JP2007116081A - Ternary composite oxide abrasive and method of polishing substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ternary composite oxide abrasive with which a surface of an SiO<SB>2</SB>insulating film etc., to be polished can be polished fast by a CMP technique without a decrease in mechanical polishing operation nor a polishing flaw caused by an abrasive grain, and to provide a method of polishing a substrate. <P>SOLUTION: The abrasive contains ternary composite oxide particles having a monoclinic brannerite structure and including a CeTi<SB>2</SB>O<SB>6</SB>phase, and the method of polishing the substrate with the abrasive. The substrate is preferably a semiconductor wafer on which a silica film is formed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an abrasive containing ternary composite oxide particles and a method for polishing a substrate.

In recent years, chemical mechanical polishing (CMP) for planarizing an inorganic insulating film layer such as a SiO ₂ insulating film formed by a method such as plasma-CVD or low-pressure CVD in a manufacturing process of a semiconductor device. The method is applied to mass production.
For the CMP abrasive for the SiO ₂ insulating film, a slurry-like silica abrasive and cerium oxide abrasive are generally used.

The SiO ₂ insulating film is used for an interlayer insulating film (ILD: Inter Layer Dielectric) for insulating between wirings and a narrow element isolation (STI: Shallow Trench Isolation) for separating elements. The CMP for ILD is to flatten the unevenness of the insulating film formed on the Al wiring.

On the other hand, in the STI process, a trench is formed in the Si substrate, SiN is formed as a stopper film on the upper portion of the element portion, and SiO ₂ (silica) is embedded in the trench portion, and the SiO ₂ film is removed by CMP. . At that time, it is necessary to have a selective polishing characteristic that only the SiO ₂ film is polished without cutting the stopper film, and it is essential that the recess (trench) SiO ₂ film is not excessively sharpened. In particular, for STI CMP, a cerium oxide-based abrasive in which cerium oxide particles and an additive are combined for the purpose of providing high selectivity between a SiO ₂ film and a SiN film is becoming mainstream. The cerium oxide particles have a lower hardness than silica particles and alumina particles, and therefore are less likely to scratch the polished surface. Further, there is an advantage that the polishing rate is faster than that of the silica abrasive. In recent years, CMP abrasives for semiconductors using high-purity cerium oxide abrasive grains have been used. For example, this technique is disclosed in Patent Document 1. Moreover, the technique which adds an additive to a cerium oxide polishing liquid is disclosed by patent document 2, for example.

Since CMP for STI polishes a portion close to the element, it is particularly necessary to reduce polishing scratches caused by abrasive grains. Since polishing flaws lead to a reduction in device yield, further reduction of polishing flaws is demanded as design rules are reduced.
Japanese Patent Laid-Open No. 10-106994 JP-A-8-22970

The development of abrasive grains for cerium oxide-based abrasives is being promoted so as to further reduce the polishing scratches introduced by the abrasive grains on the SiO ₂ insulating film surface and maintain the conventional polishing rate. The most effective method is micronization, but in this case, the mechanical polishing action decreases as the size is reduced, which causes a new problem of increased CMP processing time.

The present invention provides a polishing agent and a substrate polishing method capable of polishing a surface to be polished such as an SiO ₂ insulating film at high speed without damage.

The present invention relates to an abrasive containing ternary composite oxide particles containing a CeTi ₂ O ₆ phase having a monoclinic blannelite structure (Brannerite structure).
The present invention also relates to a method for polishing a substrate, wherein the substrate is polished with the complex oxide abrasive.
Furthermore, the present invention relates to the method for polishing a substrate, wherein the substrate is a semiconductor wafer on which a silica film is formed.
Hereinafter, the Brunelite structure represents a Brannerite structure.

According to the ternary composite oxide abrasive of the present invention, it is possible to increase the number of abrasive grains per mass while maintaining the chemical activity of cerium oxide. As a result, the surface to be polished such as the SiO ₂ insulating film can be polished at high speed without damage, which is extremely suitable industrially.

The ternary composite oxide abrasive of the present invention is a ternary composite oxide particle containing a CeTi ₂ O ₆ phase having a monoclinic blannelite structure (hereinafter also referred to as composite oxide particle or particle). .)including. The CeTi ₂ O ₆ phase has a monoclinic blannelite structure in Journal of Alloys and Compounds, 376 (2004) p. 262-267 and the like.

The phase phase diagram of the ternary system of Ce—Ti—O includes Ce ₂ Ti0 ₅ , Ce ₂ Ti ₂ O ₇ , Ce ₄ Ti ₉ O ₂₄ , CeTiO ₄ , Ce ₂ Ti ₃ O ₉ and CeTi ₂ O ₆ . Although there are six different phases, CeTi ₂ O ₆ focused on in the present invention is said to have Ce ⁴⁺ like CeO ₂ , and its crystal structure is Journal of Solid State Chemistry, 110 (1994) p. It is clarified in 364-369.

The density of CeTi ₂ O ₆ is 4.96 g / cc, which is as low as 70% of 7.2 g / cc of cerium oxide, so the number of particles acting as abrasives per mass is 1.4 times. Become.

The CeTi ₂ O ₆ phase can be a single phase when _x of the Ce _1-x Ti _x O ₂ composition is around 0.3. When the value of x is 0.2, it is a mixed phase of CeTi ₂ O ₆ phase and TiO ₂ (rutile phase), and when it is 0.4, it becomes a cerium oxide phase. In order to obtain a CeTi ₂ O ₆ phase at a synthesis temperature of 600 ° C. or more and 950 ° C. or less, the value of x is preferably 0.15 or more and 0.35 or less.

The method of synthesizing the ternary composite oxide particles is to mix and mix cerium oxide powder and titanium oxide powder so that the value of x in the Ce _1-x Ti _x O ₂ composition is 0.15 or more and 0.35 or less. And a synthesis method obtained by baking at 600 ° C. or more and 950 ° C. or less.
Moreover, a precursor can be obtained by mixing a cerium salt and an aqueous titanium salt solution, neutralizing and precipitating with an alkaline solution such as an aqueous ammonia solution and drying it. This precursor can also be obtained by firing at 600 ° C. or higher and 950 ° C. or lower.

  Furthermore, it can also be obtained by synthesizing a precursor by the Pechini method and firing the precursor. For example, M.M. Kakihana; Journal of Sol-Gel Science and Technology, 6 (1996) p. 7-55.

  As a method for preparing the precursor, for example, cerium nitrate hexahydrate, titanium tetraisopropoxide and citric acid, ethylene glycol and methanol are mixed and stirred at a predetermined ratio, and heated at 100 ° C. for 15 hours for esterification. do. Then, it concentrates at 200 degreeC until it becomes a polymer form, and carbonizes at 450 degreeC after that, and a precursor is obtained. Any of the precursor firing methods is preferably performed at 600 ° C. to 950 ° C. in air.

（例えば、Ｉｎｔｅｒｎａｔｉｎａｌ Ｔａｂｌｅｓ ｆｏｒ Ｃｒｙｓｔａｌｌｏｇｒａｐｈｙ Ｖｏｌ.Ａ， Ｔｈ． Ｈａｈｎ， 第５版参照）で、格子定数がａ＝９．８２Å、ｂ＝３．７５Å、ｃ＝６．８８Å、α＝９０．０°、β＝１１８．９７８°、γ＝９０．０°であることが知られている。 The crystal structure analysis of the obtained particles is preferably performed by a powder X-ray Rietveld method. CeTi ₂ O ₆ phase with monoclinic blannelite structure has space group

(See, for example, International Tables for Crystallography Vol. A, Th. Hahn, 5th edition), and lattice constants a = 9.82９, b = 3.75Å, c = 6.88Å, α = 90.0 °, It is known that β = 118.978 ° and γ = 90.0 °.

The atomic position can be determined with reference to a ThTi ₂ O ₆ phase having a similar structure (see Acta. Cryst. (1966) 21, p. 974).

  In addition to phase identification from the analysis method, the crystallite size can be estimated. That is, the crystallite size parameter x can be obtained from the analysis, and the crystallite size is estimated by substituting x into the following formula (1).

(Equation 2)
Crystallite size (nm)
= {0.15418 (nm) · 180 (degree) · K} / {π · x} (1)
K is a constant and generally 0.9 is used. When polishing a SiO ₂ insulating film formed by TEOS-CVD or the like, if the crystallite size is too large as in the case of cerium oxide abrasive grains, it will cause polishing scratches, and if it is too small, an appropriate polishing rate can be obtained. Absent. Therefore, an appropriate crystallite size is preferably 50 nm or more and 200 nm or less.

  Further, a parameter value y representing crystal distortion can be obtained from Rietveld analysis, and this distortion also affects the polishing characteristics. The y value is preferably from 0.01 to 0.3. It shows that distortion is so small that y value is small. If it is larger than 0.3, the strain is large and an appropriate polishing rate tends not to be obtained.

  Since it is also used for semiconductor wafer polishing, the alkali metal and halogen content of the ternary composite oxide particles is preferably suppressed to 1 ppm or less. Further, the ternary composite oxide particles preferably have high purity such that Na, K, Si, Mg, Ca, Zr, Ti, Ni, Cr and Fe are each 1 ppm or less and Al is 10 ppm or less.

  The ternary composite oxide particles obtained by firing can be agglomerated by dry pulverization such as a jet mill or wet pulverization such as a liquid jet mill or planetary bead mill. The jet mill is described, for example, in Chemical Engineering Papers Vol. 6 No. 5 (1980) pp. 527-532. It is preferable that the pulverization is performed up to crystallite size particles so that there is no pulverization residue.

  The abrasive of the present invention is obtained from an aqueous solution containing the ternary composite oxide particles produced by the above method, or the particles recovered from this aqueous solution are dispersed in, for example, water as a main dispersion medium. Obtained by. Furthermore, if necessary, a composition comprising a dispersant or the like may be added and dispersed. Although there is no restriction | limiting in the density | concentration of particle | grains here, the range of 0.1-10 mass% is preferable from the ease of handling of a slurry-like abrasive | polishing agent.

  In addition, the dispersant does not contain metal ions, and includes acrylic acid polymer and ammonium salt thereof, methacrylic acid polymer and ammonium salt thereof, water-soluble organic polymers such as polyvinyl alcohol, ammonium lauryl sulfate, polyoxy Water-soluble anionic surfactants such as ethylene lauryl ether ammonium sulfate, water-soluble nonionic surfactants such as polyoxyethylene lauryl ether and polyethylene glycol monostearate, and water-soluble amines such as monoethanolamine and diethanolamine Can be mentioned. Polyacrylic acid ammonium salts, particularly polyacrylic acid ammonium salts having a weight average molecular weight of 5,000 to 20,000 are preferred.

  The amount of these dispersants added is preferably in the range of 0.01 to 5 parts by mass with respect to 100 parts by mass of the composite oxide particles from the viewpoint of the dispersibility of particles in the slurry abrasive and the anti-settling property. In order to enhance the dispersion effect, it is preferable to place the particles in the disperser simultaneously with the dispersion process.

  As a method of dispersing the composite oxide particles in water, a homogenizer, an ultrasonic disperser, a ball mill, or the like can be used in addition to a dispersion treatment using a normal stirrer. In particular, in order to disperse the composite oxide particles in the present invention as fine particles of 1000 nm or less, it is preferable to use a wet disperser such as a ball mill, a vibration ball mill, a planetary ball mill, or a medium stirring mill.

Moreover, when it is desired to increase the alkalinity of the abrasive, an alkaline substance containing no metal ions such as aqueous ammonia can be added during or after the dispersion treatment.
In addition, nitric acid can be added to increase the acidity of the abrasive.

Large particles of composite oxide particles dispersed in the abrasive of the present invention are related to abrasive scratches. The particle diameter of the particles in the abrasive is measured by a photon correlation method (for example, product name Zeta Sizer 3000H manufactured by Malvern Instruments). It is preferable that the particle size of D99% is 1000 nm or less. Here, D99% means the particle diameter when the volume ratio of the particles is accumulated from the finer particle diameter distribution in the volume particle diameter distribution and reaches 99%.
The abrasive of the present invention may further contain additives such as a water-soluble polymer, a solvent other than water, and a colorant as long as the action of the abrasive is not impaired.

The substrate polishing method of the present invention is characterized in that the substrate is polished using the abrasive of the present invention. As the substrate, a semiconductor substrate, that is, a semiconductor substrate on which a circuit element and a wiring pattern are formed, a substrate on which a SiO ₂ insulating film layer is formed on a semiconductor substrate such as a semiconductor substrate on which a circuit element is formed can be used. In particular, the substrate is preferably a semiconductor wafer on which an SiO ₂ film is formed. Hereinafter, such a semiconductor substrate will be described as an example. By polishing the SiO ₂ insulating film layer formed on the substrate with the cerium oxide abrasive, unevenness on the surface of the SiO ₂ insulating film layer can be eliminated and the entire surface of the semiconductor substrate can be made smooth. Here, as an apparatus for polishing, a general polishing having a holder for holding a semiconductor substrate and a polishing surface plate to which a polishing cloth (pad) can be attached and a motor or the like whose rotation speed can be changed is attached. The device can be used.

As an abrasive cloth, a general nonwoven fabric, a polyurethane foam, a porous fluororesin, etc. can be used, and there is no restriction | limiting in particular.
Further, it is preferable that the polishing cloth is subjected to groove processing so that an abrasive is collected. The polishing conditions are not limited, but the rotation speed of the polishing surface plate is preferably low rotation of 100 min ⁻¹ or less so that the semiconductor substrate does not pop out, and the pressure (working load) applied to the semiconductor substrate does not cause scratches after polishing. Thus, 1 kg / cm ² or less is preferable. During polishing, an abrasive is continuously supplied to the polishing cloth with a pump or the like. Although there is no restriction | limiting in this supply amount, It is preferable that the surface of polishing cloth is always covered with the abrasive | polishing agent.

The semiconductor substrate after completion of polishing is preferably washed in running water and then dried after removing water droplets adhering to the semiconductor substrate using a spin dryer or the like. On this way, the SiO ₂ insulating film layer which is flattened, forming an aluminum wiring of the second layer, after forming the SiO ₂ insulating film again by the above method on the inter-wiring and the wiring, the composite oxide By polishing with an object polishing agent, unevenness on the surface of the insulating film is eliminated, and the entire surface of the semiconductor substrate is made smooth. By repeating this process a predetermined number of times, a desired number of semiconductor layers are manufactured.

The composite oxide abrasive and polishing method of the present invention are not limited to SiO ₂ insulating film formed on a semiconductor substrate, but also inorganic such as SiO ₂ insulating film formed on a wiring board having predetermined wiring, glass, silicon nitride, etc. Optical glass such as insulating films, photomasks, lenses and prisms, inorganic conductive films such as ITO, optical integrated circuits / optical switching elements / waveguides composed of glass and crystalline materials, end faces of optical fibers, scintillators, etc. It is used for polishing optical single crystals, solid state laser single crystals, blue laser LED sapphire substrates, semiconductor single crystals such as SiC, GaP, and GaAs, glass substrates for magnetic disks, magnetic heads, and the like.

Examples of a method for manufacturing an inorganic insulating film in which the composite oxide abrasive and the polishing method of the present invention are used include a low pressure CVD method and a plasma CVD method. In the formation of the SiO ₂ insulating film by the low pressure CVD method, monosilane: SiH _{4 is} used as the Si source, and oxygen: O ₂ is used as the oxygen source. It can be obtained by performing this SiH ₄ —O ₂ -based oxidation reaction at a low temperature of about 400 ° C. or less. When doping phosphorus: P in order to achieve surface flattening by high-temperature reflow, it is preferable to use a SiH ₄ —O ₂ —PH ₃ reaction gas.

The plasma CVD method has an advantage that a chemical reaction requiring a high temperature can be performed at a low temperature under normal thermal equilibrium. There are two plasma generation methods, capacitive coupling type and inductive coupling type. The reaction as a gas, SiH ₄ as an Si source, an oxygen source as _{N 2} O was used was _SiH 4 -N ₂ O-based gas and _{TEOS-O 2} based gas using tetraethoxysilane (TEOS) in an Si source (TEOS- Plasma CVD method). The substrate temperature is preferably 250 to 400 ° C., and the reaction pressure is preferably 67 to 400 Pa. Thus, the SiO ₂ insulating film of the present invention is phosphorus, elemental boron, and the like de - may be up.

Hereinafter, the present invention will be described more specifically with reference to examples.
Example 1
(Synthesis of ternary composite oxide particles containing CeTi ₂ O ₆ phase)
200 ml of methanol, 200 ml of ethylene glycol, 153 g of anhydrous citric acid, 63 g of cerium nitrate hexahydrate and 96.2 g of titanium tetraisopropoxide were mixed and stirred in a beaker and heat-treated at 100 ° C. for 15 hours for esterification. It was. Thereafter, concentrated at about 200 ° C. until a polymeric, then 6 hours at 450 ° C., precursor is thermally decomposed becomes _Ce 0.3 _Ti 0.7 _{O 2} composition was prepared 52 g. The precursor was calcined at 850 ° C. for 2 hours to obtain ternary composite oxide particles containing a CeTi ₂ O ₆ phase.

格子定数がａ＝９．８２７（１）Å、ｂ＝３．７５１（３）Å、ｃ＝６．８８３（１）Å、α＝９０°、β＝１１８．９８（１）°、γ＝９０°であった。 XRD measurement was performed on the obtained composite oxide particles, and X-ray Rietveld analysis was performed using the data. For the Rietveld analysis, the Rietveld analysis program RIETAN-2000 was used.

The lattice constants are a = 9.827 (1) Å, b = 3.751 (3) Å, c = 6.883 (1) Å, α = 90 °, β = 118.98 (1) °, γ = It was 90 °.

  The atomic positions are Ce (0.0 0.0 0.0), Ti (0.883 (1) 0.0 0.303 (1)), and O1 (0.978 (2). 0 0.303 (1)), O2 is (0.654 (1) 0.0 0.104 (3)) and O3 is (0.276 (2) 0.0 0.40182)). confirmed. The value of the crystallite parameter x was 126 nm from the above formula (1) for obtaining the crystallite size at 0.063. Moreover, the value of the crystallite strain parameter y was 0.10.

(Preparation of composite oxide abrasive)
50 g of the composite oxide particles produced above, 2.5 g of ammonium polyacrylate aqueous solution (40% by mass) and 447.5 g of deionized water were mixed, and pulverized and dispersed in a planetary bead mill for 30 minutes to obtain a slurry. Non-alkaline glass beads with a diameter of 0.8 mm were used as the bead media. The obtained slurry was filtered with a 1 micron filter, and deionized water was further added to obtain a slurry-like composite oxide abrasive having a solid content of 1% by mass. The pH of the abrasive was 8.0.

  In order to examine the particle size distribution of the slurry in the slurry-like abrasive by the photon correlation method, the particle size distribution was measured using a particle size distribution measuring apparatus Zeta Sizer 3000H manufactured by Malvern Instruments. The median was 230 nm and the maximum particle size was 980 nm. Further, in order to investigate the dispersibility of the abrasive and the charge of the particles in the abrasive, the zeta potential of the abrasive was examined by the particle size distribution measuring apparatus. It was negatively charged and confirmed to have a large absolute value of -78 mV and good dispersibility.

(Polishing the insulating film layer)
A SiO ₂ insulating film was formed on the Si wafer surface by TEOS-plasma CVD. Set this Si wafer in the holder of the polishing device to which the suction pad for attaching the holding substrate is pasted, and place the insulating film side down on the polishing surface plate on which the porous urethane resin polishing pad is pasted In addition, the processing load was set to 30 kPa. While the above polishing agent (solid content: 1% by mass) is dropped onto the polishing surface plate at a rate of 150 cc / min, the polishing surface plate is rotated in the same direction at 50 min ⁻¹ and the wafer-mounted holder is rotated in the same direction at 50 min ^−1. The insulating film was polished for 1 minute.

  After polishing, the wafer was removed from the holder, washed thoroughly with running water, and further washed with an ultrasonic cleaner for 20 minutes. After washing, water droplets were removed from the wafer with a spin dryer, and the wafer was dried with a dryer at 120 ° C. for 10 minutes. As a result of measuring the film thickness change before and after polishing using an optical interference type film thickness measuring apparatus, each of the insulating films having a thickness of 352 nm (polishing rate: 352 nm / min) was shaved by this polishing, and the thickness was uniform over the entire surface of the wafer. I found out that Further, when the surface of the insulating film was observed using an optical microscope, no clear scratch was found.

Example 2
(Synthesis of ternary composite oxide particles containing CeTi ₂ O ₆ phase)
154 g of aqueous cerium ammonium nitrate solution (50%) and 260 g of aqueous titanium sulfate solution (30%) were mixed and stirred, and 25% aqueous ammonia solution was added to neutralize and precipitate. The point at which the pH of the suspension reached 10.0 was taken as the end point, and then solid-liquid separation was performed with a centrifuge (3000 min ⁻¹ , 15 minutes). The solid content was dried at 110 ° C. for 3 hours, pulverized in a mortar, and then fired at 850 ° C. for 2 hours to obtain about 50 g of composite oxide particles.

格子定数がａ＝９．８２３（１）Å、ｂ＝３．７５７（３）Å、ｃ＝６．８８８（１）Å、α＝９０°、β＝１１８．９８（１）°、γ＝９０°であった。 The obtained composite oxide particles were subjected to XRD measurement and X-ray Rietveld analysis in the same manner as in Example 1.

Lattice constants are a = 9.823 (1) Å, b = 3.757 (3) Å, c = 6.888 (1) Å, α = 90 °, β = 118.98 (1) °, γ = It was 90 °.

  The atomic positions are Ce (0.0 0.0 0.0), Ti (0.873 (1) 0.0 0.313 (1)), and O1 (0.971 (2). 0 0.300 (1)), O2 is (0.634 (1) 0.0 0.098 (3)) and O3 is (0.271 (2) 0.0 0.3980 (2)). It was confirmed. The value of the crystallite parameter x was 109 nm from the above formula (1) for obtaining the crystallite size at 0.073. Moreover, the value of the crystallite strain parameter y was 0.10.

(Preparation of composite oxide abrasive)
A slurry-like composite oxide abrasive having a solid content of 1% by mass was obtained in the same manner as in Example 1 except that 50 g of the prepared composite oxide particles were used. The pH of the abrasive was 8.1.

  The particle size distribution and zeta potential of the particles in the abrasive were measured in the same manner as in Example 1. The particle size distribution had a median value of 210 nm and a maximum particle size of 980 nm. It was confirmed that the zeta potential was negatively charged, had an absolute value of -78 mV and a large dispersibility.

(Polishing the insulating film layer)
The insulating film was polished for 1 minute under the same conditions as in Example 1 except that the abrasive prepared above (solid content: 1% by mass) was used.

After polishing, the film was washed and dried in the same manner as in Example 1. As a result of measuring the change in film thickness before and after polishing, the insulating film of 332 nm (polishing rate: 332 nm / min) was cut by this polishing, and the entire surface of the wafer was removed. It was found that the thickness was uniform.
Further, when the surface of the insulating film was observed using an optical microscope, no clear scratch was found.

Comparative Example 1
(Method for producing cerium oxide particles)
200 ml of methanol, 200 ml of ethylene glycol, 153 g of citric acid and 177 g of cerium nitrate hexahydrate were mixed and stirred in a beaker and subjected to heat treatment for 15 hours at 100 ° C. for esterification. Then, it concentrated at about 200 degreeC until it became polymer form, and it thermally decomposed at 450 degreeC for 6 hours after that, and the precursor of cerium oxide was produced. Then, it baked at 850 degreeC and obtained 70g of cerium oxides.

The obtained cerium oxide particles were subjected to XRD measurement and X-ray Rietveld analysis in the same manner as in Example 1. Rietveld analysis confirmed that it was cubic cerium oxide having a CaF ₂ type structure. The value of the crystallite parameter x was 120 nm from the above formula (1) for obtaining the crystallite size at 0.060. Moreover, the value of the crystallite strain parameter y was 0.005.

(Production method of cerium oxide abrasive)
A slurry-like abrasive having a solid content of 1% by mass was obtained in the same manner as in Example 1 except that 50 g of the particles prepared above were used. The pH of the abrasive was 8.5.

  The particle size distribution and zeta potential of the particles in the slurry abrasive were measured in the same manner as in Example 1. The median value of the particle size distribution was 199 nm, and the maximum particle size was 980 nm. It was confirmed that the zeta potential was negatively charged and had a large absolute value of -65 mV and good dispersibility.

(Polishing the insulating film layer)
The insulating film was polished for 1 minute under the same conditions as in Example 1 except that the above abrasive (solid content: 1% by mass) was used.

After polishing, the substrate was washed and dried in the same manner as in Example 1. As a result of measuring the change in film thickness before and after polishing, the insulating film having a thickness of 293 nm (polishing rate: 293 nm / min) was removed by this polishing, and a CeTi ₂ O ₆ phase was obtained. It was about 84% of the speed of the composite oxide polishing agent containing. It was found that the thickness was uniform over the entire wafer surface. Further, when the surface of the insulating film was observed using an optical microscope, no clear scratch was found.

Comparative Example 2
(Production method of titanium oxide abrasive)
Titanium hydroxide was prepared by adding ammonium aqueous solution (25%) to titanium sulfate aqueous solution (30%) and neutralizing and precipitating. After solid-liquid separation by this titanium hydroxide centrifugal separation, it was fired at 850 ° C. for 2 hours to produce titanium oxide particles. An abrasive having a solid content of 1% by mass was obtained in the same manner as in Example 1 except that 50 g of the obtained titanium oxide particles were used. The abrasive pH was 7.9.

  The particle size distribution and zeta potential of the abrasive particles were measured in the same manner as in Example 1. The median value of the particle size distribution was 280 nm, and the maximum particle size was 980 nm. It was confirmed that the zeta potential was negatively charged and had a large absolute value of −60 mV and good dispersibility.

(Polishing the insulating film layer)
The insulating film was polished for 1 minute under the same conditions as in Example 1 except that the above abrasive (solid content: 1% by mass) was used.

  After polishing, the film was washed and dried in the same manner as in Example 1, and the change in film thickness before and after polishing was measured. As a result, only 15 nm (polishing rate: 15 nm / min) was removed by this polishing.

Comparative Example 3
(Method for producing a mixed abrasive of cerium oxide and titanium oxide particles)
The two types of abrasives produced in Comparative Examples 1 and 2 were mixed so as to be 48 parts by mass and 52 parts by mass, and the composition of Ce _0.3 Ti _0.7 O ₂ to become a CeTi ₂ O ₆ phase as a composition. did. When this mixed abrasive was used to polish the insulating film layer in the same manner as in the above-described Examples and Comparative Examples, only 101 nm / min was removed.

Claims (3)

A ternary composite oxide abrasive comprising ternary composite oxide particles containing a CeTi ₂ O ₆ phase having a monoclinic blannelite structure.   A method for polishing a substrate, comprising polishing the substrate with the abrasive according to claim 1.   The method for polishing a substrate according to claim 2, wherein the substrate is a semiconductor wafer on which a silica film is formed.