediately after molding, the polishing pad had abrasive grains embedded in the resin, so it was sharpened with a #800 grindstone before a polishing test was carried out.

(Polishing test)
The polishing test was performed by mounting a polishing pad on a polishing apparatus 200 as shown in Fig. 3. Specifically, the polishing pad was attached to a platen 210 (polishing plate) using a double-sided adhesive film (e.g., AS ONE OCA50-A4). The double-sided adhesive sheet was attached using a rubber roller or the like so as to prevent air bubbles from being trapped when the sheet was attached to the polishing pad and the polishing plate.

Next, a 15×15 mm square Si substrate, which is the object to be polished 220, was pressed against the rotating polishing pad to perform polishing. The polishing conditions were as follows: At this time, the load of the jig (polishing head 230) and the weight 240 was applied to the substrate.
(Polishing conditions)
Polishing device: Dialap ML-150P (manufactured by Marutoh)
Polishing plate rotation speed: 100 rpm
Polishing disk diameter: 150mm in diameter
Forced driving or oscillation of the workpiece: None Surface pressure: 440 gf/ ^cm2
Flow rate of polishing liquid: 100 mL/min.
Polishing liquid: NaOH aqueous solution (20°C)

The polishing solution was prepared by varying the concentration of NaOH to have pH values of 13, 12, and 9. The pH was then changed in the order of 13, 12, and 9, and the polishing speed, protrusion height, and surface roughness of the workpiece at each pH were measured using the following method.

(1) Polishing speed The polished object was attached to a jig with wax and polished. In this state, the thickness of the polished object was measured using an electric micrometer Millimar 1240 (manufactured by Mahr).
The thickness of the workpiece was measured at five points and the average value was used. The polishing rate was calculated from the polishing time (min) and the thickness reduction (removal amount, μm).

(2) Surface roughness of the workpiece to be polished Using a laser microscope VK-X260 (manufactured by Keyence Corporation), the arithmetic mean height Sa (μm) of the surface of the Si substrate to be polished after 1 hour of polishing was measured and used as the surface roughness. The measurement was performed using an objective lens of 20x and N.A. = 0.46.

(3) Protruding height of abrasive grains For Example 1, Comparative Example 1, and Comparative Example 2, the polishing pads used for 60 minutes of polishing were removed from the polishing device, and ion-exchanged water was poured over them three times to remove the polishing liquid and shavings from the surface. A paper towel was placed on the polishing pad to remove moisture, and then the pad was air-dried.

After drying, 3D data of the outermost surface of the polishing pad was obtained at the position of the convex portion of the polishing layer using a laser microscope VK-X260 (manufactured by Keyence Corporation). At this time, an objective lens of 50x and N.A. = 0.95 was used.
Specifically, the center of the polishing pad is O, the distance from the center O to the edge of the polishing pad (polishing layer) is 1, a circle with a radius of 0.6 is drawn from the center O, and the circumference of the circle is divided into 6 equal parts, and each of the 6 points on the circumference is used as the measurement point. The arithmetic mean of the measurement points is used as the representative value of the protruding height of the abrasive grains on the surface of the polishing layer. The protruding height of the abrasive grains at each measurement point is observed by observing the field of view including each measurement point with a laser microscope having an objective lens N.A. = 0.95 at an observation magnification of 50 times, and the protruding height of the abrasive grains observed in the same field of view is Ha, and the protruding height of the nth abrasive grain in order of the height is Ha (n). Next, when the height display is set based on the apex of the protruding part of the abrasive grain, when the height of the flat area (height of the binder resin) observed in the nearest vicinity of Ha (n) due to the difference in contrast is Hb (n), the protruding height H (n) of the abrasive grains is obtained by subtracting Hb (n) from Ha (n). The height H of the abrasive grains was determined as the arithmetic mean value of the heights of the abrasive grains for n=1 to 5, and was calculated using the above-mentioned formula 1.

(4) Thickness reduction rate (preparation of test specimen)
A composition was prepared in the same manner as above, except that no abrasive grains were added to the composition obtained in the kneading step. A 10 mm x 10 mm x 120 mm square pillar was obtained by kneading this resin composition, and a cubic test piece (molded body) with a side length of 10 mm was obtained from the square pillar.

(Immersion test)
The obtained test piece was placed in a 1 L autoclave. The autoclave was then filled with water (deionized water) at a temperature of 60° C. or 80° C., and the test piece was completely immersed in the water at normal pressure to perform an immersion test.
The test pieces were taken out after immersion at a predetermined time interval to prepare test pieces with different immersion times, and each test piece was cut to expose the cross section. Then, after leaving it overnight in a dry room to dry, the thickness of the core (hard part) of the test piece was measured. The thickness reduction was measured from the difference from the thickness before immersion (initial thickness, specifically 10 mm). The time change in the reduced thickness of the test piece was calculated based on the measured values of the reduced thickness of the test piece measured by different immersion times. Then, the thickness reduction rate of the test piece with a thickness of 10 mm was calculated from the time change in the reduced thickness of the test piece in the range where the linearity of the time change in the reduced thickness of the test piece was observed (unit: mm/h).

(5) Tensile Strength The tensile strength of the composition prepared in (4) above was measured in accordance with ISO 527.

The evaluation results for Examples 1 to 3 and Comparative Example 1 are shown in Table 1. Note that Fig. 5A shows a graph of the pH dependence of the protruding height of the abrasive grains for Example 1, and Fig. 5B shows that for Comparative Example 1. In Figs. 5A and 5B, each plot shows the protruding height of each abrasive grain at each pH.

As shown in Table 1, in the polishing pad of Comparative Example 1, which uses non-hydrolyzable PPS as the binder resin, even when the pH of the polishing liquid is changed to 13, 12, or 9, the protruding height of the abrasive grains does not change significantly for any of the abrasive grains, indicating that the pH dependency is low (see Figure 5B).

In contrast, in the polishing pads of Examples 1 to 3, which use hydrolyzable PGA as the binder resin, the proportion of abrasive grains with large protruding heights increases as the pH of the polishing liquid increases, indicating high pH dependency (see Figure 5A).

From these findings, it can be seen that in polishing pads that use a hydrolyzable resin as the binder resin, the surface roughness of the polishing layer can be changed by changing the pH of the polishing liquid.

This application claims priority from Japanese Patent Application No. 2023-091782, filed June 2, 2023. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety.

The present invention provides a method for polishing an object that can change the degree of polishing with a single polishing pad and improve processing efficiency.

REFERENCE SIGNS LIST 100 Polishing pad 110 Polishing layer 110A Groove 111 Hydrolyzable resin 112 Abrasive grains 200 Polishing device 210 Plate 220 Object to be polished 230 Polishing head 230A Rotating shaft 240 Weight 250 Supply nozzle 301 Ferro plate 302 Aluminum foil 303 Aluminum punching sheet 304 SUS mold 305 Composition

Claims (9)

A method for polishing an object to be polished, comprising the steps of:
The method includes a step of polishing an object by sliding a polishing pad having a polishing layer including a composition including a hydrolyzable resin and an abrasive grain against the object to be polished,
The step of polishing the object to be polished includes:
a first step of polishing the workpiece while supplying a first polishing liquid containing a hydrolysis promoter that promotes hydrolysis to a surface of the polishing layer;
and a second step of polishing the workpiece while supplying a second polishing liquid having a lower concentration of a hydrolysis promoter than the first polishing liquid to the surface of the polishing layer after the first step.
A method for polishing an object to be polished. In the first step, the first polishing liquid is supplied to polish the workpiece while adjusting the height of protruding abrasive grains on the surface of the polishing layer to H1,
In the second step, the workpiece is polished in a state where a protruding height of the abrasive grains on the surface of the polishing layer is adjusted to H2 lower than H1 by supplying the second polishing liquid.
The method for polishing an object to be polished according to claim 1. The hydrolysis promoter is an alkaline substance.
3. The method for polishing an object to be polished according to claim 1 or 2. The hydrolyzable resin is mainly composed of a glycolic acid polymer.
The method for polishing an object to be polished according to any one of claims 1 to 3. the pH of the first polishing liquid is higher than 12;
The pH of the second polishing liquid is 12 or less.
The method for polishing an object to be polished according to any one of claims 1 to 4. 1. A polishing pad comprising:
a polishing layer including a composition including a hydrolyzable resin and an abrasive grain;
When the height of protruding abrasive grains on the surface of the polishing layer when polished with a polishing liquid having a pH of 13 is H1', and the height of protruding abrasive grains on the surface of the polishing layer when polished with a polishing liquid having a pH of 12 is H2', H2'/H1' is 0.79 or less.
Polishing pad. The median diameter of the abrasive grains is 2 μm or more and 50 μm or less.
The polishing pad of claim 6. a thickness reduction rate of 12 μm/h or more when a molded body of the composition excluding the abrasive grains is immersed in water at 60° C.;
8. The polishing pad according to claim 6 or 7. The tensile strength of a molded body made of the composition excluding the abrasive grains is 55 MPa or more.
The polishing pad according to any one of claims 6 to 8.

Images