JP5172867B2 - Coating composition comprising polysilazane - Google Patents

Description

  The present invention relates to a coating composition for forming a siliceous film in a semiconductor manufacturing process. More specifically, the present invention relates to a coating composition containing polysilazane for forming a siliceous film used as an insulating film in a semiconductor manufacturing process.

  In recent years, higher integration density has been demanded for semiconductor devices, and manufacturing technology has been improved to meet this demand. In the process of forming an insulating film, which is one of the manufacturing processes of such a semiconductor device, it is necessary to bury a narrow gap.

  It is known to use coating compositions containing perhydropolysilazane to fill such narrow gaps. Perhydropolysilazane is a polymer whose basic skeleton is composed of Si—N, Si—H, and N—H bonds. By baking in an atmosphere containing oxygen and / or water vapor, Si—N bonds become Si—O bonds. Thus, a siliceous film having a high purity can be obtained.

  However, the gap is becoming narrower as the integration density required for semiconductors becomes higher. Conventionally known coating compositions containing perhydropolysilazane are generally said to have excellent embedding properties, but improvements are required to achieve the high integration density required recently. ing. Specifically, with conventional coating compositions, it has become difficult to achieve both embedding and coating properties.

  One of the causes of such problems is known to be the molecular weight distribution of perhydropolysilazane. For example, Patent Document 1 discloses a spin-on glass composition using perhydropolysilane having a weight average molecular weight of 4000 to 8000 and a ratio of the weight average molecular weight to the number average molecular weight of 3.0 to 4.0. ing. Patent Document 2 discloses a spin-on glass containing polysilazane having a weight average molecular weight of 3000 to 6000. Further, Patent Document 3 discloses a coating solution for forming a silica-based film in which the amount of polysilazane having a polystyrene-equivalent molecular weight of 700 or less is 10% or less of the total amount of polysilazane. These are all intended to improve the coatability and the like by controlling the molecular weight distribution of polysilazane.

  According to the study by the present inventors, when perhydropolysilazane having a small weight average molecular weight is used, embedding tends to be improved. When polysilazane is used, the occurrence of striation is suppressed and the coating property is improved, but the embedding property tends to deteriorate. As a result, there is a problem in that the depth of the gap is not sufficiently embedded, and when the siliceous film is formed by baking after coating, the etching rate of the gap deep due to hydrofluoric acid tends to increase. . For such problems, it is not sufficient to control the molecular weight distribution as described in Patent Documents 1 to 3, and further improvement has been desired.

JP 2001-319927 A Japanese Patent Application Laid-Open No. 2005-150702 JP-A-8-269399 Japanese Patent No. 1474685 Japanese Patent No. 2613787

  As described above, in the conventional coating composition, when trying to form a siliceous film on a substrate having a narrow gap as required recently, embedding property and applicability cannot be sufficiently achieved. It was. In view of such problems, an object of the present invention is to provide a siliceous film for a semiconductor device in which a narrow gap, in other words, a gap having a large aspect ratio can be sufficiently embedded, and no striation occurs during coating. Is to provide a coating composition.

  The coating composition according to the present invention is a coating composition comprising perhydropolysilazane and a solvent, wherein the molecular weight distribution curve of the perhydropolysilazane has a molecular weight in the range of 800-2,500 and a molecular weight of 3,000- Each has a maximum in the range of 8,000, and the ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn is 6-12.

The method for forming a siliceous film according to the present invention includes:
A coating composition comprising perhydropolysilazane and a solvent on the surface of an uneven substrate, wherein the molecular weight distribution curve of the perhydropolysilazane has a molecular weight in the range of 800 to 2,500 and a molecular weight of 3,000. A coating step of applying a coating composition having a maximum in the range of ˜8,000 and a ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of 6 to 12, and a coated substrate at 1000 ° C. It is characterized by comprising a curing step in which the composition is converted into a silicon dioxide film by heat treatment in an oxygen atmosphere or an oxidizing atmosphere containing water vapor.

  According to the coating composition of the present invention, the coating property and embedding property of the coating composition containing a polysilazane compound can be made compatible, and the physical properties of the resulting siliceous film can be improved.

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

Coating Composition The coating composition according to the present invention comprises perhydropolysilazane and a solvent capable of dissolving the perhydropolysilazane.

The perhydropolysilazane used in the present invention is required to have a specific molecular weight and molecular weight distribution as will be described later. However, the structure is not particularly limited, and may have any structure as long as the effects of the present invention are not impaired. Can be selected. Perhydropolysilazane, which is an inorganic compound, consists only of silicon, nitrogen, and hydrogen, and has a feature that impurities are hardly mixed when a siliceous film is formed by firing. The specific structure of such perhydropolysilazane can be represented by the following general formula (I).
_{- (SiH 2 -NH) n -} (I)
In the formula, n is a number representing the degree of polymerization.

  It should be noted that part or all of the hydrogen in the formula (I) is substituted with an alkyl group, alkenyl group, cycloalkyl group, aryl group, alkylsilyl group, alkylamino group, alkoxy group or the like within a range not impairing the effects of the present invention. A small amount of polysilazane compound can also be included.

  The polysilazane composition according to the present invention comprises the above-described perhydropolysilazane. The molecular weight distribution curve of the perhydropolysilazane has a molecular weight of 800 to 2,500 and a molecular weight of 3,000 to 8,000. It has a maximum in the region. In this case, there is one or more, preferably one minimum, between the two maximums.

  A perhydropolysilazane having such a molecular weight distribution curve can be prepared by any method, but most simply, a perhydropolysilazane having a relatively high molecular weight and a perhydropolysilazane having a relatively low molecular weight Can be obtained by mixing. More specifically, a perhydropolysilazane having a weight average molecular weight of 800 to 2,500, particularly 1,000 to 2,200 (hereinafter referred to as low molecular weight polysilazane for simplicity), and a weight average molecular weight of 3, It is preferably obtained by mixing with perhydropolysilazane (hereinafter referred to as high molecular weight polysilazane for simplicity) of 000 to 8,000, particularly 3,500 to 7,000. The method for synthesizing perhydropolysilazane before mixing is not particularly limited, but can be synthesized by the method described in Patent Document 4 or 5, for example.

  Since not only perhydropolysilazane but a polymer compound has a wide molecular weight distribution, when two kinds of polymer compounds having different molecular weights are mixed, the maximum position of the molecular weight distribution may change before and after mixing. This is particularly likely to occur when the molecular weights that are maximal are close in the molecular weight distribution of two types of polymer compounds, and the molecular weight having the maximum value tends to approach by mixing. In some cases, the maximum value may be one. However, when two types of perhydropolysilazane having a weight average molecular weight as described above are mixed, the difference in molecular weight is large, so that the maximum value is generally not one. In the present invention, since it is considered that the effect of the present invention is manifested by reducing the number of components having a molecular weight between two maximum values, two types have a minimum between at least two maximum values. Of perhydropolysilazane must be mixed.

  In the present invention, when two kinds of perhydropolysilazane are mixed in order to achieve the target molecular weight distribution, it is preferable that the molecular weight distribution of each perhydropolysilazane is narrow. This is because if one or both of the perhydropolysilazanes mixed has a wide molecular weight distribution, it is difficult for the minimum to appear between the two maximums of the distribution curve, and the effect of the present invention tends to be small. Because. Specifically, the ratio Mw / Mn of the weight average molecular weight Mw and the number average molecular weight Mn is preferably 1.1 to 1.8 for each of the two types of perhydropolysilazane before mixing.

  In order to narrow the molecular weight distribution of perhydropolysilazane, it is convenient to remove the high molecular weight component and / or the low molecular weight component contained in perhydropolysilazane. As a simple method for removing the high molecular weight component and / or the low molecular weight component in this manner, a method utilizing the molecular weight dependency of solubility can be mentioned. That is, perhydropolysilazane generally tends to have lower solubility as the molecular weight increases, and higher solubility as the molecular weight decreases. By using such a difference in solubility, the perhydropolysilazane is dissolved in a solvent having a solubility sufficient to dissolve a part of the perhydropolysilazane, and the insoluble component is separated by filtration, so that it is filtered as an insoluble component. The high molecular weight component can be separated from the low molecular weight component dissolved in the solvent. That is, removing the insoluble component separated by filtration removes the high molecular weight component, and removing the dissolved component removes the low molecular weight component.

  Here, since the solubility of perhydropolysilazane varies depending on the solvent used, after removing the high molecular weight component with one solvent, the low molecular weight is removed with another solvent with different solubility, and the width of the molecular weight distribution is further increased. Can be narrowed. In many cases, such a method cannot completely remove the high molecular weight component or the low molecular weight component, but it is convenient for narrowing the molecular weight distribution of the high molecular weight compound that is a mixture of compounds having different molecular weights, that is, different degrees of polymerization. And it is an effective method. As a solvent used for such an application, for example, a hydrocarbon is suitable. For example, alkanes tend to dissolve perhydropolysilazane having a higher molecular weight as the number of carbon atoms increases. In general, hydrocarbons having about 5 to 10 carbon atoms can be used.

  Further, in order to narrow the molecular weight distribution of the polymer compound, it can be classified according to the molecular weight of perhydropolysilazane by commonly used chromatography or the like. However, when chromatography is used, the treatment time may be long, and from the viewpoint of production efficiency, a method using the above-described difference in solubility in a solvent is preferable.

  In addition, it is also effective to synthesize perhydropolysilazane having a narrow molecular weight distribution by adjusting the synthesis method and synthesis raw materials, instead of performing a treatment for narrowing the molecular weight distribution of perhydropolysilazane.

  When the high molecular weight component or low molecular weight component contained in each perhydropolysilazane is to be removed before mixing the two types of perhydropolysilazane, the high molecular weight component of the low molecular weight perhydropolysilazane is added to the high molecular weight component. It is preferred to remove the low molecular weight component of the molecular weight perhydropolysilazane. Thus, by reducing the components corresponding to the two intermediate regions of the molecular weight distribution curve, the effect of the present invention is more strongly expressed.

  When perhydropolysilazane having different molecular weights is prepared and mixed by the above method, the mixing ratio is such that the weight ratio of low molecular weight polysilazane to high molecular weight polysilazane is 3: 7 to 6: 4. It is preferable that the ratio is 4: 6 to 6: 4. This is because if the mixing ratio is outside this range, the balance between applicability and embedding property may be deteriorated.

  The perhydropolysilazane having a molecular weight distribution specified in the present invention can be easily obtained by mixing two types of perhydropolysilazanes having different molecular weights as described above, but can be obtained by other methods. May be. For example, a desired molecular weight distribution can be achieved by preparing perhydropolysilazane having a relatively broad molecular weight distribution, and then removing intermediate region components having a molecular weight of about 2,500 to 3,000 by chromatography.

  Further, the perhydropolysilazane used in the present invention needs to have a ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of 6 to 12, and preferably 7 to 10. Such a ratio Mw / Mn is a weight ratio of 3: 7 to 6: 4 of low molecular weight perhydropolysilazane and high molecular weight perhydropolysilazane when mixing two kinds of perhydropolysilazane as described above. This can be achieved when mixing at a ratio.

The coating composition according to the present invention comprises a solvent capable of dissolving the perhydropolysilazane. Such a solvent is not particularly limited as long as it can dissolve each of the above-mentioned components. Specific examples of preferable solvents include the following:
(A) Aromatic compounds such as benzene, toluene, xylene, ethylbenzene, diethylbenzene, trimethylbenzene, triethylbenzene, etc. (b) Saturated hydrocarbon compounds such as n-pentane, i-pentane, n-hexane, i-hexane , N-heptane, i-heptane, n-octane, i-octane, n-nonane, i-nonane, n-decane, i-decane, etc. (c) alicyclic hydrocarbon compounds such as ethylcyclohexane, methylcyclohexane , Cyclohexane, cyclohexene, p-menthane, decahydronaphthalene, dipentene, limonene and the like, (d) ethers such as dipropyl ether, dibutyl ether, diethyl ether, methyl tertiary butyl ether, anisole and the like, and (e) ketones, For example methyl isobut Ruketo down, and the like. Of these, (b) saturated hydrocarbon compounds, (c) alicyclic hydrocarbon compounds (d) ethers, and (e) ketones are more preferred.

  These solvents may be used by appropriately mixing two or more of them in order to adjust the evaporation rate of the solvent, to reduce the harmfulness to the human body, or to adjust the solubility of each component.

  The coating composition used for this invention can also contain another additive component as needed. Examples of such components include viscosity modifiers and crosslinking accelerators. In addition, a phosphorus compound such as tris (trimethylsilyl) phosphate may be contained for the purpose of obtaining a sodium gettering effect when used in a semiconductor device.

  Moreover, although content of each said component changes with uses of the target composition, it is preferable that the content rate of perhydropolysilazane is 10 to 25 weight%, and it shall be 12 to 22 weight%. More preferred. In general, when the content of perhydropolysilazane is excessively high, the viscosity of the coating composition tends to be high and the embedding property and coating property tend to be deteriorated. There is a tendency to run out.

Production method of siliceous film According to the production method of siliceous film according to the present invention, a gap surface such as a groove or a hole is sufficiently buried to the deep part of the gap, the film surface is flat, and the film quality is uniform. Can be formed. Therefore, it can be formed as a planarizing insulating film (pre-metal insulating film) for a transistor part or a capacitor part of an electronic device, or by forming a siliceous film on a grooved substrate and embedding the groove, The structure can also be formed. Hereinafter, the present invention will be described based on a method of forming a trench isolation structure.

(A) Coating process The coating composition according to the present invention is suitable for forming a trench isolation structure on a substrate. In the case of forming a trench isolation structure, a substrate such as silicon having a desired groove pattern is prepared. Although any method can be used for forming the groove, for example, the groove can be formed by the following method.

  First, a silicon dioxide film is formed on the surface of a silicon substrate by, for example, a thermal oxidation method. The thickness of the silicon dioxide film formed here is generally 5 to 30 nm.

  If necessary, a silicon nitride film is formed on the formed silicon dioxide film by, for example, a low pressure CVD method. This silicon nitride film can function as a mask in a later etching process or a stop layer in a polishing process described later. The silicon nitride film is generally formed with a thickness of 100 to 400 nm when formed.

  A photoresist is applied on the silicon dioxide film or silicon nitride film thus formed. The photoresist film is dried or cured as necessary, and then exposed and developed with a desired pattern to form a pattern. The exposure method can be performed by any method such as mask exposure or scanning exposure. Also, any photoresist can be selected and used from the viewpoint of resolution and the like.

  Using the formed photoresist film as a mask, the silicon nitride film and the underlying silicon dioxide film are sequentially etched. By this operation, a desired pattern is formed on the silicon nitride film and the silicon dioxide film.

  Using the silicon nitride film and silicon dioxide film on which the pattern is formed as a mask, the silicon substrate is dry etched to form trench isolation grooves.

  The width of the trench isolation groove to be formed is determined by the pattern for exposing the photoresist film. The trench isolation groove in the semiconductor element varies depending on the target semiconductor element, but the width is generally 0.02 to 10 μm, preferably 0.05 to 5 μm, and the depth is 200 to 1000 nm, preferably 300 to 700 nm. The method according to the present invention makes it possible to uniformly embed a narrower and deeper portion than a conventional trench isolation structure formation method, so that a narrower and deeper trench isolation structure is formed. It is suitable for forming. In particular, in the conventional siliceous film forming composition and the siliceous film forming method, it is difficult to form a uniform siliceous film up to the deep part of the groove. The groove width is generally 0.5 μm or less, particularly 0. In the case of forming a trench isolation structure having an aspect ratio of 5 or more, a siliceous film in the groove can be formed uniformly by using the composition for forming a siliceous film according to the present invention.

  Subsequently, the coating film of the said coating composition used as the material of a siliceous film | membrane is formed on the silicon substrate prepared in this way.

  The coating composition can be applied onto the substrate by any method. Specific examples include spin coating, curtain coating, dip coating, and others. Of these, spin coating is particularly preferable from the viewpoint of uniformity of the coating surface.

  In order to achieve both trench groove embedding and coating properties after application of the siliceous film-forming composition, the thickness of the applied coating is generally 10 to 1,000 nm, preferably 50 to 800 nm.

  The application conditions vary depending on the concentration of the composition, the solvent, the application method, and the like, and are as follows by taking spin coating as an example.

  Recently, in order to improve the manufacturing yield, devices are often formed on a large substrate, but in order to uniformly form a coating film of a siliceous film forming composition on a silicon substrate of 8 inches or more, Spin coating that combines multiple stages is effective.

  First, in general, 0.5 to 20 cc of a composition per silicon substrate is dropped at several locations including the central portion such that a coating film is formed on the entire surface of the silicon substrate or on the entire surface of the substrate.

  Next, in order to spread the dropped composition over the entire surface of the silicon substrate, the composition is rotated at a relatively low speed for a short time, for example, at a rotational speed of 50 to 500 rpm for 0.5 to 10 seconds (press pin).

  Next, in order to make the coating film have a desired thickness, the coating film is rotated at a relatively high speed, for example, at a rotational speed of 500 to 4500 rpm for 0.5 to 800 seconds (main spin).

  Furthermore, in order to reduce the swelling of the coating film around the silicon substrate and to dry the solvent in the coating film as much as possible, the rotational speed is higher than the main spin rotational speed by 500 rpm or more, for example, the rotational speed. Rotate at 1000-5000 rpm for 5-300 seconds (final spin).

  These application conditions are appropriately adjusted according to the size of the substrate to be used, the performance of the target semiconductor element, and the like.

(B) Curing process After apply | coating a coating composition, it can attach | subject to a prebaking process as needed.
In the pre-baking step, the purpose is to completely remove the solvent contained in the coating film and to pre-cure the coating film. In particular, in the method for forming a siliceous film of the present invention using a composition containing polysilazane, the pre-baking treatment improves the denseness of the formed siliceous film.

  Usually, in the prebaking process, a method of heating at a substantially constant temperature is employed. In addition, to prevent the coating film from shrinking during curing and the gap to become dents or voids to form inside the gap, the temperature in the prebaking process is controlled and prebaked while increasing over time. Is preferred. The temperature in a prebaking process is in the range of 50 to 400 degreeC normally, Preferably it is 100 to 300 degreeC. The time required for the prebaking step is generally 10 seconds to 30 minutes, preferably 30 seconds to 10 minutes.

  In order to increase the temperature in the pre-bake process over time, a method of increasing the temperature of the atmosphere in which the substrate is placed in a stepwise manner or a method of increasing the temperature in a monotonically increasing manner can be mentioned. Here, the maximum prebaking temperature in the prebaking step is generally set to a temperature higher than the boiling point of the solvent used in the composition for forming a siliceous film from the viewpoint of removing the solvent from the coating.

When the prebaking process is combined in the method according to the present invention, the substrate heated to a high temperature by prebaking is preferably subjected to a curing process at a temperature of 50 ° C. or higher and lower than the maximum temperature during prebaking before the temperature decreases. It is preferable to attach. By subjecting the substrate before the temperature to the curing step, energy and time for raising the temperature again can be saved.
Next, in order to convert the coating film containing polysilazane into a siliceous film and cure it, the entire substrate is subjected to a curing step. Usually, the entire substrate is generally put into a curing furnace and heated.

  Curing is preferably performed in an inert gas or oxygen atmosphere containing water vapor using a curing furnace or a hot plate. The water vapor is important for sufficiently converting the polysilazane into a siliceous film (ie, silicon dioxide), preferably 30% or more, more preferably 50% or more, and most preferably 70% or more. In particular, a water vapor concentration of 80% or more is preferable because conversion of an organic compound to a siliceous film is likely to proceed, defects such as voids are reduced, and characteristics of the siliceous film are improved. When an inert gas is used as the atmospheric gas, nitrogen, argon, helium, or the like is used.

  The temperature conditions for curing vary depending on the type of siliceous film-forming composition to be used and how the processes are combined. However, the higher the temperature, the higher the rate at which polysilazane is converted into a siliceous film, and the lower the temperature, the less adverse effects on device characteristics due to oxidation of the silicon substrate or changes in crystal structure. . From such a viewpoint, in the curing step in the present invention, heating is usually performed at 1000 ° C. or lower, preferably 400 to 700 ° C. Here, the temperature raising time to the target temperature is generally 1 to 100 ° C./min, and the curing time after reaching the target temperature is generally 1 minute to 10 hours, preferably 15 minutes to 3 hours. If necessary, the curing temperature or the composition of the curing atmosphere can be changed stepwise. By this heating, the polysilazane is converted into silicon dioxide to form a siliceous film.

  The method for forming a siliceous film according to the present invention requires the above-described steps, but further steps such as a polishing step and an etching step can be combined as necessary.

  The present invention will be described below with reference to various examples.

Composition Example 1 Synthesis of Low Molecular Weight Polysilazane 400 g of dichlorosilane having a purity of 99% or more was poured into 5 kg of dehydrated pyridine at 0 ° C. with stirring. While maintaining the temperature of this mixture at 0 ° C., 1.22 kg of 99.9% purity ammonia gas was injected into the mixture with stirring.

  While maintaining the temperature of the mixture at 0 ° C., the reaction was continued for 12 hours with continued stirring. Excess ammonia was removed by blowing dry nitrogen into the mixture after the reaction for 30 minutes, and then ammonium chloride was filtered off from the slurry-like reaction mixture to obtain a filtrate A. Xylene was mixed with the obtained filtrate A, heated to 50 ° C., and distilled under a reduced pressure of 20 mmHg to remove pyridine, thereby obtaining a 20 wt% concentration solution containing a polymer having a weight average molecular weight of 1450.

  The resulting 20 wt% xylene solution was heated to 50 ° C. and distilled under a reduced pressure of 10 mmHg to remove xylene. N-Pentane was added to the resulting colorless transparent liquid to give a white solution having a concentration of 10% by weight. This solution was filtered through a filter having a filtration accuracy of 0.2 μm to obtain a polymer solution. Dibutyl ether was mixed with this polymer solution and heated to 50 ° C., and distilled under a reduced pressure of 20 mmHg to remove n-pentane. The weight average molecular weight was 1100, and the ratio Mw / weight average molecular weight Mw to number average molecular weight Mn A 20 wt% polymer solution 1 containing a polymer having a Mn of 1.45 was obtained.

Synthesis Example 2 Synthesis of High Molecular Weight Polysilazane A filtrate A was prepared in the same manner as in Synthesis Example 1, and further heated at 150 ° C. for 3 hours in a closed system. After cooling to room temperature, the pressure is returned to normal pressure, and the resulting solution is mixed with xylene, heated to 50 ° C., distilled under a reduced pressure of 20 mmHg to remove pyridine, and 20% by weight containing a polymer with a weight average molecular weight of 6000 The solution was a concentration.

The resulting 20 wt% xylene solution was heated to 50 ° C. and distilled under reduced pressure of 10 mmHg to remove xylene. N-Heptane was added to the obtained white powder to prepare a dispersion having a concentration of 10% by weight. This dispersion was filtered under reduced pressure using a glass filter (manufactured by Advantech Toyo Co., Ltd .: GF-75 (trade name)) to remove the solvent. The resulting et a white powder was dissolved in dibutyl ether, weight average molecular weight of 6400, with the polymer solution 2 in 20% strength by weight comprises a ratio Mw / Mn of 1.22 polymer having a weight average molecular weight Mw to the number average molecular weight Mn did.

Synthesis Example 3 Synthesis of Ultra High Molecular Weight Polysilazane A filtrate A was prepared in the same manner as in Synthesis Example 1 and heated at 150 ° C. for 6 hours in a closed system. After cooling to room temperature, the pressure is returned to normal pressure, and the resulting solution is mixed with dibutyl ether and heated to 50 ° C., distilled under a reduced pressure of 20 mmHg to remove pyridine, and 20 weight containing a polymer having a weight average molecular weight of 9,200. % Concentration of polymer solution 3 was obtained.

Example 1
60 g of polymer solution 1 and 40 g of polymer solution 2 were mixed. The polymer solution after mixing had a maximum in the molecular weight distribution curve at positions 6300 and 650, and Mw / Mn was 10.

  As a silicon grave plate, a substrate was prepared in which grooves having a depth of 0.5 μm and widths of 0.05, 0.1, 0.2, and 0.5 μm were formed, and the surface was coated with a silicon nitride liner layer. . The prepared polymer solution was applied to this substrate by spin coating as a coating composition. The coating conditions were as follows: press pin: 300 rpm / 5 seconds, main spin: 1000 rpm / 20 seconds, final spin: 1,500 rpm / 10 seconds. When the film surface after coating was observed, it was confirmed that no striation occurred and excellent coating properties were achieved.

Furthermore, the substrate after this application was pre-baked on a hot plate at 150 ° C. for 3 minutes, and subsequently introduced into a firing furnace in a pure oxygen atmosphere without cooling. The mixture was heated to 800 ° C. at a heating rate of 10 ° C./min in a baking furnace, and further baked for 30 minutes in an oxygen atmosphere with a water vapor concentration of 80%. When the FT-IR of the obtained fired film was measured, absorption at a wave number of 1080 cm ⁻¹ attributed to the Si—O bond was observed, and it was confirmed that a siliceous film was obtained. On the other hand, the absorption wave numbers 3380 cm ^-1 and 2200 cm ^-1 attributed to N-H bonds and Si-H bonds are not observed, the perhydropolysilazane was converted to silica has been confirmed.

  Further, when an aqueous solution containing 0.5% by weight of hydrofluoric acid and 30% by weight of ammonium fluoride was used as an etching solution, etching was performed at 23 ° C., and the relative etching rate with respect to the thermally oxidized silica film was measured. .48.

After cutting in the direction perpendicular to the substrate after firing with respect to the longitudinal direction of the grooves, the aqueous solution to crush immersed for 30 seconds with 0.5 wt% hydrofluoric acid and 30% by weight of ammonium fluoride, further net After thoroughly washing with water, it was dried.

The cross-section of the substrate was observed with a scanning electron microscope from the top at an elevation angle of 30 ° in the direction perpendicular to the cross-section at a magnification of 50,000 times, and the etching depth was evaluated. Even when the groove width was changed, the change in the etching amount was slight, and it was confirmed that a sufficiently dense siliceous film was formed even at the deepest part of the groove having a width of 0.05 μm.

Example 2
40 g of polymer solution 1 and 60 g of polymer solution 2 were mixed . The polymer solution after mixing had a maximum in the molecular weight distribution curve where the molecular weight was 6250 and 680, and Mw / Mn was 10.

  The prepared polymer solution was applied as a coating composition on a silicon substrate in the same manner as in Example 1. When the film surface after coating was observed, it was confirmed that no striation occurred and excellent coating properties were achieved.

Further, the substrate after this application was fired in the same manner as in Example 1. When the FT-IR of the obtained fired film was measured, absorption at a wave number of 1080 cm ⁻¹ attributed to the Si—O bond was observed, and it was confirmed that a siliceous film was obtained. On the other hand, the absorption wave numbers 3380 cm ^-1 and 2200 cm ^-1 attributed to N-H bonds and Si-H bonds are not observed, the perhydropolysilazane was converted to silica has been confirmed. Further, when the relative etching rate with respect to the thermally oxidized silica film was measured in the same manner as in Example 1, it was 1.50.

  The cross section of the substrate after firing was observed by the same method as in Example 1, and the etching amount was evaluated. Even when the groove width was changed, the change in the etching amount was slight, and it was confirmed that a sufficiently dense siliceous film was formed even at the deepest part of the groove having a width of 0.05 μm.

Comparative Example 1
Polymer solution 1 was used as a coating composition, and was applied onto a silicon substrate in the same manner as in Example 1. When the film surface after application was observed, a large number of striations from the central part toward the peripheral part occurred, and it was confirmed that the application property was insufficient.

  Furthermore, the substrate after this application was fired in the same manner as in Example 1, and the cross section was observed with an electron microscope. In the groove having a width of 0.1 μm or more, the change in the etching amount was slight, and it was confirmed that a sufficiently dense siliceous film was formed even in the deepest part. However, it was confirmed that the etching amount was large in the deepest portion of the groove having a width of 0.05 μm, and a dense siliceous film was not formed in that portion.

Comparative Example 2
Polymer solution 2 was used as a coating composition, and was applied onto a silicon substrate in the same manner as in Example 1. When the film surface after coating was observed, it was confirmed that no striation occurred and excellent coating properties were achieved.

  Furthermore, the substrate after this application was fired in the same manner as in Example 1, and the cross section was observed with an electron microscope. In the groove having a width of 0.2 μm or more, the change in the etching amount was slight, and it was confirmed that a sufficiently dense siliceous film was formed even in the deepest part. However, the etching amount was large in the deepest part of the grooves having a width of 0.05 μm and 0.1 μm, and it was confirmed that a dense siliceous film was not formed in that part.

Comparative Example 3
Polymer solution 3 was used as a coating composition, and was applied onto a silicon substrate in the same manner as in Example 1. When the film surface after coating was observed, it was confirmed that no striation occurred and excellent coating properties were achieved.

Furthermore, the substrate after this application was fired in the same manner as in Example 1, and the cross section was observed with an electron microscope. A void was observed in the deepest part of the groove having a width of 0.2 μm or less, and it was confirmed that there was room for improvement in embedding property.

Claims (6)

  A coating composition comprising perhydropolysilazane and a solvent, wherein the molecular weight distribution curve of the perhydropolysilazane has a molecular weight of 800 to 2,500 and a molecular weight of 3,000 to 8,000, respectively. A coating composition having a maximum and a ratio Mw / Mn of weight average molecular weight Mw to number average molecular weight Mn of 6 to 12.   The coating composition according to claim 1, wherein the content of perhydropolysilazane is 10 to 25% by weight, based on the total weight of the coating composition.   3. The perhydropolysilazane according to claim 1, wherein the perhydropolysilazane is a mixture of a low molecular weight polysilazane having a weight average molecular weight of 800 to 2,500 and a high molecular weight polysilazane having a weight average molecular weight of 3,000 to 8,000. Coating composition.   The coating composition of Claim 3 whose weight ratio of the said low molecular weight polysilazane and the said high molecular weight polysilazane is 3: 7-6: 4. A coating composition comprising perhydropolysilazane and a solvent on the surface of an uneven substrate, wherein the molecular weight distribution curve of the perhydropolysilazane has a molecular weight in the range of 800 to 2,500 and a molecular weight of 3,000. A coating step of applying a coating composition having a maximum in the range of ˜8,000 and a ratio Mw / Mn of the weight average molecular weight Mw to the number average molecular weight Mn of 6 to 12, and a coated substrate at 1000 ° C. A method for forming a siliceous film, comprising a curing step in which the composition is converted into a silicon dioxide film by heat treatment in an oxygen atmosphere or an oxidizing atmosphere containing water vapor.   The method for forming a siliceous film according to claim 5, further comprising a prebaking step of heating the coated substrate at 50 ° C to 400 ° C for 10 seconds to 30 minutes between the coating step and the curing step.