JPH0450731B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a projection exposure method, particularly for projecting an image of a circuit pattern of a reticle onto a wafer, which is used to manufacture semiconductor devices such as ICs and LSIs. The present invention relates to a projection exposure method for exposing a wafer to light according to a circuit pattern.

[Prior art] The conventional method of projecting and exposing a circuit pattern image onto a wafer using a reticle is to move the XY stage on which the wafer is placed and send the shot area on the wafer to the exposure position directly below the projection optical system. By stopping the stage, shining light on the shot area on the wafer at the exposure position, and detecting the reflected light from the surface of the shot area, the deviation of the circuit pattern of the reticle on the surface of the shot area from the imaging plane is detected. However, by adjusting the height of the wafer to correct this deviation, the imaging plane and the surface of the shot area are matched, and then the circuit pattern image of the reticle is projected onto the shot area by a projection optical system.

[Problems to be Solved by the Invention] In the conventional projection exposure method described above, after the shot area on the wafer is sent to the exposure position, the deviation of the reticle circuit pattern from the imaging plane in the shot area on the wafer is optically corrected. Since the method includes a step of detecting the height of the wafer and a step of adjusting the height of the wafer, it takes a relatively long time to complete the exposure.

Therefore, an object of the present invention is to shorten the time required to expose a shot area on a wafer.

[Means for Solving the Problems] In order to achieve the above object, the present invention moves the wafer to send the shot area of the wafer to an exposure position, and injects a reticle pattern onto the shot area at the exposure position. when projecting the image of the reticle pattern, the step includes the step of optically detecting a deviation of the shot area from the imaging plane of the reticle pattern, and correcting the deviation so that the shot area substantially coincides with the imaging plane. In the projection exposure method,
The optical detection is performed before the exposure position without stopping the movement of the wafer.

The present invention optically detects the deviation of the shot area of the wafer from the imaging plane of the reticle pattern in front of the exposure position without stopping the movement of the wafer, so that the operation of feeding the shot area on the wafer to the exposure position is possible. In parallel with this, it is possible to detect the deviation of the shot area from the imaging plane, and it is also possible to adjust the wafer height at the same time as the movement of the shot area to the exposure position. It can save time.

[Example] Hereinafter, an example of the present invention will be described using the drawings.

FIG. 1 shows a schematic configuration of an exposure apparatus in which the projection exposure method of the present invention is used.

In the figure, 1 is an illumination system, 2 is a reticle (original plate) on which a pattern to be exposed is drawn, 3 is a light source of detection light for detecting the position of the wafer in the Z direction, 4 is a Z direction position detection mechanism, 5 is a projection lens which is an imaging optical system; 6 is a mirror; 7 is an X-Y stage movable in the XY direction, that is, in the left-right direction of the page and in a direction perpendicular to the page; 8 is movable in the Z direction, that is, in the vertical direction of the page. 9 is a wafer that is an object to be exposed, 10 is a sensor (light receiving element) for detecting the position of the wafer in the Z direction, 11 is a control unit of the exposure apparatus, 12 is a laser interferometer, and 13 is an X-Y The stage drive motor is shown.

In the above configuration, the light beam emitted from the illumination system 1 illuminates the reticle 2 and projects an image of the pattern of the reticle 2 onto the wafer 9 via the projection lens 5. Then, in order to align the wafer 9 with the imaging position of the pattern image formed by the projection lens 5, the positions of the Z stage 8 and the wafer 9, which can place the wafer 9 and move in the Z direction, are measured. The Z-direction position detection mechanism 4 is provided.

The Z-direction position detection mechanism 4 optically detects the surface position of the wafer 9, and is composed of a light source 3, a mirror 6, a sensor (light receiving element) 10, and the like. Then, the sensor 10 outputs a position signal indicating the deviation of the pattern of the reticle 2 from the image plane, which corresponds to the position of the wafer 9 in the Z direction.

Furthermore, an XY stage 7 is provided to enable exposure at any location on the wafer 9. This X-Y stage 7 is operated by a drive motor 13 etc.
Driven in the XY direction, its position is determined by the laser interferometer 1
Guaranteed by 2nd place.

The control unit 11 of the exposure apparatus obtains the Z position signal of the wafer 9 output from the Z direction position detection mechanism 4, and
Based on the detection result, the drive amount of the Z stage 8 is calculated and applied to the Z stage 8 in order to match the pattern image of the reticle 2 formed by the projection lens 5 with the wafer 9. In addition, the control unit 11
receives the output of a laser interferometer 12 that measures the current position of the stage 7 as a feedback signal in order to accurately position the X-Y stage 7,
It has a control function to give a drive signal to the XY stage 7. Furthermore, the control system 11 controls the Z of the wafer in the region where semiconductor integrated circuits are formed, as will be described later.
It is assumed that the controller has a function of determining whether or not directional position detection is possible, calculating the amount of movement for corrective driving of the X-Y stage 7, and instructing the X-Y stage 7. In addition, when actually performing exposure, the X-Y stage 7 is corrected and the wafer 9 is
Then, based on the detection result, the wafer 9 is moved in the Z direction and the XY stage 7 is moved to the exposure position to perform exposure.

FIG. 2 is an enlarged view of a part of the shot layout on the wafer 9. As shown in FIG.

In the figure, 14 indicates the center of the wafer, and 15 and 16 indicate the n-th and (n+1)-th shots, respectively. The shots 15 and 16 are multi-chips in which two chips are arranged in one row and two columns. That is, the shot 15 contains chips 15a and 15b, and the shot 16 contains chips 16.
Contains chips a and 16b.

17 is the detection light irradiation position for Z-direction position detection in the n-th shot 15, 18, 19, 2
0 is a candidate for the detection light irradiation position in the (n+1)th shot 16. That is, the Z-direction position of the n-th shot 15 of the wafer 9 is obtained by making the detection light incident on the position 17 and detecting the reflected light. Further, the Z direction position of the n+1th shot 16 is such that the detection light is directed to positions 18, 19, 20.
It is obtained by making the light incident on one of the positions and detecting the reflected light. S _x and S _y indicate the length of the side of the shot.

The exposure ranges of shots 15 and 16 are rectangles with side lengths S _x and S _y , respectively, and detection light irradiation positions 17 and
Contains 20. That is, the position detected on the wafer surface by the Z-direction position detection mechanism 4 in FIG. 1 is position 17 within the exposure range in shot 15 (nth shot). Also, shot 16 (n+
In the first shot), the detection position in the normal case without correction drive is position 20. The distance traveled from shot 15 to shot 16 is the distance between detection light irradiation position 17 and (candidate) detection light irradiation position 20, and is expressed as S _x .

By the way, this position 20 is outside the wafer 9, and the position in the Z direction cannot be detected. This is because the range that can be irradiated with the detection light is within the wafer surface. on the other hand,
Candidates 18 and 19 for the detection light irradiation positions are positions in place of the position 20 where the detection light cannot be irradiated at the n+1-th shot 16. These positions 1
8 and 19 are the same wafer reflectances as position 20,
This is a position where the Z-direction position can be detected without any error due to reflectance.

FIG. 3 is a diagram showing a range in which the detection light irradiation position and wafer reflectance of the normal shot stored in advance in the control section are the same in the shot 16 of FIG. 2.

In the figure, 21 to 23 indicate a range in which the Z-direction position can be detected, where the wafer surface has the same reflectance as the normal detection light irradiation position. This range 21-23
If the detection light is irradiated at
The same detection signal is obtained as when using .

FIG. 4 is a flowchart showing the procedure of projection exposure using the apparatus shown in FIG.

Next, a specific correction drive operation will be described with reference to FIGS. 1 to 4.

In the above configuration, the detection position 17 of the n-th shot 15 by the Z-direction position detection mechanism 4 is on the wafer surface, as described above, and is therefore within the range where detection light can be irradiated. Therefore, this position 17
Based on the detection result in , the reticle 2 and wafer 9 can be accurately positioned at the conjugate optical reference plane position of the imaging optical system.

However, when the wafer 9 is moved by S _x in order to expose the next (n+1)th shot 16, the detection position 20 on the wafer surface by the Z direction position detection mechanism 4 is
is outside the wafer surface and cannot be detected. For this reason, the reticle 2 and the wafer 9 cannot be positioned at conjugate positions of the imaging optical system, and the n+1th shot 1
Even though there is a valid chip 16a in the shot 6, the shot 16 becomes an invalid chip, resulting in a decrease in yield.

Therefore, in this embodiment, the n+1st shot 1
If the position cannot be detected as in case 6, the position is within the range (on the wafer surface) where detection light can be irradiated between the n-th shot 15 and the n+1-th shot 16, and the X-Y The wafer reflectance is the same as the detection light irradiation position in the case of a normal shot in which the stage 7 is not driven for correction (position 17 for the n-th shot 15, and original position 20 for the n+1-th shot 16 if detection is possible). The XY stage 7 is corrected and driven so as to perform position detection in the Z direction within the range. Thereafter, the wafer 9 is moved to an exposure position and exposed. This makes it possible to make a chip that has been disabled due to inability to detect a position in the Z direction into a valid chip. Furthermore, detection errors due to the reflectance of the wafer 9 can also be eliminated.

Next, with reference to FIG. 3, a description will be given of what position should be the irradiation position of the detection light.

First, as shown in the figure, the range 2 of the wafer reflectance is the same as the detection light irradiation position 20 when no correction drive is performed.
The positions 1 to 23 are stored in advance in the control unit 11 before exposing the wafer 9 to light. After the exposure of the n-th shot 15 in FIG.
Before moving to the first shot 16 in the X-Y direction, when the control unit 11 determines that Z-direction position detection is impossible at the detection light irradiation position 20, the pre-stored range 21 to 21 of the same wafer reflectivity is determined. 23 location information is called. Among the positions within ranges 21 to 23, ranges 22 and 2 are inside the detection light irradiation range.
It is 3. Positions 18 and 19 in FIG. 2 are within ranges 22 and 23, respectively.

Next, by minimizing the driving distance of the X-Y stage 7, in order to suppress a decrease in throughput, a correction drive is performed to set position 18 as the target position for detection light irradiation, and a correction drive is performed to set position 19 as the target position. Calculate in which case the driving distance is smaller. In this example, X-Y stage 7
If you move from position 17 → 18 → 20, it becomes 17 → 1
The distance traveled is shorter than moving from 9 to 20, so
17→18→20 are selected. and position 1
The X-Y stage 7 is driven for correction in order to make the detection light irradiation position 8, Z-direction position detection is executed, and then the entire range of the shot 16 is exposed.

Next, the procedure of projection exposure will be explained with reference to FIG.

First, after the exposure of the n-th shot 15 is completed, and before the wafer 9 moves to expose the next shot 16, the next shot 16 is placed in the Z position at the normal position.
Step 3: Check whether direction position detection is possible.
Judging by 1. If possible, the X-Y stage 7 is moved to the exposure position in step 35, the position in the Z direction is detected at position 20, and exposure is performed in step 36.

On the other hand, if position detection is not possible at position 20 as shown in Figure 2, then the wafer reflectance shown above is in the same range, and the conditions under which position detection is possible and the correction drive amount is minimum are established. A satisfactory detection light irradiation position is determined in step 32. And step 3
In step 3, move the X-Y stage 7 to detect the position in the Z direction at the corrected position.
Position detection is performed in step 4. Thereafter, in step 35, the X-Y stage 7 is driven to the exposure position, and in step 36, exposure is performed. Here, the position in the Z direction is detected without stopping the XY stage 7. That is, during the correction drive in step 33, the speed is decelerated near the detection position, and the position detection timing is obtained from the read value of the laser interferometer provided on the X-Y stage 7 to perform detection.

In this way, by detecting the position in the Z direction before the exposure position without stopping the XY stage 7, that is, without stopping the movement of the wafer 9, the time required to reach the exposure can be shortened.

[Effects of the Invention] As described above, the present invention detects the Z-direction position (deviation from the imaging plane) of the shot area of the wafer before the exposure position without stopping the movement of the XY stage, that is, the movement of the wafer. The position in the Z direction can be detected in parallel with the movement of the shot area on the wafer to the exposure position, and it is also possible to adjust the height of the wafer at the same time as the movement of the shot area to the exposure position. You can shorten the time it takes.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an exposure apparatus using the projection exposure method of the present invention, FIG. 2 is a partially enlarged view of a shot layout on a wafer, and FIG. FIG. 4, which is a diagram showing the same range of wafer reflectance as the detection light irradiation position of a normal shot, is a flowchart showing the procedure of projection exposure. 1...Lighting system, 2...Reticle (original plate), 3...
...Light source, 4...Z direction position detection mechanism, 5...Imaging optical system (projection lens), 6...Mirror, 7...X
-Y stage, 8... Z stage, 9... Wafer (exposed object), 10... Sensor (light receiving element), 11
...Control unit, 12...Laser interferometer, 13...X
-Y stage drive motor.

Claims (1)

[Scope of Claims] 1. When a shot area of the wafer is sent to an exposure position by moving the wafer, and an image of a reticle pattern is projected onto the shot area at the exposure position, the image of the reticle pattern in the shot area is A projection exposure method including the step of optically detecting a deviation from an imaging plane and correcting the deviation to make the shot area substantially coincide with the imaging plane, wherein A projection exposure method characterized in that the optical detection is performed before the exposure position. 2. The projection exposure method according to claim 1, wherein the optical detection is performed while the moving speed of the wafer is reduced.