JP2000047103A - Adjusting method of projection optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection optical system adjusting method capable of attaining comparatively high working efficiency and a comparatively high image forming performance. SOLUTION: As for the method for adjusting the projection optical system for forming a pattern image on an original plate onto photosensitive agent on a substrate, the method comprises a 1st process (a) for measuring the wave surface of radiation passing through the projection optical system, 2nd processes (d) to (f) for executing an image forming simulation in the projection optical system based on the measurement data on the wave surface and the adjustment quantity of the projection optical system so as to obtain an image forming evaluation quantity and then calculating the adjustment quantity required when the image forming evaluation quantity is put into the prescribed extent and a 3rd process (g) for adjusting the projection optical system based on the calculated adjustment quantity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for adjusting a projection optical system in a projection exposure apparatus used for manufacturing circuits such as semiconductors and liquid crystal displays.

[0002]

2. Description of the Related Art Conventionally, when adjusting the projection optical system of a projection exposure apparatus, the projection optical system is adjusted while actually forming a predetermined pattern under a predetermined exposure condition through the projection optical system. . That is, an image such as a resist image or an aerial image is observed through a projection optical system, a lens to be adjusted and an adjustment amount thereof are obtained from aberrations generated in the image, and adjustment is performed based on the lens. With reference to FIG. 10, a procedure for adjusting a conventional projection optical system will be described. First, an image such as a resist image or an aerial image via the projection optical system is measured (u in FIG. 10). Then, the aberration amount of the image is obtained (v). Next, based on the aberration amount, a lens to be adjusted (adjustment procedure) and an interval correction amount are calculated (w). Then, the lens is corrected based on the calculated value (g), and the resist image is measured (h). When the measured value satisfies a predetermined standard (i), the projection optical system is incorporated into an exposure apparatus as a finished product (j). On the other hand, when the measured value does not satisfy the standard (i), the aberration amount is obtained again from the measured value (h) (v). Thereafter, FIGS. 7A to 7I are repeated until the measured value of the resist image satisfies the standard and the projection optical system is a completed product. Here, the standard is determined by the accuracy required for an exposure apparatus in which the projection optical system is incorporated. Next, FIG.
The relationship between the image height of the projection optical system adjusted by the conventional adjustment method and various aberrations will be described below. The horizontal axis in the figure represents the image height, and the vertical axis represents the amount of aberration. The unit of the amount of aberration on the vertical axis is an arbitrary unit. Point A represents spherical aberration, line B represents coma, line C represents astigmatism, line D represents field curvature, and line E represents distortion. In addition to the aberrations, the line R in the figure shows the RMS of the wavefront for each image height.

[0003]

The above-mentioned conventional method of adjusting the projection optical system has a low working efficiency and does not have a very high imaging performance of the projection optical system. That is, the above-described adjustment method is an adjustment method that relies on the experience and intuition of the worker, and is a work that involves many trials and errors. Since the lens correction amount is determined after actually exposing through the projection optical system, much time is required for the adjustment process including the inspection. Further, even if apparent aberrations can be corrected under predetermined exposure conditions at the time of adjustment, large aberrations may actually remain in some cases.
That is, aberrations may occur under exposure conditions different from the exposure conditions at the time of adjustment. In addition, the above-described adjustment method is disadvantageous for driving in the aberrations, because the predetermined lens is only moved (interval correction) with respect to the aberration under the predetermined exposure condition. Therefore, an object of the present invention is to provide a method for adjusting a projection optical system having relatively high work efficiency and relatively high imaging performance of the projection optical system.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem. That is, when the reference numerals in FIG.
In a method of adjusting a projection optical system for forming an image of a pattern on an original onto a photosensitive agent on a substrate, a first step (a) of measuring a wavefront of radiation passing through the projection optical system, and measuring the wavefront Performs an imaging simulation of the projection optical system based on the data and the adjustment amount of the projection optical system to obtain an imaging evaluation amount, and calculates an adjustment amount when the imaging evaluation amount falls within a predetermined range. And a third step (g) of adjusting the projection optical system based on the calculated adjustment amount. At that time, the first step (a) and the second step (d to
Preferably, a step (c) of calculating an adjustment amount when the aberration of the wavefront is driven into a predetermined range is provided between the step (c) and the step (f).

[0005] With the above configuration, it is possible to provide a method of adjusting a projection optical system having relatively high work efficiency and relatively high imaging performance of the projection optical system. Hereinafter, a method for calculating the adjustment amount of the projection optical system will be described in detail. First, with respect to the measured wavefront W, to calculate the wavefront W ₀ simulated the corresponding (wavefront of the optical system data as computable numeric data). Therefore, the difference dW between the wavefronts W and W ₀ is dW = W−W ₀ (1). Then, in the subsequent calculations, every time the wavefront W _{0 in the} simulation is calculated, the difference dW of the equation (1) is added. Thus, simply by calculating the wavefront W _0, is obtained measurement wavefront W as follows. W = W ₀ + dW (2)

Further, when any change is made to the adjustment amount of the optical system, the simulated wavefront W ₀ ′ that changes by the change has the same change as that when the same change is made to the actual optical system. Joins W ₀ . Therefore, by simply adding the difference dW as in the equation (2), the wavefront W ′ that the real optical system will have can be calculated as in the following equation. W ′ = W ₀ ′ + dW = W ₀ ′ + (W−W ₀ ) (3) Here, in general, a wavefront used for calculation is a four-dimensional function based on XY coordinates and pupil coordinates.

[0007] Note that 'Another way of calculating the wavefront of the variation dW of the simulation of the formula _0, dW ₀ = W _0' wavefront W would actual optical system has -W ₀ (4) Is added to the wavefront W measured as follows. W ′ = W + dW ₀ = W + (W ₀ ′ −W ₀ ) (5) However, considering the efficiency of the calculation, the calculation of the expression (3) is more efficient than the expression (5). That is, in the calculation of the expression (3), the difference dW does not depend on the later deformation of the optical system data. Once the difference dW is obtained by the equation (1),
Subsequent processing is performed on the wavefront W ₀ ′ of the changed optical system data.
Only the difference dW is added. On the other hand, in the calculation of Expression (5), the wavefront change dW ₀ of the optical system data of Expression (4) depends on the deformation of the optical system data. Therefore, every time W ₀ ′ changes, d
W ₀ must be determined. Thus, it is efficient to use equation (3).

Next, automatic correction (run-in) by wavefront aberration is performed. The automatic correction of the wavefront aberration is to select various quantities that can be evaluated with the wavefront aberration as a target. For example, it is the RMS of the wavefront, or the optimal focus shift amount at which the RMS is minimized, or This is a coefficient for each component when the detailed wavefront undulation is decomposed into a function series such as a Zernike function. Of course, after the component decomposition, the wavefront may be divided into a rotationally symmetric component, an even symmetric component, and an odd symmetric component, and each RMS may be targeted.

By such automatic correction based on the wavefront aberration, the imaging performance of the projection optical system is almost satisfied. However, under the actual exposure condition of the projection optical system, the intensity distribution of the light source may not be uniform in the pupil, but may be distributed only near the center of the pupil, or the size of the distribution may vary depending on the exposure condition. . As a result, even if the wavefront is numerically improved as compared with the initial state, if it is not a sufficiently small value, the imaging performance may not be satisfied.
Therefore, fine adjustment of parameters is further performed by automatic correction using an imaging simulation.

[0010] The imaging simulation performed after the automatic correction by the wavefront aberration is performed by HH Hopkins.
Coherent Imaging Theory (Proc. Roy. Soc., A, 20
8 (1951), 263). The image forming simulations are roughly classified into two types: an aerial image simulation in which the calculation processing is fast, and a resist simulation in which the processing speed is slow but the photolithography is better reproduced. A latent image simulation is intermediate between the two. Any of these can faithfully simulate the above-described exposure conditions of the projection optical system. Automatic correction using such an imaging simulation is performed to further drive the aberration of the optical system. And
Finally, a specific adjustment amount for the actual optical system is calculated. The adjustment amount is an amount such as the shape (curvature, aspherical shape, and the like), interval, eccentricity, inclination, and the like of the optical member constituting the projection optical system.

Examples of a method used for automatic correction of the imaging simulation include a local optimization method represented by the DLS method and a global optimization method represented by the GA method (genetic algorithm) and simulated annealing. Is raised. In the case of the local optimization method, generally, various aberrations of the optical system are targeted. Then, using a physical quantity related to the imaging performance of the optical system as a parameter, such as a curvature, a surface interval, or a glass refractive index, a change rate of the target by the parameter is calculated. Then, the amount of parameter correction that minimizes the aberration of the optical system at the time when the rate of change is calculated is sequentially and approximately determined. The details of this method are described, for example, in the document “Lens Design” (written by Tomotaka Takahashi, published by Tokai University).

Next, a description will be given of a target of automatic correction using an imaging simulation. The target of the automatic correction using the imaging simulation is the imaging evaluation amount itself. For example, it is an imaging evaluation amount corresponding to the following five Seidel aberrations. A. Spherical aberration: the difference between the best focuses of two or more types of image patterns having different periods on the same point. B. Coma: the ratio of the line width difference between the left and right ends of the five isolated lines. C. Astigmatism: the difference between the best focuses of line and space patterns in two different directions on the same point. D. Field curvature: the difference in the best focus of the image pattern between the center point of the exposure field and the periphery. E. FIG. Distortion: The relative displacement of an image forming pattern with the origin at the center of the exposure field.

It should be noted that there are various evaluation quantities other than the Seidel aberration described above, and these can be set as targets. For these evaluation amounts, the rate of change with respect to the parameter is calculated, and automatic correction is performed by the local optimization method, as in the case of the wavefront aberration described above. At this time,
In order not to deteriorate the wavefront, it is more effective to set the RMS or the like of the wavefront as a target.

[0014]

Embodiments of the present invention will be described with reference to the drawings. A first embodiment of a method for adjusting a projection optical system according to the present invention will be described with reference to FIGS. FIG. 1 is a flowchart showing a method for adjusting a projection optical system according to a first embodiment of the present invention. First, the wavefront aberration of the projection optical system is measured by a Fizeau interferometer or the like (FIG. 1A). Based on the wavefront measurement data at that time (b), aberration correction is performed (c). Here, the drive-in refers to an operation of optimizing the aberration of the projection optical system by a computer. Further, in FIG. 3B, the difference dW between the wavefront of the optical system data and the measured wavefront is obtained.

Next, an image formation evaluation of the projection optical system is performed by an image formation simulation, and aberration is driven in based on the image formation evaluation (d). Then, it is determined whether the wavefront aberration and the aberration obtained by the imaging simulation have sufficient values (e). If the aberration falls within a predetermined range, the correction amount of the distance between the constituent lenses of the projection optical system is calculated (f). If the aberration does not fall within the predetermined range, the wavefront aberration and the imaging simulation are performed until the aberration falls within the predetermined range (c to e).

Next, the lens is corrected based on the distance correction amount calculated in c to f in FIG. 1 (g), and the resist image is measured (h). When the measured value satisfies a predetermined standard (i), the projection optical system is incorporated into an exposure apparatus as a finished product (j). On the other hand, when the measured value does not satisfy the standard (i), the wavefront aberration is measured again (a). Thereafter, a to i in the same drawing are repeated until the measured value of the resist image satisfies the standard and the projection optical system is a completed product. Through these steps,
Finally, a projection exposure apparatus is manufactured. In FIG. 1,
Although the correction parameter of the projection optical system is only the correction amount of the distance between the lenses, for example, the rotation amount or the eccentric amount of the lens may be selected as the parameter.

Next, FIG. 2 shows the aberration of the projection optical system after being adjusted by the adjustment method of FIG. As in FIG. 11 described above, the horizontal axis of FIG. 2 represents the image height, and the vertical axis represents the amount of aberration. The scale of each aberration on the vertical axis in FIGS. 2 and 11 is the same. Point A represents spherical aberration, line B represents coma, line C represents astigmatism, line D represents field curvature, and line E represents distortion. In addition to the aberrations, the line R in the figure shows the RMS of the wavefront for each image height.
Here, various aberrations (A to E) and RMS (R) of the projection optical system adjusted by the adjustment method in the first embodiment shown in FIG. 2 and various aberrations and RMS in the prior art shown in FIG. Compare. The RMS is significantly improved in the first embodiment. Also, with respect to various aberrations, the first embodiment has a more uniform overall balance than the conventional technology.

Further, in addition to the above-mentioned effects on various aberrations and RMS, the working efficiency of the first embodiment is greatly improved as compared with the prior art. For example, the number of loops in the flowchart shown in FIG. 1 is less than half the number of loops in the flowchart in FIG. Here, evaluation and run-in by the imaging simulation shown in the flowchart of FIG.
FIG. 3 shows an aberration diagram when the projection optical system is adjusted without performing evaluation and focusing by image forming simulation in order to confirm the effect d). When FIG. 3 is compared with FIG. 11, the RMS is improved as a whole as compared with FIG. However, as for various aberrations, the coma aberration B in FIG. 3 is deteriorated on the low image height side, and the field curvature D is also deteriorated on the high image height side. The astigmatism C in FIG. 11 has a bad result on the high image height side. Thus, it is not clear which of the various aberrations in FIG. 3 and FIG. 11 is superior. Therefore, in the flowchart of FIG. 1, it can be seen that the fine adjustment by the imaging simulation has a great effect on the improvement of various aberrations.

As described above, in the first embodiment, the adjustment amount is calculated by using the automatic optimization method based on the measured wavefront aberration of the projection optical system, and the projection optical system is adjusted accordingly. I have. At this time, optimization targeting only the wavefront aberration is performed first, and thereafter, an imaging evaluation amount is calculated by applying an imaging simulation, and the aberration is again balanced using the target as the target. As described above, in the first embodiment, since the optimum adjustment amount of the projection optical system can be calculated based on the wavefront measured first, the adjustment operation of the projection optical system is greatly improved.

Next, a second embodiment of the method of adjusting the projection optical system according to the present invention will be described with reference to FIGS. FIG. 4 is a flowchart showing a method for adjusting a projection optical system according to a second embodiment of the present invention. In the second embodiment, in addition to the correction of the distance between the lenses constituting the projection optical system performed in the first embodiment, aspheric polishing is an adjustment item. First, the first
As in the embodiment, the wavefront aberration of the projection optical system is measured (FIG. 4A). Based on the wavefront measurement data at that time (b), aberration correction is performed (c).

Next, an image formation evaluation of the projection optical system is performed by an image formation simulation, and aberrations are driven in based on the image formation evaluation (d). Then, it is determined whether the wavefront aberration and the aberration obtained by the imaging simulation have sufficient values (e). When the aberration is within a predetermined range, the distance correction amount and the aspherical polishing amount of the constituent lenses of the projection optical system are calculated (f). However, the aspheric polishing amount at this time is zero. On the other hand, if the aberration does not fall within the predetermined range, it is determined whether or not to perform aspherical polishing (k in the above). When performing aspherical surface polishing, aspherical surface polishing is selected (the same m), and the aspherical surface polishing amount is added to the parameter (the same n). Then, the steps c to e in the same drawing are repeated again. When the aspherical surface polishing is not performed, the steps c to e in FIG.

These steps are repeated until the aberration falls within the predetermined range. When the aberration falls within the predetermined range, based on the interval correction amount and the aspherical polishing amount calculated by the computer, The lens is corrected (g), and the resist image is measured (h). When the measured value satisfies a predetermined standard (i), the projection optical system is incorporated into an exposure apparatus as a finished product (j). On the other hand, when the measured value does not satisfy the standard (i),
The wavefront aberration is measured again (a). Thereafter, a to i in the same drawing are repeated until the measured value of the resist image satisfies the standard and the projection optical system is a completed product. In the second embodiment, the aspherical surface optimization using the aspherical surface polishing as a parameter
To n) are performed after image formation evaluation and drive-in by image formation simulation are performed, but actual wavefront measurement (a) is performed.
It may be performed at any later stage.

Next, FIG. 5 shows the aberration of the projection optical system after being adjusted by the adjustment method shown in FIG. It can be seen that both the various aberrations and the RMS are significantly improved as compared with FIG. 2 of the first embodiment. That is, by using the aspherical polishing amount as a parameter in addition to the interval correction amount, the imaging performance is remarkably improved. As described above, also in the second embodiment, the optimum adjustment amount of the projection optical system can be calculated based on the wavefront measured first, as in the first embodiment.
The adjustment work of the projection optical system is made much more efficient.

Next, a third embodiment of the method for adjusting the projection optical system according to the present invention will be described with reference to FIGS. FIG.
9 is a flowchart illustrating a method for adjusting a projection optical system according to a third embodiment of the present invention. In the second embodiment, the lens needs to be polished again. In the third embodiment, the imaging performance is improved without performing the lens repolishing. The imaging performance of the projection optical system changes when minute deformation on the order of wavelength occurs. The deflection of the lens that occurs when assembling the optical system, the polishing error of the lens that occurs two-dimensionally, and the optical non-uniformity inside the lens cause a large asymmetry error in the imaging of the optical system. Becomes However, if such error data is measured using an interferometer, and the error data is added to numerically calculable optical system data and then corrected based on the measured wavefront, an asymmetric image can be formed to some extent. Can be avoided.

More specifically, first, the wavefront aberration of the projection optical system is measured as in the first embodiment (FIG. 6A).
In addition to the wavefront measurement data at this time (b), error data measured by the interferometer is input to the computer (p). Here, the error data is data such as the surface deformation of the lens of the projection optical system and the error aspherical surface. Next, based on the wavefront measurement data and the error data, the interval due to the wavefront aberration, the rotation of the lens, and the eccentricity are adjusted (q). Further, an image formation evaluation is performed by an image formation simulation, and based on the image formation evaluation, the distance, the rotation of the lens, and the eccentricity are adjusted (r). Then, the optimum distance correction amount, rotation amount, and eccentric amount of the projection optical system are calculated (s).

Then, the interval correction amount calculated by the computer,
The lens is corrected based on the rotation amount and the eccentric amount (g),
The resist image is measured (h). When the measured value satisfies a predetermined standard (i), the projection optical system is incorporated into an exposure apparatus as a finished product (j). On the other hand, when the measured value does not satisfy the standard (i), the wavefront aberration is measured again (a). Thereafter, a to i in the same drawing are repeated until the measured value of the resist image satisfies the standard and the projection optical system is a completed product.

Next, the effects of the third embodiment will be described with reference to FIGS. FIG. 7 shows the distribution of aberration in each direction of the projection optical system after being adjusted by the adjustment method of FIG. FIG. 8 shows the distribution of aberration in each direction of the projection optical system before being adjusted by the adjustment method of FIG. The numbers (0 to 330) attached to the radial lines in FIGS. 7 and 8 represent angles (°) and correspond to the azimuths in the projection optical system. The dotted line P is a virtual line when the projection optical system has no aberration. Lines J to N
Represents the percentage (%) of the image height, and the line J is 2
0%, line K represents 40%, line L represents 60%, line M represents 80%, and line N represents 100% image height. When the two figures are compared, it is clear that FIG. 7 has better symmetry in the rotation direction than FIG. Thus, in the third embodiment, a projection optical system having good rotational symmetry can be adjusted efficiently.

In the third embodiment, as in the first and second embodiments, the optimum adjustment amount of the projection optical system can be calculated based on the first measured wavefront. The adjustment work is made much more efficient. In addition, even when the aspherical surface processing is introduced as in the second embodiment described above, the asymmetric component can be suppressed as in the third embodiment. However, in that case, a rotationally asymmetric aspherical surface processing must be performed. Even in such a case, according to the present invention, it is possible to simulate or may be subjected in advance what the aspherical surface processing, reliably, processed efficiently projection optical system can be adjusted.

Next, FIG. 9 shows an embodiment of a projection exposure apparatus equipped with a projection optical system adjusted by the adjustment method shown in the above embodiment. A light beam emitted from a KrF excimer laser light source 1 having a band-narrowing element passes through an illumination optical system 2,
The pattern surface Pa of the reticle P placed on the reticle stage 3 is uniformly illuminated. Exposure light emitted from the pattern surface Pa of the reticle P passes through the projection optical system 4 to the photosensitive surface Wa of the wafer W placed on the wafer stage 5,
An image of the pattern surface Pa is formed. The projection optical system 4 is adjusted by the adjustment method described in the above embodiment. Therefore, a projection exposure apparatus having extremely high imaging performance can be provided.

[0030]

As described above, according to the present invention, the optimum adjustment amount of the projection optical system is calculated, and a method of adjusting the projection optical system having high imaging performance can be provided. Further, since the working efficiency is extremely high, a relatively inexpensive method for adjusting the projection optical system can be provided.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for adjusting a projection optical system according to a first embodiment of the present invention.

FIG. 2 is an aberration diagram of the projection optical system after being adjusted by the adjustment method according to the first embodiment of the present invention.

FIG. 3 is an aberration diagram of the projection optical system when the adjustment is performed by the adjustment method according to the first embodiment of the present invention without performing a run-in by an imaging simulation.

FIG. 4 is a flowchart illustrating a method of adjusting a projection optical system according to a second embodiment of the present invention.

FIG. 5 is an aberration diagram of the projection optical system after being adjusted by the adjustment method according to the second embodiment of the present invention.

FIG. 6 is a flowchart illustrating a method for adjusting a projection optical system according to a third embodiment of the present invention.

FIG. 7 is a radar diagram of the amount of aberration in each direction of the projection optical system after being adjusted by the adjustment method according to the third embodiment of the present invention.

FIG. 8 is a radar diagram of the amount of aberration in each direction of the projection optical system before adjustment by the adjustment method according to the third embodiment of the present invention.

FIG. 9 is a schematic view showing a projection exposure apparatus according to one embodiment of the present invention.

FIG. 10 is a flowchart showing a conventional method of adjusting a projection optical system.

FIG. 11 is an aberration diagram of a projection optical system after being adjusted by a conventional adjustment method.

[Explanation of symbols]

 A: spherical aberration B: coma aberration C: astigmatism D: field curvature E: distortion R: RMS 1: light source 2: illumination optical system 3: reticle stage 4: projection optical system 5: wafer stage P: reticle Pa ... Pattern surface W ... Wafer Wa ... Photosensitive surface

Claims (8)

[Claims] 1. A method for adjusting a projection optical system for forming an image of a pattern on an original on a photosensitive agent on a substrate, comprising: a first step of measuring a wavefront of radiation passing through the projection optical system; Based on the measurement data of the wavefront and the adjustment amount of the projection optical system, an imaging simulation is performed on the projection optical system to obtain an imaging evaluation amount, and the imaging evaluation amount is driven into a predetermined range. And a third step of adjusting the projection optical system based on the calculated adjustment amount. 2. The method according to claim 1, further comprising the step of calculating the adjustment amount when the aberration of the wavefront falls within a predetermined range between the first step and the second step. The method for adjusting a projection optical system according to claim 1. 3. A measurement wavefront by the first step and is W, the wave front by imaging simulation simulating the measurement wavefront W and W _0, the wave front by imaging simulation after adjusting the adjustment amount and W ₀ ' _{when, W '= W 0' +} (W-W 0) by a method of adjusting a projection optical system according to claim 1 or 2, wherein the predicting the measurement wavefront W 'after adjusting the adjustment amount . 4. The method according to claim 1, wherein the imaging simulation calculates an aerial image of the pattern. 5. The method according to claim 1, wherein the image forming simulation calculates a latent image or a resist image formed on the photosensitive agent. 6. The imaging evaluation amount includes spherical aberration, coma aberration,
The method for adjusting a projection optical system according to any one of claims 1 to 5, wherein the method includes at least one of astigmatism, field curvature, and distortion. 7. The projection optical system adjusting method according to claim 1, wherein the calculation method used in the run-in by the imaging simulation is a local optimization method. 8. The method of adjusting a projection optical system according to claim 1, wherein the calculation method used in the run-in by the imaging simulation is a global optimization method.