JPH04208514A - Device and method of determining optical axis of alignment optical system - Google Patents

Abstract

PURPOSE:To improve the accuracy of axial alignment and adjustment by conducting the axial alignment of each optical central axis and the adjustment of the position of projection and projection angle of the alignment light or each alignment optical system by regulating an entrance pupil in a space. CONSTITUTION:When the entrance pupil 41 of a reduction projection lens 40 is positioned outside the reduction projection lens 40, when the entrance pupil 41 is positioned at a section lower than the surface of a wafer, an optical-axis determining device 45, to which a plane mirror 44 is installed so as to run parallel with a reticle and the wafer and so that reference beams 42 are projected vertically, is used. According to the optical-axis determining device, the entrance pupil 41 is shifted to a position 46 symmetric regarding the plane mirror 45 by reflecting reference beams by the plane mirror 45. The axial alignment, etc., of an optical central axis are enabled similarly by placing a pinhole plate 47 having a pinhole having the same diameter as the diameter of reference beams at the position 46. Consequently, the axial alignment of each optical central axis and the adjustment of the position of projection and projection angle of the alignment light of each alignment optical system are performed simply with high accuracy.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an optical axis alignment device and optical axis alignment method for an alignment optical system in an optical transfer device using a projection lens, and in particular to an optical axis alignment device and an optical axis alignment method for an optical transfer system using a projection lens. The present invention relates to an optical axis alignment device and an optical axis alignment method for an alignment optical system, which can easily and accurately align the optical center axis of the optical system, the projection position of alignment light, and the projection angle.

(Prior Art) Conventionally, in the manufacturing process of semiconductor integrated circuits, optical transfer apparatuses typified by reduction projection exposure apparatuses have been frequently used. In a reduction projection exposure apparatus, a wafer, which is a photosensitive substrate, is usually placed below a reduction projection lens, and a reticle on which a circuit pattern is formed is placed above the reduction projection lens.

By irradiating exposure light from above the reticle, the circuit pattern formed on the reticle is transferred onto the wafer via a reduction projection lens. In the current manufacturing process of semiconductor integrated circuits, many types of circuit patterns are overlapped, so this transfer must be performed with high positional accuracy. For this reason, a reduction projection exposure apparatus usually has a reticle alignment optical system for aligning the reticle with the reduction projection lens, and a wafer alignment optical system for aligning the wafer with the reduction projection lens. We are prepared. Each alignment optical system is configured to detect the position based on coordinates set with the optical center axis of each optical system as a reference, and perform alignment with the optical center axis of the reduction projection lens. Furthermore, the alignment light of each optical system must be incident toward the center position of the entrance pupil of the reduction projection lens. Therefore, a positional shift may occur between the optical center axis of each alignment optical system and the optical center axis of the reduction projection lens, or the alignment light of each optical system may be incident toward the center position of the entrance pupil of the reduction projection lens. If this is not done, there is a problem in that the alignment accuracy of transfer deteriorates and pattern deviation occurs when circuit patterns are superimposed.

In order to solve this problem, a reduction projection exposure apparatus as shown in FIG. 8 is used. In the figure, 50 is a vibration isolation table. A surface plate 51 is placed on the vibration isolation table 50. A wafer table 52 is installed on the surface plate 51, and a first pedestal 53 is placed thereon. Positioning blocks 54a and 54b are attached to the reference surface of the first pedestal 5B. This positioning block 54a154b
Accordingly, a lens holder 57 holding a transfer light illumination optical system 55 and a reduction projection lens 56, respectively, is positioned and placed on the first pedestal 53. Lens holder 5
A positioning block 54c is attached to the reference plane 7. The second pedestal 58 is positioned and placed on the lens holder 57 by the positioning block 54c. A positioning block 54d is attached to the reference surface of the second pedestal 58. The reticle table base 59 is positioned and placed on the second pedestal 58 by the positioning block 54d. A positioning block 54 is provided on the reference surface of the reticle table base 59.
e is attached. The reticle alignment optical system 60 is positioned and placed on the reticle table base 59 by the positioning block 54e.

Further, a wafer alignment optical system 61 is attached to the transfer light illumination optical system 55 so as to be positioned by fitting.

As described above, the conventional reduction projection exposure apparatus uses a positioning block or is configured by a fitting method, and thereby the reduction projection lens 56, the reticle alignment optical system 60, and the wafer alignment optical system 6.
1 can be aligned. Further, the projection position and projection angle of each alignment light beam with respect to the center position of the entrance pupil of the reduction projection lens 56 are adjusted by actually performing transfer and checking.

However, in aligning the optical center axis using such a reduction projection exposure apparatus, the alignment accuracy depends on the machining accuracy of each frame, base, and block. This alignment error is an accumulation of machining errors of each member. Normally, it is impossible to reduce machining errors of these members to zero, so errors inevitably occur in axis alignment. Furthermore, since the entrance pupil of the alignment light does not physically exist in space but exists within the reduction projection lens 56, the projection position and projection angle of the alignment light of each alignment optical system can be adjusted as described above. Since the transfer is repeated and adjusted through the reduction projection lens 56 mounted with accumulated machining errors, the overlay accuracy of the transferred patterns decreases, and
There is also the problem that this takes a lot of time.

The reason why the overlay accuracy of the transferred patterns decreases due to the positional deviation of each optical center axis is as follows. here,
An example will be described in which a positioning mark provided on a wafer is detected by the wafer alignment optical system 61, and the wafer table 52 is moved based on this position information to align the wafer.

As shown in FIG. 9(A), alignment light from the wafer alignment optical system 61 is irradiated onto the wafer 62 on the wafer table 52 via the reduction projection lens 56. In the figure, 63 is a condenser lens for transfer light, and 64 is a lens for correcting chromatic aberration between the transfer light and alignment light 65. The correction lens 64 and the condenser lens 63 are set so that the alignment light 65 passes therethrough and is condensed at the center P of the position of the entrance pupil 66 of the reduction projection lens 56 . The alignment light 65 is irradiated so that the alignment light enters the center P of the entrance pupil 66 of the reduction projection lens 56 at a predetermined angle with respect to the lens center axis 67 of the reduction projection lens 56 . This is adjusted based on coordinates set with reference to the optical center axis of the wafer alignment optical system 61. That is, FIG. 9(B)
As shown in FIG.
The alignment light 65 is made incident at a position far away from the target.

If there is a positional deviation between the optical center axis of the wafer alignment optical system 61 and the lens center axis 67 of the reduction projection lens 56 due to machining errors, it is indicated by a broken line 65' in FIG. 9(B). The alignment light 65 is Δε
Then, the light beam is shifted and incident on the reduction projection lens 56. Therefore, as shown in FIG. 9(A), the alignment light 65
is an angle α to the normal line of the wafer 62 on the upper surface of the wafer 62.
It is irradiated at an angle. The top surface of the wafer 62 is located at the first position.
The position indicated by the solid line in Figure 0, that is, the reduction projection lens 56
When the alignment light 65 is at the focal position (Z-0) 62, even if the alignment light 65 is irradiated at a certain angle, there is no problem because the reflected light returns to the incident position. However, due to irregularities on the surface of the wafer table 52, pitching changes, etc., the position of the upper surface of the wafer 62 is shifted upward or downward from the position 62' indicated by the two-dot chain line in FIG. When the alignment light 65 is deviated by ΔZ in the direction, the reflected light does not return to the incident position if the alignment light 65 is irradiated at a certain angle. Therefore, according to Atsube's principle, an error of X-ΔZα occurs in the alignment direction (here, the X direction). A position with this error will be determined as an offset position by the system. As a result, the accuracy of overlapping the transferred patterns is reduced.

Next, a case where the alignment light 65 with respect to the position of incidence @66 of the reduction projection lens 56 is shifted by an angle Δθ on the reticle 68 will be described. Figure 11 (A).

As shown in solid line 65 and broken line 65-' in (B),
The alignment light 65 is incident on the reduction projection lens 560 with an angle Δθ deviation on the reticle 68 due to the machining error of the component.
66, the upper surface of the wafer 62 is irradiated with a shift of Δε. A position with this error will be determined as an offset position by the system. As a result, the overlay accuracy of the transferred patterns is reduced.

Note that in the reticle alignment optical system 6o, as well as the wafer alignment optical system 61, an error in the position or angle of the alignment light with respect to the position of incidence l1166 of the reduction projection lens 56 becomes an alignment error and reduces the overlay accuracy of transferred patterns. let However, the alignment light of the reticle alignment optical system 60 is ultraviolet light, the same as the transfer light, and the wafer alignment optical system 60
Since this light has a different wavelength from the first alignment light, the position of the entrance pupil is also different.

(Issue 8 to be solved by the invention) As described above, in the method of aligning the optical axis in a conventional optical transfer device, typified by a reduction projection exposure device, the alignment accuracy of each optical center axis depends exclusively on the machining accuracy. As a result, the alignment accuracy deteriorates due to accumulated machining errors. Therefore, the error in overlapping the transferred patterns becomes relatively large. Another problem is that it takes a lot of time to align the optical center axis and adjust the projection position and projection angle of the alignment light.

The present invention has been made in view of these points, and allows alignment of each optical center axis and adjustment of the projection position and projection angle of the alignment light of each alignment optical system to be performed easily and with high precision. It is an object of the present invention to provide an optical axis alignment method and an optical axis alignment device used in this method.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a transfer optical system for transferring a pattern formed on a reticle onto a photosensitive substrate via a projection lens, and a reticle alignment optical system for positioning the reticle. system and
An optical axis alignment device for an alignment optical system of an optical transfer device, comprising an alignment optical system for a photosensitive substrate for positioning a photosensitive substrate, which is installed in place of the projection lens, and includes an alignment optical system for the projection lens and the reticle. The optical center axes of the alignment optical system and the photosensitive substrate alignment optical system are aligned, and the projection position and projection angle of the alignment light of the reticle alignment optical system and the photosensitive substrate alignment optical system are performed. Provided is an optical axis alignment device for an alignment optical system, characterized in that it is equipped with means for defining an entrance pupil in space for adjusting.

The present invention also provides a transfer optical system for transferring a pattern formed on a reticle onto a photosensitive substrate via a projection lens, a reticle alignment optical system for positioning the reticle, and a photosensitive substrate for positioning the photosensitive substrate. The projection lens of the optical transfer device equipped with an alignment optical system for a reticle is replaced with an optical axis alignment device having a means for defining an entrance pupil in space, and the projection lens, the alignment optical system for a reticle, and the The optical center axis of each of the photosensitive substrate alignment optical systems is aligned, and the projection position and projection angle of the alignment light of the reticle alignment optical system and the photosensitive substrate alignment optical system are adjusted. The present invention provides a method for determining the optical axis of an alignment optical system.

(Operation) According to the present invention, the alignment of each optical center axis and the adjustment of the projection position and projection angle of the alignment light of each alignment optical system are performed by defining an entrance pupil in space. . Since these axis alignments and adjustments are performed without depending on the machining accuracy of each member of the optical transfer device, more accurate axis alignment and adjustments can be performed.

Further, since the optical axis alignment device of the present invention adopts the same mounting method as the projection lens of the optical transfer device,
It is easy to attach and detach from the optical transfer device, and there is no need to increase the size of the device.

(Example) Hereinafter, an example of the present invention will be specifically described with reference to the drawings.

FIG. 1 is an explanatory diagram showing an example of the case where the optical axis alignment device of the present invention is applied to a reduction projection exposure device.

In the figure, 10 is a vibration isolation table. A surface plate 11 is placed on the vibration isolation table 10. A wafer table 12 is installed on the surface plate 11, and a first pedestal 13 is also placed. A plane mirror (optical flat) 14 is placed on the wafer table 12 . Positioning blocks 15a and 15b are attached to the reference surface of the first pedestal 13. The transfer light illumination optical system 16 is positioned and held by this positioning block 15a.

When aligning the optical axis, an optical axis aligning device 17 is attached in place of the reduction projection lens, and a holder 18 that holds the centering device 17 is positioned on the first pedestal 13 by the positioning block 15b. . A pinhole portion 19 is formed in the optical axis alignment device 17 . Note that the diameter of one pinhole portion is the same as the diameter of the reference beam 20 irradiated from the transfer light illumination optical system 16. Further, the pinhole portion 19 coincides with the optical center axis of the reduction projection lens, and also spatially coincides with the center position of the entrance pupil. The optical axis alignment device 17 and the reduction projection lens are mounted in the same manner so that they are compatible with each other. Here, the mounting method to the holder 18 is a fitting method. A positioning block 15c is attached to the reference surface of the holder 18. The second pedestal 21 is positioned and placed on the holder 18 by the positioning block 15c. A positioning block 15d is attached to the reference surface of the second pedestal 21. The reticle table base 22 is positioned by the positioning block 15d and placed on the second mount 21.
is placed on top. A positioning block 15e is attached to the reference surface of the reticle table base 22. Further, a reticle table 23 is placed on the reticle table base 22. A reticle alignment optical system 24 is positioned and placed on the reticle table base 22 by the positioning block 15e. Further, a wafer alignment optical system 25 is attached to the transfer light illumination optical system 16 so as to be positioned by fitting. A pinhole plate 27 having a pinhole 26 having the same diameter as the reference beam 20 is removably attached to the transfer light illumination optical system 16 so as to coincide with the transfer optical axis.

In the apparatus configured as described above, a method for aligning the optical center axes of each alignment optical system, that is, aligning the optical axis will be described.

First, the reference beam 20, which is visible light, is irradiated from the transfer light illumination optical system 16. At this time, the reference beam 20 passes through the pinhole 26 and passes through the pinhole section 19 of the optical axis alignment device 17.
The position of the optical axis alignment device 17 is adjusted so that the light reflected by the plane mirror 14 follows the same path and passes through the pinhole portion 19 and the pinhole 26. Figure 2 shows the reference beam 20 and the optical axis alignment device 1.
7 is a diagram showing the positional relationship with the pinhole portion 19. FIG. While visually checking from above the optical axis aligning device 17, move the optical axis aligning device 17 so that one pinhole portion matches the reference beam 20 and the reflected light of the reference beam follows the same path.
Adjust the position. Thereby, the optical center axis of the optical axis alignment device 17 can be aligned with respect to the reference beam 20. Therefore, the optical center axis of the reduction projection lens compatible with the optical axis alignment device 17 is aligned with the reference beam 20.

Next, as shown in FIG. 3, a first auxiliary member 29 having a pinhole 28 having the same diameter as the reference beam 20 is inserted so that the pinhole 28 coincides with the optical center axis of the reticle alignment optical system 24. Attach it to the reticle alignment optical system 24 in this way.

Further, a second auxiliary member 31 having a pinhole 30 having the same diameter as the reference beam 20 is attached to the wafer alignment optical system 25 so that the pinhole 30 coincides with the optical center axis of the wafer alignment optical system 25. Attach. Note that the transfer light illumination optical system 16 includes a dichroic mirror 32.
or installed. In the device configured in this way,
The reference beam 20 is irradiated again from the transfer light illumination optical system 16. The reference beam 20 deflected by the dichroic mirror 32 sequentially passes through the pinholes 26 and 28 and the pinhole section 19 and enters the plane mirror 14, and the reflected light from the plane mirror 14 follows the same path and enters the pinhole section. 1
The positions of the reticle alignment optical system 24 and the wafer alignment optical system 25 are adjusted so that the reticle alignment optical system 24 and the wafer alignment optical system 25 sequentially pass through the dichroic mirror 32 and the pinholes 28 and 26. The position of the alignment optical system is adjusted in the same way as the optical center axis of the optical axis alignment device is aligned.

In this way, the optical center axes of the reticle alignment optical system 24 and the wafer alignment optical system 25 are aligned with the reference beam 20.

Next, the projection beam of the alignment light of the alignment optical system is adjusted so as to be incident on the pinhole portion 19 of the optical axis alignment device W17, and the projection position and the projection angle are adjusted. The projection beam of the alignment light of the reticle alignment optical system 24 is the same ultraviolet light as the transfer light, so the projection position and projection angle can be adjusted by hitting the projection beam instead of using a pinhole. It is preferable to use a mark that emits fluorescence. In addition, an excimer laser or the like is used for the alignment light of the reticle alignment optical system 24, and a He-Ne laser or the like is used for the alignment light of the wafer alignment optical system 25, and since each wavelength is different, it is inevitable that The position of the entrance pupil is different.

In this way, the optical central axes of the optical axis alignment device 17, that is, the reduction projection lens, the reticle alignment optical system 24, and the wafer alignment optical system 25, are aligned with the reference beam 20 that serves as a reference for alignment. . Further, the projection position and projection angle of the alignment light are almost completely adjusted.

The accuracy of alignment of the optical center axis can be easily increased by reducing the diameter of the reference beam 20. Thereby, the alignment accuracy of the transfer pattern can be further improved.

As shown in FIG. 4(A), when the position of the entrance pupil 41 of the reduction projection lens 40 is outside the reduction projection lens 40, that is, when the entrance pupil 41 is located below the wafer surface, the fourth As shown in Figure (B), an optical axis alignment device 45 is used in which a plane mirror 44 is installed so that it is parallel to the reticle and the wafer and the reference beam 42 is perpendicularly incident thereon.

According to this optical axis alignment device, the reference beam is aligned with the plane mirror 4.
By reflecting at 5, the incident @41 becomes a plane mirror 45
is moved to a symmetrical position 46 with respect to. By placing a pinhole plate 47 having a pinhole with the same diameter as the diameter of the reference beam at this point W46, the optical center axis can be aligned in the same way.

Furthermore, as described above, when using a mark that emits fluorescence when exposed to transfer light (ultraviolet light) instead of using the pinhole plate 47, for example, as shown in FIG. In order to confirm the size and optical center axis, an optical axis alignment device 52 is used, which is equipped with ground glass 50 having a mark that emits light when it is hit by transfer light. Thereby, it can be confirmed whether the imaging position of the transfer light by the transfer light illumination optical system matches the position of the entrance pupil of the reduction projection lens and whether the optical center axis is aligned.

The present invention can also be applied when alignment is performed using the optical heterodyne method. FIG. 6 is an explanatory diagram showing a wafer alignment optical system using the optical heterodyne method. Frequency f from first frequency shift mechanism 60
The first alignment light is transmitted and diffracted by the alignment mark 62 of the reticle 61, and becomes a +1st order (or -1st order) diffracted light 1 and a 0th order diffracted light L1. Further, the alignment light of frequency f2 from the second frequency shift mechanism 63 is transmitted and diffracted by the alignment mark 64 of the reticle 61, and becomes 11th-order (or +1st-order) diffracted light g2 and 0th-order diffracted light L2. . The projection position and projection angle of the alignment light are adjusted so that the diffracted light g and the diffracted light g2 are imaged onto the wafer 65. Therefore, the diffracted light g1 and the diffracted light g2 do not pass through the incident @66. However, since the diffracted light L1 and the diffracted light L2 are incident on the entrance pupil 66, optical center axis alignment etc. can be performed in the same manner.

In this example, a plane mirror was placed on the wafer table when aligning the optical center axis.
A photoelectric sensor may be placed on the wafer table instead of the plane mirror. In this case, alignment is performed while adjusting the optical axis alignment device and alignment optical system so that the output of the photoelectric sensor is maximized. Thereby, alignment can be performed with higher precision.

Further, in this embodiment, a single-telecentric projection lens is used to adjust the projection position and projection angle of the alignment light of each optical system, but a double-telecentric projection lens may be used. In this case, the entrance pupil is at an infinite position, so for example, as shown in FIG. 7, a plane mirror 76 is mounted so that it is parallel to the reticle 70 and the wafer and that the reference beam 74 is incident perpendicularly thereto. The optical axis alignment device 78 is used. Therefore, the alignment light reflected by the plane mirror 76 returns to its projection position. Therefore, by adjusting the reflected light to match the incident light, alignment of the optical center axis can be performed in the same way.

When aligning the optical center axis and adjusting the projection position and projection angle of the alignment light in each alignment optical system independently, the alignment optical system must be installed in one method or the optical transfer device that aligns the optical axis must be aligned. It is possible to use an optical axis adjustment device that is the same as that of the optical system and is compatible with each alignment optical system equipped with an optical axis alignment device. By using this device, assembly and adjustment steps for the device can be reduced.

The present invention is not limited to application to a reduction projection exposure apparatus, but includes a transfer optical system that transfers a pattern formed on a reticle to a photosensitive substrate via a projection lens, and a reticle alignment optical system that positions the reticle. The present invention can be applied to any optical transfer device including a photosensitive substrate alignment optical system for positioning a photosensitive substrate.

[Effects of the Invention] As explained above, the optical axis alignment device and optical axis alignment method of the alignment optical system of the present invention are capable of aligning each optical center axis, and determining the projection position and projection position of the alignment light of each alignment optical system. The angle can be adjusted easily and with high precision, thereby improving the overlay accuracy of the transferred patterns.

Furthermore, since the optical axis alignment device of the alignment optical system of the present invention can be attached to and removed from an existing device, it is possible to avoid increasing the size and complexity of the device.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram showing an example of applying the optical axis alignment device of the present invention to a reduction projection exposure apparatus, and FIG. 2 is a diagram showing the positional relationship between the reference beam and the pinhole portion of the optical axis alignment device. ,
FIG. 3 is a schematic explanatory diagram of aligning the optical center axis using the optical axis alignment device of the present invention, and FIGS. A schematic explanatory diagram showing another aspect of aligning the central axes; FIG. 8 is a schematic explanatory diagram showing a conventional reduction projection exposure apparatus; FIGS. 9(A), 10, and 11(A) 9 is a schematic explanatory diagram for explaining the deviation of the projection position and projection angle of alignment light in a conventional reduction projection exposure apparatus, and FIG. 9(B) is the X of FIG.
FIG. 11(B) is an enlarged view of the Y section in FIG. 11(A). 10... Vibration isolation table, 11... Surface plate, 12... Wafer table, 13. First mount, 14, 45.76... Plane mirror, 15a to 15e... Positioning block, 1
6...Transfer light illumination optical system, 17,52.78...Optical axis alignment device, 18...-Holder, 19...Pinhole section, 20,42.74...Reference beam, 21.Second 22. Reticle table base, 23. Reticle table, 24. Reticle alignment optical system.
25. Wafer alignment optical system, 26.28.30
...Pinhole, 27.47 ...Pinhole plate, 29
...First auxiliary member, 31...Second auxiliary member, 32
・Dichron clock mirror, 40 ・Reduction projection lens,
41.66... Entrance pupil, 44... Wafer, 46...
- Symmetrical position, 50 - Ground glass, 60... First frequency shift mechanism, 61.70... Reticle, 62.6
4. Alignment mark, 63... Second frequency shift mechanism, 65... Wafer. Applicant's representative Patent attorney Takehiko Suzue 1o Figure 1 Figure 2 No. 10 Figure 3 41-/ Figure 4 (B) Figure 4 (A)), 1. ．． 1 Figure 5 Figure 6 Father Figure 8 Figure 9 (B) Figure 10 Figure 11 (A) Figure 11 (8)

Claims (2)

[Claims] (1) A transfer optical system that transfers a pattern formed on a reticle onto a photosensitive substrate via a projection lens, a reticle alignment optical system that positions the reticle, and a photosensitive substrate alignment optical system that positions the photosensitive substrate. an optical axis alignment device for an alignment optical system of an optical transfer device, which is installed to replace the projection lens;
The optical center axes of the projection lens, the reticle alignment optical system, and the photosensitive substrate alignment optical system are aligned, and the alignment light of the reticle alignment optical system and the photosensitive substrate alignment optical system is aligned. An optical axis determining device for an alignment optical system, comprising means for defining an entrance pupil in space for adjusting a light projection position and a light projection angle. (2) A transfer optical system that transfers the pattern formed on the reticle onto the photosensitive substrate via a projection lens, a reticle alignment optical system that positions the reticle, and a photosensitive substrate alignment optical system that positions the photosensitive substrate. The projection lens of the optical transfer device having a system is replaced with an optical axis alignment device having a means for defining an entrance pupil in space, and the projection lens, the alignment optical system for the reticle, and the alignment optical system for the photosensitive substrate are installed. An alignment optical system characterized by aligning the optical center axes of each of the alignment optical systems and adjusting the projection position and projection angle of the alignment light of the reticle alignment optical system and the photosensitive substrate alignment optical system. How to align the optical axis of the system.