JP2000091207A - Projection aligner and cleaning method of projection optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove cleanly and effectively contaminants sticking on the surface of an optical element of a projection optical system. SOLUTION: There is provided on a wafer table 15 a concave mirror 19 for reflecting the light (ultraviolet ray) emitted from a projection optical system PL toward an optical element (lens, etc.), 18 of a plurality of optical elements constituting the projection optical system PL which is closest to the image surface of the projection optical system PL. By changing the direction of the concave mirror 19 through a swing device 20, and by scanning with the reflection light of the concave mirror 19 the surface of the optical element 18, the contaminants on the surface of the optical element 18 are decomposed and vaporized to remove therefrom. A gas containing ozone is jetted from a jet nozzle 22 to suck the gas containing the vaporized contaminants in a suction nozzle 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus for manufacturing a semiconductor device, a liquid crystal display, an image pickup device such as a CCD, and a micro device such as a thin film magnetic head, and a method for cleaning a projection optical system.

[0002]

2. Description of the Related Art With the advance of high integration in micro devices such as semiconductor elements, the wavelength of light sources of projection exposure apparatuses used in photolithography processes has been shortened, and so-called vacuum ultraviolet rays, for example, KrF excimer laser (wavelength 248 nm), ArF excimer laser (wavelength 193 nm), more _{F 2} laser (wavelength 1
57 nm) has been used as exposure light.

As a photoresist applied to a substrate (such as a semiconductor wafer or a glass plate) in such a short wavelength region, a photoresist mainly composed of a novolak resin generally used for conventional i-rays and the like is used. It cannot be used because it becomes opaque, and a chemically amplified resist is used instead.

[0004]

However, since light in such a short wavelength region has extremely high energy, organic substances contained in the chemically amplified resist are chemically decomposed and gasified by the irradiation, and this is generated. The projection optical system arranged opposite to the substrate has a problem that the lens surface is contaminated by aggregating and adhering on the surface of the lens closest to the substrate.

When this type of contamination occurs, the light transmittance of the projection optical system is reduced, the exposure time is prolonged to secure an appropriate exposure amount, and the throughput is reduced. In addition, the contamination on the lens surface is uniform. However, there is a problem that illumination unevenness occurs and a high-quality and highly reliable microdevice may not be manufactured in some cases (for example, the amount of adhesion in the center of the lens is large).

Although an apparatus for mechanically wiping such contaminants has been proposed, there is a problem that a brush or the like comes into contact with the optical element, which may damage an antireflection film or the like.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to effectively clean and remove contaminants adhering to the surface of an optical element of a projection optical system. That is.

[0008]

Means for Solving the Problems In the following description, in order to facilitate understanding, each constituent element of the present invention will be described with reference numerals shown in the drawings of the embodiments. The constituent elements of the invention are not limited by these reference numerals.

In order to achieve the above object, a projection exposure apparatus according to the present invention is arranged such that an image of a pattern of a mask (R) illuminated by illumination light is projected onto a substrate (W) by a projection optical system (PL). Reflecting the light emitted from the projection optical system toward the optical element (18) closest to the image plane of the projection optical system among the plurality of optical elements constituting the projection optical system. A member (19) is provided.

In order to achieve the above object, a method for cleaning a projection optical system according to the present invention provides a projection optical system for projecting an image of a pattern of a mask (R) illuminated by illumination light onto a substrate (W). PL) cleaning method, the light emitted from the projection optical system is used to convert the light emitted from the projection optical system to the optical element (1) closest to the image plane of the projection optical system among the plurality of optical elements constituting the projection optical system.
The surface of the optical element is optically cleaned by being reflected toward 8).

A contaminant such as an organic substance attached to the surface of an optical element such as a lens breaks a chemical bond by radiating ultraviolet rays, and generates a molecule of the contaminant whose bond has been dissociated by irradiation with ultraviolet rays. Oxidation by separately supplied ozone or excited oxygen atoms can be removed by light cleaning, which decomposes and vaporizes.

Therefore, according to the present invention, the light emitted from the projection optical system is reflected toward the optical element closest to the substrate of the projection optical system, and is guided to the surface of the optical element, whereby the surface of the optical element is Was light washed to remove contaminants. This prevents a decrease in light transmittance of the projection optical system, thereby suppressing a decrease in throughput and
The occurrence of uneven illumination is also prevented, and a high-quality and highly reliable microdevice can be manufactured.

The reflecting member for guiding the light emitted from the projection optical system to the surface of the optical element includes, for example,
A concave mirror can be adopted, and according to such a concave mirror,
Since the light energy density on the surface of the optical element can be set appropriately high, the time required for light cleaning can be reduced.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a reduction projection type exposure apparatus (stepper) according to an embodiment of the present invention.

Referring to FIG. 1, an illumination optical system 11 has a KrF
Exposure light source that emits excimer laser light (wavelength 248 nm), fly-eye lens or rod for uniformizing illuminance distribution
It comprises an optical integrator (homogenizer) such as an integrator, an illumination system aperture stop, a reticle blind (variable field stop), and a condenser lens system.

A reticle R as a photomask on which a pattern to be transferred is formed is attracted and held on a reticle stage (not shown), and is carried into a predetermined reticle setting position during exposure processing. Irradiation is performed on the reticle R set at the reticle setting position. In the illumination optical system 11, a half mirror 12 for splitting a laser beam from an exposure light source is provided.
The laser light transmitted through is used as illumination light as it is,
The laser light reflected by the half mirror 12 is incident on the incident light amount sensor 13. The detection signal of the incident light amount sensor 13 is sent to the transmittance detector 14.

The image of the pattern in the illumination area of the reticle R is reduced via the projection optical system PL at a reduction ratio of 1 / α (α is, for example, 4 or 5) at the wafer W coated with a chemically amplified photoresist. Projected onto the surface of Hereinafter, a description will be given with the Z axis taken parallel to the optical axis AX1 of the projection optical system PL, the X axis taken parallel to the plane of FIG. 1 in a plane perpendicular to the Z axis, and the Y axis taken perpendicular to the plane of FIG. I do.

The wafer W is held on a wafer holder (not shown) by negative pressure suction, and the wafer holder is detachably sucked and held on a wafer table (substrate stage) 15.
The wafer table 15 is installed on the XY stage via a plurality of actuators displaced in the Z direction.
The wafer table 15 adjusts the surface of the wafer W to the image plane of the projection optical system PL by controlling the focus position (position in the direction of the optical axis AX1) and the tilt angle of the wafer W by an autofocus method.

An emission light sensor (illuminance sensor) 16 is provided near the wafer holder of the wafer table 15. The outgoing light quantity sensor 16 is positioned in the projection area by the projection optical system PL by moving the wafer table 15, and emits light (illuminance) on the image plane of the projection optical system PL.
And sends the detection signal to the transmittance detector 14.
The transmittance detecting device 14 detects the half mirror 1 based on detection signals from the incident light amount sensor 13 and the output light amount sensor 16.
The light transmittance from 2 to the output light quantity sensor 16 is calculated.

By comparing the transmittance obtained by the transmittance detector 14 with a comparison value stored and held in advance, it is possible to know the state of attachment of contaminants to the projection optical system PL. Based on such a change in light transmittance, execution of light cleaning by a light cleaning device described later is controlled. In addition, an illuminance sensor (irregularity sensor) for detecting illuminance unevenness (illuminance distribution) in the projection area of the projection optical system PL is provided on the wafer table 15, and cleaning is performed by an optical cleaning device described below based on the occurrence state of the illuminance unevenness. May be controlled.

Next, the optical cleaning device will be described. An optical cleaning device 17 is provided on the wafer table 15 as shown in an enlarged manner in FIG. Light cleaning device 17
Converts the light emitted from the projection optical system PL into the projection optical system PL.
Of the plurality of optical elements constituting the optical element closest to the image plane of the projection optical system PL (such as a lens or a glass plate) 1
A concave mirror 19 is provided as a reflecting member that reflects light toward the mirror 8.

In this embodiment, the concave mirror 19 is
As shown in the perspective view of FIG. 3, a cylindrical light beam IL1 emitted from the projection optical system PL and incident on the concave mirror 19 (in this embodiment, it is assumed to be parallel light) is condensed on its axis AX2. It is a concave mirror of a type. The concave mirror 19 is configured such that the converging axis AX2 is the optical axis AX of the projection optical system PL.
It is supported by the wafer table 15 via the swinging device 20 so as to be substantially orthogonal to the direction parallel to the direction 1.

The focusing axis AX2 of the concave mirror 19 extends from the surface to be cleaned (exposed surface) of the optical element (hereinafter referred to as an optical element to be cleaned) 18 closest to the image plane of the projection optical system PL. Is set at a position separated from the object surface side.

As described above, the converging axis AX2 of the concave mirror 19 is spaced apart from the surface of the optical element 18 to be cleaned because the optical element 18 itself to be cleaned due to energy concentration or an antireflection film coated on the surface thereof. The separation amount is appropriately determined such that the damage can be sufficiently prevented and the light cleaning efficiency is maximized. Note that the concave mirror 19 may be a spherical reflecting mirror that condenses reflected light at one point. Further, instead of the concave mirror 19, a flat reflecting mirror or a convex mirror having a diverging property to the reflected light can be adopted.

The swinging device 20 supports a shaft 21 provided integrally with the concave mirror 19 so as to be rotatable, as shown in FIG. This is a device for swinging the concave mirror 19 within a predetermined angle range by a connected stepping motor (not shown). By appropriately energizing the stepping motor of the oscillating device 20, the directivity of the concave mirror 19 can be continuously changed, that is, the surface of the optical element to be cleaned 18 can be scanned by the light reflected by the concave mirror 19. ing.

Referring again to FIG. Wafer table 1
An ejection nozzle 22 is provided on the 5 adjacent to the concave mirror 19 so as to obliquely direct the optical element 18 to be cleaned. A gas ejection device (not shown) is connected to the ejection nozzle 22, and a predetermined gas is ejected from the ejection nozzle 22 toward the optical element 18 to be cleaned.

As the gas to be ejected, the optical to be cleaned
Types of contaminants adhering to the element 18 (photoresist used
Type) and the wavelength of illumination light
And an inert gas such as argon (Ar)
Dzong (O₃) And oxygen (O₂ ) Including active gas
Can be That is, the adhered contaminants
The nature of which promotes photolysis
Use ozone-mixed products,
If a significant acceleration effect is not observed,
Considering the adverse effects of wastewater and the labor required to remove ozone at the destination
Then, the combined use of ozone may be avoided.

Further, even when the presence of ozone promotes photodecomposition, ultraviolet rays having a shorter wavelength (for example, Ar
In the case of an F excimer laser, the supply of ozone is not necessarily required because ultraviolet light itself decomposes and activates oxygen in the atmosphere to generate ozone. In this embodiment, an active gas containing ozone is ejected because a KrF excimer laser is used as exposure light.

The ejection nozzle 2 of the wafer table 15
A suction nozzle 23 is provided at a position opposing the concave mirror 19 across the concave mirror 19 so as to obliquely point the optical element 18 to be cleaned. The suction nozzle 23 is connected to a gas suction device (not shown), The gas including the gas ejected from the ejection nozzle 22 in the portion between the wafer table 15 and the optical element to be cleaned 18 can be sucked.

When the reticle R is set at the reticle setting position and the wafer W coated with the chemically amplified resist is exposed as shown in FIG. Organic substances contained in the chemically amplified resist are chemically decomposed into gas G by light irradiation,
This is the optical element 1 to be cleaned, which is disposed opposite the wafer W.
As shown in FIG. 5 (B), the contaminants 1 are condensed and adhered on the surface of the optical element 18 to be cleaned.
8a adheres.

The occurrence of such contamination lowers the light transmittance, necessitating an increase in the exposure time in order to secure a proper exposure amount, and lowers the throughput. Therefore,
The light transmittance is obtained by the transmittance detection device 14, and light cleaning is performed by the light cleaning device 17. That is, the emission light amount sensor 16 is moved to the projection position of the projection optical system PL (immediately below the optical axis AX1).
When the transmittance calculated from the detection signals of the incident light amount sensor 13 and the output light amount sensor 16 by the transmittance detection device 14 becomes smaller than a comparison value stored and held in advance, the value becomes, for example, 90%. When this is found, light cleaning by the light cleaning device 17 is performed.

First, the wafer table 15 is moved to position the concave mirror 19 below the optical element 18 to be cleaned, and the exposure light source of the illumination optical system 11 is operated to start illumination for light cleaning. At this time, it is assumed that the reticle R is not set at the reticle setting position, and that the illumination system aperture stop and the like are appropriately adjusted so that substantially parallel light falls from the projection optical system PL. At the same time or before or after this, the gas ejection device and the gas suction device are operated, and the ejection nozzle 22
A predetermined gas is ejected from the nozzle and the gas is sucked from the suction nozzle 23.

Next, the oscillating device 20 is operated to gradually change the directing direction of the concave mirror 19, and
The surface 8 is scanned by light (ultraviolet light) reflected by the concave mirror 19. As a result, the chemical bond of the organic substance or the like on the surface of the optical element 18 to be cleaned is cut, and the molecule of the organic substance having the bond dissociated is converted into ozone in the active gas from the ejection nozzle 22 or ozone generated by ultraviolet irradiation. The organic matter is decomposed and vaporized and removed by oxidation. The vaporized contaminants are sucked into the suction nozzle 23 together with the surrounding gas.

According to the above-described embodiment of the present invention, the ultraviolet light emitted from the projection optical system PL is reflected toward the optical element 18 to be cleaned by the concave mirror 19 supported by the oscillating device 20, and is thus cleaned. By scanning the surface of the optical element 18, contaminants adhering to the surface of the optical element 18 are optically cleaned. This prevents a decrease in the light transmittance of the projection optical system PL, thereby suppressing a decrease in the throughput and preventing the occurrence of uneven illumination, thereby manufacturing a high-quality and highly reliable microdevice. become able to.

Also, since the ultraviolet light emitted from the projection optical system PL is reflected by the concave mirror 19, the light energy density of the ultraviolet light on the surface of the optical element 18 to be cleaned is high, and the time required for cleaning is short.

Further, when the light cleaning is performed, the ejection nozzle 22
Activated gas containing ozone is ejected from
The decomposition and vaporization of the contaminants are promoted, and the suction nozzle 23 sucks and removes the nearby gas including the vaporized contaminants. Adherence is prevented.

In addition, the concave mirror 19 is
Is changed so that the surface of the optical element to be cleaned 18 is scanned, so that the entire surface of the optical element 18 to be cleaned can be cleaned. Also, the incident light amount sensor 1
3. The light transmittance is detected by the output light amount sensor 16 and the transmittance detection device 14, and when the light transmittance becomes lower than a predetermined limit value, the light cleaning by the light cleaning device 17 is performed. Therefore, cleaning can be performed only when cleaning is necessary, and highly efficient cleaning can be performed.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

For example, the projection exposure apparatus of the present embodiment is a batch exposure type stepper, but can be similarly applied to a scanning exposure type scanning stepper and other types of exposure apparatuses. Further, the exposure illumination light is not limited to KrF excimer laser (wavelength 248 nm), ArF excimer laser (wavelength 193 nm), _{F 2} excimer laser (wavelength 157 nm), or be any of the harmonics of a YAG laser Good. For example, EUV (Extrem) having an oscillation spectrum at 5 to 15 nm (soft X-ray region)
e Ultra Violet) light is used as exposure illumination light, the illumination area on the reflection mask is defined in an arc slit shape, and a reduction projection optical system including only a plurality of reflection optical elements (mirrors) is provided. The present invention can also be applied to an EUV exposure apparatus or the like that transfers the pattern of the reflection mask onto the wafer by synchronously moving the reflection mask and the wafer at a speed ratio according to the magnification of the system.

Further, in the above embodiment, the concave mirror 19, the oscillating device 20, the ejection nozzle 22 and the suction nozzle 23 of the optical cleaning device 17 are fixedly provided on the wafer table 15, but the present invention is not limited thereto. There is no limitation, and all or a part of them can be configured to be detachable, and when it is necessary to perform optical cleaning, it can be installed on the wafer table 15 to perform optical cleaning. By doing so,
The size and weight of the wafer table can be reduced. Gas ejection device including ejection nozzle 22, suction nozzle 2
It is desirable to install the gas suction device including No. 3 from the viewpoint of improving light cleaning efficiency and preventing reattachment of contaminants, but it is not necessarily essential, and one or both of them can be omitted. .

Further, in the above embodiment, the concave mirror 19
Is set so as to be located away from the surface of the optical element to be cleaned 18 on the object side of the projection optical system PL, but to be located away from the image plane side of the projection optical system PL. Can be set. Which side of the converging axis AX2 is located with respect to the surface of the optical element 18 to be cleaned can be appropriately selected depending on the tendency of the contaminant to adhere to the optical element 18 to be cleaned.

That is, the light energy density on the surface of the optical element 18 to be cleaned due to the reflected light of the concave mirror 19 is inversely proportional to the distance of the concave mirror 19 from the converging axis AX2.
As shown in FIG. 5B, when a large amount of contaminants adheres to the central portion of the optical element 18 to be cleaned, the converging axis AX
By setting the position 2 on the image side of the optical element 18 to be cleaned, the central portion (the concave mirror 19) of the surface of the optical element 18 to be cleaned is set.
The light energy density is high on the side (closer to), the light energy density decreases as the distance increases, and cleaning can be performed efficiently according to the actual state of contamination. On the other hand, when the contamination state is relatively small in the central portion and large in the peripheral portion, contrary to FIG. 5B, the converging axis AX2 of the concave mirror 19 is positioned on the object side of the optical element 18 to be cleaned. By letting
The light energy density is low at the center (the side close to the concave mirror 19), and the light energy density increases as the distance increases, which follows the actual state of contamination.

In addition, in the above embodiment, the concave mirror 1
The scanning of the surface of the optical element 18 to be cleaned by the reflected light 9 is performed by the oscillating device 20, but the present invention is not limited to this, and the wafer table is used together with the oscillating device 20 or alone. The movement may be performed by moving the concave mirror 19 with the use of the mirror 15.

Although the swinging device 20 changes the direction of the concave mirror 19 about one axis (axis 21), the direction of the concave mirror 19 may be changed biaxially. In addition, in the above-described embodiment, the light cleaning by the light cleaning device 17 is performed by detecting the light transmittance, but the light cleaning is performed when the integrated exposure time reaches a predetermined time. Is also good.

Furthermore, in the above embodiment, the active gas containing ozone is ejected by the gas ejection device to promote the photolysis. However, the gas containing oxygen is ejected, and the ejection nozzle 22 is ejected. Ozone may be generated by providing a corona discharge electrode inside or at the tip.

[0046]

As described above, the present invention has the effect that the contaminants adhering to the surface of the optical element of the projection optical system can be effectively cleaned and removed. Further, there is an effect that damage to the optical element can be prevented as compared with the case where the optical element is wiped and cleaned with a brush or the like.

[Brief description of the drawings]

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

FIG. 2 is an enlarged view of a main part of the projection exposure apparatus according to the embodiment of the present invention.

FIG. 3 is a perspective view of a concave mirror according to the embodiment of the present invention.

FIG. 4 is a diagram showing a main configuration of the optical cleaning device according to the embodiment of the present invention.

5A and 5B are diagrams for explaining a process of contamination of an optical element of the projection optical system. FIG.
(B) shows a state in which a contaminant has adhered to the optical element of the projection optical system.

[Explanation of symbols]

 R ... reticle (mask) W ... wafer (substrate) PL ... projection optical system 11 ... illumination optical system 12 ... half mirror 13 ... incident light quantity sensor 14 ... transmissivity detector 15 ... wafer table (substrate stage) 16 ... outgoing light quantity sensor DESCRIPTION OF SYMBOLS 17 ... Light cleaning device 18 ... Optical element to be cleaned 19 ... Concave mirror (reflection member) 20 ... Swinging device 22 ... Spout nozzle 23 ... Suction nozzle

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) H01L 21/30 515B

Claims (10)

[Claims] 1. A projection exposure apparatus wherein an image of a pattern of a mask illuminated by illumination light is projected onto a substrate by a projection optical system, wherein the light emitted from the projection optical system constitutes the projection optical system. A projection exposure apparatus, further comprising: a reflecting member that reflects light toward an optical element closest to an image plane of the projection optical system among the plurality of optical elements. 2. The projection exposure apparatus according to claim 1, wherein said reflection member is a concave mirror. 3. The projection exposure apparatus according to claim 2, wherein the concave mirror is provided on a substrate stage that holds the substrate. 4. The projection exposure apparatus according to claim 3, wherein the concave mirror is detachable from the substrate stage. 5. The projection exposure apparatus according to claim 2, wherein the concave mirror is supported by a swinging device so as to scan the surface of the optical element on the concave mirror side with light reflected by the concave mirror. . 6. The projection exposure apparatus according to claim 2, wherein the illumination light is ultraviolet light. 7. The projection exposure apparatus according to claim 2, further comprising a gas suction device for sucking gas in a portion between the optical element and the concave mirror. 8. The projection exposure apparatus according to claim 2, wherein a gas ejection device for ejecting gas is provided at a portion between the optical element and the concave mirror. 9. The projection exposure apparatus according to claim 8, wherein the gas ejection device ejects an active gas or an inert gas. 10. A cleaning method of a projection optical system for projecting an image of a pattern of a mask illuminated by illumination light onto a substrate, wherein a plurality of optics constituting the projection optical system emit light emitted from the projection optical system. A method of cleaning a projection optical system, comprising: reflecting light toward an optical element closest to an image plane of the projection optical system among the elements to optically clean a surface of the optical element.