JPH07211623A - Short wavelength optical system - Google Patents

Abstract

PURPOSE:To prolong the service life of an optical system by setting the width of incident light in a predetermined direction narrower than the effective width of a selected optical element in the predetermined direction and gradually shifting the region on the selected optical element, being irradiated with the incident light, in the predetermined direction. CONSTITUTION:In an optical system 4 receiving an incident light having wavelength of 450nm or less and delivering a light through one or a plurality of optical elements 5A, 5B, the width of a incident light to at least one selected optical element 5A is set narrower, in a predetermined direction, than the effective width of the selected optical element 5A in the predetermined direction. When a plurality of optical elements 5A, 5B are selected, they are classified into a plurality of optical element groups which are then provided individually with rotary means 7A, 7B for rotating the optical elements in each group synchronously.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a short-wavelength optical system for transmitting light having a short wavelength of 450 nm or less, and is one example of an illumination optical system of an exposure apparatus using a bright line of a mercury lamp or excimer laser light as exposure light. It is suitable to be applied to a part.

[0002]

2. Description of the Related Art Conventionally, various optical systems have been designed and manufactured by combining lenses, mirrors, optical filters, etc., and these optical systems are used for consumer equipment such as camera lenses, binoculars, exposure apparatuses, surveying instruments, etc. Widely used for industrial equipment. In recent years, particularly in industrial instruments, the wavelength of the light source of the optical system has been shortened in order to improve the measurement accuracy and the processing accuracy and realize the finer processing.

For example, in an exposure apparatus for manufacturing a semiconductor element or a liquid crystal display element, the wavelength of the exposure light used is from the g-line (wavelength 436 nm) to the i-line (wavelength 3) of a mercury lamp.
65 nm), and recently, the wavelength has been further shortened to KrF excimer laser light (wavelength 249 nm) and ArF excimer laser light (wavelength 193 nm).

[0004]

As the wavelength of the light used in the optical system is shortened in this way, the following new disadvantages, which have not occurred in the conventional optical system, occur. Has occurred. By reducing the wavelength of the light used, the number of glass types that can be used as optical elements (lenses, optical filters, mirrors, etc.) in the optical system will decrease, and the glass types that can be used will also have reduced transmittance due to continuous light irradiation. (Solarization) increases.

Materials of optical thin films such as antireflection films and reflection increasing films coated on the surfaces of various optical elements are limited, and optical thin films formed of usable materials are destroyed (peeled) by irradiation of light. , Cracks, etc.) easily occur. Impurities in the air cause a photochemical reaction by light having a short wavelength and adhere to the surface of the optical element, resulting in a decrease in transmittance.

Due to the inconveniences described above, the useful life of the optical system is decreasing as the wavelength of light used is shortened. FIG. 7 shows BK7, which is a typical glass type as optical glass, and i-line (wavelength 365n) of a mercury lamp.
The change with time of the transmittance when the light of m) is irradiated at an intensity of 4 W / cm ² is shown. In this case, the thickness of the glass material is set to 1 cm, and the loss due to the surface reflection of the glass material is corrected. As shown in FIG. 7, the light of the i-line is 200
It can be seen that a decrease in transmittance of about 1.6% occurs when irradiated for a long time.

Assuming that the decrease in the transmittance of the glass material is proportional to the energy product, which is the product of the intensity of light and time, ten lenses made of a glass type having the same light resistance as BK7 (the center thickness of each lens is 10 mm) and an optical system composed of
If you continue to irradiate the light of the line with the intensity of 400 mW / cm ² ,
The light transmittance of this optical system drops to about 58% of the initial value after two years. Therefore, there is a possibility that the entire optical system needs to be replaced.

Next, FIG. 8 shows the durability of the antireflection film for KrF excimer laser light (wavelength 249 nm) against KrF excimer laser light. The excimer laser light is pulsed light, the horizontal axis in FIG. 8 represents the number of shots (pulse number) of laser irradiation, and the vertical axis represents irradiation energy per pulse of laser light. In FIG. 8, it is considered that the condition that the antireflection film is destroyed is marked with X, and that the damage occurs in the antireflection film under the condition that the straight line connecting these X marks is exceeded. As described above, there is a certain relationship between the irradiation energy at which the antireflection film is broken and the number of shots. For example, it can be seen that the irradiation energy of 1.5 J / cm ² causes breakage in 10 ¹⁰ shots. For example, the laser oscillation frequency is 500 Hz
Then, the optical system will be destroyed in about 230 days.

Table 1 shows, by way of example, main chemical substances used in semiconductor factories.

[0010]

[Table 1]

It is conceivable that a small amount of these substances floats in the semiconductor factory, and they undergo a photochemical reaction by light of a short wavelength and adhere to the surface of the optical element. It is considered that the impurities attached to the surface scatter light and the transmittance of the optical system is lowered.
In Table 1, the substances with wavy lines below, that is, the ammonia gas (NH ₃ ) and the sulfuric acid gas (H ₂ SO ₄ ) are considered to be the substances that particularly contribute to the reduction of the transmittance of the optical element.

As the wavelength of the light used is shortened as described above, the service life of the optical system is rapidly decreasing. In order to fundamentally solve this inconvenience, (a) development of optical glass whose transmittance does not decrease even when irradiated with light,
It is desirable to take measures such as (b) development of a coating material or coating technology that does not cause damage even when irradiated with light, or (c) complete removal of impurities in the air. However, on the other hand, these measures are (d) optical design restrictions due to the limited glass types that can be used, (e) optical thin film property limitations due to limited coating materials, and special coatings. Inconveniences such as an increase in cost for realizing the technology or (f) an increase in cost for removing impurities in the air are brought about.

In view of such a point, the present invention is, for example, 450n
An object of the present invention is to extend the service life of an optical system for an optical system that handles light with a short wavelength of m or less without adding much to the current technology.

[0014]

As shown in FIG. 1, for example, an optical system for short wavelengths according to the present invention is provided with one or a plurality of optical elements (5A, 5A, 5A, 5A, 5A, 5A, 5A, 5A, 5C, 5C, 5D, 5E, 5F, 5E, 5F, 5E, 5E, 5E, 5E, 5E, 5E, 5E, 5E, 5C, 5E, and 5C, respectively.
In the optical system (4) which emits through B),
The width of the incident light in a predetermined direction when it is incident on at least one optical element (5A) selected from one or a plurality of optical elements is defined as the width of the selected optical element (5A) in the predetermined direction. It is set smaller than the effective width.

In this case, the width of the incident light in the predetermined direction when entering the optical element (5A) selected from the one or more optical elements is determined by the selected optical element (5).
It is desirable to set it to 1/2 or less of the effective width of A) in the predetermined direction. Further, it is desirable to provide a rotating means (7A) for rotating the optical element (5A) selected from the one or a plurality of optical elements.

When there are a plurality of optical elements selected from the one or a plurality of optical elements, the selected plurality of optical elements (5A, 5B) is one or a plurality of optical elements. It is desirable that the optical element group is divided into groups, and the rotating means (7A, 7B) is provided for each of the one or more optical element groups, and the rotating means synchronously rotates the optical elements belonging to the respective optical element groups. .

[0017]

According to the present invention, the optical element (5A, 5B) constituting the optical system (5) is arranged at a portion where the irradiation power of the incident light is increased by, for example, narrowing the light beam. Select the optical element (5A). Then, the width of the light beam incident on the selected optical element (5A) in the predetermined direction is set to be smaller than the effective width of the optical element (5) in the predetermined direction, and the light beam enters the optical element (5A). Secure an area that is not illuminated by light.

After that, the transmittance of the optical element (5A) is lowered, the coating is broken, or a scattering substance is attached to the surface of the optical element (5A), so that the optical element (5A) has an optical property. When the characteristic deteriorates, the selected optical element (5A) is rotated to irradiate the area where the light is not yet irradiated with the incident light. This allows
The life of the optical system (5) is extended and the service life is extended.

At this time, the selected optical element (5A)
It is also possible to put a stop in front of so that the width of the light beam incident on the optical element (5A) in the predetermined direction is smaller than the effective width of the optical element (5A). Incidentally, among the optical elements constituting the optical system, for example, when only the optical element arranged in the portion where the irradiation power is increased by narrowing the light beam is selected, and only the selected optical element is rotated, It is not necessary to make the width of the light beam incident on the other non-rotating optical element smaller than the effective width of the optical element.

In this case, the width in the predetermined direction of the incident light when entering the selected optical element (5A) is ½ of the effective width of the selected optical element (5A) in the predetermined direction. If set below, first the optical element (5A)
Of the incident light of the optical element (5) by irradiating the right half of the predetermined direction with incident light, and when the optical characteristic of the right half of the same falls below the allowable range. To the left half. As a result, the life of the optical system (5) can be doubled or longer. However, optical element (5A)
It is necessary to prevent the irradiation areas of the light beams from overlapping when rotating.

Generally, the selected optical element (5A)
The width of the incident light in the predetermined direction when it is incident on the lens is 1 / n of the effective width of the selected optical element (5A) in the predetermined direction.
When (n is an integer of 2 or more) or less, the irradiation area of the optical element (5A) is gradually shifted in the predetermined direction so that the life of the optical element (5A) is n.
Can be doubled.

Next, rotating means (7) for rotating the optical element (5A) selected from the one or a plurality of optical elements.
When A) is provided, the life of the optical system can be extended by automatic control by rotating the optical element (5A) by a predetermined amount via the rotating means (7A) according to the irradiation time of incident light. Further, when there are a plurality of optical elements (5A, 5B) selected in this way, all the optical elements may be independently rotated, or these optical elements may be divided into several groups and each group may be rotated. You may rotate independently. In that case, the light beam incident on each optical element forming each group must have a shape that does not cause vignetting or the like when the optical elements are synchronously rotated. Alternatively, the entire optical system may be regarded as one group and the entire optical system may be rotated. Which of these rotation methods is adopted depends largely on the optical design, but it does not cause great technical difficulties.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a short wavelength optical system according to the present invention will be described below with reference to FIGS. This embodiment is a mirror projection type exposure apparatus that transfers a circuit pattern on a photomask or reticle (hereinafter, a reticle is used as an example) onto a photosensitive substrate such as a wafer through a projection type optical system such as a reflection type. The present invention is applied to an illumination optical system. A mirror projection type exposure apparatus includes a projection optical system having two reflecting mirrors, a concave mirror and a convex mirror, and scans a reticle and a wafer in a predetermined direction in synchronization with each other to form a circuit pattern image on the reticle. It is an exposure apparatus that sequentially exposes a wafer, and can transfer an image of a relatively large circuit pattern on a reticle onto a wafer with high throughput.

In this mirror projection system, since the good image area of the projection image of the projection optical system is an off-axis arc-shaped area, the entire arc-shaped illumination area on the reticle has a uniform illuminance and a constant numerical aperture. An illumination optical system capable of illuminating with (NA) is required. FIG. 1 shows a mirror projection type exposure apparatus including such an illumination optical system, and FIG. 1 is a configuration diagram including a partial cross-sectional view of the exposure apparatus when viewed from the lateral direction. 2 is a plan view of FIG.
In FIG. 1, an i-line (wavelength 365) emitted from a light source 1 including a mercury lamp, an elliptic mirror, and a collimator lens is used.
The illumination light IL made up of a substantially parallel light beam of (nm) enters the optical integrator 2 made up of a fly-eye lens, for example. A plurality of light source images (secondary light sources) are formed in the vicinity of the exit surface of the optical integrator 2, and the light flux from this secondary light source is reflected by the toric reflector 3
Is reflected and condensed by.

In this case, the surface on which the secondary light source is formed is a plane P1 perpendicular to the plane of FIG. 1, and the optical axis AX3 of the optical integrator 2 is perpendicular to the plane P1 and within the plane of FIG.
There is. Further, using a predetermined constant α, the surface P
The plane P2 is set at a position perpendicular to 1 and at a distance of 1 / (2α) from the optical axis AX3. Within the plane P2, the y axis is in the direction parallel to the paper surface of FIG. 1, and within the plane P2 is the y axis. The z axis is taken vertically (that is, perpendicular to the plane of FIG. 1). Then, the origin O is set at a position where the distance from the plane P1 is 3 / (4α) on the y-axis, and the origin O
Take the x axis perpendicular to the yz plane.

Next, a parabola PA defined by y = αx ² is assumed in the xy plane using the above-mentioned constant α. The symmetry axis AX0 of this parabola PA is the y axis itself. The parabola PA is rotated about the reference axis AX1 that passes through the optical axis AX3 in the plane P1 and is perpendicular to the y-axis to form a parabolic toric surface of rotation, and the parabolic toric surface of rotation and the light. A region surrounded by two parallels 3a and 3b and two meridians 3c and 3d (see FIG. 2) on the paraboloidal toric surface about the intersection with the axis AX3 is a toric reflector 3. As the reflective surface. On the reflecting surface of the toric reflector 3, a dielectric multilayer film for increasing the reflectance with respect to i-line is formed.

In this case, the light beam from one point on the secondary light source by the optical integrator 2 is converted into a parallel light beam by the toric reflector 3 as shown by the dotted line,
An arcuate illumination area BF is formed on the surface P2 while maintaining the telecentricity. The light parallel to the optical axis AX3 is reflected by the toric reflection mirror 3, and then is separated from the origin O by 1 / (4α) on the y-axis on the surface P2, that is, the surface P1 is 1 / (2α). The illumination area BF is also formed with that position as the center because it passes through a position separated by only.

In FIG. 1, the focal length f of the toric reflector 3 is 1 / (2α), and the toric reflector 3 is
Is on the surface P1 which is the secondary light source forming surface by the optical integrator 2, and the focal position on the illuminated object side of the toric reflector 3 is on the surface P2. The surface P2 on which the arc-shaped illumination area BF is formed has an illumination area BF _R on the reticle _R.
A slit plate S as a field stop having an arcuate opening is provided in order to accurately form a desired arcuate shape. The light flux that has passed through the opening of the slit plate S is condensed again on the pattern surface of the reticle R via the re-imaging optical system 4, and the arc surface illumination is maintained on the pattern surface while maintaining the telecentricity. Region BF _R is formed.

The reticle R is held on the reticle stage RS, and the reticle stage RS has an arc-shaped illumination area BF.
_The reticle R is scanned at a constant speed in a direction (short side direction) indicated by an arrow parallel to _{R with} respect to the y-axis. Below the reticle R, a projection optical system 9 of equal magnification and both sides telecentric is provided, and this projection optical system 9 is constituted by combining, for example, a concave mirror, a convex mirror and two plane mirrors.

Then, the pattern image of the reticle _R in the illumination area BF _R is transferred via the projection optical system 9 to the wafer stage W.
An image is projected on the wafer W placed on S. At this time, in synchronization with scanning the reticle R parallel to the y-axis,
By scanning the wafer W through the wafer stage WS in the direction indicated by the arrow parallel to the y-axis, the pattern of the reticle R is successively transferred and exposed onto the wafer W by the scanning exposure method.

At this time, the surface P1 which is the surface for forming the secondary light source by the optical integrator 2 is substantially conjugate with the entrance pupil of the re-imaging optical system 4 and the entrance pupil of the projection optical system 9. . Moreover, the secondary light source (surface light source) formed by the optical integrator 2, the entrance pupil of the re-imaging optical system 4, and the entrance pupil of the projection optical system 9 are both circular. Therefore, the arc-shaped illumination area BF _R is maintained on the reticle R while maintaining the telecentricity.
It can be seen that not only is formed but also Koehler illumination is realized. Therefore, the reticle R is illuminated in a circular arc shape with a high illumination efficiency and with a uniform illuminance, and the circuit pattern on the reticle R can be faithfully transferred to the wafer W in a circular arc shape in a short exposure time. Moreover, since the scanning exposure speed can be increased, the exposure can be performed with higher throughput.

Now, the re-imaging optical system 4 of this embodiment includes the first and second axially symmetric first lenses 5A and 2A, which are convex lenses, respectively.
The illumination light, which is composed of the lens 5B and is emitted from one point inside the opening of the slit plate S, is converted into a substantially parallel light flux by the first lens 5A, and then is converted into an arc shape on the reticle R by the second lens 5B. It is focused on one point in the illumination area BF _R.
That is, the re-imaging optical system 4, and the illumination area BF _R on the pattern formation surface of the opening and the reticle R in a slit plate S has become a conjugate, the magnification is 1x, for example. First lens 5
Each of the A and the second lens 5B is formed of optical glass having light resistance equivalent to BK7, and an anti-reflection film for i-line is applied to both surfaces thereof.

Further, the first lens 5A and the second lens 5B
Are fixed to the metal lens frames 6A and 6B by adhesion or so-called crimping, respectively.
The re-imaging optical system 4 is assembled by stacking B in a lens barrel (not shown) made of metal or synthetic resin via a washer or the like. Further, the lens frames 6A and 6B
Are rotated by the rotating units 7A and 7B, respectively.
Is independently rotatably supported around the optical axis AX4. The two rotary parts 7A and 7B are connected to the synchronous drive part 8, and the synchronous drive part 8 drives the two rotary parts 7A and 7B in synchronization in response to an instruction from an operator, for example, to thereby drive the first lens 5A. And the second lens 5B through the optical axis A
Rotate around X4 synchronously by the same angle.

In this case, in the present embodiment, the longitudinal width (maximum width) of the luminous flux of the illumination light entering the first lens 5A from the slit plate S is 1/3 or less of the effective diameter of the first lens 5A. The illumination light which is set to and which is incident on the first lens 5A from the slit plate S irradiates the right half surface from the optical axis AX4 on the first lens 5A in FIG. The optical axis AX4 is positioned. Further, the width (maximum width) in the longitudinal direction of the luminous flux of the illumination light emitted from the first lens 5A and incident on the second lens 5B is also the second lens 5
It is set to 1/3 or less of the effective diameter of B and the second lens 5
The illumination light incident on B is the second lens 5B in FIG.
The left half surface is illuminated from the optical axis AX4.

FIG. 3 shows the structure of the rotating portion 7A in FIG. 1. In FIG. 3, the lens frame 6A accommodating the first lens 5A on the convex portion 10a in the lens barrel 10 rotates around the optical axis AX4. A gear 11A is formed around the lens frame 6A so as to be freely rotatable. For this gear 11A,
A gear 12A installed outside engages with a slit-shaped opening 10b on the side surface of the lens barrel 10, and the gear 12A is connected to the shaft 1
It is rotatably supported by a motor 14A via 3A. Then, the synchronous drive unit 8 of FIG.
When A is rotated, the gears 12A and 11A rotate and the first lens 5A rotates around the optical axis AX4. In this case, the rotating portion 7A is composed of the gears 11A and 12A, the shaft 13A and the motor 14A, and the rotating portion 7B of FIG. 1 has the same structure.

Next, as shown in FIG. 2, the optical integrator 2 to the toric reflector 3 of this embodiment are used.
The width of the illumination area 3f in the circumferential direction of the illumination light incident on is set to be ⅓ or less of the length of the arc-shaped center line 3e centered on the axis AX1 of the toric reflector 3. There is. Then, a rotating unit 7C for rotating the reflecting mirror 3 about the axis AX1 is also attached to the toric reflector 3, and the operation of the rotating unit 7C is also controlled by the synchronous drive unit 9 in FIG.

In FIG. 2, an arc gear 11C is fixed to the periphery of the toric reflector 3 and the arc gear 1 is provided.
1C is an arc-shaped guide centered on the axis AX1 (not shown)
It is slidably supported along. A worm gear 12C fixed to the outside meshes with the gear 11C, the worm gear 12C is rotatably supported by a motor 14C, and the operation of the motor 14C is controlled by the synchronous drive unit 8 in FIG. In this case, by rotating the worm gear 12C by the motor 14C, the arc-shaped gear 11
C and the toric reflector 3 rotate about axis AX1. Gear 11C, worm gear 12C, and motor 14
The rotating portion 7C is composed of C.

Next, returning to FIG. 1, the operation of this embodiment will be described. First, when starting to use the exposure apparatus of FIG. 1, the toric reflector 3 is rotated about the axis AX1 in FIG. The illumination area 3f is the toric reflector 3
So that it is in contact with one meridian 3c of the contour. afterwards,
After the use of the exposure apparatus of FIG. 1 is started, when the reflectance of the toric reflection mirror 3 with respect to the illumination light decreases, the toric reflection mirror 3 is circled around the axis AX1 through the rotating portion 7C in FIG. Rotate 1/3 of the circumference. After that, when the use of the exposure apparatus is started and the reflectance of the toric reflector 3 with respect to the illumination light decreases again, the axis AX is rotated via the rotating unit 7C in FIG.
1 is the center, and the toric reflector 3 is 1/3 of the circumferential angle.
Just rotate. As a result, the continuous use time (lifetime) of the toric reflector 3 can be tripled as compared with the conventional one, and the frequency of replacement or rework of the illumination optical system can be reduced.

On the other hand, when the transmittance of the re-imaging optical system 4 with respect to the illumination light decreases after the use of the exposure apparatus of FIG. 1, the rotating portions 7A and 7B are driven synchronously to make The one lens 5A and the second lens 5B are each rotated by 1/3 of one rotation. After that, when the use of the exposure apparatus is started and the transmittance of the re-imaging optical system 4 with respect to the illumination light decreases again, the rotating unit 7A
1/3 rotation of lens 5A and 5B through 1 and 7B
Just rotate. Thereby, the continuous use time (lifetime) of the re-imaging optical system 4 can be tripled conventionally, and the frequency of replacement or repair of the illumination optical system can be reduced.

In the above embodiment, it is assumed that the first lens 5A and the second lens 5B have the same transmittance lowering characteristics.
The two lenses 5A and 5B were rotated in synchronization with each other. However, when the two lenses 5A and 5B have different transmittance lowering characteristics, the two lenses 5A and 5B are independently rotated in different cycles. Good. Further, in the above-described embodiment, the lenses 5A and 5B are rotated by the motor, but as shown in FIG. 4, the operator may manually rotate the lenses. In FIG. 4, the lens barrel 10
The fixed part 15A of the bearing is fixed on the convex part 10a on the inner side of the bearing, and the rotating part 1 of the bearing is fixed on the fixed part 15A.
6A is placed, and the first lens 5A is placed inside the rotating portion 16A.
The lens frame 6A storing the is fixed. in this case,
The operator manually operates the rotating portion 16A of the bearing through the slit-shaped opening 10b on the side surface of the lens barrel 10 from the outside.
By rotating the first lens 5A, the first lens 5A moves along the optical axis AX4.
It can be rotated about a desired angle.

The mechanism for rotating the lenses 5A and 5B and the toric reflector 3 is not limited to the above-mentioned embodiment, and various mechanisms such as a mechanism using an ultrasonic motor can be used. Next, FIG. 5 shows the result of monitoring changes in the illumination light that is actually applied to the reticle R via the re-imaging optical system 4 in the illumination optical system of the exposure apparatus of FIG. Specifically, after adjusting the emission power of the light source 1 so that the toric reflector 3 is irradiated with the illumination light IL of the i-line (wavelength 365 nm) having the intensity of 4 W / cm ² , the toric reflector 3 is adjusted. And the irradiation to the re-imaging optical system 4 was started. Then, on the reticle R on which the illumination light is condensed, the light amount of the illumination light with which the reticle R is irradiated is monitored. In this case, the amount of light monitored on the reticle R immediately after starting the light emission of the light source 1 is 100%, and the amount of light monitored on the reticle R thereafter is the transmittance (%) with the initial amount of light as a reference. It is shown on the vertical axis of FIG.

In the example of FIG. 5, the amount of light on the reticle R gradually decreased with time, and the transmittance became about 85% when the irradiation time was 800 hours. At this point, when the toric reflector 3, the first lens 5A, and the second lens 5B in FIG. 1 are rotated to positions where the irradiation areas do not overlap, the monitored light amount returns to 100% which is the initial state. did. After that, the amount of light monitored on the reticle R gradually decreased again, and the transmittance became about 85% at the total irradiation time of 1600 hours as in the first time. At this point, when the optical elements in FIG. 1 are rotated again, the reticle R
The light intensity above returned to the initial state.

On the other hand, FIG. 6 shows changes in transmittance in the case of the comparative example in which the respective optical elements of FIG. 1 are not rotated, that is, the same case as the conventional example. That is, also in the case of FIG. 6, the emission power of the light source 1 is adjusted so that the toric reflector 3 is irradiated with the i-line illumination light having an intensity of 4 W / cm ² , and then the irradiation is started. The amount of light was monitored on Reticle R4 of No. 1. As shown in FIG. 6, the monitored light amount gradually decreases with time, and the irradiation time is 800 hours and the transmittance is 85%.
It has become a degree. In this comparative example, irradiation was continued without rotating each optical element, so the amount of light being monitored was further reduced, and the transmittance was 70% or less at the total irradiation time of 1600 hours. After that, when the irradiation was further continued, the lens 5A or 5B was broken in the vicinity of 1600 hours. That is, by periodically rotating each optical element shown in FIG. 1 as shown in FIG. 5, the irradiation power with respect to the object to be illuminated can always be kept within a predetermined range, and the life of the illumination optical system can be extended. it can.

In the above embodiment, the i-line of the mercury lamp is used as the illumination light, but other than that, the g-line (wavelength 436 nm), the KrF excimer laser light (wavelength 249 nm), the ArF excimer laser of the mercury lamp are used. Light (wavelength 1
93 nm), or YAG laser harmonics (wavelength 450 n
m or less), the life of the optical system can be extended by applying the present invention.

Further, the present invention can be applied to a laser processing device, a surveying instrument and the like. As described above, the present invention is not limited to the above-described embodiments, and various configurations can be taken without departing from the gist of the present invention.

[0046]

According to the present invention, since the width of the incident light in the predetermined direction is set narrower than the effective width of the selected optical element in the predetermined direction, the selected optical element is irradiated with the incident light. The life of the optical element can be extended by gradually shifting the area in the predetermined direction. Therefore, in an optical system that handles light with a short wavelength of 450 nm or less, there is an advantage that the service life of the optical system can be extended without significantly modifying the current technology.

Further, when the width of the incident light when entering the selected optical element in the predetermined direction is set to 1/2 or less of the effective width of the selected optical element in the predetermined direction, The life of the selected optical element can be doubled as compared with the conventional one. Further, when a rotating means for rotating the selected optical element is provided, for example, when the transmittance or the reflectance of the optical element is lowered, the rotating means rotates the selected optical element. By this, the life of the optical element can be automatically extended.

When there are a plurality of selected optical elements, the selected plurality of optical elements are divided into one or a plurality of optical element groups, and the one or a plurality of optical element groups are divided. In the case where the rotating means for rotating the optical elements belonging to the respective optical element groups in synchronization with each other is provided,
For example, by rotating the optical elements having the same deterioration characteristics with respect to the incident light as the same optical element group in synchronization, the configuration and control are facilitated.

[Brief description of drawings]

FIG. 1 is a block diagram showing an exposure apparatus to which an embodiment of a short wavelength optical system according to the present invention is applied.

FIG. 2 is a plan view of FIG.

FIG. 3 is an enlarged cross-sectional view showing a configuration example of a rotating unit 7A in FIG.

FIG. 4 is an enlarged sectional view showing an example of a mechanism for manually rotating a first lens 5A in FIG.

FIG. 5 is a diagram showing changes in the amount of light applied to the reticle when each optical element is rotated at regular intervals in the example.

FIG. 6 is a diagram showing a change in the amount of light applied to the reticle when each optical element is left fixed in FIG.

FIG. 7 is a diagram showing a change with time in transmittance when the glass type BK7 is irradiated with light of i-line (wavelength 365 nm).

FIG. 8: KrF excimer laser light (wavelength 2
It is a figure which shows the durability with respect to (49 nm).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 light source 2 optical integrator 3 toric reflector 4 re-imaging optical system 5A first lens 5B second lens 6A, 6B lens frame 7A, 7B, 7C rotating unit 8 synchronous drive unit R reticle 9 projection optical system W wafer 11A , 12A gear

Claims (4)

[Claims] 1. An optical system for emitting incident light having a wavelength of 450 nm or less through one or a plurality of optical elements, wherein at least one optical element selected from the one or a plurality of optical elements is used. A short-wavelength compatible optical system, wherein a width of the incident light in a predetermined direction upon incidence is set to be smaller than an effective width of the selected optical element in the predetermined direction. 2. The width of the incident light in the predetermined direction when entering the optical element selected from the one or a plurality of optical elements is defined as the effective width of the selected optical element in the predetermined direction. The short wavelength optical system according to claim 1, wherein the width is set to 1/2 or less. 3. The short-wavelength compatible optical system according to claim 1, further comprising rotating means for rotating an optical element selected from the one or a plurality of optical elements. 4. When there are a plurality of optical elements selected from the one or a plurality of optical elements, the selected plurality of optical elements are divided into one or a plurality of optical element groups, A rotating means is provided for each of the one or more optical element groups, and the rotating means rotates the optical elements belonging to each of the optical element groups in synchronization.
Alternatively, the optical system corresponding to the short wavelength described in 2.