JP7138273B2 - Method for forming silicon film on substrate to be processed - Google Patents

Description

The present invention relates to a method for forming a silicon film on a substrate to be processed.

2. Description of the Related Art Silicon, such as amorphous silicon, is used for thin films for filling contact holes and lines of semiconductor integrated circuit devices and for forming elements and structures. As a method for forming a silicon film, for example, in Patent Documents 1 to 3 and Non-Patent Document 1, a photopolymerizable silane compound such as a cyclic silane compound is irradiated with light to obtain a silane polymer, and then the silane polymer is used as a solvent. describes a method of forming a silicon film by coating a substrate to be treated with a solution dissolved in , and heating the solution.

JP 2009-259958 A JP 2009-102224 A Japanese Patent Application Laid-Open No. 2001-262058

Shimoda T, Masuda T.; Liquid silicon and its applications in electronics. Jpn. J. Appl. Phys. 2014 Jan; 53, 02 BA01

The present disclosure provides techniques that can form silicon films from silane polymers of a wide range of molecular sizes.

A method for forming a silicon film on a substrate to be processed according to one aspect of the present disclosure includes (A) a first solvent having a 6- to 8-membered monocyclic saturated carbocyclic ring in the molecule and a boiling point of less than 160°C and a molecule A step of coating a substrate to be treated with a solution obtained by dissolving a silane polymer in a mixed solvent containing a second solvent containing a saturated or partially saturated carbocyclic ring or a partially saturated carbocyclic ring and having a boiling point of 160° C. or higher to form a coating film. and (B) a step of heating the coating film.

According to one aspect of the disclosed method for forming a silicon film on a substrate to be processed, there is an effect that the silicon film can be formed from silane polymers having a wide range of molecular sizes.

FIG. 1 is a diagram showing film formation properties of a silicon film. (a) shows an example of poor film-forming properties, and (b) shows an example of good film-forming properties. FIG. 2 shows an example of forming a silicon film on a patterned substrate (pattern pitch: 52 nm). (a) is an SEM photograph of a substrate to be processed (before silicon film formation) having a pattern, (b) to (d) are SEM photographs of a silicon film formed by applying a silane polymer solution once, (e) to ( g) is an SEM photograph of a silicon film formed by applying the silane polymer solution twice. FIG. 3 shows an example of forming a silicon film on a patterned substrate (pattern pitch: 64 nm). (a) is an SEM photograph of a substrate to be processed (before silicon film formation) having a pattern, (b) to (d) are SEM photographs of a silicon film formed by applying a silane polymer solution once, (e) to ( g) is an SEM photograph of a silicon film formed by applying the silane polymer solution twice.

Hereinafter, a method for forming a silicon film on a substrate to be processed disclosed in the present application (hereinafter also simply referred to as a "method for forming a silicon film") will be described in detail according to preferred embodiments. Note that the present embodiment does not limit the disclosed method for forming a silicon film.

[Method for Forming Silicon Film]
A method for forming a silicon film according to one aspect of the present disclosure includes (A) a first solvent having a 6- to 8-membered monocyclic saturated carbocyclic ring in the molecule and a boiling point of less than 160°C, and a saturated carbocyclic ring in the molecule. Alternatively, a step of coating a substrate to be processed with a solution obtained by dissolving a silane polymer in a mixed solvent containing a second solvent containing a partially saturated carbocyclic ring and having a boiling point of 160° C. or higher to form a coating film; A step of heating the coating film is included.

<Step (A)>
In step (A), a first solvent containing a 6- to 8-membered monocyclic saturated carbocyclic ring in the molecule and a boiling point of less than 160°C and a solvent containing a saturated or partially saturated carbocyclic ring in the molecule and a boiling point of 160°C A solution (also referred to as “silane polymer solution”) obtained by dissolving a silane polymer in a mixed solvent containing a second solvent having a temperature of 10° C. or higher is applied to a substrate to be processed to form a coating film.

(mixed solvent)
-First solvent-
The first solvent contains a 6- to 8-membered monocyclic saturated carbocyclic ring in the molecule and has a boiling point of less than 160°C. The use of the first solvent allows the silane polymer solution to be prepared with a wide range of molecular size silane polymers. In addition, in this specification, a "boiling point" means the boiling point under atmospheric pressure.

From the viewpoint of the solubility of the silane polymer, particularly the ability to dissolve a silane polymer having a large molecular size, the first solvent preferably contains one 6- to 8-membered monocyclic saturated carbocyclic ring in the molecule. more preferably contains one 7- or 8-membered monocyclic saturated carbocyclic ring.

The 6- to 8-membered monocyclic saturated carbocyclic ring may have a substituent as long as it does not inhibit the solubility of the silane polymer. The substituent is not particularly limited, and examples thereof include alkyl groups having 1 to 4 carbon atoms (preferably 1 to 3 carbon atoms, more preferably 1 or 2 carbon atoms). The number of substituents is not limited, and when there are multiple substituents, they may be the same or different.

Examples of the first solvent include cyclohexane (81°C), cycloheptane (112°C), cyclooctane (151°C), methylcyclohexane (101°C), ethylcyclohexane (132°C), dimethylcyclohexane (120-130°C), ), n-propylcyclohexane (157° C.), isopropylcyclohexane (155° C.), trimethylcyclohexane (136-145° C.), and methylethylcyclohexane (148° C.) (boiling points are in parentheses).

Among them, from the viewpoint of being able to dissolve silane polymers with a wide range of molecular sizes, the first solvent is preferably a cycloalkane having 6 to 8 carbon atoms, more preferably a cycloalkane having 7 or 8 carbon atoms, particularly preferably It is a cycloalkane having 8 carbon atoms. Therefore, in one particularly preferred embodiment, the first solvent is cyclooctane.

The lower limit of the boiling point of the first solvent is preferably 100° C. or higher, more preferably 110° C. or higher, 120° C. or higher, or 130° C. °C or higher.

-Second solvent-
The second solvent contains a saturated carbocyclic ring or a partially saturated carbocyclic ring in its molecule and has a boiling point of 160° C. or higher. By using the second solvent in combination with the first solvent, it becomes possible to form a silicon film with good film-forming properties from silane polymers having a wide range of molecular sizes. As used herein, the term "partially saturated carbocyclic ring" refers to a carbon in which any number of double bonds excluding at least one double bond of an unsaturated carbocyclic ring are converted to single bonds by hydrogenation. ring.

Here, with reference to FIG. 1, the film formation properties of the silicon film will be described. FIG. 1(a) shows an example in which the silicon film is formed only on a part of the substrate to be processed, that is, the film forming property of the silicon film is poor. In the rectangular substrate to be processed, the silicon film (light colored portion in FIG. 1) is not formed in the region near the edge, and the substrate to be processed (dark colored portion in FIG. 1) is exposed. Although the silicon film is partially formed in the central portion, there are scattered portions where the substrate to be processed is exposed. Not only in the case of FIG. 1A, but when the silicon film is formed only on a part of the substrate to be processed, the film formability is poor. On the other hand, FIG. 1B shows an example in which a silicon film is formed on the entire surface of the substrate to be processed, in which the silicon film has good film-forming properties.
The silicon film is required to have a desired thickness and be formed over the entire surface of the substrate to be processed. In this regard, in the case of forming a silicon film from a silane polymer having a large molecular size or in the case of forming a silicon film using a low-concentration silane polymer solution, conventionally, a silicon film is formed on the entire surface of the substrate to be processed. tended to be difficult. On the other hand, according to the method of forming a silicon film of the present disclosure using the second solvent in combination with the first solvent, as described below, when using a silane polymer with a large molecular size or when using a low-concentration silane polymer solution, is used, it is possible to form a silicon film with a desired thickness on the entire surface of the substrate to be processed.

From the viewpoint of being able to form silicon films with good film-forming properties from silane polymers with a wide range of molecular sizes, especially from silane polymers with large molecular sizes that have been considered difficult to form, the second solvent contains 8 to 12 molecules in the molecule. It preferably contains one membered saturated or partially saturated carbocyclic ring. The saturated carbocyclic ring or partially saturated carbocyclic ring is a polycyclic saturated carbocyclic or partially A saturated carbocyclic ring is preferred, and a bicyclic saturated carbocyclic ring or partially saturated carbocyclic ring is more preferred. When the second solvent contains a polycyclic partially saturated carbocyclic ring in the molecule, at least one ring constituting the polycyclic ring preferably has a saturated carbocyclic structure (that is, the degree of unsaturation is 0). . For example, when the second solvent contains a bicyclic partially saturated carbocyclic ring in the molecule, it is preferable that one ring of the bicyclic ring has a saturated carbocyclic structure and the other ring has an unsaturated carbocyclic structure. .
Among them, in combination with the first solvent, the second solvent contains a polycyclic saturated carbocyclic ring in the molecule from the viewpoint that a silicon film can be formed with particularly good film-forming properties from silane polymers with a wide range of molecular sizes. are preferred, and those containing bicyclic saturated carbocycles are particularly preferred.

In the second solvent, the saturated carbocyclic ring or partially saturated carbocyclic ring may have a substituent as long as it does not inhibit the film-forming properties of the silicon film. The substituent is not particularly limited, and examples thereof include alkyl groups having 1 to 4 carbon atoms (preferably 1 to 3 carbon atoms, more preferably 1 or 2 carbon atoms). The number of substituents is not limited, and when there are multiple substituents, they may be the same or different.

Examples of the second solvent include decahydronaphthalene (decalin) (193° C.), 1,2,3,4-tetrahydronaphthalene (tetralin) (207° C.), methyl decahydronaphthalene (210° C.), dimethyl decahydro naphthalene (224° C.), ethyl decahydronaphthalene (226° C.), and isopropyl decahydronaphthalene (241° C.) (boiling points in parentheses).

Among them, in combination with the first solvent, the second solvent is preferably a bicycloalkane having 8 to 12 carbon atoms from the viewpoint that a silicon film can be formed with particularly good film-forming properties from silane polymers of a wide range of molecular sizes. , more preferably bicycloalkanes having 10 to 12 carbon atoms, particularly preferably bicycloalkanes having 10 carbon atoms. Therefore, in one particularly preferred embodiment, the second solvent is decahydronaphthalene.

The boiling point of the second solvent is higher than that of the first solvent by 20° C. or more from the viewpoint of forming a silicon film with good film-forming properties from silane polymers having a wide range of molecular sizes in combination with the first solvent. It is preferably 30° C. or higher, more preferably 40° C. or higher. The upper limit of the boiling point of the second solvent is not particularly limited as long as a mixed solvent can be prepared in combination with the first solvent.

From the viewpoint of forming a silicon film with particularly good film-forming properties from silane polymers having a wide range of molecular sizes, in the mixed solvent, when the volume of the first solvent is 1, the volume of the second solvent is preferably 2 or less. , more preferably 1 or less, still more preferably 0.7 or less, or 0.5 or less. In particular, when the volume of the first solvent is 1 and the volume of the second solvent is 0.5 or less, a molecular size such that the weight average molecular weight (Mw) exceeds 100,000 is obtained. Even when using a very large silane polymer, it is possible to form a silicon film with good film-forming properties.

Advantages of using a mixed solvent can be obtained if the mixed solvent contains even a small amount of the second solvent. For example, in the mixed solvent, when the volume of the first solvent is 1, the volume of the second solvent may be 0.001 or more, preferably 0.005 or more, more preferably 0.01 or more, and 0 0.02 or more, or 0.03 or more. In this specification, the volume ratio of the first solvent and the second solvent is a value calculated based on the volume of the first solvent and the volume of the second solvent at room temperature.

(silane polymer)
The silane polymer is not particularly limited as long as it can form a silicon film by heating. For example, a silane polymer (preferably polydihydrosilane) produced by a conventionally known method obtained by irradiating a photopolymerizable silane compound with light is used. you can According to the method for forming a silicon film according to one aspect of the present disclosure, a silicon film can be formed from silane polymers with a wide range of molecular sizes, including silane polymers with extremely large molecular sizes, which have conventionally been difficult to form. Therefore, when producing silane polymers, it is possible to enjoy the advantage of widening the selection tolerance of conditions such as light irradiation conditions.

In one embodiment, the method for forming a silicon film according to one aspect of the present disclosure may include a step of irradiating a photopolymerizable silane compound with light to prepare a silane polymer before step (A).

Examples of photopolymerizable silane compounds include chain silane compounds, cyclic silane compounds, and cage-like silane compounds (see, for example, Patent Document 2). Among them, a cyclic silane compound is preferable because of its excellent photopolymerizability. Examples of cyclic silane compounds include cyclic silane compounds having one cyclic silane structure, such as cyclotrisilane, cyclotetrasilane, cyclopentasilane, cyclohexasilane, cycloheptasilane, neopentasilane, and trisilane; '-bicyclobutasilane, 1,1'-bicyclopentasilane, 1,1'-bicyclohexasilane, 1,1'-bicycloheptasilane, spiro[2,2]pentasilane, spiro[3,3]heptasilane, spiro cyclic silane compounds having two cyclic silane structures such as [4,4]nonasilane; and silane compounds in which some or all of the hydrogen atoms in these cyclic silane compounds are substituted with silyl groups or halogen atoms.

In particular, cyclopentasilane, cyclohexasilane, and cycloheptasilane are preferred, and cyclohexasilane is more preferred, from the viewpoint of easy synthesis with high purity. Accordingly, in one embodiment, a method of forming a silicon film according to one aspect of the present disclosure may include irradiating cyclohexasilane with light to prepare a silane polymer.

Light irradiation can be carried out under any conventionally known conditions. For example, the irradiation wavelength can range from 300 to 420 nm, and the irradiation time can range from 0.1 second to 600 minutes.

As noted above, the method of forming a silicon film according to one aspect of the present disclosure can form silicon films from silane polymers of a wide range of molecular sizes. Therefore, the weight-average molecular weight (Mw) of the silane polymer used in step (A) is not particularly limited, and may range, for example, from 1,000 to 500,000. Here, in this specification, the "weight average molecular weight" of the silane polymer is the polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography (GPC).

According to the method for forming a silicon film of the present disclosure using a specific mixed solvent, it is possible to form a silicon film from a silane polymer having a large molecular size, which has been difficult to form in the past. For example, the weight average molecular weight (Mw) is 5,000 or more, 10,000 or more, 20,000 or more, 30,000 or more, 50,000 or more, 70,000 or more, 80,000 or more, 90,000 or more, Alternatively, silicon films can be formed from 100,000 or more silane polymers. A silane polymer with a large molecular size tends to be able to form a silicon film even at a low concentration. This is a significant contribution.

The upper limit of the weight average molecular weight (Mw) of the silane polymer is preferably 450,000 or less, 400,000 or less, 350,000 or less, or 300,000 or less from the viewpoint of forming a silicon film with even better film-forming properties. is.

(Silane polymer solution)
The silane polymer solution can be prepared by dissolving the silane polymer in the mixed solvent. In the method of the present disclosure using a particular solvent mixture, a wide range of molecular size silane polymers can be used to prepare the silane polymer solution.

The concentration of the silane polymer in the silane polymer solution (hereinafter also simply referred to as "solution concentration") depends on the molecular size of the silane polymer, but can be adjusted, for example, within the range of 30% by volume or less. From the viewpoint of forming a thin silicon film, the solution concentration is preferably 20% by volume or less, more preferably 10% by volume or less, and even more preferably 5% by volume or less. Conventionally, it has tended to become difficult to form a silicon film on the entire surface of a substrate to be processed when the solution concentration is low. In contrast, according to the method of forming a silicon film of the present disclosure using a specific mixed solvent, it is possible to form a silicon film over the entire surface of the substrate to be processed even when the concentration of the solution is low. Combined with the advantage of being able to use a silane polymer with a large molecular size (which can form a silicon film even at a low concentration, as described above), the method for forming a silicon film of the present disclosure enables an extremely thin silicon film to be formed. It can be formed on the entire surface of the substrate to be processed. In the method of forming a silicon film of the present disclosure, the solution concentration can be lowered to 4% by volume or less, 3% by volume or less, or 2% by volume or less without deteriorating film-forming properties. The lower limit of the concentration of the solution is not particularly limited, but from the viewpoint of the film-forming property of the silicon film, it can be usually 0.1% by volume or more, 0.3% by volume or more, or 0.5% by volume or more. As used herein, the concentration of the silane polymer in the silane polymer solution is a value calculated based on the volume of the mixed solvent and the volume of the silane polymer at room temperature.

According to the method of the present disclosure using a specific mixed solvent, the silane polymer is mixed with the mixed solvent in a mild environment (preferably at room temperature and under atmospheric pressure) and stirred to easily obtain a predetermined concentration of the silane polymer. A solution can be prepared.

The silane polymer solution may contain other components as long as they do not impair the film forming properties of the silicon film. Such other components include, for example, dopants, surface tension modifiers, and the like. As a dopant, a known dopant conventionally used for forming n-type and p-type silicon films may be used. As the surface tension modifier, conventionally known surface tension modifiers such as fluorine-based and silicone-based surface tension modifiers may be used.

(Application of silane polymer solution)
Examples of the method for applying the silane polymer solution to the substrate to be processed include spin coating, roll coating, curtain coating, dip coating, spraying, and inkjet. Among them, it is preferable to apply the silane polymer solution by a spin coating method from the viewpoint of forming a silicon film on the substrate to be processed with good film-forming properties.

The conditions for application by the spin coating method are not particularly limited, and may be appropriately determined in consideration of the molecular size of the silane polymer, the concentration of the solution, and the desired thickness of the silicon film. For example, the rotation speed of the main spin may range from 100 to 5,000 rpm, and the rotation time may range from 1 to 20 seconds.

The amount of the silane polymer solution to be applied may be appropriately determined in consideration of the molecular size and solution concentration of the silane polymer, the dimensions and structure of the substrate to be treated, the desired thickness of the silicon film, and the like. In addition, when the silane polymer solution is applied twice or more as described later, each application amount may be the same or different.

The substrate to be processed, which is the object to be coated, is not particularly limited, and any substrate on which a silicon film is to be further formed may be used in manufacturing a semiconductor integrated circuit device. Examples of substrates to be treated include silicon substrates; glass substrates; transparent electrodes such as ITO; metal substrates such as gold, silver, copper, palladium, nickel, titanium, aluminum, and tungsten; plastic substrates; substrates. The substrate to be processed may have a surface pattern, as described below.

The application of the silane polymer solution to the substrate to be processed may be performed only once, or may be performed twice or more. As described above, according to the method of forming a silicon film of the present disclosure using a specific mixed solvent, a thin silicon film can be formed on the entire surface of the substrate using a low-concentration silane polymer solution. Therefore, it is also possible to form a silicon film with a desired thickness by applying a low-concentration silane polymer solution to the substrate to be processed two or more times. Combined with the advantage of being able to use a silane polymer with a large molecular size, the method of forming a silicon film of the present disclosure enables an extremely thin silicon film to be formed on the entire surface of the substrate to be processed with high accuracy. Further, as will be described later, by repeating the steps (A) and (B) two or more times, fine surface patterns of the substrate to be processed can be satisfactorily embedded with a silicon film.

After the silane polymer solution is applied to the substrate to be treated to form a coating film, heat treatment may be performed to remove low boiling point components such as the solvent. The heat treatment may be performed in a temperature range lower than that of the heating in step (B) described below, for example, in the range of 100 to 200°C.

<Step (B)>
In step (B), the coating film is heated. Thereby, the coating film (silane polymer film) can be converted into a silicon film.

The heating conditions are not particularly limited, and conditions conventionally used for forming a silicon film from a silane polymer may be employed. For example, when forming an amorphous silicon film, the coating film may be heated at 300 to 550° C. (preferably 350 to 500° C.) for 30 seconds to 300 minutes.

According to the method of forming a silicon film of the present disclosure using a specific mixed solvent, silane polymers with a wide range of molecular sizes can be used to form a silicon film with a desired thickness. In one embodiment, the thickness of the silicon film formed is 0.5-100 nm. The thickness of the silicon film is preferably 80 nm or less, more preferably 50 nm or less, still more preferably 40 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less. Although the lower limit of the thickness of the silicon film is not particularly limited, it can be usually 1 nm or more, 3 nm or more, or the like.

In the method of forming a silicon film of the present disclosure, step (A) and step (B) may be performed only once each, or may be performed twice or more each. Here, in converting the silane polymer film to a silicon film in step (B), the film tends to shrink. Such film shrinkage becomes an obstacle in embedding a minute surface pattern with a silicon film. Specifically, due to shrinkage of the film, a gap occurs between the surface pattern and the silicon film. Such a phenomenon tends to become remarkable when step (A) and step (B) are performed only once (see FIGS. 2(b) to (d) and FIGS. 3(b) to (d). ; there is a gap between the wall or bottom of the surface pattern and the silicon film). Conventionally, in order to form a silicon film on the entire surface of a substrate to be processed, it was necessary to use a silane polymer solution with a relatively high solution concentration, and it was difficult to avoid the problem of poor embedding properties due to such film shrinkage. This is because, in order to form a thin silicon film using a silane polymer solution having a high solution concentration, the number of coatings of the silane polymer solution tends to be limited to one.

In this respect, according to the method of forming a silicon film of the present disclosure using a specific mixed solvent, as described above, a low-concentration silane polymer solution is applied to a substrate to be processed two or more times to form a silicon film having a desired thickness. It is possible to form As a result, it is possible to form a silicon film having a desired thickness by performing the steps (A) and (B) two or more times each, and to form a fine surface pattern of the substrate to be processed in a desired manner. A thicker silicon film enabled better embedding. According to the method for forming a silicon film of the present disclosure, the height is 30 to 100 nm (preferably 40 nm or more, 50 nm or more, or 60 nm or more and 90 nm or less), the width is 5 to 50 nm (preferably 40 nm or less, A surface pattern having grooves of 30 nm or less and 10 nm or more can be satisfactorily embedded with a silicon film having a desired thickness.

In the method for forming a silicon film of the present disclosure, in order to suppress the denaturation of the silane polymer and the silane polymer solution (also the photopolymerizable silane compound when synthesizing), an atmosphere with extremely low concentrations of oxygen and moisture (preferably oxygen concentration) It is preferable to perform the series of steps under an atmosphere of 1 ppm or less and a water concentration of 5 ppm or less. In one embodiment, a series of steps including step (A) and step (B) are performed in an inert gas atmosphere such as nitrogen, helium, argon and the like. A series of steps may be performed in an atmosphere in which a reducing gas such as hydrogen is added to an inert gas.

Hereinafter, a method for forming a silicon film according to one aspect of the present disclosure will be specifically described with reference to examples. However, the disclosed method for forming a silicon film is not limited to the examples shown below.

In the following description, "parts" and "%" representing amounts mean "parts by volume" and "% by volume", respectively, unless otherwise specified. In addition, reagent preparation, solution application (step (A)), and coating film heating (step (B)) are carried out in a glove box (manufactured by Miwa Seisakusho Co., Ltd. “DBO-1KH special-OSC” with a gas circulation purifier It was carried out inside a glove box device). The internal environment of the glove box was maintained at an oxygen concentration of 1 ppm or less and a water concentration of 5 ppm or less.

[Example 1]
1. Formation of Silicon Film on Substrate to be Processed 1.1. Preparation of Silane Polymer Solution A silane polymer derived from cyclohexasilane was prepared as the silane polymer. A plurality of silane polymers having different weight-average molecular weights (Mw; converted to polystyrene) were prepared by changing the light irradiation conditions for cyclohexasilane. Three types of silane polymers with Mw of about 2,000, about 20,000, and about 200,000 were used in this evaluation.
At room temperature, 20 parts of the silane polymer was added to 80 parts of the solvent, and the mixture was stirred to prepare a stock solution of the silane polymer solution. Table 1 shows the composition of the solvent used in this evaluation. Since the silane polymer having a very large molecular size of about 200,000 Mw did not dissolve in Single Solvent 2 and Mixed Solvent 4, further evaluation of these systems was discontinued.

1.2. Application of Silane Polymer Solution to Substrate to be Processed As a substrate to be processed, a 2 cm square silicon substrate (without surface pattern) was prepared. 80 μL of the silane polymer solution was dropped onto the substrate to be treated using a micropipette and applied by spin coating. The spin coating conditions were main spin: 500 rpm, 8 sec. The silane polymer solution is the same as in 1.1. A diluted solution (silane polymer concentration: 1 to 10%) obtained by diluting the undiluted solution of each silane polymer solution prepared in 1 to a concentration such that the thickness of the formed silicon film is about 20 nm was used. For dilution, the same solvent as that used to prepare the stock solution was used.

1.3. Heating of coating film (formation of silicon film)
After spin coating, the coating film on the substrate to be processed was heated at 400° C. for 15 minutes to form a silicon film.
"○" indicates that a uniform silicon film is formed on the entire surface of the substrate to be processed, "Δ" indicates that the thickness of the silicon film is uneven although the silicon film is formed on the entire surface of the substrate to be processed, and silicon A case in which the silicon film was formed only partially on the substrate to be processed, such as when the film was torn, was evaluated as "x". Table 2 shows the results.

It was confirmed that a mixed solvent of cyclooctane and decahydronaphthalene can be used to form silicon films from silane polymers with a wide range of molecular sizes. Particularly noteworthy is that even when a silane polymer having a molecular size as large as Mw of about 200,000 is used, a uniform silicon film can be formed on the entire surface of the substrate by using a mixed solvent. became possible.

[Example 2]
2. Formation of a silicon film on a substrate to be processed (evaluation of surface pattern embedding properties)
2.1. Preparation of silane polymer solution 1.1. A plurality of silane polymers having different weight-average molecular weights (Mw; polystyrene equivalent) were prepared in the same manner as above. Three silane polymers with Mw of about 2,200, about 9,000, and about 86,000 were used in this evaluation.
At room temperature, 20 parts of silane polymer was added to 80 parts of mixed solvent 2 (cyclooctane:decahydronaphthalene=1:0.33 (volume ratio)) and stirred to prepare a stock solution of a silane polymer solution.

2.2. Application of Silane Polymer Solution to Substrate to be Processed As a substrate to be processed, a 2 cm square silicon substrate (with a surface pattern) was prepared. In this evaluation, a silicon substrate having a surface pattern (pattern pitch of 52 nm) having grooves of 20 nm width (see FIG. 2(a); hereinafter also referred to as “silicon substrate having a pattern pitch of 52 nm”) and a 34 nm width silicon substrate. A silicon substrate (see FIG. 3A; hereinafter also referred to as "silicon substrate with a pattern pitch of 64 nm") on which a surface pattern having grooves (pattern pitch of 64 nm) was formed was used. The surface pattern is composed of Si ₃ N ₄ at the bottom of the pattern and SiO ₂ at the top of the pattern, and the entire surface of the substrate including the surface pattern is coated with an atomic layer deposited silicon film (1.5 nm thick). We used a substrate with
160 μL of the silane polymer solution was dropped onto the substrate to be treated using a micropipette and applied by spin coating. The spin coating conditions were main spin: 500 rpm, 8 sec. The silane polymer solution is the same as in 2.1. A diluted solution (silane polymer concentration: 1 to 10%) obtained by diluting the undiluted solution of each silane polymer solution prepared in 1 to a concentration such that the thickness of the formed silicon film is about 20 nm was used. At the time of dilution, mixed solvent 2 was used in the same manner as the stock solution.

2.3. Heating of coating film (formation of silicon film)
After spin coating, the coating film on the substrate to be processed was heated at 400° C. for 15 minutes to form a silicon film.

2.4. Evaluation of Embedability of Surface Pattern Above 2.2. and the above 2.3. Heating was performed only once each (coating → heating), and evaluation substrates were made by repeating coating and heating twice (coating → heating → coating → heating). The state of the film was observed by SEM.
FIG. 2 shows an SEM photograph of an evaluation substrate using a silicon substrate with a pattern pitch of 52 nm, and FIG. 3 shows an SEM photograph of an evaluation substrate using a silicon substrate with a pattern pitch of 64 nm.
It was confirmed that in the evaluation substrate on which coating and heating were performed only once, gaps were generated between the walls and the bottom of the surface pattern due to the shrinkage of the silicon film (FIGS. 2(b) to (d), 3(b)-(d)).
On the other hand, in the evaluation substrate on which the coating and heating were repeated twice, there was no gap between the formed silicon film and the wall or bottom of the surface pattern, and the surface pattern was satisfactorily embedded with the silicon film. (Figs. 2(e)-(g), Figs. 3(e)-(g)).
From the above, it was confirmed that when a mixed solvent of cyclooctane and decahydronaphthalene is used, a fine surface pattern of the substrate to be processed can be satisfactorily embedded using silane polymers having a wide range of molecular sizes.

Claims (7)

(A)a cycloalkane having 8 carbon atoms, anda first solvent having a boiling point of less than 160°C;, a bicycloalkane having 10 carbon atoms, andA second solvent having a boiling point of 160° C. or higherWhenin a mixed solvent containing, Sia step of applying a solution in which a run polymer is dissolved to a substrate to be processed to form a coating film;
(B)SaidProcess of heating the coating film
includesfruit,
In the mixed solvent, when the volume of the first solvent is 1, the volume of the second solvent is 2 or less,
A method of forming a silicon film on a substrate to be processed. Said The boiling point of the second solvent isSaid20 ° C. or more higher than the boiling point of the first solvent, claimto 1described method. Said Claim 1, wherein the first solvent is cyclooctane.or 2The method described in . Said Claims 1-, wherein the second solvent is decahydronaphthalene3The method according to any one of . Said Claim 1-4The method according to any one of . Said Claims 1 to 1, wherein the weight average molecular weight (Mw) of the silane polymer is 10,000 or more5The method according to any one of . Said Step (A) andSaidClaims 1-, wherein step (B) is repeated two or more times6The method according to any one of .

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