JP2004071780A - Method for fabricating projection optical system and aligner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for fabricating a projection optical system capable of adjusting the lens aberration to the optimums by using projection lens image performance prediction considering the changes in image characteristics caused by deviation in the band-pass filter central wavelength, and to provide an aligner using the method. <P>SOLUTION: In an aligner having this projection optical system, a circuit pattern is projected onto a photosensitive substrate by an illuminating optical system that illuminates the circuit pattern with light from a light source having a plurality of emission spectra. The illuminating optical system has a band-pass filter that transmits only one bright line spectrum out of the emission spectra of the light source, and is capable of adjusting the aberration in the projection optical system in correspondence to the central wavelength of the band-pass filter. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exposure apparatus for manufacturing a semiconductor and a liquid crystal using a bright line having a bandwidth as exposure light and using a bandpass filter for narrowing the band of the exposure light.
[0002]
[Prior art]
The projection lens of a conventional exposure apparatus uses a wavefront aberration measuring device to measure the wavefront aberration of the lens, and in an experimental apparatus equipped with a projection lens, reduces or equalizes the circuit pattern and prints it on a photosensitive substrate, and transfers the image of the transferred pattern. The imaging performance is evaluated by SEM (hereinafter, this method is referred to as "image performance printing") to grasp the performance of the projection lens and adjust the distance, eccentricity, rotation, etc. of the lens based on the information. Thus, a projection lens was manufactured.
[0003]
However, this method takes a lot of time, and it is difficult to grasp the original performance of the projection lens because it may include a reticle error or a process error in image performance printing. The production of the projection lens using this method is the best method. I couldn't say.
[0004]
In addition, when a bright line used as exposure light has a spectral intensity distribution having a certain width, in order to use this bright line as illumination light, the spectral intensity distribution is narrowed, and an extra amount of light that is considered to deteriorate image performance is made. It is necessary to cut the spectrum through a band pass filter.
[0005]
However, there is a difference in image performance between the case where the center line wavelength is used as a bright line spectrum passing through a band-pass filter different from the desired value and the case where the center line wavelength uses a bright line spectrum passing through a band-pass filter having an ideal center wavelength as illumination light. There is an adverse effect such as that
[0006]
This is because the projection lens is designed and adjusted as an exposure wavelength using a spectrum passed through a band-pass filter (ideal band-pass filter) whose center wavelength does not deviate from the i-line reference wavelength. In the production of the lens, the influence on the image performance due to the wavelength shift at the center of the bandpass filter could be considered only in the image performance printing.
[0007]
[Problems to be solved by the invention]
In the prior art, the only way to consider the effect on the image performance due to the wavelength shift at the center of the bandpass filter is to burn the image performance. However, it takes a long time. However, there is a problem that it is difficult to accurately grasp the performance of the projection lens because it includes a reticle error, a process error, and the like.
[0008]
Therefore, if an attempt is made to adjust the lens using only the wavefront aberration data without performing image performance printing, the band-pass filter may be incorrect because the filter center wavelength may differ from the desired reference wavelength in the exposure light as a manufacturing error. It has been difficult to predict and predict the lens performance and manufacture and adjust the projection lens.
[0009]
Therefore, the present invention provides a method of manufacturing a projection optical system that adjusts the lens aberration to an optimal state by predicting the image performance of a new projection lens, taking into account the image performance change caused by the center wavelength shift of the bandpass filter, and It is an exemplary object to provide an exposure apparatus using such a method.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, a method for manufacturing a projection optical system according to one aspect of the present invention includes: a light source having a plurality of emission spectra; an illumination optical system for illuminating a circuit pattern with light from the light source; An exposure apparatus having a projection optical system for projecting a pattern on a photosensitive substrate, wherein the illumination optical system has a band-pass filter that transmits only one emission line spectrum from the emission spectrum of the light source; Wherein the state of aberration of the projection optical system is changed according to the center wavelength. The aberration change amount of the projection optical system with respect to the center wavelength of the band filter is calculated in advance, and the aberration of the projection optical system measured by a wavefront aberration measuring device and the aberration change amount of the projection optical system based on the aberration change amount. The state of aberration is determined. With respect to the center wavelength of the bandpass filter, the aberration change amount of the projection optical system is calculated in advance from an exposure experiment, and the aberration of the projection optical system measured by a wavefront aberration measuring device, based on the aberration change amount, An aberration state of the projection optical system is determined.
[0011]
An exposure apparatus according to another aspect of the present invention includes a projection optical system manufactured by the above-described manufacturing method.
[0012]
Other objects and other features of the present invention will be made apparent by preferred embodiments described below with reference to the accompanying drawings.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, with reference to the accompanying drawings, a description will be given of a method of accurately predicting the image performance of a projection lens by considering the center wavelength of a bandpass filter in the present invention, and a method of producing a lens for adjusting a lens aberration to an optimum state.
[0014]
When the projection lens is manufactured, in advance, the half-value center wavelength of the emission line spectrum due to the band-pass filter shift is ideally determined by a simulation or an experiment in consideration of a shift of the center wavelength of the band-pass filter from a desired center reference wavelength in the exposure light. The wavefront aberration change amount (wavefront aberration sensitivity) at the time of shifting from a proper value is calculated.
[0015]
The band-pass filter used here measures the deviation from the center wavelength of the ideal filter, and determines the band-pass filter's sensitivity from the wavefront aberration sensitivity determined in advance according to the amount of the deviation. The change amount of the wavefront aberration due to the center wavelength shift can be obtained. The amount of aberration obtained by adding this value and the wavefront aberration data of the lens itself measured by the wavefront aberration measuring device becomes the total aberration amount when the main body is mounted, and becomes the target value when adjusting the projection lens.
[0016]
With this method, it is possible to know a target value when adjusting the projection lens without performing image performance printing, and to obtain a desired image performance when mounted on the main body without generating a problem associated with image performance printing. There is an advantage that becomes possible. Further, it is possible to simultaneously perform image performance printing as in the related art.
[0017]
Here, the band filter used to measure the shift amount of the center wavelength used in the simulation or the experiment and the projection lens adjusted according to the filter are used as a pair when mounted on the main body.
[0018]
When replacing the bandpass filter mounted on the projection exposure apparatus, a bandpass filter having a center wavelength having the same performance as when mounted on the main body is selected and used according to the adjustment state of the projection optical system.
[0019]
In the present embodiment, an example in which a mercury lamp is used as a light source having a bandwidth will be described in detail. However, needless to say, the present invention is not limited by the embodiments described below.
[0020]
A method of calculating the sensitivity to wavefront aberration and a method of ascertaining the performance of the projection lens when the center wavelength of the bandpass filter is different from the center wavelength of the mercury lamp will be described below. The image performance depends on various factors, but also on the half-value center wavelength of the illumination light used for exposure. Since the center wavelength at half maximum of the light passing through the bandpass filter is determined by the center wavelength of the bandpass filter and the transmittance distribution, the shift amount of the center wavelength at half maximum from the center wavelength of the mercury lamp can be obtained relatively easily.
[0021]
First, an example of a method of calculating wavefront aberration sensitivity, a method of grasping lens performance, and a method of adjusting a lens using simulation will be described.
[0022]
The difference between the wavefront aberration in the bandpass filter having the center wavelength of the i-line reference wavelength and the wavefront aberration in the exposure light by the bandpass filter in which the center wavelength of the bandpass filter deviates from the reference value (wavelength) is calculated by simulation. , The sensitivity of the wavefront aberration to the half value center wavelength shift amount is obtained (step 1002).
[0023]
Wavefront aberration data of the projection lens is obtained by measuring the wavefront aberration (step 1004).
[0024]
Under the condition (mode) in which the exposure apparatus is used, the center wavelength shift amount of the band-pass filter mounted on the main body is measured and multiplied by the wavefront aberration sensitivity with respect to the half-value center wavelength change amount obtained in step 1002 to obtain the filter center wavelength. The amount of aberration due to the shift is obtained (step 1006).
[0025]
Here, a method of optimizing aberration by adjusting a lens will be described by taking the field curvature as an example. FIG. 1 is a graph showing an adjustment amount of a projection lens taking field curvature as an example. Here, the reference value is a band-pass filter (ideal filter) whose center wavelength does not deviate from the i-line reference wavelength, and the field curvature at this time is measured by a wavefront aberration measuring device at the length determined in step 1004. Only the aberration amount is obtained, and the lens may be adjusted so as to correct the aberration amount (see FIG. 1A). However, when a bandpass filter having a shifted center wavelength is used, an aberration amount due to the filter center wavelength shift in step 1006 occurs in addition to step 1004, and the adjustment amount of the lens changes. (See FIG. 1B). A projection lens can be manufactured by performing such adjustment for various aberrations by using conditions (mode) using an exposure apparatus, a reticle, and a device pattern (step 1008).
[0026]
Next, an example of a method of grasping the performance of the projection lens and a method of adjusting the lens by experiments, which is another method, which requires much time and may include various errors as compared with the method by simulation, will be described.
[0027]
The center wavelength of the band-pass filter is shifted by about several nm before and after the reference wavelength of the i-line in advance, and the performance under the use condition of the exposure apparatus is measured by an experiment to check the image performance sensitivity to the filter shift amount (step 2002).
[0028]
The parameters that determine the conditions at this time include each illumination mode (NA, σ), reticle (binary, halftone, Levenson), and device pattern, and the performance under each condition is the focus by image height. The difference, left and right line width difference, distortion, CD change amount, etc. are measured and evaluated.
[0029]
The center wavelength shift amount of the band pass filter to be used from the i-line reference wavelength is measured (step 2004).
[0030]
From the above, the amount of change in image performance per shift amount of the center wavelength of the band-pass filter under the use condition is obtained, and the wavefront aberration data measured by the wavefront aberration measuring device is added to this to obtain the shift amount of the bandpass filter center. The corresponding accurate projection lens performance can be calculated, and the projection lens can be manufactured in the same manner as in the lens adjustment method described above (step 2006).
[0031]
Hereinafter, an example of an exposure apparatus using the projection lens manufactured by the above method will be described. FIG. 2 is a schematic cross-sectional view illustrating an exemplary embodiment of the exposure apparatus 100 according to one aspect of the present invention. The exposure apparatus 100 is an exposure apparatus that exposes device patterns on a plurality of regions on the wafer 10 by a step-and-repeat method or a step-and-scan method.
[0032]
In FIG. 2, reference numeral 1 denotes a light source, which extracts a light beam in a range of 300 nm to 400 nm from a light beam of a mercury lamp having a spectral output characteristic as shown in FIG. In step 3, a light beam having a width of several nm near the i-line is extracted. Here, FIG. 3 is a graph showing the spectral output of the mercury lamp as the light source 1 shown in FIG.
[0033]
However, when the center of the narrow band i-line filter used is shifted from the reference wavelength of the i-line as shown in FIG. 4A, the i-line is used as shown in FIG. Is shifted from the desired value. As described above, the fact that the center wavelength of the band-pass filter used for the i-line is shifted from the i-line reference wavelength leads to a phenomenon that the half-value center wavelength shifts as shown in FIG. On the surface to be exposed (such as a wafer) in the exposure apparatus showing the exposure procedure, a difference occurs in the image performance as compared with the case where the half-value center wavelength of the band-pass filter used for i-line is the i-line reference wavelength. Here, FIG. 4A is a graph showing the cut characteristics of the filter when the center of the band-pass filter in the exposure apparatus shifts, and FIG. 4B shows the graph when the center of the band-pass filter in the exposure apparatus shifts. 3 is a graph showing an i-line spectrum of the above.
[0034]
Therefore, what is needed here is to calculate in advance by simulation or experiment the amount of change in image performance due to the amount by which the spectral half-value center wavelength of the band-pass filter shifts from the i-line reference wavelength, so that the band mounted on the main body can be calculated. By adding the change amount of image performance according to the shift amount of the center wavelength of the pass filter to the wavefront aberration data, the projection lens can be formed by adjusting the interval, eccentricity, rotation, aspherical processing, and the like.
[0035]
With this, when the projection lens is mounted on the main body of the exposure apparatus 100, if the band-pass filter used at the time of manufacturing the lens is used, even when the spectral half-value center wavelength of the exposure light is different from the i-line reference wavelength, It is possible to obtain a result with the same accuracy as the image performance obtained with ideal exposure light.
[0036]
In the main body of the exposure apparatus 100, the i-ray spectrum that has passed through the i-line filter 3, which is a band-pass filter, is once collected by a lens (not shown), enters the in-plane reflecting member 4, and is formed on the light exit surface of the inner reflecting member 4. The light beam having the uniform light intensity distribution is projected onto the light incident surface of the fly-eye lens 5 by a lens system (not shown). Then, the converging point group formed on the light exit surface of the fly-eye lens 5 is used as a secondary light source to uniformly illuminate the illumination area, and a uniform light intensity distribution at the position of the stop 6 is relayed. The system projects the size and shape of the reticle 7 to illuminate the reticle 7. The pattern on the reticle 7 is imaged by a projection optical system 8 on a substrate 10 coated with a resist such as a semiconductor wafer.
[0037]
Although the projection optical system 8 is a known one, it is assumed here that a projection lens manufactured in consideration of the center wavelength of the bandpass filter is mounted. The band-pass filter mounted on the exposure apparatus 100 is used when adjusting the projection lens.
[0038]
The projection optical system 8 includes a system basically including a refraction system, a system including a lens and a concave mirror, and a catadioptric system including a lens and a concave mirror. The position of the reticle 7 and the position of the substrate 10 are adjusted in the optical axis direction. , Both the reticle 7 side and the substrate 10 side where the projection magnification does not change are telecentric systems.
[0039]
Further, the projection optical system 8 is provided with an aperture stop 9 having a variable aperture diameter, and by adjusting the aperture diameter of the aperture stop 9 to adjust the numerical aperture (NA), the brightness, resolution, and depth of focus are improved. Control.
[0040]
In the present invention, since the projection optical system 8 is configured by the projection lens adjusted in consideration of the center wavelength of the band-pass filter, the center wavelength shift of the i-line spectrum has changed due to the center wavelength shift of the band-pass filter. Even in this case, a result is obtained in which there is no difference in image performance from the case where a bandpass filter having an ideal i-line center wavelength is used in image formation performance.
[0041]
Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the gist.
[0042]
【The invention's effect】
According to the present invention, the aberration of the lens can be adjusted to an optimum state by calculating the amount of change in image performance in consideration of the influence on the image performance due to the difference in the center wavelength of the bandpass filter by simulation or experiment. It becomes. In addition, it is possible to grasp the performance of the projection lens without performing image performance printing which is time-consuming and may include various errors. Therefore, it is possible to greatly reduce the manufacturing time and to manufacture a projection lens with a minimum error.
[Brief description of the drawings]
FIG. 1 is a graph showing an adjustment amount of a projection lens taking field curvature as an example.
FIG. 2 is a schematic cross-sectional view illustrating an exemplary embodiment of an exposure apparatus according to one aspect of the present invention.
FIG. 3 is a graph showing a spectral output of a mercury lamp as a light source shown in FIG.
FIG. 4A is a graph showing a filter cut characteristic when the center of the band-pass filter in the exposure apparatus shifts, and FIG. 4B is a graph when the center of the band-pass filter in the exposure apparatus shifts. It is a graph which shows an i-line spectrum.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 light source 2 elliptical mirror 3 i-line filter 4 internal reflection member 5 fly-eye lens 6 stop 7 reticle 8 projection optical system 9 aperture stop 10 substrate 100 exposure apparatus

Claims (4)

A light source having a plurality of emission spectra, an illumination optical system that illuminates a circuit pattern with light from the light source, and an exposure apparatus that includes a projection optical system that projects the circuit pattern onto a photosensitive substrate.
The illumination optical system has a bandpass filter that transmits only one emission line spectrum from the emission spectrum of the light source,
A method of manufacturing a projection optical system, comprising changing an aberration state of the projection optical system according to a center wavelength of the bandpass filter. With respect to the center wavelength of the band filter, the amount of change in aberration of the projection optical system is calculated in advance, and the aberration of the projection optical system measured by a wavefront aberration measuring device, and the amount of change in aberration of the projection optical system is determined based on the amount of change in aberration. 2. The method of manufacturing a projection optical system according to claim 1, wherein an aberration state is determined. With respect to the center wavelength of the band-pass filter, the aberration change amount of the projection optical system is calculated in advance from an exposure experiment, and the aberration of the projection optical system measured by a wavefront aberration measuring device, based on the aberration change amount, 2. The method according to claim 1, wherein an aberration state of the projection optical system is determined. An exposure apparatus equipped with a projection optical system manufactured by the manufacturing method according to claim 1.

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