JPH08234138A - Projection exposure apparatus and method - Google Patents

Abstract

(57) Abstract: When a mask pattern is projected and exposed on a photosensitive substrate, if the distribution of a light source image generated on the pupil plane of the projection optical system is changed, good imaging characteristics are maintained. There was an inconvenience that it was not possible. SOLUTION: When the distribution of the light source image generated on the pupil plane of the projection optical system 24 is changed, the image forming characteristic adjusting means (32, 34, 36, 38) is adapted to the changed light source image distribution. To work.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus and a projection exposure method used, for example, in the manufacture of integrated circuits, and more particularly to improvement of correction control for changes in imaging characteristics.

[0002]

2. Description of the Related Art One of the important optical characteristics of a projection optical apparatus, for example, a reduction projection type exposure apparatus, is overlay accuracy. An important factor affecting this is a magnification error of the projection optical system. . In recent years, the degree of integration of integrated circuits has improved and patterns have tended to become finer, and along with this, there has been an increasing demand for improvement in overlay accuracy. Therefore, there is a growing need to maintain the projection magnification at a predetermined value.

By the way, the magnification of the projection optical apparatus is predetermined due to a slight temperature change of the apparatus, a slight atmospheric pressure change of the atmosphere in a clean room in which the apparatus is arranged, a temperature change, or irradiation of energy rays to the projection optical system. It varies near the magnification. For this reason, some recent reduction projection type exposure apparatuses have a magnification correction mechanism for finely adjusting the magnification of the projection optical system to realize a required predetermined magnification. For example, the distance between the reticle and the projection lens may be changed, the distance between the lenses in the projection lens may be changed, or as disclosed in Japanese Patent Laid-Open No. 61-78454, a suitable air chamber in the projection lens may be provided. There is a mechanism for adjusting the pressure.

Further, the focus also moves due to the same reason as the above-mentioned variation factor relating to the magnification. Therefore, there is an exposure apparatus having such a focus correction mechanism. By the way, among the above-mentioned factors for changing the imaging characteristics, the accumulation of heat by the irradiation of energy rays to the projection optical system is a thermal diffusion phenomenon having a predetermined specific number. In general, the numerical aperture of the illumination system in the conventional exposure apparatus is often constant. Therefore, the manner of incidence of energy rays on the projection optical system is constant, and the time constant of such thermal diffusion is constant. Therefore, the magnification and focus fluctuation characteristics that are image formation characteristics are also constant, and a single method may be used for adjusting and controlling them.

[0005]

However, recently, an exposure apparatus has been proposed in which a higher resolution can be obtained for projection of a specific pattern by changing the numerical aperture of the illumination system. Has been done. In such an apparatus, the distribution state of the light flux on the pupil of the projection optical system changes as the numerical aperture changes, and as a result,
It was confirmed as a result of the experiment that the time constant also changes. Therefore, even if the control method for the constant time constant described above is applied, it is not possible to satisfactorily adjust the imaging characteristics, and it is not possible to cope with such a change in the time constant.

Further, when the total amount of incident energy rays (illuminance) on the projection optical system is measured on the image plane (exposed substrate) side of the projection optical system and the value is used as a parameter to correct the imaging characteristics, correction control is performed. Is treated as a simple change in the amount of incident energy. Generally, when the numerical aperture of the illumination system is changed, the illuminance on the image plane changes accordingly, but at the same time, the distribution state of the light flux on the pupil, that is, the energy density near the pupil plane changes as described above. . Therefore, it is expected that not only the above-mentioned time constant but also the coefficient term such as the model formula for specifying the fluctuation of the optical characteristics will change. Therefore, if such a change in the coefficient is not taken into consideration, there arises a disadvantage that the correction control becomes inaccurate.

The present invention has been made in view of the above point, and satisfactorily adjusts the imaging characteristics, particularly the variation of the magnification and the focus even if the distribution of the energy rays incident on the projection optical system changes. It is an object of the present invention to provide a projection exposure apparatus and a method capable of performing the same.

[0008]

According to the present invention, in projecting an image of a pattern of a mask illuminated with exposure illumination light onto a photosensitive substrate with a predetermined image forming characteristic through a projection optical system, The distribution changing means changes the distribution of the light source image generated on the pupil plane of the projection optical system as needed. Further, the image forming characteristic of the projection optical system is adjusted by adjusting the characteristic of at least a part of the optical elements constituting the projection optical system by the image forming characteristic adjusting means.

Since the control means controls the image forming characteristic adjusting means in accordance with the changed light source image distribution, the image forming state is maintained well even if the light source image distribution is changed.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, a first embodiment of the present invention will be described with reference to FIGS. First, the overall configuration of the first embodiment of the present invention will be described with reference to FIG. In FIG. 1, a light source 10 for exposure illumination
The light emitted from the lens 1 is transmitted through the shutter 12 to the lens 1
It is configured so that it is incident on the optical integrator 4 and is made into a parallel light flux by this, and then is incident on the optical integrator or fly-eye lens 16.

The light transmitted through the fly-eye lens 16 passes through an illumination aperture stop 18 whose numerical aperture can be changed automatically or manually, and then enters a dichroic mirror 20, and its optical axis is bent downward in the figure. After entering the main condenser lens 22, the optical path is bent again, and after passing through the reticle R having a required pattern, the projection lens 24 is further provided.
To reach the wafer W on the stage 26, so that the pattern of the reticle R is projected onto the wafer W. The illumination aperture stop 18 is arranged conjugate with the entrance pupil of the projection lens 24.

Next, the projection lens 24 has typical lens elements 24A, 24B, 24C and 24D, respectively.
Between these, the sealed lens chambers 24E, 24F, 24G
Are respectively formed. Of these, the sealed lens 24
The pressure of F is controlled by means described later, and the image forming characteristic of the projection lens 24 is adjusted and controlled. Next, the control system will be described. The control of the imaging characteristics is performed mainly by the main controller 28. A shutter control circuit 30 is connected to the main controller 28. The shutter control circuit 30 controls opening / closing of the shutter 12.

The sealed lens chamber 2 of the projection lens 24 described above.
4F is connected to a pressure adjuster 32, and a pressurization system 34 for supplying pressurized air and an exhaust system 36 for vacuum evacuation are connected to the pressure adjuster 32, respectively. The pressure inside the sealed lens chamber 24F is controlled by an electromagnetic valve. A pressure sensor 38 is connected to the lens sealing chamber 24F, and the pressure sensor 38 and
Each of the pressure regulators 32 is connected to the main controller 28. As a result, the sealed lens chamber 2
The pressure in 4F is detected, and the pressure controller 32 is driven by the main controller 28 so that the pressure becomes a predetermined value.

Next, a selector 40 as an input means is connected to the above-mentioned illumination aperture stop 18, and this selector 40 is connected to the main controller 28 via a memory 42. The selector 40 is for selecting from the memory 42 a time constant that changes according to a σ (sigma) value of the illumination aperture stop 18 described later. Further, the memory 42 stores a time constant of a change in the imaging characteristic which is experimentally obtained in advance corresponding to each σ value or numerical aperture. It should be noted that, of the above-mentioned respective constituent elements, respective portions excluding the illumination aperture stop 18, the selector 40 and the memory 42 are disclosed in JP-A-60-78454.
The above-mentioned σ value represents the degree of the aperture, and is represented by the ratio of the numerical aperture of the illumination optical system and the numerical aperture of the projection optical system on the object (reticle R) side.

Next, the change in the light distribution in the projection optical system when the numerical aperture changes will be described with reference to FIG. 2 (A) and 2 (B) are the same as the device of FIG.
It is a simplified view of the illumination optical system and the projection optical system. In FIGS. 2A and 2B, the solid line L
Reference numerals A and LB denote the paths of the light flux, PA denotes the position of the entrance pupil, PB denotes the main surface, and PC denotes the image plane. The broken line indicates the object-side or image-side opening of the projection optical system.

Here, the numerical aperture will be described with reference to FIG. The angle of the incident light L with respect to the reticle R is θ ₁
Let θ ₂ be the angle of the light transmitted from the reticle R, θ ₃ be the incident angle with respect to the image plane PC, and n be the refractive index of air with respect to vacuum. The numerical aperture is represented by nsin θ ₁ , similarly, the numerical aperture on the reticle R side of the projection optical system, that is, the projection lens 24 is nsin θ ₂ , and the numerical aperture on the image plane PC side is nsin θ ₃ . Since the refractive index n is usually about 1, the numerical aperture is substantially sin
It is represented by θ ₁ , sin θ ₂ , and sin θ ₃ .

FIG. 2A shows the case where the illumination aperture stop 18 is opened relatively wide, and the numerical aperture is also large. As shown in this figure, the path LA to the image formation of the 0th-order light flux that travels straight without being diffracted among the illumination light fluxes collected at the three points on the reticle R spreads throughout the projection lens 24. . Next, FIG. 2B shows a case where the illumination aperture stop 18 is relatively closed, and the numerical aperture is small. In this case, as is clear from the path LB of the 0th-order light flux, the light flux will be concentrated in the vicinity of the optical axis inside the projection lens 24.
However, in reality, since there is diffracted light on the R surface of the reticle, the light flux spreads outside the range shown in the figure. Even if this point is taken into consideration, the light flux is larger than that when the numerical aperture is large. Tend to gather near the optical axis.

As described above, the light flux distribution or the optical image area on the pupil position PA (or the principal surface position PB) in the projection lens 24 changes with the change of the numerical aperture or σ value of the illumination optical system. Become. When such a change in the luminous flux distribution occurs, the time constant of the change in the imaging characteristics caused by the temperature rise due to the absorption of a part of the luminous flux by the projection lens 24 also changes.

Next, the selector 40 and the memory 42 will be described. As described above, the time constant of the change in the imaging characteristics also changes in accordance with the aperture or the σ value of the illumination aperture stop 18. FIG. 4 shows the change over time in the amount of change in the magnification (or focus) of the projection lens 24 when the σ value is changed as a parameter. The amount of fluctuation is standardized with its saturation point set to 100%. In this figure, the σ value is the value at α ₁ > the value at α ₂ >
There is a relationship of the value at α ₃ > the value at α ₄ , and at time t ₀
To shutter 12 is "open" to t _C, after the time t _C is a state of the shutter 12 is "closed". Α ₁ having the largest σ value is saturated at time t ₁ , and at the same time, α ₂ is saturated at time t ₂ , α ₃ is saturated at time t ₃ , and α ₄ is saturated at time t ₄ . Also, after time t _C , the degree of decrease is different as indicated by β ₁ to β ₄ . In this way, the time constant of the change in the imaging characteristics changes in accordance with the change in the σ value corresponding to the numerical aperture. Therefore, as shown in FIG. 7 (A), data of the change in the imaging characteristics is acquired in advance for several σ values or numerical apertures of the illumination aperture stop 18, and the time constant τ _i in each case is obtained. deep. These time constants τ _i are stored in the memory 42, and necessary ones are selected by the selector 40 and input to the main controller 28.

Next, the overall operation of the above embodiment will be described. First, the illumination light emitted from the light source 10 is incident on the lens 14 in response to the opening / closing of the shutter 12 under the control of the shutter control circuit 30, is made into a parallel light flux by this, and then is incident on the fly-eye lens 16. Further, it passes through the illumination aperture stop 18. At this time, the illumination aperture stop 18
The divergence of the luminous flux is appropriately adjusted depending on the σ value or the numerical aperture. The illumination light whose divergence is adjusted is incident on the reticle R via the dichroic mirror 20 and the main condenser lens 22, respectively, and further passes through the projection lens 24 to reach the wafer W, where the pattern of the reticle R is projected. Be seen.

On the other hand, with respect to the set numerical aperture of the illumination aperture stop 18, the corresponding time constant is selected by the selector 40 from the memory 42.
Is selected from For example, when the numerical aperture is 0.6, the time constant τ ₆ is selected (see FIG. 7A). The selected time constant is input to the main controller 28, and the variation amount of the magnification as shown in FIG. 4 is obtained based on the time constant. Then, a control signal is output from the main controller 28 to the pressure adjuster 32 based on this variation amount and the pressure in the sealed lens chamber 24F detected by the pressure sensor 38, and the pressurization system 34 and the exhaust system 36 are used. Thus, the pressure inside the sealed lens chamber 24F is controlled. Thereby, the magnification of the projection lens 24 is controlled to be a predetermined value. As described above, the method of controlling the pressure by using the time constant on the variation characteristic of the projection lens 24 may be the method disclosed in Japanese Patent Laid-Open No. 60-78454. The selector 40 may manually accept the input at the operator's discretion.

Next, a second embodiment of the present invention will be described with reference to FIGS. The same reference numerals are used for the same components as those in the above-described embodiment. In this embodiment, as disclosed in Japanese Patent Laid-Open No. 58-160914, a Galilean lens group is used instead of the above-mentioned illumination aperture stop 18, which is advantageous for improving the throughput without vignetting of the light quantity. Is an example. FIG. 5 shows an example in which the numerical aperture is increased, and the concave-convex lens 5 is provided on the incident side of the fly-eye lens 16.
The lens 14 (Fig.
Expand the illumination luminous flux collimated by the reference (see). When the Galileo system is not arranged, it is as shown by the broken line in the figure, and the size of the secondary light source image is IP ₀ . This image is formed on the image plane 16 which is a position conjugate with the pupil of the projection lens 24.
Formed in A. Next, when the Galileo system is arranged, as shown by the solid line in the figure, the size of the secondary light source image becomes IP ₁ and the numerical aperture increases.

Next, when the concavo-convex lenses 50 and 52 are replaced with each other, the result is as shown in FIG. 6, and the size of the secondary light source image is IP ₂ as shown by the solid line in the figure, and the numerical aperture is reduced. It becomes the same state as. As described above, according to the second embodiment, since the σ value of the illumination system can be changed without using the illumination aperture stop 18, there is no vignetting of the light quantity and improvement in throughput can be measured. When the σ value is continuously variable, a zoom lens system may be provided in front of the fly-eye lens 16.

Next, a third embodiment of the present invention will be described with reference to FIG. The device configuration in this embodiment is
It is similar to the above-described first or second embodiment, but the method of obtaining the numerical aperture and the corresponding time constant is different. In the first embodiment,
As shown in FIG. 7A, the relationship between the numerical aperture and the time constant is stored in the memory 42 as a table, and the necessary one is read by the selector 40.

However, in this embodiment, the relationship between the numerical aperture and the time constant is approximated by an appropriate function, for example, an nth-order function, as shown in FIG. 7B, and this function is stored in the memory 42. Then, the corresponding time constant is calculated from the set numerical aperture. In this case, the selector 40 acts as a means for inputting the change in numerical aperture. In the case of FIG. 7 (A),
Although the numerical aperture only changes stepwise, this embodiment of FIG. 7B can also deal with the case where the numerical aperture changes continuously.

In the above embodiment, the change in the imaging characteristic is represented by one time constant, but in some cases, the variation characteristic (attenuation characteristic or the like) may be represented by two or more parameters. . In this case, two or more required parameters are made to correspond to each numerical aperture. For example, in the example shown in FIG. 7A, the required number of parameters (time constants) such as τ _i1 , τ _i2 , τ _i3 ...
2 is stored in the memory 42. In the example shown in FIG. Further, the numerical aperture and the σ value correspond to each other, and either one may be used.

As the fluctuation characteristics, the fluctuation amount of the magnification and the focus with respect to the instantaneous energy ray irradiation is ΔP, the time constants are T ₁ , T ₂ , T ₃ , (T ₁ > T ₂ > T ₃ ), and the coefficients are a
Assuming ₁ , a ₂ , and a ₃ ,

[0028]

In the case of the expression, if the coefficient a ₁ also needs to be corrected, it may be changed in accordance with the numerical aperture (or σ value). In the above embodiment, the change of the time constant was considered as a problem, but the change of the time constant may hardly occur even if the σ value is changed.

FIG. 8 shows the incidence of illumination light on the projection lens 24.
Illumination aperture stop 1 when the total amount (image surface illuminance) is constant
Magnification when changing the value of σ of 8 as a parameter
(Or focus) variation characteristics. In Figure 8, the horizontal axis is hour
Represents time t and time t₀To t_CShutter 12 open until
It is in the state, and time t_CAfter that, it is in the closed state. And FIG.
The vertical axis represents the amount of change in magnification (or focus). In this figure
Therefore, the relationship between the values of the illumination system is the characteristic γ₁Σ value> characteristic γ
₂Σ value> characteristic γ₃Σ value> characteristic γ_FourAnd the σ value at
ing. This characteristic is the structure of the projection lens, the lens glass material, etc.
However, the change in the time constant is
Almost nothing, the coefficient term as a parameter changed
Recognized. In such a case, the memory shown in FIG.
As shown in FIG. 9 (A), there are several illumination openings 42.
The σ value (or numerical aperture) of the diaphragm 18 is linked in advance.
Acquired data of image characteristic change and corresponded to each σ value
Coefficient C _i(A in the above equation_i) And memorize
deep. Then, the desired coefficient is selected by the selector 40 in FIG.
C_iWill be selected and sent to the main controller 28.
I will Also, as in the case of FIG. 7B, the σ value
And coefficient C_iAs shown in Fig. 9 (B),
Number, for example, n-degree function or hyperbola
It is stored in the memory 42 and corresponds to the set σ value of the illumination system.
The coefficient may be calculated. Mochiro
Hmm, store both time constant and coefficient in memory 42,
Depending on the change in σ value, both or one of them may be read and controlled as appropriate.
You may use it.

In each of the above-described embodiments, the method of correcting the optical characteristics of the projection lens 24 itself is used as the means for correcting the image formation state, but other methods may be used. For example, if the reticle side of the projection lens 24 is non-telecentric, the magnification on the wafer can be changed by automatically moving the reticle R in the optical axis direction. Therefore, if the amount of movement is changed in accordance with the calculated variation characteristic, the magnification can always be maintained at a constant value. Further, when the focus fluctuation of the projection lens 24 poses a problem, the automatic focusing mechanism for keeping the distance between the projection lens 24 and the wafer W constant has an offset according to the fluctuation characteristics, and the projection lens 24 The position of the wafer W which is considered to be in focus may be changed by following the change of the image forming surface in the optical axis direction. That is, in the present invention, as long as it is possible to correct the image formation state of the projected image on the wafer W,
Any method may be used.

Also, when the shape of the light source image (image of the aperture stop or the like) on the pupil of the projection lens changes from a circular shape to another shape, it is desirable to similarly change the parameters such as the time constant and the coefficient. Furthermore, even when the numerical aperture (pupil size) of the projection optical system itself is changed by a diaphragm or the like, the parameters (time constant, coefficient) are changed in exactly the same way as when the numerical aperture of the illumination system is changed. It goes without saying that the same effect can be obtained by doing so. Also in this case, it works as a means for inputting a change in the numerical aperture (σ value) of the selector 40.

[0032]

As described above, according to the present invention, even if the distribution state of incident light in the projection optical system changes, the change of the image forming characteristic is adjusted well, and the image forming characteristic is maintained with high accuracy. The effect is that you can.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a change in a light distribution in a projection lens when a numerical aperture is changed.

FIG. 3 is a diagram for explaining a numerical aperture.

FIG. 4 is a diagram showing an example of changes in image forming characteristics when the numerical aperture is changed.

FIG. 5 is a diagram for explaining a second embodiment in which the numerical aperture is changed by using a Galileo system.

FIG. 6 is a diagram for explaining a second example in which the numerical aperture is changed by using a Galileo system.

FIG. 7 is a diagram for explaining an example of correspondence of a time constant with a numerical aperture.

FIG. 8 is a diagram showing an example of changes in image forming characteristics when the numerical aperture is changed.

FIG. 9 is a diagram for explaining a correspondence example of a coefficient with respect to a numerical aperture (σ value).

[Description of sign]

10 ... Light source, 12 ... Shutter, 16 ... Fly-eye lens, 18 ... Illumination aperture stop, 22 ... Main condenser lens, 24 ... Projection lens, 24A, 24B, 24C, 24
D ... Lens element, 24E, 24F, 24G ... Sealed lens chamber, 26 ... Stage, 28 ... Main controller, 30
... Shutter control circuit, 32 ... Pressure regulator, 38 ... Pressure sensor, 40 ... Selector, 42 ... Memory, R ... Reticle,
W ... Wafer

Claims (13)

[Claims] 1. An illumination system for illuminating a mask with illumination light for exposure, a projection optical system for projecting an image of the pattern of the mask on a photosensitive substrate with a predetermined image forming characteristic, and illumination light from the illumination system. A distribution changing means for changing the distribution of the light source image generated on the pupil plane of the projection optical system by means of the above, and the characteristics of at least a part of the optical elements forming the projection optical system to adjust the image of the projection optical system. In a projection exposure apparatus provided with an image forming characteristic adjusting unit for finely adjusting the characteristic, a change from a predetermined state of the image forming characteristic of the projection optical system caused in response to the change of the light source image distribution by the distribution changing unit is corrected. Storage means for storing in advance the correction information of the characteristics of the optical element necessary for the operation; when the light source image distribution is changed by the distribution changing means, it corresponds to the distribution state of the light source image after the change. Correction information above A projection exposure apparatus comprising: a control unit that reads out from a storage unit and controls an adjusting operation of the image formation characteristic adjusting unit based on the correction information. 2. The illumination system has an optical integrator, and the distribution changing unit is arranged on the exit side of the optical integrator and changes the shape of the light source image distribution. Projection exposure device. 3. The projection exposure apparatus according to claim 2, wherein the distribution changing means is composed of an illumination aperture stop member arranged on the exit side of the optical integrator. 4. The projection exposure apparatus according to claim 2, wherein the distribution changing unit is composed of a lens group that changes the distribution of the illumination light flux incident on the optical integrator. 5. The projection exposure apparatus according to claim 1, wherein the image forming characteristic adjusting means is a mechanism for adjusting the pressure in a part of the air chamber that constitutes the projection optical system. 6. An illumination system for illuminating a mask with illumination light for exposure, a projection optical system for projecting an image of the pattern of the mask on a photosensitive substrate with a predetermined image forming characteristic, and illumination light from the illumination system. A distribution changing means for changing the distribution of the light source image generated on the pupil plane of the projection optical system by means of the above, and the characteristics of at least a part of the optical elements forming the projection optical system to adjust the image of the projection optical system. A projection exposure apparatus comprising: an image forming characteristic adjusting unit for finely adjusting the characteristic; and a control unit for controlling the image forming characteristic adjusting unit according to a state after the light source image distribution is changed by the distribution changing unit. A projection exposure apparatus characterized by the above. 7. A method for illuminating a mask with illumination light from an exposure illumination system to expose a pattern of the mask on a photosensitive substrate with a predetermined image formation characteristic through a projection optical system, the projection optical system comprising: Changing the light source image distribution generated on the pupil plane of the system; adjusting the light source image distribution of the projection optical system so as to correct the change of the image forming characteristic of the projection optical system caused by the change of the light source image distribution. Correcting the characteristics of at least some of the optical elements constituting the projection optical system in response to the change; and after the correction, project and expose a mask pattern on the photosensitive substrate in the changed light source image distribution state. And a projection exposure method. 8. The illumination system has an optical integrator, and the change of the light source image distribution changes the shape of the secondary light source image generated on the exit side of the optical integrator. The projection exposure method according to. 9. The projection exposure method according to claim 8, wherein the light source image distribution is changed by changing an illumination aperture stop arranged in a predetermined plane on the exit side of the optical integrator. 10. The projection exposure method according to claim 7, wherein the change of the light source image distribution changes the numerical aperture of the projection optical system. 11. The correction information of the characteristic of the optical element necessary for correcting the variation of the image forming characteristic of the projection optical system which occurs after the change of the light source image distribution is stored in advance. Item 7. The projection exposure method according to Item 7. 12. The step of correcting the characteristics of at least a part of optical elements constituting the projection optical system adjusts a gas pressure in an air space formed between a plurality of lens elements constituting the projection optical system. 8. The projection exposure method according to claim 7, wherein the projection exposure method is performed as follows. 13. The step of correcting the characteristic of at least a part of optical elements constituting the projection optical system is performed by adjusting a distance between lens elements in the projection optical system. The projection exposure method according to.