JPH04350925A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To shorten the focusing motion by detecting the position and the inclination of the surface of a plate-shaped substance such as a wafer, etc., during the shifting of a stage on which to place said plate-shaped substance. CONSTITUTION:This device is equipped with a stage 3 capable of shifting two- dimensionally, which shifts a plate-shaped substance (wafer) 2 placed on itself in the direction orthogonal to the optical axis AX of a projecting lens system 1 and sends in the specified face of the wafer 2 to the side of the image face of the projecting lens system 1. Moreover, it is equipped with a detection means 11 which can detect the shape of, at least, one face out of the position and the inclination pertaining to the optical axis AX direction of the specified face of the wafer 2 and can detect the shape of the face in cooperation with the shifting of the stage 3. And the detection by the detection means 11 is performed during the shifting of the stage 3, and based on the face shape sought by the detection means 11, the specified face is set to the focusing face of the projecting lens system 1. Hereby, the focusing action can be shortened.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing apparatus, and in particular, in a reduction projection exposure apparatus (stepper) for manufacturing semiconductor devices, each exposed area of a semiconductor wafer placed on a wafer stage is The present invention relates to an automatic focusing device used to focus on the focal plane of a lens system (projection optical system).

0002

[Prior Art] Currently, circuit patterns are becoming finer in line with the increasing integration of VLSIs, and along with this, stepper reduction projection lens systems are becoming higher in NA. The allowable depth of the lens system in the circuit pattern transfer process is becoming narrower. Furthermore, the size of the exposed area to be exposed by the reduction projection lens system also tends to increase.

In order to make it possible to transfer a good circuit pattern over the entire enlarged exposed area, it is necessary to ensure that the exposed area of the wafer is within the allowable depth of the reduction projection lens system. (Shot) You have to position the whole thing.

In order to achieve this, the position and inclination of the wafer surface with respect to the focal plane of the reduction projection lens system, that is, the plane on which the circuit pattern image of the reticle is focused, is detected with high precision, and the position and inclination of the wafer surface are determined. It is important to make adjustments.

[0005] As a method for detecting the position of the wafer surface in a stepper, there is a method of detecting the surface positions of a plurality of points on the wafer surface using an air microsensor, and determining the position of the wafer surface based on the results. A method of detecting the position of the wafer surface using a detection optical system that makes a light beam incident on the wafer surface from an oblique direction and detects the positional deviation of the reflection point of the reflected light from the wafer surface as the positional deviation of the reflected light on the sensor. It has been known.

Conventional steppers move the wafer stage to a target position using servo drive while measuring the amount of displacement of the wafer stage using a laser interferometer, thereby sending the exposed area on the wafer directly below the projection lens system. After the wafer stage is stopped, the surface position of the surface of the exposed region is detected by the method described above, and the position of the surface of the exposed region is adjusted. That is, operations such as driving the wafer stage, stopping the wafer stage, detecting the surface position, and adjusting the surface position are sequentially performed.

[0007]

However, a detector for detecting the shape of the wafer surface can only detect the position of the wafer surface at the mounting position of the sensor (light receiving element). Therefore, there is a problem in that the entire surface of the shot to be exposed cannot be detected. For example, if the measurement point of the sensor is extremely small, it becomes impossible to accurately calculate the surface shape of the shot due to the influence of minute irregularities on the wafer surface.

Furthermore, when a series of operations such as driving the wafer stage on which the wafer is placed, stopping it, detecting the surface position, and adjusting the surface position are performed in sequence, the exposed area is brought into focus on the focal plane of the projection lens system. The amount of time it takes to complete the process is relatively long, which causes a reduction in the number of wafers that can be processed per unit time (throughput) by the reduction projection exposure apparatus.

Furthermore, there is a problem in that when the exposed area is changed, the measurement point cannot be changed.

[0010] The present invention provides an automatic focusing device that can measure the surface shape of a predetermined surface of a flat object with high accuracy, complete the operation to move the predetermined surface to a predetermined position in a short time, and perform a focusing operation. With the goal.

[0011]

[Means for Solving the Problems] The automatic focusing device of the present invention moves a flat object mounted thereon along a direction perpendicular to the optical axis of a projection lens system (projection optical system), and focuses the flat object at a predetermined position. a two-dimensionally movable stage that sends a surface to the image plane side of the projection lens system; a surface shape of at least one of the position and inclination of the predetermined surface with respect to the optical axis direction; and a detection means that can cooperate with each other to measure the surface shape.

Detection by the detection means is performed while the stage is moving, and the predetermined surface is focused on the focal plane of the projection lens system based on the surface shape determined by the detection means. Furthermore, the detection means is provided with a movable mechanism so that the surface shape can be measured even when the stage is stationary.

Further, even when the exposed area is changed, a detection means having a scanning optical system capable of measuring the surface shape by moving measurement is used to cope with the change in the exposed area.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram of a part of a reduction projection exposure apparatus equipped with an automatic focusing device according to the present invention.

In FIG. 1, reference numeral 1 denotes a reduction projection lens system, the optical axis of which is indicated by AX in the figure. The reduction projection lens system 1 converts the circuit pattern of the reticle (not shown) into a 1/
A circuit pattern image is formed on the focal plane by projecting the image at a 5-fold reduction. Further, the optical axis AX is parallel to the z-axis direction in the figure. 2 is a wafer whose surface is coated with resist, and a large number of exposed areas (shots) in which the same pattern has been formed in the previous exposure process are arranged.

3 is a wafer stage on which a wafer is placed. The wafer 2 is attracted and fixed to the wafer stage 3. The wafer stage 3 includes an X stage that moves in the x-axis direction, a Y stage that moves in the y-axis direction, and a Z stage that rotates around axes parallel to the z-axis direction and the x, y, and z-axis directions. Furthermore, the x, y, and z axes are set to be orthogonal to each other. Therefore, by driving the wafer stage 3, the position of the surface of the wafer 2 is adjusted in the direction of the optical axis AX of the reduction projection lens system 1 and in the direction along the plane orthogonal to the optical axis AX. The tilt with respect to the pattern image is also adjusted.

Reference numerals 4 to 11 in FIG. 1 indicate each element of a detection means provided for detecting the surface position and inclination of the wafer 2. 4 is a light emitting diode, which is a high-intensity light source such as a semiconductor laser. 5 is an illumination lens.

The light emitted from the light source 4 is turned into a parallel beam by the illumination lens 5, and illuminates a mask 6 in which a plurality of (seven) pinholes are formed. The plurality of light beams that have passed through each pinhole in the mask 6 pass through an imaging lens 7 and enter a bending mirror 8, and after being changed in direction by the bending mirror 8, they enter the surface of the wafer 2.

Here, the imaging lens 7 and the bending mirror 8 form images of the plurality of pinholes in the mask 6 on the wafer 2. The light flux passing through multiple pinholes is shown in Figure 2.
As shown in FIG. 2, seven locations (21 to 27) including the center of the exposed region 100 of the wafer 2 are irradiated, and the light is reflected at each location. That is, in this embodiment, seven pinholes are formed in the mask 6.
The positions of seven measurement points (21 to 27) including the central portion are measured within the exposed area 100, as will be described later.

In FIG. 2, the irradiation positions 26 and 27 are shifted inward in a diagonal direction with a step difference from other measurement points because the surface of a wide area of the wafer 2 is shifted in cooperation with the stage movement described later. This is because they were placed in the most suitable state so that their shapes could be measured. With such an arrangement, the surface shape of the wafer 2 can be accurately determined over a wide range as the stage moves. Further, the irradiation positions 24 and 25 are used even when the stage is stationary. Irradiation positions 21, 22,
By arranging 23, 24, and 25, measurements are made over the widest range. Note that the detected values from the irradiation positions 24 and 25 may be used when measuring stage movement.

The light beam reflected at each measurement point (21 to 27) on the wafer 2 is changed in direction by a bending mirror 9, and then passes through a detection lens 10 onto a position detection element 11 in which elements are arranged two-dimensionally. incident. Here, the detection lens 10 cooperates with the imaging lens 7, the bending mirror 8, the wafer 2, and the bending mirror 9 to form an image of the pinhole of the mask 6 on the position detection element 11. That is, the mask 6, the wafer 2, and the position detection element 11 are located at mutually optically conjugate positions. Although shown schematically in FIG. 1, if optical arrangement is difficult, a plurality of position detection elements 11 may be arranged corresponding to each pinhole.

The position detection element 11 is composed of a two-dimensional CCD or the like, and is capable of independently detecting the incident positions of a plurality of light beams onto the light receiving surface of the position detection element 11 via a plurality of pinholes. It has become. A change in the position of the reduction projection lens system 1 on the wafer 2 in the optical axis AX direction can be detected as a shift in the incident position of a plurality of light beams on the position detection element 11. The position of the wafer surface in the optical axis AX direction at the measurement points 21 to 27 can be detected based on the output signal from the position detection element 11. Further, the output signal from the position detection element 11 is input to the control device 13 via a signal line.

The displacement of the wafer stage 3 in the x-axis and y-axis directions is measured by a well-known method using a reference mirror provided on the wafer stage and a laser interferometer, and a signal indicating the amount of displacement of the wafer stage 3 is detected by laser interference. The signal is input from the meter to the control device 13 via a signal line. Further, the movement of the wafer stage 3 is controlled by a stage drive device 12,
The stage drive device 12 is connected to the control device 13 via a signal line.
The wafer stage 3 is servo driven in response to a command signal from the wafer stage 3.

The stage driving device 12 has a first driving means and a second driving means, and the first driving means controls the position (x, y) and rotation (of the wafer 2 in a plane perpendicular to the optical axis AX).
θ), and the position (z) and inclination (φx, y) of the wafer 2 in the optical axis AX direction are adjusted by the second driving means.

The control device 13 processes the output signal (surface position data) from the position detection element 11 by a method described later, and detects the position of the surface of the wafer 2. Then, a predetermined command signal is input to the stage drive device 12 based on this detection result. In response to this command signal, the stage drive device 12
The second driving means operates, and the second driving means adjusts the position and inclination of the wafer 2 in the optical axis AX direction.

Next, the method of detecting the surface shape of the wafer 2 in this embodiment will be explained in order.

First, as shown in FIG.
Seven measurement points 21 to 27 are set within the area. The measurement point 21 is located approximately at the center of the exposed region 100, and intersects with the optical axis AX during surface position detection. Further, the remaining measurement points 22 to 25 are located at the periphery of the exposed area 100, and assuming that the measurement point 21 is located at the point (x, y) on the x-y coordinates, each of the measurement points 22 to 2
The positions of 5 are (x+Δx, y+Δy), (x−Δx,
y+Δy), (x-Δx, y-Δy), (x+Δx, y
−Δy).

Measurement point 26 is It is at the point where it becomes.

Further, as shown in FIG. 3, the exposed regions 100 are regularly arranged on the wafer 2 along the x-axis and the y-axis.

Next, the wafer stage 3 is moved to the target position, and the exposed area (shot) 10 on the wafer 2 is
The detection means (4 to 1) shown in FIG.
Perform the settings in 1). At this time, exposed area 1
00 is positioned directly below the reduction projection lens system 1, and the measurement point 21 intersects the optical axis AX.

In this embodiment, the wafer stage 3 is moved so that the first exposed area 100a on the wafer 2 is directly below the reduction projection lens system 1, and the first exposed area 100a is aligned with the reticle pattern. . After the alignment is completed, the first exposed area 1 is detected by the detection means (4 to 11).
The surface position of five measurement points (21 to 25) of 00a is detected, and surface position data of each measurement point is formed in the control device 13 based on the output signal from the position detection element 11. At this time, measurement points 26 and 27 are not used.

The control device 13 controls the first exposed area 100a based on the five surface position data Zi (i=1 to 5).
The distance between this least squares plane and the reticle pattern image in the optical axis AX direction, and the direction and amount of tilt of the wafer 2 are calculated.

[0033]The position z of the least squares plane is

[0034]

[Math 1] It satisfies the following.

The control device 13 inputs a command signal according to the calculation result to the stage drive device 12, and the stage drive device directs the optical axis AX of the wafer 2 on the wafer stage 3.
The position and tilt of the direction are adjusted (corrected). This positions the surface of the wafer 2, that is, the first exposed region 100a, at the best imaging plane (focal plane) of the reduction projection lens system 1 while the stage is moving. After that, wafer stage 3
movement to the target position is completed. After this surface position adjustment is completed, the first exposed area 100a is exposed to transfer the circuit pattern image.

When the exposure of the first exposed area 100a is completed, the wafer stage 3 is driven so that the second exposed area 100b on the wafer 2 is located directly below the reduction projection lens system 1.

In this embodiment, the measurement point 24, just before transitioning from the first exposed area 100a to the second exposed area 100b,
25 has been abolished and the measurement points 26 and 27 have been switched to use. Furthermore, the measurement mode is switched to the moving measurement mode. This mode switching is performed by the control device 13.

FIG. 4 shows the relationship between stage movement and measurement points. In FIGS. 4(A) and 4(B), arrows indicate the loci of measurement points. While the stage is moving, the position of the wafer surface is measured sequentially until the stage movement is completed. By changing the measurement point, the middle of measurement points 21 and 22 and the measurement point 21,
It is possible to measure at a position between 24 and 24. That is, 5
Five rows of measurements are taken at the measurement points.

Next, when moving from the first exposed area 100a to the second exposed area 100b, for example, the measuring point 21 has an unmeasured area 21b in the second exposed area 100b. However, while the stage is moving, the first exposed area 100a
The measurement has been completed in the range 21a within the shot. The surface shapes of adjacent shots of wafers that have been processed through the same process rarely vary greatly.

Therefore, the range of the unmeasured part 21b is defined as the range 21a.
It is quite possible to replace it with As a result, in this embodiment, in cooperation with the stage movement, the measurement point 21 can measure all shots of the second exposed area 100b in the stage movement direction. This means that measurement points 22, 24, 26
, 27 as well.

The stage position is stored in synchronization with the timing of measuring the wafer surface within the shot while the stage is moving. For example, from the first exposed area 100a to the second exposed area 100a,
If measurements are taken five times while moving to the exposed area 100b, the second
When the measurement points of the exposed area 100b are plotted, FIG.
B). At this time, the value Zxy (x=1 to 5,
y=1 to 5), the least squares plane of the exposure area 100b is determined, and the amount of inclination between the exposure surface and the wafer is calculated. The obtained inclination amount is adjusted in the same manner as in the shot of the first exposed area 100a, and the circuit pattern on the reticle is transferred. Although the movement in the X direction has been described here, the same applies to movement in the Y direction.

FIG. 5 is a flowchart of this embodiment. In step S501, the wafer 2 is carried onto the wafer stage 3 and fixed to the wafer chuck. Step S5
In step 02, surface calculation, tilt driving, exposure, etc. for the first shot are performed. A flowchart at this time is shown in FIG.

Next, the flowchart shown in FIG. 6 will be explained. In the case of the first shot, movement measurement is not performed because the feed may not be from an adjacent shot. When the stage movement is completed in step SB521, step SB521
At 522, the position of the wafer surface is measured using measurement points 21, 22, 23, 24, and 25. A least squares plane calculation is performed from the measured values in step SB523, and the distance and inclination between the focal plane of the projection lens system 1 and the wafer 2 are detected. In step SB524, the control device 13 inputs a command signal corresponding to the interval and inclination to the stage driving device 12, and performs inclination driving.

[0044] At step SB525, the driving is completed, and after the difference in focal plane between the wafer and the lens is corrected, exposure is performed.

Next, returning to the flowchart of FIG. 5, in step S502, when the exposure of the first shot is completed, the control device 1
3 mode to moving measurement mode, measuring points 21 and 2.
Switch to 2, 24, 26, 27. Step SB504
After that, the stage 3 is started to be driven, and the counter j is initialized to 1. In step S505, focus measurement is performed at predetermined time intervals in the moving measurement mode, and Zji (i=2
1, 22, 24, 26, 27) and the stage position Pj are stored in the memory of the control device 13.

In step S507, step S505 is repeated until the stage 3 passes a predetermined position.
Add. After passing the predetermined position in step S508, Zji
A least squares plane is calculated in the control device 13 from Pj and Pj. In step S509, the distance and inclination between the reduction projection lens system 1 and the wafer 2 are determined. This value is sent to the control device 13 to drive the tilt.

When the movement of the stages that were being moved at the same time is completed in step S510, exposure is performed in step S511 since the difference in focal plane between the reduction projection lens 1 and the wafer 2 has already been corrected. If the exposure of all shots is not completed in step S512, the process moves to step S504 and steps S504 to S512 are repeated. When the exposure of the final shot is completed, the wafer 2 is removed from the wafer chuck in step S513, and the wafer 2 is carried out.

In this example, seven measurement points were fixed in advance,
A configuration in which seven light beams are irradiated onto a wafer has been described. The measurement points are selected in two modes: stationary state and moving measurement, but the measurement light beams for measurement points 23 and 26 and the measurement light beam for measurement points 25 and 27 are each treated as one light beam. You can also measure it. In that case, the position of the mask 6 provided with the pinhole should be moved, or the imaging lens 7 should be moved.
The position of the measurement point may be changed using a mechanism that changes the position of the light beam.

Furthermore, for the measurement of the first shot, a measurement point for static measurement is not selected, and moving measurement is also possible for the exposure of the first shot. In this case, the operation of the wafer stage 3 on which the wafer 2 is placed may be completed by passing through the shot of the second exposed area 100b, which is an adjacent shot, before the shot of the first exposed area 100a. In this case, the number of measurement light beams may be five. That is, measurement point 23,2
5 may not be used.

In this embodiment, a case has been described in which an LED is used as the light source 4 to illuminate seven or five pinholes on the mask 6 to form seven or five light beams.
An ED may be individually provided for each pinhole to illuminate the corresponding pinhole.

FIG. 7 is a schematic diagram of a part of a second embodiment of a reduction projection exposure apparatus equipped with an automatic focusing device of the present invention. In the figure, 601 is a light source such as a laser or high-intensity LED;
602 is a scanning optical system (scanning optical system). For example, it has a polygon mirror, a galvano mirror, etc. This scanning optical system 602 is controlled by the control device 13. The other configurations are similar to the embodiment shown in FIG.

A laser beam emitted from a light source 601 is scanned by a scanning optical system 602, and a spot of light is scanned on the wafer surface in the Y direction as shown in FIG. This method cannot measure the two-dimensional surface shape within the shot, but by scanning the laser beam while moving the stage as described above, it is possible to scan the entire surface within the shot with a spot of light, as shown in Figure 9. Become. This allows measurement at each point in the position shown in FIG. 4(B). The subsequent calculation of the surface shape and driving of the inclination are the same as those described in the previous embodiment. If the scanning optical system 602 is made capable of scanning not only in the Y direction but also in the X direction, two-dimensional scanning is possible. In this case, the surface shape can be measured in a stationary state. Furthermore, in the case of movement measurement, it can also be used when moving the stage in the Y direction.

[0053] Furthermore, when the range of the exposed area is changed,
This can be handled by changing the scan width of the scan optical system. Alternatively, this may be achieved by providing a blade in the scanning optical system to control the scanning width and opening/closing the blade. The position of this blade is preferably placed at a position conjugate with the surface to be measured. Or detect light 2
The inspection and processing area of the dimensional CCD sensor 11 may be aligned with the exposed area.

[0054] As the position detection element in each of the above embodiments, it is possible to use not only an air sensor and an optical sensor, but also various well-known sensors such as a capacitance sensor and other types of optical sensors. be done. still,
In order to detect the inclination of a predetermined surface of a flat object, multiple air sensors or optical sensors are used to measure the height (surface position) of different points on the predetermined surface. Alternatively, parallel light may be irradiated, the parallel light reflected from a predetermined surface may be collected, and the incident position of the collected light on the photodetector may be measured.

Furthermore, in each of the above embodiments, the detection means (4 to 11) or (601, 602,
7 to 11) are preferably constantly driven to continuously monitor the surface position of the exposed area that is the object of exposure.

In each of the above embodiments, the surface position and inclination of the surface of the wafer 2 are detected and corrected, but the present invention provides an apparatus that only detects and corrects the surface position of the surface of the wafer 2,
Conversely, the present invention is similarly applied to an apparatus that only detects and corrects the inclination of the surface of the wafer 2.

Further, the position detection element for detecting the surface position and inclination of the surface of the wafer 2 includes the detection means (4 to 11) shown in FIG.
) or the detection optical system (601, 602, 7) shown in FIG.
-11) Well-known position detection elements other than those described above can also be used. Furthermore, the mechanism for focusing the surface of the wafer 2 on the focal plane of the projection lens system includes, in addition to moving the Z stage of the wafer stage 3, changing the focal length of the projection lens system 1.
A mechanism may also be adopted in which the projection lens system 1 and a reticle (not shown) are moved up and down in the direction of the optical axis AX.

In each of the embodiments described above, the present invention is applied to a reduction projection exposure apparatus, but the present invention also applies to an exposure apparatus of a type other than the apparatus shown in FIG. The present invention can be similarly applied to devices that project pattern images using a projection optical system composed of lenses and mirrors. Furthermore, the present invention is applicable to other than optical exposure devices, such as electron beam exposure devices and X-ray exposure devices that use an electron beam and an electron lens to draw a circuit pattern or project a circuit pattern. The same can be applied.

Furthermore, the present invention can be similarly applied to optical equipment other than exposure apparatuses that require automatic focusing.

[0060]

[Effects of the Invention] As described above, according to the present invention, since the position and inclination of the surface of a flat object such as a wafer are detected while the stage on which the flat object such as a wafer is placed is moved, the focusing operation can be shortened. . Moreover, since the measurement points are arranged so that all planes within the shot can be observed, an extremely accurate two-dimensional plane shape can be detected. Further, by adjusting the position and inclination of the surface of the flat object while the stage is moving, the focusing operation can be further shortened. Furthermore, it is possible to achieve an automatic focusing device that has the feature of being able to respond to changes in the exposed area by using a detector having a scanning optical system.

[Brief explanation of drawings]

[Fig. 1] A schematic diagram of the main parts of Embodiment 1 of a reduction projection exposure apparatus to which the present invention is applied.

[Figure 2] Explanatory diagram showing the arrangement of each measurement point set in the exposed area

[Figure 3] Plan view showing the arrangement of exposed areas (shots) on a wafer

[Figure 4] Diagram showing an example of the trajectory of each distance measurement point while the wafer stage is moving and the measurement points obtained by movement measurement

[Figure 5]
A flowchart diagram showing an example of a focusing operation by the device of FIG. 1.

[Figure 6] Flowchart diagram showing an example of focusing operation by the device in Figure 1.

[Fig. 7] A schematic diagram of main parts of a second embodiment of a reduction projection exposure apparatus to which the present invention is applied.

[Fig. 8] An explanatory diagram of the light spot of the exposed area in the scanning optical system of Fig. 7

[Figure 9] An explanatory diagram of the light spot of the exposed area in the scanning optical system in Figure 7

[Explanation of symbols]

1. Reduction projection lens system 2 Wafer 3 Wafer stage 4 High brightness light source 5.Lens for lighting 6. Mask with pinholes 7 Imaging lens 8,9　Folding mirror 10 Detection lens 11 Two-dimensional position detection element 12 Stage drive device 13 Control device 21-27 Measurement points 100 Exposed area (shot) 601 Laser light source 602 Scan optical system

Claims (4)

[Claims] 1. A two-dimensional device in which a flat object is placed and moved along a direction substantially perpendicular to the optical axis of the projection optical system, and a predetermined surface of the flat object is sent to the image plane side of the projection optical system. a stage movable in the optical axis direction, and a detection means for detecting at least one of the position and inclination of the predetermined surface with respect to the optical axis direction while cooperating with the stage and/or while stationary, the detection means An automatic focusing device, characterized in that the predetermined surface is focused on a focal plane of the projection optical system based on detection by means. 2. The automatic focusing device according to claim 1, wherein an operation for focusing the predetermined surface on the focal plane of the projection optical system is started while the stage is moving. 3. Before the movement of the stage is completed,
3. The automatic focusing device according to claim 2, wherein said focusing operation is completed. 4. Claim 1, further comprising a mechanism for moving a measurement point of the detection means for measuring a surface shape.
, 2 or 3 automatic focusing devices.