Polysilazane, a silica-based film-forming composition containing the same, and a method for producing a silica-based film using the same

Abstract

To provide a polysilazane capable of suppressing film thickness changes and void formation even in an ozone environment, and a siliceous film-forming composition containing the same. The present invention provides a polysilazane containing N-Si bonds, the number of N atoms having three N-Si bonds (NA 3 ) and the number of N atoms with two N-Si bonds (NA 2 ) and the ratio (NA 3 / NA 2 ) is 1.8 to 6.0.

Description

Technical Field

[0001] The present invention relates to polysilazane and a silica film-forming composition containing the same. The present invention also relates to a method for producing a silica film using them, a silica film, and an electronic device including the silica film.

Background Art

[0002] In the production of electronic devices, particularly semiconductor devices, an interlayer insulating film may be formed between a transistor element and a bit line, between a bit line and a capacitor, between a capacitor and a metal wiring, between a plurality of metal wirings, etc. Further, an insulating material may be embedded in an isolation groove provided on the substrate surface or the like. Furthermore, after forming a semiconductor element on the substrate surface, a coating layer may be formed using a sealing material to form a package. Such interlayer insulating films and coating layers are often formed from silica-based materials.

[0003] In the field of electronic devices, device rules are gradually being miniaturized, and miniaturization is also required for the size of insulating structures that separate each element incorporated in the device. However, as the miniaturization of the insulating structure progresses, the occurrence of defects in the silica film constituting a trench or the like has increased, and the problem of a decrease in the manufacturing efficiency of electronic devices has become significant.

[0004] As methods for forming a silica-based film, a chemical vapor deposition method (CVD method), a sol-gel method, a method of applying and firing a composition containing a silicon-containing polymer, etc. are used. Among these, since it is relatively simple, the method for forming a silica-based film using a composition is often adopted. In order to form such a silica-based film, a composition containing a silicon-containing polymer such as polysilazane, polysiloxane, polysiloxazane, or polysilane is applied to the surface of a substrate or the like and fired to oxidize the silicon contained in the polymer to form a silica-based film. In such a case, a method for reducing defects in the formed silica-based film has been studied. For example, it has been studied to form a silica-based film with few defects by using a composition containing perhydropolysilazane, which has high stability against oxidation (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present inventors have discovered that a composition containing polysilazane forms a silica-based film in an atmosphere containing oxygen, but when ozone also coexists in the atmosphere, ozone has an adverse effect on the properties of the silica-based film. And there has been a demand for a polysilazane that can form a silica-based film capable of suppressing changes in film thickness and defects even in the presence of ozone.

Means for Solving the Problems

[0007] The present invention is a polysilazane containing an N-Si bond, the number of N atoms having three N-Si bonds (NA 3 ), and the number of N atoms having two N-Si bonds (NA 2 ), and the ratio (NA 3 / NA 2) is a polysilazane with a value of 1.8 to 6.0. Here, Regarding the infrared absorption spectrum of the polysilazane, the peak intensity corresponding to the N-H bond existing at 3500 - 3250 cm -1 and the peak intensity corresponding to the Si-N bond existing at 1065 - 695 cm -1 are taken as the absorbances corresponding to the N-H bond and the Si-N bond respectively. By the following formula, the bonding amounts of the N-H bond and the Si-N bond per cm of the film thickness d (cm) present in the thin film are calculated as 3 (N), N = A∫α(ω) / ω·dω (Here, A is a proportionality constant. For the N-H bond, A N-H : 2.6×10 20 (cm -2 ) is used, and for the Si-N bond amount, A Si-N : 7.7×10 18 (cm -2 ) is used. α(ω) is the absorption coefficient, ω is the wave number (cm -1 ) and α(ω) = 1 / d × absorbance × ln10), and NA 2 is taken as the N-H bond amount, and NA 3 is taken as [(Si-N bond amount) - (N-H bond amount) × 2)] / 3

[0008] The silica film-forming composition according to the present invention comprises the above polysilazane and a solvent.

[0009] The method for producing a silica film according to the present invention comprises applying the above silica film-forming composition to a substrate and heating it.

[0010] The silica film according to the present invention is produced by the above method.

[0011] The electronic device according to the present invention comprises the silica film produced by the above method.

Advantages of the Invention

[0012] The polysilazane according to the present invention can form a silica-based film with suppressed film thickness change and few voids even in an ozone environment. Furthermore, the obtained silica-based film also has the characteristics of small shrinkage during curing and being less likely to crack. Therefore, by forming an electronic device using the composition containing the polysilazane, the manufacturing efficiency of the electronic device can be improved.

Brief Description of the Drawings

[0013]

Figure 1

Embodiments for Carrying Out the Invention

[0014] [Definitions] In this specification, unless otherwise particularly limited, the definitions and examples described in this paragraph shall apply. The singular form includes the plural form, and "one" and "the" mean "at least one". The elements of a certain concept can be expressed by multiple types, and when the amount (for example, mass% or mol%) is described, the amount means the sum of these multiple types. "And / or" includes all combinations of elements and also includes use alone. When indicating a numerical range using "~" or "-", these include both endpoints and the units are common. For example, 5~25 mol% means 5 mol% or more and 25 mol% or less. "C x-y ", "C x ~C y " and "C x " and the like indicate the number of carbons in a molecule or substituent. For example, C 1-6 alkyl means an alkyl chain having 1 to 6 carbons (such as methyl, ethyl, propyl, butyl, pentyl, hexyl, etc.). When the polymer has multiple types of repeating units, these repeating units copolymerize. These copolymerizations can be any of alternating copolymerization, random copolymerization, block copolymerization, graft copolymerization, or a mixture thereof. When representing a polymer or resin by a structural formula, n, m, etc. noted in parentheses indicate the number of repetitions. The unit of temperature is Celsius. For example, 20 degrees means 20 degrees Celsius.

[0015] Hereinafter, embodiments of the present invention will be described in detail.

[0016] [Polysilazane] Polysilazane contains an N-Si bond as a repeating unit. Focusing on the nitrogen atoms contained in polysilazane, they can be roughly classified into three types. That is, a nitrogen atom having three N-Si bonds (hereinafter also referred to as a trifunctional nitrogen atom), a nitrogen atom having two N-Si bonds (hereinafter also referred to as a bifunctional nitrogen atom), and a nitrogen atom having one N-Si bond (also referred to as a monofunctional nitrogen atom). [Chemical formula] (In the formula, R is hydrogen or an organic group) In polysilazane, the trifunctional nitrogen atom brings about a branched structure, the bifunctional structure brings about a linear structure, and the monofunctional nitrogen atom brings about a terminal structure. The polysilazane according to the present invention has the number of N atoms having three N-Si bonds (trifunctional nitrogen atoms) (NA 3 ) and the number of N atoms having two N-Si bonds (bifunctional nitrogen atoms) (NA 2 ) and the ratio (NA 3 / NA 2 ) is 1.8 to 6.0, preferably 2.0 to 5.5, and more preferably 3.5 to 5.0. Although not restricted by theory, the N-R bond of the difunctional nitrogen atom reacts with ozone, and the resulting OR radical forms an oxide film near the coating film surface, causing a film thickness change. In the coating film, it is considered that the OR radical generates chemical species that vaporize due to the cleavage of the polysilazane bond and expand during the heating process to form voids. On the other hand, since the trifunctional nitrogen atom without an N-R bond does not generate an OR radical by reacting with ozone, it is considered that when the ratio of the trifunctional nitrogen atom to the difunctional nitrogen atom is the above specific ratio, the effect of suppressing the generation of voids and film thickness change is brought about in an ozone environment. In addition, it is preferable that the monofunctional nitrogen atom is less in the polysilazane. Specifically, based on the total number of all nitrogen atoms contained in the polysilazane, the number of monofunctional nitrogen atoms is preferably 0.1% or less, and more preferably not contained at all (0%). In particular, when the polysilazane is perhydropolysilazane described later, usually, the monofunctional nitrogen atom does not exist in the molecule, that is, the number of monofunctional nitrogen atoms is 0%.

[0017] NA 3 / NA 2 can be measured as follows. A coating solution containing the polysilazane according to the present invention and a solvent is applied onto a substrate, and the solvent is volatilized by spin drying or the like to form a coating film. In the infrared absorption spectrum obtained by measuring the coating film with a Fourier transform infrared spectrophotometer, the peak intensity corresponding to the N-H bond present at 3500 - 3250 cm -1 and the peak intensity corresponding to the Si-N bond present at 1065 - 695 cm -1 are taken as the absorbances corresponding to the N-H bond and the Si-N bond, respectively. For each range, the bond amount / cm 3 (N) of the N-H bond and the Si-N bond present in the thin film with a film thickness d (cm) is calculated by the following formula. N = A∫α(ω) / ω·dω (where A is a proportionality constant, and for the N-H bond, A N-H : 2.6×10 20 (cm-2 ) is used with the Si-N bond content of A Si-N : 7.7×10 18 (cm -2 ), where α(ω) is the absorption coefficient, ω is the wave number (cm -1 ), and α(ω) = 1 / d × absorbance × ln10). From the above results, NA 2 is taken as the N-H bond content, and NA 3 is set as [(Si-N bond content) - (N-H bond content) × 2] / 3. The obtained NA 3 and NA 2 are used to determine NA 3 / NA 2 .

[0018] The polysilazane according to the present invention is preferably perhydropolysilazane (hereinafter also referred to as PHPS). PHPS contains Si-N bonds as repeating units and consists only of Si, N, and H. Except for the Si-N bonds, all the elements bonded to Si and N in this PHPS are H, and it substantially does not contain other elements such as carbon and oxygen.

[0019] The polysilazane according to the present invention preferably comprises at least any one of repeating units selected from the group consisting of the groups represented by formulas (Ia) to (If), and a terminal group represented by formula (Ig).

[0020]

Chemical formula

[0021] The polysilazane according to the present invention preferably consists of at least any one of the repeating units represented by the formulas (Ia) to (If) and the terminal group represented by the formula (Ig) substantially. In the present invention, "substantially" means that 95% by mass or more of all the constituent units contained in the polysilazane are the groups represented by the formulas (Ia) to (If) and the terminal group represented by the formula (Ig). More preferably, the polysilazane does not contain constituent units other than the groups represented by the formulas (Ia) to (If) and the terminal group represented by the formula (Ig), that is, it consists of at least any one of the repeating units represented by the group consisting of the groups represented by the formulas (Ia) to (If) and the terminal group represented by the formula (Ig).

[0022] When the polysilazane according to the present invention is PHPS, it shows specific characteristic values when evaluated by quantitative NMR. Specifically, the analysis is performed by comparing the integral values of the signals derived from the internal standard substance and the substance to be measured (internal standard method). For PHPS, 1 1H-NMR is measured using xylene as the internal standard substance, and the relative value of the total amount of SiH2 (corresponding to (Ia) and (Ib) in the above formula) and SiH1 (corresponding to (Ic) and (Id) in the above formula) based on the aromatic ring hydrogen of xylene in the PHPS molecule (hereinafter referred to as R(SiH 1,2 )) is preferably 0.220 or less, more preferably 0.200 or less, and even more preferably 0.190 or less. (2) The relative value of the total amount of NH (corresponding to (Ia), (Ic) and (Ie) in the above formula) based on the aromatic ring hydrogen of xylene (hereinafter referred to as R(NH)) is preferably 0.055 or less. Note that (If) in the above formula 1 cannot be detected by 1H-NMR and can be ignored.

[0023] Examples of such specific partial structures of the polysilazane are shown in the following general formula.

Chemical formula

[0024] The weight average molecular weight of the polysilazane according to the present invention is not particularly limited. However, when converting to silica, in order to reduce the low molecular weight components that scatter (evaporate) and prevent volume shrinkage caused by the scattering of the low molecular weight components, and thus prevent the low density inside the fine grooves, it is preferable that the weight average molecular weight of the polysilazane is large. From such a viewpoint, the weight average molecular weight of the polysilazane according to the present invention is preferably 4,000 or more, and more preferably 6,000 or more. On the other hand, when the polysilazane is dissolved in a solvent to form a composition, it is necessary to improve the coatability of the composition. Specifically, it is necessary to prevent the viscosity of the composition from becoming excessively high and to control the curing rate of the composition in order to ensure the permeability to the uneven portions. From such a viewpoint, the weight average molecular weight of the polysilazane according to the present invention is preferably 20,000 or less, and more preferably 18,000 or less. Here, the weight average molecular weight is the polystyrene-equivalent weight average molecular weight and can be measured by gel permeation chromatography based on polystyrene.

[0025] [Silica film-forming composition] The silica film-forming composition according to the present invention (hereinafter sometimes referred to as the composition) comprises the polysilazane according to the present invention and a solvent. As the solvent used in the present invention, there may be mentioned, but not limited to, (a) aromatic compounds such as benzene, toluene, xylene, ethylbenzene, diethylbenzene, trimethylbenzene, triethylbenzene, etc., (b) saturated hydrocarbon compounds such as cyclohexane, decahydronaphthalene, dipentene, n-pentane, i-pentane, n-hexane, i-hexane, n-heptane, i-heptane, n-octane, i-octane, n-nonane, i-nonane, n-decane, ethylcyclohexane, methylcyclohexane, cyclohexane, p-menthane, etc., (c) unsaturated hydrocarbons such as cyclohexene, etc., (d) ethers such as dipropyl ether, dibutyl ether, anisole, etc., (e) esters such as n-butyl acetate, i-butyl acetate, n-amyl acetate, i-amyl acetate, etc., (f) ketones such as methyl isobutyl ketone (MIBK), etc. Also, by using a plurality of solvents, the solubility of polysilazane and the evaporation rate of the solvent can be adjusted.

[0026] The blending amount of the solvent in the composition can be appropriately selected according to the mass average molecular weight, its distribution and structure of the polysilazane used, considering workability depending on the coating method employed, and also considering the permeability of the solution into fine grooves and the film thickness required outside the grooves. The composition according to the present invention preferably contains 0.10 to 70% by mass, more preferably 1.0 to 30% by mass of polysilazane based on the total mass of the composition.

[0027] [Method for forming a silica-based film] The method for forming a silica-based film according to the present invention comprises applying the composition according to the present invention to a substrate and heating it. In the present invention, "to the substrate" shall include the case where the composition is directly applied to the substrate and the case where the composition is applied to the substrate via one or more intermediate layers. The shape of the substrate is not particularly limited and can be arbitrarily selected according to the purpose. However, since the composition according to the present invention has the characteristic that it can easily penetrate into narrow groove portions and the like and can form a uniform silica film even inside the grooves, it is preferably applied to a substrate having groove portions or holes with a high aspect ratio. Specifically, it is preferably applied to a substrate having at least one groove with a width of 0.02 μm or less at the deepest part and an aspect ratio of 20 or more. Here, the shape of the groove is not particularly limited, and the cross section may be any shape such as a rectangular shape, a forward taper shape, a reverse taper shape, or a curved surface shape. Also, both end portions of the groove may be open or closed.

[0028] In the conventional method, even when attempting to seal a groove with a width of 0.02 μm or less at the deepest part and an aspect ratio of 20 or more with a silica material, due to the large volume shrinkage during the conversion to silica, the inside of the groove becomes less dense than the outside of the groove, and it was difficult to seal the groove so that the material is homogeneous inside and outside the groove. In contrast, according to the present invention, a uniform silica film can be obtained inside and outside the groove. Such an effect of the present invention becomes even more remarkable when using a substrate having very fine grooves with a width of 0.01 μm or less at the deepest part.

[0029] As a representative example of a substrate having at least one groove with a high aspect ratio, a substrate for an electronic device including a transistor element, a bit line, a capacitor, etc. can be mentioned. For the production of such an electronic device, a through-hole forming step of forming a hole that penetrates the upper and lower sealing materials for the fine grooves may be included following steps such as forming an insulating film between a transistor element and a bit line called PMD, between a transistor element and a capacitor, between a bit line and a capacitor, or between a capacitor and a metal wiring, or forming an insulating film between a plurality of metal wirings called IMD, or sealing an isolation groove.

[0030] The present invention is suitable for any other application that requires embedding a high aspect ratio substrate with a homogeneous silica-based material both inside and outside the grooves. Such applications include, for example, an undercoat for liquid crystal glass (a passivation film such as Na), an overcoat for a liquid crystal color filter (an insulating planarization film), a gas barrier for a film liquid crystal, a hard coating for a substrate (metal, glass), a heat-resistant and oxidation-resistant coating, an antifouling coating, a water-repellent coating, a hydrophilic coating, an ultraviolet cut coating for glass and plastic, and a coloring coating.

[0031] There is no particular limitation on the method of applying the composition for curing to such a substrate, and ordinary coating methods such as spin coating, dipping, spraying, transfer printing, slit coating, etc. can be mentioned.

[0032] After applying the composition for curing, for the purpose of drying or pre-curing the coating film, a drying process is carried out under treatment conditions of a temperature of 50 to 400 °C for 10 seconds to 30 minutes in the air, an inert gas, or an oxygen gas. By drying, the solvent is removed, and the fine grooves are substantially embedded with polysilazane.

[0033] According to the present invention, the polysilazane contained inside and outside the grooves is converted into a silica-based material by heating. It is preferable to heat in a water vapor atmosphere when heating.

[0034] The water vapor atmosphere means an atmosphere in which the water vapor partial pressure is in the range of 0.50 to 101 kPa, preferably having a water vapor partial pressure in the range of 1.0 to 90 kPa, more preferably 1.5 to 80 kPa. The heating can be carried out in a temperature range of 300 to 1200 °C.

[0035] In addition, when heating at a high temperature, for example, a temperature exceeding 600°C, in an atmosphere containing water vapor, there may be concerns about adverse effects on other elements such as electronic devices that are simultaneously subjected to the heat treatment. In such a case, the silica material conversion process can be divided into two or more stages. First, heat in an atmosphere containing water vapor at a relatively low temperature, for example, in the temperature range of 300 to 600°C, and then heat in an atmosphere without water vapor at a higher temperature, for example, in the temperature range of 500 to 1200°C.

[0036] As a component other than water vapor (hereinafter referred to as a dilution gas) in an atmosphere containing water vapor, any gas can be used. Specific examples include air, oxygen, nitrogen, helium, argon, etc. It is preferable to use oxygen in terms of the film quality of the resulting silica material. However, the dilution gas is appropriately selected in consideration of the influence on other elements such as electronic devices that are subjected to the heat treatment. In addition, as an atmosphere without water vapor in the above two-stage heating method, in addition to an atmosphere containing any of the above dilution gases, a reduced pressure of less than 1.0 kPa or a vacuum atmosphere can also be adopted.

[0037] Examples of suitable heating conditions set in consideration of these circumstances are given below. (1) After applying the composition according to the present invention to a predetermined substrate and drying, heat in an atmosphere where the temperature is in the range of 300 to 600°C and the water vapor partial pressure is in the range of 0.50 to 101 kPa, and then heat in an atmosphere where the temperature is in the range of 400 to 1200°C and the oxygen partial pressure is in the range of 0.50 to 101 kPa; (2) After applying the composition according to the present invention to a predetermined substrate and drying, heat in an atmosphere where the temperature is in the range of 300 to 600°C and the water vapor partial pressure is in the range of 0.50 to 101 kPa, and then heat in an atmosphere of one or more inert gas selected from nitrogen, helium, and argon where the temperature is in the range of 400 to 1200°C, and (3) Apply the composition according to the present invention to a predetermined substrate. After drying, heat it in an atmosphere where the temperature ranges from 300 to 600 °C and the water vapor partial pressure ranges from 0.50 to 101 kPa, and then continue to heat it in a reduced pressure or vacuum atmosphere of less than 1.0 kPa where the temperature ranges from 400 to 1200 °C.

[0038] There are no particular restrictions on the heating rate and cooling rate to the target temperature during heating, but generally, it can be in the range of 1 °C to 100 °C / min. Also, there are no particular restrictions on the heating holding time after reaching the target temperature, and generally, it can be in the range of 1 minute to 10 hours.

[0039] Through the above heating process, polysilazane is converted into a silica-based material mainly composed of Si-O bonds through a hydrolysis reaction with water vapor. When a silica film is formed on the surface of a substrate having grooves with a high aspect ratio using the composition according to the present invention, it becomes uniform both inside and outside the grooves. Also, according to the method of the present invention, since there is no conformality like the CVD method, it can be uniformly embedded inside the fine grooves. Furthermore, in the conventional method, the densification of the silica film was insufficient, but according to the method of the present invention, the densification of the film after the conversion of the silica material is promoted, and cracks are less likely to occur.

[0040] As described above, since the silica film according to the present invention is obtained by the hydrolysis reaction of polysilazane, it mainly consists of Si-O bonds, but also contains some Si-N bonds depending on the degree of conversion. That is, the fact that the silica material contains Si-N bonds indicates that the material is derived from polysilazane. Specifically, the silica film according to the present invention contains nitrogen in the range of 0.005 to 5% by atomic percentage. In fact, it is difficult to make this nitrogen content less than 0.005%. The atomic percentage of nitrogen can be measured by secondary ion mass spectrometry.

[0041] In conventional sol-gel methods, siloxane-based polymer solution coating methods, or methods using polysilazane containing organic groups, a large volume shrinkage occurs during the conversion to a silica-based material. Therefore, when grooves with a high aspect ratio are encapsulated with a silica-based material by these methods, the silica-based material inside the grooves tends to be inhomogeneous in terms of density, and the film density decreases. The silica-based film according to the present invention has almost no volume shrinkage during the conversion to a silica-based material, the silica-based material becomes more homogeneous inside and outside the grooves, and by stabilizing the oxidation reactivity, the film density of the film formed by the conversion of the silica-based material can be improved. Also, between a plurality of grooves with different groove widths, when volume shrinkage occurs during the conversion to a silica-based material, the finer the grooves, the greater the influence of the restraint by the groove wall surface, and the density of the silica-based material tends to be lower. Since the silica-based film according to the present invention has almost no volume shrinkage during the conversion to a silica-based material, the density is uniform even if the groove widths are different.

[0042] In the method for forming a silica-based film according to the present invention, there is no particular limitation on the thickness of the silica-based film formed on the substrate surface and the thickness of the coating film formed on the surface outside the grooves. Generally, it can be set to any thickness within a range where no cracks occur in the film during the conversion to a silica-based material. As described above, according to the method of the present invention, even when the film thickness is 0.5 μm or more, cracks are less likely to occur in the film. Therefore, for example, a contact hole with a width of 1000 nm and a groove with a depth of 2.0 μm can be substantially defectlessly encapsulated.

[0043] Further, the method for manufacturing an electronic device according to the present invention includes the above manufacturing method.

Examples

[0044] The present invention will be described by way of examples as follows. Note that the aspects of the present invention are not limited to only these examples.

[0045] [Synthesis of Intermediate (A)] After replacing the inside of a 10 L reaction vessel equipped with a cooling condenser, a mechanical stirrer, and a temperature control device with dry nitrogen, 7,500 ml of dry pyridine is charged into the reaction vessel and cooled to -3°C. Then, 500 g of dichlorosilane is added, and a white solid adduct (SiH2Cl2·2C5H5N) is formed. After confirming that the reaction mixture has reached -3°C or lower, 350 g of ammonia is slowly blown into it while stirring. Subsequently, after continuously stirring for 30 minutes, dry nitrogen is blown into the liquid layer for 30 minutes to remove excess ammonia. The resulting slurry-like product is subjected to pressure filtration using a 0.2 μm Teflon (registered trademark) filter in a dry nitrogen atmosphere to obtain 6,000 ml of filtrate. Pyridine is distilled off using an evaporator, xylene is added, and a xylene solution of polysilazane with a concentration of 39.8% by mass is obtained. The mass average molecular weight (hereinafter referred to as Mw) of the obtained polysilazane is measured by gel permeation chromatography and is 1280 in terms of polystyrene conversion. The polysilazane obtained according to this formulation is hereinafter referred to as intermediate (A).

[0046] GPC is measured using an allianceTM e2695 type high-speed GPC system (manufactured by Waters Japan K.K.) and a Super Multipore HZ-N type GPC column (manufactured by Tosoh Corporation). The measurement is carried out under the measurement conditions of a flow rate of 0.6 milliliters per minute and a column temperature of 40°C, using monodisperse polystyrene as a standard sample and chloroform as a developing solvent, and then the mass average molecular weight is calculated as the relative molecular weight to the standard sample. The same measurement method is applied to the following Mw.

[0047] [Synthesis Example 1: Synthesis of Polysilazane 1] After replacing the inside of a 10 L reaction vessel equipped with a cooling condenser, a mechanical stirrer, and a temperature control device with dry nitrogen, 4710 g of dry pyridine, 150 g of dry xylene, and 1650 g of the intermediate (A) with a concentration of 39.8 mass% obtained above are charged, and while bubbling with nitrogen gas at 0.5 NL / min, stirring is carried out to make it uniform. Subsequently, a reforming reaction is carried out at 100 °C for 12.6 hours to obtain polysilazane 1. Mw is 4,600. The relative value (R(SiH 1,2 )) of the total amount with SiH2 and SiH1 based on the aromatic ring hydrogen of xylene is 0.195, and the relative value (R(NH)) of the amount of NH based on the aromatic ring hydrogen of xylene is 0.048. NA 3 / NA 2 is 2.52.

[0048] In the examples, NA 3 / NA 2 is calculated as follows. The coating solution is prepared by adjusting the concentration so that the film thickness after coating polysilazane 1 with xylene becomes 250 nm. Using a spin coater 1HDX2 (manufactured by Mikasa Co., Ltd.), the coating solution is coated on a 4-inch high-resistance n-type Si wafer, spin-dried, and a 250-nm coating film is produced. The film thickness is measured with an M-44 type spectroscopic ellipsometer (manufactured by JA Woollam Co., Ltd.). Using a Fourier transform infrared spectrophotometer FTIR-6600FV (manufactured by JASCO Corporation), measurement is carried out by the transmission method, integration times: 100 times, measurement temperature: room temperature, measurement atmosphere: vacuum to obtain an infrared absorption spectrum. In the obtained infrared absorption spectrum, a baseline is drawn at 3500 - 3250 cm -1 to calculate the absorbance of the N-H bond, and a baseline is drawn at 1065 - 695 cm -1 to measure the absorbance of the Si-N bond. According to the following formula, the bonding amount / cm 3 (N) of the N-H bond and the Si-N bond present in the thin film with a film thickness d (cm) is calculated over each of the above ranges, N = A∫α(ω) / ω·dω (where, A is a proportionality constant, and for the N-H bond, A N-H: 2.6×10 20 (cm -2 ) is used for the Si-N bond amount of A Si-N : 7.7×10 18 (cm -2 ). And α(ω) is the absorption coefficient, ω is the wave number (cm -1 ), and α(ω) = 1 / d × absorbance × ln10), and NA 2 is defined as the N-H bond amount, and NA 3 is set as [(Si-N bond amount) - (N-H bond amount) × 2] / 3. The obtained NA 3 and NA 2 are used to determine NA 3 / NA 2 .

[0049] [Synthesis Example 2: Synthesis of Polysilazane 2] For Synthesis Example 1, the conditions of the modification reaction are changed to 110 °C for 9.1 hours for synthesis to obtain polysilazane 2. Mw 5,800, R(SiH 1,2 ) is 0.195, R(NH) is 0.045, NA 3 / NA 2 is 3.37.

[0050] [Synthesis Example 3: Synthesis of Polysilazane 3] For Synthesis Example 1, the conditions of the modification reaction are changed to 110 °C for 10.0 hours for synthesis to obtain polysilazane 3. Mw 8,300, R(SiH 1,2 ) is 0.185, R(NH) is 0.043, NA 3 / NA 2 is 3.95.

[0051] [Synthesis Example 4: Synthesis of Polysilazane 4] For Synthesis Example 1, the conditions of the modification reaction are changed to 120 °C for 8.2 hours for synthesis to obtain polysilazane 4. Mw 12,400, R(SiH 1,2 ) is 0.180, R(NH) is 0.040, NA 3 / NA 2 is 4.34.

[0052] [Comparative Synthesis Example 1: Synthesis of Polysilazane 5] For Synthesis Example 1, the conditions of the modification reaction were changed to 100 °C for 11.2 hours for synthesis to obtain polysilazane 5. Mw 2,200, R(SiH 1,2 ) is 0.242, R(NH) is 0.058, NA 3 / NA 2 is 1.48.

[0053] [Film Thickness Change in Ozone Environment] The polysilazane obtained in the synthesis example was adjusted in concentration using xylene so that the coating film would be 580 nm, and a coating solution was prepared. The obtained coating solution was spin-coated on a 4-inch wafer at a rotational speed of 1000 rpm using a spin coater 1HDX2 (manufactured by Mikasa Co., Ltd.). The obtained coating film was heat-treated at 150 °C for 3 minutes under an ozone concentration of 10 ppb generated by a uvistare ozone deodorizer. The ozone concentration was measured with an EG-3000F (manufactured by Ebara Jitsugyo Co., Ltd.). The film thickness before and after the heat treatment was measured with an M-44 type spectroscopic ellipsometer (manufactured by JA Woollam Co., Ltd.) and used as the film thickness change in the ozone environment.

[0054] [Number of Voids] A coating solution was applied to an 8-inch wafer having trenches with a width of 20 nm and a depth of 500 nm at 1000 rpm using a spin coater Mark8 (manufactured by Tokyo Electron Limited). The obtained coating film was baked at 150 °C for 3 minutes under an ozone concentration of 10 ppb and then fired in a firing furnace VF1000LP (manufactured by Koyo Thermo System Co., Ltd.) in a steam atmosphere at 400 °C for 30 minutes, followed by firing in a nitrogen atmosphere at 600 °C. After the fired wafer sample was cut perpendicular to the trench direction at the trench pattern portion, it was immersed in an aqueous solution containing 5 mass% ammonium fluoride and 0.5 mass% hydrofluoric acid for 30 seconds, washed with pure water and dried, and then observed with a scanning electron microscope S-4700 (manufactured by Hitachi High-Technologies Corporation). 300 trenches were observed, and the number of trenches in which voids were confirmed was taken as the number of voids.

[0055] The obtained results are as shown in Table 1. For Synthesis Example 2, the results regarding the film thickness change and the number of voids in an environment where the ozone concentration is 0 ppb are also shown.

Table 1

Claims

1. A polysilazane containing an N—Si bond, wherein the number of N atoms having three N—Si bonds (NA ３ ), and the number of N atoms having two N—Si bonds (NA ２ ), and the ratio thereof (NA ３ / NA ２ ) is 1.8 to 6.0, the polysilazane. where The peaks corresponding to the N-H bonds present at 3500 - 3250 cm －１ in the infrared absorption spectrum of the polysilazane, and the peaks corresponding to the Si-N bonds present at 1065 - 695 cm －１ are taken as the absorbances corresponding to the N-H bonds and the Si-N bonds, respectively, The bond amount / cm of N-H bonds and Si-N bonds present in a thin film with a film thickness d (cm) is calculated by the following formula: ３ (N), N = A∫α(ω) / ω・dω where A is a proportionality constant. For the N-H bond, A Ｎ－Ｈ : 2.6×10 ２０ (cm －２ ) is used. For the Si-N bond, A Ｓｉ－Ｎ : 7.7×10 １８ (cm －２ ) is used. α(ω) is the absorption coefficient, ω is the wave number (cm －１ ), and α(ω) = 1 / d × absorbance × ln10), and NA ２ is taken as the N-H bond amount, and NA ３ is taken as [(Si-N bond amount)-(N-H bond amount)×2)] / 3

2. The polysilazane according to Claim 1, wherein the polysilazane is perhydropolysilazane.

3. The polysilazane according to Claim 1 or 2, comprising at least any one of repeating units selected from the group consisting of groups represented by formulas (Ia) to (If), and a terminal group represented by formula (Ig). 【Chemical 1】

4. NA ３ / NA ２ The polysilazane according to any one of claims 1 to 3, wherein the [specific content related to 'NA / NA'] is 2.0 to 5.

5.

5. The polysilazane according to any one of Claims 1 to 4, wherein the mass average molecular weight in terms of polystyrene measured by gel permeation chromatography is 4,000 to 20,000.

6. A silica film-forming composition comprising the polysilazane according to any one of Claims 1 to 5 and a solvent.

7. A method for producing a silica film, comprising applying the silica film-forming composition according to Claim 6 to a substrate and heating.

8. The method for producing a silica film according to Claim 7, wherein the heating is performed in a steam atmosphere.

9. A method for producing an electronic device, comprising the method for producing a silica film according to Claim 7 or 8.

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