JPH08241860A - Photolithography device and exposure method - Google Patents

Abstract

PURPOSE: To lessen a projected image in distortion errors attendant on the change of a pattern injection region in shape or size by a method wherein a photolithography device is controlled in a projection multiplying factor to a substrate so as to make image high spots, which are located in a pattern projection region adjusted by a blind, small in amount of distortion on an average. CONSTITUTION: Blinds BL1 and BL2 are each equipped with a movable blade to control illuminating light which irradiates masks (reticle) R1 and R2 in an illuminating range conforming to pattern regions PA1 and PA2 on the masks (reticle) R1 and R2. Multiplying factor controlling means BC1 and BC2 control a photolithography device in a projection multiplying factor to a substrate so as to make image high spots, which are located in the effective pattern projection regions of projection optical systems PL1 and PL2 corresponding to illuminating ranges adjusted by the blinds BL1 and BL2, small in amount of distortion on an average. By this setup, a projected image can be lessened in distortion error attendant on the change of a pattern projection region in shape or size.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photolithography apparatus for transferring a mask pattern onto a substrate for photolithography (a photosensitive substrate such as a semiconductor wafer) by a step-and-repeat method, and such an apparatus. And a method of exposing a substrate using the same.

[0002]

2. Description of the Related Art In recent years, a reduction projection type exposure apparatus has been used for manufacturing a VLSI, and has made great achievements in improving productivity. This type of projection exposure apparatus is designed to have a finer line width of a pattern on a reticle to be projected for exposure, and a higher integration of the pattern itself. Is required to be improved. This is particularly remarkable between different devices.

Recently, various types of projection exposure apparatuses having different numerical apertures, magnifications, or exposure areas (projection fields of view) have appeared, and the super LS
In the manufacturing factory of I, in consideration of the required resolution and throughput, it is becoming more and more common to use different exposures for different layers in one VLSI manufacturing process. Mixing of exposure apparatuses having different projection magnifications and projection fields, or apparatuses having different exposure methods such as a refraction system or a reflection system in the photolithography process of semiconductor manufacturing, so-called mix and match (Mix an
In d Match), overlay accuracy becomes especially important. Distortion (image distortion) of the projection optical system is one of the factors that influence the overlay accuracy.

In general, even in a projection optical system having the same structure, the distortion characteristic (aberration curve) is slightly different for each line, and even if the projection optical systems are different in magnification and field size, the distortion characteristics are different. Can vary significantly. Therefore, even if such devices are used for mix and match, it is not always possible to obtain sufficient overlay accuracy.
Therefore, a serious problem such as a decrease in productivity due to a defective overlay may occur.

The 1/5 reduction or 1 / 2.5 reduction projection optical system used in the step-and-repeat type projection exposure apparatus has a diameter of 28 mm or 42 mm on a semiconductor wafer, although it depends on the numerical aperture. Has a circular visual field area. On the other hand, the pattern area to be exposed formed on the reticle is generally 20 × 20 mm, 30 × 30.
It has a rectangular shape such as mm. Therefore, this type of projection exposure apparatus is provided with an illumination field diaphragm that limits the size of the exposure illumination light that illuminates the reticle in a rectangular shape in accordance with the pattern area on the reticle. This field stop has a movable blade that adjusts the shape and size of the illumination area according to the change in the size of the pattern area on the reticle.

[0006]

By the way, the change of the size of the pattern area on the reticle means that the size of the effective pattern projection area in the circular visual field of the projection optical system changes, that is, the pattern. It also means that the effective image height range that contributes to the projection (distance from the center of the circular visual field of the projection optical system) also changes within the circular visual field. The distortion characteristic for each image height point in the circular visual field of the projection optical system tends to be in the initial state, and the effective image height range changes means that the image according to a part of the entire distortion characteristic This means that projection exposure is performed with distortion.

For this reason, when projecting and exposing a relatively small pattern area with respect to the circular visual field of the projection optical system, for example, a projection optical system which is originally capable of projecting up to a pattern area of 30 × 30 mm is used. When a mask with a small pattern area of 20 × 20 mm is projected and exposed, there is a problem that the entire projected image of the pattern area is transferred to a slightly smaller size than the original projection magnification. .

Therefore, the present invention solves such a problem,
An object of the present invention is to provide an exposure method and a photolithography apparatus capable of reducing distortion error of a projected image due to a change in shape and size of a pattern projection area occupied in a circular visual field of a projection optical system and obtaining higher overlay accuracy. And

[0009]

Therefore, the first invention of the present application is to provide a pattern area (PA1) of a mask (reticle R1 or R2) on a substrate (wafer W or the like) for photolithography.
Alternatively, it is applied to a photolithography apparatus (projection exposure apparatus A or B) that transfers an image of PA2) through the circular visual field of the projection optical system (PL1 or PL2). In the first invention, the pattern area (P
A blind (BL1 or BL2) provided with a movable blade that adjusts the illumination range of the illumination light irradiated on the mask according to A1 or PA2) and the illumination range adjusted by this blind (BL1 or BL2) Magnification for adjusting the projection magnification with respect to the substrate (wafer W, etc.) so that the amount of distortion at each of the plurality of image height points in the effective pattern projection area of the projection optical system (PL1 or PL2) becomes small on average. The adjusting means (BC1 or BC2) is provided.

In the second invention of the present application, the mask (R1
Or a blind (BL1 or BL2) provided with a movable blade that changes the illumination range of the illumination light that illuminates the mask (R1 or R2) according to the size of the pattern area (PA1 or PA2) of R2), and this blind ( In response to a change in BL1 or BL2, the projection optical system (PL1 or PL2
2) Adjusting means for adjusting the imaging characteristics (BC1 or BC
2) and are provided.

Further, a third invention of the present application is the mask (R1
Or, the pattern area (PA1 or PA2) of R2) is irradiated with the illumination light for exposure, and the image of the pattern area is superimposed on the exposed area on the substrate (wafer W or the like) via the projection optical system (PL1 or PL2). It is applied to the method of performing combined exposure. In the third invention, the projection optical system (PL1 or PL2)
Characteristic data (data DS1 stored in the main controller CNT1 or CNT2) defining the relationship between the image height position of the projection optical system (PL1 or PL2) and the distortion amount obtained when the image forming characteristics of The step of pre-storing DS2 or the distortion functions Fa (γ), Fb (γ) and the irradiation range of the illumination light is restricted according to the size of the pattern area (PA1 or PA2) of the mask (R1 or R2). Illumination field stop (BL1 or BL
2) Adjusting the movable blade, projection based on the size of the irradiation range limited by the illumination field stop and prestored characteristic data (data DS1 or DS2, or distortion function Fa, Fb) Optical system (PL1
Or, the imaging characteristics of the projection optical system (PL1 or PL2) are initialized so that the amount of distortion generated at each point in the effective pattern projection area corresponding to the irradiation range within the projection field of view (PL2) becomes small on average. From the stage to adjust and to execute.

[0012]

With the above-described structure, in each invention of the present application, an exposure image that changes according to a change in the size and shape of the effective pattern exposure region that contributes to exposure within the circular visual field of the projection optical system. Dispersion variation is reduced, and the amount of distortion at each image height point in the exposure image of the pattern area can be averaged and minimized regardless of the size of the projected pattern area. Therefore, it is possible to improve the overlay accuracy with the exposed region formed on the substrate such as a wafer on average.

Further, in the third invention of the present application, since the distortion characteristic peculiar to the projection optical system is stored in advance, the best result is immediately obtained for the mask mounted on the exposure apparatus having the projection optical system. It is possible to command to create an image state. Therefore, an exposure method and apparatus according to an embodiment to which the present invention is applied will be described below with reference to FIG. FIG. 1 is a perspective view showing a schematic configuration of two projection type exposure apparatuses (hereinafter referred to as steppers) A and B having different projection visual field sizes. In this embodiment, the projection lens PL1 of the stepper A has the reduction magnification of 1/5 and the wafer W
The projection visual field on the top is 20 × 20 mm square (circular area with a diameter of 28 mm), and the projection lens PL2 of the stepper B has a reduction magnification of 1 / 2.5 and the projection visual field on the wafer W is 30 × 3.
It is assumed to be 0 mm square (circular region having a diameter of 42 mm).

The stepper A is provided with a blind BL1 as a field stop for illuminating only the pattern area PA1 to be exposed on the reticle R1, and the shape and size of the opening are adjusted by four movable blades. . Reticle R
1, the center of the pattern area PA1 is the projection lens PL1.
It is mounted so as to coincide with the optical axis (center of visual field) AX1 of. The wafer W loaded on the stepper A is placed on the stage ST1 that moves two-dimensionally, and the projection image of the pattern area PA1 by the projection lens PL1 is sequentially exposed on the wafer W by the step-and-repeat method.

The projection lens PL1 in this embodiment includes
A pressure controller BC1 for controlling the pressure (atmospheric pressure) in an air gap between a plurality of lenses forming the projection lens to finely adjust the magnification of the projection lens PL1 is provided, and the main controller C
It operates so as to obtain a desired projection magnification according to the setting information from NT1. Regarding the specific configuration, operation and usage of the pressure regulator BC1 and the main controller CNT1, JP-A-60-28613 or JP-A-60-
The detailed description is omitted here because it is disclosed in Japanese Patent No. 78454.

On the other hand, with respect to the stepper B, only the size of the projection visual field of the projection lens PL2 is different, and the blind BL2, the stage ST2, the pressure regulator BC2, and the main controller CNT2, which are other basic configurations, are the same as those of the stepper A. Is the same as. The pattern area PA2 of the reticle R2 mounted on the stepper B has the same size as the pattern area PA1 of the reticle R1. That is, the size of the pattern area PA1 corresponds to the maximum field of view (20 × 20 mm) that can be projected by the projection lens PL1 and is 100 × 100.
If it is mm square, the projection lens PL2 will be used after being narrowed down to a region of 20 × 20 mm square in the maximum projection visual field (30 × 30 mm). In this embodiment, such steppers A and B are used together for overlay exposure between different layers formed on the wafer W.

In order to simplify the description here, after the exposure of the first layer on the wafer W is performed by the stepper A,
It is assumed that the predetermined process E for forming the first layer is performed, and the stepper B performs overlay exposure on the second layer of the wafer W. Therefore, the main controller CNT2 of the stepper B receives the data DS regarding the distortion of the projection lens PL1 from the main controller CNT1 of the stepper A.
Enter 1. The data DS1 is stored in the main controller CNT1 in advance as inspection data when the stepper A is manufactured.

Alternatively, as disclosed in Japanese Patent Laid-Open No. 60-18738, a photoelectric sensor with a slit is provided on the stage ST1 to project cross marks formed at a plurality of positions on a reticle for distortion inspection. By scanning the slit in the projection screen and obtaining the projection position of each mark, the distortion amounts at a plurality of points in the projection field may be detected and stored as data DS1. By using the slits on the stage in this way, the distortion at that time can be accurately measured at any time during the operation of the stepper, and it is possible to cope with the temporal change of the distortion characteristics. Similarly, the data D regarding the distortion of the projection lens PL2 of the stepper B
S2 is stored in the main controller CNT2, and the stepper A
Main controller CNT as data when adjusting the magnification of
Sent to 1.

Further, when the main control devices CNT1 and CNT2 are comprehensively controlled by a higher-order main control device (large computer), the distortion data DS1 of the projection lens PL1 and the projection lens PL2.
Even if both data of the distortion data DS2 of (1) are sent to the host control device and are centrally managed there, the same is true.

FIG. 2 is an exaggerated chart showing an example of overlay accuracy (hereinafter referred to as matching accuracy) when overlay exposure is performed without performing magnification correction on the two steppers A and B. In the figure, the solid line is a chart showing the deviation from the ideal grid point of the stepper A,
The broken line is a chart showing the deviation of the stepper B from the ideal grid point.

The center of the projected field of view of the stepper A and the center of the projected field of view of the stepper B are the origin P0 of the orthogonal coordinate system xy.
In the first quadrant of the coordinate system xy, the projection point of the ideal lattice point by the stepper A is P1a,
P2a, P3a ... And the projection points of the ideal lattice points by the stepper B are P1b, P2b, P3b. As is clear from this example, when two steppers are mixed and matched with their centers (optical axes) aligned, a matching accuracy near the center P0 is sufficiently obtained, but a point distant from the center P0, for example, a point P2a. At P2b, or at points P3a and P3b, the relative shift amount may become too large to be ignored. This amount of deviation depends on the distortion characteristics between the two projection lenses, and does not always increase at each peripheral point.

FIG. 3A shows an example of the distortion characteristic of the projection lens PL1. Data D is added to the main control CNT1.
It is stored as S1, and FIG.
This is an example of the distortion characteristic of L2, and is stored as data DS2 in main controller CNT2. FIG.
In (a) and (b), the vertical axis represents the distortion amount, and the horizontal axis represents the image height (optical axis, that is, the distance from the center P0 in the radial direction). The positive / negative of the distortion amount is negative when the projection point of the ideal lattice point is shifted toward the center P0, and positive when the projection point is opposite.

Although the curves of the distortion characteristics of both projection lenses are similar in overall tendency, the amount of distortion at the same image height position is greatly different depending on the image height. In this type of projection lens, distortion correction is performed so that the maximum value in the positive direction of distortion and the maximum value in the negative direction are substantially equal. This is to improve (distribute) the distortion on average over the entire exposure area.

FIG. 4 shows the two distortion characteristics as described above, which are centered and overlapped.
It is only necessary to consider within the projected field of view (20 × 20 mm). In FIG. 4, the projection magnifications of both steppers A and B are assumed to be standard values (initial values). As is clear from this figure, from the point where the image height is about 9 mm to the periphery,
The absolute value of the deviation between the distortion characteristics DS1 and DS2 becomes extremely large, and the absolute value of the deviation ΔD at the image height position Px |
ΔD | is maximized.

The amount of the deviation | ΔD | may be larger than the maximum value of the distortion amount on either the distortion characteristic DS1 or DS2. Therefore, a pattern located at the image height position of about 9 mm or more can hardly obtain sufficient matching accuracy. The case shown in FIG. 4 corresponds to the chart shown in FIG.

Therefore, in the present embodiment, the distortion characteristic DS1 of the stepper A is left as it is, and the distortion characteristic DS2 of the stepper B is changed by finely adjusting the magnification to change the two distortion characteristics in the projection visual field. The maximum value of the absolute value of the deviation ΔD caused by is minimized. Therefore, the mathematical analysis for superimposing the two distortion characteristics and optimizing the matching accuracy will be described below.

The following analysis is based on the main controller C of the stepper B.
It can be easily executed by a computer such as NT2 or a host controller. Assuming that the image height is γ, the distortion curve is f (γ), and the magnification adjustment coefficient is C, the deviation amount Δ from the ideal grid point obtained by adjusting the magnification is Δ.
(Γ) is expressed as in equation (1). Δ (γ) = f (γ) + C · γ (1) Corresponding to this equation (1), the deviation from the ideal grid point is calculated by the vector (ΔXa, ΔY) for each of the steppers A and B.
When expressed by a) and (ΔXb, ΔYb) respectively, the equation for equation (2) for stepper A and the equation (3) for stepper B are obtained.

[0028]

[Equation 1]

[0029]

[Equation 2]

However, the subscripts a and b are steppers A and B, respectively.
Corresponds to B. Therefore, the final deviation vector (ΔX, ΔY) of the distortion when the steppers A and B are superimposed and exposed by centering is expressed by the equation (4) from the equations (2) and (3). (ΔX, ΔY) = (ΔXa, ΔYa) − (ΔXb, ΔYb) (4) From equation (4), the absolute value of the deviation ΔX, the absolute value of the deviation ΔY in the overlay exposure area (projection field of view), and The maximum values of the scalar quantity of the vector (ΔX, ΔY) are Dx and D, respectively.
Assuming y and Dk, they are expressed by the following equations (5), (6) and (7).

Dx = MAX (| ΔX |) (5) Dy = MAX (| ΔY |) (6)

[0032]

(Equation 3)

Therefore, if the magnification adjustment coefficients Ca and Cb are set so that either one of Dx, Dy and Dk is minimized or both Dx and Dy are both minimized, the optimum condition can be obtained. Will be done. When the magnification correction is performed only by the stepper B as in this embodiment, the coefficient Ca
May be zero. Therefore, from the equations (2), (3), and (4), the deviation vector (ΔX, ΔY) is expressed as in equation (8).

[0034]

[Equation 4]

(However, here, Ca = 0.) Therefore, the main controller CNT2, for each of a large number of points in the projection exposure region, the distortion characteristics DS1 (function fa) and DS2 (function fb) stored in advance. ) And, while changing the adjustment coefficient Cb, the vector (ΔX, ΔY),
And the maximum values Dx, Dy, Dk are calculated, and one of Dx, Dy, Dk or a coefficient Cb that minimizes both Dx, Dy is found from the accuracy required for the layer to be subjected to overlay exposure. Then, main controller CNT2 outputs a command value for correcting the magnification of projection lens PL2 by a value corresponding to coefficient Cb to pressure adjuster BC2. The pressure adjuster BC2 controls the pressure by taking into account the irradiation history of the projection lens PL2 and the magnification variation due to the atmospheric pressure variation, as well as the command value thereof.

In the above analysis, an exact solution is obtained by mathematical analysis in order to improve the matching accuracy over the entire exposure area. However, even if only the distortion curve is used, there will be no significant error. You can get a solution. Therefore, an analysis using the distortion curve will be described with reference to FIG. FIG. 5 shows a state in which the distortion characteristics DS1 and DS2 are overlapped with each other with the magnification of the projection lens PL2 being changed, and the distortion characteristic of the projection lens PL2 after the magnification adjustment is represented by DS2 ′. First, the main controller CNT2 calculates the difference in distortion amount between the characteristics DS1 and DS2 before magnification adjustment as follows.
Calculation is performed for a large number of points (for example, every 0.5 mm) between the center P0 and the image height of 15 mm, for example. As a result, the maximum absolute value of the deviation ΔD is obtained as shown in FIG.

In order to reduce the absolute value of the deviation ΔD, the magnification of the projection lens PL2 is corrected as shown in FIG.
The characteristic DS2 may be lifted (tilted) in the positive direction at a predetermined image height point. In FIG. 5, the straight line L passing through the center P0 corresponds to the original image height axis of the characteristic DS2, and the slope Cb of the straight line L corresponds to the magnification adjustment coefficient C in the above equation (1). .

The main controller CNT2 calculates the characteristic DS2 'after the magnification adjustment based on the equation (1) in a state where the inclination Cb is increased from zero by a certain amount. Then, the absolute value of the deviation between the corrected characteristic DS2 'and the characteristic DS1 is calculated again for each image height position, and the deviation having the maximum absolute value is obtained. The above calculation is repeated after increasing the gradient Cb by a certain amount. Eventually, as shown in FIG. 5, the deviation | ΔD1 | near the position Px becomes | ΔD in FIG.
Is smaller than |, and conversely the deviation at another image height position | ΔD
2 | becomes larger.

In the case of the characteristics as shown in FIG. 5, if the characteristics DS2 'is lifted a little further from the state shown in the figure, |
ΔD2 |> | ΔD2 |, and conversely, if it is further lowered, | ΔD2 | <| ΔD1 |. Therefore, in the example shown here, the inclination Cb may be set so that | ΔD1 | = | ΔD2 |. Then, when the inclination is Cb, the deviation amount ΔM of the straight line L obtained from the position of the image height of 15 mm from the image height axis is the deviation amount caused by the magnification correction on the actual projected image plane.

In this way, the two distortion characteristics are compared while changing the relative magnification, the maximum value of the deviation (absolute value) of the distortion amount is obtained at each magnification, and the magnification that minimizes the maximum value is obtained. By determining, the best matching accuracy can be obtained over the entire exposure area within the image height of 15 mm. FIG. 6 is a chart showing an example of a matching state when the stepper B is used to perform overlay exposure with the magnification adjusted as described above. In the figure, the solid line is due to stepper A, and the broken line is due to stepper B. Compared to the chart shown in FIG. 2, the deviation amounts of the projected points of the ideal lattice points (P1a and P1b, P2a and P2b, P3a and P3b) become smaller on average,
It can be seen that the matching accuracy is improved.

As shown in FIG. 1, the wafer W that has undergone the process E after exposure by the stepper A may undergo linear deformation (expansion / contraction) due to heat or chemical treatment. Therefore, when overlay exposure is performed by the stepper B, it is desirable to perform magnification correction in consideration of its deformation. For that purpose, the amount of deformation can be obtained by measuring the positions of alignment marks formed at a plurality of points on the wafer W by an alignment device provided in the stepper B and comparing each position with a design value.

Next, another embodiment of the present invention will be described. When the stepper A shown in FIG. 1 does not use the entire projection field of 20 mm square as an exposure area, or the wafer W
If you want to match the absolute magnification of the above exposure area accurately,
In consideration of the overlay exposure by the stepper B, the stepper A may be adjusted in magnification in advance. Although it is not a practical use, if the exposure area of the first layer by the stepper A is narrowed down to an image height of 11 mm, the magnification of only the stepper B is adjusted as in the previous embodiment. Then, as shown in FIG. 7, the matching degree on the distortion characteristic is generally biased in the negative direction. This becomes a big problem when trying to control the absolute magnification on the wafer W.

In FIG. 7, the image height position where the absolute value of the difference between the distortion amounts of the characteristics DS2 'and DS1 can be the maximum is at a point of about 8 mm and a point of about 11 mm, and the deviations ΔD4 and ΔD3 near this point. If both absolute values are equal,
This means that the absolute value of the maximum deviation is minimized. However, in the exposure area up to an image height of about 11 mm, the distortion at the time of superposition is biased in the negative direction, so if the characteristics DS1 and DS2 are raised in the positive direction by the same value at a certain image height point, the exposure area It becomes possible to divide the distortion into positive and negative.

FIG. 8 shows the characteristics under the optimum condition where | ΔD3 | = | ΔD4 | and the distribution of distortion is performed from the superposed state as shown in FIG.
In FIG. 8, the straight line L2 is the same as the straight line L in FIGS. 5 and 7, and the straight line L1 represents the original image height axis inclined by the coefficient Ca by the magnification adjustment of the stepper A, and the characteristic DS1 ′.
Represents the distortion of the projection lens PL1 after the magnification adjustment.

In order to obtain such a characteristic, first, the characteristic DS1 is fixed and the characteristic DS2 is raised, that is, in the same manner as in the previous embodiment, the magnification is such that both absolute values of the deviations ΔD3 and ΔD4 become equal. The adjustment coefficient Cb is obtained. After that, further, in order to make the maximum value of the positive distortion amount and the maximum value of the negative distortion amount equal in absolute value on the superimposed distortion characteristic, straight lines L1 and L
Both slopes of 2 are changed by the same amount.

The slope Ca of the straight line L1 obtained by this
Is a magnification adjustment coefficient of the stepper A. Therefore, at the time of exposure of the first layer, for example, a magnification offset of + ΔMa may be added to the stepper A at an image height of 10 mm, and at the time of overlay exposure of the second layer, an image height of 10 mm.
At this point, the stepper B may be used with a magnification offset of +4 Mb. When such a magnification correction is performed,
Not only the relative difference in distortion between different layers can be reduced, but also the absolute amount of distortion (magnification error) of the pattern region formed on the wafer W can be reduced.

In each of the embodiments of the present invention described above, the mix-and-match of steppers having different projection visual field sizes was considered. However, even if the projection lenses have the same size of the projection visual field, the distortion characteristics are usually slightly different due to the difference in the lens configuration, the manufacturing error or the variation. Accordingly, FIG. 9 shows an example in which the sizes of the projected visual fields are the same.
Will be described with reference to.

FIG. 9A shows a characteristic in which the distortion characteristic DS2 of one of the two steppers and the distortion characteristic DS3 of the other stepper are overlapped without adjusting the magnification. Here, it is assumed that the characteristic DS2 has poor distortion even in the same stepper, and the characteristic DS3 has good distortion. If these two steppers are used by narrowing down the exposure area with an image height of 16 mm, for example, the absolute value of the difference in distortion amount will be the maximum value ΔD near an image height of 11 mm, and the distribution of distortion will be somewhat unbalanced. Come on.

Therefore, in such a case, the characteristics DS2 and DS3 are both raised in the positive direction in consideration of the distribution of distortion, and DS2 'and D2 shown in FIG.
If S3 'is used, the best matching accuracy can be obtained. The characteristic DS2 changes like the characteristic DS2 'by the magnification adjustment corresponding to the inclination of the straight line L2, and the characteristic DS3 changes like the characteristic DS3' by the magnification adjustment corresponding to the inclination of the straight line L3. By doing so, the maximum deviation can be obtained between the point with an image height of 16 mm and the point near 8 mm. However, by minimizing the maximum absolute value of these deviations, the relative amount of distortion between the steppers is increased. 9 is much smaller than that in the case of FIG. 9 (a).

Although each of the embodiments of the present invention has been described only with respect to a stepper equipped with a reduction projection lens, the present invention can be carried out in the same manner for a mixed use with a reflection projection type stepper using a mirror. It is a thing. Further, in each of the above-described embodiments, only matching of two steppers is considered, but the same can be applied to any n or more steppers. In this case, a matching computer is used to calculate the matching accuracy by using the distortion characteristics of the n steppers, and the magnification of each stepper is adjusted so that the best matching accuracy can be obtained throughout the photolithography process of semiconductor device manufacturing. You just need to adjust.

When the object (reticle) side of the projection lens is a non-telecentric optical system, the magnification can be adjusted by finely adjusting the distance between the reticle and the projection lens, and the same effect can be obtained. In this case, a drive unit for moving the reticle stage holding the reticle up and down by a small amount along the optical axis is provided as the magnification adjusting unit. Further, in the embodiment described above, the two distortion characteristics are compared, for example, every 0.5 mm on the image height axis, and the maximum absolute value of the deviation is obtained.
However, this is 0.5 within the predetermined exposure range.
Since the maximum value is searched after obtaining the deviations at all image height points for each mm, the accuracy is low, and some error occurs with respect to the true maximum.

For this reason, if the point to be compared is made finer than 0.5 mm, the accuracy will be improved, but the processing time will be increased in proportion to it. Therefore, a method for quickly obtaining an accurate maximum value from two distortion curves by mathematical analysis will be briefly described below. Now, assuming that the distortion characteristics of the two steppers are fa (γ) and fb (γ), respectively, the distortion function Fa considering the magnification adjustment coefficients Ca and Cb will be described.
(Γ) and Fb (γ) are expressed by equations (9) and (10), respectively.

Fa (γ) = fa (γ) + Ca · γ (9) Fb (γ) = fb (γ) + Cb · γ (10) where the characteristics fa (γ) and fb (γ) are It is assumed that they are stored in the main controller of each stepper or a host computer in a form approximated by the Na-th order curve and the Nb-th order curve, respectively.

The characteristics fa (γ) and fb (γ) are normally fa (γ) = 0, when γ = 0 so that the distortion characteristics of this type of projection lens are line-symmetric with respect to the optical axis.
Since it is designed so that fb (γ) = 0, the general formula is expressed as formula (11), and there is no constant term.

[0055]

(Equation 5)

Here, Kn, Kn-1, ... K2, K1 are constants. Therefore, two distortion functions Fa
When the difference between (γ) and Fb (γ) is represented by the function G (γ), the function G (γ) is represented by the equation (12). G (γ) = Fb (γ) −Fa (γ) = fb (γ) −fa (γ) + (Cb−Ca) · γ (12) where C = Cb−Ca and the function G (γ ) Maximum point,
In order to obtain the minimum point, the function G (γ) is differentiated by the image height γ as in the equation (13).

[0057]

(Equation 6)

Here, Kan represents the constant of the n-th term of the characteristic fa (γ), and Kbn represents the constant of the n-th term of the characteristic fb (γ). Therefore, if the image height γ that satisfies dG (γ) / (dγ) = 0 is obtained, the maximum point and the minimum point of the function G (γ) can be found, and the absolute value of the deviation becomes maximum at either of these points. ing. If both Na and Nb are third or lower,
Equation (13) becomes a quadratic equation and the solution can be analytically obtained. However, if either Na or Nb is a quaternary or higher, the solution cannot be analytically obtained, so the numerical solution is used. Will be asked.

When the solution of the image height γ satisfying dG (γ) / (dγ) = 0 is γ1, γ2, ..., γn and the maximum image height point in the exposure area is γmax, The value is (1
Substituting into equation (2), G (γ1), G (γ2), ... G (γn),
Each value of G (γmax) is calculated. Then, of the calculated values, select the one with the maximum absolute value, and set this to Gma
If x is set, Gmax is expressed as in equation (14).

Gmax = Max {| G (γ1) |, | G (γ2) |, ... | G (γn) |, | G (γmax) |} (14) where γ1, γ2 ... γn Among them, those larger than γmax or those with a negative value are excluded.
By doing so, the maximum absolute value of the deviation can be uniquely obtained without making a comparison every 0.5 mm on the image height axis. Based on the above calculation, the relative magnification difference C (Cb−
The optimum magnification adjustment coefficients Ca and Cb can be determined by changing Ca) only by a small amount and repeating the calculation.

Based on the above method, an example in which both Na and Nb are cubic is described below. Therefore, the characteristic fa
(Γ) and fb (γ) are defined as in equations (15) and (16), respectively.

[0062]

(Equation 7)

[0063]

(Equation 8)

Therefore, the function G (γ) of the difference between the functions Fa (γ) and Fb (γ) is expressed by the equation (17).

[0065]

[Equation 9]

When this equation (17) is differentiated by γ, (18)
The formula is obtained.

[0067]

[Equation 10]

Here, Kb3-Ka3 = K3, Kb2-Ka2
= K2, Kb1−Ka1 = K1, Cb−Ca = C, the solution satisfying G ′ (γ) = 0 is as follows (19),
As shown in the equation (20), there are two, γ1 and γ2.

[0069]

[Equation 11]

[0070]

(Equation 12)

Therefore, if the value of C is changed by a small amount, (1
9) and (20) are calculated to obtain γ1 and γ2, and further, the absolute values of G (γ1), G (γ2) and G (γmax) are obtained from the equation (17), which are repeatedly executed. At this time, γ 1, γ
If both 2 are larger than γ max, or γ 1, γ
If both 2 are negative or complex, | G
(γmax) | is the maximum value (| Gm corresponding to the value of C at that time
ax |). In this way, all values of | Gmax | calculated every time the value of C is changed are compared, and the value of C corresponding to the minimum | Gmax | is the solution to be obtained. Therefore, to satisfy the value of C, Ca, C
It suffices to determine b.

[0072]

As described above, according to the present invention, the distortion performance at the time of overlay exposure using a projection type exposure apparatus is improved, and even if masks having pattern regions of various sizes are used for projection exposure. Since the transfer can always be performed under the best distortion characteristics regardless of the size of the region, the productivity of the semiconductor device having the finer line width pattern can be remarkably improved.

Further, according to the present invention, the adjustment can be made so that the best distortion performance can be obtained within the pattern projection range used for exposure, so that it is always created from the beginning in consideration of matching between a plurality of exposure apparatuses. Also, there is no limitation that the exposure apparatuses are used together, and an effect that a plurality of apparatuses can be relatively freely combined on the semiconductor element manufacturing line can be obtained.

[Brief description of drawings]

FIG. 1 shows a mix and
The perspective view which shows the schematic structure of two projection type exposure apparatuses suitable for the method of a match.

FIG. 2 is a chart diagram exaggerating a deviation of projection points of ideal lattice points when two exposure apparatuses perform overlapping exposure without performing magnification correction.

FIG. 3 is a characteristic diagram showing distortion curves of projection lenses of two exposure apparatuses, respectively.

FIG. 4 is a characteristic diagram when the distortion curves in FIGS. 3A and 3B are superimposed.

FIG. 5 is a characteristic diagram when the characteristics shown in FIG. 4 are adjusted in magnification and overlapped.

FIG. 6 is a chart diagram exaggerating the deviation of projection points of ideal lattice points when overlay exposure is performed after adjusting the magnification.

FIG. 7 is a characteristic diagram showing a state of matching when the image height is changed with the characteristic shown in FIG.

FIG. 8 is a characteristic diagram showing a case where the magnifications of the two exposure apparatuses are adjusted to the best from the characteristics of FIG.

FIG. 9 is a characteristic diagram for explaining an improvement in matching accuracy in the case where the exposure apparatuses have the same projection visual field size.

[Explanation of symbols]

A ... First projection type exposure apparatus B ... Second projection type exposure apparatus E ... Wafer process R1, R2 ... Reticles PL1, PL2 ... Projection lens W ... Wafer BC1, BC2 ... Pressure regulator (Magnification adjustment unit) CNT1, CNT2 ... Main control device DS1, DS2, DS3 ... Distortion characteristics DS1 ', DS2', DS3 '... Distortion characteristics after magnification adjustment

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Koichi Matsumoto 1-6-3 Nishioi, Shinagawa-ku, Tokyo Nikon Oi Manufacturing Co., Ltd.

Claims (3)

[Claims] 1. A photolithography apparatus for transferring an image of a pattern area of a mask onto a substrate for photolithography through a circular visual field of a projection optical system, wherein the mask is irradiated in accordance with the pattern area on the mask. A blind having a movable blade for adjusting the illumination range of the illumination light; and at each of a plurality of image height points in the effective pattern projection area of the projection optical system corresponding to the illumination range adjusted by the blind. A photolithography apparatus comprising: a magnification adjusting unit that adjusts a projection magnification with respect to the substrate so that the amount of distortion is reduced on average. 2. A photolithography apparatus which transfers an image of a pattern area of a mask onto a substrate for photolithography through a circular visual field of a projection optical system, and irradiates the mask according to the size of the pattern area of the mask. A photolithography apparatus comprising: a blind provided with a movable blade for changing the illumination range of the illuminating light; and adjusting means for adjusting the imaging characteristic of the projection optical system according to the change of the blind. 3. A method of irradiating a pattern area of a mask with illumination light for exposure, and superimposing and exposing an image of the pattern area onto an exposed area on a substrate through a projection optical system. Pre-storing characteristic data defining the relationship between the image height position and the distortion amount of the projection optical system, which is obtained when the image forming characteristic is in the initial state; Adjusting the movable blade of the illumination field stop so as to limit the irradiation range of the illumination light; the projection optics based on the size of the irradiation range limited by the illumination field stop and the characteristic data stored in advance. Imaging characteristics of the projection optical system such that the amount of distortion generated at each point in the effective pattern projection area corresponding to the irradiation range in the projection field of the system becomes small on average. Exposure method characterized by including the step of adjusting the initial state.