JPH08330212A - Exposure device - Google Patents

Abstract

PURPOSE: To drastically reduce the difference of resolution between vertical and horizontal directions within an exposure surface. CONSTITUTION: An exposure device for exposing a photosensitive substrate W to a mask pattern is provided with a light source means 10 for supplying light, multiple light source image forming means 30 and 60 for forming a plurality of light source images by dividing light from the light source means into a plurality of parts, and a focusing optical system 6 for overlappingly lighting a mask M with a specific pattern by focusing light from the multiple light source image forming means. Then, aperture stops AS1 and AS2 are arranged at a light development position or near the light development position which is formed by the multiple light source image forming means and the length of the aperture of the aperture stop corresponding to a first direction and that of the aperture of the aperture stop corresponding to a second direction are allowed to differ to compensate the difference in resolution in the specific first direction (X direction) on the photosensitive substrate and the second direction (Y direction) which is vertical to the first direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical device for uniformly illuminating an object to be illuminated, and more particularly to an illumination optical device suitable for manufacturing semiconductor elements, liquid crystal elements and the like.

[0002]

2. Description of the Related Art Conventionally, for example, an illumination optical device as shown in FIG. 7 applied to an exposure apparatus for semiconductor manufacturing is known. As shown in FIG. 7A, the light flux from the light source 1 such as a mercury arc lamp is condensed by the elliptical mirror 2 and then converted into a parallel light flux by the collimator lens 3.
Then, as shown in FIG. 7B, the parallel light flux passes through a fly-eye lens 4 composed of an assembly of lens elements 4a having a quadrangular cross section, thereby forming a plurality of light source images on the exit side thereof. To be done. An aperture stop 5 having a circular opening is provided at this light source image position. The light fluxes from the plurality of light source images are condensed by the condenser lens 6 and uniformly illuminate the mask M as an irradiation object in a superimposed manner.

The circuit pattern on the mask M is transferred onto the wafer W by the projection optical system 7 including the lenses 71 and 72 by the above illumination optical device. This wafer W is placed on a wafer stage WS that moves two-dimensionally. In the exposure apparatus of FIG. 14, when the exposure of one shot area on the wafer is completed, the exposure to the next shot area is performed. Then, so-called step-and-repeat type exposure in which the wafer stage is two-dimensionally moved is sequentially performed.

[0004]

By the way, in recent years, the mask M is irradiated with a rectangular or arc-shaped light beam, and the mask M and the wafer W, which are arranged conjugate with respect to the projection optical system, are scanned in a certain direction. Therefore, a scanning exposure method has been proposed in which the circuit pattern of the mask M is transferred onto the wafer under high throughput.

Here, in order to apply the scanning optical system by applying the illumination optical device as shown in FIG. 7, it is necessary to illuminate the reticle with, for example, a rectangular light beam. Therefore, for example,
As shown in FIG. 7C, it is conceivable to configure the fly-eye lens 4. That is, since the light fluxes from the individual lens elements forming the fly-eye lens 4 illuminate the mask M in a rectangular shape, the lenses forming the fly-eye lens 4 are formed as shown in FIG. In order to make the cross section of the element 4a into a rectangular shape similar to the shape of the irradiation area, and to make the numerical aperture of the illumination optical system for the illumination area on the mask M equal, a lens element having this rectangular lens cross section 4a is bundled into a square so that the circular aperture of the aperture stop 5 is inscribed as a whole. As a result, the mask M can be illuminated in a rectangular shape with high illumination efficiency.

However, in the fly-eye lens 4 having a sectional shape as shown in FIG.
Since the cross section of a has a rectangular shape, the number of lens elements arranged in the vertical direction is significantly different from the number of lens elements arranged in the horizontal direction. As a result, as shown in FIG. 7C, the light source image is not evenly distributed inside the circular aperture 5a of the aperture stop 5, and the light source is not vertically (Y direction) and horizontally (X direction). There is a problem that the density of the light intensity of the image is different. Here, the shape of the aperture stop plays the role of a σ stop that determines the coherence of the illumination optical system, and the fact that the light intensity density of the light source image is different in each direction causes variation in the σ value. Means Therefore, the difference between the σ values in the vertical and horizontal directions occurs due to the difference in the light intensity density of the light source image in the vertical and horizontal directions, and finally the vertical and horizontal directions of the exposure apparatus itself. There is a problem that the marginal resolutions of and differ greatly.

In view of the above, the present invention solves the above-mentioned problems and significantly reduces the difference in resolution between the vertical and horizontal directions within the exposure plane, that is, the difference in resolution between the respective directions. Is intended to provide.

[0008]

In order to achieve the above object, the present invention provides a light source means for supplying light and a multi-light source for dividing light from the light source means into a plurality of light source images. An image forming unit and a condensing optical system that condenses light from the multi-light source image forming unit and illuminates a mask having a predetermined pattern in a superimposed manner, and exposes the pattern of the mask on a photosensitive substrate. In the exposure apparatus, an aperture stop is arranged at or near the light source image position formed by the multi-light source image forming means, and a predetermined first direction on the photosensitive substrate is perpendicular to the first direction. In order to correct the difference in resolution in the second direction, the length of the aperture of the aperture stop corresponding to the first direction and the length of the aperture of the aperture stop corresponding to the second direction are made different. It is what

In this case, it is desirable that the aperture of the aperture stop has an elliptical shape. Further, based on the above structure, a projection optical system for transferring the pattern image of the mask onto the photosensitive substrate may be arranged between the mask and the photosensitive substrate.

[0010]

[Operation] In the present invention, in order to reduce the variation in resolution in each direction within the exposure surface on the photosensitive substrate, the light intensity distribution, the light intensity distribution, and the light intensity distribution for forming a plurality of light source images in the illumination optical system in the exposure apparatus The focus is on deforming the shape of the aperture of the aperture stop by varying the intensity density in each direction.

[0011]

1 shows an example in which the illumination optical device according to the first embodiment of the present invention is applied to an exposure apparatus for semiconductor manufacturing. 1A is a diagram showing a configuration of the device of the first embodiment as seen from directly above, and FIG. 1B is a diagram showing a cross-sectional configuration of the device of FIG. 1A as seen from a lateral direction. Is. Less than,
The first embodiment will be described in detail with reference to FIG.

As shown in FIG. 1, the light source means for supplying a parallel light flux having a rectangular light flux cross section is composed of a parallel light flux supply section 10 and a light flux shaping section 20, and an excimer laser or the like is used as the parallel light flux supply section. The light source 10 outputs a parallel light flux of wavelength light of 248 nm (KrF) or 192 nm (ArF), and the cross-sectional shape of the parallel light flux at this time is rectangular. This light source 1
The parallel light flux from 0 is incident on the beam shaping optical system 20 as a light flux shaping unit that shapes the light flux to have a predetermined cross-sectional shape.
The beam shaping optical system 20 is composed of two cylindrical lenses (21, 22) having a refractive power in a direction perpendicular to the paper surface of FIG. 1A (direction of the paper surface of FIG. 1B). The cylindrical lens 21 on the light source side has a positive refractive power, and collects the light flux in the paper surface direction of FIG. 1B, while the cylindrical lens 22 on the illuminated surface side has a negative refractive power. , The condensed light flux from the cylindrical lens 21 on the light source side is diverged and converted into a parallel light flux. Therefore, the parallel light flux from the light source 1 via the beam shaping optical system 20 is
The light flux width in the paper surface direction of FIG. 1B is reduced and the light flux cross section is shaped into a rectangular shape. The beam shaping optical system 20
As the above, a combination of cylindrical lenses having a positive refractive power may be used, and further, an anamorphic prism or the like may be used.

The shaped light flux from the beam shaping optical system 20 enters an optical integrator 30 as a first multi-light source image forming means for forming a plurality of light source images linearly arranged in three rows. As shown in FIG. 2A, the optical integrator 30 includes a plurality of biconvex lens elements 30a having a substantially square lens cross section.
Are arranged (3 columns × 9 rows = 27), and the optical integrator 30 as a whole has a rectangular cross section. Each biconvex lens element 30a has the same curvature (refractive power) in the paper surface direction of FIG. 1A and the paper surface direction of FIG. 1B.

Therefore, the optical integrator 3
The parallel light fluxes that pass through the individual lens elements 30a forming 0 are collected, and a light source image is formed on the exit side of each lens element 30a. Therefore, at the exit side position A ₁ of the optical integrator 30, the lens element 30
A plurality of (3 columns × 9 rows = 27) light source images corresponding to the number of a are formed, and substantially secondary light sources are formed here.

The light beams from the plurality of secondary light sources formed by the optical integrator 30 are condensed by the relay optical system 40 to further form a plurality of light source images, and an optical integrator 50 as a second multi-light source image forming means. Incident on. As shown in FIG. 2B, the optical integrator 50 is configured by arranging a plurality of biconvex lens elements 50a having a rectangular lens cross section (9 columns × 3 rows = 27). Cage,
The lens element 50a is configured such that the sectional shape (aspect ratio) of the element 50a is similar to the sectional shape (aspect ratio) of the optical integrator 30. The optical integrator 50 as a whole has a square cross section. In addition, each lens element 50
a has the same curvature (refractive power) in the paper surface direction of FIG. 1A and the paper surface direction of FIG. 1B.

Therefore, the optical integrator 5
The light fluxes from the optical integrators 30 that pass through the individual lens elements 50a that form 0 are focused, and a light source image is formed on the exit side of each lens element 30a. Therefore, at the exit side position A ₂ of the optical integrator 30, a plurality of light source images arranged in a square shape are formed, and a tertiary light source is substantially formed here.

Here, the optical integrator 50 is used.
In the number of the plurality of light source images arranged in a square shape, the number of lens elements 30a forming the optical integrator 30 is N and the number of lens elements 50a forming the optical integrator 50 is M. At this time, N × M pieces are formed. That is, the plurality of light source images formed by the optical integrator 30 are transferred to the optical integrator 5 by the relay optical system 40.
Since the image is formed at the light source image positions of the respective lens elements 50a forming 0, a total of N × M light source images are formed at the exit side position A ₂ of the optical integrator 50.

The relay optical system 40 is an optical
Incident surface position B of integrator 30 ₁And optical
Incident surface position B of the integrator 50₂When and are conjugated,
To the exit surface position A of the optical integrator 30.₁
And the exit surface position A of the optical integrator 50₂When
Are conjugated. Position A where this tertiary light source is formed₂
Or, in the vicinity thereof, an opening of a predetermined shape described later
Aperture stop AS₁Is provided and this aperture stop
AS₁From the tertiary light source formed into a circular shape by
Is due to the condenser optical system 60 as the condensing optical system.
It is condensed and slit-shaped on the mask M as the illuminated object.
Uniformly illuminate (rectangular shape with long side and short side).

The mask M is held by the mask stage MS, and the wafer W as a photosensitive substrate is held by the wafer stage. Then, the mask M held on the mask stage MS and the wafer W placed on the wafer stage WS.
Are arranged conjugate with respect to the projection optical system 80, and the circuit pattern portion of the mask M illuminated in a slit shape is projected onto the wafer W by the projection optical system 80.

In the actual exposure with the above configuration,
The mask stage MS and the wafer stage WS are shown in FIG.
As shown in (b), they move in the opposite directions in the directions of the arrows.
Then, the circuit pattern on the reticle is transferred onto the wafer W.
It Now, the aperture stop according to this embodiment will be described in detail.
I do. In this embodiment, the second optical in shown in FIG.
Light source image position A formed by the integrator₂Or
As shown in FIG. 3A, the aperture stop AS in the X direction₁Open
Mouth A_P1Length Φ_X1And the opening in the Y direction orthogonal to the X direction
Aperture AS₁Opening A_P1Length Φ_Y1And are different (Φ_X1<
Φ_Y1), Or in the X direction, as shown in FIG.
Aperture stop AS ₂Opening A_P2Length Φ_X2And orthogonal to the X direction
Aperture stop AS in Y direction₂Opening A_P2Length Φ_Y2
And are different (Φ_X2> Φ_Y2), That is, an elliptical opening (A
_P1Or A_P2) Aperture stop (AS₁Or AS₂) Is set
Have been killed.

Here, FIG. 4A shows the second optical
A circle is placed at the position of the light source image formed by the integrator 50.
Shape A_P0If you place an aperture stop with
Circular opening from the exit side of the optical integrator 50
A_P0Each lens element 50 when looking at the aperture stop with
Light source image I formed on a₃₀Figure 4 shows the situation of
(B) is obtained by the second optical integrator 50.
At the position of the formed light source image, the elliptical shape shown in FIG.
Opening A_P1Aperture stop AS₁If you place
2 Elliptical shape from the exit side of the optical integrator 50
Shaped opening A_P1Aperture stop AS₁Ren when I saw
Source image I formed on the element 50a ₃₀Shows the situation
are doing. Further, FIG. 4C shows the second optical in
The position of the light source image formed by the integrator 50 is shown in FIG.
Elliptical opening A shown in (b)_P2Aperture stop AS
₂2nd optical integrator
Elliptical opening A from the exit side of 50_P2Aperture stop with
AS₂Formed on each lens element 50a when viewed
Light source image I₃₀Is shown. In addition, in FIG.
The lens of the second optical integrator 50.
The shaded light source image I shown in the element 50a₃₀Each ren
First image re-formed on the exit side of the zoom element 50a
Simplified appearance of the light source image of the entire Tikal Integrator
Shows.

From the comparison of (a) to (c) of FIG.
In (a), it can be understood that the light intensity distribution or the light density distribution of the light source image is different in the X direction and the Y direction due to the difference in the number of the light source images I _{30 in} the X direction and the Y direction. However, as shown in FIGS. 4B and 4C, the elliptical opening (A
_When an aperture stop (AS ₁ or AS ₂ ) having _P1 or A _P2 ) is arranged, the elliptical aperture in the X direction is changed in the X direction due to the difference in the number of the light source images I _{30 in} the X direction and the Y direction. Since the length Φ _X2 is different from the length Φ _{Y2 in the} Y direction, it can be seen that the light intensity distribution or the light density distribution of the light source image can be made substantially equal in the X direction and the Y direction.

In other words, the aperture diameter Φ of the normal aperture stop (σ stop) can be calculated by the following equation. Φ = 2f · σ · NA / β (1) where f is the focal length of the condenser optical system 60, NA
Is the numerical aperture of the projection optical system PL, and β is the magnification of the projection optical system PL. It should be noted that in an optical system for forming an image of the field stop on the mask surface by using a relay optical system, the expression (1) is multiplied by the magnification of the relay optical system. Normally, the NA is axisymmetric with respect to the chief ray, so the aperture stop is circular. However, if there is a difference in the light source image distribution inside the aperture stop, NA
Is no longer axisymmetric. Therefore, it can be seen from the view shown in FIG. 4A that the distribution of the light source image I ₃₀ is different vertically and horizontally. Due to the difference in the density of the light source image, the aperture stop (A
S ₁ or AS ₂ ) is arranged on the side A ₂ of the optical integrator 5 on which the light source image is formed, as shown in FIG. 3, to reduce the variation in resolution in each direction in the exposure surface on the wafer W. You can The aperture of the aperture stop (AS ₁ or AS ₂ ) (A _P1 or A _P2 )
The optimum shape of is determined by sufficiently considering the points that change depending on the position where the light source image is cut depending on the σ value, that the light source image I ₃₀ is not uniform, and that various aberrations of the illumination optical system are affected. However, in practice, it is possible to easily perform the trial exposure or the simulation to easily obtain the optimum values of Φ _X1 and Φ _Y1 of the aperture stop (AS ₁ or AS ₂ ) or Φ _X2 and Φ _Y2 . The optimum value can be determined.

In the first embodiment shown in FIG. 1, an excimer laser or the like for supplying a parallel light beam is used as the parallel light beam supplying portion, but the present invention is not limited to this, and for example, g-line (436 nm) or i-line (365 nm). ), Etc., and a collimator lens system for converting the light flux condensed by this elliptic mirror into a parallel light flux. You may comprise a supply part. Further, it goes without saying that the projection optical system 80 in the present embodiment may be constituted by a refractive optical system, a reflective optical system or a catadioptric optical system.

Now, a second embodiment will be described with reference to FIGS. 5 and 6. 5 is similar to the configuration of the prior art shown in FIG. 7A, but in FIG.
It differs from (a) in the configuration of the optical integrator 4 ′ and the configuration of the aperture stop (AS ₁ or AS ₂ ). First, the optical integrator 4'in FIG.
As shown in FIG. 5, the lens element 4a ′ having a rectangular lens cross section having long sides and short sides is 5 columns × 6 rows (30 pieces).
The optical integrator 4'is arranged in a square shape as a whole. In the optical integrator 4'of FIG. 5, the lens element 4 is
a ′ has an aspect ratio slightly deviated from the square, and the total number is different in the vertical and horizontal directions. Therefore, if a normal circular aperture stop is used as the aperture stop, the distribution of the light source image inside the aperture will be different vertically and horizontally, and the σ value and the numerical aperture of the projection lens will be slightly different vertically and horizontally. Occurs.

Therefore, also in the second embodiment shown in FIG. 5, the aperture in the X direction is formed at the light source image position formed by the optical integrator 4'or in the vicinity thereof, as shown in FIG. 3 (a). the length [Phi _Y1 of the opening a _P1 of the aperture stop aS ₁ in the Y-direction perpendicular to the length [Phi _X1 and X direction of the opening a _P1 of the diaphragm aS ₁ is different (Φ _X1 <Φ _Y1), or, As shown in FIG. 3B, the aperture stop A in the X direction
The length Φ _X2 of the aperture A _P2 of S ₂ is different from the length Φ _Y2 of the aperture A _P2 of the aperture stop AS ₂ in the Y direction orthogonal to the X direction (Φ _X2 > Φ _Y2 ), that is, an elliptical shape. The aperture stop (AS ₁ or AS ₂ ) having the aperture (A _P1 or A _P2 ) is provided.

Here, FIG. 6A shows that when an aperture stop having a circular aperture A _P0 is arranged at the position of the light source image formed by the optical integrator 4'of FIG. 5, the emission of the optical integrator 4'is performed. Circular opening A from the side
Each lens element 4a 'when looking at the aperture stop with _P0
6 shows the state of the light source image I _4a 'formed in FIG.
(B), when arranging the aperture stop AS ₁ has an opening A _P1 of the elliptical shape shown in FIGS. 3 (a) to the position of the light source images formed by the optical integrator 4 'in FIG. 5,
It shows a state of a light source image I _4a ′ formed on each lens element 4 a ′ when the aperture stop AS ₁ having an elliptical aperture A _P1 is seen from the exit side of the optical integrator 4 ′. 6C shows the position of the light source image formed by the optical integrator 4'of FIG.
Aperture stop AS having an elliptical aperture A _P2 shown in (b)
Optical integrator 4'when ₂ is installed
Aperture stop AS having an elliptical aperture A _P2 from the exit side of
₂ shows a state of a light source image I ₃₀ formed on each lens element 4a ′ when ₂ is viewed.

From the comparison of FIGS. 6A to 6C, FIG.
In (a), it is understood that the light intensity distribution or the light density distribution of the light source image is different in the X direction and the Y direction due to the difference in the number of the light source images I _{4a in} the X direction and the Y direction. However, as shown in FIGS. 6B and 6C, the elliptical opening (A
_When an aperture stop (AS ₁ or AS ₂ ) having _P1 or A _P2 ) is arranged, the ellipse-shaped aperture in the X direction is changed in the X direction due to the difference in the number of light source images I _{4a in} the X direction and the Y direction. Since the length Φ _X2 is different from the length Φ _{Y2 in the} Y direction, it can be seen that the light intensity distribution or the light density distribution of the light source image can be made substantially equal in the X direction and the Y direction.

As described above, even when one optical integrator 4'consisting of a plurality of lens elements 4a 'having an aspect ratio slightly deviated from a square is used, the elliptical aperture stop (AS ₁ or AS _{2) is used.} ), It is possible to make the density of the light source image inside the opening constant in the vertical and horizontal directions.

[0030]

As described above, according to the present invention, it is possible to greatly reduce the difference in resolution between the vertical direction and the horizontal direction within the exposure surface, that is, the variation in the resolution in each direction. Therefore, a high-performance exposure apparatus can be realized.

[Brief description of drawings]

FIG. 1A is a diagram showing a configuration of an exposure apparatus of a first embodiment according to the present invention, and FIG. 1B is a diagram showing a configuration of the exposure apparatus of FIG. .

2A is a diagram showing a state of a cross-sectional shape of the first optical integrator 30 of FIG. 1, and FIG. 2B is a diagram showing FIG.
It is a figure which shows the mode of the cross-sectional shape of the 2nd optical integrator 50 of FIG.

FIG. 3A shows the length Φ _X1 of the opening A _P1 in the X direction as Y.
Is a plan view showing a state of the aperture stop AS ₁ having openings of elliptical shape when shorter than the length [Phi _Y1 of the opening A _P1 in the direction, (b) the opening A _P2 in the X-direction Length of Φ _X2 to Y
7 is a plan view showing a state of an aperture stop AS ₂ having an elliptical aperture when it is made longer than the length Φ _Y2 of the aperture A _P2 in the direction.

4 is a diagram showing the relationship between the light source image distribution and the aperture of the aperture stop when the aperture stop of each shape is arranged on the exit side of the second optical integrator 50 shown in FIG.

FIG. 5 is a view showing the arrangement of an exposure apparatus according to the first embodiment of the present invention.

FIG. 6 is an optical integrator 4 ′ shown in FIG.
6 is a diagram showing the relationship between the light source image distribution and the aperture of the aperture stop when the aperture stop of each shape is arranged on the exit side of FIG.

FIG. 7 is a diagram showing a configuration of a conventional exposure apparatus.

[Explanation of symbols for main parts]

10 ... Excimer laser 20 ... Beam shaping optical system 4 ', 30, 50 ... Optical integrator 40 ... Relay optical system 60 ... Condenser optical system AS ₁ 、 AS ₂・ ・ ・ ・ ・ Aperture stop PL ・ ・ ・ ・ ・ Projection optical system

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 21/30 518

Claims (3)

[Claims] 1. A light source means for supplying light, a multi-light source image forming means for dividing the light from the light source means into a plurality of light source images to form a plurality of light source images, and a light source for collecting the light from the multi light source image forming means. A light source image formed by the multi-light source image forming means, comprising: a condensing optical system that illuminates a mask having a predetermined pattern in a superimposed manner to expose the pattern of the mask onto a photosensitive substrate. An aperture stop is arranged at a position or in the vicinity of the light source image position, and in order to correct a difference in resolution between a predetermined first direction on the photosensitive substrate and a second direction perpendicular to the first direction, the first An exposure apparatus, wherein the length of the opening of the aperture stop corresponding to the direction is different from the length of the opening of the aperture stop corresponding to the second direction. 2. The illumination optical apparatus according to claim 1, wherein the aperture of the aperture stop has an elliptical shape. 3. An exposure apparatus, wherein a projection optical system for transferring the pattern image of the mask onto the photosensitive substrate is arranged between the mask and the photosensitive substrate.