Patent Number: 062953346
Section: summary

This application is based on Japanese Patent Applications No. HEI-9-115871 and No. HEI-9-115872 both filed on May 6, 1997 and No. HEI-10-45506 filed on Feb. 26, 1998, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION a) Field of the Invention The present invention relates to a transmission system for synchrotron light (SR light), and more particularly to an SR light transmission system capable of giving an intensity distribution to SR light in a cross sectional plane perpendicular to its optical axis and to an SR light transmission system for irradiating a certain area by swinging up and down a transporting direction of the SR light using a swinging mirror. b) Description of the Related Art PA1 An output window made of a beryllium thin film is formed in a window flange 37 which is hermetically mounted on an output end of the outgoing vacuum duct 30. SR light entering the outgoing vacuum duct 30 transmits through the output window formed in the window flange 37 and is radiated to the outside of the vacuum duct 30. An X-ray stepper 50 is disposed facing the window flange 37. The X-ray stepper 50 holds a semiconductor substrate 51 at the position where SR light radiated from the window flange 37 is applied. An exposure mask 52 is supported in front of the semiconductor substrate 51. With reference to FIG. 1, the structure of a conventional X-ray exposure system will be described. Reference to FIG. 1 is also made when embodiments of the invention are described later. The X-ray exposure system comprises an SR light generator unit 1, an SR light transmission unit 10 and an X-ray stepper 50. The SR light generator unit 1 comprises a vacuum room 2 and an electron beam circular orbit 3 formed therein. SR light is radiated from electrons moving along the circular orbit 3. This SR light is output from a beam output port of the vacuum room 2. The SR light transmission unit 10 has an incoming vacuum duct 11, a mirror box 12 and an outgoing vacuum duct 30. Incoming opening 13 and outgoing opening 14 are formed in the wall of the mirror box 12. The incoming vacuum duct 11 hermetically communicates the beam output port of the SR light generator unit 1 with the incoming opening 13. In the vacuum duct 11, a vacuum shielding valve (not shown), an SR light shielding shutter (not shown) and the like are mounted. The input port of the outgoing vacuum duct 30 is hermetically coupled to the outgoing opening 14. A reflection mirror 15 is disposed in the mirror box 12 and supported by a mirror swinging mechanism 16. SR light entering the mirror box 12 via the incoming opening 13 is reflected by the mirror 15 and enters the outgoing vacuum duct 30 via the outgoing opening 14. The mirror 15 is disposed such that its incidence plane contains an optical center axis of incidence SR light and a normal to a reflection plane at the reflection point and such that an angle between the optical center axis and the reflection plane is about 1 to 2.degree., i.e., such that the incidence angle is about 89 to 88.degree.. The swinging mechanism 16 swings the mirror 15 a long an axis vertical to the incidence plane and passing the reflection point of SR light, i.e., a horizontal rotary shaft is used as a swing axis. As the mirror 15 swings, reflected SR light is swung up and down. The swing axis may be set to a position different from the reflection point of SR light. Although SR light is irradiated omnidirectionally in the horizontal plane, it only has a spread of about +/-1 mrad (mili-radian) in the vertical plane. By swinging the mirror 15, SR light is swung in the vertical direction so that SR light can be applied to a broad surface area of the semiconductor substrate 51. SR light diverges in the horizontal direction. This SR light is therefore converged in the horizontal direction to make it parallel light fluxes, so that SR light radiated from the light source can be more efficiently used. If the intensity of X-ray is increased, the X-ray exposure time can be shortened. In order to converge SR light in the horizontal direction, as the mirror 15 shown in FIG. 1, a cylindrical mirror or a toroidal mirror is used. A substantial focal length of a cylindrical mirror or toroidal mirror changes with an incidence angle of SR light. As the mirror 15 is swung, the incident angle changes and the focal length with respect to the horizontal plane changes with the incidence angle correspondingly. As the focal length changes, an energy density of SR light on the surface of the semiconductor substrate 51 changes. It is therefore difficult to uniformly apply X-rays to the surface of the semiconductor substrate 51. SR light reflected by a cylindrical mirror or a toroidal mirror has a shape extending along generally a circular line in the cross sectional plane (cross beam section) perpendicular to the optical axis. Therefore, an SR light radiation area on the exposure surface of the semiconductor substrate 51 also has a shape extending along generally a circular line. SR light can be applied to a broad area by moving this radiation area in the radial direction passing through a center point of the circular line. A length of the circular radiation area cut along a straight line parallel to the motion direction of the area becomes longer at a position more remote from the center of the radiation area in the horizontal direction. In addition, the exposure amount on the exposure plane obtained by swinging the mirror and moving such an exposure area in the vertical direction on the exposure plane becomes larger at a position more remote from the center of the exposed area. It is therefore difficult to uniformly expose the exposure plane by using SR light having a circular radiation area. SUMMARY OF THE INVENTION It is an object of the present invention to provide an SR light transmission system capable of improving an exposure performance of an exposure apparatus using SR light. It is another object of the present invention to provide a synchrotron radiation light transmission system capable of making a distribution of exposure amounts in an exposure area nearly uniform. According to one aspect of the present invention, there is provided a synchrotron radiation light transmission system, comprising: a mirror box formed with an incoming opening and an outgoing opening through which synchrotron radiation light having a horizontally elongated cross section passes; a mirror disposed in the mirror box for reflecting the synchrotron radiation light; and a swinging mechanism for supporting the mirror so as to allow the synchrotron radiation light entering the mirror box via the incoming opening to be reflected by the mirror and to change a travelling direction in a vertical plane and for swinging the mirror to change a change angle of the travelling direction, wherein a swing axis is on a cross line, or on its extension, between an incidence plane of the synchrotron radiation light and a tangential plane of the mirror at a reflection point and also on an incidence side of the synchrotron radiation light from the reflection point, the reflection point of the synchrotron radiation light moves on a reflection plane of the mirror as the mirror swings, and the mirror is swung so that an incidence angle becomes larger as a distance between a light source of the synchrotron radiation light and the reflection point becomes longer. If the mirror is a cylindrical surface mirror, a toroidal mirror, a conical surface mirror or the like, a focal length in the horizontal plane changes with an incidence angle of synchrotron radiation light. A change in the focal length is compensated by changing the position of the reflection point to thereby form suitable reflected SR light. According to another aspect of the present invention, there is provided a synchrotron radiation light transmission system, comprising: a mirror box formed with an incoming opening and an outgoing opening through which synchrotron radiation light having a horizontally elongated cross section passes; a light source for making the synchrotron radiation light incident upon the incoming opening of the mirror box; a mirror disposed in the mirror box for reflecting the synchrotron radiation light; and a swinging mechanism for supporting the mirror so as to allow the synchrotron radiation light entering the mirror box via the incoming opening to be reflected by the mirror and to change a travelling direction in a vertical plane and for swinging the mirror to change a change angle of the travelling direction, wherein a reflection point on the mirror of the synchrotron radiation light moves on a reflection plane of the mirror as the mirror swings, the mirror is swung so that an incidence angle becomes larger as a distance between a light source of the synchrotron radiation light and the reflection point becomes longer, and a distance between the reflection point of the synchrotron radiation light and a swing axis of the mirror is not shorter than a distance between the reflection point and the light source. As the swing radius is set longer than the distance between the reflection point and light source, the energy density of synchrotron radiation light on the exposure plane can be made more uniform. According to another aspect of the present invention, there is provided a synchrotron radiation light transmission system comprising: an optical system for transmitting synchrotron radiation light; and a thin film disposed in an optical path of the synchrotron radiation light, made of material capable attenuating the synchrotron radiation light, and formed so that an optical path length in the thin film of the synchrotron radiation light transmitting through the thin film is not uniform in an in-plane of the thin film. Since the optical path length in the thin film of synchrotron radiation light is different at each point in the in-plane of the thin film, the synchrotron radiation light can be attenuated by different amounts at respective points in the in-plane of the thin film. According to a further aspect of the present invention, there is provided a synchrotron radiation light transmission system, comprising: a mirror box formed with an incoming opening and an outgoing opening through which synchrotron radiation light having a horizontally elongated beam cross section passes; a mirror disposed in the mirror box for reflecting the synchrotron radiation light; a duct coupled to the outgoing opening of the mirror box for defining a hollow space through which the synchrotron radiation light output from the outgoing opening passes; and a thin film mounted at an output port of the duct for attenuating and transmitting the synchrotron radiation light, wherein an optical path length in the thin film of the synchrotron radiation light transmitting through the thin film is made different in each point in an in-plane of the thin film to change an attenuation amount of the synchrotron radiation light in the in-plane. Since the transmission optical path length of the thin film is different at each point, the attenuation amount of synchrotron radiation light also become different. By controlling the transmission optical path length distribution, a desired intensity distribution of the synchrotron radiation light transmitted through the thin film can be obtained. As above, an attenuation amount distribution of SR light can be provided in a plane perpendicular to the optical axis. If the invention is applied to X-ray exposure using SR light, uniform exposure is possible by attenuating SR light so as to compensate for a variation of SR light intensities in the beam cross section.