JPH10154672A - Cerium oxide abrasive material and polishing method of substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To polish the polished surface of a prescribed substrate quickly without contaminating it with alkaline metal and making any marks on it by a method wherein the surface of the wafer is polished with cerium oxide abrasive material. SOLUTION: Composition composed of cerium oxide particles and dispersant which contains ammonium polyacrylate is dispersed into water for obtaining cerium oxide slurry. Cerium oxide slurry is used as abrasive material. An SiO2 insulating layer is formed on a semiconductor substrate where circuit elements and wiring patterns are formed, and the SiO2 insulating layer formed on the semiconductor substrate is polished with cerium oxide abrasive material, whereby the irregularities of the SiO2 insulating layer surface are turned smooth throughout all the surface of the substrate.

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 glass surfaces such as photomasks and lenses.
Cerium oxide particles have a lower hardness than silica particles and alumina particles and are therefore less likely to scratch the polished surface, and are therefore useful for finishing mirror polishing. 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, since a cerium oxide abrasive for polishing a glass surface uses a dispersant containing a Na salt, it cannot be directly used as a semiconductor abrasive. Furthermore, if the cerium oxide abrasive for polishing the glass surface is applied to the polishing of the inorganic insulating film as it is, the cerium oxide particle size (primary particles or aggregated particles) is large, and a polishing scratch that can be visually observed is formed on the insulating film surface.

[0004]

SUMMARY OF THE INVENTION The present invention relates to a cerium oxide abrasive and a substrate for polishing a surface to be polished such as a SiO2 insulating film, etc., at a high speed without fouling without causing alkali metal contamination such as Na. A polishing method is provided.

[0005]

The cerium oxide abrasive of the present invention contains cerium oxide particles, ammonium polyacrylate, and water. The addition amount of the ammonium polyacrylate is preferably a necessary effective amount to 2.0 parts by weight based on 100 parts by weight of the cerium oxide particles. The effective necessary amount is preferably 0.01 part by weight. The molecular weight (weight average molecular weight) of the ammonium polyacrylate is from 1000 to 100
00 is preferable, and 3000 to 8000 is more preferable.
The pH of the cerium oxide abrasive is more preferably 7 or more and 10 or less. The substrate polishing method of the present invention is characterized in that a predetermined substrate, for example, a substrate on which an SiO ₂ insulating film is formed is polished with the cerium oxide abrasive. The present invention has been made by finding that a surface to be polished such as an SiO ₂ insulating film is polished at high speed without being damaged by alkali metal contamination such as Na.

[0008]

DETAILED DESCRIPTION OF THE INVENTION Generally, cerium oxide is a carbonate,
It is obtained by calcining cerium compounds such as nitrates, sulfates and oxalates. As the SiO ₂ insulating film formed by the TEOS-CVD method or the like has a large primary particle diameter and a small crystal distortion, that is, a high crystallinity, high-speed polishing can be performed, but polishing scratches tend to occur. Therefore, the cerium oxide particles used in the present invention are not limited to a production method, but are preferably produced without increasing crystallinity so much. Cerium oxide primary particle size is 5n
It is preferably from m to 100 nm. Further, since it is used for polishing a semiconductor chip, the content of alkali metals and halogens is preferably suppressed to 1 ppm or less.

In the present invention, a firing method can be used as a method for producing cerium oxide powder. Firing temperature is 350
The temperature is preferably in the range of ℃ to 800 ° C. Since the cerium oxide particles produced by the above method are agglomerated, it is preferable to mechanically pulverize the particles. As the pulverization method, a dry pulverization method using a jet mill or the like or a wet pulverization method using a planetary bead mill or the like is preferable.

The cerium oxide slurry of the present invention can be obtained, for example, by dispersing a composition comprising cerium oxide particles having the above-described characteristics, a dispersant containing ammonium polyacrylate, and water. Here, the concentration of the cerium oxide particles is not limited, but is preferably in the range of 0.5 to 20% by weight from the viewpoint of easy handling of the suspension. As a dispersant, an alkali metal such as Na or K, and ammonium polyacrylate are preferable because they do not contain halogen or sulfur because they are used for polishing semiconductor chips. In addition, ammonium polyacrylate and water-soluble organic polymers (such as polyglycerin fatty acid ester),
At least one selected from a water-soluble anionic surfactant (alkyl ether carboxylate), a water-soluble nonionic surfactant (polyethylene glycol monostearate, etc.), and a water-soluble amine (monoethanolamine, etc.) May be used. The addition amount of these dispersants is 0.01 to 2.0 parts by weight based on 100 parts by weight of cerium oxide particles from the relationship between the dispersibility of the particles in the slurry and the prevention of sedimentation, and the relationship between the polishing scratches and the addition amount of the dispersant. Is preferable. The molecular weight (weight average molecular weight) of the ammonium polyacrylate is 1,000 to 10,000.
Is preferable, and 3000 to 8000 is more preferable. As a method for dispersing these cerium oxide particles in water, a homogenizer, an ultrasonic disperser, or the like can be used in addition to the dispersion treatment using a usual stirrer.

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. In some cases, heat treatment is performed at a temperature of 1000 ° C. or lower after CVD. When doping phosphorus: P for planarizing the surface by high temperature reflow,
It is preferable to use a SiH ₄ -O ₂ -PH ₃ 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 TEOS using tetraethoxysilane (TEOS) as a Si source
-O ₂ system gas (TEOS-plasma CVD method). The substrate temperature is 250 ° C to 400 ° C, and the reaction pressure is 67
The range of -400 Pa is preferable. As described above, the elements such as phosphorus and boron may be doped in the SiO2 insulating film of the present invention.

As a predetermined substrate, a semiconductor substrate, that is, a semiconductor substrate in which 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, 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
Optical single crystal such as laser, single laser single crystal, blue laser L
It is used for polishing a sapphire substrate for ED, a semiconductor single crystal such as SiC, GaP, GaAs, a glass substrate for a magnetic disk, a magnetic head, and the like. 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,
Substrate on which inorganic insulating film such as silicon nitride is formed, optical glass such as photomask, lens, prism, etc .; inorganic conductive film such as ITO; optical integrated circuit / optical switching element / optical waveguide composed of glass and crystalline material Optical fiber end face, optical single crystal such as scintillator, solid laser single crystal, blue laser LED sapphire substrate, SiC, Ga
Includes semiconductor single crystals such as P and GaAs, glass substrates for magnetic disks, and magnetic heads.

[0016]

【Example】

(Preparation of cerium oxide particles 1) Cerium carbonate hydrate 2k
g was placed in a platinum container and calcined at 700 ° C. for 2 hours in the air to obtain about 1 kg of a yellow-white powder. When this powder was subjected to phase identification by an X-ray diffraction method, it was confirmed that the powder was cerium oxide. Cerium oxide powder was mixed with deionized water so as to have a concentration of 10% by weight, and pulverized at 1400 rpm for 120 minutes using a horizontal wet-type ultrafine particle pulverizer.
The obtained suspension was dried at 110 ° C. for 3 hours to obtain cerium oxide particles. Observation with a transmission electron microscope revealed that the particles had a size of 10 to 60 nm, and that the specific surface area measured by the BET method was 39.5 m ² / g.

(Preparation of Cerium Oxide Particles 2) 2 kg of cerium carbonate hydrate was placed in a platinum container and calcined at 700 ° C. for 2 hours in air to obtain about 1 kg of yellowish white powder. When this powder was subjected to phase identification by an X-ray diffraction method, it was confirmed that the powder was cerium oxide. Cerium oxide powder 1k
g was dry-ground using a jet mill. 41. The particle size is 10 to 60 nm as observed by a transmission electron microscope, and the specific surface area is measured by a BET method.
It was found to be ² m ² / g.

(Preparation of Cerium Oxide Slurry) 125 g of the cerium oxide particles of Preparations 1 and 2, 3 g of an aqueous solution of ammonium polyacrylate (40% by weight), and deionized water 2
372 g were mixed and subjected to ultrasonic dispersion while stirring. The ultrasonic frequency was 40 kHz and the dispersion time was 10 minutes. The resulting slurry was filtered through a 0.8 micron filter, and 3 wt.
% Abrasive was obtained. The slurry pH was both 8.5. Examination of the particle size distribution of the slurry revealed that both the average particle size was as small as 290 nm, and the half-value width was 300 nm, and the distribution was relatively narrow. The maximum particle diameter was 99.9% for particles having a diameter of 800 nm or less.

(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 attaching a substrate to be held was attached.
An i-wafer was set, and a holder was placed with the insulating film surface down on a surface plate to which a polishing pad made of a porous urethane resin was attached, and a weight was further placed so that the processing load was 300 g / cm ² . . While the cerium oxide slurry (solid content: 3% by weight) was dropped on the platen at a rate of 35 cc / min, the platen was rotated at 30 rpm for 1 minute to polish the insulating film. After polishing, remove the wafer from the holder,
After being thoroughly washed with running water, it was further washed for 20 minutes by an ultrasonic washing machine. 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 device, two types of abrasives were obtained by this polishing.
It was found that the insulating film of 0 nm / min was shaved and had a uniform thickness 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 polished by polishing for 3 minutes (25
nm / min).

[0021]

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

Claims (6)

[Claims] 1. A cerium oxide abrasive containing cerium oxide particles, ammonium polyacrylate and water. 2. The cerium oxide abrasive according to claim 1, wherein the polyacrylic acid ammonium salt is added in a required effective amount to 2.0 parts by weight based on 100 parts by weight of the cerium oxide particles. 3. The cerium oxide abrasive according to claim 1, wherein the molecular weight (weight average molecular weight) of the ammonium polyacrylate is from 1,000 to 10,000. 4. The method according to claim 1, wherein the pH is from 7 to 10.
3. The cerium oxide abrasive according to any one of the above items. 5. A method for polishing a substrate, comprising polishing a predetermined substrate with the cerium oxide abrasive according to any one of claims 1 to 4. 6. The method according to claim 5, wherein the predetermined substrate is a substrate on which an SiO ₂ insulating film is formed.