JPH0888164A - Projection aligner - Google Patents

Abstract

PURPOSE: To maintain imaging characteristics of optimum precision, by comparing the reference value which is previously set according to imaging performance with the change of imaging characteristics which can be known by an inspection means, and performing at least one operation out of the display of alarm and the interruption of exposure operation. CONSTITUTION: A measurement equipment 19 is installed in the vicinity of a projection aligner, and measures atmospheric pressure, temperature, etc. The measure results are outputted to a detection part 28, as the data about environmental condition changing in the course of exposure operation. From a key board 25, an operator of the equipment inputs data to an input part 27 which data are concerned with the kind of photosensitizer and whether an optical filter is used. About the change of the respective imaging characteristics and the change of the respective environmental conditions, a plurality of references for the display of alarm and for the interruption of exposure operation are set according to the values of imaging performance to be required. When the value exceeds the previously set reference, a control part 26 outputs at least one command out of the display of alarm and the interruption of exposure operation.

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,
In particular, the present invention relates to a projection exposure apparatus for manufacturing semiconductor integrated circuits and liquid crystal devices, which requires highly accurate imaging characteristics.

[0002]

2. Description of the Related Art In a photolithography process for forming a circuit pattern of a semiconductor element or the like, a reticle (mask) is irradiated with, for example, i-line (wavelength 365 nm) of a mercury lamp as illumination light. Then, the transmitted light of the circuit pattern on the reticle is condensed via a projection optical system onto a substrate (semiconductor wafer, glass plate, etc.) coated with a photosensitive photoresist to form the circuit pattern on the substrate. A projection exposure apparatus (for example, a stepper) that forms an image and transfers the image is used.

With respect to this type of projection exposure apparatus, it has been increasingly required in recent years to maintain the imaging performance of the projection optical system with high accuracy. However, the higher the required accuracy, the more the imaging characteristics are improved. It is more susceptible to changes in environmental conditions.
For this reason, in particular, with respect to the focus position and the projection magnification, a method is adopted in which a change in environmental conditions is measured and correction is constantly made based on the change.

The environmental conditions that affect the imaging characteristics are mainly those caused by the projection optical system absorbing the illumination light beam and causing a temperature change, and those caused by a change in the atmospheric pressure and the air temperature. It is caused by a change in the refractive index. A method for correcting the fluctuation of the image forming characteristic is disclosed in, for example, Japanese Patent Laid-Open No. 60-78454. There, the amount of energy (heat amount) accumulated in the projection optical system due to the incidence of illumination light on the projection optical system is sequentially calculated, and the change amount of the imaging characteristic due to this accumulated energy amount is obtained, and a predetermined correction mechanism is set. Has proposed a method for finely adjusting the image forming characteristic. As this correction mechanism, for example, there is a method of sealing a space sandwiched by two lens elements of a plurality of lens elements forming a projection optical system and adjusting the pressure of the sealed space. In addition, when correcting the fluctuation of the imaging characteristics caused by the change of the refractive index of air due to the change of atmospheric pressure or temperature, the atmospheric pressure or the temperature is measured and the atmospheric pressure or the temperature previously obtained is measured. Based on the relationship between the image forming characteristics and the like, the amount of change in the image forming characteristics due to the change in atmospheric pressure, temperature, etc. is estimated and corrected by a predetermined correction mechanism.

Further, instead of measuring the cause (illumination light absorption amount, atmospheric pressure or air temperature) of changing the image forming characteristics as described above, the change of the aerial image of the projection optical system is measured to determine the focus position. A method of directly obtaining a change in the image forming characteristic such as a projection magnification and correcting the image forming characteristic by a predetermined correction mechanism is also proposed in, for example, Japanese Patent Laid-Open No. 5-41344. According to this method, it is possible to increase the correction accuracy by increasing the frequency of measurement, but at the same time, the productivity (throughput) of the device is reduced. Therefore, in practice, it is used in combination with the above-mentioned method of cause measurement. It is often done.

By the way, the above-mentioned correction method can be applied only to the correction of the image formation characteristic such as the focus position and the projection magnification which is relatively easy to correct. This is because if the number of correction items (focal position, magnification, etc.) increases, the apparatus becomes more complicated, and the correction items are closely related to each other, and it is difficult to correct each correction item independently. Therefore, for an item for which direct correction is difficult, a corresponding technique is proposed by providing a function of temporarily stopping the exposure operation when it is determined that the imaging condition exceeds the allowable range. There is. This technique is disclosed in detail, for example, in Japanese Patent Laid-Open No. 63-291417. Further, with respect to the correctable items such as the focus position and the projection magnification, it is not possible to perform the infinitely accurate correction, and there is a range in which the predetermined correction accuracy can be maintained, and if the range deviates, the correction accuracy deteriorates. An apparatus having a function of temporarily stopping exposure when the range is exceeded is disclosed in, for example, Japanese Patent Laid-Open No. 25199/1993. More specifically, a technique has been proposed in which an error or warning is displayed or the exposure operation is stopped according to the energy amount of the illumination light absorbed by the projection optical system, the atmospheric pressure, the temperature change amount, or the like.

On the other hand, various high resolution techniques have been developed in recent years because there is a limit to the high precision of the image forming performance defined by the wavelength of illumination light and the numerical aperture of the projection optical system. For example, in Japanese Examined Patent Publication No. 62-50811, the phase of the transmitted light from a specific portion of the transmitted portion of the circuit pattern of the reticle is π (ra.
A method of using a phase shift reticle with a phase shifter, which is offset by d) is disclosed. When this phase shift reticle is used, a finer pattern can be transferred as compared with the case where a normal reticle is used, so that the resolution can be increased and the depth of focus can be deepened.

Recently, attempts have been made to enable transfer of fine patterns by optimizing the illumination conditions or devising the exposure method. For example, the optimum numerical aperture of the illumination optical system for a pattern having a specific line width. There has been proposed a method of improving resolution and depth of focus by selecting a combination of (σ value) and numerical aperture (NA) of the projection optical system for each pattern line width. Further, the light quantity distribution of the illumination light flux on the surface of the illumination optical system (hereinafter referred to as the pupil surface), which is the Fourier transform surface of the surface on which the pattern on the reticle exists, or in the vicinity of the surface is defined as a ring-shaped reticle pattern. For example, an annular illumination method for irradiating an illuminating light flux on the surface of the reticle, or an inclined illumination method for irradiating the illuminating light flux with a predetermined angle in a specific direction corresponding to the pattern of the reticle, is disclosed in, for example, Japanese Patent Laid-Open No. Hei 4
It is proposed in Japanese Patent Publication No. 225514.

[0009]

By the way, in the prior art for maintaining the accuracy of the exposure performance within a predetermined allowable range as described above, the product which requires the highest accuracy that can be manufactured by the apparatus is used. The reference value for stopping the exposure or issuing a warning is uniquely set so that the imaging performance with sufficient accuracy is guaranteed. However, when the apparatus is not always used in a process requiring the highest accuracy, and when it is used in a sufficient process even with a lower accuracy, the exposure operation is unnecessarily stopped and the throughput is increased. There was a problem of getting worse.

Further, by using the various high resolution techniques as described above, even when the same projection optical system as the conventional one and the same wavelength of the illumination light are used, a higher resolution and a deeper depth of focus can be obtained. Therefore, when the same reference value as the conventional reference value is applied, the exposure operation is unnecessarily stopped and the throughput is deteriorated.

On the contrary, when higher accuracy is required for the image forming performance, there is a possibility that the stop of the exposure operation may be delayed with the initial reference value. Therefore, when higher accuracy is required, there has been a problem that the initial setting regarding the reference value for stopping the exposure operation must be changed each time.

According to the present invention, in order to maintain a predetermined image forming performance, the conventional exposure apparatus has problems such as displaying a warning and stopping the exposure operation according to a uniquely set reference value. In view of the above, it is an object of the present invention to provide a new and improved projection exposure apparatus capable of maintaining an image forming characteristic with optimum accuracy according to a required image forming performance. is there.

[0013]

In order to solve the above problems, in the present invention, the illumination light (I) from the light source (1) is used.
L) is shaped into a substantially uniform intensity distribution and the illumination optical system (2, 5) for irradiating the mask (R), and the image of the pattern formed on the mask is projected onto the photosensitive substrate (W) by projection exposure. In a projection exposure apparatus having a projection optical system (PL), the imaging performance required for the projection optical system (for example, the depth of focus in the exposure area,
Information about the amount of image distortion) and the required imaging performance (for example, the target line width to be exposed, the illumination condition of the illumination optical system, the numerical aperture of the projection optical system, the presence or absence of a mask phase shifter, the step of the photosensitive substrate, Input means for inputting at least one of the type of the photosensitizer applied to the photosensitive substrate and the presence or absence of an optical filter provided in the projection optical system, and a change in the imaging characteristics of the projection optical system (for example, in the exposure area) Depth of focus, the amount of image distortion) and changes in environmental conditions that affect its imaging characteristics (for example, changes related to the amount of illumination light absorbed by the projection optical system, changes in atmospheric pressure, changes in temperature). Detection means to detect (2
(8, 17, 18, 19, 20, 24, etc.), and at least one of the change in the imaging characteristics and the change in the environmental conditions detected by the detecting means is set to the reference value set according to each change. Exposure operation control means (26) for displaying a warning and / or stopping the exposure operation when it reaches
A plurality of reference values are set, and a selection means (selection means for selecting an optimum reference value from the plurality of reference values according to at least one of the imaging performance and the information relating to the imaging performance input to the input means. 32) and are provided.

[0014]

According to the present invention, at least one of the image forming performance of the projection optical system necessary for the present exposure and the information concerning the image forming performance such as the line width, which is the basis of the judgment, is obtained by the input means before the exposure operation is performed. Since one is input, the required imaging performance can be known in advance. Thereafter, during the actual exposure operation, the detection means detects a value capable of estimating at least one of the change in the image forming characteristic and the change in the image forming characteristic such as the atmospheric pressure, thereby to know the change in the image forming characteristic moment by moment. be able to. Further, the exposure operation control means compares the reference value preset according to the necessary imaging performance known in advance with the change in the imaging characteristics that can be known by the detection means, and the required imaging is performed. When it is determined that the performance cannot be maintained, good exposure can be performed by performing at least one operation of displaying a warning and stopping the exposure operation. Further, according to the present invention, a plurality of reference values are set in advance, and the selecting means selects the optimum reference value according to the imaging performance required for the present exposure, so that the exposure is unnecessary. The inconvenience that the throughput is lowered due to the suspension is eliminated.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a projection exposure apparatus constructed according to the present invention will be described in detail below with reference to the accompanying drawings. First, a projection exposure apparatus according to an embodiment of the present invention will be described with reference to FIG. The light source 1 emits illumination light IL that sensitizes a resist layer such as a bright line of an ultra-high pressure mercury lamp, a laser beam of a KrF or ArF excimer laser, a metal vapor laser, or a high frequency of a YAG laser. The illumination light IL enters the illumination optical system 2 including a collimator lens and a fly-eye lens and is shaped into a substantially uniform intensity distribution. The revolver 3 is located at a position conjugate with the Fourier transform plane of the pattern surface of the reticle R of the projection optical system PL, a so-called pupil plane, and the aperture can be selected by holding and rotating the aperture for changing the illumination condition. As the stop on the revolver 3, for example, a stop for changing the Uherence factor (σ value) of the illumination light beam, or a ring-shaped stop for high resolution technology or a stop for inclined illumination is prepared. Such a diaphragm is disclosed in, for example, Japanese Patent Laid-Open No. 5-175100. Since the final imaging characteristic of the projection optical system PL also changes due to such illumination conditions, the state of the revolver 3 is
As information regarding the illumination conditions of the illumination optical system, the input unit 27
And to the detection unit 28. Details will be described later. The illumination light passing through the revolver 3 passes through the half mirror 4 and enters the illumination optical system 5 including a relay lens or a variable blind.

The half mirror 4 is a photosensitive substrate (wafer) W.
It receives reflected light from the side, and it is possible to measure the amount of light that enters the projection optical system PL as reflected light.
The light amount information measured here is sent to the detection unit 28 as a change in environmental conditions that occurs during the exposure operation. The illumination light emitted from the illumination optical system 5 is folded downward by the dichroic mirror 6 to illuminate a mask (reticle) R on which a semiconductor circuit pattern or the like is drawn. Reticle R
Are vacuum-adsorbed on the reticle holder 7. Further, outside the pattern area of the reticle R, a bar code in which information about the pattern of the reticle (for example, the target line width for exposure) and the type of the reticle (for example, the presence or absence of a phase shifter) is written is attached. This bar code can be read by the bar code reader 30 into the apparatus before R is loaded into the reticle holder 7.
Since the information about the pattern and type of the reticle R also affects the imaging performance and the like, the input unit 27 and the detection unit 2
8 respectively. The illumination light that has passed through the reticle R is projected and exposed onto a silicon wafer W coated with a photosensitive material (resist), which is a photosensitive substrate, via a projection optical system PL.

In the present embodiment, a part of the lens elements constituting the projection optical system PL, that is, the lens element 10 in FIG. 1, together with the holder 11 holding the lens element 10, drive element 1 according to a command from the correction section 29.
It is configured so that it can be driven perpendicularly to the optical axis direction of the projection optical system PL by moving 2, and is used for correcting the projection magnification of the projection optical system. The permissible drive distance of the magnification correction optical system also affects the imaging performance of the apparatus, and is therefore sent to the input unit 27 and the detection unit 28 as information regarding the imaging performance. The lenses below the lens element 13 are the projection optical system P.
It is fixed to the L body. Further, the projection optical system PL is provided with a temperature control unit 14 outside so as not to be affected by an external temperature change, and the gas or the liquid is temperature-controlled to flow. In the example of FIG. 1, the liquid that has flowed in from the lower IN of the projection optical system PL flows out from the upper OUT, is returned to the temperature controller (not shown), and returns to IN again after the temperature control. Although the temperature of the fluid is controlled by the output of the temperature sensor 31, a change in the temperature of the fluid also affects the imaging performance, and therefore is output to the detection unit 28 as a change in the environmental condition that occurs during the exposure operation. .

An aperture stop 21 is provided on the pupil plane EP of the projection optical system PL (that is, an optical Fourier transform plane for the reticle), so that the numerical aperture (NA) of the projection optical system PL can be changed. . The information about the numerical aperture (NA) of the projection optical system PL is also output to the input unit 27 and the detection unit 28 as the information about the imaging performance. Further, in order to improve the resolution and the depth of focus when transferring an isolated contact hole pattern, an optical filter O is provided on or near the pupil plane EP of the projection optical system PL.
In some cases, F (hereinafter, referred to as a pupil filter) may be arranged. In the case of such a configuration, as shown in FIG. 3, the pupil filter storage cassette 33 is provided near the pupil plane EP of the projection optical system PL.
The pupil filter insertion / removal mechanism 34 is configured such that the pupil filter OF can be inserted into or removed from the pupil plane EP of the projection optical system PL according to the exposure target pattern. The pupil filter OF that can be used here is, for example, a projection optical system PL such as the Super-FLEX method announced in the Proceedings 28a-ZC-8, 9 of the Society of Applied Physics, 1981.
Which forms a concentric amplitude transmittance distribution (phase difference) centered on the optical axis on the pupil plane (hereinafter referred to as a phase difference type pupil filter), or is disclosed in Japanese Patent Application Laid-Open No. 4-179958. As described above, a device that shields a circular area near the optical axis on the pupil plane of the projection optical system PL (hereinafter referred to as a light-shielding type pupil filter), or JP-A-6-12011.
As disclosed in Japanese Laid-Open Patent Publication No. 6-124870 and Japanese Laid-Open Patent Publication No. 6-124870, a type of reducing the mutual coherence of transmitted light fluxes between concentric regions in the pupil plane EP of the projection optical system PL. (Hereinafter referred to as SFINCS type pupil filter). Information regarding the presence or absence of an optical filter provided in the projection optical system is also output to the input unit 27 and the detection unit 28 as information regarding the imaging performance.

The wafer W is a wafer holder (θ table) 8
It is vacuum-sucked to and is held on the wafer stage WS via the wafer holder 8. Wafer stage WS
Can be tilted in any direction with respect to the best image plane of the projection optical system PL by the motor 9, and can be finely moved in the optical axis direction (Z direction), and can be two-dimensionally moved by a step-and-repeat method. 1 on the wafer W.
When the transfer exposure of the reticle R to one shot area is completed, the stepping is performed to the next shot position.
The structure of the wafer stage WS is disclosed in, for example, Japanese Patent Laid-Open No. 62-274201.

Further, on the wafer stage WS, a photoelectric sensor 17 as a dose monitor is provided at a height which substantially coincides with the height of the surface of the wafer W. Photoelectric sensor 17
Is composed of, for example, a photoelectric conversion element having a light receiving surface having substantially the same area as the image field of the projection optical system PL or the projection area of the reticle pattern, and the optical information regarding the irradiation amount is used as environmental conditions generated during the exposure operation. Is output to the detection unit 28. This light information serves as basic data for obtaining the amount of change (aberration amount) in the imaging characteristics corresponding to the amount of energy accumulated in the projection optical system PL with the incidence of illumination light.

Further, in FIG. 1, irradiation for supplying an image forming light beam for forming an image of a pinhole or a slit toward the best image forming surface of the projection optical system PL obliquely with respect to the optical axis AX. An oblique incidence type wafer position detection system is provided which includes an optical system 15 and a light receiving optical system 16 which receives the reflected light flux of the imaged light flux on the surface of the wafer W through a slit. The configuration of the wafer position detection system is disclosed in, for example, Japanese Patent Laid-Open No. 60-168112, and the position of the wafer surface in the vertical direction (Z direction) with respect to the image plane is detected to detect the wafer W and the projection optical system. It is used when the wafer stage WS is driven in the Z direction so as to maintain a predetermined distance from the system PL.

In this embodiment, the angle of a parallel flat glass (plane parallel) (not shown) provided inside the light receiving optical system is adjusted in advance so that the image plane becomes the zero point reference, and the wafer position detecting system is adjusted. Shall be calibrated. That is, in this embodiment, the lens element 1
The magnification can be changed by driving 0, and the focal position can be corrected by the plane parallel angle. Further, since the height (step) of the wafer W can be measured from the output of the light receiving optical system 16, the output of the light receiving optical system 16 is also output to the input unit 27 as information regarding the step of the wafer W.

On the wafer stage WS, a pattern plate 18 for detecting the focus position as an actual measurement value in an aerial image.
Is also placed. The upper surface of the pattern plate 18 is shown in FIG.
As shown in (A), an opening pattern including a light shielding portion 71 and a light transmitting portion 72 is formed. The opening pattern is composed of four diffraction gratings each of which is formed by sequentially rotating an amplitude type diffraction grating having a predetermined pitch line and space pattern by 90 °.

Returning to FIG. 1, the pattern plate 18 is fixed on the wafer stage WS such that the surface on which the opening pattern is formed is substantially level with the surface of the wafer W in the Z direction, and the lower part of the pattern plate 18 is fixed. Is provided with an input / output unit 22 of the detection illumination optical system. Further, by moving the wafer stage WS in the XY plane perpendicular to the optical axis AX of the projection optical system PL, the pattern plate 18 is placed at the center of the image field of the projection optical system PL or at a position of an arbitrary image height. Can be positioned.

The same as the illumination light IL that illuminates the reticle R,
Alternatively, the illumination light EL in the wavelength range in the vicinity enters the one branch end 23a of the fiber bundle 23. As the illumination light EL, for example, a portion of the illumination light IL that is split by a beam splitter or the like is used. The illumination light EL enters the input / output unit 22 inside the wafer stage WS from the branch end 23a of the fiber bundle 23 through the congruent end 23b. Further, the illumination light EL illuminates the opening pattern of the pattern plate 18 from below via the input / output unit 22 including a relay lens, a field stop, a mirror, a condenser lens and the like. The light flux that has passed through the pattern plate 18 forms an image of the opening pattern of the pattern plate 18 on the lower surface (pattern surface) of the reticle R via the projection optical system PL. The light reflected by the pattern surface of the reticle R returns to the inside of the wafer stage WS via the projection optical system PL and the pattern plate 18, and enters the congruent end 23b of the fiber bundle 23 again through the optical path opposite to that at the time of incidence. . Further, the reflected light exits from the other branch end 22c of the fiber bundle 23 and enters the photoelectric sensor 24.

A photoelectric signal F output from the photoelectric sensor 24
S corresponds to the amount of light that the reflected light from the pattern surface of the reticle R is limited by the opening pattern of the pattern plate 18, and is supplied to the detection unit 28. FIG. 2B shows the pattern plate 15
Shows the photoelectric signal FS output from the photoelectric sensor 24 when the lens is slightly moved in the Z direction, the vertical axis represents the signal level (voltage value), and the horizontal axis represents the output signals AFS of the wafer position detection systems 15 and 16. That is, it represents the position in the Z direction. Therefore, the detection unit 10 obtains the position BS in the Z direction where the photoelectric signal FS is maximum as the optimum focus position.

A measuring device 19 is provided near the projection exposure apparatus.
The measuring device 19 measures atmospheric pressure, temperature and the like in the vicinity of the apparatus, and outputs it to the detection unit 28 as information regarding environmental conditions that change during the exposure operation. Further, from the keyboard 25, the operator of the apparatus can obtain various information, for example, the type of the photosensitizer applied on the photosensitive substrate, the information about the presence or absence of an optical filter provided in the projection optical system, or an illumination optical system as described later. Information about the waiting time until the exposure process is restarted after switching the illumination conditions of 2 and 5 can be input to the input unit 27.

Here, the conventional exposure operation control means, which has been described in the prior art, will be briefly described. When the projection magnification, focus position, field curvature, spherical aberration, distortion, etc. are considered as the imaging characteristics of the projection optical system PL,
According to the projection exposure apparatus according to the above embodiment, as described above, the change in the projection magnification and the focus position is calculated or based on the actually measured value using the pattern plate 18, for example, by the command of the correction unit 29, the driving element is driven. It is possible to make a correction by finely adjusting 12. However, other imaging characteristics other than projection magnification and focus position, such as field curvature,
Since it is difficult to directly correct spherical aberration, distortion, etc., the detection means (28, 17, 18,
(19, 20, 24, etc.), the change in the imaging characteristics and / or the change in the environmental condition that causes the change in the imaging characteristics reaches a preset constant reference value, and the exposure is temporarily performed. The operation is stopped, and the image forming characteristic of the projection exposure system PL or the change of the environmental condition causing the change of the image forming characteristic is
It is necessary to wait until it falls within the reference value and then start the exposure operation again. Note that, for example, if the field curvature, the spherical aberration, and the like are deteriorated in the image forming characteristics, the depth of focus in the exposure area becomes low. Moreover, the overlay accuracy deteriorates due to the change in the distortion curve.

By the way, as the change of the environmental condition which affects the above-mentioned image forming characteristic, there can be considered a change in the absorption amount of the illumination light of the projection optical system PL, a change in the atmospheric pressure, a change in the temperature, etc. A change in the image forming characteristic related to the absorption of the illumination light of the projection optical system PL will be described.

As an example of the operation, first, the energy of the illumination light incident on the projection optical system PL is obtained. This is the measurement of the energy of the illumination light on the image plane by the dose monitor 17,
This is performed by receiving the reflected light from the wafer W with the photoelectric sensor 20. That is, the amount of light incident on the projection optical system PL from above is determined by the irradiation amount monitor 17, and the amount of light reflected by the wafer W and incident from below is determined by the photoelectric sensor 20. When the illumination light enters the projection optical system PL, the temperature thereof gradually rises with time, and when the exposure is stopped, the temperature thereof also falls with time. As shown in FIG. 4, this characteristic can be represented by a differential equation, for example, as a variation characteristic of a temporary delay system. That is, the variation characteristic of the magnification due to the absorption of the illumination light of the projection optical system PL is determined by two values, that is, the ratio ΔM / E of the variation amount ΔM of the magnification to the irradiation energy and the time constant T indicating the temporal change. In the above example, the time constant T can be represented by the time that changes by ΔM × (1−e ⁻¹ ) with respect to the final change amount ΔM. That is, the smaller the time constant T, the faster the change. Then, the amount of change can be calculated by previously obtaining this characteristic by an experiment or a simulation calculation and solving the differential equation inside the detecting unit 28 based on a numerical solution method. Note that FIG. 4A is a graph showing the change characteristic of the magnification, in which the vertical axis represents the magnification change and the horizontal axis represents the time. Further, FIG. 4B shows the projection optical system P.
It shows the irradiation energy incident on L, the vertical axis represents the irradiation energy, and the horizontal axis represents the time. Similarly, the imaging characteristics of the projection optical system PL of the present embodiment, that is, the amount of change depending on the illumination light energy, such as the projection magnification, the focus position, the field curvature, the spherical aberration, and the distortion,
It can be obtained by the above calculation. However, in reality, the structure of the projection optical system PL is complicated, a large number of lens elements are present inside, the respective heat capacities are different, and the effects on the image forming characteristics are different.
Strictly speaking, the variation characteristic differs for each imaging characteristic, and there are some that cannot be expressed by a simple temporary delay system as shown in FIG. 4, for example, but these may be calculated separately, or they may be simplified and the same. It is also possible to consider only as one calculation.

According to the above method, for example, one image forming characteristic which has the greatest influence on the accuracy of the image forming performance is selected, and the change amount thereof is measured or calculated, and the value thereof exceeds a preset constant reference value. In this case, the control unit 26 may be configured to issue at least one of a warning display instruction and an exposure operation stop instruction. Of course, when a plurality of image forming characteristics are selected and the measured or calculated change amount of the image forming characteristics exceeds a preset constant reference value, at least a warning is displayed and the exposure operation is stopped. The control unit 26 may be configured to issue one command. And
If the exposure operation is stopped, the temperature of the projection optical system PL naturally lowers and exposure can be performed again. As described above, in the conventional projection exposure apparatus, the exposure operation is temporarily stopped and the throughput is reduced to reduce the average incident energy amount and maintain the imaging characteristics. Then, at that time, the constant reference value, which is an index for displaying a warning and stopping the exposure operation, is usually set on the premise that the product with the strictest accuracy required for the exposure apparatus is exposed. Was there.

Further, in addition to the method of obtaining the change amount of the predetermined image formation characteristic by the above calculation, for example, in the case of the field curvature, the pattern plate 18 measures the focal positions at a plurality of points inside the exposure area. Since it can be obtained, it is possible to use this measured value as an index for displaying a warning or stopping the exposure operation. However, since this method requires a long time for measurement, throughput is deteriorated. In addition, the projection optical system PL is determined by the presence or absence of the diaphragm of the revolver 3, the aperture diaphragm 21, or the phase shifter of the pattern of the reticle R.
Since the internal light amount distribution changes, the change characteristics may change when these conditions change. Therefore, it is necessary to have a change characteristic for each condition.

Next, the change in atmospheric pressure will be described. The change in atmospheric pressure is measured by the atmospheric pressure sensor inside the measuring device 19. Since the atmospheric pressure does not change gradually with time like the absorption amount of illumination light, the measured value can be used as it is. Similar to the illumination light absorption, the imaging characteristics other than the focus position and the projection magnification that are easily corrected, such as field curvature, spherical aberration, and distortion,
When the amount of change exceeds a predetermined allowable level, the exposure operation is stopped, and the process waits until the amount of change falls within the allowable level. However, in the case of changes in atmospheric pressure, it is difficult to preliminarily examine the fluctuation characteristics relating to each imaging characteristic in an experiment, and even for the focus position and the magnification, in atmospheric pressure environments other than a certain range, the device, sensor, etc. Since it is difficult to maintain the accuracy of the imaging performance on the manufacturing apparatus side, it is preferable to determine the allowable level of atmospheric pressure from the viewpoint of correcting the focus position and the projection magnification. However, when the exposure operation is stopped due to the atmospheric pressure exceeding the allowable level, the throughput cannot be recovered immediately and the throughput is seriously deteriorated.

Next, the temperature change will be described. With respect to the temperature change, the output of the temperature sensor 31 of the temperature control unit 14 of the projection exposure system PL and the air temperature sensor inside the measuring device 19 (between the reticle R and the projection optical system PL, between the projection optical system PL and the wafer W). (Related to the refractive index of air). Similarly to the case of the atmospheric pressure, the temperature change is not necessarily integrated over time, and thus the measured value can be used as it is. However, even if the temperature of the temperature control unit 14 changes, the internal temperature of the projection optical system PL does not change immediately because of the heat capacity of the projection optical system PL. In addition, the display of a warning and the exposure operation are stopped.

As described above, in the conventional projection exposure apparatus,
Depending on illumination light absorption, atmospheric pressure change, and temperature change, a fixed reference value is set in advance for the amount of change in each imaging characteristic, and exposure is stopped when the amount of change in the imaging characteristic exceeds the reference value. Alternatively, it is configured to issue a warning. However,
As described above, in the conventional projection exposure apparatus, the above-mentioned constant reference value is set so as to meet the highest precision required for the imaging performance of the apparatus. For this reason, the exposure operation is performed in the case of a process in which only relatively moderate accuracy is required, or in the process in which the resolution and the depth of focus are improved by the super resolution technique and the accuracy requirement is relatively relaxed. Was unnecessarily stopped and the throughput decreased. In this respect, the present invention is configured to eliminate unnecessary stop by making the reference value, which is an indicator of warning display and exposure operation stop, variable depending on conditions. A specific description will be given below.

First, when the imaging performance required for the process is known in advance by an experiment or the like, the operator can directly input the value using the keyboard 25 or the like. In the apparatus of the present invention, a plurality of reference values for displaying a warning and stopping the exposure operation are provided in accordance with the required imaging performance value for each change in each imaging characteristic and each environmental condition. It is set. Therefore, the selection means 32 selects the optimum reference value from the plurality of reference values for each imaging characteristic and each environmental condition in response to the operator's input of the keyboard 25, so that the warning is displayed only in accordance with a certain reference value. Unlike the conventional apparatus in which the exposure operation is stopped, the unnecessary stop of the exposure operation is avoided. The reference value according to the value of the imaging performance is the control unit 26 or the selection unit 32.
It is also possible to calculate each time based on the input value by a mathematical formula stored in advance, or it may be stored in advance in the form of a table in the control unit 26 or the selection unit 32, and based on the input value, a plurality of criteria may be used. It is also possible to configure to select the optimum reference value from among the values.

This point will be described with reference to FIG. 5, taking as an example the case of correction in accordance with a change in the amount of illumination light absorption. Note that FIG. 5 shows how the amount of illumination light absorption changes with irradiation energy. FIG. 5A shows a change characteristic of the amount of illumination light absorption, the vertical axis represents the amount of illumination light absorption, and the horizontal axis represents time. FIG. 5B shows a change characteristic of irradiation energy, in which the vertical axis represents irradiation energy and the horizontal axis represents time. Then, assuming that the reference value corresponding to the imaging performance required for the process currently being exposed is stored in the form of a table in advance, when the accuracy of the imaging performance input by the operator is critical, When the reference value A (reference value regarding the amount of illumination light absorption) is selected from the reference table and the amount of illumination light absorption calculated based on the measured values of the irradiation amount monitor 17 and the photoelectric sensor 20 reaches the reference value A ( t ₁ ), since the operation with sufficient accuracy is not guaranteed, the control unit 26 commands the display of a warning and the stop of the exposure operation. Then, the exposure operation is restarted at the time (t ₂ ) when the absorption amount of the illumination light decreases. On the other hand, when the accuracy of the imaging performance input by the operator is relatively gentle, the standard value B is selected from the reference table and calculated based on the measured values of the irradiation amount monitor 17 and the photoelectric sensor 20. Only after the amount of absorbed illumination light reaches the reference value B (t ₃ ), the control unit 26 commands the display of a warning and the stop of the exposure operation. As a result, unlike the conventional apparatus, the critical reference value A is applied regardless of the required accuracy, and the exposure operation is stopped at the time point (t ₁ ). For example, since the reference value B is applied and the display of the warning and the stop point of the exposure operation can be delayed by (t ₃ −t ₁ ), the throughput can be improved. further,
When the reference value B is applied, the total energy is higher than that of the reference value A, and the waiting time until the exposure operation is restarted can be shortened, so that the throughput is further improved. That is, as shown in FIG. 5A, when the reference value A has a high total energy, the cooling is slow (L ₂ ) and the heating is fast (L ₁ ), whereas the reference value B is Has
This is because it cools quickly (H ₂ ) and warms slowly (H ₁ ).

Next, a method for determining the accuracy of the required imaging performance on the side of the apparatus when the operator cannot predetermine the required imaging performance will be described. First, as a material for determining the required accuracy, there is some minimum line width of the pattern of the reticle R to be exposed. The minimum line width may be input directly by the operator from the keyboard 25 or may be entered in the bar code of the reticle R and read by the bar code reader 30. Alternatively, there is also a method of detecting the angle of the diffracted light generated from the reticle R. Next, it is conceivable that the depth of focus is increased by the high resolution technique even with the same line width, and the required depth of focus varies depending on whether or not the high resolution technique is used or the type thereof. Therefore, it is necessary to take in the information of the illumination condition from the revolver 3, or to directly input the information regarding whether it is a reticle with a phase shifter from the keyboard 25 or read it by the barcode reader 30. Since the depth of focus also changes depending on the numerical aperture (NA) of the projection lens, the information about the numerical aperture (NA) is read from the aperture diaphragm 21. Furthermore, since the depth of focus also changes depending on whether or not a pupil filter is inserted in the projection optical system PL, information regarding the presence / absence of a pupil filter is also read. Then, also in these cases, the reference value according to the above information that affects the imaging performance is the control unit 26 or the selection unit 3.
2 is calculated each time based on the input value by the mathematical formula stored in advance, or is stored in advance in the control unit 26 or the selection unit 32 in the form of a table, and the optimum reference value is selected based on the input value. It

As a material for determining the required accuracy other than the above, a step difference in the exposure area of the wafer W may be considered.
In recent years, a DRAM has adopted a stack structure in order to save the area, and as a result, the step difference of the wafer W in the exposure area is large and the focus margin is small, which greatly affects the required accuracy of image quality. The step size of the wafer W can be input in advance from the keyboard 25, or can be measured using the light receiving optical system 16 that measures the distance between the projection optical system PL and the wafer W. Is. That is, the step in the exposure area can be measured by monitoring the output of the light receiving optical system 16 while moving the wafer stage WS in the direction perpendicular to the optical axis. Alternatively, the waviness in the height direction in the exposure area due to the flatness of the wafer W can also be measured, and the necessary amount of the imaging characteristics relating to the depth of focus such as field curvature and astigmatism can be determined. Then, each reference value corresponding to these pieces of information is calculated each time based on an input value by a mathematical formula stored in advance in the control unit 26 or the selection unit 32, or the control unit 26 or the selection unit 32 stores a table. In advance, the optimum reference value is selected based on the input value.

In addition, it is conceivable that the characteristics of the resist, for example, the type of the photosensitive agent applied to the photosensitive substrate, influences the accuracy of the imaging performance. For such information,
For example, the operator can input from the keyboard 25, and the reference value according to the characteristics of the resist is also stored in advance in the form of a table in the control unit 26 or the selection unit 32, and is optimized based on the input value. A standard value is selected.

As described above, according to the present invention, in consideration of various requirements as described above, the imaging performance required for the exposure process currently performed, such as the depth of focus and the amount of image distortion, can be determined. The projection optical system P is determined according to the accuracy of the imaging performance determined.
An optimum reference value for displaying a warning and stopping the exposure operation in response to a change in the image forming characteristic of L or a change in the environmental condition affecting the image forming characteristic is selected from a plurality of reference values.
When determining the amount of image distortion allowed in this exposure operation, consider the overlay accuracy expected in that process or the amount of image distortion of the exposure machine used in the previous process. It is possible.

In addition to the above, there are correction conditions in which it is preferable to display a warning and stop the exposure operation. For these conditions as well, the optimum reference value according to the required accuracy should be selected based on the present invention. You can

For example, the change characteristic due to the absorption of the illumination light changes as described above immediately after the change of the illumination condition due to the change of the revolver 3 or the like. However, as described above, the change characteristic is calculated by the numerical solution method of the differential equation. There is. For this reason, when the illumination conditions are switched, the change characteristic becomes discontinuous and cannot be calculated by the differential equation, and the change amount of the characteristic to be corrected such as the focus position and the magnification becomes unknown. For this reason,
As shown in FIG. 6, after the illumination condition is switched (t ₁ ), the exposure operation is stopped for a while, and when the projection optical system PL is cooled and the change amount is close to the initial value of detection (t ₂ ), exposure is performed. A method of resuming has been devised. 6. Note that FIG. 6 is a graph for explaining the waiting time after changing the illumination conditions. FIG. 6A shows the change characteristic of the illumination absorption amount after the illumination condition is changed, the vertical axis shows the illumination light absorption amount, and the horizontal axis shows the time. FIG. 6B shows changes in irradiation conditions, the vertical axis shows irradiation energy, and the horizontal axis shows time. However, also in this case, in the conventional projection exposure apparatus, the critical reference value A is applied in all cases, and even when the required accuracy is low (t
_The exposure operation had to be stopped for _2- t ₁ ). However, according to the present embodiment, a plurality of reference values (A, B) are obtained according to the illumination condition and stored in the control failure 26 or the reference value selection unit 32. Since the exposure operation suspension time can be shortened by (t ₂ −t ₃ ) by applying the different reference value B, the throughput is not lost due to unnecessary waiting time.

Further, when a pattern with a phase shifter and a pattern without a phase shifter coexist on the same reticle, the change characteristics due to the absorption of illumination light are different.
It is conceivable that optimal correction cannot be performed for both patterns. Even in such a case, there is a projection exposure apparatus having a function of temporarily suspending the exposure operation and cooling the projection optical system PL to wait for the recovery of accuracy. However, by applying the present method to the standby time, It is possible to prevent the throughput from decreasing due to unnecessary waiting time.

Further, in the embodiment shown in FIG. 1, the lens element 1 is driven by the driving element 12 when correcting the projection magnification.
Although the projection magnification is corrected by driving 0, it is usual that the drive range of the lens element 10 has a certain limit. That is, it is usually difficult to correct only the projection magnification completely independently of the other imaging characteristics, and the other imaging characteristics also change with the correction of the projection magnification, so the correction is acceptable. The lens element 10 can be driven only within the level. Also regarding this drive allowable range, since there is a difference between the case where critical accuracy is required and the case where moderate accuracy is applied, the optimum allowable range is set according to the accuracy of the required imaging performance according to the present embodiment. It is also possible to make a configuration such that a warning is displayed and the exposure operation is stopped when the selected value deviates from the allowable range.

[0046]

As described above, according to the present invention, in order to maintain the accuracy of the imaging performance required for the projection optical system in each exposure process, the change of the imaging characteristics or the With respect to changes in environmental conditions that affect the imaging characteristics, the optimal reference value that serves as an indicator for displaying a warning or stopping the exposure operation is selected from among multiple reference values, so it is unnecessary to set a critical reference value. Is applied, the exposure operation is stopped,
It is possible to effectively prevent a situation where the throughput is reduced. On the contrary, it is possible to prevent the situation where the reference value is set too low and the stop of the exposure operation is delayed.

[Brief description of drawings]

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

2A is a diagram showing an example of an opening of a pattern plate 18 in FIG. 1, and FIG. 2B is a diagram showing a photoelectric signal output from a photoelectric sensor 24.

FIG. 3 is a diagram showing a schematic configuration of a projection exposure apparatus having a mechanism capable of inserting and removing an optical filter in a projection optical system.

FIG. 4 is a diagram showing an outline of a plurality of reference values set with respect to changes in imaging characteristics (magnification of the projection optical system PL);
(A) shows a time series change of magnification, and (B) is a diagram showing a time series change of irradiation energy.

FIG. 5 is a diagram showing an outline of a plurality of reference values set with respect to changes in the amount of illumination light absorption set according to the present invention, (A) showing a time-series change in the amount of illumination light absorption;
(B) is a figure which shows the time series change of irradiation energy.

FIG. 6 is a diagram showing an outline of a plurality of reference values set with respect to a standby time after a change in illumination condition set according to the present invention, in which (A) shows a time-series change of an illumination light absorption amount. , (B) are diagrams showing time series changes of irradiation energy.

[Explanation of symbols]

 1 ... Light source 2, 5 ... Illumination optical system R ... Mask PL ... Projection optical system W ... Photosensitive substrate 25 ... Keyboard 27 ... Input section 30 ... Bar code reader 28 ... Detection section 17 ... Irradiation amount monitor 18 ... Pattern board 19 ... Measurement Unit 26 ... Exposure operation control unit 32 ... Reference value selection unit

Claims (5)

[Claims] 1. An illumination optical system for forming illumination light from a light source into a substantially uniform intensity distribution and irradiating it on a mask, and a projection optical system for forming an image of a pattern formed on the mask on a photosensitive substrate. In the projection exposure apparatus, an input means for inputting information regarding at least one of the image forming performance required for the projection optical system and the required image forming performance; and a change in image forming characteristic of the projection optical system. Detection means for detecting at least one of changes in environmental conditions affecting the imaging characteristics; and at least one of changes in imaging characteristics and changes in environmental conditions detected by the detection means. An exposure operation control means for displaying at least one of a warning and a stop of the exposure operation when the reference value set in accordance therewith is reached; a plurality of the reference values are set, and the reference values are input to the input means. A projection exposure apparatus comprising: a selecting unit that selects one of the plurality of reference values according to at least one of the image forming performance and the information regarding the image forming performance. 2. The imaging performance input to the input means is
The projection exposure apparatus according to claim 1, wherein the projection exposure apparatus is one of a depth of focus within an exposure area and an amount of image distortion. 3. The information relating to the imaging performance input to the input means includes a target line width for exposure, an illumination condition of the illumination optical system, a numerical aperture of the projection optical system, and a phase shifter of the mask. Presence or absence, a step of the photosensitive substrate, a type of the photosensitive agent applied to the photosensitive substrate, and the presence or absence of an optical filter provided in the projection optical system. The projection exposure apparatus according to claim 1. 4. The change in the imaging characteristic detected by the detection means is a change relating to at least one of the depth of focus and the amount of image distortion in the exposure area. The projection exposure apparatus according to any one of 1. 5. The change in the environmental condition detected by the detection means is at least one of a change relating to the illumination light absorption amount of the projection optical system, a change in atmospheric pressure, and a change in temperature.
The projection exposure apparatus according to claim 1, 2 or 3, wherein