JP2584925Y2 - Parabolic mirror device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a parabolic mirror device for collimating divergent rays such as SOR light (synchrotron radiation), and to reduce unevenness of ray density due to collimation. It is.

[0002]

2. Description of the Related Art SOR light is high-power light emitted from a synchrotron, and is expected to be applied to various fields such as the production of ultra-super LSI circuits, diagnosis in the medical field, molecular analysis, and structural analysis.

FIG. 2 shows an outline of a small SOR device. An electron beam generated by a charged particle generator (such as an electron gun) 10 is accelerated to near the speed of light by a linear accelerator (linac) 12 and deflected by a deflection electromagnet 16 of a beam transport unit 14.
The light enters the storage ring 22 via the inflector 18. The electron beam incident on the storage ring 22 is supplied with energy by the high-frequency
The light is converged at 25 (for the vertical direction) and 25 (for the horizontal direction), deflected by the bending electromagnet 24, and continues to go around the storage ring 22. Synchrotron radiation generated when deflected by the deflection electromagnet 24 passes through the beam channel 26 to the exposure unit 2.
8 and used as a light source for lithography and the like for creating an ultra-super LSI circuit.

The SOR light is divergent light whose light source is on the orbit of the electron beam in the storage ring 22. If this light is used as it is as a light source for lithography, a run-out error occurs. Therefore, it is necessary to collimate the SOR light using a parabolic mirror. FIG. 3 is a plan view showing how the SOR light 32 is made parallel in the horizontal direction. The SOR light 32 emitted from the light source 30 on the electron beam orbit and diverging in the horizontal direction is incident on an oblique incidence mirror 34 disposed in the beam channel 26 (FIG. 2). The oblique incidence mirror 34 has a reflection surface 36 formed on a paraboloid having the light source 30 as a focal position, and collimates and emits the SOR light 32. By using the collimated SOR light 32 'as a light source for lithography, it is possible to prevent a run-out error from occurring.

[0005] However, in the arrangement of FIG.
Assuming that 2 is θ1 = θ2, on the D surface, D1 = D2, while after being reflected by the oblique incidence mirror 34,
Due to the difference in the incident angle between the a side and the b side, d1> d2. Therefore, the light ray density (the number of light rays per unit length) becomes dense on the a side and coarse on the b side. Therefore, when lithography is performed using the SOR light 32 'as it is, the entire exposed surface is not uniformly exposed, and there is a problem that uneven exposure occurs in the horizontal direction.

Conventionally, to solve such a problem, there is a device proposed in Japanese Utility Model Application No. 3-102610 filed by the present applicant. FIG. 4 is a plan view showing an outline of a lithography exposure system configured by using this. The SOR light 32 emitted and diverged from the deflection position of the storage ring of the synchrotron on the electron beam trajectory 38 as the light source 30 is reflected by the parabolic mirror 34 and parallelized in the horizontal direction. S emitted from parabolic mirror 34
The light density of the OR light 32 'is coarse on the b side and dense on the a side.

The SOR light 32 ′ is further transmitted to the parabolic mirror 4.
The light is reflected at 0 and is also parallelized in the vertical direction. SOR light 3
2 has a small spread in the vertical direction.
By swinging 0 around the swing shaft 42, the SOR light 32 ″ is swung up and down to secure an exposure area required for lithography.

[0008] The SOR light 32 "is
The lithography is performed by irradiating an exposure object (mask and wafer) 46 in the exposure apparatus 28 (FIG. 2) through a beryllium window 44 provided at the end of (FIG. 2).

The beryllium window 44 is formed in a curved shape with a constant thickness, and the intensity is equal on the a-side and the b-side by utilizing the difference in the optical path length of the SOR light 32 ″ passing through the beryllium window 44. (I.e., so that the attenuation amount is larger on the a side).

FIG. 5 shows a state of each part in FIG. SOR light 3 emitted from parabolic mirror 34
The light ray density in the horizontal direction of 2 '(same for 32 ") is dense on the a side and coarse on the b side as shown in (a), but the transmission amount through the beryllium window 44 is as shown in (b). Since the b-side is larger than the a-side, the light density of the SOR light 32 ″ ′ emitted from the beryllium window 44 becomes substantially uniform in the horizontal direction as shown in FIG. The exposure unevenness in the vertical direction is eliminated by swinging the parabolic mirror 40 to swing the SOR light 32 ″ in the vertical direction.

[0011]

According to the horizontal unevenness eliminating structure shown in FIG. 4, there is a problem that the emission window 44 needs to have a special shape.

This invention is intended to solve the above-mentioned problems in the prior art and to provide a parabolic mirror device capable of reducing the unevenness of the light beam density without using a specially shaped exit window. .

[0013]

According to the present invention, there is provided a parabolic mirror device in which a reflecting surface is constituted by a parabolic surface, and a divergent light beam enters and exits as substantially parallel light. The angle between the reflected light and the reflecting surface is set to an angle near the critical angle at which the reflectance characteristic changes.

[0014]

According to this invention, the angle between the incident light beam and the reflection surface is set to an angle near the critical angle where the reflectance characteristic changes, so that the incident light beam is located at a position where the density of the reflected light is coarse. The angle of the incident light becomes deeper and the reflectivity becomes lower at the position where the density of the reflected light becomes denser, and the light density becomes almost uniform as a whole. Unevenness can be reduced.

[0015]

FIG. 1 is a plan view showing an embodiment in which the present invention is applied to an exposure apparatus for performing lithography using SOR light. Electron beam trajectory 38 of the synchrotron storage ring
SO that is emitted and diverged using the upper deflection position as the light source 30
The R light 32 is reflected by the parabolic mirror 34 (oblique incidence mirror) and is parallelized in the horizontal direction.

The SOR light 32 ′ is further transmitted to the parabolic mirror 4.
The light is reflected by 0 (oblique incidence mirror) and parallelized in the vertical direction. Since the SOR light 32 has a small spread in the vertical direction, by swinging the parabolic mirror 40 about the swing shaft 42, the SOR light 32 "is swung up and down to secure an exposure area required for lithography. .

The SOR light 32 ″ is transmitted to the beam channel 26.
The lithography is performed by irradiating an exposure object (mask and wafer) 46 in the exposure apparatus 28 (FIG. 2) through a beryllium window 44 provided at the end of (FIG. 2). The beryllium window 44 has a constant thickness and is formed in a flat plate shape.

The parabolic mirror 34 is made of oxygen-free copper, SiC, A
u, Pt, and the like, and the reflection surface 36 is formed as a uniaxial paraboloid having the light source 30 as a focal position. Incident SOR light 32 and reflection surface 36 on parabolic mirror 34
FIG. 6 shows the relationship between the angle α and the reflectance. According to this, the reflectance is large at an angle smaller than the critical angle α ₀ , and the reflectance sharply decreases at an angle deeper than the critical angle α ₀ . In the related art (FIG. 4), a region D1 that is shallower than the critical angle α _{0 and} has a large reflectance is used.

On the other hand, the parabolic mirror 34 shown in FIG. 1 uses a region D2 near the critical angle α _{0 and a} deeper angle.

FIG. 7 shows the state of each part in FIG. 1 in the case of such an arrangement. In FIG. 7, (a) shows a reflectance of 1
The output light density of the parabolic mirror 34 assuming 00%, (b) is the reflectance of the parabolic mirror 34, and (c) is the actual light density at the B position.

The light density of the reflected light emitted from the reflecting surface 36 is higher on the a side than on the b side as shown in FIG. On the other hand, the angle α1 on the a side and the angle α2 on the b side are α1> α
2, the reflectance on the b side becomes higher as shown in (b). Accordingly, when these relationships are combined, the light beam density at the position B in FIG. 1 becomes substantially uniform as shown in (c), and the uneven exposure in the horizontal direction on the exposure target 46 can be eliminated. Therefore, the beryllium window 44 does not need to have a special shape as shown in FIG.

The parabolic mirror 40 is also made of oxygen-free copper, Si
The reflection surface 41 is formed of a paraboloid in one axis direction having the light source 30 as a focal position.

Further, since the unevenness of exposure in the vertical direction by the parabolic mirror 40 is eliminated by the swing itself of the parabolic mirror 40, the parabolic mirror 40 has an area which is shallower than the critical point and has a high reflectance. (D1 in FIG. 6) can be used.

[0024]

[Modification] In the above embodiment, the case where the present invention is applied to lithography using an SOR apparatus has been described.
The present invention can also be applied to other devices that collimate divergent light with a parabolic mirror.

[0025]

As described above, according to the present invention, since the angle between the incident light beam and the reflecting surface is set to an angle near the critical angle where the reflectance changes, the density of the reflected light is low. In the position where becomes, the angle of the incident light beam becomes shallower and the reflectance increases, and in the position where the density of the reflected light becomes dense, the angle of the incident light beam becomes deeper and the reflectance decreases, and as a whole, it is almost uniform. The light density can be reduced to reduce exposure unevenness.

[Brief description of the drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 is a plan view showing an outline of the SOR device.

FIG. 3 is a diagram illustrating a state in which divergent light from a light source is collimated by a parabolic mirror, and a ray density at that time.

FIG. 4 is a plan view showing a conventional exposure unevenness eliminating method.

FIG. 5 is a diagram showing a state of each unit in FIG. 4;

FIG. 6 is a diagram showing a reflectance characteristic of the parabolic mirror shown in FIG. 1;

FIG. 7 is a diagram showing a state of each unit in FIG. 1;

[Explanation of symbols]

 32 SOR light (divergent light beam) 34 Parabolic mirror 36 Reflecting surface

Claims (1)

(57) [Scope of request for utility model registration] 1. A parabolic mirror device wherein a reflecting surface is constituted by a parabolic surface, and a divergent light beam enters and is emitted as substantially parallel light. A parabolic mirror device in which the angle formed is set to an angle near the critical angle at which the reflectance characteristic changes.