JPH0588348A - Production of phase shift mask - Google Patents

Abstract

PURPOSE:To allow the production of the phase shift mask having high fineness with a high throughput by using a positive type electron beam resist essentially consisting of a specific copolymer. CONSTITUTION:A resist pattern is formed by electron beam lithography by using the positive type electron beam resist essentially consisting of the 2- cyclohexyl cyanoacrylate-methacrylate copolymer expressed by formula I. Silicon dioxide which is a shifter layer is worked by dry etching. In the formula I, R denotes 1 to 8C chain or cyclic alkyl group; (m), (n) denote positive integers. The copolymn. mol ratio is 2-cyclohexyl cyanoacrylate:methacrylate = 95:5 to 50:50, more preferably 90:10 to 70:30. The production of the phase shift mask master of the high fineness to be used for production of semiconductor integrated circuits with the high throughput is allowed in this way and the high productivity and cost reduction are attained in the production of semiconductors.

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 for manufacturing a semiconductor integrated circuit,
More specifically, it relates to a method of manufacturing a phase shift mask having 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 on which chromium or the like is formed on the entire surface, irradiating with an electron beam, developing the resist, forming a resist pattern, and then etching. It is produced 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 patterns, 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 produced 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, but silicon dioxide is used because of its durability.
The patterning method of silicon dioxide, which is the phase shift layer, is performed by applying an electron beam resist as in the case of the light-shielding film, developing the resist, forming a resist pattern, and etching the silicon dioxide.

The thickness of the phase shift layer is such that the phase difference of light is 18
It is necessary to set it so that it changes 0 degrees. The condition at this time is d = λ / {2 (n−) where n is the refractive index of the phase shift layer, λ is the exposure light source wavelength, and d is the film thickness of the phase shift layer.
1)}. Specifically, n of silicon dioxide is 1.4
7. If λ is 365 nm, the thickness of the phase shift layer is 390 nm.
Becomes

When etching the light-shielding film such as chromium, there is no problem even with wet etching which is isotropic because the light-shielding film has a relatively thin film thickness of 100 nm. However, since the phase shift layer is thicker than the light-shielding film,
Side etching is involved in isotropic wet etching, and it is difficult to control the dimensions of the phase shift layer.
The pattern is tapered. For this reason, anisotropic dry etching is suitable for etching the silicon dioxide that is the phase shift layer.

However, the resistance of the resist is a problem in dry etching. In general, positive electron beam resists are incompatible with dry etching resistance, and resists having high dry etching resistance have low sensitivity and low throughput. For example, resists such as PBS (trade name of Chisso Co., Ltd.) and EBR-9 (trade name of Toray Co., Ltd.) have high sensitivity, but dry etching resistance is methacrylic acid which is a standard of positive type electron beam resist. Methyl polymer (P
It is 1/2 or less of MMA). Further, a resist containing an aromatic ring such as φ-MAC (trade name, manufactured by Daikin Industries, Ltd.) and MP2400 (trade name, manufactured by Shipley, USA) is PMMA.
However, the sensitivity is low and an electron beam irradiation dose of ²⁰ μC / cm ² or more is required. That is, it is not possible to manufacture a high-definition phase shift mask with a high throughput by using a commercially available resist at present.

The sensitivity of cyclohexyl 2-cyanoacrylate polymer is as high as ^{2 to} 6 μC / cm ² (accelerating voltage 20 kV), and its dry etching resistance is more than twice as high as PBS and other acrylic electron beam resists. It has the same dry etching resistance as a low-sensitivity resist containing an aromatic ring.
This cyclohexyl 2-cyanoacrylate polymer causes no problem when patterned on a metal such as chromium, aluminum, or silicon, but when patterned on silicon dioxide which is the above-mentioned phase shift layer, cracks occur in the resist pattern. There was a problem that it would end up.

[0008]

The object of the present invention is to prevent the generation of cracks on a silicon dioxide of 2-cyanoacrylate cyclohexyl polymer, and to provide a phase shift mask of high definition with high throughput. It is to provide a manufacturing method.

[0009]

Means for Solving the Problems The present invention uses a positive type electron beam resist containing a 2-cyanoacrylic acid cyclohexyl-methacrylic acid ester copolymer represented by the formula (Chem. 1) as a main component to form a resist by electron beam lithography. It is a method of manufacturing a phase shift mask, characterized in that a pattern is formed and silicon dioxide, which is a shifter layer, is processed by dry etching.

The 2-cyanoacrylic acid cyclohexyl-methacrylic acid ester copolymer according to the present invention is obtained by radically polymerizing a 2-cyanoacrylic acid cyclohexyl monomer and a methacrylic acid ester monomer. The molecular weight of the obtained copolymer is generally 10,000 to 3,000,000. However, if the molecular weight is too high, the coatability will be lowered, and if the molecular weight is low, the sensitivity will decrease.
A molecular weight of 0,000 to 1,000,000 is preferred.

The 2-cyanoacrylic acid cyclohexyl monomer used in the present invention is represented by the following formula (Formula 2).

[0012]

[Chemical 2]

The methacrylic acid ester monomer is represented by the following formula (Formula 3).

[0014]

[Chemical 3]

However, R in the formula is a chain or cyclic alkyl group having 1 to 8 carbon atoms, and specifically, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, methacrylic acid. Examples thereof include n-butyl acidate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, and n-octyl methacrylate.

The copolymerization molar ratio is 2-cyanoacrylic acid cyclohexyl: methacrylic acid ester = 95: 5 to 50:
50, preferably 90:10 to 70:30. If the content of the methacrylic acid ester is 5% or less, cracks will occur, but if the content of the methacrylic acid ester is too large, the dry etching resistance will be reduced.

[0017]

Table 1 shows a comparison between the 2-cyanoacrylic acid cyclohexyl-methacrylic acid ester copolymer used in the present invention and various positive type electron beam resists. The sensitivity is an acceleration voltage of 20 kV, and the dry etching resistance is a reactive ion etching device as a dry etching device.
C ₂ F ₆ as etching gas, pressure 0.03 Tor
It was carried out under the conditions of r and power of 300W.

[0018]

[Table 1]

As is clear from Table 1, the resist used in the present invention has practically sufficient sensitivity and dry etching resistance, and is applicable to silicon dioxide.
Therefore, silicon dioxide, which is the shifter layer of the phase shift mask, can be processed with high precision by dry etching, and the phase shift mask can be manufactured with high throughput.

[0020]

【Example】

<Example 1> Chromium was sputtered on a glass substrate to a thickness of 100 nm, and 390 n of silicon dioxide was further added.
A film-formed photomask blank having a thickness of m was prepared. 10 g of cyclohexyl 2-cyanoacrylate, 3 g of n-butyl methacrylate, 2 g of acetic acid, and 0.05 g of azobisisobutyronitrile were charged in a glass sealed tube and reacted in a nitrogen stream at 60 ° C. for 10 hours. This was poured into methanol to precipitate the reaction product, and 7.4 g of a white powdery copolymer was obtained. The molecular weight of this copolymer was 430,000 (converted to polystyrene by GPC).

A 5% by weight cyclohexanone solution of 2-cyanocyclohexyl acrylate / n-butyl methacrylate copolymer was prepared and spin-coated on the prepared photomask blank at 700 rpm, followed by heat treatment at 120 ° C. for 30 minutes, and 500 nm. A resist coating of Irradiation amount 6μ
After electron beam irradiation at C / cm ² and accelerating voltage of 20 kV, it was immersed in a mixed solvent of isopropyl cellosolve: 2-propanol = 9: 1 at 20 ° C. for 5 minutes, rinsed in 2-propanol, and dried to positive A mold resist pattern was obtained.

Then, using a reactive ion etching apparatus, etching of silicon dioxide was performed with an etching gas of C ₂ F ₆ (50 SCCM) at a pressure of 0.03 Torr and a power of 300 W for 20 minutes. Removal of the resist coating with acetone resulted in a taper-free vertical profile silicon dioxide pattern.

Example 2 Cyclohexyl 2-cyanoacrylate 10 g, ethyl methacrylate 3.5 g, acetic acid 2
g and azobisisobutyronitrilo (0.05 g) were charged in a glass sealed tube and reacted in a nitrogen stream at 60 ° C. for 10 hours. This was poured into methanol and the reaction product was precipitated to obtain 8.2 g of a white powdery copolymer. The molecular weight of this copolymer was 350,000 (converted to polystyrene by GPC).

A 5 wt% cyclohexanone solution of 2-cyanocyclohexyl acrylate-ethyl methacrylate copolymer was prepared and spin-coated at 700 rpm on a photomask blank coated with silicon dioxide.
It heat-processed at 20 degreeC for 30 minute (s), and obtained the resist film of 500 nm. After irradiation with an electron beam at an irradiation dose of 6 μC / cm ² and an accelerating voltage of 20 kV, it was immersed in a mixed solvent of methyl isobutyl ketone: 2-propanol = 1: 1 at 20 ° C. for 1 minute, and then 2
A positive resist pattern was obtained by rinsing in propanol and drying. Next, silicon dioxide was dry-etched in the same manner as in Example 1 to obtain a silicon dioxide pattern on the substrate.

Comparative Example 1 A 5% by weight cyclohexanone solution of a cyclohexyl 2-cyanoacrylate polymer was prepared and applied onto a photomask blank coated with silicon dioxide at 1100 rpm at 120 ° C. for 3 times.
Prebaking was performed for 0 minutes to form a 500 nm resist film. After irradiation with an electron beam at an irradiation amount of 6 μC / cm ² and an acceleration voltage of 20 kV, methyl isobutyl ketone: 2-propanol =
The developing treatment was carried out by immersing the mixed solvent of 3: 2 in a developing solution at 20 ° C. for 3 minutes. Next, a resist pattern was obtained by rinsing with 2-propanol and drying, but cracks had occurred.

<Comparative Example 2> A positive electron beam resist EBR-9 having a thickness of 500 nm was formed on the manufactured photomask blank.
A film having a thickness of 3 μm was formed, prebaked at 200 ° C. for 30 minutes, and irradiated with an electron beam of 3.2 μC / cm ² . After electron beam irradiation, it was immersed in methyl isobutyl ketone at 20 ° C. for 3 minutes, then rinsed with 2-propanol and dried. As in Example 1, the reactive ion etching apparatus was used to etch the silicon dioxide, but all the resist pattern disappeared and the selection ratio between silicon dioxide and the resist could not be obtained.

[0027]

INDUSTRIAL APPLICABILITY The resist used in the present invention has practically sufficient sensitivity and dry etching resistance, and is applicable to silicon dioxide without causing cracks. Therefore, the silicon dioxide that is the shifter layer of the phase shift mask can be processed with high definition by dry etching. 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 a high throughput, and it is possible to obtain a great effect on high productivity and cost reduction in the manufacture of a semiconductor. Can bring

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Claims (2)

[Claims] 1. The following chemical formula: A method for producing a phase shift mask, which comprises using a positive electron beam resist containing a 2-cyanoacrylic acid cyclohexyl-methacrylic acid ester copolymer represented by the following as a main component. 2. The method of manufacturing a phase shift mask according to claim 1, wherein reactive ion etching is used in the step of etching the silicon dioxide which is the shifter layer in the phase shift mask.