JP2005012231A - Ceric dioxide abrasive and substrate-polishing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ceric dioxide abrasive that polishes the surface of an object to be polished, such as an SiO<SB>2</SB>insulating film, without faults. <P>SOLUTION: An Si wafer, to which an SiO<SB>2</SB>insulating film produced by the TEOS-CVD method is formed, is polished using slurry abrasive, onto which cerium dioxide particles whose diameter aspect ratio is equal to or larger than 1 and equal to or smaller than 2, and whose primary particles showing contours not including corners smaller than 120<SP>o</SP>C are equal to or higher than 90% of the total, are distributed over a medium by means of the observation of a transmission electron microscope. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides a cerium oxide abrasive and a method for polishing a substrate.

Conventionally, colloidal silica-based abrasives have been used as chemical mechanical abrasives for planarizing inorganic insulating film layers such as SiO ₂ insulating films formed by methods such as plasma-CVD and low-pressure CVD in the manufacturing process of semiconductor devices. Generally considered. Colloidal silica-based abrasives are produced by growing silica particles by a method such as thermal decomposition of tetrachlorosilicic acid and adjusting the pH with an alkaline solution containing no alkali metal such as ammonia. However, such an abrasive does not have a sufficient polishing rate for the inorganic insulating film, and there is a technical problem of a low polishing rate for practical use.

  On the other hand, a cerium oxide abrasive is used for photomask glass surface polishing. Cerium oxide particles have a lower hardness than silica particles and alumina particles, and are therefore useful for finishing mirror polishing because they do not easily scratch the polished surface. Moreover, cerium oxide has a chemically active property as known as a strong oxidizing agent. Taking advantage of this advantage, application to a chemical mechanical polishing agent for insulating films is useful. However, if the cerium oxide abrasive for polishing a glass surface for a photomask is applied to an inorganic insulating film as it is, polishing scratches that can be visually observed will enter the insulating film surface.

The present invention provides a cerium oxide abrasive capable of polishing a surface to be polished such as a SiO ₂ insulating film without scratches and a method for polishing a substrate.

  The cerium oxide abrasive of the present invention has a particle diameter aspect ratio of 1 or more and 2 or less as observed with a transmission electron microscope, and 90% or more of primary particles exhibiting a contour that does not include corners smaller than 120 ° C. And a slurry in which cerium oxide particles are dispersed in a medium.

  The substrate polishing method of the present invention is characterized in that a predetermined substrate is polished with the cerium oxide abrasive.

The present invention relates to a cerium oxide particle in which the aspect ratio of the particle diameter is 1 or more and 2 or less and the primary particle showing the outline not including the corner portion smaller than 120 ° C. is 90% or more of the total number as observed with a transmission electron microscope. By using this, it has been found that the surface to be polished such as the SiO ₂ insulating film can be polished without scratching.

The polishing agent of the present invention makes it possible to polish a surface to be polished such as a SiO ₂ insulating film without scratching.

In general, cerium oxide is obtained by firing a cerium compound such as carbonate, sulfate, or oxalate. The SiO ₂ insulating film formed by TEOS-CVD or the like has a larger primary particle diameter and a smaller crystal distortion, that is, a higher crystallinity allows higher-speed polishing, but there is a tendency for polishing flaws to occur. . Therefore, the cerium oxide particles used in the present invention are produced without increasing crystallinity. Moreover, since it uses for semiconductor chip grinding | polishing, it is preferable to suppress the content rate of an alkali metal and halogens to 1 ppm or less.

  In the present invention, a firing method can be used as a method for producing cerium oxide particles. Since the oxidation temperature of the cerium compound is 300 ° C, the firing temperature is preferably 350 ° C or higher and 700 ° C or lower.

  The cerium oxide slurry in the present invention is obtained by dispersing an aqueous solution containing cerium oxide particles produced by the above method, or cerium oxide particles recovered from this aqueous solution, water and, if necessary, a composition comprising a dispersant. It is done. Here, although there is no restriction | limiting in the density | concentration of a cerium oxide particle, The range of 0.5 to 10 weight% is preferable from the ease of handling of suspension. The dispersant does not contain metal ions, and includes acrylic acid polymer and its ammonium salt, methacrylic acid polymer and its ammonium salt, water-soluble organic polymers such as polyvinyl alcohol, ammonium lauryl sulfate, and polyoxyethylene. Water-soluble anionic surfactants such as ammonium lauryl ether sulfate, water-soluble nonionic surfactants such as polyoxyethylene lauryl ether and polyethylene glycol monostearate, and water-soluble amines such as monoethanolamine and diethanolamine It is done. The amount of these dispersants added is preferably in the range of 0.01 to 5 parts by weight with respect to 100 parts by weight of the cerium oxide particles in view of the dispersibility of the particles in the slurry and the anti-settling property. In order to achieve this, it is preferable to place the particles in the disperser simultaneously with the particles during the dispersion treatment.

  As a method for dispersing these cerium 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 cerium oxide particles as fine particles having a size of 1 μm 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. When it is desired to increase the alkalinity of the slurry, an alkaline substance that does not contain metal ions such as aqueous ammonia can be added during or after the dispersion treatment.

  The cerium oxide abrasive of the present invention may use the above slurry as it is, but an additive such as N, N-diethylethanolamine, N, N-dimethylethanolamine, aminoethylethanolamine is added. Thus, an abrasive can be obtained.

Examples of a method for manufacturing an inorganic insulating film in which the cerium oxide abrasive of the present invention is used include a constant pressure CVD method and a plasma CVD method. In the formation of the SiO ₂ insulating film by the constant 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 -based reactive 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, elements such as phosphorus and boron may be doped in the SiO ₂ insulating film of the present invention.

As the predetermined substrate, a semiconductor substrate, that is, a semiconductor substrate in which a circuit element and a wiring pattern are formed, or a substrate in which a SiO ₂ insulating film layer is formed on a semiconductor substrate such as a semiconductor substrate in which a circuit element is formed is used. it can. By polishing the SiO ₂ insulating film layer formed on such a semiconductor substrate with the cerium oxide abrasive, unevenness on the surface of the SiO ₂ insulating film layer is eliminated and a smooth surface is formed over the entire surface of the semiconductor substrate. . Here, as a polishing apparatus, a general polishing apparatus having a surface plate with a holder for holding a semiconductor substrate and a polishing cloth (pad) attached (a motor etc. capable of changing the number of rotations) is used. it can. 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 slurry is accumulated. The polishing conditions are not limited, but the rotation speed of the surface plate is preferably low rotation of 100 rpm or less so that the semiconductor does not jump out, and the pressure applied to the semiconductor substrate is 1 kg / cm ² or less so that no scratches are generated after polishing. preferable. During polishing, slurry 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 slurry.

The semiconductor substrate after the 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. A second-layer aluminum wiring is formed on the thus planarized SiO ₂ insulating film layer, and the SiO ₂ insulating film is formed again between the wirings and on the wiring by the above method, and then the cerium oxide. By polishing with an abrasive, unevenness on the surface of the insulating film is eliminated, and a smooth surface is formed over the entire surface of the semiconductor substrate. By repeating this process a predetermined number of times, a desired number of semiconductor layers are manufactured.

Cerium oxide abrasive of the present invention is not only SiO ₂ insulating film formed on a semiconductor substrate, SiO ₂ insulating film formed on the wiring board having a predetermined wiring, glass, inorganic insulating films such as silicon nitride, Photo Optical glass for masks, lenses, prisms, etc., optical conductive circuits such as ITO, inorganic conductive films such as ITO, glass and crystalline materials, optical switching elements, optical waveguides, end faces of optical fibers, scintillators, etc. It is used to polish single crystals, solid laser single crystals, LED sapphire substrates for blue lasers, semiconductor single crystals such as SiC, GaP, and GaAS, glass substrates for magnetic disks, magnetic heads, and the like. The predetermined substrate in the present invention as described above, SiO ₂ semiconductor substrate on which an insulating film is formed, SiO ₂ insulating film is formed wiring board, glass, inorganic insulating films such as silicon nitride, photomask lenses and prisms Optical glass such as ITO, inorganic conductive films such as ITO, optical integrated circuits / optical switching elements / waveguides composed of glass and crystalline materials, optical fiber end faces, optical single crystals such as scintillators, solid layers, etc. -The single crystal, LED sapphire substrate for blue laser, semiconductor single crystal such as SiC, GaP, GaAS, etc., glass substrate for magnetic disk, magnetic head, etc.

Example (Preparation of cerium oxide particles: Part 1)
600 g of cerium carbonate hydrate (99.9%) was placed in a platinum container and baked in air at 400 ° C. for 2 hours to obtain a yellowish white powder. When this powder was phase-identified by X-ray diffraction, it was confirmed to be cerium oxide. Furthermore, it was confirmed by observation with a transmission electron microscope that the primary particle diameter is a spherical primary particle having an aspect ratio of 1 or more and 2 or less and showing a contour that does not include a corner portion smaller than 120 ° C. . Further, it was confirmed by observation with a transmission electron microscope that the primary particle diameter was 5 nm or more and 10 nm or less.

(Preparation of cerium oxide particles: Part 2)
600 g of cerium carbonate hydrate (99.9%) was placed in a platinum container and calcined in air at 600 ° C. for 2 hours to obtain a yellowish white powder. When this powder was phase-identified by X-ray diffraction, it was confirmed to be cerium oxide. Furthermore, it was confirmed by observation with a transmission electron microscope that the primary particle diameter is a spherical primary particle having an aspect ratio of 1 or more and 2 or less and showing a contour that does not include a corner portion smaller than 120 ° C. . Further, it was confirmed by observation with a transmission electron microscope that the primary particle diameter was more than 10 nm and less than 100 nm.

(Preparation of cerium oxide slurry)
Disperse 80g of the above two kinds of cerium oxide powder in 800g of deionized water, add 8g of polyacrylic acid ammonium salt to this, and then disperse for 30 minutes at 2300rpm using planetary ball mill (P-5 type, manufactured by Fritche). By performing the treatment, a milky white cerium oxide slurry was obtained. The slurry pH was 9.7 and 9.1, respectively. When the particle size distribution of the slurry was examined (manufactured by Master Sizer), it was found that the average particle diameter was as small as 300 nm and 260 nm, respectively, and the half-value width was 300 nm and the distribution was relatively narrow.

(Polishing the insulating film layer)
A surface plate on which a Si wafer on which a SiO ₂ insulating film produced by TEOS-plasma CVD method is formed is set in a holder on which a holding pad for attaching a substrate to be held is attached, and a polishing pad made of porous urethane resin is attached. A holder was placed thereon with the insulating film face down, and a weight was placed so that the processing load was 160 g / cm ² . While the two kinds of cerium oxide slurries (solid content: 2.5 wt.%) Were dropped on the surface plate at a rate of 35 cc / min, the surface plate was rotated at 30 rpm for 3 minutes to polish the insulating film. 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 device, the slurry of Part 1 of the slurry preparation was scraped by 200 nm by this polishing, and the part of the slurry of 240 nm was the insulating film of 240 nm. Was shaved. After polishing each slurry, it was found that the thickness was uniform over the entire wafer surface. In addition, no scratch was found on the surface of the insulating film by visual observation.

For Si wafer having formed an SiO ₂ insulating film was prepared in the same manner as in Comparative Example Example in TEOS-CVD method, it was polished using a commercially available silica slurry (manufactured by Cabot Corporation, trade name SS225). This commercially available slurry has a pH of 10.3 and contains 12.5 wt% of SiO ₂ particles. The polishing conditions are the same as in the example. As a result, scratches due to polishing were not observed, and polishing was performed uniformly, but only 75 nm of the insulating film layer was removed by polishing for 3 minutes.

Claims (7)

  Dispersed in the medium cerium oxide particles having a particle diameter aspect ratio of 1 or more and 2 or less and 90% or more of primary particles showing an outline not including corners smaller than 120 ° C. as observed by a transmission electron microscope The cerium oxide abrasive | polishing agent containing the made slurry.   The cerium oxide abrasive according to claim 1, wherein the slurry contains a dispersant.   The cerium oxide abrasive according to claim 1 or 2, wherein the medium is water.   The cerium oxide abrasive according to claim 2, wherein the dispersant is at least one selected from a water-soluble organic polymer, a water-soluble anionic surfactant, a water-soluble nonionic surfactant and a water-soluble amine.   The cerium oxide abrasive according to any one of claims 1 to 4, wherein the slurry has a pH of 7 or more and 10 or less.   A method for polishing a substrate, comprising polishing a predetermined substrate with the cerium oxide abrasive according to any one of claims 1 to 5. The method for polishing a substrate according to claim 6, wherein the predetermined substrate is a substrate on which an SiO ₂ insulating film is formed.