JP2004297046A - Method of aberration measurement - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of aberration measurement capable of measuring wave aberration with high accuracy over the whole area of the effective numerical aperture of a lens to be inspected. <P>SOLUTION: The method comprises steps of: entering light flux condensed by a condenser-lens optical system into the optical system to be inspected 400; reflecting the light flux through the optical system to be inspected 400 on a reflection optical system 168 having a center of curvature located at the focus point on the light exit side of the optical system to be inspected 400 and again entering the reflected light flux in the optical system to be inspected 400; and when detecting the wave aberration of the optical system to be inspected 400 as an interference fringe by making use of the light flux transmitted again through the optical system to be inspected 400, setting the numerical aperture of the optical system to be inspected 400 to the value larger than the value of the numerical aperture when the optical system to be inspected 400 is actually used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention generally relates to an aberration measuring method, and more particularly to an aberration measuring method for measuring wavefront aberration of a projection optical system or the like that transfers a pattern on a mask to a photosensitive substrate. Such a projection optical system is used, for example, in a lithography process when exposing an object to be processed such as a single crystal substrate such as a semiconductor wafer or a glass substrate for a liquid crystal display (LCD).

  When manufacturing a fine semiconductor device such as a semiconductor memory or a logic circuit by using a photolithography technique, a circuit pattern drawn on a reticle or a mask (in this application, these terms are used interchangeably) Conventionally, a projection exposure apparatus that projects a circuit pattern by projecting onto a wafer or the like by a projection optical system has been used.

  In a projection exposure apparatus, it is required to accurately transfer a pattern on a reticle onto a wafer at a predetermined magnification (reduction ratio). In order to meet such a requirement, the aberration is minimized and imaging performance is improved. It is important to use an excellent projection optical system. In particular, due to rapid miniaturization of semiconductor devices in recent years, patterns that exceed normal imaging performance have been increasingly transferred, and the transferred patterns have become sensitive to aberrations in the optical system. On the other hand, the projection optical system is required to enlarge the exposure area and increase the numerical aperture (NA), making aberration correction more difficult. In order to perform good aberration correction, it is necessary to measure wavefront aberration with high accuracy.

  As an apparatus for measuring the wavefront aberration of an optical system with high accuracy, an apparatus using a Fizeau type or Twiman Green type interferometer has been conventionally used (Patent Documents 1 and 2).

  The principle of wavefront aberration measurement will be described below with reference to FIGS. 7 to 9 using a Fizeau interferometer as a projection lens mounted on the projection optical system of the projection exposure apparatus. Here, FIG. 7 is a schematic configuration diagram showing a conventional aberration measuring apparatus 1000.

  The light from the light source 1100 is guided to the interferometer unit 1200, passes through the half mirror 1210, is converted into parallel light by the collimator lens 1220, and is reflected by the RS mirror 1500 through the TS lens 1300 and the test lens 1400. . The light reflected by the RS mirror 1500 travels in the opposite direction to the test lens 1400 and the TS lens 1300, is reflected by the half mirror 1210, and enters the CCD camera 1240 as test light by the imaging lens 1230.

  On the other hand, the light reflected by the final surface (ie, Fizeau surface) of the TS lens 1300 is also reflected by the half mirror 1210 and is incident on the CCD camera 1240 as reference light by the imaging lens 1230. Interference fringes are detected on the CCD camera 1240 by the interference of these two light beams (that is, the test light and the reference light). Based on the interference fringes, the wavefront aberration can be obtained by calculation. The TS lens 1300 and the RS mirror 1500 are scanned in the optical axis direction, and wavefront aberration can be continuously measured by a so-called fringe scanning method. In addition, in FIG. 7, since the member which does not attach | subject the code | symbol is demonstrated by below-mentioned embodiment, description is abbreviate | omitted here.

  Here, the aperture stop 1410 for determining the numerical aperture of the test lens 1400 is disposed so as to be optically conjugate with the CCD camera 1240. Such an arrangement will be described in detail with reference to FIG. FIG. 8 is a schematic block diagram showing the positional relationship between the aperture stop 1410 and the CCD camera 1240 shown in FIG.

  As shown in FIG. 8A, the aperture stop 1410 of the test lens 1400 includes a TS lens 1300 by a rear optical system (lens system on the image plane side of the aperture stop 1410) 1600 and the TS lens 1300. This is conjugate to the front focal plane FP (interferometer unit 1200 side). Further, the front focal plane FP of the TS lens 1300 is conjugated to the detection surface 1240a of the CCD camera 1240 by the interference optical system (collimator lens 1220 and imaging lens 1230 constituting the interferometer unit 1200) 1700. To be precise, the TS lens 1300 is arranged at the measurement position on the axis, and the position of the detection surface 1240a is adjusted at the assembly adjustment stage so that the aperture stop 1410 and the detection surface 1240a have an optically conjugate relationship.

As a result, the diameter of the aperture stop 1410 of the test lens 1400 matches the effective numerical aperture of the test lens 1400, but diffracted light from the edge of the aperture stop 1410 forms an image on the detection surface 1240a. The wavefront aberration detected from the interference fringes is not affected.
JP 2000-277411 A Japanese Patent Laid-Open No. 2000-277412

  However, when the TS lens 1300 is moved to the off-axis measurement position, as shown in FIG. 8B, the optical conjugate of the aperture stop 1410 of the lens 1400 to be detected and the detection surface 1240a of the CCD camera 1240. The relationship is broken. This is because when the TS lens 1300 moves, the interference optical system 1700 moves relative to the test lens 1400, and the distance between the TS lens 1300 and the interference optical system 1700 is only ΔL (the amount of movement of the TS lens 1300). Because it changes.

  As described above, when the optical conjugate relationship between the aperture stop 1410 of the lens 1400 to be examined and the detection surface 1240a of the CCD camera 1240 is broken, the diffracted light spreads on the detection surface 1240a, as shown in FIG. In the vicinity of the effective numerical aperture NA0 (ie, pupil) of the lens 1400 to be examined, a sudden phase change occurs in the wavefront aberration measured due to the influence of the diffracted light from the aperture stop 1410, resulting in a large measurement error. Here, FIG. 9 is a schematic diagram showing the wavefront aberration around the pupil of the lens 1400 to be measured in the conventional aberration measuring apparatus 1000.

  In particular, when the measurement light is incident from the object plane side like the aberration measuring apparatus 1000 shown in FIG. 7, the amount of movement between the on-axis and the off-axis of the TS lens 1300 is the measurement light from the image plane side. (For example, in the case of a 5 × projection lens, ΔL has a movement amount of 25 ×), so that the error of the wavefront aberration around the pupil due to the spread of diffracted light becomes large.

  On the other hand, the CCD camera 1240 or the imaging lens 1230 can be moved in the optical axis direction according to the measured image height, so that the optical conjugate relationship between the aperture stop 1410 and the detection surface 1240a can always be maintained. It is. However, since the interference fringes move on the CCD camera 1240 due to the eccentricity when the CCD camera 1240 or the imaging lens 1230 moves, it is necessary to perform correction for each image height of the center coordinates in the wavefront aberration calculation region. It is not desirable.

  An object of the present invention is to provide an aberration measuring method capable of measuring wavefront aberration with high accuracy over the entire effective numerical aperture of a lens to be examined.

  In order to achieve the above object, the aberration measuring method of the present invention causes a light beam condensed by a condensing optical system to enter the test optical system, and the light beam via the test optical system is emitted from the test optical system. Reflected by a reflective optical system with a center of curvature at the condensing point on the side, re-entered into the test optical system, and again used the light beam through the test optical system to reduce the wavefront aberration of the test optical system as interference fringes Is an aberration measuring method to detect as In particular, the numerical aperture of the test optical system is set to the maximum numerical aperture when the test optical system is actually used (for example, when the test optical system is a projection optical system for an exposure apparatus, during actual exposure). And a step of measuring the wavefront aberration of the optical system to be measured at the set numerical aperture.

  Further objects and other features of the present invention will become apparent from the preferred embodiments described below with reference to the accompanying drawings.

  According to the present invention, it is possible to provide an aberration measuring method capable of measuring wavefront aberration with high accuracy over the entire effective numerical aperture of a lens to be examined.

  Hereinafter, an aberration measuring apparatus 100 and an exposure apparatus 200 according to one aspect of the present invention will be described with reference to the accompanying drawings. In addition, the same reference number is attached | subjected about the same member in each figure, and the overlapping description is abbreviate | omitted. Here, FIG. 1 is a schematic configuration diagram showing an exemplary form of the aberration measuring apparatus 100 as one aspect of the present invention.

  The aberration measuring apparatus 100 constitutes a Fizeau interferometer using a light beam 110 having a coherent light beam (for example, laser light) having an oscillation wavelength close to the use wavelength of the lens 400 to be tested. The wavefront aberration of the test lens 400 such as a projection optical system is measured. Hereinafter, in this embodiment, the test lens 400 will be described as a projection optical system.

  As shown in FIG. 1, the aberration measuring apparatus 100 includes a light source 110, an interferometer unit 120, a routing optical system 130, a TS-XYZ stage 140, a TS lens 150, an RS-XYZ stage 160, and a numerical aperture. A change unit 170 and a main controller 180 are included.

  The aberration measuring apparatus 100 forms interference fringes by superimposing the test light and the reference light, and measures the wavefront aberration of the test lens 400. First, the test light will be described. Referring to FIG. 1, the light beam from the light source 110 is guided to the interferometer unit 120. Inside the interferometer unit 120, the light beam is collected on the spatial filter 122 by the condenser lens 121. Here, the diameter of the spatial filter 122 is set to about ½ of the Airy disk diameter determined by the numerical aperture (NA) of the collimator lens 124. As a result, the light emitted from the spatial filter 122 becomes an ideal spherical wave, passes through the half mirror 123, is converted into parallel light by the collimator lens 124, and is emitted from the interferometer unit 120. Thereafter, the optical system 130 guides the optical system 130 to the upper part of the object surface (corresponding to the reticle surface when placed on the exposure apparatus) of the lens 400 to be tested, and the TS-XYZ stage 140 (the TS-XYZ stage 140 is an X-axis). Including the stage 142, the Y stage 144, and the Z stage 146).

  The parallel light incident on the TS-XYZ stage 140 is reflected in the Y direction by the mirror M1 fixedly arranged on the stage surface plate SB, and in the X direction by the mirror M2 arranged on the Y stage 144 and movable in the Y direction. The light is reflected and reflected in the Z direction by a mirror M3 arranged on the X stage 142 and movable in the X direction. Further, the light is condensed on the object surface of the test lens 400 by the TS lens 150 disposed on the Z stage 146, and after passing through the test lens 400, the image plane (wafer surface when placed on the exposure apparatus). The image is condensed and re-imaged.

  Thereafter, the re-imaged light is reflected by an RS mirror 168 disposed on an RS-XYZ stage 160 (the RS-XYZ stage 160 includes an X stage 162, a Y stage 164, and a Z stage 166), The test lens 400, the TS lens 150, the mirror M3, the mirror M2, the mirror M1, and the routing optical system 130 are reversed in substantially the same optical path, and again enter the interferometer unit 120 again. As can be seen, the center of curvature of the RS mirror 168 exists on the image plane (condensing point) of the test lens 400.

  The light after entering the interferometer unit 120 is transmitted through the collimator lens 124, reflected by the half mirror 123, and collected on the spatial filter 125. Here, the spatial filter 125 is for blocking stray light and steeply inclined wavefronts. The light after passing through the spatial filter 125 is incident on the CCD camera 127 as a substantially parallel light beam by the imaging lens 126.

  On the other hand, for the reference light, the TS lens 150 reflects a part of the light beam incident on the TS lens 150 in the forward path. Specifically, surface reflected light from the Fizeau surface, which is the final surface of the TS lens 150, is obtained, and the reflected light is converted into a mirror M3, a mirror M2, a mirror M1, a routing optical system 130, a collimator lens 124, a half mirror 123, The beam is reversed along the optical path of the spatial filter 125 and the imaging lens 126 and is incident on the CCD camera 127 as reference light. That is, the CCD camera 127 detects interference fringes formed by superimposing the test light and the reference light.

  Here, the TS-XYZ stage 140 (X stage 142, Y stage 144, Z stage 146) and RS-XYZ stage 160 (X stage 162, Y stage 164, Z stage 166) are the numerical aperture changing means 170 described later. Under the control of the control unit 174, the wavefront aberration at an arbitrary image point (arbitrary object point) of the test lens 400 can be continuously measured via the TS-XYZ stage driving unit 140a and the RS-XYZ driving stage 160a. ing.

  In the aberration measuring apparatus 100 of this embodiment, as described above, the light condensed by the TS lens 150 on the object side (the side on which the reticle is placed) of the test lens 400 is first incident on the test lens 400. However, light may be first incident from the image side (side on which the wafer is placed). In this case, the light condensing point by the TS lens 150 is set on the image plane of the test lens 400, and the center of curvature of the RS mirror 168 is set on the object plane of the test lens 400.

  Here, the numerical aperture changing means 170 will be described. The numerical aperture changing means 170 includes a drive unit 172 that drives an aperture stop 410 provided in the lens 400 to be tested and a control unit 174 that controls the drive unit 172, and light passes through the aperture stop 410. The numerical aperture of the test lens 400 is changed by changing the aperture diameter of the aperture stop 410 so as to reduce the influence of the phase change received by the interference fringes detected by the CCD camera 127 by the generated diffracted light. In the present embodiment, the control unit 174 is configured to also control the TS-XYZ stage driving unit 140a and the RS-XYZ driving stage 160a. However, a control unit that controls each of them independently may be provided. .

The numerical aperture changing means 170 makes the numerical aperture of the lens 400 to be measured variable so that the diffracted light does not affect the wavefront aberration measurement value even at the most off-axis measurement position, and the maximum effective numerical aperture when actually used. A predetermined numerical aperture NA ₁ sufficiently larger than NA ₀ can be set. Before the measurement, the numerical aperture changing means 170 enlarges the aperture stop 410 of the lens 400 to be measured larger than the maximum effective numerical aperture during actual use, and in this state, the wavefront aberration is measured. Here, the “maximum effective numerical aperture during actual use” refers to the maximum numerical aperture within a range in which imaging performance is guaranteed when the lens 400 to be tested is used in accordance with an actual purpose. For example, when the test lens 400 is a projection optical system of an exposure apparatus for manufacturing a semiconductor device or the like, the maximum numerical aperture that can be used when the exposure apparatus actually performs projection exposure (during actual exposure) is indicated. .

In addition, the effective diameter of each lens constituting the test lens 400 is also secured so that the aperture stop 410 can be changed to the maximum diameter exceeding the effective numerical aperture NA ₀ in actual use. Further, the diameter of the aperture stop 410 can be changed as necessary before measurement by the main controller 180 via the drive unit 172 and the control unit 174. The diameter of the aperture stop 410 may be changed by manually operating the drive unit 172 before measurement.

Hereinafter, the flow of measurement will be described. First, the aperture diameter of the aperture stop 410 is changed by the numerical aperture changing means 170 so that the numerical aperture of the test lens 400 is larger than the maximum effective numerical aperture NA _{0 in} actual use. Next, wavefront aberration is sequentially measured at a plurality of measurement points on and off the axis. When the TS lens 150 and the RS mirror 168 are moved to an off-axis measurement position, the optical conjugate relationship between the aperture stop 410 of the test lens 400 and the test surface of the CCD camera 127 is broken, but the aperture is not measured before measurement. Since the number is larger than the maximum effective numerical aperture NA ₀ , it is possible to measure wavefront aberration with high accuracy at all measurement positions without being affected by the diffracted light at the aperture stop 410. Hereinafter, the reason will be described in detail.

  FIG. 2 is a graph showing the phase change of the test light due to the influence of diffraction near the edge when the edge position of the aperture stop 410 of the test lens 400 is 1.0. This is a result of calculating a Fresnel diffraction image with a defocus amount of 80 mm, assuming a movement amount of the TS lens 150 of 80 mm. Further, the pixel size of the CCD camera 127 on the pupil is set to 0.5% of the pupil diameter, and the diffraction image is averaged in the pixel of the CCD camera 127.

Referring to FIG. 2, when the movement amount ΔL of the TS lens 150 is 80 mm (sum of the movement amounts in the X direction and the Y direction), a phase change occurs up to 0.5% from the edge. It can be seen that no phase change has occurred. In consideration of securing 0.5% larger numerical aperture NA ₁ at the time of wavefront aberration measurement than the maximum effective numerical aperture NA _{0 of the} test lens 400, the maximum effective numerical aperture NA ₀ and numerical aperture NA ₁ are as follows: The control unit 174 may control the drive unit 172 so as to satisfy the relational expression expressed by Equation 1 below.

NA ₀ / NA ₁ <0.995
By measuring the wavefront aberration at any point on the axis and off-axis in a state where the numerical aperture of the lens 400 to be tested satisfies Expression 1, it is possible to measure the wavefront aberration with high accuracy. Here, the influence of diffracted light on the measurement of wavefront aberration in the state of the numerical aperture NA ₁ will be described with reference to FIG. FIG. 3 is a diagram showing wavefront aberration in one section of a circular pupil. The horizontal axis represents the pupil coordinates of one section passing through the pupil center, and the vertical axis represents the value of wavefront aberration. As shown in FIG. 3, the phase change is _{only in} the range of the numerical apertures NA _{0 to} NA ₁ of the test lens 400 (the range in which the wavefront aberration changes in FIG. 3), and the effective numerical aperture of the test lens 400 Does not occur inside. As a result, the wavefront aberration can be measured with high accuracy over the entire pupil within the effective numerical aperture of the lens 400 to be examined. Here, FIG. 3 is a schematic diagram showing the wavefront aberration around the pupil of the test lens 400 in the aberration measuring apparatus 100.

  Hereinafter, with reference to FIG. 4, an exposure measure 200 according to one aspect of the present invention will be described. FIG. 4 is a schematic block diagram showing an exemplary embodiment of an exposure apparatus 200 that is one aspect of the present invention. The exposure apparatus 200 is obtained by applying the aberration measuring apparatus 100 to an exposure apparatus. The exposure apparatus 200 is a projection exposure apparatus that exposes a circuit pattern formed on the mask 220 onto the wafer 224 by, for example, a step-and-scan method or a step-and-repeat method. Such an exposure apparatus is suitable for a lithography process of submicron or quarter micron or less, and in the present embodiment, a step-and-scan exposure apparatus (also referred to as a “scanner”) will be described as an example. Here, the “step and scan method” means that the wafer is continuously scanned (scanned) with respect to the mask to expose the mask pattern onto the wafer, and the wafer is stepped after the exposure of one shot is completed. The exposure method moves to the next exposure area. The “step-and-repeat method” is an exposure method in which the wafer is stepped and moved to the next exposure area for every batch exposure of the wafer.

  The basic configuration of the exposure apparatus 200 is the same as that of the published Japanese Patent Application No. 277412 which is the prior application. Referring to FIG. 4, the laser light emitted from the light source 210 is converted into a beam shape symmetric with respect to the optical axis by the beam shaping optical system 212 and guided to the optical path switching mirror 214. The optical path switching mirror 214 is disposed outside the optical path during normal exposure.

  The light beam emitted from the beam shaping optical system 212 enters the incoherent optical system 216, reduces coherence, passes through the illumination optical system 218, and illuminates the mask (or mask surface) 220. The light that passes through the mask 220 and reflects the mask pattern is imaged by the projection optical system 222 at the wafer surface position 224a where the wafer 224 is disposed. In FIG. 4, since the time of exposure is not shown, the wafer 224 is not positioned at the wafer surface position 224a, but is moved to the wafer surface position 224a by the wafer stage 226 at the time of exposure.

On the other hand, when measuring the wavefront aberration of the projection optical system 222, the optical path switching mirror 214 is disposed in the optical path. Further, the control unit 174 of the numerical aperture changing means 170 drives the aperture diameter of the aperture stop 222a that makes the numerical aperture of the projection optical system 222 variable via the drive unit 172, and the numerical aperture of the projection optical system 222 is normally set. The numerical aperture NA ₁ is larger than the maximum numerical aperture NA ₀ at the time of exposure (during actual exposure). Note that the control unit 174 controls the drive unit 172 so that the numerical aperture NA ₀ and the numerical aperture NA ₁ of the projection optical system satisfy the relationship of Equation 1. In this state, the light beam from the beam shaping optical system 212 is reflected by the optical path switching mirror 214, guided to the routing optical system 230, and guided to the vicinity of the interferometer unit 120 disposed in the vicinity of the mask 220. . The light beam emitted from the drawing optical system 230 is collected at one point by the condenser lens 232. Here, a pinhole 234 is disposed in the vicinity of the focal point of the condenser lens 232.

  The light beam that has passed through the pinhole 234 is converted into parallel light by the collimator lens 236. The diameter of the pinhole 234 is set to be approximately the same as the Airy disk diameter determined by the numerical aperture (NA) of the collimator lens 236. As a result, the light beam emitted from the pinhole 234 is an almost ideal spherical wave. The parallel light from the collimator lens 236 is reflected by the half mirror 238 and enters the TS lens 150 arranged on the TS-XYZ stage 140 via the mirror M4. As described above, the light beam incident on the TS lens 150 is divided into the test light and the reference light, and the interferometer unit 120 forms interference fringes. With such interference fringes, the wavefront aberration of the projection optical system 222 can be obtained with high accuracy.

  After measuring the wavefront aberration of the projection optical system 222, the aperture stop 222a is driven by the numerical aperture changing means 170, the projection optical system 222 is returned to the numerical aperture during normal exposure, and the optical path switching mirror 214 is moved to the illumination optical system 218 side. Switch and perform exposure. However, when the projection optical system 222 is required to have a more accurate optical performance, after measuring the wavefront aberration, for example, by adjusting the lens interval and position of the projection lens to be configured, A correcting unit 250 that corrects aberration may be configured.

  Next, an embodiment of a device manufacturing method using the exposure apparatus 200 will be described with reference to FIGS. FIG. 5 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, etc.). Here, the manufacture of a semiconductor chip will be described as an example. In step 1 (circuit design), a device circuit is designed. In step 2 (mask production), a mask on which the designed circuit pattern is formed is produced. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the mask and the wafer. Step 5 (assembly) is called a post-process, and is a process for forming a semiconductor chip using the wafer created in step 4, and includes processes such as an assembly process (dicing and bonding) and a packaging process (chip encapsulation). . In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).

  FIG. 6 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the surface of the wafer is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like. Step 14 (ion implantation) implants ions into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus 200 to expose a circuit pattern on the mask onto the wafer. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeatedly performing these steps, multiple circuit patterns are formed on the wafer. According to the device manufacturing method of the present embodiment, it is possible to manufacture a higher quality device than before. Thus, the device manufacturing method using the exposure apparatus 200 and the resulting device also constitute one aspect of the present invention.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist. For example, in this embodiment, light is incident from the object plane side of the lens to be examined, but may be incident from the image plane side.

1 is a schematic configuration diagram showing an exemplary form of an aberration measuring apparatus 100 as one aspect of the present invention. It is a graph which shows the phase change of the test light by the influence of the diffraction in the edge vicinity when the edge position of the aperture stop of a test lens is 1.0. It is a schematic diagram which shows the wavefront aberration around the pupil of the test lens in the aberration measuring apparatus shown in FIG. It is a schematic block diagram which shows one exemplary form of the exposure apparatus which is one side of this invention. It is a flowchart for demonstrating manufacture of devices (semiconductor chips, such as IC and LSI, LCD, CCD, etc.). 6 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 5. It is a schematic block diagram which shows the conventional aberration measuring device. FIG. 8 is a schematic block diagram showing a positional relationship between the aperture stop and the CCD camera shown in FIG. 7. It is a schematic diagram which shows the wavefront aberration around the pupil of the test lens in the conventional aberration measuring device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Aberration measuring apparatus 110 Light source 120 Interferometer unit 121 Condensing lens 122 Spatial filter 123 Half mirror 124 Collimator lens 125 Spatial filter 126 Imaging lens 127 CCD camera 130 Drawing optical system 140 TS-XYZ stage 150 TS lens 160 RS-XYZ stage 168 RS mirror 170 Numerical aperture changing means 172 Drive unit 174 Control unit 180 Main control unit 200 Exposure unit 210 Light source 212 Beam shaping optical system 214 Optical path switching mirror 216 Incoherent optical system 218 Illumination optical system 220 Mask 222 Projection optical system 222a Aperture Diaphragm 224 Wafer 226 Wafer stage 230 Route optical system 232 Condensing lens 234 Pinhole 236 Collimator lens 238 Half Ra 250 correction unit 400 subjects the lens 410 aperture

Claims (5)

A reflective optical system in which a light beam collected by a condensing optical system is incident on a test optical system, and the center of curvature is set at a light condensing point on the light exit side of the test optical system. Is an aberration measurement method for detecting the wavefront aberration of the test optical system as an interference fringe by using the light beam that has passed through the test optical system again and reflected again by the test optical system.
Setting the numerical aperture of the test optical system to a numerical aperture larger than the maximum numerical aperture when the test optical system is actually used;
Measuring the wavefront aberration of the optical system under test at the set numerical aperture. When the maximum numerical aperture when actually using the test optical system is NA ₀ and the set numerical aperture is NA ₁ ,
NA ₀ / NA ₁ <0.995
The aberration measurement method according to claim 1, wherein the following condition is satisfied. An exposure apparatus that has a projection optical system with a variable numerical aperture, and projects a pattern formed on a reticle by the projection optical system onto a wafer,
A condensing optical system disposed on the light incident side of the projection optical system, a reflection optical system disposed on the light exit side of the projection optical system, and detection optics for detecting wavefront aberration of the projection optical system as interference fringes An aberration measurement system comprising: a light beam condensed by the light collecting optical system is incident on the projection optical system, and the light beam that has passed through the projection optical system is incident on the projection optical system. Reflected by the reflection optical system with the center of curvature set at the condensing point on the light exit side and made incident again on the projection optical system, and again using the light flux through the projection optical system to form interference fringes An exposure apparatus characterized in that the numerical aperture of the projection optical system is set to a numerical aperture larger than the maximum numerical aperture during actual exposure, and the wavefront aberration of the projection optical system is measured at the set numerical aperture.   4. An exposure apparatus according to claim 3, further comprising correction means for correcting wavefront aberration of the projection optical system based on the wavefront aberration measured by the aberration measurement system. 4. A device comprising: a step of applying a resist to a wafer; a step of exposing a wafer coated with a resist using the exposure apparatus according to claim 3; and a step of developing the exposed resist. Production method.

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