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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a projection exposure apparatus used for forming fine patterns in, for example, semiconductor integrated circuits, liquid crystal displays, etc. More particularly, the present invention relates to a projection
exposure apparatus having a mechanism for maintaining the image-forming performance of its projection optical system in a favorable condition.
A photolithography process for forming a circuit pattern in a semiconductor device or the like uses a projection exposure apparatus (e.g., stepper) in which a pattern formed on a mask (a reticle) is transferred to a photosensitive substrate
(e.g., a semiconductor wafer, glass plate, etc.), which has been coated with a photoresist, through a projection optical system. The projection optical system of such a projection exposure apparatus is incorporated in the apparatus after high-level
optical designing, careful selection of a vitreous material, superfine processing of the vitreous material, and precise assembly adjustment. The present semiconductor manufacturing process mainly uses a stepper in which a reticle (or a photomask, etc.)
is irradiated with the i-line (wavelength: 365 nm) of a mercury-vapor lamp as illuminating light, and light passing through a circuit pattern on the reticle is passed through a projection optical system to form an image of the circuit pattern on a wafer
(or a glass plate, etc.), which has been coated with a photoresist. An excimer stepper that employs an excimer laser (KrF laser of wavelength 248 nm) as an illuminating light source has also been used for evaluation or research purposes.
With the steady increase of the degree of integration of VLSI and other similar devices, various methods have been developed for projection exposure apparatuses in order to perform transfer of finer patterns, such as optimization of illuminating
conditions, new schemes of exposure method, etc. For example, there has been proposed a method of improving the resolution and DOF (Depth of Focus) by previously obtaining the most suitable combination of a coherence factor of the illuminating optical
system (i.e., .sigma. value: the ratio of the numerical aperture (N.A.) of the illuminating optical system to the numerical aperture of the projection optical system) and the numerical aperture of the projection optical system for each specific pattern
line width, and selecting the most suitable combination for each pattern line width.
Among projection exposure apparatuses which are presently put to practical use, those which are designed for the i-line include a projection optical system having a numerical aperture (NA) of about 0.6. In general, for the same wavelength of
illuminating light used, as the numerical aperture of the projection optical system is increased, the resolution improves correspondingly. However, as the numerical aperture NA increases, the focal depth DOF becomes shallower in proportion to
.lambda./NA.sup.2, where .lambda. is the wavelength of illuminating light.
Incidentally, the resolution can be improved by increasing the image-side numerical aperture NAw (cf. the object-side numerical aperture NAr) of the projection optical system. That is, the resolution can be improved by increasing the pupil
diameter of the projection optical system and also increasing the effective aperture of an optical element, e.g., lens, which constitutes the projection optical system. However, the focal depth DOF decreases in inverse proportion to the square of the
numerical aperture NAw. Accordingly, even if a projection optical system of high numerical aperture can be produced, the required focal depth cannot be obtained; this is a considerable problem in practical use.
Assuming that the wavelength of illuminating light is 365 nm of the i-line and the numerical aperture NAw is 0.6, the focal depth DOF decreases to about 1 .mu.m (.+-.0.5 .mu.m) in total range. Accordingly, a resolution failure occurs in a
portion where the surface unevenness or the curvature is greater than DOF within one shot area (which is about 20 by 20 mm to 30 by 30 mm square) on the wafer.
In order to cope with these problems, the following various methods have been devised:
First, super-high resolution techniques, e.g., an annular zone illuminating method, modified light source method, phase shift method, etc., have been proposed. Among them, the annular zone illuminating method is a technique whereby the light
intensity distribution of an illuminating light beam in a pupil plane of an illuminating optical system or a plane neighboring it is regulated to an annular zone shape, and a reticle pattern is illuminated with such an illuminating light beam, as
disclosed in Japanese Patent Application Public Disclosure (KOKAI) No. Sho 61-91662. The modified light source method (also known as SHRINC method or inclined illuminating method) is a technique whereby the light intensity distribution of an
illuminating light beam in a pupil plane of an illuminating optical system or a plane neighboring it is made maximum at least at one position that is a predetermined amount off from the optical axis of the illuminating optical system, and thus the
illuminating light beam is applied to a reticle pattern at a predetermined angle of inclination, as disclosed in Japanese Patent Application Public Disclosure (KOKAI) Nos. Hei 04-101148, Hei 04-180612, Hei 04-225358, Hei 04-180613 and Hei 04-225514.
The phase shift method is carried out by using a phase shift reticle having a phase shifter (e.g., a dielectric thin film) whereby the phase of light passing through a specific one of light-transmitting portions of a circuit pattern formed on the
reticle is shifted by .pi.[rad] with respect to the phase of light passing through another light-transmitting portion, as disclosed, for example, in Japanese Patent Application Publication (KOKOKU) No. Sho 62-50811. The use of such a phase shift reticle
enables the resolution to be improved in comparison to the use of an ordinary reticle (i.e., a conventional reticle composed only of a light-transmitting portion and a light-blocking portion) for a predetermined pattern. It should be noted that typical
phase shift reticles include a spatial frequency modification type (Japanese Patent Application Publication No. Sho 62-50811), a half-tone type (Japanese Patent Application Public Disclosure (KOKAI) No. Hei 04-162039), a shifter shielding type, and an
edge enhancement type.
However, none of the above-described methods are effective for all reticle patterns, that is, all line widths and configurations. Therefore, it is necessary to select an illuminating method and conditions which are most suitable for each reticle
or reticle pattern. Accordingly, the projection exposure apparatus needs to have a structure which enables illuminating conditions (.sigma. value and other conditions) in the illuminating optical system to be varied. For example, when the phase shift
method is used, it is necessary to optimize the .sigma. value of the illuminating optical system.
Further, with the above-described methods, advantages such as an improvement in the resolution and an increase in the focal depth can be effectively obtained when a circuit pattern to be transferred is a periodic pattern having a relatively high
density. However, substantially no effect can be obtained for discrete patterns (isolated patterns) such as those called "contact hole patterns".
To enlarge the apparent focal depth for isolated patterns, e.g., contact hole patterns, an exposure method has been proposed, for example, in U.S. Pat. No. 4,869,999, in which exposure for one shot area on a wafer is carried out in a plurality
of successive exposure operations, and the wafer is moved along the optical axis of the projection optical system by a predetermined amount during the interval between each pair of successive exposure operations. This exposure method is called FLEX
(Focus Latitude enhancement Exposure) method and provides satisfactory focal depth enlarging effect for isolated patterns, e.g., contact hole patterns. However, since the FLEX method indispensably requires multiple exposure of contact hole pattern
images which are slightly defocused, a resist image obtained after development inevitably lowers in sharpness (the rise of the edge of the resist layer).
There has also been proposed a technique whereby the focal depth is increased during projection of contact hole patterns by a method different from the FLEX method wherein the wafer is moved along the optical axis during the exposure operation.
In the Super-FLEX method published in Extended Abstracts (Spring Meeting, 1991) 29a-ZC-8, 9, Japan Society of Applied Physics, a phase filter having a concentric amplitude transmittance distribution centered at the optical axis is provided on the pupil
plane (i.e., a Fourier transform plane with respect to the reticle) of the projection optical system so as to increase the effective resolution and focal depth of the projection optical system by the action of the filter.
The method wherein the transmittance distribution or phase difference is changed by filtering at the pupil plane of the projection optical system to thereby improve the focal depth as in the case of the Super FLEX method is generally known as
"multifocus filter method". The multifocus filter method is detailed in the paper entitled "Study of Imaging Performance of Optical System and Method of Improving the Same", pp. 41-55, in Machine Testing Institute Report No. 40, issued on Jan. 23,
1961. The method of improving the image quality by spatial filtering at the pupil plane is generally called a "pupil filter method". The assignee has proposed, as a new type of filter usable for such pupil filter method, a filter of the type that
blocks light only in a circular area in the vicinity of the optical axis (this filter will hereinafter be referred to as "light-blocking pupil filter") in Japanese Patent Application Public Disclosure (KOKAI) No. Hei 04-179958. The assignee has further
proposed a pupil filter method named "SFINCS method" that uses a pupil filter designed to reduce the spatial coherence of a bundle of image-forming rays from a contact hole pattern which passes through the pupil plane in U.S. patent application Ser.
No. 128,685 (Sep. 30, 1993).
Separately from the above-described pupil filters for contact hole patterns, pupil filters which are effective for relatively dense periodic patterns, e.g., line and space (L&S) patterns, have also been reported, for example, in "Projection
Exposure Method Using Oblique Incidence Illumination: Principle" (Matsuo et al.: 12a-ZF-7) in Extended Abstracts (Autumn Meeting, 1991), Japan Society of Applied Physics, and in "Optimization of Annular Zone Illumination and Pupil Filter" (Yamanaka et
al.: 30p-NA-5) in Extended Abstracts (Spring Meeting, 1992), Japan Society of Applied Physics. These filters are adapted to reduce the transmittance (i.e., the transmitted light intensity) of a circular or annular area centered at the optical axis (this
type of filter will hereinafter be referred to as "filter for L&S patterns"). In the L&S pattern filter method, the phase of light passing through the filter is not changed, unlike in the Super FLEX method.
Incidentally, the exposure apparatus is required to provide not only high resolution but also high alignment accuracy in formation of fine patterns of semiconductor integrated circuits, etc. That is, patterns of successive layers must be
transferred such that the pattern of the subsequent layer is accurately superimposed one the pattern of the preceding layer. Accordingly, the exposure apparatus is required not only to perform accurate detection of alignment marks on the wafer and
accurate alignment between the reticle and the wafer but also to use a projection optical system having minimal distortion. It is assumed that the distortion includes not only ordinary barrel form distortion and pincushion distortion but also random
variation of the image position caused mainly by possible manufacturing errors of lens elements.
Among various exposure methods using pupil filters, the Super FLEX method, the light-blocking pupil filter exposure method and the SFINCS method enable the resolution and focal depth to be effectively increased with respect to isolated contact
hole patterns among fine patterns which are to be transferred by exposure, as described above. However, for relatively dense (periodic) patterns, e.g., L&S patterns, these methods cause the resolution to lower undesirably. Therefore, when L&S patterns
or other relatively dense patterns are to be exposed, it is necessary to unload the pupil filter from the projection optical system or to exchange it for a filter for L&S patterns.
As has been described above, the projection optical system is completed through a combination of high-level designing and production, together with strict adjustment, to obtain a favorable projected image. Accordingly, if the pupil filter, which
changes the optical characteristics of the bundle of image-forming rays, is merely loaded, unloaded or exchanged, the image-forming characteristics of the projection optical system are undesirably changed and cannot accurately be maintained at the
desired level.
In the case of an exposure apparatus designed on the premise that it will be used only for specific patterns, e.g., contact hole patterns, the projection optical system may be adjusted with a specific pupil filter incorporated thereinto when the
system is set up, as a matter of course. However, the above-described problems inevitably arise in such a case where a single exposure apparatus is used for pattern transfer by exposure at various steps in order to increase the production efficiency as
in the case of the present production lines for semiconductor devices or the like.
Further, there may be cases where exposure is carried out by combining together information as to whether or not a pupil filter is present and about the type of pupil filter used, and the change of illuminating conditions (i.e., change of the
.sigma. value or use of annular zone illumination, etc.). In such cases, the condition of variation of the image-forming characteristics changes under each set of conditions. The condition of variation of the image-forming characteristics also changes
when the pupil filter method and a conventional high-resolution technique are employed in combination. When such a change of the image-forming characteristics is corrected through a correcting mechanism using parameters corrected as described above, no
problem will arise from the long-term standpoint. However, there is a problem that the image-forming characteristics have past hysteresis on account of the phenomenon of heat accumulation in the projection optical system. Accordingly, when the
illuminating conditions or the pupil filters are changed from one to another according to the type of reticle or reticle pattern, even if the amount of change of the image-forming characteristics is calculated and the characteristic change is corrected
immediately on the basis of the parameters corrected under the new conditions, the image-forming characteristics cannot accurately be corrected as long as the hysteresis according to the previous conditions remains in the projection optical system. This
problem may occur in the following two forms:
Firstly, owing to the distribution of heat generated under the illuminating conditions before the change of the operating conditions and by the pupil filter used under these conditions, image-forming characteristics obtained under the new
illuminating conditions and pupil filter (used after the condition change) do not coincide with the actual image-forming characteristics even if they are obtained by taking into consideration an offset component attendant on the change of the conditions. That is, since the offset component is determined under conditions where the projection optical system is not affected by the absorption of illuminating light, if the influence of the absorption of illuminating light before the change of the conditions
remains, it is necessary to additionally give an offset corresponding to the influence of the absorption of illuminating light. In other words, since the amount of change of the image-forming characteristics becomes discontinuous before and after the
change of illuminating conditions and pupil filters, the image-forming characteristics cannot be accurately corrected continuously when the illuminating conditions, together with the pupil filters, are changed from one to another.
Secondly, even if the first problem is solved by some method, a second problem arises from the exposure carried out under the new illuminating conditions and pupil filter. That is, immediately after the change of illuminating conditions and
pupil filters, the heat distribution condition under the previous conditions and that under the new conditions overlap each other, forming a state of being neither of the two heat distribution conditions, at a lens element in the vicinity of a pupil
plane of the projection optical system. Accordingly, even if an amount of change of the image-forming characteristics is calculated on the basis of the parameters under either of the illuminating conditions, the result of the calculation is not
coincident with the actual amount of image-forming characteristic change. The image-forming characteristics (i.e., the heat distribution condition in the projection optical system) in such a transient state cannot be expressed simply by a sum of the
characteristics before and after the change of illuminating conditions and pupil filters, and it is extremely difficult to calculate and correct a change of the image-forming characteristics in the transient state.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a projection exposure apparatus capable of obtaining favorable image-forming characteristics at all times even in a case where a plurality of pupil filters, which are different in optical
performance from each other, such as a pupil filter suitable for projection exposure of isolated patterns, e.g., contact hole patterns, and a pupil filter suitable for projection exposure of relatively dense patterns, e.g., L&S patterns, are exchangeably
used in the vicinity of a pupil plane of a projection optical system of the apparatus.
Another object of the present invention is to provide a projection exposure apparatus capable of correcting optical aberrations, particularly distortion and field curvature, which occur according to the combination of a projection optical system
and an optical filter when an optical filter suitable for a particular exposure method is used in a system which is provided with members for changing optical filters from one to another and members for changing image-forming characteristic correcting
members respectively corresponding to the optical filters, thereby enabling a single projection exposure apparatus to be used for various types of exposure method.
Still another object of the present invention is to provide a projection exposure apparatus capable of canceling distortion by previously measuring distortion of a projection optical system in a state where an optical filter is loaded, and
disposing an image-forming characteristic correcting member, which has been deformed so as to correct the distortion of the projection optical system, between a mask and the projection optical system or in the projection optical system.
A further object of the present invention is to provide a projection exposure apparatus capable of correcting field curvatures of a projection optical system, which are produced by respective optical characteristics of different types of optical
filter (including light-transmitting members), by disposing an image-forming characteristic correcting member formed from a concave (or convex) lens according to the type of optical filter used.
A still further object of the present invention is to provide a projection exposure apparatus capable of minimizing variation of image-forming characteristics due to difference in optical characteristics of various types of optical filter when
exchangeably used in the single projection exposure apparatus, and hence readily compatible with various types of exposure method.
A still further object of the present invention is to provide a projection exposure apparatus designed so that the effective resolution and focal depth of a projection optical system further increase when the apparatus uses an optical filter for
changing at least either the amplitude distribution or phase distribution of light passing therethrough, that is, a pupil filter of the type that blocks light incident on the center thereof, a pupil filter for L&S patterns, or a super FLEX pupil filter.
A still further object of the present invention is to provide a projection exposure apparatus designed so that when it uses an optical filter for reducing coherence, that is, a SFINCS pupil filter, the spatial coherence of a bundle of
image-forming rays from a contact hole pattern is reduced, and thus the resolution and the depth of focus increase.
A still further object of the present invention is to provide a projection exposure apparatus compatible with an exposure method requiring no optical filter when an optical filter changing member has a light-transmitting member which does not
change optical characteristics, that is, a simple plane-parallel plate.
A still further object of the present invention is to provide a projection exposure apparatus designed so that, even when a pupil filter is loaded into or unloaded from a projection optical system or exchanged in a case where the resolution and
the depth of focus are controlled by employing a pupil filter method, image-forming characteristics of the projection optical system are maintained in conditions which are close to the desired conditions by taking into consideration the accumulation of
heat in the projection optical system, thereby enabling pattern exposure to be satisfactorily effected with respect to a photosensitive substrate.
A still further object of the present invention is to provide a projection exposure apparatus designed so that image-forming characteristics of a projection optical system are constantly maintained in conditions which are close to the desired
conditions by correcting a change of the image-forming characteristics through an image-forming condition adjusting device, thereby enabling pattern exposure to be satisfactorily effected with respect to a photosensitive substrate.
A still further object of the present invention is to provide a projection exposure apparatus capable of accurately correcting image-forming characteristics of a projection optical system in a quantitative manner by changing parameters with a
parameter changing circuit according to the type of pupil filter set in the projection optical system, obtaining an amount of change of the image-forming characteristics with an image-forming characteristic computing device using the parameters which
have been changed, and correcting the image-forming characteristics through an image-forming condition adjusting device on the basis of the determined amount of change of the image-forming characteristics.
A still further object of the present invention is to provide a projection exposure apparatus having an image-forming characteristic computing device capable of accurately calculating an amount of change of image-forming characteristics by using
an accumulated energy measured with an accumulated energy measuring device, thus enabling the image-forming characteristics to be maintained in conditions which are closer to the desired conditions.
A still further object of the present invention is to provide a projection exposure apparatus designed so that, in a case where distortion as one of image-forming characteristics of a projection optical system is aggravated by unloading or
exchange of a pupil filter, a distortion correcting plate that cancels the aggravated distortion is inserted into, for example, a space between a mask and the projection optical system, thereby making it possible to prevent aggravation of the
image-forming characteristics.
In order to attain the above-described objects, the present invention provides a projection exposure apparatus having an illuminating system (1 to 14) for irradiating a mask (R), which has a pattern to be transferred, with illuminating light
(ILB) for exposure, and a projection optical system (PL) for projecting an image of the pattern of the mask (R) onto a photosensitive substrate (W) with predetermined image-forming characteristics under the illuminating light (ILB). The projection
exposure apparatus is provided with an optical filter changing member (40 to 42) for selecting one of a plurality of optical filters (PF1 and PF2) that change at least one of optical characteristics of light from the mask (R) by respective amounts which
are different from each other. The optical characteristics include an amplitude distribution, a phase distribution and a condition of polarization. The optical filter changing member further disposes the selected optical filter on a pupil plane (FTP)
in the projection optical system (PL) or on a plane in the neighborhood of the pupil plane (FTP). The projection exposure apparatus is further provided with a correcting member-changing member (15 and 16) for selecting one of a plurality of
image-forming characteristic correcting members (CP) that correct the image-forming characteristics of the projection optical system (PL) by respective amounts which are different from each other in accordance with the optical filter (PF1 or PF2)
selected by the optical filter changing member, and for disposing the selected image-forming characteristic correcting member (CP) between the mask (R) and the substrate (W).
In this case, one of the plurality of optical filters (PF1 and PF2) may be an optical filter that changes at least either the amplitude distribution or phase distribution of light from the mask (R) according to the position on a plane in the
projection optical system (PL) where it is disposed.
One of the plurality of optical filters (PF1 and PF2) may be an optical filter that reduces coherence between light passing through a predetermined area of a plane in the projection optical system (PL) where it is disposed and light passing
through the other area of the plane.
The optical filter changing member (40 to 42) preferably has a light-transmitting member (PF3) that does not change the optical characteristics of light from the mask (R).
The plurality of image-forming characteristic correcting members (CP) may be adapted to correct distortion of the image projected by the projection optical system (PL) by respective amounts which are different from each other.
Alternatively, the image-forming characteristic correcting members (CP) may be adapted to correct the curvature of field of the image projected by the projection optical system (PL) by respective amounts which are different from each other.
In addition, the present invention provides a projection exposure apparatus having, as shown for example in FIGS. 8 and 9, an illuminating system (1 to 4, 11A and 11B) for illuminating a mask (R) having a pattern to be transferred, and a
projection optical system (PL) for projecting an image of the mask pattern onto a photosensitive substrate (W) with predetermined image-forming characteristics under the illuminating light applied from the illuminating system. The projection exposure
apparatus is provided with an optical characteristic varying member (31) for changing at least one of optical characteristics on a pupil plane in the projection optical system (PL) or on a plane in the neighborhood of the pupil plane. The optical
characteristics include polarizing characteristic distribution, transmittance distribution and phase distribution. The projection exposure apparatus is further provided with an image-forming condition adjusting device (24, 14, 18, 21, 36 and 38) for
adjusting the condition of image formation of the image projected onto the photosensitive substrate (W) by the projection optical system (PL), and an image-forming characteristic correcting member (6) for correcting through the image-forming condition
adjusting device a change of a predetermined image-forming characteristic of the image projected onto the photosensitive substrate (W) by the projection optical system (PL), which is caused when the optical characteristic varying member is used to change
the corresponding optical characteristic.
In this case, the image-forming characteristic correcting member (6) may have a parameter changing member (62), an image-forming characteristic computing device (64), and a controller (65). The parameter changing member (62) changes a parameter
used to calculate an amount of change of the predetermined image-forming characteristic in accordance with the optical characteristic changed by the optical characteristic varying member (30A and 31). The image-forming characteristic computing device
(64) obtains an amount of change of the predetermined image-forming characteristic by using the parameter changed by the parameter changing member. The controller (65) corrects the change of the predetermined image-forming characteristic through the
image-forming condition adjusting device on the basis of the amount of change of the image-forming characteristic obtained by the image-forming characteristic computing device (64).
In this case, it is preferable to provide an accumulated energy measuring device (27 and 24) for obtaining an amount of energy accumulated in the projection optical system (PL) by the illuminating light applied from the illuminating system, so
that the image-forming characteristic computing device (64) calculates a change of the predetermined image-forming characteristic on the basis of the accumulated energy obtained by the accumulated energy measuring device and the parameter set by the
parameter changing member.
It is also possible to provide an accumulated energy measuring device (27 and 24) for obtaining an amount of energy accumulated in the projection optical system (PL) by the illuminating light applied from the illuminating system, and an exposure
judging device (64) which suspends exposure of the mask pattern from the time the optical characteristic varying member changes the corresponding optical characteristic until the accumulated energy obtained by the accumulated energy measuring device
reduces to a level lower than a predetermined allowable energy level by thermal diffusion.
In each of the above-described arrangements, a distortion correcting plate (33A) may be inserted into the space between the mask (R) and the photosensitive substrate (W) to correct distortion of the image projected onto the photosensitive
substrate (W) by the projection optical system (PL), which is caused when the optical characteristic varying member is used to change the corresponding optical characteristic.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the arrangement of one embodiment of the projection exposure apparatus according to the present invention.
FIG. 2 is a plan view showing pupil filters as shown in FIG. 1, together with a pupil filter exchanging mechanism.
FIG. 3 is a sectional view taken along the line A--A' line in FIG. 2.
FIG. 4 illustrates the way in which distortion is corrected by a filter correcting member in the embodiment of the present invention.
FIG. 5 shows a part of the filter correcting member shown in FIG. 4.
FIG. 6 is a fragmentary sectional enlarged view showing another example of the filter correcting member used in the embodiment of the present invention.
FIG. 7 is a sectional view showing still another example of the filter correcting member used in the embodiment of the present invention.
FIG. 8 is a partly-cutaway schematic view showing the arrangement of another embodiment of the projection exposure apparatus according to the present invention.
FIG. 9 is a functional block diagram showing the arrangement of a main control system (6) used in the embodiment shown in FIG. 8.
FIG. 10 is a partly-cutaway view showing the arrangement of a mechanism for correcting spherical aberration in a projection optical system (PL) used in the embodiment shown in FIG. 8.
FIGS. 11(a) and 11(b) are enlarged plan views showing examples of the arrangement of a pupil filter used in the embodiment shown in FIG. 8.
FIG. 12 is an enlarged plan view showing one example of an aperture stop disposed on a turret plate (4) in the arrangement shown in FIG. 8.
FIGS. 13(a) and 13(b) illustrate the way in which image-forming characteristics change depending upon the illuminating light intensity distribution at a pupil plane in the projection optical system.
FIGS. 14(a) and 14(b) show a change in the amount of shift of the best focus plane when the operating condition is changed from an exposure condition where no pupil filter is present through an exposure suspending condition to an exposure
condition where a pupil filter is present.
FIG. 15 shows a change in the amount of shift of the best focus plane immediately after the operating condition has been changed between an exposure condition where no pupil filter is present and an exposure condition where a pupil filter is
present without providing an exposure suspending condition therebetween.
FIG. 16 shows an advantageous effect obtained by providing an exposure suspending condition as an intermediary condition when the operating condition is changed between an exposure condition where no pupil filter is present and an exposure
condition where a pupil filter is present.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
One embodiment of the projection exposure apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. The projection exposure apparatus of this embodiment transfers a pattern drawn
on a pattern surface, which is defined on the lower side (projection optical system side) of a reticle, onto a wafer through a projection optical system by the stepper method.
FIG. 1 shows the projection exposure apparatus of this embodiment. Referring to FIG. 1, illuminating light beam emitted from a light source 101, which is a mercury-vapor lamp, enters an interference filter 106 through an elliptical mirror 102, a
collimator lens 104 and a short-wavelength cut filter 105. The interference filter 106 selects illuminating light ILB consisting of only the i-line (wavelength: 0.365 .mu.m), for example, and the illuminating light ILB then enters a fly-eye lens 107.
The illuminating light is selectively passed or intercepted under the control of a shutter 103 which is disposed in the vicinity of the secondary focal point of the elliptical mirror 102. It should be noted that the illuminating light ILB is not
necessarily limited to the i-line, and a wavelength other than the i-line or a plurality of wavelengths may be used. Further, the light source 101 for exposure is not necessarily limited to an emission line lamp such as a mercury-vapor lamp. For
example, an excimer laser light source, a metal vapor laser or YAG laser harmonic generator, etc. may be used.
The exit-side surface of the fly-eye lens 107 forms a Fourier transform plane in the illuminating optical system with respect to the reticle pattern, where a surface illuminant image (i.e., a plane composed of the set of a plurality of point
light sources corresponding to the element lenses of the fly-eye lens 107) is formed, and where an aperture stop of an illuminating system (hereinafter referred to as ".sigma. stop") 108, which defines the shape and size of the surface illuminant image,
is also provided.
The illuminating light emanating from the fly-eye lens 107 and passing through the .sigma. stop 108 illuminates a reticle R on a reticle stage RST via a mirror 109, a first relay lens 110, a reticle blind (field stop) 111, a second relay lens
112, a mirror 113 and a condenser lens 114. The reticle blind 111 is placed in conjugate relation to the pattern surface of the reticle R with respect to a composite system of the relay lens system 112 and the condenser lens 114. Thus, the illuminating
field on the reticle R can be varied by the action of the reticle blind 111. The first relay lens system 110 is set so that the .sigma. stop 108 (surface illuminant image) forms a Fourier transform plane with respect to the reticle blind 111 or the
pattern surface of the reticle R.
A filter correcting member CP for correcting image-forming characteristics is disposed between the reticle R and the projection optical system PL. The filter correcting member CP is secured to a load arm 115 which is controlled by a load arm
controller 116. The filter correcting member CP may be exchanged for another filter correcting member according to need. The action and effect of the filter correcting member CP will be described later. The bundle of rays passing through the filter
correcting member CP is converged to form an image of the pattern of the reticle R on a wafer W. It should be noted that in FIG. 1 the optical path from the reticle R to the wafer W shows a chief ray in a bundle of image-forming rays from each pattern on
the reticle R. In this embodiment, a pupil plane FTP in the projection optical system PL, i.e., an optical Fourier transform plane with respect to the reticle R, is set so as to lie in a hollow space (where no lens or other element is present) between
the reticle R and the wafer W, and a pupil filter PF1 is provided on the pupil plane FTP or a plane neighboring to it. The pupil filter PF1 will also be described later. Although the system shown in FIG. 1 employs Koehler illumination in which the
position of the pupil plane FTP (conjugate to the surface illuminant image | | |
