Cerium oxide and abrasives

Abstract

Provided are a cerium oxide that is capable of high-speed polishing of a silicon nitride film, and a polishing agent that includes said cerium oxide. In this cerium oxide, the BET diameter is 15nm to 100nm, said BET diameter being the particle diameter as calculated from the specific surface area measured according to a nitrogen gas adsorption method, the Scherrer diameter is 10nm to 50nm, said Scherrer diameter being the crystal diameter as obtained from an X-ray powder diffraction method, and the value of the BET diameter divided by the Scherrer diameter is 1.4 to 3.5. This polishing agent includes said cerium oxide and water.

Description

[Technical Field]

[0001] The present invention relates to cerium oxide and an abrasive. [Background technology]

[0002] In recent years, with the increasing integration and functionality of semiconductor integrated circuits, the development of microfabrication technologies for miniaturizing and densifying semiconductor elements has been progressing. Conventionally, in the manufacture of semiconductor integrated circuit devices (hereinafter also referred to as semiconductor devices), chemical mechanical polishing (hereinafter referred to as CMP) has been used to planarize interlayer insulating films, buried wiring, etc., in order to prevent problems such as unevenness (steps) on layer surfaces exceeding the depth of focus of lithography, making it impossible to obtain sufficient resolution. As the demand for higher definition and miniaturization of elements becomes stricter, the importance of high planarization using CMP is increasing.

[0003] Furthermore, in recent years, in the manufacture of semiconductor devices, an isolation method using shallow trenches with small element isolation widths (hereinafter referred to as STI) has been introduced in order to advance the further miniaturization of semiconductor elements. STI is a technique for forming an electrically isolated device region by forming trenches (grooves) in a silicon substrate and filling the trenches with an insulating film. An example of STI will be described with reference to FIGS. 1A and 1B. As shown in FIG. 1A, after the device region of silicon substrate 1 is masked with a silicon nitride film 2 or the like, trenches 3 are formed in silicon substrate 1, and an insulating film such as a silicon dioxide film 4 is deposited to fill trench 3. Next, by using CMP, the silicon dioxide film 4 on the silicon nitride film 2 (the protruding portion) is polished and removed while leaving the silicon dioxide film 4 in the trenches 3 (the recessed portion), thereby obtaining a device isolation structure in which the silicon dioxide film 4 is filled in trench 3, as shown in FIG. 1B.

[0004] One known abrasive for CMP is one containing cerium oxide particles. For example, Patent Document 1 discloses a polishing agent containing a specific water-soluble polymer, cerium oxide particles, and water, and having a pH of 4 to 9. The polishing agent of Patent Document 1 can maintain a high polishing rate for silicon oxide films while suppressing the polishing rate for silicon nitride films. In the example of Figures 1A and 1B, the silicon nitride film 2 acts as a polishing stopper film, resulting in a highly flat surface.

[0005] Separately, Patent Document 2 discloses a specific method for preparing a metal-doped cerium composition having excellent thermal stability and used in catalysts for treating exhaust gases, in which a solution containing a cerium (III) salt, cerium (IV) and a metal salt is prepared in the presence of nitrate ions, the solution is brought into contact with a base to form a precipitate, and the precipitate is then heat-treated. Furthermore, Non-Patent Document 1 discloses a nitrogen gas adsorption method, which will be described later. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2019-87660 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-529296 [Non-patent literature]

[0007] [Non-Patent Document 1] Brunauer, S., Emmett, PT and Teller, E.: Adsorption Gases in Multimolecular Layers, J. Amer. Che. Soc., Vol.60, No.2, pp.309-319, 1938 Summary of the Invention [Problem to be solved by the invention]

[0008] 1A and 1B, an example of STI different from that shown in FIGS. 1A and 1B will be described with reference to FIGS. 2A and 2B. As shown in FIG. 2A, a titanium nitride film 5 and a silicon nitride film 2 are stacked in this order on an element region of a silicon substrate 1, which is different from that shown in FIG. 1A. In the example shown in FIG. 2A, it may be necessary to polish and remove the silicon nitride film 2 together with the silicon oxide film 4. In contrast, conventional abrasives containing cerium oxide particles are generally used to polish silicon oxide films at high speed and reduce the polishing rate with silicon nitride films, but are not designed to polish silicon oxide films and silicon nitride films at high speed simultaneously. One possible solution is to add an additive that acts on silicon oxide films, which have a high polishing rate, to suppress the polishing of the silicon oxide film and achieve a uniform polishing rate. However, this method has the problem of hindering the speed of the polishing process. In CMP, in order to polish a silicon oxide film and a silicon nitride film at the same speed while maintaining a sufficiently high polishing rate, a polishing agent capable of polishing a silicon nitride film at high speed is required.

[0009] The present invention has been made in view of the above circumstances, and has as its object to provide cerium oxide capable of polishing silicon nitride films at high speeds and an abrasive containing said cerium oxide. [Means for solving the problem]

[0010] A first embodiment of cerium oxide according to the present invention has a BET diameter, which is a particle diameter calculated from a specific surface area measured by a nitrogen gas adsorption method, of 15 nm or more and 100 nm or less, a Scherrer diameter, which is a crystallite diameter obtained by an X-ray powder diffraction method, of 10 nm or more and 50 nm or less, and a value obtained by dividing the BET diameter by the Scherrer diameter of 1.4 or more and 3.5 or less.

[0011] The second embodiment of the cerium oxide according to the present invention has a true density of 5.0 to 6.8 g / cm 3 is a particle.

[0012] The cerium oxide may contain one or more metals selected from the group consisting of alkaline earth metals and lanthanoids (excluding cerium).

[0013] The cerium oxide may contain 1 to 20 mol % of the metal.

[0014] In the cerium oxide, the lanthanoid may include lanthanum.

[0015] The alkaline earth metal in the cerium oxide may include at least one selected from the group consisting of barium and strontium.

[0016] The value obtained by subtracting the lattice constant of the cerium oxide not containing the metal from the lattice constant of the cerium oxide containing the metal may be 0.003 Å to 0.05 Å.

[0017] The present invention provides an abrasive containing the above cerium oxide and water. [Effects of the Invention]

[0018] The present invention provides cerium oxide capable of polishing silicon nitride films at high speeds and an abrasive containing said cerium oxide. [Brief explanation of the drawings]

[0019] [Figure 1A] 1 is a cross-sectional view showing an example of a semiconductor substrate before being polished by CMP in STI. [Figure 1B] 1 is a cross-sectional view showing an example of a semiconductor substrate after polishing by CMP in STI. [Figure 2A] FIG. 10 is a cross-sectional view showing another example of a semiconductor substrate. [Figure 2B] 2B is a cross-sectional view showing an example of the semiconductor substrate of FIG. 2A after polishing. [Figure 3] FIG. 1 is a schematic diagram illustrating an example of a polishing apparatus. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following describes embodiments of the present invention. The present invention is not limited to the following embodiments, and other embodiments may also fall within the scope of the present invention as long as they are consistent with the spirit of the present invention.

[0021] In the present invention, the term "surface to be polished" refers to the surface to be polished of an object to be polished, for example, the front surface. In this specification, the term "surface to be polished" also includes intermediate surfaces that appear on a semiconductor substrate during the process of manufacturing a semiconductor device. In the present invention, "silicon oxide" specifically refers to silicon dioxide, but is not limited thereto and also includes silicon oxides other than silicon dioxide. In the present invention, the "selectivity" refers to the polishing rate (R SiN ) to the polishing rate of silicon oxide film (R SiO2 ) ratio (R SiO2 / R SiN ) means Furthermore, the symbol "~" indicating a range of numerical values ​​includes the numerical values ​​before and after it as the lower and upper limits.

[0022] [BET diameter and Scherrer diameter] First, the BET diameter and Scherrer diameter, which specify the cerium oxide of the first embodiment, will be described. The BET diameter is a value calculated by the following formula (1) assuming that the particles are spherical, from the nitrogen gas adsorption volume measured by the nitrogen gas adsorption method and the specific surface area calculated from the Brunauer-Emmett-Teller equation (BET equation). d B =6 / ρs Equation (1) where d B is the particle diameter (BET diameter), ρ is the density of cerium oxide, and s is the specific surface area.

[0023] In the present invention, the nitrogen gas adsorption method uses the BET flow method (single-point method) with reference to Non-Patent Document 1. The cerium oxide to be measured is preliminarily treated at 200°C for 20 minutes to remove adsorbates. The nitrogen gas adsorption isotherm of the cerium oxide is then measured, and the specific surface area is calculated from the isotherm using the BET equation (Equation (2) below). The isotherm can be measured using a fully automatic specific surface area measuring device (such as Macsorb (trade name) manufactured by Mountech Co., Ltd.).

[0024]

number

[0025] The Scherrer diameter is a value calculated from the line width of a powder X-ray diffraction peak and the like using the Scherrer formula (the following formula (4)). d S =Kλ / βcosθ Equation (4) where d S is the crystallite diameter (Scherrer diameter), K is the Scherrer constant, λ is the wavelength of the X-ray, θ is the Bragg angle, and β is the full width at half maximum. In the present invention, the Scherrer diameter is determined from the half-width of the 111 plane diffraction peak at about 28.5°, which is the main peak of cerium oxide.

[0026] The cerium oxide of the first embodiment has a BET diameter, which is a particle diameter calculated from a specific surface area measured by a nitrogen gas adsorption method, of 14 nm or more and 210 nm or less, and a Scherrer diameter, which is a crystallite diameter obtained by an X-ray powder diffraction method, of 10 nm or more and 60 nm or less, and the BET diameter d B The Scherrer diameter d S The value divided by (d B / d S ) is between 1.4 and 3.5. A polishing agent using the present cerium oxide as an abrasive grain has a high polishing rate for silicon nitride films, and for example, it is possible to polish silicon oxide films and silicon nitride at the same speed while maintaining a sufficiently high polishing rate.

[0027] The reason why cerium oxide has excellent polishing properties for silicon nitride films is still not fully understood, but is speculated to be as follows. The cerium oxide particles exist as agglomerated particles (secondary particles) in the abrasive. Such agglomerated particles are expected to have a smaller measured BET diameter relative to non-agglomerated cerium oxide particles, i.e., d B / d S is estimated to be a value that reflects the aggregation state of cerium oxide particles. d B / d S Cerium oxide particles with a ρ of 1.4 or more and 3.5 or less have an excellent balance between the particle size and the ratio of the surface area that chemically interacts with silicon nitride, and are therefore presumed to improve the polishing rate of silicon nitride films while suppressing the occurrence of polishing scratches on silicon nitride films and silicon oxide films. d B / d S The lower limit of d is preferably 1.5 or more, more preferably 1.6 or more, even more preferably 1.7 or more, and particularly preferably 2.0 or more. B / d S The upper limit of the value is preferably 3.5 or less, more preferably 3.0 or less.

[0028] [True density] Next, the true density that specifies the cerium oxide of the second embodiment will be described. Density includes true density, apparent density, and bulk density. True density is defined as the density where only the volume occupied by the substance itself is used to calculate density. Known methods for measuring true density include the liquid displacement method and gas displacement method. Apparent density is defined as the density where the volume occupied by the substance itself and internal voids is used to calculate density. However, in reality, the volume used to calculate density also includes the volume of the unevenness of the particle surface that is not wetted by liquid. Known methods for measuring apparent density include the Le Chatelier pycnometer method, submerged weighing method, Archimedes' method, and mercury intrusion method. Bulk density is defined as the density where the volume occupied by the substance itself and internal voids and pores is used to calculate density. However, in reality, the volume used to calculate density also includes the volume of the unevenness of the particle surface, the volume of the gaps between particles, and the volume of the gaps between particles and the container. Known methods for measuring bulk density include the container method and funnel method. In the cerium oxide of the second embodiment, the density is defined as true density. In the present invention, true density is measured by gas displacement spectrometry. Because gas phase displacement spectrometry uses a gas as a probe, extremely minute spaces between particles and in pores on the particle surfaces, such as closed pores, are more likely to be reflected in the volume for density measurement than liquid phase displacement spectrometry, which uses a liquid as a probe. Therefore, gas phase displacement spectrometry is the optimal method for measuring the density of aggregates of particles of about several tens of nanometers in size. The density of the cerium oxide of the second embodiment is the density measured by a gas phase substitution method using He as a probe, that is, the true density is 5.0 g / cm 3 More than 6.8g / cm 3 It is preferable that the true density is 5.5 g / cm or less. 3 More than 6.7g / cm 3 Preferably less than 6.0 g / cm 3 More than 6.6g / cm 3 More preferably, the true density is 6.8 g / cm or less. 3 If the true density is 5.0 g / cm or less, scratches on the silicon nitride film can be suppressed even when polishing a hard film such as a silicon nitride film at high speed. 3 As a result, it is possible to suppress scratches occurring on the silicon oxide film and the like while maintaining a desired polishing rate for the silicon oxide film. The true density of the cerium oxide of the second embodiment is 7.215 g / cm, which is the literature value for the density of cerium oxide. 3 The main factors that cause the true density of this cerium oxide to be significantly lower are (1) lattice defects, i.e., oxygen vacancies, and (2) the difference in atomic weight due to the substitution of metal elements other than cerium. However, because the true density of this cerium oxide is even lower than the theoretical value that takes into account the above (1) and (2), it is presumed that other factors also exist.

[0029] [Lattice constant] Next, the lattice constant (a) that specifies cerium oxide will be described. In the present invention, the lattice constant is determined from the pattern obtained by X-ray diffraction and the assigned Miller index (hkl). The following can be determined from the value (Δa = a1 - a0) obtained by subtracting the lattice constant (a0) of cerium oxide without a metal from the lattice constant (a1) of cerium oxide with a metal. That is, if the value of Δa is positive, it indicates that ions with a radius larger than the ionic radius of cerium ions are incorporated into the lattice of the cerium oxide, causing the lattice to expand. On the other hand, if the value of Δa is negative, it indicates that ions with a radius smaller than the ionic radius of cerium ions are incorporated into the lattice of the cerium oxide, causing the lattice to shrink. Furthermore, a larger absolute value of Δa indicates that ions with a radius different from the ionic radius of cerium ions are incorporated into the lattice, or that a larger amount of ions are incorporated into the lattice. In this way, Δa can be used to determine how heterogeneous elements are incorporated into the lattice. Δa is preferably 0.003 Å to 0.05 Å, and more preferably 0.004 Å to 0.03 Å. If Δa is within this range, a high polishing rate for the silicon nitride layer can be obtained.

[0030] The cerium oxide of the present invention may satisfy the requirements of both the first and second embodiments. That is, the cerium oxide of the present invention has a BET diameter d B is 14 nm or more and 210 nm or less, and the Scherrer diameter d Sis 10 nm or more and 60 nm or less, and d B / d S is 1.4 or more and 3.5 or less, and the true density is 5.0 to 6.8 g / cm 3 It is preferable that the particles are of the formula: Preferred embodiments and production methods of cerium oxide will be described below, but unless otherwise specified, they are common to the cerium oxide of the first embodiment and the cerium oxide of the second embodiment.

[0031] The cerium oxide may be composed of cerium and oxygen, or may further contain other atoms. In terms of ease of adjusting the BET diameter, Scherrer diameter, and true density to specific ranges, and ease of adjusting the Δa to the above range, it is preferable that the cerium oxide contains a metal selected from alkaline earth metals and lanthanoids other than cerium. Examples of alkaline earth metals include beryllium, magnesium, calcium, strontium, barium, and radium, and from the viewpoint of the polishing properties of silicon nitride, strontium or barium is preferred. Examples of lanthanoids include lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium, with lanthanum being preferred from the standpoint of polishability of silicon nitride. These metals may be used alone or in combination of two or more. In the present cerium oxide, the content of the above metals is preferably 1 to 20 mol %, more preferably 1 to 18 mol %, based on the total amount of the present cerium oxide including the metals.

[0032] The cerium oxide may further contain other atoms as long as the effects of the present invention are achieved. Examples of such other atoms include fluorine, carbon, nitrogen, aluminum, and silicon. From the viewpoint of the polishing properties of silicon nitride, the content of these other atoms is preferably 5 mol % or less, and more preferably 1 mol % or less, based on the total amount of cerium oxide. Among these, fluorine atoms increase the hardness of cerium oxide and may damage the polishing surface, so the content is preferably 1 mol % or less, more preferably 0.1 mol % or less, based on the total amount of cerium oxide.

[0033] The crystal structure of cerium oxide is not particularly limited, but a cubic fluorite structure is preferred from the viewpoint of polishability. Note that, according to the manufacturing method described below, cerium oxide having a cubic fluorite structure can be obtained.

[0034] [Method of producing cerium oxide] The method for producing cerium oxide is to obtain a BET diameter d B is 14 nm or more and 210 nm or less, and the Scherrer diameter d S is 10nm or more and 60nm or less, d B / d S A method for obtaining cerium oxide having a true density of 5.0 to 6.8 g / cm 3 Any method can be selected from among methods that can obtain cerium oxide of the above formula. One example of such a production method is a production method including the following steps 1 to 3 (hereinafter also referred to as the present production method). The present production method is characterized by including the following steps 1 to 3. Step 1: A step of adding an aqueous solution containing a dopant containing one or more metals selected from the group consisting of alkaline earth metals and lanthanoids (excluding cerium) to a slurry in which a poorly soluble cerium-containing compound is dispersed. Step 2: A step of drying the slurry to adhere the dopant to the surface of the cerium-containing compound. Step 3: A step of firing the cerium-containing compound to which the dopant has been attached.

[0035] According to this production method, the cerium oxide can be suitably synthesized. Each step will be described below.

[0036] In this production method, first, a slurry in which a poorly soluble cerium-containing compound is dispersed and an aqueous solution containing a dopant containing one or more metals selected from the group consisting of alkaline earth metals and lanthanoids are prepared. Examples of poorly soluble cerium include cerium oxide, cerium carbonate, cerium hydroxide, cerium sulfate, cerium phosphate, cerium oxalate, cerium carbonate hydroxide, etc. The dispersion medium for poorly soluble cerium is usually water. The aqueous solution is an aqueous solution in which the specific metal is dissolved. Examples of water-soluble compounds containing the metal include nitrates, carbonates, acetates, sulfates, oxalates, chlorides, hydroxides, and halides. The pH of the aqueous solution may be adjusted. For example, even compounds that are poorly soluble in water, such as oxides, can be used as long as they can be dissolved by adjusting the pH. Among these, compounds with high solubility in water are preferred for the manufacturing process, and compounds in which the counter anions of the metal elements decompose or volatilize at low temperatures are preferred in terms of polishing characteristics, particularly the stability of the polishing rate. Examples of compounds that satisfy these characteristics include oxalates and acetates. Furthermore, aqueous solutions in which carbonates and organic acids are dissolved, and aqueous solutions in which hydroxides and organic acids are dissolved, are also suitable. After the slurry and the aqueous solution are prepared, the aqueous solution is added to the slurry. The aqueous solution may be added at room temperature or may be heated.

[0037] The slurry is then dried. Any drying method can be selected from methods that evaporate water. For example, the slurry may be heated using a heater or furnace, heated in a hot bath, or sprayed with dry air. In order to uniformly attach the dopant to the surface of the cerium-containing compound, it is preferable to stir the slurry during the drying process. The slurry is dried and solidified by this drying process.

[0038] The dried cerium-containing compound with the dopant attached thereto is optionally pulverized and then calcined. From the viewpoint of crystallinity, the heating temperature is preferably 500°C or higher, more preferably 600°C or higher, and even more preferably 700°C or higher. On the other hand, the upper limit of the heating temperature is not particularly limited, but is usually 1000°C or lower. From the viewpoint of suppressing the increase of coarse particles, the upper limit is preferably 950°C or lower, and even more preferably 900°C or lower.

[0039] When a large amount of Sr or Ba is used as the alkaline earth metal, the resulting cerium oxide may contain strontium carbonate or barium carbonate as an impurity. In this case, the carbonate can be removed by washing with an acidic aqueous solution, such as hydrochloric acid or nitric acid, adjusted to a pH of about 2, as needed.

[0040] According to the above production method, the BET diameter, which is the particle diameter calculated from the specific surface area measured by nitrogen gas adsorption method, is 14 nm or more and 210 nm or less, the Scherrer diameter, which is the crystallite diameter obtained by X-ray powder diffraction method, is 10 nm or more and 60 nm or less, the value obtained by dividing the BET diameter by the Scherrer diameter is 1.4 or more and 3.5 or less, and the true density is 5.0 to 6.8 g / cm 3 The cerium oxide particles obtained have a value (Δa) of 0.003 Å to 0.05 Å, which is obtained by subtracting the lattice constant of cerium oxide that does not contain a metal from the lattice constant of cerium oxide that does contain a metal.

[0041] <Uses of cerium oxide> This cerium oxide can be suitably used, for example, as an abrasive grain in a polishing agent for CMP, particularly STI. Because this cerium oxide improves the polishing rate of silicon nitride surfaces, it is possible to perform constant speed polishing while suppressing a decrease in the polishing rate, particularly in CMP of polished surfaces including silicon oxide and silicon nitride surfaces.

[0042] When using the present cerium oxide as an abrasive, it is preferable to use the present cerium oxide particles dispersed in a dispersion medium. The dispersion medium may be appropriately selected from liquids in which the present cerium oxide is insoluble or poorly soluble. In CMP applications, water is particularly preferred as the dispersion medium. Furthermore, the abrasive containing the present cerium oxide may contain known additives as needed. The additive is not particularly limited, but examples thereof include polymers that adjust the polishing rate of silicon oxide films or silicon nitride films, pH adjusters, chelating agents, and the like.

[0043] The pH adjuster can be appropriately selected from known inorganic acids, organic acids, basic compounds, amphoteric compounds such as amino acids, and salts thereof. Examples of inorganic acids include nitric acid, sulfuric acid, hydrochloric acid, and phosphoric acid, and ammonium salts, sodium salts, potassium salts, and the like of these acids may also be used. Examples of organic acids include carboxylic acids such as picolinic acid, organic sulfonic acids, and organic phosphoric acids, and ammonium salts, sodium salts, potassium salts, etc. Examples of organic base compounds include basic compounds such as ammonia, potassium hydroxide, tetramethylammonium hydroxide, and ethylenediamine, which contain nitrogen. Examples of amphoteric compounds include glycine, alanine, and phenylalanine.

[0044] The chelating agent can be appropriately selected from known chelating agents used in abrasive applications, and examples thereof include dicarboxylic acid chelating agents, tricarboxylic acid chelating agents, gluconic acid chelating agents, nitrilotriacetic acid chelating agents, and iminosuccinic acid chelating agents.

[0045] A polishing method using the present cerium oxide-containing abrasive includes, for example, bringing the surface of an object to be polished into contact with a polishing pad while supplying the abrasive, and polishing the surface by relative movement of the two. The surface to be polished includes, for example, a semiconductor substrate surface on which a silicon oxide film and a silicon nitride film are arranged in a pattern. When polishing a silicon nitride film using an abrasive containing this cerium oxide, it is preferable that the film has an underlayer such as a titanium nitride film or a polysilicon film. Because this cerium oxide has a low polishing rate for the underlayer, a planarized surface is formed in which the underlayer is exposed on the surface.

[0046] Examples of silicon dioxide films for STI substrates include so-called PE-TEOS films formed by plasma CVD using tetraethoxysilane (TEOS) as a raw material. Other examples of silicon dioxide films include so-called HDP films formed by high-density plasma CVD. Other CVD methods, such as HARP films and FCVD films, and SOD films formed by spin coating, can also be used. Examples of silicon nitride films include those formed by low-pressure CVD or plasma CVD using silane or dichlorosilane and ammonia as raw materials, or those formed by ALD.

[0047] A known polishing apparatus can be used in the polishing method of the present invention. Fig. 3 is a schematic diagram showing an example of a polishing apparatus. The polishing apparatus 20 shown in Fig. 3 includes a polishing head 22 that holds a semiconductor substrate 21 such as an STI substrate, a polishing platen 23, a polishing pad 24 attached to the surface of the polishing platen 23, and a polishing agent supply pipe 26 that supplies a polishing agent 25 to the polishing pad 24. While supplying a polishing agent 25 from the abrasive agent supply pipe 26, the polishing surface of the semiconductor substrate 21 held by the polishing head 22 is brought into contact with the polishing pad 24, and the polishing head 22 and the polishing platen 23 are rotated relative to each other to perform polishing.

[0048] The polishing head 22 may move linearly as well as rotaryly. Furthermore, the polishing platen 23 and polishing pad 24 may be approximately the same size as or smaller than the semiconductor substrate 21. In this case, it is preferable to move the polishing head 22 and polishing platen 23 relative to each other so that the entire surface to be polished of the semiconductor substrate 21 can be polished. Furthermore, the polishing platen 23 and polishing pad 24 do not have to be of the type that moves rotary, and may be, for example, of the type that moves in one direction as a belt.

[0049] Although there are no particular limitations on the polishing conditions for such a polishing apparatus 20, applying a load to the polishing head 22 and pressing it against the polishing pad 24 can increase the polishing pressure and improve the polishing rate. The polishing pressure is preferably about 0.5 to 50 kPa, and more preferably about 3 to 40 kPa from the viewpoints of uniformity of the polishing rate across the polished surface of the semiconductor substrate 21, flatness, and prevention of polishing defects such as scratches. The rotation speed of the polishing platen 23 and the polishing head 22 is preferably about 50 to 500 rpm. The supply amount of the abrasive 25 is appropriately adjusted depending on the composition of the abrasive, the above-mentioned polishing conditions, etc.

[0050] The polishing pad 24 can be made of a material such as nonwoven fabric, polyurethane foam, porous resin, or non-porous resin. To facilitate the supply of abrasive 25 to the polishing pad 24 or to allow a certain amount of abrasive 25 to accumulate on the polishing pad 24, the surface of the polishing pad 24 may be grooved in a grid, concentric circle, spiral, or other pattern. If necessary, a pad conditioner may be brought into contact with the surface of the polishing pad 24 to condition the surface of the polishing pad 24 while polishing. [Example]

[0051] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following examples, "%" means mass % unless otherwise specified. Furthermore, property values ​​were measured and evaluated by the following methods. Examples 1 to 4 are examples of cerium oxide and its production method according to the present invention, and Examples 5 to 7 are comparative examples.

[0052] [Synthesis of cerium oxide] (Example 1) 42.4 g of anhydrous cerium carbonate was placed in a calcination furnace and calcined for 1 hour at 800°C while blowing air through. The resulting slurry, containing 31.7 g of cerium oxide powder, was placed in an evaporating dish. Next, 8.834 g of lanthanum nitrate hexahydrate was dissolved in 40 mL of pure water. The evaporating dish containing the slurry was placed on a hot stirrer, set to 200°C, and stirred with a stirrer. After confirming that steam had begun to emerge from the evaporating dish, an aqueous solution of lanthanum nitrate was added little by little over approximately 3 minutes and allowed to dry completely while stirring. The agglomerated precursor was crushed to powder in an agate mortar and then calcined in an electric furnace. The calcination temperature was 800°C for 8 hours. The temperature was raised to 800°C over 2 hours, and the mixture was allowed to cool naturally after calcination. The resulting powder was crushed in an agate mortar and washed with 300 mL of pure water. Using a 0.1 μm membrane filter and a suction filter, the particles were washed with pure water until the pH of the filtrate was close to neutral, and then recovered. The recovered particles were dried in a thermostatic chamber at 80°C for 12 hours to completely remove moisture. The resulting powder was again pulverized in an agate mortar to obtain the cerium oxide of Example 1.

[0053] (Example 2) Cerium oxide of Example 2 was obtained in the same manner as in Example 1, except that 4.317 g of strontium nitrate was used instead of lanthanum nitrate hexahydrate.

[0054] (Example 3) Cerium oxide of Example 3 was obtained in the same manner as in Example 1, except that 2.665 g of strontium nitrate was used instead of lanthanum nitrate hexahydrate.

[0055] (Example 4) Cerium oxide of Example 4 was obtained in the same manner as in Example 1, except that 5.331 g of barium nitrate was used instead of lanthanum nitrate hexahydrate.

[0056] (Example 5) 42.4 g of cerium carbonate anhydride was placed in a calcination furnace and calcined for 1 hour at 800 °C while blowing air through. The resulting slurry, containing 31.7 g of cerium oxide powder, was placed in an evaporating dish. The evaporating dish containing the slurry was placed on a hot stirrer, set to 200 °C, and stirred with a stirrer until completely dried. The agglomerated precursor was ground to powder in an agate mortar and then calcined in an electric furnace. The calcination temperature was 800 °C for 8 hours. The temperature was raised to 800 °C over 2 hours, and the temperature was allowed to cool naturally after calcination. The resulting powder was ground in an agate mortar and washed with 300 mL of pure water. The particles were recovered by washing with pure water using a 0.1 μm membrane filter and a suction filter until the pH of the filtrate was near neutral. The recovered particles were dried in a thermostatic chamber at 80 °C for 12 hours to completely remove moisture. The obtained powder was again pulverized in an agate mortar to obtain cerium oxide of Example 5.

[0057] (Example 6) Cerium oxide of Example 6 was obtained in the same manner as in Example 1, except that 4.35 g of aluminum nitrate was used instead of lanthanum nitrate hexahydrate.

[0058] (Example 7) Cerium oxide of Example 7 was obtained in the same manner as in Example 1, except that 0.188 g of potassium nitrate was used instead of lanthanum nitrate hexahydrate.

[0059] [BET diameter and Scherrer diameter] The BET diameter and Scherrer diameter of the cerium oxides obtained in Examples 1 to 7 were calculated using the above-mentioned formulas (1) to (4). The specific surface area was measured using a Mountec Macsorb and evaluated using the BET flow method (single point method), a physical adsorption method. The sample was pretreated at 200°C for 20 minutes to remove any adsorbates adsorbed on the sample surface. Pure nitrogen was used as the gas. X-ray diffraction (XRD) measurements were performed using a Rigaku SmartLab high-speed X-ray diffractometer. The measurement conditions were: X-ray tube: Cu, voltage: 40 kV, current: 200 mA, scan mode: Step Scan, measurement angle range: 10°-150°, sampling interval: 0.01°, scan time per step: 2 s. The obtained XRD profile was compared with a database (JCPDS No.: 34-0394), confirming that the target cerium oxide with a cubic fluorite structure had been obtained.

[0060] [True density] The true density of the cerium oxides obtained in Examples 1 to 7 was measured using an AccuPycII1340 manufactured by Shimadzu Corporation. He gas was used as the probe, and the temperature of the circulating thermostatic bath was set to 25°C. After purging the sample with He gas 30 times as a pretreatment, measurements were repeated 10 times, and the average value of the 10 measurements was taken as the true density. The purging and measurement pressures for the He gas in the measurement cell were 135 kPa, and purging was stopped when the pressure change reached 0.05 kPa / min.

[0061] Approximately 30 g of each of the cerium oxides obtained in Examples 1 to 7 was placed in a container containing 270 mL of pure water and subjected to 5 minutes of ultrasonic homogenization to disintegrate and disperse. Next, 5 mm diameter zirconia balls were added to the container so that the volume was approximately the same as the pure water, and the mixture was ball milled for 30 minutes to disintegrate and disperse. Next, injection collision treatment was repeated five times to disintegrate and disperse the mixture, yielding slurries in which the cerium oxides of Examples 1 to 8 were dispersed. During the various crushing and dispersion processes, nitric acid was added as a pH adjuster as needed to maintain a pH of 3 to 5. The homogenizer used was a US-600TCVP (device name) manufactured by NIHONSEIKI KAISHA, and the wet jet mill used was a Starburst Mini (device name) manufactured by Sugino Machine.

[0062] [Polishing speed evaluation] The polishing speed of silicon nitride was measured using the slurries of Examples 1 to 7 obtained above. A fully automatic CMP device (Applied Materials, device name: Mirra) was used as the polishing machine. A two-layer pad (DuPont, product name: IC-1000 K-groove) was used as the polishing pad, and conditioning was performed using a diamond disc (3M, product name: A165). The supply speed of the slurry, which was an abrasive, was set to 200 cm 3 The silicon nitride was polished for 1 minute at a rotation speed of 77 rpm / min, a polishing platen rotation speed of 77 rpm, and a polishing pressure of 3 psi. The removal rate was measured using an optical film thickness meter (KLA-Tencor, device name: UV-1280SE). The amount of film thickness removed per minute was evaluated as the removal rate (RR). The removal rate of each example was compared with the removal rate of Example 5 (100). The results are shown in Table 1.

[0063] [Table 1]

[0064] As shown in Table 1, the cerium oxides of Examples 1 to 4, which have a BET diameter of 15 nm or more and 100 nm or less, a Scherrer diameter of 10 nm or more and 50 nm or less, and a value obtained by dividing the BET diameter by the Scherrer diameter of 1.4 or more and 3.5 or less, were shown to have a high polishing rate for silicon nitride films.

[0065] [Lattice constant evaluation] The lattice constant (a) of each of the cerium oxides of Examples 1 to 7 obtained above was determined from the X-ray diffraction patterns and assigned Miller indices (hkl). Subsequently, the value (Δa) was calculated by subtracting the lattice constant of the metal-free cerium oxide (Example 5) from the lattice constant of the metal-containing cerium oxides (Examples 1 to 4, 6, and 7). These results are shown in Table 2. From the results in Tables 1 and 2, the cerium oxides of Examples 1 to 4 have a BET diameter of 15 nm or more and 100 nm or less, a Scherrer diameter of 10 nm or more and 50 nm or less, and d B / d S The value of the BET diameter, Scherrer diameter, and d B / d S was not within the above range, a high polishing rate for the silicon nitride film could not be obtained.

[0066] [Table 2] [Industrial Applicability]

[0067] The cerium oxide of the present invention has a high polishing rate not only for silicon oxide films but also for silicon nitride films, so that, for example, in CMP of a surface to be polished in which silicon oxide and silicon nitride are arranged in a pattern, it is possible to polish the silicon oxide film and silicon nitride at a constant speed or by adjusting the selectivity to a desired value while maintaining a sufficiently high polishing rate. Therefore, the cerium oxide of the present invention is suitable for planarizing insulating films for STI in semiconductor device manufacturing.

[0068] This application claims priority based on Japanese Patent Application No. 2020-148694, filed on September 4, 2020, the disclosure of which is incorporated herein in its entirety. [Explanation of symbols]

[0069] 1...silicon substrate, 2...silicon nitride film, 3...trench, 4...silicon oxide film, 5...titanium nitride film, 20...polishing device, 21...semiconductor substrate, 22...polishing head, 23...polishing surface plate, 24...polishing pad, 25...abrasive, 26...abrasive supply pipe

Claims

1. A composition comprising 1 to 20 mol % of one or more metals selected from the group consisting of alkaline earth metals and lanthanides (excluding cerium), True density is 5.0 to 6.8 g / cm ３ is a particle of Cerium oxide having a BET diameter, which is a particle diameter calculated from a specific surface area measured by a nitrogen gas adsorption method, of 14 nm or more and 210 nm or less, a Scherrer diameter, which is a crystallite diameter obtained by an X-ray powder diffraction method, of 10 nm or more and 60 nm or less, and a value obtained by dividing the BET diameter by the Scherrer diameter of 1.4 or more and 3.5 or less.

2. 2. The cerium oxide of claim 1, wherein the lanthanoid comprises lanthanum.

3. 3. The cerium oxide according to claim 1, wherein the alkaline earth metal comprises at least one selected from the group consisting of barium and strontium.

4. The cerium oxide according to any one of claims 1 to 3, wherein a value obtained by subtracting the lattice constant of the cerium oxide not containing the metal from the lattice constant of the cerium oxide containing the metal is 0.003 Å to 0.05 Å.

5. An abrasive comprising cerium oxide and water, The cerium oxide contains 1 to 20 mol % of one or more metals selected from the group consisting of alkaline earth metals and lanthanoids (excluding cerium), and has a true density of 5.0 to 6.8 g / cm ３ The abrasive has a BET diameter, which is a particle diameter calculated from a specific surface area measured by a nitrogen gas adsorption method, of 14 nm or more and 210 nm or less, a Scherrer diameter, which is a crystallite diameter obtained by an X-ray powder diffraction method, of 10 nm or more and 60 nm or less, and a value obtained by dividing the BET diameter by the Scherrer diameter is 1.4 or more and 3.5 or less.

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