JPH08313842A - Lighting optical system and aligner provided with the optical system - Google Patents

Abstract

PURPOSE: To obtain a uniform illuminance distribution on irradiated surfaces and to obtain a lighting optical system which is compact in size and right in weight by providing the light deflecting means having many minute reflection surfaces whose directions are made to be independently changed each other. CONSTITUTION: Illuminating light from a light source 1 is guided to a mask 8 and a wafer 10 being irradiated surfaces by making all micromirrors consisting of a DMD 4 as a light deflecting means ON-states and, moreover, is guided to another optical system like an alignment system by making them OFF-states. That is, the DMD 4 serves functions of shutters and mirrors of a conventional lighting optical system. Further, this system can stitpulate the sectional form of the parallel luminous flux made incident on fly eye lenses 5 and in its turn the lighting area on the mask 8 and the wafer 10 by making only micromirrors of a specific area among micromirrors consisting of the DMD 4 ON-states by a control means 14. That is, the DMD 4 serves the function of a rectile blind in the conventional lighting optical system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an illumination optical system and an exposure apparatus equipped with the optical system, and more particularly to a mask on which a transfer pattern is formed in an exposure apparatus for manufacturing a semiconductor element, a liquid crystal display element or the like. The present invention relates to an illumination optical system for illuminating a reticle or the like with uniform illuminance.

[0002]

2. Description of the Related Art An illumination optical system used in an exposure apparatus for manufacturing a highly integrated semiconductor device or the like is required to have excellent illuminance uniformity on an illuminated object surface. Therefore, the conventional illumination optical system of this type employs a configuration in which the illuminated surface is superimposedly illuminated via a multi-light source image forming unit such as an optical integrator.

FIG. 5 is a diagram schematically showing the structure of a conventional exposure apparatus. The illustrated apparatus includes a light source 51 for supplying illumination light, for example. The illumination light flux emitted from the light source 51 is once condensed through the elliptical mirror 52, and then,
It is incident on the mirror 54. The illumination light reflected on the right side in the drawing by the mirror 54 is converted into a parallel light flux by the collimator lens 55, and then enters a fly-eye lens 57 as an optical integrator.

Illumination light that has passed through the fly-eye lens 57 passes through a mirror 58 and a condenser lens 59, and then has a pattern formed thereon, that is, a mask.
Illuminate 60 in a superimposed manner. The light transmitted through the mask 60 is
The wafer 62, which is a photosensitive substrate, is reached via the projection optical system 61. Thus, the pattern image of the reticle 60 is formed on the wafer 62. A shutter 53 is provided in the optical path between the light source 51 and the mirror 54. A reticle blind 56 is provided in the parallel optical path between the collimator lens 55 and the fly-eye lens 57.

FIG. 6 is a perspective view schematically showing the structure of a shutter in a conventional exposure apparatus. As shown in FIG. 6, the conventional shutter is a mechanical blade rotating type, and includes a shutter substrate 67 and a rotating blade 66 connected to an output shaft of a motor 68. The shutter substrate 67 allows the illumination light 65 from the light source 51 to pass and allows the mirror 54 to pass through.
An opening portion 69 for leading to is formed. The opening 69 is shielded at any time by the rotation of the rotary blade 66 driven by the motor 68. When the opening 69 is blocked by the rotary blade 66, the illumination light 65 from the light source 51 is reflected by the rotary blade 66 and is guided to another appropriate optical system such as an alignment optical system.

On the other hand, FIG. 7 is a diagram schematically showing the structure of a reticle blind in a conventional exposure apparatus. Note that FIG. 7 shows the configuration of the reticle blind on the plane perpendicular to the optical axis AX of FIG. As shown in FIG.
The conventional reticle blind includes a pair of L-shaped blind blades 71 and 72. Blind blade 71
Are driven to slide in the horizontal direction in the figure by the drive motor 73 and vertically in the vertical direction by the drive motor 74 along guide rails (not shown).

Further, the blind blades 72 are slid by a drive motor 75 in the horizontal direction in the figure and vertically by a drive motor 76 along a guide rail (not shown). In this way, the opening 77 formed by the pair of L-shaped blind blades 71 and 72 can be formed into a desired rectangular shape. As described above, the reticle blind 56 is a field stop having a variable opening, and an illumination area having a desired shape can be obtained on the reticle 60 by appropriately changing the shape of the opening.

[0008]

However, in the illumination optical system of the conventional exposure apparatus as described above, the shutter 5 is used.
3, the mirror 54, and the reticle blind 56 are separately configured. Therefore, the total number of parts in the optical system is large and it is difficult to reduce the cost. Also, space for many parts is required,
It was difficult to make the device compact and lightweight. Moreover, during the assembly of the optical system, it is difficult to adjust the positioning of the shutter 53, the mirror 54, and the reticle blind 56, and the reticle 60 and the wafer 6 that are the irradiated surface are not adjusted.
It was difficult to obtain a uniform illuminance distribution on No. 2.

In the illumination optical system of the exposure apparatus, the latest super LS is used.
With the further increase in the integration degree of I, more strict specifications are required for the uniformity of illumination. However, in the illumination optical system having the above-described configuration, the uniformity of illumination changes over time due to, for example, the shift of the light source, so-called change in the uniformity of illumination over time occurs. Further, there is a so-called fixed non-uniformity of the illumination that the uniformity of the illumination is impaired regardless of the passage of time due to the fly-eye lens or the like. The conventional illumination optical system has no means for correcting the above-mentioned temporal change of illumination uniformity and fixed nonuniformity of illumination.

The present invention has been made in view of the above problems, and is a compact and lightweight illumination optical system capable of obtaining a uniform illuminance distribution on a surface to be illuminated, and an exposure apparatus provided with the optical system. The purpose is to provide.

[0011]

In order to solve the above-mentioned problems, in the first invention, a light source for supplying a substantially parallel illumination light flux in an illumination optical system for illuminating a predetermined object plane substantially uniformly. Means, and a light deflecting means having a large number of minute reflecting surfaces whose directions can be changed independently of each other, each of the plurality of minute reflecting surfaces reflecting and deflecting the illumination light flux from the light source means. A multi-light source image forming means for forming a plurality of light source images based on the illumination light flux reflected by the light deflecting means, and a light flux from the multi-light source image forming means is condensed and superposed on the object plane. The present invention provides an illumination optical system characterized by comprising: a condenser optical system for selectively illuminating.

According to a preferred aspect of the first invention, the detecting means for detecting the illuminance distribution on the object plane and the output of the detecting means so that the illuminance distribution on the object plane becomes substantially uniform. And a control means for controlling the orientation of each of the plurality of minute reflection surfaces of the light deflection means.

In order to solve the above problems, in the second invention, an illumination optical system for illuminating a mask on which a predetermined pattern is formed, and an image of the pattern of the mask are formed on a photosensitive substrate. In the exposure apparatus including a projection optical system for performing the above, the illumination optical system includes a light source unit for supplying a substantially parallel illumination luminous flux and a large number of minute reflecting surfaces capable of changing their directions independently of each other. And a plurality of light source images based on the illumination light flux reflected by the light deflection means, and the light deflection means for reflecting and deflecting the illumination light flux from the light source means by each of the plurality of minute reflection surfaces. An exposure, comprising: a multi-light source image forming means for forming the light source; and a condenser optical system for converging a light flux from the multi-light source image forming means to illuminate the object surface in a superimposed manner. Provide equipment .

According to a preferred aspect of the second aspect of the present invention, the detection means for detecting the illuminance distribution on the photosensitive substrate and the output of the detection means so that the illuminance distribution on the photosensitive substrate becomes substantially uniform. And a control means for controlling the orientation of each of the plurality of minute reflection surfaces of the light deflection means.

[0015]

In the present invention, the light deflecting means having a large number of minute reflecting surfaces whose directions can be changed independently of each other is provided, and the illumination light from the light source means is reflected and deflected by each of the plurality of minute reflecting surfaces. To do. As such a light deflecting means, for example, a DMD (Digital Micromirror Device or
Deformable Micromirror Device) can be used

The DMD is a microdevice newly proposed in recent years. For example, solid state
Technology (Solid State Technology) 1994 7
Monthly issue, pages 63 to 68, SID (SI
D) 1993 digest version, pages 1012 to 10
As disclosed in p. 15, p. 86 to p. 102 of SPIE Critical Reviews Series, Volume 1150, etc., the DMD has a large number of micromirrors arranged in a grid pattern. It consists of (a minute reflection mirror).

As described above, the DMD is an integration of minute micromirrors, and the angle (that is, the direction) of the micromirrors is changed by the electrostatic attraction between the electrodes and the micromirrors provided for each micromirror. Change. That is, the direction of each micro mirror is configured to be individually drive-controlled. Incidentally, each micromirror has a square shape of, for example, about 20 μm × 20 μm, and one DMD is composed of, for example, hundreds of thousands to millions of micromirrors.

In the present invention, each DMD micromirror reflects the illumination light from the light source and guides it to a multi-light source image forming means such as a fly-eye lens, and reflects the illumination light to a fly-eye lens. Are individually controlled to be driven in the OFF state where they are not made incident. Therefore,
By turning on all the micromirrors that make up the DMD, the illumination light from the light source is guided to the surface to be illuminated, and by turning off all the micromirrors, the illumination light from the light source can be used as in an alignment system. Can be led to the optical system. That is, the DMD can function as a shutter and a mirror in the illumination optical system of the conventional exposure apparatus.

Further, among the micromirrors constituting the DMD, by turning on only the micromirrors in a specific area, the cross-sectional shape of the parallel light beam incident on the fly-eye lens and thus the illumination area on the illuminated surface is defined. can do. That is, the DMD can function as a reticle blind in the illumination optical system of the conventional exposure apparatus. Thus, according to the present invention, the functions of the shutter, the mirror and the reticle blind in the prior art can be achieved by using the DMD which is one optical component. As a result, it is not necessary to adjust the positions of the shutter, mirror, and reticle blind components, and a uniform illuminance distribution can be obtained on the illuminated surface. Further, it is possible to realize a compact and lightweight illumination optical system and an exposure apparatus equipped with the optical system.

Furthermore, the illuminance distribution on the surface to be illuminated is detected,
By appropriately controlling the direction of each micromirror of the DMD based on the result, the illuminance distribution on the irradiated surface can be corrected almost uniformly at any time. That is, the uniformity of the illuminance distribution on the surface to be illuminated can be further improved by correcting the above-mentioned temporal change in the uniformity of illumination and the fixed nonuniformity of illumination as needed. Note that the number of permissible driving of each micromirror of the DMD is about 1.2 × 10 ¹⁰ and has much higher durability than the reticle blind in the conventional technique.

[0021]

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing the configuration of an illumination optical system and an exposure apparatus having the optical system according to an embodiment of the present invention. The illustrated exposure apparatus is provided with a light source 1 which is, for example, an ultrahigh pressure mercury lamp. The light source 1 is the first of the elliptical mirror 2.
It is positioned at the focal position. The illumination light flux emitted from the light source 1 enters the collimator lens 3 while being condensed toward the second focal position of the elliptical mirror 2. Then, the illumination light flux converted into the parallel light flux by the collimator lens 3 enters the DMD 4.

Each micromirror that constitutes the DMD 4 is
The control system 14 individually controls the driving between the ON state and the OFF state. And
The light beam reflected by the micro mirror in the ON state is guided in the horizontal direction on the right side in the figure, and the light beam reflected by the micro mirror in the OFF state is guided in the direction indicated by the broken line A in the figure. The light reflected by the DMD 4 in the direction indicated by the broken line A in the figure is guided to another suitable optical system (not shown) such as an alignment system. On the other hand, the light reflected by the DMD 4 in the horizontal direction in the figure enters the fly-eye lens 5.

The light beam incident on the fly-eye lens 5 is two-dimensionally divided by a plurality of lens elements constituting the fly-eye lens 5 to form a plurality of light source images at the rear focal position of the fly-eye lens 5. In this way, the fly-eye lens 5 constitutes a multi-light source forming unit that forms a plurality of light source images based on the light flux from the DMD 4.

Light fluxes from a plurality of light source images are limited by an aperture stop (not shown), and then reflected by the bending mirror 6 downward in the drawing. The light flux reflected by the folding mirror 6 is condensed by the condenser lens 7 and illuminates the mask 8 such as a reticle in a superimposed manner. As described above, the light source 1, the elliptic mirror 2, the collimating lens 3, the DMD 4, the fly-eye lens 5, the bending mirror 6 and the condenser lens 7 constitute an illumination optical system for uniformly illuminating the mask 8.

The light flux transmitted through the mask 8 is projected by the projection optical system 9.
The wafer 10 which is a photosensitive substrate is reached through the. Thus, the pattern image of the mask 8 is formed on the wafer 10. The wafer 10 is supported on a wafer stage 11 which is two-dimensionally movable in a plane perpendicular to the optical axis of the projection optical system 9. The wafer stage 11 is further supported on the surface plate 12. Therefore, the wafer 1
By performing exposure while moving 0 two-dimensionally,
The pattern of the mask 8 can be sequentially transferred to each exposure region of the wafer 10.

The exposure apparatus of FIG. 1 is equipped with an illuminance sensor 13 as a detection means for detecting the illuminance distribution on the exposure surface of the wafer 10, that is, the image plane of the projection optical system 9. The illuminance sensor 13 is provided on the wafer stage 11 that holds the wafer 10 and is two-dimensionally movable. The illuminance distribution detected by the illuminance sensor 13 is sent to the control means 14.

In the present embodiment, each micromirror of the DMD 4 is turned on by the control means 14 so as to reflect the illumination light from the light source 1 to the fly-eye lens 5, and the fly-eye lens 5 to reflect the illumination light. The drive is controlled individually between the OFF state in which the light is not incident on. Therefore, turn on all the micromirrors that make up the DMD4.
In this state, the illumination light from the light source 1 is guided to the mask 8 or the wafer 10, which is the surface to be illuminated, and the micromirror is turned on
By setting the FF state, the illumination light from the light source 1 can be guided to another optical system such as an alignment system. That is, the DMD 4 functions as a shutter and a mirror in the illumination optical system of the conventional exposure apparatus.

Further, the control means 14 turns on only the micromirrors in a specific region among the micromirrors constituting the DMD 4, so that the cross-sectional shape of the parallel light flux incident on the fly-eye lens 5 and thus the mask 7 and the like. An illuminated area on the wafer 10 can be defined. That is, the DMD 4 functions as a reticle blind in the illumination optical system of the conventional exposure apparatus. As described above, according to this embodiment, the functions of the shutter, the mirror, and the reticle blind in the related art can be achieved by using the light deflecting means such as the DMD 4. As a result, it becomes unnecessary to adjust the positioning of these components, and a uniform illuminance distribution can be obtained in the illumination area on the mask 7 or the wafer 10. Further, the illumination optical system can be made compact and lightweight.

FIG. 2 is a perspective view schematically showing the structure of each micromirror of the DMD. 3 is a view corresponding to FIG. 2 and is a cross-sectional view schematically showing the configuration of each micromirror formed side by side on the DMD substrate. As shown in FIGS. 2 and 3, the upper surface in the figure is a reflective surface (mirror surface).
The micro mirror 21 formed on the substrate is supported by the hinge member 22. Both ends of the hinge member 22 are swingably supported at the upper ends of the pair of column members 23.

In this case, the swing axis line coincides with the longitudinal direction of the hinge member 22, and the four electrodes 24 from the hinge member 22 are arranged along the direction orthogonal to the longitudinal direction and parallel to the reflecting surface.
Are formed so as to project. Also, the DMD substrate 2
Four electrodes 26 are formed on the position 5 corresponding to the four electrodes 24. In this way, a potential difference is applied between the corresponding electrodes 24 and 26, and the hinge member 2 is caused by the electrostatic force acting based on the potential difference between the electrodes.
Therefore, the micro mirror 21 can be appropriately swung between the ON state and the OFF state.

In the DMD shown in FIGS. 2 and 3, the micromirrors are arranged vertically and horizontally close to each other. Therefore, it is possible to secure a high uniform reflectance as the entire DMD. Further, since each hinge member is shielded by the corresponding micromirror, damage to the hinge member due to energy irradiation to the micromirror can be minimized. As described above, the DMD configurations shown in FIGS. 2 and 3 are optimal for the illumination optical system and the exposure apparatus including the optical system as in the present embodiment.

As mentioned above, the DMD 4 has a large number of micromirrors. Then, the illumination light reflected by the micromirror group included in one divided reflection area that is a part of the reflection area on the DMD 4 is one divided illumination area that is a part of the illumination area on the image plane of the projection optical system 9. It corresponds to. Therefore, by referring to the illuminance distribution detected by the illuminance sensor, and turning off a predetermined number of micromirrors in a predetermined distribution in the micromirror group of the DMD 4 corresponding to the specific divided illumination area with high illuminance, It can be reduced to the desired value.

In other words, by controlling the number of micromirrors in the OFF state in each micromirror group corresponding to each divided illumination area, the entire illumination area on the image plane of the projection optical system 9 is controlled. The illuminance distribution can be made uniform. That is, in this embodiment, the projection optical system 9
By detecting the illuminance distribution on the image plane, it is possible to correct the temporal change in the uniformity of the illumination due to the shift of the light source and the fixed nonuniformity of the illumination due to the fly-eye lens or the like. As a result, it is possible to further improve the uniformity of the illuminance distribution in the illumination area on the wafer 10.

Further, as described above, the DMD 4 comprises a large number of micromirrors whose directions can be controlled independently of each other. Therefore, by turning off a specific micromirror of the DMD 4 to form a light-shielding portion on the wafer surface, it is possible to additionally expose the numbers, letters, and patterns as shown in FIG. In addition, the numbers, letters, and patterns formed on the wafer 10 are
It can be used as an indication of the product lot number. In this case, in order to obtain a sharp (high-resolution) number, character, or pattern on the wafer 10, the DMD 4 is positioned at a position optically conjugate with the wafer 10, that is, near the incident surface of the fly-eye lens 5. Is preferred.

In the above embodiments, the present invention is applied to an exposure apparatus using an ultrahigh pressure mercury lamp as a light source, but the present invention is applied to a general exposure apparatus using another light source such as an excimer laser. The invention can be applied. Further, in the above embodiment, the illuminance distribution is detected on the image plane of the projection optical system, but when the present invention is applied to a general illumination optical system, the illuminance distribution is detected on the surface corresponding to the mask surface. Therefore, the illuminance distribution can be made uniform.

[0036]

As described above, according to the present invention, by using the DMD as the light deflecting means, the shutter, the mirror and the reticle blind in the prior art are unnecessary. Therefore, it is possible to realize a compact and lightweight illumination optical system capable of obtaining a uniform illuminance distribution on the illuminated surface and an exposure apparatus equipped with the optical system. Furthermore, it detects the illuminance distribution on the illuminated surface,
By appropriately controlling the direction of each micromirror of the DMD based on the detection result, the illuminance distribution on the irradiated surface can be corrected almost uniformly at any time.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a configuration of an illumination optical system and an exposure apparatus having the optical system according to an embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a configuration of each micromirror of the DMD shown in FIG.

FIG. 3 is a cross-sectional view corresponding to FIG. 2 and schematically showing the configuration of each micromirror formed side by side on the DMD substrate.

FIG. 4 is a diagram showing numbers, characters, and patterns formed on a wafer by the action of DMD.

FIG. 5 is a diagram schematically showing a configuration of a conventional exposure apparatus.

FIG. 6 is a perspective view schematically showing the structure of a shutter in a conventional exposure apparatus.

FIG. 7 is a diagram schematically showing a configuration of a reticle blind in a conventional exposure apparatus.

[Explanation of symbols]

 1 Light Source 2 Elliptical Mirror 3 Collimating Lens 4 DMD 5 Fly-eye Lens 6 Bending Mirror 7 Condenser Lens 8 Mask 9 Projection Optical System 10 Wafer 11 Wafer Stage 12 Surface Plate 13 Illuminance Sensor 14 Control System

Claims (6)

[Claims] 1. An illumination optical system for illuminating a predetermined object plane substantially uniformly, comprising: a light source means for supplying a substantially parallel illumination light flux; and a large number of minute reflecting surfaces capable of changing their directions independently of each other. And a plurality of light source images based on the illumination light flux reflected by the light deflection means, and the light deflection means for reflecting and deflecting the illumination light flux from the light source means by each of the plurality of minute reflection surfaces. An illumination characterized by comprising: a multi-light source image forming means for forming the light source; and a condenser optical system for condensing a light flux from the multi-light source image forming means to illuminate the object surface in a superimposed manner. Optical system. 2. A detecting means for detecting an illuminance distribution on the object plane, and a plurality of the light deflecting means based on the output of the detecting means so that the illuminance distribution on the object plane becomes substantially uniform. The illumination optical system according to claim 1, further comprising: a control unit for controlling the orientation of each of the minute reflection surfaces of. 3. The light deflecting means is a DMD, and the DM
The illumination optical system according to claim 1 or 2, wherein D is positioned near the multi-light source image forming means. 4. An exposure apparatus comprising an illumination optical system for illuminating a mask on which a predetermined pattern is formed, and a projection optical system for forming an image of the pattern of the mask on a photosensitive substrate, The illumination optical system has a light source means for supplying a substantially parallel illumination light flux, and a plurality of minute reflecting surfaces whose directions can be changed independently of each other. The light source means is provided by each of the plurality of minute reflecting surfaces. A light deflecting means for reflecting and deflecting the illumination light flux from the light source, a multi-light source image forming means for forming a plurality of light source images based on the illumination light flux reflected by the light deflecting means, and the multi-light source image An exposure apparatus comprising: a condenser optical system that condenses a light beam from the forming unit and illuminates the object surface in a superimposed manner. 5. A detector for detecting an illuminance distribution on the photosensitive substrate, and a plurality of the light deflectors based on the output of the detector so that the illuminance distribution on the photosensitive substrate becomes substantially uniform. 5. The exposure apparatus according to claim 4, further comprising: a control unit for controlling the direction of each of the minute reflection surfaces of. 6. The light deflecting means is a DMD, and the DM
The exposure apparatus according to claim 4, wherein D is positioned near the multi-light source image forming means.