Polishing pad and method for polishing object to be polished

Abstract

A polishing pad according to the present invention comprises a polishing layer. The polishing layer includes a composition that contains a glycolic acid polymer and abrasive grains.

Description

Polishing pad and method for polishing object

[0001] The present invention relates to a polishing pad and a method for polishing an object to be polished.

[0002] In the manufacturing process of substrates used in semiconductor devices, a cylindrical single crystal (ingot) is sliced ​​into discs to form wafers, which are then roughly polished (lapping, primary polishing) to ensure that both sides of the wafer are parallel and to the specified thickness. The roughly polished wafers then undergo chemical etching and precision mechanical polishing (secondary polishing, mechanical polishing) to achieve a highly flat mirror surface. Finally, a chemical process is added to achieve atomic-level flatness by finishing polishing (chemical mechanical polishing, CMP).

[0003] In rough polishing, a polishing method using a fixed-abrasive polishing pad having a polishing layer containing a binder resin and abrasive grains fixed by the binder resin is known.

[0004] As the binder resin, a curable resin such as a phenol resin, an epoxy resin, or an acrylic phenol resin is usually used (see, for example, Patent Document 1).

[0005] JP 2018-51733 A

[0006] Rough polishing with a fixed-abrasive polishing pad (sometimes simply referred to as "rough polishing") is carried out by abrasive grains exposed on the surface of the polishing pad. During polishing, abrasive grains may fall off the polishing pad or wear away due to wear, causing dulling (a condition in which the tips of the abrasive grains are worn away and flattened), reducing the polishing ability of the polishing pad. Therefore, it is desirable for the polishing pad to have a structure in which abrasive grains are fixed by a binder resin, and the binder resin is appropriately removed from the polishing surface of the polishing pad, causing the abrasive grains to fall off appropriately, replacing the abrasive grains and changing the grain size, so that undulled abrasive grains are always exposed. However, in polishing pads using the binder resin described above, the binder resin is only worn away by friction with the wafer during polishing. Therefore, continuous use of the polishing pad reduces the proportion of abrasive grains exposed on the polishing surface, i.e., grain change is unlikely to occur. Furthermore, because the abrasive grains on the polishing surface are firmly fixed to the binder resin, dulling occurs over the course of polishing, resulting in a problem of a decrease in the polishing rate.

[0007] In particular, silicon carbide (SiC) and gallium nitride (GaN) substrates used in next-generation power semiconductor devices are harder than silicon (Si) substrates and require a long time for polishing. Therefore, there is a need for a polishing pad that does not require dressing (sharpening) during long-term polishing processes and does not experience a significant decrease in polishing rate.

[0008] The present invention has been made in view of the above circumstances, and has as its object to provide a polishing pad in which the reduction in polishing rate is small even without dressing, and a method for polishing an object to be polished using the same.

[0009] [1] A polishing pad comprising a polishing layer containing a composition containing a glycolic acid polymer and abrasive grains. [2] The polishing pad according to [1], wherein the median diameter of the abrasive grains is 2 μm or more and 50 μm or less. [3] The polishing pad according to [1] or [2], wherein the weight-average molecular weight of the glycolic acid polymer is 70,000 or more. [4] The polishing pad according to any one of [1] to [3], wherein the polishing layer further contains a hydrolysis accelerator that accelerates hydrolysis of the glycolic acid polymer. [5] The polishing pad according to any one of [1] to [4], wherein the hydrolysis accelerator comprises a cyclic ester. [6] The polishing pad according to any one of [1] to [5], wherein a molded product of the composition excluding the abrasive grains exhibits a thickness reduction rate of 12 μm / h or more when immersed in water at 60°C. [7] The polishing pad according to any one of [1] to [6], wherein a molded product of the composition excluding the abrasive grains has a tensile strength of 55 MPa or more. [8] A method for polishing an object to be polished, comprising the step of polishing the object to be polished by sliding the polishing pad and the object to be polished relative to each other while supplying a polishing liquid containing water to the surface of the polishing layer of the polishing pad according to any one of [1] to [7]. [9] The method for polishing an object to be polished according to [8], wherein the polishing liquid is an alkaline aqueous solution.

[0010] According to the present invention, it is possible to provide a polishing pad with a small decrease in polishing rate and a method for polishing an object using the same.

[0011] Fig. 1A is a schematic plan view of a polishing pad according to one embodiment of the present invention, and Fig. 1B is a schematic cross-sectional view of the polishing pad of Fig. 1A taken along line 1B-1B. Fig. 2 is a schematic cross-sectional view showing a polishing method for a polished object according to one embodiment of the present invention. Figs. 3A to 3C are schematic cross-sectional views showing a molding process in an example. Figs. 4A and 4B are graphs showing the thickness reduction rate of compositions used in the examples and comparative examples.

[0012] The inventors have investigated various binder resins for fixing abrasive grains in polishing pads and found that by using a hydrolyzable resin that disintegrates appropriately when polished with water, the abrasive grains buried in the binder resin are easily exposed to the surface of the polishing layer, thereby exhibiting a dressing effect. Furthermore, among hydrolyzable resins, glycolic acid polymers have higher strength and a faster hydrolysis rate than other hydrolyzable resins such as polylactic acid, and therefore exhibit a high dressing effect and thus exhibit a high polishing rate. As a result, the decrease in polishing rate can be significantly reduced even without a dressing treatment.

[0013] That is, the polishing pad according to one embodiment of the present invention includes a polishing layer containing a glycolic acid polymer and abrasive grains. The configuration of the polishing pad will be described in detail below.

[0014] 1. Polishing Pad FIG. 1A is a schematic plan view of a polishing pad 100 according to one embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view of the polishing pad 100 of FIG. 1A taken along line 1B-1B.

[0015] The polishing pad 100 according to this embodiment includes a polishing layer 110 containing a glycolic acid polymer and abrasive grains (see FIG. 1B ). The polishing layer 110 includes a matrix portion 111 (base material) containing the glycolic acid polymer, and abrasive grains 112 fixed by the matrix portion 111. In this embodiment, grooves 110A are arranged on the surface of the polishing layer 110, forming an uneven pattern. While FIG. 1 shows an example in which the polishing pad 100 is made up of the polishing layer 110, the polishing pad 100 may further include other layers.

[0016] 1-1. Abrasive Layer The abrasive layer contains a composition containing a glycolic acid polymer and abrasive grains.

[0017] 1-1-1. Glycolic acid polymer Glycolic acid polymer is a polymer consisting of a structural unit (-(-O-CH ２The glycolic acid polymer is a polymer containing a structural unit derived from glycolic acid, and is a polymer containing a structural unit derived from glycolic acid as a main component. The glycolic acid polymer may be a homopolymer of glycolic acid or a copolymer of glycolic acid and a monomer copolymerizable therewith.

[0018] 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; and carbonates such as trimethylene carbonate.

[0019] The term "mainly composed of glycolic acid-derived structural units" means that the content of glycolic acid-derived structural units is 50% by mass or more relative to the total amount of structural units constituting the glycolic acid polymer. The content of glycolic acid-derived structural units is preferably 70% by mass or more, more preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95% by mass or more. When the content of the structural units constituting the glycolic acid polymer is 50% by mass or more, the strength of the glycolic acid polymer can be better maintained, so that sufficient strength can be obtained when used in a polishing pad. Furthermore, when the content of the structural units constituting the glycolic acid polymer is 70% by mass or more, hydrolysis is more likely to proceed, so that the decrease in polishing rate can be reduced.

[0020] Among these, from the viewpoint of higher strength and ease of hydrolysis, the glycolic acid polymer is preferably a homopolymer of glycolic acid.

[0021] The weight-average molecular weight of the glycolic acid polymer is not particularly limited, but is preferably 70,000 or more and 500,000 or less. When the weight-average molecular weight of the glycolic acid polymer is 70,000 or more, the strength of the glycolic acid polymer can be increased, thereby further improving the abrasive grain retention and durability. In addition, sufficient strength can be 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 a polishing device. When the weight-average molecular weight of the glycolic acid polymer is 500,000 or less, not only can moldability be further maintained, but the time until disintegration by hydrolysis can also be shortened. From the same viewpoint, the weight-average molecular weight of the glycolic acid polymer is more preferably 90,000 or more and 400,000 or less, even more preferably 100,000 or more and 350,000 or less, and particularly preferably 110,000 or more and 300,000 or less.

[0022] The weight-average molecular weight of the glycolic acid polymer can be measured by gel permeation chromatography (GPC). The measurement conditions can be as follows: (Measurement conditions) Apparatus: "Shodex-104" manufactured by Showa Denko Column: Two HFIP-606M columns connected in series with one HFIP-G column as a pre-column 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

[0023] The content of the glycolic acid polymer 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 polishing layer (or the total amount of the composition). A glycolic acid polymer content of 20% by mass or more is preferred because it increases the strength of the polishing layer containing abrasive grains. A glycolic acid polymer content of 90% by mass or less is preferred because it prevents the proportion of abrasive grains from becoming too small, thereby preventing a decrease in the polishing rate. When the glycolic acid polymer is at the above content, excessive collapse of the polishing layer is suppressed, and a more stable polishing rate is likely to be obtained due to the dressing effect.

[0024] 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 further increasing the polishing rate, and diamond is more preferred from the viewpoint of facilitating processing of high-hardness substrates such as SiC substrates.

[0025] The median diameter of the abrasive grains depends on the required polishing degree, but is preferably, for example, 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. If the median diameter of the abrasive grains is 2 μm or more, the polishing speed of the workpiece can be increased, which is preferable. If the median diameter of the abrasive grains is 50 μm or less, the depth of the damaged layer of the workpiece can be reduced, which is preferable.

[0026] 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 size analyzer (e.g., Malvern Mastersizer 3000) at a measurement temperature of 21°C, using ion-exchanged water as the dispersion medium, with a refractive index of 1.330, and using the Mie theory as the light scattering model.

[0027] 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 also be measured in the same manner as above.

[0028] The content of the abrasive grains is not particularly limited, but is preferably 10% by mass or more and 80% by mass or less relative 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 rate can be further increased. When the content of the abrasive grains is 80% by mass or less, the formability or processability into a polishing pad can be further improved. From the same viewpoint, the content of the abrasive grains is more preferably 20% by mass or more and 70% by mass or less relative 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.

[0029] The content of abrasive grains can be measured by thermogravimetric analysis (TGA).Specifically, on the surface of the polishing layer of unused polishing pad, when any straight line passing through the center O of the polishing layer is designated as line L, and the straight line passing through the center O of the polishing layer perpendicular to line L is designated as line M, the center O of the polishing layer, the midpoint between the center O of the polishing layer and the end of the polishing layer on line L are designated as a1 and a2, and the midpoint between the center O of the polishing layer and the end of the polishing layer on line M are designated as b1 and b2, then, from the range including the measurement points of O, a1, a2, b1 and b2, 100 mg or more of measurement samples are taken from the polishing layer, and suitably pulverized, and used as the measurement samples from each measurement point.20±2 mg of measurement sample is placed in a platinum pan, and heated from room temperature to 800 ° C at a rate of 10 ° C / min under air atmosphere, and kept at 800 ° C for 30 minutes, and components other than abrasive grains are burned off, and the remaining sample weight is divided by the mass of the measurement sample to determine 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.

[0030] 1-1-3. Other Components The composition may further contain other components in addition to the glycolic acid polymer and abrasive grains. Examples of other components include resins other than the glycolic acid polymer 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. One type of hydrolysis accelerator may be used alone, or two or more types may be used in combination.

[0031] The hydrolysis accelerator is a compound that accelerates the hydrolysis reaction of the glycolic acid polymer, and is preferably a compound that dissolves in the polishing solution to accelerate the penetration of the solution into the glycolic acid polymer, and more preferably a compound that generates an acid or alkali in the presence of water. Examples of such decomposition accelerators include carboxylic acid anhydrides, phosphorus compounds, cyclic esters, and basic metal oxides.

[0032] 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, butanetetracarboxylic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, diphenylsulfonetetracarboxylic dianhydride, biphenyltetracarboxylic dianhydride, ethylene glycol bisanhydrotrimellitate, and glycerin bisanhydrotrimellitate monoacetate. Among these, phthalic anhydride, trimellitic anhydride, benzoic anhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and benzene-1,2,4,5-tetracarboxylic anhydride (pyromellitic anhydride) are preferred.

[0033] The phosphorus compound is preferably an organic phosphorus compound such as a phosphate ester or a phosphite ester, and more preferably an organic phosphorus compound 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.

[0034] Examples of phosphate esters 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 phosphites having an aromatic ring include tris(nonylphenyl)phosphite. Examples of phosphites 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.

[0035] Examples of cyclic esters include glycolide, lactide, ε-caprolactone, γ-valerolactone, δ-valerolactone, diglycolic anhydride, and glutaric anhydride.

[0036] Examples of basic metal oxides include magnesium oxide, zinc oxide, calcium oxide, sodium oxide, and copper oxide.

[0037] Among these, cyclic esters are preferred, and glycolide is more preferred, from the viewpoints of being relatively stable during molding and further promoting hydrolysis of glycolic acid polymers in the polishing layer permeated with water.

[0038] The content of the hydrolysis accelerator is preferably 0.5% by mass or more and 50% by mass or less relative to the total amount of the glycolic acid polymer. When the content of the hydrolysis accelerator is 0.5% by mass or more, the hydrolysis of the glycolic acid polymer can be further accelerated, and the decrease in the polishing rate can be further reduced. When the content of the hydrolysis accelerator is 50% by mass or less, not only can the bleed-out of the hydrolysis accelerator be more unlikely to occur, but excessive collapse due to excessive hydrolysis can also be further suppressed. From the same viewpoint, the content of the hydrolysis accelerator 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.

[0039] The thickness of the polishing layer is not particularly limited, but when used for processing a substrate of a semiconductor device, for example, it is preferably 0.1 mm or more and 50 mm or less, more preferably 0.3 mm or more and 30 mm or less, even more preferably 0.4 mm or more and 10 mm or less, and particularly preferably 0.5 mm or more and 5 mm or less. A thickness of 0.1 mm or more is preferable from the viewpoint that the polishing layer can sufficiently hold abrasive grains.

[0040] 1-1-4. Physical Properties (Thickness Reduction Rate) When a molded body of the composition (base material) excluding the abrasive grains is immersed in water at 60°C, the thickness reduction rate is preferably 12 μm / h or more. A polishing layer containing a composition having such a thickness reduction rate is easily hydrolyzed by supplying a polishing liquid, and the dressing effect is more easily obtained. There is no particular limit on 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.

[0041] The rate of thickness reduction can be measured by the following procedure. 1) The above composition containing no abrasive grains is injection molded to obtain a 10 mm x 10 mm x 120 mm prism, and a cubic test piece (molded body) with a side length of 10 mm is obtained from the prism. Molded bodies of the above composition containing no abrasive grains can also be obtained by heating and melting a molded body of a composition containing abrasive grains, i.e., the abrasive layer. The abrasive layer is heated and melted, and the resulting molten material is passed through a filter to separate the abrasive grains and the composition containing the other hydrolyzable resin, i.e., the abrasive grain-free composition, and the abrasive grain-free composition is molded to produce a molded body, which can be used as a test piece. 2) Next, the test piece is placed in a 1 L autoclave, the autoclave is filled with water (deionized water) at 60°C, and the test piece is completely immersed at normal pressure. The above procedure is repeated to prepare test pieces 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 thickness reduction is measured from the difference with the thickness (10 mm) before immersion. 3) The time change in the thickness reduction of the test piece is determined based on the measured values ​​of the thickness reduction of the test piece measured after different immersion times. Then, 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 within the range where the time change in the thickness reduction of the test piece is linear.

[0042] The rate of thickness reduction of the composition excluding the abrasive grains can be adjusted, for example, by the type of binder resin and the type and content of the hydrolysis accelerator. For example, when the binder resin is a glycolic acid polymer, the rate of thickness reduction tends to be high. Furthermore, when the content of the hydrolysis accelerator is high, the rate of thickness reduction tends to be high.

[0043] (Tensile strength) The tensile strength of the composition excluding the abrasive grains at 25°C is preferably 55 MPa or more. A tensile strength of 55 MPa or more can further increase the retention of the abrasive grains. From the same viewpoint, the tensile strength is more preferably 60 MPa or more. The tensile strength can be measured in accordance with ISO 527.

[0044] (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 workpiece and a load is applied, the abrasive grains protruding from the surface are less likely to be pushed back into the base material. This can further reduce the decrease in polishing rate. In addition, it can reduce the edge sagging of the workpiece after polishing (a phenomenon in which the edge is intensively scraped off, resulting in a decrease in dimensional accuracy). From the same perspective, the tensile modulus of the composition 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 ISO 527.

[0045] The tensile strength and tensile modulus can be adjusted by the type and content of the hydrolyzable resin, the type and content of the hydrolysis promoter, the weight average molecular weight, the cooling step during molding, etc. For example, if the content of the hydrolysis promoter is low, the tensile strength tends to be high.

[0046] In this embodiment, as described above, grooves 110A may be formed on the surface of polishing layer 110 as needed (see FIGS. 1A and 1B). This allows the polishing liquid containing water to be easily spread over the entire surface of polishing layer 110 via grooves 110A, and also allows shavings generated by hydrolysis of the glycolic acid polymer to be easily discharged to the outside via grooves 110A.

[0047] 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 substrate layer and an adhesive layer. The substrate 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 platen (platen 210, described below).

[0048] 2. Method for Manufacturing Polishing Pad The polishing pad according to this embodiment can be manufactured by any method. For example, the polishing pad can be manufactured through 1) a step of obtaining a composition containing a glycolic acid polymer and abrasive grains, and 2) a step of molding the obtained composition.

[0049] The composition can be obtained by any method. For example, the composition can be obtained by kneading the glycolic acid polymer with the abrasive grains. Examples of kneading machines that can be used include rolls, kneaders, Banbury mixers, and extruders (single-screw or multi-screw).

[0050] From the viewpoint of improving processability, the kneading is preferably carried out under heating. The heating temperature can be, for example, 180° C. or higher and 270° C. or lower. In particular, when the composition contains a hydrolysis accelerator, the heating temperature is preferably a temperature at which the hydrolysis accelerator can be dispersed in a stable state.

[0051] The form of the resulting composition is not particularly limited, and may be, for example, pellets, powder, or filaments.

[0052] Step 2) Next, the obtained composition is molded into a predetermined shape. The molding method is not particularly limited, and may be, for example, any of injection molding, melt extrusion molding, solidification extrusion molding, vacuum molding, transfer molding, and compression molding. Molding may also be performed using a 3D printer.

[0053] When producing a molded product by compression molding, pellets of the composition are fed into a mold, and the mold temperature is set to 180°C or higher and 270°C or lower, followed by press molding to obtain a polishing pad containing the molded product.

[0054] In this embodiment, grooves may be formed on the surface of the polishing layer obtained by molding. The method for forming the grooves is not particularly limited, and the grooves may be formed by cutting the surface of the molded product of the composition, or by molding the composition using a mold or die on which a pattern corresponding to the grooves is formed. Furthermore, in order to improve the dimensional stability of the molded product, annealing may be performed as necessary.

[0055] 2 is a schematic diagram showing a polishing apparatus 200 using the polishing pad 100 according to the present embodiment. In this figure, detailed illustration of the polishing pad 100 is omitted.

[0056] 2, polishing apparatus 200 includes polishing pad 100, a disc-shaped surface plate 210 that supports polishing pad 100, a disc-shaped polishing head 230 that holds workpiece 220, a weight 240, and a supply nozzle 250 that supplies polishing liquid W. Surface plate 210 is rotatable by a rotation shaft (not shown), and polishing head 230 is rotatable by a rotation shaft 230A.

[0057] In this embodiment, the polishing pad 100 and the object to be polished 220 are slid relative to each other while a polishing liquid W containing water is supplied to the surface of the polishing pad 100, thereby polishing the object to be polished 220.

[0058] Specifically, first, the polishing pad 100 is attached to the surface plate 210. Next, the workpiece 220 held by the polishing head 230 is pressed against the polishing surface of the polishing pad 100, and the surface plate 210 and / or the polishing head 230 are rotated while supplying the polishing liquid W 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 (surface to be polished) of the workpiece 220.

[0059] The type of the object to be polished 220 is not particularly limited, and examples thereof 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.

[0060] The polishing solution W contains at least water. From the viewpoint of promoting hydrolysis of the glycolic acid polymer contained in the polishing pad 100 and further enhancing the dressing effect, the polishing solution W is preferably an alkaline or acidic aqueous solution, and an alkaline aqueous solution is more preferable. In an alkaline aqueous solution, the carboxylic acid terminals generated by hydrolysis remain as carboxylate ions, and oligomers of the polymer generated by hydrolysis are easily eluted into the solution. Therefore, an alkaline aqueous solution can promote hydrolysis more than an acidic aqueous solution.

[0061] The alkaline aqueous solution contains water and an alkaline substance. Examples of the alkaline substance include alkali metal hydroxides such as sodium hydroxide (NaOH) and potassium hydroxide (KOH), and organic alkalis such as tetramethylammonium hydroxide. From the viewpoint of further promoting the hydrolysis of the glycolic acid polymer, the pH of the alkaline aqueous solution is preferably 9 or higher, more preferably 12 or higher, and even more preferably 13 or higher. The upper limit of the pH can be, for example, 14. The pH is a value measured with a pH meter at 20°C. The pH of the alkaline aqueous solution can be adjusted by the amount of the alkaline substance.

[0062] The temperature of the polishing liquid W is not particularly limited, but can be set to 1°C or higher and 60°C or lower.

[0063] The polishing liquid W may further contain other components than those mentioned above, for example, a hydrolysis accelerator.

[0064] 4. Modifications Although in the above embodiment, grooves are arranged on the surface of the polishing layer, the present invention is not limited to this, and grooves may not be arranged.

[0065] In the above embodiment, the polishing pad is composed of only the polishing layer, but is not limited thereto and may further include other layers. When the polishing pad further includes a base layer, the polishing layer may be disposed uniformly on the base layer or may be disposed in a pattern.

[0066] In addition, in the above embodiment, an example was shown in which glycolic acid polymer was used as the binder resin for the polishing layer, but this is not limited to this, and a hydrolyzable resin can also be used in which the rate of reduction in the thickness of the composition excluding the abrasive grains falls within the above range.

[0067] The present disclosure will be described below with reference to examples, which should not be construed as limiting the scope of the present disclosure.

[0068] 1. Materials 1-1. Binder resins PGA-1 (homopolymer of glycolic acid, weight-average molecular weight 298,000) PGA-2 (homopolymer of glycolic acid, weight-average molecular weight 115,000) PLA (Natureworks 7000D, polylactic acid, weight-average molecular weight 246,000, manufactured by Natureworks) PPS (polyphenylene sulfide, weight-average molecular weight 60,400)

[0069] The weight average molecular weight of each resin was measured by gel permeation chromatography (GPC).

[0070] (Weight average molecular weight of PGA and PLA) Apparatus: "Shodex-104" manufactured by Showa Denko K.K. Column: Two HFIP-606M columns connected in series with one HFIP-G column as a pre-column 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

[0071] (Weight average molecular weight of PPS) Apparatus: High temperature GPC SSC-7000 manufactured by Senshu Scientific 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

[0072] 1-2. Abrasive grain: #800 GC fine grain abrasive (silicon carbide abrasive, manufactured by Naniwa Kenma Kogyo Co., Ltd.)

[0073] 1-3. Hydrolysis accelerator: glycolide: pyromellitic anhydride = 14:5 (weight ratio)

[0074] 2. Preparation and Evaluation of Polishing Pads 2-1. Preparation of Polishing Pads (Examples 1 to 3, Comparative Examples 1 and 2) (1) Kneading Step The binder resin shown in Table 1 was weighed to 67% by volume (Examples 1 to 3: 50% by mass, Comparative Example 1: 44% by mass, Comparative Example 2: 46% by mass), and #800 GC fine abrasive (manufactured by Naniwa Abrasive Industries Co., Ltd.) was weighed to 33% by volume (Examples 1 to 3: 50% by mass, Comparative Example 1: 56% by mass, Comparative Example 2: 54% by mass), and kneaded using a Labo Plastomill (manufactured by Toyo Seiki Seisakusho) 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, 200 ° C. for PLA, and 320 ° C. for PPS.

[0075] 3A to 3C are schematic cross-sectional views showing the molding process in the example. In the figures, reference numeral 301 denotes a ferroelectric plate, and 302 denotes an aluminum foil.

[0076] As shown in Figure 3, a 0.3 mm thick aluminum punched sheet 303 with 3 mm diameter through-holes arranged at 5 mm intervals was prepared. A 0.5 mm thick SUS mold 304 with 150 mm diameter holes was placed on this aluminum punched sheet 303 as shown in Figure 3, and the kneaded composition 305 was placed in the SUS mold 304 and press-molded to obtain a polishing pad 100 consisting of a 0.8 mm thick polishing layer with grooves arranged on the surface, as shown in Figures 1A and 1B. The temperature of the press was set to the same temperature as the heater temperature of the Labo Plastomill.

[0077] 2-2. Evaluation Immediately after molding, the polishing pad had abrasive grains embedded in the resin, so it was sharpened with an #800 grindstone before a polishing test was carried out.

[0078] 2, the polishing test was performed by mounting a polishing pad on a polishing apparatus 200. Specifically, the polishing pad was attached to a surface plate 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 to prevent air bubbles from being trapped when attached to the polishing pad and polishing plate.

[0079] Next, a 15×15 mm square Si substrate, which was the workpiece 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 weight 240 was applied to the substrate.

[0080] (Polishing Test 1) Polishing device: Dialap ML-150P (manufactured by Marutoh Co., Ltd.) Polishing disc rotation speed: 100 rpm Polishing disc diameter: 150 mm diameter Forced drive or oscillation of polished object: None Surface pressure: 440 gf / cm ２ Polishing solution flow rate: 100 mL / min. Polishing solution: NaOH aqueous solution (20°C) with pH = 9

[0081] (Polishing Test 2) Polishing device: Dialap ML-150P (manufactured by Marutoh Co., Ltd.) Polishing disc rotation speed: 100 rpm Polishing disc diameter: 150 mm diameter Forced drive or oscillation of polished object: None Surface pressure: 440 gf / cm ２ Polishing solution flow rate: 100 mL / min. Polishing solution: NaOH aqueous solution (20°C) with pH = 13

[0082] The polishing rate when polishing was performed using each polishing liquid was measured by the following method.

[0083] (Polishing Rate) The workpiece was attached to a jig with wax and polished. In this attached state, the thickness of the workpiece was measured using an electric micrometer Millimar 1240 (manufactured by Mahr). The thickness of the workpiece was measured at five locations and the average value was used. The polishing rate was calculated from the polishing time (min) and the thickness reduction value (removal amount, μm).

[0084] The construction and tensile strength of the polishing pads of Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 1. The tensile strength indicates the tensile strength measured in accordance with ISO 527 for the above composition without the abrasive grains. Table 2 also shows the results of polishing test 1 and polishing test 2 conducted using the polishing pads obtained in Examples 1 to 3 and Comparative Examples 1 and 2.

[0085]

[0086]

[0087] As shown in Tables 1 and 2, the polishing pads of Comparative Examples 1 and 2, which used PLA or PPS as the binder resin, had low polishing rates at both pH 9 and 13, and the polishing rate gradually decreased from the polishing rate in the first 15 minutes. This indicates that initially, the abrasive grains exposed on the surface of the polishing pad acted on the polishing, but the abrasive grains acting on the polishing gradually decreased. In other words, it is thought that the polishing rate decreased because the decomposition ability of the binder resin was insufficient and the abrasive grains did not change.

[0088] In contrast, the polishing pads of Examples 1 to 3, which used PGA as the binder resin, had a high removal rate, and at pH 13, no significant decrease in removal rate was observed from the first 15 minutes to 60 minutes.

[0089] From these facts, it can be seen that with a polishing pad using PGA as the binder resin, the decrease in polishing rate can be reduced even without dressing.

[0090] It is also clear that the addition of a hydrolysis inhibitor (GL) to PGA can significantly increase the removal rate, particularly at pH 13 (comparison between Examples 1 and 3).

[0091] 3. Immersion test (Preparation of test pieces) A ​​composition was prepared in the same manner as in Examples 1 to 3 and Comparative Examples 1 and 2, except that abrasive grains were not added to the compositions used to prepare the polishing pads. This resin composition was injection molded to obtain a 10 mm × 10 mm × 120 mm square pillar, and a cubic test piece (molded body) with a side length of 10 mm was obtained from the square pillar.

[0092] (Immersion Test) The obtained test specimens were placed in a 1 L autoclave. The autoclave was then filled with water (deionized water) at 60°C or 80°C, and the test specimens were completely immersed at normal pressure to perform an immersion test. Test specimens with different immersion times were prepared by removing the test specimens after immersion at predetermined time intervals, and each test specimen was cut to expose its cross section. After leaving the specimens to dry overnight in a dry room, the thickness of the core (hard part) of each test specimen was measured. The thickness loss was measured as the difference from the thickness before immersion (initial thickness, specifically 10 mm). The time change in the thickness loss of the test specimen was calculated based on the measured values ​​of the thickness loss of the test specimens measured for different immersion times. The thickness loss rate of a 10 mm thick test specimen was calculated (unit: mm / h) from the time change in the thickness loss of the test specimen within the range in which the time change in the thickness loss of the test specimen was linear.

[0093] The evaluation results at 60°C for Examples 1 to 3 and Comparative Examples 1 and 2 are shown in Table 3. Also, Fig. 4 is a graph showing the evaluation results for Example 1 and Comparative Example 1, where Fig. 4A shows the evaluation results at 60°C and Fig. 4B shows the evaluation results at 80°C.

[0094]

[0095] As shown in Table 3, the molded bodies of Examples 1 to 3 had a high thickness reduction rate of 12 μm / h or more, whereas the molded bodies of Comparative Examples 1 and 2 had a lower thickness reduction rate. In other words, as shown in Table 2, the reason why the processing rate was not maintained in the polishing pads of Comparative Examples 1 and 2 is thought to be due to insufficient decomposition of the binder resin.

[0096] Furthermore, as shown in Figure 4, the PGA of Example 1 exhibits surface degradability, with its thickness decreasing at a constant rate even in water at 60°C and 80°C. On the other hand, the PLA of Comparative Example 1 exhibits a significantly slower decomposition rate than PGA at 60°C. Furthermore, when the temperature was raised to 80°C to promote hydrolysis, the thickness loss rate accelerated over time, demonstrating bulk degradability. In other words, even if hydrolysis was further promoted when PLA was used as a binder resin, excessive disintegration occurred due to bulk decomposition, which not only shortened the life of the polishing pad but also prevented stable dressing effects from being obtained. These findings demonstrate that PGA exhibiting surface degradability is suitable for polishing pads that maintain stable dressing effects and polishing rates.

[0097] This application claims priority based on Japanese Patent Application No. 2023-91781, filed June 2, 2023. The contents of the specification and drawings of that application are incorporated herein by reference in their entirety.

[0098] According to the present invention, it is possible to provide a polishing pad with a small decrease in polishing rate and a method for polishing an object using the same.

[0099] REFERENCE SIGNS LIST 100 Polishing pad 110 Polishing layer 110A Groove 111 Matrix portion 112 Abrasive grains 200 Polishing device 210 Surface 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

1. a polishing layer including a composition containing a glycolic acid polymer and abrasive grains; Polishing pad.

2. The median diameter of the abrasive grains is 2 μm or more and 50 μm or less. The polishing pad of claim 1 .

3. The weight average molecular weight of the glycolic acid polymer is 70,000 or more. The polishing pad of claim 1 .

4. The polishing layer further contains a hydrolysis promoter that promotes hydrolysis of the glycolic acid polymer. The polishing pad of claim 1 .

5. The hydrolysis promoter includes a cyclic ester. The polishing pad of claim 4.

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; The polishing pad of claim 1 .

7. The tensile strength of a molded body made of the composition excluding the abrasive grains is 55 MPa or more. The polishing pad of claim 1 .

8. The method includes a step of polishing an object by sliding the polishing pad and the object to be polished relatively while supplying a polishing liquid containing water to the surface of the polishing layer of the polishing pad according to any one of claims 1 to 7. A method for polishing an object.

9. The polishing liquid is an alkaline aqueous solution. The method for polishing an object to be polished according to claim 8.