JP2012186339A - Polishing liquid and polishing method of substrate using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing liquid which can enhance the polishing speed ratio of silicon oxide and silicon nitride of a polished film in the CMP technology for polishing the polished film formed on the surface of a substrate, and to provide a polishing method of a substrate using the polishing liquid.SOLUTION: The polishing liquid contains cerium oxide particles, a hydroxy acid compound and/or its salt, and water. In a state where a polished film formed on a substrate is pressed against the polishing cloth of a polishing surface plate, the substrate and the polishing surface plate are moved relatively while supplying the polishing liquid containing cerium oxide particles, a hydroxy acid compound and/or its salt, and water between the polished film and the polishing cloth thus polishing the polished film.

Description

  The present invention relates to a polishing liquid and a method for polishing a substrate using the polishing liquid. More specifically, the present invention is a semiconductor element manufacturing technique, a planarization process of a substrate surface, in particular, a planarization process of an interlayer insulating film and a BPSG film (boron, phosphorus-doped silicon dioxide film), shallow trench isolation. The present invention relates to a polishing liquid and a substrate polishing method using the polishing liquid, which are used in the forming process (hereinafter referred to as “STI”).

  In the current ULSI semiconductor device manufacturing process, processing technology for high density and miniaturization of semiconductor devices has been researched and developed. CMP (Chemical Mechanical Polishing) technology, which is one of the processing technologies, is indispensable when performing planarization of interlayer insulation films, STI formation, plugs and buried metal wiring formation, etc. in the semiconductor device manufacturing process. Has become a technology.

  Conventionally, in a semiconductor device manufacturing process, an inorganic insulating film such as a silicon oxide film is formed by a method such as plasma-CVD (chemical vapor deposition) or low-pressure CVD (chemical vapor deposition). As a chemical mechanical polishing liquid for planarizing the inorganic insulating film, it has been generally studied to use a fumed silica-based polishing liquid. The fumed silica-based polishing liquid is produced by adjusting the pH of a slurry containing particles obtained by grain growth by a method such as thermal decomposition of silicon tetrachloride. However, such a fumed silica-based polishing liquid has a technical problem that the polishing rate is low.

  In the generations after the design rule 0.25 μm, STI is used for element isolation in the integrated circuit. In STI, CMP technology is used to remove an excess silicon oxide film formed on a substrate. In this case, in order to stop the polishing at an arbitrary depth, a stopper film having a low polishing rate is formed under the silicon oxide film. A silicon nitride film or the like is used for the stopper film. It is desirable that the polishing rate ratio between the silicon oxide film and the stopper film is large in order to efficiently remove the excess silicon oxide film and sufficiently suppress the subsequent polishing. However, the conventional colloidal silica-based polishing liquid has a polishing rate ratio between the silicon oxide film and the stopper film as small as about 3, and does not have a characteristic that can be practically used for STI.

  On the other hand, a cerium oxide polishing liquid containing cerium oxide particles is used as a polishing liquid for glass surfaces such as photomasks and lenses. Cerium oxide particles have a lower hardness than silica particles and alumina particles, and are difficult to scratch on the polished surface during polishing, and thus are useful for finish mirror polishing. Further, the cerium oxide polishing liquid has an advantage that the polishing rate is faster than the silica polishing liquid such as fumed silica type or colloidal silica type.

  As a cerium oxide polishing liquid, the following Patent Document 1 describes a semiconductor CMP polishing liquid using high-purity cerium oxide abrasive grains. Patent Document 2 below describes a technique of adding an additive to control the polishing rate of a cerium oxide polishing liquid and improve global flatness.

Japanese Patent Laid-Open No. 10-106994 Japanese Patent No. 3278532

  However, with the progress of miniaturization of design rules for wiring and STI, further improvement in flatness is required for the cerium oxide polishing liquid as described above. For this purpose, it is required to increase the polishing rate difference between the silicon oxide film and the silicon nitride film as the stopper film.

  The present invention has been made in view of the above circumstances, and in a CMP technique for polishing a film to be polished formed on the surface of a substrate, polishing of a silicon oxide film as a film to be polished and a silicon nitride film as a stopper film An object is to provide a polishing liquid capable of greatly improving the speed difference.

  The present invention provides a polishing liquid comprising cerium oxide particles, at least one additive selected from the group consisting of hydroxy acid compounds and salts of hydroxy acid compounds, and water.

  According to the polishing liquid of the present invention, in a CMP technique for polishing a film to be polished (STI film) formed on the surface of a substrate, a polishing rate difference between a silicon oxide film as a film to be polished and a silicon nitride film as a stopper film. Can be improved.

  The polishing liquid of the present invention preferably contains at least one selected from the group consisting of malic acid, citric acid, lactic acid, glycolic acid, glyceric acid, tartaric acid, and salicylic acid as the hydroxy acid compound. In this case, the polishing rate difference between the silicon oxide film as the film to be polished and the silicon nitride film as the stopper film can be further improved.

  The hydroxyl group in the hydroxy acid is preferably not a phenolic hydroxyl group.

  The content of the hydroxy acid compound is preferably 0.0001 to 5% by mass based on the total mass of the polishing liquid.

  Moreover, it is preferable that the polishing liquid of the present invention does not contain an alcohol compound.

  The polishing liquid of the present invention may be stored as a two-part polishing liquid in which constituent components are divided into a first liquid containing cerium oxide particles and water and a second liquid containing an additive and water.

  Further, the present invention provides the polishing liquid of the present invention between the film to be polished and the polishing cloth in a state where the film to be polished of the substrate on which the film to be polished is pressed against the polishing cloth of the polishing platen. Accordingly, a substrate polishing method is provided in which a film to be polished is polished by relatively moving a substrate and a polishing surface plate.

  According to the substrate polishing method of the present invention, in the CMP technique for polishing a film to be polished (for example, an STI film) formed on the surface of the substrate by using the polishing liquid of the present invention, silicon oxide that is the film to be polished The polishing rate difference between the film and the silicon nitride film as the stopper film can be improved.

  According to the present invention, in a CMP technique for polishing a film to be polished (for example, an STI film) formed on the surface of a substrate, the polishing rate difference between a silicon oxide film as a film to be polished and a silicon nitride film as a stopper film is improved. And a polishing method for a substrate using the polishing liquid.

  Hereinafter, embodiments of the present invention will be described in detail. The polishing liquid according to the present invention contains cerium oxide particles, an additive, and water. Hereinafter, each component contained in the polishing liquid according to the present invention will be described in detail.

(Cerium oxide particles)
There is no restriction | limiting in particular as a cerium oxide particle, A well-known thing can be used. In general, cerium oxide is obtained by oxidizing a cerium compound such as carbonate, nitrate, sulfate, or oxalate. Examples of the method for producing the cerium oxide particles include firing or oxidation using hydrogen peroxide.

  When cerium oxide particles are used for polishing a silicon oxide film formed by TEOS-CVD using tetraethoxysilane (hereinafter referred to as “TEOS”) as a Si source, the crystallite diameter (crystallite) of the cerium oxide particles The larger the diameter) and the smaller the crystal distortion, that is, the better the crystallinity, the faster the polishing is possible, but there is a tendency that polishing scratches are likely to enter the film to be polished. From this point of view, the cerium oxide particles are preferably composed of two or more crystallites, particles having a crystal grain boundary, and more preferably particles having a crystallite diameter of 5 to 300 nm.

  The content of alkali metal and halogens in the cerium oxide particles is preferably 10 ppm or less because it is suitably used for polishing in the manufacture of semiconductor elements.

  The average particle diameter of the cerium oxide particles is preferably 1 to 500 nm, more preferably 1 to 400 nm, and still more preferably 1 to 300 nm. When the average particle size of the cerium oxide particles is 1 nm or more, a good polishing rate tends to be obtained, and when the average particle size is 500 nm or less, the film to be polished tends not to be damaged.

  Here, the average particle diameter of the cerium oxide particles is measured with a laser diffraction particle size distribution analyzer (for example, manufactured by Malvern, trade name: Master Sizer Microplus, refractive index: 1.93, light source: He—Ne laser, absorption 0). Means the value of D50 (median diameter of volume distribution, cumulative median value). For the measurement of the average particle diameter, a sample in which the polishing liquid is diluted to an appropriate concentration (for example, a concentration at which the measurement transmittance (H) with respect to the He—Ne laser is 60 to 70%) is used. In addition, when the cerium oxide polishing liquid is stored separately as a cerium oxide slurry in which cerium oxide particles are dispersed in water and an additive solution in which an additive is dissolved in water, as will be described later, Can be diluted to an appropriate concentration and measured.

  The content of the cerium oxide particles is preferably 0.1 to 20% by mass, more preferably 0.1 to 5% by mass, and still more preferably 0.5 to 1.5% by mass based on the total mass of the polishing liquid. If the content of the cerium oxide particles is 0.1% by mass or more, a good polishing rate tends to be obtained. If the content is 20% by mass or less, the aggregation of the particles is suppressed and the film to be polished is damaged. There is a tendency to become difficult.

(Additive)
[Hydroxy acid compound]
The polishing liquid according to the present invention contains a hydroxy acid compound and / or a salt thereof as an additive. As a result, the polishing rate difference between the silicon oxide film as the film to be polished and the silicon nitride film as the stopper film can be improved. This effect can be obtained more efficiently by using a hydroxy acid compound and cerium oxide particles in combination.

  A hydroxy acid compound is a compound having at least one alcoholic hydroxyl group and carboxyl group. Such a compound is preferably at least one selected from the group consisting of malic acid, citric acid, lactic acid, glycolic acid, glyceric acid, tartaric acid, and salicylic acid. These can be used alone or in combination of two or more.

  The content of the hydroxy acid compound and / or salt thereof is preferably 0.0001 to 5% by mass, more preferably 0.001 to 2% by mass based on the total mass of the polishing liquid. If the content of the hydroxy acid compound is 0.0001% by mass or more, the difference in polishing rate between the silicon oxide film and the silicon nitride film tends to be easily improved, and if it is 5% by mass or less, the polishing rate of the film to be polished The difference tends to improve further.

[Other additives]
In the polishing liquid according to the present invention, a water-soluble polymer can be used as an additive different from the hydroxy acid compound and its salt. Examples of such water-soluble polymers include polysaccharides such as alginic acid, pectic acid, carboxymethylcellulose, agar, curdlan and pullulan; polyaspartic acid, polyglutamic acid, polylysine, polymalic acid, polyamic acid, polyamic acid ammonium salt And polycarboxylic acids such as polyamic acid sodium salt and polyglyoxylic acid and salts thereof; and vinyl polymers such as polyvinyl alcohol, polyvinyl pyrrolidone and polyacrolein.

  These water-soluble polymers preferably have a weight average molecular weight of 500 or more. The weight average molecular weight is a value obtained by measuring with GPC (Gel Permeation Chromatography) and converting to standard polyoxyethylene. Further, the content of these water-soluble polymers is preferably 0.01 to 5% by mass based on the total mass of the polishing liquid.

(water)
Although it does not restrict | limit especially as water, Deionized water, ion-exchange water, ultrapure water, etc. are preferable. The water content is not particularly limited as long as it is the remainder of the content of each of the above-described components and is contained in the polishing liquid. Note that the polishing liquid may further contain a solvent other than water, for example, a polar solvent such as ethanol, acetic acid, and acetone, if necessary.

(Dispersant)
In the polishing liquid according to the present invention, a dispersant for dispersing cerium oxide particles can be used. Examples of the dispersant include a water-soluble anionic dispersant, a water-soluble nonionic dispersant, a water-soluble cationic dispersant, a water-soluble amphoteric dispersant, and the like, among others, a water-soluble anionic dispersant. Is preferred. These can be used individually by 1 type or in combination of 2 or more types.

  As the water-soluble anionic dispersant, a polymer containing acrylic acid as a copolymerization component and a salt thereof are preferable, and a salt of the polymer is more preferable. Polymers containing acrylic acid as a copolymerization component and salts thereof include, for example, polyacrylic acid and ammonium salts thereof, copolymers of acrylic acid and methacrylic acid and ammonium salts thereof, and acrylic amides and acrylic acids. And copolymers thereof and ammonium salts thereof.

  Examples of other water-soluble anionic dispersants include lauryl sulfate triethanolamine, lauryl ammonium sulfate, polyoxyethylene alkyl ether sulfate triethanolamine, and special polycarboxylic acid type polymer dispersants.

  Examples of the water-soluble nonionic dispersant include polyethylene glycol monolaurate, polyethylene glycol monostearate, polyethylene glycol distearate, polyethylene glycol monooleate, polyoxyethylene alkylamine, and polyoxyethylene hydrogenated castor oil. , 2-hydroxyethyl methacrylate, alkyl alkanolamide and the like.

  Examples of the water-soluble cationic dispersant include polyvinyl pyrrolidone, coconut amine acetate, stearyl amine acetate and the like.

  Examples of the water-soluble amphoteric dispersant include lauryl betaine, stearyl betaine, lauryl dimethylamine oxide, 2-alkyl-N-carboxymethyl-N-hydroxyethylimidazolinium betaine and the like.

  From the viewpoint of improving the dispersibility of the cerium oxide particles to suppress sedimentation and further reducing the polishing scratches on the film to be polished, the content of the dispersant is in the range of 0.01 to 10% by mass based on the total mass of the polishing liquid. preferable.

  Although the weight average molecular weight of a dispersing agent does not have a restriction | limiting in particular, 100-150,000 are preferable and 1000-20000 are more preferable. When the molecular weight of the dispersant is 100 or more, a good polishing rate tends to be easily obtained when a film to be polished such as a silicon oxide film or a silicon nitride film is polished. If the weight average molecular weight of the dispersant is 150,000 or less, the storage stability of the polishing liquid tends to be difficult to decrease. The weight average molecular weight is a value measured by GPC and converted to standard polyoxyethylene.

  When the polishing liquid according to the present invention is used for polishing in the production of semiconductor elements, the content of alkali metals such as sodium ions, halogen, and sulfur in the dispersant is preferably 10 ppm or less.

(Preparation / storage / polishing method of polishing liquid)
The polishing liquid according to the present invention can be obtained, for example, by blending cerium oxide particles and water to disperse the particles, and further adding a hydroxy acid compound. The polishing liquid according to the present invention may be stored as a one-part polishing liquid containing cerium oxide particles, a hydroxy acid compound, water, and optionally a water-soluble polymer, and a cerium oxide slurry containing cerium oxide particles and water. You may preserve | save as a 2 component type polishing liquid which divided | segmented the structural component into (1st liquid) and the addition liquid (2nd liquid) containing a hydroxy acid compound and water.

  In the case of a two-component polishing liquid, the dispersant is preferably contained in the cerium oxide slurry. Additives other than the hydroxy acid compound may be included in either the cerium oxide slurry or the additive liquid, but are preferably included in the additive liquid in that the dispersion stability of the cerium oxide particles is not affected.

  When storing as a two-component polishing liquid in which the cerium oxide slurry and the additive liquid are separated, the planarization characteristics and the polishing rate can be adjusted by arbitrarily changing the combination of these two liquids. When polishing with a two-part polishing liquid, the cerium oxide slurry and additive liquid are sent through separate pipes, and these pipes are joined just before the outlet of the supply pipe to mix both liquids. A method of supplying the cerium oxide slurry and an additive solution immediately before polishing can be used.

  The polishing liquid according to the present invention can be adjusted to a desired pH and used for polishing. Although there is no restriction | limiting in particular as a pH adjuster, Alkali metals, ammonia water, and an acid component are mentioned. When the polishing liquid is used for semiconductor polishing, ammonia water and an acid component are preferably used rather than alkali metals. As the pH adjuster, an ammonium salt of a water-soluble polymer that has been partially neutralized with ammonia in advance can be used.

  The pH of the polishing liquid of the present invention is preferably in the range of 3-12. By being in the above range, the storage stability of the polishing liquid tends to be improved, and the number of scratches on the film to be polished tends to decrease. From this point of view, the pH is more preferably 4 or more, further preferably 5 or more, particularly preferably 5.5 or more, and extremely preferably 6 or more. From the same viewpoint, the pH is more preferably 11 or less, still more preferably 10 or less, particularly preferably 9 or less, and extremely preferably 8 or less. The pH of the polishing liquid can be measured with a pH meter (for example, Yokogawa Electric Corporation, trade name: Model PH81). For example, after calibrating two points using a standard buffer solution (phthalate pH buffer solution pH: 4.21 (25 ° C.), neutral phosphate pH buffer solution pH: 6.86 (25 ° C.)), the electrode Is measured in the polishing liquid after 2 minutes or more has elapsed and stabilized.

  In the method for polishing a substrate according to the present invention, the polishing liquid is supplied between the film to be polished and the polishing cloth in a state where the film to be polished of the substrate on which the film to be polished is pressed against the polishing cloth of the polishing surface plate. Meanwhile, the film to be polished is polished by relatively moving the substrate and the polishing surface plate.

  As the substrate, a substrate related to semiconductor element manufacture, for example, a semiconductor substrate in which a circuit element and a wiring pattern are formed, a substrate in which inorganic insulation is formed on a semiconductor substrate such as a semiconductor substrate in which a circuit element is formed, and the like. Can be mentioned. Examples of the film to be polished include an inorganic insulating film such as a silicon oxide film or a composite film of a silicon nitride film and a silicon oxide film. By polishing the inorganic insulating film formed on such a semiconductor substrate with the polishing liquid according to the present invention, unevenness on the surface of the inorganic insulating film can be eliminated, and the entire surface of the semiconductor substrate can be made smooth. The polishing liquid according to the present invention can also be used for shallow trench isolation.

  Hereinafter, the method for polishing a substrate will be described in more detail by taking the case of a semiconductor substrate on which an inorganic insulating film is formed as an example.

  As a polishing apparatus, a holder for holding a substrate having a film to be polished such as a semiconductor substrate, a polishing platen to which a motor capable of changing the number of rotations and the like, and a polishing cloth (pad) can be attached, A general polishing apparatus can be used. As a polishing apparatus, for example, trade name: EPO-111 manufactured by Ebara Corporation can be used.

  As the polishing cloth, a general nonwoven fabric, foamed polyurethane, porous fluororesin and the like can be used without particular limitation. Moreover, it is preferable that the polishing cloth is subjected to groove processing so that the polishing liquid is accumulated.

  The polishing conditions are not limited, but the rotation speed of the surface plate is preferably low rotation of 200 rotations / minute or less so that the semiconductor substrate does not pop out, and the pressure (working load) applied to the semiconductor substrate is scratched after polishing. 100 kPa or less is preferable. During polishing, the polishing liquid 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 polishing liquid.

  The semiconductor substrate after polishing is preferably washed in running water, and then dried by removing water droplets adhering to the semiconductor substrate using a spin dryer or the like.

  By polishing the inorganic insulating film, which is the film to be polished, with the polishing liquid in this way, surface irregularities can be eliminated and a smooth surface can be obtained over the entire surface of the semiconductor substrate. After the planarized shallow trench is formed, an aluminum wiring is formed on the inorganic insulating film, an inorganic insulating film is formed again between the wirings and on the wiring, and then the inorganic insulating film is polished with a polishing liquid. To obtain a smooth surface. By repeating this step a predetermined number of times, a semiconductor substrate having a desired number of layers can be manufactured.

  Examples of the inorganic insulating film polished by the polishing liquid according to the present invention include a silicon oxide film and a silicon nitride film. The silicon oxide film may be doped with an element such as phosphorus or boron. As a method for manufacturing the inorganic insulating film, a low pressure CVD method, a plasma CVD method, or the like can be given.

The silicon oxide film formation by the low pressure CVD method uses monosilane: SiH ₄ as the Si source and oxygen: O ₂ as the oxygen source. A silicon oxide film can be obtained by performing this SiH ₄ —O ₂ -based oxidation reaction at a low temperature of 400 ° C. or lower. In some cases, the silicon oxide film obtained by CVD is heat-treated at a temperature of 1000 ° C. or lower. In order to planarize the surface by high-temperature reflow, when doping silicon: P with phosphorus: P, 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. As the reaction gas, a TEOS-O-based gas (TEOS-plasma CVD) using SiH ₄ -N ₂ O-based gas using SiH ₄ as a Si source and N ₂ O as an oxygen source and tetraethoxysilane (TEOS) as a Si source. Law). The substrate temperature is preferably 250 to 400 ° C., and the reaction pressure is preferably 67 to 400 Pa.

Silicon nitride film formation by the low pressure CVD method uses dichlorosilane: SiH ₂ Cl ₂ as a Si source and ammonia: NH ₃ as a nitrogen source. This SiH ₂ Cl ₂ —NH ₃ -based oxidation reaction can be obtained by carrying out at a high temperature of 900 ° C. Silicon nitride film formed by plasma CVD method, as the reaction gas, SiH ₄ as an Si source, _SiH 4 -NH ₃ series gas using NH ₃ and the like as a nitrogen source. The substrate temperature is preferably 300 to 400 ° C.

  The polishing liquid and substrate polishing method according to the present invention can be applied not only to an inorganic insulating film formed on a semiconductor substrate but also to manufacturing processes of various semiconductor devices. The polishing liquid and the substrate polishing method according to the present invention include, for example, a silicon oxide film formed on a wiring board having predetermined wiring, an inorganic insulating film such as glass and silicon nitride, polysilicon, Al, Cu, Ti, and TiN. , W, Ta, TaN, etc., optical glass such as photomask, lens, prism, etc., inorganic conductive film such as ITO, optical integrated circuit composed of glass and crystalline material, optical switching element, optical waveguide Polishing optical fiber end faces, scintillator and other optical single crystals, solid state laser single crystals, blue laser LED sapphire substrates, semiconductor single crystals such as SiC, GaP, and GaAs, glass substrates for magnetic disks, magnetic heads, etc. Can also be applied.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not restrict | limited to these Examples.

(Production of cerium oxide powder)
Commercially available cerium carbonate hydrate: 40 kg was placed in an alumina container and baked in air at 830 ° C. for 2 hours to obtain 20 kg of yellowish white powder. When the phase of this powder was identified by the X-ray diffraction method, it was confirmed to be cerium oxide. The obtained cerium oxide powder: 20 kg was dry pulverized using a jet mill to obtain powdered cerium oxide.

(Production of cerium oxide slurry)
200 g of the cerium oxide prepared above and 795 g of deionized water are mixed, 5 g of an aqueous solution of ammonium polyacrylate (weight average molecular weight: 8000, 40% by mass) is added, and ultrasonic dispersion is performed with stirring. A cerium oxide dispersion was obtained. The ultrasonic dispersion was performed at an ultrasonic frequency of 400 kHz and a dispersion time of 20 minutes.

  Thereafter, 1 kg of a cerium oxide dispersion was placed in a 1 liter container (height: 170 mm) and allowed to stand to perform sedimentation classification. Classification time: After 15 hours, the height from the bottom of the container: 10 mm or more of the supernatant was pumped up. The obtained supernatant cerium oxide dispersion was then diluted with deionized water to obtain a cerium oxide slurry so that the solid content concentration was 5% by mass.

  In order to measure the average particle diameter (D50) of cerium oxide in the cerium oxide slurry, the slurry was diluted so that the transmittance (H) at the time of measurement with respect to the He—Ne laser was 60 to 70%. did. When this measurement sample was measured using a laser diffraction particle size distribution analyzer (trade name: Master Sizer Microplus, manufactured by Malvern) as a refractive index of 1.93 and an absorption of 0, the value of D50 was 200 nm.

Example 1
As a hydroxy acid compound, 30 g of malic acid and 250 g of deionized water were mixed, and 20 g of aqueous ammonia (25% by mass) was added to adjust the pH to 6.5. The pH was measured using a pH meter (trade name: Model PH81, manufactured by Yokogawa Electric Corporation), standard buffer solution (phthalate pH buffer solution pH: 4.21 (25 ° C.), neutral phosphate. After calibrating two points using a pH buffer solution (pH: 6.86 (25 ° C.)), the electrode was placed in the measurement object, and the value after 2 minutes had passed and stabilized was measured. Further, deionized water was added to obtain 2700 g of malic acid additive solution.

  Here, 300 g of the cerium oxide slurry was added to prepare 3000 g of a cerium oxide polishing liquid (abrasive grain concentration: 0.5 mass%, hydroxy acid compound: 1 mass%).

  In addition, a measurement sample was prepared in the same manner as described above, and the average particle size of the particles in the polishing liquid was measured with a laser diffraction particle size distribution meter. As a result, the value of D50 was 200 nm. Moreover, when pH was measured like the above, pH was 7.3.

(Insulating film polishing)
As a polishing test wafer, a silicon oxide blanket wafer in which silicon oxide was formed on a silicon substrate and a silicon nitride film blanket wafer (diameter: 200 mm) in which silicon nitride was formed on a silicon substrate were used.

A polishing apparatus (trade name: EPO-111, manufactured by Ebara Corporation) was used for polishing the polishing test wafer. A polishing test wafer was set in a holder on which a suction pad for mounting the substrate was attached. A polishing cloth made of porous urethane resin (groove shape = perforate type: manufactured by Rohm and Haas, trade name: IC1000) was attached to a polishing surface plate having a diameter of 600 mm of a polishing apparatus. Further, each of the blanket wafers is placed on the polishing platen with the silicon oxide film surface or silicon nitride film surface as the film to be polished facing down, and the processing load is set to 350 gf / cm ² (34.3 kPa). Set.

  While dropping the cerium oxide polishing liquid on the polishing platen at a rate of 200 ml / min, the polishing platen and the polishing test wafer were each operated at 50 rpm to polish the polishing test wafer for 60 seconds. . The polished test wafer after polishing was thoroughly washed with pure water and then dried.

  For each polished test wafer after polishing, the residual film thickness of the silicon oxide film and the silicon nitride film was measured using an interference film thickness measuring apparatus (trade name: Nanospec / AFT5100, manufactured by Nanometrics Co., Ltd.). The polishing rate of the silicon film was 3200 分 / min, the polishing rate of the silicon nitride film was 32 Å / min, and the polishing rate ratio between the silicon oxide film and the silicon nitride film was as large as 100, and good results were obtained.

(Example 2)
As a hydroxy acid compound, 30 g of citric acid and 243 g of deionized water are mixed, 27 g of ammonia water (25% by mass) is added to adjust the pH to 6.5, and 1100 g of deionized water is further added to add citric acid. A liquid was prepared.

  Moreover, the cerium oxide slurry produced in Example 1 (solid content: 5 mass%): It diluted by adding 1200 g of deionized water to 300 g, and produced the cerium oxide slurry whose cerium oxide solid content concentration is 1 mass%. . A measurement sample was prepared in the same manner as in Example 1, and the average particle size of the particles in the polishing liquid was measured with a laser diffraction particle size distribution analyzer. As a result, the value of D50 was 200 nm. Moreover, when pH was measured like the above, pH was 7.3.

(Insulating film polishing)
Example except that 1% by mass of the cerium oxide slurry prepared above: 1000 g and hydroxy acid addition liquid: 1000 g were mixed immediately before polishing to obtain a cerium oxide polishing liquid (solid content: 0.5% by mass). In the same manner as in Example 1, the polishing test wafer was polished. The polishing rate of the silicon oxide film was 3340 Å / min, the polishing rate of the silicon nitride film was 35 Å / min, and the polishing rate ratio between the silicon oxide film and the silicon nitride film was as large as 95, and good results were obtained.

(Comparative Example 1)
A cerium oxide polishing liquid was prepared in the same manner as in Example 1 except that 30 g of propionic acid was used in place of malic acid as the hydroxy acid compound. A measurement sample was prepared in the same manner as in Example 1, and the average particle size of the particles in the polishing liquid was measured with a laser diffraction particle size distribution analyzer. As a result, the value of D50 was 200 nm. Moreover, when pH was measured like the above, pH was 7.3. The polishing test wafer was polished in the same manner as in Example 1. The polishing rate of the silicon oxide film was 1552 Å / min, the polishing rate of the silicon nitride film was 120 Å / min, and the polishing rate ratio between the silicon oxide film and the silicon nitride film was 13, which was smaller than that containing the hydroxy acid compound.

(Comparative Example 2)
Ammonium polyacrylate aqueous solution (mass average molecular weight: 8000, 40% by mass): 23 g and deionized water: 2673 g were mixed, and 4 g of aqueous ammonia (25% by mass) was added to adjust the pH to 4.8. Furthermore, 300 g of the cerium oxide slurry prepared in Example 1 (solid content: 5% by mass) was added to prepare a cerium oxide polishing liquid (solid content: 0.5% by mass). A measurement sample was prepared in the same manner as in Example 1, and the average particle size of the particles in the polishing liquid was measured with a laser diffraction particle size distribution analyzer. As a result, the value of D50 was 200 nm. Moreover, when pH was measured similarly to the above, it was 5.1.

(Insulating film polishing)
The polishing test wafer was polished in the same manner as in Example 1 except that the polishing liquid prepared above was used. The polishing rate of the silicon oxide film was 2700 Å / min, the polishing rate of the silicon nitride film was 68 Å / min, and the polishing rate ratio between the silicon oxide film and the silicon nitride film was 40, which was smaller than that containing the hydroxy acid compound.

Claims (6)

  A polishing liquid comprising cerium oxide particles, at least one additive selected from the group consisting of hydroxy acid compounds and salts of hydroxy acid compounds, and water.   The polishing liquid according to claim 1, wherein the hydroxy acid compound is at least one selected from the group consisting of malic acid, citric acid, lactic acid, glycolic acid, glyceric acid, tartaric acid, and salicylic acid.   The polishing liquid according to claim 1 or 2, wherein the content of the additive is 0.0001 to 5% by mass based on the total mass of the polishing liquid.   The polishing liquid according to claim 1, which does not contain an alcohol compound.   Any one of Claims 1-4 preserve | saved as a 2 component type polishing liquid which divided the component into the 1st liquid containing the said cerium oxide particle and water, and the 2nd liquid containing the said additive and water. The polishing liquid described in 1.   The polishing liquid according to any one of claims 1 to 5 is applied between the film to be polished and the polishing cloth in a state where the film to be polished of the substrate on which the film to be polished is formed is pressed against a polishing cloth of a polishing platen. A method for polishing a substrate, wherein the film to be polished is polished by relatively moving the substrate and the polishing surface plate while supplying the substrate.