JPH11258498A5 - - Google Patents

Description

This will be explained in more detail. Here, we will take as an example a case where the illumination area is a rectangle (rectangle) elongated in the non-scanning direction. FIG. 11 shows a projection optical system PL' used in a scanning exposure apparatus as viewed from the optical axis direction. The area IA indicated by the dotted line in this figure is the illumination area. Generally, a projection optical system absorbs the exposure illumination light during exposure, resulting in a temperature distribution. However, in a scanning exposure apparatus, the illumination area IRA is rectangular, so the temperature distribution becomes dependent on the illumination area, as shown in FIG. 12. As is clear from FIG. 12 , in the non-scanning direction, the temperature distribution is such that the temperature gradually increases from the periphery to the center, and illumination is uniform. However, in the scanning direction, the temperature changes rapidly from the low-temperature area in the periphery to the high-temperature area in the center, and the illumination area is quite limited. For this reason, while the curvature of the projection optical system PL' changes in the non-scanning direction as shown schematically in Fig. 13, which is a cross-sectional view taken along line A-A in Fig. 12, the change in curvature becomes larger within the illumination area in the scanning direction as shown schematically in Fig. 14, which is a cross-sectional view taken along line B-B in Fig. 12. Although Figs. 13 and 14 show the projection optical system PL' as a single lens, it is also acceptable to consider each lens element that makes up the projection optical system to undergo the above-mentioned thermal deformation, or to consider the projection optical system PL' itself as a single large lens that undergoes the above-mentioned thermal deformation.

In the projection lens described in claim 2 or 3, various imaging characteristics may be initially adjusted. For example, as described in claim 4, the imaging characteristic to be initially adjusted may be rectangular distortion whose longer side is in the first direction. In this case, as described in claim 5, the initial adjustment of the rectangular distortion is preferably performed by shifting the magnification in the second direction from the desired magnification more significantly than in the first direction. Rectangular distortion whose longer side is in the first direction typically occurs when the illumination area has a long shape in the first direction, and the projection lens is illuminated almost evenly in the first direction and a limited range in the second direction. Therefore, the change in magnification of the projection lens due to illumination light absorption is larger in the second direction and smaller in the first direction. Therefore, rectangular distortion can be effectively suppressed by shifting the magnification in the second direction from the desired magnification more significantly than in the first direction.

In the scanning exposure apparatus according to any of the tenth to thirteenth aspects of the present invention, it is possible to resume exposure after a certain time has elapsed since the exposure was interrupted. However, if the certain time is too short, the anisotropic imaging characteristic will reach the threshold value immediately after the resumption. Conversely, if the certain time is too long, the exposure will be interrupted for an unnecessarily long period, unnecessarily deteriorating throughput. Therefore, as in the fourteenth aspect of the present invention, it is desirable that the imaging characteristic monitoring device (21) continues to monitor changes in the anisotropic imaging characteristic of the projection optical system even after the exposure operation is interrupted, and resumes the exposure operation when the imaging characteristic has decayed to a predetermined standard. In such a case, the above-mentioned inconveniences can be avoided, the interruption time can be set to the minimum necessary, throughput can be minimized, and exposure defects due to deterioration of the anisotropic imaging characteristic can be reliably prevented.

The scanning exposure apparatus of claim 9 may further comprise an imaging characteristic correction device (14, 15) that corrects changes in rotationally symmetric imaging characteristics other than focus of the projection optical system (PL), as in claim 15. In such a case, the imaging characteristic correction device can correct rotationally symmetric imaging characteristics other than focus (magnification, distortion, field curvature, coma aberration, spherical aberration, etc.), thereby further improving exposure accuracy such as line width controllability and overlay accuracy.
The invention of claim 16 is an exposure apparatus that illuminates a mask (R) with illumination light and transfers a pattern of the mask onto a substrate (W) via a projection optical system (PL), and is characterized by comprising: an arithmetic unit (21) that calculates changes in anisotropic imaging characteristics due to absorption of the illumination light by the projection optical system; and a focus correction unit (42) that adjusts the positional relationship between the image plane of the projection optical system and the substrate in the optical axis direction of the projection optical system, taking into account the changes in anisotropic imaging characteristics due to absorption of the illumination light by the projection optical system calculated by the arithmetic unit.
This allows the positional relationship between the imaging plane of the projection optical system and the substrate to be adjusted taking into account changes in the anisotropic imaging characteristics due to absorption of illumination light by the projection optical system, thereby improving exposure accuracy.
According to the invention of claim 18, an exposure apparatus that illuminates a mask (R) with illumination light and transfers a pattern of the mask onto a substrate (W) via a projection optical system (PL) is characterized by comprising an imaging characteristic monitoring device (21) that monitors changes in the anisotropic imaging characteristics due to absorption of the illumination light by the projection optical system, and interrupts the exposure operation when the amount of this change reaches a predetermined threshold value.
This makes it possible to prevent exposure defects caused by the anisotropic imaging characteristics of the projection optical system.

The XY stage 18 is actually driven in two dimensions (X and Y) on a base (not shown) by a two-dimensional planar motor or the like, and the Z stage 17 is driven in the Z direction within a predetermined range (for example, a range of 100 μm) by a drive mechanism (not shown). In FIG. 1, these two-dimensional planar motor, drive mechanism, etc. are shown as a wafer drive device 42.

Next, a method for measuring the wafer reflectivity R _{W ,} which is also a prerequisite, will be described.
First, two reflectors (not shown) having known reflectivities R _H and R _L , respectively, are placed on wafer stage WST. Next, as with the above-described irradiation light intensity measurement, main controller 21 sets the exposure conditions (reticle R, reticle blind 7, illumination conditions) to the same as those during actual exposure, and drives wafer stage WST to move the placed reflector with reflectivity R _H directly below projection optical system PL. Next, main controller 21 oscillates light source 1 to synchronously move reticle stage RST and wafer stage WST under the same conditions as actual exposure, while simultaneously capturing output V _H0 of reflectance sensor 10 and output I _H0 of integrator sensor 6 at predetermined sampling intervals. This allows output V _H0 of reflectance sensor 10 corresponding to the synchronous movement position (scanning position), and corresponding output I _H0 of integrator sensor 6, to be stored in memory. As a result, output V _H0 of reflectance sensor 10 and output I _H0 of integrator sensor 6 are stored in memory as functions corresponding to the scanning position of reticle R. Next, the main controller 21 drives the wafer stage WST to move the installed reflector with reflectance R _L to directly below the projection optical system PL, and similarly to the above, stores the output V _L0 of the reflectance sensor 10 and the output I _L0 of the integrator sensor 6 in memory as functions corresponding to the scanning position of the reticle R.

Claims (20)

A projection lens for projecting an image of a first object onto a second object,
A projection lens that is initially adjusted so that its imaging characteristics differ between a first direction perpendicular to its optical axis and a second direction perpendicular to the optical axis and the first direction. 2. The projection lens according to claim 1, wherein the imaging characteristics in the first and second directions are initially adjusted taking into account variations that occur due to absorption of illumination light when illuminated with illumination light of a predetermined shape. 3. The projection lens according to claim 2, wherein the initial adjustment of the imaging characteristics in the first and second directions is performed by shifting the imaging characteristics from the desired imaging characteristics so as to cancel half of the change in the imaging characteristics in the first and second directions caused by the absorption of the illumination light. 4. The projection lens according to claim 2, wherein the imaging characteristic to be initially adjusted is a rectangular distortion having a long side in the first direction. 5. The projection lens according to claim 4, wherein the initial adjustment of the rectangular distortion is performed by making the magnification in the second direction larger than the desired magnification in the first direction. 4. The projection lens according to claim 2, wherein the imaging characteristic to be initially adjusted is a deviation of the imaging position in the first direction and the second direction about the center of the optical axis. The projection lens according to claim 6, characterized in that the initial adjustment of the deviation of the imaging position in the first direction and the second direction around the optical axis center is performed by shifting a predetermined one of the imaging plane of the periodic pattern in the first direction and the imaging plane of the periodic pattern in the second direction closer to the projection optical system than the other. 1. A scanning exposure apparatus that illuminates a mask with illumination light of a predetermined shape while synchronously moving a mask and a substrate, and transfers a pattern of the mask onto the substrate via a projection optical system,
8. A scanning exposure apparatus, comprising: a projection lens according to claim 1, as said projection optical system; and a synchronous movement direction in said second direction. 1. A scanning exposure apparatus that illuminates a mask with illumination light of a predetermined shape while scanning a mask and a substrate relative to each other in a synchronous manner in a predetermined scanning direction, and transfers a pattern of the mask onto the substrate via a projection optical system,
the projection optical system has different imaging characteristics in the scanning direction and in a non-scanning direction perpendicular to the scanning direction,
a focus correction device that adjusts the positional relationship between the image plane of the projection optical system and the substrate in the optical axis direction of the projection optical system by positioning the substrate, taking into account the deviation of the image position in the non-scanning direction and the scanning direction of the projection optical system. 10. The scanning exposure apparatus according to claim 9, further comprising an imaging characteristic monitoring device that monitors changes in anisotropic imaging characteristics due to absorption of the illumination light by the projection optical system, and interrupts the exposure operation when the amount of change reaches a predetermined threshold value. 1. A scanning exposure apparatus that illuminates a mask with illumination light of a predetermined shape while scanning a mask and a substrate relative to each other in a synchronous manner in a predetermined scanning direction, and transfers a pattern of the mask onto the substrate via a projection optical system,
a scanning exposure apparatus comprising an imaging characteristic monitoring device that monitors changes in anisotropic imaging characteristics due to absorption of the illumination light by the projection optical system, and interrupts exposure operation when the amount of change reaches a predetermined threshold. 12. A scanning exposure apparatus according to claim 10, wherein the anisotropic imaging characteristic of the object to be monitored is at least one of rectangular distortion and deviation of the imaging position in the non-scanning direction and the scanning direction from the center of the optical axis. 13. The scanning exposure apparatus according to claim 12, wherein the imaging characteristic monitoring device monitors the change in the rectangular distortion based on the difference between the magnification change in the non-scanning direction and the magnification change in the scanning direction, and monitors the deviation of the imaging position in the non- scanning direction and the scanning direction from the center of the optical axis based on the difference between the imaging plane of the periodic pattern in the non-scanning direction formed on the mask and the imaging plane of the periodic pattern in the scanning direction. 14. A scanning exposure apparatus according to claim 10, wherein the imaging characteristic monitoring device continues to monitor changes in the anisotropic imaging characteristics of the projection optical system even after the exposure operation is interrupted, and resumes the exposure operation when the imaging characteristics have decayed to a predetermined standard. 10. A scanning exposure apparatus according to claim 9, further comprising an imaging characteristic correction device that corrects changes in rotationally symmetric imaging characteristics other than focus of the projection optical system. An exposure apparatus that illuminates a mask with illumination light and transfers a pattern of the mask onto the substrate via a projection optical system,
a calculation unit that calculates a change in anisotropic imaging characteristics due to absorption of the illumination light by the projection optical system;
and a focus correction device that adjusts the positional relationship between the image plane of the projection optical system and the substrate along the optical axis of the projection optical system, taking into account changes in the anisotropic imaging characteristics of the projection optical system due to absorption of the illumination light, which is determined by the calculation device. 17. The exposure apparatus according to claim 16, further comprising an imaging characteristic monitoring device that monitors changes in anisotropic imaging characteristics due to absorption of the illumination light by the projection optical system, and interrupts the exposure operation when the amount of change reaches a predetermined threshold value. An exposure apparatus that illuminates a mask with illumination light and transfers a pattern of the mask onto the substrate via a projection optical system,
an imaging characteristic monitoring device that monitors changes in the anisotropic imaging characteristics caused by absorption of the illumination light by the projection optical system, and interrupts the exposure operation when the amount of change reaches a predetermined threshold. 19. The exposure apparatus according to claim 16, wherein the anisotropic imaging characteristic is at least one of distortion and focus. The exposure apparatus of claim 16 , wherein the anisotropic imaging characteristics include non-rotationally symmetric imaging characteristics.