JPH05217851A - Projection aligner - Google Patents

Abstract

PURPOSE:To obtain a high resolution, a large focus depth and an excellent illuminance uniformity by installing a beam splitter which splits an illumination light flux and causes the splited light fluxes to be cast on each of the plurality of second fly's-eye lenses and by installing an optical path difference generating member which generates an optical path difference, in an optical path of any one of the divided light fluxes. CONSTITUTION:Laser beam 1 is cast on beam splitters 20 and 21 through a parallel light flux bending mirror 3 after its beam cross section is shaped into the proper form and size by a beam shaping optical system 2. The illumination light flux is divided into two by bending action of these two prisms and the divided light fluxes are cast on second fly's-eye lens groups 40a and 40b respectively. Here, in an optical path of either of the light fluxes divided by the beam splitters 20 and 21, a parallel flat glass 30 is located as an optical path difference generating member. By this method, a projection aligner of a high resolution and a large focus depth can be materialized and furthermore, the illuminance uniformity can be more and more enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus for transferring a mask or reticle pattern used in a lithographic process for manufacturing a semiconductor integrated circuit or a liquid crystal display device onto a photosensitive substrate, and more particularly to a coherent exposure light source. The present invention relates to a projection exposure apparatus equipped with a simple laser light source.

[0002]

2. Description of the Related Art For forming a circuit pattern of a semiconductor element or the like,
Generally, a process called photolithography is required. In this step, a method of transferring a reticle (mask) pattern onto a substrate such as a semiconductor wafer is usually adopted.
A photosensitive photoresist is coated on the substrate,
The circuit pattern is transferred to the photoresist according to the irradiation light image, that is, the pattern shape of the transparent portion of the reticle pattern. Generally, in a projection exposure apparatus (eg stepper), an image of a circuit pattern to be transferred drawn on a reticle is projected and imaged on a substrate (wafer) via a projection optical system.

In addition, an optical integrator such as a fly-eye lens or a fiber is used in an illumination optical system for illuminating the reticle, and the intensity distribution of the illumination light with which the reticle is irradiated is made substantially uniform. .. In order to perform this homogenization optimally, when a fly-eye lens is used, the reticle side focal plane (emission surface side) and the reticle surface (pattern surface) are connected by a Fourier transform relationship.
Further, the reticle side focal plane and the light source side focal plane (incident surface side) are also connected by a Fourier transform relationship. Therefore, the pattern surface of the reticle and the light source side focal plane of the fly eye lens (more precisely, the light source side focal plane of each lens of the fly eye lens) are connected in an image forming relationship (conjugate relationship). Therefore, on the reticle, the illumination light from each optical element (secondary light source image) of the fly-eye lens is added (superposed) by passing through the condenser lens etc., and is averaged, so that the illuminance on the reticle is uniform. It is possible to improve the sex. In principle, this does not change whether it is a high-pressure mercury lamp that is generally used as a light source for exposure at present or a laser light source such as a KrF or ArF excimer laser that has recently been attracting attention. ..

In the conventional projection exposure apparatus, the light quantity distribution of the illumination light beam incident on the incident surface of the optical integrator such as the fly-eye lens described above is within a substantially circular shape (or within a rectangular shape) about the optical axis of the illumination optical system. So that it was almost uniform. FIG. 11 shows a schematic configuration of a conventional projection exposure apparatus (stepper) as described above, and an illumination light flux L140 emitted from an excimer laser light source (not shown).
Illuminates the pattern 9 of the reticle 8 via the beam shaping optical system in the illumination optical system, the fly-eye lens 41c, the spatial filter (aperture stop) 4a, and the condenser lens 7. Here, the spatial filter 4a is arranged on the reticle-side focal plane 414c of the fly-eye lens 41c, that is, on the Fourier transform plane 17 (hereinafter abbreviated as a pupil plane) for the reticle pattern 9 or a plane in the vicinity thereof and the projection optical system. 10 has a substantially circular opening centered on the optical axis AX, and limits the secondary light source (surface light source) image formed in the pupil plane 17 to a circular shape. The illumination light that has passed through the pattern 9 of the reticle 8 is imaged on the resist layer of the wafer 12 via the projection optical system 10. At this time, the ratio of the numerical aperture of the illumination optical system (41c, 4a, 7) and the numerical aperture on the reticle side of the projection optical system 10, that is, the so-called σ value is determined by the aperture stop (for example, the aperture diameter of the spatial filter 4a). Generally, the value is about 0.3 to 0.6.

The illumination light L140 is diffracted by the pattern 9 patterned on the reticle 8, and the pattern 9
The 0th-order diffracted light D ₀ , the + 1st-order diffracted light D _p , and the −1st-order diffracted light D _m are generated. Each diffracted light (D ₀ , D _p , D _m )
Are condensed by the projection optical system 10 and generate interference fringes on the wafer 12. This interference fringe is an image of pattern 9.
At this time, the angle θ (reticle side) formed between the _0th-order diffracted light D ₀ and the ± 1st-order diffracted lights D _p and D _m is sin θ = λ / P
(Λ: exposure wavelength, P: pattern pitch).

By the way, if the pattern pitch becomes finer,
When sin θ becomes larger and sin θ becomes larger than the reticle-side numerical aperture (NA _R ) of the projection optical system 10, the ± first-order diffracted lights D _p and D _m of the pupil plane (Fourier transform surface) 11 of the projection optical system 10 become. It is limited by the effective diameter and cannot pass through the projection optical system 10. At this time, only the _0th-order diffracted light D ₀ reaches the wafer 12 and no interference fringes occur. That is, sin
When θ> NA _R , the image of pattern 9 cannot be obtained,
The pattern 9 cannot be transferred onto the wafer 12.

From the above, in the conventional projection exposure apparatus, the pitch P at which sin θ = λ / P≈NA _R is given by the following equation. P≈λ / NA _{R From} this, the minimum pattern size is half the pitch P, so the minimum pattern size is about 0.5 × λ / NA _R , but in the actual photolithography process, the wafer curvature, process A certain depth of focus is required due to the influence of the step difference of the wafer due to the above or the thickness of the photoresist itself. Therefore, the practical minimum resolution pattern size is expressed as k × λ / NA _R. here,
Although k is called a process coefficient and depends on the characteristics of the resist and the like, it is usually about 0.6 to 0.8. Since the ratio between the reticle-side numerical aperture NA _R and the wafer-side numerical aperture NA _W is the same as the imaging magnification of the projection optical system 10, the minimum resolution pattern size on the reticle is k × λ / NA _R , The minimum pattern size is k × λ / NA _W = k × λ / B
NA _R (where B is the imaging magnification (reduction ratio)).

Therefore, in order to transfer a finer pattern, it was necessary to select whether to use an exposure light source having a shorter wavelength or to use a projection optical system having a larger numerical aperture. Of course, efforts can be made to optimize both the exposure wavelength and the numerical aperture. However, in the conventional projection exposure apparatus as described above, it is difficult at this time to shorten the wavelength of the illumination light source (for example, 200 nm or less) because there is no suitable optical material that can be used as the transmissive optical member. Is. Further, the numerical aperture of the projection optical system is already close to the theoretical limit even at present, and it is almost impossible to expect a larger aperture. Furthermore, even if a larger aperture than the current one is possible, the depth of focus represented by ± λ / 2NA ² will decrease sharply as the numerical aperture increases, and the depth of focus required for actual use will increase. There is a problem that it will decrease. This naturally becomes more serious as the wavelength of the light source is shortened.

Further, a so-called phase shift reticle, which shifts the phase of the transmitted light from a specific portion of the transmitted portion of the circuit pattern of the reticle by π from the phase of the transmitted light from other transmitted portions, is disclosed in, for example, Japanese Patent Publication No. It is proposed in Japanese Laid-Open Patent Publication No. 62-50811. By using this phase shift reticle, it becomes possible to transfer a finer pattern than the conventional one. However, the phase shift reticle has many problems because the manufacturing process is complicated and the cost is high, and the inspection and correction methods have not been established yet.

Therefore, as a projection exposure technique that does not use a phase shift reticle, attempts have been made to improve the transfer resolution by improving the reticle illumination method. One of the illumination methods is, for example, the spatial filter 4a shown in FIG.
Is an annular aperture, and the illumination light flux distributed around the optical axis of the illumination optical system on the pupil plane (Fourier transform surface) 17 of the illumination optical system is partially cut so that the illumination light flux reaching the reticle 8 is formed. It has a certain inclination.

[0011]

However, in the prior art as described above, when the light source is a laser having spatial coherence such as an excimer laser, it is formed on the reticle side focal plane of the fly-eye lens. Considering the secondary light source, the illumination light fluxes corresponding to the respective lens elements have coherence to some extent. For this reason, random interference fringes (speckle interference fringes) are formed on the reticle surface or the wafer surface conjugate with the reticle surface, and the illuminance uniformity may be reduced. Here, considering the spatial frequency, the Fourier component corresponding to the minimum distance between the lens elements is dominant. That is, this is because the number of combinations of light fluxes that contribute to interference is the largest. Therefore, on the reticle surface or the wafer surface, fringes having a relatively low frequency (long pitch) are observed in comparison with the limit resolution, corresponding to the arrangement direction of the lens elements. In the case of a KrF excimer laser, since the spatial coherence is relatively low, the contrast of the interference fringes formed is also low, but it acts as harmful noise to the original pattern, and the illuminance uniformity will become even more demanding in the future. However, the occurrence of interference fringes is a serious problem. Further, in the case of considering the above-mentioned annular illumination, the noises are concentrated in the vicinity of the limit resolution, and the noise is superposed, which is more influential than the ordinary illumination method.

Further, if a special illumination method is adopted in which the illumination luminous flux distribution in the Fourier transform plane of the illumination optical system is made into a ring shape, although the improvement of the resolving power is certainly recognized even with the ordinary reticle, the entire surface of the reticle is confirmed. However, there is a problem that it becomes difficult to guarantee a uniform illuminance distribution. Further, as shown in FIG. 11, in a system in which a member that partially cuts the illumination light flux such as a spatial filter is provided, as a matter of course, the illumination intensity (illuminance) on the reticle or wafer is significantly increased. This leads to the problem of an increase in exposure processing time associated with a decrease in illumination efficiency.
Further, since the light flux from the light source is concentrated and passes through the Fourier transform surface in the illumination optical system, the temperature rise due to the light absorption of the light shielding member such as the spatial filter becomes remarkable, and the performance due to the thermal fluctuation of the illumination optical system is caused. It is also necessary to consider measures against deterioration (air cooling, etc.).

The present invention has been made in view of the above problems, and it is possible to obtain a high resolution and a large depth of focus even if a normal reticle is used, and it is excellent in illuminance uniformity and is represented by an excimer laser. An object of the present invention is to provide a projection exposure apparatus which is less affected by harmful speckle noise even when a laser is used as a light source.

[0014]

In order to solve such a problem, in the present invention, the exit side focal plane is arranged in the Fourier transform plane (17) for the mask in the optical path of the illumination optical system, or in the plane in the vicinity thereof. And a plurality of first fly-eye lenses (41a, 41b) whose centers are arranged at a plurality of positions decentered from the optical axis (AX) of the illumination optical system.
And the exit side focal plane is arranged on the Fourier transform surface with respect to the incident end of each of the plurality of first fly-eye lenses (41a, 41b) or in the vicinity thereof, and the first fly-eye lenses (41a, 41b) A plurality of second fly-eye lenses (40a, 40b) provided corresponding to each of the
Between the plurality of second fly-eye lenses (40a, 40b), the light splitter (20, 21) that splits and enters the illumination light flux from the light source, and between the split arbitrary light fluxes.
An optical path difference generating member (30) that gives an optical path difference longer than the coherence length (coherence length) of the illumination light flux is provided. Further, the guide optical element is provided so that the light emitted from one of the plurality of second fly-eye lenses is incident on the corresponding one of the plurality of first fly-eye lenses.

[0015]

The operation of the present invention will be described with reference to FIG.
In FIG. 10, the second fly-eye lens groups 40a and 40b corresponding to the second fly-eye lens of the present invention are the projection optical system 10
Are arranged in a plane perpendicular to the optical axis AX of, and the light beams emitted from the light beams are guided to the first fly-eye lens groups 41a and 41b corresponding to the first fly-eye lens of the present invention by the guide optical systems 42a and 42b, respectively. Incident. The illuminance distribution on the incident surface of the first fly-eye lens is made uniform by the second fly-eye lens group.

The light flux emitted from the first fly-eye lens group is applied to the reticle 8 by the condenser lens 7. The illuminance distribution on the reticle 8 is made uniform by the first and second fly-eye lens groups described above, and has extremely good uniformity. Here, the centers of the first fly-eye lens groups 41a and 41b are both present at positions apart from the optical axis AX. In addition, the first fly-eye lens group 41
The reticle side focal planes 414a and 414b of a and 41b are
Since it substantially matches the Fourier transform surface 17 of the reticle pattern 9, the angle of incidence of the light flux emitted from the first fly-eye lens on the reticle 8 is determined by the distance between the optical axis AX and the center of the first fly-eye lens. To be done.

The circuit pattern 9 drawn on the reticle (mask) generally contains many periodic patterns. Therefore, from the reticle pattern 9 irradiated with the illumination light from one fly-eye lens group 41a, the 0th-order diffracted light component D ₀ and the ± 1st-order diffracted light components D _p , D _m , and higher-order diffracted light components are It occurs in the direction according to the fineness of the pattern. At this time, since the illumination light beam (main light beam) is incident on the reticle 8 at an inclined angle, the generated diffracted light components of each order also have an inclination (angle deviation) from the reticle pattern 9 as compared with the case of being illuminated vertically. Occur. Figure 10
The inside illumination light L130 is incident on the reticle 8 with an inclination of ψ with respect to the optical axis.

The illumination light L130 is diffracted by the reticle pattern 9, and the 0th-order diffracted light D ₀ that advances in a direction inclined by ψ with respect to the optical axis AX and the + 1st-order diffracted light that advances by θ _p with respect to the _0th- order diffracted light D ₀ . D _p, and 0-order diffracted light D ₀ relative theta _m proceeds inclined by -1st-order diffracted light D _m is generated. However, since the illumination light L130 is incident on the reticle pattern 9 with an angle ψ with respect to the optical axis AX of the projection optical system 10 which is telecentric on both sides, the 0th-order diffracted light D ₀ is also relative to the optical axis AX of the projection optical system 10. And proceed in a direction inclined by an angle ψ.

Therefore, the + 1st-order diffracted light D _p proceeds in the direction of (θ _p + ψ) with respect to the optical axis AX, and the −1st-order diffracted light D _m is (θ _m −ψ) on the opposite side with respect to the optical axis AX. ) Angle. At this time, the diffraction angles θ _p and θ _m are sin (θ _p + ψ) −sin ψ = λ / P sin (θ _m −ψ) + sin ψ = λ / P, respectively. However, here, it is assumed that both the + 1st-order diffracted light D _p and the −1st-order diffracted light D _m are transmitted through the pupil plane 11 of the projection optical system 10.

When the diffraction angle increases with the miniaturization of the reticle pattern 9, first, the + 1st order diffracted light D _p that travels in the direction of the angle (θ _p + ψ) cannot pass through the pupil 11 of the projection optical system 10. That is, the relationship of sin (θ _p + ψ)> NA _R is established. However, since the illumination light L130 is obliquely incident on the optical axis AX, the diffraction angle at this time is −
The first-order diffracted light D _m can pass through the projection optical system 10.
That is, sin (θ _m −ψ) <NA _R.

Therefore, the 0th-order diffracted light D ₀ is formed on the wafer 12.
And interference fringes are generated by the two light fluxes of the −1st order diffracted light D _m . This interference fringe is an image of the reticle pattern 9, and when the reticle pattern 9 has a 1: 1 line and space pattern, it is about 9
It becomes possible to pattern the image of the reticle pattern 9 on the resist coated on the wafer 12 with a contrast of 0%.

The resolution limit at this time is when sin (θ _m −ψ) = NA _R , so that N _R + sin ψ = λ / P P = λ / (NA _R + sin ψ) can be transferred. It is the pitch on the reticle side of the smallest pattern.

Assuming that sin ψ is set to about 0.5 × NA _R as an example, the minimum pitch of the pattern on the transferable reticle is P = λ / (NA _R + 0.5 × NA _R ) = 2λ / 3NA It becomes _R. On the other hand, as shown in FIG.
In the case of the conventional exposure apparatus in which the above distribution is in the circular area centered on the optical axis AX of the projection optical system 10, the resolution limit is P≈λ / NA _{R as} described above. Therefore, it can be seen that higher resolution can be realized than the conventional exposure apparatus.

Next, the present method of irradiating the reticle pattern with exposure light in a specific incident direction and incident angle and forming an imaged pattern on the wafer using the 0th-order diffracted light component and the 1st-order diffracted light component. The reason why the depth of focus also increases will be described. When the wafer 12 is aligned with the focus position (best image plane) of the projection optical system 10 as shown in FIG.
Each diffracted light that exits one point in the reticle pattern 9 and reaches one point on the wafer 12 has the same optical path length regardless of which part of the projection optical system 10 passes. For this reason,
As in the conventional case, the 0th-order diffracted light component is the pupil plane 1 of the projection optical system 10.
Even when penetrating almost the center of 1 (near the optical axis), the optical path lengths of the 0th-order diffracted light component and other diffracted light components are equal,
Therefore, the wavefront aberration is also zero. However, when the wafer 12 is in a defocused state where it does not coincide with the focal position of the projection optical system 10, the optical path length of obliquely incident high-order diffracted light is in front of the focal point with respect to the 0th-order diffracted light passing near the optical axis ( Projection optical system 1
It is short in the direction approaching 0) and is behind the focus (projection optical system 10
(Direction away from) becomes longer, and the difference depends on the difference in incident angle. Therefore, the 0th order, ± 1st order, and other diffracted lights form wavefront aberrations, causing blurring before and after the focus position.

With respect to the wavefront aberration due to the defocus described above, the deviation amount from the focus position of the wafer 12 is ΔF, and the sine of the incident angle θ _W when each diffracted light is incident on one point on the wafer is r.
When (r = sinθ _W), it is an amount given by ΔFr ^2/2. At this time, r represents the distance from the optical axis AX on the pupil plane 11 of each diffracted light. In the conventional projection exposure apparatus shown in FIG. 11, since the 0th-order diffracted light D ₀ passes in the vicinity of the optical axis AX, r (0th) = 0, while the ± 1st-order diffracted lights D _p , D
_m is r (first order) = M · λ / P (M is the magnification of the projection optical system). Therefore, zero-order diffracted light D ₀ and ± 1-order diffracted light D _p, the wavefront aberration due to defocusing of the D _m becomes ^{ΔF · M 2 (λ / P} ) 2/2.

On the other hand, in the projection exposure apparatus according to the present invention,
As shown in 10, the 0th-order diffracted light component D ₀Is the angle from the optical axis AX
It occurs in the direction inclined by ψ, so the distance from the optical axis AX
The separation is r (0th order) = M · sin ψ. On the other hand, -1st order diffraction
Light component D_mFor r (−1st order) = M · sin (θ_m−
ψ). Therefore, sin ψ ＝ sin (θ_m−ψ) become
For example, the 0th order diffracted light component D₀And -1st order diffracted light component D_mWith
There is no difference in optical path length due to focus, and the wavefront aberration is zero.
And the wafer 12 is slightly displaced from the focus position in the optical axis direction.
However, the image blur of the pattern does not occur as much as before.
It That is, the depth of focus is increased. Also,
As above sin (θ_m-Ψ) + sin ψ = λ / P
The incident angle ψ of the illumination light flux L130 to the reticle 8 by
The relation of sin ψ = λ / 2P with respect to the pattern of switch P
If defined, the depth of focus can be increased significantly
It

Further, according to the present invention, after the illumination light flux emitted from the light source is divided into a plurality of light fluxes, a phase difference (optical path length) longer than the coherence length (coherent length) of the illumination light is generated between each of the plurality of light fluxes. Difference). Here, the coherent length L of the illumination light is represented by L = λ ² / Δλ, where λ is the illumination wavelength and Δλ is the spectral width thereof.

In other words, if there is a difference in the optical path length of the coherent length L or more between the two light beams emitted from the same light source, the two light beams do not interfere with each other. For example, in the case of a KrF excimer laser whose light source is a narrow band, the coherent length L is about 20 mm, and it is relatively easy to give such a light path difference between a plurality of light beams. Therefore, even with a laser having a certain degree of coherence, it is possible to effectively reduce the speckle interference fringes superimposed on the original pattern as noise.

[0029]

FIG. 1 is a diagram showing a schematic configuration of a projection exposure apparatus (stepper) according to an embodiment of the present invention. In this embodiment, two polyhedral prisms are used as an optical splitter, and an optical path is further provided. A parallel plate glass is used as the difference generating member. In FIG. 1, the exposure light source 1 is Kr.
F, ArF excimer laser, or a harmonic vapor of a metal vapor laser or a YAG laser or the like is generated to generate illumination light in a wavelength range that sensitizes the resist layer. This illumination light (laser beam) is a substantially parallel light beam, and after the beam shaping optical system 2 including a beam expander or the like shapes the beam cross section into an appropriate shape (usually square) and size, it remains a parallel light beam. It is incident on the light splitter (20, 21) via the folding mirror 3. Here, the optical splitter of the present embodiment has a first polyhedral prism 20 having a V-shaped concave portion and a second polyhedral prism having a V-shaped convex portion.
It is a combination of the polyhedron prism 21 of FIG.
Due to the refraction of these two prisms, the illumination light flux is 2
The light beam is divided into two light beams, and the respective light beams are incident on different second fly-eye lens groups 40a and 40b.

Here, as shown in FIG. 1, the optical splitter 20,
A parallel plate glass 30 as an optical path difference generating member is arranged in the optical path of either one of the two light beams split by 21 (in the optical path of the light beam incident on the second fly-eye lens group 40a in FIG. 1). Has been done. Therefore, the light flux entering the second fly-eye lens group 40a is delayed in phase by a predetermined amount with respect to the light flux entering the second fly-eye lens group 40b, that is, there is a difference in optical path length between the two light fluxes. Will occur. In the present embodiment, the parallel plate is arranged so that the optical path difference between the two light beams becomes longer than the coherent length L (L = λ ² / Δλ) of the illumination light (however, the optical path difference does not become an integral multiple of the coherent length L). The thickness of the glass 30 is defined. Here, the parallel plate glass 30 is arranged only in one optical path of the two light beams, but if the optical path difference between the two light beams is always longer than the coherent length L, the parallel plate glass 30 is arranged in both optical paths. Glass may be placed. Further, the optical path difference generating member may be a member other than the parallel flat plate glass, for example, a mirror that draws a light beam to give an optical path difference.

By the way, in this embodiment, the number of the second fly-eye lens is two, but the number may be arbitrary. The light splitter also divides the illumination light flux into two in accordance with the number of second fly-eye lens groups, but the second fly-eye lens group is configured so that the light flux enters each of the plurality of second fly-eye lens groups. It may be divided into any number depending on the number of eye lens groups.
Further, the optical path difference generating member may be any member as long as the phase difference between the light fluxes is appropriately given, and the number of the light path difference generating members may be different from each other among the plurality of light fluxes divided by the light splitter. As given, the same number as the number of the second fly-eye lens groups or a number smaller by one may be prepared and arranged in the optical path of each light flux. For example, if the second fly-eye lens group is composed of four, the light splitter is the first polyhedral prism 20 having a quadrangular pyramid (pyramid) concave portion.
And a second polyhedral prism 21 having a quadrangular pyramid-shaped (pyramid-shaped) convex portion, and four light beams have different phase differences (optical path differences) from each other.
It suffices to dispose four (or three) parallel plate glasses having different thicknesses according to the coherent length L in the optical path of each light beam.

Now, the second fly-eye lens groups 40a, 4
The illumination light emitted from 0b is the guide optical system 42a,
The light beams 43a, 42b, 43b enter the first fly-eye lens groups 41a, 41b. At this time, only the light flux from the second fly-eye lens 40a enters the first fly-eye lens 41a, and only the light flux from the second fly-eye lens group 40b enters the first fly-eye lens group 41b. Further, the respective light fluxes emitted from the first fly-eye lenses 41a and 41b are guided to the condenser lenses 5 and 7 and the bending mirror 6, and illuminate the pattern 9 formed on the lower surface of the reticle 8 with a substantially uniform illuminance. The light transmitted through the pattern 9 and diffracted is focused and imaged by the projection optical system 10 to form an image of the pattern 9 on the wafer 12.

Reference numeral 11 in the figure denotes a Fourier transform plane (hereinafter referred to as the pupil plane of the projection optical system) for the pattern 9 in the projection optical system 10, and a variable diaphragm (N A. Aperture) may be provided. On the other hand, although the pupil plane 17 of the illumination optical system corresponding to the Fourier transform plane for the pattern 9 also exists in the illumination optical system, the reticle side focal plane (emission side focal plane) of the first fly-eye lenses 41a and 41b described above. Is at a position substantially coincident with the pupil plane 17 of the illumination optical system. The exit surfaces of the second fly-eye lenses 40a and 40b are Fourier transform surfaces with respect to the entrance surfaces of the first fly-eye lenses 41a and 41b by the guide optical systems 42 and 43. However, it is not necessary to strictly maintain the relationship of the Fourier transform, and the point is that the light flux emitted from each element of the second fly-eye lens group is superposed on the incident surface of the first fly-eye lens group. It is good if the relationship is maintained.

Further, the first fly-eye lens groups 41a, 4
Since 1b is located away from the optical axis AX, it is possible to make the depth of focus of the projected image of the pattern having a specific direction and pitch in the reticle pattern 9 extremely large. However, the direction and pitch of the reticle pattern 9 are
It is expected to vary depending on the reticle 8 used. Therefore, the drive system 51 drives the first fly-eye lens groups 41a, 41b and 41a, 41b so that the respective center positions of the first fly-eye lens groups 41a, 41b in the pupil plane are optimal for each reticle pattern. Guide optical system 42a, 42
b, 43a, 43b, or the positions of the second fly-eye lens groups 40a, 40b, the parallel plate glass 00, the light splitters 20, 21 and the like may be changed. still,
The drive system 51 operates according to the operation command of the main control system 50, and the setting conditions such as the position at this time are input from the keyboard 52. Alternatively, the barcode pattern on the reticle may be read by a barcode reader and the setting may be performed based on the information.

FIG. 2 is an enlarged view of the light splitters 20 and 21 to the first fly-eye lens groups 41a and 41b in FIG. Here, it is assumed that the surfaces of the first polyhedron prism 20 and the second polyhedron prism 21 facing each other are parallel to each other, and the incident surface of the prism 20 and the exit surface of the prism 21 are perpendicular to the optical axis AX. And The first polyhedral prism 20 is held by a holding member 22, and the second polyhedral prism 21 is held by a holding member 23.
The holding members 22 and 23 are movable members 24a and 24, respectively.
b, and 25a, 25b, and fixed member 26
It is movable in the left and right directions in the figure on the a and 26b, that is, in the direction warped to the optical axis AX. This operation is performed by active members 27a, 27b, 28a, 28b such as motors. Further, since the first polyhedron prism 20 and the second polyhedron prism 21 can be moved independently, the interval between the two light beams emitted by changing the interval between the two prisms is set to the optical axis A.
It can be changed in the radial direction around X.

Now, the plurality of light beams emitted from the polyhedral prism 21 enter each of a plurality (the same number as the light beams) of the second fly-eye lens group. In FIG. 2, one of the second fly-eye lens group, one of the first fly-eye lens group, and one of
The one guide optical system and the parallel flat glass are integrally held by one holding member 44a, 44b (however, in this embodiment, the parallel flat glass is not arranged on one of the holding members (44b in the figure) as described above). ing. In addition, the holding member 44
Since a and 44b are held by the movable members 45a and 45b, respectively, they are movable with respect to the fixed members 46a and 46b. This operation is performed by the active members 47a and 47b.

By holding and moving the second fly-eye lens, the first fly-eye lens, the guide optical system, and the parallel plate glass as a unit, the first fly-eye lens and the second fly-eye lens
The position of the light flux emitted from the first fly-eye lens is arbitrarily changed within the plane perpendicular to the optical axis AX (that is, the pupil plane of the illumination optical system) without shifting the optical positional relationship with the fly-eye lens. can do. The holding member 44a,
The members 48a and 48b protruding from 44b are light shielding plates. This blocks stray light generated from the light splitter,
Prevents unwanted light from reaching the reticle. Also,
Since the light shielding plates 48a and 48b are displaced from each other in the optical axis AX direction, it is possible to reduce restrictions on the movable range of the holding members 44a and 44b.

In FIG. 2, an optical splitter (polyhedral prism) is used.
The position of each divided light flux can be changed in the radial direction with respect to the optical axis AX by changing the distance between the light fluxes 20 and 21 in the optical axis direction. It is also possible to change. FIG. 6 shows an embodiment in that case, and the holding member 23 holding the second polyhedral prism (pyramid prism) 21 is held by the fixture 25, but the holding member 23 is shown in FIG. 6 (A). It is rotatable in the plane of the drawing with respect to the fixture 25. Further, this rotation is performed by a driving member 29 such as a motor provided on the fixture 29. Further, a gear 201 is provided around the holder 23 so as to correspond to the position of the motor 29. 6B is a cross-sectional view taken along the line 3A of FIG. 6A.

Here, the fixture 25 may be further held as shown in FIG. 2 and movable in the optical axis AX direction. Further, although FIG. 6 shows only an example in the case of the second polyhedral prism 21, the first polyhedral prism 20 can be similarly configured to be rotatable (with respect to the optical axis AX). Further, instead of rotating the polyhedral prisms 20 and 21 separately, the fixing members 26a and 26b in FIG. 2 are integrated with another fixing portion (exposure apparatus main body) around the optical axis AX. It may be configured to be rotatable. In the rotating mechanism in this case, for example, the holding member 23 in FIG. 6 is replaced with the fixing members 26 a and 26 shown in FIG. 1 instead of the polyhedral prism 21.
It may be configured so as to hold b.

As described above, when the plurality of light beams emitted from the light splitters 20 and 21 change their positions in the radial direction and the concentric direction about the optical axis AX, the second fly's eye on which these light beams are incident. The positions of the lens groups 40a and 40b also need to be variable accordingly. FIG. 7 shows an example of a mechanism that enables a two-dimensional (in-plane direction perpendicular to the optical axis AX) operation for this purpose. In FIG. 7, as shown in FIG.
Fly-eye lenses 40a and 40b, guide optical system 42
a, 42b, 43a, 43b and the first fly-eye lens 41a, 41b integrally held (holding member 4
4a, 44b) as viewed from the reticle side of the optical axis AX. Each synthetic fly-eye lens 41A-41
D is held by holding members 44A to 44D, which are held by movable members 45A to 45D, and are movable in the radial direction about the optical axis AX by active members 46A to 46D. Also, active members 46A to 46D
Is movable on the fixing members 49A to 49D in a direction substantially orthogonal to the radial direction (almost concentric direction),
The synthetic fly's eye lenses 41A to 41D have optical axes A, respectively.
It is two-dimensionally movable in the plane perpendicular to X (the plane of the paper). As a result, the light beams split by the light splitter can be efficiently applied to the reticle.

The moving direction of the movable members 45A to 45D in FIG. 7 is not limited to the radial direction about the optical axis AX, but may be any direction perpendicular to the optical axis AX. Further, even in the case of a system that is movable only in one dimension as shown in FIG. 2, the direction may be any direction perpendicular to the optical axis AX. Although the parallel flat plate glass 30 is not described in the above description, since it is held by the holding member 44a and can move integrally with the second fly-eye lens group 40a (FIG. 2), there is no problem. Further, the parallel flat plate glass 30 may be independently movable without being fixed to the holding member 44a, and the parallel flat plate glass 30 may be driven in association with the movement of the holding member 44a. Or
Optical axis A of the light beam incident on the second fly-eye lens group 40a
If the area of the parallel plate glass 30 is made larger than the moving range in the plane perpendicular to X, it is not necessary to provide a moving mechanism, and it is not necessary to fix the holding member 44a integrally. Simply mechanically fix it to the device.

When the light beams split by the light splitters 20 and 21 are changed to the concentric direction about the optical axis AX, the parallel plate glass 30 also moves along the optical axis A as the light beams move.
It is desirable to rotate around X. Further, when the positions of the plurality of light beams emitted from the light splitters 20 and 21 are changed in the radial direction and the concentric direction with respect to the optical axis AX, particularly when the positions are changed in the concentric direction, as described above. It is desirable to move the positions of the second fly-eye lens groups 40a and 40b on which the light flux is incident such that the arrangement direction of each element forming the fly-eye lens group and the periodic direction of the reticle pattern are substantially aligned with each other. At this time, each fly-eye lens group may be configured to be independently rotatable, or a plurality of combined fly-eye lenses (holding members 44a and 44b) may be integrally configured to be rotatable about the optical axis AX. good. The position of each of the plurality of light beams is changed in the concentric direction by changing the reticle pattern from a one-dimensional line-and-space pattern regularly arranged in the X direction to 45 in the X and Y directions.
This is when the pattern is changed to a one-dimensional line-and-space pattern that is regularly arranged in a direction inclined by °.

Next, a modified example of the optical path difference generating member of the present invention will be described with reference to FIGS. 3, 4 and 5. In each of the drawings, members having the same functions and functions as those of FIG. 2 are designated by the same reference numerals. In the example of FIG. 3, parallel plate glass is used as the optical path difference generating member as in the above-described embodiment (FIG. 2), but here the illumination light flux from the light source is divided by the light splitters 20, 21.
Before the incident on the parallel plate glass 30, the parallel plate glass 30 is arranged in a part of the illumination optical path (upper half of the optical axis AX in the figure) corresponding to one of the two slopes of the light splitters 20 and 21. .. Therefore, of the two light fluxes split by the light splitters 20 and 21, only the light flux entering the second fly-eye lens group 40a is delayed in phase, and the optical path difference between them is made longer than the coherent length L. It becomes possible. Figure 3
Since the parallel plate glass 30 is held by the holding member 31 and the holding member 31 is held by the movable member 32, the parallel plate glass 30 is movable with respect to the fixed member 33. This operation is performed by the active member 34. Since the parallel flat plate glass 30 is configured to be movable in the direction perpendicular to the optical axis AX as described above, the parallel flat plate glass 30 is moved to the optical axis A.
It can be accurately arranged in the illumination optical path with X as a boundary, and it is possible to change only the phase (optical path length) of either one of the two light beams. The rest of the apparatus shown in FIG. 3 is basically the same as that shown in FIG. 2 and will not be described here. In addition, the parallel plate glass 30 in this example
May be arranged anywhere in the optical path between the light source 1 and the light splitters 20 and 21. As is clear from FIGS. 2 and 3, the parallel plate glass 30 may be arranged anywhere in the optical path between the light source 1 and the second fly-eye lens groups 40a and 40b. Furthermore, the first fly-eye lens group 41a,
Although it can be arranged in the optical path between 41b and the reticle 8,
Here, it is necessary to dispose the light beams from the first fly-eye lens groups 41a and 41b at positions where they do not overlap (for example, near the exit-side focal plane of the first fly-eye lens groups 41a and 41b or near their conjugate planes). is there.

FIG. 4 shows an example in which a mirror is used instead of the parallel plate glass as the optical path difference generating member.
In the same way as in the example of FIG.
Before entering 1, the phase difference (optical path length difference) is given to the light flux portion corresponding to either one of the two split light fluxes. In FIG. 4, the illumination light flux from the light source 1 is split by a beam splitter (half mirror) 30a into two light fluxes (the light amount ratio is 1: 1), and the light flux that has passed therethrough goes straight to the light splitters 20 and 21. The incident and reflected light flux is bent upward in the figure, and then reflected by the reflection mirror 30b.
Then, it is bent again and enters the light splitters 20 and 21.
As a result, the light flux reflected by the half mirror 30a is delayed (the phase is delayed) by the distance from the half mirror 30a to the reflection mirror 30b. Therefore, also in this example, it is possible to change the optical path length of only one of the two light beams split by the light splitters 20 and 21.
The half mirror 30a and the reflection mirror 30b are integrally fixed to a holding member (not shown) at a distance such that the optical path difference between the two light fluxes is longer than the coherent length L, and the half mirror 30a The transmitted light flux and the reflected light flux are arranged in the illumination optical path so as to enter the light splitter 20 symmetrically with the optical axis AX in between. As is clear from FIG. 4, in this example, the mirror 30 is used as the optical path difference generating member.
Since a and 30b are used, the illumination light flux from the light source 1 is decentered with respect to the optical axis AX of the illumination optical system. Further, the mirrors 30a and 30b may be integrally configured so as to be movable in a direction perpendicular to the optical axis AX so that the incident positions of the transmitted light flux and the reflected light flux on the optical splitter 20 can be finely adjusted. desirable. In FIG. 4, the remaining device parts are exactly the same as in the example of FIG.

In the example of FIG. 5, the optical path difference generating members 30a and 30 are provided.
The configuration including b and the light splitters 20 and 21 is exactly the same as the example of FIG. 4, but here an example in which the image rotator 35 is arranged in the optical path of one light beam is shown.
By this image rotator 35, only one light beam (reflected light beam in the figure) divided by the half mirror 30a is rotated, for example, by 180 ° in a plane perpendicular to the optical axis AX. With the above configuration, the coherence of each luminous flux is further reduced, and the contrast of speckle interference fringes that are noise components is further reduced, which is advantageous. The image rotator may be other than the combination of prisms shown in FIG.

When the image rotator 35 is arranged in the optical path as in this example, the phase of the reflected light beam is delayed a little, so the distance (spacing) between the half mirror 30a and the reflective mirror 30b is taken into consideration in consideration of this delay. It is desirable to set. Further, the installation position of the image rotator 35 is not limited to this example, and may be arranged anywhere in the optical path between the light source 1 and the reticle 8 like the optical path difference generating member, for example, the optical splitter. It may be installed behind 20 and 21 (on the side of the second fly-eye lens group). Further, the image rotator 35 includes an optical path difference generating member (30 or 3).
0a, 30b) to the light source side or the second fly-eye lens group side. Also, in FIG.
The image rotator 3 is also used for the configuration shown in FIG.
5 can be arranged to obtain the same effect. In other words, the conditions regarding the installation positions and the number of the image rotators 35 are exactly the same as the conditions for the optical path difference generating member,
For example, when the illumination light flux from the light source 1 is divided into four, an image rotator is arranged in each of the optical paths of three of the four divided light fluxes, and 90 ° and 180 ° are respectively set around the optical axis direction. It is preferable to rotate by 270 degrees each (degrees of rotation of the other one light beam is 0 degree). Alternatively, an image rotator is arranged in each of the optical paths of the four light fluxes, and 90 °, 180 °, 270 °, 36 with the optical axis directions as axes.
You may rotate by 0 degree.

Next, a modification of the optical splitter will be described with reference to FIGS. In each figure, members having the same functions and functions as those of FIG. 2 are designated by the same reference numerals, and description thereof will be omitted here. 8 and 9 show examples in which an optical fiber 20c and a plurality of mirrors 20d to 20f are used as the light splitter. In FIG. 8, the incident portion 20b of the fiber 20c is shown.
The illumination light flux incident on is split into two light fluxes at the emission units 21b and 21c. The ejection parts 21b and 21c are the holding members 4
4a and 44b are integrally held, and the position of each luminous flux automatically moves (follows) as each synthetic fly-eye lens moves.
Will be done.

In FIG. 9, the illumination luminous flux is divided into two by the V-shaped first mirror 20d. The second mirrors 21e and 21f are plane mirrors and guide each light beam to the first fly-eye lens groups 40a and 40b. Further, the second mirrors 21e, 21
f is integrally held by holding members 44a and 44b that integrally hold the synthetic fly-eye lens, and in this example, the position of each light beam is also automatically moved (followed) as the synthetic fly-eye lens is moved. become.

By the way, even when the optical splitters shown in FIGS. 8 and 9 are used, the optical path difference generating member (parallel plate glass 30) is replaced with the fiber emitting portions 21b and 21c as in the example of FIG. Second fly-eye lens group 40a, 4
0b, the first mirror 20d and the second mirror 21e, 2
1f (or the second fly-eye lens group 40a, 40)
It may be arranged in the optical path between the fiber entrance portion 20f and the first mirror 20d in the optical path between the fiber entrance portion 20f and the first mirror 20d as in the example of FIG. Further, the number of each synthetic fly-eye lens and the number of divisions by the optical divider are not limited to two, and may be any number. In FIG. 8, the number of divisions (the number of emission parts) of the fiber 20c may be changed, and in FIG. 9, a pyramid mirror (four divisions) or the like may be used as the first mirror 21d. still,
The configuration of the light splitter is not limited to these, and may be, for example, a combination of a concave polyhedron prism and a convex lens (or a lens group having positive power), a diffraction grating, particularly a phase type diffraction grating, or a convex lens. An array or the like may be used.

Next, how to optimize these systems according to the reticle pattern to be exposed will be described.
Each position of the first fly-eye lens group (position within a plane perpendicular to the optical axis) is preferably determined (changed) according to the reticle pattern to be transferred. The position determining method in this case is, as described in the action section, the optimum resolution for the fineness (pitch) of the pattern to be transferred by the illumination light flux from each first fly-eye lens group, and the effect of improving the depth of focus. The position (incident angle ψ) that is incident on the reticle pattern may be set so as to obtain

Next, a specific example of determining each position of the first fly-eye lens group will be described with reference to FIGS. 12 and 13.
FIG. 12 is a diagram schematically showing the portion from the first fly-eye lens groups 41a and 41b to the reticle pattern 9, and the reticle-side focal planes 414a and 414b of the first fly-eye lens groups 41a and 41b are the reticle pattern 9. Coincides with the Fourier transform plane 17 of. Further, at this time, a lens or a lens group that brings them into a Fourier transform relationship is represented as one lens 5. further,
It is assumed that the distance from the fly eye lens side principal point of the lens 5 to the reticle side focal planes 414a and 414b of the first fly eye lens group 41 and the distance from the reticle side principal point of the lens 5 to the reticle pattern 9 are both f. To do.

13A and 13C are diagrams showing an example of a partial pattern formed in the reticle pattern 9, and FIG. 13B shows the case of the reticle pattern of FIG. 13A. Shows the optimum position on the Fourier transform surface 17 (pupil surface of the projection optical system) of the center of the first fly's eye lens group, and FIG. 13D shows the optimum position for the reticle pattern of FIG. 13C. It is a figure showing the position of 1 fly eye lens group (center position of each fly eye lens group).

FIG. 13A shows a so-called one-dimensional line-and-space pattern in which the transmissive portion and the light-shielding portion are arranged in strips in the Y direction with the same width, and they are arranged in a pitch P in the X direction.
It is lined up regularly. At this time, the optimum position of each first fly-eye lens is on the line segment Lα in the Y direction, which is assumed in the Fourier transform plane, and on the line segment L, as shown in FIG. 13B.
It is an arbitrary position on β. FIG. 13B is a view of the Fourier transform surface 17 with respect to the reticle pattern 9 as viewed from the optical axis AX direction, and the coordinate system XY in the surface 17 is the view of the reticle pattern 9 viewed from the same direction as FIG. 13A. Same as.

In FIG. 13B, the distances α and β from the center C through which the optical axis AX passes to the line segments Lα and Lβ are α.
= Β, and when λ is the exposure wavelength, α = β = f ·
It is equal to (1/2) · (λ / P). This distance α ・ β is f
・ If expressed as sin ψ, sin ψ = λ / 2P, which is in agreement with the numerical value described in the section of action. Therefore, each center of the first fly-eye lens group (each centroid of the light amount distribution of the secondary light source image formed by each of the first fly-eye lens group)
If the positions are on the line segments Lα and Lβ, either the 0th-order diffracted light or the ± 1st-order diffracted light generated by the illumination light from each fly-eye lens group with respect to the line-and-space pattern as shown in FIG. The two diffracted lights, one of which and the other one, pass through the position on the pupil plane 11 of the projection optical system 10 at a position substantially equidistant from the optical axis AX. Therefore, as described above, the depth of focus for the line and space pattern (FIG. 13A) can be maximized and high resolution can be obtained.

Next, FIG. 13C shows the case where the reticle pattern is a so-called isolated space pattern, and the X direction (horizontal direction) pitch of the pattern is Px and the Y direction (vertical direction) pitch is Py. .. FIG. 13D is a diagram showing the optimum position of each first fly-eye lens in this case, and the position and rotation relationship with FIG. 13C are shown in FIG.
This is the same as the relationship between (A) and (B). When the illumination light is incident on the two-dimensional pattern as shown in FIG.
Diffracted light is generated in a two-dimensional direction according to the periodicity (X: Px, Y: Py) in the dimensional direction. Even in the two-dimensional pattern as shown in FIG. 13C, one of the ± 1st-order diffracted lights in the diffracted light and the 0th-order diffracted light are arranged to be substantially equidistant from the optical axis AX on the pupil plane 12 of the projection optical system 10. By doing so, the depth of focus can be maximized. Since the pitch in the X direction is Px in the pattern of FIG. 13C, the line segment Lα that satisfies α = β = f · (1/2) · (λ / Px), as shown in FIG. 13D. If the center of each fly-eye lens group is located on Lβ, the depth of focus can be maximized for the X-direction component of the pattern. Similarly, r = ε = f · (1/2) ·
If the centers of the fly-eye lens groups are on the line segments Lγ and Lε that are (λ / Py), the depth of focus can be maximized for the Y-direction component of the pattern as well.

As described above, when the illumination light flux from the fly-eye lens group arranged at each position shown in FIG. 13 (B) or (D) enters the reticle pattern 9, the 0th-order diffracted light component D
₀ and + 1st order diffracted light component D _p or −1st order diffracted light component D
Any one of _m passes through an optical path that is substantially equidistant from the optical axis AX on the pupil plane 11 of the projection optical system 10. Therefore, as described in the section of the operation, a projection exposure apparatus having a high resolution and a large depth of focus can be realized.

The reticle pattern 9 shown in FIG.
Although only the two examples shown in (A) and (C) are considered, the + 1st-order diffracted light component or the -1st-order diffracted light component from the pattern is paid attention to the periodicity (fineness) of other patterns. The center of each fly-eye lens group may be arranged at a position where two light fluxes of either one of the above and the 0th-order diffracted light component pass through the optical path on the pupil plane 11 of the projection optical system that is substantially equidistant from the optical axis AX. .. In the pattern examples of FIGS. 13A and 13C, the ratio (duty ratio) of the line portion and the space portion is 1:
Since the pattern is 1, the ± first-order diffracted light becomes strong in the diffracted light generated here. Therefore, attention was paid to the positional relationship between one of the ± first-order diffracted lights and the zero-order diffracted light. However, in the case where the pattern is different from the duty ratio of 1: 1 or the like, in the case of other diffracted light, for example, in the case of the pattern with the duty ratio of 1: 3, the positional relationship between any one of the ± 2nd order diffracted light and the 0th order diffracted light becomes The optical axis A on the pupil plane 11 of the system
The distance from X may be substantially equal.

The reticle pattern 9 is shown in FIG.
In the case of including a two-dimensional periodic pattern as shown in FIG.
On 1, the first-order and higher-order diffracted light components distributed in the X direction (first direction) centering on the one zero-order diffracted light component,
There may be first-order or higher-order diffracted light components distributed in the Y direction (second direction). Therefore, assuming that a two-dimensional pattern is satisfactorily formed on one specific 0th-order diffracted light component, one of the higher-order diffracted light components distributed in the first direction,
One of the higher-order diffracted light components distributed in the second direction and a specific 0
The three 0th-order diffracted light components are distributed on the pupil plane 11 at substantially equal distances from the optical axis AX.
The positions of the two first fly-eye lenses) may be adjusted.
For example, in FIG. 13D, each center position of the first fly-eye lens may be matched with any of the points Pζ, Pη, Pκ, and Pμ. The points Pζ, Pη, Pκ, and Pμ are all line segments Lα or Lβ (the optimum position for periodicity in the X direction,
That is, the 0th-order diffracted light and one of the ± 1st-order diffracted lights in the X direction are located on the pupil plane 12 of the projection optical system at substantially equal distances from the optical axis, and line segments Lγ and Lε (optimal positions for periodicity in the Y direction). ), The light source position is optimal in both the X-direction and Y-direction pattern directions.

In the above description, a pattern having a two-dimensional directivity at the same location on the reticle is assumed as a two-dimensional pattern. However, when a plurality of patterns having different directivities exist at different positions in the same reticle pattern. Also, the above method can be applied. When the pattern on the reticle has a plurality of directions and / or fineness, the optimum position of the fly-eye lens group corresponds to each direction and fineness of the pattern as described above. However, for example, the first fly-eye lens may be arranged at the average position of the optimum positions. Here, this average position may be a weighted average in which a weight corresponding to the fineness or importance of the pattern is added.

Further, the 0th-order diffracted light component of the light flux emitted from each first fly-eye lens group is obliquely incident on the wafer. At this time, if the direction of the light amount center of gravity of these inclined incident light beams (plurality) is not perpendicular to the wafer,
When the wafer 12 is slightly defocused, the position of the transferred image shifts in the in-plane direction of the wafer. In order to prevent this, the direction of the light amount centroid on the image plane of the illumination light flux (plurality) from each fly-eye lens group or on the plane in the vicinity thereof is perpendicular to the wafer, that is, parallel to the optical axis AX. To be there. That is, when an optical axis (center line) is assumed for each first fly-eye lens group, a position vector in the Fourier transform plane of the optical axis (center line) with reference to the optical axis AX of the projection optical system 10, It suffices that the vector sum of the products of the light quantities emitted from the fly-eye lens groups becomes zero. As a simpler method, the number of the first fly-eye lens group is set to 2 m (m is a natural number), and
Individual positions are determined by the optimization method described above (FIG. 12),
The remaining m pieces may be arranged at positions symmetrical to the m pieces with respect to the optical axis AX.

As described above, when the position of each first fly's eye lens group is determined, the state of the light splitter (FIGS. 2, 8 and 9) is determined accordingly. At this time, the guide optical system, the light splitting optical system, the position of the second fly-eye lens group, and the like are determined so that the illumination light is incident on the first fly-eye lens group most efficiently (without loss of light amount). It should be noted that in the above system, each operation unit may be provided with a position detector such as an encoder. The main control system 50 or drive system 51 in FIG. 1 moves, rotates, or replaces each component based on the position information from these position detectors. Further, although it is the shape of the lens element of each fly-eye lens group, the effective area of the reticle or the circuit pattern area is usually rectangular. Therefore, the incident surface of each element of the first fly-eye lens (reticle pattern and imaging relationship: because the exit surface and the reticle pattern surface have a Fourier transform relationship, the entrance surface (light source side focal plane) and the exit surface (reticle side) (Focus) is also related to the Fourier transform, of course)
Is a rectangle corresponding to the planar shape of the reticle pattern surface, it is possible to efficiently illuminate only the pattern portion of the reticle.

The first fly's eye lens group is composed of a set of elements, but the total of all incident surfaces thereof may be any shape. However, since the total of all the incident surfaces and the incident surface of one element of the second fly-eye lens group have an image-forming relationship, it is similar to the incident surface of one element of the second fly-eye lens group. With the shape, light loss is small. For example, if the entrance surface of one element of the second fly-eye lens group is rectangular, then the total entrance surface of each first fly-eye lens group is also rectangular. Alternatively, if the entrance surface of one element of the second fly-eye lens group is a regular hexagon, all entrance surfaces of each first fly-eye lens group may be inscribed in a regular hexagon.

When the image of the incident surface shape of one element of the second fly-eye lens group is projected by the guide optical system so as to be slightly larger than the entire incident surface of each first fly-eye lens group, The illuminance uniformizing effect in the one fly-eye lens group is further enhanced. Further, the size of the exit surface of each first fly-eye lens group is such that the numerical aperture (one width of the angular distribution on the reticle) of each of the outgoing light beams is relative to the reticle-side numerical aperture of the projection optical system. 0.1 to 0.3 times is preferable. This is because the fidelity of the transfer pattern (image) is reduced at 0.1 times or less, and the effects of high resolution and large depth of focus are weakened at 0.3 times or more.

Further, in the device shown in the embodiment of the present invention, each optical system of the first fly-eye lens group, the guide optical system, and the second fly-eye lens group (the configuration shown in FIG. 2) from the light splitter is A corresponding part in the conventional illumination optical system, that is, a relay lens and one fly's eye lens may be exchangeable. In the above embodiment, in order to improve the illuminance uniformity, a two-stage integrator structure is provided in which two sets of fly-eye lens groups are provided for each of the plurality of light beams split by the light splitters 20 and 21. For example, a prismatic rod-type integrator may be used as the optical integrator, or two sets of rod-type integrators or a combination of a rod-type integrator and a fly-eye integrator may be used to form the above two-stage integrator structure. Incidentally, such a configuration is disclosed in, for example, Japanese Patent Laid-Open No. 1-271718. Further, in addition to the two-stage integrator structure, for example, each of the plurality of light beams divided by the light splitters 20 and 21 is further divided into a plurality of light beams by using a polyhedral prism, a mirror, or the like, and the plurality of light beams are divided. May be configured so as to be superposed on the entrance surface of one fly-eye lens group (or may be a rod-type integrator) to be incident. According to such a configuration, even if only one optical integrator is used, the effect of improving the illuminance uniformity can be obtained to some extent. Further, for example, if the size (cross-sectional area) of each element that constitutes the fly-eye lens is reduced, even if a two-stage integrator structure is not used, only one mesh-shaped fly-eye lens can be used to achieve uniform illuminance. Can be improved to some extent. Further, in the above embodiment, the optical splitters 20 and 21 are
Although two sets of fly-eye lens groups (40a, 41a) and (40b, 41b) are arranged for each of the plurality of light beams divided by, for example, the first fly-eye lens group and the second fly-eye lens group are arranged.
At least one of the fly-eye lens groups may be one large fly-eye lens that spreads over the entire surface of a region through which each light flux passes in a plane perpendicular to the optical axis AX of the illumination optical system. At this time, considering the moving range of each light flux in the plane perpendicular to the optical axis AX according to the periodicity and fineness of the reticle pattern,
It is desirable to determine the size of the fly-eye lens. This also applies when only one set of fly-eye lenses is used. 2 to 5, FIG. 8 and FIG.
In the illumination optical system shown in, the light flux incident on each fly-eye lens group is illuminated to a certain extent wider than the entrance end face of each fly-eye lens group, and the light amount distribution incident on each fly-eye lens group is The uniformity is preferable because the illuminance uniformity on the reticle pattern surface can be further enhanced.

As is clear from the above, regardless of the configuration of the light splitter, the fly-eye lens group, etc., at least 2 in the pupil plane 17 of the illumination optical system or in the vicinity thereof.
In the case of a projection exposure apparatus having an illumination optical system that forms two light quantity distributions (secondary light source image of the fly's eye lens group), an optical path difference generating member such as a parallel plate glass is used to obtain a coherent length L By generating a long optical path difference, the effect of improving the illuminance uniformity on the reticle pattern surface can be obtained.

By the way, in the above embodiment, the optical splitter 20,
The parallel plate glass 30 as the optical path difference generating member is arranged in the optical path of either one of the two light beams divided by 21, but its thickness is set so that the optical path difference of the two light beams becomes longer than the coherent length L. May be arranged in each optical path, or two parallel plate glasses may be integrally formed. For example, when the illumination light flux is divided into four by the light splitters 20 and 21, FIG.
It is also possible to use an optical member 60 as shown in FIG. 5, that is, an integrated combination of four parallel plate glasses 60a to 60d having different thicknesses. At this time, the thickness of each parallel flat glass is determined so that the mutual optical path differences of the light beams passing through each of the parallel flat glasses 60a to 60d are all longer than the coherent length L. As described above, the parallel flat plate glass need not be arranged in the optical path of one of the four light fluxes. Further, instead of using the parallel plate glass as the optical path difference generating member, a step prism 61 as shown in FIG. 14B may be used. Step prism 61
Is a combination of prisms of the same number of prisms as the number of elements forming the fly-eye lens group, and the optical path differences of the light fluxes passing through the prisms are all longer than the coherent length L, The length of each prism is defined. By arranging the step prism 61 as described above in the optical path of one light flux, it is possible to reduce the interference generated between the respective elements of the fly-eye lens group and further improve the illuminance uniformity. In the optical member 60 and the step prism 61, the optical path difference is generated by making the thickness (length) different. However, not only the thickness (length) of the parallel plate glass and the prism but also the refractive index Even if each parallel plate glass or prism is made of different optical materials, it is possible to generate an optical path difference between mutual light beams.

In the above embodiment, the pupil plane 1 of the illumination optical system is
7 or a projection exposure apparatus including an illumination optical system that forms at least two light amount distributions (secondary light source image of the fly's eye lens group) in the plane is described, for example, as shown in FIG. When the optical path difference generating member 60 described above is applied to a projection exposure apparatus that employs an annular illumination method, improvement in illuminance uniformity on the reticle pattern surface can be expected. Hereinafter, a brief description will be given with reference to FIG. In FIG. 15, an illumination light flux from a light source (not shown) is incident on the prism 70, and after being shaped into an annular shape, the optical path difference generating member 6 is formed.
It is incident on the second fly-eye lens group 71 via 0. Further, the illumination light flux passes through the lens 73 and the first fly-eye lens group 72, and then is irradiated onto the reticle pattern with a substantially uniform illuminance by the condenser lens. Note that FIG.
It is assumed that the apparatus configuration is the same as that shown in FIG. 1 except for the configuration shown in FIG. By the way, the prism 70 is a so-called cone prism having a conical slope on each of the incident surface and the exit surface, and the illumination light flux is shaped into a ring zone by the refraction of the prism 70 and is irradiated on the optical path difference generating member 60. Will be. In addition, the first and second fly-eye lens group 7
Both 2 and 71 are one large fly-eye lens that spreads over the entire area of the passage area of the annular luminous flux in the plane perpendicular to the optical axis AX, and each element has a very small cross-sectional area. ing. The above-mentioned configuration, that is, a two-stage integrator structure is adopted, and the ring-shaped illumination luminous flux is divided into four by the optical path difference generating member 60, and the mutual optical path difference between the divided luminous fluxes is determined to be longer than the coherent length L. As a result, it is possible to improve the illuminance uniformity on the reticle pattern surface. Although FIG. 15 shows an example in which the ring-shaped illumination light flux is divided into four, the number of divisions may be arbitrary (at least two). Further, during the exposure, the optical path difference generating member 6
If 0 is rotated about the optical axis AX, further improvement in illuminance uniformity can be expected. Further, when changing the inner diameter or outer diameter of the annular illumination light flux according to the periodicity or fineness of the reticle pattern, for example, a plurality of cone prisms having different thicknesses should be replaceably arranged in the illumination optical path. In addition, the size (diameter) of the circular illumination light flux incident on the cone prism 70 can be changed by the variable aperture stop.

[0068]

As described above, according to the present invention, while using a reticle having a normal transmission and light shielding pattern,
It is possible to realize a projection exposure apparatus having a higher resolution and a larger depth of focus than ever before. Moreover, the present invention is particularly suitable for a projection exposure apparatus that uses a laser such as an excimer laser as a light source, and has a simple structure, that is, the speckle interference fringes are reduced by the optical path difference generating member, and the illuminance uniformity on the reticle pattern surface is improved. Can be improved. Furthermore, by adopting a two-stage integrator structure, further improvement in illuminance uniformity can be expected.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a specific configuration of part of the illumination optical system in FIG.

FIG. 3 is a diagram showing a modified example of a part of the configuration of the illumination optical system in FIG.

FIG. 4 is a diagram showing a modified example of a part of the configuration of the illumination optical system in FIG.

5 is a diagram showing a modified example of a part of the configuration of the illumination optical system in FIG.

FIG. 6 is a diagram showing a configuration of a prism when the light splitter in the illumination optical system is divided into four.

FIG. 7 is a diagram showing a structure of a moving mechanism of a fly-eye lens group.

FIG. 8 is a diagram showing a modification of the light splitter in the illumination optical system.

FIG. 9 is a diagram showing a modification of the light splitter in the illumination optical system.

FIG. 10 is a diagram showing a device configuration for explaining the principle of the present invention.

FIG. 11 is a view for explaining the projection principle of a conventional projection exposure apparatus.

FIG. 12 is a diagram illustrating a principle of arrangement of a fly-eye lens in an illumination optical system.

FIG. 13 is a diagram illustrating a method of arranging a fly-eye lens.

FIG. 14 is a diagram showing a modification of the optical path difference generating member in the illumination optical system.

FIG. 15 is a diagram showing an example in which an optical path difference generating member is applied to a projection exposure apparatus adopting a ring illumination method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 7 condenser lens 8 reticle 10 projection lens 11 pupil 12 wafer 20, 21 polyhedral prism 30 parallel plate glass 35 image rotator 41a, 41b first fly-eye lens group 40a, 40b second fly-eye lens group 42a, 42b, 43a, 43b Guide optical element

Claims (8)

[Claims] 1. An illumination optical system that shapes illumination light from a light source into a substantially uniform intensity distribution and irradiates the mask on which a predetermined pattern is formed with the uniform illumination light, and an image of the pattern of the mask. In a projection exposure apparatus provided with a projection optical system for image-forming projection on a photosensitive substrate, an exit side focal plane is arranged in a Fourier transform plane for the pattern of the mask in the optical path of the illumination optical system or in a plane in the vicinity thereof. And a plurality of first centers whose centers are arranged at a plurality of positions decentered from the optical axis of the illumination optical system.
A fly-eye lens; an exit-side focal plane is disposed on a Fourier transform surface with respect to an incident end of each of the plurality of first fly-eye lenses, or in a plane in the vicinity thereof, and
A plurality of second fly-eye lenses provided corresponding to each of the fly-eye lenses; and a light splitting device that splits the illumination light from the light source into a plurality of light beams to enter each of the plurality of second fly-eye lenses. And a light path difference generating member that gives different light path differences to the light path lengths of the light beams emitted from each of the plurality of first fly-eye lenses. 2. The optical path difference generating member is arranged in an optical path between the light source and the second fly-eye lens, and an optical path from the light source to an incident end of each of the second fly-eye lenses. The projection exposure apparatus according to claim 1, wherein an optical path difference between the plurality of light fluxes in length is set to be longer than a coherence length of the illumination light. 3. The number of the optical path difference generating members is the same as the number of sets of the first fly-eye lens and the second fly-eye lens,
Alternatively, the projection exposure apparatus according to claim 2, wherein only one lesser number is provided. 4. The projection exposure apparatus according to claim 3, wherein the optical path difference generating member is a parallel plate glass. 5. The illumination optical system outputs a light beam from each of a plurality of light source images formed on one exit end side of the second fly-eye lens to a corresponding one of the first fly-eye lenses. A guide optical element to be superposed on the incident surface side, and one of the first fly-eye lenses and a corresponding one
A plurality of holding members for integrally holding one second fly-eye lens, the guide optical element, and the optical path difference generating member are provided corresponding to the number of sets of the first fly-eye lens and the second fly-eye lens. 4. The projection exposure apparatus according to claim 3, wherein the plurality of holding members are provided and movable in a plane perpendicular to the optical axis. 6. The illumination optical system is a set of the first fly-eye lens and the second fly-eye lens in an optical path to the incident end of each of the light splitter and the plurality of second fly-eye lenses. 2. The projection exposure apparatus according to claim 1, further comprising at least one image rotator corresponding to the number of N. 7. An illumination optical system for shaping illumination light from a light source into a substantially uniform intensity distribution and irradiating the mask on which a predetermined pattern is formed with the uniform illumination light, and an image of the pattern of the mask. In a projection exposure apparatus including a projection optical system for image-forming projection on a photosensitive substrate, in the optical path of the illumination optical system, the illumination light is divided into a plurality of light fluxes, and a Fourier transform plane for the pattern of the mask, or A light beam splitting member that creates at least two light amount distributions that are separated from each other in the vicinity thereof; an optical path difference that gives different optical path differences to the respective optical path lengths of a plurality of light beams emitted from the light beam splitting member A projection exposure apparatus comprising: a member. 8. The projection exposure apparatus according to claim 1, wherein the light source is a laser light source.