JP3218478B2 - Projection exposure apparatus and method - Google Patents

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, projection exposure apparatuses such as semiconductor manufacturing-related apparatuses have been required to have extremely high imaging performance.
This type of conventional apparatus is equipped with a projection optical system in which various aberrations are highly corrected. Normally, 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 dedicated pattern is exposed on a test substrate, developed, and 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 position of a pattern having a plurality of different line widths.
Specifically, the stage is sequentially positioned in the optical axis direction,
While sequentially moving the test substrate coated with the photosensitive agent in the optical axis direction, a pattern having a plurality of line widths is exposed and developed. As a result, a pattern having a line width corresponding to the distance from the projection optical system in the optical axis direction is formed on the substrate. For each line width pattern formed on the substrate, the line width is measured using 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. Midpoint of substrate position where predetermined line width is maintained (intermediate point between maximum position and minimum position of substrate position where predetermined line width is maintained)
Is determined as the best focus, the best focus position of each line width is obtained from the curve of the plotted data. Here, when spherical aberration occurs, a deviation occurs in the best focus position of each line width. The astigmatism can be checked by calculating the difference between the best focus positions of the patterns having different directions. Next, as an example of checking coma aberration, there is a method of observing a difference between line widths at both ends of a plurality of continuous marks having the same line width.

[0003] Each aberration is obtained by the above-described method, and the imaging characteristics of the projection optical system are optimized. For example, the distance between lens elements inside the projection optical system is adjusted to finally make each aberration equal to or less than an allowable value. However, each aberration is not always constant, and can be changed by a temperature change, an atmospheric pressure change, and a rise in the temperature of the projection optical system due to absorption of the illumination light by the projection optical system. In particular, a change in the temperature of the projection optical system due to absorption of the illumination light causes a temperature distribution in a lens element inside the projection optical system, which may cause a non-negligible change in aberration. In such a case, it is impossible to check the aberration amount during the exposure operation by the above method.

Therefore, a method has conventionally been proposed in which the amount of exposure energy accumulated in the projection optical system is calculated, and when the amount of accumulation exceeds a certain reference value, the exposure operation is temporarily stopped, and is not used where the aberration is deteriorated. I was Specifically, the relationship between the amount of aberration generated and the amount of heat accumulated in the projection optical system and the heat absorption characteristics of the projection optical system are determined in advance. At the time of actual exposure operation, the amount of heat accumulated in the projection optical system is sequentially calculated from the numerical model of the heat absorption characteristic obtained in advance, the mask transmittance, and the shutter opening / closing signal to calculate the amount of generated aberration. 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 falls below the allowable value, so that 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 obtained amount of aberration is a predicted value to the last, and the actual amount of aberration is unknown. In particular, in recent years, techniques for increasing the resolving power include annular illumination, Japanese Patent Application Laid-Open Nos. 4-180612 and 4-180.
No. 613 discloses an oblique illumination from a plurality of directions, and a phase shift mask disclosed in Japanese Patent Publication No. 62-50811 has also been proposed. When these techniques are used, the intensity distribution of the illumination light inside the projection optical system differs. For this reason, even if the illumination energy is the same, the amount of aberration generated by the illumination condition or the reticle is different, and it is difficult to predict the amount of aberration generated.
Therefore, there is a problem that the conventional method of estimating the amount of aberration cannot cope with a desired exposure operation. The present invention has been made in view of such conventional problems, and has an apparatus which can measure an actual amount of aberration and can cope with a change in imaging characteristics.
And a method .

[0006]

In order to solve the above-mentioned problems, according to the present invention, illumination light from a light source (1) is masked by a mask (R).
Optical system (6, 7, 10) for irradiating the light, a projection optical system (PL) for forming an image of a mask pattern (PA) on a photosensitive substrate (W), a 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; Light receiving means for illuminating the aperture pattern from the stage side while moving in the direction of the optical axis, and receiving the light reaching the mask via the projection optical system and reflected by the mask via the projection optical system and the aperture pattern; A stage position measuring means for measuring the position of the stage in the axial direction; and an aberration calculating means for calculating an aberration amount of the projection optical system from a signal waveform obtained from the photoelectric detecting means are provided. Ma
Further, the present invention is based on the fact that the pattern of the mask is based on a projection optical system.
A projection exposure apparatus that exposes a substrate by projecting onto a plate
The projection optical system is a second optical system fixed to the lens barrel (52).
First and second fixed lens elements (37, 50);
First fixed lens (37) and second fixed lens (50)
Is movable between the lens barrel and
And a movable lens element (44).
Driving means (48) for moving the projection lens and a projection optical system.
Detecting means (20 to 26, 28) for detecting spherical aberration;
The driving hand is operated based on the spherical aberration detected by the detecting means.
Control means for controlling the step and moving the movable lens element
(29). Further
In the present invention, the mask pattern is based on a projection optical system.
A projection exposure method that exposes a substrate by projecting it on a plate
Method to detect and detect spherical aberration of the projection optical system.
Fixed to the barrel of the projection optical system based on the spherical aberration
A mirror disposed between the first and second fixed lens elements;
Move the movable lens element that is movable with respect to the cylinder
It is characterized by that.

[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 incident on the mask via the projection optical system. Then, the illumination light reflected by the mask is made incident on the photoelectric detector via the projection optical system and the aperture pattern. The amount of aberration is obtained using the waveform of the photoelectric detection signal from the photoelectric detector. Therefore, procedures such as exposure, development, and measurement on the test substrate can be omitted, and there is no need to provide a dedicated pattern on the mask. it can. As a result, exposure is performed while aberration is occurring,
There is no inconvenience of taking out defective products.

[0008]

FIG. 1 is a plan view showing a schematic configuration of a projection exposure apparatus according to one 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 for exposing a resist layer. As a light source for exposure, in addition to an emission line such as a mercury lamp, a laser light source such as a KrF or ArF excimer laser, or a metal vapor laser or YA
A harmonic of the G laser may be used. The illumination light IL is reflected by the elliptical mirror 2 and condensed at its second focal point f ₀ , and then enters the mirror 5, the collimator lens 6, and the fly-eye lens 7. A variable stop 8 is provided on the exit side of the fly-eye lens, so that illumination conditions can be changed according to the type of reticle and the periodicity of the pattern. The change of the illumination condition is executed by driving the variable aperture 8 by the motor 9.

A shutter (for example, a rotary shutter with four blades) 3 for closing and opening the optical path of the illumination light IL by a motor 4 is disposed near the second focal point f ₀ . The illumination light IL that has passed through the variable aperture 8 is
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 and reach a mirror 14, where the reticle R Pattern area PA
Is illuminated with substantially uniform illuminance. Reticle R is mounted on reticle stage RS, and reticle stage RS
Is capable of finely moving the reticle R in the XY directions. The reticle stage RS can finely move the reticle R in the Z direction (optical axis direction) by the drive unit 51, and can change the distance between the reticle R and the projection optical system PL, or move the reticle R in 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 a projection optical system PL that is telecentric on both sides, and the projection optical system PL forms a projection 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 moved so that the surface substantially matches the best image forming plane.
The circuit pattern is held on the wafer W and is image-formed and projected on one shot area on the wafer W so as to overlap. (FIG. 1 does not form an image on the wafer W for the sake of explanation.) The wafer W is vacuum-adsorbed on the wafer holder 16 and is held on the wafer stage 15 via the holder 16. The wafer stage 15 can be tilted in any direction with respect to the best image forming 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, When the transfer exposure of the reticle R to one shot area on the wafer W is completed, stepping is performed to the next shot position.

FIG. 1 shows an irradiation optical system which supplies an image forming light beam for forming an image of a pinhole or a slit obliquely to the optical axis AX toward the best image plane of the projection optical system PL. System 17 and light receiving optical system 1 for receiving, via a slit, a light beam reflected by the surface of wafer W of the image forming light beam
A focusing system (wafer position detection system) of the oblique incidence type comprising 8 is provided. The configuration and the like of this focusing system are disclosed in, for example, Japanese Patent Laid-Open No. 60-168112.
The position of the wafer surface in the direction (Z direction) with respect to the imaging plane is detected, and the focus state of the wafer W and the projection optical system PL is detected. In this embodiment, an unillustrated parallel flat glass (plane parallel) provided in advance in the light receiving optical system 18 so that the best imaging plane in design becomes the zero point reference.
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 detecting aberration is drawn on the pattern plate 19 as shown in FIG. Here, the pattern plate 19
Is provided with a pattern plate 19 so as to be substantially flush with the surface of the wafer W. The light beam IL ′ having substantially the same wavelength range as the illumination light IL is split into a two-branch fiber 20, a variable stop 21, relay lenses 23a and 23b, a mirror 24,
The pattern plate 19 is illuminated from the wafer stage 15 side (below) through the condenser lens 25. Illumination light IL '
May split the illumination light IL from the light source 1 or may separately provide a light source that emits light having the same wavelength as the illumination light IL.
The light beam emitted from the pattern opening of the pattern plate 19 forms an image on the pattern surface PA of the reticle R via the projection optical system PL, and the reflected light forms an image on the pattern plate 19 again via the projection optical system PL. . The light flux reaching the pattern plate 19 passes through the opening of the pattern 19 again, passes through the condenser lens 25, the mirror 24, the relay lenses 23a and 23b, the variable stop 21, and the two-branch 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. At the same time, the aberration detection system 28 in the main control system 29 receives the signal S3 from the photoelectric conversion element 26 and receives light from the focus detection system. Received in synchronization with the signal from the 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 driving the variable aperture 8 and the motor 22 driving the variable aperture 21. The aberration detection system 28 can be used for TTL (through-the-lens) type focus position detection (detection of the imaging plane of the projection optical system PL), and can simultaneously detect the focus position and the aberration. The main control system 29 controls the entire device in addition to the control of the drive unit 51. Here, the aperture pattern is a combination of multi-directional patterns as shown in FIG. 2 in consideration of astigmatism.

The principle by which the focus position is determined 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 reflected by the mask R when the reticle R and the pattern plate 19 are slightly displaced from the conjugate position, and re-imaged via the projection optical system PL. FIG. 3B shows an image of the aperture pattern 19 reflected by the mask R and re-formed through the projection optical system PL when the mask R and the pattern plate 19 are at conjugate positions. FIG. 3C is a diagram showing a light amount distribution, and FIG.
9 shows an example. In FIG. 3C, reference numeral 19a denotes 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 at conjugate positions, the intensity distribution of the image of the reference pattern plate 19 becomes as shown in a distribution Ca of FIG.
The distribution substantially matches the light and dark distribution of the reference pattern plate 19 itself, and almost all of the light returns to the wafer stage 15 via the transmission part of the reference pattern plate 19. On the other hand, when the reference pattern plate 19 is slightly displaced from the plane 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 has a distribution shown in FIG. The contrast decreases as indicated by Cb. In this case, FIG.
The hatched portion in the distribution Cb of (a) overlaps the light-shielding portion (non-transmissive portion) 19a of the reference pattern 19 in FIG. 3C, cannot pass through the reference pattern 19, and the photoelectric conversion element 26 Is reduced.

FIG. 4 shows a detection signal S from the photoelectric conversion element 26.
3 is a diagram illustrating the output value from the photoelectric conversion element 26 when the opening pattern 19 is moved in the Z direction, with the output value of No. 3 as the vertical axis and the Z coordinate of the pattern plate 19 as the horizontal axis. 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. When the output value S3 of the photoelectric conversion element 26 is the largest (peak value) in FIG. 4, the Z coordinate Za indicates the case where the reticle R and the pattern plate 19 are substantially conjugate with each other. ). In FIG. 4, the Z coordinate Zb when the output value from the photoelectric conversion element 26 is at a point lower than the peak value indicates that the reticle R and the pattern plate 19 are slightly displaced from the conjugate position. This corresponds to the case (a).

As described above, when the reference pattern plate 19 comes to 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 becomes a waveform that falls in a concave shape on both sides of the peak, for example, as shown in FIG. Next, the configuration of the correction means for correcting the imaging state will be described. In the present embodiment, the imaging characteristics (such as spherical aberration, coma, astigmatism, and field curvature) are corrected by driving the lens elements of the projection optical system PL or changing the pressure between the lens elements. It has a configuration. Therefore, some of the optical elements of the projection optical system PL can be moved. Further, the pressure between the optical elements of the projection optical system PL is variable. FIG. 5 is a diagram partially illustrating the apparatus of FIG. 1, and is a diagram illustrating a mechanism for varying the pressure between the driving unit of the reticle R, the driving unit of the optical element of the projection optical system PL, and the optical element. The lens element 33 closest to the reticle R is fixed by a support member 34 and provided on a support member 36 via a drive element 35. The support member 36 is fixed to the lens barrel 52 of the projection optical system PL. The driving elements 35 are composed of driving elements 35a, 35b, and 35c (only 35a and 35b are shown in FIG. 5) arranged at positions rotated by 120 °, and each driving element can be independently controlled by a driving element control unit 38. Has become. Although the lens element 33 is shown as one lens in FIG. 5, it is assumed that the lens element is a lens element including three (or two) lens groups, and each lens group constituting the lens element 33 is a driving element. (Not shown) enables independent fine movement.

A lens element 44 near the pupil plane P1 of the projection optical system PL is fixed by a support member 45 and provided on a support member 47 via a drive element 46. The support member 47 is fixed to the lens barrel 52 of the projection optical system PL. Driving elements 46a, 46b, 46c are arranged at positions rotated by 120 °, respectively.
(Only 46a and 46b are shown in FIG. 5), and each drive element can be independently controlled by a drive element control unit 48. As the driving elements 35 and 46, for example, an electrostrictive element or a magnetostrictive element is used, and a displacement amount of the driving element according to a voltage or a magnetic field applied to the driving element is obtained in advance. Although not shown here, in consideration of the hysteresis of the driving element, a capacitive displacement sensor,
A differential transformer or the like is provided near the driving element.
Thereby, the position of the driving element corresponding to the voltage or the magnetic field applied to the driving element can be monitored, so that highly accurate driving can be performed. The fine movement of the lens elements 33 and 44 changes the distance between the lens elements, tilts the lens element with respect to a plane perpendicular to the optical axis AX, and moves the lens element in a plane perpendicular to the optical axis AX. Done. The configuration and operation for driving such an optical element are disclosed in detail in Japanese Patent Application Laid-Open No. 4-134814.

In this embodiment, the reticle R is controlled by controlling the driving element 35 by the driving element control section 38.
The lens element 33 close to is movable.
The lens element 33 is selected so that the influence on the imaging characteristics such as coma aberration and curvature of field is large and easy to control as compared with other lens elements. In addition, since the movable lens element 33 has a three-group configuration, the range of movement can be increased by moving the lens element while suppressing variations in other aberrations. Further, by controlling the above-described driving element 46 by the driving element control unit 48, the lens element 44 close to the pupil plane P1 can be moved, and the effect of the lens element 44 on the spherical aberration is affected by other lens elements. Those that are larger and easier to control are selected.

The lens elements 37 and 50 are connected to a lens barrel 52.
, The air pressure adjusting device 39 adjusts the pressure of the air in the lens chamber between the lens element 33 and the lens element 37, and the air pressure adjusting device 49 adjusts the pressure in the lens chamber between the lens element 44 and the end element 50. Adjust the air pressure. Japanese Patent Laid-Open No. 60-78 discloses a technique for correcting the aberration 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.

Further, two cylindrical lenses 40 and 41 are provided near the pupil plane P1, and these two lenses are relatively rotated by driving units 42 and 43 or the distance between the lenses is changed. Controls astigmatism. The cylindrical lenses 40 and 41 are arranged in directions orthogonal to each other, and change the refractive index in the X and Y directions by relatively rotating them. Then, these lenses are relatively rotated so that the X and Y components cancel each other, and astigmatism components generated by other lens elements are removed. The main control system 29 includes these drive element control units 38 and 48, drive units 42 and 43, an air pressure adjustment device 39,
49 is controlled.

Next, the above-mentioned variable stop 8 and projection optical system PL
The variable aperture 30 will be briefly described. Generally, the numerical value indicating the characteristic of the illumination system is the numerical aperture N of the projection optical system.
A and a value representing the coherency of the illumination light are used. The numerical aperture and the 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 through which the light beam from the reticle R side of the projection optical system PL can pass. θ _R and the maximum angle θ _W of the light beam falling from the projection optical system PL toward the wafer W (pattern plate 19) are limited to predetermined values. Projection optical system PL
The numerical aperture _PL of a sin [theta _W, when the projection magnification and 1 / m, a relation of sinθ _R = sinθ _W / m.

[0021]

## EQU1 ## σ _IL = sin θ _IL / sin θ _R = m · sin θ
_IL / sin θ _{W In} general, 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, the better the coherency of the exposure light IL. 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, when the σ value changes, the projection optical system PL
The illuminance distribution on the pupil plane P1 changes.

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

The apertures 135, 136, 13 of the rotary plate 8
When using No. 7, it is desirable to set so that the σ value of the illumination light beam from each opening is about 0.1 to 0.3. Further, it is desirable that the position of each opening in each of the apertures 135 to 137 can be finely adjusted according to the fineness (pitch or the like) of the reticle pattern. Further, when the stops 133 to 137 are used, the uniformity of the illuminance on the reticle or the wafer may be deteriorated. Therefore, it is desirable to make each element of the fly-eye lens 7 fine (reduce the sectional area). Further, another integrator (fly-eye type or rod type) may be added to form a two-stage integrator structure.

When the stops 135 to 137 are used, a large amount of light is lost. Therefore, 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 stop. . Further, as an example of the selection criteria of the aperture stop of the rotating plate 8, the aperture stops 135, 136, and 137 (especially, these three usages may be selected according to the periodicity of the reticle pattern) particularly for fine patterns. When the line width is not severe, the aperture stop 132 is used, and for the phase shift reticle, for example, the aperture stop 133 (or the aperture stop 141 may be used) is used. Aperture stop 13
5 is, for example, a periodic pattern arranged in the X direction, the aperture stop 36 is a periodic pattern arranged in the Y direction,
7 is effective for a two-dimensional pattern.

The optimum positions of the apertures of the aperture stops 135, 136 and 137 are described in JP-A-4-180612.
JP-A-4-180613 and JP-A-4-22551
No. 4 and the like. 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 opening 137a, one of the ± 1st-order diffracted lights by the pattern in the X direction and one of the ± 1st-order diffracted lights by the pattern in the Y direction and the 0th-order diffracted light are projected optically. The position of the opening 137a is determined so as to be equidistant from the optical axis on the pupil plane P1 of the system PL. If the positions of the other openings (137b to 137d) are determined under the same conditions, each of the openings (13
7a to 137d) are set at positions equidistant from the optical axis.

Here, when obtaining the aberration from the signal waveform from the photoelectric conversion element 26, the illumination light I from the illumination optical system 10 is used.
L and the illumination light IL ′ that has passed through the pattern plate 19 match the two light amount distributions when passing through the projection optical system PL.
It is necessary to make 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 equal to the illuminance distribution on the pupil plane P1. Therefore, for example, a rotating plate 21 is provided near the joint end 20b of the fiber bundle,
The aperture stops provided on the rotary plate 21 are six types of aperture stops similar to the aperture stops (132 to 137) shown in FIG. 7, and the aperture stop of the rotary plate 21 is selected according to the aperture stop of the rotary plate 8. What should I do?

Next, a method for obtaining aberration from the signal waveform from the photoelectric conversion element 26 will be described. The principle of obtaining each aberration amount from the waveform of the photoelectric detection signal can be explained as follows. When the NA of the illumination light source is reduced (partial coherent illumination) in order to improve the resolution of the specific pattern line width, the light flux is concentrated (converged) 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. However, since the intensity of the diffracted light other than the 0th-order light is generally weaker than that of the 0th-order diffracted light, the tendency that the light flux is biased toward the center of the lens remains unchanged.

Therefore, if the lens constituting the projection optical system has very little heat absorption, when the projection optical system is irradiated with light, heat is generated according to the amount of light transmitted through the lens.
When the lens generates heat, the refractive index increases in many cases with expansion (however, the refractive index may decrease due to heat generation). That is, in a convex lens having a positive power (refractive power) due to heat generation, the power at the lens central portion is increased as compared with the peripheral portion due to the deformation of the lens central portion and the effect of the distributed index lens. FIG. 8 shows this state, FIG. 8A shows a state without spherical aberration, and FIG. 8B shows a state in which spherical aberration is overcorrected (state in which spherical aberration occurs).
When the spherical aberration has been corrected in the initial state as shown in FIG. 8A, the power of the central portion of the lens 32 increases as shown by the oblique lines in FIG. The focus position fluctuates because the image is overcorrected by M (the focus is out of focus).

FIG. 9 shows an output signal S3 from the photoelectric detector 26.
FIG. 5 is a diagram showing the signal intensity on the vertical axis as in FIG.
The horizontal axis indicates the position of the pattern plate 19 in the Z direction. FIG.
9A shows the output signal S3 when there is no spherical aberration, and FIG. 9B shows the output signal S3 when spherical aberration occurs.
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 a state where there is no spherical aberration, the light beam diameter has a symmetrical diameter along the optical axis.
Half-width of the illustrated signal waveform in FIG. 9 (a) is a W _1,
Z position Z ₀ at the center and the peak value of the half width W ₁ is consistent. That is, the signal waveform of FIG. 9A is a signal waveform symmetrical with respect to the peak value.

On the other hand, in FIG. 9B, the light beam diameter before and after the minimum confusion circle position (Z _{1 in} FIG. 9B) is asymmetric along the optical axis due to the spherical aberration overcorrection. The diameter. Therefore distribution of the signal light intensity as shown in FIG. 9 (b) is asymmetric with respect to Z _1. The above is the process in which the lens is asymmetrically deformed and has a distributed refractive index due to light irradiation, and the focus detection signal is distorted. Note that the lens includes a concave lens, but the above description qualitatively applies since it is a convex lens as a whole. At that time, the half-value width w ₂ of the signal according to (excessively corrected by) the spherical aberration amount generated becomes larger than the half-value width W _1, can measure the spherical aberration by measuring the half-width w _2. Further, since the asymmetry of the signal also increases according to the amount of spherical aberration, the amount of spherical aberration can be measured from the asymmetry of the signal. It is possible to measure the spherical aberration by measuring the output difference I ₂ between the bottom value I ₁ of the right sides of the peak value P ₀ of the bottom value I ₀ and the signal waveform of the left signal waveform in particular . In addition, the bottom value includes not only the bottom values I ₀ and I ₁ but also a plurality of bottom values as high-order components appearing right and left across the peak value P ₀ . By comparing the left and right bottom values over a plurality of sets, the spherical aberration amount can be measured with high accuracy.
Note that the relationship between the change in the half-value width W of the signal and the amount of generation of spherical aberration,
Alternatively, the relationship between the difference between the bottom values and the generation amount of spherical aberration is obtained by performing trial printing or the like in advance. This relationship is input to the main control system 29 by the input means 53, and is stored in the memory in the main control system 29. The curvature of field 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 case, a case has been described in which a light beam impinges on the projection lens in an axisymmetric manner. However, when the mask has a pattern in one direction, the diffracted light is generated not axisymmetrically but asymmetrically. Therefore, it is conceivable that the deformation of the lens due to irradiation occurs asymmetrically about the axis. That is, the irradiation causes astigmatism (astigmatic difference). In this case, the pattern 19a of the projection pattern plate 19 is aligned in the same direction, and the focus position is measured in at least two different directions (radiation direction centering on the optical axis of the projection optical system and 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 by measuring the difference, the astigmatic difference can be measured.

In the above example, spherical aberration, field curvature,
Although astigmatism has been described, other coma and the like can also be detected by the aberration detection system. That is, it is only necessary to detect that the focus position and the detection signal in the optical axis direction have a spread due to the coma aberration. More specifically, as shown in FIG. 10, an aperture pattern 19a is formed by radiating a radial pattern (S image) around the optical axis AX of the projection optical system PL and a pattern perpendicular to the radial pattern (M image).
And a pattern having two directions. Then, coma aberration can be measured by comparing asymmetric components of signals obtained from the respective patterns. FIG. 11 shows a signal waveform obtained from the pattern shown in FIG. 10. Here, FIG. 11 (a) shows the pattern (S
11B. FIG. 11B shows a signal obtained from a pattern (M image) in a direction perpendicular to the radiation direction. FIG. 11 shows a case where the radial component (S image) is asymmetric due to coma aberration.
The coma aberration amount is measured by comparing the asymmetric components of these two signals by the aberration detection system 28. 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 determined by comparing two bottom values. The relationship between the difference between the asymmetric components and the coma aberration amount is obtained by performing trial printing or the like in advance.
This relationship is input to the main control system 29 by the input means 53, and is stored in the memory in the main control system 29.

When measuring spherical aberration and coma aberration, the pattern 19a in two different directions may be provided with a plurality of focus measuring systems shown in FIG.
May be provided with marks in different directions, and these may be switched and selected with a diaphragm or the like. Next, a method for measuring the imaging characteristics of the projection optical system PL such as spherical aberration and coma aberration in the present embodiment will be described. The wafer stage 15 is moved by the motor 27 so that the center of the opening 19a on the reference member 19 is located on the optical axis AX of the projection optical system. At this time, the motor 27 is simultaneously driven to move the wafer stage 15 to a focus variation amount (a variation amount of the imaging characteristic) expected from a position considered to be the design best focus position (the best imaging plane) of the projection optical system PL. Decrease or increase by several times. This is, for example, about twice the depth of focus (± DOF) (2 · DOF).
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 again passes through the projection optical system PL and the opening 19,
Lens 25, mirror 24, lens 23, optical fiber 20
And enters the photoelectric detector 26 via the. Thereafter, in this state, the wafer stage 15 is scanned upward (or downward) by about twice the expected focus fluctuation amount described above. At this time, the aberration detector 28 simultaneously outputs the output of the photoelectric detector 26 and the output of the light receiving optical system 18 of the focusing system, for example, on the wafer stage 1.
The sample is sampled for each unit movement amount of 5 (for example, 0.02 μm) and A / D converted to obtain a relationship as 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 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 correction of the spherical aberration is performed by changing the lens interval between the lens elements 44 and 50 (FIG. 5) near the pupil P2 of the projection optical system PL. Also, the lens element 44,
The aberration correction may be performed by changing the pressure of the air in the lens chamber between 50 by the air pressure adjusting device 49. [Correction of Coma Aberration and Field Curvature] Correction of coma aberration and field curvature is performed by changing the distance between lenses away from the pupil P2. In the present embodiment, aberration correction is performed by moving and tilting the lens element 33. Further, the correction of coma may be performed by the air pressure adjusting device 39 by adjusting the pressure of the air in the lens chamber between the lens elements 33 and 37. [Correction of Astigmatism] The correction of astigmatism is performed by relatively rotating 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 a lens element having little influence on other aberrations. 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 or achromatic in a certain wavelength band, it is possible to irradiate a plurality of wavelengths from the focusing system (irradiation optical system 17) in FIG. 1 and perform measurement using a plurality of wavelengths. The respective aberrations can be measured independently and the above-described various aberrations can be measured based on the signal from the photoelectric conversion element 26. In that case, a band-pass filter is inserted into the light source unit, and each is exchanged so as to transmit a plurality of wavelengths.

It is conceivable that the driving of the lens elements 33 and 44 may cause the image plane to move up and down. However, an offset is added to the output value from the light receiving optical system 18 of the focusing system according to the amount of change. If given, the wafer W is always set to the best image plane. Next, an exposure sequence for interrupting the exposure based on the result from the aberration detection system 28 will be described.

The half width w ₂ of the signal from the photoelectric conversion element 26
There becomes larger than a certain, because imaging condition worsens, is determined in advance an upper limit in advance w _2, it is conceivable to be interrupted exposure operation when exceeding it. As described above, the aberration condition deteriorates 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 replaced, the aberration is checked by the aberration measuring means, and it is determined whether the aberration exceeds an allowable value obtained in advance by experiment or simulation. Of course, at this time, it is desirable to perform the calibration of the focal position at the same time. If the tolerance 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, for 30 seconds)
Each time), the aberration is measured, and it is determined whether or not the allowable value is exceeded. When the amount of heat accumulated in the projection optical system PL is released to the outside due to the interruption of the exposure operation, 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 equal to or less than the allowable value. Start operation.
Since the above-mentioned allowable value differs depending on the line width, pattern type, and the like of the reticle pattern to be exposed, the conditions must be set in advance by the input means 5.
It is also conceivable to input to the main control system 29 by 3 to make the permissible condition variable. Further, the measurement interval of the aberration is not necessarily limited to a fixed interval, and the measurement interval is increased immediately after the irradiation of the illumination light IL, and the measurement interval is shortened as the irradiation time becomes longer. Further, the pattern 19 may be exchangeable so as to match the actual exposure pattern.

Next, a method of correcting the calibration of the focal position determined by the aberration detection system will be described. As described above, the focal position can be measured using the reference pattern plate 19. Normally, the pattern on the pattern plate 19 is matched with the line width to be actually exposed, but the pattern to be exposed varies in size and does not always match. In this case, when spherical aberration occurs due to illumination light absorption, the focal position differs depending on the line width, and there is a problem that the focal position measurement result does not match the focal position of the actual exposure pattern. Here, correction can be performed if the exposure line width and the amount of spherical aberration are known. Regarding the line width, for example, a method of inputting from a keyboard or the like, or a method of writing and reading with a reticle bar code or the like can be considered. The relationship between the spherical aberration and the focal position shift amount may be measured in advance or obtained by simulation, and stored in the form of a table or a mathematical expression. Alternatively, an allowable value is set such that the influence of the spherical aberration amount on the focus detection is sufficiently negligible. If the allowable value is larger than the allowable value, the focus position is not measured. For example, the exposure operation is interrupted to sufficiently cool the projection optical system. There is also a way to wait.

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, the trouble of exposing the pattern using a special mask and the like is not required. The amount of aberration can be easily determined when using the apparatus. Based on the actually measured aberration, it is possible to stop the exposure operation when the aberration occurs, correct the error of the focus detection system 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 38 for changing the distance between lens elements 38, 4
Any one of 8, 42 and 43 may be provided. 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, the exposure can be performed in a state where the aberration is corrected, and the exposure operation according to the aberration can be performed. In addition, since the amount of aberration can be measured, even if the amount of generated aberration such as a phase shift reticle or a plurality of oblique illuminations cannot be predicted, exposure according to the generated aberration can be performed. In addition, measure the spherical aberration
Move lens elements that affect spherical aberration
This enables accurate spherical aberration correction.

[Brief description of the drawings]

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

FIG. 2 is a view showing an opening pattern provided on a reference pattern plate by the apparatus of FIG. 1;

FIG. 3 is a view for explaining the principle of determining a focal position using the aperture pattern of FIG. 2;

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.

FIG. 5 is a diagram partially showing an aberration correcting unit of the apparatus of FIG. 1;

FIG. 6 is a diagram for explaining that the amount of aberration differs depending on the illumination conditions.

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

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

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

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

11A is a diagram showing a signal waveform from a photoelectric conversion element 26 in a state where coma is present in an S image. FIG. FIG. 5B is a diagram illustrating a signal waveform from the photoelectric conversion element 26 in an M image in a state where there is no coma aberration.

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/027

Claims (10)

(57) [Claims] An illumination optical system for irradiating a mask with illumination light from a light source; a projection optical system for imaging a pattern of the mask on a photosensitive substrate; and a light for the projection optical system for holding the photosensitive substrate and for holding 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; while moving the stage in the optical axis direction Light receiving means for illuminating the aperture pattern from the stage side, reaching the mask via the projection optical system, and receiving light reflected by the mask via the projection optical system and the aperture pattern; Stage position measuring means for measuring the position of the stage with respect to the optical axis direction; and obtaining the amount of aberration of the projection optical system from a signal waveform obtained from the photoelectric detecting means. Projection exposure apparatus characterized by having a Saryou calculating means. 2. The projection exposure apparatus according to claim 1, further comprising an aberration correcting unit that corrects aberration of the projection optical system based on a result of the aberration amount calculating unit. 3. The projection exposure apparatus according to claim 1, further comprising an exposure operation control unit for interrupting the exposure operation based on a result of the aberration amount calculation unit. 4. The projection exposure apparatus according to claim 1, further comprising a stage position correcting unit for correcting a position of the photosensitive substrate in the optical axis direction based on a result of the aberration amount calculating unit. 5. A pattern of a mask is projected through a projection optical system.
Projection to expose the substrate by projecting onto the substrate
An exposure apparatus, The projection optical system includes first and second fixed members fixed to a lens barrel.
A fixed lens element and the first fixed lens element
Between the lens and the second fixed lens element
A movable lens element movable with respect to the lens barrel;
Have Driving means for moving the movable lens element, Detecting means for detecting spherical aberration of the projection optical system, Based on the spherical aberration detected by the detecting means,
Control the driving means Move the movable lens element
Control means for performing A projection exposure apparatus comprising: 6. When illuminating the mask with exposure light
Both have a lighting system that can change the lighting conditions, The detecting means is configured to control the sphere in response to a change in the lighting condition.
6. The projection device according to claim 5, wherein the surface aberration is detected.
Shadow exposure device. 7. The illumination system according to claim 1, wherein the illumination system is provided on a pupil plane of the projection optical system.
Characterized by having a changing member for changing the illuminance distribution in
The projection exposure apparatus according to claim 6, wherein 8. The projection optical system according to claim 8, wherein said detecting means is a spherical surface of said projection optical system.
Claims characterized in that aberrations other than aberrations can be detected.
Item 8. The projection exposure apparatus according to any one of Items 5 to 7. 9. The projection optical system of the substrate in an optical axis direction.
Position information on the substrate, and according to the detection result, the substrate
Focusing means for matching the best imaging plane of the projection optical system
Further having The control means responds to the movement of the movable lens element.
The same offset is given to the focusing means.
The projection exposure apparatus according to claim 5. 10. A pattern of a mask is projected through a projection optical system.
Exposure to expose the substrate by projecting it onto the substrate
A shadow exposure method, The spherical aberration of the projection optical system is detected, and the detected spherical aberration is detected.
Based on the difference, the first fixed to the lens barrel of the projection optical system
And the mirror disposed between the second fixed lens element and
Move the movable lens element that is movable with respect to the cylinder
A projection exposure method.