JPH06177002A - Projection exposure device - Google Patents

Abstract

(57) [Summary] [Object] To provide an X-ray projection exposure method and apparatus capable of obtaining a high exposure intensity according to a pattern dimension. A wavelength region is variable in projection exposure in which a pattern on a mask illuminated by X-rays or vacuum ultraviolet rays is transferred onto a substrate by an imaging optical system composed of a reflecting mirror. [Effect] When the pattern size is large, it is possible to increase the exposure intensity by using X-rays or vacuum ultraviolet rays in the long wavelength region, and the effect of improving productivity is great.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithography technique in a manufacturing process of semiconductor integrated circuits and the like, and more particularly to a projection exposure apparatus using an X-ray or vacuum ultraviolet ray and a reflection type imaging optical system.

[0002]

2. Description of the Related Art Resolution and depth of focus are important in projection exposure for transferring a pattern of a semiconductor integrated circuit or the like drawn on a mask onto a substrate. Generally, the numerical aperture of the imaging optical system is NA,
When the exposure wavelength is λ, the resolution R and the depth of focus DOF are given by the following equations.

[0003]

[Formula 1] R = k ₁ λ / NA (Formula 1)

[0004]

(2) DOF = k ₂ λ / NA ² (2) where k ₁ and k ₂ are constants, for example, k ₁ = 0.5
It is considered that k ₂ = 0.5. Currently, wavelength is 365n
A resolution of 0.35 μm and a depth of focus of 1 μm are realized by using a mercury i-line of m and a lens optical system of NA 0.5.

In order to increase the density of semiconductor integrated circuits, a projection exposure method with higher resolution is required. As shown in Formula 1, the resolution increases as the NA increases or the exposure wavelength decreases. However, if NA is increased,
Since the depth of focus decreases as shown in Formula 2, there is a limit to increase the resolution by this method. On the other hand, the exposure wavelength is a dozen n
When the wavelength is shortened to the X-ray region of m to several nm, it is possible to achieve a resolution of 0.1 μm or less while securing a focal depth of 1 μm. However, since the refractive index of the substance is extremely close to 1 in the X-ray region, it is difficult to apply the refraction type optical system, and it is necessary to use the reflection type optical system. In recent years, a multilayer mirror in which a large number of thin films of two kinds of substances having different refractive indexes are alternately laminated has been put into practical use, and X-ray reflection with high reflectance has become possible. Therefore, an X-ray projection exposure method using a multilayer film reflection type optical system has been actively studied.

The conventional X-ray projection exposure method is disclosed in, for example, Journal of Vacuum Science Technology (J.Vac.Sci.Technol.) B7, p. 1648-p. 165.
1 (1989). FIG. 5 shows a conventional X-ray projection exposure method. Synchrotron radiation 1 emitted from an electron storage ring (not shown) is a continuous wavelength light extending from the X-ray region to the visible region. The long-wavelength component unnecessary for exposure to the synchrotron radiation is absorbed by the carbon thin film filter 2, and the short-wavelength component is incident on the reflective mask 3. The reflective mask has a pattern of a reflective surface formed on a non-reflective substrate. The illuminated pattern on the reflective mask is reduced and projected onto the substrate 6 by the imaging optical system including the reflecting mirrors 4 and 5. Here, the reflective mask and the reflective surface of the reflecting mirror are all Mo / a in which a large number of thin films of molybdenum (Mo) and silicon (Si) are alternately laminated.
A Si multilayer film 7 is formed. When the multilayer film satisfies the Bragg condition given by Equation 3, the phases of the reflected waves at the respective interfaces match each other, so that a high reflectance is obtained.

[0007]

## EQU00003 ## 2d cos .theta. =. Lamda. (Formula 3) where d is the period length of the multilayer film, .theta. Is the incident angle, and .lamda. Is the wavelength. In the above-mentioned conventional example, X-rays having a narrow band width centered at a wavelength of 13 nm are imaged on the substrate, and NA0.
A resolution of 0.1 μm is achieved at 1.

[0008]

In a semiconductor integrated circuit, a large number of layers having various patterns are formed on a wafer. However, the same pattern size is not used for all layers. DRAM (Dynamic Random Access Memor)
The pattern size of y) is reduced by about 0.6 to 0.7 times for each generation, but about 50% of layers require the size of that generation. About the remaining 50%, the dimensions of the previous generation and the generation before the next generation are applied. For example, the minimum size of 4 Gbit DRAM is about 0.1 μm, but 0.15 to 0.25 μm
Pattern dimensions of some degree are also used.

When a 0.1 μm pattern is transferred, considering the reflectance of the multilayer film, the exposure wavelength is 13 as described above.
nm is suitable. On the other hand, since the reflective optical system has no chromatic aberration, a pattern of about 0.25 μm can be resolved even if the exposure wavelength is lengthened to about 50 nm using the same optical system.

However, since the conventional X-ray projection exposure method uses only the Bragg reflection of the multilayer film, the wavelength band is extremely narrow and the wavelength continuity of the X-ray source is not effectively used.

It is an object of the present invention to provide an X-ray projection exposure method and apparatus which can obtain a high exposure intensity according to the pattern size.

[0012]

In order to achieve the above object, the X-ray projection exposure method and apparatus of the present invention provide a pattern on a mask illuminated by X-rays or vacuum ultraviolet rays,
In projection exposure for transferring onto a substrate by an imaging optical system composed of a reflecting mirror, the exposure wavelength region is made variable.

[0013]

The multi-layer film has a high reflectance only at and near the wavelength satisfying the Bragg condition. However, about 25 nm
In the above wavelength range, the reflectance increases even if the Bragg condition is not satisfied. Therefore, when the pattern size is large, a high exposure intensity can be obtained by using X-rays or vacuum ultraviolet rays that satisfy the Bragg condition and X-rays or vacuum ultraviolet rays that do not satisfy the Bragg condition.

[0014]

EXAMPLES First, the wavelength dependence of the imaging performance of the optical system will be described. FIG. 2 shows the relationship between the resolution and the wavelength given by Equation 1. In reflective optics, if NA is set too large, the reflector will block the beam, so the upper limit of NA is 0.
It is about 1. If NA is 0.1 and k ₁ is 0.5, it is necessary to set the wavelength to 20 nm or less in order to obtain the resolution of 0.1 μm, but to obtain the resolution of 0.25 μm, the wavelength is set to 50 nm or less. The wavelength can be made longer.

FIG. 1 shows an X-ray projection exposure apparatus according to the present invention. Synchrotron radiation 1 is emitted from an electron storage ring (not shown). The electron storage ring deflects electrons having energy of 350 MeV with a magnetic field intensity of 1 T and circulates the electrons, and the synchrotron radiation light has high brightness at wavelengths of 10 nm to 50 nm. The two types of transmission filters 2a and 2b are silicon thin films having thicknesses of 0.5 μm and 0.2 μm, respectively, and one of them is inserted in the optical path.
When transferring a 0.1 μm pattern, the filter 2a is used to remove the wavelength component of about 15 nm or more of the synchrotron radiation. Therefore, the wavelength component of about 15 nm or less enters the reflective mask 3. The illuminated pattern on the reflective mask is reduced and projected onto the substrate 6 by the imaging optical system including the reflecting mirrors 4 and 5. Here, the reflective mask and the reflective surface 7 of the reflective mirror are all formed with a Mo / Si multilayer film. The cycle length of each multilayer film is 13 nm
Was determined according to Equation 3 so that the Bragg condition was satisfied. For example, in a reflective mask, a Mo thin film having a thickness of 3.4 nm and a Si thin film having a thickness of 3.4 nm are alternately laminated in 60 layers. The exposure wavelength was 13 nm, and a 0.1 μm pattern could be resolved at NA 0.1 of the imaging optical system.

Next, a transfer experiment was conducted using the filter 2b. In this case, about 50 nm of synchrotron radiation
The above wavelength components are removed, and wavelength components of about 50 nm or less enter the reflective mask. X-rays having a wavelength of 13 nm that satisfy the Bragg condition are imaged on the substrate in the same manner as above. Further, X-rays having a wavelength of about 25 to 50 nm are also reflected by the respective multilayer films, although they have a low reflectance, and form an image on the substrate. Since the reflective optical system has no chromatic aberration, it has virtually no aberration at any wavelength, and a 0.25 μm pattern can be resolved.

Next, the increase in exposure intensity according to the present invention will be described. FIG. 3 shows the reflectance when the above Mo / Si multilayer film satisfies the Bragg condition. A peak reflectance of 70% is obtained at a wavelength of 13 nm, but the bandwidth is about 0.4.
nm is extremely small. FIG. 4 shows the reflectance when the Mo / Si multilayer film does not satisfy the Bragg condition. A reflectance of several% can be obtained in the wavelength region of about 25 nm or more.
This reflectance is smaller than that in the case where the Bragg condition is satisfied, but since the wavelength region is wide, the effect of increasing the exposure intensity is large.

The present invention is not limited to the above embodiment. That is, as the X-ray source, a high-intensity and continuous wavelength X-ray source such as laser plasma can be used. Also,
Be, B, C, etc. can be used for the filter. further,
As the constituent material of the multilayer film, a heavy element such as Mo, Ru, Rh, W, and Re and a light element such as Be, B, C, and Si may be combined.

[0019]

According to the present invention, in projection exposure using X-rays or vacuum ultraviolet rays, the exposure intensity can be increased when the pattern size is large.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an X-ray projection exposure method of the present invention.

FIG. 2 is a characteristic diagram of image formation of an optical system.

FIG. 3 is an explanatory diagram of reflectance in a multilayer film when the Bragg condition is satisfied.

FIG. 4 is an explanatory diagram of reflectance in a multilayer film when the Bragg condition is not satisfied.

FIG. 5 is an explanatory diagram of a conventional X-ray projection exposure method.

[Explanation of symbols]

1 ... Synchrotron radiation, 2a, 2b ... Filter, 3
... Reflective mask, 4,5 ... Reflecting mirror, 6 ... Substrate, 7 ... Multilayer film.

Claims (4)

[Claims] 1. A projection exposure in which a pattern on a mask illuminated by X-rays or vacuum ultraviolet rays is transferred to a substrate by an imaging optical system composed of a reflecting mirror, wherein a wavelength region is variable. Projection exposure device. 2. A projection exposure for transferring a pattern on a mask illuminated by X-rays or vacuum ultraviolet rays onto a substrate by an imaging optical system composed of a reflecting mirror, wherein a plurality of filters having different wavelength regions are provided. And a projection exposure apparatus. 3. In projection exposure, in which a pattern on a reflective mask illuminated by X-rays or vacuum ultraviolet rays is transferred onto a substrate by an imaging optical system composed of a reflective mirror, the reflective mask and the reflective mirror are exposed. The reflecting surface is formed of a multilayer film in which thin films of plural kinds of substances having different refractive indexes are alternately laminated, and X-rays or vacuum ultraviolet rays satisfying the Bragg condition with the multilayer film and Bragg condition with the multilayer film are not satisfied. A projection exposure apparatus, which forms an image of X-rays or vacuum ultraviolet rays on a substrate. 4. The projection exposure apparatus according to claim 1, wherein the X-rays or the vacuum ultraviolet rays are synchrotron radiation emitted from an electron storage ring.