JPH06235863A - Cata-dioptric system - Google Patents

Abstract

PURPOSE:To improve image forming function by reducing flare and ghost generated from a cata-dioptric system. CONSTITUTION:In the cata-dioptric system provided with a 1st optical system K1 having a positive refractive power and for forming a primary image I1 of an object and a 2nd optical system K2 having a positive refractlve power and for forming a secondary image I2 with light from the primary image I1 arranged in this order from the object side, a field diaphragm B provided with an aperture formed to a prescribed shape is arranged on a position where the primary image I1 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catadioptric optical system suitable for projecting and transferring a circuit pattern on a mask onto a photosensitive substrate.

[0002]

2. Description of the Related Art Conventionally, as the above-mentioned catadioptric optical system, the one disclosed in, for example, JP-A-61-29815 is known. The catadioptric optical system disclosed in Japanese Patent Application Laid-Open No. 61-29815 includes a partial optical system for forming a primary image and a partial optical system for forming a secondary image by light from the primary image. Is configured to have.

[0003]

However, in the catadioptric optical system disclosed in JP-A-61-29815 as described above, no consideration has been given to the prevention of flare and ghost. Therefore, on the image plane (on the secondary image plane)
However, there is a problem that flare and ghosts occur and the image forming performance deteriorates.

Therefore, an object of the present invention is to provide a catadioptric optical system that improves the imaging performance by reducing the flare and ghost generated from the catadioptric optical system.

[0005]

In order to achieve the above object, for example, as shown in FIG. 1, a catadioptric optical system according to the present invention comprises a primary image of an object having positive refractive power in order from the object side. the first partial optical system K ₁ to form an I _1, as a second partial optical system K ₂ for forming a secondary image I ₂ by light from the primary image I ₁ has a positive refractive power arrangement And the primary image I
A field stop B having an opening having a predetermined shape is arranged at a position where ₁ is formed.

[0006]

As described above, in the present invention, since the field stop having the opening of the predetermined shape is arranged at the conjugate point (primary image plane) of the object plane and the secondary image plane, it contributes to the image formation. Not harmful light can be blocked by this field stop. Therefore,
The influence of flare and ghost is reduced, and the imaging performance of the catadioptric optical system can be improved.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration and optical path of a first embodiment of a catadioptric optical system according to the present invention. The first embodiment is an example in which the catadioptric optical system according to the present invention is applied to the projection optical system of a projection exposure apparatus. Note that an illumination optical system for illuminating the object plane O is omitted in FIG.

As shown in FIG. 2 (a), a predetermined circuit pattern area PA is formed on the mask Ma serving as the object plane O, and this mask Ma and an arc-shaped illumination optical system (not shown) are formed. The illumination area LA is relatively moved along the scanning direction. At this time, the circuit pattern area PA of the mask Ma is illuminated while being scanned in the arc-shaped illumination area LA.

Here, the above-mentioned arc-shaped illumination area LA.
2A, an arc having a predetermined radius r and a radius r translated from the arc by a distance a _{1 in the} scanning direction are shown in FIG.
The area is surrounded by the circular arc and the straight line with the interval b ₁ . Here, it referred to the distance a ₁ between the slit width a ₁ of the illumination area LA of the arc, called the distance b ₁ between the slit length b ₁ of the illumination area LA. As the arc-shaped illumination area, a concentric area centered on a predetermined point can be considered, but it is not desirable because the exposure amount at the time of scan exposure differs between the center and the end of the exposure area.

In the catadioptric optical system shown in FIG.
A photosensitive substrate having a surface coated with a photoresist or the like is provided at a position where the next image I ₂ is formed. Then, as shown in FIG. 2B, the circuit pattern PA illuminated in the illumination area LA is projected onto the photosensitive substrate as an arc-shaped exposure area EA by the catadioptric optical system.
Here, if the exposure area EA and the photosensitive substrate are relatively moved in the scanning direction, the scanning exposure, so-called step.
And-scan type projection exposure can be realized. By performing this scanning exposure, the shot area S is formed on the photosensitive substrate.
A is formed. The shape of the exposure area EA is similar to the shape of the illumination area LA.

Returning to FIG. 1, the light from the mask surface (object surface O) illuminated in the illumination area as described above passes through the lens components L _{1 to} L ₃ arranged along the optical axis Ax _1. Then, it is deflected by approximately 45 ° by the plane reflecting mirror MP ₁ and is reflected by the first concave reflecting mirror M ₁ which is arranged along the optical axis Ax ₂ which is perpendicular to the optical axis Ax ₁ and whose concave surface faces the incident side of the light beam. To be done. Then, a primary image I ₁ of the object plane O is formed on the reflection side of the first concave reflecting mirror M ₁ . Here, the lens components L _{1 to} L ₃ and the first concave reflecting mirror M
₁ and ₁ constitute the first partial optical system K ₁ .

The light from the primary image I ₁ has an optical axis Ax ₂
The light beam is deflected by approximately 45 ° by the plane reflecting mirror MP ₂ via the lens components L _{4 to} L ₆ arranged along. _On the reflection side (light emission side) of this flat reflecting mirror MP ₂ , along the optical axis Ax ₃ (parallel to the optical axis Ax ₁ ) perpendicular to the optical axis Ax ₂ , the lens component L ₇ and the second concave surface are formed. a reflecting mirror M ₂ is disposed, light emitted from the plane reflecting mirror MP ₂ is reflected by the second concave reflecting mirror M ₂ via the lens component L _7, through a lens component L ₇ again To the lens components L _{8 to} L ₁₄ . The lens components L _{8 to} L ₁₄ have positive refracting power as a whole, and light from the lens component L ₇ causes a secondary image I ₂ which is a reduced image of the _primary image I ₁ on the substrate. Form. Here, the lens component L ₄ ~L _6, the lens component L _7, the second concave reflecting mirror M ₂ and the lens component L ₈ ~L ₁₄ constitutes a second partial optical system K _2. The imaging magnification of the entire catadioptric optical system according to the present embodiment is a reduction magnification of 1/5.

In the catadioptric system according to this embodiment, the field stop B having an opening of a predetermined shape is arranged at the position where the primary image I ₁ is formed. Hereinafter, a specific configuration of the field stop B will be described. FIG. 3 is a plan view showing the shape of the opening of the field stop B. This Figure 3
In, the arc-shaped opening portion BA is surrounded by an arc (partial circle) having a predetermined radius R, an arc translated from the arc by a predetermined distance a ₃ and a straight line with a predetermined interval b _3. Is. The distance a ₃ is the slit width a ₃ and the interval b ₃ is the slit length b ₃ .

Here, since a light ray (harmful light) that does not contribute to image formation and that passes through the optical path of the catadioptric optical system does not pass through the opening BA of the field stop B, the secondary image plane I ₂ (photosensitive substrate).
Don't reach the top As a result, the image (secondary image) of the circuit pattern PA is formed while the influence of flare and ghost is reduced. Further, the field stop B causes the exposure area EA formed on the shot area SA on the photosensitive substrate.
Is accurately defined without blurring of the peripheral portion.

The slit width a ₂ of the exposure area EA shown in FIG. 2B is the slit width a ₂ of the opening BA shown in FIG.
_{It is} uniquely determined by ₃ . Here, the width a of the opening BA
_{If 3} is made variable, the slit width a ₂ of the exposure area can be made variable. Specifically, as shown in FIG.
The light-shielding member 10 having an arc having a predetermined radius and the light-shielding member 20 having an arc having the same radius as that of the light-shielding member 10 constitute the field stop B. Then, the light blocking member 10
Is provided movably in the arrow direction (slit width direction) in the figure by the motor 11 and the feed screw 12, and the light shielding member 20 is movably provided in the arrow direction (slit width direction) in the figure by the motor 21 and the feed screw 22. The slit width of the arc-shaped opening can be made variable. This makes it possible to change the slit width of the exposure area EA.

In this embodiment, since scanning exposure is performed while moving the photosensitive substrate and the exposure area relatively, if the slit width of the exposure area EA is made variable, the exposure on the photosensitive substrate is performed. The amount can be adjusted. In order to make the width of the opening of the field stop B variable, for example, the field stop B is configured by arranging a plurality of openings having different shapes in a turret shape, and one of the plurality of openings is formed. It is also conceivable to arrange the two in a position where the primary image I ₁ is formed. Also by such a method, the shape of the opening of the field stop B can be made variable.

When the illuminance uniformity in the illumination area LA is poor, the shape of the opening BA of the field stop B is the same as the illumination area LA.
It is desirable to make the shape according to the illuminance distribution. For example, as shown in FIG. 5 (a), when the illumination area LA has an illuminance distribution in which the illuminance decreases in the slit length direction (direction orthogonal to the scanning direction), as shown in FIG. 5 (b), The field stop B having the openings BA having different slit widths at both ends may be used. As a result, it is possible to obtain a uniform distribution of the exposure amount on the photosensitive substrate that is scanned and exposed.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a diagram showing the configuration and the optical path of this embodiment. The present embodiment is an application of the present invention to the catadioptric optical system disclosed in the first embodiment of JP-A-61-29815. In FIG. 6, the light ray from the object plane O is sequentially reflected by the first concave mirror M ₁ and the first convex mirror M ₂ , and reaches the second concave mirror having the same curvature as the first concave mirror M ₁ . The light beam reflected by the second concave mirror is
A primary image I ₁ is formed on the exit side of the lens group G ₁ through the lens group G ₁ . Here, the first and second concave mirrors M ₁ ,
M ₃ , the first convex mirror M _2, and the lens group G ₁ constitute a first partial optical system K ₁ .

The first partial optical system K₁Formed by
Primary image I₁From the third concave mirror M_FourReflected at
And then the second lens group G₂This second lens through
Group G ₂Secondary image I on the exit side of₂To form. Where the third
Concave mirror M_FourAnd the second lens group G ₂Is the second partial optical system K₂
Make up. The entire catadioptric optical system according to the present embodiment
The image forming magnification of is a reduction ratio of 1 / 2.25 times.
It

In the present embodiment as well, the first partial optical system is used.
System K₁Primary image I formed by₁At the position of
A field stop B having a circular opening is arranged. this
With the field stop B, harmful light that becomes flare or ghost
Shielding light to improve the imaging performance of catadioptric systems
You can In addition, as in the first embodiment described above, the secondary image I ₂
And the photosensitive substrate are scanned, the aperture of the field stop B
Of the secondary image plane I by changing the width of₂Adjust the exposure amount at
be able to. Furthermore, the illuminance of the illumination area on the object plane O
Specify the shape of the aperture of the field stop B according to the cloth.
For example, the secondary image plane I₂Exposure can be made uniform
It

As described above, according to the present invention, the catadioptric system has the first partial optical system for forming the primary image of the object and the second partial optical system for relaying the primary image to form the secondary image. Any optical system can be applied.
Further, in the present embodiment, one set of field stop B is arranged at the position where the primary image is formed.
Is not limited to one set, and for example, in addition to the first and second partial optical systems, a third partial optical system that relays a secondary image formed by the second partial optical system to form a tertiary image Is provided, two sets of field diaphragms can be arranged at the position where the primary image is formed and the position where the secondary image is formed.

[0022]

As described above, according to the present invention, it is possible to reduce the influence of the ghost and flare generated from the catadioptric optical system, so that the imaging performance of the catadioptric optical system can be improved. Further, since the field stop is arranged at a position conjugate with the secondary image plane, the exposure range can be strictly defined. Furthermore, if you change the shape of the aperture of the field stop,
It is possible to adjust the exposure amount on the secondary image plane. Then, if the shape of the field stop is made to correspond to the illuminance distribution on the object plane, there is also an effect that the exposure amount on the secondary image plane can be made uniform.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration and an optical path of a first embodiment according to the present invention.

FIG. 2 is a plan view showing the shapes of an illumination area on the object plane and an exposure area on the image plane.

FIG. 3 is a plan view showing the configuration of a field stop.

FIG. 4 is a schematic diagram showing a configuration in which a field diaphragm is a movable diaphragm.

FIG. 5 is a diagram showing an example of correspondence between an illuminance distribution and a shape of an opening of a field stop.

FIG. 6 is a diagram showing a configuration and an optical path of a second embodiment according to the present invention.

[Explanation of symbols]

K ₁ ... 1st partial optical system, K ₂ ... 2nd partial optical system, O ... object plane, I ₁ ... primary image, I ₂ ... secondary image, B ... field stop,

Claims (3)

[Claims] 1. A first partial optical system having a positive refracting power and forming a primary image of the object in order from the object side, and a secondary image having a positive refracting power and light from the primary image forming a secondary image. In a catadioptric optical system having a second partial optical system to be formed, a field diaphragm having an opening of a predetermined shape is arranged at a position where the primary image is formed. system. 2. The field stop has a plurality of openings having different shapes, and one of the plurality of openings is arranged at a position where the primary image is formed. The catadioptric optical system according to claim 1, which is characterized in that: 3. The catadioptric system according to claim 1, wherein the field stop is configured such that the shape of the opening is variable.