JPH07271011A - Positive electron beam resist and production of phase shift mask using same - Google Patents

Abstract

PURPOSE:To provide a method by which a problem of occurrence of cracks in a resist pattern of 2-cyclohexyl cyanoacrylate polymer on silicon dioxide and a high-precision phase shift mask is produced with high throughput. CONSTITUTION:In the production method of a phase shift mask using silicon dioxide as a phase shift layer, a positive electron beam resist essentially comprising a copolymer of 2-cyclohexyl cyanoacrylate and 2-alkoxyethyl cyanoacrylate having alkoxy groups of 1 to 4 carbon number is used. The phase shift layer is processed by dry etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a photomask used in manufacturing a semiconductor integrated circuit, and more particularly to a method for manufacturing a phase shift mask having silicon dioxide as a phase shift layer. .

[0002]

2. Description of the Related Art In general, a photomask is formed by coating an electron beam resist on a transparent substrate having a chromium film formed on the entire surface, irradiating with an electron beam and then developing the resist pattern to form a resist pattern, followed by etching. It is manufactured by
However, in the conventional exposure method using a photomask, there has been a problem that light leaking from the transmissive portion of the mask interferes with each other in the approaching pattern, resulting in poor resolution.

Therefore, a phase shift mask for reversing the phase of the projection light passing through the adjacent pattern by 180 degrees and improving the resolution of a fine pattern has been developed and attracted attention. The phase shift mask is manufactured by forming a film of the phase shift layer on the entire surface of the substrate on which the pattern of the light shielding film is formed, and then processing only the phase shift layer into a predetermined pattern.

The phase shift layer may be made of a transparent material,
Silicon dioxide is used because of its durability. The patterning of silicon dioxide is formed by the same method as the light shielding film. First, after coating an electron beam resist on silicon dioxide, irradiating with an electron beam, a developing process is performed to form a resist pattern, and silicon dioxide is etched.

When the refractive index of the phase shift layer is n, the wavelength of the exposure light source is λ, and the thickness of the phase shift layer is d, d = λ /
It is represented by (2 (n-1)). Specifically, when n of silicon dioxide is 1.47 and λ is 365 nm, the film thickness of the phase shift layer is 390 nm. When etching chrome or the like of the light-shielding film, the thickness of the light-shielding film is 100 nm, which is relatively thin, and therefore there is no problem even if it is isotropic wet etching. However, since the thickness of the phase shift layer is thicker than that of the light shielding layer, side etching occurs in the isotropic wet etching, which makes it difficult to control the dimensions of the phase shift layer and further taper the pattern. Therefore, anisotropic dry etching is suitable for etching the silicon dioxide that is the phase shift layer.

However, in the dry etching, the etching resistance of the resist poses a problem. Generally, the relationship between dry etching resistance and sensitivity of positive electron beam resists is contradictory,
A resist having high dry etching resistance has the drawbacks of low sensitivity and low throughput. For example, "PB
The resists such as "S" (trade name of Chisso Co., Ltd.) and "EBR-9" (trade name of Toray Co., Ltd.) have high sensitivity, but the dry etching resistance is methacrylic acid which is a standard of positive electron beam resist. 1 / Methyl polymer (hereinafter referred to as PMMA)
It is 2 or less. Further, resists having an aromatic ring such as “φ-MAC” (trade name of Daikin Industries, Ltd.) and “MP2400” (trade name of Shipley, USA) have dry etching resistance twice or more that of PMMA. However, the sensitivity is low and an electron beam irradiation dose of ²⁰ μC / cm ² or more is required.
That is, it was not possible to manufacture a high-definition phase shift mask with a high throughput using the resist currently on the market.

The sensitivity of the main chain scission type 2-cyanoacrylic acid cyclohexyl polymer as a positive type electron beam resist is as high as ^{2 to} 10 μC / cm ² (accelerating voltage 20 kV), and the dry etching resistance is higher than that of other acrylics. It has a higher dry etching resistance than that of the electron beam resist of the type and the above-mentioned "PBS", and has almost the same dry etching resistance as the resist containing a benzene ring.

However, this cyclohexyl 2-cyanoacrylate polymer causes no problem when a film is formed on a metal such as chromium, aluminum, or silicon and irradiated with an electron beam and then developed, but a resist pattern is formed on silicon dioxide. There is a problem that cracks occur in the.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve these problems, and it is an object of the present invention to form a resist pattern of 2-cyanoacrylate cyclohexyl polymer on silicon dioxide. Another object of the present invention is to provide a method for solving the problem of crack generation and manufacturing a high-definition phase shift mask with high throughput.

[0010]

In order to solve this problem, the present invention is a copolymer of cyclohexyl 2-cyanoacrylate and alkoxyethyl 2-cyanoacrylate having an alkoxy group having 1 to 4 carbon atoms. To provide a positive electron beam resist characterized by containing as a main component, also, in the method of manufacturing a phase shift mask having a phase shift layer of silicon dioxide, using the positive electron beam resist, by dry etching Provided is a method for manufacturing a phase shift mask, which is characterized by processing a phase shift layer.

The copolymer of cyclohexyl 2-cyanoacrylate and alkoxyethyl 2-cyanoacrylate according to the present invention can be obtained by copolymerizing both monomers by anion polymerization or radical polymerization.

The alkoxyethyl 2-cyanoacrylate has an alkoxy group with 1 to 4 carbon atoms, and specifically, methoxyethyl 2-cyanoacrylate, ethoxyethyl 2-cyanoacrylate, and 2-cyanoacrylic acid. Propoxyethyl, butoxyethyl 2-cyanoacrylate and the like.

As the initiator of the radical polymerization method, those used in ordinary radical polymerization are specifically used, such as benzoyl peroxide and azobisisobutyronitrile.
The radical polymerization method can be bulk polymerization or solution polymerization. Examples of the polymerization solvent used in the solution polymerization include organic solvents such as benzene, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, tetrahydrofuran, and methyl cellosolve acetate. The polymerization temperature and the polymerization time naturally vary depending on the type and amount of the polymerization initiator and the polymerization solvent used, but are 40 to 8
0 degreeC and 1 to 24 hours are preferable.

As an initiator of the anionic polymerization method, an organic amine which is a weak base is preferable. Specifically, it is aniline, diethylamine, N, N-dimethyl-p-toluidine, or the like. The reaction temperature is preferably −70 to 20 ° C. in order to control the polymerization rate of the monomer and suppress side reactions. The same solvent as that used in radical polymerization can be used as the polymerization solvent.

Cyclohexyl 2-cyanoacrylate and 2
The copolymerization ratio of -alkoxyethyl cyanoacrylate is preferably 95/5 to 50/50 (molar ratio), and more preferably 90/10 to 60/40. If the content of cyclohexyl 2-cyanoacrylate is high, the dry etching resistance is high, but the adaptability on silicon dioxide is insufficient. On the contrary, if the content of alkoxyethyl 2-cyanoacrylate is high, it does not adhere to silicon dioxide. Although it is possible to completely prevent the cracks, the dry etching resistance and the resolution are deteriorated.

The copolymer having a molecular weight of 10,000 to 2,000,000 can be used, and more preferably 100,000 to 1
It is one million. If the molecular weight is too high, the filterability and coatability will decrease, and if the molecular weight is low, the sensitivity will decrease. The molecular weight mentioned here is a polystyrene-equivalent weight average molecular weight by GPC.

The positive type electron beam resist of the present invention is used as a main component of the above-mentioned copolymer by dissolving it in a solvent which dissolves it. The solvent is not particularly limited, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, isobutyl acetate, methyl cellosolve acetate, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, ethyl lactate, toluene, xylene, 1,2-dichloroethane and the like. Cyclohexanone, ethyl cellosolve acetate, propylene glycol monomethyl ether acetate, and ethyl lactate are particularly preferable from the viewpoints of coating property and resolution.

In the method of manufacturing a phase shift mask using the positive type electron beam resist of the present invention, the dry etching method of silicon dioxide which is the shifter layer of the phase shift mask includes plasma etching, reactive ion etching and ion beam. Etching or the like can be used. Reactive ion etching is particularly preferable in view of the high etching selectivity between the workpiece and the resist film and the small amount of side etching. A fluorine-based gas such as CF ₄ or C ₂ F ₆ is used as the reactive gas, and hydrogen is added to improve etching selectivity.
It is also possible to add oxygen to prevent the deposition of side reaction products.

[0019]

Although it has been difficult to achieve both sensitivity and dry etching resistance with the conventional main chain breaking type positive electron beam resist, 2-cyanoacrylate cyclohexyl polymer has both sensitivity and dry etching resistance. Is possible. However, when a resist consisting of a cyclohexyl 2-cyanoacrylate homopolymer is applied on silicon dioxide and subjected to electron beam irradiation and development, a resist pattern is cracked. It is considered that this is because the six-membered ring has a high stereoregularity and internal stress is applied to the cracks.

However, as shown in Table 1, in the positive type electron beam resist of the present invention, the internal stress is relaxed by the alkoxyethyl group, and the generation of cracks on silicon dioxide can be prevented. Further, since it has a cyano group and a cyclohexyl ring, it has excellent sensitivity and dry etching resistance. From this, it becomes possible to process silicon dioxide by dry etching, and it is possible to manufacture a high-definition phase shift mask with high throughput.

Table 1 shows a comparison between the positive electron beam resist of the present invention and various other positive electron beam resists. The sensitivity is an acceleration voltage of 20 kV, and the dry etching resistance is C ₂ F ₆ : H ₂ = 50 as an etching gas by using a reactive ion etching device as a dry etching device.
sccm: 5 sccm, pressure 0.03 Torr, power 300W
It carried out on condition of.

[0022]

[Table 1]

[0023]

【Example】

<Example 1> Cyclohexyl 2-cyanoacrylate 0.
06 mol, methoxyethyl 2-cyanoacrylate 0.
04 mol, azobisisobutyronitrile 5 × 10 ⁻⁴ m
and 1 ml of acetic acid were reacted at 60 ° C. for 12 hours in a nitrogen stream. This was poured into methanol and the reaction product was precipitated to obtain a white powdery copolymer. The copolymerization ratio of this copolymer is measured by nuclear magnetic resonance spectrum (NM
R) as a result, cyclohexyl 2-cyanoacrylate / 2-methoxyethyl 2-cyanoacrylate = 58/4
It was 2 (molar ratio). The weight average molecular weight is 28.
It was 50,000 (polystyrene conversion by GPC).

A 5 wt% cyclohexanone solution of this copolymer was prepared and filtered with a filter having a pore size of 0.2 μm. On the other hand, a glass substrate was prepared in which chromium was sputtered to a thickness of 80 nm, and silicon dioxide was sputtered to a thickness of 400 nm on chromium to prepare a glass substrate.
It was applied as a resist film having a thickness of 950 rpm and 500 nm by a spin coating method, heat-treated at 120 ° C. for 30 minutes, and then irradiated with an electron beam at an irradiation dose of 0.8 to 100 μC / cm ² (accelerating voltage 20 kV).

After electron beam irradiation, methyl isobutyl ketone /
20 with a mixed solvent of isopropyl alcohol = 70/30
A resist pattern was obtained by immersing at ℃ for 1 minute, rinsing in isopropyl alcohol and drying. The minimum irradiation dose required to completely dissolve the electron beam irradiation part, that is, the sensitivity was 6.4 μC / cm ² , which was high sensitivity. Further, the obtained resist pattern was not cracked at all.

Next, using a reactive ion etching apparatus, with a mixed gas of C ₂ F ₆ : H ₂ = 50 sccm: 5 sccm,
Dry etching of silicon dioxide was performed at a pressure of 0.03 Torr and a power of 300 W for 20 minutes. When the resist film was removed with acetone and the etching shape of silicon dioxide was observed by an electron microscope, a vertical cross-sectional shape pattern without taper was confirmed. While the etching rate of silicon dioxide is 24.6 nm / min,
The etching rate of cyclohexyl cyanoacrylate-2-methoxyethyl cyanoacrylate copolymer is 20.5.
nm / min, and had a selection ratio of 1 or more.

For comparison, the etching rate of cyclohexyl 2-cyanoacrylate homopolymer was measured to be 16.2 nm / min, and PMMA was 32.1.
nm / min. The positive electron beam resist of the present invention has a slightly lower dry etching resistance than the cyclohexyl 2-cyanoacrylate homopolymer.
It had a sufficient dry etching resistance.

<Example 2> Using 0.07 mol of cyclohexyl 2-cyanoacrylate and 0.03 mol of ethoxyethyl 2-cyanoacrylate as a polymerization initiator, 1 x ^10-4 mol of N, N-dimethyl-p-toluidine was used. Reaction was carried out in 100 ml of tetrahydrofuran at 0 ° C. for 10 hours. This was poured into petroleum ether and the reaction product was precipitated to obtain a copolymer. The copolymerization ratio was cyclohexyl 2-cyanoacrylate / 2-ethoxyethyl 2-cyanoacrylate = 69/31 (molar ratio). The molecular weight of this polymer was 462,000 (converted to polystyrene by GPC).
Met.

Further, as in Example 1, a 5% by weight solution of this copolymer in cyclohexanone was prepared, a film was formed on a substrate on which silicon dioxide was sputtered, and electron beam irradiation was carried out. After electron beam irradiation, 2 with a mixed solvent of methyl isobutyl ketone / isopropyl alcohol = 65/35
It was immersed at 0 ° C. for 1 minute and rinsed in isopropyl alcohol to obtain a resist pattern.

The residual film sensitivity was 4.2 μC / cm ² , and no crack was generated in the resist pattern. Next, as a result of performing dry etching in the same manner as in Example 1, a silicon dioxide pattern having a vertical cross-sectional shape without taper was obtained. The dry etching rate of the resist film was 18.2 nm / min and had high dry etching resistance.

Example 3 In 100 ml of toluene, 0.08 mol of cyclohexyl 2-cyanoacrylate, 0.02 mol of n-butoxyethyl 2-cyanoacrylate, 1 ml of acetic acid, 5 × 10 ⁻⁴ mo of azobisisobutyronitrile were used.
1 was added, and the mixture was reacted at 60 ° C. for 10 hours in a nitrogen stream. This was poured into petroleum ether and the reaction product was precipitated to obtain a white powdery copolymer. The copolymerization ratio was cyclohexyl 2-cyanoacrylate / 2-n-butoxyethyl 2-cyanoacrylate = 83/17 (molar ratio).
The molecular weight of this copolymer was 247,000 (converted to polystyrene by GPC).

A film of this copolymer was formed on a substrate and irradiated with an electron beam in the same manner as in Example 1. After electron beam irradiation, methyl isobutyl ketone / isopropyl alcohol = 50/50
It was dipped in the mixed solvent of 20 ° C. for 30 seconds, developed, and then dry-etched. Sensitivity is 3.2 μC /
At cm ² , no crack was observed in the resist pattern. Dry etching rate of resist film is also 1
It was good at 7.6 nm / min.

Comparative Example 1 A cyclohexanone 2-cyanoacrylate homopolymer having a molecular weight of 481,000 was dissolved in cyclohexanone to prepare a 5% by weight resist solution, and silicon dioxide was sputtered in the same manner as in Example 1. A resist film was formed on the substrate and irradiated with an electron beam. After electron beam irradiation, a resist pattern was obtained by immersing in a mixed solvent of methyl isobutyl ketone / isopropyl alcohol = 60/40 at 20 ° C. for 3 minutes, rinsing in isopropyl alcohol and drying. However, many cracks were found in the obtained resist pattern.

Comparative Example 2 After forming a resist pattern on silicon oxide in the same manner as in Example 2, wet etching of silicon dioxide was performed using buffered hydrofluoric acid (manufactured by Daikin Corp.). However, side etching enters,
A silicon oxide pattern having a vertical cross-sectional shape could not be obtained, and the taper shape was formed. In some places, peeling of the resist pattern was also observed.

[0035]

As described above, according to the present invention, it is possible to provide a high-definition phase shift mask used at the time of manufacturing a semiconductor integrated circuit with high throughput,
It is possible to bring great effects to high productivity and cost reduction in semiconductor manufacturing.

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Claims (2)

[Claims] 1. Cyclohexyl 2-cyanoacrylate,
A positive-type electron beam resist containing a copolymer with 2-cyanoalkoxyethyl 2-cyanoacrylate having an alkoxy group having 1 to 4 carbon atoms as a main component. 2. A method for manufacturing a phase shift mask using silicon dioxide as a phase shift layer, wherein cyclohexyl 2-cyanoacrylate and alkoxyethyl 2-cyanoacrylate having an alkoxy group having 1 to 4 carbon atoms are used. A method of manufacturing a phase shift mask, characterized in that a positive type electron beam resist containing a polymer as a main component is used and the phase shift layer is processed by dry etching.