JP2000114150A - Alignment method and overlay measuring method in lithography process, aligner, and overlay measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make abnormal data removable with high accuracy by finding the medium value of a plurality of residual data, and removing measured data corresponding to the residual data which exceed a preset allowable value as abnormal data on the basis of the medium value. SOLUTION: When an aligner makes alignment, the positional deviated amounts of alignment marks formed on a wafer from prescribed positions are measured (ST1). Then alignment correcting amounts are found (ST2), and a plurality of residual data are obtained by removing the linear error components of the wafer from each obtained measured data (ST3). After obtaining the residual data, the medium value of the data is found (ST4) and whether the residual data exceed a preset allowable value is discriminated on the basis of the medium value and the residual data exceeding the allowable value are decided as being abnormal data (ST6). Finally, the measured data corresponding to the residual data which were discriminated as being abnormal data are removed from stored measured data (ST7).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aligning method and an overlay measuring method for an exposure apparatus in a lithography process for manufacturing a semiconductor device, an exposure apparatus, and an overlay measuring apparatus.

[0002]

2. Description of the Related Art In a conventional lithography process in the manufacture of a semiconductor device, prior to exposure, an alignment mark formed on a wafer is used to align a design pattern of the next process with a pattern existing on the wafer, and then the exposure is performed. To suppress the occurrence of misalignment with the existing pattern on the wafer. After exposure and development,
The overlay measurement mark formed on the wafer and the resist pattern formed on the wafer by this exposure and development are measured for the amount of misalignment, and the obtained overlay measurement data is reflected in the next alignment. .

In recent years, the pattern size of semiconductor devices has been miniaturized, and accordingly, the overlay accuracy between patterns required in a lithography process has become strict. However, for example, when the measurement mark composed of the alignment mark and the overlay measurement mark becomes rough due to a process trouble or the like caused in the previous process, or when foreign matter adheres, abnormal measurement occurs, and the data obtained as a result is obtained. That is, the accuracy of the alignment correction amount and overlay measurement data of the exposure apparatus may be reduced.

[0004] Therefore, a data processing method for removing abnormal data obtained by abnormal measurement has been studied and attempted. For example, in the case of alignment of an exposure apparatus, as shown in the flowchart of FIG. 7, first, in step (hereinafter, referred to as ST) 21, preliminary measurement (pre-alignment) is performed prior to alignment to determine a temporary shot array lattice ( ST22). Next, alignment measurement at the first point is performed (ST23), and the measurement data and ST
The amount of deviation from the array lattice determined in 2 is obtained (ST2).
4).

[0005] Then, it is determined whether or not the deviation exceeds a predetermined allowable value (ST25). If it is determined that the deviation does not exceed the allowable value, the measurement data at that point is left as normal data, and the process proceeds to ST23. Returning to the second point and thereafter, the same procedure is repeated. If it is determined in ST25 that the deviation amount exceeds the allowable value, the measurement data at that point is deleted as abnormal data,
Return to

As another processing method for removing abnormal data obtained by abnormal measurement, a standard deviation of a deviation amount is obtained, and XX times (eg, 2.75σ) or more of the standard deviation is excluded as abnormal data. Is adopted.

[0007]

However, in all of the above-described conventional methods for removing abnormal data, it is necessary to set the allowable value for determining abnormal data to be rather loose, for example, about several μm. This is because the measured data contains a linear error component such as an error in the elongation (scaling) of the wafer that actually exists, and if the allowable value is set strictly, it is not abnormal data. This is because there is a risk that the data may be erroneously determined as abnormal data.

When the average value of the deviation amount is used as in the method of removing abnormal data from the standard deviation, for example, when large abnormal data is generated, the average value itself is pulled by the abnormal data. Would. as a result,
There is a risk that even normal data may be erroneously determined as abnormal data. Therefore, it is impossible to remove abnormal data with high accuracy by the conventional method, and it is hardly practical. Therefore, in alignment and overlay measurement of an exposure apparatus, development of a technology capable of removing abnormal data with high accuracy, thereby always performing proper alignment correction and improving overlay accuracy is desired.

[0009]

In order to solve the above-mentioned problems, an alignment method in a lithography process according to the present invention provides a method of aligning a position of an alignment mark formed on a wafer from a specified position. The measurement is performed for a plurality of positions in the wafer, a linear error component of the wafer is removed from each of the obtained plurality of measurement data to obtain a plurality of residual data, and then a median of the plurality of residual data is obtained. On the basis of the reference, the measurement data corresponding to the residual data exceeding the preset allowable value is excluded as abnormal data.

Further, the method for measuring overlay in a lithography process according to the present invention includes the steps of:
The position of the overlay measurement mark formed on the wafer after exposure is deviated from the position of the overlay measurement mark formed on the wafer. A plurality of residual data is obtained by removing the linear error component of the wafer from each of the data. Then, similarly to the above invention, the configuration is such that abnormal data is removed from measurement data based on a plurality of residual data.

Further, in the exposure apparatus according to the present invention, at the time of alignment, a measuring means for measuring a deviation amount of a position of an alignment mark formed on a wafer from a specified position at a plurality of positions in the wafer, and a measuring means, Removing means for removing abnormal data using the measured data obtained, wherein the removing means removes a linear error component of the wafer from each of the plurality of measured data obtained by the measuring means and removes a plurality of residual data. And a median value of a plurality of residual data is obtained, and it is determined whether or not each of the plurality of residual data exceeds a preset allowable value based on the median value. When it is determined that the measured value has exceeded the threshold value, the measurement data corresponding to the residual data is excluded as abnormal data. It has become had a determination function of the measured data and normal data structure.

Further, the overlay measuring apparatus according to the present invention comprises:
Measuring means for measuring the amount of deviation of the position of the overlay measurement mark formed on the wafer through exposure from the position of the overlay measurement mark formed on the wafer at a plurality of positions in the wafer during the overlay measurement; ,
Removing means for removing abnormal data using the measurement data obtained by the measurement means, wherein the removal means removes a linear error component of the wafer from each of the plurality of measurement data obtained by the measurement means. Error component removal function to obtain a plurality of residual data, determine the median of the plurality of residual data, each of the plurality of residual data based on the median,
It is determined whether or not a predetermined allowable value has been exceeded.If it is determined that the allowable value has been exceeded, measurement data corresponding to the residual data is removed as abnormal data, and if it is determined that the allowable value has not been exceeded, the residual data is determined. It has a function of determining a measurement data corresponding to data as normal data.

In the alignment method and the overlay measurement method in the lithography step of the present invention, the linear error component of the wafer is removed from the measurement data before obtaining the median value. Therefore, even if the measurement data contains a large linear error component. Also, the linear error component does not affect the subsequent setting of the median. In addition, the median value obtained from the plurality of residual data from which the linear error component has been removed is compared with the case where the average value of the residual data is obtained, even if some of the plurality of residual data include other large error components. This value is hardly affected by the error component. Then, in order to perform the removal of the abnormal data using the residual data from which the linear error component has been removed based on such a median value, it is necessary to strictly set a predetermined allowable value for removing the abnormal data. Will be possible. Therefore, abnormal data is removed with high accuracy.

Further, in the exposure apparatus and the overlay measuring apparatus according to the present invention, the error component removing function of the removing means removes the linear error component of the wafer from each of the plurality of measurement data obtained by the measuring means to obtain a plurality of residual data. The determination function determines the median of the plurality of obtained residual data, and determines whether each of the plurality of residual data exceeds a preset allowable value based on the median, When it is determined that the allowable value is exceeded, the residual data is removed as abnormal data, and when it is determined that the allowable value is not exceeded, the residual data is regarded as normal data. Therefore, since the alignment method and the overlay measurement method according to the above-described invention can be reliably performed, the same operation as these methods can be obtained.

[0015]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a main part of an embodiment of an exposure apparatus according to the present invention. In particular, the present invention is applied to an alignment correction amount calculation unit built in the exposure apparatus in a lithography process of semiconductor device manufacturing. FIG. As shown in FIG.
Are the measuring means 2, the storing means 3, the calculating means 4, and the removing means 5.
It is comprised including.

The measuring means 2 measures the amount of deviation of the position of the alignment mark formed on the wafer from the specified position when aligning the exposure apparatus. It is configured similarly. The storage unit 3 stores the measurement data obtained by the measurement unit 2, the calculated alignment correction amount, an allowable value described later, and the like. For example, a storage unit such as a random access memory (RAM) or a floppy disk is used. It is made up of media. Further, the calculating means 4 includes the storage means 3
Has the function of reading the measurement data stored in the memory and calculating the amount of alignment correction.

The removing means 5 uses the measured data obtained by the measuring means 2 to remove abnormal data from the measured data, and has an error component removing function 5a and a judging function 5b. I have. Error component removal function 5a
Is a function of removing a linear error component of a wafer from each of the plurality of measurement data obtained by the measurement means 2 to obtain a plurality of residual data. The linear error component is a component that can be corrected by the exposure apparatus, and includes, for example, a scaling error.

The determining function 5b determines a median value of the plurality of residual data, and determines whether each of the plurality of residual data exceeds a preset allowable value based on the median value to determine the allowable value. The residual data exceeding
It has a function of removing measurement data corresponding to residual data determined to be abnormal data from the measurement data stored in the storage means 3. In the present embodiment, it is determined whether or not the absolute value of the value obtained by subtracting the median from the plurality of residual data exceeds an allowable value.

Next, an embodiment of the alignment method in the lithography process of the present invention based on the operation of the calculation unit 1 will be described with reference to the flowchart shown in FIG.
Here, in the alignment in the reduction projection exposure apparatus (stepper), the deviation amount of the position of the alignment mark formed on the wafer from the specified position is measured only by one point in the shot generally adopted at present. Is described.

First, as shown in ST1 of FIG. 2, measurement is performed a plurality of times to determine the amount of deviation of the position of the alignment mark formed on the wafer from the specified position, and a plurality of measurement data is obtained. That is, the measuring unit 2 measures the amount of deviation of the position of the alignment mark from the specified position in each of the shots in the plurality of shot areas in the wafer plane. Then, the measurement unit 2 sends the obtained result to the storage unit 3, and the storage unit 3 stores the sent data as measurement data.

Next, the calculation means 4 reads the measurement data from the storage means 3, and calculates an alignment correction amount based on the measurement data (ST2). The calculated alignment correction amount is output to the storage means 3 and stored therein.

Next, the error component removing function 5a reads the measurement data of each shot from the storage means 3, removes a linear error component from each of the read measurement data, and obtains residual data as a residual value (ST3). ). Subsequently, the determination function 5b obtains a median from the plurality of residual data obtained in ST3 (ST4), and subtracts the median from each residual data (ST5). Then, the judgment function 5 b
Is read, and it is determined whether or not the absolute value of the value obtained by subtracting the median value from the residual data of each shot exceeds the allowable value (ST6).

Here, the residual data includes error components such as the stage accuracy of the exposure apparatus and the measurement reproducibility of the measuring machine constituting the measuring means 2. The value of the error component is approximately 20 nm to 30 n based on the recent accuracy of equipment accuracy.
m. Therefore, a value exceeding this may be considered as some alignment measurement error. That is, a value exceeding about 30 nm is adopted as the allowable value.
However, as a matter of course, since the measurement reproducibility of the measuring instrument differs depending on the process, it is necessary to set an allowable value accordingly.

When the determining function 5b determines that the absolute value of the value obtained by subtracting the median from the residual data exceeds the allowable value, the value is regarded as an abnormal value, and the value corresponding to the residual data obtained by adding the median to this value is determined. From the measurement data stored in the storage means 3 as abnormal data (ST
7). Thereafter, returning to ST2, the calculating means 4 calculates the alignment correction amount based on the measurement data from which the abnormal data has been removed. In the exposure apparatus, the alignment is corrected by adjusting the position of the stage that holds the wafer based on the obtained alignment correction amount.

On the other hand, when the determination function 5b determines that the absolute value of the value obtained by subtracting the median from the residual data does not exceed the allowable value, the value is regarded as a normal value, and the residual data obtained by adding the median to this value is determined. Is kept stored in the storage means 3 as normal data. Then, in the exposure apparatus, exposure is performed in a state where the alignment is corrected based on the alignment correction amount obtained in ST2.

In the above embodiment, since the error component removing function 5a removes the linear error component of the wafer from the measurement data before the determination function 5b finds the median value, even if the measurement data contains a large linear error component. However, it is possible to avoid such a disadvantage that the subsequent setting of the median value is affected by the linear error component. In addition, the median value obtained from the plurality of residual data obtained by the correction by removing the linear error component is used to calculate the average value of the residual data even if some of the plurality of residual data include other large error components. This value is less likely to be affected by the error component than in the case. Then, since the determination function 5b removes the abnormal data using the median as a reference and using the residual data from which the linear error component has been removed, an allowable value set in advance for removing the abnormal data is set. Can be set strictly.

FIG. 3 is a diagram (part 1) showing a result obtained by simulating the removal of abnormal data from the measurement data in the alignment of the stepper by the method of the above embodiment (part 1). FIG. In this drawing, 1 and 2 on the left side represent measured data and residual data when there is no abnormal value, and 1 and 2 on the right side represent measured data (nm) and residual data (nm) when there is an abnormal value. .

As shown in the figure, the value obtained by subtracting the median from the residual data in shot (1, 2) is an abnormal value.
Therefore, the measurement data in shot (1, 2) becomes abnormal data. On the other hand, in the conventional method in which the tolerance is set to a relatively low value, the difference between the normal data and the abnormal data in the shot (1, 2) is as small as about 80 nm in the measurement data indicating the amount of displacement of the alignment mark position. The measurement data in the shot (1, 2) cannot be captured as abnormal data.

That is, the measurement data may be normal data but have a larger value than that of the shot (1, 2), such as the measurement data of the shot (6, 1), which is another shot area. is there. Therefore, if the allowable value is made stricter to catch the abnormal data, even the measurement data that is the normal data may be removed as the abnormal data. The method requires the tolerances to be set fairly loose, resulting in shots (1,
The measurement data in 2) cannot be caught as abnormal data.

In the example shown in FIG. 3, the median value when there is no abnormal value is -7 nm and 7 nm, respectively, for the X coordinate and the Y coordinate, and the median value when there is an abnormal value is -13 nm for the X coordinate and the Y coordinate, respectively. , 11 nm. As a result, when there is no abnormal value, the maximum difference from the median is 15 nm and 14 nm, respectively, when there is an abnormal value. When there is an abnormal value, the maximum difference from the median is X coordinate and Y coordinate, respectively. 91n
m, 81 nm.

Therefore, the allowable value is previously set to, for example, 50 nm.
In this case, the value obtained by subtracting the median from the residual data in shot (1, 2) can be determined as an abnormal value, and the measurement data in shot (1, 2) can be removed as abnormal data. As described above, according to the present embodiment, it is confirmed that the allowable value can be set to a strict value, whereby abnormal data can be accurately removed.

FIG. 4 is a diagram (part 2) showing a result obtained by simulating the removal of abnormal data from the measurement data in the alignment of the stepper by the method of the above embodiment (part 2). Is shown in comparison with the average value standard. Also in this drawing, 1 and 2 on the left are measurement data and residual data when there is no abnormal value, and 1 and 2 on the right are measurement data (nm) and residual data (nm) when there is an abnormal value.
Is shown. Also, the result is obtained when the allowable value is set to 50 nm.

In the example shown in FIG. 4, in the case of the median value reference, the median value is 17 nm and 17 nm, respectively, in the X coordinate and the Y coordinate. In the case of the average value reference, the average value is about -4 nm in the X coordinate and the Y coordinate, respectively. , 6 nm. As a result, the maximum difference from the median value is 171 nm and 164 nm, respectively, in the case of the median value reference, and the maximum difference from the average value is the X coordinate, Y coordinate in the case of the average value, respectively. Fifteen
0 nm and 153 nm.

Therefore, in practice, only the value obtained by subtracting the median from the residual data in shot (1, 2) is an abnormal value, and therefore only the measurement data in shot (1, 2) is abnormal data. On the other hand, in the case of the average value standard, a value obtained by subtracting the median value from the residual data is determined as an abnormal value even for a normal shot (2, 0). This can be said to be due to the fact that the average value is pulled by the abnormal data as described above. In the example shown in FIG. 4, the difference between the two determination results is relatively low, but if the value of the abnormal data in the shot (1, 2) is further increased (to the minus side), the difference between the determination results becomes obvious. Not even.

As is apparent from the above simulation results, in the above embodiment, the median is obtained from the residual data obtained by removing the linear error component, and the abnormal data is removed based on the obtained median. Thus, the allowable value set in advance for removing abnormal data can be set strictly, so that abnormal data can be removed from the measured data with extremely high accuracy. Therefore, proper alignment correction can always be performed, and the overlay accuracy can be improved. As a result, it is expected that the manufacturing yield of the semiconductor device using the exposure apparatus including the method and the calculation unit 1 of the present embodiment is improved, and that the overall productivity is improved by reducing the rework work.

Next, an embodiment of the overlay measuring apparatus according to the present invention will be described. FIG. 5 is a block diagram showing a main configuration of an embodiment of the overlay measuring apparatus according to the present invention.

The overlay measuring apparatus 10 is used for measuring an overlay after exposure in a lithography process for manufacturing a semiconductor device. In the overlay measurement apparatus 10 of this embodiment, the calculation unit 1 of the exposure apparatus shown in FIG.
The difference from the above is that the measuring unit 11 is formed separately from the exposure apparatus, and that the measurement contents of the measuring unit 11 are different from those of the measuring unit 2 of the calculating unit 1.

That is, the measuring means 11 determines that the position of the overlay measurement mark formed of, for example, a resist formed on the wafer after exposure is shifted from the position of the overlay measurement mark formed on the wafer during the overlay measurement. The measurement of the amount is performed at a plurality of positions in the wafer. Such a measuring means 11 is configured similarly to that provided in the conventional overlay measuring apparatus. The other components of the overlay measuring device 10, namely, the storage unit 3, the calculation unit 4, and the removal unit 5, are configured in the same manner as the calculation unit 1 described above, and thus description thereof will be omitted.

Next, an embodiment of the overlay measuring method in the lithography process of the present invention based on the operation of the overlay measuring apparatus 10 will be described with reference to the flowchart shown in FIG. Here, a case will be described in which the displacement of the position of the overlay measurement mark on the wafer is measured at only one point in the shot.

As shown in FIG. 6, the overlay measurement method of this embodiment is different from the alignment method shown in FIG.
Except that the eleven steps are different, it can be basically considered almost the same. That is, in ST11, first, the measurement of the amount of deviation of the position of the overlay measurement mark formed on the wafer through the exposure from the position of the overlay measurement mark formed on the wafer is performed a plurality of times. Obtain measurement data of That is, the measuring unit 11 measures the amount of displacement of the position of the overlay measurement mark in each of the shots on the plurality of shot areas in the wafer plane. Then, the measuring unit 11 stores the obtained result in the storage unit 3
And the storage means 3 stores the transmitted data as measurement data.

Thereafter, the process goes through ST12 to ST16 corresponding to ST2 to ST6 shown in FIG. And S
At T16, when the determination function 5b determines that the absolute value of the value obtained by subtracting the median from the residual data exceeds the allowable value,
This value is regarded as an abnormal value, and the measurement data in the shot having this value is removed from the storage means 3 as abnormal data (ST1).
7) Return to ST12. If the determination function 5b determines that the absolute value of the value obtained by subtracting the median from the residual data does not exceed the allowable value, this value is regarded as a normal value, and the measurement data at the shot coordinates is regarded as normal data.
To be stored. Then, the measurement is completed.

As described above, also in the overlay measuring apparatus and method of the above embodiment, after the error component removing function 5a removes the linear error component and obtains the residual data, the determining function 5b sets the abnormal value based on the median value. Since the data is removed, an allowable value set in advance for removing abnormal data can be strictly set. Therefore, the abnormal data can be removed from the measurement data with high accuracy, and can be reflected in the alignment at the time of the next wafer exposure, so that the overlay accuracy can be improved. The effect can be obtained.

In this embodiment, the case of measuring one point in a shot has been described. However, the present invention can be applied to the case of multipoint measurement in a shot, which may be performed recently.

[0044]

As described above, according to the alignment method and the overlay measurement method in the lithography process according to the present invention, after removing the linear error component of the wafer from the measurement data, the median value is calculated from the residual data without the linear error component. Is obtained, and abnormal data is removed based on the median value. Therefore, an allowable value set in advance for removing abnormal data can be set strictly. Therefore, abnormal data can be removed with high accuracy, and proper alignment correction can always be performed, so that overlay accuracy can be improved. As a result, it is expected that the production yield of the semiconductor device is improved, and that the overall productivity is improved by reducing the rework work.

According to the exposure apparatus and the overlay measuring apparatus of the present invention, an error component removing function for removing a linear error component of a wafer from measurement data, and a median value is obtained from residual data obtained by removing a linear error component. Since there is provided a removing unit having a determination function of determining abnormal data based on the median, the alignment method and overlay measurement method according to the above invention can be reliably performed. Therefore, effects similar to those of the method of the present invention can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing an embodiment of an alignment method in a lithography step according to the present invention.

FIG. 3 is a diagram (part 1) illustrating a result obtained by simulating removal of abnormal data from measurement data in stepper alignment by the method of the embodiment.

FIG. 4 is a diagram (part 2) illustrating a result obtained by simulating removal of abnormal data from measurement data in stepper alignment by the method of the embodiment.

FIG. 5 is a block diagram illustrating a main configuration of an embodiment of an overlay measurement device according to the present invention.

FIG. 6 is a flowchart illustrating an embodiment of an overlay measurement method according to the present invention.

FIG. 7 is a flowchart illustrating an example of a method for removing abnormal data during alignment in a conventional lithography process.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Calculation part, 2, 11 ... Measurement means, 4 ... Calculation means, 5 ...
Removing means, 5a: error component removing function, 5b: determining function,
10 ... Overlay measuring device

Claims (4)

[Claims] In an alignment of an exposure apparatus in a lithography process of manufacturing a semiconductor device, a measurement of a deviation amount of a position of an alignment mark formed on a wafer from a predetermined position is performed at a plurality of positions in the wafer. The linear error component of the wafer is removed from each of the measurement data to obtain a plurality of residual data.Then, a median of the plurality of residual data is obtained, and a predetermined allowable value is exceeded based on the median. An alignment method in a lithography process, wherein measurement data corresponding to residual data is excluded as abnormal data. 2. When overlay measurement is performed after exposure in a lithography process of manufacturing a semiconductor device, a position of an overlay measurement mark formed on a wafer after the exposure is shifted from a position of an overlay measurement mark formed on the wafer. The deviation amount is measured for a plurality of positions in the wafer, and a plurality of residual data is obtained by removing a linear error component of the wafer from each of the plurality of obtained measurement data. An overlay measurement method in a lithography process, wherein the measured data corresponding to residual data exceeding a predetermined allowable value is determined as abnormal data with reference to the median value. 3. A measuring means for measuring an amount of deviation of a position of an alignment mark formed on a wafer from a specified position at a plurality of positions in a wafer during alignment of an exposure apparatus in a lithography process of manufacturing a semiconductor device. Removing means for removing abnormal data using the measurement data obtained by the measurement means, wherein the removal means removes a linear error component of the wafer from each of the plurality of measurement data obtained by the measurement means. An error component removing function of obtaining a plurality of residual data by calculating a median value of the plurality of residual data, and determining whether each of the plurality of residual data exceeds a predetermined allowable value based on the median value. If it is determined that the value exceeds the allowable value, the measurement data corresponding to the residual data is removed as abnormal data, and it is determined that the value does not exceed the allowable value. Exposure apparatus, characterized in that it has a determination function, a to the normal data measurement data corresponding to the remaining data if the. 4. When overlay measurement is performed after exposure in a lithography process of manufacturing a semiconductor device, a position of an overlay measurement mark formed on a wafer after the exposure is shifted from a position of an overlay measurement mark formed on the wafer. Measuring means for measuring the amount of displacement at a plurality of positions within the wafer, and removing means for removing abnormal data using the measurement data obtained by the measuring means, wherein the removing means comprises: An error component removing function of removing a linear error component of the wafer from each of the plurality of measurement data obtained in the above to obtain a plurality of residual data; and finding a median value of the plurality of residual data. Is determined based on the median value as to whether or not a predetermined allowable value has been exceeded. If it is determined that the allowable value has been exceeded, the residual data is determined. A measurement function that removes measurement data to be performed as abnormal data and determines that measurement data corresponding to the residual data is normal data when it is determined that the measured data does not exceed an allowable value. .