JP2006261405A - Manufacturing method of projective optical system for euv exposure apparatus, and euv exposure apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a projective optical system for an EUV exposure apparatus which has a desired optical performance. <P>SOLUTION: The manufacturing method of the projective optical system for an EUV exposure apparatus has processes of: manufacturing a plurality of non-spherical-surface mirrors for constituting the projective optical system to assemble the optical system, by integrating the manufactured non-spherical-surface mirrors into it on the basis of designing values: evaluating the optical performance of the assembled optical system; determining, the shape correcting quantities of the mirrors (replaced mirrors) to be replaced on the basis of the evaluated optical performance with new non-spherical-surface mirrors which are included in the originally assembled non-spherical-surface mirrors that the optical performance falls in a toleranc; manufacturing the new non-spherical-surface mirrors (replacement mirrors) on the basis of the determined shape correcting quantities and the shapes of the replaced mirrors; replacing the replaced mirrors with the manufactured replacement mirrors; and manufacturing the projective optical system by using the unreplaced and left non-spherical-surface mirrors and the replaced-off non-spherical-surface mirrors. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a projection optical system mounted on an EUV exposure apparatus (also referred to as an extreme ultraviolet exposure apparatus, and in the present specification and claims, refers to an exposure apparatus using ultraviolet light having a wavelength of 50 nm or less). The present invention relates to a manufacturing apparatus and an EUV exposure apparatus having a projection optical system manufactured by this method.

  In recent years, with the miniaturization of semiconductor integrated circuits, EUV light having a shorter wavelength (11 to 14 nm) is used in place of conventional ultraviolet rays in order to improve the resolving power of the optical system limited by the diffraction limit of light. Projection lithography techniques have been developed (see, for example, D. Tichenor, et al, SPIE 2437 (1995) 292). This technique is recently called EUV (Extreme UltraViolet) lithography, and is expected as a technique that can obtain a resolution that cannot be achieved by conventional optical lithography using light having a wavelength of about 190 nm.

  In a wavelength region of EUV light, a transmission / refraction type optical element such as a conventional lens cannot be used, and an optical system utilizing reflection is used.

  An outline of the EUV exposure apparatus is shown in FIG. The EUV light 32 emitted from the EUV light source 31 enters the illumination optical system 33 to form a substantial surface light source. The light from the substantial surface light source is deflected by the plane mirror 36 and then forms an elongated arc-shaped illumination area on the mask M. The light from the pattern of the illuminated mask M forms an image of the mask pattern on the wafer W through the projection optical system PL composed of a plurality of mirrors (six mirrors M1 to M6 in FIG. 3 exemplarily). .

  In order to form a desired pattern on the wafer, it is preferable to sufficiently reduce the aberration of the projection optical system. In particular, the wavefront aberration (rms value) of the projection optical system is reduced to 1/30 or less of the wavelength, and the pattern distortion is reduced. If the line width is kept at 1/10 or less, a fine pattern with high contrast can be formed. For example, when the exposure wavelength is 13.5 nm and the NA of the projection optical system is 0.25, if the wavefront aberration is 0.5 nm (rms) or less and the pattern distortion is 5 nm or less, a good resist having a size of about 45 nm is obtained. A pattern can be formed.

  In order to manufacture a projection optical system having such a minute wavefront aberration and pattern distortion, it is necessary to manufacture an aspherical mirror having a reflection surface shape with extremely high accuracy. For example, in order to manufacture the projection optical system, the shape accuracy of the mirror must be 0.1 nm (rms) or less. However, it is very difficult to manufacture such a mirror even if the current high-precision mirror manufacturing technology is used.

  A manufacturing process of a conventional projection optical system is shown in FIG. First, an aspherical mirror substrate constituting the projection optical system is manufactured. As the substrate material, it is preferable to use low thermal expansion glass with small thermal deformation. The polishing process and the reflection surface shape measurement are alternately performed, and the polishing process is repeatedly performed until the reflection surface gradually becomes a desired shape. When the aspherical substrate is completed, a multilayer coating for increasing the reflectance of EUV light is applied to the surface. The optical system is assembled using the optical system mechanical parts produced in parallel with the produced aspherical mirror. A projection optical system is completed by adjusting the position of the mirror while evaluating optical performance such as wavefront aberration. The projection optical system is mounted on an EUV exposure apparatus, and finally exposure evaluation is performed to confirm final performance.

JP 2000-91209 A

  The projection optical system produced by the conventional process may not obtain a desired optical performance in the optical performance evaluation. This is mainly caused by a mirror shape error, and cannot be sufficiently corrected only by adjusting the mirror position. Although it is possible to calculate the mirror shape error or the mirror shape correction amount for correcting the optical performance from the result of the optical performance evaluation, it is very difficult to change the shape of the mirror coated with the multilayer coating. Some multilayer films cannot be removed by wet etching. When the multilayer film is peeled from the mirror by polishing or the like, the shape accuracy of the mirror is greatly deteriorated. As described above, in the conventional process, it is difficult to correct the optical performance due to the mirror shape error.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a method for manufacturing a projection optical system for an EUV exposure apparatus having desired optical performance, and an EUV exposure apparatus having the projection optical system. To do.

A first means for solving the above-described problem is a method for manufacturing a projection optical system for an EUV exposure apparatus, characterized by comprising the following steps.
(1) Manufacturing a plurality of aspherical mirrors constituting the projection optical system based on the design values, and assembling the optical system by incorporating the manufactured aspherical mirrors
(2) A step of evaluating the optical performance of the assembled optical system
(3) Based on the evaluated optical performance, the shape correction amount of the aspherical mirror to be replaced with a new aspherical mirror (a mirror to be exchanged) is adjusted so that the optical performance falls within an allowable range. Decision process
(4) A step of manufacturing a new aspherical mirror (exchange mirror) based on the determined shape correction amount and the shape of the exchanged mirror
(5) Step of replacing the manufactured replacement mirror with the replacement mirror
(6) A step of manufacturing a projection optical system using the aspherical mirror remaining without being replaced and the replaced aspherical mirror.

  In this means, after manufacturing a plurality of aspherical mirrors that make up the projection optical system based on the design values, an optical system is assembled using these aspherical mirrors, and the deviation of the optical characteristics from the design values is measured. To do. Then, the aspherical mirror to be replaced is determined (may be determined in advance), and the shape correction amount (difference between the shape of the replacement mirror and the replacement mirror) necessary for setting the optical characteristics to the design value is determined. .

  Then, based on the shape correction amount and the shape of the exchanged mirror, a new aspherical mirror (exchanged mirror) is manufactured, the exchanged mirror is exchanged with the exchanged mirror, and the remaining aspherical mirror remains. And an exchange mirror are used to manufacture a projection optical system.

  In this means, even if the target optical characteristics are not obtained due to the shape error of the aspherical mirror, the shape of the aspherical mirror is not corrected, and a new mirror is considered in consideration of the shape correction amount. Since it is manufactured and exchanged for it, the time-consuming process of shape correction can be omitted.

  A second means for solving the problem is the first means, wherein the optical system is an actual projection optical system for an EUV exposure apparatus (claim 2). is there.

  In this means, since the actual projection optical system for the EUV exposure apparatus is used to detect the optical characteristics, the measurement can be performed in a state closer to the actual use state.

  The third means for solving the above-mentioned problem is the first means, and when the exchange mirror is manufactured, the shape of the reflection surface of the exchange mirror and the reflection of the substrate of the exchanged mirror corresponding thereto are reflected. The shape of the surface to be a surface is measured with a laser interference shape measuring device, and based on the difference between the measurement data of the two and the shape correction amount, the shape of the surface to be the reflective surface of the substrate of the exchanged mirror is the target value It has the process which processes so that it may become (Claim 3).

  With the laser interference shape measuring device, precise measurement is possible by measuring the difference between the shape of the reflective surface of the interchangeable mirror and the shape of the corresponding mirror surface of the mirror to be replaced. By alternately and repeatedly processing the substrate of the exchange mirror, the shape of the exchange mirror can be made close to the target value.

  A fourth means for solving the problem is the third means, wherein the laser interference shape measuring apparatus has a reference surface, and the laser light reflectance of the reference surface is equal to that of the mirror to be exchanged. It is lower than the laser beam reflectance of the reflecting surface and higher than the reflectance of the surface that becomes the reflecting surface of the substrate of the exchange mirror (claim 4).

  When the surface shape is measured by the laser interference shape measuring apparatus, the difference in reflectance between the surface serving as the reflective surface of the substrate of the exchange mirror and the reflective surface of the exchanged mirror becomes a problem. That is, although the reflection film is formed on the reflection surface of the exchanged mirror, the reflection film is not yet formed on the surface that becomes the reflection surface of the substrate of the exchange mirror. growing. In the laser interference shape measuring apparatus, if the difference between the amount of light reflected from the reference surface and the amount of light reflected from the measurement surface is large, clear interference fringes are not formed and measurement error increases.

  In this means, the reflectance of the reference surface is such that the reflectance of the laser beam is lower than the reflectance of the laser beam of the reflecting surface of the exchanged mirror and higher than the reflectance of the surface of the substrate of the exchange mirror. Therefore, it is possible to accurately measure the shapes of both the reflection surface of the exchanged mirror and the reflection surface of the exchange mirror substrate.

  According to a fifth aspect of the present invention, there is provided a projection optical system manufactured by the method of manufacturing a projection optical system for an EUV exposure apparatus according to any one of the first to fourth means. An EUV exposure apparatus (claim 5).

  In this means, an EUV exposure apparatus having desired optical performance can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the projection optical system for EUV exposure apparatuses which has desired optical performance, and the EUV exposure apparatus which has this projection optical system can be provided.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings, taking as an example a projection optical system composed of six aspherical mirrors as shown in FIG. This projection optical system is an optical system that forms an intermediate image in the middle of the optical path, and a third mirror (hereinafter referred to as an M3 mirror) is disposed at a position closest to the intermediate image along the optical path from the image side. .
Example 1
FIG. 1 is a flowchart showing manufacturing steps of a first embodiment of a method for manufacturing a projection optical system for an EUV exposure apparatus according to the present invention. The manufacturing method according to the present embodiment includes a step of correcting the optical performance after the optical performance evaluation.

  First, an aspherical mirror substrate constituting the projection optical system was manufactured (step S1). As the substrate material, ceramic glass having a thermal expansion coefficient of 1 ppb / K or less was used. The substrate was polished using an ion beam, and its shape was measured with a Fizeau type laser interferometer. Since ion beam processing can remove substrate material at the atomic level, it is suitable for high-precision substrate processing. The Fizeau type laser interferometer has a reference reference surface (Fizeau surface) in the apparatus, and performs comparative measurement between the Fizeau surface and the surface of the mirror to be measured. It is relatively insensitive to air fluctuations and vibrations, and is suitable for highly accurate shape measurement.

  After the substrate processing was completed, a multilayer film made of molybdenum and silicon was coated on the surface (step S2). As a means for forming the multilayer film, a magnetron sputtering method capable of forming a multilayer film having a high reflectance was employed. After completing the six mirrors constituting the projection optical system, the optical system was assembled (step S4) in combination with mechanical parts (step S3) manufactured in parallel. The mechanical parts include a mount mechanism that holds the mirror and a stage mechanism that positions the mirror with high accuracy. Thus, the mirror can be held so as not to change the shape of the mirror, and the positional relationship between the mirrors can be adjusted with high accuracy.

  The mirror position was adjusted based on the evaluation results of the optical performance. The optical performance was evaluated by measuring the wavefront aberration of the optical system using an interferometer using EUV light. The wavefront aberration was measured at a plurality of locations in the exposure field of the projection optical system. At the same time, image distortion and field curvature were also measured (step S4). From these measurement results, the amount of deviation in the mirror positional relationship was calculated, and the mirror position was adjusted. Further, a mirror shape correction amount for correcting the optical performance was calculated (step S6). Although the mirror shape correction amount differs depending on the number of mirrors to be corrected, in this embodiment, the correction amount for correcting three of the six mirrors was calculated.

  As a method for calculating the correction amount of the mirror shape from the measurement data of the wavefront aberration, a known method as described in, for example, Japanese Patent Application Laid-Open No. 2000-91209 (Patent Document 1) can be used.

  In other words, by expanding wavefront aberrations to Zernike polynomials, distortion, focus, astigmatism, coma, and other aberrations are obtained. Whether it changes to some extent is obtained by simulation. Then, by calculating back the simulation result, it is determined how much the corresponding mirror shape should be corrected in order to correct each aberration.

  After the optical performance evaluation, the optical system was disassembled, and three mirrors out of the six mirrors (hereinafter referred to as “replaced mirrors”) were taken out (step S7). One mirror of the same type as the three mirrors to be exchanged (hereinafter, this mirror is referred to as an exchange mirror) was manufactured (step S8). The exchange mirror was made of the same substrate material as the exchanged mirror, and was polished by the same technique as the exchange mirror substrate. However, the polishing process was performed so that the shape of the substrate of the exchange mirror was a shape obtained by adding the above-described mirror shape correction amount to the shape of the exchange mirror.

  That is, assuming that the measured value when the shape of the exchange mirror removed from the optical system is measured with a Fizeau interferometer is A and the calculated shape correction amount is B, the target measurement value of the shape of the exchange mirror is A + B. In other words, the processing was performed so that the shape of the replacement mirror was driven to the shape offset by the shape correction amount. For example, when the shape measurement value of the exchange mirror is C, the remaining polishing amount is A + B−C.

After the fabrication of the exchange mirror substrate was completed, a multilayer film was coated on the substrate surface (step S9). Next, the three replacement mirrors were mounted on mechanical parts instead of the mirrors to be replaced, and the optical system was reassembled (step S10). The characteristics of the optical system were evaluated again and the position of the mirror was adjusted. As a result, it was possible to obtain optical performance superior to that of the optical system constituted by the original mirror (step S11). These mirrors were mounted on the projection optical system of the EUV exposure apparatus (step S12), and exposure evaluation was performed (step S13). As a result, a desired resist pattern could be obtained.
(Example 2)
FIG. 2 is a flowchart showing manufacturing steps of the second embodiment of the method for manufacturing a projection optical system for an EUV exposure apparatus according to the present invention. In the present embodiment, in the first embodiment, the optical system is assembled and the optical performance is evaluated, and the mirror shape correction amount is calculated based on the result, but the actual EUV exposure apparatus is used. The mirror shape correction amount is calculated based on the exposure result. When the latter measurement accuracy is better than the former, it is possible to create a projection optical system that is even better than the first embodiment.

  In the following description, description of the same steps as those in the first embodiment will be omitted, and only steps different from those in the first embodiment will be described.

  After evaluating the optical performance of the optical system constituted by the exchange mirror (step S25), these mirrors were mounted on the projection optical system of the actual EUV exposure apparatus (step S26). Using this EUV exposure apparatus, the resist on the wafer was actually exposed with a mask having a predetermined pattern, the obtained resist pattern was measured, and optical performance was obtained from the result (step S27).

  That is, exposure was performed without scanning the stage to obtain a static exposure pattern. The positional relationship of the resist pattern was measured with a coordinate measuring machine to obtain image distortion. In general, an interferometer using EUV light is suitable for measurement of wavefront aberration, but the measurement accuracy of image distortion is often inferior to that of still exposure evaluation. This step is effective when it is desired to reduce image distortion with higher accuracy.

  The method for obtaining the mirror shape correction amount from the image distortion is to calculate the degree of change in the image distortion when the shape of each mirror is changed by a small amount in advance, and then reversely calculate this relational expression. Thus, it is possible to use a method for obtaining the mirror shape correction amount corresponding to the obtained image distortion.

  A mirror shape correction amount was calculated from the wavefront aberration obtained from the optical performance evaluation and the image distortion obtained from the exposure evaluation (step S28). Thereafter, a projection optical system was manufactured in the same manner as in the first example. When this projection optical system was mounted on an EUV exposure machine and exposure evaluation was performed, a desired resist pattern could be obtained.

  In the first and second embodiments described above, when the substrate of the exchange mirror was manufactured, a comparative measurement of the shape of the mirror to be exchanged and the substrate of the exchange mirror was performed with a Fizeau interferometer. At this time, since the mirror to be exchanged is coated with a multilayer film, the laser light reflectance is often higher than the light reflectance of the substrate of the exchange mirror. When the difference in reflectance is large, it is difficult to obtain the interference fringe contrast.

  The contrast of the interference fringes is determined by the ratio of the intensity of the laser beam reflected by the Fizeau surface and the intensity of the laser beam reflected by the surface of the mirror to be measured. If the reflectivity of the Fizeau surface is approximately the same as the reflectivity of the mirror substrate, sufficient contrast can be obtained when measuring the mirror substrate, but when measuring a multilayer mirror, the contrast is low and the measurement accuracy is low. Is lacking.

  In the first embodiment and the second embodiment, the reflectivity of the Fizeau surface is higher than the reflectivity of the mirror substrate and lower than the reflectivity of the multilayer film. That is, a surface reflection increasing film was formed on the Fizeau surface to control the reflectance. By using such a Fizeau interferometer, it was possible to obtain a sufficient contrast in any measurement of the exchanged mirror and the exchange mirror.

  In the second embodiment, the optical performance was evaluated from the shape of the resist pattern that was actually exposed. However, the present invention is not limited to such a measurement method. For example, an interferometer is mounted on an EUV exposure apparatus, and wavefront aberration is achieved. May be measured and the optical performance may be evaluated based on the result. Further, the aerial image may be measured by a photo sensor or the like, and wavefront aberration and image distortion may be acquired based on the result.

It is a flowchart which shows the manufacturing process of the 1st Example of the manufacturing method of the projection optical system for EUV exposure apparatuses of this invention. It is a flowchart which shows the manufacturing process of the 2nd Example of the manufacturing method of the projection optical system for EUV exposure apparatuses of this invention. It is a figure which shows schematic structure of an EUV exposure apparatus. It is a figure which shows the manufacturing process of the conventional projection optical system.

Claims (5)

The manufacturing method of the projection optical system for EUV exposure apparatuses characterized by having the following processes.
(1) Manufacturing a plurality of aspherical mirrors constituting the projection optical system based on the design values, and assembling the optical system by incorporating the manufactured aspherical mirrors
(2) A step of evaluating the optical performance of the assembled optical system
(3) Based on the evaluated optical performance, the shape correction amount of the aspherical mirror to be replaced with a new aspherical mirror (a mirror to be exchanged) is adjusted so that the optical performance falls within an allowable range. Decision process
(4) A step of manufacturing a new aspherical mirror (exchange mirror) based on the determined shape correction amount and the shape of the exchanged mirror
(5) Step of replacing the manufactured replacement mirror with the replacement mirror
(6) A step of manufacturing a projection optical system using the aspherical mirror remaining without being replaced and the replaced aspherical mirror. The method for manufacturing a projection optical system for an EUV exposure apparatus according to claim 1, wherein the optical system is an actual projection optical system for an EUV exposure apparatus. The method for manufacturing a projection optical system for an EUV exposure apparatus according to claim 1, wherein when manufacturing the exchange mirror, the shape of the reflection surface of the exchange mirror and the reflection surface of the substrate of the exchanged mirror corresponding thereto The shape of the surface to be formed is measured with a laser interference shape measuring device, and the shape of the surface to be the reflection surface of the substrate of the exchanged mirror becomes the target value based on the difference between the measurement data of the two and the shape correction amount. A process for producing a projection optical system for an EUV exposure apparatus, characterized by comprising a step of processing as described above. 4. The method for manufacturing a projection optical system for an EUV exposure apparatus according to claim 3, wherein the laser interference shape measuring device has a reference surface, and the laser light reflectance of the reference surface is a reflection surface of the exchanged mirror. A method of manufacturing a projection optical system for an EUV exposure apparatus, characterized in that the reflectance is lower than the laser light reflectance of the first mirror and higher than the reflectance of the surface of the exchange mirror substrate. An EUV exposure apparatus comprising a projection optical system manufactured by the method for manufacturing a projection optical system for an EUV exposure apparatus according to any one of claims 1 to 4.

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