JPH09106983A - Semiconductor device and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain an insulation film from being side-etched by oxygen plasma when a resist pattern is removed and from generating moisture even if it is heated. SOLUTION: An insulating film formed on a semiconductor substrate provided with a metal film is made up with a composite layer where first silanol condensate fine particles 1 and second silanol condensate fine particles 2 are mixedly scattered. The first silanol condensate fine particles 1 contain at least either bonds of fluorine and silicon or bonds of an organic group and silicon. The second silanol condensate fine particles 2 contain only bonds of oxygen and silicon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device, and more particularly to a semiconductor device having an insulating film made of an SOG film on a semiconductor substrate having a metal layer formed thereon and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional insulating film made of an SOG film having a low dielectric constant is an aggregate layer made of organic silanol condensate particles having a structure shown in FIG. That is, in the organic silanol condensate fine particles, the bond between silicon and an alkyl group (organic part) is uniformly dispersed at the molecular level in the bond between silicon and oxygen (inorganic part), and the silanol group ( Si-OH). In addition, in FIG. 10, R represents an alkyl group such as CH ₃ , C ₂ H ₅ , and C ₆ H ₅ .

The conventional insulating film is formed as follows. That is, TEO having an alkyl group as a substituent
After applying a silica sol solution obtained by hydrolyzing an S derivative (wherein a silicon-alkyl group bond is substantially uniformly dispersed in a silicon-oxygen bond at the molecular level) and then dehydration condensation, onto a semiconductor substrate, It is formed by heat-treating the silica sol solution.

[0004]

However, the conventional SO
As described above, the organic silanol condensate fine particles forming the insulating film made of the G film have a structure in which silicon-alkyl group bonds (organic part) are uniformly dispersed at the molecular level in silicon oxygen bonds (inorganic part). Thus, the bond between silicon and an alkyl group is less stable than the bond between silicon and oxygen.
Therefore, various problems as described below occur, but as a premise therefor, a process of forming a contact hole in an insulating film made of an SOG film formed on a semiconductor substrate having a metal layer will be described.

First, as shown in FIG. 11A, a first aluminum film formed on a semiconductor substrate 100 is used.
A first-layer SiO ₂ film 102 having a film thickness of 50 nm is deposited on the entire surface of the metal wiring 101 of the layer by the CVD method.
Next, as shown in FIG. 11B, the interlayer insulating film 103 made of the SOG film is formed on the first layer SiO ₂ film 102.
After depositing, a second layer SiO ₂ film 104 having a film thickness of 100 nm is deposited on the interlayer insulating film 103 by the CVD method.

Next, as shown in FIG. 11C, after forming a resist pattern 105 made of an organic material on the second layer SiO ₂ film 104, as shown in FIG.
First layer of SiO ₂ film 1 using resist pattern 105
02, interlayer insulating film 103 and second layer SiO ₂ film 104
Etching to contact holes 106
To form

Next, as shown in FIG. 12B, the resist pattern 105 is removed by oxygen plasma.

However, as described above, the bond between silicon and an alkyl group is more unstable than the bond between silicon and oxygen, so that the oxidative decomposition of the silicon-alkyl group bond causes the side wall of the contact hole 106 in the interlayer insulating film 103. Go deep into. Therefore, as shown in FIG. 12B, the contact hole 106 in the interlayer insulating film 103.
There is a problem that side etching occurs in the exposed portion.

Next, as shown in FIG. 12C, moisture from the interlayer insulating film 103 is removed by the heat of the surface heat treatment performed when the second layer metal wiring 107 (see FIG. 13) is buried in the contact hole 106. Occurs. Therefore, the interlayer insulating film 103 absorbs moisture to increase the dielectric constant, or the surface of the first-layer metal wiring 101 made of aluminum is oxidized,
There is a problem that the contact resistance is increased.

Next, as shown in FIG. 13, when the metal wiring 107 of the second layer is deposited, a void 108 is generated in the metal wiring 107 of the second layer due to the side etching, and the second metal wiring 107 is formed. There is a problem that the metal wiring 107 of the layer is thinned or broken.

In view of the above, the present invention provides an insulating film which is less likely to be side-etched by oxygen plasma when removing a resist pattern and which is less likely to generate moisture even when heated, whereby an upper metal layer in a semiconductor device is provided. It is an object of the present invention to prevent thinning and disconnection of wiring, reduce contact resistance between a lower metal wiring and an upper metal wiring, and suppress an increase in dielectric constant due to moisture absorption.

[0012]

In order to achieve the above-mentioned object, a solution means provided by the invention of claim 1 is a metal film formed on a semiconductor substrate and an insulating film formed around the metal film. Assuming a semiconductor device including a film, the insulating film is
A first silanol condensate fine particle containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon, and a second silanol condensate fine particle containing only a bond of oxygen and silicon. The structure is composed of composite layers mixed in a dispersed state.

According to the structure of the first aspect, in the first silanol condensate fine particles located on the outermost surface of the insulating film, the oxygen-plasma causes oxidative decomposition of the silicon-alkyl group bond. The second silanol condensate fine particles containing only a bond between oxygen and silicon are present inside the silanol condensate fine particle No. 1 and the second silanol condensate fine particles are composed of only a silicon-oxygen bond. Since it is not oxidatively decomposed by the oxygen plasma, it is possible to avoid the situation where the oxidative decomposition deeply progresses in the insulating film, and it is difficult for moisture to be generated from the insulating film. In addition, since the first silanol condensate fine particles containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon are dispersed in the insulating film, the density and polarizability of the insulating film are reduced. Decreases and the relative dielectric constant decreases.

According to a second aspect of the present invention, there is provided a solving means, which is premised on a semiconductor device comprising a metal film formed on a semiconductor substrate and an insulating film formed around the metal film. Is a collection of capsule-like particles in which fine particles of a silanol condensate containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon are chemically modified by silanol containing only a bond between oxygen and silicon. It is configured by layers.

According to the second aspect of the present invention, the capsule-shaped particles are such that the silanol condensate fine particles containing at least one bond of fluorine-silicon bond and organic group-silicon bond are only oxygen-silicon bond. Since it has a structure chemically modified with silanol containing, the silanol condensate fine particles do not come into direct contact with oxygen plasma, and the silanol containing only the bond between surface oxygen and silicon is not oxidatively decomposed by oxygen plasma. It is possible to avoid the situation where the insulating film is oxidized and decomposed, and it is difficult for moisture to be generated from the insulating film. Further, since the insulating film is composed of fine particles of a silanol condensate containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon, the density of the insulating film decreases and the relative dielectric constant decreases. .

According to a third aspect of the present invention, a means for solving the problems is based on a semiconductor device including a metal film formed on a semiconductor substrate and an insulating film formed around the metal film. Is a capsule-like particle in which fine particles of a silanol condensate containing only a bond between oxygen and silicon are chemically modified with a silanol containing at least one bond between a bond between fluorine and silicon and a bond between an organic group and silicon. It is configured by an assembly layer.

According to the third aspect of the invention, in the capsule-shaped particles located on the outermost surface of the insulating film, the silanol containing at least one of the bond between fluorine and silicon and the bond between an organic group and silicon is oxygen. It is oxidatively decomposed by plasma, but since the silanol condensate fine particles made of an inorganic substance are present inside the capsule-shaped particles and the silanol condensate fine particles made of the inorganic substance are not oxidatively decomposed by the oxygen plasma, the oxidative decomposition by the oxygen plasma is carried out. Does not progress into the insulating film, and moisture is unlikely to be generated from the insulating film. In addition, since the insulating film is composed of capsule-like particles chemically modified with silanol containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon, the density of the insulating film decreases and Dielectric constant decreases.

According to a fourth aspect of the present invention, a means for solving the problems is based on a semiconductor device including a metal film formed on a semiconductor substrate and an insulating film formed around the metal film. Is composed of an aggregate layer of fine particles of silanol condensate containing only bonds of oxygen and silicon and at least a part of the hydroxyl groups on the surface being substituted with silyl groups.

According to the structure of claim 4, the silyl group on the surface of the fine particles of the silanol condensate located on the outermost surface of the insulating film is eliminated by oxygen plasma, but the fine particles of the silanol condensate contain a bond between oxygen and silicon. Since it is not oxidatively decomposed by the oxygen plasma, the oxidative decomposition by the oxygen plasma does not proceed into the insulating film, and moisture is hardly generated from the insulating film. Further, since the insulating film is made of silanol condensate fine particles or siloxane polymer in which at least a part of hydroxyl groups is substituted with a silyl group, the density of the insulating film is reduced and the relative dielectric constant is reduced.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a semiconductor device according to the first aspect, which comprises at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon. A first silica sol solution containing 1 silanol condensate fine particles and a second silica sol solution containing second silanol condensate fine particles containing only a bond between oxygen and silicon are mixed in a liquid phase to form a mixed silica sol solution. The step of obtaining and the mixed silica sol solution are supplied onto the semiconductor substrate on which the metal film is formed, and then the semiconductor substrate is subjected to heat treatment to obtain the first silanol condensate fine particles and the second silanol condensate fine particles. And a step of forming an insulating film made of a composite layer in which they are mixed in a dispersed state.

According to the structure of claim 5, a first silica sol solution containing fine particles of first silanol condensate containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon, and oxygen. A mixed silica sol solution obtained by mixing a second silica sol solution containing second silanol condensate fine particles containing only the bond between silicon and silicon is supplied onto the semiconductor substrate, and then the semiconductor substrate is subjected to heat treatment, A composite layer in which the first silanol condensate fine particles and the second silanol condensate fine particles are mixed in a dispersed state is formed on the semiconductor substrate.

A sixth aspect of the present invention is a method of manufacturing a semiconductor device according to the second aspect of the present invention, wherein the silanol contains at least one of a bond between fluorine and silicon and a bond between an organic group and silicon. A silica sol solution containing condensate fine particles, a step of mixing a silicon alkoxide containing no bond between silicon and an alkyl group to obtain a mixed silica sol solution, and the mixed silica sol solution was supplied onto a semiconductor substrate on which a metal film was formed. After that, the semiconductor substrate is subjected to heat treatment to form an insulating film composed of an aggregate layer of capsule-shaped particles in which the silanol condensate fine particles are chemically modified with silanol containing only a bond between oxygen and silicon. The configuration is as follows.

According to the structure of claim 6, a silica sol solution containing fine particles of a silanol condensate containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon is bonded to the silicon and an alkyl group. After supplying the mixed silica sol solution obtained by mixing the silicon alkoxide containing no to the semiconductor substrate, and subjecting the semiconductor substrate to heat treatment, the silanol condensate fine particles on the semiconductor substrate only bond with oxygen and silicon. An aggregate layer of the capsule-like particles chemically modified by the silanol containing is formed.

According to the invention of claim 7, in the structure of claim 6, the silicon alkoxide contains at least one of tetraethoxysilane, tetramethoxysilane, triethoxysilane, trimethoxysilane and triethoxyfluorosilane. The configuration is added.

The invention of claim 8 is the method of manufacturing a semiconductor device according to claim 3, wherein a silica sol solution containing fine particles of a silanol condensate containing only bonds between oxygen and silicon is added with silicon and an alkyl group. Mixing the silicon alkoxide containing the bond to obtain a mixed silica sol solution, and supplying the mixed silica sol solution onto the semiconductor substrate on which the metal film is formed, and then subjecting the semiconductor substrate to a heat treatment to perform the silanol condensation. A step of forming an insulating film in which the body particles are composed of an aggregate layer of capsule-like particles chemically modified with silanol containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon. It is configured to be.

According to the structure of claim 8, a mixed silica sol solution obtained by mixing a silica sol solution containing fine particles of a silanol condensate containing only a bond between oxygen and silicon with a silicon alkoxide containing a bond between silicon and an alkyl group is obtained. When the semiconductor substrate is subjected to heat treatment after being supplied onto the semiconductor substrate, the silanol condensate fine particles form at least one bond among the bond between fluorine and silicon and the bond between an organic group and silicon on the semiconductor substrate. An aggregate layer of the capsule-like particles chemically modified by the silanol containing is formed.

According to a ninth aspect of the invention, in addition to the constitution of the eighth aspect, the constitution in which the silicon alkoxide contains triethoxymethylsilane is added.

A tenth aspect of the present invention is a method for manufacturing a semiconductor device according to the fourth aspect, wherein the silanol condensate fine particles are contained in a silica sol solution containing silanol condensate fine particles containing only a bond between oxygen and silicon. The first step of silylating the surface of the above, and after supplying a silica sol solution containing fine particles of silanol condensate whose surface is silylated onto the semiconductor substrate on which the metal film is formed, heat-treating the semiconductor substrate And a second step of forming an insulating film composed of an aggregate layer of silanol condensate fine particles in which at least a part of hydroxyl groups on the surface containing only bonds of oxygen and silicon are substituted with silyl groups. It is configured to be.

According to the structure of claim 10, a silica sol solution containing fine particles of silanol condensate having only a bond between oxygen and silicon and having a silylated surface is supplied onto the semiconductor substrate, and then the semiconductor substrate is subjected to heat treatment. Then, on the semiconductor substrate, an aggregate layer of silanol condensate fine particles containing only bonds between oxygen and silicon and having at least a part of the hydroxyl groups on the surface substituted with silyl groups is formed.

According to an eleventh aspect of the invention, in the structure of the tenth aspect, in the first step, the silica sol solution and the silylating agent are reacted in a liquid phase to remove hydroxyl groups on the surface of the silanol condensate fine particles. A structure including a step of substituting at least a part of them with a silyl group is added.

A twelfth aspect of the present invention is a method of manufacturing a semiconductor device according to the fourth aspect, wherein a silanol condensate containing only a bond between oxygen and silicon is provided on a semiconductor substrate having a metal film formed thereon. A first step of supplying a silica sol solution containing fine particles, a second step of silylating the surface of the silanol condensate fine particles in the silica sol solution, and a heat treatment on the semiconductor substrate to obtain oxygen and silicon. And a third step of forming an insulating film composed of an aggregate layer of silanol condensate fine particles in which at least some of the hydroxyl groups on the surface thereof are substituted with silyl groups. .

According to the structure of claim 12, a silica sol solution containing fine particles of silanol condensate containing only a bond between oxygen and silicon is supplied onto a semiconductor substrate, and the surface of the fine particle of silanol condensate is silylated on the semiconductor substrate. ,
When a semiconductor substrate is subjected to heat treatment, an aggregate layer of silanol condensate fine particles is formed on the semiconductor substrate, which contains only bonds between oxygen and silicon and in which at least some of the hydroxyl groups on the surface are substituted with silyl groups. .

According to a thirteenth aspect of the present invention, in addition to the configuration of the twelfth aspect, the second step includes a step of supplying a gas-state silylating agent to the heated semiconductor substrate. .

According to a fourteenth aspect of the present invention, in the structure of the twelfth aspect, the second step is to react the silica sol solution and the silylating agent in a liquid phase on the semiconductor substrate to form the silanol condensate fine particles. A configuration including a step of substituting a hydroxyl group on the surface with a silyl group and a step of heating the semiconductor substrate to substitute a residual hydroxyl group on the surface of the silanol condensate fine particles with a silyl group is added.

The invention of claim 15 is the invention of claim 13 or 14.
In addition to the above configuration, the second step adds a configuration including a step of silylating the surface of the silanol condensate fine particles under high pressure.

The invention of claim 16 is the structure of claims 12 to 15, wherein the silylating agent is hexamethyldisilazane,
A structure containing at least one of hexamethyldisiloxane and trimethylchlorosilane is added.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, in an insulating film in a semiconductor device according to a first embodiment of the present invention, organic silanol condensate fine particles 1 and inorganic silanol condensate fine particles 2 are mixed substantially uniformly. It is a bulk composite layer formed by. The organic silanol condensate fine particles 1 have the same molecular structure as that shown in FIG. 10, and the inorganic silanol condensate fine particles 2 have a silicon-alkyl group bond as shown in FIG. However, it has only a silicon-oxygen bond and has a silanol group (Si-OH) on the surface.

According to the first embodiment, in the organic silanol condensate fine particles 1 located on the outermost surface of the insulating film,
As described in the section of the problem to be solved by the invention, the silicon-alkyl group bond is oxidatively decomposed by the oxygen plasma. However, the inorganic silanol condensate fine particles 2 are present inside the organic silanol condensate fine particles 1 located on the outermost surface of the insulating film. Since the inorganic silanol condensate fine particles 2 are silicon-oxygen bonds, Not oxidatively decomposed by plasma. Therefore, oxidative decomposition by oxygen plasma does not proceed deep into the insulating film.

In the insulating film in the semiconductor device according to the second embodiment of the present invention, as shown in FIG. 2, the organic silanol condensate fine particles 3 containing a bond between an organic group and silicon have only a bond between oxygen and silicon. It is an assembly layer in which a large number of capsule-shaped particles 5 chemically modified with an inorganic silanol 4 containing is assembled.

According to the second embodiment, since the capsule-shaped particles 5 have a structure in which the organic silanol condensate fine particles 3 are covered with the inorganic silanol 4, the organic silanol condensate fine particles 3 are exposed to oxygen plasma. Not oxidatively decomposed. Therefore, the insulating film is not oxidized and decomposed by oxygen plasma.

In the insulating film in the semiconductor device according to the third embodiment of the present invention, as shown in FIG. 3, the inorganic silanol condensate fine particles 6 containing only the bond between oxygen and silicon are bonded to the organic group and silicon. It is an assembly layer in which a large number of capsule-shaped particles 8 chemically modified with an organic silanol 7 containing are assembled.

According to the third embodiment, in the capsule-shaped particles 8 located on the outermost surface of the insulating film, the organic silanol 7 is oxidatively decomposed by oxygen plasma, but the inside of the capsule-shaped particles 8 is an inorganic silanol. Since the condensate fine particles 6 are present and the inorganic silanol condensate fine particles 6 are not oxidatively decomposed by oxygen plasma, the oxidative decomposition by oxygen plasma does not proceed into the insulating film.

In place of the organic silanol condensate fine particles in the first or second embodiment, fluorinated silanol condensate fine particles containing a bond of fluorine and silicon as shown in FIG. 5 may be used. Instead of the organic silanol in the third embodiment, a fluorinated silanol containing a bond between fluorine and silicon may be used.

The method of manufacturing the semiconductor device according to the first embodiment will be described below.

First, a solution of an inorganic silica sol (commercially available inorganic SOG solution having an SiO ₂ concentration of 3 to 20 wt.
%. ) 100 ml and an organic silica sol solution (commercially available organic SOG solution having a SiO ₂ -concentration of 3 to
20 wt%. ) 50 ml are mixed to obtain a mixed silica sol solution.

Next, after the mixed silica sol solution was stirred at room temperature for 3 hours, 3000 rpm was formed on the semiconductor substrate 10 on which the metal wiring 11 and the first SiO ₂ film 12 were formed as shown in FIG. 6A. Spin coat with. Next, the spin-coated mixed silica sol solution was baked on a hot plate at a temperature of 100 ° C. for 1 minute and then at a temperature of 150 ° C. for 1 minute, and then the semiconductor substrate 10 was baked. When a heat treatment was performed for 30 minutes at a temperature of 400 ° C. in a nitrogen atmosphere with an electric furnace, a film thickness of 3 was formed on the semiconductor substrate 10.
An interlayer insulating film 13 made of an 80 nm SOG film was formed.

The interlayer insulating film 13 thus formed
Was analyzed by infrared spectroscopy, it was confirmed that a silicon-methyl group bond was observed, and that a composite layer was formed in which organic silanol condensate fine particles and inorganic silanol condensate fine particles were mixed. . Further, when the dielectric constant of this interlayer insulating film 13 was measured by the CV method, the relative dielectric constant was about 2.8.

Next, after depositing a _second SiO ₂ film 14 having a film thickness of 100 nm on the interlayer insulating film 13 by the CVD method, the photoresist 1 is formed by a normal lithography process.
The contact hole pattern is formed by using the pattern No. 5, and then the first and second SiO ₂ films 12 and 14 and the interlayer insulating film 13 are dry-etched to obtain the pattern shown in FIG.
A contact hole 16 is formed as shown in FIG.
Next, after removing the photoresist 15 by ashing with oxygen plasma, the contact hole 16 is removed by an electron microscope.
As a result of observing the shape of, the side etching was hardly recognized as shown in FIG.

Further, when the contact resistance of the contact hole 16 formed in the interlayer insulating film 13 obtained by the method for manufacturing a semiconductor device according to the first embodiment was measured,
No increase in contact resistance was observed as compared with the interlayer insulating film made of the SiO ₂ film (plasma TEOS film) formed by the ordinary CVD method. Further, even if the humidification test was performed, almost no change in the dielectric constant was recognized.

By increasing or decreasing the amount of organic silica sol added to the inorganic silica sol, hygroscopicity, oxygen plasma resistance and relative dielectric constant can be adjusted. That is,
When the amount of organic silica sol is increased, the hygroscopicity is decreased, the oxygen plasma resistance is less deteriorated, and the relative dielectric constant is decreased.

Instead of the organic silica sol solution, a solution of fluorinated silica sol synthesized by hydrolysis and dehydration condensation of trimethoxyfluorosilane may be added to the inorganic silica sol. By doing so, fine particles of a fluorine-silanol condensate having a fluorine-silicon bond as shown in FIG. 5 can be obtained.

The method of manufacturing the semiconductor device according to the second embodiment will be described below.

First, a solution of organic silica sol (commercially available organic SOG solution having a SiO ₂ concentration of 3 to 20 wt.
%. ) 100 ml of tetraethoxysilane 0.
2 ml and 0.05 ml of water are added to obtain an organic silica sol solution.

Next, the organic silica sol solution was added at room temperature for 48 hours.
After stirring for a time, as shown in FIG.
And the semiconductor substrate 10 on which the first SiO ₂ film 12 is formed
Spin coat at 3000 rpm. Next, the spin-coated organic silica sol solution is baked on a hot plate at a temperature of 150 ° C. for 2 minutes, and then the semiconductor substrate 10 is heated by an electric furnace at 450 ° C. in a nitrogen atmosphere for 30 minutes. When the heat treatment was performed, an interlayer insulating film 13 made of an SOG film having a film thickness of 450 nm was formed on the semiconductor substrate 10.

FIG. 7 is a schematic view showing a partially enlarged structure of the capsule-shaped particles forming the interlayer insulating film 13, in which the organic silanol condensate fine particles 3 are covered with the inorganic silanol 4.

The interlayer insulating film 13 thus formed
When the dielectric constant of was measured by the CV method, the relative dielectric constant was about 2.5.

Next, after depositing a _second SiO ₂ film 14 having a film thickness of 100 nm on the interlayer insulating film 13 by the CVD method, the photoresist 1 is formed by a normal lithography process.
The contact hole pattern is formed by using the pattern No. 5, and then the first and second SiO ₂ films 12 and 14 and the interlayer insulating film 13 are dry-etched to obtain the pattern shown in FIG.
A contact hole 16 is formed as shown in FIG.
Next, after removing the photoresist 15 by ashing with oxygen plasma, the contact hole 16 is removed by an electron microscope.
As a result of observing the shape of, the side etching was hardly recognized as shown in FIG.

When the contact resistance of the contact hole 16 formed in the interlayer insulating film 13 obtained by the method for manufacturing a semiconductor device according to the second embodiment was measured,
No increase in contact resistance was observed as compared with the interlayer insulating film made of the SiO ₂ film (plasma TEOS film) formed by the ordinary CVD method. Further, even if the humidification test was performed, almost no change in the dielectric constant was recognized.

The hygroscopicity, oxygen plasma resistance and relative permittivity can be adjusted by increasing or decreasing the amount of tetraethoxysilane added to the organic silica sol. That is, when the amount of tetraethoxysilane is increased, the hygroscopicity is increased, the oxygen plasma resistance is significantly improved, and
The relative permittivity increases.

The method of manufacturing the semiconductor device according to the third embodiment will be described below.

First, a solution of an inorganic silica sol (commercially available organic SOG solution having an SiO ₂ conversion concentration of 3 to 20 wt.
%. ) To 100 ml, 0.2 ml of triethoxymethylsilane and 0.05 ml of water are added to obtain an inorganic silica sol solution.

Next, the inorganic silica sol solution was added at room temperature for 48 hours.
After stirring for a time, as shown in FIG.
And the semiconductor substrate 10 on which the first SiO ₂ film 12 is formed
Spin coat at 3000 rpm. Next, the spin-coated inorganic silica sol solution was baked on a hot plate at a temperature of 150 ° C. for 2 minutes, and then the semiconductor substrate 10 was heated by an electric furnace at a temperature of 450 ° C. for 30 minutes in a nitrogen atmosphere. When the heat treatment was performed, an interlayer insulating film 13 made of an SOG film having a film thickness of 450 nm was formed on the semiconductor substrate 10.

The interlayer insulating film 13 thus formed
When the dielectric constant of was measured by the CV method, the relative dielectric constant was about 2.5.

Next, after depositing a _second SiO ₂ film 14 having a film thickness of 100 nm on the interlayer insulating film 13 by the CVD method, the photoresist 1 is formed by a normal lithography process.
The contact hole pattern is formed by using the pattern No. 5, and then the first and second SiO ₂ films 12 and 14 and the interlayer insulating film 13 are dry-etched to obtain the pattern shown in FIG.
A contact hole 16 is formed as shown in FIG.
Next, after removing the photoresist 15 by ashing with oxygen plasma, the contact hole 16 is removed by an electron microscope.
As a result of observing the shape of, the side etching was hardly recognized as shown in FIG.

Further, the contact resistance of the contact hole 16 formed in the interlayer insulating film 13 obtained by the method of manufacturing the semiconductor device according to the third embodiment was measured,
No increase in contact resistance was observed as compared with the interlayer insulating film made of the SiO ₂ film (plasma TEOS film) formed by the ordinary CVD method. Further, even if the humidification test was performed, almost no change in the dielectric constant was recognized.

The humidity resistance, oxygen plasma resistance and relative dielectric constant can be adjusted by increasing or decreasing the amount of tetraethoxysilane added to the inorganic silica sol. That is, when the amount of tetraethoxysilane is increased, the hygroscopicity is decreased, the oxygen plasma resistance is less deteriorated, and the relative dielectric constant is decreased.

As shown in FIG. 8, the insulating film in the semiconductor device according to the fourth embodiment of the present invention is a silanol condensate in which at least a part of the OH groups constituting the silanol groups on the surface are replaced by silyl groups. It is an aggregate layer of fine particles. In FIG. 8, X represents a silyl group, and FIG. 9 lists examples of silyl groups.

The first method of manufacturing the semiconductor device according to the fourth embodiment will be described below.

Solution of inorganic silica sol (commercially available inorganic SOG
It is a solution and has a SiO ₂ conversion concentration of 3 to 20 wt%. ) 10 ml of hexamethyldisiloxane in 100 ml
1 is added to obtain a silica sol solution.

Next, the silica sol solution is stirred at room temperature for 3 hours and then spin-coated on the semiconductor substrate at 3000 rpm. Next, the spin-coated inorganic silica sol solution was applied to a hot plate at 1
After baking for 1 minute, the semiconductor substrate was baked for 1 minute at a temperature of 150 ° C., and then the semiconductor substrate was heat-treated for 30 minutes at a temperature of 450 ° C. in a nitrogen atmosphere in an electric furnace. An interlayer insulating film made of an SOG film having a film thickness of 380 nm was formed on the top.

When the interlayer insulating film thus formed was analyzed by infrared spectroscopy, it was confirmed that a silicon-methyl group bond was observed and that a silylation reaction had occurred on the surface of the silanol condensate fine particles. It was Further, when the dielectric constant of this interlayer insulating film was measured by the CV method, the relative dielectric constant was about 2.8.

Next, after depositing a SiO ₂ film having a film thickness of 100 nm on the interlayer insulating film by a CVD method, contact holes are patterned by a photoresist by a normal lithography process, and then the SiO ₂ film and A contact hole is formed by dry etching the interlayer insulating film. Next, after removing the photoresist by ashing with oxygen plasma, when observing the shape of the contact hole with an electron microscope, almost no side etching was observed.

When the contact resistance of the contact hole formed in the above-mentioned interlayer insulating film was measured, it was found that the SiO ₂ film (plasma TEO) formed by the usual CVD method was used.
No increase in contact resistance was observed as compared with the interlayer insulating film made of S film).

Moisture resistance can be improved by increasing or decreasing the amount of hexamethyldisiloxane added to the inorganic silica sol solution.
The oxygen plasma resistance and the relative dielectric constant can be adjusted.

The same effect can be obtained by using triethylchlorosilane or hexamethyldisilazane as the silylating agent instead of hexamethyldisiloxane.

In order to adjust the coatability of the silica sol, the silylating agent may be dissolved in a suitable non-aqueous solvent such as hexane, acetone, ethanol and then mixed with the inorganic silica sol solution.

The second method of manufacturing the semiconductor device according to the fourth embodiment will be described below.

Solution of inorganic silica sol (commercially available inorganic SOG
It is a solution and has a SiO ₂ conversion concentration of 3 to 20 wt%. ) On a semiconductor substrate by spin coating
After coating at rpm to form a wet gel film, the semiconductor substrate is heated to 160 ° C. and exposed to a gas obtained by vaporizing hexamethyldisilazane as a silylating agent for 10 minutes.
After that, when the semiconductor substrate was heat-treated in an electric furnace in a nitrogen atmosphere at a temperature of 450 ° C. for 30 minutes, an interlayer insulating film made of an SOG film having a film thickness of 380 nm was formed on the semiconductor substrate.

When the interlayer insulating film thus formed was analyzed by infrared spectroscopy, it was confirmed that a silicon-methyl group bond was observed and that a silylation reaction had occurred on the surface of the inorganic silanol condensate fine particles. did it. Also,
When the dielectric constant of this interlayer insulating film was measured by the CV method, the relative dielectric constant was about 2.9.

Next, after depositing a SiO ₂ film having a film thickness of 100 nm on the interlayer insulating film by a CVD method, contact holes are patterned by a photoresist by a usual lithography process, and then the SiO ₂ film and A contact hole is formed by dry etching the interlayer insulating film. Next, after removing the photoresist by ashing with oxygen plasma, when observing the shape of the contact hole with an electron microscope, almost no side etching was observed.

Further, when the contact resistance of the contact hole formed in the above-mentioned interlayer insulating film was measured, the SiO ₂ film (plasma TEO) formed by the ordinary CVD method was measured.
No increase in contact resistance was observed as compared with the interlayer insulating film made of S film).

The rate of silylation of residual silanol groups can be adjusted by changing the exposure temperature and exposure time by the gasified silylating agent. In this way, the humidity resistance, oxygen plasma resistance, and relative dielectric constant can be adjusted.

The same effect can be obtained by using triethylchlorosilane or hexamethyldisilazane as the silylating agent instead of hexamethyldisilazane.

The third manufacturing method of the semiconductor device according to the fourth embodiment will be described below.

Solution of inorganic silica sol (commercially available inorganic SOG
It is a solution and has a SiO ₂ conversion concentration of 3 to 20 wt%. ) On a semiconductor substrate by spin coating
After coating at rpm to form a wet gel film, hexamethyldisilazane as a silylating agent is dropped on the semiconductor substrate, and then left for 10 minutes, followed by spin drying. Then, using an electric furnace, 450 in a nitrogen atmosphere
When heat treatment was performed at a temperature of 30 ° C. for 30 minutes, an interlayer insulating film made of an SOG film having a film thickness of 380 nm was formed on the semiconductor substrate.

When the interlayer insulating film thus formed was analyzed by infrared spectroscopy, it was confirmed that a silicon-methyl group bond was observed and a silylation reaction had occurred on the surface of the inorganic silanol condensate fine particles. did it. Also,
When the dielectric constant of this interlayer insulating film was measured by the CV method, the relative dielectric constant was about 3.0.

Next, after depositing a SiO ₂ film having a thickness of 100 nm on the interlayer insulating film by a CVD method, a contact hole pattern is formed by a photoresist by an ordinary lithography process, and then the SiO ₂ film and A contact hole is formed by dry etching the interlayer insulating film. Next, after removing the photoresist by ashing with oxygen plasma, when observing the shape of the contact hole with an electron microscope, almost no side etching was observed.

Further, when the contact resistance of the contact hole formed in the above-mentioned interlayer insulating film was measured, the SiO ₂ film (plasma TEO) formed by the ordinary CVD method was measured.
No increase in contact resistance was observed as compared with the interlayer insulating film made of S film).

The rate of silylation of the residual silanol groups can be adjusted by changing the reaction temperature and reaction time with the silylating agent. In this way, moisture resistance,
Oxygen plasma resistance and relative permittivity can be adjusted.

In place of the third manufacturing method, the silylating agent may be dissolved in a non-aqueous solvent and then dropped on the wet gel film on the semiconductor substrate. Further, the semiconductor substrate on which the wet gel film is formed may be immersed in a silylating agent or a solution of the silylating agent heated to a boiling point or lower.

The same effect can be obtained by using triethylchlorosilane or hexamethyldisiloxane as the silylating agent instead of hexamethyldisilazane.

The fourth manufacturing method of the semiconductor device according to the fourth embodiment will be described below.

Solution of inorganic silica sol (commercially available inorganic SOG
It is a solution and has a SiO ₂ conversion concentration of 3 to 20 wt%. ) On a semiconductor substrate by spin coating
After coating at rpm to form a wet gel film, the semiconductor substrate is placed in an airtight container filled with a gas of hexamethyldisilazane as a silylating agent. After that, a silylation reaction is caused to occur in the airtight container at a temperature of 200 ° C. and a pressure of 50 atm for 10 minutes, and then the pressure is returned to 1 atm with the temperature kept constant to dry the wet gel film. I did. After that, when the semiconductor substrate was heat-treated in an electric furnace in a nitrogen atmosphere at a temperature of 450 ° C. for 30 minutes, an interlayer insulating film made of an SOG film having a film thickness of 380 nm was formed on the semiconductor substrate.

When the interlayer insulating film thus formed was analyzed by infrared spectroscopy, it was confirmed that a silicon-methyl group bond was observed and a silylation reaction occurred on the surface of the inorganic silanol condensate fine particles. did it. Also,
When the dielectric constant of this interlayer insulating film was measured by the CV method, the relative dielectric constant was about 3.0.

Next, after depositing a SiO ₂ film having a thickness of 100nm by CVD on the interlayer insulating film layer performs pattern out of contactee holes due photoresist by conventional lithography process, then, the SiO ₂ film and A contact hole is formed by dry etching the interlayer insulating film. Next, after removing the photoresist by ashing with oxygen plasma, when observing the shape of the contact hole with an electron microscope, almost no side etching was observed.

When the contact resistance of the contact hole formed in the above-mentioned interlayer insulating film was measured, the SiO ₂ film (plasma TEO) formed by the ordinary CVD method was measured.
No increase in contact resistance was observed as compared with the interlayer insulating film made of S film).

The rate of silylation of residual silanol groups can be adjusted by changing the reaction temperature, reaction pressure and reaction time with the silylating agent. In this way, the humidity resistance, oxygen plasma resistance, and relative dielectric constant can be adjusted.

Instead of the fourth manufacturing method, the semiconductor substrate on which the wet gel film is formed may be immersed in a solution in which a silylating agent is dissolved in a non-aqueous solvent, and reacted at high temperature and high pressure. . Hexane, acetone, ethanol and the like can be used as the non-aqueous solvent.

The same effect can be obtained by using triethylchlorosilane or hexamethyldisiloxane as the silylating agent instead of hexamethyldisilazane.

[0100]

According to the semiconductor device of the first aspect of the present invention, since the second silanol condensate fine particles are composed of only silicon-oxygen bonds and are not oxidatively decomposed by oxygen plasma, oxidative decomposition proceeds deeply into the insulating film. It is possible to avoid the situation and it is difficult for moisture to be generated from the insulating film.
It is possible to prevent thinning and disconnection of the upper metal wiring in the semiconductor device, and reduce contact resistance between the lower metal wiring and the upper metal wiring. Also,
A first insulating film containing at least one bond between fluorine and silicon and an organic group and silicon;
Since the fine particles of the silanol condensate are dispersed, the relative dielectric constant becomes small.

According to the semiconductor device of the second aspect of the present invention, the silanol condensate particles forming the capsule-shaped particles do not come into direct contact with oxygen plasma, and the silanol containing only the bond between surface oxygen and silicon is oxygen plasma. Since it is not oxidatively decomposed by the above, it is possible to avoid a situation in which the insulating film is oxidatively decomposed, and it is difficult for moisture to be generated from the insulating film. It is possible to reduce the contact resistance between the wiring and the upper metal wiring. Further, since the insulating film is made of silanol condensate fine particles containing at least one bond of the bond between fluorine and silicon and the bond between the organic group and silicon, the relative dielectric constant becomes small.

According to the semiconductor device of the third aspect of the present invention, in the capsule-shaped particles located on the outermost surface of the insulating film, at least one of the bond between fluorine and silicon and the bond between an organic group and silicon is bonded. Silanol containing is oxidatively decomposed by oxygen plasma, but the silanol condensate fine particles present inside the capsule-shaped particles are not oxidatively decomposed by oxygen plasma. Since moisture is unlikely to be generated, it is possible to prevent thinning and disconnection of the upper metal wiring in the semiconductor device, and it is possible to reduce the contact resistance between the lower metal wiring and the upper metal wiring. Further, since the insulating film is composed of capsule-like particles chemically modified with silanol containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon, the relative dielectric constant becomes small.

According to the semiconductor device of the fourth aspect of the invention, the silyl groups on the surface of the silanol condensate fine particles located on the outermost surface of the insulating film are eliminated by oxygen plasma, but the silanol condensate fine particles are oxidized by oxygen plasma. Since it is not decomposed, oxidative decomposition by oxygen plasma does not proceed in the insulating film and moisture is less likely to be generated from the insulating film.Thus, thinning and disconnection of the upper metal wiring in the semiconductor device can be prevented and the lower metal wiring and the upper metal wiring can be prevented. The contact resistance with the metal wiring can be reduced. Moreover, since the insulating film is made of silanol condensate fine particles or siloxane polymer in which at least a part of hydroxyl groups is substituted with a silyl group, the relative dielectric constant becomes small.

According to the semiconductor device manufacturing method of the fifth aspect of the present invention, the composite layer in which the first silanol condensate fine particles and the second silanol condensate fine particles are mixed in a dispersed state is formed on the semiconductor substrate. Therefore, the semiconductor device according to the first aspect of the invention can be reliably manufactured.

According to the method for manufacturing a semiconductor device of the sixth aspect of the present invention, an aggregate layer of capsule-like particles is formed on a semiconductor substrate in which fine particles of a silanol condensate are chemically modified with silanol containing only a bond between oxygen and silicon. Therefore, the semiconductor device according to the second aspect of the invention can be reliably manufactured.

According to the method of manufacturing a semiconductor device of the eighth aspect, the silanol condensate fine particles have at least one bond selected from the bonds of fluorine and silicon and the bonds of organic groups and silicon on the semiconductor substrate. Since the aggregate layer of the capsule-like particles chemically modified by the silanol contained therein is formed, the semiconductor device according to the invention of claim 3 can be reliably manufactured.

According to the method for manufacturing a semiconductor device of the tenth aspect of the present invention, a silanol condensation in which only a bond between oxygen and silicon is contained and at least a part of the hydroxyl groups on the surface is substituted with a silyl group on the semiconductor substrate. Since the aggregated layer of body particles is formed, the semiconductor device according to the invention of claim 4 can be reliably manufactured.

According to the semiconductor device manufacturing method of the eleventh aspect of the present invention, the silica sol solution containing the silylated condensate of fine particles of the silanol can be supplied onto the semiconductor substrate.

According to the semiconductor device manufacturing method of the twelfth aspect of the present invention, the surface of the silanol condensate fine particles can be silylated on the semiconductor substrate.

According to the method for manufacturing a semiconductor device of the thirteenth aspect of the present invention, the gas-state silylation is performed while heating the semiconductor substrate to which the silica sol solution containing the silanol condensate fine particles containing only the bond between oxygen and silicon is supplied. Since the agent is supplied, silylation of the silanol condensate fine particles is promoted.

According to the semiconductor device manufacturing method of the fourteenth aspect of the present invention, after the hydroxyl groups on the surface of the silanol condensate fine particles on the semiconductor substrate are replaced with silyl groups, the semiconductor substrate is heated to produce the surface of the silanol condensate fine particles. Since the residual hydroxyl group of (3) is substituted with a silyl group, silanol condensate fine particles can be reliably silylated.

According to the semiconductor device manufacturing method of the fifteenth aspect, the second step includes a step of silylating the surface of the silanol condensate fine particles under high pressure.
Silylation of silanol condensate fine particles is promoted well.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a structure of an insulating film in a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing the structure of an insulating film in a semiconductor device according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view showing a structure of an insulating film in a semiconductor device according to a third embodiment of the present invention.

FIG. 4 is a schematic diagram showing a molecular structure of fine particles of an inorganic silanol condensate in each embodiment of the present invention.

FIG. 5 is a schematic view showing the molecular structure of fine particles of a fluorinated silanol condensate in each embodiment of the present invention.

FIG. 6 is a cross-sectional view showing each step of the method for manufacturing the semiconductor device according to each embodiment of the present invention.

FIG. 7 is a schematic diagram showing a molecular structure of capsule-shaped particles in a semiconductor device according to a second embodiment of the present invention.

FIG. 8 is a schematic diagram showing a molecular structure of silylated silanol condensate fine particles in a semiconductor device according to a fourth embodiment of the present invention.

9 is a chemical formula showing an example of a silyl group in the molecular structure of the silylated silanol condensate fine particles shown in FIG.

FIG. 10 is a schematic view showing a molecular structure of organic silanol condensate fine particles in the related art and each embodiment of the present invention.

FIG. 11 is a cross-sectional view showing each manufacturing step of a conventional semiconductor device manufacturing method.

FIG. 12 is a cross-sectional view showing each manufacturing step of a conventional semiconductor device manufacturing method.

FIG. 13 is a cross-sectional view showing each manufacturing step of a conventional semiconductor device manufacturing method.

[Explanation of symbols]

1 Organic Silanol Condensate Fine Particles 2 Inorganic Silanol Condensate Fine Particles 3 Organic Silanol Condensate Fine Particles 4 Inorganic Silanol 5 Capsule Particles 6 Inorganic Silanol Condensate Fine Particles 7 Organic Silanol 8 Capsule Particles 10 Semiconductor Substrate 11 Metal Wiring 12 First SiO ₂ Film 13 Interlayer insulating film 14 Second SiO ₂ film 15 Photoresist 16 Contact hole

Claims (16)

[Claims] 1. A semiconductor device comprising a metal film formed on a semiconductor substrate and an insulating film formed around the metal film, wherein the insulating film comprises a bond between fluorine and silicon and an organic group. A composite layer in which fine particles of first silanol condensate containing at least one bond of silicon and fine particles of second silanol condensate containing only bond of oxygen and silicon are mixed in a dispersed state. A semiconductor device characterized by the above. 2. A semiconductor device comprising a metal film formed on a semiconductor substrate and an insulating film formed around the metal film, wherein the insulating film comprises a bond between fluorine and silicon and an organic group. A semiconductor device, wherein the silanol condensate fine particles containing at least one bond with silicon are composed of an assembly layer of capsule-like particles chemically modified with silanol containing only bonds with oxygen and silicon. 3. A semiconductor device comprising a metal film formed on a semiconductor substrate and an insulating film formed around the metal film, wherein the insulating film is a silanol containing only a bond of oxygen and silicon. A semiconductor device, wherein the condensate fine particles are an aggregate layer of capsule-like particles chemically modified with silanol containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon. 4. A semiconductor device comprising a metal film formed on a semiconductor substrate and an insulating film formed around the metal film, wherein the insulating film contains at least a bond of oxygen and silicon, A semiconductor device comprising a silanol condensate fine particle in which at least a part of surface hydroxyl groups is substituted with a silyl group or an aggregate layer of siloxane polymers. 5. A first silica sol solution containing first silanol condensate fine particles containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon, and a bond between oxygen and silicon. Mixing a second silica sol solution containing second silanol condensate fine particles containing only the liquid phase to obtain a mixed silica sol solution; and supplying the mixed silica sol solution onto a semiconductor substrate having a metal film formed thereon. Then, a heat treatment is applied to the semiconductor substrate to form an insulating film composed of a composite layer in which the first silanol condensate fine particles and the second silanol condensate fine particles are mixed in a dispersed state. A method of manufacturing a semiconductor device, comprising: 6. A silica sol solution containing fine particles of a silanol condensate containing at least one bond of a bond between fluorine and silicon and a bond between an organic group and silicon, and a silicon alkoxide containing no bond between silicon and an alkyl group. And a step of obtaining a mixed silica sol solution by mixing the above, after supplying the mixed silica sol solution onto the semiconductor substrate on which the metal film is formed, by subjecting the semiconductor substrate to a heat treatment, the silanol condensate fine particles become oxygen and silicon. And a step of forming an insulating film made of an aggregate layer of capsule-like particles chemically modified with silanol containing only a bond with. 7. The semiconductor according to claim 6, wherein the silicon alkoxide includes at least one of tetraethoxysilane, tetramethoxysilane, triethoxysilane, trimethoxysilane, and triethoxyfluorosilane. Device manufacturing method. 8. A step of mixing a silica sol solution containing fine particles of a silanol condensate containing only a bond of oxygen and silicon with a silicon alkoxide containing a bond of silicon and an alkyl group to obtain a mixed silica sol solution; After the solution is supplied onto the semiconductor substrate on which the metal film is formed, the semiconductor substrate is subjected to heat treatment so that the silanol condensate fine particles form at least one of a bond between fluorine and silicon and a bond between an organic group and silicon. And a step of forming an insulating film composed of an aggregate layer of capsule-like particles chemically modified with silanol containing one bond. 9. The method of manufacturing a semiconductor device according to claim 8, wherein the silicon alkoxide contains triethoxymethylsilane. 10. A method for silylating the surface of the silanol condensate fine particles in a silica sol solution containing the silanol condensate fine particles containing only a bond between oxygen and silicon.
And the step of, on the semiconductor substrate on which the metal film is formed, after supplying a silica sol solution containing silanol condensate fine particles whose surface is silylated, heat-treating the semiconductor substrate to obtain oxygen and silicon. A second step of forming an insulating film comprising an aggregate layer of fine particles of silanol condensate containing only bonds and at least a part of the hydroxyl groups on the surface of which are substituted with silyl groups. Manufacturing method. 11. The first step is a step of reacting the silica sol solution with a silylating agent in a liquid phase to replace at least a part of hydroxyl groups on the surface of the silanol condensate fine particles with a silyl group. 11. The method for manufacturing a semiconductor device according to claim 10, further comprising: 12. A first step of supplying a silica sol solution containing fine particles of a silanol condensate containing only a bond of oxygen and silicon onto a semiconductor substrate having a metal film formed thereon, and the silanol in the silica sol solution. The second step of silylating the surface of the condensate particles and the heat treatment of the semiconductor substrate resulted in substitution of at least a part of the hydroxyl groups on the surface containing only the bond between oxygen and silicon with a silyl group. And a third step of forming an insulating film composed of an aggregate layer of fine particles of a silanol condensate. 13. The method of manufacturing a semiconductor device according to claim 12, wherein the second step includes a step of supplying a silylating agent in a gas state to the heated semiconductor substrate. 14. The second step, wherein the silica sol solution and the silylating agent are reacted in a liquid phase on the semiconductor substrate to substitute hydroxyl groups on the surface of the silanol condensate fine particles with silyl groups, Heating the semiconductor substrate to replace residual hydroxyl groups on the surface of the silanol condensate fine particles with silyl groups.
2. The method for manufacturing a semiconductor device according to 2. 15. The method of manufacturing a semiconductor device according to claim 13, wherein the second step includes a step of silylating the surface of the silanol condensate fine particles under high pressure. 16. The semiconductor according to claim 12, wherein the silylating agent contains at least one of hexamethyldisilazane, hexamethyldisiloxane, and trimethylchlorosilane. Device manufacturing method.