JPH1041226A - Projection optical device and method for adjusting image forming characteristic - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always adjust the image forming characteristic of a projection optical device in an excellent state by eliminating the thermal influence of printing light by adjusting the optical characteristic of the device based on a model formula for the variation of the optical characteristic containing the parameter corresponding to the time constant on the changing characteristic of the optical characteristic and the variation data of the optical characteristic. SOLUTION: The quantity of lighting light is outputted to an arithmetic section 52B from a main control system 46 as the hourly rate, namely, the duty ratio of the lighting light passed through a projection lens per, for example, 5 seconds. The section 52B finds the variation of the focal point and magnification of a projection lens 26 by solving an equation of state and an output equation (model formula) by utilizing the parameter, etc., corresponding to the time constant on the peculiar changing characteristic of the lens 26 stored in a parameter storing section 52A. Then a correction value output section 52C outputs a specific correction value, based on the variation outputted from the arithmetic section 52B to a photoreceptor 54 and a pressure controller 60.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus having a projection optical system,
More particularly, the present invention relates to a projection optical apparatus for controlling a projected mask pattern image to a desired projection state regardless of a change in optical characteristics of a projection optical system in an exposure apparatus for manufacturing a semiconductor element.

[0002]

BACKGROUND OF THE INVENTION Exposure apparatuses, in particular, reduction projection type exposure apparatuses,
In recent years, it has become indispensable for the production of integrated circuits. In such an exposure apparatus, a circuit pattern on a reticle is usually formed on a semiconductor wafer by I / 5 or 1/10.
A projection lens is used which obtains a resolution of 1 μm or more in line width.

In particular, at present, in order to improve the degree of integration of semiconductor devices, there is a demand for a projection lens that increases the resolving power while maintaining a large projection exposure area. Generally, such an exposure apparatus uses a gap sensor that detects the distance between the projection lens and the wafer in order to cope with a change in the thickness of the wafer and unevenness of the surface when forming a predetermined pattern in the lithography process. Focus detector is incorporated. Based on the detection signal of the focus detector, automatic focusing is performed such that the image plane of the projection lens, that is, the image plane of the projection pattern and the wafer surface are matched.

FIG. 2 shows a schematic configuration of a reduction projection type exposure apparatus having such a gap sensor, that is, a so-called stepper. In FIG. 2, a reticle R on which a circuit pattern or the like to be projected is drawn is a reticle stage 2
01. This reticle stage 2
An opening 201 through which the illumination light passing through the pattern area Pr of the reticle R enters the projection lens 202
a is formed. The opening 201a allows an optical image of a circuit pattern drawn on the reticle R to be projected onto a wafer W described later. Further, the reticle stage 201 is provided with a plurality of holding portions 201b for vacuum-sucking the peripheral portion of the reticle R, and the reticle R is sucked and held on the reticle stage 201 by these holding portions 201b. Reticle stage 201
Is slightly moved in the illustrated xy directions, and positioning is performed such that the center of the reticle R is aligned with the optical axis AX of the projection lens 202. Next, below the projection lens 202, a two-dimensional moving stage unique to a stepper is provided. First, a wafer W as a substrate to be projected is placed in a wafer check 2.
03 is vacuum-adsorbed. This wafer check 20
Reference numeral 3 is provided on a Z stage 204 that moves up and down in the optical axis AX direction of the projection lens 202, that is, in the Z direction.
The Z stage 204 moves on a Y stage 205 moving in the y direction and on an X stage 206 moving in the x direction.
It is provided to move up and down by a motor 207. The motors 208 and 209 are respectively connected to the Y stage 20
5, for performing a one-dimensional drive of the X stage 206.

Further, movable mirrors 210 and 211 for a laser interference side elongate for detecting the coordinate position of the stage are provided on the sides of the Z stage 204 in the x and y directions, respectively. In the above apparatus, when the reticle R is illuminated by the illumination optical means (not shown), the pattern area P
The pattern image in r is formed on the image plane of the projection lens 202. A light projector 220 and a light receiver 221 are provided as gap sensors for detecting the positional relationship between the image plane and the surface of the wafer W, that is, the distance between the projection lens 202 and the wafer W.

[0006] Among them, the light projector 220 projects the slit light image obliquely so as to form an image on the image plane of the projection lens 202, and the light receiver 221 receives the light from the wafer W positioned on the image plane. It has a function of receiving the reflected light of the slit light image and detecting the position of the wafer W in the Z direction, that is, the distance between the projection lens 202 and the wafer W. An oblique incident light type focus detector for detecting a focus by projecting a slit-like or rectangular light beam obliquely onto the wafer W as described above is basically disclosed in Japanese Patent Application Laid-Open No. Sho 56-42205. Is the same as

Further, the photodetector 221 synchronously rectifies the photoelectric signal of the reflected light from the wafer W, thereby
And outputs a focus signal indicating the surface position. Since this focus signal is a signal that is synchronously rectified, it has an s-curve characteristic similar to the output characteristic of a photoelectric microscope or the like, and is input to the control circuit 222 for focusing. This control circuit 2
Reference numeral 22 has a function of outputting a control signal for servo-controlling the motor 207 for vertically moving the Z stage 204 based on the focus signal. By this control, the Z stage 204 is adjusted so that the surface of the wafer W is positioned at a height position at which the focus signal indicates focus and the surface of the next wafer W indicates focus. Will be

FIG. 3 shows a detailed configuration example of the gap sensor of the above embodiment. In FIG. 3, a light emitting diode (hereinafter, simply referred to as “LED”) 340 outputs light having a predetermined wavelength width that does not expose the photoresist on the wafer W as illumination light. This illumination light is condensed by a condenser lens 341 and is incident on a slit plate 342 having an elongated rectangular slit 342a. The light transmitted through the slit 342a is
The light is reflected by the mirror 343 and converged by the imaging lens 344.

The converged illumination light is incident on the surface of the wafer W near the optical axis AX of the projection lens 202,
The light image SI of the slit 242a is formed. LE above
D340, condenser lens 341, slit plate 34
2, the mirror 343 and the imaging lens 344 constitute the light projector 220 of FIG. Next, the reflected light from the wafer W is guided to the slit plate 348 via the imaging lens 345, the parallel plate glass (plane parallel) 346, and the vibration mirror 347. That is, an enlarged image of the optical image SI described above is formed on the slit plate 348.

The slit plate 348 has a slit 348
The light transmitted through the slit 348 a is received by the photoelectric detector 349. The above imaging lens 345, parallel plate glass 345,
The vibrating mirror 347, the slit plate 348, and the photoelectric detector 349 constitute the light receiver 221 in FIG.

Note that the vibration mirror 347 is
Accordingly, the enlarged image of the optical image SI is driven on the slit plate 348 so as to make a single oscillation in a direction parallel to the slit 348a and in a direction orthogonal to the longitudinal direction. Next, the photoelectric signal from the photoelectric detector 349 is connected so as to be amplified by an amplifier 351 and then input to a synchronous rectification (synchronous detection) circuit (hereinafter referred to as “PSD”) 352. This P
The SD 352 has a function of receiving a reference frequency signal from an oscillator (hereinafter, referred to as “OSC”) 353 for determining a vibration frequency of the vibration mirror 347, and outputting a focus signal FPS by synchronously rectifying the photoelectric signal with the signal. Having.

The driving circuit 350, the amplifier 351, the synchronous detection circuit 352, and the oscillator 353 constitute the control circuit 222 shown in FIG. The driving unit 56
The present invention relates to the present invention, which will be described later. Incidentally, the position in the Z direction detected by the gap sensor as the in-focus position as described above is mechanically determined so as to be at a constant distance from the projection lens 202 at the time of manufacturing the apparatus. If the focus change occurs due to the temperature change, the surface of the wafer W will be displaced from the image plane even if the focus state is adjusted by the focus signal FPS. In particular, in order to obtain higher resolution, the number of apertures (NA) of the projection lens must be increased, but this necessarily results in a shallower depth of focus.

The depth of focus for obtaining a predetermined pattern line width accuracy becomes smaller as the minimum pattern to be projected becomes smaller.
When projecting a μm line-and-space pattern, the depth of focus is about ± 1 μm. However, when a reticle or mask pattern is projected, the projection optical system, especially the projection lens, absorbs a part of the thermal energy of the printing light and rises in temperature. As a result, the optical performance changes and the best imaging position fluctuates. It is known to

FIG. 4 shows the relationship between the timing of irradiation of printing light in the conventional apparatus, the displacement of the imaging position (or the displacement of the magnification) of the projection optical system, and ΔZ. In this figure, the printing light irradiation starts at time T1 and ends at T3 (see FIG. 1A). The change ΔZ in the image forming position of the projection lens due to the influence of the printing light occurs from time T1 and saturates at time T2. Thereafter, it occurs again from the time T3 at which the printing ends, and a time T4 after a lapse of substantially the same time as T2-T1.
To return to the initial state (see FIG. 3B).

Such a change in the imaging position due to a change in the projection lens itself cannot be corrected only by the above-described conventional focus detector using a gap sensor that detects the distance between the projection lens and the wafer. This variation can be eliminated by using an optical focus detection means via a projection lens, but it has various problems. On the wafer to be projected, there is a patterned film layer of about 1 μm. The patterned film layer may be optically transparent, such as SiO2, or optically, such as Si or aluminum. Some are opaque. Furthermore, a resist film on the order of several microns at the most exists thereon. In addition to such a situation, if printing light is used for such an optical focus detection means, the resist on the wafer is exposed, so this point must be taken into consideration. A means using printing light of a non-photosensitive wavelength of the resist is also possible, but in this case, the aberration of the projection lens is poor, and a high quality image cannot be formed.

In addition, such thermal influences not only change the imaging position but also the magnification of the projection optical system, and cause a failure to form an image with good reproducibility. Further, fluctuations in the imaging characteristics of the projection optical system also occur due to fluctuations in outside air temperature, atmospheric pressure, and the like.

[0017]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and is a projection capable of always adjusting the imaging characteristics satisfactorily without being affected by thermal effects of printing light. It is an object to provide an optical device.

[0018]

According to the present invention, in a projection optical apparatus for projecting a predetermined pattern onto a substrate to be projected via a projection optical system, information relating to a cause of a change in optical characteristics of the projection optical system is obtained. Data collection means, adjustment means for adjusting the optical characteristics of the projection optical system, and projection optical system model formulas and data collection means for fluctuations in optical characteristics including a parameter corresponding to a time constant on a change characteristic of the optical characteristics. And calculating means for calculating an adjustment amount instructed to the adjusting means based on the received data.

The change in the optical characteristics of the projection optical system is
A mathematical expression representing a linear model is calculated and calculated predictively, and the optical characteristics are adjusted based on the calculation result.

[0020]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, in order to facilitate understanding of the present embodiment, an outline thereof will be described. Generally, a system is configured by combining a number of components, and is represented, for example, as shown in FIG.

In FIG. 5, Ui is an input variable, Yi is an output variable, and Xk is a state variable. These variables are generally a function of time t, as they change over time. When a linear system is expressed using these variables, it is expressed by a state equation in the form of a recurrence equation and an output equation for deriving a physical quantity corresponding to a fluctuation value.

The present invention deals with the case where the focus change and magnification change of the projection optical system occur due to the change of the environment such as the incidence of the illumination light, the outside air temperature and the outside pressure. Therefore, the input variable U
i corresponds to the incidence of illumination light and environmental change, and the output variable Y
i corresponds to the focus variation and the magnification. Then, the characteristic change of each element constituting the projection optical system corresponds to the state variable Xk.

Next, the outline of the focus correction will be described.
First, the temperature rise due to the illumination light depends on the amount of illumination light passing through the projection lens. The amount of illumination light is the product of the intensity of the illumination light passing through the projection lens and the open / close duty ratio of the shutter that controls the exposure. Of these,
The illumination light intensity is measured by an illuminance sensor (SPD) on the stage.
Is measured at the beginning of a series of exposure operations such as when the reticle is replaced.

On the other hand, the opening / closing duty ratio of the shutter is determined, for example, by monitoring the opening / closing of the shutter for 5 seconds, and calculating the average value of the duty ratio (the shutter opening time within 5 seconds / 5).
Second). Based on the information on the amount of illumination light obtained as described above, the correction control system 52 shown in FIG. 1 indirectly obtains the amount of change in focus and magnification based on the above-described state equation and output equation. Then, an offset is added to the gap sensor shown in FIGS. 2 and 3 based on the variation.

The magnification correction is basically performed by the same operation, but the correction value is input to the pressure control device 60 for changing the air pressure in the lens chamber of the projection lens, whereby the control is performed. It is. If you change the air pressure,
Since the refractive index of air changes, the magnification of the projection lens 26 itself changes. The focus variation and the magnification variation are controlled by the above method. As described above, the focus and magnification of the projection lens change due to the change in the atmospheric pressure, but corrections are also made to this. The influence of atmospheric pressure is corrected using an atmospheric pressure sensor.

Next, the state of the focal point after the above correction is shown in FIG.
Alternatively, a focus detection mechanism (hereinafter, referred to as “TTLFA”) 58, 59 as a direct fluctuation measuring means shown in FIG.
(See FIG. 1). When it is recognized that the TTLFA is not in a well-focused state, the TTLFA shown in FIG.
Is given to the correction control system 52 shown in (1), and the parameters of the state equation and the output equation are corrected. Then, the amount of change of the focus is obtained again by the corrected equation, and a predetermined correction is performed.

As described above, after the fluctuation correction is performed by the correction control system, the state after correction is checked by the TTLFA. That's why. Therefore, the state in which the fluctuation correction has been performed well in both cases,
The control is performed on the assumption that the state is most matched.

Next, referring to FIG. 6, a focus detection mechanism (hereinafter referred to as "TTLF") for performing focus detection via a projection optical system will be described.
A ”). FIG. 6 shows a state in which the pattern of the reticle R is imaged at the point F. Since the projection target substrate is the reflection plate 28 and is not a wafer, it is not necessary to consider the resist exposure, and Illumination light having a photosensitive wavelength at which chromatic aberration is the best can be used with a sufficient amount of light.

In FIG. 6, the illumination light (the same wavelength as the exposure light) output from the light source 10 is transmitted via a relay lens 12 to a line-and-space (lattice-shaped) pattern PA.
And the transmitted light is incident on the half mirror 16 via the lens 14. The illumination light reflected by the half mirror 16 passes through the field lens 18, the field stop 20, and the relay lens 22 and enters the mirror 24, where it is reflected and enters the reticle R.

Next, the illumination light transmitted through the reticle R reaches the reflector 28 via the projection lens 26 and is reflected there. The light reflected by the reflector 28 enters the mirror 24 via the projection lens 26 and the reticle R, is reflected there, and passes through the relay lens 22, the field stop 20, the field lens 18, and the half mirror 16, respectively. The reflected light provided at a position conjugate with the pupil of the projection lens 26 and split by the splitting prism 30 passes through the relay lens 32 and the cylindrical 33 and passes through the linear ray sensor 34.
A pupil division image is formed in a different upper portion. FIG. 7 shows the above-described array sensor 34, cylindrical lens 33, relay lens 32, split prism 30, field lens 18, and field stop 20 in an enlarged manner. The generatrix of the cylindrical lens 33 corresponds to the direction in which the light receiving elements of the array sensor 34 are arranged. The cylindrical lens 33 has a function of increasing the amount of light by compressing the line direction of the reflection image of the pattern PA and performing averaging.

The optical element in the TTLFA section constitutes the section 58 of the alignment optical system as shown in FIG. 1, and the TTLFA system 59 is constituted in the other sections. In FIG. 6, a broken line indicates an imaging light beam (principal ray) of the illumination light from the light source 10, and a solid line indicates the principal ray of the imaging light beam of the reticle R, the reflector 28, and the like. In the apparatus as described above, the angle formed by the imaging light flux imaged at the point F is ± θ1 if the numerical aperture NA is sin θ1. In this example, the light beam of 2θl is split into two by a splitting prism 30 on a plane including the optical axis, and the focus is detected by using the properties of the split light beam.

In FIG. 6, a lattice pattern PA is
The reticle R and the reflector 28 are disposed between the condenser lens 12 and the relay lens 14 at a position conjugate with the reticle R, and the pattern PA is illuminated by the light source 10 and projected onto the reflector 28. The pattern image reflected by the reflection plate 28 is split into two by a split prism 30 located at a position conjugate with the aperture stop (pupil) eP of the projection lens 26.

As is well known, each of the split light beams is shifted laterally from each other by a front pin and a rear pin. Therefore, by measuring the interval between the two divided images on the array sensor 34, the in-focus state can be detected. That is, as shown by the solid line in FIG. 7, if the distance between the two images is L during focusing, the distance L 'is smaller than L in the case of the back focus as shown by the dotted line.
In the case of the front focus, it becomes wider than the image interval L.

In order to accurately extract the lateral displacement of the image, for example, there is a method in which the image on the array sensor 34 is subjected to Fourier transform, the phase portion thereof is extracted, and the lateral shift is obtained by the transition theorem of Fourier transform. . First, the intensity of the light image on the array sensor 34 is determined by the function f of the position x in the arrangement direction of the elements of the sensor 34, that is, the direction perpendicular to the optical axis.
(X). Then, the Fourier transform F1 of the intensity f (x) before the light image shifts can be expressed as in equation (1), where S is the spatial frequency.

[0035]

(Equation 1)

Next, the Fourier transform in the case where the light image is displaced by a in the horizontal direction is expressed by the equation (2) based on the transition theorem.

[0037]

(Equation 2)

Comparing the above equations (1) and (2),
Since only the phase shifts by 2πas without changing the magnitude of the Fourier component due to the displacement a, if the phase of the shift is Δθ, the displacement a is expressed as in equation (3).

[0039]

(Equation 3)

In practice, the integration interval cannot be infinite. Therefore, integration is performed on the array sensor 34 for a section having an appropriate sample length l. Next, a correction control system for obtaining the amount of change in focus or the like based on the above-described state equation or the like will be described with reference to FIG. In FIG. 1, the illumination light output from the light source 40 is:
The light enters the wafer W via the shutter 42, the reticle R, and the projection lens 26. The drive of the shutter 42 is performed by a shutter control system 44, and the shutter control system 44 is connected to a main control system 46.

Next, the main control system 46 is connected to the motors 48 and 50 for driving the X and Y stages, and is also connected to the correction control system 52. This correction control system 52
Is composed of a parameter storage unit 52A, a calculation unit 52B, a correction value output unit 52C, and a parameter correction unit 52D. Among them, the information relating to ON and OF of the shutter 42 and the information from the parameter storage unit 52A corrected by the parameter correction unit 52D are input to the calculation unit 52B from the main control system 46. Arithmetic unit 5
The output of 2B is output to a correction value output unit 52C, and the output of the correction value output unit 52C is output to a light receiver (or pressure control device 60) 54. I have. Specifically, a correction value is input to the driving unit 56 for rotating the parallel flat glass 346 shown in FIG. 3 so that an offset is applied at the time of oblique incidence type focus detection.

More specifically, the parallel plate glass 34 described above is used.
Numeral 6 is arranged in the light collecting system after the magnifying lens 345, and is configured to be tiltable within a predetermined angle range by the driving unit 56. When the degree of inclination of the parallel plate glass 346 changes, the vibration center of the enlarged image of the optical image SI formed on the slit plate 348 is oriented in a direction orthogonal to the longitudinal direction of the slit 348a (in FIG. 3, the horizontal direction on the paper). Shift to
The shift of the vibration center with respect to the slit 348a is equivalent to shifting the position of the wafer W in the Z direction when the focus signal FPS is focused, that is, when it is determined to be the zero point position on the S-curve characteristic waveform. In this embodiment, the parallel plate glass 346 and the driving unit 56 correct the focus variation.

Next, the reflected light from the reflecting plate 28 on the Z stage 204 is reflected by the projection lens 26 and the reticle R
Through the alignment optical system 58, is taken out from the part of the alignment optical system 58, and enters the TTLFA system 59 shown in detail in FIG. The information of the defocus detected by the TTLFA system 59 is transmitted to the parameter correction unit 52D of the correction control system 52 described above.
To be entered.

The output of the correction value output section 52C is also connected to a pressure control device 60 for controlling the pressure in the lens chamber of the projection lens 26.
The control of the magnification change of the projection lens 26 is performed by the pressure control according to the above. In this example,
Part 5 of the alignment optical system provided above the reticle R
8 through the TTLFA system 5
9, any method may be used as long as the reflected light can be detected through the projection lens 26, and other optical means, for example, non-photosensitive laser light may be applied to the wafer W without passing through a reticle. The reflected light may be guided using an alignment system (LSA system) that supplies the reflected light.

Of the above components, first, the shutter control system 44 is operated by the command from the main control system 46.
For controlling the opening and closing of. For information on shutter opening and closing,
The data is input from the main control system 46 to the calculation unit 52B, and is used as data for obtaining the amount of illumination light. Since the illumination light intensity changes depending on the transmittance of the reticle and the lamp light intensity, the illumination light intensity is detected by a photoelectric element (not shown) provided on the wafer stage. Information detected by the elements is also input to the calculation unit 52B as data for obtaining the amount of illumination light. This photoelectric element is not always necessary in the present invention.

Next, the operation unit 52B uses the information on the input amount of illumination light and the parameters stored in the parameter storage unit 52A to generate a state equation and an output equation (hereinafter referred to as a “model equation”). To obtain the amount of change in focus and magnification. The parameters of the parameter storage unit 52A are, as described later,
The parameter is corrected by the parameter correcting section 52D.

Next, the correction value output section 52C is
A specific correction value based on the fluctuation amount output from B is output to each of the light receiver 54 and the pressure control device 60. Next, a model equation for the projection optical system used in the calculation unit 52B, that is, a state equation and an output equation will be described. The projection lens 26 is configured to
The temperature changes every moment. Therefore, the variables “U, Y, X
i "should be expressed as a function of time, but here, we consider discretizing time,
"U (K), Y (K), Xi (K)". Where K
= 0, 1, 2,....

That is, in this embodiment, since the duty of the time during which the shutter is open is measured at intervals of 5 seconds as described above, K which is a discrete value of K is used instead of time. For the above K, if the equation for the projection lens 26 is expressed in two dimensions,

[0049]

(Equation 4)

[0050]

(Equation 5)

In these equations (4) and (5), the input variable U (K) is the amount of illumination light that has passed through the projection lens 26 for 5 seconds, that is, the amount of energy. It is expressed as the product of the ratio and the irradiation light intensity. The output variable Y (K) is the focus to be obtained or the amount of change in magnification. State variables X1 (K), X
2 (K), X1 (K + 1) and X2 (K + 1) correspond to physical quantities in this case. In this embodiment, a new focus and magnification change amount Y (K) is calculated every 5 seconds, so that the state variable after 5 seconds is X1 (X1 (K), X2 (K). K + 1) and X2 (K + 1).

Next, α, β, a, b, m, and L are constants (parameters) determined so as to reproduce the fluctuation characteristics of the projection lens 26 shown in FIG. Of these, the parameters α and β correspond to the time constant on the change characteristic inherent to the projection lens 26, the parameters a and b correspond to the coefficient terms on the characteristic, and m is the same even if the illumination light amount is the same. In view of the fact that the characteristic is slightly different for each projection lens, it is a unique constant determined for each projection lens. L corresponds to the light intensity of the lamp.

Next, the parameters α, β, a,
A specific method for obtaining b and m will be described. These parameters can be measured by a method such as performing a pseudo-exposure operation before the actual exposure operation, but can be measured using the above-described TTLFA during the exposure operation or during the operation. Monkey In this embodiment, α, β, a,
A method of determining b and m in advance from experiments and sequentially estimating “L” using the measurement result by TTLFA as described later will be described.

Α, β, a, b, and m are determined in advance as follows. First, a reflector 28 is placed immediately below the projection lens 26, and the gap between the projection lens 26 and the reflector 28 is kept constant by a gap sensor. Then, when the illumination light is passed through the projection lens 26, a change in the output of the TTLFA is obtained as shown in FIG. The amount of change Δ in FIG.
The rising curve of Z is represented by the sum of exponential functions. For example

[0055]

(Equation 6)

Is represented by In this equation (6), 1 / T
1, 1 / T2 correspond to the parameters α and β, respectively, and A and B
Correspond to parameters a and b, respectively. It should be noted that the above parameters are obtained for a change in focus and a change in magnification. These parameters are stored in the parameter storage unit 52A shown in FIG. 1, and are used for calculating the model formulas of the calculation units 52B (4) and (5).

Next, the overall operation of the above embodiment will be described. First, a description will be given of how the arithmetic unit 52B (see FIG. 1) of the correction control system 52 captures information regarding the amount of illumination light. First, in the case of the step-and-repeat method, exposure is performed in a pulsed manner at predetermined intervals, as shown in FIG. Then, as shown in FIG.
The illumination light amount is output from the main control system 46 to the calculation unit 52B as a time ratio of the illumination light transmitted through the projection lens 26 during 5 seconds, that is, a duty ratio. This ratio corresponds to the ratio of the opening time of the shutter 42 for a predetermined 5 seconds.

It should be noted that the duty ratio detected at a certain point in time is a value up to 5 seconds before the detection point, and no value before that is detected at all. The reason why the past influence is not considered is that the projection optical system is assumed to be a linear system. As described above, the illumination light intensity is measured by an illuminance sensor (not shown) provided on the stage.
And is input to the calculation unit 52B.

Next, the fluctuation correction will be specifically described with reference to FIG. FIG. 7A shows the above-described duty ratio, and FIG. 7B shows the calculated value (predicted value) Yi of the fluctuation. First, time t = t0
Then, the exposure has not started yet. Therefore, (5)
The input variables X1 and X2 of the expression are both 0, and the fluctuation calculation value Yj is 0.

Next, at time t = t1, the exposure is started and the duty ratio DT = D1, the calculation by the equations (4) and (5) is performed, and Y = Y1, and the value Y1 after 5 seconds is obtained. Is calculated. Next, at time t = t2, the exposure is further continued and the duty ratio DT = D2,
The calculation based on the equations (4) and (5) is performed to obtain the sum Y2 with the value Y1 '5 seconds after the previous time, and the value Y further 5 seconds later.
2 'is required.

As described above, the variation Yj is repeatedly calculated every 5 seconds. As described above, the fluctuation amount Yj is performed based only on the calculated value five seconds before, and is not considered before that. Note that these variations are relative to the focus,
Each of the factors relating to the magnification is calculated.

The variation calculated by the calculation section 52B as described above is output to the correction value output section 52C. In the correction value output unit 52C, a specific degree of inclination of the parallel flat glass 346 (see FIG. 3) and a pressure control value in the lens chamber of the projection lens 26 are obtained based on the input fluctuation amount. 54, pressure control device 60
(See FIG. 1).

At this time, a focus fluctuation also occurs in the pressure control. For this reason, the correction value output unit 52C determines the degree of inclination of the parallel flat glass 346 in consideration of the focus variation due to the pressure control, and based on this, offsets the drive unit 56 (see FIG. 3). Therefore, both the focus variation and the magnification variation are ideally corrected to zero.However, when a certain amount of time elapses due to a setting error of a parameter in an arithmetic expression or a cumulative error due to repetitive arithmetic, etc.
An error occurs between the calculated fluctuation prediction amount and the actual fluctuation amount (the characteristic of the fluctuation actual measurement value in FIG. 9B), and the correction is not always satisfactorily performed.

Therefore, in this embodiment, the parameters of the equations (4) and (5) are corrected using the TTLFA of FIG. Hereinafter, the correction method will be described. The check by the TTLFA is performed each time one wafer is exposed or each time one wafer is processed. First, focusing is performed on the reflector 28 on the stage by the gap sensor shown in FIG. Next, while maintaining this state, the defocus is detected with respect to the reflection plate 28 using TTLFA. When the deviation is equal to or larger than the allowable value, the parameter is corrected by the parameter correcting unit 52D.

Here, a case where the parameter L of the equation (4) is modified will be described. This correction is made by the following equation.

[0066]

(Equation 7)

Here, G is called an adaptive gain, and is determined so that the sequence Li converges. Yi
Is the result of measurement by the i-th TTLFA, and Y
Are (4) and (5) at the time of measurement as described above.
Is the calculated value. Such parameter correction is performed by the parameter correction unit 52D of FIG.
The corrected parameters are input from the parameter storage unit 52A to the calculation unit 52B, and the calculations of the equations (4) and (5) using the new parameters are performed. Note that parameters other than L, a, b, and m, may be modified.

As described above, the parameters are sequentially adjusted to appropriate values by performing the check by the TTLFA. Therefore, the interval between checks by the TTLFA can be gradually increased. Next, another method of capturing information regarding the amount of illumination light will be described. In this method, for example, the open / closed state of the shutter 42, that is, the ON / OF state, is input from the main control system 46 to the calculation unit 52B every 1 ms for an opening time of 200 ms of the shutter 42. More specifically, the open / closed state of the shutter 42 shown in FIG. 10A is sampled every lmS and input to the arithmetic unit 52B as shown in FIG.

Next, the variation amount Y is calculated by the equations (4) and (5).
Find (K). First, at time t1, the shutter is turned off.
Therefore, no exposure is performed. Therefore, the fluctuation amount Y (1) is 0. At time t = t2, shutter is ON
And exposure is being performed. Therefore, the sampled value becomes a logical value "T", and U (K
The variation amount Y (2) is obtained by 2).

Next, at time t = t3, the variation Y (3) is similarly obtained based on the incident light amount U (K3). The offset for the gap sensor in FIG. 3 is added based on the amount of change obtained by repeating the above operation. The offset may be performed every 1 mS, or may be performed every 5 seconds as in the method described above.

However, in the above method, an error in correction may occur due to a large number of operations and an error in parameter setting. Therefore, T shown in FIGS.
The actual position of the image plane is occasionally checked by the TLFA, and based on the result, the parameters of the equations (4) and (5) are corrected by the parameter correction unit 52D to reduce the occurrence of errors.

In some cases, the initial value of the state variable Xk may be incorrect. In this case,
The estimation is performed by a so-called observer. Observers are

[0073]

(Equation 8)

The configuration is as follows. Thereby, Xk
Is corrected to Xka using the measurement result Ye by TTLFA. f is a constant called an observer gain. The following equations (4) and (5) are operated by the corrected state variable Xka. More specifically, first, the actual measured value Ye of the focus change is measured using TTLFA (see FIGS. 6 and 7). The interval is an interval at which the value of the state variable Xk is updated n times. That is, TT
By LFA, Ye (Ko), Ye (Ko + n), Ye
(Ko + 2n). The value of... Will be known. Next, the average value Ua of the parameter U between K = K0 and K = K0 + n is obtained by solving the equation (4) from Ye (Ko) and Y (Ko + n). Next, using this Ua, the state variables X, K between K = K0 + n and K = K0 + 2n are used.
The estimated values Xa and Ya of the output variable Y are sequentially obtained by the following recurrence formula.

[0075]

(Equation 9)

[0076]

(Equation 10)

This Ya (K) is the estimated value of focus variation Yj ′.
Will correspond. In the above method, T
The measurement interval of the TLFA need not always be a constant value. For example, the method may be performed for each exposure of one wafer W, or may be performed when the focus variation is large, and when the focus variation is small, the interval may be increased. In the above embodiment, the description has been made with a focus on the temperature change due to the illumination light. Can be corrected in the same manner. In particular, parameter correction by TTLFA is effective.

In the above embodiment, both the focus and the magnification of the projection lens are corrected, but only one of them may be used. Further, by detecting a reference mark provided on a portion of the reflecting plate 28 using the TTL alignment system 58 (see FIG. 1), the magnification change of the projection lens can be measured. For this purpose, a plurality of alignment systems 58 are provided so as to detect marks at different positions on the reticle R, respectively. Then, by moving the reference mark in the image plane of the projection lens and measuring the positional relationship between the projection points of the two marks on the reticle R, a magnification error can be detected. Therefore, when such measurement is possible, the alamement system and the reference mark work together as the variation measuring means of the present invention.

Alternatively, as disclosed in JP-A-59-94032, a photoelectric sensor having a slit on an XY stage is provided, and the contrast of a projected image of a reticle pattern is detected by the photoelectric sensor, and projection is performed. A method of obtaining the actual image plane position of the lens is also effective as the fluctuation measuring means of the present invention. Further, as the adjusting means of the present invention, when the reticle side of the projection lens is a non-telecentric type, a method of adjusting the magnification by changing the distance between the reticle R and the projection lens is also effective.

[0080]

As described above, according to the present invention,
Correction of the change of the projection optical system itself, especially the focus fluctuation of the projection optical system due to temperature change, enables accurate focusing at all times, so that the line width of the pattern to be exposed becomes more precise, and the This has the effect of improving reproducibility. Further, according to the present invention, not only thermal changes due to light absorption of the projection optical system, but also environmental changes such as changes in atmospheric pressure, changes in device temperature, and the release of distortion that the device has structurally can be caused. What kind of effect can be obtained even with respect to the focus fluctuation that occurs.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention,

FIG. 2 is a perspective view showing a schematic configuration of an exposure apparatus.

FIG. 3 is a configuration diagram showing a detailed configuration example of a gap sensor.

FIG. 4 is a diagram showing a change in optical characteristics of a projection lens due to incidence of illumination light;

FIG. 5 is an explanatory diagram showing a general system,

FIG. 6 is a configuration diagram showing a TTLFA;

FIG. 7 is a configuration diagram showing a main part of a TTLFA;

FIG. 8 is a diagram illustrating the capture of information regarding the amount of incident light,

FIG. 9 is a diagram for explaining a variation calculation.

FIG. 10 is a view for explaining a variation calculation.

[Explanation of symbols]

 Reference numeral 25: Projection lens, 28: Reflector, 30: Split prism, 34: Array sensor, 40: Light source, 42: Shutter, 52: Correction control system, 54: Light receiver, 55: Drive unit, 60: Pressure control device

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 7, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Patent application title: Projection optical apparatus and imaging characteristic adjustment method

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical apparatus and an image forming characteristic adjusting method, and more particularly, to a projection optical apparatus in an exposure apparatus for manufacturing a semiconductor device or a liquid crystal display element and an image forming characteristic adjusting method of the projection optical apparatus. is there.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0007

[Correction method] Change

[Correction contents]

Further, the photodetector 221 synchronously rectifies the photoelectric signal of the reflected light from the wafer W, thereby
And outputs a focus signal indicating the surface position. Since this focus signal is a signal that is synchronously rectified, it has an s-curve characteristic similar to the output characteristic of a photoelectric microscope or the like, and is input to the control circuit 222 for focusing. This control circuit 2
Reference numeral 22 has a function of outputting a control signal for servo-controlling the motor 207 for vertically moving the Z stage 204 based on the focus signal. By this control, the Z stage 204 is adjusted so that the surface of the wafer W is located at a height position such that the focus signal indicates focus.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

The converged illumination light is incident on the surface of the wafer W near the optical axis AX of the projection lens 202,
The light image SI of the slit 242a is formed. LE above
D340, condenser lens 341, slit plate 34
2, the mirror 343 and the imaging lens 344 constitute the light projector 220 of FIG. Next, the reflected light from the wafer W is guided to the slit plate 348 via the imaging lens 345, the parallel plate glass (plane parallel) 346, and the vibration mirror 347. That is, an enlarged image of the optical image SI described above is formed on the slit plate 348.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

In addition, such thermal influences not only change the imaging position but also the magnification of the projection optical system, and cause a failure to form an image with good reproducibility. Further, the fluctuation of the image forming characteristic of the projection optical system also occurs due to the fluctuation of the outside air temperature and the atmospheric pressure.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

[0018]

According to the present invention, in a projection optical apparatus for projecting a predetermined pattern onto a substrate to be projected via a projection optical system, information relating to a cause of a change in imaging characteristics of the projection optical system is obtained. Data collection means for obtaining, adjustment means for correcting the imaging characteristics of the projection optical system, and model formulas and data of the projection optical system with respect to fluctuations in the imaging characteristics including a parameter corresponding to a time constant on a change characteristic of the imaging characteristics. And calculating means for calculating an adjustment amount instructed to the adjusting means based on the data collected by the collecting means. Further, in an imaging characteristic adjusting method for adjusting an imaging characteristic of a projection optical device that projects a predetermined pattern onto a projection target substrate via a projection optical system, information on a cause of an imaging characteristic variation of the projection optical system is obtained. Predict the fluctuation of the imaging characteristic based on the model formula of the projection optical system and the information on the cause of the fluctuation of the imaging characteristic with respect to the fluctuation of the imaging characteristic including the parameter corresponding to the time constant on the change characteristic of the imaging characteristic. And adjusting the imaging characteristic of the projection optical device based on the prediction result.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

Next, the state of the focal point after the above correction is shown in FIG.
Alternatively, a focus detection mechanism (hereinafter, referred to as “TTLFA”) 58, 59 as a direct fluctuation measuring means shown in FIG.
(See FIG. 1). When it is recognized by the TTLFA that the subject is not in a well-focused state, FIG.
Is given to the correction control system 52 shown in (1), and the parameters of the state equation and the output equation are corrected. Then, the amount of change of the focus is obtained again by the corrected equation, and a predetermined correction is performed.

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction contents]

Next, the main control system 46 is connected to the motors 48 and 50 for driving the X and Y stages, and is also connected to the correction control system 52. This correction control system 52
Is composed of a parameter storage unit 52A, a calculation unit 52B, a correction value output unit 52C, and a parameter correction unit 52D. Among them, the information relating to ON and OF of the shutter 42 and the information from the parameter storage unit 52A corrected by the parameter correction unit 52D are input to the calculation unit 52B from the main control system 46. Arithmetic unit 5
The output of 2B is output to a correction value output unit 52C, and the output of the correction value output unit 52C is output to a light receiver (or pressure control device 60) 54. I have. Specifically, a correction value is input to the driving unit 56 for rotating the parallel flat glass 346 shown in FIG. 3 so that an offset is applied at the time of oblique incidence type focus detection.

[Procedure amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0051

[Correction method] Change

[Correction contents]

In these equations (4) and (5), the input variable U (K) is the amount of illumination light that has passed through the projection lens 26 for 5 seconds, that is, the amount of energy. It is expressed as the product of the ratio and the irradiation light intensity. The output variable Y (K) is the focus to be obtained or the amount of change in magnification. State variables X1 (K), X
2 (K), X1 (K + 1) and X2 (K + 1) do not correspond to physical quantities in this case. In this embodiment, a new focus and magnification change amount Y (K) is calculated every 5 seconds, so that the state variable after 5 seconds is X1 (X1 (K), X2 (K). K + 1) and X2 (K + 1).

[Procedure amendment 11]

[Document name to be amended] Statement

[Correction target item name] 0053

[Correction method] Change

[Correction contents]

Next, the parameters α, β, a,
A specific method for obtaining b and m will be described. These parameters can be measured by a method such as performing a pseudo-exposure operation before the actual exposure operation, but can be measured using the above-described TTLFA during the exposure operation or during the operation. it can. In this embodiment, α, β, a,
A method of determining b and m in advance from experiments and sequentially estimating “L” using the measurement result by TTLFA as described later will be described.

[Procedure amendment 12]

[Document name to be amended] Statement

[Correction target item name] 0072

[Correction method] Change

[Correction contents]

In some cases, the initial value of the state variable Xk may be incorrect. In this case,
The estimation is performed by a so-called observer. Observers are

[Procedure amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0077

[Correction method] Change

[Correction contents]

This Ya (K) is the estimated value of focus variation Yj ′.
Will correspond. In the above method, T
The measurement interval of the TLFA need not always be a constant value. For example, the method may be performed for each exposure of one wafer W, or may be performed when the focus variation is large, and when the focus variation is small, the interval may be increased. In the above embodiment, the description has been made by focusing on the temperature change caused by the illumination light. Can be corrected in the same manner. In particular, parameter correction by TTLFA is effective.

[Procedure amendment 14]

[Document name to be amended] Statement

[Correction target item name] 0078

[Correction method] Change

[Correction contents]

In the above embodiment, both the focus and the magnification of the projection lens are corrected, but only one of them may be used. Further, by detecting a reference mark provided on a portion of the reflecting plate 28 using the TTL alignment system 58 (see FIG. 1), the magnification change of the projection lens can be measured. For this purpose, a plurality of alignment systems 58 are provided so as to detect marks at different positions on the reticle R, respectively. Then, by moving the reference mark in the image plane of the projection lens and measuring the positional relationship between the projection points of the two marks on the reticle R, a magnification error can be detected. Therefore, when such measurement is possible, the alamement system and the reference mark work together as a variation measuring means.

[Procedure amendment 15]

[Document name to be amended] Statement

[Correction target item name] 0079

[Correction method] Change

[Correction contents]

Alternatively, as disclosed in JP-A-59-94032, a photoelectric sensor having a slit on an XY stage is provided, and the contrast of a projected image of a reticle pattern is detected by the photoelectric sensor, and projection is performed. A method of obtaining the actual image plane position of the lens is also effective as a fluctuation measuring means. Further, as the adjusting means of the present invention, when the reticle side of the projection lens is a non-telecentric type, a method of adjusting the magnification by changing the distance between the reticle R and the projection lens is also effective.

[Procedure amendment 16]

[Document name to be amended] Statement

[Correction target item name] 0080

[Correction method] Change

[Correction contents]

[0080]

As described above, according to the present invention,
In particular, it is possible to correct image forming characteristics (focus fluctuation, magnification fluctuation) of the projection optical system, and to form an image with good quality and good reproducibility. Further, since accurate focusing can always be performed, there is an effect that the line width of the pattern to be exposed is more precisely controlled and the reproducibility is improved. Further, according to the present invention, not only a thermal change due to light absorption of the projection optical system, but also an environmental change such as a change in atmospheric pressure, a change in apparatus temperature, and a release of a structural distortion of the apparatus. Whatever effect can be obtained even with respect to a change in focus and a change in magnification.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shoichi Tanimoto 1-6-3 Nishioi, Shinagawa-ku, Tokyo Nikon Oi Works Co., Ltd.

Claims (1)

[Claims] 1. A projection optical apparatus for projecting a predetermined pattern onto a substrate to be projected via a projection optical system, wherein: data collection means for obtaining information on a cause of a change in optical characteristics of the projection optical system; Adjusting means for adjusting the optical characteristics of the optical characteristics, and a model formula of the projection optical system with respect to the fluctuation of the optical characteristics including a parameter corresponding to a time constant on the change characteristics of the optical characteristics, and data collected by the data collecting unit. Calculating means for calculating an adjustment amount instructed to the adjusting means based on the calculating means.