JPH07142331A - Projection aligner - Google Patents

Abstract

PURPOSE:To speedily control a relative misalignment during the scanning exposure of a mask stage and a substrate stage. CONSTITUTION:In a step and scan system aligner, a relative misalignment is calculated from the original position relationship being scanned of a reticle 14 and a wafer 5 according to the position information of a reticle stage interferometer 16 and that of a wafer stage interferometer 9. Transparent plates 20 and 21 are inclined according to the operation result, thus shifting a projection image onto the wafer 5 of the reticle 14 and compensating a relative misalignment during scanning exposure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning type projection exposure apparatus used for manufacturing semiconductor elements, liquid crystal display elements and the like, and more particularly to a positioning method during scanning exposure.

[0002]

2. Description of the Related Art Conventionally, there are roughly two types of exposure methods for this type of projection exposure apparatus. One is a method of exposing a photosensitive substrate such as a wafer or a plate by a step-and-repeat method through a projection optical system having an exposure field that can include the entire pattern of an original image pattern.
The other is a scanning method in which the original image pattern and the photosensitive substrate are opposed to each other with the projection optical system interposed therebetween, and the original image pattern and the photosensitive substrate are relatively scanned and exposed under the arcuate slit illumination light. The former step-and-repeat type stepper is a mainstream device in recent lithography processes. This is because the resolution, overlay accuracy, throughput, etc. are all higher than those of the latter aligner employing the scan exposure method, and it is considered that steppers will be the mainstream for some time to come.

In this step-and-repeat method, an alignment device provided in the exposure device is used to correct the positional deviation between the original image pattern placed on the mask stage and the photosensitive substrate placed on the substrate stage before exposure. Then do. Then, when the relative alignment between the original image pattern and the photosensitive substrate is completed by the alignment device, the original image pattern is irradiated with illumination light from the exposure illumination system for a predetermined time, during which no positional deviation between the original image pattern and the photosensitive substrate occurs. In this state, the photosensitive substrate is exposed.

Incidentally, a new method for achieving high resolution even in the recent projection scan exposure method is SPIE Vol.
Fourth of 1088 Optical / Laser Microlithography II (1989)
On pages 24-433, it was proposed as a step-and-scan method. The step-and-scan method includes a scan method in which the original image pattern is scanned in a one-dimensional direction while the wafer is one-dimensionally scanned at a speed synchronized with it, and a method in which the wafer is step-moved in a direction orthogonal to the scanning exposure direction. It is a mixture.

FIG. 4 is a diagram for explaining the concept of the step-and-scan method. Here, X on the photosensitive substrate W is used.
It is assumed that a row of shot regions (one chip or multi-chips) in the direction is scanned and exposed by the arcuate slit illumination light RIL, and the photosensitive substrate (wafer) W is stepped in the Y direction. In the figure, the arrow shown by the broken line represents the exposure route of step-and-scan (hereinafter referred to as S & S), and the S & S exposure is performed in the order of the shot areas SA ₁ , SA ₂ , ..., SA ₆ , and then the wafer. Similarly, S & S exposure is performed in the order of shot areas SA ₇ , SA ₈ , ... SA ₁₂ arranged in the center of W in the Y direction. S & S disclosed in the above document
In the aligner of the method, since the image of the reticle pattern illuminated by the arc-shaped slit illumination light RIL is imaged on the wafer W via the 1/4 × reduction projection optical system, the reticle stage is scanned in the X direction. Speed is X of wafer stage
It is precisely quadrupled with respect to the directional scanning speed. Further, the arc-shaped slit illumination light RIL is used as a projection optical system using a reduction system in which a refraction element and a reflection element are combined, and various aberrations in a narrow range of image height (annular zone) apart from the optical axis by a certain distance. This is to obtain the advantage that is almost zero. An example of such a catoptric reduction projection system is, for example, USP.
4,747,678.

[0006]

In the step-and-repeat type exposure apparatus, since the mask stage and the substrate stage need only be stationary in a predetermined positional relationship during exposure, a factor that disturbs the positional relationship (stage The structure for suppressing the static accuracy can be easily realized.
On the other hand, in the step-and-scan method, the mask stage and the substrate stage move relative to each other at a constant speed ratio during exposure. Therefore, during this movement, the mask stage (original pattern) A relative displacement may occur between the substrate and the substrate stage (photosensitive substrate).

In this step-and-scan method, as a method of correcting the relative positional deviation that occurs during exposure, a fine movement mechanism is placed on the scanning mask stage or the substrate stage, and the relative positional deviation amount between the mask stage and the substrate stage is set. It is conceivable to drive the fine movement mechanism in accordance with the above and constantly correct the exposure. However, in this method, it is difficult to reduce the weight of the fine movement mechanism because of the structure, and the response is not always good. Therefore, it is an object of the present invention to provide a highly responsive device that corrects a positional deviation (uneven speed) that occurs during exposure.

[0008]

According to the present invention, in a step-and-scan type projection exposure apparatus, it is possible to tilt in a first direction that is the same as the scanning direction of the mask stage, or in a second direction that is orthogonal to the first direction. Transparent plates 20 and 21 are provided in the imaging optical path between the mask and the photosensitive substrate, and a mask stage position detection device (reticle stage interferometer) 16 and a substrate stage position detection device (wafer stage interferometer) 9 are provided. A controller for detecting the relative positional deviation amount during scanning exposure based on the position information output from the device, or the variation amount of the speed ratio based on the speed signals output from the reticle stage driving device 17 and the wafer stage driving device 8. 23 and a transparent plate drive device 22 for inclining the transparent plate according to the amount of positional deviation.

[0009]

According to the present invention, the original image pattern image projected on the photosensitive substrate is projected by the projection optical system by inclining the transparent plate provided between the mask (reticle) on which the original image pattern is formed and the photosensitive substrate. Uses the function to shift a minute amount within the field of view. Therefore, a transparent plate, which is generally lighter than that in which a fine movement mechanism is placed on the mask stage and the position of the original image pattern is corrected during scanning exposure, can be used, so that high-speed response can be obtained.

Further, when the transparent plate is provided in the step-and-repeat system, a transparent plate that covers the entire exposure range (projection field of view) is required, whereas in the step-and-scan system, only the exposure slit area needs to be covered. The area of the plate can be reduced, and the responsiveness can be increased.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The step-and-scan type device configuration described in the present embodiment is basically disclosed in Japanese Patent Laid-Open No. 4-196513.
Since the device configuration is the same as that disclosed in the publication, the basic part thereof will be briefly described. FIG. 1 shows the configuration of a projection exposure apparatus according to an embodiment of the present invention. Illumination light emitted from a light source such as a mercury lamp or an excimer laser is shaped into a rectangular slit-shaped illumination field by an imaging illumination field diaphragm. Then, it is projected onto the reticle 14.
The pattern existing in the illumination area on the reticle 14 is projected and exposed on the wafer 5 via the projection lens 10. Here, the reticle 14 scans from the left side to the right side at a constant speed V in the plane of FIG. 1, and at the same time, the wafer 5 moves from right to left on the plane at a constant speed V / M (1 / M is the projection lens reduction magnification). The scanning exposure is achieved by scanning.

The structure relating to the driving of the reticle 14 and the wafer 5 will be described. On the reticle support 11, a reticle Y-axis stage that can be driven in the Y-axis direction (left-right direction with respect to the paper surface) for scanning exposure. A reticle fine movement stage 13 capable of highly precise fine position control in the X, Y, and θ directions is provided on the reticle 14.
Is held on the reticle fine movement stage 13. A movable mirror 15 is arranged on the reticle fine movement stage 13, and a two-dimensional coordinate position is constantly monitored by a reticle stage interferometer 16 arranged on the reticle support 11. On the other hand, a Y-axis stage 2 that can be driven in the Y-axis direction for scanning exposure is placed on the wafer stage support 1, and an X-axis stage 3 that can be driven in the X-axis direction is provided thereon. And on top of that, Z perpendicular to the XY plane
Z that moves parallel to the direction and makes a minute rotation in the XY plane
A θ-axis stage 4 is provided. The wafer 5 is held on this by vacuum. A movable mirror 7 is provided on the Zθ axis stage 4, and the wafer stage is driven to drive the wafer 5 at an arbitrary position or speed based on the two-dimensional coordinate position of the movable mirror 7 monitored by the wafer stage interferometer 9. A device 8 is provided. Further, as will be described later, a wafer coordinate system determined by the wafer stage interferometer 9,
There is a fiducial mark plate 6 (hereinafter referred to as FM6) on the Zθ axis stage 4 in order to correspond to the reticle coordinate system determined by the reticle stage interferometer 16. The reticle alignment device 18 for observing the mark on the FM 6 and the mark on the reticle 14 is provided by the deflection mirror 1.
It is provided together with 9.

Further, a wafer alignment device 24 for observing the mark on the wafer 5 is provided near the projection lens 10. The alignment between the reticle 14 and the wafer 5 is performed by obtaining the relative positional relationship between the projected position of the center point of the reticle 14 and the detection center point of the wafer alignment device 24 via the FM 6, and the wafer alignment device 24 immediately before the exposure to the wafer 5 This is done by aligning (detecting) the upper alignment mark.

Now, the transparent plate 21 provided in the projection optical path between the reticle 14 and the projection lens 10 is constructed so as to be tiltable in the direction orthogonal to the scanning direction, and the transparent plate 20 is arranged in the scanning direction. It is designed to be tiltable. Then, the transparent plate driving device 22 drives the transparent plates 20 and 21 from the original position by the tilt amount based on the instruction from the control device 23.

At the time of reticle alignment, the control device 23 controls the reticle stage drive device based on the alignment signal received from the reticle alignment device 18 and indicating the positional relationship between the FM 6 and the position information from the wafer stage interferometer 9. 17 has a function of instructing the positions of the scanning start point and the end point, and the correspondence with the wafer coordinate system. Further, the control device 23 gives an operation command to the wafer stage driving device 8 and the reticle stage driving device 17 at the time of exposure so as to perform scanning at a predetermined speed ratio, and also the two-dimensional coordinates of the wafer coordinate system and the reticle coordinate system during exposure. The position change is monitored by the wafer stage interferometer 9 and the reticle stage interferometer 16, and the reticle 1
4 has a function of calculating the relative positional deviation amount from the original positional relationship during scanning exposure of the wafer 4 and the wafer 5 in real time, and giving an instruction of the inclination amount of the transparent plate 20 or 21 based on the calculation result.

FIG. 2A shows an arrangement example of the transparent plate with respect to the visual field 26 of the projection lens when the transparent plate 27 of this kind is provided in the case of the step-and-repeat method, but it is effective on the reticle. While a transparent plate having a size that covers the entire exposure range 25 is required, the step-and-scan method requires a transparent plate 2 as shown in FIG.
It can be seen that 0 and 21 may have a size that covers the rectangular slit illumination area that illuminates the reticle. Therefore, in the step-and-scan method, the size and weight of the transparent plate can be reduced, controllability is improved, and high speed control during exposure becomes possible.

FIG. 3 shows the alignment errors generated during step-and-scan exposure classified into three types. FIG. 3A shows an offset in the X and Y directions of the entire shot, which is caused by an error in specifying the relative positional relationship between the reticle and the wafer during alignment. In this figure, the relationship between the ideal shot area A and the actually exposed shot area B is shown. Next, FIG. 3B shows a case where the reticle and the wafer fluctuate relative to each other in the longitudinal direction of the slit illumination region 28, and the shot region D actually exposed with respect to the ideal shot region C is distorted. Has occurred. In FIG. 3B, when the relative scanning of the reticle and the wafer advances by the width L of the slit illumination region 28 in the scanning direction, the fluctuation in the direction orthogonal to the scanning becomes the allowable value or more. Furthermore, FIG. 3 (3) to (5)
Indicates the fluctuation within the width L of the slit illumination region 28. FIG. 3 (4) shows that the slit moves in the shot area E from the position F to the position G by the distance of the slit width L. If fluctuation occurs in the X direction perpendicular to the scanning direction as shown in the graph of FIG. 3C during this period, the image projected on the point H in the ideal shot area E of FIG. Image obtained as an integration with the resist image) is an ideal pattern image I as shown in FIG.
On the other hand, it can be seen that the intensity distribution deteriorates like the pattern image J. This also applies to fluctuations generated in the scanning direction.

These errors are caused by the wafer stage interferometer 9
And the reticle stage interferometer 16 can be read from the difference between the measured position values, the difference between the measured values of the wafer stage interferometer 9 and the reticle stage interferometer 16 is calculated by the controller 23 during exposure, and the difference is calculated. When the transparent plate driving device 22 tilts the transparent plates 20 and 21 at a high speed when the allowable value is exceeded, the above various errors can be removed.

Here, a method of correcting an error in the scanning direction using the transparent plate 20 will be specifically described. For example, a 1/5 times reduction projection optical system is used for the projection lens 10, and the reading resolution of the wafer stage interferometer 9 is 0.01 μm.
Read resolution of reticle stage interferometer 16 is 0.0
In the case of 2 μm, the ratio P _w / P _{r of the} number of pulses per unit time between the pulse signal P _w output from the wafer stage interferometer 9 and the pulse signal P _r output from the reticle stage interferometer 16 during exposure. Is 5/2. Control device 2
3 constantly monitors this ratio, for example, every few milliseconds, and when a preset allowable value is exceeded, a drive signal corresponding to the deviation amount is sent to the transparent plate driving device 22 to drive the transparent plate 20. The above arithmetic processing requires high-speed processing, so it is better than processing using software.
A control method using a digital arithmetic circuit (hardware) that is a combination of a divider, a comparator and the like is desirable.

In the above embodiment, the wafer stage interferometer 9 is used.
Position detection with the reticle stage interferometer 16 and
The amount of relative positional deviation from the original positional relationship during the scanning of the wafer and reticle is detected, and control is performed so as to correct it. Aside from this method, for positional deviation control in the scanning direction, a circuit for detecting the ratio of speed signals obtained from speed sensors provided in each of the reticle stage driving device 17 and the wafer stage driving device 8 (speed fluctuation detection circuit). ) Is provided, and the position shift control can be performed by inclining the transparent plate 20 when the ratio fluctuates from a predetermined value.

Further, if the position correction of the transparent plate of the present invention is used in combination with the reticle fine movement stage 13 arranged on the reticle Y-axis stage 12, the fluctuation amplitude is large and the low frequency fluctuation is corrected by the reticle fine movement stage 13. If high-frequency fluctuations with a small amplitude are corrected by the transparent plates 20 and 21, the amount of rotation of the transparent plates 20 and 21 can be reduced, and a configuration using a piezo element that can handle high frequencies can be adopted. Higher accuracy and higher speed can be expected. Also,
The transparent plates 20 and 21 do not necessarily have to be provided between the reticle 14 and the projection lens 10, and may be provided between the wafer 5 and the projection lens 10.

Instead of the transparent plates 20 and 21, the lens element of the projection optical system 10 can be tilted to perform the positional deviation control.

[0023]

As described above, according to the present invention, in the step-and-scan exposure apparatus, by inclining the transparent plate placed between the mask stage and the substrate stage,
A relative displacement between the mask and the exposure substrate during scanning exposure, or speed unevenness can be corrected with high responsiveness. Therefore, it is possible not only to shift the entire shot area to be exposed, but also to reduce shot distortion and image deterioration.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram comparing the sizes of transparent plates used in the step-and-repeat exposure method and the step-and-scan exposure method.

FIG. 3 is a diagram for explaining various errors that occur in the step-and-scan exposure method.

FIG. 4 is a diagram illustrating the concept of a conventional step-and-scan exposure method.

[Explanation of symbols]

 1 Wafer Stage Support 2 Y-Axis Stage 3 X-Axis Stage 4 Zθ-Axis Stage 5 Wafer 6 Fiducial Mark Plate 7 Moving Mirror 8 Wafer Stage Drive 9 Wafer Stage Interferometer 10 Projection Lens 11 Reticle Support 12 Reticle Y-axis Stage 13 reticle fine movement stage 14 reticle 15 moving mirror 16 reticle stage interferometer 17 reticle stage drive device 20, 21 transparent plate 22 transparent plate drive device 23 control device

Claims (3)

[Claims] 1. A mask stage that holds a mask on which an original image pattern is formed and is movable in at least a first direction along a surface of the original image pattern;
Alternatively, a projection optical system that projects a part of the projection optical system at a predetermined magnification, and a substrate that holds the photosensitive substrate so that the photosensitive substrate is positioned on the image plane of the projection optical system and is movable at least in the first direction. An apparatus that includes a stage, a drive unit that moves the mask stage and the substrate stage at a speed ratio according to the magnification, and scans and exposes the projected image of the original image pattern onto the photosensitive substrate, wherein the mask stage and A transparent plate which is disposed between the substrate stages and can be tilted to displace the projection image in the first direction or a second direction orthogonal to the first direction; the mask stage and the substrate stage during scanning exposure And a positional deviation detecting means for outputting a detection signal corresponding to the positional deviation amount from the predetermined relative positional relationship in the first direction or the second direction, and, according to the detection signal, Projection exposure apparatus characterized in that a control means for tilting the serial transparent plate said first direction, or in the second direction. 2. The projection exposure apparatus according to claim 1, wherein the positional deviation detection means is a detection signal in accordance with a change in speed ratio between the mask stage and the substrate stage. 3. The positional deviation detecting means outputs a detection signal corresponding to the positional deviation amount in a first direction and a detection signal corresponding to the positional deviation amount in a second direction, and the transparent plate is A first transparent plate that can be tilted to displace the projection image in the first direction, and a second transparent plate that can be tilted to displace the projection image in the second direction,
The first transparent plate and the second transparent plate are arranged in parallel in the optical axis direction of the projection optical system.
The projection exposure apparatus according to the item.