JP6732402B2 - Abrasive, abrasive set, and method for polishing substrate - Google Patents

Description

The present invention relates to an abrasive, an abrasive set, and a method for polishing a substrate. Particularly, the present invention relates to an abrasive for chemical mechanical polishing (CMP), an abrasive set, and a method for polishing a substrate.

In recent years, further miniaturization of wiring has been required in the manufacturing process of semiconductor devices, and polishing scratches generated during polishing have become a problem. For example, even if minute polishing scratches are generated when polishing is performed using a conventional cerium oxide-based polishing agent, it is not a problem as long as the size of the polishing scratches is smaller than the conventional wiring width. However, when further miniaturization of the wiring is to be achieved, even if the polishing scratches are minute, there is a problem.

To solve this problem, abrasives using particles of hydroxide of a tetravalent metal element have been studied (see, for example, Patent Documents 1 to 3 below). In addition, a method for producing particles of a hydroxide of a tetravalent metal element has also been studied (see, for example, Patent Documents 4 and 5 below). These techniques are intended to reduce polishing scratches caused by particles by making the mechanical action as small as possible while making full use of the chemical action of particles of a hydroxide of a tetravalent metal element.

By the way, in recent years, there is a semiconductor element in which silicon nitride is used as a constituent material of a hard mask or a cap. In the manufacturing process of such a semiconductor device, it is necessary to remove a part or all of silicon nitride. Examples of the method for removing silicon nitride include dry etching. However, if the silicon nitride can be removed by the CMP process, the process can be simplified, so that the throughput can be improved and the cost can be reduced.

As a CMP polishing agent for removing silicon nitride, a polishing agent composition in which polishing abrasive grains (for example, abrasive grains containing fumed silica, colloidal silica, ceria, etc.), a pH adjusting agent, an additive, etc. are combined. Have been studied (for example, see Patent Documents 6 to 8 below).

International Publication No. 2002/067309 International Publication No. 2012/070541 International Publication No. 2012/070542 JP, 2006-249129, A International Publication No. 2012/070544 JP, 2010-041037, A Japanese Patent Publication No. 2009-530811 Patent No. 5188980

However, further improvement is required for the polishing rate of silicon nitride, and it is required to polish silicon nitride at high speed.

The present invention is intended to solve the above problems, and an object of the present invention is to provide an abrasive capable of polishing silicon nitride at high speed, an abrasive set, and a method for polishing a substrate.

The present inventor has found that silicon nitride can be polished at high speed by using abrasive grains containing a hydroxide of a tetravalent metal element in combination with a triazine compound having a triazine skeleton.

That is, the present invention provides an abrasive containing a liquid medium, abrasive grains containing a hydroxide of a tetravalent metal element, and a triazine compound having a triazine skeleton. According to the polishing agent of the present invention, silicon nitride can be polished at high speed.

By the way, a surface to be polished containing various materials to be polished such as silicon oxide, polysilicon, etc. in addition to silicon nitride, such as a FinFET structure which is a transistor structure which has been actively researched in recent years, and a gate portion of a semiconductor element. May be polished. In such a case, it is necessary to control the polishing rate of the object depending on the situation, such as removing only silicon nitride or removing both silicon nitride and another material to be polished (eg, silicon oxide). May be required. However, since silicon nitride is difficult to obtain a sufficient polishing rate (hard to be removed) as compared with a material to be polished such as silicon oxide or polysilicon, it is a problem to adjust the polishing rate between silicon nitride and another material to be polished. It is said that. On the other hand, according to the polishing agent of the present invention, it is possible to adjust the polishing rate between silicon nitride and another material to be polished (eg, an insulating material such as silicon oxide; a silicon material such as polysilicon or silicon). it can.

The content of the triazine compound is preferably 0.001% by mass or more based on the total mass of the abrasive. This makes it possible to polish silicon nitride at a higher speed.

The tetravalent metal element is preferably tetravalent cerium. This makes it possible to suppress the occurrence of polishing scratches on the surface to be polished while further improving the polishing rate of silicon nitride.

The abrasive grains have a nonvolatile content of 300 ppm or more when an aqueous dispersion in which the content of the abrasive grains is adjusted to 1.0% by mass is centrifuged at a centrifugal acceleration of 1.59×10 ⁵ G for 50 minutes. It is preferable to give it. This makes it possible to polish silicon nitride at a higher speed. In addition, "ppm" shall mean mass ppm, ie, "parts per million mass".

One aspect of the present invention relates to the use of the abrasive for polishing a surface to be polished containing silicon nitride. That is, the polishing agent according to the present invention is preferably used to polish a surface to be polished containing silicon nitride.

In the present invention, the constituents of the abrasive are stored separately in a first liquid and a second liquid, the first liquid contains the abrasive grains and a liquid medium, and the second liquid is the triazine. An abrasive set is provided that includes a compound and a liquid medium. According to the polishing agent set of the present invention, the same effects as those of the polishing agent of the present invention can be obtained.

The present invention provides a method for polishing a substrate, which comprises a step of polishing a surface to be polished of a substrate using the polishing agent, wherein the surface to be polished contains silicon nitride. According to such a substrate polishing method, the same effects as those of the polishing agent according to the present invention can be obtained.

The present invention comprises a step of polishing a surface to be polished of a substrate using an abrasive obtained by mixing the first liquid and the second liquid in the abrasive set, wherein the surface to be polished is nitrided. Provided is a method of polishing a substrate containing silicon. According to such a substrate polishing method, the same effects as those of the polishing agent according to the present invention can be obtained.

According to the present invention, it is possible to provide an abrasive, an abrasive set, and a method for polishing a substrate that can polish silicon nitride at high speed. The present invention can also provide the use of an abrasive or an abrasive set for polishing silicon nitride. According to the present invention, while polishing silicon nitride on a surface to be polished containing silicon nitride and another material to be polished (eg, an insulating material such as silicon oxide; silicon such as polysilicon and silicon), another material to be polished is polished. The use of an abrasive or abrasive set in the polishing process to control the amount of material abraded can be provided.

It is a cross-sectional schematic diagram which shows an example of an angle rotor. It is a cross-sectional schematic diagram which shows a part of High-k metal gate manufacturing process. It is a cross-sectional schematic diagram which shows a part of manufacturing process of the multi-gate element called Fin-FET. It is a cross-sectional schematic diagram which shows a part of manufacturing process of the gate structure in a transistor.

Hereinafter, a polishing agent, a polishing agent set, and a method for polishing a substrate using the polishing agent or the polishing agent set according to an embodiment of the present invention will be described in detail.

<Definition>
In the present specification, the term “process” is included in this term as long as the intended action of the process is achieved not only as an independent process but also when it cannot be clearly distinguished from other processes. Be done.

In the present specification, the amount of each component in the composition refers to the total amount of the plurality of substances present in the composition, unless a plurality of substances corresponding to each component are present in the composition. means.

In the present specification, “polishing rate” means a rate at which a material is removed per unit time (removal rate=Removal Rate).

In the present specification, the "abrasive" is defined as a composition that comes into contact with the surface to be polished during polishing. The phrase "abrasive" by itself does not limit the components contained in the abrasive. As described later, the polishing agent according to the present embodiment contains abrasive grains (Abrasive Grain). The abrasive grains are also called “abrasive particles”, but in the present specification, they are referred to as “abrasive grains”. Abrasive grains are generally solid particles. In this case, it is considered that the object to be removed is removed (removed) by the mechanical action of the abrasive grains and the chemical action of the abrasive grains (mainly the surface of the abrasive grains) during polishing. It is not limited to this.

<Abrasive and abrasive set>
The polishing agent according to this embodiment is, for example, a polishing agent for CMP. Specifically, the polishing agent according to the present embodiment contains at least a liquid medium, abrasive grains containing a hydroxide of a tetravalent metal element, and a triazine compound having a triazine skeleton. According to the polishing agent of the present embodiment, silicon nitride can be polished at a high speed, and the polishing rate of silicon nitride and another polishing target material can be adjusted. Examples of other materials to be polished include an insulating material (in this specification, "silicon nitride" is not included in the insulating material), a silicon material, and the like. Examples of the insulating material include silicon oxide. Examples of the silicon material include polysilicon and silicon such as silicon.

The essential components and the components that can be optionally added will be described below.

(Abrasive)
The polishing agent according to this embodiment contains abrasive grains containing a hydroxide of a tetravalent metal element. The “hydroxide of tetravalent metal element” is a compound containing a tetravalent metal (M ⁴⁺ ) and at least one hydroxide ion (OH ⁻ ). The hydroxide of the tetravalent metal element may contain anions other than hydroxide ions (for example, nitrate ion NO ₃ ⁻ , sulfate ion SO ₄ ²⁻ ). For example, the hydroxide of a tetravalent metal element may include an anion (eg, nitrate ion, sulfate ion) bonded to the tetravalent metal element. The abrasive grains containing the hydroxide of the tetravalent metal element can polish silicon nitride at a higher polishing rate than conventional abrasive grains such as silica particles, alumina particles, and ceria particles. Further, since the reactivity with the insulating material is high, the insulating material can also be polished at a high polishing rate.

The tetravalent metal element preferably contains at least one selected from the group consisting of rare earth elements and zirconium from the viewpoint of polishing silicon nitride at a higher speed and suppressing the occurrence of polishing scratches on the surface to be polished. The tetravalent metal element is preferably a rare earth element from the viewpoint of polishing silicon nitride at a higher speed and further suppressing the occurrence of polishing scratches on the surface to be polished. Examples of the rare earth element capable of having a valence of 4 include lanthanoids such as cerium, praseodymium, and terbium. Cerium (tetravalent cerium) is more preferable because it is easily available and has a further excellent polishing rate for silicon nitride. A rare earth element hydroxide and a zirconium hydroxide may be used in combination, or two or more kinds of rare earth elements may be selected and used.

The hydroxide of a tetravalent metal element can be prepared by reacting a salt containing a tetravalent metal element with a basic compound (alkali source). For example, as a method for producing abrasive grains containing a hydroxide of a tetravalent metal element, a method of mixing a salt containing a tetravalent metal element and an alkaline solution containing a basic compound can be used. This method is described, for example, in "Science of Rare Earths" [edited by Adachi Ginya, Kagaku Dojin, 1999], pages 304-305. Further, as a method for producing abrasive grains containing a hydroxide of a tetravalent metal element, the method described in Patent Document 5 may be used.

As the salt containing a tetravalent metal element, conventionally known salts can be used without particular limitation, and M(SO ₄ ) ₂ , M(NH ₄ ) ₂ (NO ₃ ) ₆ and M(NH ₄ ) ₄ (SO ₄ ) can be used. ₄ (M represents a rare earth element), Zr(SO ₄ ) ₂ .4H ₂ O and the like, among which M(NH ₄ ) ₂ (NO ₃ ) ₆ is preferable. As M, chemically active cerium (Ce) is preferable. From the above, Ce(NH ₄ ) ₂ (NO ₃ ) ₆ is more preferable as the salt containing a tetravalent metal element.

As the basic compound, conventionally known compounds can be used without particular limitation. Examples of the basic compound include imidazole, tetramethylammonium hydroxide (TMAH), guanidine, triethylamine, pyridine, piperidine, pyrrolidine, chitosan, and other organic bases; ammonia, potassium hydroxide, sodium hydroxide, calcium hydroxide, and other inorganic bases. And so on. Of these, at least one selected from the group consisting of ammonia and imidazole is preferable, and imidazole is more preferable, from the viewpoint of further improving the polishing rate of silicon nitride and the insulating material.

The abrasive grains containing the hydroxide of a tetravalent metal element synthesized by the above method can be washed to remove metal impurities. As a method for cleaning the abrasive grains, a method in which solid-liquid separation is repeated several times by centrifugation or the like can be used. The abrasive grains can also be washed in steps such as centrifugation, dialysis, ultrafiltration, and ion removal using an ion exchange resin or the like.

When the abrasive particles obtained above are aggregated, it is preferable to disperse the abrasive particles in a liquid medium (for example, water) by an appropriate method. As a method for dispersing the abrasive grains in the liquid medium, a dispersion treatment using an ordinary stirrer; a mechanical dispersion treatment using a homogenizer, an ultrasonic disperser, a wet ball mill, etc.; centrifugation, dialysis, ultrafiltration, ion exchange An example is a treatment of removing contaminant ions with a resin or the like. For the dispersion method and the particle size control method, for example, the method described in "Dispersion Technology Daizenshu" [Information Agency, Inc., July 2005], Chapter 3, "Latest Development Trends of Various Dispersers and Selection Criteria". Can be used. By performing the cleaning treatment to reduce the electric conductivity of the dispersion liquid containing the abrasive particles containing the hydroxide of the tetravalent metal element (for example, 500 mS/m or less), the hydroxide of the tetravalent metal element can be removed. The dispersibility of the contained abrasive grains can be increased. The cleaning treatment may be applied as a dispersion treatment, or the cleaning treatment and the dispersion treatment may be used in combination.

In the polishing agent according to the present embodiment, the abrasive containing a hydroxide of a tetravalent metal element may be used in combination with another abrasive. Examples of such other abrasive grains include silica particles, alumina particles, and ceria particles. As the abrasive grains containing a hydroxide of a tetravalent metal element, composite particles containing hydroxide particles of a tetravalent metal element and silica particles can be used.

The lower limit of the content of the hydroxide of the tetravalent metal element is preferably 80 mass% or more, more preferably 90 mass% or more, further preferably 95 mass% or more, and 98 mass% based on the total mass of the abrasive grains. The above is particularly preferable, and 99% by mass or more is extremely preferable. The abrasive grains are composed of a hydroxide of the tetravalent metal element (substantially 100% by mass of the abrasive grains is the tetravalent metal element, from the viewpoint of easy preparation of an abrasive and further excellent polishing characteristics). Hydroxide) is preferred.

From the viewpoint of further improving the polishing rate of silicon nitride, the abrasive containing a hydroxide of a tetravalent metal element is a water dispersion liquid in which the content of the abrasive is adjusted to 1.0% by mass, and light having a wavelength of 400 nm is used. It is preferable to give an absorbance of 1.00 or more. The "water dispersion liquid" having the content of abrasive grains adjusted to a predetermined amount means a liquid containing a predetermined amount of abrasive grains and water. The reason why the effect of improving the polishing rate can be obtained is not always clear, but the present inventor thinks as follows. That is, a tetravalent metal (M ⁴⁺ ), 1 to 3 hydroxide ions (OH ⁻ ), and 1 to 3 anions (X ^{c −} ) according to the production conditions of a hydroxide of a tetravalent metal element and the like. It is considered that particles containing M(OH) _a X _b (in the formula, a+b×c=4) are formed as a part of the abrasive grains (these particles are also referred to as “tetravalent metal”). "Abrasive grains containing elemental hydroxide"). In M(OH) _a X _b , the electron-withdrawing anion (X ^c− ) acts to improve the reactivity of the hydroxide ion, and the abundance of M(OH) _a X _b increases. It is considered that the polishing rate is improved as a result. Since the M _(OH) particles containing a _{X b} is the absorbance of light of wavelength 400nm, with the absorbance increases with respect to light having a wavelength of 400nm abundance of M _(OH) a _{X b} is increased, the polishing rate Is expected to improve.

The abrasive grains containing a hydroxide of a tetravalent metal element may be, for example, _a multinuclear compound or a multinuclear complex such as M _d (OH) _a X _b (in the formula, a+b×c=4d). Good. In the following, M(OH) _a X _b will be described as an example.

Abrasive grains containing a hydroxide of a tetravalent metal element may include not only M(OH) _a X _b, but also M(OH) ₄ , MO _{2 and the} like. Examples of the anion (X ^c− ) include NO ₃ ⁻ and SO ₄ ²⁻ .

It should be noted that the fact that the abrasive grains include M(OH) _a X _b means that after the abrasive grains are thoroughly washed with pure water, the FT-IR ATR method (Fourier transform Infra Red Spectrometer Attenuated Total Reflection method, Fourier transform infrared spectrophotometer) is used. It can be confirmed by a method of detecting a peak corresponding to an anion (X ^c− ) by a total reflection measurement method). The presence of anions (X ^c− ) can also be confirmed by the XPS method (X-ray Photoelectron Spectroscopy).

From the viewpoint of further improving the polishing rate of silicon nitride, the abrasive grains have an absorbance of 1.000 or more for light with a wavelength of 290 nm in an aqueous dispersion in which the content of the abrasive grains is adjusted to 0.0065 mass %. It is preferable to give it. The reason why such an effect of improving the polishing rate is obtained is not always clear, but the present inventor thinks as follows. That is, the particles containing M(OH) _a X _b generated according to the production conditions of the hydroxide of the tetravalent metal element or the like have a peak of absorption in the vicinity of a wavelength of 290 nm in calculation, and for example, Ce ⁴⁺ (OH ⁻ ) Particles of ₃ NO ₃ ^— have an absorption peak at a wavelength of 290 nm. Therefore, it is considered that the polishing rate is improved as the abundance of M(OH) _a X _b increases and the absorbance with respect to the light having a wavelength of 290 nm increases.

The hydroxide of the tetravalent metal element (for example, M(OH) _a X _b ) tends not to absorb light having a wavelength of 450 nm or more, particularly 450 to 600 nm. Therefore, from the viewpoint of suppressing the adverse effect on polishing due to the inclusion of impurities and polishing silicon nitride at a further excellent polishing rate, the abrasive grains have a content of the abrasive grains of 0.0065 mass. It is preferable that the aqueous dispersion liquid adjusted to 50% gives an absorbance of 0.010 or less with respect to light having a wavelength of 450 to 600 nm.

From the viewpoint of further improving the polishing rate of silicon nitride, the abrasive grains have a light transmittance of 50%/50% with respect to light having a wavelength of 500 nm in an aqueous dispersion in which the content of the abrasive grains is adjusted to 1.0% by mass. It is preferable that it gives cm or more. The reason why such an effect of improving the polishing rate is obtained is not always clear, but the present inventor thinks as follows. That is, it is considered that the chemical action is more dominant than the mechanical action in the action of the abrasive grains containing the hydroxide of the tetravalent metal element as the abrasive grains. Therefore, it is considered that the number of abrasive grains contributes more to the polishing rate than the size of the abrasive grains.

When the light transmittance is low in an aqueous dispersion in which the content of the abrasive is adjusted to 1.0% by mass, the abrasive present in the aqueous dispersion has a large particle size (hereinafter referred to as "coarse particle"). Are considered to exist relatively in large numbers. When an additive is added to the abrasive containing such abrasive grains, other particles are aggregated with the coarse particles as the core. As a result, the number of abrasive grains acting on the surface-to-be-polished per unit area (the number of effective abrasive grains) decreases, and the specific surface area of the abrasive grains in contact with the surface-to-be-polished decreases, so that the polishing rate may decrease. Conceivable.

On the other hand, when the light transmittance is high in the water dispersion liquid in which the content of the abrasive grains is adjusted to 1.0% by mass, it is considered that the abrasive grains present in the water dispersion liquid are in a state where the “coarse particles” are small. To be In this way, when the amount of coarse particles is small, even if an additive is added to the polishing agent, there are few coarse particles that become nuclei for aggregation, so that aggregation of the abrasive grains is suppressed, or aggregation. The size of the particles becomes smaller. As a result, the number of abrasive grains acting on the surface-to-be-polished per unit area (effective number of abrasive grains) is maintained, and since the specific surface area of the abrasive grains in contact with the surface-to-be-polished is maintained, the polishing rate is less likely to decrease, It is considered that the polishing rate of silicon nitride is likely to be improved.

The absorbance and light transmittance that the abrasive grains contained in the abrasive give in the aqueous dispersion can be measured using, for example, a spectrophotometer (device name: U3310) manufactured by Hitachi, Ltd. Specifically, for example, an aqueous dispersion in which the content of abrasive grains is adjusted to 1.0% by mass or 0.0065% by mass is prepared as a measurement sample. This measurement sample is placed in a 1 cm square cell in an amount of about 4 mL (L indicates “liter”; the same applies hereinafter), and the cell is installed in the device. Next, the absorbance is measured in the wavelength range of 200 to 600 nm, and the absorbance and the light transmittance are judged from the obtained chart.

Absorbance and light transmittance that the abrasive particles contained in the abrasive give in the aqueous dispersion, solid components other than the abrasive particles, and, after removing the liquid component other than water, the aqueous dispersion of the content of the predetermined abrasive Can be prepared and measured using the aqueous dispersion. Depending on the components contained in the polishing agent, solid components or liquid components can be removed by centrifugation using a centrifuge that can apply a gravitational acceleration of several thousand G or less, or by applying a gravitational acceleration of tens of thousands G or more. Centrifugation methods such as ultracentrifugation using a centrifuge; chromatography methods such as partition chromatography, adsorption chromatography, gel permeation chromatography, ion exchange chromatography; natural filtration, vacuum filtration, pressure filtration, ultrafiltration. And the like; distillation methods such as vacuum distillation and atmospheric distillation can be used, and these may be appropriately combined.

For example, when a compound having a weight average molecular weight of tens of thousands or more (for example, 50,000 or more) is included, a chromatography method, a filtration method and the like can be mentioned, and gel permeation chromatography and ultrafiltration are preferable. When the filtration method is used, the abrasive grains contained in the abrasive can be passed through the filter by setting appropriate conditions. When the compound having a weight average molecular weight of tens of thousands or less (for example, less than 50,000) is included, chromatography method, filtration method, distillation method and the like can be mentioned, and gel permeation chromatography, ultrafiltration and vacuum distillation are preferable. When a plurality of types of abrasive grains are contained, a filtration method, a centrifugal separation method and the like can be mentioned. Abrasives containing a hydroxide of a tetravalent metal element in the filtrate in the case of the filtration method and in the liquid phase in the case of the centrifugal separation method. Contains more grains.

As a method of separating the abrasive grains by the chromatography method, for example, the abrasive grains and/or other components can be separated under the following conditions.

Sample solution: Abrasive 100 μL
Detector: Hitachi Ltd., UV-VIS detector, trade name "L-4200", wavelength: 400 nm
Integrator: Hitachi, Ltd., GPC integrator, product name "D-2500"
Pump: Hitachi, Ltd., trade name "L-7100"
Column: Hitachi Chemical Co., Ltd., packing column for aqueous HPLC, trade name "GL-W550S"
Eluent: Deionized water Measuring temperature: 23℃
Flow rate: 1 mL/min (pressure: about 40-50 kg/cm ² )
Measurement time: 60 minutes

It should be noted that it is preferable to degas the eluent using a degasser before performing the chromatography. When the degassing device cannot be used, it is preferable that the eluent is degassed by ultrasonic waves or the like in advance.

Depending on the components contained in the abrasive, the abrasive grains may not be separated under the above conditions. In this case, the separation can be performed by optimizing the sample solution amount, column type, eluent type, measurement temperature, flow rate, and the like. Further, by adjusting the pH of the polishing agent, it is possible to adjust the distillation time of the components contained in the polishing agent and separate them from the abrasive grains. When the abrasive contains an insoluble component, it is preferable to remove the insoluble component by filtration, centrifugation, or the like, if necessary.

From the viewpoint of obtaining a more excellent polishing rate of silicon nitride, the abrasive grains are centrifuged for 50 minutes at a centrifugal acceleration of 1.59×10 ⁵ G with an aqueous dispersion liquid in which the content of the abrasive grains is adjusted to 1.0 mass %. It is preferable to give a supernatant (liquid phase) having a nonvolatile content of 300 ppm or more when separated.

The present inventor considers the reason why the polishing rate improving effect is obtained when the content of non-volatile matter in the supernatant after centrifugation is high. Generally, in an abrasive containing abrasive grains, almost all the abrasive grains settle when centrifugally separated for 50 minutes at a centrifugal acceleration of 1.59×10 ⁵ G. However, the abrasive according to the present embodiment contains a large amount of fine particles that do not settle even if centrifugation is performed under the above conditions, because the abrasive particles contained therein have a sufficiently small particle size. That is, it is considered that the proportion of fine particles in the abrasive grains increases as the nonvolatile content increases, and the surface area of the abrasive grains in contact with the surface to be polished increases. It is considered that this promotes the progress of polishing due to the chemical action and improves the polishing rate.

The lower limit of the nonvolatile content of the supernatant liquid when the aqueous dispersion in which the content of the abrasive grains is adjusted to 1.0% by mass is centrifuged is 400 ppm from the viewpoint of easily obtaining a more excellent polishing rate of silicon nitride. The above is more preferable, 500 ppm or more is further preferable, 600 ppm or more is particularly preferable, 700 ppm or more is extremely preferable, and 750 ppm or more is very preferable. The upper limit of the nonvolatile content of the supernatant is, for example, 10,000 ppm (1.0% by mass).

As the apparatus for performing the centrifugal separation, both an angle rotor in which tubes are arranged at a predetermined angle and a swing rotor in which the tubes have a variable angle and the tubes are horizontal or nearly horizontal during centrifugation are used. be able to.

FIG. 1 is a schematic sectional view showing an example of an angle rotor. The angle rotor AR is symmetrical with respect to the rotation axis A1. In FIG. 1, only one side (left side in the figure) of the angle rotor AR is shown and the other side (right side in the figure) is omitted. In FIG. 1, A2 is the tube angle, R _min is the minimum radius from the rotation axis A1 to the tube, and R _max is the maximum radius from the rotation axis A1 to the tube. R _av is an average radius from the rotation axis A1 to the tube, and is calculated as “(R _min +R _max )/2”.

In such a centrifugal separator, the centrifugal acceleration [unit: G] can be calculated from the following equation (1).
Centrifugal acceleration [G]=1118×R×N ² ×10 ⁻⁸ (1)
[In the formula, R represents the radius of rotation (cm), and N represents the number of revolutions per minute (rpm=min ⁻¹ ). ]

In the present embodiment, the value of the average radius R _{av in} FIG. 1 is used as the rotation radius R in Expression (1), and the rotation speed N is set so that the centrifugal acceleration is 1.59×10 ⁵ G. Centrifuge. When a swing rotor is used instead of the angle rotor as shown in FIG. 1, the minimum radius R _min , the maximum radius R _max , and the average radius R _av are obtained from the state of the tube during centrifugation to set the conditions. ..

The abrasive grains can be separated into large particles and fine particles using, for example, an ultracentrifuge 70P-72 manufactured by Hitachi Koki Co., Ltd. as an angle rotor. The centrifugation of the aqueous dispersion liquid using 70P-72 can be specifically performed as follows, for example. First, an aqueous dispersion in which the content of abrasive grains is adjusted to 1.0% by mass is prepared, and this is filled in a centrifuge tube, and then the centrifuge tube is installed in a rotor. Then, after rotating at a rotation speed of 50,000 min ⁻¹ for 50 minutes, the centrifuge tube is taken out from the rotor, and the supernatant liquid in the centrifuge tube is collected. The nonvolatile content of the supernatant can be calculated by weighing the mass of the collected supernatant and the mass of the residue after drying the supernatant.

The lower limit of the average particle size of the abrasive grains is preferably 1 nm or more, more preferably 2 nm or more, still more preferably 3 nm or more, and particularly preferably 5 nm or more, from the viewpoint of obtaining a more excellent polishing rate for silicon nitride and the insulating material. The upper limit of the average particle size of the abrasive grains is preferably 300 nm or less, more preferably 250 nm or less, and further preferably 200 nm or less, from the viewpoint of further suppressing scratches on the surface to be polished. From the above viewpoint, the average grain size of the abrasive grains is more preferably 1 nm or more and 300 nm or less.

The "average particle size" of the abrasive grains means the average secondary particle size of the abrasive grains. The average particle size of the abrasive grains can be measured, for example, by a photon correlation method for an abrasive or a slurry in an abrasive set described below. Specifically, for example, the average particle size of the abrasive grains can be measured by a device name: Zetasizer 3000HS manufactured by Malvern Instruments Ltd., a device name: N5 manufactured by Beckman Coulter Ltd., or the like. The measuring method using N5 is as follows. Specifically, for example, an aqueous dispersion in which the content of abrasive grains is adjusted to 0.2 mass% is prepared, and about 4 mL of this aqueous dispersion is placed in a 1 cm square cell, and the cell is installed in the apparatus. It is possible to set the refractive index of the dispersion medium to 1.33 and the viscosity to 0.887 mPa·s, perform the measurement at 25° C., and use the displayed average particle size value as the average particle size of the abrasive grains.

The lower limit of the content of abrasive grains is preferably 0.005 mass% or more, and more preferably 0.01 mass% or more, based on the total mass of the polishing agent, from the viewpoint of obtaining a more excellent polishing rate for silicon nitride and the insulating material. It is preferably 0.02 mass% or more, more preferably 0.04 mass% or more. The upper limit of the content of abrasive grains is preferably 20% by mass or less, more preferably 15% by mass or less, and further preferably 10% by mass or less, based on the total mass of the abrasive, from the viewpoint of increasing the storage stability of the abrasive. preferable. From the above viewpoint, the content of the abrasive grains is more preferably 0.005 mass% or more and 20 mass% or less based on the total mass of the abrasive.

Further, by further reducing the content of the abrasive grains, the cost and polishing scratches can be further reduced, which is preferable. Conventionally, when the content of abrasive grains decreases, the polishing rate of silicon nitride or the like tends to decrease. On the other hand, an abrasive containing a hydroxide of a tetravalent metal element can obtain a predetermined polishing rate even with a small amount, so that the polishing rate is balanced with the advantage obtained by reducing the content of the abrasive. The content of abrasive grains can be further reduced. From such a viewpoint, the upper limit of the content of the abrasive grains is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, further preferably 1.0% by mass or less, and 0.5% by mass or less. Is particularly preferable, and 0.3% by mass or less is extremely preferable.

(Liquid medium)
The liquid medium in the polishing agent according to the present embodiment is not particularly limited, but water such as deionized water or ultrapure water is preferable. The content of the liquid medium may be the balance of the abrasive excluding the contents of the other constituents, and is not particularly limited.

(Additive)
The polishing agent according to this embodiment contains an additive. Here, the "additive" means polishing properties other than the liquid medium and the abrasive grains in order to adjust the polishing properties such as polishing rate and polishing selectivity; abrasive properties such as dispersibility of abrasive grains and storage stability. Refers to the substance contained in the agent. The additives may be used alone or in combination of two or more.

[First additive]
The polishing agent according to this embodiment contains a triazine compound having a triazine skeleton as a first additive. The first additive has the effect of increasing the polishing rate of silicon nitride. It is presumed that the reason why this effect is obtained is that the first additive increases the polishing rate by increasing the affinity between silicon nitride and the abrasive grains.

As the triazine compound, a triazine compound having a 1,3,5-triazine skeleton (hereinafter referred to as "1,3,5-triazine compound"), a triazine compound having a 1,2,4-triazine skeleton (hereinafter referred to as "1 , 2,4-triazine compound"), a triazine compound having a 1,2,3-triazine skeleton (hereinafter referred to as "1,2,3-triazine compound"), and the like.

Examples of the 1,3,5-triazine compound include 1,3,5-triazine and 1,3,5-triazine derivatives. Examples of the 1,3,5-triazine derivative include 1,3,5-triazine-2,4,6-triamine (conventional name: melamine) and 2,4,6-tris[bis(methoxymethyl)amino]-1. ,3,5-Triazine, 2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-1,3,5-triazine, 4,6-diamino-2-hydroxy-1, 3,5-triazine, 6-amino-2,4-dihydroxy-1,3,5-triazine, 2,4,6-trifluoro-1,3,5-triazine, 2,4-diamino-6-methyl -1,3,5-triazine, 6-fluoro-1,3,5-triazine-2,4-diamine, 1,3,5-triazine-2,4-diamine, N,N-dimethyl-1,3 ,5-Triazine-2,4-diamine, 2,4-bis(methylamino)-1,3,5-triazine, 1,3,5-triazine-2-amine, 2,4,6-trimethyl-1 ,3,5-Triazine, 2-amino-4,6-dimethyl-1,3,5-triazine, N-methyl-1,3,5-triazine-2,4,6-triamine, 2,4-dimethyl -1,3,5-triazine, 2-methylamino-1,3,5-triazine, 2-dimethylamino-1,3,5-triazine, 2-ethylamino-1,3,5-triazine, 4- (Methylamino)-6-methyl-1,3,5-triazin-2-amine, 4-methyl-1,3,5-triazin-2-amine, 2-ethyl-4,6-dimethyl-1,3 , 5-triazine, N-ethyl-4-methyl-s-triazin-2-amine, 4-ethyl-s-triazin-2-amine and the like can be mentioned.

Examples of the 1,2,4-triazine compound include 1,2,4-triazine and 1,2,4-triazine derivatives. As the 1,2,4-triazine derivative, 3-amino-5,6-dimethyl-1,2,4-triazine, 1,2,4-triazine-3-amine, 1,2,4-benzotriazine, 3-methyl-1,2,4-benzotriazine, 3-methyl-1,2,4-triazine, 5-methyl-1,2,4-triazine, 6-methyl-1,2,4-triazine, 3 ,5-dimethyl-1,2,4-triazine, 5,6-dimethyl-1,2,4-triazine, 3,5,6-trimethyl-1,2,4-triazine, 6-methyl-1,2 , 4-triazin-3-amine and the like.

Examples of the 1,2,3-triazine compound include 1,2,3-triazine and 1,2,3-triazine derivatives. Examples of the 1,2,3-triazine derivative include 4,6-dimethyl-1,2,3-triazine, 4-methyl-1,2,3-triazine and 2,5-dihydro-2,4,6-trimethyl. Examples include -1,2,3-triazine, 5-methyl-1,2,3-triazine and 4,5-dimethyl-1,2,3-triazine.

The triazine compounds may be used alone or in combination of two or more. Each of the triazine compounds has an effect of increasing the polishing rate of silicon nitride. The triazine compound has an effect of increasing or decreasing the polishing rate of the material to be polished other than silicon nitride depending on the type of the triazine compound. Examples of other materials to be polished include an insulating material (in this specification, "silicon nitride" is not included in the insulating material), a silicon material, and the like. Examples of the insulating material include silicon oxide. Examples of the silicon material include polysilicon and silicon such as silicon.

Examples of the triazine compound capable of decreasing the polishing rate of the insulating material while increasing the polishing rate of silicon nitride include melamine and 2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-1,3. , 5-triazine and the like.

Examples of the triazine compound capable of increasing the polishing rate of the insulating material while increasing the polishing rate of silicon nitride include 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine and 3-amino- 5,6-dimethyl-1,2,4-triazine and the like can be mentioned.

Examples of triazine compounds that can increase the polishing rate of silicon nitride and decrease the polishing rate of silicon materials (silicon such as polysilicon and silicon) include melamine and 2,4-diamino-6-[2-(2-methyl -1-Imidazolyl)ethyl]-1,3,5-triazine and the like can be mentioned.

The lower limit of the content of the triazine compound is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, based on the total mass of the polishing agent, from the viewpoint of obtaining a further excellent polishing rate of silicon nitride. 0.01% by mass or more is more preferable, 0.03% by mass or more is particularly preferable, and 0.05% by mass or more is extremely preferable. The upper limit of the content of the triazine compound is not particularly limited, but from the viewpoint of excellent dissolution stability, 10% by mass or less is preferable, 5.0% by mass or less is more preferable, and 3.0% by mass or less is based on the total mass of the abrasive. It is more preferably not more than mass%, particularly preferably not more than 2.0 mass%, very preferably not more than 1.0 mass%, very preferably not more than 0.5 mass%, and even more preferably not more than 0.3 mass%. From the above viewpoint, the content of the triazine compound is more preferably 0.001% by mass or more and 10% by mass or less based on the total mass of the abrasive.

[Second additive]
In addition to the first additive, the polishing agent according to the present embodiment is used for the purpose of adjusting polishing characteristics such as polishing rate and polishing selectivity; polishing agent characteristics such as dispersibility of abrasive grains and storage stability. , And may further contain a second additive.

Examples of the second additive include carboxylic acid and amino acid. These may be used alone or in combination of two or more. By using these compounds, the dispersibility of abrasive grains and the balance of polishing characteristics are improved. Although amino acids have a carboxyl group, carboxylic acids exclude compounds corresponding to amino acids. Further, as the carboxylic acid and amino acid, carboxylic acid and amino acid having a triazine skeleton are excluded.

The carboxylic acid has the effects of stabilizing the pH and further improving the polishing rate of silicon nitride and the insulating material. Examples of the carboxylic acid include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid and lactic acid.

Amino acids have the effects of improving the dispersibility of the abrasive grains containing the hydroxide of the tetravalent metal element and further improving the polishing rate of silicon nitride and the insulating material. The amino acids include arginine, lysine, aspartic acid, glutamic acid, asparagine, glutamine, histidine, proline, tyrosine, tryptophan, serine, threonine, glycine, α-alanine, β-alanine, methionine, cysteine, phenylalanine, leucine, valine, isoleucine. Etc.

When using the second additive, the lower limit of the content of the second additive, from the viewpoint of obtaining the effect of addition of the second additive while suppressing the sedimentation of the abrasive grains, based on the total mass of the abrasive Is preferably 0.001 mass% or more, more preferably 0.003 mass% or more, still more preferably 0.005 mass% or more. The upper limit of the content of the second additive is preferably 10% by mass or less, based on the total mass of the abrasive, from the viewpoint of obtaining the effect of adding the second additive while suppressing the sedimentation of the abrasive grains. 0 mass% or less is more preferable, and 3.0 mass% or less is still more preferable. From the above viewpoint, the content of the second additive is more preferably 0.001% by mass or more and 10% by mass or less based on the total mass of the abrasive.

[Water-soluble polymer]
The polishing agent according to the present embodiment has flatness, in-plane uniformity, polishing selectivity of silicon nitride with respect to silicon oxide (polishing rate of silicon nitride/polishing rate of silicon oxide), polishing selectivity of silicon nitride with respect to polysilicon ( A water-soluble polymer may be contained for the purpose of adjusting polishing characteristics such as polishing rate of silicon nitride/polishing rate of polysilicon). Here, the "water-soluble polymer" is defined as a polymer that dissolves in 0.1 g or more in 100 g of water at 25°C. The polymer corresponding to the first additive is not included in the "water-soluble polymer".

The water-soluble polymer is not particularly limited, and polysaccharides such as alginic acid, pectic acid, carboxymethylcellulose, agar, curdlan, guar gum, dextrin, cyclodextrin and pullulan; polyvinyl alcohol, polyvinylpyrrolidone, polyacrolein and other vinyl-based polymers Polymers: glycerin-based polymers such as polyglycerin and polyglycerin derivatives can be mentioned. The water-soluble polymer may be used alone or in combination of two or more.

In the case of using a water-soluble polymer, the lower limit of the content of the water-soluble polymer is from the viewpoint of obtaining the effect of adding the water-soluble polymer while suppressing the settling of abrasive grains, based on the total mass of the abrasive. 0001 mass% or more is preferable, 0.001 mass% or more is more preferable, and 0.01 mass% or more is still more preferable. The upper limit of the content of the water-soluble polymer is preferably 10% by mass or less based on the total mass of the abrasive, and 5.0% by mass, from the viewpoint of obtaining the effect of adding the water-soluble polymer while suppressing the sedimentation of the abrasive grains. % Or less is more preferable, 1.0% by mass or less is further preferable, and 0.5% by mass or less is particularly preferable. From the above viewpoint, the content of the water-soluble polymer is more preferably 0.0001% by mass or more and 5.0% by mass or less based on the total mass of the abrasive.

[Other additives]
The abrasive according to the present embodiment may further contain other additives in addition to the first additive, the second additive and the water-soluble polymer for the purpose of adjusting polishing characteristics. Good. Examples of other additives include an oxidizing agent (for example, hydrogen peroxide), and a pH adjusting agent and a buffering agent described later. These may be used alone or in combination of two or more.

(Characteristics of abrasives)
From the viewpoint of further improving the polishing rate of silicon nitride and the insulating material, the lower limit of the pH of the polishing agent according to the present embodiment is preferably 3.0 or more, more preferably 3.5 or more, still more preferably 4.0 or more. , 4.5 or higher is particularly preferable. The upper limit of the pH of the polishing agent is preferably 9.0 or less, more preferably 8.5 or less, still more preferably 8.0 or less, and 7.5 or less from the viewpoint of further improving the polishing rate of silicon nitride and the insulating material. Is particularly preferable. From the above viewpoint, the pH of the polishing agent is more preferably 3.0 or more and 9.0 or less. The pH is defined as the pH at a liquid temperature of 25°C.

The pH of the polishing agent can be adjusted with acid components such as inorganic acids and organic acids; alkali components such as ammonia, sodium hydroxide, potassium hydroxide, tetramethylammonium hydroxide (TMAH), imidazole and 2-methylimidazole. In addition, a buffer solution may be added to stabilize the pH. Examples of such buffer solution include acetate buffer solution and phthalate buffer solution.

The pH of the polishing slurry according to this embodiment can be measured with a pH meter (for example, model number PHL-40 manufactured by Electrochemical Instruments Co., Ltd.). Specifically, for example, a phthalate pH buffer (pH 4.01) and a neutral phosphate pH buffer (pH 6.86) are used as standard buffers to calibrate the pH meter at two points, and then the pH meter is calibrated. The electrode is put in an abrasive and the value is measured after 2 minutes or more has been stabilized and then measured. At this time, both the standard buffer solution and the polishing agent have a liquid temperature of 25°C.

The abrasive according to the present embodiment may be stored as a one-liquid type abrasive containing at least abrasive grains, a first additive, and a liquid medium, and a slurry (first liquid) and an additive liquid (second liquid). ) May be mixed and stored as a two-component type polishing agent set (for example, CMP polishing agent set) in which the constituents of the polishing agent are divided into a slurry and an additive liquid so as to form the polishing agent. The slurry contains, for example, at least abrasive grains and a liquid medium. The additive liquid contains, for example, at least a first additive and a liquid medium. The first additive, the second additive, the water-soluble polymer, and the buffer solution are preferably contained in the additive solution among the slurry and the additive solution. The constituents of the abrasive may be stored as an abrasive set divided into three or more liquids.

In the polishing agent set, a slurry and an additive solution are mixed immediately before or during polishing to prepare a polishing agent. Further, the one-liquid type polishing agent may be stored as a storage solution for polishing agent in which the content of the liquid medium is reduced, and may be used by diluting with the liquid medium during polishing. The two-liquid type polishing agent set may be stored as a slurry storage liquid and an additive liquid storage liquid in which the content of the liquid medium is reduced, and may be used by diluting with the liquid medium during polishing.

In the case of polishing using a one-liquid type polishing agent, the method of supplying the polishing agent onto the polishing surface plate is a method of directly feeding and supplying the polishing agent; a storage liquid for polishing agent and a liquid medium are provided in separate pipes. It is possible to use a method in which the liquid is fed in, and these are combined, mixed and supplied; a method in which the storage liquid for abrasive and the liquid medium are mixed and supplied in advance.

When the slurry is stored as a two-component type abrasive set divided into a slurry and an additive liquid, the polishing rate can be adjusted by arbitrarily changing the composition of these two liquids. When polishing is performed using an abrasive set, examples of the method for supplying the abrasive onto the polishing platen include the following methods. For example, a method in which a slurry and an additive liquid are sent through separate pipes, and these pipes are joined, mixed and supplied; a slurry storage liquid, an additive liquid storage liquid and a liquid medium are sent through separate pipes. , A method of merging, mixing and supplying these; a method of previously mixing and supplying the slurry and the additive liquid; a method of previously mixing and supplying the slurry storage liquid, the additive liquid storage liquid and the liquid medium be able to. It is also possible to use a method in which the slurry and the additive liquid in the above-mentioned polishing agent set are respectively supplied onto the polishing platen. In this case, the surface to be polished is polished using the polishing agent obtained by mixing the slurry and the additive liquid on the polishing platen.

<Substrate polishing method>
The method for polishing a substrate according to the present embodiment may include a polishing step of polishing the surface to be polished of the substrate using the one-liquid type polishing agent, and mixing the slurry and the additive liquid in the polishing agent set. A polishing step of polishing the surface to be polished of the substrate using the polishing agent obtained as described above may be provided.

In the method for polishing a substrate according to this embodiment, the surface to be polished contains, for example, silicon nitride. In the polishing step, the one-liquid type polishing agent or the polishing agent obtained by mixing the slurry and the additive liquid in the polishing agent set is used to polish the surface to be polished containing silicon nitride and another polishing target material. It may be a polishing step of selectively polishing a specific material to be polished (eg, silicon nitride). In this case, the base may have, for example, a member containing silicon nitride and a member containing another material to be polished. Examples of other materials to be polished include an insulating material (in this specification, "silicon nitride" is not included in the insulating material), a silicon material, and the like. Examples of the insulating material include silicon oxide. Examples of the silicon material include polysilicon and silicon such as silicon.

The polishing rate of silicon nitride is preferably 75 nm/min or more, more preferably 100 nm/min or more, further preferably 120 nm/min or more, particularly preferably 130 nm/min or more. When the polishing rate is 75 nm/min or more, it can greatly contribute to improvement in throughput in device manufacturing.

In the polishing step, for example, in a state where the material to be polished of the substrate having the material to be polished (silicon nitride and/or material to be polished other than silicon nitride) is pressed against the polishing pad (polishing cloth) of the polishing platen, The polishing agent is supplied between the material to be polished and the polishing pad, and the substrate and the polishing platen are relatively moved to polish the material to be polished. In the polishing step, for example, at least a part of the material to be polished is removed by polishing. The material to be polished may be in the form of a film (film to be polished), for example.

Examples of the substrate to be polished include a substrate and the like. Examples of the base include a base on which a material to be polished is formed on a substrate (for example, a semiconductor substrate on which an STI pattern, a gate pattern, a wiring pattern, etc. are formed) related to semiconductor device manufacturing.

A specific example of the method for polishing a substrate according to this embodiment will be described in detail with reference to the drawings.

FIG. 2 is a schematic cross-sectional view showing a part of the high-k metal gate manufacturing process. First, the substrate 100a shown in FIG. 2A is prepared. In the substrate 100a, convex portions made of a dummy gate material 2 such as polysilicon are provided on the silicon substrate 1 at intervals. A cap material 3 of silicon nitride is provided so as to follow the uneven shape formed of the dummy gate material 2. An insulating material (for example, an insulating film) 4 such as silicon oxide is provided so as to fill the recess and cover the entire cap material 3.

Next, the substrate 100a is polished using a known CMP polishing agent that can remove the insulating material and has a low polishing rate for silicon nitride. As a result, the surface layer portion of the insulating material 4 is removed to expose the cap material 3 of the convex portion, thereby obtaining the substrate 100b shown in FIG. 2B.

Subsequently, the cap material 3 of the convex portion is removed by using the polishing agent according to the present embodiment, and the polishing is stopped when the dummy gate material 2 is exposed to obtain the substrate 100c shown in FIG. 2C. .. As the polishing agent used here, it is preferable to use a polishing agent having a high polishing rate for silicon nitride and a low polishing rate for a dummy gate material such as polysilicon.

FIG. 3 is a schematic sectional view showing a part of a manufacturing process of a multi-gate element called Fin-FET. As shown in FIG. 3A, a substrate 110a having a silicon substrate 11 processed into a predetermined shape, an insulating material 12 such as silicon oxide, and a hard mask 13 of silicon nitride is prepared. The hard mask 13 is provided on the silicon substrate 11. The insulating material 12 is provided so as to cover the silicon substrate 11 and the hard mask 13.

Next, the substrate 110a is polished using a known CMP polishing agent that can remove the insulating material and has a low polishing rate for silicon nitride. As a result, the surface layer portion of the insulating material 12 is removed to expose the hard mask 13 to obtain the substrate 110b shown in FIG. 3B.

Subsequently, the hard mask 13 is removed using the polishing agent according to the present embodiment, and polishing is stopped when the silicon substrate 11 is exposed to obtain a substrate 110c shown in FIG. 3C. As the polishing agent used here, it is preferable to use a polishing agent having a high polishing rate for silicon nitride and a low polishing rate for an insulating material such as silicon oxide.

FIG. 4 is a schematic sectional view showing a part of the manufacturing process of the gate structure in the transistor. As shown in FIG. 4A, it has a silicon substrate 21 processed into a predetermined shape, an insulating material 22 such as silicon oxide, a cap material 23 of silicon nitride, and a dummy gate material 24 such as polysilicon. A substrate 120a is prepared. The insulating material 22 and the dummy gate material 24 are provided on the silicon substrate 21. The cap material 23 is provided so as to cover the silicon substrate 21, the insulating material 22, and the dummy gate material 24.

Next, the surface layer portion of the cap material 23 is removed using the polishing agent according to the present embodiment, and polishing is stopped when the insulating material 22 is exposed to obtain the substrate 120b shown in FIG. 4B. As the polishing agent used here, it is preferable to use a polishing agent having a high polishing rate for silicon nitride and a low polishing rate for an insulating material such as silicon oxide.

Hereinafter, the method for polishing the substrate (semiconductor substrate or the like) according to this embodiment will be further described. In the polishing method according to the present embodiment, as a polishing apparatus, a general polishing apparatus having a holder capable of holding a substrate (semiconductor substrate or the like) having a surface to be polished and a polishing surface plate to which a polishing pad can be attached Can be used. Each of the holder and the polishing platen is provided with, for example, a motor whose rotation speed can be changed. Examples of the polishing device include a polishing device manufactured by APPLIED MATERIALS (trade name: Mirara-3400, Reflexion LK), a polishing device manufactured by EBARA CORPORATION (trade name: FREX-300), and the like.

As the polishing pad, general non-woven fabric, foam, non-foam or the like can be used. Materials for the polishing pad include polyurethane, acryl, polyester, acryl-ester copolymer, polytetrafluoroethylene, polypropylene, polyethylene, poly-4-methylpentene, cellulose, cellulose ester, polyamide (for example, nylon (trademark) and Resins such as aramid), polyimide, polyimide amide, polysiloxane copolymer, oxirane compound, phenol resin, polystyrene, polycarbonate, and epoxy resin can be used. As the material of the polishing pad, foamed polyurethane and non-foamed polyurethane are preferable from the viewpoint of further excellent polishing rate and flatness. The polishing pad may be grooved so that the polishing agent may accumulate.

Although the polishing conditions are not limited, the rotation speed of the polishing platen is preferably 200 min ⁻¹ or less so that the substrate does not jump out, and the polishing pressure (processing load) applied to the substrate is sufficient to cause polishing scratches. From the viewpoint of easy suppression, 100 kPa or less is preferable. During polishing, it is preferable to continuously supply the polishing agent to the polishing pad with a pump or the like. Although the supply amount is not limited, it is preferable that the surface of the polishing pad is always covered with the abrasive.

It is preferable that the substrate after polishing is thoroughly washed in running water to remove particles attached to the substrate. For cleaning, dilute hydrofluoric acid or aqueous ammonia may be used in addition to pure water, and a brush may be used to enhance cleaning efficiency. After washing, it is preferable to dry off the substrate after removing water droplets attached to the substrate using a spin dryer or the like.

Hereinafter, the present invention will be specifically described based on Examples, but the present invention is not limited to these Examples.

<Synthesis of hydroxide of tetravalent metal element>
After putting 7.603 L of water in a container, a cerium ammonium nitrate aqueous solution having a concentration of 50% by mass (chemical formula: Ce(NH ₄ ) ₂ (NO ₃ ) ₆ , formula weight: 548.2 g/mol, Nippon Kagaku Sangyo Co., Ltd. (Manufactured under the trade name of 50% CAN solution) (0.715 L) was added and mixed. Then, the liquid temperature was adjusted to 40° C. to obtain an aqueous metal salt solution (metal salt concentration: 0.114 mol/L).

Next, imidazole was dissolved in water to prepare 4.566 L of an aqueous solution having a concentration of 0.7 mol/L, and then the liquid temperature was adjusted to 40° C. to obtain an alkaline liquid.

The container containing the metal salt aqueous solution was placed in a water tank filled with water. The water temperature of the water tank was adjusted to 40° C. using an external circulation device Coolnix circulator (manufactured by Tokyo Rika Kikai Co., Ltd. (EYELA), product name Cooling Thermo Pump CTP101). While maintaining the water temperature at 40° C., while stirring the metal salt aqueous solution at a stirring rate of 400 min ⁻¹ , the alkaline liquid was mixed in a container at a mixing rate of 8.5×10 ⁻⁶ m ^{3 /} min (8.5 mL/min). In addition to the above, a slurry precursor 1 containing abrasive grains containing a hydroxide of tetravalent cerium was obtained. The pH of the slurry precursor 1 was 2.2. The aqueous metal salt solution was stirred using a 3-blade pitch paddle having a blade length of 5 cm.

The slurry precursor 1 is subjected to ultrafiltration using a hollow fiber filter having a molecular weight cut-off of 50,000 to circulate the slurry precursor 1 to remove an ionic component until the conductivity becomes 50 mS/m or less, thereby obtaining a slurry precursor. Got 2. The ultrafiltration was performed using a liquid level sensor while adding water so that the water level in the tank containing the slurry precursor 1 was kept constant. An appropriate amount of the obtained slurry precursor 2 was taken and the mass before and after drying was measured to calculate the nonvolatile content of the slurry precursor 2 (content of abrasive grains containing hydroxide of tetravalent cerium). In addition, when the nonvolatile content was less than 1.0 mass% at this stage, ultrafiltration was further performed without adding water to concentrate to a level exceeding 1.1 mass %. Finally, an appropriate amount of water was added to prepare a storage solution for cerium hydroxide slurry (abrasive grain content: 1.0% by mass).

<Measurement of average particle size>
An appropriate amount of a storage liquid for cerium hydroxide slurry was sampled and diluted with water so that the content of the abrasive grains was 0.2% by mass to obtain a measurement sample (water dispersion liquid). About 4 mL of the measurement sample was placed in a 1 cm square cell, and the cell was installed in a device name: N5 manufactured by Beckman Coulter. The dispersion medium was set to have a refractive index of 1.33 and a viscosity of 0.887 mPa·s, the measurement was carried out at 25° C., and the displayed average particle size was taken as the average secondary particle size. The result was 21 nm.

<Measurement of absorbance and light transmittance>
Measure an appropriate amount of a storage liquid for cerium hydroxide slurry (abrasive grain content: 1.0% by mass) and dilute it with water so that the abrasive grain content will be 0.0065% by mass (65 ppm). A sample (aqueous dispersion) was obtained. About 4 mL of the measurement sample was put in a 1 cm square cell, and the cell was installed in a spectrophotometer (device name: U3310) manufactured by Hitachi, Ltd. The absorbance was measured in the wavelength range of 200 to 600 nm, and the absorbance with respect to the light with a wavelength of 290 nm and the absorbance with respect to the light with a wavelength of 450 to 600 nm were measured. The absorbance for light having a wavelength of 290 nm was 1.248. The absorbance for light having a wavelength of 450 to 600 nm was 0.010 or less.

About 4 mL of a storage solution for cerium hydroxide slurry (content of abrasive grains: 1.0% by mass) was put into a 1 cm square cell, and the cell was placed in a spectrophotometer (device name: U3310) manufactured by Hitachi, Ltd. installed. The absorbance was measured in the wavelength range of 200 to 600 nm, and the absorbance for light having a wavelength of 400 nm and the light transmittance for light having a wavelength of 500 nm were measured. The absorbance for light having a wavelength of 400 nm was 1.436. The light transmittance for light with a wavelength of 500 nm was 99%/cm.

<Measurement of the nonvolatile content of the supernatant>
The cerium hydroxide slurry storage solution (abrasive grain content: 1.0% by mass) was placed in a centrifuge tube (tube) attached to the Hitachi Koki ultracentrifuge (apparatus name: 70P-72). It was filled and centrifuged for 50 minutes at a rotation speed of 50,000 min ⁻¹ using the ultracentrifuge. In the ultracentrifuge, the tube angle was 26°, the minimum radius R _min was 3.53 cm, the maximum radius R _max was 7.83 cm, and the average radius R _av was 5.68 cm. The centrifugal acceleration calculated from the average radius R _av was 158756 G≈1.59×10 ⁵ G. After centrifugation, 5.0 g of the supernatant was taken from the centrifuge tube, placed in an aluminum petri dish, and dried at 150° C. for 1 hour. The non-volatile content (content of abrasive grains containing hydroxide of tetravalent cerium) in the supernatant was calculated by measuring the mass before and after drying, and it was 764 ppm.

<Preparation of CMP Abrasive>
[Example 1]
1,3,5-triazine-2,4,6-triamine (hereinafter referred to as "melamine") [manufactured by Tokyo Chemical Industry Co., Ltd.] 0.2% by mass, acetic acid 0.06% by mass and water 99.74% by mass. % Of the additive-containing stock solution, 100 g of the cerium hydroxide slurry stock solution, and 400 g of water were mixed to prepare a CMP abrasive (1000 g) having the composition shown in Table 1. .. The CMP abrasive contains 0.1% by mass of abrasive grains containing cerium hydroxide, 0.1% by mass of melamine, and 0.03% by mass of acetic acid.

[Example 2]
The melamine was changed to 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine, and 0.06% by mass of acetic acid in the stock solution for additive liquid was added to 0.004% by mass of imidazole. An abrasive for CMP having the composition shown in Table 1 was prepared in the same manner as in Example 1 except that the content was changed to %. The abrasive for CMP is 0.1 mass% of abrasive grains containing cerium hydroxide and 0.1 mass% of 2,4,6-tris[bis(methoxymethyl)amino]-1,3,5-triazine. %, and 0.002 mass% of imidazole.

[Example 3]
As shown in Table 1, in the same manner as in Example 1 except that melamine was changed to 2,4-diamino-6-[2-(2-methyl-1-imidazolyl)ethyl]-1,3,5-triazine. A polishing agent for CMP having the above composition was prepared. The abrasive for CMP is 0.1% by mass of abrasive grains containing cerium hydroxide, 2,4-diamino-6-[2-(2-methyl-1-imidazoyl)ethyl]-1,3,5. -Containing 0.1% by weight of triazine and 0.03% by weight of acetic acid.

[Example 4]
Other than changing melamine to 3-amino-5,6-dimethyl-1,2,4-triazine and changing 0.06% by mass of acetic acid in the stock solution for additive liquid to 0.004% by mass of imidazole. In the same manner as in Example 1, a CMP abrasive having the composition shown in Table 1 was prepared. The polishing agent for CMP contained 0.1% by mass of abrasive grains containing cerium hydroxide, 0.1% by mass of 3-amino-5,6-dimethyl-1,2,4-triazine, and 0.1% by mass of imidazole. 002 mass% is contained.

[Comparative Example 1]
500 g of a storage solution for an additive solution containing 0.004% by mass of imidazole, 0.2% by mass of tris(2-hydroxyethyl) isocyanurate and 99.796% by mass of water, and 100 g of a storage solution for a cerium hydroxide slurry, An abrasive (1000 g) for CMP having the composition shown in Table 1 was prepared by mixing with 400 g of water. The CMP abrasive contains 0.1% by mass of abrasive grains containing cerium hydroxide, 0.1% by mass of tris(2-hydroxyethyl) isocyanurate, and 0.002% by mass of imidazole.

[Comparative example 2]
Changed tris(2-hydroxyethyl) isocyanurate to 1,3,5-tris(4,5-epoxypentyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione Except for the above, a CMP abrasive having the composition shown in Table 1 was prepared in the same manner as in Comparative Example 1. The polishing agent for CMP contains 0.1% by mass of abrasive grains containing cerium hydroxide and 1,3,5-tris(4,5-epoxypentyl)-1,3,5-triazine-2,4. It contains 0.1% by mass of 6(1H,3H,5H)-trione and 0.002% by mass of imidazole.

[Comparative Example 3]
It is described in Table 1 by mixing 500 g of the stock solution for the additive solution containing 0.004% by mass of imidazole and 99.996% by mass of water, 100 g of the stock solution for cerium hydroxide slurry, and 400 g of water. An abrasive for CMP having the composition (1000 g) was prepared. The CMP abrasive contains 0.1% by mass of abrasive grains containing cerium hydroxide and 0.002% by mass of imidazole.

[Comparative Example 4]
An abrasive for CMP having the composition shown in Table 1 was prepared in the same manner as in Comparative Example 1 except that tris(2-hydroxyethyl) isocyanurate was changed to pyrazine amide. The CMP abrasive contains 0.1% by mass of abrasive grains containing cerium hydroxide, 0.1% by mass of pyrazine amide, and 0.002% by mass of imidazole.

[Comparative Example 5]
An abrasive for CMP having a composition shown in Table 1 was prepared in the same manner as in Comparative Example 1 except that tris(2-hydroxyethyl) isocyanurate was changed to 1-aminobenzotriazole. The abrasive for CMP contains 0.1 mass% of abrasive grains containing cerium hydroxide, 0.1 mass% of 1-aminobenzotriazole, and 0.002 mass% of imidazole.

<Liquid property evaluation>
The pH of the CMP polishing agent obtained above was evaluated under the following conditions.

(PH measurement conditions)
Measurement temperature: 25±5℃
Measuring device: manufactured by Electrochemical Instruments Co., Ltd., model number PHL-40
Measurement method: After performing two-point calibration using a standard buffer solution (phthalate pH buffer solution, pH: 4.01 (25°C); neutral phosphate pH buffer solution, pH 6.86 (25°C)), The electrode was put in a polishing agent for CMP and the pH after being stabilized for 2 minutes or more was measured by the measuring device.

<CMP evaluation: blanket wafer evaluation>
Each of the CMP polishing agents was used to polish a substrate to be polished under the following CMP conditions.

(CMP condition)
Polishing device: Mira-3400 (manufactured by APPLIED MATERIALS)
・CMP abrasive flow rate: 200 mL/min
Substrate to be polished: As a blanket wafer on which no pattern is formed, a substrate in which a silicon oxide film having a thickness of 1000 nm is formed on a silicon substrate by a plasma CVD method, and a silicon nitride film having a thickness of 200 nm is formed on a silicon substrate by a CVD method. The substrate formed in 1. and the substrate in which a 200 nm-thick polysilicon film was formed on the silicon substrate by the CVD method were used.
Polishing pad: foamed polyurethane resin having closed cells (Rohm and Haas Japan Co., Ltd., model number IC1010), Shore D hardness=60
・Polishing pressure: 20 kPa (3.0 psi)
-Number of rotations of substrate and polishing platen: substrate/polishing platen = 93/87 min ^-1
・Polishing time: 1 min
-Wafer cleaning and drying: After CMP treatment, cleaning with a PVC (polyvinyl chloride) brush was performed, and subsequently, drying was performed with a spin dryer.

(Measurement of blanket wafer polishing rate)
Polishing rate of each film to be polished (silicon oxide film, silicon nitride film, polysilicon film) polished and washed under the above conditions (polishing rate of silicon oxide film: SiO ₂ RR, polishing rate of silicon nitride film: SiNRR, polysilicon) The polishing rate of the film: p-SiRR) was calculated from the following formula. Further, to determine the polishing selectivity ratio _{SiNRR / p-SiRR / SiO 2} RR. The film thickness difference between the films to be polished before and after polishing was determined using an optical interference film thickness device (manufactured by Filmetrics, Inc., trade name: F80).
(Polishing rate: RR)=(difference in film thickness of each film to be polished before and after polishing (nm))/(polishing time (min))

Table 1 shows each measurement result obtained in Examples and Comparative Examples. The symbols in Table 1 are as follows.
A1: 1,3,5-triazine-2,4,6-triamine (conventional name: melamine)
A2: 2,4,6-Tris[bis(methoxymethyl)amino]-1,3,5-triazine A3:2,4-diamino-6-[2-(2-methyl-1-imidazoyl)ethyl]- 1,3,5-Triazine A4:3-Amino-5,6-dimethyl-1,2,4-triazine A5: Tris(2-hydroxyethyl) isocyanurate
A6:1,3,5-tris(4,5-epoxypentyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione A7:pyrazineamide A8:1-aminobenzo Triazole

According to the present invention, it is possible to provide an abrasive, an abrasive set and a polishing method capable of polishing silicon nitride at high speed. Further, according to the present invention, by adjusting the type of the triazine compound, it is possible to maintain the polishing rate of silicon nitride at a high level and adjust the polishing rates of other materials to be polished.

1, 11, 21... Silicon substrate, 2, 24... Dummy gate material, 3, 23... Cap material, 4, 12, 22... Insulating material, 13... Hard mask, 100a, 100b, 100c, 110a, 110b, 110c, 120a, 120b... Substrate, AR... Angle rotor, A1... Rotation axis, A2... Tube angle, R _min ... Minimum radius, R _max ... Maximum radius, R _av ... Average radius.

Claims (6)

A polishing agent used for polishing a surface to be polished containing silicon nitride,
Containing a liquid medium, abrasive grains containing a hydroxide of a tetravalent metal element, and a triazine compound having a triazine skeleton,
An abrasive containing the triazine compound in an amount of 0.001 to 0.3% by mass. The polishing agent according to claim 1, wherein the tetravalent metal element is tetravalent cerium. The abrasive grains have a nonvolatile content of 300 ppm or more when an aqueous dispersion in which the content of the abrasive grains is adjusted to 1.0% by mass is centrifuged at a centrifugal acceleration of 1.59×10 ⁵ G for 50 minutes. The abrasive according to claim 1, which is provided. The constituents of the polishing agent according to any one of claims 1 to 4 are separately stored in a first liquid and a second liquid, and the first liquid contains the abrasive grains and a liquid medium, An abrasive set, wherein the second liquid contains the triazine compound and a liquid medium. Using the polishing agent according to any one of claims 1 to 3 comprising the step of polishing the surface of the substrate, the surface to be polished containing silicon nitride, a substrate polishing method. 5. A step of polishing a surface to be polished of a substrate using an abrasive obtained by mixing the first liquid and the second liquid in the polishing agent set according to claim 4 , wherein the surface to be polished is A method of polishing a substrate containing silicon nitride.

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