JPH0684757A - Projection aligner - Google Patents

Abstract

PURPOSE:To measure the actual quantity of aberration so as to cope with the variation of the image forming characteristic of a projection exposing device by making light to incident to a mask by irradiating an opening pattern on a stage from the stage side and making reflected light from the mask to incident to a photoelectric conversion element through a projecting optical system and the opening pattern, and then, finding the quantity of aberration. CONSTITUTION:A pattern plate provided on a stage 15 and having a prescribed opening pattern is irradiated from a stage 15 side while the stage 15 is moved in the direction of the optical axis AX. Then reflected light IL' from a mask R through a projecting optical system PL is received by means of a photoelectric conversion element 26. In addition, the quantity of aberration of the optical system PL is found by inputting the signal of a light receiving optical system 18 which measures the position of the stage 15 in the direction of the optical axis AX and a signal obtained from the element 26 to an aberration detecting system 28. Therefore, the quantity of aberration can be actually measured and the exposure can be performed in an aberration-corrected state or exposing operation can be performed in accordance with the aberration.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus, and more particularly to a projection exposure apparatus used for manufacturing semiconductor integrated circuits, liquid crystal substrates, thin film magnetic heads and the like.

[0002]

2. Description of the Related Art In recent years, extremely high imaging performance has been required in projection exposure apparatuses such as semiconductor manufacturing related apparatuses.
A conventional apparatus of this type is equipped with a projection optical system in which various aberrations are highly corrected. Usually, the amount of aberration of the projection optical system is checked by using a special mask. A special pattern for aberration check is drawn on this special mask, and this special pattern is exposed on a test substrate, and after development, the amount of aberration is checked by observing the exposed pattern with a microscope or the like. . For example, the spherical aberration is checked by obtaining the best focus positions of patterns having different line widths.
Specifically, the stages are sequentially positioned in the optical axis direction,
While the test substrate coated with the photosensitizer is sequentially moved in the optical axis direction, a pattern having a plurality of line widths is exposed and developed. As a result, a pattern having each line width corresponding to the distance from the projection optical system in the optical axis direction is formed on the substrate. The line width of each pattern formed on the substrate is measured with an electron microscope or the like, and the actual dimension of the measured line width and the distance from the optical axis of the projection optical system are plotted. The midpoint of the position of the board where the predetermined line width is maintained (the midpoint between the maximum position and the minimum position of the board position where the predetermined line width is maintained)
If is determined to be the best focus, the best focus position of each line width can be obtained from the curve of the plotted data. Here, when spherical aberration occurs, a shift occurs in the best focus position of each line width. The astigmatism can be checked by finding the difference between the best focus positions of patterns having different directions. Next, as an example of checking coma aberration, there is a method of observing a difference in line width between both ends of a plurality of continuous marks having the same line width.

The respective aberrations are obtained by the above method, and the image forming characteristics of the projection optical system are optimized. For example, the distance between the lens elements inside the projection optical system is adjusted so that each aberration is finally set to the allowable value or less. However, each aberration is not always constant, and may change due to temperature change, atmospheric pressure change, and temperature rise of the projection optical system due to absorption of illumination light by the projection optical system. Particularly, the temperature change of the projection optical system due to the absorption of the illumination light may cause a temperature distribution in the lens element inside the projection optical system, which may cause a non-negligible aberration change. In such a case, it is impossible to check the aberration amount during the exposure operation by the above method.

Therefore, conventionally, a method has been proposed in which the amount of exposure energy accumulated in the projection optical system is calculated, and when the accumulated amount exceeds a certain reference value, the exposure operation is temporarily stopped and the exposure operation is not used in a place where the aberration has deteriorated. Was there. Specifically, the relationship between the amount of aberration generated in advance and the amount of heat accumulated in the projection optical system and the heat absorption characteristics of the projection optical system are obtained. During the actual exposure operation, the amount of heat accumulated in the projection optical system is sequentially calculated from the numerical model of the heat absorption characteristics, the mask transmittance, and the shutter opening / closing signal that have been obtained in advance, and the amount of generated aberration is calculated. When the amount of aberration exceeds the allowable value, if the exposure operation is temporarily stopped, the amount of heat accumulated in the projection optical system is attenuated and the amount of aberration becomes less than the allowable value, and the exposure operation can be performed again. Such an exposure method is disclosed in, for example, JP-A-63-291417.

[0005]

In the prior art as described above, the calculated aberration amount is merely a predicted value, and the actual aberration generation amount is unknown. Particularly in recent years, as a technique for increasing the resolution, ring-shaped illumination, or JP-A-4-180612 or JP-A-4-180.
The tilt illumination from a plurality of directions as disclosed in Japanese Patent No. 613 is proposed, and the phase shift mask as disclosed in Japanese Patent Publication No. 62-50811 is also proposed. When these techniques are used, the intensity distribution of illumination light inside the projection optical system differs. Therefore, even if the illumination energy is the same, the amount of aberration generated depending on the illumination condition or the reticle is different, and it is difficult to predict the amount of aberration generation.
Therefore, the conventional method of predicting the amount of aberration cannot cope with a desired exposure operation. The present invention has been made in view of such conventional problems, and an object of the present invention is to provide an apparatus capable of measuring an actual amount of aberration and capable of coping with fluctuations in imaging characteristics.

[0006]

In order to solve the above problems, in the present invention, the illumination light from the light source (1) is masked (R).
The illumination optical system (6, 7, 10) for irradiating the substrate, the projection optical system (PL) for forming an image of the mask pattern (PA) on the photosensitive substrate (W), and the projection optical system for holding the photosensitive substrate and In a projection exposure apparatus having a stage (15) movable in an optical axis (AX) direction and a direction perpendicular to the optical axis, a reference member (19) provided on the stage and having a predetermined opening pattern; A light receiving unit that illuminates the opening pattern from the stage side while moving in the optical axis direction, and receives the light that reaches the mask through the projection optical system and is reflected by the mask through the projection optical system and the opening pattern; A stage position measuring means for measuring the position of the stage in the axial direction; and an aberration amount calculating means for obtaining the aberration amount of the projection optical system from the signal waveform obtained from the photoelectric detecting means are provided.

[0007]

In the present invention, a predetermined opening pattern provided on the stage is illuminated from the stage side with light having a wavelength substantially equal to the exposure light, and this illumination light is made incident on the mask through the projection optical system. Then, the illumination light reflected by the mask is made incident on the photoelectric detector through the projection optical system and the aperture pattern. The amount of aberration is obtained using the waveform of the photoelectric detection signal from this photoelectric detector. Therefore, it is possible to omit the steps such as exposure to the test substrate, development, and measurement, and it is not necessary to provide a dedicated pattern on the mask. it can. As a result, exposure is performed with aberration occurring,
There is no inconvenience of releasing defective products.

[0008]

1 is a plan view showing a schematic structure of a projection exposure apparatus according to an embodiment of the present invention. In the figure, a light source 1 such as an ultra-high pressure mercury lamp generates illumination light (i-line or the like) IL in a wavelength range that sensitizes a resist layer. As the light source for exposure, in addition to bright lines such as mercury lamps, laser light sources such as KrF and ArF excimer lasers, metal vapor lasers and YAs
A harmonic of G laser may be used. The illumination light IL is reflected by the elliptical mirror 2 and focused on the second focal point f ₀ thereof, and then enters the mirror 5, the collimator lens 6, and the fly-eye lens 7. A variable diaphragm 8 is provided on the exit side of the fly-eye lens, so that the illumination condition can be changed according to the type of reticle and the periodicity of the pattern. This change of the illumination condition is executed by driving the variable diaphragm 8 with the motor 9.

Further, a shutter 3 (for example, a rotary shutter having four blades) 3 for closing and opening the optical path of the illumination light IL by a motor 4 is arranged near the second focal point f ₀ . The illumination light IL that has passed through the variable diaphragm 8 is relay lens 1
2a, 12b and a variable blind 11 for limiting an illumination area on the reticle R, and an optical system 10 including a condenser lens 13 are incident on the reticle R after reaching a mirror 14 where they are reflected almost vertically downward. Pattern area PA
To illuminate with a substantially uniform illuminance. The reticle R is mounted on the reticle stage RS, and the reticle stage RS
Can finely move the reticle R in the XY directions. Further, the reticle stage RS is capable of finely moving the reticle R in the Z direction (optical axis direction) by the drive unit 51, changing the distance between the reticle R and the projection optical system PL, and setting the reticle R on a plane perpendicular to the optical axis AX. Can be tilted against. The illumination light IL that has passed through the pattern area PA enters the projection optical system PL that is telecentric on both sides, and the projection optical system PL forms a projected image of the circuit pattern of the reticle R on the wafer W. A resist layer is formed on the surface of the wafer W, and the wafer stage 15 is placed so that the surface of the wafer W substantially matches the best image plane.
The circuit pattern is held on the upper surface of the wafer W and is image-projected so as to be superimposed on one shot area on the wafer W. (FIG. 1 is not imaged on the wafer W for convenience of explanation.) The wafer W is vacuum-sucked by the wafer holder 16 and held on the wafer stage 15 via this holder 16. The wafer stage 15 can be tilted in any direction with respect to the best image plane of the projection optical system PL and can be finely moved in the optical axis direction (Z direction), and can be moved in a two-dimensional direction (X, X-axis) by a step-and-repeat method. When the transfer exposure of the reticle R onto one shot area on the wafer W is completed, it is stepped to the next shot position.

Further, in FIG. 1, irradiation optics for supplying an imaging light beam for forming an image of a pinhole or a slit toward the best image plane of the projection optical system PL from an oblique direction with respect to the optical axis AX. System 17 and light-receiving optical system 1 for receiving the reflected light flux of the image-formed light flux on the surface of the wafer W through the slit.
An oblique incidence type focusing system (wafer position detection system) 8 is provided. The structure of this focusing system is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-168112.
The position of the wafer surface in the direction (Z direction) with respect to the image plane is detected, and the focus state of the wafer W and the projection optical system PL is detected. In the present embodiment, a parallel flat glass plate (plane parallel) (not shown) provided in advance inside the light receiving optical system 18 so that the best image plane in the design becomes the zero point reference.
The angle of is adjusted and the focusing system is calibrated.

Next, the aberration detection system will be described. A pattern plate 19 is provided on the wafer stage 15, and a predetermined aperture pattern for aberration detection is drawn on the pattern plate 19 as shown in FIG. Here, the pattern plate 19
The pattern plate 19 is provided so that the surface of the is substantially flush with the surface of the wafer W. The light beam IL ′ having substantially the same wavelength range as the illumination light IL has a bifurcated fiber 20, a variable diaphragm 21, relay lenses 23a and 23b, a mirror 24,
The pattern plate 19 is illuminated from the wafer stage 15 side (downward) via the condenser lens 25. Illumination light IL '
The illumination light IL from the light source 1 may be branched, or a light source that emits light having the same wavelength as the illumination light IL may be separately provided.
The light flux emitted from the pattern opening of the pattern plate 19 is imaged on the pattern surface PA of the reticle R via the projection optical system PL, and the reflected light is imaged again on the pattern plate 19 via the projection optical system PL. . The light flux reaching the pattern plate 19 again passes through the opening of the pattern 19, passes through the condenser lens 25, the mirror 24, the relay lenses 23a and 23b, the variable diaphragm 21, and the bifurcated fiber 20, and reaches the photoelectric conversion element 26. The main control system 29 controls the motor 27 to move the wafer stage 15 in the Z direction, and at the same time, the aberration detection system 28 in the main control system 29 transmits the signal S3 from the photoelectric conversion element 26 to the light receiving optical system of the focus detection system. Received in synchronism with the signal from system 18. Thereby, the aberration detection system 28 obtains the output of the photoelectric conversion element 26 with respect to the position of the wafer stage 15 in the Z direction. The main control system 29 also controls the motor 9 that drives the variable diaphragm 8 and the motor 22 that drives the variable diaphragm 21. The aberration detection system 28 can be used for focus position detection (detection of the image plane of the projection optical system PL) of the TTL (through-the-lens) method, and can detect focus position and aberration at the same time. The main control system 29 controls not only the drive unit 51 but also the entire device. Here, the aperture pattern is a combination of patterns in multiple directions as shown in FIG. 2 in consideration of astigmatism.

The principle of finding the focal position by the aberration detection system 28 will be briefly described with reference to FIG. FIG. 3A shows the light amount distribution of the image of the aperture pattern 19 which is reflected by the mask R when the reticle R and the pattern plate 19 are slightly displaced from the conjugate position and is imaged again through the projection optical system PL. FIG. 3B shows an image of the aperture pattern 19 which is reflected by the mask R and is imaged again through the projection optical system PL when the mask R and the pattern plate 19 are in a conjugate position. FIG. 3C is a diagram showing a light amount distribution, and FIG. 3C shows a reference pattern plate 1.
9 shows an example. In FIG. 3C, reference numeral 19a is a light shielding portion made of a chromium vapor deposition film or the like.

When the reference pattern plate 19 and the pattern surface of the reticle R are in a conjugate position, the intensity distribution of the image of the reference pattern plate 19 is as shown by distribution Ca in FIG. 3B.
The light and dark distribution of the reference pattern plate 19 itself substantially matches, and almost the most of the light returns to the wafer stage 15 via the transmissive part of the reference pattern plate 19. On the other hand, when the reference pattern plate 19 is slightly deviated from the surface conjugate with the pattern surface of the reticle R, the image of the reference pattern plate 19 re-imaged by the reflected light from the reticle R is distributed as shown in FIG. The contrast decreases as shown by Cb. In this case,
The shaded portion in the distribution Cb of (a) overlaps the light-shielding portion (non-transmissive portion) 19a of the reference pattern 19 of FIG. 3C, cannot pass through the reference pattern 19, and the photoelectric conversion element 26 The amount of light that reaches is reduced.

FIG. 4 shows a detection signal S from the photoelectric conversion element 26.
3 is a diagram showing output values from the photoelectric conversion element 26 when the output value of 3 is the vertical axis and the Z coordinate of the pattern plate 19 is the horizontal axis, and the aperture pattern 19 is moved in the Z direction. The position of the pattern plate 19 in the Z direction can be obtained from the output from the light receiving optical system 18 of the focus detection system. In FIG. 4, the Z coordinate Za when the output value S3 of the photoelectric conversion element 26 is the largest (the peak value) is shown when the reticle R and the pattern plate 19 are at substantially conjugate positions. ). In FIG. 4, the Z coordinate Zb when the output value from the photoelectric conversion element 26 is below the peak value is shown when the reticle R and the pattern plate 19 are slightly displaced from the conjugate position. This corresponds to the case of (a).

As described above, when the reference pattern plate 19 reaches the focal position of the projection optical system PL, the detection signal S3 output from the photoelectric conversion element 26 becomes maximum. The signal waveform of the detection signal S3 is a waveform that falls in a concave shape on both sides of the peak as shown in FIG. 4, for example, due to the interference phenomenon of the light flux. Next, the configuration of the correction means for correcting the image formation state will be described. In this embodiment, the imaging characteristics (spherical aberration, coma aberration, astigmatism, curvature of field, etc.) are corrected by driving the lens elements of the projection optical system PL or changing the pressure between the lens elements. It is composed. Therefore, some of the optical elements of the projection optical system PL are movable. Further, the pressure between the optical elements of the projection optical system PL is variable. FIG. 5 is a view for partially explaining the apparatus of FIG. 1, and is a view showing a drive unit of the reticle R, a drive unit of optical elements of the projection optical system PL, and a mechanism for varying the pressure between the optical elements. The lens element 33 closest to the reticle R is fixed by a supporting member 34, and is provided on a supporting member 36 via a driving element 35. The support member 36 is fixed to the lens barrel 52 of the projection optical system PL. The drive element 35 is composed of drive elements 35a, 35b, 35c (only 35a, 35b are shown in FIG. 5) arranged at positions rotated by 120 °, and each drive element can be independently controlled by the drive element control unit 38. Has become. Although the lens element 33 is shown as one lens in FIG. 5, it is assumed that it is a lens element composed of three (or two) lens groups, and each lens group forming the lens element 33 is a driving element. (Not shown) allows fine movement independently.

The lens element 44 near the pupil plane P1 of the projection optical system PL is fixed by a supporting member 45, and is provided on a supporting member 47 via a driving element 46. The support member 47 is fixed to the lens barrel 52 of the projection optical system PL. The driving elements 46 are arranged at positions rotated by 120 °, and the driving elements 46a, 46b, 46c are arranged at the positions.
(Only 46a and 46b are shown in FIG. 5), and each drive element can be independently controlled by the drive element controller 48. As the driving elements 35 and 46, for example, an electrostrictive element or a magnetostrictive element is used, and the displacement amount of the driving element according to the voltage or magnetic field applied to the driving element is obtained in advance. Although not shown here, in consideration of the hysteresis of the drive element, a capacitive displacement sensor as a position detection device,
A differential transformer or the like is provided near the drive element.
As a result, the position of the drive element corresponding to the voltage or magnetic field applied to the drive element can be monitored, so that highly accurate drive is possible. The fine movements of the lens elements 33 and 44 change the distance between the lens elements, incline the lens elements with respect to the plane perpendicular to the optical axis AX, or move the lens elements within the plane perpendicular to the optical axis AX. Done. The configuration and operation of driving such an optical element are disclosed in detail in Japanese Patent Laid-Open No. 4-134813.

In this embodiment, the reticle R is controlled by controlling the drive element 35 described above by the drive element controller 38.
It is possible to move the lens element 33 close to
The lens element 33 is selected so that the influence of the coma aberration, the curvature of field, and the like on the image forming characteristics can be controlled more easily than other lens elements. Further, since the movable lens element 33 is composed of three groups, it is possible to widen the movement range by moving the lens element while suppressing variations of other various aberrations. Further, by controlling the drive element 46 described above by the drive element control unit 48, the lens element 44 near the pupil plane P1 can be moved, and the lens element 44 affects the spherical aberration to other lens elements. The one that is larger and easier to control is selected.

The lens elements 37 and 50 are a lens barrel 52.
The air pressure adjusting device 39 adjusts the air pressure in the lens chamber between the lens element 33 and the lens element 37, and the air pressure adjusting device 49 controls the air pressure inside the lens chamber between the lens element 44 and the ends element 50. Adjust the air pressure of. As described above, it is possible to correct aberrations and the like by changing the image forming characteristics of the projection optical system by changing the pressure of the air portion between the lens elements.
454.

Two cylindrical lenses 40 and 41 are provided in the vicinity of the pupil plane P1, and these are relatively rotated by the drive units 42 and 43 or the lens interval is changed. Controls astigmatism. The cylindrical lenses 40 and 41 are arranged in directions orthogonal to each other, and by rotating them relatively, the refractive index in the X and Y directions is changed. Then, these lenses are relatively rotated so that the X and Y components cancel each other out, and the astigmatism components generated in the other lens elements are removed. The main control system 29 includes the drive element control units 38 and 48, the drive units 42 and 43, the atmospheric pressure adjusting device 39,
Control 49.

Next, the aforementioned variable diaphragm 8 and projection optical system PL
The variable diaphragm 30 will be briefly described. Generally, the numerical value indicating the characteristics of the illumination system is the numerical aperture N of the projection optical system.
A and the σ value representing the coherency of the illumination light are used. The numerical aperture and σ value will be described with reference to FIG. In FIG. 6, since the aperture stop 30 is provided on the pupil plane P1 of the projection optical system PL, that is, the Fourier transform plane of the mask pattern PA, the maximum angle at which the light flux from the reticle R side of the projection optical system PL can pass. θ _R and the maximum angle θ _W of the light flux incident on the wafer W (pattern plate 19) side from the projection optical system PL are limited to predetermined values. Projection optical system PL
The numerical aperture _PL is sin θ _W , and assuming that the projection magnification is 1 / m, sin θ _R = sin θ _W / m.

[0021]

## EQU1 ## σ _IL = sin θ _IL / sin θ _R = m · sin θ
_IL / sin θ _W Generally, the larger the numerical aperture NA, the higher the resolution, but the shallower the depth of focus. On the other hand, the smaller the σ value is, the better the coherency of the exposure light IL is. Therefore, when the σ value is small, the edge of the pattern is emphasized, and when the σ value is large, the edge of the pattern is blurred. become able to. Therefore, if the σ value changes, the projection optical system PL
The illuminance distribution on the pupil plane P1 changes.

This means that the temperature distribution inside the projection optical system PL changes depending on the illumination condition as described above, and the aberration generated due to the temperature rise differs. Specifically, as shown in FIG. 7, on the rotary plate 8, for example, six types of aperture stops 132 to 137 are formed at equal angular intervals. Among these aperture stops, circular aperture stops 132 and 133
Has ordinary circular openings 132a and 133a having different diameters, and the annular aperture stop 134 has an annular opening 134a. Further, the aperture stops 135 and 136 for a plurality of oblique illuminations are a pair of minute apertures 135a, 135b and 136 arranged in directions orthogonal to each other.
a and 136b, and aperture stop 137 for multiple tilt illumination
Has four minute openings 137a to 137d arranged equidistantly about the optical axis.

The diaphragms 135, 136, 13 of the rotary plate 8
When 7 is used, it is desirable to set the σ value of the illumination light flux from each opening to be about 0.1 to 0.3. Further, it is desirable that the positions of the openings in each of the diaphragms 135 to 137 can be finely adjusted according to the fineness (pitch or the like) of the reticle pattern. Further, when the diaphragms 133 to 137 are used, it is desirable to make each element of the fly-eye lens 7 fine (to reduce the cross-sectional area) because the illuminance uniformity on the reticle or wafer may be deteriorated. Further, another integrator (fly-eye type or rod type) may be added to form a two-stage integrator structure.

Since the loss of light amount is large when the diaphragms 135 to 137 are used, it is preferable to use an optical splitter such as an optical fiber or a polygonal prism to guide the exposure light to each opening on the diaphragm. . Further, as an example of the selection criterion of the aperture diaphragm of the rotary plate 8, the aperture diaphragms 135, 136, 137 (these three usages may be selected according to the periodicity of the reticle pattern) particularly for a fine pattern. The aperture stop 132 is used when the line width is not severe, and the aperture stop 133 (or the aperture stop 141 may be used) is used as the phase shift reticle. Aperture stop 13
5 is a periodic pattern arranged in the X direction, for example, the aperture stop 36 is a periodic pattern arranged in the Y direction, and the aperture stop 13 is
7 is effective for a two-dimensional pattern.

The optimum positions of the apertures of the aperture stops 135, 136, 137 are disclosed in Japanese Patent Laid-Open No. 4-180612.
JP-A-4-180613 and JP-A-4-22551
No. 4, for example. For example, the aperture stop 137
Is an aperture stop effective for a two-dimensional periodic pattern,
Regarding the aperture stop 137, when focusing on one aperture 137a, either one of the ± first-order diffracted light due to the pattern in the X direction and either one of the ± first-order diffracted light due to the pattern in the Y direction and the zero-order diffracted light are projected optics. The position of the opening 137a is determined so that it is equidistant from the optical axis on the pupil plane P1 of the system PL. When the positions of the other openings (137b to 137d) are determined under the same conditions, the respective openings (13
7a to 137d) are set at positions equidistant from the optical axis.

When the aberration is determined from the signal waveform from the photoelectric conversion element 26, the illumination light I from the illumination optical system 10 is used.
Since L and the illumination light IL 'that has passed through the pattern plate 19 have the same two light amount distributions when passing through the projection optical system PL, the projection optical system PL by the illumination light from the fiber 20 is used.
The illuminance distribution on the pupil plane P1 must be equal to the illuminance distribution on the pupil plane P1 of the projection optical system PL by the illumination light emitted from the fly-eye lens 7. Therefore, for example, a rotary plate 21 is provided near the conjoining end 20b of the fiber bundle,
The aperture diaphragms provided on the rotary plate 21 are six types of aperture diaphragms similar to the aperture diaphragms (132 to 137) shown in FIG. 7, and the aperture diaphragm of the rotary plate 21 is selected according to the aperture diaphragm of the rotary plate 8. You can do it like this.

Next, a method of obtaining the aberration from the signal waveform from the photoelectric conversion element 26 will be described. The principle that each aberration amount is obtained from the waveform of the photoelectric detection signal can be explained as follows. When the NA of the illumination light source is made small (in the case of partial coherent illumination) to improve the resolution of the line width of the specific pattern, the light beam is hardened (collected) at the center of the lens of the projection optical system. When there is a mask pattern, the diffracted light reaches the periphery of the lens, but since the intensity of diffracted light other than the 0th order is generally weaker than that of the 0th order diffracted light, the tendency that the light beam is deviated to the center of the lens remains unchanged.

Therefore, when a slight amount of heat is absorbed by the lens forming the projection optical system, when the projection optical system is irradiated with light, heat is generated according to the amount of light passing through the lens.
When the lens heats up, the index of refraction often increases with expansion (although it may decrease due to heat generation). That is, in a convex lens having a positive power (refractive power) due to heat generation, the power of the central part of the lens is increased compared to the peripheral part due to the deformation of the central part of the lens and the effect of the distributed index lens. FIG. 8 shows this state, FIG. 8A shows a state in which there is no spherical aberration, and FIG. 8B shows a state in which spherical aberration is overcorrected (a state in which spherical aberration occurs).
When the spherical aberration is corrected in the initial state as shown in FIG. 8A, the power of the central portion of the lens 32 increases after the irradiation of light as shown by the slanted line in FIG. Since the state is overcorrected by M, the focus position changes (out of focus).

FIG. 9 shows the output signal S3 from the photoelectric detector 26.
FIG. 5 is a diagram showing the signal strength, and the vertical axis represents the signal strength as in FIG.
The horizontal axis represents the position of the pattern plate 19 in the Z direction. Figure 9
9A shows the output signal S3 when there is no spherical aberration, and FIG. 9B shows the output signal S3 when there is spherical aberration.
Is shown. When a signal is detected by the focus detection device in this state, a signal spread along the optical axis direction is obtained as shown in FIG. 9B. In the state where there is no spherical aberration, the diameter of the light flux becomes a diameter symmetrical with respect to the optical axis.
The full width at half maximum of the signal waveform shown in FIG. 9A is W ₁ ,
The center of the half-value width W ₁ and the Z position Z ₀ at the peak value match. That is, the signal waveform of FIG. 9A has a symmetrical signal waveform with respect to the peak value.

On the other hand, in FIG. 9B, the beam diameter before and after the position of the minimum circle of confusion (Z _{1 in} FIG. 9B) is asymmetrical along the optical axis due to the spherical aberration overcorrection. It becomes the diameter. Therefore, as shown in FIG. 9B, the distribution of the amount of signal light is asymmetric with respect to Z ₁ . The above is the process in which the lens has asymmetric deformation and distributed refractive index due to light irradiation, and the focus detection signal is distorted. Although the lens includes a concave lens, the above description qualitatively applies because it is a convex lens as a whole. At this time, the half-value width w _{2 of the} signal becomes larger than the half-value width W _{1 in} accordance with the amount of spherical aberration generated (due to overcorrection), so the half-value width w ₂ can be measured to measure the spherical aberration amount. Further, since the asymmetry of the signal also increases according to the amount of spherical aberration, it is possible to measure the amount of spherical aberration from the asymmetry of the signal. Specifically, the spherical aberration can also be measured by measuring the output difference I ₂ between the bottom value I ₀ on the left side of the signal waveform and the bottom value I ₁ on the right side across the peak value P ₀ of the signal waveform. . Further, the bottom value is not only the bottom values I ₀ and I ₁ , but a plurality of bottom values appear as high-order components on the left and right sides of the peak value P ₀ . The spherical aberration amount can be measured with high accuracy by comparing the left and right bottom values over a plurality of sets.
The relationship between the change in the half-width W of the signal and the amount of spherical aberration generated,
Alternatively, the relationship between the difference in bottom value and the amount of spherical aberration generated is obtained by performing trial baking in advance. It is assumed that this relationship is input to the main control system 29 by the input means 53 and stored in the memory in the main control system 29. The field curvature is also obtained by measuring the focus position in the image plane using the multidirectional aperture pattern 19a as shown in FIG.

In the above cases, the case where the light beam impinges on the projection lens in axial symmetry has been described. However, when the mask has a pattern in one direction, the diffracted light is not axisymmetric but asymmetric. Therefore, the deformation of the lens due to irradiation may occur asymmetrically about the axis. That is, irradiation causes astigmatism (astigmatism). In this case, the patterns 19a of the projection pattern plate 19 are aligned in the same direction, and the focus position is measured in at least two different directions (a radial direction around the optical axis of the projection optical system and a direction perpendicular thereto). Like Then, when there is an astigmatic difference, the value of the peak position Z ₀ shown in FIG. 7 differs in each direction, and the astigmatic difference can be measured by measuring the difference.

In the above example, spherical aberration, field curvature,
Although astigmatism has been described, other coma aberrations can be detected by the aberration detection system. That is, it is sufficient to detect that the focus position in the optical axis direction and the detection signal have a spread due to the coma aberration. Specifically, as shown in FIG. 10, the aperture pattern 19a has a radial pattern (S image) centered on the optical axis AX of the projection optical system PL and a pattern (M image) perpendicular thereto.
And a pattern having two directions. Then, coma can be measured by comparing the asymmetrical components of the signals obtained from the respective patterns. FIG. 11 shows a signal waveform obtained from the pattern shown in FIG. 10. Here, FIG. 11A shows a pattern in the radial direction (S
11B shows a signal obtained from the image), and FIG. 11B shows a signal obtained from the pattern (M image) in the direction perpendicular to the radial direction. FIG. 11 shows a case where the radial direction component (S image) is asymmetric due to coma aberration,
The aberration detection system 28 compares the asymmetrical components of these two signals to measure the amount of coma. Asymmetry detection using similarly to the case half width W of the detection of the spherical aberration described with reference to FIG. 9, or compared to half width W ₁ and W ₂ of the two signals, across the peak value 2 It may be obtained by comparing two bottom values. The relationship between the difference between the asymmetric components and the amount of coma aberration is obtained by performing trial baking or the like in advance.
It is assumed that this relationship is input to the main control system 29 by the input means 53 and stored in the memory in the main control system 29.

When measuring spherical aberration and coma, the pattern 19a may be measured in two different directions by providing a plurality of focus measuring systems shown in FIG.
Alternatively, marks may be provided in different directions, and the marks may be selected by switching them with a diaphragm or the like. Next, a method of measuring the image forming characteristics of the projection optical system PL such as spherical aberration and coma in this embodiment will be described. The motor 27 moves the wafer stage 15 so that the center of the opening 19a on the reference member 19 is on the optical axis AX of the projection optical system. At this time, the motor 27 is driven at the same time to move the wafer stage 15 to the expected focus variation amount (variation amount of the image forming characteristic) from the position considered to be the best focus position (best image forming surface) in the design of the projection optical system PL. Lower or raise it by several times. This is, for example, about twice the depth of focus (± DOF) (2 · DO
F) It may be lowered or raised. At the same time, the back surface (pattern surface) of the reticle R is illuminated via the opening 19 and the projection optical system PL. The illumination light reflected from the reticle R passes through the projection optical system PL and the opening 19 again,
Lens 25, mirror 24, lens 23, optical fiber 20
It is incident on the photoelectric detector 26 via. Thereafter, in this state, the wafer stage 15 is scanned upward (or downward) by about twice the expected amount of focus fluctuation described above. At this time, the aberration detecting unit 28 simultaneously outputs the output of the photoelectric detector 26 and the output of the focusing optical system 18 to, for example, the wafer stage 1.
The unit movement amount of 5 (for example, 0.02 μm) is sampled and A / D converted to obtain the relationship shown in FIG.
Then, as described above, based on the signal waveform from the photoelectric conversion element 26, the aberration is measured from its symmetry and the like.

Next, a method of correcting the aberration of the projection optical system PL according to this embodiment will be described. When the amount of aberration is detected as described above, the aberration can be corrected by adjusting the projection lens or the like. [Correction of spherical aberration] A method of correcting spherical aberration will be described. The spherical aberration is corrected by changing the lens interval of the lens elements 44 and 50 (FIG. 5) near the pupil P2 of the projection optical system PL. In addition, the lens element 44,
Aberration correction may be performed by changing the pressure of air in the lens chamber between 50 by the atmospheric pressure adjusting device 49. [Correlation of coma aberration and curvature of field] Correction of coma aberration and curvature of field is performed by changing the distance between the lenses away from the pupil P2. In this embodiment, aberration correction is performed by moving and tilting the lens element 33. Further, the coma aberration may be corrected by adjusting the pressure of the air in the lens chamber between the lens elements 33 and 37 by the atmospheric pressure adjusting device 39. [Correction of Astigmatism] Correction of astigmatism is performed by relatively rotating the two cylindrical lenses 40 and 41 provided in the lens. Further, the interval between the two cylindrical lenses may be changed.

As described above, each aberration correction is performed by selecting the lens element that has little influence on other aberrations. Moreover, the measurement and correction of these aberrations are performed in conjunction with the change of each illumination condition. Here, if the projection lens is achromatic in a plurality of wavelength bands or in a certain wavelength band, it is possible to irradiate a plurality of wavelengths from the focusing system (irradiation optical system 17) of FIG. 1 and perform measurement using a plurality of wavelengths. It is possible to measure each of the above-mentioned aberrations based on the signal from the photoelectric conversion element 26 independently of each other. In that case, a bandpass filter is inserted in the light source unit, and each of them is replaced so as to transmit a plurality of wavelengths.

Although it is possible that the image plane moves up and down by driving the lens elements 33 and 44, an offset is added to the output value from the light receiving optical system 18 of the focusing system according to this variation. If given, the wafer W is always set on the best image plane. Next, an exposure sequence for interrupting the exposure will be described based on the result from the aberration detection system 28.

Width at half maximum w ₂ of the signal from the photoelectric conversion element 26
Is larger than a certain level, the image formation state deteriorates. Therefore, it is possible to set an upper limit of w ₂ in advance and interrupt the exposure operation when it exceeds the upper limit. As described above, the aberration condition becomes worse due to the absorption of the illumination light of the projection optical system PL. For this reason, during the exposure operation, for example, when the wafer is exchanged, the aberration is checked by the aberration measuring means, and it is determined whether or not it exceeds the allowable value obtained in advance by experiments or simulations. Of course, at this time, it is desirable to perform the calibration of the focus position at the same time. If the allowable value is exceeded, the aberration detection system 2
8 issues a warning to the main control system 29, and the main control system 29 stops the exposure operation. Periodically in this state (for example, 30 sec
Each time), the aberration is measured and it is determined whether or not it exceeds the allowable value. Due to the interruption of the exposure operation, the amount of heat accumulated in the projection optical system PL is released to the outside, and the aberration detection system 28 sends an exposure OK signal to the main control system 29 in the order in which the amount of heat becomes less than the allowable value, and the main controller again exposes. Start operation.
Since the above-mentioned allowable value differs depending on the line width of the reticle pattern to be exposed, the pattern type, etc., the condition is input in advance by the input means 5.
It is also conceivable that the permissible condition is made variable by inputting to the main control system 29 according to No. 3. Further, the measurement interval of the aberration is not necessarily limited to a constant interval, and the measurement interval is lengthened immediately after the irradiation of the illumination light IL and is shortened as the irradiation time increases. Further, the pattern 19 may be made replaceable so as to match the actual exposure pattern.

Next, a method for correcting the calibration of the focus position obtained by the aberration detection system will be described. As described above, the focus position can be measured using the reference pattern plate 19. Normally, the pattern of the pattern plate 19 is made to match the line width to be actually exposed, but the pattern to be exposed is not necessarily the same as it is large or small. In this case, when spherical aberration occurs due to absorption of illumination light, the focal position differs depending on the line width, and there is a problem that the focal position measurement results of the actual exposure pattern do not match. Here, correction is possible if the exposure line width and the amount of spherical aberration are known. Regarding the line width, for example, a method of inputting with a keyboard or the like, or a method of writing and reading with a reticle barcode or the like can be considered. Regarding the spherical aberration and the focal position shift amount, the relationship may be measured in advance or obtained by simulation, and stored in the form of a table or a mathematical formula. Alternatively, an allowable value is set so that the influence of the spherical aberration amount on the focus detection can be sufficiently ignored, and when the allowable value is equal to or larger than the allowable value, focus position measurement is not performed, for example, the exposure operation is interrupted and the projection optical system is sufficiently cooled. A method of waiting for is also possible.

As described above, since the aberration of the projection optical system PL can be actually measured based on the signal waveform from the photoelectric conversion element 26, it does not take time to expose the pattern using a special mask, The amount of aberration can be easily known when using the device. Based on the measured aberration, it is possible to stop the exposure operation when the aberration occurs, correct the focus detection system error due to the aberration amount, or correct the aberration in real time.

In the above-described embodiment, the mechanisms 39, 4 for changing the pressure of the air chamber between the lens elements as described with reference to FIG.
Mechanisms 38, 48 for changing the distance between 9 and the lens element,
However, it is not necessary to provide all the aberration correction mechanisms. For example, a mechanism 39 for changing the pressure,
49 or a mechanism for changing the distance between lens elements 38, 4
You may make it have any one of 8, 42, and 43. Further, it is effective to provide only a part of these for specific aberration correction.

[0041]

As described above, according to the present invention, since the amount of aberration can be measured, it is possible to perform exposure in a state in which the aberration is corrected, or to perform an exposure operation according to the aberration. Further, since the amount of aberration can be measured, even if the amount of aberration generated by the phase shift reticle, multiple tilt illumination, etc. cannot be predicted, exposure can be performed according to the generated aberration.

[Brief description of drawings]

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

FIG. 2 is a diagram showing an opening pattern provided on a reference pattern plate by the apparatus of FIG.

FIG. 3 is a diagram illustrating a principle of obtaining a focal position by using the aperture pattern of FIG.

FIG. 4 is a diagram showing a relationship between an output signal from a photoelectric conversion element 26 and a Z position of an aperture pattern.

5 is a diagram partially showing an aberration correction means of the apparatus of FIG.

FIG. 6 is a diagram illustrating that the amount of aberration varies depending on the illumination condition.

FIG. 7 is a diagram showing an aperture stop for changing illumination conditions.

FIG. 8 is a diagram illustrating a spherical aberration occurrence state.

9A is a diagram showing a signal waveform from the photoelectric conversion element 26 in a state where there is no aberration. FIG. (B) It is a figure which shows the signal waveform from the photoelectric conversion element 26 in the state with spherical aberration.

FIG. 10 is a diagram illustrating an aperture pattern used to measure coma.

11 (a) is a diagram showing a signal waveform from the photoelectric conversion element 26 in a state where an S image has coma aberration. FIG. (B) is a diagram showing a signal waveform from the photoelectric conversion element 26 in a state in which there is no coma aberration in the M image.

[Explanation of symbols]

 8, 21 ... Rotating plate 15 ... Wafer stage 17 ... Irradiation optical system 18 ... Receiving optical system 19 ... Pattern plate 19a ... Aperture pattern 20 ... Optical fiber 26 ... Photoelectric conversion element 28 ... Aberration detection system 29 ... Main control system R ... Reticle W … Wafer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G11B 5/31 M 8947-5D

Claims (4)

[Claims] 1. An illumination optical system that irradiates a mask with illumination light from a light source, a projection optical system that forms an image of the pattern of the mask on a photosensitive substrate, and a light of the projection optical system that holds the photosensitive substrate. In a projection exposure apparatus having a stage movable in an axial direction and a direction perpendicular to the optical axis, a reference member provided on the stage and having a predetermined opening pattern; A light receiving unit that illuminates the opening pattern from the stage side, reaches the mask through the projection optical system, and receives the light reflected by the mask through the projection optical system and the opening pattern; Stage position measuring means for measuring the position of the stage with respect to the optical axis direction; and obtaining an aberration amount of the projection optical system from a signal waveform obtained from the photoelectric detecting means. Projection exposure apparatus characterized by having a quantity computing means. 2. The projection exposure apparatus according to claim 1, further comprising an aberration correction unit that corrects the aberration of the projection optical system based on the result of the aberration amount calculation unit. 3. The projection exposure apparatus according to claim 1, further comprising exposure operation control means for interrupting the exposure operation based on the result of the aberration amount calculation means. 4. The projection exposure apparatus according to claim 1, further comprising stage position correction means for correcting the position of the photosensitive substrate in the optical axis direction based on the result of the aberration amount calculation means.