JPH10303097A - Projection exposure device, exposure method, manufacture of semiconductor device, and manufacture of projection optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain high optical performance even when water content and an organic material is stuck onto the surface of an optical element, by controlling a changing means which changes numerical aperture of an illuminating optical system based on an output from an measurement means for performing measurement for transmittance of a projection optical system. SOLUTION: A control system 21 discriminates whether light transmittance of a projection optical system 10 of a projection exposure device is a specified value or not, based on an output from a second detector 12 provided to one end of a wafer stage WS and an output from a third detector 31 provided to one end of a reticule stage RS. And the control system 21 sets the size of a variable aperture stop 6 with a driving system 22, to execute optical cleaning process. At this time, when a numerical aperture of an illuminating optical system 10 is made NAi , and that of the projection optical system 10 is made NA0 , the control system 21 rotates a turret plate 60 with the driving system 22 so as to satisfy a relation Nai >=NA0 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention manufactures devices such as semiconductor devices such as LSIs, imaging devices such as CCDs, liquid crystal display devices, and thin-film magnetic heads (hereinafter collectively referred to as semiconductor devices). Exposure apparatus for exposing a pattern of an original such as a mask (or reticle) to a photosensitive substrate such as a wafer in a photolithography process for
The present invention relates to an exposure method using the exposure apparatus, a method for manufacturing a semiconductor device using the exposure method, and a method for manufacturing a projection optical system used for the projection exposure apparatus.

[0002]

2. Description of the Related Art Along with the high integration of semiconductor devices, projection exposure apparatuses used in optical lithography processes, which are important for manufacturing the semiconductor devices, have made great progress. The resolving power of the projection optical system mounted on the projection exposure apparatus is represented by the relationship of R = k × λ / NA, as is well known by the Rayleigh equation. Here, R is the resolution of the projection optical system,
λ is the wavelength of light for exposure, NA is the numerical aperture of the projection optical system, k
Is a constant determined by the process in addition to the resolution of the resist.

In order to realize the required resolution in the projection optical system in response to the high integration of semiconductor elements, as can be seen from the above equation, the wavelength of the light source for exposure and the numerical aperture of the projection optical system must be increased. So-called efforts to increase the NA have been continued.
In recent years, an exposure apparatus using a krypton fluoride excimer laser (KrF excimer laser) having an output wavelength of 248 nm as a light source for exposure and having a numerical aperture of a projection optical system of 0.6 or more has been commercialized, reaching 0.25 μm. Exposure of fine patterns has been realized.

In particular, recently, as a light source following the krypton fluoride excimer laser, an argon fluoride excimer laser (ArF excimer laser) having an output wavelength of 193 nm is used.
Is attracting attention. If an exposure apparatus using this argon fluoride excimer laser as an exposure light source can be realized, 0.1
It is expected that microfabrication ranging from 8 μm to 0.13 to 0.15 μm will be possible, and vigorous R & D has been actively conducted.

In the wavelength range of the output wavelength (193 nm) of this argon fluoride excimer laser, the material usable as a lens from the viewpoint of transmittance is synthetic quartz glass at this stage.
As it is limited to two kinds of calcium fluoride (fluorite),
As an optical material for an exposure apparatus of this kind, a material having a sufficient transmittance and internal uniformity has been energetically developed. Synthetic quartz glass has an internal transmittance of 0.9
At 95 / cm or more, calcium fluoride reaches a negligible level of internal absorption.

[0006] The material for the anti-reflection film coated on the surface of the optical material has a very narrow selection range as compared with that of the output wavelength (248 nm) of the krypton fluoride excimer laser, and the degree of freedom in design is increased. Subject to major restrictions. However, the problem has been overcome by vigorous development efforts, and the loss on each lens surface has been realized to a level of 0.005 or less.

[0007]

In this type of exposure apparatus, a change in thermal characteristics of an optical member such as a lens due to absorption of an optical material or an anti-reflection film causes a change in imaging characteristics. It is an essential task to realize the above and to make the thermal characteristic change as small as possible. However,
For light in the deep ultraviolet region of 200 nm or less, even if the absorption of the optical material and the antireflection film is achieved to the above-mentioned level, when the optical components for the exposure apparatus are handled in the working environment in the air, the moisture and the moisture in the air may be reduced. Experiments by the present inventors have revealed that there is a problem that the transmittance of an optical component such as a lens rapidly decreases due to the attachment of an organic substance. The absorption amount reaches, for example, 0.01 per lens surface, and the maximum absorption becomes easy.

Conventionally, a method of irradiating ultraviolet rays as a method of cleaning the surface deposits is known, for example, in Japanese Patent Application Laid-Open No. 7-294705. However, although a temporary cleaning effect is exhibited by the irradiation of the ultraviolet light, the surface of the optical component is activated by the ultraviolet light, and when the optical component is left in a normal working environment thereafter, it becomes easier to adsorb ambient moisture and organic substances. This has been found by the inventors' experiments.

Therefore, even if the optical components are cleaned with ultraviolet rays, it is necessary to consider a process of assembling optical components such as lenses for forming a projection optical system in a state where the optical components are completely isolated from moisture and organic substances. Is practically impossible, and this is a major obstacle in realizing an optical system of an exposure apparatus for an argon fluoride excimer laser.

Therefore, the present invention has been made in view of the above problems, and even if moisture or an organic substance adheres to the surface of an optical element constituting a projection optical system used in an optical lithography process, these problems can be solved. A method of manufacturing a projection optical system capable of maintaining high optical performance by eliminating attached substances,
It is an object of the present invention to provide an exposure method capable of exposing a good image on a photosensitive substrate, a projection exposure apparatus using the exposure method, and a method of manufacturing a semiconductor device for manufacturing a good semiconductor device.

[0011]

According to an embodiment of the present invention, there is provided an illumination optical system for illuminating an original having a predetermined pattern with light for exposure, and A projection optical system having a projection optical system for projecting the pattern of the original illuminated by an optical system onto a photosensitive substrate; and a transmittance of the projection optical system, or at least a part of an illumination optical system and the projection optical system. A measuring means for measuring the transmittance of the light, a changing means for changing a numerical aperture of the illumination optical system, and a control means for controlling the changing means based on an output from the measuring means. It is.

According to another embodiment of the present invention, in an exposure method, an original having a predetermined pattern is illuminated with light for exposure by an illumination optical system to project the pattern of the original into a projection optical system. An exposure step of sequentially projecting onto a plurality of photosensitive substrates through the first and second exposure steps before the start of the exposure step or the exposure of the (n + 1) th photosensitive substrate after the exposure of the nth photosensitive substrate is completed. And a light cleaning step of irradiating the projection optical system with the light for exposure to restore the transmittance of the projection optical system.

According to still another embodiment of the present invention, in a method of manufacturing a semiconductor device, an original having a predetermined pattern is illuminated with light for exposure by an illumination optical system to change the pattern of the original. An exposure step of sequentially projecting a plurality of photosensitive substrates through a projection optical system, and before the start of the exposure step, or after the exposure of the n-th photosensitive substrate is completed, the next (n + 1) -th photosensitive substrate And a light cleaning step of irradiating the projection optical system with the light for exposure to restore the transmittance of the projection optical system before the exposure is performed.

According to still another embodiment of the present invention, in a method of manufacturing a projection optical system, a predetermined pattern formed on an original is projected onto a photosensitive substrate under light for exposure. An assembling step of assembling a projection optical system, and irradiating the projection optical system with light having the same wavelength as the light for exposure toward the projection optical system after the assembling step, thereby restoring the transmittance of the projection optical system. And a light cleaning step.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of a projection exposure apparatus according to the present invention. As shown in FIG. 1, for example, an ArF excimer laser light source 1 oscillating pulse light having an output wavelength of 193 nm is supplied with a laser beam as a substantially parallel light beam, and is guided to a light transmission window 2 on the projection exposure apparatus main body side. I will Here, the main body of the projection exposure apparatus is housed in a chamber 30. In order to prevent the optical elements and the like in the chamber 30 from adhering moisture and organic substances in the atmosphere to the optical elements, for example, nitrogen is used. And the like.

The laser light that has passed through the light transmission window 2 is reflected by a reflection mirror 3 and guided to a fly-eye lens 5 as an optical integrator. Fly eye lens 5
Is configured by bundling a number of lens elements, and a light source image is formed on the exit surface side of the lens elements. Therefore, a large number of light source images (secondary light sources) corresponding to the number of lens elements constituting the fly-eye lens 5 are provided on the exit surface side of the fly-eye lens 5.
Is formed.

In this embodiment, one fly-eye lens 5 is provided.
A fly-eye lens as a second optical integrator may be provided between the F-excimer laser light source 1 (or the reflection mirror 3), and an internal reflection type rod-shaped optical member is provided instead of the fly-eye lens. It may be used as an optical integrator.

As will be described in detail later, a plurality of aperture stops having a predetermined shape or a predetermined size can be set at positions where a large number of secondary light sources formed by the fly-eye lens 5 are formed. A variable aperture stop (changing means or changing device for changing the numerical aperture of the illumination optical system) 6 is arranged. Now, light beams from a number of secondary light sources formed by the fly-eye lens 5 are reflected by a reflection mirror 7 and then collected by a condenser optical system 8 composed of refractive lenses such as a plurality of lenses. Be lighted. This allows
The circuit pattern formed on the reticle 9 is uniformly illuminated in a superimposed manner. Then, an image of the circuit pattern on the reticle 9 is formed on the wafer 11 by the projection optical system 10. Therefore, the resist applied on the wafer is exposed to light, and the circuit pattern image is transferred onto the wafer 11.

The projection optical system 10 of the present embodiment is composed entirely of optical elements such as a refracting lens.
An aperture stop 10a is arranged at the position of the pupil 0 (entrance pupil). The aperture stop 10a and the variable aperture stop 6 are
They are arranged at optically conjugate positions. Here, the reticle 9 is held by a reticle stage RS that moves two-dimensionally along a plane orthogonal to the paper surface of FIG. 1, and a measurement of an interference system or the like (not shown) that measures the position of the reticle stage RS. The control system 21 as the control means uses the position information from the system.
The control system 21 controls the position of the reticle stage RS via a drive system (not shown) based on the position information.

The wafer stage W moves two-dimensionally along a plane orthogonal to the plane of FIG.
The wafer stage WS is mounted on a measurement system 3 such as an interference system for measuring the position of the wafer stage WS.
0 is input to a control system 21 as control means, and based on this position information, the control system 21
9, the position of the wafer stage WS is controlled.

The projection exposure apparatus shown in FIG. 1 is provided with an illumination optical system (3 to 8) and a transmittance measuring system for measuring the transmittance of the projection optical system 10. A first detector 4 relating to the transmittance measurement system is disposed below the first stage, and a second detector 12 relating to the transmittance measurement system is disposed at one end of the wafer stage WS. Further, at one end of reticle stage RS, a third detector 31 relating to a transmittance measurement system is arranged.

First, the first detector 4 provided below the reflection mirror 3 is provided below the reflection mirror 3 and photoelectrically measures the amount of light leaked from the reflection mirror 3 and the illuminance. And the output of the ArF excimer laser light source 1 is detected. Then, the output from the first detector 4 is input to a control system 21 as control means. Further, the second detector 12 provided at one end of the wafer stage WS is set, via a drive system 29, on a surface on which a wafer as an irradiated surface is arranged (or an image forming surface of the projection optical system). As a result, the amount of light, the illuminance, and the like on the surface on which the wafer is arranged (or the imaging surface of the projection optical system) are detected. Then, the output from the second detector 12 is input to a control system 21 as control means.

Further, a third detector 31 provided at one end of the reticle stage RS is connected via a drive system (not shown).
When the reticle 9 is set in the plane where the reticle 9 is to be arranged, the light amount, the illuminance, and the like of the illumination light beam supplied to the reticle surface are detected. The output from the third detector 31 is input to a control system 21 as control means. A division unit and a determination unit are provided inside the control system 21. The division unit divides the output from the second detector 12 by the output from the first detector 4 (the reflection mirror 7, A value corresponding to the light transmittance of the condenser optical system 9 and the projection optical system 10) or a value obtained by dividing the output from the third detector 31 by the output from the second detector 12 (projection optical system 1).
(A value corresponding to a light transmittance of 0) is output to the determination unit. Then, the determination unit determines whether or not the transmittance of the predetermined optical system constituting the projection exposure apparatus has decreased by determining whether or not the output from the division unit has reached a predetermined threshold. Then, the determination unit determines whether to start the exposure operation or to continuously execute the exposure operation, or to start the light cleaning operation.

Further, outside the chamber 30, a plurality of spaces formed between a plurality of optical members inside the projection optical system 10 and a gas suction device 23 for supplying an inert gas such as nitrogen to the chamber 30. And a discharge device 26 for discharging gas inside a plurality of spaces formed between the plurality of optical members inside the projection optical system 10 and gas inside the chamber 30 to the outside. The inert gas is not limited to nitrogen, but may be a gas such as helium or argon.

The gas suction device 23 is connected to a pipe 24
A dry inert gas such as nitrogen (dry inert gas) is supplied to the chamber 30 through the
And supplies an inert gas such as nitrogen (dry inert gas) to the inside of the projection optical system 10 through the. The discharge device 26 discharges the gas inside the chamber 30 to the outside through the pipe 27 and discharges the gas inside the projection optical system 10 to the outside through the pipe 27.

The gas suction device 23 and the discharge device 2
6 is controlled by the control system 21. Next
The opening of the illumination optical system in the projection exposure apparatus described above
Variable as changing means or changing device to change the number of mouths
The aperture stop 6 will be described. Now, as shown in FIG.
Parallel to the optical axis AX from the outermost edge (outermost diameter) of the variable aperture stop 6
Light ray R_iOf the illumination optical system (3 to 7) determined by
NA_i(= sinθ _i) And the opening in the projection optical system 10
Parallel to the optical axis AX from the outermost edge (outermost diameter) of the aperture stop 10a
Light ray R_OOptics of the projection optical system 10 determined by
The numerical aperture on the system side is NA_O(= sinθ_O)
The value of σ as the ratio factor is defined by the following equation.
You.

Σ = NA _i / NA _O Note that the aperture stop 10a disposed at the position of the pupil (entrance pupil) of the projection optical system 10 and the variable aperture stop 6 in the illumination optical system are optically conjugate, Since the image of the variable aperture stop 6 (the image of the secondary light source) is formed on the pupil of the projection optical system 10, the diameter of the image of the variable aperture stop 6 is D _6, and the diameter of the aperture stop 10 a of the projection optical system 10 is when the diameter and D _10a, sigma value as coherence factor can be defined even in the following equation.

Σ = D ₆ / D _{10a In} general, the σ value of the projection exposure apparatus in the photolithography process is set to be in the range of 0.3 to 0.8. In this example, the variable aperture stop 6 shown in FIG. 1 is provided so that a stop having a different aperture shape or another size aperture shape can be set at a secondary light source position formed by the fly-eye lens 5. .

FIG. 2 shows a more specific configuration of the variable aperture stop 6 shown in FIG. As shown in FIG. 2, the variable aperture stop 6 shown in FIG. 1 has a turret plate 60 having eight aperture stops (60a to 60h) formed on a transparent substrate such as quartz. Here, five aperture stops (60a, 60e to 60h) having a circular aperture are for positively changing the σ value, and three aperture stops (60e, 60f, 60g) among them are: This is an aperture used during an actual exposure operation. The remaining two aperture stops (6
Reference numerals 0a and 60h) denote apertures used in the light cleaning operation.

An aperture stop having three other deformed apertures is used during the exposure operation to improve the resolving power of the projection optical system 10. Two of the aperture stops (60c, 60d) have orbital apertures having different orbital ratios, and the remaining one aperture stop 60b forms four eccentric secondary light sources. Therefore, the diaphragm has four eccentric apertures.

Now, eight aperture stops (60a-60h)
The turret plate 60 is rotated via a drive system 22 such as a motor shown in FIG. 1 and one of the three aperture stops, that is, the stop having a desired aperture shape is set to the secondary light source position. Is done. This drive system 22 is driven by the control system 2
1 is controlled. In FIG. 3, aperture stops (60a, 60e to 60e) having circular apertures of different sizes from each other are shown.
FIG. 2H shows a state when the image of FIG. 1H is formed on the aperture stop 10 a in the projection optical system 10.

[0032] First, when the aperture stop 60e with the smallest round opening is set on the illumination light path, it reduces the numerical aperture NA _i of the illumination optical system is best, this time, an aperture stop having an opening diameter D _10a An image of the aperture stop 60e having the aperture diameter _D60e is formed inside 10a, and the σ value is set to 0.4.
That is, σ = D _60e / D _10a = NA _i / NA _O = 0.
4 holds. Therefore, when the aperture stop 60e is set in the illumination optical path, the reticle 9 is set under the σ value of 0.4.
Can be transferred onto the wafer 11.

When an aperture stop 60f having a circular aperture larger than the aperture stop 60e is set in the illumination optical path,
Numerical aperture NA _i of the illumination optical system becomes larger than when the aperture stop 60e is set on the illumination light path. At this time, the inside of the aperture stop 10a having the aperture diameter D _10a, the aperture diameter D _60f
Is formed, and the σ value is set to 0.6. That is, σ = D _60f / D _10a = NA _i / NA
The relationship of _O = 0.6 holds. Therefore, the aperture stop 60f
Is set in the illumination light path, the pattern of the reticle 9 can be transferred onto the wafer 11 under the σ value of 0.6.

When an aperture stop 60g having a circular aperture larger than the aperture stop 60f is set in the illumination optical path,
The numerical aperture NA _i of the illumination optical system is larger than when the aperture stop 60f is set in the illumination optical path. At this time, inside the aperture stop 10a having the aperture diameter _D10a , an aperture diameter _{D60g is provided.}
Is formed, and the σ value is set to 0.8. That is, σ = D _60g / D _10a = NA _i / NA
The relationship of _O = 0.8 holds. Therefore, the aperture stop 60g
Is set in the illumination light path, the pattern of the reticle 9 can be transferred onto the wafer 11 under the σ value of 0.8.

Furthermore, the aperture stop 60h having a large circular opening of the aperture stop 60g is set on the illumination light path, the numerical aperture NA _i of the illumination optical system, when the aperture stop 60g is set on the illumination light path Larger than. At this time,
Opening diameter D of the same size as the opening diameter D _10a of the aperture stop 10a
An image of the aperture stop 60g having _60h is formed, and the σ value is 1.
Set to 0. That is, σ = D _60h / D _10a = NA
The relationship of _i / NA _O = 1.0 holds. Therefore, when the aperture stop 60h is set in the illumination optical path, the effective diameter of an optical element such as a lens constituting the condenser optical system 8 of the illumination optical system and the effective diameter of an optical element such as a lens constituting the projection optical system 10 are effective. The illumination light flux can be guided sufficiently to the diameter, and even to the portion exceeding the effective diameter of these optical elements. For this reason, moisture, organic substances, and the like attached to the surfaces of these optical elements can be eliminated by the light cleaning effect of the illumination light beam for exposure.

When an aperture stop 60a having a circular aperture larger than the aperture stop 60h is set in the illumination optical path,
The numerical aperture NA _i of the illumination optical system is larger than when the aperture stop 60h is set in the illumination optical path. At this time, as an aperture stop 10a having the aperture diameter D _10a, the aperture diameter D
_60a an image of the aperture stop 60a is formed of, sigma value is set to 1.2. That is, σ = D _60a / D _10a = NA _i /
The relationship of NA _O = 1.2 holds. Therefore, the aperture stop 6
When 0a is set in the illumination optical path, the effective diameter of the optical element such as a lens constituting the condenser optical system 8 of the illumination optical system and the effective diameter of the optical element such as the lens constituting the projection optical system 10 are of course. That is, the illumination light flux can be sufficiently guided to the peripheral portion of the lens exceeding the effective diameter of these optical elements. Therefore, it is possible to sufficiently obtain the effect of optically cleaning water, organic substances, and the like attached to the surfaces of these optical elements.

Next, the operation of this embodiment will be described. First, as shown in FIG. 1, when the illumination light flux as exposure light is not guided to the optical system portion of the projection exposure apparatus even when the chamber 30 is filled with a dry inert gas such as nitrogen and is isolated from the atmosphere. Various experiments have revealed that the transmittance of the optical system of the projection exposure apparatus is reduced. Therefore, when performing an optical lithography process for manufacturing a semiconductor device, before starting the projection exposure apparatus shown in FIG. 1 and shifting to the exposure operation, the optical system portion of the projection exposure apparatus (reflection of the illumination optical system) must be used. Mirror 7, condenser optical system 8, projection optical system 10, etc.)
A first step of confirming the transmittance of the sample by the transmittance measurement system is executed. The condenser optical system 8 and the projection optical system 10
The phenomenon that the transmittance of the transmissive optical element such as decreases,
The reflection type optical element such as the reflection mirror 7 appears as a phenomenon that the reflectance is reduced. [Step 1] First, in a first step, the projection exposure apparatus is started up via a power supply (not shown), and a laser beam is emitted from the ArF excimer laser light source in a state where the reticle 9 is not set. Is supplied, the control system 2
1 sets the second detector 12 provided at one end of the wafer stage WS to the exposure surface of the projection optical system 10 via the drive system 29.

Next, the control system 21 is based on the output from the first detector 4 provided below the reflection mirror 3 and the output from the second detector 12 provided at one end of the wafer stage WS. Predetermined optical system parts of the projection exposure apparatus (reflection mirror 7, condenser optical system 8, and projection optical system 10)
It is determined whether or not the light transmission of each of the pixels has a predetermined value. In other words, the division unit inside the control system 21 is based on the output from the first detector 4 and the output from the second detector 12,
Calculate the ratio of both outputs. Thereafter, based on the calculation result, the determination unit inside the control system 21 determines whether or not the output from the division unit has reached a predetermined threshold. When the output from the division unit has reached the predetermined threshold value by the determination unit, the process proceeds to step 3 as an exposure operation described later. If the output from the division unit has reached the predetermined threshold value by the determination unit, the process proceeds to a second step as a light cleaning step.

In the first step, the control system 21
Are based on the output from the second detector 12 provided at one end of the wafer stage WS and the output from the third detector 31 provided at one end of the reticle stage RS. It is desirable to determine whether or not the light transmittance of the projection optical system 10 has reached a predetermined value, and to further determine the light transmittance of the projection optical system 10, and then determine whether or not to proceed to the second step. At this time, in order to obtain the output from the third detector 31, the control system 21 controls the third detector 31 provided at one end of the reticle stage RS via a drive system (not shown) to dispose a reticle. It is necessary to set it to the surface that should be. [Step 2] In the second step, the control system 21 first sets the size of the aperture of the variable aperture stop 6 via the drive system 22 to execute the optical cleaning process. Here, the control system 21 rotates the turret plate 60 via the drive system 22 and sets an appropriate aperture stop 60a so that the σ value becomes 1 or more.
Alternatively, 60h is set in the illumination light path.

In other words, let the numerical aperture of the illumination optical system be NA _i
When the numerical aperture of the projection optical system 10 is NA _O , the control system 21 rotates the turret plate 60 via the drive system 22 so as to satisfy the relationship of NA _i ≧ NA _O , and an appropriate aperture stop. 60
a or 60h is set in the illumination light path.

Thus, the effective diameter of an optical element such as a lens constituting the condenser optical system 8 of the illumination optical system, the effective diameter of an optical element such as a lens constituting the projection optical system 10,
Further, the illumination light flux can be sufficiently guided to a portion exceeding the effective diameter of these optical elements. As a result, moisture, organic substances, and the like adhering to the surfaces of these optical elements can be eliminated by the light cleaning effect of the illumination light beam for exposure.

Also, due to the light cleaning effect of the irradiation of the illumination light beam for exposure, moisture and organic substances separated from the surface of the optical element enter inside a plurality of predetermined spaces formed between the plurality of optical elements. There is a possibility of floating in the chamber 30. For this reason, the control system 21 performs the light cleaning step, and simultaneously, forcibly discharges water and organic substances separated from the surface of the optical element to the outside of the apparatus.
Then, the discharge device 26 is operated. That is, the control system 2
The gas supply device 23 supplies fresh and dry inert gas such as nitrogen into the chamber 30 via the pipe 24 and into the projection optical system 10 via the pipe 25, respectively, based on the command from 1. At the same time, based on a command from the control system 21, the discharging device 26 controls the moisture in the chamber 30 through a pipe 27, an inert gas containing an organic substance, and the like, the water in the projection optical system 10 through a pipe 28, and the like. An inert gas containing an organic substance or the like is discharged to the outside of the projection exposure apparatus.

As a result, an inert gas such as nitrogen, which has been cleaned by removing moisture and organic substances, is supplied to the chamber 30.
Since it is filled into the inside of the projection optical system 10, the transmittance of the optical system portion of the projection exposure apparatus (such as the reflection mirror 7 of the illumination optical system, the condenser optical system 8, and the projection optical system 10) returns to the original state. It will be possible to recover. During the light cleaning step of the second step, the gas supply device 23
A fresh dry inert gas such as nitrogen is supplied to the chamber 30.
The gas supply unit 23 supplies oxygen (O ₂ ) and ozone (O ₂ ) as strongly oxidizing gases to an inert gas such as nitrogen. ₃ ) Alternatively, it is desirable to adopt a configuration in which active oxygen (O ^* ) or the like is mixed. As a result, the action of the gas having a strong oxidizing property promotes the light cleaning effect, and a greater effect can be expected.

Further, at the same time as the exposure step of the first step is shifted to the optical cleaning step of the second step, the barge of an inert gas such as nitrogen is opened in at least one of the inside of the chamber 30 and the inside of the projection optical system 10. Then, the air may be caused to flow in, and then the second step of the optical cleaning process may be started in an air environment to gradually replace the inert gas with the inert gas.

When the light cleaning step of the second step is completed, the operation shifts to an exposure operation as a third step. [Step 3] In step 3, an actual exposure operation is performed. First, when the reticle 9 is set on the reticle stage RS, that is, when the pattern surface of the reticle 9 is set on the object surface of the projection optical system 10, the control system 21
The exposure surface of the wafer 11 held on the wafer stage WS is set as the image forming surface of the projection optical system 10 via. At the same time, the control system 21 sets the size of the aperture of the variable aperture stop 6 via the drive system 22.

Here, the storage unit inside the control system 21 stores the exposure map such that the wafer 11 to be exposed is sequentially conveyed every time the exposure is completed and the exposure condition such as the σ value in the input system 20 such as a console. Has been input in advance. On the basis of the input information, the control system 21 rotates the turret plate 60 via the drive system 22 so that a desired one of the six aperture stops (60b to 60g) for exposure is set in the illumination optical path. Set to. Thereby, under the situation where the transmittance of the predetermined optical system of the projection exposure apparatus has been recovered, the desired σ
The pattern of the reticle 9 can be transferred onto the wafer 11 under the condition of the value. As a result, a good fine pattern image can be faithfully transferred onto the wafer 11 under a high throughput, and a good semiconductor device with a high degree of integration can be manufactured.

It should be noted that even if the exposure operation in the third step described above is being executed, the chamber 30 may be exposed for some reason.
In some cases, water, organic substances, and the like as contaminants adhere to the inside of the projection optical system 10 and reduce the transmittance of the optical system in the exposure apparatus. Therefore, if n is an integer of 1 or more, the exposure operation is performed once before the exposure of the n-th photosensitive substrate is completed from the start of exposure and before the exposure of the next (n + 1) -th photosensitive substrate is performed. The operation is stopped, and the process returns to step 1 to execute transmittance measurement. For example, the process returns to the transmittance measurement process of step 1 at a regular stage when the exposure of every 300 to 500 wafers 11 is completed. And the control system 21 again
Predetermined optical system parts of the projection exposure apparatus (reflection mirror 7 of illumination optical system, condenser optical system 8, projection optical system 10
Etc.) is checked with a transmittance measurement system.

If no decrease in the transmittance of the predetermined optical system of the projection exposure apparatus is confirmed, the flow returns to step 3 again to continue the exposure operation. If it is confirmed that the transmittance of the predetermined optical system of the projection exposure apparatus has decreased, the process returns to step 2 to execute the optical cleaning process. As can be understood from the above, in order to guide the illumination light flux to a portion exceeding the effective diameter of each optical element of the optical system at the time of exposure, the numerical aperture of the illumination optical system in the light cleaning step in step 2 is required. When the numerical aperture of the illumination optical system in the exposure step of step 2 is NA _i2 , N _i1 is set in this example.
It is preferable to change the numerical aperture of the illumination optical system so as to satisfy the condition of A _i1 > NA _i2 .

Further, the exposure of each optical element of the optical system at the time of exposure is
Reliable and sufficient illumination luminous flux even beyond the effective diameter
Lighting in the light cleaning process of step 2 above.
NA of the numerical aperture of the optical system_i1And the illumination light of the projection optical system 10
Maximum numerical aperture NA on the academic side _OAnd NA_i1≧ N
A_O(That is, the condition of σ ≧ 1),
It is more preferable to change the numerical aperture of the illumination optical system.

In the embodiment described above, the value of σ is set to 1 or more in the optical cleaning step. However, the present invention is not limited to this, and the maximum σ value at the time of the exposure operation may be increased. The numerical aperture of the illumination optical system in the light cleaning step may be set so that the σ value also becomes large. In this case, in order to obtain a better Naru optical cleaning effect, the numerical aperture of the illumination optical system and NA _i, the numerical aperture of the illumination optical system in the optical cleaning process NA _i1, the illumination optical system side of the projection optical system 10 when the maximum numerical aperture NA _O at, NA _i ≧ 0.85NA _O, or N
It is preferable to satisfy the relationship of A _i1 ≧ 0.85NA _O.

In the above-described embodiment, when light cleaning is performed using a light cleaning reticle having a predetermined pattern such as a diffraction grating in the light cleaning step, diffracted light of the light cleaning reticle and the like can be obtained. Light can be guided to the entire optical system, so that a large light cleaning effect can be expected. In the above embodiment, the case has been described where the projection optical system 10 is entirely composed of a refractive optical element. However, the present invention is not limited to this, and a reflective optical element such as a mirror and a refractive optical element such as a lens may be used. A catadioptric projection optical system may be used. Further, almost or all of the projection optical system 10 may be configured by a reflective optical element such as a mirror. This projection optical system 10
Is mainly composed of a reflective optical element such as a mirror, the second detector 12 becomes dominant in measuring the reflectance of the optical system rather than the transmittance of the optical system. Is included in the concept of measuring the transmittance of the optical system of the present invention.

Further, the wavelength of the light required to perform the optical cleaning is a short wavelength of 200 nm or less.
It is extremely effective to provide an exposure apparatus that performs exposure with light having a short wavelength of 0 nm or less to have a light cleaning function. In the above embodiment, the example in which the projection exposure apparatus itself has the light cleaning function has been described. Next, an example relating to a method for manufacturing a projection optical system for the projection exposure apparatus will be described. [Step 1] In step 1, as shown in FIG. 4, lens elements (L _{1 to} L ₅ ) as optical members constituting the projection optical system according to design values such as predetermined lens data and the like, and each lens element are held. producing barrel of (B ₁ ~B ₅₎ to.

Specifically, first, each lens element (L ₁ to L ₁ )
L ₅₎ is a known lens edger a predetermined radius of curvature, each of the optical material according to a predetermined design value by using, it is processed to have on-axis thickness. Thereafter, the surfaces of the processed lens elements (L _{1 to} L ₅ ) are processed by a well-known vapor deposition device or the like.
An anti-reflection film for efficiently transmitting light having an exposure wavelength (light of 193 nm, which will be described later) is formed.

On the other hand, a lens barrel (B ₁₎ holding each lens element
.About.B ₅₎ is machined into a shape each having a predetermined size from a predetermined material (stainless steel, brass, etc.) using known metalworking machine. In addition, a predetermined lens barrel (B ₁ , B ₂ , B ₃ )
, A through hole for injecting and discharging an inert gas such as nitrogen is formed by a metal working machine. As mentioned above,
When the production of the components constituting the projection optical system 10 is completed, the process proceeds to a step 2 of assembling the projection optical system 10. [Step 2] As shown in FIG. 4, the lens elements (L _{1 to} L ₅ ) manufactured in Step 1
Embedded within the manufactured lens barrel (B ₁ .about.B ₅₎ at, to produce a five divided tube unit. At this time, a predetermined three lens barrel _{(B 1, B 2, B} 3) a number of through holes formed in the injection-side valve (V ₁₁ ~V ₁₄₎ injection pipe is mounted (25a ～25D) and the discharge side valve (V ₂₁ discharge pipe ~V ₂₄₎ is mounted (28a-
28d).

[0055] or more over five divided tube unit production is completed, as shown in FIG. 4, Wasshiya (WA ₁ to W-
While interposing A _4), successively each divided tube unit,
We will assemble while adjusting. Then, when the projection optical system is assembled, in order to check the optical performance of this, for example,
By placing a test pattern on the object plane of the projection optical system 10,
A test pattern image formed on the image plane of the projection optical system 10 is observed via a television camera.

When the process of assembling the projection optical system 10 in step 2 is completed, the process proceeds to a light cleaning process. [Step 3] The above steps 1 and 2 must basically be performed in the atmosphere (air). In such an environment, moisture and organic substances contained in the atmosphere may It adheres to the surfaces of the elements (L _{1 to} L ₅ ) and greatly reduces the transmittance of the projection optical system 10 incorporated.

Therefore, in step 3, the projection optical system 10 assembled in step 2 is irradiated with light having the same wavelength as the exposure light to remove water and organic substances adhering to the surface of the lens element constituting the projection optical system 10. Remove. Since the wavelength of light that requires light cleaning is a short wavelength of 200 nm or less, a light cleaning step is required when manufacturing a projection optical system for an exposure apparatus that performs exposure with light having a short wavelength of 200 nm or less. It is effective to use

FIG. 5 is a diagram showing a schematic configuration of an optical cleaning apparatus for irradiating the projection optical system 10 assembled in step 2 with light having the same wavelength as the exposure light. FIG.
In the drawing, members having the same functions in the projection exposure apparatus of FIG. 1 are denoted by the same reference numerals. As shown in FIG. 5, first, the projection optical system 10 assembled in step 2 is incorporated into the champer 30 of the optical cleaning device. That is, the projection optical system 10 is incorporated so that the irradiation surface IP at the rear focal position of the condenser optical system 8 in the illumination optical system coincides with the object plane of the projection optical system 10.

Next, the injection side valve (V ₁₁ to V ₁₁₎ shown in FIG.
V ₁₄ ) and four injection pipes (25a-
The 25d) connected to the injection pipe 25 shown in FIG. 5, also four discharge pipes discharge side valve (V ₂₁ ~V ₂₄₎ is attached to (28a to 28d) to the discharge pipe 28 shown in FIG. 5 Connecting. When the above settings are completed, as shown in FIG. 5, the control system 21 operates the gas supply device 23 and the discharge device 26 to cause the inert gas such as nitrogen dried by the gas supply device 23 to be in the chamber 30 and The air is supplied to the inside of the projection optical system 10, and the air inside the chamber 30 and inside the projection optical system 10 is exhausted to the outside by the exhaust device 26. Then, air and an inert gas are exchanged inside the chamber 30 and inside the projection optical system 10.

The inside of the chamber 30 and the projection optical system 10
Is sufficiently filled with an inert gas, light from the ArF excimer laser light source 1 oscillating pulse light having an output wavelength (for example, 193 nm) equal to the wavelength for exposure is transmitted through the light transmission window. Guide to the cleaning device body side. The laser light that has passed through the light transmission window 2 is reflected by the reflection mirror 3 to form a fly-eye lens 5 as an optical integrator.
And a number of light source images (secondary light sources) are formed on the exit surface side of the fly-eye lens 5.

At a position where a number of secondary light sources formed by the fly-eye lens 5 are formed, an aperture stop 32 having a circular aperture of a predetermined size is provided. When the numerical aperture of the illumination optical system in this step (light cleaning step) is NA _i1 and the maximum numerical aperture NA _{O of} the projection optical system 10 on the illumination optical system side described later is NA _i1 ≧ N
It is configured to satisfy the condition of A _O (that is, the condition of σ ≧ 1).

Now, the luminous flux from these many secondary light sources is
After being reflected by the reflection mirror 7, the light is condensed by the condenser optical system 8 and uniformly illuminates the irradiated surface IP in a superimposed manner. The light beam passing through the irradiated surface IP is projected onto the projection optical system 1.
0, whereby moisture, organic substances, and the like adhering to the surfaces of the plurality of optical elements (L _{1 to} L ₅ ) constituting the projection optical system 10 can be eliminated by the light washing effect of the illumination light beam for exposure. it can.

Due to the light cleaning effect by the irradiation of the illumination light beam for exposure, the moisture and organic substances separated from the surfaces of the plurality of optical elements (L _{1 to} L ₅ ) constituting the projection optical system 10 are removed by the plurality of optical elements. There is a possibility of floating in a predetermined plurality of spaces formed between the device and the inside of the chamber 30. For this reason, the control system 21 operates the gas supply device 23 and the discharge device 26 in order to forcibly discharge moisture, organic substances, and the like separated from the surface of the optical element to the outside of the device simultaneously with the execution of the optical cleaning process. Let it. That is, based on a command from the control system 21, the gas supply device 23 supplies a new inert gas such as nitrogen to the chamber 3 through the pipe 24.
0 and through the pipe 25 to the inside of the projection optical system 10, respectively. At the same time, based on a command from the control system 21, the discharging device 26 controls the moisture in the chamber 30 through a pipe 27, an inert gas containing an organic substance, and the like, the water in the projection optical system 10 through a pipe 28, and the like. An inert gas containing an organic substance or the like is discharged to the outside of the projection exposure apparatus.

As a result, an inert gas such as nitrogen, which has been cleaned by removing moisture and organic substances, is supplied to the chamber 30.
Since the inside and inside of the projection optical system 10 are filled, the transmittance of the projection optical system 10 can be restored to the original state. In the third step of the optical cleaning step, fresh and inert gas such as nitrogen is supplied into the chamber 30 and into the projection optical system 10 by the gas supply device 23. Reference numeral 23 denotes oxygen (O ₂ ), ozone (O ₃ ), or active oxygen (O ^* ) as an oxidizing gas in an inert gas such as nitrogen.
It is desirable to adopt a configuration that mixes the like. As a result,
By the action of the gas having a strong oxidizing property, the light cleaning effect is promoted, and a larger effect can be expected.

It is desirable to measure the transmittance of the projection optical system 10 before and after the third step of the optical cleaning process is performed. In this case, a first detector 31 movable along an irradiated surface IP of the illumination optical system and a second detector 12 movable along an imaging plane of the projection optical system 10 are arranged.
When measuring the transmittance of the projection optical system 10, the first detector 31 is set in the irradiation target surface IP, and the second detector 12 is set in the imaging surface of the projection optical system 10.

Then, based on the output from the first detector 31 and the output from the second detector 12, the control system 21 determines whether or not the light transmittance of the projection optical system 10 has a predetermined value. It is good to be constituted so that it may be judged. by this,
By measuring the light transmittance of the projection optical system 10 before performing the light cleaning step of the third step, it is possible to predict how long the light from the ArF excimer laser light source should be irradiated, and If the light transmittance of the projection optical system 10 is measured after executing the three-step light cleaning process, the state of recovery of the light transmittance of the projection optical system 10 can be confirmed.

If the adjustment of the projection optical system 10 is necessary again at the stage when the light cleaning step in the above third step is completed, the projection optical system 10 is taken out of the chamber 30 of the optical cleaning apparatus of FIG. Return to step 2 again. When the third step is completed, the projection optical system 10
When it is confirmed that the imaging performance of the above is sufficiently obtained, the projection optical system is taken out from the chamber 30 of the optical cleaning apparatus shown in FIG. 5 and attached to the main body of the projection exposure apparatus as shown in FIG. Complete the device.

[0068]

As described above, according to the present invention, moisture and organic substances adhering to the optical system constituting the projection exposure apparatus can be removed by light washing, so that a good reticle pattern image can be formed. It can be transferred onto a substrate. Moreover, in the optical lithography process including the exposure method, even if the transmittance of the projection optical system is reduced, the transmittance of the projection optical system can be sufficiently recovered by newly adopting the light cleaning process. Since a fine pattern can be used as a photosensitive substrate, a semiconductor device such as an LSI having a higher degree of integration can be manufactured.

Further, if the optical cleaning step according to the present invention is used in manufacturing a projection optical system, the assembly and adjustment work of the projection optical system can be performed under a normal working environment, and the transmittance of the projection optical system can be reduced. It can be sufficiently secured.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing a configuration of a variable aperture stop in the projection exposure apparatus shown in FIG.

3 is a diagram showing a state of an image of a variable aperture stop formed at a pupil position of a projection optical system in the projection exposure apparatus of FIG.

FIG. 4 is a diagram showing a state when a projection optical system is incorporated.

FIG. 5 is a view showing a schematic configuration of a light cleaning apparatus for light cleaning the projection optical system shown in FIG. 4;

[Explanation of symbols]

 1 ArF excimer laser light source 4, 12, 31 Detector 6 Variable aperture stop 8 Condenser optical system 10 ... Projection optical system 21 ... Control system

Claims (17)

[Claims] 1. A projection system comprising: an illumination optical system for illuminating an original having a predetermined pattern with light for exposure; and a projection optical system for projecting the pattern of the original illuminated by the illumination optical system onto a photosensitive substrate. In the exposure apparatus, a measuring unit for measuring a transmittance of the projection optical system or a transmittance of at least a part of the illumination optical system and the projection optical system, and a change for changing a numerical aperture of the illumination optical system And a control unit for controlling the changing unit based on an output from the measuring unit. 2. The method according to claim 1, wherein the control unit determines whether the transmittance of the projection optical system or the transmittance of at least a part of the illumination optical system and the projection optical system is reduced based on an output from the measurement unit. 2. The projection exposure apparatus according to claim 1, wherein it is determined whether or not the change is made, and the changing unit is controlled based on the determination information. 3. When the control means determines that the transmittance has decreased, the changing means sets the numerical aperture of the illumination optical system to be larger than the numerical aperture of the illumination optical system based on the output of the control means. 3. The projection exposure apparatus according to claim 2, wherein a numerical aperture of the illumination optical system is changed. 4. When the control means determines that the transmittance has decreased, the changing means sets the numerical aperture of the illumination optical system based on the output of the control means so as to satisfy the following condition. The projection exposure apparatus according to claim 2, wherein the projection exposure apparatus is changed. NA _i ≧ NA _O where NA _i is the numerical aperture of the illumination optical system and NA _O is the numerical aperture of the projection optical system. 5. An exposure step of illuminating an original having a predetermined pattern with light for exposure by an illumination optical system and sequentially projecting the pattern of the original onto a plurality of photosensitive substrates via a projection optical system; Before the start of the exposure step, or before the exposure of the (n + 1) th photosensitive substrate is completed after the exposure of the nth photosensitive substrate is completed, the light for exposure is projected into the projection optical system. A light cleaning step of recovering the transmittance of the projection optical system by irradiating light to the projection optical system. 6. The numerical aperture of the illumination optical system in the optical cleaning process and NA _i1, when the numerical aperture of the illumination optical system in the exposure step and the NA _i2, the condition NA _i1> NA _i2 The exposure method according to claim 5, wherein the above condition is satisfied. 7. When the numerical aperture of the illumination optical system in the light cleaning step is NA _i1 and the maximum numerical aperture NA _O of the projection optical system on the illumination optical system side is NA _i1 ≧ NA _O. The exposure method according to claim 6, wherein the following condition is satisfied. 8. An exposure step of illuminating an original having a predetermined pattern with light for exposure by an illumination optical system and projecting the pattern of the original onto a plurality of photosensitive substrates sequentially via a projection optical system; Before the start of the exposure step, or before the exposure of the (n + 1) th photosensitive substrate is completed after the exposure of the nth photosensitive substrate is completed, the light for exposure is projected into the projection optical system. And a light cleaning step of recovering the transmittance of the projection optical system by irradiating the semiconductor device with light. 9. The numerical aperture of the illumination optical system in the optical cleaning process and NA _i1, when the numerical aperture of the illumination optical system in the exposure step and the NA _i2, the condition NA _i1> NA _i2 The method for manufacturing a semiconductor device according to claim 8, wherein the following conditions are satisfied. 10. When the numerical aperture of the illumination optical system in the light cleaning step is NA _i1 and the maximum numerical aperture NA _O of the projection optical system on the illumination optical system side is: _{10. The} method of manufacturing a semiconductor device according to claim 9, wherein the following condition is satisfied: NA _i1 ≧ NA _O. 11. The light cleaning step includes: injecting a predetermined inert gas into a plurality of predetermined spaces formed between the plurality of optical elements forming the projection optical system; 9. The method according to claim 8, further comprising the step of discharging gas.
The method of manufacturing a semiconductor device according to claim 10. 12. The optical cleaning step comprises injecting a predetermined inert gas containing a predetermined active gas into a plurality of spaces formed between the plurality of optical elements constituting the projection optical system. 11. The method according to claim 8, further comprising a step of discharging gas from the plurality of spaces.
13. The method for manufacturing a semiconductor device according to item 9. 13. An assembling step for assembling a projection optical system for projecting a predetermined pattern formed on an original onto a photosensitive substrate under light for exposure, and said projection optical system having passed through said assembling step. A light cleaning step of recovering the transmittance of the projection optical system by irradiating light having the same wavelength as the light for exposure toward the projection optical system. 14. The projection optical system according to claim 12, wherein the light having the same wavelength as the exposure light used in the light cleaning step is light having a wavelength of 200 nm or less. Production method. 15. The optical cleaning step according to claim 1, wherein a predetermined inert gas is injected into a plurality of predetermined spaces formed between the plurality of optical elements constituting the projection optical system, and the plurality of optical elements are included in the plurality of optical elements. 2. The method according to claim 1, further comprising the step of discharging gas.
The method of manufacturing a projection optical system according to claim 2 or 14. 16. In the light cleaning step, a predetermined inert gas containing a predetermined active gas is injected into a plurality of predetermined spaces formed between the plurality of optical elements constituting the projection optical system. 15. The method of manufacturing a projection optical system according to claim 13, further comprising a step of exhausting gas from the plurality of spaces. 17. Light having the same wavelength as the light for exposure in the light cleaning step is supplied by an illumination optical system, and the numerical aperture of the illumination optical system in the light cleaning step is NA _i1 .
The maximum numerical aperture N of the projection optical system on the illumination optical system side
_{17. The method according} to claim 13, wherein when A _O satisfies the condition of NA _i1 ≧ NA _O.
13. The method for manufacturing a projection optical system according to item 9.