JPS63114186A - Lighting apparatus - Google Patents

Abstract

PURPOSE:To enable scanning and lighting in a short time even when the area of scanning is large by forming a plurality of beam spots on approximately the same plane and directing beams from the beam spot onto the surface to be irradiated through a beam-condensing optical system while the surface is scanned simultaneously by the beam spot. CONSTITUTION:A plurality of mutually incoherent luminous flux are shaped by a luminous flux divider 12, a plurality of beam spots are formed onto approximately the same plane by a fly-eye lens 14 by using a plurality of luminous flux, and the surface to be irradiated is scanned simultaneously with a plurality of beam spots by a rotating reflecting mirror 15 while beams from a plurality of the beam spots are directed onto the surface to be irradiated. Accordingly, since an incoherent light source having spread can be acquired, the distance of scanning of each point source (image), beam spots, is shortened extremely, and a predetermined scanning range can be scanned with beam spots by scanning in an extremely short time even when a large area is scanned.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an illumination device, and particularly to an illumination device that illuminates an object by scanning a beam of light from a coherent light source such as a laser.

[Prior art] In an imaging optical system, it is necessary to set the illumination coherency to an appropriate value in order to obtain the necessary resolving power, and for this purpose, the coherency of the illumination system must be set to a 0 value (the coherency of the illumination system with respect to N and A of the objective lens). It is known to control the ratio of N and A. When a coherent light source such as a laser beam is used as the illumination light source, the required coherency is achieved by condensing the light source into a spot and scanning it by an appropriate distance at the pupil position of the imaging optical system. can be obtained.

FIG. 4 is a schematic diagram showing a conventional example of an illumination device using the above-mentioned Cohey and Rhett light sources as an illumination light source.

The device shown in FIG. 4 is an illumination device for an excimer stepper that has been attracting attention in recent years. In the figure, 1 is a laser light source such as an excimer laser, and L and L2 are lenses each having positive power. 2 is a pinhole, Mr is a rotating or rotatable reflecting mirror, and L3 and L4 are lenses each having positive power. Further, A is the pupil plane of the lens L4, and is located at the front focal position of the lens L4.

B is the irradiated surface and is located at the rear focal position of the lens L4. Specifically, if the focal length flow of lens L4 is f4,
The pupil plane A and the irradiated surface B are located at a distance of f4 from the front and rear principal planes of the lens L4.

In FIG. 6, a parallel beam of light emitted from a laser light source 1 is once focused on a pinhole 2 by a lens L1, and then becomes a diverging beam of light and enters a lens L2. The lens L2 has a function as a so-called collimator lens, converts the diverging light into a parallel light beam, and directs the parallel light beam toward the reflecting mirror Mr. reflection fiM
The light beam reflected by r is focused on the pupil plane A by the lens L3, and by turning or rotating the reflector Mr in the direction of the arrow, the spot of the focused light beam moves on the pupil plane A.
scanned in the direction. Furthermore, the scanning light beam condensed on the pupil plane A enters the lens L4 as a diverging light beam, and is sequentially converted into a parallel light beam by the lens L4 to illuminate the same illumination area of the illuminated surface B.

According to this device, the required coherence range can be obtained by condensing the light beam emitted from the laser light source 1 onto the pupil plane A and deflecting and scanning it with the reflecting mirror Mr.

This type of device is disclosed in, for example, Japanese Patent Application Laid-Open No. 59-226317, and is suitable as a device for obtaining a desired coherence range when using a coherent light source such as an excimer laser.

However, depending on the required coherence, etc., the area to be scanned becomes large, resulting in disadvantages such as an increase in the size of the scanning optical system and an increase in the time required for scanning. Particularly, when this type of illumination device is used in semiconductor manufacturing equipment such as the above-mentioned excimer stepper, a longer scanning time is undesirable because it causes deterioration of the throughput of the manufacturing equipment.

[Summary of the invention]

SUMMARY OF THE INVENTION In view of the above conventional problems, an object of the present invention is to provide an illumination device that can scan and illuminate in a short time even when the scanning area is large.

In order to achieve the above object, an illumination device according to the present invention includes a light beam forming means that forms a plurality of mutually incoherent light beams, and an optical system that forms a plurality of light spots on substantially the same plane using the plurality of light beams. The apparatus is characterized in that it has a scanning means for simultaneously scanning the plurality of light spots, and a condensing means for directing the light from the plurality of light spots onto a surface to be irradiated.

Further features of the invention are detailed in the Examples below.

(Embodiment) FIG. 1 is a schematic configuration diagram showing an embodiment of the illumination device according to the present invention, and shows a case where the illumination device is applied to a semiconductor exposure device called a so-called stepper.

In the figure, 11 is a coherent light source such as an excimer laser,
Reference numeral 12 denotes a beam splitting device that divides the coherent light emitted from the light source 11 into a plurality of beams and emits each of the divided beams as a mutually incoherent beam. 13
is a fly-eye lens consisting of multiple lens elements,
14 is a condenser lens, and the rear focus of the fly's eye lens 13 and the front focus of the condenser lens 14 coincide (arrow P in the figure). 15 is a rotating reflector that can be rotated in any direction, 16 is an F-θ lens whose exit side is telecentric, and A is a surface conjugate with the entrance pupil of the imaging optical system (described later).
Hereinafter, it will be referred to as "pupil A." ), the light flux passing through the F-θ lens 16 is focused on the pupil A to form a light spot. 17
18 is a condensing optical system, 18 is a reticle with a predetermined circuit pattern, 19 is an imaging optical system, and 20 is an entrance pupil of the imaging optical system 19, which is in a conjugate relationship with the pupil A described above. 21 is reticle 1
The circuit pattern No. 8 is projected onto the wafer through the imaging optical system 19, and exists at a position conjugate with the reticle 21 through the imaging optical system 19. Also, 0 is the optical axis, x and y are the rotating reflector 1
5 shows the rotation axis.

The coherent light emitted from the light source 11 is transmitted to the beam splitter 1
2, this coherent light is split into a plurality of light beams by the light beam splitter 12, and each of the plurality of light beams becomes incoherent light with respect to the light beam splitter 1.
2 is emitted as a parallel beam of light. Note that the specific configuration of this beam splitting device 12 will be explained in detail later using the drawings.

A plurality of mutually incoherent parallel light beams emitted from the light beam splitter 12 enter a fly's eye lens 13 .

A plurality of lens elements and a plurality of parallel light beams constituting the fly-eye lens 13 have a 1:1 correspondence, and each light beam incident on each corresponding lens element is reflected by the fly-eye lens 13 after the fly-eye lens 13. The light is focused on the side focal point. In this case, since the plurality of light beams emitted from the light beam splitter 12 were parallel light beams, the fly-eye lens 1
Although the light is focused at the rear focal point of No. 3, the light focusing position P may be any position.

For example, if the light beam is emitted from the light beam splitter 12 in a converging or diverging state, it will not be focused on the focal point of the fly's eye lens 13. Further, although the illustrated fly's eye lens 13 is made of a lens element having a positive refractive power, it may be made of a lens element such as a concave lens having a negative refractive power.

Now, since the rear focal point of the fly's eye lens 13, that is, the condensing position P of the plurality of light beams mentioned above, coincides with the front focal point of the condenser lens 14, The light beams enter the condenser lens 14 as divergent light beams, and become parallel light beams via the condenser lens 14, respectively. However, the plurality of parallel light beams obtained by the condenser lens 14 are tilted at different angles with respect to the optical axis 0, and the plurality of parallel light beams are incident on the rotating reflecting mirror 15 at different angles. Each parallel light beam reflected by the rotating reflector 15 is directed to the F-theta lens 16, and is focused by the F-theta lens 16 on the back focal plane of the F-theta lens 16, that is, IA, so that they are on the same plane in space. A light spot is formed at a position corresponding to the angle of incidence on the upper F-θ lens 16. Here, F
Since the -θ lens 16 is telecentric on the exit side, the principal rays of the plurality of light beams condensed by the F-〇 lens 16 are parallel to the optical axis.

Through the above process, a plurality of light spots (images) are formed on the pupil A using a plurality of mutually incoherent light beams obtained from the light beam splitter 12.

Here, when the above-mentioned plurality of parallel light beams are scanned by rotating the rotating reflector 15 around the two rotation axes indicated by x and y, the plurality of light spots formed in the pupil A are on the same parallel plane. are simultaneously scanned two-dimensionally. Figure 2 is pupil A
It is a schematic diagram showing how multiple light spots are two-dimensionally scanned at , and each symbol indicates a different time To, T I,
T2.

T3. The position of the light spot at T4 is shown. At this time, light spots at different times are incoherent, and multiple light spots at the same time are also incoherent as described above, so all light spots formed on pupil A within a predetermined time interval The light spot becomes incoherent light. Therefore, multiple point light sources (images) that are scannable and incoherent are formed on the IA,
A wide incoherent light source can be obtained. For this reason, as can be seen from Figure 2, the scanning distance of each point light source (image), that is, the light spot, becomes extremely short, and even when scanning a large area, a predetermined scanning range can be covered by the light spot in an extremely short period of time. It becomes possible to scan.

Returning to FIG. 1, [the light from the plurality of light spots formed on the IA enters the condensing optical system 17 as a diverging light flux,
The light beams are converged by the condensing optical system 17 and overlap each other to illuminate the reticle 18.

The circuit pattern of the reticle 18 illuminated in this manner is imaged onto the wafer 21 at a predetermined magnification via the imaging optical system 19, and the circuit pattern of the reticle 18 is transferred onto the wafer 21.

In addition, since the entrance pupil 2o of the imaging optical system 19 and [IA are related to military service, a plurality of incoherent light spots (images)
is formed at the entrance pupil 2° of the imaging optical system 190, and the wafer 21 receives so-called Koehler illumination. If the wafer 21 is illuminated with Kohler illumination in this manner, non-uniformity in the illuminance distribution caused by the brightness distribution of the light source image (light spot) can be avoided. However, if the brightness distribution of the light source image is not much of a problem, it is not necessarily necessary to configure this type of Koehler illumination. Therefore, the position of the light spot formed through the F-θ lens 16 is not limited to []IItA, and the light spot can be formed at any position on the optical path of the illumination light beam.

According to this embodiment, it is reflected by the rotating reflecting mirror 15.

By condensing the scanned parallel light flux through the F-θ lens 16, the light spot formed at @A moves at a constant speed, making it possible to constantly illuminate the same area of the reticle 17. Therefore, when the illumination area is defined, the illumination light flux can be efficiently guided to the illumination area. However, if the intensity of the illumination luminous flux is sufficient and effective use of the illumination luminous flux is not a problem, a normal condensing optical system (F t a n θ lens system) may be arranged in place of the F-θ lens system 16. I do not care. Similarly, the refractive power (focal length) of the focusing optical system
Also, the distance between the plane on which the light spot is formed and the reticle 18, etc. are determined as appropriate in accordance with the specifications of the apparatus. For example, if the imaging optical system 19 is a telecentric optical system on the entrance and exit sides, the plane (pupil A) on which the light spot is formed and the condensing optical system 1
7 and the distance between the focusing optical system 17 and the reticle 18, respectively, as the focal length (f) of the focusing optical system 17.
In view of lighting efficiency, etc., this can be said to be a preferable configuration.

Further, in this embodiment, the light spot is scanned by scanning a parallel light beam using the rotating reflecting mirror 15, but the scanning means is not limited to the rotating reflecting mirror. For example, instead of the above-mentioned rotating reflector 15, an Elo or A10 optical deflector using an electro-optic crystal, an elastic wave transmission medium, etc. may be arranged in the optical path of the parallel light beam to scan the light beam using physical optics. I can do it.

In addition, in the optical path of a plurality of parallel beams emitted from the beam splitting device 12 shown in FIG. 1, separate Elo,
It is also possible to arrange an A10 optical deflector to deflect and scan each light beam individually.

In this case, the number of optical deflectors increases, but compared to arranging this type of optical deflector at the position of the rotating reflector 15 in FIG. The deflector can be easily manufactured and the entire lighting device can be downsized.

As mentioned above, there are various means for scanning a plurality of light beams in the present invention. That is, in the present invention, any configuration can be selected as long as it is possible to form a plurality of mutually incoherent light spots on the same plane and scan these light spots.

Furthermore, in the present invention, the plurality of mutually incoherent spots formed on the same plane do not need to be formed at exactly the same time, but each light spot may be formed within a short enough time to be considered as the same time. It doesn't matter if it is For example, in FIG. 1, the coherent light emitted from the light source 11 may be deflected at high speed using an Elo or A/○ optical deflector, and the light beam may be directed to the rotating reflecting mirror 15 via the condenser lens 14. do not have.

In this case, it goes without saying that the deflection speed of the coherent light by the optical deflector is much faster than the scanning speed of the light beam by the rotating reflecting mirror 15.

Furthermore, by appropriately setting this deflection speed, it is possible to make the respective deflected coherent lights into a mutually incoherent beam.

According to the illumination device of the present invention, if the optical arrangement is determined as shown in FIG. 1, the coherency of illumination mainly depends on the scanning range of the light spot. Therefore, by controlling a scanning means such as a rotating reflector to define the scanning range of the light spot, illumination with a desired coherency can be achieved, and since multiple light spots are used, each light spot can be scanned. The distance is short, and a predetermined scanning range can be scanned in a short time. In other words, it becomes possible to perform illumination with desired coherency in a short time.

FIG. 3 is a schematic diagram showing a specific configuration example of the beam splitting device 12, FIG. 3(A) is a perspective view showing the entire device, and FIG.
B) is a principle diagram showing the function of a splitting prism, which is one element of the device, and FIG. 3(C) is a schematic diagram showing the arrangement of a plurality of split light beams.

In FIG. 3, 31 is a beam splitting/incoherent optical system (hereinafter referred to as "optical system 31"), 32 is a beam expander, 31a and 31b are splitting prisms, and 32a and 32b are cylindrical lenses. In addition, 33, 34, and 35 show cross sections of the light beam at different positions in the optical path of the present light beam splitter 12,
is the luminous flux emitted from the light source 11 in FIG. 1, and 34 is the optical system 3.
1, and 35 is the luminous flux after passing through the beam expander 32.

Furthermore, d and 3d are split prisms 31b, respectively.

Symbols indicating the dimensions of the plurality of person exit surfaces of 31a, 11 to 1
g is a symbol indicating a plurality of divided luminous fluxes.

The split prisms 31a and 31b each have three exit surfaces, and each exit surface of the split prism 31a is rectangular.
Each exit surface of the splitting prism 31b has a square shape. However, although the dimensions and shapes are different, the functions of dividing the light beam and making it incoherent are the same for the two splitting prisms. This principle will be explained below.

The principle diagram in FIG. 3(B) shows an optical path diagram in a cross section of the dividing prism 31a taken along a plane perpendicular to the incident surface of the light beam and perpendicular to the long side of the prism. Split prism 31
The light beam incident on the splitting prism 31a is separated by three incident surfaces (long side length 9d, short side length d) and directed into three different optical paths. The three optical paths are parallel to each other, and have reflective surfaces Rl+R2+R3 located at different distances from the incident surface. Therefore, the three sets of light beams traveling along each optical path are changed in direction by 90 degrees by the reflecting surfaces RI + R2 + R3 arranged in each optical path, and the three sets of light beams i
It is divided into In i2+i3 and emitted.

Three sets of light beams 11+1 after passing through the splitting prism 31a
The optical path difference of 2+13 is Jl jz = 2nd j2-js = 4nd, where Jnx is the optical path length within the prism of the light beam in, and n is the refractive index of the prism. Therefore, if the optical path difference 2nd is longer than the coherence length of the coherent light incident on the splitting prism 31a, the light beam is split! ! +'2+13 becomes a mutually incoherent light flux.

For example, when a KrF excimer laser with a wavelength width of 0.005 nm is used as a light source, the coherence length of this laser light is 12 mm. Therefore, when a glass material with a refractive index n=1.5 is used as the prism material, incoherence can be achieved if the dimension d in FIG. 3 is d=4 mm or more.

By using two dividing prisms having functions as shown in FIG. 3(B) and configuring as shown in FIG. 3(A), three sets of light beams divided into three by the dividing prism 31b are transmitted to the dividing prism 31a. Each group is further divided into three parts, and the result is shown in Figure 3 (C).
As shown in the figure, nine divided light beams 11 to i are obtained.

Needless to say, based on the above-mentioned principle, each of the light beams from il to 19 becomes a mutually incoherent light beam. The optical path difference between each luminous flux and the luminous flux 11 is determined by the optical path length of the luminous flux 11.
When, J+ jm=2n-m-d.

Hereinafter, the functions of the beam splitting device 12 shown in FIG. 3(A) will be briefly explained.

A light beam 33 having a rectangular cross section emitted from a coherent light source such as an excimer laser is first directed toward an optical system 31 . The dividing prism 31b of the optical system 31 divides the luminous flux 33 into three parts along the long side of its rectangular cross section, and divides the beam into three parts (11°Z21 13) and ('4-Is) shown in FIG.
+ is ) and (17+ 16 + 1 *
) are emitted from the splitting prism 31b with their traveling directions bent by 90'. Subsequently, these three sets of light beams enter the splitting prism 31a, and are divided into three along the short side of the rectangular cross section of the light beam 33.

Therefore, the luminous flux 34 emitted from the splitting prism 31a is i
,, f2+ j! +i4. is, ia.

'? + ia + 19 sets of light beams, and the overall shape maintains a rectangular shape as shown in FIG. 3(C). Further, the nine sets of light beams are mutually incoherent light beams as explained using FIG. 3(B).

Subsequently, the nine sets of light beams emitted from the splitting prism 31a are directed to the beam expander 32. A cylindrical lens 32a that constitutes the beam expander 32,
32b has refractive power only in the short side direction of the rectangular beam 34 (7), and the beam 35 that has passed through the beam expander 32 is emitted as a beam having a square cross section.

As explained above, the coherent light that has entered the present beam splitting device 12 is split into a plurality of beams and output as mutually incoherent beams. The plurality of incoherent light beams are then directed to the fly's eye lens 13 shown in FIG. 1, respectively.

The beam splitting device shown in FIG. 3 has different optical path lengths within the splitting prisms 31a and 31b to achieve incoherence. Therefore, if the splitting prism has absorption, there will be a difference in the amount of light between the split light beams, which is not preferable. In this case, by making the light beams that have passed through the beam expander 32 further enter the image rotator prism and rotating the image rotator prism, it is possible to eliminate the non-uniformity in the amount of light of each light beam.

As mentioned above, the beam splitting device shown in Fig. 3 achieves beam splitting and incoherence in the same device, but the device for beam splitting and the device for making incoherent are configured separately. Good too. Therefore, the elements constituting this type of beam splitting or incoherent device are not limited to the splitting prism of the above embodiment, but also various optical elements such as light transmission members such as fibers, multiple reflecting mirrors, and half mirrors. obtain. Furthermore, when using a split prism, it goes without saying that the configuration is not limited to that shown in FIG. 3, and that various configurations may be adopted.

The lighting device according to the present invention has been described above in detail based on specific configuration examples, but as described above, the structure of the lighting device is not limited to the above embodiments.

That is, various forms of lighting devices can be constructed based on the idea of the present invention, and various members can be used for each component.

The illumination device of the present invention is particularly suitable for application to a device that uses a coherent light source to illuminate a desired coherence range, and supplies a predetermined amount of light to an irradiated object in a short time with a desired coherence range. It is something that can be done. Therefore, the reticle (
(or a mask) When used as a lighting device, great effects can be obtained.

(Effects of the Invention) As described above, the illumination device according to the present invention forms a plurality of light spots on substantially the same plane, scans the plurality of light spots simultaneously, and converts the light spots from the plurality of light spots through the condensing optical system. By directing the light onto the irradiated surface, even when the scanning area is large, the light can be directed to the irradiated surface in an extremely short period of time, and illumination light with desired coherence can be obtained. Therefore, if used in a lighting device such as an excimer stepper, it is possible to provide a stepper with a high throughput.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of a lighting device according to the present invention. FIG. 2 is a schematic diagram showing how a plurality of light spots formed on the same plane are scanned. 3(A), 3(B), and 3(C) are schematic diagrams showing an example of the configuration of a beam splitting device. FIG. 3(A) is a perspective view of the entire device, and FIG. 3(B) is a diagram of a splitting prism. FIG. 3(C) is a diagram showing the arrangement of a plurality of divided light beams. FIG. 4 is a schematic mechanical diagram showing a conventional spot light scanning type illumination device. 11 ----------One light source 12---One beam splitter 13---Fly eye lens 14------
----Condenser lens 15 -1----Rotating reflector 16 -------F-θ lens 17 -11-
---Condensing optical system t a --------- Reticle 19 ---1 --- Imaging optical system 20 ----1 Imaging optical system human projection 21 ---
------Wafer

Claims (1)

[Claims] A light beam forming means for forming a plurality of mutually incoherent light beams, an optical means for forming a plurality of light spots on substantially the same plane using the plurality of light beams, a scanning means for simultaneously scanning the plurality of light spots, and the plurality of light beams. An illumination device comprising: an optical means for directing light from a light spot onto a surface to be illuminated.