KR102246692B1 - Compound, organic layer composition, organic layer, and method of forming patterns - Google Patents

Abstract

상기 화학식 1에서, A B 및 n의 정의는 명세서 내 기재한 바와 같다.It relates to a compound including 1 to 4 structural units represented by Formula 1 below, an organic layer composition including the compound, and a pattern formation method using the organic layer composition.
[Formula 1]

In Formula 1, the definitions of AB and n are as described in the specification.

Description

Compound, organic film composition, organic film and pattern formation method {COMPOUND, ORGANIC LAYER COMPOSITION, ORGANIC LAYER, AND METHOD OF FORMING PATTERNS}

It relates to a novel compound, an organic film composition comprising the compound, an organic film formed from the organic film composition, and a pattern forming method using the organic film composition.

Recently, the semiconductor industry is developing from a pattern of several hundred nanometers to an ultra-fine technology having a pattern of several to tens of nanometers. Effective lithographic techniques are essential to realize such ultra-fine technology.

A typical lithographic technique involves forming a material layer on a semiconductor substrate, coating a photoresist layer thereon, exposing and developing to form a photoresist pattern, and then etching the material layer using the photoresist pattern as a mask. do.

In recent years, as the size of the pattern to be formed decreases, it is difficult to form a fine pattern having a good profile using only the above-described typical lithographic technique. Accordingly, a fine pattern may be formed by forming an organic layer called a hardmask layer between the material layer to be etched and the photoresist layer. The hard mask layer serves as an interlayer that transfers the fine pattern of the photoresist to the material layer through a selective etching process. Therefore, the hard mask layer needs heat resistance and corrosion resistance so that it can withstand multiple etching processes.

In addition, when there is a step difference in the substrate to be processed in the multiple patterning process, or when a pattern dense portion and an area without a pattern exist together on the wafer, the hard mask layer filled in the pattern has a planarization characteristic that can minimize the step difference between patterns. This is especially important.

Therefore, there is a need for a material for a film structure that can satisfy the above-described properties.

One embodiment provides a novel compound having excellent etch resistance while securing solubility.

Another embodiment provides an organic film composition comprising the compound.

Another embodiment provides an organic film formed by curing the organic film composition.

Another embodiment provides a pattern formation method using the organic film composition.

According to one embodiment, there is provided a compound containing 1 to 4 structural units represented by the following formula (1).

[Formula 1]

In Formula 1,

A and B are each independently a substituted or unsubstituted hexagonal ring or a pentagonal ring,

When A is a hexagonal ring, n is an integer from 3 to 6, and when A is a pentagonal ring, n is an integer from 3 to 5:

However, when the compound includes two or more structural units represented by Chemical Formula 1, the connection point is not particularly limited.

In Formula 1, A and B may each independently be a substituted or unsubstituted benzene ring.

The structural unit represented by Formula 1 may be represented by the following Formula 2.

[Formula 2]

In Chemical Formula 2,

R ¹ to R ⁶ are each independently a hydroxy group, a halogen group, a substituted or unsubstituted C1 to C30 alkoxy group, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C2 to C30 alkenyl group, a substituted or unsubstituted A C2 to C30 alkynyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C1 to C30 heteroalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,

a to f are each independently an integer of 0 to 4.

According to another embodiment, an organic film composition including the above-described compound and a solvent is provided.

The compound may be included in an amount of 0.1% to 30% by weight based on the total content of the organic layer composition.

According to another embodiment, an organic film formed by curing the above-described organic film composition is provided.

The curing may be performed by heat treatment at a temperature of 100 to 1,000°C.

The curing may be performed by heat treatment at a temperature of 600 to 1,000°C.

The heat treatment may be performed while purging with nitrogen.

According to another embodiment, the step of forming a material layer on a substrate, applying the above-described organic film composition on the material layer, forming a hardmask layer by heat treatment of the organic film composition, on the hardmask layer Forming a silicon-containing thin film layer, forming a photoresist layer on the silicon-containing thin film layer, exposing and developing the photoresist layer to form a photoresist pattern, the silicon-containing thin film layer and It provides a pattern forming method comprising selectively removing the hardmask layer, exposing a portion of the material layer, and etching the exposed portion of the material layer.

The step of applying the organic film composition may be performed by a spin-on coating method.

It may further include forming a bottom anti-reflective layer (BARC) before forming the photoresist layer.

The heat treatment may be performed at a temperature of 100 to 1,000°C.

The heat treatment may be performed at a temperature of 600 to 1,000°C.

The heat treatment may be performed while purging with nitrogen.

The compound according to the present invention has a structure including 1 to 4 structural units containing a plurality of hexagonal rings or pentagonal rings, and each of the single rings included in the compound may be fused to each other in the heat treatment process. The compound has excellent etch resistance and etch selectivity. Since the compound exists in the form of a single ring rather than a fused ring before heat treatment, the solubility is relatively excellent compared to a compound that already contains a fused ring in its structure, and therefore, the compound can satisfy not only etch resistance but also solubility properties at the same time. have.

1 is a flowchart illustrating a method of forming a pattern according to an exemplary embodiment.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the embodiments of the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

Unless otherwise defined herein, the term'substituted' means that the hydrogen atom in the compound is a halogen atom (F, Br, Cl, or I), a hydroxy group, a nitro group, a cyano group, an amino group, an azido group, an amidino group, Hydrazino group, hydrazono group, carbonyl group, carbamyl group, thiol group, ester group, carboxyl group or salt thereof, sulfonic acid group or salt thereof, phosphoric acid or salt thereof, C1 to C30 alkyl group, C2 to C30 alkenyl group, C2 to C30 alky Nyl group, C6 to C30 aryl group, C7 to C30 arylalkyl group, C1 to C30 alkoxy group, C1 to C20 heteroalkyl group, C3 to C20 heteroarylalkyl group, C3 to C30 cycloalkyl group, C3 to C15 cycloalkenyl group, C6 to C15 It means substituted with a substituent selected from a cycloalkynyl group, a C3 to C30 heterocycloalkyl group, and combinations thereof.

In addition, unless otherwise defined in the specification,'hetero' means containing 1 to 3 heteroatoms selected from N, O, S, and P.

In addition, unless otherwise defined in the specification,'*' indicates a connection point of a compound or a compound moiety.

Hereinafter, a compound according to an embodiment will be described.

The compound according to an embodiment includes 1 to 4 structural units represented by the following formula (1).

[Formula 1]

In Formula 1,

A and B are each independently a substituted or unsubstituted hexagonal ring or a pentagonal ring,

When A is a hexagonal ring, n is an integer of 3 to 6, and when A is a pentagonal ring, n is an integer of 3 to 5.

However, when the compound includes two or more structural units represented by Formula 1, the connection point between the structural units is not particularly limited.

The structural unit represented by Formula 1 has a structure in which 3 to 6 substituents represented by B are connected to the core represented by A. Each of A and B is independently a hexagonal ring or a pentagonal ring, and A and B may be an aliphatic ring group or an aromatic ring group. For example, A may be independently a substituted or unsubstituted benzene ring, but is not limited thereto. For example, in Formula 1, both A and B may be substituted or unsubstituted benzene rings, for example, 3, 4, 5, or 6 benzene rings may be substituted on the benzene ring of the core. .

For example, the structural unit may be represented by Formula 2 below, but is not limited thereto.

[Formula 2]

In Chemical Formula 2,

R ¹ to R ⁶ are each independently a hydroxy group, a halogen group, a substituted or unsubstituted C1 to C30 alkoxy group, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C2 to C30 alkenyl group, a substituted or unsubstituted A C2 to C30 alkynyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C1 to C30 heteroalkyl group, a substituted or unsubstituted C2 to C30 heteroaryl group, or a combination thereof,

a to f are each independently an integer of 0 to 4.

For example, when the compound includes one structural unit represented by Formula 2, the compound may be represented by Formula 2, for example.

For example, when the compound includes two structural units represented by Formula 2, the compound may be represented by Formula 3 below.

[Formula 3]

In Chemical Formula 3,

The definitions of R ¹ to R ⁶ , and a to f are the same as in Formula 2,

The definition of R ⁷ to R ¹² is the same as R ¹ to R ⁶ , and the definition of g to l is the same as the definition of a to f.

It is natural that the compound may include three or four structural units represented by Formula 2, and the arrangement of each structural unit is not limited, for example, each structural unit may be connected in parallel with each other, for example, one Other structural units may be connected so that they extend radially around the structural unit of.

Since the compound is a high carbon compound containing 1 to 4 structural units represented by the above-described Chemical Formula 1, it is basically excellent in etch resistance. In addition, each of the single rings included in the compound may be fused to each other in the heat treatment process, for example, when heat is applied to the compound at a predetermined temperature or higher in a baking or annealing process (e.g., 100 to 1.000°C, more specifically 600 to 1.000°C) The compound causes a dehydrogenation reaction (see Scheme 1 below), so that the compound can form a dense structure close to that of graphene. do. Accordingly, when the compound is used as an organic film material, an organic film having more enhanced etch resistance can be provided.

[Scheme 1]

In addition, since the compound exists in the form of a single ring rather than a fused ring before heat treatment, the solubility is relatively excellent compared to a compound that already contains a fused ring in its structure. I can be satisfied.

The number of structural units represented by Formula 1 can be selected within the range of 1 to 4, and the number of structural units within the range is selected to determine the carbon content and solvent of the organic film composition (eg, hardmask composition). It can be optimized by adjusting the solubility for

For example, the compound may be prepared by reacting a compound having a Cyclopentadienone structure (Compound 1) and Diethynyl benzene, diphenylacetylene or 1,4-Bis-phenylethynyl-benzene (hereinafter, Compound 2) with each other, for example Compound 1 may be Tetraphenylcyclopentadienone, but this is only an example and is not limited thereto.

According to another embodiment, an organic film composition including the above-described compound and a solvent is provided.

The solvent is not particularly limited as long as it has sufficient solubility or dispersibility in the compound, for example, propylene glycol, propylene glycol diacetate, methoxy propanediol, diethylene glycol, diethylene glycol butyl ether, tri(ethylene glycol) mono Methyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, cyclohexanone, ethyl lactate, gamma-butyrolactone, N,N-dimethylformamide, N,N-dimethylacetamide, methylpyrrolidone , Methylpyrrolidinone, acetylacetone, and ethyl 3-ethoxypropionate.

The compound may be included in an amount of about 0.1 to 50% by weight, about 0.1 to 30% by weight, or about 0.1 to 15% by weight based on the total content of the organic layer composition. When the compound is included in the above range, the thickness, surface roughness, and level of planarization of the organic film can be controlled.

The organic film composition may further include additives such as a surfactant, a crosslinking agent, a thermal acid generator, and a plasticizer.

The surfactant may be, for example, a fluoroalkyl-based compound, an alkylbenzene sulfonate, an alkylpyridinium salt, a polyethylene glycol, or a quaternary ammonium salt, but is not limited thereto.

Examples of the crosslinking agent include melamine-based, substituted urea-based, or these polymers. Preferably, a crosslinking agent having at least two crosslinking substituents, for example, methoxymethylated glycoruryl, butoxymethylated glycoruryl, methoxymethylated melamine, butoxymethylated melamine, methoxymethylated benzoguanamine, butoxy Compounds such as methylated benzoguanamine, methoxymethylated urea, butoxymethylated urea, methoxymethylated thiourea, or butoxymethylated thiourea may be used.

In addition, as the crosslinking agent, a crosslinking agent having high heat resistance may be used. As a crosslinking agent having high heat resistance, a compound containing a crosslinking substituent having an aromatic ring (for example, a benzene ring or a naphthalene ring) in the molecule can be used.

The thermal acid generator is an acidic compound such as p-toluenesulfonic acid, trifluoromethanesulfonic acid, pyridinium p-toluenesulfonic acid, salicylic acid, sulfosalicylic acid, citric acid, benzoic acid, hydroxybenzoic acid, naphthalenecarboxylic acid or/and 2,4 ,4,6-tetrabromocyclohexadienone, benzointosylate, 2-nitrobenzyltosylate, and other organic fonate alkyl esters may be used, but the present invention is not limited thereto.

The additive may be included in an amount of about 0.001 to 40 parts by weight based on 100 parts by weight of the organic layer composition. By including it in the above range, solubility can be improved without changing the optical properties of the organic film composition.

According to another embodiment, an organic film manufactured using the organic film composition described above is provided. The organic film may be in a form cured through a heat treatment process after coating the above-described organic film composition on a substrate, for example, and may include an organic thin film used in electronic devices such as a hard mask layer, a planarization film, a sacrificial film, and a filler. have. The curing may include heat treatment at a temperature of about 100 to 1,000°C, and specifically, heat treatment at a temperature of about 600 to 1,000°C. The heat treatment may be performed while purging with nitrogen.

Hereinafter, a method of forming a pattern using the above-described organic film composition will be described with reference to FIG. 1.

1 is a flowchart illustrating a method of forming a pattern according to an exemplary embodiment.

A pattern formation method according to an embodiment includes forming a material layer on a substrate (S1), applying the above-described organic film composition on the material layer (S2), and forming a hardmask layer by heat-treating the organic film composition. (S3), forming a silicon-containing thin film layer on the hardmask layer (S4), forming a photoresist layer on the silicon-containing thin film layer (S5), and exposing and developing the photoresist layer to form a photoresist pattern Forming (S6), selectively removing the silicon-containing thin film layer and the hardmask layer using the photoresist pattern, and exposing a portion of the material layer (S7), and the exposed portion of the material layer And etching (S8).

The substrate may be, for example, a silicon wafer, a glass substrate, or a polymer substrate.

The material layer is a material to be finally patterned, and may be, for example, a metal layer such as aluminum or copper, a semiconductor layer such as silicon, or an insulating layer such as silicon oxide or silicon nitride. The material layer can be formed, for example, by a chemical vapor deposition method.

The organic film composition is as described above, and may be prepared in a solution form and applied by a spin-on coating method. At this time, the coating thickness of the organic layer composition is not particularly limited, but may be applied to a thickness of, for example, about 50 to 200,000 Å.

The step of heat-treating the organic film composition may be performed at, for example, about 100 to 1,000° C. for about 10 seconds to 1 hour, and more specifically, may be performed at a temperature of about 600 to 1,000° C. By heat-treating the organic film composition at a high temperature, a single ring of the compound contained in the organic film composition forms a fused ring, so that the etching resistance of the thin film may be further improved. The heat treatment process may be performed while purging with nitrogen, for example.

The silicon-containing thin film layer may be formed of, for example, a material such as SiCN, SiOC, SiON, SiOCN, SiC, SiO and/or SiN.

In addition, before forming the photoresist layer, a bottom anti-reflective coating (BARC) may be further formed on the silicon-containing thin film layer.

The step of exposing the photoresist layer may be performed using, for example, ArF, KrF, or EUV. In addition, after exposure, a heat treatment process may be performed at about 100 to 800°C.

The step of etching the exposed portion of the material layer may be performed by dry etching using an etching gas, and the etching gas may be, for example, CHF ₃ , CF ₄ , Cl ₂ , BCl _3, and a mixed gas thereof.

The etched material layer may be formed in a plurality of patterns, and the plurality of patterns may be various, such as a metal pattern, a semiconductor pattern, and an insulating pattern, and may be applied as various patterns in, for example, a semiconductor integrated circuit device.

The embodiments of the present invention described above will be described in more detail through the following examples. However, the following examples are for illustrative purposes only and do not limit the scope of the present invention.

Synthesis example

Synthesis example One

Add 40 g of benzophenone to a 100 ml flask, and add 0.021 mol of tetraphenylcyclopentadienone and 0.043 mol of diphenylacetylene. When heated to 300℃, CO gas is generated. After 1 hour, the reaction was terminated and diphenyl ether was added, followed by washing with benzene to obtain a compound.

Synthesis example 2

In a 100 ml flask, 10 g (0.028 mol) of 4,4-bis (phenylethynyl)-biphenyl, 21.7 g (0.056 mol) of tetraphenylcyclopentadienone, and 20 g of benzophenone were heated to 280° C. in argon atmospheric conditions, and the reaction was carried out for 3 hours. Cool to room temperature to terminate the reaction, stir with 1 liter of dichloromethane, and filter. After washing the powder with additional dichloromethane and acetone, it is extracted with hot benzonitrile to obtain the desired compound.

Comparative Synthesis Example One

1-naphthol 28.83 g (0.2 mol), benzoperylene 41.4 g (0.15 mol), and paraformaldehyde 12.0 g (0.34 mol) were added to the flask, followed by propylene glycol monomethyl ether acetate (PGMEA) 162 g. Next, 0.19 g of p-toluene sulfonic acid monohydrate was added, followed by stirring at a temperature of 90 to 100°C for 5 to 12 hours. Samples are collected from the polymerization reaction product at 1 hour intervals, the weight average molecular weight of the sample is measured, and the reaction is completed when the weight average molecular weight is 1,800 to 2,500. After the polymerization reaction was completed, the reaction product was gradually cooled to room temperature, and the reaction product was added to 40 g of distilled water and 400 g of methanol, stirred vigorously, and allowed to stand. The supernatant was removed and the precipitate was dissolved in 80 g of propylene glycol monomethyl ether acetate (PGMEA), stirred vigorously with 320 g of methanol, and allowed to stand (1st). At this time, the obtained supernatant is removed again, and the precipitate is dissolved in 80 g of propylene glycol monomethyl ether acetate (PGMEA) (secondary). The first and second processes are referred to as a one-time purification process, and this purification process is performed three times in total. After dissolving the purified polymer in 80 g of propylene glycol monomethyl ether acetate (PGMEA), methanol and distilled water remaining in the solution are removed under reduced pressure to obtain a compound containing a structural unit represented by the following formula (A).

[Formula A]

Comparative Synthesis Example 2

In a 500 mL 2-neck round bottom flask equipped with a condenser, 4,4'-(9H-fluoren-9-ylidene)bisphenol 35.0g(0.10mol), 1,4-bis(methoxymethyl)benzene 16.6g(0.10mol), diethyl After adding 15.4 g (0.10 mol) of sulfate and 134 g of PGMEA, the mixture was stirred at 110° C. for 24 to 48 hours to proceed with polymerization. When the weight average molecular weight is 1,000 to 1,500, the reaction is completed. After the reaction, the reaction product was cooled to room temperature, diluted with 400 g of ethyl acetate, and washed with distilled water (400 g x 10 times). After the organic layer was concentrated under reduced pressure, it was diluted with 200 g of THF and added dropwise to 1 kg of hexane to obtain a precipitate. After filtering and drying the precipitate, a compound containing a structural unit represented by the following formula (B) is obtained (Mw: 1,700).

[Formula B]

Hard mask Preparation of the composition

Example One

1.5 g of the compound obtained in Synthesis Example 1 was dissolved in 10 g of a mixed solvent of propylene glycol monomethyl ether acetate and cyclohexanone (7:3 (v/v)), and filtered to a hard mask. The composition was prepared.

Example 2

A hardmask composition was prepared in the same manner as in Example 1, except that the compound obtained in Synthesis Example 2 was used instead of the compound obtained in Synthesis Example 1.

Comparative example One

A hardmask composition was prepared in the same manner as in Example 1, except that the compound obtained in Comparative Synthesis Example 1 was used instead of the compound obtained in Synthesis Example 1.

Comparative example 2

A hardmask composition was prepared in the same manner as in Example 1, except that the compound obtained in Comparative Synthesis Example 2 was used instead of the compound obtained in Synthesis Example 1.

Evaluation 1: Corrosion resistance

After spin-coating the hardmask compositions according to Examples 1 to 2 and Comparative Examples 1 to 2 on a silicon wafer, heat treatment at 400° C. for 90 seconds on a hot plate to form a 4,000 Å-thick thin film, K-MAC The thin film thickness was measured with a thin film thickness meter of.

Meanwhile, the hardmask compositions according to Examples 1 to 2 and Comparative Examples 1 to 2 were spin-coated on a silicon wafer, and then heat-treated at 800° C. for 1 hour in a furnace while purging with _{N 2 to form a film.} After that, the thickness of the thin film was measured by the same method.

Subsequently, the formed thin film _{was dry-etched for 100 seconds and 60 seconds using a CHF 3} /CF ₄ mixed gas and an N ₂ /O ₂ mixed gas, respectively, and then the thickness of the thin film was measured again. From the thickness and etching time of the thin film before and after dry etching, the bulk etch rate (BER) was calculated according to the following formula 1

[Calculation 1]

Etch rate (bulk etch rate, BER) = (initial thin film thickness-thin film thickness after etching)/etching time (Å/sec)

The results are shown in Table 1.

CHF ₃ /CF ₄ bulk etch rate (Å/sec) N ₂ /O ₂ bulk etch rate
(Å/sec) Example 1 22.21 22.15 Example 2 23.13 22.35 Example 1 (N ₂ purging performed) 20.14 22.20 Example 2 (N ₂ purging performed) 21.36 22.75 Comparative Example 1 28.42 26.98 Comparative Example 2 29.03 29.19 Comparative Example 1 (N ₂ purging performed) 27.21 28.64 Comparative Example 2 (N ₂ purging performed) 30.13 29.41

Referring to Table 1, the thin film formed from the hardmask composition according to Examples 1 to 2 has sufficient etch resistance to the etching gas compared to the thin film formed from the hardmask composition according to Comparative Examples 1 to 2, so that the bulk etch characteristics are improved. can confirm.

Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention defined in the following claims are also present. It is within the scope of the invention.

Claims (17)

A compound containing 1 to 4 structural units represented by the following formula (2), and
menstruum
Hardmask composition comprising a.
[Formula 2]

In Chemical Formula 2,
R ¹ to R ⁶ are each independently a hydroxy group, a halogen group, a substituted or unsubstituted C1 to C30 alkoxy group, a substituted or unsubstituted C1 to C30 alkyl group, a substituted or unsubstituted C2 to C30 alkenyl group, a substituted or unsubstituted Is a C2 to C30 alkynyl group, a substituted or unsubstituted C6 to C30 aryl group, or a combination thereof,
In this case, the hydrogen atom is halogen, hydroxy group, nitro group, cyano group, amino group, azido group, amidino group, hydrazino group, hydrazono group, carbonyl group, carbamyl group, thiol group, ester group, carboxyl group or salt thereof, sulfonic acid Group or its salt, phosphoric acid or its salt, C1 to C30 alkyl group, C2 to C30 alkenyl group, C2 to C30 alkynyl group, C6 to C30 aryl group, C7 to C30 arylalkyl group, C1 to C30 alkoxy group, C1 to C20 heteroalkyl group, A C3 to C20 heteroarylalkyl group, a C3 to C30 cycloalkyl group, a C3 to C15 cycloalkenyl group, a C6 to C15 cycloalkynyl group, a C3 to C30 heterocycloalkyl group, or a combination thereof,
a to f are each independently an integer of 0 to 4. delete delete delete delete delete In claim 1,
The compound is a hardmask composition that is contained in an amount of 0.1% to 30% by weight based on the total content of the hardmask composition. A hard mask layer formed by curing the hard mask composition according to claim 1. In clause 8,
The curing is a hard mask layer made by heat treatment at a temperature of 100 to 1,000 ℃. In claim 9,
The curing is a hard mask layer made by heat treatment at a temperature of 600 to 1,000 ℃. In claim 10,
The heat treatment is performed while purging with nitrogen. Providing a layer of material over the substrate,
Applying the hardmask composition according to any one of claims 1 and 7 on the material layer,
Heat treating the hardmask composition to form a hardmask layer,
Forming a silicon-containing thin film layer on the hardmask layer,
Forming a photoresist layer on the silicon-containing thin film layer,
Exposing and developing the photoresist layer to form a photoresist pattern,
Selectively removing the silicon-containing thin film layer and the hardmask layer using the photoresist pattern and exposing a portion of the material layer, and
Etching the exposed portion of the material layer
Including
How to form a pattern. In claim 12,
The step of applying the hardmask composition is a pattern forming method performed by a spin-on coating method. In claim 12,
Forming a bottom anti-reflective layer (BARC) prior to forming the photoresist layer. In claim 12,
The heat treatment is a pattern forming method performed at a temperature of 100 to 1,000 ℃. In paragraph 15,
The heat treatment is a pattern forming method performed at a temperature of 600 to 1,000 ℃. In paragraph 16,
The heat treatment is performed while purging with nitrogen.

Images