JP4389887B2 - Polishing agent and substrate polishing method - Google Patents

Description

  The present invention relates to a polishing agent suitably used in a planarization process of a substrate surface in a manufacturing process of a semiconductor device, in particular, a shallow trench isolation formation process, and a substrate using the polishing agent. The present invention relates to a polishing method.

  In the present ultra-large scale integrated circuit, there is a tendency to increase the mounting density, and various fine processing techniques are being researched and developed. Already, the design rules are on the order of sub-half microns. One of the techniques that have been developed in order to satisfy such demands for strict miniaturization is a CMP (chemical mechanical polishing) technique. Since this technology can completely planarize the layer to be exposed in the manufacturing process of the semiconductor device, reduce the burden of the exposure technology, and stabilize the yield, for example, planarization of the interlayer insulating film, shallow trench This technique is essential when performing separation or the like.

  Conventionally, CMP polishing for planarizing an inorganic insulating film layer such as a silicon oxide insulating film formed by a method such as plasma-CVD (Chemical Vapor Deposition) or low-pressure CVD in a manufacturing process of a semiconductor device. Colloidal silica-based abrasives have been generally studied as agents. Colloidal silica-based abrasives are produced by growing silica particles by a method such as thermal decomposition of tetrachlorosilicic acid and adjusting pH.

  In generations with a design rule of 0.5 μm or more, LOCOS (silicon local oxidation) was used for element isolation in an integrated circuit. Thereafter, when the processing dimensions are further miniaturized, a technology with a narrow element isolation width is required, and shallow trench isolation is being used. In shallow trench isolation, CMP is used to remove an excess silicon oxide film formed on the substrate, and a stopper film having a low polishing rate is formed under the silicon oxide film in order to stop polishing. Silicon nitride or the like is used for the stopper film, and it is desirable that the polishing rate ratio between the silicon oxide film and the stopper film is large. Conventional colloidal silica-based abrasives have a polishing rate ratio of the above-described silicon oxide film and stopper film as small as about 3, and have no practical characteristics for shallow trench isolation.

  On the other hand, cerium oxide abrasives are used as glass surface abrasives for photomasks and lenses. Cerium oxide particles have a lower hardness than silica particles and alumina particles, and are therefore useful for finishing mirror polishing because they do not easily scratch the polished surface. However, since a cerium oxide abrasive for polishing a glass surface uses a dispersant containing a sodium salt, it cannot be directly applied as an abrasive.

  The inventions of claims 1 and 2 provide an abrasive that is highly practical for shallow trench isolation and can be polished without scratches. In addition to the invention described in claim 1 or 2, the invention described in claim 3 provides an abrasive capable of increasing the ratio of the silicon oxide insulating film polishing rate and the silicon nitride insulating film polishing rate and improving the dispersion stability. To do. The invention according to claim 4 provides an abrasive capable of sufficiently increasing the ratio of the silicon oxide insulating film polishing rate to the silicon nitride insulating film polishing rate in addition to the invention according to claim 1, 2 or 3.

  The invention described in claim 5 provides a method for polishing a substrate, which is highly practical for shallow trench isolation and can be polished without scratches. The invention described in claim 6 provides a method for polishing a substrate capable of polishing a surface to be polished of a silicon oxide film or a silicon nitride film without scratches. The invention described in claim 7 provides a method for polishing a substrate capable of polishing a surface to be polished of a silicon oxide film or a silicon nitride film formed in a pattern without any scratches.

  The present invention relates to an abrasive containing abrasive grains, a surfactant and water, wherein the ratio of the silicon oxide film polishing rate to the silicon nitride film polishing rate is 100 or more. Further, the present invention is a mixture of a cerium oxide slurry containing cerium oxide particles, a dispersant and water, and an additive solution containing a surfactant and water, and has a silicon oxide film polishing rate and a silicon nitride film polishing rate. It is related with the abrasive | polishing agent whose ratio is 100 or more. The present invention also relates to the above abrasive, wherein the surfactant is an amino acid surfactant. Moreover, this invention relates to the said abrasive | polishing agent whose pH (25 degreeC) is 5-10.

  In addition, the present invention presses the substrate on which the film to be polished is pressed against the polishing cloth of the polishing surface plate and pressurizes the substrate, while supplying the abrasive between the polishing film and the polishing cloth, The present invention relates to a method for polishing a substrate for polishing a film to be moved and polished. The present invention also relates to the method for polishing a substrate, wherein the substrate is a substrate on which at least a silicon oxide film or a silicon nitride film is formed. The present invention also relates to the method for polishing a substrate, wherein the substrate is a substrate in which a silicon oxide film or a silicon nitride film is formed in a pattern.

  The abrasive according to claims 1 and 2 is highly practical for shallow trench isolation and can be polished without scratches. In addition to the invention of claim 1 or 2, the polishing agent according to claim 3 can increase the ratio of the silicon oxide insulating film polishing rate to the silicon nitride insulating film polishing rate and improve the dispersion stability. . The polishing agent according to claim 4 can sufficiently increase the ratio of the silicon oxide insulating film polishing rate to the silicon nitride insulating film polishing rate in addition to the invention according to claim 1, 2 or 3.

  The method for polishing a substrate according to claim 5 is highly practical for separating the surface of the substrate to be used for shallow trench isolation and can be polished without scratches. According to the substrate polishing method of the sixth aspect, the surface to be polished of the silicon oxide film or the silicon nitride film can be polished without scratches. According to a seventh aspect of the present invention, the polished surface of the silicon oxide film or silicon nitride film formed in a pattern can be polished without scratches.

  The abrasive of the present invention contains abrasive grains, a surfactant and water, and the ratio of the silicon oxide film polishing rate to the silicon nitride film polishing rate is 100 or more. If this ratio is less than 100, it cannot withstand practical use for shallow trench isolation. This ratio is preferably 150 or more, more preferably 200 or more, particularly preferably 500 or more, extremely preferably 1000 or more, and most preferably 1500 or more. The polishing agent having a ratio of the silicon oxide film polishing rate to the silicon nitride film polishing rate of 100 or more is, for example, a cerium oxide slurry containing cerium oxide particles, a dispersant and water, and an additive liquid containing a surfactant and water. Can be mixed and adjusted.

  Examples of the abrasive grains in the present invention include cerium oxide, aluminum oxide, zirconium oxide, tin oxide, silicon dioxide, silicone carbide, titanium dioxide, and titanium carbide. Cerium oxide is preferable from the viewpoint of increasing the ratio of the silicon oxide film polishing rate to the silicon nitride film polishing rate and high flatness. The production method of cerium oxide particles is not limited, but can be obtained by oxidizing a cerium compound of carbonate, nitrate, sulfate or oxalate. The cerium oxide primary particle diameter is preferably 5 nm or more and 300 nm or less. Moreover, since it uses for semiconductor chip grinding | polishing, it is preferable to suppress the content rate of an alkali metal and halogens to 10 ppm or less in a cerium oxide particle.

  In the present invention, as a method for producing the cerium oxide powder, an oxidation method by baking, hydrogen peroxide treatment, or the like can be used. The firing temperature is preferably 350 ° C. or higher and 900 ° C. or lower. Since the cerium oxide particles produced by the above method are agglomerated, it is preferably mechanically pulverized. As the pulverization method, a dry pulverization method such as a jet mill or a wet pulverization method such as a planetary bead mill is preferable.

  The cerium oxide slurry in the present invention is obtained, for example, by dispersing a composition comprising cerium oxide particles having the above characteristics, a dispersant, and water. Here, although there is no restriction | limiting in the density | concentration of a cerium oxide particle, The range of 0.5 to 20 weight% is preferable from the ease of handling of a dispersion liquid.

  As the dispersant in the present invention, the content of alkali metals such as sodium ions and potassium ions and halogen and sulfur is preferably suppressed to 10 ppm or less from the point of use for semiconductor chip polishing. A polymer dispersant containing an ammonium salt is preferred. In addition, as a dispersant, a polymer dispersant containing an ammonium acrylate salt as a copolymerization component, a water-soluble anionic surfactant, a water-soluble nonionic surfactant, a water-soluble cationic surfactant, a water-soluble You may use 1 or more types, such as an amphoteric surfactant.

  Examples of water-soluble anionic surfactants include, for example, triethanolamine lauryl sulfate, ammonium lauryl sulfate, triethanolamine lauryl benzene sulfonate, triethanolamine polyoxyethylene lauryl ether sulfate, polycarboxylic acid type polymer surfactant, Coconut oil fatty acid acylalanine triethanolamine, coconut oil fatty acid glutamic acid triethanolamine, lauric acid glutamic acid triethanolamine, coconut oil fatty acid alaninate triethanolamine, sarcosine derivatives, lauric acid triethanolamine, etc. Examples of the surfactant include polyoxyethylene lauryl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, and polyoxyethylene ether. Yl ether, polyoxyethylene higher alcohol ether, polyoxyethylene octyl phenyl ether, polyoxyethylene nonyl phenyl ether, polyoxyalkylene alkyl ether, polyoxyethylene derivative, polyoxyethylene sorbitan monolaurate, polyoxyethylene sorbitan monopalmitate , Polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan tristearate, polyoxyethylene sorbitan monooleate, polyoxyethylene sorbitan trioleate, polyoxyethylene sorbite tetraoleate, polyethylene glycol monolaurate, polyethylene glycol monostearate Rate, polyethylene glycol distearate, polyethylene glycol mono Examples include water, polyoxyethylene alkylamine, polyoxyethylene hydrogenated castor oil, alkyl alkanolamide, and water-soluble cationic surfactants such as coconut amine acetate and stearyl amine acetate. Examples of the amphoteric surfactant include lauryl betaine, stearyl betaine, lauryl dimethylamine oxide, 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine and the like.

  These dispersants are added in an amount of 0.01 parts by weight or more and 2.0 parts by weight with respect to 100 parts by weight of cerium oxide particles due to the dispersibility of particles in the slurry and settling prevention, and also the relationship between polishing scratches and the amount of dispersant added. The range of parts by weight or less is preferred. The molecular weight of the dispersant is preferably 100 to 50,000, more preferably 1,000 to 10,000. When the molecular weight of the dispersant is less than 100, a sufficient polishing rate cannot be obtained when polishing the silicon oxide film or the silicon nitride film, and when the molecular weight of the dispersant exceeds 50,000, the viscosity is high. This is because the storage stability of the cerium oxide slurry is lowered.

  On the other hand, surfactants in an additive solution containing a surfactant and water are water-soluble anionic surfactants, water-soluble nonionic surfactants, water-soluble cationic surfactants, water-soluble amphoteric surfactants. Although an agent or the like can be used, an amino acid-based surfactant among water-soluble anionic surfactants is particularly preferable from the viewpoint of increasing the ratio of the silicon oxide film polishing rate to the silicon nitride film polishing rate. The amino acid-based surfactant is not particularly limited, but N-substituted amino acids and N-substituted amino acid salts are used from the viewpoint of increasing the ratio of the silicon oxide film polishing rate to the silicon nitride film polishing rate and high flatness. Among them, N acylamino acid and N acylmino acid salts are preferable. Here, examples of the base for forming the salt include alkali metal hydroxides such as NaOH and KOH, and organic alkalis such as triethanolamine, but organic alkali is preferable.

  Specific examples of such amino acid surfactants include coconut oil fatty acid acylalanine triethanolamine, coconut oil fatty acid glutamic acid triethanolamine, lauric acid glutamic acid triethanolamine, coconut oil fatty acid alaninate triethanolamine, and sarcosine derivatives. Etc. In addition, as commercial products, trade names from Ajinomoto Co., Inc., such as trade name Amisoft LT-12, Amilite ACT-12, etc., from Lion Corporation as trade names, Energol L-30ANT, etc., from Toho Chemical Industries, Inc. It is available as SCT-30 or the like.

  This amino acid-based anionic surfactant is added in an amount of 0.01 to 100 parts by weight of the cerium oxide particles due to the dispersibility of the particles in the slurry and the prevention of settling, and the relationship between the polishing scratches and the added amount of the surfactant. The range of not less than 1000 parts by weight is preferred. When the cerium oxide slurry and the additive solution are mixed and stored, the cerium oxide particles may aggregate or settle, resulting in generation of polishing flaws and fluctuations in the polishing rate. For this reason, the additive solution is supplied separately from the cerium oxide slurry on the polishing platen and mixed on the polishing platen, or mixed with the cerium oxide slurry and supplied onto the polishing platen immediately before polishing. Sometimes taken.

  The pH of the abrasive of the present invention is preferably 5 or more and 10 or less. When the pH is less than 5 or when the pH exceeds 10, the ratio of the silicon oxide film polishing rate to the silicon nitride film polishing rate may not be 100 or more. For adjusting the pH, a method of mixing and stirring triethanolamine, aqueous ammonia, acetic acid, or the like can be used.

  As a method for dispersing these cerium oxide particles in water, a homogenizer, an ultrasonic disperser, a wet ball mill or the like can be used in addition to a dispersion treatment using a normal stirrer. The average particle size of the cerium oxide particles in the slurry thus prepared is preferably 0.01 μm to 1.0 μm. This is because if the average particle size of the polishing liquid is less than 0.01 μm, the polishing rate becomes too low, and if it exceeds 1.0 μm, the film to be polished is easily damaged.

  The abrasive of the present invention may use the cerium oxide slurry and additive liquid as they are, but an additive such as N, N-diethylethanolamine, N, N-dimethylethanolamine, aminoethylethanolamine is added. Thus, an abrasive can be obtained.

Examples of a method for manufacturing an inorganic insulating film in which the abrasive of the present invention is used include a low pressure CVD method and a plasma CVD method. 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. It can be obtained by performing this SiH ₄ —O ₂ oxidation reaction at a low temperature of 400 ° C. or lower. In some cases, heat treatment is performed at a temperature of 1000 ° C. or lower after CVD. When doping phosphorus: P in order to achieve surface flattening by high-temperature reflow, 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. The reaction as a gas, SiH ₄ as an Si source, an oxygen source as _{N 2} O was used was _SiH 4 -N ₂ O-based gas and _{TEOS-O 2} based gas using tetraethoxysilane (TEOS) in an Si source (TEOS- Plasma CVD method). The substrate temperature is preferably 250 to 400 ° C., and the reaction pressure is preferably 67 to 400 Pa.

Thus, the silicon oxide film of the present invention may be doped with elements such as phosphorus and boron. Similarly, silicon nitride film formation by low pressure CVD uses dichlorosilane: SiH ₂ Cl ₂ as a Si source and ammonia: NH ₃ as a nitrogen source. It can be obtained by performing this SiH ₂ Cl ₂ —NH ₃ oxidation reaction at a high temperature of 900 ° C. In the plasma CVD method, examples of the reactive gas include SiH ₄ —NH ₃ based gas using SiH ₄ as the Si source and NH ₃ as the nitrogen source. The substrate temperature is preferably 300 ° C to 400 ° C.

  As the substrate, a substrate in which a silicon oxide film layer or a silicon nitride film layer is formed on a silicon substrate, or a semiconductor substrate in which a circuit element and a wiring pattern are formed, a stage in which a circuit element is formed A substrate in which a silicon oxide film layer or a silicon nitride film layer is formed on a semiconductor substrate such as a semiconductor substrate can be used. By polishing the silicon oxide film layer or silicon nitride film layer formed on such a semiconductor substrate with the above-mentioned polishing agent, unevenness on the surface of the silicon oxide film layer is eliminated, and the entire surface of the semiconductor substrate is made smooth. Can do. It can also be used for shallow trench isolation. In order to use for shallow trench isolation, the ratio of the silicon oxide film polishing rate to the silicon nitride film polishing rate and the silicon oxide film polishing rate / silicon nitride film polishing rate must be 10 or more. When this ratio is less than 10, the difference between the silicon oxide film polishing rate and the silicon nitride film polishing rate is small, and polishing cannot be stopped at a predetermined position when performing shallow trench isolation. When this ratio is 100 or more, the polishing rate of the silicon nitride film is further reduced and the polishing can be stopped more easily, which is preferable for shallow trench isolation. In addition, in order to use for shallow trench isolation, it is necessary that the generation of scratches is small during polishing.

Here, as a polishing apparatus, a general polishing apparatus having a surface plate with a holder for holding a semiconductor substrate and a polishing cloth (pad) attached (a motor etc. capable of changing the number of rotations) is used. it can. As an abrasive cloth, a general nonwoven fabric, a polyurethane foam, a porous fluororesin, etc. can be used, and there is no restriction | limiting in particular. Further, it is preferable that the polishing cloth is grooved so that the CMP abrasive is accumulated. The polishing conditions are not limited, but the rotation speed of the surface plate is preferably low rotation of 200 rpm or less so that the semiconductor substrate does not jump out, and the pressure applied to the semiconductor substrate is 1 kg / cm ² or less so that no scratches are generated after polishing. Is preferred. During polishing, slurry 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 the slurry.

  The semiconductor substrate after completion of polishing is preferably washed in running water and then dried after removing water droplets adhering to the semiconductor substrate using a spin dryer or the like. After forming the flattened shallow trench in this way, an aluminum wiring is formed on the silicon oxide insulating film layer, and after forming the silicon oxide insulating film again between the wirings and on the wiring by the above method, By polishing with a CMP abrasive, unevenness on the surface of the insulating film is eliminated, and a smooth surface is obtained over the entire surface of the semiconductor substrate. By repeating this process a predetermined number of times, a desired number of semiconductor layers are manufactured.

  The abrasive of the present invention includes not only a silicon oxide film and a silicon nitride film formed on a semiconductor substrate, but also an inorganic insulating film such as a silicon oxide film, glass, and a silicon nitride film formed on a wiring board having a predetermined wiring, Optical glass such as photomasks, lenses, and prisms, inorganic conductive films such as ITO, optical integrated circuits composed of glass and crystalline materials, optical switching elements, optical waveguides, end faces of optical fibers, optical single crystals such as scintillators, Solid laser single crystals, blue laser LED sapphire substrates, semiconductor single crystals such as SiC, GaP, and GaAS, magnetic disk glass substrates, magnetic heads, and the like can be polished.

  Next, an example explains the present invention.

[Preparation of cerium oxide particles 1]
About 1 kg of yellowish white powder was obtained by putting 2 kg of cerium carbonate hydrate into a platinum container and firing in air at 800 ° C. for 2 hours. When this powder was phase-identified by X-ray diffraction, it was confirmed to be cerium oxide. It mixed with pure water so that it might become 10 weight% of cerium oxide powder, and it pulverized for 120 minutes at 1400 rpm using the horizontal wet ultrafine particle dispersion pulverizer. The obtained polishing liquid was dried at 110 ° C. for 3 hours to obtain cerium oxide particles. The cerium oxide particles were found to have a weight average crystal diameter of 80 nm from observation with a transmission electron microscope.

[Preparation of cerium oxide particles 2]
About 1 kg of yellowish white powder was obtained by putting 2 kg of cerium carbonate hydrate in a platinum container and firing in air at 800 ° C. for 2 hours. When this powder was phase-identified by X-ray diffraction, it was confirmed to be cerium oxide. 1 kg of cerium oxide powder was dry pulverized using a jet mill. The cerium oxide particles were found to have a weight average crystal diameter of 80 nm from observation with a transmission electron microscope.

[Preparation of cerium oxide slurry 1]
Acrylic acid / methyl acrylate copolymer ammonium salt aqueous solution (40% by weight) having a molecular weight of 10,000 obtained by copolymerizing 125 g of the cerium oxide particles prepared in Preparation 1 of the above cerium oxide particles and acrylic acid and methyl acrylate in a ratio of 3: 1. ) 3 g and 2372 g of pure water were mixed and subjected to ultrasonic dispersion while stirring. The ultrasonic frequency was 40 kHz, and dispersion was performed with a dispersion time of 10 minutes. The obtained slurry was filtered with a 0.8 micron filter, and further deionized water was added to obtain a 2 wt% cerium oxide slurry (A-1). The pH of the cerium oxide slurry (A-1) was 8.5. When the particle size distribution of the cerium oxide slurry (A-1) was examined with a laser diffraction particle size distribution meter (Mastersizer Microplus, measured by Malvern Instruments, refractive index: 1.928), the average particle size was as small as 0.20 μm. I understood. Moreover, the particle | grains of 1.0 micrometer or less were 95.0%.

[Preparation of cerium oxide slurry 2]
The cerium oxide slurry (A-2) was prepared in the same manner as in the preparation of cerium oxide slurry 1 except that the cerium oxide particles prepared in Preparation 2 of cerium oxide particles were used instead of the cerium oxide particles prepared in Preparation 1 of cerium oxide particles. ) Was produced. The pH of this cerium oxide slurry (A-2) was 8.7. When the particle size distribution of the cerium oxide slurry (A-2) was examined, it was found that the average particle size was as small as 0.21 μm. Moreover, the particle | grains of 1.0 micrometer or less were 95.0%.

Examples 1-5 and Comparative Examples 1-3
The cerium oxide slurry and the additive liquid were mixed as shown in Table 1 and Table 2 below to produce an abrasive, and the insulating film layer was polished. The results are shown in Tables 1 and 2. The pH and dispersion stability of the abrasive are also shown in Tables 1 and 2.

[Polishing the insulating film layer]
A silicon oxide film (SiO ₂ film) produced by TEOS-plasma CVD method was formed on a holder with a suction pad for attaching a substrate on a surface plate on which a polishing pad made of porous urethane resin was attached. Diameter 125 mm The silicon wafer was set with the insulating film face down, and a weight was applied so that the polishing load was 300 g / cm ² . While feeding the above cerium oxide slurry (solid content: 2% by weight) and additive liquid on the surface plate at a rate of 25 ml / min, adjusting the nozzle so that it becomes one liquid just before the surface plate, The surface plate was rotated at 40 rpm for 2 minutes to polish the insulating film. After polishing, the wafer was removed from the holder, washed thoroughly with running water, and further washed with an ultrasonic cleaner for 20 minutes. After washing, water droplets were removed with a spin dryer and dried for 10 minutes with a 120 ° C. dryer.

The change in film thickness before and after polishing was measured using an optical interference type film thickness measuring device, and the polishing rate was calculated. Similarly, a silicon nitride film (Si ₃ N ₄ film) produced by low-pressure CVD instead of a silicon oxide film produced by TEOS-plasma CVD is polished under the same conditions, and the change in film thickness before and after polishing is measured. The polishing rate was calculated. From the results of film thickness measurement, it was confirmed that the silicon oxide film produced by the TEOS-plasma CVD method and the silicon nitride film produced by the low pressure CVD method had a uniform thickness over the entire surface of the wafer. Further, the polishing scratches were observed by visual observation under a mercury lamp light source. In addition, the dispersion stability was determined by measuring the average particle size after 7 days with a laser diffraction particle size distribution meter, and judging that 0.27 μm or less was good and 0.28 μm or more was bad.

  As is apparent from Table 1, by using the polishing agent and substrate polishing method of the present invention, the surface to be polished such as a silicon oxide film or a silicon nitride film is contaminated with alkali metal such as sodium ions on the surface to be polished. An abrasive that can be polished without scratches and that has a ratio of a silicon oxide film polishing rate / a silicon nitride film polishing rate of 100 or more, and can be reliably stopped by a stopper film, and these abrasives It can be seen that polishing of the used substrate can be achieved.

Claims (6)

Abrasive, a polishing liquid for polishing a substrate having a water soluble anionic surfactant and water including, a silicon oxide film and a silicon nitride film,
The water-soluble anionic surfactant is an N-substituted amino acid or a salt of an N-substituted amino acid,
A polishing load of 300 g / cm ² for a silicon wafer with a diameter of 125 mm formed with a silicon oxide film manufactured by TEOS-plasma CVD method and a silicon wafer with a diameter of 125 mm formed with a silicon nitride film prepared by TEOS-plasma CVD method, respectively. The relationship between the polishing rates of the two films when polishing using a porous urethane resin pad at a platen rotational speed of 40 rpm is an amount of water-soluble anions such that the silicon oxide film polishing rate / silicon nitride film polishing rate ≧ 100 A polishing agent containing a surfactant .   The abrasive according to claim 1, having a pH (25 ° C) of 5 or more and 10 or less. The water-soluble anionic surfactant is a salt of an N-substituted amino acid;
The polishing agent according to claim 1, wherein the base for forming the salt is an alkali metal hydroxide or an organic alkali. A polishing method for a substrate , wherein the polishing liquid according to claim 1 is supplied between a substrate on which a film to be polished is formed and a polishing cloth to polish the film to be polished . The method for polishing a substrate according to claim 4 , wherein the substrate is a substrate on which at least a silicon oxide film and a silicon nitride film are formed. 6. The method for polishing a substrate according to claim 5 , wherein the substrate is a substrate in which a silicon oxide film or a silicon nitride film is formed in a pattern.