JP2003051467A - Cerium oxide abrasive and polishing method of substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cerium oxide abrasive that can polish the surface to be polished of an silicon oxide insulating film or the like flat and quickly, and to provide a polishing method of a semiconductor device substrate, using the cerium oxide abrasive. SOLUTION: A cerium abrasive contains slurry, where cerium oxide, with a ratio of a/b being equal to or larger than 2.5 is used, is dispersed into a medium, where (a) and (b) indicate the intensity by the (111) face and that by the (200) obtained by X-ray diffraction, respectively. Also, a specific substrate is polished by the cerium oxide abrasive.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD 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 process of manufacturing a semiconductor device,
As a chemical mechanical polishing agent for flattening an inorganic insulating film layer such as a silicon oxide 2 insulating film formed by a method such as plasma-CVD or low-pressure-CVD, a colloidal silica-based polishing agent is generally studied. . The colloidal silica-based abrasive is manufactured by growing silica particles into 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 has a technical problem of low polishing rate for practical use.

On the other hand, a cerium oxide polishing agent is used for polishing the glass surface of a photomask. Cerium oxide particles have lower hardness than silica particles and alumina particles,
Therefore, the polished surface is less likely to be scratched, which is useful for finishing mirror polishing. Further, cerium oxide has a chemically active property, as is known as a strong oxidant. Taking advantage of this advantage, application to chemical mechanical polishing agents for insulating films is useful. However, when the cerium oxide abrasive for polishing the glass surface for a photomask is directly applied to the polishing of the inorganic insulating film, the primary particle (crystallite) diameter is large, and therefore the surface of the insulating film has visible scratches. Further, since the cerium oxide particles have a large theoretical specific gravity of 7.2, they tend to settle. As a result, problems such as uneven concentration of the polishing agent supplied during polishing and clogging of the supply pipe occur.

[0004]

DISCLOSURE OF THE INVENTION The present invention uses a cerium oxide abrasive capable of polishing a surface to be polished such as a silicon oxide insulating film at high speed and flatly, and this cerium oxide abrasive. A method of polishing a semiconductor device substrate is provided.

[0005]

The present invention relates to the following. (1) Cerium oxide having a (111) plane diffraction intensity a and a (200) plane diffraction intensity b obtained by an X-ray diffraction method of 2.5 or more in an integrated intensity ratio of a / b is dispersed in a medium. Cerium oxide abrasive containing slurry. (2) The cerium oxide abrasive according to item (1), wherein the slurry contains a dispersant. (3) The cerium oxide abrasive according to item (1) or (2), wherein the slurry contains water as a medium. (4) Item wherein the dispersant is at least one compound selected from water-soluble organic polymers, water-soluble anionic surfactants, water-soluble nonionic surfactants and water-soluble amines (2)
The cerium oxide abrasive described. (5) The cerium oxide abrasive according to any one of items (1) to (4), which has a pH of 7 or more and 10 or less.

(6) A method of polishing a substrate, which comprises polishing a predetermined substrate with the cerium oxide abrasive according to the items (1) to (5). (7) The method for polishing a substrate according to item (6), wherein the predetermined substrate is a semiconductor element having a silicon oxide insulating film formed thereon.

[0007]

DETAILED DESCRIPTION OF THE INVENTION Generally, cerium oxide is a carbonate,
It is obtained by firing a cerium compound such as a sulfate or an oxalate. A silicon oxide insulating film formed by the TEOS-CVD method or the like has a large primary particle (crystallite) diameter and a small crystal strain, that is, the higher the crystallinity, the higher the speed of polishing is possible, but polishing scratches are likely to occur. Tend. Therefore, the cerium oxide particles used in the present invention are produced without raising the crystallinity so much. Since it is used for polishing semiconductor chips, it is preferable to keep the content of alkali metals and halogens to 1 ppm or less. The polishing agent of the present invention is of high purity and comprises Na, K, Si, Mg, Ca, Z.
r, Ti, Ni, Cr, Fe are each 1 ppm or less, A
It is preferable that l is 10 ppm or less.

In the present invention, a firing method can be used as a method for producing cerium oxide particles. However, in order to produce particles that are free from polishing scratches, low temperature firing that does not increase the crystallinity as much as possible is preferable. Since the oxidation temperature of the cerium compound is 300 ° C, the firing temperature is 600 ° C or higher 9
It is preferably 00 ° C or lower. Cerium carbonate over 600 ℃ 9
It is preferable to perform baking at 00 ° C. or lower for 5 to 300 minutes in an oxidizing atmosphere such as oxygen gas.

The calcined cerium oxide can be pulverized by dry pulverization such as a jet mill or wet pulverization such as a bead mill. Jet mills are described, for example, in Chemical Industry Proceedings Vol. 6, No. 5 (1980), pages 527-532. Cerium oxide particles obtained by pulverizing calcined cerium oxide by dry pulverization using a jet mill or the like include particles having a small primary particle (crystallite) size and polycrystals not pulverized to a primary particle (crystallite) size, This polycrystal is a primary particle (crystallite)
Is different from the reaggregated aggregate, and is composed of two or more primary particles (crystallites) and has a crystal grain boundary. It is presumed that polishing with an abrasive containing a polycrystal having grain boundaries will cause active surfaces to be destroyed by the stress during polishing, and the surface to be polished such as a silicon oxide insulating film will be polished at high speed without scratches. It is thought that it contributes to doing.

The cerium oxide slurry in the present invention is
It is obtained by dispersing the aqueous solution containing the cerium oxide particles produced by the above method or the composition comprising the cerium oxide particles recovered from the aqueous solution, water and, if necessary, a dispersant. Here, there is no limitation on the concentration of the cerium oxide particles, but a range of 0.5 to 10% by weight is preferable from the viewpoint of easy handling of the suspension (abrasive). further,
In order to obtain storage stability, the range of 1 to 5% by weight is preferable. Examples of the dispersant include water-soluble organic polymers, water-soluble anionic surfactants, water-soluble nonionic surfactants and water-soluble amines. For example, a copolymer of ammonium acrylate and methyl acrylate, particularly a weight average molecular weight (measured by gel permeation chromatography using a calibration curve of standard polystyrene, the same applies hereinafter) 100
There are 0 to 20,000 ammonium acrylate and methyl acrylate copolymers. The amount of these dispersants added is, from the dispersibility of particles in the slurry and the anti-settling property,
The range of 0.01 to 5 parts by weight is preferable with respect to 100 parts by weight of the cerium oxide particles, and in order to enhance the dispersing effect, it is preferable to put the particles together with the particles in the dispersing machine during the dispersion treatment.

As a method for dispersing these cerium oxide particles in water, an ultrasonic disperser, a homogenizer, a ball mill or the like can be used in addition to the usual dispersion treatment with a stirrer. In order to disperse the submicron-order cerium oxide particles, it is preferable to use a wet disperser such as a ball mill, a vibrating ball mill, a planetary ball mill, or a medium stirring mill. Further, when it is desired to increase the alkalinity of the slurry, an alkaline substance containing no metal ions, such as aqueous ammonia, can be added during or after the dispersion treatment.

When a copolymer of ammonium acrylate and methyl acrylate is used as the dispersant contained in the slurry of the present invention, the dispersant is 0.01 to 5.00 parts by weight with respect to 100 parts by weight of the cerium oxide particles. It is preferable to add the following, and the weight average molecular weight is 1,000 to 20,000.
Is preferred. The molar ratio of ammonium acrylate salt to methyl acrylate is preferably 0.1 or more and 0.9 or less. If the copolymer of ammonium acrylate and methyl acrylate is less than 0.01 parts by weight with respect to 100 parts by weight of cerium oxide particles, it tends to settle, and if it exceeds 5 parts by weight, a change in particle size distribution due to re-aggregation easily occurs. . Further, if the weight average molecular weight exceeds 20,000, a change with time in the particle size distribution due to reaggregation is likely to occur.

The median diameter of cerium oxide particles having crystal grain boundaries dispersed in the slurry of the present invention is 60 to 1500 nm.
Is preferred, and the median value of primary particle (crystallite) diameter is 30 to 2
50 nm is preferred. If the median value of cerium oxide particles having crystal grain boundaries is less than 60 nm or the median value of primary particles (crystallites) is less than 30 nm, the surface to be polished such as a silicon oxide insulating film can be polished at high speed. Tends to be difficult to do,
The median diameter of cerium oxide particles having a grain boundary is 150.
It exceeds 0 nm, or the median value of primary particles (crystallites) is 25
If it exceeds 0 nm, scratches are likely to occur on the surface to be polished such as a silicon oxide insulating film. When the maximum diameter of cerium oxide particles having crystal grain boundaries exceeds 3000 nm, scratches are likely to occur on the surface to be polished such as a silicon oxide insulating film. The cerium oxide particles having a grain boundary are 5 to 100% by volume of the total cerium oxide particles.
Is preferable, and when it is less than 5% by volume, scratches are likely to occur on the surface to be polished such as a silicon oxide insulating film. In the above cerium oxide particles, the maximum diameter of primary particles (crystallites) is 60.
0 nm or less is preferable, and the primary particle (crystallite) diameter is 10 to 6
It is preferably 00 nm. 6 primary particles (crystallites)
If it exceeds 00 nm, scratches are likely to occur, and if it is less than 10 nm, the polishing rate tends to be low.

The diffraction intensity a by the (111) plane and the diffraction intensity b by the (200) plane obtained by the X-ray diffraction method of the cerium oxide particles dispersed in the slurry of the present invention are respectively:
Obtain the integrated value of the diffraction peaks of the (111) plane and the (200) plane by measuring the cerium oxide particles by the powder X-ray diffraction method and plotting the results with the diffraction angle on the horizontal axis and the diffraction line intensity on the vertical axis. And the ratio of these (integrated intensity ratio, a /
b) is 2.5 or more, preferably 3.00 or more. If a / b becomes too small, the polishing rate tends to be low. Further, the larger a / b is, the higher the polishing rate is, which is preferable. However, cerium oxide particles having a large ratio are difficult to form, so that it is preferably 3.70 or less.

The pH of the slurry of the present invention is preferably 7 or more and 10 or less, more preferably 8 or more and 9 or less.

As a method for producing an inorganic insulating film in which the cerium oxide abrasive of the present invention is used, a constant pressure CVD method, a plasma CVD method and the like can be mentioned. The silicon oxide insulating film is formed by the constant pressure CVD method using monosilane: SiH4 as the Si source and oxygen: O2 as the oxygen source. It can be obtained by carrying out this SiH4—O2 type oxidation reaction at a low temperature of about 400 ° C. or lower. When phosphorus: P is doped to achieve surface flattening by high temperature reflow, SiH 4 --O 2 --P
It is preferable to use an H3 based reaction gas. Plasma CD
The method has the advantage that chemical reactions that require high temperatures under normal thermal equilibrium can occur at low temperatures. There are two plasma generation methods, a capacitive coupling type and an inductive coupling type. As the reaction gas, SiH4 was used as the Si source, and SiH4-N2O-based gas using N2O as the oxygen source and tetraethoxysilane (TE).
TEOS-O2-based gas (TE) used as the Si source.
OS-plasma CVD method). Substrate temperature is 2
The range of 50 to 400 ° C. and the reaction pressure of 67 to 400 Pa are preferable. As described above, the silicon oxide insulating film of the present invention may be doped with elements such as phosphorus and boron.

As a predetermined substrate, a silicon oxide insulating film layer is formed on a semiconductor substrate, that is, a semiconductor substrate in which a circuit element and aluminum wiring are formed, a semiconductor substrate in which a circuit element is formed, and the like. A substrate or the like can be used. By polishing the silicon oxide insulating film layer formed on such a semiconductor substrate with the cerium oxide abrasive, the unevenness of the surface of the silicon oxide insulating film layer is eliminated, and a smooth surface is formed over the entire surface of the semiconductor substrate. To do. Here, as a polishing device, a general polishing device having a holder for holding a semiconductor substrate and a surface plate to which a polishing cloth (pad) is attached (a motor or the like whose rotation speed is changeable) is used is used. it can. As the polishing cloth, general non-woven cloth, foamed polyurethane, porous fluororesin, etc. can be used without any particular limitation. Further, it is preferable that the polishing cloth is grooved so that the slurry is accumulated. The polishing conditions are not limited, but the rotation speed of the holder and the surface plate is preferably low rotation of 100 rpm or less so that the semiconductor substrate does not jump out, and the pressure applied to the semiconductor substrate is such that scratches do not occur after polishing. 1 kg / c
It is preferably m2 or less. During polishing, slurry is continuously supplied to the polishing cloth with a pump or the like. Although the supply amount is not limited, it is preferable that the surface of the polishing cloth 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 droplets adhering to the semiconductor substrate are removed by using a spin dryer or the like and then dried. The aluminum wiring of the second layer is formed on the thus-planarized silicon oxide insulating film layer, and the silicon oxide insulating film is formed again between the wirings and on the wiring by the above method, and then the above-mentioned oxidation is performed. By polishing with 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 polishing agent of the present invention is applicable not only to a silicon oxide insulating film formed on a semiconductor substrate but also to a silicon oxide insulating film formed on a wiring board having predetermined wiring, glass,
Inorganic insulating film such as silicon nitride, optical glass such as photomask, lens and prism, inorganic conductive film such as ITO, optical integrated circuit composed of glass and crystalline material, optical switching element, optical waveguide, optical fiber End face, optical single crystal for scintillator, solid laser single crystal, blue laser L
It is used for polishing an ED sapphire substrate, a semiconductor single crystal such as SiC, GaP and GaAs, a glass substrate for a magnetic disk, a magnetic head and the like.

As described above, the predetermined substrate in the present invention means a semiconductor substrate on which a silicon oxide insulating film is formed, a wiring board on which a silicon oxide insulating film is formed, glass, an inorganic insulating film such as silicon nitride, a photomask, Optical glass such as lenses and prisms, inorganic conductive films such as ITO, optical integrated circuits, optical switching elements and optical waveguides composed of glass and crystalline materials, end faces of optical fibers, optical single crystals such as scintillators , A solid-state laser single crystal, a blue laser LED sapphire substrate, a semiconductor single crystal such as SiC, GaP, or GaAs, a magnetic disk glass substrate, and a magnetic head.

[0021]

EXAMPLES Next, the present invention will be described with reference to examples. Preparation Example 1 (Preparation of Cerium Oxide Particles: Part 1) 2 kg of cerium carbonate hydrate was placed in a platinum container and heated to 830 ° C.
About 1 kg of yellowish white powder was obtained by firing in air for 1 hour. When this powder was subjected to phase identification by X-ray diffraction, it was confirmed to be cerium oxide. The particle size of the calcined powder was 30-100 microns. When the surface of the calcined powder particles was observed with a scanning electron microscope, grain boundaries of cerium oxide were observed. 1 kg of cerium oxide powder was dry-ground using a jet mill. The specific surface area of the thus obtained polycrystal was measured by the BET method and found to be 10 m2 / g.

Preparation Example 2 (Preparation of Cerium Oxide Particles: Part 2) 2 kg of cerium carbonate hydrate was placed in a platinum container and heated to 850 ° C.
About 1 kg of yellowish white powder was obtained by firing in air for 1 hour. When this powder was subjected to phase identification by X-ray diffraction, it was confirmed to be cerium oxide. The particle size of the calcined powder was 30-100 microns. When the surface of the calcined powder particles was observed with a scanning electron microscope, grain boundaries of cerium oxide were observed. 1 kg of cerium oxide powder was dry-ground using a jet mill. As a result of measuring the specific surface area of the thus obtained polycrystal by the BET method, it was found to be 12 m2 / g.

Preparation Example 3 (Preparation of Cerium Oxide Particles: Part 3) 2 kg of cerium carbonate hydrate was placed in a platinum container and heated to 800 ° C.
About 1 kg of yellowish white powder was obtained by firing in air for 2 hours. When this powder was subjected to phase identification by X-ray diffraction, it was confirmed to be cerium oxide. The particle size of the calcined powder was 30-100 microns. When the surface of the calcined powder particles was observed with a scanning electron microscope, grain boundaries of cerium oxide were observed. 1 kg of cerium oxide powder was dry-ground using a jet mill. The specific surface area of the thus obtained polycrystal was measured by the BET method, and it was found to be 17 m2 / g.

(Preparation of Cerium Oxide Slurry) 1000 g of the cerium oxide particles prepared in the above-mentioned preparation examples 1 to 3 of cerium oxide particles, acrylic acid and methyl acrylate were mixed at 3:
Weight average molecular weight of 10,000 (molar ratio)
Aqueous solution of ammonium salt of polyacrylic acid copolymer (4
0% by weight) (23 g) and deionized water (8977 g) were mixed and ultrasonically dispersed with stirring. Ultrasonic frequency is 40
Dispersion was carried out at kHz with a dispersion time of 10 minutes. The obtained slurry was filtered through a 1-micron filter, and deionized water was further added to obtain a 5.0 wt% cerium oxide slurry. The pH of the cerium oxide slurry is from Preparation Example 1 to
For No. 3, the values were 8.4, 8.5 and 8.5 in that order. The abrasive was stored for 6 months at 5 ° C to 40 ° C.

After that, the mixture was returned to a cerium oxide slurry having a uniform concentration distribution by stirring, and laser diffraction particle size distribution measurement was carried out. As a result, it was confirmed that the particle size distribution was the same as that immediately after preparation. As a result of measuring the specific surface area of the slurry particles by the BET method, for the preparation examples 1 to 3, 10 m2 /
g, 12 m2 / g and 17 m2 / g. By stirring during polishing, the cerium oxide slurry did not have uneven concentration. The concentration of the cerium oxide slurry was calculated from the ratio of the weight of the cerium oxide particles to the weight of the slurry. The weight of cerium oxide particles is 15
Heat at 0 ° C. to evaporate the water to the remaining solid weight.

(Measurement of Integrated Strength Ratio) 20 g of the three types of cerium oxide slurries prepared in the above-mentioned preparation of cerium oxide slurries were heated at 150 ° C. to evaporate water to obtain the remaining solid content. What was made into a powder in a mortar was measured by a powder X-ray diffraction method. The ratio of the integrated values of the diffraction peaks of the (111) plane and the (200) plane obtained by plotting the measurement results on the horizontal axis and the diffraction line intensity on the vertical axis (integrated intensity ratio,
a / b) is 3.0 for Manufacturing Examples 1 to 3 in that order.
It was 0, 3.34 and 3.70. The measurement of X-ray diffraction was performed using RAD-2C manufactured by Rigaku Electric Co., Ltd.

(Polishing of Insulating Film Layer) TEOS-Plasma C
Set the Si wafer on which the silicon oxide insulating film formed by the VD method is set, and place the holder with the insulating film face down on the surface plate to which the polishing pad made of porous urethane resin is attached. A weight was placed so that the weight became 300 g / cm2. The above cerium oxide slurry is deionized water to 5
A double-diluted slurry (solid content: 1% by weight) was put in a container, and it was possible to supply the slurry on a platen through a pipe with a pump while stirring. At this time, no sedimentation was observed in the container and the pipe. The insulating plate was polished by rotating the platen at 30 rpm for 1 minute while dropping the slurry on the platen at a rate of 50 cc / min. After polishing, remove the wafer from the holder and wash it thoroughly with running water.
Washed for minutes. After washing, water drops were removed from the wafer with a spin dryer, and the wafer was dried with a dryer at 120 ° C. for 10 minutes.

The change in film thickness before and after polishing was measured using an optical interference type film thickness measuring device.
-3 nm to 364 nm and 416 nm respectively
And 541 nm (for the polishing rates of Preparation Examples 1 to 3, 364 nm / min, 416 nm / min and 541 nm / mi in that order).
It was found that the insulating film of n) was shaved and the thickness was uniform over the entire surface of the wafer. Further, when the surface of the insulating film was observed using an optical microscope, no clear scratch was seen.

[0029]

According to the polishing agent of the present invention, the surface to be polished such as a silicon oxide insulating film can be polished flat and at high speed.

Claims (7)

[Claims] 1. A diffraction intensity a by a (111) plane and a diffraction intensity b by a (200) plane obtained by an X-ray diffraction method are a / b.
A cerium oxide abrasive containing a slurry in which cerium oxide having an integrated intensity ratio of 2.5 or more is dispersed in a medium. 2. The cerium oxide abrasive according to claim 1, wherein the slurry contains a dispersant. 3. The slurry contains water as a medium.
Alternatively, the cerium oxide abrasive according to item 2. 4. The dispersant is at least one selected from water-soluble organic polymers, water-soluble anionic surfactants, water-soluble nonionic surfactants and water-soluble amines.
The cerium oxide abrasive described. 5. The method according to claim 1, wherein the pH is 7 or more and 10 or less.
The cerium oxide abrasive according to any one of 4 above. 6. A method of polishing a substrate, which comprises polishing a predetermined substrate with the cerium oxide abrasive according to any one of claims 1 to 5. 7. The method of polishing a substrate according to claim 6, wherein the predetermined substrate is a semiconductor element having a silicon oxide insulating film formed thereon.