X-ray or gamma ray systems or devices – Specific application – Lithography
Reexamination Certificate
1999-09-14
2001-07-24
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Lithography
Reexamination Certificate
active
06266389
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exposure apparatus for manufacturing devices such as semiconductor devices, liquid crystal display devices, or thin-film magnetic head by means of the lithography process. Also, the present invention relates to a method for manufacturing an exposure apparatus, and a method for manufacturing a device using an exposure apparatus.
2. Description of the Related Art
A conventional exposure apparatus is generally used for manufacturing semiconductor devices, liquid crystal display devices, or thin-film magnetic heads. This is a projection exposure apparatus which projects a predetermined pattern formed on a mask as a projection master onto a photosensitive substrate through a projection optical system. There are three types of conventional projection optical systems. A refraction type projection optical system comprises a refraction optical element having the optical property of transmitting an exposure light such as a lens. A reflection type projection optical system comprises a reflection optical element having an optical property of reflecting an exposure light such as a mirror. A conventional reflection and refraction type projection optical system comprises both reflection and refraction optical elements.
In order to manufacture highly integrated semiconductor devices the wave length of the exposure light has been shifted from the g-line toward the i-line, until the KrF excimer laser light had a wave length of 248 nm. Recently, an exposure light having a wave length of 193 nm can be produced by an ArF excimer laser. In the future, the more highly integrated semiconductor devices will be developed, the higher the resolution of a projection optical system in an exposure apparatus is required. A resolution of a projection optical system is represented by the formula below:
(resolution)=
k*&lgr;/NA,
where k denotes the k factor which is a positive constant, k<1, which varies with the properties of the resist, &lgr; denotes the wave length of an exposure light, NA denotes a numerical aperture of a projection optical system.
As it is obvious from the above mentioned formula, reducing the wavelength &lgr; is a very efficient technique for increasing the resolution of a projection optical system. As a result, an exposure apparatus using a soft X-ray having a wave length of 5-15 nm (Extreme Ultra Violet radiation, or EUV radiation) as an exposure light has been developed recently. This exposure apparatus using EUV radiation is very prominent at the moment as a potential example of the technology of an exposure apparatus of the future.
The U.S. Pat. No. 5,917,879 discloses a projection optical system for an exposure apparatus using an EUV radiation.
In a projection optical system of an exposure apparatus using EUV radiation, a refraction optical device such as a lens cannot be used because no hyaline material can transmit EUV radiation. Moreover, the number of reflection optical elements must be minimized because reflection optical elements such as mirrors are extremely inefficient in their reflectivity, reflecting only about 65% of light. For example, a projection optical system disclosed in the U.S. Pat. No. 5,917,879 has four mirrors.
In the case of actual manufacture of a projection system, there are manufacturing errors of each optical member constituting a projection optical system (a refraction optical element, a reflection optical element), and structural errors. Therefore the required image resolution properties according to design rules of the future generations cannot be achieved without adjustments. The manufacturing errors of each optical member must be reduced to a negligible value to satisfy the required image properties.
When the size of an optical member is small, it is difficult to adjust the position of each optical member of a projection system after assembly in accordance with the measured image property. This is because the degree of freedom for adjustment is small.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method for manufacturing an exposure apparatus, an exposure apparatus itself, and a method for manufacturing a device using the exposure apparatus which overcomes the above issues in the related art. This object is achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, a method for manufacturing an exposure apparatus which transcribes an image of a projection master on a substrate by a projection system having a plurality of reflection mirrors is provided. This manufacturing method comprises a first step for measuring an image property of a projection system having a plurality of reflection mirrors, a second step for selecting an image property component to be adjusted from an image property, a third step for selecting at least one of reflection mirrors which can adjust an image property component selected in a second step, a fourth step for calculating a surface shape which adjusts substantially an image property component based on an image property measured in a first step, a fifth step for giving a surface shape calculated in a fourth step to a reflection mirror, a sixth step for embedding a reflection mirror having a surface shape given in a fifth step into a projection system.
An image property component may include an image magnification error, a skew of an image, a curvature of an image plane, a gradient of an image plane, a displacement of a focal point caused by a direction in an aperture, a displacement of a focal point caused by a numerical aperture, and a telecentric error.
A method for manufacturing an exposure apparatus may further comprise a seventh step for selecting positions of reflection mirrors in a projection system, and positions of reflection mirrors may be selected so that an image property is adjusted substantially.
An image property may be measured using a light having a wave length used in a projection system in a first step.
An image property may be measured by using a light having a wave length other than used in a projection system in the first step.
A surface shape may be given to a reflection mirror having essentially the same shape as selected reflection mirror in a fifth step, and a reflection mirror in a projection system may be interchanged with a reflection mirror given a surface shape in a sixth step. A reflection mirror placed near a projection master or a substrate may be selected in the third step.
A reflection mirror placed near an aperture stop of a projection system is selected in said third step.
According to the second aspect of the present invention, an exposure apparatus is provided. This exposure apparatus comprises an X-ray source, an illumination system for guiding an X-ray from an X-ray source to a mask, a projection system for projecting a pattern on a mask by guiding an X-ray to an exposed plane through a mask, where a projection system is manufactured by a method according to one of the above mentioned methods.
According to the third aspect of the present invention, an exposure apparatus is provided. This exposure apparatus comprises an X-ray source, an illumination system for guiding an X-ray from an X-ray source to a mask, a projection system for guiding an X-ray to an exposed plane through a mask and projecting a pattern on a mask, where a projection system comprises a plurality of reflection mirrors, and at least one reflection mirror among the reflection mirrors is interchangeable with a reflection mirror having a surface shape different from that of the one reflection mirror.
A certain aberration component among a plurality of aberration components in a projection system may be changed by interchanging a reflection mirror without substantially influencing other aberration components.
The reflection mirror which is interchangeable may be a reflection mirror placed near a projection master or a su
Komatsuda Hideki
Murayama Norio
Chapman and Cutler
Church Craig E.
Nikon Corporation
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