JP3640012B2 - Method for measuring level of mask or wafer in exposure apparatus and measurement control apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a mask or wafer leveling measurement method and a measurement control apparatus in an exposure apparatus.
[0002]
[Prior art]
In an exposure apparatus, for example, an exposure (lithographic) apparatus using X-rays, as shown in FIGS. 5 and 6, a mask 41 having an exposure pattern and a wafer 42 to be exposed are opposed to each other with a gap G1 of about 30 μm. Then, exposure is performed by irradiating an X-ray beam from the mask 41 side. On the other hand, in the alignment apparatus for controlling the positions and postures of the mask 41 and the wafer 42, the control is performed so that the mask 41 and the wafer 42 are parallel (the gap G1 is constant). Here, since it is difficult to directly measure the gap G1, a method of controlling the mask 41 and the wafer 42 so as to be parallel to the drive surface of the XY stage 43 is generally used. . Such a method is called “mask leveling” or “wafer leveling”.
[0003]
Hereinafter, the case of mask leveling will be described, but the wafer leveling is theoretically the same.
[0004]
The position / orientation of the mask 41 is obtained by measuring the distance from the XY stage 43 at three points on the mask 41 using a laser displacement meter or a capacitance sensor. In this case, as shown in FIG. 7, the three distance sensors 45 and 46 are used in order to perform measurement in as wide an area as possible with a mechanical constraint on the mask 41 (also for the purpose of shortening the measurement time). 47 may be used. In that case, the XY stage 43 is driven, and the distances to the same place (initial offset amount measurement point P1) on the mask 41 determined in advance by the three distance sensors 45, 46, 47 are respectively measured. Usually, the initial offset amount of each of the distance sensors 45 to 47 is corrected.
[0005]
[Problems to be solved by the invention]
However, there may be a case where the position is shifted by several μm to several 100 μm although the measurement is performed at the same place due to an error in the mounting position of the distance sensors 45 to 47. In this case, the slight deviation of the measurement location adversely affects the leveling accuracy (which requires accuracy on the order of μm).
[0006]
In particular, when the surface shape of the mask 41, which is the object, is uneven, and the initial offset amount measurement point P1 is located where the slope happens to be large (or has a peak), an error may be included. Sexuality will increase. There is currently no automatic detection / correction method.
[0007]
SUMMARY OF THE INVENTION An object of the present invention is to provide a leveling measurement method that can improve the alignment (positioning) accuracy of a mask or wafer in an exposure apparatus.
[0008]
Specifically, the present invention detects the position and orientation of a mask (wafer) using three sensors in a measurement called mask (wafer) leveling performed during alignment processing, and determines the initial offset amount of these sensor signals. The aim is to improve alignment accuracy by matching them accurately.
[0009]
Another object of the present invention is to provide a leveling measurement control apparatus suitable for the measurement method.
[0010]
[Means for Solving the Problems]
In the leveling measurement method according to the present invention, when leveling a mask or wafer so that it is parallel to a movable stage at least in the X-axis and Y-axis directions in the exposure apparatus, the stage is driven and installed there. In the leveling measurement method for measuring the distance to the same point of the mask or wafer by a plurality of leveling sensors and calculating an initial offset amount from the sensor signals of the plurality of sensors, for each of the plurality of sensors, Creating a measurement area map for scanning the vicinity of the same point of the mask or wafer a plurality of times, driving the stage based on the measurement area map, and detecting the same mask or wafer by each of the plurality of sensors. Scanning the vicinity of a point multiple times Holding a plurality of pattern measurement information obtained by a plurality of scans obtained from each of the plurality of sensors as three-dimensional information, and performing a pattern matching process on the three-dimensional information by the held plurality of sensors , Estimating the same point of the mask or wafer from the matched pattern, and referring to the three-dimensional information by the plurality of sensors using the estimated same point of the mask or wafer, respectively. Calculating the initial offset amount of the sensor.
[0011]
The leveling measurement control apparatus according to the present invention drives the stage when the mask or wafer is leveled at least in the X-axis and Y-axis directions parallel to the movable stage in the exposure apparatus. In the leveling measurement control device for measuring the distance to the same point of the mask or wafer by a plurality of leveling sensors and calculating the initial offset amount from the sensor signals of the plurality of sensors, the leveling measurement control device Has a function of executing a predetermined initial offset measurement algorithm, and the initial offset measurement algorithm scans the vicinity of the same point on the mask or wafer a plurality of times for each of the plurality of sensors. To create a measurement area map A step of driving the stage based on the measurement area map and scanning the vicinity of the same point of the mask or wafer a plurality of times by each of the plurality of sensors, and a plurality of scans obtained from each of the plurality of sensors Holding a plurality of pattern measurement information by the three-dimensional information, and performing a pattern matching process on the three-dimensional information by the plurality of held sensors, so that the mask or wafer is identified from the matched pattern. Estimating one point, and calculating the initial offset amount of the plurality of sensors by referring to the three-dimensional information by the plurality of sensors using the estimated same point of the mask or wafer, respectively. To do.
[0012]
In any of the inventions, the measurement area map is created based on the known attachment position coordinates of the plurality of sensors and the known position coordinates of the same point on the mask or wafer.
[0013]
Further, it is preferable that three sensors as the plurality of sensors are installed at positions separated from each other on the stage.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a configuration of a leveling measurement system according to the present invention, which can be applied to both the mask leveling and the wafer leveling described above. Three distance sensors 45, 46, 47 are mounted on the XY stage 43 at positions separated from each other, and sensor signals from the respective distance sensors 45 to 47 are taken into the measuring device 10. The measuring device 10 is connected to the XY stage driving device 30 so that the distance sensors 45 to 47 can be moved to desired positions. A feature of the present invention resides in that an initial offset amount measuring algorithm as described below is mounted on the measuring apparatus 10.
[0015]
FIG. 2 is a functional block diagram showing an initial offset amount measurement algorithm mounted on the measurement apparatus 10. First, in order to facilitate understanding of the present invention, a conventional leveling measurement method will be briefly described. In order to move one certain distance sensor to the initial offset amount measurement point P1 (see FIG. 7), an XY stage drive command 13 is created from the sensor attachment position coordinate 11 and the initial offset amount measurement point coordinate 12. The XY stage 43 is driven by the generated XY stage drive command 13, and one certain distance sensor is moved to the initial offset amount measurement point P1. Then, the sensor signal 14 at that time is read. Such processing is performed for each distance sensor, and the initial offset amount 15 of the other distance sensor is obtained from the sensor signal of the other distance sensor based on the sensor signal of a certain distance sensor. The sensor attachment position coordinate 11 and the initial offset amount measurement point coordinate 12 are both known.
[0016]
In any case, as described above, in this measurement method, if there is an error in the mounting positions of the distance sensors 45 to 47, the leveling accuracy is adversely affected.
[0017]
On the other hand, the initial offset amount measurement algorithm according to the present embodiment is characterized in that it has a measurement area map 16, sensor signal three-dimensional information 17, and matching processing 18.
[0018]
In FIG. 2, first, a measurement area map 16 is created from the sensor attachment position coordinates 11 and the initial offset amount measurement point coordinates 12. This is to determine the trajectory (coordinates) for driving the XY stage 43 in order to perform distance measurement on the surrounding two-dimensional plane including the initial offset amount measurement point P1. Here, as shown in FIG. 3, a trajectory (coordinates) is determined for each distance sensor so as to scan the nearby drive range area including the initial offset amount measurement point P <b> 1 five times. This drive range can be determined from the measurement spot diameter of the distance sensor, the machining accuracy such as the distance sensor attachment, and the like. As shown in FIG. 3, when scanning is performed in a reciprocating motion, the scanning directions are different between the forward path and the backward path. In this case, for example, it is necessary to perform processing for reversing the start point and the end point of the scan in the return path to have the same signal pattern as the scan in the forward path. Of course, for example, if scanning is performed only in the forward path, the above processing is unnecessary.
[0019]
Next, the XY stage drive command 13 is calculated based on the determined coordinates, and the XY stage 43 is driven. As a result, the three-dimensional information 17 of the sensor signal 14 is created by holding the signal pattern from the distance sensor by five scans as the sensor signal 14.
[0020]
These are performed for each of the three distance sensors 45 to 47. Then, a signal pattern matching process 18 is performed on the basis of the three-dimensional information 17 of each sensor signal to extract a match for the five signal patterns from the three distance sensors 45 to 47, and the extracted three signals The same point (initial offset amount measurement point P1) is estimated from the pattern.
[0021]
Note that the algorithm of the matching process 18 may be as simple as performing a correlation process or obtaining a peak value (maximum or minimum value).
[0022]
Finally, a sensor signal value at the estimated same point is extracted, and an initial offset amount 15 of another distance sensor is calculated based on one sensor signal value.
[0023]
FIG. 4 shows an example of three-dimensional information of sensor signals from the distance sensors 45 to 47. In the conventional method, the initial offset amount is calculated based on the values of 19a, 19b, and 19c. This is because the same point P1 of the mask 41 is not measured, and thus the calculated value has an error. Will be included. When leveling control is performed using such an offset amount, the measurement value always includes this error.
[0024]
On the other hand, in the initial offset amount measurement algorithm according to this embodiment, the maximum value of the signal pattern is detected by performing the matching process 18, and the same point on the mask 41 as 20a, 20b, and 20c is extracted. . This means that the surface shape of the mask 41 is convex and the initial offset amount measurement point P1 happens to be located at the peak.
[0025]
Next, the level in the Z-axis direction (vertical axis in FIG. 4) is detected as a distance from the signal pattern having the extracted points 20a, 20b, and 20c, and the remaining two levels when a certain level is used as a reference. Is calculated as the initial offset amount. These initial offset amounts are sent to an alignment apparatus for subsequent alignment processing.
[0026]
In the alignment apparatus, since the initial offset amount sent is a value obtained by correcting an error caused by the surface state of the mask 41 and the installation position shift of each of the distance sensors 45 to 47, the alignment (positioning) accuracy is improved. Can do.
[0027]
As mentioned above, although the embodiment of the present invention has been described for the case of mask leveling, it is needless to say that it can also be applied to wafer leveling.
[0028]
【The invention's effect】
According to the present invention, since the initial offset amount of each distance sensor can be accurately measured at the same place of the measurement object (mask / wafer), the leveling accuracy can be improved. This is particularly effective in leveling when the accuracy of mounting the distance sensor cannot be strictly guaranteed or when the surface shape of the measurement object is rough.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a leveling measurement system according to the present invention.
FIG. 2 is a functional block diagram of an initial offset amount measurement algorithm installed in the measurement apparatus shown in FIG.
FIG. 3 is a diagram for explaining an operation of scanning a nearby drive range area including an initial offset amount measurement point by a distance sensor in the present invention.
4 is a diagram illustrating an example of three-dimensional information of sensor signals obtained from the three distance sensors in FIG. 1. FIG.
FIG. 5 is a view for explaining an outline of an X-ray exposure apparatus;
6 is a view showing a relationship among a mask, a wafer, and an XY stage in the X-ray exposure apparatus of FIG.
FIG. 7 is a diagram for explaining a method of measuring the position and orientation of a mask using three distance sensors.
[Explanation of symbols]
41 Mask 42 Wafer 43 XY Stages 45, 46, 47 Distance Sensor G1 Initial Offset Amount Measurement Point 10 Measuring Device 11 Sensor Mounting Position Coordinate 12 Initial Offset Amount Measurement Point Coordinate 13 XY Stage Drive Command 14 Sensor Signal 15 Initial Offset Quantity 16 Measurement area map 17 Three-dimensional information 18 of sensor signal Matching process 30 XY stage driving device

Claims (6)

When leveling a mask or wafer in an exposure apparatus so as to be parallel to a stage that is movable in at least the X-axis and Y-axis directions, the mask is driven by a plurality of leveling sensors installed on the stage by driving the stage. Alternatively, in the leveling measurement method for measuring the distance to the same point on the wafer and calculating the initial offset amount from the sensor signals of the plurality of sensors,
For each of the plurality of sensors, creating a measurement area map for scanning the vicinity of the same point of the mask or wafer a plurality of times;
Driving the stage based on the measurement area map and scanning the vicinity of the same point of the mask or wafer a plurality of times by each of the plurality of sensors;
Holding a plurality of pattern measurement information obtained by a plurality of scans obtained from each of the plurality of sensors as three-dimensional information;
Performing a pattern matching process on the three-dimensional information by the held sensors and estimating the same point of the mask or wafer from the matched pattern;
And calculating the initial offset amount of the plurality of sensors by referring to the three-dimensional information by the plurality of sensors using the estimated same point of the mask or wafer, respectively. Measurement method. The leveling measurement method according to claim 1, wherein the measurement area map is based on a known attachment position coordinate of the plurality of sensors and a known position coordinate of the same point of the mask or wafer. A measuring method for leveling, characterized by being created. 3. The leveling measurement method according to claim 1, wherein three sensors as the plurality of sensors are installed at positions separated from each other on the stage. When leveling a mask or wafer in an exposure apparatus so as to be parallel to a stage that is movable in at least the X-axis and Y-axis directions, the mask is driven by a plurality of leveling sensors installed on the stage by driving the stage. Alternatively, in the leveling measurement control device for measuring the distance to the same point on the wafer and calculating the initial offset amount from the sensor signals of the plurality of sensors,
The leveling measurement control device has a function of executing a predetermined initial offset measurement algorithm,
The initial offset amount measurement algorithm is:
For each of the plurality of sensors, creating a measurement area map for scanning the vicinity of the same point of the mask or wafer a plurality of times;
Driving the stage based on the measurement area map and scanning the vicinity of the same point of the mask or wafer a plurality of times by each of the plurality of sensors;
Holding a plurality of pattern measurement information obtained by a plurality of scans obtained from each of the plurality of sensors as three-dimensional information;
Performing a pattern matching process on the three-dimensional information by the held sensors and estimating the same point of the mask or wafer from the matched pattern;
The leveling measurement control apparatus, wherein the initial offset amount of the plurality of sensors is calculated by referring to the three-dimensional information by the plurality of sensors using the estimated same point of the mask or wafer. 5. The leveling measurement control device according to claim 4, wherein the measurement area map is based on a known attachment position coordinate of the plurality of sensors and a known position coordinate of the same point of the mask or wafer. Leveling measurement control device, characterized by being created by 6. The leveling measurement control apparatus according to claim 4, wherein three sensors as the plurality of sensors are installed at positions separated from each other on the stage.

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