JP2004172440A - Exposure apparatus and exposure method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure apparatus which is capable of preventing optical members in an illuminating optical system from deteriorating even when a mask is irradiated with exposure light for a long term, and carrying out a stable exposure process for a long term. <P>SOLUTION: The exposure system is equipped with a light source means 10 supplying exposure light and an illuminating optical system guiding light emitted from the light source means 10 onto the mask M where a prescribed pattern is formed. The exposure apparatus projects the image of the pattern of the mask M onto a photosensitive substrate W for exposing the substrate W, and lenses provided in the illuminating optical system are all formed of fluorite. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exposure apparatus and an exposure method for transferring a predetermined mask pattern onto a photosensitive substrate, and more particularly to an exposure apparatus and an exposure method using an ultraviolet light source suitable for semiconductor manufacturing.
[0002]
[Prior art]
Conventionally, for example, an exposure apparatus for manufacturing a semiconductor as shown in FIG. 3 is known. As shown in FIG. 3A, a light beam from a light source 1 such as a mercury arc lamp is condensed by an elliptical mirror 2 and then converted by a collimator lens 3 into a parallel light beam. Then, as shown in FIG. 3 (b), the parallel light beam passes through a fly-eye lens 4 composed of an aggregate of lens elements 4a having a rectangular cross section, thereby forming a plurality of light source images on the exit side thereof. Is done. An aperture stop 5 having a circular opening is provided at this light source image position. Light beams from the plurality of light source images are condensed by the condenser lens 6 and uniformly illuminate the mask M as an object to be irradiated in a superimposed manner.
[0003]
The circuit pattern on the mask M is transferred onto the resist-coated wafer W by the projection optical system 7 including the lenses 71 and 72 by the above illumination optical device. This wafer W is mounted on a wafer stage WS which moves two-dimensionally. In the exposure apparatus of FIG. 5, when exposure of one shot area on the wafer is completed, exposure to the next shot area is performed. Then, a so-called step-and-repeat type exposure for sequentially moving the wafer stage two-dimensionally is performed.
[0004]
In recent years, the mask M is irradiated with a rectangular or arc-shaped light beam, and the mask M and the wafer W arranged conjugately with respect to the projection optical system are scanned in a certain direction, thereby achieving high throughput. A scanning exposure method for transferring a circuit pattern of a mask M onto a wafer has been proposed.
[0005]
[Problems to be solved by the invention]
In recent years, in order to transfer a finer mask pattern image on a wafer surface, the output wavelength of a light source for exposure has been shortened. For example, in a so-called projection exposure apparatus that transfers a mask pattern onto a resist-coated wafer via a projection optical system, the output wavelength of an exposure light source is shortened to improve the resolution of the projection optical system. Can be done.
[0006]
However, when a light source that outputs exposure light having a shorter wavelength, for example, a pulse light source in the ultraviolet region that oscillates ultraviolet light, is used, an optical glass material that transmits ultraviolet light (hereinafter referred to as “light glass”) , Glass material) is generally used, because it is easy to process like a glass material that transmits light in the visible range.
[0007]
However, a light source that emits light in the ultraviolet region, such as a pulsed light source of ultraviolet light, has a high output. There is considerable energy damage to the quartz glass that constitutes the illumination optical system due to the presence and high energy density at that location. Further, as the wavelength of the light source is shortened, the energy is further increased, and the damage to the quartz glass is further increased. Thus, there is a problem in the durability of the quartz glass.
[0008]
Further, in an exposure apparatus, it is desired to increase the number of processed substrates such as wafers per hour, that is, to improve the throughput. In order to increase the illuminance on a substrate such as a wafer, the power of a light source is required. An effective means is to increase the intensity, but the energy density for quartz glass present in the illumination optical system where the beam diameter becomes smaller becomes higher and the durability of this quartz glass becomes more serious. I do.
[0009]
Therefore, the present invention provides an exposure apparatus and an exposure method that can prevent deterioration of an optical member in an illumination optical system even when a mask is irradiated with exposure light for a long time, and can realize stable exposure for a long time. It is intended to provide.
[0010]
[Means for Solving the Problems]
The exposure apparatus according to claim 1, further comprising: a light source unit that supplies light for exposure; and an illumination optical system that guides light from the light source unit onto a mask on which a predetermined pattern is formed. In an exposure apparatus for exposing a photosensitive substrate, all the lenses in the illumination optical system are made of fluorite.
[0011]
An exposure apparatus according to a second aspect is characterized in that the light source unit supplies light having a wavelength of 157 nm as the exposure light.
[0012]
The exposure apparatus according to claim 3, wherein the illumination optical system forms multiple light sources based on light from the light source means, and multiple light sources formed by the multiple light source forming means. And a condenser optical system for condensing the light from the light sources and illuminating the mask in a superimposed manner.
[0013]
The exposure apparatus according to claim 4 is characterized in that the multiple light source forming means has an optical integrator in which a plurality of lens elements are arranged.
[0014]
6. The exposure apparatus according to claim 5, wherein the projection optical system projects the image of the pattern of the mask onto the photosensitive substrate, a mask stage on which the mask is mounted, and a substrate stage on which the photosensitive substrate is mounted. And transferring the mask pattern to the photosensitive substrate by moving the mask stage and the substrate stage.
[0015]
According to a sixth aspect of the present invention, there is provided an exposure method comprising exposing the pattern of the mask onto the photosensitive substrate using the exposure apparatus according to any one of the first to fifth aspects.
[0016]
The present invention focuses on the physical property that fluorite is highly durable even at high energy densities, and with the above configuration, even if the mask is irradiated with exposure light for a long time, It has been found that deterioration of an optical member in an optical system can be prevented, and stable exposure can be realized for a long period of time.
[0017]
In particular, regarding the determination method regarding fluoridation in the illumination optical system of the exposure apparatus, the energy density of the light beam irradiated on the optical member can be obtained from the area ratio of the light beam from the original light source. At the stage of designing an illumination optical system using the optical member, the energy density of a light beam applied to the optical member may be calculated in advance. In this case, it is desirable to perform irradiation experiments on the fluorite in advance and measure its durability. Based on the above calculation results and the prediction of the total irradiation time, use fluorite in places where the energy density is high. It is more desirable to design the system.
[0018]
From such a viewpoint, the inventor of the present application performed various simulations and various experiments using a light source that supplies pulsed light, and as a result, pulsed light was incident on each optical member constituting the illumination optical system. When the light energy per pulse at the time is ES (mJ), and the cross-sectional area of a light beam passing through each optical member in the illumination optical system is AB (cm2),
(1) AB <ES / [25 (mJ / cm2)]
It has been found that it is preferable that the optical member in the illumination optical system disposed at a position having a cross-sectional area of the light beam satisfying the relationship of fluorite is made of fluorite. Thus, in the illumination optical system of the exposure apparatus, there is a portion where the light beam diameter is small, and the energy density at that portion is increased, thereby solving the problem of damaging the optical members constituting the illumination optical system. A device with excellent durability is guaranteed.
[0019]
In order to make the illumination optical system of the exposure apparatus durable, it is desirable that the above condition (1) be satisfied. If the optical members at other locations are made of fluorite and the entire illumination system is fluorinated, the durability of the illumination optical system of the exposure apparatus can be further increased.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows a configuration of an exposure apparatus for manufacturing a semiconductor according to an embodiment of the present invention. FIG. 1A is a diagram showing the configuration of the exposure apparatus according to this embodiment when viewed from directly above, and FIG. 1B is a cross-sectional configuration of the exposure apparatus of FIG. 1A when viewed from the side. FIG. Hereinafter, this embodiment will be described in detail with reference to FIG.
[0021]
As shown in FIG. 1, a light source 10 that supplies light of a predetermined wavelength, such as an excimer laser, emits substantially parallel light having a wavelength of 222 nm (KrCl), 248 nm (KrF), 192 nm (ArF), or 157 nm (F2). The parallel light beam at this time has a rectangular cross section. The parallel light beam from the light source 10 enters a beam shaping optical system 20 as a light beam shaping unit that shapes the light beam into a light beam having a predetermined cross-sectional shape. This beam shaping optical system 20 is composed of two cylindrical lenses (20A, 20B) having a refractive power in a direction perpendicular to the paper surface of FIG. 1A (the paper surface direction of FIG. 1B). The cylindrical lens 20A on the light source side has a negative refractive power and diverges the luminous flux in the paper plane direction of FIG. 1B, while the cylindrical lens 20B on the illuminated surface side has a positive refractive power, The divergent light beam from the cylindrical lens 20A on the light source side is collected and converted into a parallel light beam. Accordingly, the parallel light beam from the light source 1 via the beam shaping optical system 20 is shaped into a rectangular shape having a predetermined light beam cross-section, with the light beam width in the paper plane direction of FIG. The beam shaping optical system 20 may be a combination of a cylindrical lens having a positive refractive power, and may be an anamorphic prism or the like.
[0022]
Now, the shaped light beam from the beam shaping optical system 20 enters the first relay optical system 21. Here, the first relay optical system 21 includes a front group (21A, 21B) of two positive lenses having positive refractive power and a rear group (21C, 21D) of two positive lenses having positive refractive power. The front group (21A, 21B) of the first relay optical system 21 forms a condensing point (light source image) I at the focal position on the mask M side (rear side) of the front group. The rear group (21C, 21D) of the first relay optical system 21 is arranged such that the focal position on the light source side (front side) matches the focal position of the front group (21A, 21B). The first relay optical system 21 has a function to conjugate the exit surface of the light source 10 with the entrance surface of an optical integrator 30 as a first multiple light source image forming unit described later. The function of the first relay optical system 21 corrects the shift of the light beam illuminating the optical integrator 30 due to the angle shift of the light from the light source 10, and increases the tolerance for the angle shift of the light from the light source 10. . The light guiding optical system according to this embodiment for guiding the light from the light source 10 to the first multiple light source forming unit includes a beam shaping optical system 20 and a first relay optical system 21.
[0023]
The light beam having passed through the first relay optical system 21 enters an optical integrator 30 as first multi-source image forming means for forming a plurality of light source images arranged in three rows in a straight line. As shown in FIG. 2A, the optical integrator 30 is configured by arranging a plurality of (3 columns × 9 rows = 27) bi-convex lens elements 30a each having a substantially square lens cross section. The optical integrator 30 has a rectangular cross section as a whole. Each biconvex lens element 30a has the same curvature (refractive power) in the direction of the paper of FIG. 1A and the direction of the paper of FIG. 1B.
[0024]
Therefore, the parallel light beams passing through the individual lens elements 30a constituting the optical integrator 30 are respectively condensed, and a light source image is formed on the exit side of each lens element 30a. Accordingly, a plurality of (3 columns × 9 rows = 27) light source images corresponding to the number of lens elements 30a are formed at the emission side position A1 of the optical integrator 30, and a secondary light source is substantially formed here. Is done.
[0025]
The light beams from the plurality of secondary light sources formed by the optical integrator 30 are condensed by the second relay optical system 40, and are further transmitted to an optical integrator 50 as a second multi-light source image forming means for forming a plurality of light source images. Incident. As shown in FIG. 2B, the optical integrator 50 includes a plurality of (9 columns × 3 rows = 27) bi-convex lens elements 50 a having a rectangular lens cross section. The lens element 50a is configured such that the cross-sectional shape (aspect ratio) of the element 50a is similar to the cross-sectional shape (aspect ratio) of the optical integrator 30. The optical integrator 50 as a whole has a square cross section. Each lens element 50a has the same curvature (refractive power) in the direction of the paper surface of FIG. 1A and the direction of the paper surface of FIG. 1B.
[0026]
Therefore, the light fluxes from the optical integrators 30 passing through the individual lens elements 50a constituting the optical integrator 50 are respectively condensed, and a light source image is formed on the exit side of each lens element 30a. Therefore, a plurality of light source images arranged in a square shape are formed at the emission side position A2 of the optical integrator 30, and a tertiary light source is substantially formed here.
[0027]
Here, the number of the plurality of light source images arranged in a square shape formed by the optical integrator 50 is such that the number of the lens elements 30a constituting the optical integrator 30 is N and the number of the lens elements 50a constituting the optical integrator 50 is N. When the number is M, N × M are formed. That is, since a plurality of light source images formed by the optical integrator 30 are formed at the light source image positions of the respective lens elements 50a constituting the optical integrator 50 by the relay optical system 40, the light source images are located at the emission side position A2 of the optical integrator 50. Form a total of N × M light source images.
[0028]
The second relay optical system 40 conjugates the incident surface position B1 of the optical integrator 30 with the incident surface position B2 of the optical integrator 50, and also sets the exit surface position A1 of the optical integrator 30 and the exit surface position of the optical integrator 50. A2 and A2 are conjugated. An aperture stop AS having an opening of a predetermined shape is provided at or near the position A2 where the tertiary light source is formed, and a light beam from the tertiary light source formed in a circular shape by the aperture stop AS is provided. Is condensed by a condenser optical system 60 as a condensing optical system and uniformly illuminates a mask M as an object to be illuminated in a slit shape (a rectangular shape having a long side and a short side).
[0029]
The mask M is held on a mask stage MS, and a wafer W as a photosensitive substrate is held on a wafer stage. The mask M held on the mask stage MS and the wafer W mounted on the wafer stage WS are arranged conjugate with respect to the projection optical system PL, and the circuit pattern portion of the mask M illuminated in a slit shape is projected. The light is projected onto the wafer W by the optical system PL.
[0030]
In the actual exposure with the above configuration, the mask stage MS and the wafer stage WS move in the directions opposite to each other in the direction of the arrow as shown in FIG. 1B, and the circuit pattern on the reticle is transferred onto the wafer W. You.
[0031]
Next, the lens configuration of the illumination optical system according to this embodiment will be described in detail. In the embodiment shown in FIG. 1, when the light flux from the light source 10 such as an excimer laser is routed, a portion where the energy density becomes particularly high is in the first relay optical system 21. The reason is that the energy density is inversely proportional to the area of the cross section of the light beam, so that the energy density of the lens element on which light with a small light beam diameter is incident increases. Accordingly, the first relay optical system 21 forms a condensing point (light source image) I of all light fluxes from the light source 10 in an optical path between the front group (21A, 21B) and the rear group (21C, 21D). Therefore, the energy density of the positive lens 21B of the front group and the positive lens 21C of the rear group in the first relay optical system 21 in which the area of the cross section of the light beam becomes small becomes considerably high.
[0032]
Therefore, this embodiment will be described with specific numerical examples. The light source 10 supplies light having a light cross-sectional area of output light of 1.25 cm 2 and a light energy ES per pulse of 10 mJ, and performs beam shaping. The optical system 20 has a magnification of 1.6 times, and the focal length of the front group (21A, 21B) in the first relay optical system 21 and the focal length of the rear group (21C, 21D) in the first relay optical system 21. Are both 100 mm 2, and the first relay optical system 21 is configured as an equal magnification system. The positive lens 21B is arranged at a position 43.6 mm from the position of the light source image I formed by the front group (21A, 21B) of the first relay optical system 21 toward the light source. The relay optical system 21 is arranged at a position of 43.6 mm from the position of the light source image I formed by the front group (21A, 21B) to the mask side. In this case, the cross-sectional area of the light beam passing through the beam shaping optical system 20 is 2.0 cm 2, the cross-sectional area AB1 of the light beam passing through the positive lens 21B is 0.38 cm 2, and the cross-sectional area of the light beam passing through the positive lens 21C AB2 is 0.38 cm2. Here, since there is almost no loss in the amount of light from the light source 10 passing through the beam shaping optical system 20 and the first relay optical system 21, the light energy ES when entering the positive lens 21B and the positive lens 21C is both 10 mJ. Become. Therefore, from the above numerical examples, it is understood that both the front group positive lens 21B and the rear group positive lens 21C in the first relay optical system 21 satisfy the above condition (1). Therefore, in this embodiment, the positive lens 21B and the positive lens 21C having the luminous flux cross-sectional area of the portion satisfying the above condition (1) are made of fluorite, so that the configuration has excellent durability. I have.
[0033]
In this embodiment, the positive lens 21B of the front group and the positive lens 21C of the rear group in the first relay optical system 21 are made of fluorite, but in order to achieve more sufficient aberration correction, It is possible to configure the first relay optical system 21 with a larger number of lenses. In this case, it is necessary to arrange a plurality of lenses in the vicinity of the converging point I where the energy density becomes high due to spatial restrictions, but all the lenses located in the vicinity of the converging point I are made of fluorite. Just do it.
[0034]
Therefore, in FIG. 1, the energy density is considerably high, and the positive lens 21B of the front group and the positive lens 21C of the rear group in the first relay optical system 21 are made of fluorite. It is needless to say that all the optical members such as the lens are preferably made of fluorite. In addition to the first relay optical system 21, it is preferable to use fluorite for a high energy portion, for example, the optical integrators (30, 50). Further, the light source 10 is provided with an excimer laser that oscillates light of higher output. When used, the durability of the device can be further increased by using fluorite for the entire illumination system.
[0035]
Further, in the embodiment of the present invention, an example is shown in which a part of the lens constituting the first relay optical system 21 is formed of fluorite. However, the present invention provides a beam shaping optical system 20 and a first relay optical system. The lens constituting the optical integrator 4 and the condenser optical system 6 of the illumination optical system shown in FIG. 3 without the system 21 may be made of fluorite. In this case as well, it is preferable that the above condition (1) is satisfied. At this time, the light energy ES of the above condition (1) is a light amount loss due to, for example, a luminous flux incident on the optical integrator 4 or the condenser optical system 6. There is a possibility that the light energy will be incident on the optical integrator 4 and the condenser optical system 6, respectively.
[0036]
In the embodiment of the present invention, the example of the step scan type exposure apparatus has been described. However, even in the batch exposure type exposure apparatus, the durability of the illumination system can be increased by using fluorite in a portion having a high energy density. Needless to say. Although an excimer laser is used as the light source 10 in the embodiment of the present invention, for example, a solid-state laser having a wavelength of 250 nm or less using harmonics may be used as the light source.
[0037]
【The invention's effect】
As described above, according to the present invention, even when the object to be exposed (mask) is irradiated with high-output exposure light for a long period of time, it is possible to prevent deterioration of the optical members in the illumination optical system of the exposure apparatus. A durable exposure apparatus capable of achieving stable exposure over a long period of time can be achieved. Further, even if a light source with a higher output is used, it is possible to realize exposure capable of maintaining a high throughput, as long as deterioration of an optical member in the illumination optical system of the exposure apparatus is prevented.
[Brief description of the drawings]
FIG. 1A is a diagram illustrating a configuration of an exposure apparatus according to an embodiment of the present invention, and FIG. 1B is a diagram illustrating a configuration of the exposure apparatus of FIG. .
2A is a diagram showing a state of a cross-sectional shape of a first optical integrator 30 of FIG. 1, and FIG. 2B is a diagram showing a state of a cross-sectional shape of a second optical integrator 50 of FIG.
FIG. 3 is a diagram showing a configuration of a conventional exposure apparatus.
[Explanation of symbols]
Reference Signs List 10: excimer laser, 20: beam shaping optical system, 21: first relay optical system, 30, 50: optical integrator, 40: second relay optical system, 60: condenser optical system, AS: aperture stop, PL: projection optical system

Claims (6)

Exposure apparatus comprising: light source means for supplying light for exposure; and an illumination optical system for guiding light from the light source means onto a mask on which a predetermined pattern is formed, and exposing the pattern of the mask onto a photosensitive substrate. At
An exposure apparatus, wherein all the lenses in the illumination optical system are made of fluorite. The exposure apparatus according to claim 1, wherein the light source supplies light having a wavelength of 157 nm as the exposure light. The illumination optical system, based on light from the light source means, a multi-light source forming means for forming a number of light sources, and collects light from a number of light sources formed by the multi-light source forming means, respectively, 3. The exposure apparatus according to claim 1, further comprising a condenser optical system that illuminates the mask in a superimposed manner. 4. The exposure apparatus according to claim 1, wherein the multiple light source forming unit has an optical integrator in which a plurality of lens elements are arranged. 5. A projection optical system for projecting an image of the pattern of the mask onto the photosensitive substrate,
A mask stage for mounting the mask,
Further comprising a substrate stage on which the photosensitive substrate is mounted,
The exposure apparatus according to any one of claims 1 to 4, wherein the mask stage and the substrate stage are moved to transfer the pattern of the mask onto the photosensitive substrate. An exposure method, comprising: exposing the pattern of the mask onto the photosensitive substrate using the exposure apparatus according to claim 1.

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