Polishing slurry and polishing method

Abstract

To provide a chemical mechanical polishing (CMP) slurry and a CMP method that reduce the amount of abrasive particles remaining after cleaning.SOLUTION: Hydroxyapatite (HAp) is used as an abrasive in a CMP slurry containing abrasive grains, water, and a pH adjuster. When cleaning a substrate after CMP, the remaining HAp can be removed by contacting the substrate with acid.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a slurry for chemical mechanical polishing. Further, the present invention relates to a chemical mechanical polishing method using this polishing slurry.

Background Art

[0002] In order to planarize the surface of a substrate used in the manufacture of semiconductor elements, chemical mechanical polishing (CMP) is performed. In CMP, the surface of the substrate is polished using a suspension (slurry) containing abrasive grains and a polishing aid. In CMP, a large amount of particles are generated due to polishing debris and abrasive grains in the slurry, and subsequently, a cleaning process for removing these foreign substances is performed. If the cleaning process is not appropriate, defects occur in the structure of the substrate, resulting in poor characteristics of the semiconductor element. Therefore, more reliable removal of foreign substances is required.

[0003] As CMP abrasive grains, generally, abrasive grains made of silica particles (for example, Patent Document 1) and abrasive grains made of ceria (cerium oxide) particles (for example, Patent Document 2) are used. Further, as a cleaning method after CMP, an alkaline cleaning solution obtained by mixing ammonia water and hydrogen peroxide water at an arbitrary ratio is used, and the adhered particles are lifted off by etching the substrate surface. Further, a method of removing particles while suppressing reattachment to the substrate by utilizing electrostatic repulsion (SC1 cleaning), a method of using a cleaning solution obtained by mixing hydrochloric acid and hydrogen peroxide water at an arbitrary ratio to dissolve and remove trace metal impurities on the substrate surface (SC2 cleaning), etc. are known to be used in combination according to the purpose (Patent Document 3). Further, in combination with such a cleaning solution, physical cleaning for physically sweeping out particles using a cleaning member such as a roll brush or a pen brush, and non-contact physical cleaning such as ultrasonic cleaning are used.

[0004] However, due to requirements such as miniaturization in the semiconductor industry in recent years, the size of abrasive grains used has been decreasing. Along with this, the size and number of foreign substances allowed after substrate cleaning have become more stringent, and there is a possibility that the cleaning performance may not be sufficient with the above conventional methods.

[0005] On the other hand, hydroxyapatite is a major component of teeth and bones of vertebrates such as humans and is widely used as a medical device and dental material. Also, it has been reported as an example of particles that can be used as a polishing agent for the glossing of painted surfaces of automobiles etc. by utilizing its appropriate hardness (Patent Document 4). However, there is no report on using hydroxyapatite as an abrasive grain for CMP.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a slurry for CMP and a CMP method with reduced residue of abrasive grains after cleaning.

Means for Solving the Problems

[0008] The inventors of the present invention have intensively studied to significantly reduce the residue of abrasive grains for CMP after cleaning. As a result, they came up with the idea of reducing the residue of abrasive grains on the substrate after cleaning by dissolving the abrasive grains during cleaning. However, silica and ceria, which are conventionally used as abrasive grains for CMP, are hardly soluble, and a very strong acid such as hydrofluoric acid is required to dissolve silica, and there is also a problem that high temperature is required in addition to sulfuric acid and hydrogen peroxide to dissolve ceria. As a result of further studies on abrasive grains that can be more easily removed by dissolution, it was found that hydroxyapatite can be dissolved with an acid that is relatively easy to handle, such as citric acid, at room temperature, and when used as an abrasive grain for CMP, it can be easily dissolved and removed by cleaning with an acidic aqueous solution, and the residue of abrasive grains on the substrate can be reduced. The present invention includes, but is not limited to, the following. (1) A slurry for chemical mechanical polishing, comprising abrasive grains, water, and a pH adjuster, wherein the abrasive grains are hydroxyapatite. (2) The slurry for chemical mechanical polishing according to (1), having a pH of 6.0 to 14.0. (3) The slurry for chemical mechanical polishing according to (1) or (2), wherein the average particle size of hydroxyapatite is 1 to 1000 nm. (4) The slurry for chemical mechanical polishing according to (1) or (2), wherein the pH adjuster is potassium hydroxide, calcium hydroxide, or ammonia. (5) The slurry for chemical mechanical polishing according to (1) or (2) for polishing a semiconductor element. (6) Performing chemical mechanical polishing on a substrate using the slurry for chemical mechanical polishing according to (1) or (2), and cleaning the substrate after chemical mechanical polishing, wherein the cleaning includes bringing the substrate into contact with an acid to remove residual hydroxyapatite A chemical mechanical polishing method. (7) The chemical mechanical polishing method according to (6), wherein the acid is an aqueous solution of an organic acid. (8) The chemical mechanical polishing method according to (6), wherein the aqueous solution of an organic acid is an aqueous solution of citric acid.

Advantages of the Invention

[0009] In the present invention, by using hydroxyapatite as the abrasive grains of the CMP slurry, the substrate after polishing is brought into contact with an acid such as citric acid at room temperature to dissolve the hydroxyapatite, making it possible to easily remove the abrasive grains. In physical cleaning using a brush or the like combined with a conventional cleaning liquid, it was sometimes difficult to completely remove the abrasive grains with a small particle size. However, the abrasive grains using hydroxyapatite of the present invention can be easily dissolved in an acid, so even with a small particle size, it can be more reliably removed by cleaning with an acid.

Brief Description of the Drawings

[0010]

Figure 1

Mode for Carrying Out the Invention

[0011] The slurry for chemical mechanical polishing (CMP) of the present invention contains abrasive grains, water, and a pH adjuster, and the abrasive grains are hydroxyapatite. CMP is a method of polishing the surface of a substrate by utilizing the surface chemical action of the abrasive grains and / or the action of the chemical components in the slurry and the mechanical action caused by the contact between the slurry and the substrate.

[0012] The hydroxyapatite (HAp) used as the abrasive grains in the CMP slurry of the present invention is a compound having a basic composition of Ca 10 (PO4)6(OH)2, which is also called calcium phosphate hydroxide. In the present invention, HAp may be derived from natural products or may be synthesized. From the viewpoint of obtaining homogeneous HAp, synthesized ones are preferred. The synthesis method of HAp is not particularly limited, and it may be obtained by any known method such as a dry method, a wet method, a hydrothermal method, or a spray pyrolysis method. As starting materials for HAp synthesis, for example, but not limited to, calcium carbonate, calcium hydroxide, acid Calcium hydroxide, calcium nitrate, calcium organic acid, calcium hydrogen phosphate, phosphoric acid, ammonium hydrogen phosphate, etc. are used.

[0013] HAp is used as an abrasive grain in the CMP slurry of the present invention and exists as particles in the dispersion medium of the slurry. In the present invention, when removing HAp, which is an abrasive grain, by washing after polishing, it can be removed by dissolving it in an acid, so although not limited thereto, it is also possible to use abrasive grains with a small particle size that were difficult to remove by conventional washing methods. The abrasive grains with a small particle size have advantages such as being less likely to scratch the surface of the substrate and being able to more precisely control the surface roughness of the substrate. Therefore, from the viewpoints of polishing performance and ease of removal in washing after polishing, the average particle size of HAp in the slurry is preferably 1000 nm or less, more preferably 500 nm or less, still more preferably 300 nm or less, and even more preferably 150 nm or less. The lower limit of the average particle size is not particularly limited, and it may be 1 nm or more, for example, 5 nm or more, or 10 nm or more. In this specification, as the average particle size of HAp, the average particle size obtained using the cumulant method based on the dynamic light scattering method of JIS Z 8828 is used.

[0014] The concentration of HAp (solid content) in the slurry of the present invention is not particularly limited as long as the amount allows the abrasive grains to flow sufficiently in the slurry. However, from the viewpoint of polishing performance, it is preferably about 1.0 to 35.0% by mass, more preferably 3.0 to 30.0% by mass, still more preferably 7.0 to 25.0% by mass, and even more preferably 10.0 to 20.0% by mass.

[0015] The slurry for CMP of the present invention contains water as a dispersion medium for abrasive grains. Further, the slurry for CMP of the present invention contains a pH adjuster. The pH of the slurry is adjusted within a predetermined range using the pH adjuster. Examples of the pH adjuster include, but are not limited to, inorganic bases such as potassium hydroxide, calcium hydroxide, ammonia, and sodium hydroxide, and organic bases such as tetramethylammonium hydroxide, triethylamine, triethanolamine, monoethanolamine, imidazole, and 2-methylimidazole. Among them, potassium hydroxide or ammonia is preferable.

[0016] From the viewpoints of storage stability of the slurry, polishing rate, and removal performance during cleaning, the pH of the slurry for CMP of the present invention is preferably about 6.0 to 14.0, more preferably 6.0 to 12.0, and even more preferably 6.5 to 11.0. The pH of the slurry can be measured using a commercially available pH meter with the liquid temperature set at 25°C.

[0017] The slurry for CMP may further contain additives other than abrasive grains, water, and the pH adjuster for the purpose of improving the dispersibility of abrasive grains and enhancing storage stability. Examples of such additives include a dispersant, a surfactant, a pH stabilizer, and a solvent other than water.

[0018] Examples of the dispersant include, but are not limited to, sodium tripolyphosphate, sodium polyacrylate, ammonium polyacrylate, sodium n-silicate, sodium pyrophosphate, sodium hexametaphosphate, sodium polyaluminate, sodium tetraborate, sodium triphosphate, sodium polystyrene sulfonate, or a combination thereof.

[0019] Examples of surfactants include, but are not limited to, alkyl sulfate salts, alkyl ether sulfate salts, higher alcohol sulfate salts, alkyl phosphate salts, α-olefin sulfonates, alkyl sulfonates, styrene sulfonates, alkyl naphthalene sulfonates, taurine-based surfactants, sarcosinate-based surfactants, isethionate-based surfactants, N-acyl acidic amino acid-based surfactants, higher fatty acid salts, acylated polypeptides, or combinations thereof.

[0020] Examples of pH stabilizers include various buffer solutions. Further, as solvents other than water, solvents such as ethanol and acetone can be optionally used for the purpose of enhancing the solubility of various additives, but are not limited thereto.

[0021] In the CMP slurry, when using additives other than abrasive grains, water, and pH adjusters, the amount of the additives may be appropriately set according to the purpose and is not particularly limited. For example, it may be about 0.001 to 10.0% by mass, or may be about 0.005 to 5.0% by mass.

[0022] From the viewpoint of the dispersion stability of the abrasive grains, the zeta potential of the CMP slurry of the present invention is preferably -5 mV or less, more preferably -10 mV or less, and even more preferably -20 mV or less. The zeta potential is an index of the charge situation on the particle surface in the slurry. The farther the zeta potential value is from zero, the stronger the repulsive force between the particles becomes, and generally the particles are less likely to aggregate, so the dispersion stability during slurry storage is enhanced. The zeta potential can be measured using a commercially available zeta potential meter that uses an electrophoresis method.

[0023] The CMP slurry of the present invention can be prepared by dispersing HAp, which is an abrasive grain, in water and adding a pH adjuster and various additives as necessary. The mixing order of each component during preparation is not particularly limited. Also, the apparatus used for dispersion is not particularly limited.

[0024] The slurry for CMP of the present invention is a slurry for polishing a substrate using the CMP method. The substrate may be any object to which the CMP method can be applied and is not particularly limited. For example, a substrate having silicon oxide provided on its surface can be mentioned. In addition to silicon oxide, substrates having glass, silicon nitride, polysilicon, aluminum, copper, titanium, titanium nitride, tungsten, tantalum, tantalum nitride, etc. on their surfaces may also be used as polishing targets. Further, the substrate is not limited to these, but may also be a semiconductor element such as a diode, transistor, varistor, thyristor, memory element, logic circuit element, integrated circuit element, photoelectric conversion element, solar cell, etc.

[0025] The CMP method using the slurry for CMP of the present invention is not particularly limited. CMP may be performed using a CMP apparatus. A CMP apparatus generally includes a polishing table that supports a polishing pad having a polishing surface, and a substrate holding member for holding a substrate. The substrate is pressed against the polishing surface by the substrate holding member with a predetermined pressure, and while supplying the slurry for CMP onto the polishing pad, the polishing table and the substrate holding member are relatively moved, whereby the surface of the substrate is polished flat.

[0026] After CMP, a large amount of particles are generated due to polishing debris generated by polishing and abrasive grains in the slurry. In order to remove these foreign substances, subsequent cleaning is performed. Since the CMP slurry of the present invention uses HAp as the abrasive grain, it can be removed by dissolving the abrasive grain in an acid. Therefore, when using the CMP slurry of the present invention, it is preferable to include a step of bringing the substrate into contact with an acid during cleaning. The contact with the acid may be achieved by immersing the substrate in a treatment tank containing the acid, or by spraying the acid onto the substrate. The type of acid should be able to dissolve HAp and preferably should not corrode the substrate. The acid can be either an inorganic acid or an organic acid. However, it is preferable to use an organic acid in the form of an aqueous solution because it has a high HAp removal effect and is easy to handle. Examples of organic acids include, but are not limited to, citric acid, tartaric acid, malic acid, tricarballylic acid, malonic acid, glycolic acid, glutaric acid, succinic acid, lactic acid, acetic acid, propionic acid, n-butyric acid, etc. Among them, citric acid is preferable because of its excellent ability to dissolve HAp. The concentration of the organic acid when using the organic acid aqueous solution for cleaning is not particularly limited. For example, an organic acid aqueous solution with a concentration of 0 .1 to 10.0% by mass, preferably about 0.5 to 5.0% by mass can be used. The contact with the acid is not limited to this, and it may be carried out at room temperature. For example, it may be carried out in an environment of about 10 to 40°C, or in an environment of about 15 to 30°C. After the contact with the acid, it is preferable to wash away the acid sufficiently by washing with pure water or the like. Then, drying can be performed by a normal method.

[0027] In addition to the above contact with the acid, methods usually used for cleaning after CMP may be combined and used. Such cleaning methods include, for example, but are not limited to, SC1 cleaning and SC2 cleaning using a specific cleaning liquid, buff cleaning, contact physical cleaning that physically sweeps out particles using a cleaning member such as a roll brush or a pen brush, non-contact physical cleaning such as two-fluid cleaning and ultrasonic cleaning, pure water cleaning, etc. These can be appropriately combined and used according to the type of the substrate, etc.

Example

[0028] Hereinafter, the present invention will be specifically described using examples, but the present invention is not limited to these aspects. <Preparation of CMP Slurry> Using deionized water, HAp as abrasive grains, a dispersant, and potassium hydroxide as a pH adjuster, four types of slurries with an abrasive grain concentration of 5.0% by mass or 10.0% by mass and a pH of 7.0 or 8.0 were prepared. The average particle size of the abrasive grains in the slurry was about 150 nm in any of the slurries.

[0029] <Polishing of Substrate> As a substrate to be polished, a 30 mm square TEOS wafer was prepared. The substrate was set in a CMP apparatus, and polishing was performed three times for each of the four types of slurries prepared above at a pressure of 3 psi, a pad rotation speed of 100 rpm, and a wafer rotation speed of 101 rpm. After polishing, it was rinsed with pure water and subjected to nitrogen blowing, and then the polishing state of the substrate was confirmed. As a result, it was confirmed that the substrate could be polished in any of the slurries.

[0030] <Cleanability Test> As a cleaning solution, an aqueous citric acid solution (pH 2.17) with a concentration of 1.0% by mass was prepared. The substrate after polishing using the slurry with a HAp concentration of 10.0% by mass and a pH of 8.0 by the above method was immersed in the above aqueous citric acid solution at room temperature for 10 minutes. Also, as a control, a substrate immersed in ultrapure water for 10 minutes after polishing with the same slurry was prepared. After immersion, the substrate was taken out with tweezers, washed with pure water, and then dried by nitrogen blowing. For the dried substrate, elemental analysis of the substrate surface was performed using a fluorescent X-ray analyzer. The results are shown in Table 1. Also, the operation electron microscope (SEM) image of the substrate surface after cleaning is shown in FIG. 1.

[0031]

Table 1

[0032] As shown in Table 1, phosphorus and calcium were not detected after washing with an aqueous citric acid solution. It can be seen that phosphorus and calcium contained in HAp could be removed by washing with an aqueous citric acid solution. Also, from Fig. 1, it can be seen that most of the particles could be removed by washing with an aqueous citric acid solution.

Claims

1. A slurry for chemical mechanical polishing, comprising abrasive grains, water, and a pH adjuster, wherein the abrasive grains are hydroxyapatite.

2. The slurry for chemical mechanical polishing according to Claim 1, wherein the pH is 6.0 to 14.

0.

3. The slurry for chemical mechanical polishing according to Claim 1 or 2, wherein the average particle diameter of the hydroxyapatite is 1 to 1000 nm.

4. The slurry for chemical mechanical polishing according to Claim 1 or 2, wherein the pH adjuster is potassium hydroxide, calcium hydroxide, or ammonia.

5. The slurry for chemical mechanical polishing according to Claim 1 or 2, for polishing a semiconductor element.

6. Performing chemical mechanical polishing on a substrate using the slurry for chemical mechanical polishing according to Claim 1 or 2, and cleaning the substrate after chemical mechanical polishing, wherein the cleaning includes bringing the substrate into contact with an acid to remove residual hydroxyapatite A chemical mechanical polishing method.

7. The chemical mechanical polishing method according to Claim 6, wherein the acid is an aqueous solution of an organic acid.

8. The chemical mechanical polishing method according to Claim 6, wherein the aqueous solution of the organic acid is an aqueous solution of citric acid.

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