JP7489868B2 - Method for forming silicon film - Google Patents

Description

This disclosure relates to a method for forming a silicon film.

Silicon, for example amorphous silicon, is used to fill contact holes and lines in semiconductor integrated circuit devices and to form thin films for forming elements and structures. For example, Patent Document 1 describes a method for forming silicon in which a silane polymer solution, in which a silane polymer is dissolved in a mixed solvent containing multiple solvents, is applied to a substrate and heated to form a silicon film.

JP 2020-9826 A

This disclosure provides a technology that can form a silicon film on a patterned substrate that has good pattern embedding properties and minimal surface cracks.

A method for forming a silicon film according to one aspect of the present disclosure includes a coating step of coating a silane polymer solution onto a substrate having a pattern to form a coating film, a first heating step of heating the coating film, an irradiation step of irradiating the heated coating film with ultraviolet light, and a second heating step of heating the coating film irradiated with the ultraviolet light.

The present disclosure has the effect of forming a silicon film on a substrate having a pattern that has good embedding properties and has few surface cracks.

FIG. 1 is a flowchart showing an example of the flow of a silicon film forming method according to an embodiment. FIG. 2A is a diagram for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment. FIG. 2B is a diagram for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment. FIG. 2C is a diagram for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment. FIG. 2D is a diagram for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment. FIG. 2E is a diagram for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment. FIG. 3 is a diagram for explaining improvement in embedding properties of a pattern by the silicon film forming method according to an embodiment. FIG. 4 is a diagram for explaining the suppression of surface cracks by the silicon film forming method according to the embodiment.

Various embodiments will be described in detail below with reference to the drawings. Note that the disclosed technology is not limited to the following embodiments.

However, when a silicon film is formed on a substrate having a pattern using a silane polymer solution, spaces (voids) that are poorly filled portions may occur in the silicon film within the pattern on the substrate. Also, surface cracks may occur in the silicon film due to evaporation of the solvent in the film. For this reason, it is hoped that a silicon film that has good pattern embedding properties and few surface cracks can be formed on a substrate having a pattern.

[Example of flow of silicon film forming method according to one embodiment]
FIG. 1 is a flow chart showing an example of the flow of a method for forming a silicon film according to an embodiment. First, a substrate is provided (step S100). For example, a substrate having a pattern is provided. Next, a silane polymer solution is applied to the substrate having the pattern to form a coating film (step S101, coating process). Next, the coating film is heated (step S102, first heating process). Next, the heated coating film is irradiated with ultraviolet rays (step S103, irradiation process). Next, the coating film irradiated with ultraviolet rays is heated (step S104, second heating process). This is an example of the flow of a method for forming a silicon film according to an embodiment. Below, the details of each step of the method for forming a silicon film according to an embodiment will be described.

<Coating process>
In the coating step, a silane polymer solution is applied to a substrate having a pattern to form a coating film.

(Substrate with pattern)
The substrate having a pattern is not particularly limited as long as it has a pattern on its surface, and any substrate on which a silicon film is to be formed in the manufacture of a semiconductor integrated circuit device may be used. Examples of such substrates 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, and substrates made of composite materials thereof.

In one embodiment, the term "pattern" refers to a general shape formed on a substrate. The shape of the pattern is not particularly limited, and may be, for example, a line shape (groove) or a hole shape (hole). A plurality of patterns may be provided on the surface of the substrate. When a plurality of patterns are present, the shapes and dimensions of the plurality of patterns may be the same as each other or may be different from each other. In addition, a silicon oxide film may be formed as an undercoat film on at least a portion of the surface of the pattern.

(Silane polymer solution)
The silane polymer solution is a solution in which a silane polymer is dissolved in a mixed solvent containing a first solvent having a 6- to 8-membered monocyclic saturated carbon ring in its molecule and a boiling point of less than 160° C., and a second solvent having a saturated or partially saturated carbon ring in its molecule and a boiling point of 160° C. or higher.

(Mixed Solvent)
-First Solvent-
The first solvent contains a 6- to 8-membered monocyclic saturated carbon ring in the molecule and has a boiling point of less than 160° C. By using the first solvent, it becomes possible to prepare a silane polymer solution using silane polymers of a wide range of molecular sizes. In this specification, the "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 with a large molecular size, the first solvent preferably contains one 6- to 8-membered monocyclic saturated carbon ring in the molecule, and more preferably contains one 7- or 8-membered monocyclic saturated carbon ring in the molecule.

The 6- to 8-membered monocyclic saturated carbocyclic ring may have a substituent, so long as it does not inhibit the solubility of the silane polymer. The substituent is not particularly limited, and examples thereof include an alkyl group having 1 to 4 carbon atoms (preferably having 1 to 3 carbon atoms, more preferably having 1 or 2 carbon atoms). The number of substituents is not limited, and when multiple substituents are present, 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 these, from the viewpoint of being able to dissolve silane polymers of 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, and particularly preferably a cycloalkane having 8 carbon atoms. Therefore, in a 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 or higher, since this provides excellent silicon film forming properties when combined with the second solvent described below.

-Second Solvent-
The second solvent contains a saturated or partially saturated carbon ring in the 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 from a silane polymer having a wide range of molecular sizes with good film-forming properties. In this specification, the term "partially saturated carbon ring" refers to a carbon ring in which any number of double bonds, except for at least one double bond, of the double bonds of an unsaturated carbon ring are converted to single bonds by hydrogenation.

From the viewpoint of being able to form a silicon film with good film-forming properties from silane polymers of a wide range of molecular sizes, particularly from silane polymers of large molecular sizes that have been considered difficult to form into a film, the second solvent preferably contains one 8-12 membered saturated or partially saturated carbon ring in the molecule. From the viewpoint of being able to form a silicon film with particularly good film-forming properties from silane polymers of a wide range of molecular sizes in combination with the first solvent, the saturated or partially saturated carbon ring is preferably a polycyclic saturated or partially saturated carbon ring, and more preferably a bicyclic saturated or partially saturated carbon ring. When the second solvent contains a polycyclic partially saturated carbon ring in the molecule, it is preferable that at least one ring constituting the polycycle has a saturated carbon ring structure (i.e., the degree of unsaturation is 0). For example, when the second solvent contains a bicyclic partially saturated carbon ring in the molecule, it is preferable that one ring of the bicycle has a saturated carbon ring structure and the other ring has an unsaturated carbon ring structure.

In particular, from the viewpoint of being able to form a silicon film with particularly good film-forming properties from silane polymers of a wide range of molecular sizes in combination with the first solvent, it is preferable for the second solvent to contain a polycyclic saturated carbon ring in the molecule, and it is particularly preferable for the second solvent to contain a bicyclic saturated carbon ring.

In the second solvent, the saturated or partially saturated carbon ring may have a substituent, so long as it does not inhibit the film-forming properties of the silicon film. The substituent is not particularly limited, and examples thereof include an alkyl group having 1 to 4 carbon atoms (preferably having 1 to 3 carbon atoms, more preferably having 1 or 2 carbon atoms). The number of substituents is not limited, and when multiple substituents are present, 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), methyldecahydronaphthalene (210°C), dimethyldecahydronaphthalene (224°C), ethyldecahydronaphthalene (226°C), and isopropyldecahydronaphthalene (241°C) (boiling points are in parentheses).

In particular, from the viewpoint of being able to form a silicon film with particularly good film-forming properties from silane polymers of a wide range of molecular sizes in combination with the first solvent, the second solvent is preferably a bicycloalkane having 8 to 12 carbon atoms, more preferably a bicycloalkane having 10 to 12 carbon atoms, and particularly preferably a bicycloalkane having 10 carbon atoms. Therefore, in a particularly preferred embodiment, the second solvent is decahydronaphthalene.

From the viewpoint of being able to form a silicon film with good film-forming properties from silane polymers of a wide range of molecular sizes in combination with the first solvent, the boiling point of the second solvent is preferably at least 20°C higher than the boiling point of the first solvent, more preferably at least 30°C higher, and even more preferably at least 40°C 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, but it can usually be 250°C or lower, 240°C or lower, etc.

From the viewpoint of being able to form a silicon film with particularly good film-forming properties from silane polymers of a wide range of molecular sizes, in the mixed solvent, when the volume of the first solvent is taken as 1, the volume of the second solvent is preferably 2 or less, more preferably 1 or less, and even more preferably 0.7 or less, or 0.5 or less. In particular, when a mixed solvent is used in which the volume of the second solvent is 0.5 or less when the volume of the first solvent is taken as 1, it becomes possible to form a silicon film with good film-forming properties even when a silane polymer with a very large molecular size, such as a weight average molecular weight (Mw) exceeding 100,000, is used.

The advantage of using a mixed solvent can be enjoyed if the mixed solvent contains even a small amount of the second solvent. For example, when the volume of the first solvent in the mixed 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, 0.02 or more, or 0.03 or more. In this specification, the volume ratio of the first solvent to 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, and for example, a silane polymer (preferably polydihydrosilane) produced by a conventionally known method obtained by irradiating a photopolymerizable silane compound with light may be used. According to the method for forming a silicon film according to one aspect of the present disclosure, a silicon film can be formed from a wide range of molecular sizes of silane polymers, including silane polymers with extremely large molecular sizes that have been difficult to form into a film in the past. Therefore, when producing a silane polymer, it is also possible to enjoy the advantage of a wider range of selection allowance for light irradiation conditions, etc.

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 prior to the coating step.

Examples of photopolymerizable silane compounds include chain silane compounds, cyclic silane compounds, and cage silane compounds. Among them, cyclic silane compounds are preferred because of their 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; cyclic silane compounds having two cyclic silane structures, such as 1,1'-bicyclobutasilane, 1,1'-bicyclopentasilane, 1,1'-bicyclohexasilane, 1,1'-bicycloheptasilane, spiro[2,2]pentasilane, spiro[3,3]heptasilane, and spiro[4,4]nonasilane; and silane compounds in which some or all of the hydrogen atoms in these cyclic silane compounds have been replaced with silyl groups or halogen atoms.

In particular, from the viewpoint of ease of synthesis at high purity, cyclopentasilane, cyclohexasilane, and cycloheptasilane are preferred, and cyclohexasilane is more preferred. Therefore, in one embodiment, the method for forming a silicon film according to one aspect of the present disclosure may include a step of 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 be in the range of 300 to 420 nm, and the irradiation time can be in the range of 0.1 seconds to 600 minutes.

The weight average molecular weight (Mw) of the silane polymer used in the coating process is not particularly limited and may be, for example, in the range of 1,000 to 500,000. Here, in this specification, the "weight average molecular weight" of the silane polymer is the weight average molecular weight in terms of polystyrene measured by gel permeation chromatography (GPC).

According to the method for forming a silicon film of one embodiment using a specific mixed solvent, it is possible to form a silicon film from a silane polymer with a large molecular size, which has been difficult to form into a film in the past. For example, a silicon film can be formed from a silane polymer with a weight average molecular weight (Mw) of 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, or 100,000 or more. Silane polymers with a large molecular size tend to be able to form a silicon film even at low concentrations, and the method for forming a silicon film of one embodiment using a specific mixed solvent contributes significantly to the formation of a thin layer of silicon film with a uniform thickness.

From the viewpoint of being able to form a silicon film with even better film-forming properties, 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.

(Preparation of silane polymer solution)
The silane polymer solution can be prepared by dissolving a silane polymer in the above-mentioned mixed solvent. In the method for forming a silicon film according to an embodiment using a specific mixed solvent, the silane polymer solution can be prepared using a silane polymer having a wide range of molecular sizes.

The concentration of the silane polymer in the silane polymer solution (hereinafter, simply referred to as the "solution concentration") can be adjusted, for example, in the range of 30% by volume or less, depending on the molecular size of the silane polymer. 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, when the solution concentration is low, it tends to be difficult to form a silicon film on the entire surface of the substrate. In contrast, by using a specific mixed solvent, it is possible to form a silicon film on the entire surface of the substrate even when the solution concentration 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), the method for forming a silicon film according to one embodiment allows an extremely thin silicon film to be formed on the entire surface of the substrate. In the method for forming a silicon film according to one embodiment, the solution concentration can be reduced to 4% by volume or less, 3% by volume or less, or 2% by volume or less without deterioration of the film forming property. The lower limit of the solution concentration is not particularly limited, but from the viewpoint of the film-forming properties of the silicon film, it can usually be 0.1 vol.% or more, 0.3 vol.% or more, 0.5 vol.% or more, etc. In this specification, 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 one embodiment of the method for forming a silicon film using a specific mixed solvent, a silane polymer solution of a predetermined concentration can be easily prepared by mixing and stirring the mixed solvent with a silane polymer in a mild environment (preferably at room temperature and atmospheric pressure).

The silane polymer solution may contain other components as long as they do not inhibit the film-forming properties of the silicon film. Examples of such other components include dopants and surface tension regulators. As the dopant, a known dopant that is conventionally used in forming n-type and p-type silicon films may be used. As the surface tension regulator, a known surface tension regulator such as a fluorine-based or silicon-based one may be used.

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

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

The amount of silane polymer solution to be applied may be determined appropriately taking into consideration the molecular size and solution concentration of the silane polymer, the dimensions and structure of the substrate, the desired thickness of the silicon film, etc. Furthermore, when applying the silane polymer solution two or more times as described below, the amount of each application may be the same or different.

The silane polymer solution may be applied to the substrate once or twice or more. As described above, according to the method for forming a silicon film of one embodiment using a specific mixed solvent, a thin silicon film can be formed over the entire surface of the substrate using a low-concentration silane polymer solution. Therefore, it is also possible to form a silicon film of a predetermined thickness by applying a low-concentration silane polymer solution to the substrate twice or more. Combined with the advantage of being able to use a silane polymer with a large molecular size, according to the method for forming a silicon film of one embodiment, an extremely thin silicon film can be formed over the entire surface of the substrate with high precision.

<First heating step>
In the first heating step, the coating film is heated, whereby excess solvent can be volatilized from the coating film (silane polymer film).

The conditions for heating the coating film in the first heating step are not particularly limited. In particular, from the viewpoint of appropriately volatilizing the low-boiling point components of the solvent from the coating film, it is preferable that the first heating step is performed at a temperature lower than the temperature for heating the coating film in the second heating step. For example, when the second heating step is performed in a temperature range of 300 to 500°C, it is preferable that the first heating step is performed in a temperature range of 100 to 200°C.

<Irradiation step>
In the irradiation step, the heated coating film is irradiated with ultraviolet light. This allows the coating film (silane polymer film) to be separated into a plurality of low molecular weight components. The low molecular weight components refer to components having a lower molecular weight than the silane polymer film.

In the irradiation process, the wavelength of the ultraviolet light is preferably 172 nm. This makes it possible to break both the Si-Si bonds and the Si-H bonds contained in the coating film (silane polymer film) and separate the coating film into a larger number of multiple low molecular weight components.

In addition, in the irradiation step, the coating film may be irradiated with ultraviolet light while the coating film continues to be heated in the first heating step. This makes it possible to separate the coating film into multiple low molecular weight components while volatilizing the low boiling point components of the solvent from the coating film (silane polymer film).

<Second heating step>
In the second heating step, the coating film irradiated with ultraviolet light is heated, whereby the coating film (silane polymer film) can be converted into a silicon film.

The conditions for heating the coating film in the second heating step are not particularly limited, and may be the conditions conventionally used for forming a silicon film from a silane polymer. For example, when forming an amorphous silicon film, the second heating step is preferably performed in the temperature range of 300 to 500°C.

When converting a silane polymer film into a silicon film, low molecular weight components are released from the film. The release of low molecular weight components from the film is an obstacle to embedding the pattern of the substrate with the silicon film. In detail, due to the release of low molecular weight components, spaces (voids) that are poorly embedded portions are generated in the silicon film in the pattern of the substrate. In contrast, according to one embodiment of a method for forming a silicon film in which ultraviolet light is irradiated onto a silane polymer film, which is a coating film, prior to the formation of the silicon film, the silane polymer film is separated into a plurality of low molecular weight components in advance, and the voids can be repaired by the separated low molecular weight components. In addition, when bonds in the silicon polymer film are broken, the broken portions become active sites, which are connected to other active sites and recombined to connect the active parts, thereby repairing the voids. As a result, even if the substrate has fine patterns such as grooves and holes, a silicon film with good pattern embedding properties can be formed.

In addition, when the silane polymer film is converted into a silicon film, the solvent in the film volatilizes. The volatilization of the solvent in the film is a factor that causes surface cracks in the silicon film. In detail, stress is applied to the silicon film due to the volatilization of the solvent in the film, causing cracks on the surface of the silicon film. In contrast, according to one embodiment of a method for forming a silicon film in which the silane polymer film, which is a coating film, is heated prior to the formation of the silicon film, excess solvent is volatilized from the silane polymer film in advance, thereby reducing the stress applied to the silicon film when the silicon film is formed. This makes it possible to form a silicon film with fewer surface cracks.

[An example of a silicon film formed in an embodiment]
2A to 2E are diagrams for explaining an example of a silicon film formed by the silicon film forming method according to one embodiment.

First, in step S100, a substrate 201 having a pattern is provided (see FIG. 2A). Next, in the coating step of step S101, a silane polymer solution is applied to the substrate 201 to form a silane polymer film (an example of a coating film) 202 shown in FIG. 2B. Next, in the first heating step of step S102, the silane polymer film 202 is heated. By heating the silane polymer film 202, excess solvent 202a (see FIG. 2C) can be volatilized from the silane polymer film 202. Next, in the irradiation step of step S103, the heated silane polymer film 202 is irradiated with ultraviolet rays UV (see FIG. 2D). By irradiating the silane polymer film 202 with ultraviolet rays UV, the silane polymer film 202 can be separated into a plurality of low molecular weight components 202b. Next, in the second heating step of step S104, the silane polymer film 202 irradiated with ultraviolet rays UV is heated. By heating the silane polymer film 202 irradiated with ultraviolet rays UV, the silane polymer film 202 can be converted into a silicon film 203 (FIG. 2E). Here, the silane polymer film 202 is previously separated into a plurality of low molecular weight components 202b (see FIG. 2D) in the irradiation process of step S103. Therefore, even if a space (void) that is a defective filling portion occurs in the silicon film 203 in the pattern of the substrate 201, the void can be repaired by the low molecular weight components 202b. As a result, the silicon film 203 can be formed with good pattern filling properties. In addition, the excess solvent 202a (see FIG. 2C) is previously volatilized from the silane polymer film 202 in the first heating process of step S102. Therefore, the amount of solvent volatilized from the film when the silane polymer film 202 is converted into the silicon film 203 can be reduced, thereby suppressing the stress applied to the silicon film 203. As a result, the silicon film 203 with few surface cracks can be formed.

In this way, the method for forming a silicon film according to one embodiment involves preheating the silane polymer film, which is a coating film, and irradiating the silane polymer film with ultraviolet light, and then reheating the silane polymer film to form a silicon film. Therefore, according to the method for forming a silicon film according to one embodiment, a silicon film can be formed on a substrate having a pattern, which has good pattern embedding properties and little surface cracking.

[Improved pattern embedding]
3 is a diagram for explaining an improvement in the embedding property of a pattern by a silicon film forming method according to an embodiment of the present invention, which shows an experimental result in the case where a silicon film S1 is formed on a substrate W1 having a pattern on which a silicon oxide film is formed as an undercoat film B1.

The diagram on the left side of FIG. 3 (Comparative Example 1) shows the result of forming a silicon film S1 by applying a silane polymer solution to a substrate W1 having a pattern, and then heating the applied film (silane polymer film) without irradiating it with ultraviolet light. In Comparative Example 1, many spaces (voids) that are not filled properly are generated in the silicon film S1 within the pattern of the substrate W1. The diagram on the right side of FIG. 3 (Example 1) shows the result of forming a silicon film S1 using a silicon film forming method according to one embodiment. In Example 1, the number of voids is reduced by about 10% compared to Comparative Example 1, and the pattern of the substrate W1 is well filled by the silicon film S1.

When a silicon film is formed without irradiating it with ultraviolet light, voids occur in the silicon film within the pattern on the substrate due to the detachment of low molecular weight components from the film. As a result, the voids become an obstacle to filling, and the filling ability of the silicon film pattern deteriorates. In contrast, in one embodiment of a method for forming a silicon film, a silane polymer film, which is a coating film, is irradiated with ultraviolet light and then heated to form a silicon film. As a result, the low molecular weight components separated from the silane polymer film by the ultraviolet light repair the voids and suppress the occurrence of voids, and as a result, the filling ability of the silicon film pattern can be improved.

[Suppression of surface cracks]
4 is a diagram for explaining the suppression of surface cracks by the silicon film forming method according to one embodiment. Fig. 4 shows the experimental results when a silicon film is formed on a substrate without a pattern. In the experiment of Fig. 4, a rectangular substrate was used as the substrate without a pattern.

The leftmost figure in FIG. 4 (Comparative Example 2) shows the result of applying a silane polymer solution to a substrate, irradiating the applied film (silane polymer film) with ultraviolet light without preheating it, and then reheating the silane polymer film to form a silicon film. In Comparative Example 2, surface cracks occurred over a wide area in the formed silicon film. The second figure from the left (Example 2), the third figure from the left (Example 3), and the rightmost figure (Example 4) in FIG. 4 show the result of forming a silicon film using a method for forming a silicon film according to one embodiment. Examples 2 to 4 differ in the time (hereinafter referred to as "heating time") for preheating the applied film (silane polymer film) in the first heating step. The heating time in Example 2 is 3 minutes, the heating time in Example 3 is 5 minutes, and the heating time in Example 4 is 10 minutes. In Example 2, the occurrence of surface cracks in the silicon film is suppressed compared to Comparative Example 2. In Examples 3 and 4, no surface cracks occurred in the silicon film.

When a silicon film is formed without preheating the coating film (silane polymer film), stress is applied to the silicon film due to the evaporation of the solvent in the film, causing cracks on the surface of the silicon film. In contrast, in one embodiment of a method for forming a silicon film, the coating film (silane polymer film) is preheated prior to the formation of the silicon film. This allows excess solvent to be prevolatilized from the silane polymer film, reducing the stress applied to the silicon film, and as a result, surface cracks in the silicon film can be suppressed.

[Effects of the embodiment]
The method for forming a silicon film according to the above embodiment includes a coating step, a first heating step, an irradiation step, and a second heating step. In the coating step, a silane polymer solution is applied to a substrate having a pattern to form a coating film. In the first heating step, the coating film is heated. In the irradiation step, ultraviolet light is irradiated onto the heated coating film. In the second heating step, the coating film irradiated with ultraviolet light is heated. Therefore, according to the embodiment, a silicon film having good pattern embedding properties and few surface cracks can be formed on a substrate having a pattern.

The first heating step is performed at a temperature lower than the temperature at which the coating film is heated in the second heating step. Therefore, according to the embodiment, surface cracking of the silicon film caused by the volatilization of the solvent in the film can be suppressed.

The wavelength of the ultraviolet light is 172 nm. Therefore, according to the embodiment, the spaces (voids) that are the poorly filled portions can be repaired by low molecular weight components obtained by breaking the Si-Si bonds and Si-H bonds in the coating film (silane polymer film).

In addition, in the irradiation process, the coating film is irradiated with ultraviolet light while the coating film continues to be heated. Therefore, according to the embodiment, it is possible to repair spaces (voids) that are poorly filled while volatilizing excess solvent from the coating film.

The silane polymer solution is a solution in which a silane polymer is dissolved in a mixed solvent containing a first solvent that contains a 6- to 8-membered monocyclic saturated carbon ring in the molecule and has a boiling point of less than 160°C, and a second solvent that contains a saturated or partially saturated carbon ring in the molecule and has a boiling point of 160°C or higher. Therefore, according to the embodiment, a silicon film with good pattern embedding properties and few cracks can be formed from silane polymers of a wide range of molecular sizes.

The embodiments disclosed herein should be considered in all respects as illustrative and not restrictive. The above embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

201: Substrate 202: Silane polymer film 203: Silicon film

Claims (5)

a coating step of coating a silane polymer solution onto a substrate having a pattern to form a coating film;
a first heating step of heating the coating film;
an irradiation step of irradiating the heated coating film with ultraviolet light;
A second heating step of heating the coating film irradiated with the ultraviolet light,
The silane polymer solution is a solution in which a silane polymer is dissolved in a mixed solvent containing a first solvent having a 6- to 8-membered monocyclic saturated carbon ring in its molecule and a boiling point of less than 160° C. and a second solvent having a saturated or partially saturated carbon ring in its molecule and a boiling point of 160° C. or higher.
A method for forming a silicon film. The first heating step includes:
The method for forming a silicon film according to claim 1 , wherein the method is performed at a temperature lower than a temperature for heating the coating film in the second heating step. The method for forming a silicon film according to claim 2, wherein the temperature of the first heating step is 100 to 200°C, and the temperature of the second heating step is 300 to 500°C. The method for forming a silicon film according to any one of claims 1 to 3, wherein the wavelength of the ultraviolet light is 172 nm. The method for forming a silicon film according to any one of claims 1 to 4, wherein in the irradiation step, the coating film is irradiated with ultraviolet light while the coating film is continuously heated.

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