Cerium oxide and polishing agent

Abstract

To provide cerium oxide and a polishing agent capable of high speed polishing of a silicon nitride film.SOLUTION: Disclosed cerium oxide has a CO2 desorption amount obtained by a temperature-programmed desorption measurement of CO2 using oxygen and carbon monoxide satisfying one or more kinds selected from the following (A)-(D), wherein (A): in the CO-TPD, there exists at least one peak of the CO2 desorption amount in a range of 700°C or over, (B): in the CO-TPD, a total desorption amount of CO2 is 35 μmol / g or over, (C): in the CO-TPD, a ratio (S / T) of a total desorption amount of CO2 in a temperature range of 600°C or over, (S), to a total desorption amount of CO2, (T), is 0.3 or over, and (D): it is a grain having a true density of 5.0-6.8 g / cm3.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] In recent years, with the high integration and high functionality of semiconductor integrated circuits, the development of microfabrication technologies for miniaturization and high density of semiconductor elements has been promoted. Conventionally, in the manufacture of semiconductor integrated circuit devices (hereinafter also referred to as semiconductor devices), in order to prevent problems such as insufficient resolution due to the unevenness (steps) on the layer surface exceeding the depth of focus of lithography, a chemical mechanical polishing method (Chemical Mechanical Polishing: hereinafter referred to as CMP) is used to planarize the interlayer insulating film, embedded wiring, etc. As the requirements for high definition and miniaturization of elements become stricter, the importance of high planarization by CMP is increasing more and more.

[0003] Also in recent years, in the manufacture of semiconductor devices, in order to further advance the higher-level miniaturization of semiconductor elements, a separation method using shallow trenches with a small element isolation width (Shallow Trench Isolation: hereinafter referred to as STI) has been introduced. STI is a technique for forming electrically insulated element regions by forming trenches (grooves) in a silicon substrate and embedding an insulating film in the trenches. With reference to FIGS. 1A and 1B, an example of STI will be described. As shown in FIG. 1A, after masking the element region of the silicon substrate 1 with a silicon nitride film 2 or the like, a trench 3 is formed in the silicon substrate 1, and an insulating film such as a silicon dioxide film 4 is deposited so as to fill the trench 3. Next, by CMP, while leaving the silicon dioxide film 4 in the trench 3 which is a recess, the silicon dioxide film 4 on the silicon nitride film 2 which is a protrusion is polished and removed, so that as shown in FIG. 1B, an element isolation structure in which the silicon dioxide film 4 is embedded in the trench 3 is obtained.

[0004] As one of the abrasives for CMP, an abrasive containing cerium oxide particles is known. For example, Patent Document 1 discloses an abrasive containing a specific water-soluble polymer, cerium oxide particles, and water, with a pH of 4 to 9. According to the abrasive of Patent Document 1, while maintaining a high polishing rate for a silicon oxide film, the polishing rate for a silicon nitride film can be kept low. In the examples of FIGS. 1A and 1B, a good flat surface can be obtained because the silicon nitride film 2 serves as a polishing stopper film.

[0005] Separately from this, Patent Document 2 discloses a specific method for preparing a metal-doped cerium composition excellent in thermal stability used for a catalyst for treating exhaust gas, etc. In the presence of nitrate ions, a solution containing a cerium(III) salt, cerium(IV), and a metal salt is prepared, this solution is brought into contact with a base to form a precipitate, and the precipitate is heat-treated.

[0006] Non-Patent Document 1 discloses a method for synthesizing hexahedral cerium oxide with 100 faces exposed by a hydrothermal synthesis method.

[0007] Also, Non-Patent Document 2 shows a CO-TPD (Temperature Programmed Desorption) measurement method as a technique for examining the redox characteristics of a catalyst on the surface of a cerium oxide crystal. CO-TPD is a technique for evaluating the desorption temperature and the desorption amount when carbon dioxide (CO2) formed by oxygen (O) on the surface of cerium oxide and carbon monoxide (CO) adsorbed on the surface desorbs from the oxide surface.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0009]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0010] Referring to FIGS. 2A and 2B, another example different from FIGS. 1A and 1B of STI will be described. As shown in FIG. 2A, it is different from FIG. 1A in that a titanium nitride film 5 and a silicon nitride film 2 are laminated in this order on the element region of the silicon substrate 1. In the example of FIG. 2A, it may be required to polish and remove the silicon nitride film 2 together with the silicon oxide film 4 as shown in FIG. 2B. On the other hand, conventional abrasives containing cerium oxide particles are generally used for polishing a silicon oxide film at a high speed and suppressing the polishing rate with a silicon nitride film, and do not simultaneously polish the silicon oxide film and the silicon nitride film at a high speed. As one method, it is conceivable to suppress the polishing of the silicon oxide film and achieve equal speed by adding an additive that acts on the silicon oxide film with a high polishing rate. However, this method has a problem of hindering the speeding up of the polishing process. In CMP, in order to polish the silicon oxide film and the silicon nitride at an equal speed while maintaining a sufficiently high polishing rate, an abrasive capable of polishing the silicon nitride film at a high speed has been demanded.

[0011] The present invention has been made in view of the above circumstances, and an object thereof is to provide cerium oxide and an abrasive capable of polishing a silicon nitride film at a high speed.

Means for Solving the Problems

[0012] The first embodiment of cerium oxide according to the present invention has at least one peak in the desorption amount of CO2 in the range of 700 °C or higher in the temperature-programmed desorption measurement of CO2 using oxygen and carbon monoxide.

[0013] The second embodiment of cerium oxide according to the present invention has a total desorption amount of CO2 of 35 μmol / g or more in the temperature-programmed desorption measurement of CO2 using oxygen and carbon monoxide.

[0014] The third embodiment of cerium oxide according to the present invention has a ratio (S / T) of the total desorption amount (S) of CO2 in the temperature region of 600 °C or higher to the total desorption amount (T) of CO2 of 0.3 or more in the temperature-programmed desorption measurement of CO2 using oxygen and carbon monoxide.

[0015] The fourth embodiment of cerium oxide according to the present invention has a true density of 5.0 to 6.8 g / cm 3 and is in the form of particles.

[0016] The above cerium oxide may contain one or more metals selected from the group consisting of alkaline earth metals and lanthanoids (excluding cerium).

[0017] The above cerium oxide may contain 1 to 20 mol% of the above metal.

[0018] In the above cerium oxide, the above lanthanoid may contain lanthanum.

[0019] In the above cerium oxide, the above alkaline earth metal may contain one or more selected from the group consisting of barium and strontium.

[0020] For the cerium oxide containing the above metal, the value obtained by subtracting the lattice constant of the cerium oxide not containing the above metal from the lattice constant of the cerium oxide containing the above metal may be 0.001 Å to 0.05 Å.

[0021] The abrasive according to the present invention contains the cerium oxide and water.

Advantages of the Invention

[0022] The present invention provides cerium oxide and an abrasive capable of rapidly polishing a silicon nitride film.

Brief Description of the Drawings

[0023]

Figure 1A

Figure 1B

Figure 2A

Figure 2B

Figure 3

Figure 4A

Figure 4B

Figure 4C

Figure 4D

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments, and other embodiments may belong to the scope of the present invention as long as they conform to the gist of the present invention.

[0025] In the present invention, the "surface to be polished" refers to the surface of the object to be polished, for example, the surface. In this specification, the intermediate-stage surface that appears on the semiconductor substrate in the process of manufacturing a semiconductor device is also included in the "surface to be polished". 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 ratio" refers to the ratio (R SiN ) of the polishing rate (R SiO2 ) of the silicon nitride film to the polishing rate (R SiO2 / R SiN ) of the silicon oxide film. In addition, "~" indicating a numerical range includes the numerical values described before and after it as the lower limit value and the upper limit value.

[0026] [CO-TPD] First, the temperature-programmed desorption measurement (CO-TPD) of CO2 using oxygen and carbon monoxide to identify cerium oxide according to the present invention (hereinafter sometimes referred to as this cerium oxide) will be described. CO-TPD can be performed with reference to the non-patent document 2 and in accordance with it. It will be specifically described with reference to FIGS. 3 and 4A to 4D. FIG. 3 is a graph showing the temperature increase profile in CO-TPD including pretreatment. FIGS. 4A to 4D are schematic diagrams showing the state of cerium oxide in each step. In this measurement, as shown in FIG. 3, the furnace temperature and the gas atmosphere are adjusted in order according to the following steps (I) to (III). Note that according to the temperature-programmed desorption measurement apparatus, each step can be automatically controlled. Step (I): Weigh about 100 mg of cerium oxide to be measured and place it in the furnace. While flowing 5% by volume of oxygen at a flow rate of 30 mL / min, raise the temperature to 400 °C at a temperature increase rate of 10 °C / min and hold for 60 minutes. Step (II): After setting the temperature of the furnace to 50 °C, flow 2% by volume of carbon monoxide at a flow rate of 30 mL / min for 30 minutes, and then hold for 45 minutes while flowing helium at a flow rate of 50 mL / min. Step (III): While flowing helium at a flow rate of 50 mL / min, the temperature is raised to 900 °C at a rate of 10 °C / min and held for 30 minutes to obtain a temperature-programmed desorption spectrum. Note that steps (I) to (II) are preparatory steps, and the measurement of gas components may be performed at least during the implementation of step (III). The gas components can be detected, for example, by a quadrupole mass spectrometer or the like.

[0027] Cerium oxide is presumed to have oxygen defects on a part of its surface in the initial state as shown in Fig. 4A. It is presumed that oxygen is supplied to the oxygen defects by step (I), and the state in which the oxygen defects are reduced as shown in Fig. 4B is obtained. Then, by step (II), it is presumed that carbon monoxide is adsorbed mainly on the oxygen atoms on the surface of cerium oxide as shown in Fig. 4C. The pretreatment of this measurement is completed up to this point. Then, by raising the temperature as in step (III) above, carbon dioxide desorbs as shown in Fig. 4D, and a temperature-programmed desorption spectrum of CO2 is obtained.

[0028] Fig. 5 shows an example of the temperature-programmed desorption spectrum obtained in Example 4 described later. In the spectrum of Fig. 5, the horizontal axis represents the elapsed time (min), but it can be appropriately converted to temperature using the temperature curve (broken line). The vertical axis represents the amount of CO2 desorbed per 1 g of cerium oxide (μmol / g). As a method for detecting peaks from the obtained temperature-programmed desorption spectrum, a method of performing peak separation by a known method after performing multi-point baseline correction can be mentioned. Examples of peak separation methods include vertical division and waveform separation. When using vertical division, a line perpendicular to the horizontal axis is drawn at each point (temperature) that becomes the peak and the valley between peaks, and the range of each peak is determined. When using waveform separation, a Gauss function, a Lorentz function, a Voigt function, etc. can be used. In the case of waveform separation, for example, assuming there are 1 to 5 peaks, fitting is performed with the peak position (temperature), the full width at half maximum, and the area (desorption amount) as parameters. When performing waveform separation, when the peaks of the desorption temperature are close (about 20 °C as a guideline), they may be treated as one peak without separation. It is optional to use either vertical division or waveform separation, but peak separation by waveform separation is preferred because there are cases where peaks cannot be picked up by vertical division.

[0029] The desorption amount of CO2 can be obtained from the integrated value (area value) of the temperature-programmed desorption spectrum from the temperature-programmed desorption spectrum. For example, the total desorption amount of CO2 indicates the integrated value of the temperature-programmed desorption spectrum corresponding to the entire section of the above step (III), and the total desorption amount of CO2 in the temperature range of 600 °C or higher indicates the integrated value from the time corresponding to 600 °C of the temperature-programmed desorption spectrum to the time when the temperature is raised to 900 °C and held for 30 minutes.

[0030] In temperature-programmed desorption measurement, the desorption temperature may change slightly due to equipment differences (the presence or absence of a vacuum system in the flow where the desorbed gas is detected). Also, regarding the peak area (desorption amount), since the concentration of the gas taken in can be changed by the opening degree of the flow valve in the mass spectrometer, the peak area (desorption amount) may change significantly depending on the setting of the opening degree. To prevent such points from degrading the measurement accuracy, for example, by using the hexahedral cerium oxide with 100 exposed surfaces obtained by the hydrothermal synthesis method described in Non-Patent Document 1 and measuring based on this, accurate comparison can be made even if the equipment or equipment settings change.

[0031] Analyze the temperature-programmed desorption spectrum after the above baseline correction and waveform processing to determine the characteristics of cerium oxide, such as the peak temperature of the CO₂ desorption amount and the CO₂ desorption amount. The total desorption amount (T) of CO₂ is obtained from the area of the temperature-programmed desorption spectrum. Also, the total desorption amount (S) of CO₂ in the temperature range of 600 °C or higher is obtained from the area of the temperature-programmed desorption spectrum after the time corresponding to 600 °C in the temperature-programmed desorption spectrum.

[0032] [Cerium oxide] This cerium oxide satisfies one or more selected from the following (A) to (D). (A): In the CO-TPD, it has at least one peak of the CO₂ desorption amount in the range of 700 °C or higher. (B): In the CO-TPD, the total desorption amount of CO₂ is 35 μmol / g or more. (C): In the CO-TPD, the ratio (S / T) of the total desorption amount (S) of CO₂ in the temperature range of 600 °C or higher to the total desorption amount (T) of CO₂ is 0.3 or more. (D): It is particles with a true density of 5.0 to 6.8 g / cm 3 ³. The abrasive using the above cerium oxide as an abrasive grain has a high polishing rate for a silicon nitride film. For example, it is possible to polish the silicon oxide film and the silicon nitride at the same speed while maintaining a sufficiently high polishing rate.

[0033] Regarding the action of the above cerium oxide being excellent in the polishability of the silicon nitride film, there are still unclear parts. However, it is presumed that the cerium oxide satisfying the above (B) has many oxygen defects serving as active sites on the surface and a large interaction with the surface to be polished. Also, since the CO₂ is not desorbed until a high temperature is reached for the cerium oxide satisfying the above (A) or (C), it is presumed that it is easy to form a strong bond. As a result, it is presumed that the chemical interaction with the silicon nitride, which is the surface to be polished, becomes large and the polishing rate of the silicon nitride is improved.

[0034] In addition, the present inventors have found that the polishing rate of silicon nitride is improved by cerium oxide having a true density satisfying the above (D). The true density of the cerium oxide satisfying the (D) will be described. Densities include true density, apparent density, bulk density, etc. True density is defined as the density in which only the volume occupied by the substance itself is used as the volume for density calculation. As methods for measuring true density, the liquid displacement method and the gas displacement method are known. Apparent density is defined as the density in which the volume occupied by the substance itself and the internal voids is used as the volume for density calculation. In actuality, in addition to this, the volume of the space of the uneven portions on the surface of the particles that do not get wet with the liquid is also included in the volume for density calculation. As methods for measuring apparent density, the Le Chatelier pycnometer method, the weighing in liquid method, the Archimedes method, the mercury intrusion method, etc. are known. Bulk density is defined as the density in which the volume occupied by the substance itself, the internal voids, and the pores is used as the volume for density calculation. In actuality, in addition to this, the volume of the space of the uneven portions on the particle surface, the volume of the gaps between the particles, and the volume of the gaps between the particles and the container are also included in the volume for density calculation. As methods for measuring bulk density, the container method, the funnel method, etc. are known. In the present invention, true density is defined as the density. In the present invention, the true density is measured by the gas displacement method. Since the gas phase displacement method uses a gas as a probe, it is easier to reflect the very fine spaces of the pores between the particles and on the particle surface, such as closed pores, in the volume for density measurement compared to the liquid phase displacement method that uses a liquid as a probe. Therefore, it can be said that it is an optimal method for measuring the density of an aggregate of particles on the order of several tens of nm. The true density of this cerium oxide is the density measured by the gas phase displacement method using He as a probe, that is, the true density is 5.0 g / cm 3 or more and 6.8 g / cm 3 or less. Preferably, the true density is 5.5 g / cm 3 or more and 6.7 g / cm 3 or less, more preferably 6.0 g / cm 3 or more and 6.6 g / cm 3 or less. When the true density is 6.8 g / cm 3 or less, even when polishing a hard film such as a silicon nitride film at high speed, scratches generated on the silicon nitride film or the like can be suppressed. When the true density is 5.0 g / cm 3By the above, it is possible to suppress scratches occurring on the silicon oxide film or the like while maintaining the polishing rate of the desired silicon oxide film. The true density value of this cerium oxide is significantly lower than the literature value of the density of cerium oxide, which is 7.215 g / cm 3 The main factors for the significant decrease in the true density of this cerium oxide are (1) lattice defects, that is, oxygen defects, and (2) the difference in atomic weight due to the substitution of metal elements different from cerium. However, since the true density of this cerium oxide is even lower than the theoretical value considering the above (1) and (2), it is presumed that there are other factors.

[0035] This cerium oxide preferably satisfies one or more selected from the above (A) to (C) in terms of polishing the silicon nitride film at a higher speed, and more preferably satisfies all of the above (A) to (C).

[0036] Cerium oxide may be composed of cerium and oxygen, or may further contain other atoms. From the viewpoint of easily satisfying one or more selected from the group consisting of the above (A) to (D), it preferably contains an alkaline earth metal and a metal selected from lanthanoids other than cerium. Examples of the alkaline earth metal include beryllium, magnesium, calcium, strontium, barium, and radium. From the viewpoint of the polishability of silicon nitride, strontium or barium is preferable. Examples of the lanthanoid include lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. From the viewpoint of the polishability of silicon nitride, lanthanum is preferable. These metals may be used alone or in combination of two or more. In this cerium oxide, the content ratio of the above metal is preferably 1 to 20 mol%, more preferably 1 to 18 mol%, based on the total amount of this cerium oxide containing the metal and the like.

[0037] Next, the lattice constant (a) of cerium oxide in the case of containing a metal selected from the above-mentioned alkaline earth metals and lanthanoids other than cerium will be described. In the present invention, the lattice constant is determined by the pattern obtained by powder X-ray diffraction measurement and the assigned Miller indices (hkl). The value (Δa = a1 - a0) obtained by subtracting the lattice constant (a0) of cerium oxide not containing a metal from the lattice constant (a1) of cerium oxide containing a metal can be used to make the following judgments. That is, if the value of Δa is positive, it can be seen that ions having a radius larger than the ionic radius of cerium ions are incorporated into the lattice of cerium oxide, and the lattice is expanded. On the other hand, if the value of Δa is negative, it can be seen that ions having a radius smaller than the ionic radius of cerium ions are incorporated into the lattice of cerium oxide, and the lattice is contracted. Also, the larger the absolute value of Δa, the more it means that ions having a radius far from the ionic radius of cerium ions are incorporated into the lattice, or the larger the amount of ions incorporated into the lattice. Thus, it is possible to judge how heteroatoms are incorporated into the lattice by Δa. Δa is preferably from 0.001 Å to 0.05 Å, more preferably from 0.002 Å to 0.035 Å. If Δa is within this range, a high polishing rate of the silicon nitride film can be obtained.

[0038] This cerium oxide may further contain other atoms within the range where the effects of the present invention are exhibited. Examples of such other atoms include fluorine, carbon, nitrogen, aluminum, silicon, and the like. From the viewpoint of the polishability of silicon nitride, these other atoms are preferably 5 mol% or less, more preferably 1 mol% or less, based on the total amount of cerium oxide. Among them, since fluorine atoms harden cerium oxide and may damage the polished surface, they are preferably 1 mol% or less, more preferably 0.1 mol% or less, based on the total amount of cerium oxide.

[0039] The average particle size of the cerium oxide particles is preferably from 0.01 to 0.5 μm, more preferably from 0.03 to 0.3 μm. If the average particle size exceeds 0.5 μm, there is a risk of polishing defects such as scratches on the surface to be polished. Also, if the average particle size is less than 0.01 μm, the polishing rate may decrease.

[0040] Since the cerium oxide particles exist as agglomerated particles (secondary particles) in which primary particles are agglomerated in a liquid, the preferred particle size of the cerium oxide particles is represented by the average secondary particle size. That is, the average particle size shown in the above numerical range is usually the average secondary particle size. The average secondary particle size is measured using a particle size distribution meter such as a laser diffraction / scattering type using a dispersion liquid dispersed in a dispersion medium such as pure water.

[0041] The crystal structure of cerium oxide is not particularly limited, but a cubic fluorite structure is preferred from the viewpoint of polishability. According to the production method described later, cerium oxide having a cubic fluorite structure can be obtained.

[0042] [Production method of cerium oxide] This cerium oxide can be selected from any method among the methods capable of obtaining cerium oxide satisfying one or more selected from the above (A) to (D). As an example of such a production method, a production method including the following steps 1 to 3 (hereinafter also referred to as the present production method) can be mentioned. That is, 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 compound containing hardly soluble cerium is dispersed. Step 2: A step of drying the slurry to adhere the dopant to the surface of the compound containing cerium. Step 3: A step of firing the compound containing cerium to which the dopant has been adhered.

[0043] According to this manufacturing method, cerium oxide satisfying one or more selected from the group consisting of the above (A) to (D) can be suitably synthesized. Each step will be described below.

[0044] In this manufacturing method, first, a slurry in which a compound containing hardly soluble cerium 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 each prepared. Examples of the hardly soluble cerium include cerium oxide, cerium carbonate, cerium hydroxide, cerium sulfate, cerium phosphate, cerium oxalate, cerium hydroxocarbonate, etc. The dispersion medium of the hardly soluble cerium is usually water. The aqueous solution is an aqueous solution in which the specific metal is dissolved. Examples of the water-soluble compound containing the metal include nitrates, carbonates, acetates, sulfates, oxalates, chlorides, hydroxides, halides, etc. The pH of the aqueous solution may be adjusted. For example, even if it is a compound hardly soluble in water such as an oxide, it can be used if it can be dissolved by adjusting the pH or the like. Among these, those with high solubility in water are suitable in the manufacturing process, and those in which the counter anion of the metal element decomposes or volatilizes at low temperature are preferable from the viewpoint of polishing characteristics, particularly the stability of the polishing rate. Compounds satisfying such characteristics include oxalates, acetates, etc. Also, for example, an aqueous solution in which a carbonate and an organic acid are dissolved or an aqueous solution in which a hydroxide and an organic acid are dissolved is also suitable. After preparing the slurry and the aqueous solution, the aqueous solution is added to the slurry. The addition of the aqueous solution may be at room temperature or with heating.

[0045] Next, the slurry is dried. The drying method can be arbitrarily selected from methods in which moisture evaporates. For example, it may be heated with a heater or a furnace, heated by a warm bath, or blown with dry air. From the point of uniformly adhering the dopant to the surface of the compound containing cerium, it is preferable to perform stirring during the drying process. By this drying process, the slurry is dried to a solid.

[0046] The cerium-containing compound with the dried dopant is pulverized as necessary and then subjected to heat baking. 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 it is usually 1000 °C or lower, and from the viewpoint of suppressing the increase of coarse particles, it is preferably 950 °C or lower, and more preferably 900 °C or lower.

[0047] In addition, when a large amount of Sr or Ba is used as the alkaline earth metal, strontium carbonate or barium carbonate may be mixed as impurities in the obtained cerium oxide. In this case, the carbonate can be removed by washing with an acid aqueous solution having a pH adjusted to about 2, such as hydrochloric acid or a nitric acid aqueous solution, as necessary.

[0048] The cerium oxide obtained by the above production method satisfies at least one of the characteristics ((A) to (C)) of the cerium oxide.

[0049] <Uses of Cerium Oxide> This cerium oxide can be suitably used, for example, as abrasive grains of an abrasive for CMP, particularly for STI. Since this cerium oxide improves the polishing rate of the silicon nitride surface, in particular, in CMP of a surface to be polished including a silicon oxide surface and a silicon nitride surface, isoplanar polishing can be performed while suppressing a decrease in the polishing rate.

[0050] When using this cerium oxide as an abrasive, it is preferable to disperse the particles of this cerium oxide in a dispersion medium. The dispersion medium may be appropriately selected from liquids in which this cerium oxide is insoluble or hardly soluble. In CMP applications, water is particularly preferred as the dispersion medium. In addition, the abrasive containing this cerium oxide may contain known additives as necessary. The additive is not particularly limited, and examples thereof include polymers, pH adjusters, chelating agents, etc. that adjust the polishing rate of a silicon oxide film or a silicon nitride film.

[0051] As the pH adjuster, it can be appropriately selected and used from known inorganic acids, organic acids, basic compounds, amphoteric compounds such as amino acids, and salts thereof. Examples of the inorganic acid include nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, etc., and ammonium salts, sodium salts, potassium salts, etc. of these may be used. Examples of the organic acid include carboxylic acids such as picolinic acid, organic sulfonic acids, organic phosphoric acids, etc., and ammonium salts, sodium salts, potassium salts, etc. of these may be used. Examples of the organic base compound include nitrogen-containing compounds such as ammonia, potassium hydroxide, tetramethylammonium hydroxide, ethylenediamine, etc. as the basic compound. Examples of the amphoteric compound include glycine, alanine, phenylalanine, etc.

[0052] As the above chelating agent, it can be appropriately selected from known ones used for abrasive purposes, and examples thereof include dicarboxylic acid-based chelating agents, tricarboxylic acid-based chelating agents, gluconic acid-based chelating agents, nitrilotriacetic acid-based chelating agents, iminodiacetic acid-based chelating agents, etc.

[0053] As a polishing method using the polishing agent containing cerium oxide, for example, there is a method of bringing the polished surface of the object to be polished into contact with the polishing pad while supplying the polishing agent, and performing polishing by the relative movement of the two. Here, examples of the polished surface where polishing is performed include a surface on which a silicon dioxide film and a silicon nitride film are arranged in a pattern on the surface of a semiconductor substrate. When polishing silicon nitride using the polishing agent containing cerium oxide, it is preferable to have a silicon nitride film, a polysilicon film, etc. as the underlying film. Since the polishing rate of the underlying film is low for the cerium oxide, a planarized surface where the underlying film is exposed on the surface is formed.

[0054] As the silicon dioxide film on the STI substrate, there is a so-called PE-TEOS film formed by plasma CVD using tetraethoxysilane (TEOS) as a raw material. In addition, as the silicon dioxide film, there is a so-called HDP film formed by high-density plasma CVD. Moreover, it is also possible to use a HARP film, an FCVD film formed by other CVD methods, or a SOD film formed by spin coating. As the silicon nitride film, there are those formed by low-pressure CVD, plasma CVD, or ALD using silane or dichlorosilane and ammonia as raw materials.

[0055] For the polishing method of this embodiment, a known polishing apparatus can be used. FIG. 6 is a schematic diagram showing an example of a polishing apparatus. The polishing apparatus 20 shown in the example of FIG. 6 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 an abrasive supply pipe 26 that supplies an abrasive 25 to the polishing pad 24. While supplying the abrasive 25 from the abrasive supply pipe 26, the surface to be polished 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 relatively rotated to perform polishing.

[0056] The polishing head 22 may perform not only rotational movement but also linear movement. Further, the polishing platen 23 and the polishing pad 24 may have a size equal to or smaller than that of the semiconductor substrate 21. In that case, it is preferable to be able to polish the entire surface to be polished of the semiconductor substrate 21 by relatively moving the polishing head 22 and the polishing platen 23. Furthermore, the polishing platen 23 and the polishing pad 24 do not necessarily perform rotational movement, and for example, they may move in one direction in a belt type.

[0057] There are no particular restrictions on the polishing conditions of such a polishing apparatus 20. However, by applying a load to the polishing head 22 and pressing it against the polishing pad 24, the polishing pressure can be increased, and the polishing speed can be improved. The polishing pressure is preferably about 0.5 to 50 kPa, and more preferably about 3 to 40 kPa from the viewpoints of preventing polishing defects such as uniformity, flatness, and scratches in the polished surface of the semiconductor substrate 21 in terms of the polishing speed. The rotational speeds of the polishing platen 23 and the polishing head 22 are preferably about 50 to 500 rpm. Also, the supply amount of the abrasive 25 is appropriately adjusted according to the composition of the abrasive and the above-mentioned various polishing conditions.

[0058] As the polishing pad 24, those made of non-woven fabric, foamed polyurethane, porous resin, non-porous resin, etc. can be used. In order to promote the supply of the abrasive 25 to the polishing pad 24 or to allow a certain amount of the abrasive 25 to accumulate on the polishing pad 24, groove processing such as a lattice shape, a concentric circle shape, a spiral shape, etc. may be performed on the surface of the polishing pad 24. Further, if necessary, a pad conditioner may be brought into contact with the surface of the polishing pad 24 to perform conditioning of the surface of the polishing pad 24 while polishing.

Examples

[0059] Hereinafter, the present invention will be specifically described 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. Also, the characteristic values were measured and evaluated by the following methods. Examples 1 to 5 are examples of the cerium oxide and its manufacturing method according to the present invention, and Examples 6 to 8 are comparative examples.

[0060] [Synthesis of Cerium Oxide] (Example 1): This manufacturing method (hereinafter also referred to as synthesis method A). 42.4 g of anhydrous cerium carbonate was charged into a firing furnace and fired at 800 °C for 1 hour while blowing air. A slurry containing 31.7 g of the cerium oxide powder thus obtained was placed in an evaporating dish. Next, 8.834 g of lanthanum nitrate hexahydrate was taken and dissolved in 40 mL of pure water. The evaporating dish containing the slurry was placed on a hot stirrer, the set temperature was set to 200 °C, and it was stirred with a magnetic stirrer. After confirming that steam began to come out of the evaporating dish, the aqueous solution of lanthanum nitrate was added little by little over about 3 minutes and completely dried while stirring. The precursor that had become a lump was pulverized in an agate mortar until it became powdery and then fired in an electric furnace. The firing 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 firing. The obtained powder was pulverized in an agate mortar and then washed with 300 mL of pure water. Using a 0.1 μm membrane filter and a suction filter, the particles were recovered by washing with pure water until the pH of the filtrate was near neutral. The recovered particles were dried in a constant temperature bath at 80 °C for 12 hours to completely remove the moisture. The obtained powder was pulverized again in an agate mortar to obtain the cerium oxide of Example 1.

[0061] (Example 2) In Example 1, cerium oxide of Example 2 was obtained in the same manner as in Example 1, except that 13.251 g of lanthanum nitrate hexahydrate was changed.

[0062] (Example 3) In Example 1, cerium oxide of Example 3 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.

[0063] (Example 4) In Example 1, cerium oxide of Example 4 was obtained in the same manner as in Example 1, except that 2.665 g of barium nitrate was used instead of lanthanum nitrate hexahydrate.

[0064] (Example 5) In Example 1, cerium oxide of Example 5 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.

[0065] (Example 6): An example where no other metal is added in Synthesis Method A. Hereinafter, it is also referred to as Synthesis Method AX.) 42.4 g of anhydrous cerium carbonate was put into a firing furnace and fired at 800 °C for 1 hour while blowing air. A slurry containing 31.7 g of the thus obtained cerium oxide powder was placed in an evaporating dish. The evaporating dish containing the slurry was placed on a hot stirrer, the set temperature was set to 200 °C, and it was completely dried while stirring with a stir bar. The precursor in the form of a lump was pulverized in an agate mortar until it became powdery and then fired in an electric furnace. The firing temperature was 800 °C for 8 hours, the temperature was raised to 800 °C over 2 hours, and the temperature was allowed to drop naturally after firing. The obtained powder was pulverized in an agate mortar and then washed with 300 mL of pure water. Using a 0.1 μm membrane filter and a suction filter, the particles were recovered by washing with pure water until the pH of the filtrate was near neutral. The recovered particles were dried in a constant temperature bath at 80 °C for 12 hours to completely remove moisture. The obtained powder was pulverized again in an agate mortar to obtain the cerium oxide of Example 6.

[0066] (Example 7): Premixing method (hereinafter, also referred to as Synthesis Method B.) A method of obtaining cerium oxide by dissolving a cerium source and a hetero-element raw material together in water at the time of the crystallization reaction (coprecipitation reaction) to obtain a precipitate (cerium oxide added with a hetero-element, cerium carbonate, etc.) and firing it. Cerium oxide of Example 7 was obtained by this method using cerium carbonate and lanthanum nitrate hexahydrate as raw materials.

[0067] (Example 8): Hydrothermal synthesis method (hereinafter, also referred to as Synthesis Method C.) Referring to Non-Patent Document 1, hexahedral cerium oxide with 100 faces exposed was synthesized by the hydrothermal synthesis method. Specifically, an aqueous solution (precipitate) obtained by mixing cerium nitrate and sodium hydroxide was placed in a sealed container, and hydrothermal reaction was carried out at 180 °C for 24 hours to obtain the cerium oxide of Example 8. The obtained cerium oxide was thoroughly washed with pure water to remove unreacted components, sodium, and nitrate ions, and it was confirmed by inductively coupled plasma optical emission spectrometry (ICP), conductivity measurement, etc. that sodium, nitrate ions, etc. were sufficiently washed.

[0068] The cerium oxides obtained in Examples 1 to 8 were evaluated by measuring X-ray Diffraction (XRD) using a high-speed X-ray diffractometer SmartLab manufactured by Rigaku Corporation. The measurement conditions were set as follows: 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 profiles were compared with a database (JCPDS No.: 34 - 0394), and it was confirmed that cerium oxide with a cubic fluorite structure, which is the target substance, was obtained. It was confirmed that the cerium oxides of Examples 1 to 5 and Example 7 had each peak slightly shifted to the low-angle side because they contained La, Sr, or Ba. No peaks other than those derived from cerium oxide containing La were confirmed in the cerium oxides of Examples 1 to 2. No peak shift was confirmed in the cerium oxides of Examples 6 and 8.

[0069] Approximately 30 g of each of the cerium oxides obtained in Examples 1 to 8 was placed into a container containing 270 mL of pure water, and each was irradiated with an ultrasonic homogenizer for 5 minutes to perform crushing and dispersion treatment. Next, zirconia balls with a diameter of 5 mm were added to make the volume approximately the same as that of pure water, and ball milling was performed for 30 minutes to perform crushing and dispersion treatment. Next, the jet collision treatment was repeated 5 times to perform crushing and dispersion treatment, and slurries in which the cerium oxides of Examples 1 to 8 were dispersed were obtained. Note that during various crushing and dispersion treatments, nitric acid was appropriately added as a pH adjuster so that the pH became 3 - 5. As the homogenizer, US - 600TCVP (equipment name) manufactured by NIHONSEIKI KAISHA was used, and as the wet jet mill, Starburst Mini (equipment name) manufactured by Sugino Machine was used. The average secondary particle diameter D of the cerium oxide in the obtained slurry was measured using a laser scattering / diffraction device (manufactured by Horiba, Ltd., product name: LA - 950). The measurement results are shown in Table 1.

[0070] [Evaluation of Polishing Rate] Using the slurries of Examples 1 to 8 obtained above, the polishing rate of silicon nitride was measured. As the polishing machine, a fully automatic CMP apparatus (manufactured by Applied Materials, apparatus name: Mirra) was used. As the polishing pad, a two-layer pad (manufactured by DuPont, product name: K-groove of IC-1000) was used, and conditioning was performed using a diamond disk (manufactured by 3M, product name: A165). Then, the supply rate of the slurry as the abrasive was 200 cm 3 / min, the rotation speed of the polishing platen was 77 rpm, and the polishing pressure was 3 psi, and silicon nitride was polished for 1 minute. The measurement of the polishing rate was performed using an optical film thickness meter (manufactured by KLA-Tencor, apparatus name: UV-1280SE). The film thickness removal amount per minute was evaluated as the polishing rate (RR). Also, with the polishing rate of Example 6 as the reference (100), the polishing rates of each example were compared. The results are shown in Table 1.

[0071] [CO-TPD] Temperature-programmed desorption measurement (TPD) was evaluated using a fully automatic temperature-programmed desorption spectrometer TPD-1-ATw manufactured by MicrotracBEL Corporation. Approximately 100 mg of the sample was collected, and the measurement conditions: according to the measurement program shown in FIG. 3 described above, the details are as described above. In the temperature-programmed desorption measurement, the target gas component was detected with a quadrupole mass spectrometer. The measurement range was 50°C to 900°C, the measurement atmosphere was He 50 mL / min, and the fragments of m / z 18, 28, and 44 were detected. For the obtained temperature-programmed desorption spectrum, baseline correction and waveform analysis were performed according to the method described above, and (A) the maximum peak temperature, (B) the total desorption amount of CO2, and (C) the ratio (S / T) of the total desorption amount of CO2 (S) in the temperature region of 600°C or higher to the total desorption amount of CO2 (T) were determined. The results are shown in Table 1. [True density] The true density of the cerium oxide obtained in Examples 1 to 8 was evaluated using AccuPyc II 1340 manufactured by Shimadzu Corporation. He gas was used as a probe, and the set temperature of the circulating constant temperature bath was 25°C. After purging with He gas 30 times as a pretreatment of the sample, repeated measurements were performed 10 times, and the average value of the 10 measurements was taken as the true density. The purge filling pressure and the measurement filling pressure of He gas into the measurement cell were 135 kPa, and the purge was terminated when the pressure change reached 0.05 kPa / min.

[0072]

Table 1

[0073] As shown in Table 1, this cerium oxide, this cerium oxide, the cerium oxides of Examples 1 to 5 satisfying one or more selected from the following (A) to (D) were shown to have a high polishing rate of the silicon nitride film. (A): Having at least one peak of CO2 desorption amount in the range of 700°C or higher. (B): The total desorption amount of CO2 is 35 μmol / g or more. (C): The ratio (S / T) of the total desorption amount (S) of CO2 in the temperature range of 600°C or higher to the total desorption amount (T) of CO2 is 0.3 or more. (D): The true density is 5.0 to 6.8 g / cm 3 of the particles.

[0074] [Lattice constant evaluation] Regarding the cerium oxides of Examples 1 to 7 obtained above, the lattice constant (a) was determined for each by the pattern obtained by powder X-ray diffraction and the Miller indices (hkl) assigned thereto. The powder X-ray diffraction was evaluated using a high-speed X-ray diffractometer SmartLab manufactured by Rigaku Corporation. The measurement conditions were set as follows: 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. Also, the obtained XRD profile was compared with a database (JCPDS No.: 34-0394), and it was confirmed that cerium oxide having a cubic fluorite structure, which is the target substance, was obtained. Subsequently, the value (Δa) obtained by subtracting the lattice constant of cerium oxide without metal (Example 6) from the lattice constant of cerium oxide containing metal (Examples 1 to 5, 7) was calculated. These results are shown in Table 2.

[0075] [Table 2]

[0076] From the results of Tables 1 and 2, in the cerium oxides of Examples 1 to 5, metal ions having an ionic radius larger than that of cerium ions were sufficiently incorporated into the lattice, so that one or more selected from the above (A) to (D) were satisfied, and a high polishing rate of the silicon nitride film was obtained. On the other hand, the cerium oxides of Example 6 in which no metal ions were added and Example 7 produced by Synthesis Method B did not satisfy one or more selected from the above (A) to (D), and a high polishing rate of the silicon nitride film could not be obtained.

[0077] This application claims priority based on Japanese Patent Application No. 2020-164640 filed on September 30, 2020, and incorporates the entire disclosure thereof herein. [Explanation of Reference Signs]

[0078] 1... silicon substrate, 2... silicon nitride film, 3... trench, 4... silicon dioxide film, 5... titanium nitride film, 20... polishing apparatus, 21... semiconductor substrate, 22... polishing head, 23... polishing platen, 24... polishing pad, 25... abrasive, 26... abrasive supply pipe.

Claims

Claim 1 Cerium oxide particles having a true density of 5.0 to 6.8 g / cm ３ . Claim 2 The cerium oxide according to claim 1, comprising one or more metals selected from the group consisting of alkaline earth metals and lanthanoids (excluding cerium). Claim 3 The cerium oxide according to claim 2, containing 1 to 20 mol% of the metal. Claim 4 The cerium oxide according to claim 2 or 3, wherein the lanthanoid contains lanthanum. Claim 5 The cerium oxide according to any one of claims 2 to 4, wherein the alkaline earth metal contains one or more selected from the group consisting of barium and strontium. Claim 6 The cerium oxide according to any one of claims 2 to 5, wherein 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 is 0.001 Å to 0.05 Å. Claim 7 A polishing agent containing cerium oxide and water, wherein the cerium oxide has a true density of 5.0 to 6.8 g / cm ３ and is composed of particles.

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