JPH06181160A - Aligner - Google Patents

Abstract

PURPOSE:To control exposing energy for photosensitive substrate at a correct level even when sigma value or the like in illumination optical system is altered. CONSTITUTION:A variable diaphragm 5 is disposed on the outlet plane of a fly eye lend 3 and exposing light, passed through the variable diaphragm 5 and reflected on a beam splitter 6, is introduced to an integrating sensor 8 whereas the exposing light transmitted through the beam splitter 6 illuminates a reticle 13 through a main condenser lens 12 thus exposing a pattern image of the reticle 13 onto a wafer 15. An exposing energy conversion factor for the wafer 15 is predetermined based on the output from the integrator sensor 8 as a function of profile and size of the aperture of variable diaphragm 5 and an accurate accumulated amount of exposure for the wafer 15 is determined based on an output signal from the integrator sensor 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus used for exposing a pattern of a reticle onto a photosensitive substrate when, for example, manufacturing a semiconductor device or a liquid crystal display device by a photolithography process, and more particularly, to a photosensitive device. The present invention relates to an exposure apparatus including a control mechanism for adjusting the exposure amount for a substrate to an appropriate exposure amount.

[0002]

2. Description of the Related Art An exposure apparatus that exposes a pattern of a photomask or reticle (hereinafter referred to as a "reticle") onto a photosensitive substrate when a circuit pattern of a semiconductor device or a liquid crystal display device is manufactured by a photolithography process ( For example, a stepper) is used. What is the photosensitive substrate?
A substrate such as a semiconductor wafer or a glass substrate is coated with a photosensitive material such as photoresist, and the reticle pattern is transferred onto the photosensitive material. In this case, since the appropriate exposure amount is set for the photosensitive material, the conventional exposure apparatus controls the exposure amount for the photosensitive substrate to be the appropriate exposure amount as follows.

That is, first, a reticle on which a pattern to be exposed is drawn is mounted on an exposure apparatus,
Each condition is changed little by little to obtain the proper focus position and the proper exposure amount, and exposure (test printing) is performed on the photosensitive substrate, and the pattern on the photosensitive material formed by this is observed with an optical microscope or a scanning electron microscope. Optimal conditions are obtained by observing using the above. However, it is not necessary to perform this operation for a reticle whose optimum conditions are known in advance.

After that, when actually exposing the photosensitive substrate, the exposure amount is controlled by using an integrator sensor made up of a photoelectric conversion element provided in the illumination optical system of the exposure device. The integrator sensor is arranged at a position almost conjugate with the secondary light source forming surface of the fly-eye lens as an optical integrator in the illumination optical system, and is irradiated to the photosensitive substrate side through the fly-eye lens. Part of the exposure light is guided to the integrator sensor by the beam splitter. At this time, a conversion coefficient from the photoelectric conversion signal of the integrator sensor to the exposure energy on the photosensitive substrate is obtained in advance, and the photoelectric conversion signal of the integrator sensor is integrated and multiplied by the conversion coefficient to obtain a value on the photosensitive substrate. The integrated exposure energy is obtained. Then, when the integrated exposure energy reaches the appropriate exposure amount, the exposure light is blocked by a shutter or the like to control the exposure amount to the photosensitive substrate.

In the case of the conventional ordinary illumination optical system, the relationship between the photoelectric conversion signal of the integrator sensor and the exposure energy on the photosensitive substrate is simple and almost constant. Good results were obtained even with the method. In this regard, in recent years, miniaturization of circuit patterns such as LSI has progressed, and there is an increasing demand for exposing finer patterns on a photosensitive substrate with high resolution. One of the methods to meet that demand is the numerical aperture (NA) of the projection optical system.
However, there is a limit to it,
Recently, the following various other attempts have been made.

First, for example, in the so-called phase shift method disclosed in Japanese Patent Publication No. 62-50811, a phase film is provided between chrome patterns in order to shift the phase of light passing through a reticle. Exposure is performed using a phase shift reticle. In this phase shift method, the so-called σ value, which is the coherency factor of the illumination optical system, has a great influence on the imaging performance, and in order to form a finer pattern image, the σ value is set to a relatively small value. To be done.

Further, an actual semiconductor element is usually formed by superposing circuit patterns of 20 layers or more, but the resolution required for the circuit pattern of each layer is different, so that a normal reticle and a phase shift reticle are used. Are likely to be mixed. Therefore, for example, JP-A-2-50417
As disclosed in the publication, an exposure apparatus having an illumination optical system having a variable σ value is required. The method of changing the σ value is, for example, near the exit surface of the fly-eye lens in the illumination optical system, that is, the Fourier transform surface (pupil surface) of the illumination optical system.
A method of opening and closing an aperture stop provided in the vicinity of is used. When the σ value is changed in this way, the amount of light incident on the integrator sensor naturally changes, and the exposure amount control is performed based on the changed amount of light.

In addition, as a method of improving the image forming characteristics of the pattern exposed on the photosensitive substrate by changing the configuration of the illumination optical system, the annular illumination method (for example, Japanese Patent Laid-Open No. 61-91).
662) or a so-called modified light source method (see, for example, Japanese Patent Application Laid-Open No. 4-268715). In the annular illumination method, the distribution of the secondary light source on the Fourier transform surface of the illumination optical system becomes annular, and in the modified light source method, the distribution of the secondary light source on the Fourier transform surface of the illumination optical system is the transfer target. It becomes a discrete light source such as two or four arranged around the optical axis according to the pattern. Therefore, in any of the illumination methods, the distribution state and the coherency factor of the secondary light source on the Fourier transform plane of the illumination optical system are different from those in the normal illumination method. Therefore, the light quantity of the light incident on the integrator sensor and the distribution state of the incident angles are also changing.

[0009]

In the prior art as described above, by changing the distribution of the secondary light source on the Fourier transform plane of the illumination optical system, the distribution of the incident angle of each light flux of the exposure light guided to the integrator sensor is changed. When it changes, the photoelectric conversion signal of the integrator sensor changes due to the distribution of the incident angle even if the amount of received light is the same, and the sensitivity characteristic of the integrator sensor also changes. Therefore, there is a disadvantage that the exposure energy on the photosensitive substrate cannot be accurately calculated from the photoelectric conversion signal of the integrator sensor.

In view of such a point, the present invention takes the σ of the illumination optical system into consideration.
An object of the present invention is to provide an exposure apparatus capable of controlling the exposure energy for a photosensitive substrate to an appropriate exposure amount even when the value or the like is changed to change the light amount distribution on the Fourier transform surface of the illumination optical system.

[0011]

The exposure apparatus according to the present invention is, for example, as shown in FIG. 1, an illumination optical system (1, 3,) for illuminating a mask (13) on which a transfer pattern is formed with exposure light. 12), which exposes the transfer pattern on the photosensitive substrate (15) and controls so that the integrated exposure amount of the exposure light on the photosensitive substrate (15) becomes an appropriate exposure amount. In the apparatus, an input means (22) for inputting the distribution state of the exposure light on the Fourier transform surface of the illumination optical system, and an illumination state changing means for setting the distribution state of the input exposure light by the illumination optical system. (10,
5) and.

Further, the present invention further comprises a photoelectric conversion means (8) for receiving a part of the exposure light generated by the illumination optical system in the vicinity of a plane conjugate with the Fourier transform surface of the illumination optical system,
The conversion coefficient for obtaining the exposure amount on the photosensitive substrate (15) from the output signal of the photoelectric conversion means (8) is stored in advance as a function for the distribution state of the exposure light on the Fourier transform surface of the illumination optical system, The integrated exposure amount of the exposure light with respect to the photosensitive substrate (15) is calculated from the output signal of the photoelectric conversion means (8), the distribution state of the exposure light input from the input means (22) and the conversion coefficient stored in advance. Exposure amount calculation means (21) for performing, and when the integrated exposure amount calculated by the exposure amount calculation means (21) reaches the appropriate exposure amount,
And an exposure amount control means (4, 9) for stopping the exposure of the photosensitive substrate (15).

[0013]

In the present invention, according to the mask (13), its illumination optical system is selected from, for example, an ordinary illumination method, an illumination method corresponding to the phase shift method, an annular illumination method or a modified light source method. In order to set the illumination method, the distribution state of the exposure light on the Fourier transform plane (pupil surface) of the illumination optical system in the illumination method is input from the input means (22) to the exposure amount calculation means (21). input. In this case, when the illumination method changes, the distribution state of the incident angle of the exposure light received by the photoelectric conversion means (8) changes, so that the output signal and the photosensitive substrate (15).
The relationship with the amount of exposure in

Therefore, the exposure amount calculation means (21) outputs the output of the photoelectric conversion means (8) by using a conversion coefficient obtained in advance as a function for the distribution state of the exposure light on the Fourier transform surface of the illumination optical system. Signal to photosensitive substrate (1
5) Accurately determine the above exposure amount. When the integrated value of the exposure amount reaches the appropriate exposure amount, the exposure amount control means (4, 9) stops the exposure so that the integrated exposure of the photosensitive substrate (15) is always performed regardless of the illumination method. The amount can be adjusted to the proper exposure amount.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an exposure apparatus according to the present invention will be described below with reference to the drawings. In the present embodiment, the present invention is applied to a projection exposure apparatus capable of changing the illumination method of the illumination optical system according to the reticle. FIG. 1 shows a projection exposure apparatus of the present embodiment. In FIG. 1, the exposure light emitted from a mercury lamp 1 is condensed by an elliptical mirror 2 and then converted into a substantially parallel light flux by an input lens (not shown). It is converted and enters the fly-eye lens 3. As the light source for the exposure light, an excimer laser light source or the like can be used in addition to the mercury lamp. A shutter 4 is arranged in the optical path between the mercury lamp 1 and the fly-eye lens 3 so that it can be freely taken in and out, and the shutter 4 controls the amount of exposure to the photosensitive substrate.

Rear side of the fly-eye lens 3 (reticle side)
A large number of secondary light sources are formed on the focal plane, and the variable aperture stop 5 is arranged on the secondary light source formation surface. The arranging surface of the variable aperture stop 5 is also the Fourier transform surface (pupil surface) of the illumination optical system of this example, and by changing the distribution state of the secondary light source on the Fourier transform surface by the variable aperture stop 5, various Optimize the illumination method for the reticle. That is, the variable aperture stop 5 can set the coherency factor (σ value) of the illumination optical system to a desired value, and can also realize, for example, an annular illumination method or a so-called modified light source method. Instead of changing the shape and size of the aperture of the variable aperture stop 5, another aperture stop may be replaced.

Exposure light I passing through the aperture of the variable aperture stop 5
L is a beam splitter 6 having high transmittance and low reflectance
The exposure light incident on the beam splitter 6 and reflected by the beam splitter 6 is incident on the light receiving surface of the integrator sensor 8 formed of a photoelectric conversion element (silicon photodiode, etc.) by the condenser lens 7. In this case, the condenser lens 7 makes the arrangement surface of the variable aperture stop 5, that is, the Fourier transform surface of the illumination optical system and the light receiving surface of the integrator sensor 8 substantially conjugate. The output signal of the integrator sensor 8 is supplied to the exposure amount control unit 9, and the exposure amount control unit 9 controls the opening / closing operation of the shutter 4. Further, the illumination system controller 10 sets the shape and size of the aperture of the variable aperture stop 5 to the instructed state.

Exposure light I transmitted through the beam splitter 6
After L is reflected vertically downward by the mirror 11, it is condensed by the main condenser lens 12 and illuminates the reticle 13 with a uniform illuminance. The image of the pattern formed on the reticle 13 is reduced by a predetermined reduction magnification via the projection optical system 14 and is projected and exposed on the wafer 15 coated with the photosensitive material.

Further, a variable aperture stop 16 is arranged on the Fourier transform plane (pupil plane) of the projection optical system 14, and the numerical aperture control section 17 controls the state of the aperture of the variable aperture stop 16 to make the projection optical system. The numerical aperture (NA) of system 14 is set to a predetermined value. The wafer 15 is placed on the wafer stage 18, and the wafer stage 18 is positioned in the direction of the optical axis of the projection optical system 14 and the XY stage for positioning the wafer 15 in a plane perpendicular to the optical axis of the projection optical system 14. It is composed of a Z stage and the like for positioning the wafer 15. Further, a dose monitor 19 composed of a photoelectric conversion element is arranged near the wafer 15 on the wafer stage 18, and when the exposure energy passing through the projection optical system 14 is directly obtained, the exposure operation to the wafer 15 is started. Before that, the dose monitor 19 is moved to the exposure field of the projection optical system 14 to measure the exposure light.

The detection signal of the irradiation amount monitor 19 is supplied to the lens controller 20, and the lens controller 20
The operation of is controlled by the central controller 21. The central controller 21 controls the operations of the exposure amount controller 9, the illumination system controller 10, and the numerical aperture controller 17, and supplies the lens controller 20 with the opening / closing information of the shutter 4 from the exposure amount controller 9. Generally, when the exposure light continuously passes through the projection optical system 14, the irradiation energy of the exposure light changes the arrangement, shape, etc. of the lens elements forming the projection optical system 14, and the imaging characteristics of the projection optical system 14 are changed. Is known to fluctuate over time. Therefore, the lens controller 20 determines from the detection signal of the irradiation amount monitor 19 measured in advance and the opening / closing information of the shutter 4 which is constantly supplied,
The temporal variation of the imaging characteristics of the projection optical system 14 is constantly monitored. Further, the lens controller 20 corrects the image forming characteristic of the projection optical system 14 so that the variation of the image forming characteristic falls within a predetermined allowable range.

Examples of temporal fluctuations in the image forming characteristics of the projection optical system 14 include fluctuations in magnification and fluctuations in focus. The lens controller 2 is used to correct the variation in magnification.
0 changes the pressure of a part of the lens chamber in the projection optical system 14 to change the refractive index of the air in the lens chamber, or
Alternatively, some lenses in the projection optical system 14 are moved. Further, in order to correct the focus fluctuation, the lens controller 20 adds an offset to a focus system (not shown) so that the position of the wafer stage 18 in the optical axis direction of the projection optical system 14 at a desired height during exposure. Say it.

An input device 22 composed of a keyboard is connected to the central processing unit 21. The operator specifies the distribution state of the secondary light source on the Fourier transform plane of the illumination optical system from the keyboard 22 to the central processing unit 21. However, the type of the reticle 13 and the minimum pitch of the pattern to be transferred are input from the input device 22 to the central processing unit 21.
The optimum distribution state of the secondary light source on the Fourier transform plane of the illumination optical system may be obtained from the information on the first side. As the input device 22, for example, an input device including a CRT display and a so-called mouse, or a data file or the like that stores various exposure conditions (for example, exposure area, exposure energy, focus position offset, etc.) is used. You can also Further, in FIG. 1, the exposure amount control unit 9 and the lens controller 20 are connected via the central processing unit 21, but the exposure amount control unit 9 and the lens controller 20 may be integrated from the beginning. It is possible.

Next, an example of the exposure operation of the projection exposure apparatus of this embodiment will be described. First, in FIG. 1, when the reticle 13 is the phase shift reticle described above, it is necessary to reduce the σ value of the illumination optical system to perform exposure. Therefore, the operator inputs the σ value of the illumination optical system to the central processing unit 21 via the input device 22. However, from the input device 22, the pattern density on the reticle and information as to whether or not it is a phase shift reticle are input, and the central processing unit 1
It is also possible that 2 automatically determines the σ value. The central processing unit 12 specifies the σ value to the illumination system control unit 10, and the illumination system control unit 10 sets the aperture diameter of the variable aperture stop 5 to a value corresponding to the σ value.

Similarly, when the reticle 13 is, for example, a normal reticle and the minimum pitch of the pattern is extremely small, the illumination optical system is set to the annular illumination method or the modified light source method to perform exposure. There is a need. Therefore, when the operator designates the annular illumination method or the modified light source method or the like to the central processing unit 21 via the input device 22, the illumination system control unit 10 changes the shape of the aperture of the variable aperture stop 5 to the corresponding shape. Set to.

At this time, a part of the exposure light passing through the variable aperture stop 4 is reflected by the beam splitter 6 and is incident on the light receiving surface of the integrator sensor 8, and the photoelectric conversion signal of the integrator sensor 8 is sent to the exposure amount control section 9. Supplied. The exposure amount control unit 9 uses the photoelectric conversion signal of the integrator sensor 8 to determine the exposure amount (exposure energy) on the wafer 15.
Is calculated indirectly, and the shutter 4 is closed when this exposure amount reaches a predetermined appropriate exposure amount for the wafer 15. However, the distribution of the incident angle of the light beam incident on the integrator sensor 8 differs depending on the shape and size of the aperture of the variable aperture stop 5, and the conversion coefficient for obtaining the exposure amount on the wafer 15 from the photoelectric conversion signal of the integrator sensor 8. Is also different. Therefore, the conversion coefficient, which is obtained in advance as a function of the shape and size of the aperture of the variable aperture stop 5, is stored in the exposure amount control unit 9.

With reference to FIGS. 2 and 3, the manner in which the conversion coefficient changes will be described in detail. First, FIG.
2A shows a case where the illumination optical system has a large σ value, FIG.
3 shows the case where the σ value of the illumination optical system is small, and FIG. 3 shows the case where the illumination optical system uses the modified light source method. The light receiving surface of the integrator sensor 8 is substantially conjugate with the arrangement surface of the variable aperture stop 5. For example, comparing FIG. 2A and FIG. 2B, it can be seen that the distribution of the incident angle of the incident light on the integrator sensor 8 and the size of the light spot on the light receiving surface of the integrator sensor 8 change. Also in FIG. 3, the distribution of incident angles of light and the distribution shape of light on the light receiving surface of the integrator sensor 8 are changed.

As the integrator sensor 5, a photoelectric conversion element such as a silicon photodiode (SPD) is used. The photoelectric conversion signal of such a photoelectric conversion element is generally an angle-dependent characteristic depending on the incident angle and a light receiving surface. There is uneven sensitivity due to the position above. Therefore, FIG. 2 or FIG.
As described above, if the distribution state of the secondary light source on the Fourier transform surface of the illumination optical system changes, accurate exposure amount control cannot be performed.

Therefore, in the exposure amount control unit 9 of FIG. 1, the central processing unit 21 performs correction by simultaneously obtaining the distribution information of the secondary light source output to the illumination system control unit 10. That is, the exposure control unit 9 does not use the output of the integrator sensor 8 as it is, but obtains in advance a series of conversion coefficients that change depending on the distribution state of the secondary light source, and uses this conversion coefficient to convert the photoelectric value of the integrator sensor 8 into photoelectric values. The exposure amount on the wafer 15 is calculated from the conversion signal. Then, by controlling the open / closed state of the shutter 4 based on the integrated value of the exposure amount, accurate exposure amount control becomes possible. Further, when the annular illumination method is used in addition to the modified light source method, the state of the aperture of the variable aperture stop 5 changes, and thus the same correction can be performed to enable accurate exposure amount control. The same applies when replacing the variable aperture stop 5 instead of changing the aperture of the variable aperture stop 5.

Although the correction of the output of the integrator sensor 8 has been considered in the above embodiments, the same phenomenon occurs in the dose monitor 19. That is, for example, when a phase shift reticle is used as the reticle 13, the 0th-order component of the exposure light after passing through the reticle disappears, and the reticle pattern image is formed by the diffracted ± 1st-order diffracted light. Therefore, as the light incident on the irradiation amount monitor 19 has many components that are inclined and enter, even if the exact same amount of light passes through the projection optical system 14, the output obtained by the irradiation amount monitor 19 is different. Also in this case, the lens controller 20 may perform the same correction as that performed by the exposure control unit 9. It is also effective to perform the same correction depending on the state of the variable aperture stop 16.

The present invention is not limited to the above embodiment,
Of course, various configurations can be adopted without departing from the scope of the present invention.

[0031]

According to the present invention, since the conversion coefficient for determining the exposure amount on the photosensitive substrate is changed by the light amount distribution on the Fourier transform surface of the illumination optical system, the σ value of the illumination optical system is changed. Even when the light amount distribution on the Fourier transform surface of the illumination optical system is changed by changing the above, there is an advantage that the exposure energy for the photosensitive substrate can be controlled to an appropriate exposure amount. Therefore, it is not necessary to perform a test print for obtaining the optimum exposure condition each time the illumination optical system is changed, unlike the conventional case.

[Brief description of drawings]

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

FIG. 2A is an optical path diagram showing a state of a light flux reaching an integrator sensor 8 when the σ value of the illumination optical system is large,
(B) is an optical path diagram showing a state of a light flux reaching the integrator sensor 8 when the σ value of the illumination optical system is small.

FIG. 3 is an optical path diagram showing a state of a light beam reaching an integrator sensor 8 when the illumination optical system is a modified light source method.

[Explanation of symbols]

 3 Fly's Eye Lens 4 Shutter 5 Variable Aperture Stopper 8 Integrator Sensor 9 Exposure Control Section 10 Illumination Control Section 12 Main Condenser Lens 13 Reticle 14 Projection Optical System 15 Wafer 16 Variable Aperture Stopper 19 Irradiation Monitor 20 Lens Controller 21 Central Processing Unit 22 Input device

Claims (1)

[Claims] 1. An illumination optical system for illuminating a mask on which a transfer pattern is formed with exposure light, exposing the transfer pattern onto a photosensitive substrate, and exposing the exposure light onto the photosensitive substrate. In an exposure apparatus that controls so that the integrated exposure amount of the exposure light amount becomes an appropriate exposure amount, an input unit that inputs a distribution state of the exposure light on a Fourier transform surface of the illumination optical system, and a distribution of the input exposure light Illumination state variable means for setting a state by the illumination optical system, and photoelectric conversion means for receiving a part of the exposure light generated by the illumination optical system in the vicinity of a surface of the illumination optical system that is conjugate with a Fourier transform surface. And a conversion coefficient for obtaining the exposure amount on the photosensitive substrate from the output signal of the photoelectric conversion means is stored in advance as a function for the distribution state of the exposure light on the Fourier transform plane of the illumination optical system, An exposure amount calculation unit for calculating an integrated exposure amount of the exposure light with respect to the photosensitive substrate from the output signal of the photoelectric conversion unit, the distribution state of the exposure light input from the input unit, and the conversion coefficient stored in advance. An exposure amount control means for stopping the exposure of the photosensitive substrate when the integrated exposure amount calculated by the exposure amount calculation means reaches the appropriate exposure amount.