JPH11167004A - Optical washing method for projection optical system for aligner, and aligner and method for aligning - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the aligner which can effective remove contaminations sticking one a lens surface of the projection optical system of the aligner. SOLUTION: The device is equipped with a convex lens 7 and a concave lens 8 which have focal length such focal length (f) that |f|<=d/[tan(sin<-1> (NA0 ))- tan(sin<-1> (NAi))], where NAi is the numerical aperture of a lighting optical system 3, NA0 is the numerical aperture of the projection optical system 10, and (d) is the distance between the farthest lighting area from an optical axis 37 and the optical axis 37 at a mask arrangement position 6; and a holding device 9 holding the convex lens 7 and concave lens 8 is driven by a drive device 15 to arrange one of the convex lens 7 and concave lens 8 selectively at a position 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical cleaning method for an optical system for an exposure apparatus, an exposure apparatus, and an exposure method.

[0002]

2. Description of the Related Art In recent years, with high integration of semiconductor devices, a projection exposure apparatus used in an optical lithography process also requires high resolution. Therefore, the wavelength of the exposure light used in the projection exposure apparatus has become shorter. Recently, an exposure apparatus using light having a wavelength of 200 nm or less as the exposure light has been proposed.

[0003]

In the lens used in the above-described exposure apparatus, water and organic substances contained in air tend to adhere to the lens surface. There is a problem that the lens surface is contaminated by the contaminants.
In particular, since these contaminants have a property of strongly absorbing light of 200 nm or less, in an exposure apparatus using exposure light of 200 nm or less, a decrease in transmittance due to the contaminants attached to the lens surface poses a problem. I have.

The contaminants adhering to the lens surface are separated from the lens surface by irradiating the lens surface with ultraviolet rays as disclosed in, for example, Japanese Patent Application Laid-Open No. 7-294705. It is known that the lens surface is effectively cleaned. Since the exposure light having a wavelength of 200 nm or less used for the exposure apparatus is ultraviolet light, the exposure apparatus is operated to irradiate the exposure light to the lens of the optical system, whereby contaminants adhering to the lens surface are cleaned. There was an effect that.

However, since the numerical aperture (hereinafter referred to as NA) of the illumination optical system generally used in the projection exposure apparatus is smaller than the NA of the projection optical system, the illumination light from the illumination optical system is directly incident on the projection optical system. In this case, only a part of the NA area of the projection optical system (the area corresponding to the NA of the illumination optical system) is illuminated, and only the illuminated area is cleaned. As a result, the lens surface has a washed high transmittance area and a contaminant-adhered low transmittance area, and as a result, degradation of the resolving power and transmission due to a decrease in the effective NA of the projection optical system. There has been a problem that unevenness in the amount of light of the image forming pattern due to the unevenness of the rate causes deterioration of the image forming performance of the projection exposure apparatus.

An object of the present invention is to provide an optical cleaning method, an exposure apparatus, and an exposure method that can effectively remove contaminants attached to a lens surface of a projection optical system of an exposure apparatus.

[0007]

An embodiment of the present invention will be described with reference to FIGS. 1 and 8. FIG. (1) The first aspect of the invention is a light beam B1 from the illumination optical system 3.
Is refracted by the optical members 7 and 8 having a refracting power, and the projection optical system 10 is illuminated with the light flux B2 refracted by the optical members 7 and 8 to optically clean the lens surfaces of the lenses constituting the projection optical system 10. Thereby, the above object can be achieved. (2) To be described with reference to FIGS.
In the optical cleaning method according to the first aspect, the optical member is a positive lens 7 or a negative lens 8 disposed at the position of the object surface 6 of the projection optical system 10, and the numerical aperture of the illumination optical system 3. Where NAi is the numerical aperture of the projection optical system 10, NA is the numerical aperture of the projection optical system 10, and d is the distance between the illuminated area on the object surface farthest from the optical axis 37 and the optical axis 37. It was set as in equation (4).

| F | ≦ d / [tan {sin ⁻¹ (NAo)} − tan {sin ⁻¹ (NAi)}] (4) (3) According to the invention of claim 3, the pattern is formed. The present invention is applied to an exposure apparatus having an illumination optical system 3 for illuminating a mask with a light beam from a light source 1 and a projection optical system 10 for projecting a light beam transmitted through the mask onto a photosensitive substrate, and a light beam B1 from the illumination optical system 3 The above-described object is achieved by detachably providing the optical members 7 and 8 for refracting the light and entering the projection optical system 10. (4) In the exposure apparatus according to the fourth aspect, in the exposure apparatus according to the third aspect, the optical member is a positive lens 7 or a negative lens 8 disposed at the position of the object surface 6 of the projection optical system 10, and When the numerical aperture of the system 3 is NAi, the numerical aperture of the projection optical system 10 is NAo, and the distance between the illumination area on the object surface farthest from the optical axis 37 and the optical axis 37 is d, the lenses 7 and 8 The focal length f was set as in the following equation (5).

| F | ≦ d / [tan {sin ⁻¹ (NAo)} − tan {sin ⁻¹ (NAi)}] (5) (5) According to the invention of claim 5, the pattern is formed. The present invention is applied to an exposure apparatus having an illumination optical system 3 for illuminating a mask with a light beam from a light source 1 and a projection optical system 10 for projecting a light beam transmitted through the mask onto a photosensitive substrate. When NAi is the numerical aperture of the projection optical system 10, NAo is the numerical aperture of the projection optical system 10, and d is the distance between the illumination area farthest from the optical axis 37 on the object surface 6 of the projection optical system 10 and d, the following equation (6)

| F | ≦ d / [tan {sin ⁻¹ (NAo)} − tan {sin ⁻¹ (NAi)}] (6) A positive lens 7 and a negative lens 8 having a focal length f that satisfies (6). The above object is achieved by providing lens moving devices 9 and 15 for selectively disposing either the positive lens 7 or the negative lens 8 at the position of the object plane 6 of the projection optical system 10. (6) In the exposure apparatus according to any one of the third to fifth aspects, the incident light amount measuring device 5 for measuring the light amount of the light beam incident on the projection optical system 10, and the projection optical system An output light amount measuring device 12 for measuring the light amount of the light beam emitted from the light source 10, an incident light amount measuring device 5, and an output light amount measuring device 12
A transmittance calculating means 13 for calculating the transmittance of the projection optical system 10 based on the measured value of the projection optical system 10, and attaching / detaching of the optical member or correction by the lens moving devices 9 and 15 based on the transmittance calculated by the transmittance calculating means 13. Control means 14 for controlling the selective disposition of the lens or the negative lens. For example, the control unit 14 may terminate the light cleaning based on the transmittance,
The selection of the positive lens 7 or the negative lens 8 is controlled. (7) In the exposure apparatus according to the third aspect, in the exposure apparatus according to the third aspect, the holding device 9, which selectively arranges one of the mask and the optical members 7, 8 at the mask arrangement position 6 in the optical path,
15 were provided. (8) An optical cleaning method for an optical system for an exposure apparatus, wherein a mask on which a pattern is formed is illuminated with exposure light to form a pattern image on a photosensitive substrate. The above object is achieved by performing light cleaning performed by irradiating a light beam from a light source onto a lens surface of a lens included in the optical system 10 prior to an exposure operation using a mask. (9) According to a ninth aspect of the present invention, in the optical cleaning method for an optical system for an exposure apparatus according to the eighth aspect, a light beam from the exposure light source 1 is applied to the lens surface instead of the light cleaning light source. (10) In the optical cleaning method for an optical system for an exposure apparatus according to the ninth aspect, the invention according to the ninth aspect provides the optical system with a refractive power in an optical path between the exposure light source 1 for generating exposure light and the optical system 10. Optical members 7 and 8 are provided, and the optical members 7 and 8 refract a light beam from the exposure light source 1 and irradiate the lens surface. (11) According to an eleventh aspect of the present invention, in the optical cleaning method for an optical system for an exposure apparatus according to any one of the eighth to tenth aspects, the transmittance of the optical system 10 is started after the irradiation of the light beam onto the lens surface is started. Is greater than or equal to a predetermined value, the optical cleaning is terminated. (12) An illumination optical system 3 for illuminating a mask on which a pattern is formed with a light beam from a light source 1 (12).
A projection optical system 10 for projecting a light beam transmitted through the mask onto a photosensitive substrate; and an optical member removably provided in an optical path between the light source 1 and the projection optical system 10 for refracting the light beam from the light source 1 7, 8, detecting devices 5, 12, 13 for detecting the transmittance of the projection optical system 10, and detecting devices 5, 12, 13
Calculating means 14 for calculating the illumination unevenness on the photosensitive substrate based on the transmittance detected in step 1;
41, and a control means 14 for controlling an integrated exposure amount of exposure light applied to the photosensitive substrate based on the transmittance and time change characteristics detected by the detection devices 5, 12, and 13. (A) when the illumination unevenness of the exposure light on the photosensitive substrate exceeds a predetermined specified value, the exposure operation by the mask is stopped, and then the optical member 7 or 8 is replaced with the optical path instead of the mask. And irradiates the lens surface of the lens constituting the projection optical system 10 with a light beam refracted by the optical member 7 or 8 to perform light cleaning of the lens surface.
(B) When the transmittance of the projection optical system 10 changes and the illumination unevenness is equal to or less than a predetermined specified value, the integrated exposure by the control means 14 is performed so that the integrated exposure amount on the photosensitive substrate becomes optimal. The above object is achieved by performing exposure using a mask while controlling the amount.

In the meantime, in the section of the means for solving the above-mentioned problems which explains the constitution of the present invention, the drawings of the embodiments of the present invention are used to make the present invention easy to understand, but the present invention However, the present invention is not limited to the embodiment.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a diagram showing a schematic configuration of an exposure apparatus according to the present invention. Reference numeral 2 denotes a beam matching unit that connects the light source 1 and the illumination optical system 3. The laser light that has passed through the beam matching unit 2 and entered the illumination optical system 3 is reflected by a half mirror 4 provided in the illumination optical system 3. Into two optical paths. The laser light transmitted through the half mirror 4 is used as it is as illumination light, while the laser light reflected by the half mirror 4 enters the incident light amount measuring device 5.

A cleaning optical member 7 is provided at a position 6 on the object surface of the projection optical system 10 where the mask is to be disposed.
Reference numeral 8 denotes another cleaning optical member. The optical members 7 and 8 are held by a holding device 9, and one of the optical members 7 and 8 is rotated by driving the holding device 9 by a driving device 15. It can be arranged at the mask arrangement position 6. Although the mask is not shown in FIG. 1, the mask is provided at the mask arrangement position 6 when a normal exposure process is performed without performing optical cleaning using the optical members 7 and 8. This mask is also held by the holding device 9 together with the optical members 7 and 8.

The light beam B1 from the illumination optical system 3 is
Alternatively, the light beam B2 is refracted by the light beam 8 and becomes a light beam B2. After passing through the projection optical system 10, the light beam B2 is incident on the emission light amount measuring device 12 installed on the wafer stage 11. Reference numeral 13 denotes a transmittance measuring device, which calculates the transmittance from the half mirror 4 to the output light amount measuring device 12 based on signals from the incident light amount measuring device 5 and the output light amount measuring device 12. By comparing the calculated transmittance with the designed transmittance, the state of adhesion of the contaminants on the projection optical system 10 can be known. For example, the end timing can be determined. Reference numeral 14 denotes a control device for controlling the above. Reference numeral 141 denotes a storage unit that stores data related to exposure.
The exposure amount is controlled based on the data of 41.

FIG. 2 is a diagram showing the configuration of the illumination optical system 3 of the apparatus shown in FIG. 1, and the portion surrounded by a dashed line is the illumination optical system 3. Beam matching unit 2 shown in FIG.
From the light enters a fly-eye lens 301 as an optical integrator. The fly-eye lens 301 is configured by bundling a large number of lens elements, and a plurality of light sources (secondary light sources) corresponding to the number of lens elements constituting the fly-eye lens 301 are formed on the exit surface side of the fly-eye lens 301. You. Light beams from a number of secondary light sources formed by the fly-eye lens 301 pass through the aperture stop 302, are split into two light paths by the half mirror 4, and the reflected light enters the incident light amount measuring device 5. On the other hand, the transmitted light is
An image is formed on the field stop 305 for limiting the exposure range by the elements 04a and 304b. The light that has passed through the field stop 305 passes through the relay lens 306, the reflection mirror 307, and the main condenser lens 308 to the mask arrangement position 6.
Irradiation is performed on the cleaning optical member 7 disposed in the cleaning optical member 7. In the apparatus shown in FIG. 1, the half mirror 4 is arranged in the middle of the illumination optical system 3, but is not limited to this, and may be arranged, for example, between the illumination optical system 3 and the optical member 7.

Next, the function of the cleaning optical members 7 and 8 will be described. First, light cleaning in the case where the cleaning optical members 7 and 8 are not used will be described. FIG. 3 shows the mask arrangement position 6
FIG. 3 is a diagram for explaining bundles of rays before and after, where an illumination optical system side is above a mask arrangement position 6 and a projection optical system side is below. Reference numerals 33, 34, and 35 denote a principal ray of a light beam passing through the left end of the exposure range on the mask arrangement position 6, a principal ray of a light beam passing through the optical axis 37, and a principal ray of a light beam passing through the right end of the exposure range in order. 33a and 33b are light rays incident on the mask arrangement position 6 at an angle of the opening half angle α of the illumination optical system 3 with respect to the principal ray 33, and 34a and 34b are mask arrangement positions at an angle of the opening half angle α with respect to the principal ray 34. 6, the light rays 35a and 35b are light rays that enter the principal ray 35 at an angle of the opening half angle α. If the numerical aperture of the illumination optical system 3 is NAi, NAi = n · sin
α. Here, n is the refractive index of the atmosphere.

Here, when the mask 30 is arranged at the mask arrangement position 6, the light is diffracted by the mask 30, and diffracted light whose angles from the principal rays 33, 34, 35 are larger than the half angle α of the aperture is also generated. Will be. 33c, 33d, 34c, 34d, 35c, 35d indicated by broken lines in FIG.
Is such diffracted light, and indicates diffracted light whose angle from the principal ray is equal to the half aperture β of the projection optical system 10. As shown in FIG. 4, of the diffracted light generated by the mask 30, only light whose angle with respect to the optical axis 37 is equal to or smaller than the opening half angle β of the projection optical system 10 can pass through the projection optical system 10, and An image is formed on the photosensitive substrate 32 disposed thereon.

On the other hand, when there is no mask 30 at the mask arrangement position 6, the light beam on the projection optical system side has the same aperture half angle α as that on the illumination optical system side as shown by the solid line. for that reason,
When light cleaning of the lens surface of the projection optical system is performed with exposure light without disposing the mask 30 at the mask arrangement position 6, the lens surface included in the hatched portions in FIGS. The light is not irradiated, and the part is not cleaned.

As a method of solving such a drawback, a method of diffusing illumination light by a diffusion plate 40 provided in place of a mask in an optical path as shown in FIG. 5 is disclosed in Japanese Patent Application No. 9-155.
No. 856 proposes this. When the diffusion plate 40 is used, diffused light 41 having an angle larger than the angle α is obtained, and only the diffused light 41 having an angle equal to or smaller than the half angle β of the opening angle of the projection optical system passes through the projection optical system. As a result, optical cleaning can be performed on a lens surface in a region larger than the half opening angle α and equal to or smaller than the half opening angle β.

On the other hand, in the present invention, the projection optical system 10 in the region larger than the half-opening angle α and equal to or less than the half-opening angle β is formed by refracting a light beam with an optical member having a refractive power (for example, a convex lens or a concave lens). The lens surface was light-cleaned.

FIG. 6 is a view for explaining a case where a negative lens having a negative refractive power (hereinafter referred to as a concave lens) is used as the cleaning optical member. The cleaning concave lens 8 disposed at the mask arrangement position 6 is shown. FIG. 4 is a diagram showing how each light beam having principal rays 33, 34, and 35 is refracted by the light beam. The cleaning concave lens 8 is disposed such that its main surface 8a coincides with the mask arrangement position 6, and the central axis of the concave lens 8 coincides with the optical axis 37. The light beam having the principal rays 33 and 35 is refracted by the concave lens 8 so as to be away from the optical axis 37. At this time, the refractive power (focal length) of the concave lens 8 is set so that the rays 33b and 35a whose angle with respect to the optical axis 37 is α before refraction become equal to the half aperture β of the projection optical system 10 after refraction. . The method of setting the focal length will be described later.

On the other hand, FIG. 7 is a view for explaining a case where a positive lens having a positive refractive power (hereinafter referred to as a convex lens) is used as the cleaning optical member, and the main surface 7a coincides with the mask arrangement position 6. FIG. 4 is a view showing that each light beam having principal rays 33, 34, and 35 is refracted by the cleaning convex lens 7 arranged as described above. The light flux having the principal rays 33 and 35 is refracted by the convex lens 7 so as to approach the optical axis 37. At this time, the refracting power of the convex lens 7 is set so that the angles of the refracted light rays 33a and 35b with respect to the optical axis 37 are equal to the half aperture β of the projection optical system. Note that the angle change of the light beams 33a and 35b before and after refraction Θ
Sets the numerical apertures of the illumination optical system and the projection optical system to N
If Ai, NAo, it is expressed as the following equation (7).

７ = β−α = sin ⁻¹ (NAo) −sin ⁻¹ (NAi) (7)

Next, a method of setting the focal length f of the concave lens 8 and the convex lens 7 will be described with reference to FIG. 8A shows the case of the concave lens 8, and FIG. 8B shows the case of the convex lens 7. When the angle change Θ occurs like the light rays 33b and 35a in FIG. 6 and the light rays 33a and 35b in FIG. 7, the chief rays 33 and 35 are refracted by almost Θ. Set the distance. In FIG. 8, F is the focal point of the lens. In the case of the concave lens 8, it is the intersection point when the principal rays 33, 35 after refraction are extended to the illumination optical system side (upper side in the drawing). This is the point where the later principal rays 33 and 35 intersect on the projection optical system side (the lower side in the figure). Optical axis 37 of chief rays 33, 35
Assuming that the distance from the focal length is d, the focal length fo is given by the following equation (8).

| Fo | = d / tanΘ = d / [tan {sin ⁻¹ (NAo)} − tan {sin ⁻¹ (NAi)}] (8) In the case of the concave lens 8 which is a negative lens, Is a focal length fo <0.

Then, the magnitude | fo | of the focal length f of the cleaning optical member may be set to be equal to or less than | fo | in equation (8). FIG. 9 shows a light beam (principal rays 33 and 3) refracted by concave lens 8 or convex lens 7 where f = fo.
5) passes through the projection optical system 10 and passes through the photosensitive substrate 32.
It is a figure which shows the state which forms an image above, (a) is a case of the concave lens 8, (b) is a case of the convex lens 7. Figure 1
In FIGS. 2 and 4, the projection optical system 10 is shown by one lens, but is actually composed of a plurality of lenses. Here, the case where the lenses L1 and L2 are provided at positions as shown in FIG. Think. At this time, the regions R1 and R2 of the lens L2 shown in FIG. 9A are regions through which exposure light passes during mask exposure, but when the concave lens 8 is used as a cleaning optical member, the exposure light is not irradiated. I understand. Therefore, when the concave lens 8 is used as an optical member for cleaning, the regions R1 and R2 on the lens surface cannot be optically cleaned.

On the other hand, when the convex lens 7 is used as an optical member for cleaning as shown in FIG. 9B, the lens surfaces of the regions R3 and R4 of the lens L1 are not irradiated with the cleaning exposure light. It can be seen that light cleaning of the lens surface cannot be performed.

However, as can be seen from FIG.
The surfaces of R1 and R2 are optically cleaned by using the convex lens 7, and the surfaces of the regions R3 and R4 are optically cleaned by using the concave lens 8.
Thus, depending on the lens configuration of the projection optical system 10,
Since there is a possibility that a lens surface which cannot be optically cleaned by the exposure light with only one of the concave lens 8 or the convex lens 7 may appear, it is preferable to perform the optical cleaning using both the concave lens 8 and the convex lens 7 alternately.

Before starting the exposure process, immediately after the manufacture of the exposure apparatus, when exchanging the mask, when the exposure apparatus has not been used for a long time, or when there is a possibility that the lens surface may be contaminated due to maintenance of the exposure apparatus. Then, the above-described cleaning optical members 7 and 8 are disposed at the mask arrangement position 6 and an exposure operation is performed to perform optical cleaning. At this time, the transmittance of the projection optical system is measured using the measuring devices 5 and 12, and if the transmittance of the projection optical system is reduced to a level that does not affect the process by light irradiation for several minutes to several hours, the mask 6 is measured. The optical member is retracted from the surface, the process mask is arranged at the mask arrangement position 6, and the sensitive substrate 32 is arranged on the wafer stage 11 to start the exposure process. In the above-described embodiment, the optical members 7 and 8 for cleaning the light are provided at the mask arrangement position 6, but they are not necessarily located at this position. What is necessary is just to provide it on the projection optical system side from the aperture stop etc. which determine the numerical aperture of the system 3.

Next, a specific procedure of light cleaning will be described. By the way, the transmittance of the projection optical system 10 can be roughly classified into (1) the one caused by the reduced transmittance of the lens material itself, and (2) the one caused by the attachment of contaminants to the lens surface. Is done. In the case of (1), the transmittance of the entire lens is reduced to about 80%. In this case, only the illuminance on the photosensitive substrate is reduced, and the illumination unevenness is not deteriorated. In the case of (2), the same phenomenon as in (1) occurs when the degree of contamination is light. However, when the degree of contamination is severe, for example, the lens is directly In the case of contact with air, the transmittance is reduced to about 10% at worst as compared with the case of a lens having no contamination, and illumination unevenness is deteriorated on the photosensitive substrate due to the transmittance unevenness.

As described above, when the contamination becomes severe and the illumination unevenness deteriorates, it is necessary to uniformly light-clean the entire lens. On the other hand, in the case of (1) or in the case of slight contamination in (2), it is possible to correct a change in transmittance by performing exposure amount control as described below. When measuring illumination unevenness, the amount of exposure at each location within the exposure range is measured using the emission light amount measuring device 12, and the difference between the maximum value and the minimum value at that time is obtained. When the value exceeds the value, it is determined that the illumination unevenness has deteriorated, and light cleaning is performed.

(Explanation of Exposure by Exposure Amount Control) FIG.
FIG. 4 is a diagram showing a time change characteristic of the transmittance when the projection optical system 10 whose transmittance is uniformly reduced is irradiated with laser light. Immediately after the start of laser beam irradiation, the transmittance greatly decreases, but then gradually increases and becomes almost saturated after a certain period of time. The decrease immediately after the start of laser irradiation is due to a change in the internal properties of the glass material of the lens, and the phenomenon that gradually recovers thereafter is that contaminants (water and organic substances) attached to the lens surface are removed from the lens surface by laser light irradiation. To be removed.

In this embodiment, the time-varying characteristics of the transmittance as shown in FIG. 10 are stored in the storage unit 141 in advance, so that the exposing operation is interrupted halfway by, for example, exchanging the photosensitive substrate. Or long time (about 10 hours)
When the exposure apparatus is stopped, first, the transmittance of the projection optical system is measured using the measuring devices 5 and 12 before the exposure operation is started again. Assuming that the transmittance at that time is A, when the exposure is started again (start time t0), the transmittance becomes as shown in FIG.
It is estimated that the value changes rightward from t0 of 0. Therefore, after the start of the exposure, the exposure amount of the light source 1 is adjusted based on the time change characteristic stored in the storage device 141 so that the illuminance on the sensitive substrate becomes appropriate. Thereafter, when the change in transmittance becomes small (time at that time is t1 and transmittance is B), normal exposure without exposure amount control is performed.

FIG. 11 is a flow chart showing the procedure of light cleaning after the manufacture of the exposure apparatus or after maintenance and the above-mentioned exposure control exposure, and shows the procedure from the start to the end of the exposure operation. Step S1 is a step of determining whether or not the exposure apparatus is immediately after assembly or after maintenance. If the exposure apparatus is immediately after assembly or after maintenance, the process proceeds to step S2. If not, the process proceeds to step S11. When the process proceeds to step S2, after performing light cleaning, the process proceeds to step S3 to perform normal exposure without controlling the exposure amount.
The detailed procedure of the optical cleaning will be described later. In step S4, it is determined whether or not the exposure has been interrupted. If the exposure has been interrupted, the process proceeds to step S11. If not, the process proceeds to step S5. Step S5 is a step for determining whether or not the exposure has been completed. If YES, a series of exposure procedures is completed, and if NO, the flow returns to step S3 to perform normal exposure.

On the other hand, when the process proceeds to step S11 in step S1, the transmittance in FIG.
Is determined to be smaller than B, that is, whether or not the transmittance requires the exposure amount control. If YES, step S12 is performed.
The process proceeds to step S3 if NO, and normal exposure is performed. Step S12 is a step of judging whether or not the illumination unevenness has deteriorated beyond the specified value on the photosensitive substrate. If the illumination unevenness has deteriorated, the process proceeds to step S2 to perform light cleaning and perform illumination unevenness. If there is no deterioration, the process proceeds to step S13 to perform exposure while controlling the exposure amount.
Step S14 is a step of judging whether or not the exposure time is equal to or longer than a predetermined time (t1-t0), that is, whether or not the change in transmittance is sufficiently small and is equal to or longer than B.
If YES, the flow advances to step S3 to perform normal exposure from the next exposure. On the other hand, if the determination is NO, the process returns to step S11.

Next, a specific procedure of the optical cleaning performed in step S2 will be described with reference to FIG. Step 1
Then, immediately after device production and after maintenance of the optical system,
N2 gas (nitrogen gas) is purged into the lens barrel containing the lenses, especially between the lenses. If the optical member for optical cleaning of the concave lens is arranged at the mask arrangement position 6 in the optical path in the following step 2, the exposure light is irradiated to the lens surface of the projection optical system 10 in step 3 to perform optical cleaning. In this case, after a light cleaning optical member of a concave lens is disposed at the mask arrangement position 6, a light cleaning optical member of a convex lens is disposed, and exposure light is irradiated on the lens surface of the projection optical system 10 to perform light cleaning. Do. In step 4, the measuring device 5
The transmittance of the projection optical system 10 is measured by using the steps 12 and 13, and when the measured transmittance becomes equal to or more than a predetermined value (B in FIG. 10), the optical cleaning is completed. If the value is smaller than the predetermined value B, light cleaning is performed until the transmittance becomes equal to or more than the predetermined value B.

In the above-described embodiment, the numerical aperture NA of the projection optical system 10 is adjusted by refracting the illumination light for exposure using the concave lens 8 or the convex lens 7 which is an optical member for cleaning.
o It is possible to illuminate the entire area. As a result, contaminants adhering to the lens surface in the numerical aperture NAo region can be removed by light cleaning using exposure light. Further, in the present embodiment, since the entire numerical aperture NAo region is illuminated by refracting the light flux, the amount of light is not reduced as in the method of diffusing the illumination light using the above-described diffusion plate, and the light emission is more effectively performed. Light cleaning can be performed.

In the above embodiment, the case where the concave lens 8 and the convex lens 7 are used as the cleaning optical member has been described. However, the present invention is not limited to this, and an optical member having a positive or negative refractive power can be used. . Further, a reflecting mirror having a refractive power may be provided on the illumination optical system side as a cleaning optical member. Further, in the present embodiment, by setting the numerical aperture of the illumination optical system to be equal to or larger than the effective diameter of an optical element such as a lens constituting the projection optical system, the light cleaning effect can be further enhanced. Further, a light cleaning light source may be provided separately from the exposure light source, and light cleaning may be performed using light from the light cleaning light source. However, in this case, it is preferable to use a light source that emits light having a wavelength substantially equal to the wavelength of the exposure light. Furthermore, in the above-described embodiment, the case where the ArF laser is used as the exposure light has been described.
The present invention can be applied to an exposure apparatus using UVL.

In the correspondence between the embodiment described above and the elements of the claims, the holding device 9 and the driving device 1
5 is a lens moving device, transmittance measuring device 13 is transmittance calculating means, control device 14 is calculating means and control means,
The storage unit 141 forms a storage device, and the measuring devices 5 and 12 and the transmittance measurement device 13 form a detection device.

[0035]

As described above, according to the present invention,
Even when the numerical aperture of the illumination optical system is smaller than the numerical aperture of the projection optical system, the light beam from the illumination optical system is refracted by the optical member, thereby reducing the light amount of the light beam. Lens surface area (numerical aperture area) corresponding to
Can be illuminated, and contaminants attached to the numerical aperture region of the lens surface can be effectively removed by light cleaning. In particular, according to the fifth aspect of the present invention, the optical member includes a positive lens and a negative lens, and the positive lens and the negative lens can be selectively used according to the lens configuration of the projection optical system. Irrespective of the lens configuration, the entire numerical aperture region of the lens surface of the projection optical system can be optically cleaned. According to the seventh aspect of the present invention, the mask and the optical member are held by the holding device, and the mask and the optical member are selectively arranged at the mask arrangement position, so that the time required for optical cleaning can be reduced. According to the twelfth aspect, since exposure is performed while controlling (a) light cleaning or (b) integrated exposure amount according to the degree of illumination unevenness, high-precision exposure can be performed.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating details of an illumination optical system 3.

FIG. 3 is a view for explaining a light beam before and after a mask arrangement position 6;

FIG. 4 is a view showing a light beam from a mask 30 to a photosensitive substrate 32.

FIG. 5 is a diagram illustrating a light cleaning method using a diffusion plate.

FIG. 6 is a diagram when a negative lens having a negative refractive power is used as an optical member.

FIG. 7 is a diagram when a positive lens having a positive refractive power is used as an optical member.

FIG. 8 is a diagram illustrating a method of setting a focal length f,
(A) is the case of the concave lens 8, (b) is the case of the convex lens 7.

9A and 9B are diagrams illustrating a state of a light beam passing through the projection optical system 10, wherein FIG. 9A illustrates a case where a concave lens is used as an optical member, and FIG. 9B illustrates a case where a convex lens is used.

FIG. 10 is a diagram showing a time change characteristic of the transmittance of the projection optical system.

FIG. 11 is a flowchart showing the procedure of exposure.

FIG. 12 is a diagram showing a specific procedure of light cleaning.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 light source 2 beam matching unit 3 illumination optical system 4 half mirror 5 incident light amount measuring device 7 convex lens 8 concave lens 9 holding device 10 projection optical system 11 wafer stage 12 emission light amount measuring device 13 transmittance measuring device 14 control device 15 driving device

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/30 515D 516Z

Claims (12)

[Claims] 1. A light beam from an illumination optical system is refracted by an optical member having a refractive power, and a projection optical system is illuminated with the light beam refracted by the optical member, thereby forming a lens surface of a lens constituting the projection optical system. An optical cleaning method for a projection optical system for an exposure apparatus, comprising performing optical cleaning. 2. The optical cleaning method according to claim 1, wherein the optical member is a positive lens or a negative lens disposed at an object plane position of the projection optical system, and the numerical aperture of the illumination optical system is reduced. When the numerical aperture of the projection optical system is NAo, the distance between the illumination area on the object surface farthest from the optical axis and the optical axis is d, the focal length f of the lens is expressed by the following equation (1). | F | ≦ d / [tan {sin ⁻¹ (NAo)} − tan {sin ⁻¹ (NAi)}] (1) An optical cleaning method characterized in that: 3. An exposure apparatus comprising: an illumination optical system for illuminating a mask on which a pattern is formed with a light beam from a light source; and a projection optical system for projecting a light beam transmitted through the mask onto a photosensitive substrate. An exposure apparatus, wherein an optical member for refracting a light beam from an optical system and entering the projection optical system is detachably provided. 4. The exposure apparatus according to claim 3, wherein the optical member is a positive lens or a negative lens disposed at an object plane position of the projection optical system, and the numerical aperture of the illumination optical system is set to NAi. When the numerical aperture of the projection optical system is NAo and the distance between the illuminated area on the object surface farthest from the optical axis and the optical axis is d, the focal length f of the lens is expressed by the following equation (2). 2] | f | ≦ d / [tan {sin ⁻¹ (NAo)} − tan {sin ⁻¹ (NAi)}] (2) 5. An exposure apparatus comprising: an illumination optical system for illuminating a mask on which a pattern is formed with a light beam from a light source; and a projection optical system for projecting a light beam transmitted through the mask onto a photosensitive substrate. When the numerical aperture of the optical system is NAi, the numerical aperture of the projection optical system is NAo, and the distance between the illumination area farthest from the optical axis and the optical axis on the object plane of the projection optical system is d, the following equation is obtained. (3) | f | ≦ d / [tan {sin ⁻¹ (NA ^o )} − tan {sin ⁻¹ (NAi)}] (3) and a positive lens having a focal length f that satisfies: An exposure apparatus comprising: a negative lens; and a lens moving device that selectively disposes one of the positive lens and the negative lens at an object plane position of the projection optical system. 6. The exposure apparatus according to claim 3, wherein an incident light amount measuring device for measuring a light amount of a light beam incident on the projection optical system, and a light beam emitted from the projection optical system. An emission light amount measuring device that measures the amount of light, a transmittance calculation unit that calculates the transmittance of the projection optical system based on the measurement values of the incident light amount measurement device and the emission light amount measurement device, and the transmittance calculation unit. An exposure apparatus, comprising: control means for controlling attachment / detachment of the optical member or selective placement of a positive lens or a negative lens by the lens moving device based on the calculated transmittance. 7. The exposure apparatus according to claim 3, further comprising a holding device for selectively disposing one of the mask and the optical member at a position where the mask is disposed in an optical path. 8. A light cleaning method for an optical system for an exposure apparatus, wherein a mask on which a pattern is formed is illuminated with exposure light to form a pattern image on a photosensitive substrate. A light cleaning method for an optical system for an exposure apparatus, wherein light cleaning performed by irradiating a lens surface of a lens constituting the optical system is performed prior to an exposure operation using the mask. 9. The light cleaning method for an optical system for an exposure apparatus according to claim 8, wherein a light beam from the light source for exposure is irradiated onto the lens surface instead of the light source for light cleaning. Cleaning method for optical system. 10. The optical cleaning method for an optical system for an exposure apparatus according to claim 9, wherein an optical member having a refractive power is provided in an optical path between the exposure light source for generating exposure light and the optical system. And an optical member for refracting a light beam from the exposure light source and irradiating the light onto the lens surface. 11. The optical cleaning method for an optical system for an exposure apparatus according to claim 8, wherein the transmittance of the optical system is equal to or more than a predetermined value after starting irradiation of the light beam onto the lens surface. A light cleaning method for an optical system for an exposure apparatus, wherein the light cleaning is terminated when the condition is satisfied. 12. An illumination optical system for illuminating a mask on which a pattern is formed with a light beam from a light source, a projection optical system for projecting a light beam transmitted through the mask onto a photosensitive substrate, the light source and the projection optical system. An optical member that is removably provided in an optical path therebetween and refracts a light beam from the light source; a detection device that detects a transmittance of the projection optical system; and a transmittance that is detected by the detection device. Calculating means for calculating illumination unevenness on the photosensitive substrate; a storage device in which a time change characteristic of the exposure light transmittance of the projection optical system is stored in advance; a transmittance detected by the detection device and the time change characteristic Control means for controlling the integrated exposure amount of the exposure light applied to the photosensitive substrate based on the following conditions: (a) an illumination method of the exposure light on the photosensitive substrate; If exceeds a predetermined value, after stopping the exposure operation by the mask, the optical member is inserted into the optical path instead of the mask, and the light beam refracted by the optical member is projected into the projection optical system. (B) when the transmittance of the projection optical system changes and the illumination unevenness is equal to or less than a predetermined specified value, An exposure method, wherein the exposure using the mask is performed while controlling the integrated exposure amount by the control means so that the integrated exposure amount on the photosensitive substrate is optimized.