JPH10102039A - Cerium oxide abrasive and grinding of substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject abrasive capable of grinding without scratching a surface to be ground such as of electric insulating film, comprising a slurry prepared by dispersing cerium oxide particles each of specific aspect ratio in a medium. SOLUTION: This abrasive comprises a slurry prepared by dispersing in a medium cerium oxide particles with such size that the primary particles each 1-2 in aspect ratio having a profile with no corner <120 in angle determined by observation using a transmission electron microscope accounts for >=90wt.% of the total particles. In this case, it is preferable that the medium is water, the dispersant is at least one kind selected from esp. water-soluble organic polymers, water-soluble anionic surfactants, water-soluble nonionic surfactants and water-soluble amines, and the final abrasive is set at pH7-10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, in the manufacturing process of a semiconductor device,
Colloidal silica-based polishing agents are generally studied as chemical mechanical polishing agents 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. Colloidal silica-based abrasives are produced by growing silica particles by a method such as thermal decomposition of silicic acid tetrachloride and adjusting the pH with an alkali solution containing no alkali metal such as ammonia. However, such a polishing agent 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, cerium oxide abrasives have been used for polishing the glass surface for photomasks. Cerium oxide particles have lower hardness than silica particles and alumina particles,
Therefore, it is useful for finish mirror polishing because the polishing surface is hardly damaged. Also, cerium oxide has chemically active properties as known as strong oxidizing agents.
Taking advantage of this advantage, application to a chemical mechanical polishing agent for an insulating film is useful. However, if the cerium oxide abrasive for polishing the glass surface for a photomask is applied as it is to the polishing of the inorganic insulating film, a polishing scratch that can be visually observed is formed on the surface of the insulating film.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a cerium oxide abrasive and a substrate polishing method capable of polishing a surface to be polished such as a SiO ₂ insulating film without damage.

[0005]

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

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

According to the present invention, the aspect ratio of the particle diameter is 1 or more and 2 or less and 120 ° C.
It has been found that the use of cerium oxide particles having 90% or more of the primary particles having a contour that does not include smaller corners enables polishing without damaging the surface to be polished such as a SiO ₂ insulating film. It was done by doing.

[0008]

DETAILED DESCRIPTION OF THE INVENTION Generally, cerium oxide is a carbonate,
It is obtained by calcining cerium compounds such as sulfates and oxalates. Si formed by a TEOS-CVD method or the like
The O ₂ insulating film can be polished at a high speed as the primary particle diameter is large and the crystal distortion is small, that is, as the crystallinity is good. Therefore, the cerium oxide particles used in the present invention are produced without increasing crystallinity. Further, since it is used for polishing semiconductor chips, the content of alkali metals and halogens is 1 ppm.
It is preferable to suppress it to the following.

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 350 ° C.
The temperature is preferably from 700C to 700C.

[0010] The cerium oxide slurry in the present invention comprises:
It is obtained by dispersing an aqueous solution containing cerium oxide particles produced by the above method or a composition comprising cerium oxide particles recovered from this aqueous solution, water and, if necessary, a dispersant. Here, there is no limitation on the concentration of the cerium oxide particles, but the concentration of the cerium oxide particles is set at 0.
A range of 5 to 10% by weight is preferred. As the dispersant, those containing no metal ions include acrylic acid polymers and their ammonium salts, methacrylic acid polymers and their ammonium salts, water-soluble organic polymers such as polyvinyl alcohol, ammonium lauryl sulfate, and polyoxyethylene. Water-soluble anionic surfactants such as ammonium lauryl ether sulfate, polyoxyethylene lauryl ether, water-soluble nonionic surfactants such as polyethylene glycol monostearate, monoethanolamine,
And water-soluble amines such as diethanolamine. The addition amount of these dispersants is preferably in the range of 0.01 part by weight to 5 parts by weight based on 100 parts by weight of the cerium oxide particles in view of the dispersibility and anti-settling properties of the particles in the slurry, and enhances the dispersing effect For this purpose, it is preferable that the particles are simultaneously placed in the disperser 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 the usual dispersion treatment using a stirrer. In particular, in order to disperse cerium oxide particles as fine particles of 1 μm or less, it is preferable to use a wet disperser such as a ball mill, a vibrating ball mill, a planetary ball mill, and a medium stirring mill. When it is desired to increase the alkalinity of the slurry, an alkaline substance not containing metal ions, such as aqueous ammonia, can be added during or after the dispersion treatment.

In the cerium oxide abrasive of the present invention, the above slurry may be used as it is, but N, N-diethylethanolamine, N, N-dimethylethanolamine,
Additives such as aminoethylethanolamine can be added to make an abrasive.

As a method for forming an inorganic insulating film using the cerium oxide abrasive of the present invention, there are a constant pressure CVD method, a plasma CVD method and the like. SiO ₂ by constant pressure CVD
In forming the insulating film, monosilane: SiH _{4 is} used as a Si source, and oxygen: O ₂ is used as an oxygen source. This is obtained by performing the SiH ₄ —O ₂ -based oxidation reaction at a low temperature of about 400 ° C. or less. When doping phosphorus: P for planarizing the surface by high temperature reflow, SiH ₄ —O ₂ —PH ₃
It is preferable to use a system 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. The plasma generation method includes two types, a capacitive coupling type and an inductive coupling type. As a reaction gas, a SiH ₄ —N ₂ O-based gas using SiH ₄ as a Si source and N ₂ O as an oxygen source, and tetraethoxysilane (TEO)
S) as a Si source using a TEOS-O ₂ based gas (TEOS
-Plasma CVD method). Substrate temperature is 250
The reaction pressure is preferably in the range of 67 to 400 Pa. As described above, the elements such as phosphorus and boron may be doped in the SiO ₂ insulating film of the present invention.

A semiconductor substrate at a stage where circuit elements and wiring patterns are formed,
A substrate in which a SiO ₂ insulating film layer is formed on a semiconductor substrate such as a semiconductor substrate at a stage where circuit elements are formed can be used.
By polishing the SiO ₂ insulating film layer formed on such a semiconductor substrate with the cerium oxide polishing agent,
The unevenness on the surface of the iO 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 holder for holding a semiconductor substrate and a polishing cloth (pad) are used.
A general polishing apparatus having a surface plate on which is attached (a motor or the like whose rotation speed can be changed) is attached can be used.
As a polishing cloth, general nonwoven fabric, foamed polyurethane,
A porous fluororesin or the like can be used, and there is no particular limitation. Further, it is preferable that the polishing cloth is subjected to a groove processing for storing the slurry. Although there is no limitation on the polishing conditions, the rotational speed of the platen 100rpm or lower rotational preferably so that no semiconductor protrude, pressure applied to the semiconductor substrate is a 1 kg / cm ² or less as scratches is not generated after polishing preferable. During polishing, the slurry is continuously supplied to the polishing cloth by a pump or the like. Although the supply amount is not limited, it is preferable that the surface of the polishing pad is always covered with the slurry.

After the polishing is completed, the semiconductor substrate is preferably washed well in running water, and then dried using a spin drier or the like to remove water droplets adhering to the semiconductor substrate. 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 cerium oxide By polishing using 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 semiconductor having a desired number of layers is manufactured.

The cerium oxide abrasive of the present invention can be used not only for an SiO ₂ insulating film formed on a semiconductor substrate but also for a SiO ₂ insulating film formed on a wiring board having predetermined wiring, glass,
Inorganic insulating films such as silicon nitride, optical glasses such as photomasks, lenses, and prisms; inorganic conductive films such as ITO; optical integrated circuits, optical switching elements, optical waveguides, and optical fibers composed of glass and crystalline materials. End face, scintillation
Used for polishing optical single crystals such as lasers, solid laser single crystals, LED sapphire substrates for blue lasers, semiconductor single crystals such as SiC, GaP, GaAs, glass substrates for magnetic disks, magnetic heads, etc. Is done. Thus the predetermined substrate in the present invention, a semiconductor substrate which SiO ₂ insulating film is formed, SiO ₂ wiring board on which an insulating film is formed, glass,
Inorganic insulating films such as silicon nitride, optical glasses such as photomasks, lenses, and prisms; inorganic conductive films such as ITO; optical integrated circuits, optical switching elements, optical waveguides, and optical fibers composed of glass and crystalline materials. End face, scintillation
Optical single crystal such as laser, solid laser single crystal, blue laser LED sapphire substrate, semiconductor single crystal such as SiC, GaP, GaAs, magnetic disk glass substrate, magnetic head, etc.

[0017]

【Example】

(Preparation of Cerium Oxide Particles: Part 1) 600 g of cerium carbonate hydrate (99.9%) was placed in a platinum container, and
By baking in air at 0 ° C. for 2 hours, a yellow-white powder was obtained. When this powder was subjected to phase identification by an X-ray diffraction method, it was confirmed that the powder was cerium oxide. Further, observation with a transmission electron microscope confirmed that the primary particles were spherical primary particles having an aspect ratio of 1 to 2 and less than 120 ° C. and having a contour containing no corners smaller than 120 ° C. . In addition, when observed by a transmission electron microscope, the primary particle diameter was 5
It was confirmed that the thickness was not less than 10 nm and not more than 10 nm.

(Preparation of Cerium Oxide Particles: Part 2) 600 g of cerium carbonate hydrate (99.9%) was placed in a platinum container and calcined at 600 ° C. for 2 hours in air to produce a yellow-white powder. Obtained. When this powder was subjected to phase identification by an X-ray diffraction method, it was confirmed that the powder was cerium oxide. Further, observation with a transmission electron microscope confirmed that the primary particles were spherical primary particles having an aspect ratio of 1 to 2 and less than 120 ° C. and having a contour containing no corners smaller than 120 ° C. . In addition, observation with a transmission electron microscope confirmed that the primary particle diameter was more than 10 nm and less than 100 nm.

(Preparation of Cerium Oxide Slurry) After dispersing 80 g of the above two kinds of cerium oxide powder in 800 g of deionized water and adding 8 g of ammonium polyacrylate thereto, a planetary ball mill (P-5 type, Fritche) ), And subjected to a dispersion treatment at 2300 rpm for 30 minutes to obtain a milky white cerium oxide slurry. The slurry pH was 9.7 and 9.1, respectively. When the particle size distribution of the slurry was examined (Master Sizer
It was found that the average particle size was as small as 300 nm and 260 nm, respectively, and their half-value widths were both 300 nm and the distribution was relatively narrow.

(Polishing of Insulating Film Layer) An SiO ₂ insulating film formed by a TEOS-plasma CVD method was formed on a holder to which a suction pad for mounting a substrate to be held was attached.
The i-wafer was set, and the holder was placed with the insulating film surface down on a surface plate on which a polishing pad made of a porous urethane resin was attached, and a weight was further placed so that the processing load was 160 g / cm ² . . While the two types of cerium oxide slurries (solid content: 2.5 wt.%) Were dropped at a rate of 35 cc / min on the platen, the platen was rotated at 30 rpm for 3 minutes to polish the insulating film. After polishing, the wafer was removed from the holder, washed well with running water, and further washed with an ultrasonic cleaner for 20 minutes. After the cleaning, 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 change in film thickness before and after polishing using an optical interference type film thickness measuring apparatus, the slurry of slurry 1 was used to remove the 200 nm insulating film, and the slurry 2 was used for polishing.
With this slurry, the insulating film of 240 nm was shaved. After polishing each slurry, it was found that the thickness was uniform over the entire surface of the wafer. In addition, no scratch was observed on the surface of the insulating film visually.

Comparative Example SiO ₂ produced by the TEOS-CVD method in the same manner as in the example.
The Si wafer on which the insulating film was formed was polished using a commercially available silica slurry (manufactured by Cabot Corp., trade name SS225). The pH of this commercial slurry was 10.3,
It contains 12.5 wt% of SiO ₂ particles.
The polishing conditions are the same as in the embodiment. As a result, no scratches were found due to the polishing, and the polishing was performed uniformly, but only the insulating film layer of 75 nm was removed by the polishing for 3 minutes.

[0022]

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

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/304 321 H01L 21/304 321P

Claims (7)

[Claims] 1. A cerium oxide having an aspect ratio of particle diameter of 1 or more and 2 or less, and 90% or more of all primary particles having a contour not including a corner portion smaller than 120 ° C. observed by a transmission electron microscope. A cerium oxide abrasive containing a slurry in which particles are dispersed in a medium. 2. The cerium oxide abrasive according to claim 1, wherein the slurry contains a dispersant. 3. The cerium oxide abrasive according to claim 1, wherein the medium is water. 4. 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 as described. 5. The cerium oxide abrasive according to claim 1, wherein the slurry has a pH of 7 or more and 10 or less. 6. 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. 7. The method according to claim 6, wherein the predetermined substrate is a substrate on which an SiO ₂ insulating film is formed.