JPH11181404A - Cerium oxide abrasive and grinding of substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cerium oxide abrasive intended for high-speed grinding of the surface of SiO2 insulation films to-be-ground of the like without causing ant scratches. SOLUTION: This cerium oxide abrasive comprises a slurry which is prepared by dispersing in a medium cerium oxide particles 150-600 nm in the median of size produced by using cerium carbonate as raw material 0.3-5 μm in the median of particle size distribution. An Si wafer provided with an SiO2 insulation film made by tetraethoxysilane(TEOS)-CVD method or the like is ground with this abrasive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to 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,
As a chemical mechanical polishing agent for planarizing an inorganic insulating film layer such as an SiO ₂ insulating film formed by a method such as plasma-CVD or low-pressure-CVD, colloidal silica-based polishing agents are generally studied. Colloidal silica-based abrasives
The silica particles are produced by growing grains by a method such as thermal decomposition of tetrachlorosilicic acid and adjusting the pH with an alkaline solution.
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 thus are useful for finish mirror polishing. Cerium oxide also has chemically active properties, as is known as a strong oxidizing agent. Taking advantage of this advantage, application to a chemical mechanical polishing agent for an insulating film is useful. However, a cerium oxide abrasive for polishing a glass surface contains many impurities, and therefore cannot be used as it is as a semiconductor abrasive. Furthermore, when 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 diameter (primary particles and aggregated particles) is large, and polishing scratches that can be visually observed are formed on the insulating film surface.

[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 an SiO ₂ insulating film at a high speed without damage.

[0005]

The cerium oxide abrasive of the present invention contains cerium oxide particles, a dispersant and water. The cerium oxide particles are manufactured using cerium carbonate as a raw material, and cerium carbonate having a median particle diameter of 0.3 to less than 5 μm is used. The cerium oxide particles constituting the cerium oxide abrasive of the present invention preferably have a median particle diameter of 150 to 600 nm. The cerium oxide particles in the cerium oxide abrasive contained 99
It is preferable that the volume% or more is 3000 nm or less.
The particle size of the starting material cerium carbonate and the particle size of the cerium oxide particles contained in the cerium oxide abrasive are determined by a laser diffraction method (for example, a measuring apparatus, MalvernInstr).
Mastersizer Micro
plus, light source He-Ne laser, refractive index of particles 1.
9285, measured at absorption 0). The median value is the median value of the volume particle size distribution, and means the particle size when the volume ratio of the particles from the finer particle size is increased to 50%. That is, when particles having a volume ratio of Vi% exist in the range of the particle diameter of a certain section Δ, the section Δ
Is assumed to be di, it is assumed that particles having a particle diameter of di exist by Vi volume%. The particle existence ratio Vi (volume%) is integrated from the smaller particle diameter di, and Vi = 50%
The di at the time of is set as the median value. 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 above-mentioned cerium oxide abrasive. The present invention has been made by finding that a cerium oxide abrasive containing cerium oxide particles produced by using cerium carbonate as a raw material can polish a surface to be polished such as a SiO ₂ insulating film at high speed without damage. is there.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Cerium carbonate crystallizes as an octahydrate, but when it is heated in an oxygen-containing atmosphere such as air, it decomposes to form cerium oxide. The weight loss at this time reaches 50%, but the cerium oxide after decomposition is
It retains the form of cerium carbonate as a raw material. Therefore, cerium oxide immediately after pyrolysis has a relative density of about 50%.
And cerium oxide having low strength can be obtained.
Therefore, according to the present invention, cerium oxide is manufactured by using cerium carbonate and is used as a cerium oxide abrasive so that a polished surface such as a SiO ₂ insulating film can be polished at high speed without scratches. A polishing method for the agent and the substrate is obtained. The cerium oxide particles used in the present invention are made of cerium carbonate as a raw material, and cerium carbonate has a median particle diameter of 0.3.
~ 5 μm. Since cerium carbonate crystallizes as a hydrate, the cerium carbonate used in the present invention refers to a hydrate. The cerium oxide particles constituting the cerium oxide abrasive of the present invention preferably have a median particle diameter of 150 to 600 nm. It is preferable that 99% by volume or more of the cerium oxide particles in the cerium oxide abrasive is 3000 nm or less. Further, since it is used for polishing semiconductor chips, the content of alkali metals and halogens is 10 p.
pm or less.

In the present invention, a firing method can be used as a method for producing cerium oxide powder. The firing temperature is 6
The temperature is preferably from 00 ° C to 900 ° C. The cerium oxide particles produced by the above method are preferably mechanically pulverized because they are aggregated. 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 jet mill is described in, for example, Chemical Engineering Transactions, Vol. 6, No. 5, (1980), pp. 527-532. When the calcined cerium oxide was pulverized by dry pulverization using a jet mill or the like, generation of residual pulverization was observed.

[0008] The cerium oxide slurry in the present invention comprises:
For example, it can be obtained by dispersing a composition composed of water and a dispersant containing cerium oxide particles having the above characteristics, ammonium polyacrylate, and the like. 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), water-soluble anionic surfactant (alkyl ether carboxylate), water-soluble nonionic surfactant (polyethylene glycol monoester) Two or more dispersants including at least one selected from water-soluble amines (monoethanolamine and the like) may be used. These dispersants are added in an amount of 0.01 to 2.0 parts by weight based on 100 parts by weight of the cerium oxide particles in view of the dispersibility and prevention of sedimentation of the particles in the slurry and the relationship between the polishing scratches and the amount of the dispersant added. The following ranges are preferred. The molecular weight (weight average molecular weight) of the ammonium polyacrylate is 100
0 to 10000 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, a bead mill, a planetary ball mill, a vibration mill, or the like can be used in addition to the dispersion treatment using a normal stirrer. As a method of removing large aggregated particles in the slurry after dispersion by classification, a sedimentation separation method, a liquid cyclone, a filter filtration, or the like can be used.

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, a low pressure CVD method, a plasma CVD method and the like can be mentioned. SiO ₂ by low 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 SiH ₄ —O ₂ -based oxidation reaction is obtained by performing the 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. Phosphorus in order to surface planarization by a high temperature reflow: when doped with P, 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, Si is used as a Si source.
H _4, SiH ₄ -N ₂ O-based gas and TEOS-O ₂ based gas using tetraethoxysilane (TEOS) to Si source using N ₂ O as oxygen source (TEOS-plasma CVD
Method). The substrate temperature is preferably from 250 to 400 ° C., and the reaction pressure is preferably from 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.

The predetermined substrate is 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. The SiO ₂ insulating film layer formed on such a semiconductor substrate is polished with the above cerium oxide abrasive to eliminate irregularities on the surface of the SiO ₂ insulating film layer and to provide a smooth surface over the entire semiconductor substrate. I do. Here, as a polishing apparatus, a general polishing apparatus having a holder for holding a semiconductor substrate and a platen on which a polishing cloth (pad) is attached (a motor or the like capable of changing the number of rotations is attached) is used. it can. As the polishing cloth, a general nonwoven fabric, foamed polyurethane, 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 groove processing such that the 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 so that scratches are not generated after polishing. The following is preferred. 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.

It is preferable that the semiconductor substrate after the polishing is thoroughly washed in running water, and then water drops adhering to the semiconductor substrate are wiped off using a spin drier or the like, and then dried. On this way, the SiO ₂ insulating film layer which is flattened, forming an aluminum wiring of the second layer, again by the above method on the inter-wiring and the wiring, after forming the SiO ₂ insulating film, the oxide By polishing using a cerium 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 an 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. Single crystal for optics such as end face, scintillator, solid laser single crystal, blue laser LE
It is used for polishing a sapphire substrate for D, 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, SiO ₂ semiconductor substrate on which an insulating film is formed, SiO ₂ insulating film is formed wiring board, a glass substrate an inorganic insulating film such as silicon nitride is formed, the photo Optical glass such as masks, lenses, prisms, etc., inorganic conductive films such as ITO, optical integrated circuits, optical switching elements, optical waveguides composed of glass and crystalline materials, optical fiber end faces, scintillators, etc. Single crystal, solid laser single crystal, sapphire substrate for blue laser LED, SiC, Ga
Includes semiconductor single crystals such as P and GaAs, glass substrates for magnetic disks, magnetic heads, and the like.

[0014]

Example 1 (Preparation 1 of cerium oxide particles) Plate-like cerium carbonate was used as a raw material. Laser diffraction method (Measuring device: Malve
Mastersi made by rn Instruments
When the particle diameter was determined by zer Microplus, a light source He-Ne laser, the refractive index of the particles was 1.9285, and the absorption was 0, the median value of the volume distribution was 2.5 μm.
Met. 2 kg of cerium carbonate hydrate was placed in a platinum container and calcined at 800 ° C. for 2 hours in 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. When the surface of the fired powder particles was observed with a scanning electron microscope, grain boundaries of cerium oxide were observed. When the primary particle diameter of cerium oxide surrounded by the grain boundaries was measured, the median of the distribution was 200 nm and the maximum was 600 nm.
X-ray diffraction precision measurement is performed on the calcined powder, and the result is analyzed by the Rietveld method (Rietan-94). As a result, a structure parameter representing the primary particle diameter: a value of X of 0.080, a structure showing isotropic micro-strain Parameter: The value of Y was 0.223. Cerium oxide powder 1
The powder was dry-ground using a jet mill. Observation of the pulverized particles with a scanning electron microscope revealed that, in addition to small particles having the same size as the primary particle diameter, 1 μm to 3 μm
m and the remaining pulverized particles of 0.5 to 1 μm were mixed. The unmilled particles are not aggregates of primary particles. X-ray diffraction precision measurement was performed on the pulverized particles, and the results were analyzed using the Rietveld method (Rietan-
According to the analysis according to 94), the value of the structural parameter indicating the primary particle diameter: X was 0.083, and the value of the structural parameter indicating the isotropic micro-strain: Y was 0.264. As a result, there was almost no change in the primary particle diameter due to the pulverization, and distortion was introduced into the particles by the pulverization. Further, the specific surface area measured by the BET method was found to be 13 m ² / g.

(Preparation of cerium oxide particles 2) The same cerium carbonate hydrate 2 used in preparation of cerium oxide particles 1
The resulting powder was placed in a platinum container and calcined at 750 ° C. for 2 hours in the air to obtain about 1 kg of a yellowish white powder. When this powder was subjected to phase identification by X-ray diffraction, it was confirmed that the powder was cerium oxide. When the surface of the fired powder particles was observed with a scanning electron microscope, grain boundaries of cerium oxide were observed. When the primary particle diameter of cerium oxide surrounded by the grain boundaries was measured, the median of the distribution was 135 nm and the maximum was 450 nm. X-ray diffraction precision measurement was performed on the calcined powder, and the results were analyzed using the Rietveld method (RIRT).
According to the analysis by AN-94), the value of the structural parameter representing the primary particle diameter: X was 0.105, and the value of the structural parameter representing the isotropic micro strain: Y was 0.223.
1 kg of cerium oxide powder was dry-ground using a jet mill. Observation of the pulverized particles with a scanning electron microscope revealed that, in addition to the small particles having the same size as the primary particle diameter, large pulverized residual particles of 1 μm to 3 μm and pulverized residual particles of 0.5 to 1 μm were mixed. The unmilled particles are not aggregates of primary particles. X-ray diffraction precision measurement is performed on the pulverized particles, and the result is analyzed by the Rietveld method (Rietan-94). The structure parameter representing the primary particle diameter: the value of X is 0.110, and the structure shows isotropic micro strain. Parameter: Y value is 0.315
Met. As a result, there was almost no change in the primary particle diameter due to the pulverization, and distortion was introduced into the particles by the pulverization. Further, as a result of measuring the specific surface area by the BET method, 18 m ² /
g.

(Preparation of Cerium Oxide Slurry) 1 kg of the cerium oxide particles prepared in Preparations 1 and 2, 23 g of an aqueous solution of ammonium polyacrylate (40% by weight), and deionized water 8
977 g were mixed and subjected to ultrasonic dispersion for 10 minutes while stirring. The obtained slurry was filtered through a 1 μm filter, and 3 wt% abrasive was obtained by adding deionized water. The slurry pH was 8.3. When the particle size distribution of the slurry particles was examined using a laser diffraction method,
Each of the cerium oxide slurry preparations 1 and 2 had a median of 200 nm and a maximum particle diameter of 1480 n.
m. In order to examine the dispersibility of the slurry and the charge of the slurry particles, the zeta potential of the slurry was examined. The cerium oxide slurry was placed in a measurement cell having platinum electrodes attached to both sides, and a voltage of 10 V was applied to both electrodes. Slurry particles having a charge by applying a voltage,
The charge moves to the electrode having the opposite pole. By determining the moving speed, the zeta potential of the particles can be determined. As a result of the zeta potential measurement, it was confirmed that each of the particles was negatively charged, the absolute values were large at −45 mV and −50 mV, and the dispersibility was good.

(Polishing of Insulating Film Layer) A Si wafer having a SiO ₂ insulating film formed by a TEOS-plasma CVD method is set on a holder to which a suction pad for holding a substrate to be held is attached, and a porous urethane is formed. The holder was placed on the surface plate to which the resin polishing pad was attached, with the insulating film face down, and a weight was 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 50 cc / min, the platen was rotated at 30 rpm for 2 minutes to polish the insulating film. After polishing, the wafer is removed from the holder, washed well with running water, and then further cleaned with an ultrasonic cleaner.
Washed for 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 a change in film thickness before and after polishing using an optical interference type film thickness measuring device, the polishing results in 640 nm and 6 nm, respectively.
20 nm (polishing rate: 320 nm / min, 310 nm
/ Min) of the insulating film was removed, and the thickness was uniform over the entire surface of the wafer. When the surface of the insulating film was observed using an optical microscope, no clear damage was found.

Example 2 (Preparation of Cerium Oxide Particles) 2 kg of the same cerium carbonate hydrate used in Example 1 as a raw material was placed in a platinum container and calcined at 700 ° C. for 2 hours in the air. About 1 kg of a yellow-white powder was obtained. When this powder was subjected to phase identification by X-ray diffraction, it was confirmed that the powder was cerium oxide. When the surface of the fired powder particles was observed with a scanning electron microscope, grain boundaries of cerium oxide were observed. When the primary particle diameter of cerium oxide surrounded by the grain boundaries was measured, the median value of the distribution was 50 nm, and the maximum value was 110 nm. X-ray diffraction precision measurement is performed on the calcined powder, and the result is analyzed by the Rietveld method (Rietan-94). As a result, a structure parameter representing a primary particle diameter: a value of X is 0.300, and a structure showing isotropic micro-strain Parameter: The value of Y was 0.350. Cerium oxide powder 1
The powder was dry-ground using a jet mill. Observation of the pulverized particles with a scanning electron microscope revealed that, in addition to the small particles having the same size as the primary particle diameter, 2 μm to 4 μm
m and the remaining pulverized particles of 0.5 to 1.2 μm were mixed. The unmilled particles are not aggregates of primary particles. X-ray diffraction precision measurement was performed on the pulverized particles, and the results were analyzed using the Rietveld method (Rietan).
According to the analysis according to -94), the value of the structural parameter indicating the primary particle diameter: X was 0.305, and the value of the structural parameter indicating the isotropic micro-strain: Y was 0.412. As a result, there was almost no change in the primary particle diameter due to the pulverization, and distortion was introduced into the particles by the pulverization. Furthermore, the specific surface area measured by the BET method was 43 m ² / g.

(Preparation of Cerium Oxide Slurry) 1 kg of the cerium oxide particles prepared above, 23 g of an aqueous solution of ammonium polyacrylate (40% by weight), and 8977 of deionized water
g was mixed and subjected to ultrasonic dispersion for 10 minutes while stirring. The obtained slurry was filtered with a 2 μm filter,
Further, 3 wt% abrasive was obtained by adding deionized water. The slurry pH was 8.2. When the particle size distribution of the slurry particles was examined using a laser diffraction method, the median value was 510 nm, and 0% of the particles had a maximum particle size of 1560 nm or more. In order to examine the dispersibility of the slurry and the charge of the slurry particles, the zeta potential of the slurry was examined. The cerium oxide slurry was placed in a measurement cell having platinum electrodes attached to both sides, and a voltage of 10 V was applied to both electrodes. When a voltage is applied, the charged slurry particles move to the electrode side having the opposite pole to the charge.
By determining the moving speed, the zeta potential of the particles can be determined. As a result of the zeta potential measurement, it was confirmed that the sample was negatively charged, had a large absolute value of −39 mV, and had good dispersibility.

(Polishing of Insulating Film Layer) An Si wafer having a SiO ₂ insulating film formed by TEOS-plasma CVD method is set on a holder to which a suction pad for holding a substrate to be held is attached. The holder was placed on the surface plate to which the resin polishing pad was attached, with the insulating film face down, 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 2 minutes to polish the insulating film. After polishing, the wafer is removed from the holder, washed well with running water, and then further cleaned with an ultrasonic cleaner.
Washed for 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 polishing showed that the polishing resulted in 700 nm (polishing rate:
It was found that the insulating film of 350 nm / min) was shaved and had a uniform thickness over the entire surface of the wafer. Also,
When the surface of the insulating film was observed using an optical microscope, no clear scratch was found.

Comparative Example 1 In the same manner as in the example, the SiO
_{2. The} Si wafer on which the insulating film was formed was polished using a commercially available silica slurry (trade name: SS225, manufactured by Cabot Corporation). The pH of this commercial slurry was 10.3
And contains 12.5 wt% of SiO ₂ particles. The polishing conditions are the same as in the embodiment. As a result, no scratches due to the polishing were observed, and the polishing was performed uniformly. However, the polishing was performed for 2 minutes to 150 nm (polishing speed: 75 nm / mi).
Only the insulating film layer of n) was scraped.

[0022]

According to the polishing agent of the present invention, a surface to be polished such as an SiO ₂ insulating film can be polished at high speed without being damaged.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroki Terasaki 48 Wadai, Tsukuba, Ibaraki Prefecture, Hitachi Chemical Co., Ltd.Tsukuba R & D Co., Ltd. Within the Development Laboratory (72) Inventor Jun Matsuzawa 48 Wadai, Tsukuba, Ibaraki Prefecture Within the Hitachi Chemical Co., Ltd.Tsukuba Development Laboratory Co., Ltd. Inside the Yamazaki Plant (72) Inventor Takeshi Sakurada 4-3-1-1, Higashicho, Hitachi City, Ibaraki Prefecture Inside the Yamazaki Plant of Hitachi Chemical Co., Ltd.

Claims (4)

[Claims] 1. A cerium oxide abrasive containing cerium oxide particles produced using cerium carbonate having a median particle diameter of 0.3 to less than 5 μm as a raw material. 2. The cerium oxide abrasive according to claim 1, comprising cerium oxide having a median particle diameter of 150 to 600 nm. 3. A method for polishing a substrate, comprising polishing a predetermined substrate with the cerium oxide abrasive according to claim 1. 4. The method according to claim 3, wherein the predetermined substrate is a substrate on which an SiO ₂ insulating film is formed.