JP7489869B2 - 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 with good adhesion on a substrate having an undercoat film.

A method for forming a silicon film according to one aspect of the present disclosure includes a first coating step of coating a substrate having an undercoat film with a polysilazane solution to form a first coating film, a first heating step of heating the first coating film, a second coating step of coating the heated first coating film with a silane polymer solution to form a second coating film, and a second heating step of heating the first coating film and the second coating film.

The present disclosure has the effect of being able to form a silicon film with good adhesion on a substrate having an undercoat film.

FIG. 1 is a flowchart showing an example of the flow of a silicon film forming method according to an embodiment. FIG. 2 is a diagram showing an example of the molecular structure of polysilazane. FIG. 3A is a diagram for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment. FIG. 3B is a diagram for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment. FIG. 3C is a diagram for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment. FIG. 3D is a diagram for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment. FIG. 3E is a diagram for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment. FIG. 4 is a diagram for explaining improvement in adhesion of a silicon film formed by a silicon film forming method according to an embodiment. FIG. 5 is a diagram showing the results of an XPS (X-ray Photoelectron Spectroscopy) analysis of the surface of a substrate after a silicon film is formed using the silicon film forming method according to an embodiment. FIG. 6 is a diagram showing a result of a secondary ion mass spectrometry (SIMS) analysis of a surface of a substrate after a silicon film is formed using the silicon film forming method according to an embodiment of the present invention. FIG. 7 is a diagram showing the results of a Transmission Electron Microscope (TEM)-Energy Dispersive X-ray Spectroscope (EDX) analysis of a surface of a substrate after a silicon film is formed using a silicon film forming method according to an embodiment. FIG. 8 is a diagram showing the results of SIMS analysis of the surfaces of evaluation substrates after the second heating step according to one embodiment is performed with different oxygen concentrations.

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 coating film is formed by applying a silane polymer solution to a substrate having an undercoat film, the wettability of the silane polymer solution to the undercoat film is low, so adhesion between the coating film and the undercoat film may not be ensured. If the coating film is heated in a state in which adhesion between the coating film and the undercoat film is not ensured, there is a risk that adhesion between the silicon film formed from the coating film and the undercoat film will not be ensured. For this reason, it is expected that a silicon film with good adhesion will be formed on a substrate having an undercoat film.

[Example of flow of silicon film forming method according to one embodiment]
FIG. 1 is a flowchart showing an example of the flow of a silicon film forming method according to an embodiment.

First, a substrate is provided (step S100). For example, a substrate having an undercoat film is provided. Next, a first coating step is performed in which a polysilazane solution is applied to the substrate having the undercoat film to form a first coating film (step S101). Next, a first heating step is performed in which the first coating film is heated (step S102). Next, a second coating step is performed in which a silane polymer solution is applied to the heated first coating film to form a second coating film (step S103). Next, a second heating step is performed in which the first coating film and the second coating film are heated (step S104). This is an example of the flow of the silicon film forming method according to one embodiment. Below, each step of the silicon film forming method according to one embodiment will be described in detail.

<First Coating Step>
In the first coating step, a polysilazane solution is coated on a substrate having an undercoat film to form a first coating film.

(Substrate with Undercoat Film)
The substrate having the undercoat film is not particularly limited, 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 undercoat film is a silicon oxide film. The undercoat film may or may not have a surface pattern.

(Polysilazane)
Polysilazane is a silane-based compound having a silicon (Si)-nitrogen (N) bond, as shown in Fig. 2. Fig. 2 is a diagram showing an example of the molecular structure of polysilazane. Polysilazane can be converted into a silicon film by heating in an atmosphere with an oxygen concentration lower than that of the air.

(Polysilazane solution)
The polysilazane solution can be prepared by dissolving polysilazane in a solvent. The solvent is not particularly limited as long as it can dissolve polysilazane. The polysilazane solution has higher wettability with respect to the undercoat film of the substrate than the silane polymer solution. By applying the polysilazane solution to the substrate having the undercoat film, it is possible to form a first coating film (polysilazane film) with good adhesion.

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

The polysilazane solution may be applied to the substrate once or twice or more. According to one embodiment of the method for forming a silicon film in which a first coating film (polysilazane film) is formed prior to the formation of the silicon film, adhesion between the substrate's base film and the silicon film can be ensured regardless of the number of times the polysilazane solution is applied.

<First heating step>
In the first heating step, the first coating film is heated, whereby the first coating film (polysilazane film) can be appropriately solidified.

The conditions for heating the first coating film in the first heating step are not particularly limited. In particular, from the viewpoint of removing the low boiling point components of the solvent and appropriately solidifying the first coating film, it is preferable that the first heating step is performed at a temperature lower than the temperature for heating the first coating film and the second 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.

In addition, in the first heating step, the first coating film is heated to form a silicon nitride film at the interface between the first coating film and the base film of the substrate. That is, when the first coating film (polysilazane film) is heated, nitrogen (N) is released from the polysilazane. The released nitrogen (N) is then attracted to the base film (silicon oxide film) of the substrate and bonds with silicon on the surface of the base film. This forms a silicon nitride film at the interface between the first coating film and the base film. By forming a silicon nitride film at the interface between the first coating film and the base film, it is possible to reinforce the adhesion between the first coating film and the base film via the silicon nitride film.

<Second Coating Step>
In the second coating step, a silane polymer solution is applied to the heated first coating film to form a second coating film.

(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, it is preferable that the second solvent contains one 8-12 membered saturated carbon ring 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 carbon ring or partially saturated carbon ring is preferably a polycyclic saturated carbon ring or partially saturated carbon ring, and more preferably a bicyclic saturated carbon ring 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 a silane polymer 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 second application 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.

According to one embodiment of the method for forming a silicon film, a silicon film with good adhesion can be formed using silane polymers with a wide range of molecular sizes. Therefore, the weight average molecular weight (Mw) of the silane polymer used in the second coating step is not particularly limited, and may be in the range of, for example, 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 conventional 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 application of the silane polymer solution to the first coating film may be performed only once, or may be performed two or more times. 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 desired thickness by applying the low-concentration silane polymer solution to the substrate two or more times. 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.

<Second heating step>
In the second heating step, the first coating film and the second coating film are heated. This allows the first coating film (polysilazane film) and the second coating film (silane polymer film) to be converted into a silicon film. As described above, since a silicon nitride film is formed at the interface between the first coating film and the base film of the substrate in the first heating step, the silicon nitride film can be left at the interface between the silicon film converted from the first coating film and the base film of the substrate in the second heating step. The silicon nitride film remaining at the interface between the silicon film and the base film of the substrate can reinforce the adhesion between the silicon film and the base film.

The conditions for heating the first and second coating films in the second heating step are not particularly limited, and may be the conditions conventionally used for forming a silicon film from polysilazane and 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.

In one embodiment of the method for forming a silicon film, in order to suppress oxidation of the first coating film (polysilazane film), it is preferable to perform a series of steps under an atmosphere with a low oxygen concentration. In one embodiment, the first coating step, the first heating step, the second coating step, and the second heating step are performed under an atmosphere with an oxygen concentration lower than the oxygen concentration of the atmosphere. In addition, it is preferable that the second heating step is performed under an atmosphere with an oxygen concentration lower than the oxygen concentration when the first coating step, the first heating step, and the second coating step are performed. For example, the first coating step, the first heating step, and the second coating step may be performed under an atmosphere with an oxygen concentration of 50 ppm or less, and the second heating step may be performed under an atmosphere with an oxygen concentration of 1 ppm or less. In addition, from the viewpoint of more efficiently suppressing oxidation of the first coating film, it is preferable that the first coating step, the first heating step, the second coating step, and the second heating step are performed in a state where the substrate having the undercoat film is not exposed to the atmosphere. This makes it possible to improve the film quality of the silicon film formed by suppressing oxidation of the first coating film. Furthermore, according to one embodiment of the method for forming a silicon film, in which a silane polymer solution is applied to a first coating film to form a second coating film, the first coating film can be sealed by the second coating film, and oxidation of the first coating film can be more efficiently suppressed.

[An example of a silicon film formed in an embodiment]
3A to 3E are diagrams for explaining an example of a silicon film formed by the silicon film forming method according to an embodiment.

The substrate W shown in Figures 3A to 3E has a silicon oxide film (an example of a base film) 201 formed on a semiconductor substrate (silicon substrate) not shown. The silicon oxide film 201 has a surface pattern. First, in step S100, a substrate W having a silicon oxide film 201 is provided (see Figure 3A). Next, in a first coating step in step S101, a polysilazane solution is applied to the substrate W to form a polysilazane film (an example of a first coating film) 202 shown in Figure 3B. By performing coating using a polysilazane solution with high wettability in the first coating step, the surface pattern of the silicon oxide film 201 can be satisfactorily embedded with the polysilazane film 202. Next, in a first heating step in step S102, the polysilazane film 202 is heated. By heating the polysilazane film 202, the polysilazane film 202 is appropriately solidified, and a silicon nitride film 202a (see Figure 3C) can be formed at the interface between the polysilazane film 202 and the silicon oxide film 201 of the substrate W. Next, in the second coating step of step S103, a silane polymer solution is applied to the heated polysilazane film 202 to form a silane polymer film (an example of a second coating film) 203 (FIG. 3D). This allows the polysilazane film 202 to be sealed by the silane polymer film 203 so that the polysilazane film 202 is not exposed to oxygen. Next, in the second heating step of step S104, the polysilazane film 202 and the silane polymer film 203 are heated. By heating the polysilazane film 202 and the silane polymer film 203, the polysilazane film 202 and the silane polymer film 203 can be converted into a silicon film 204 (see FIG. 3E). Here, in the first heating step of step S102, a silicon nitride film 202a (see FIG. 3C) is formed at the interface between the polysilazane film 202 and the silicon oxide film 201 of the substrate W. Therefore, when forming the silicon film 204, the silicon nitride film 202a can be left at the interface between the silicon film 204 and the silicon oxide film 201. As a result, the silicon film 204 and the silicon oxide film 201 can be firmly adhered to each other via the silicon nitride film 202a.

In this way, in one embodiment of the method for forming a silicon film, a silicon film is formed by heating the first coating film and the second coating film in a state where a silicon nitride film is formed at the interface between the first coating film and the base film of the substrate. Therefore, according to one embodiment, a silicon film can be formed with good adhesion to a substrate having a base film.

[Improvement of adhesion]
4 is a diagram for explaining the improvement of the adhesion of the silicon film formed 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 having a silicon oxide film (undercoat film) without a surface pattern. FIG. 4(a) shows the result of forming a silicon film using the silicon film forming method according to the comparative example, and FIG. 4(b) shows the result of forming a silicon film using the silicon film forming method according to one embodiment. In the silicon film forming method according to the comparative example, a silane polymer solution is applied to a substrate having a silicon oxide film as an undercoat film to form a coating film, and then heating is performed.

As shown in FIG. 4A, when the silicon film forming method according to the comparative example is used, a silicon film is formed only on a partial area of the substrate (white area in FIG. 4A). In contrast, as shown in FIG. 4B, when the silicon film forming method according to the embodiment is used, a silicon film is formed on almost the entire surface of the substrate (white area in FIG. 4B).

When a silicon film is formed by the silicon film forming method according to the comparative example, the silane polymer solution with low wettability to the silicon oxide film (base film) is directly applied to the substrate, so the adhesion between the formed coating film and the silicon oxide film is reduced. As a result, the adhesion between the silicon film formed from the coating film and the silicon oxide film is reduced. In contrast, in the silicon film forming method according to one embodiment, a polysilazane solution with high wettability to the silicon oxide film (base film) is applied to the substrate to form a first coating film, and then a silane polymer solution is applied to the first coating film to form a second coating film. As a result, the adhesion between the first and second coating films formed and the silicon oxide film is ensured. This makes it possible to suppress the decrease in adhesion between the silicon film formed from the first and second coating films and the silicon oxide film.

Figure 5 shows the results of an XPS analysis of the surface of a substrate after a silicon film is formed using the silicon film forming method according to one embodiment. Figure 6 shows the results of a SIMS analysis of the surface of a substrate after a silicon film is formed using the silicon film forming method according to one embodiment. Figure 7 shows the results of a TEM-EDX analysis of the surface of a substrate after a silicon film is formed using the silicon film forming method according to one embodiment. In Figures 5 to 7, the vertical axis indicates atomic concentration. In Figures 5 and 6, the horizontal axis indicates the depth from the surface of the film on the substrate. In Figure 7, the horizontal axis indicates the distance from the bottom surface of the substrate. The elemental composition of the film on the substrate can be confirmed by XPS analysis, SIMS analysis, and TEM-EDX analysis.

The analysis results in Figures 5 to 7 show that a film containing nitrogen (N) and silicon (Si) (i.e., a silicon nitride film) remains at the interface between the silicon film formed using the silicon film formation method of one embodiment and the silicon oxide film (underlying film). In other words, the analysis results in Figures 5 to 7 show that by forming a silicon film using the silicon film formation method of one embodiment, the silicon film and the silicon oxide film (underlying film) can be firmly adhered to each other via the silicon nitride film.

[Oxygen concentration range in the second heating step]
Here, an experiment was conducted to evaluate the range of oxygen concentration in the second heating step. In the experiment, an evaluation substrate on which a silane polymer film, which is the second coating film, was formed was used. In the experiment, the second heating step was performed on the evaluation substrate with different oxygen concentrations, and the atomic concentration of oxygen in the silicon film formed was examined. FIG. 8 is a diagram showing the analysis result of SIMS analysis of the surface of the substrate after the second heating step according to one embodiment was performed on the evaluation substrate with different oxygen concentrations. In FIG. 8, the vertical axis indicates the atomic concentration of oxygen in the silicon film formed, and the horizontal axis indicates the depth from the surface of the film on the evaluation substrate. In FIG. 8, the dashed line indicates the result of performing the second heating step on the evaluation substrate under an atmosphere with an oxygen concentration of 50 ppm (Comparative Example 1). The solid line indicates the result of performing the second heating step on the evaluation substrate under an atmosphere with an oxygen concentration of 1 ppm or less (Example 1). It can be said that the lower the atomic concentration of oxygen in the silicon film formed, the better the film quality of the silicon film.

As shown in FIG. 8, when the oxygen concentration is 50 ppm, the oxygen atomic concentration in the silicon film is increased to a depth of about 18 nm compared to when the oxygen concentration is 1 ppm or less. From the results in FIG. 8, it was found that by performing the second heating step in an atmosphere with an oxygen concentration of 1 ppm or less, oxidation of the silicon film obtained from the second coating film (silane polymer film) can be suppressed. Therefore, from the viewpoint of improving the film quality of the silicon film formed, it is preferable to perform the second heating step in an atmosphere with an oxygen concentration of 1 ppm or less.

[Effects of the embodiment]
The method for forming a silicon film according to the above embodiment includes a first coating step, a first heating step, a second coating step, and a second heating step. In the first coating step, a polysilazane solution is applied to a substrate having an undercoat film to form a first coated film. In the first heating step, the first coated film is heated. In the second coating step, a silane polymer solution is applied to the heated first coated film to form a second coated film. In the second heating step, the first coated film and the second coated film are heated. Therefore, according to the embodiment, a silicon film can be formed with good adhesion to a substrate having an undercoat film.

The first heating step may be performed at a temperature lower than the temperature for heating the first coating film and the second coating film in the second heating step. Therefore, according to the embodiment, the low boiling point component of the solvent can be removed from the first coating film to appropriately solidify the first coating film, and the adhesion between the first coating film and the second coating film applied to the first coating film can be improved.

The first coating step, the first heating step, the second coating step, and the second heating step may be performed in an atmosphere with an oxygen concentration lower than the oxygen concentration of the atmosphere. The second heating step may be performed in an atmosphere with an oxygen concentration lower than the oxygen concentration when the first coating step, the first heating step, and the second coating step are performed. The first coating step, the first heating step, and the second coating step may be performed in an atmosphere with an oxygen concentration of 50 ppm or less, and the second heating step may be performed in an atmosphere with an oxygen concentration of 1 ppm or less. The first coating step, the first heating step, the second coating step, and the second heating step may be performed in a state where the substrate having the undercoat film is not exposed to the atmosphere. Therefore, according to the embodiment, oxidation of the first coating film can be suppressed, and the film quality of the silicon film formed can be improved.

In addition, in the first heating step, a silicon nitride film may be formed at the interface between the first coating film and the base film of the substrate by heating the first coating film. Therefore, according to the embodiment, the adhesion between the first coating film and the base film is reinforced via the silicon nitride film, thereby improving the adhesion between the silicon film converted from the first coating film and the base film.

The base film may also be a silicon oxide film. Therefore, according to the embodiment, a silicon film can be formed with good adhesion on a substrate having a silicon oxide film as a base film.

The silane polymer solution may be 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 the molecule and a boiling point of less than 160°C, and a second solvent having a saturated or partially saturated carbon ring in the molecule and a boiling point of 160°C or higher. Therefore, according to the embodiment, a silicon film with good adhesion 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.

W substrate 201 silicon oxide film 202 polysilazane film 202a silicon nitride film 203 silane polymer film 204 silicon film

Claims (10)

a first coating step of coating a substrate having an undercoat film with a polysilazane solution to form a first coating film;
a first heating step of heating the first coating film;
a second coating step of coating the heated first coating film with a silane polymer solution to form a second coating film;
a second heating step of heating the first coating film and the second coating film,
The first coating step, the first heating step, the second coating step, and the second heating step are performed in an atmosphere having an oxygen concentration lower than the oxygen concentration of the air.
A method for forming a silicon film. The first heating step includes:
2. The method for forming a silicon film according to claim 1, wherein the method is performed at a temperature lower than a temperature for performing heating of the first coating film and the second coating film in the second heating step. 2. The silicon film forming method according to claim 1 , wherein the second heating step is performed under an atmosphere having an oxygen concentration lower than the oxygen concentration when the first coating step, the first heating step, and the second coating step are performed. the first coating step, the first heating step, and the second coating step are performed in an atmosphere having an oxygen concentration of 50 ppm or less;
4. The method of forming a silicon film according to claim 3 , wherein the second heating step is performed in an atmosphere having an oxygen concentration of 1 ppm or less. The method for forming a silicon film according to any one of claims 1 to 4 , wherein the first coating step, the first heating step, the second coating step, and the second heating step are performed in a state where the substrate having an undercoat film is not exposed to the atmosphere. The silicon film forming method according to any one of claims 1 to 5 , wherein in the first heating step, a silicon nitride film is formed at an interface between the first coating film and an undercoat film of the substrate by heating the first coating film. 7. The method for forming a silicon film according to claim 1 , wherein the base film is a silicon oxide film. The method for forming a silicon film according to any one of claims 1 to 7, wherein the silane polymer solution is a solution obtained by dissolving a silane polymer in a mixed solvent containing a first solvent having a 6-8 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 first coating step of coating a substrate having an undercoat film with a polysilazane solution to form a first coating film;
a first heating step of heating the first coating film;
a second coating step of coating the heated first coating film with a silane polymer solution to form a second coating film;
a second heating step of heating the first coating film and the second coating film;
Including,
The first coating step, the first heating step, the second coating step, and the second heating step are performed in a state where the substrate having an undercoat film is not exposed to the atmosphere.
A method for forming a silicon film. a first coating step of coating a substrate having an undercoat film with a polysilazane solution to form a first coating film;
a first heating step of heating the first coating film;
a second coating step of coating the heated first coating film with a silane polymer solution to form a second coating film;
a second heating step of heating the first coating film and the second coating film;
Including,
In the first heating step, the first coating film is heated to form a silicon nitride film at the interface between the first coating film and the base film of the substrate.
A method for forming a silicon film.

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