JP2004361305A - Ultrasonic thickness measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure thickness accurately by using ultrasonic even a measuring object from which only a little reflection wave can be obtained. <P>SOLUTION: The difference in arrival time of reflection wave of emitted ultrasonic is observed between a wave from the front surface of the measuring object and a wave from the back surface of the measuring object. The thickness of the measuring object is measured for a plurality of times by calculating the distance between the front surface and the back surface from the difference of the arrival times, and a plurality of measured values showing the thickness of the measuring object at every measurement are obtained in processes from S30 to S32. In the process of measured value processing S33, the measured values regarded not affected by noise erroneously observed as reflection wave are extracted from the measured values, and the thickness of the measuring object is calculated based on the extracted measured values. The calculated values are exhibited as the measured result of the thickness of the measuring object in the process S34. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for measuring the thickness of an object using ultrasonic waves.
[0002]
[Prior art]
As an example of a technique for measuring the thickness of an object using ultrasonic waves, a technique disclosed in Patent Document 1 will be described with reference to FIG.
In FIG. 3, an ultrasonically permeable elastic body 104 is disposed on a surface of the ultrasonic probe 103 held by the handling device 101 via the pressing adjustment means 105 on the side of the object to be measured 102. Is shown. Here, the object to be measured 102 is pressed by the ultrasonic probe 103 by the pressing adjustment means 105 via the elastic body 104. In this case, the ultrasonic probe 103 is placed in contact with the measurement point of the object to be measured 102 via the elastic body 104 while maintaining the vertical state, and the pressing of the elastic body 104 The degree of elastic deformation is kept constant.
[0003]
In this state, the ultrasonic wave m is transmitted from the ultrasonic probe 103 and made to enter the object 102 through the elastic body 104 from a direction perpendicular to the surface of the object 102. This ultrasonic wave m is reflected on the bottom surface of the device under test 102, travels again in a direction perpendicular to the surface of the device under test 102, and returns to the ultrasonic probe 103 through the elastic body 104. At this time, the measurement is performed based on a time difference between detection timings of the ultrasonic waves emitted from the ultrasonic probe 103, which are received by the ultrasonic probe 103, from the front and rear surfaces of the object to be measured 102, and the like. The thickness information of the object 102 is obtained.
[0004]
Patent Literature 1 discloses a technique for automatically measuring the thickness of the DUT 102 as described above.
In the above-described thickness measurement method, for example, the waveform shown in FIG. 4A is obtained as the measurement waveform of the ultrasonic wave received by the ultrasonic probe 103. 4A and 4B, the horizontal axis represents the passage of time, and the vertical axis represents the amplitude of the ultrasonic wave.
[0005]
4A, a waveform appearing after the transmission wave waveform 10 is a surface wave waveform 11 which is a waveform of a reflected wave from the surface of the device under test 102 or a waveform of a reflected wave from the back surface of the device under test 102. A threshold value 20 is generally set as a condition for recognizing each of the reflected wave waveforms of a certain back surface wave waveform 12 as being a reflected wave waveform.
[0006]
By the way, for example, when the thickness of an object to be measured is extremely small, or due to the shape of the ultrasonic reflecting surface, when measuring the thickness of the object to be measured, the reflected wave can be obtained only minutely. Generally, the reflected waveform signal is amplified by using an amplifier.
[0007]
As shown in the example of FIG. 4A, when only the reflected wave waveform exceeds the open value 20, the distance from the intersection of the surface wave waveform 11 and the threshold value 20 to the intersection of the back wave waveform 12 and the threshold value 20 is determined. The thickness of the DUT 102 can be calculated from the time and the known sound speed.
Here, although the baseline 21 in the measurement waveform of the ultrasonic wave received by the ultrasonic probe 103 is normally flat, due to the influence of electromagnetic waves from inside and outside the measuring device, a minute noise component is actually included in the measurement waveform. Is constantly mixed in. Therefore, when a noise component having a large signal level is suddenly mixed in, the noise waveform 30 is amplified by an amplifier as shown in FIG. Sometimes. In the case of FIG. 4B, the noise waveform 30 is erroneously recognized as a waveform due to a reflected wave from the back surface, and the thickness is calculated. Therefore, an erroneous value is obtained as a thickness measurement result.
[0008]
In order to solve this problem, for example, in Patent Document 2, the time at which the surface wave waveform 11 and the back surface wave waveform 12 appear is grasped in advance, and the measured waveform is ignored except for the vicinity of the time. A method has been proposed in which a noise component is ignored by providing a prohibition gate. FIG. 5 is a flowchart showing a process of handling a measured value in the method disclosed in Patent Document 2, and by providing a prohibition gate for ignoring noise components, the method described above in the process of S60 is provided. After obtaining the calculation result of the measured thickness value, the measured value is output as it is in the step S61, so that the correct measured thickness value can be presented.
[0009]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-233952 [Patent Document 2]
Japanese Patent Application Laid-Open No. 9-152325
[Problems to be solved by the invention]
However, in the method disclosed in Patent Document 2 for removing a noise component using a forbidden gate, it is necessary to grasp the position on the measurement waveform where the waveform of the regular reflected wave appears.
[0011]
Further, in the measurement waveform, it is difficult to make the gap between the waveform of the regular reflected wave and the forbidden gate zero. Therefore, if a noise component is mixed in the gap, an error occurs in the thickness measurement result.
Also, in an object to be measured in which a reflected wave can be obtained only minutely, a small fluctuation may occur in the measurement waveform, and the fluctuation may cause a variation of about several microns in the measurement value, thereby lowering the measurement accuracy. There is a problem that.
[0012]
The present invention has been made in view of the above-described problems, and a problem to be solved is to measure the thickness using an ultrasonic wave, even if the object to be measured can obtain only a minute reflected wave. The purpose is to be able to measure the thickness well.
[0013]
[Means for Solving the Problems]
The present invention performs observation of the difference in arrival time between the reflected wave of the emitted ultrasonic wave and that arriving from the front surface of the measured object and that arriving from the back surface of the measured object, It is assumed that a thickness measurement method for measuring the thickness of the measured object by calculating the distance between the front surface and the back surface from the difference in the arrival times.
[0014]
And the ultrasonic thickness measurement method which is one of the aspects of the present invention obtains a plurality of measurement values indicating the thickness of the measured object obtained at each measurement by performing the above-described measurement a plurality of times, The value calculated based on the measurement value extracted from the plurality of measurement values, which is regarded as not being affected by noise that may be erroneously observed as the reflected wave, is used to measure the thickness of the object to be measured. The above-mentioned problem is solved by presenting as a result.
[0015]
By doing so, the measurement result of the thickness of the object to be measured is calculated based on the measurement value that is not affected by the noise contamination. The thickness can be measured.
In the above-described ultrasonic thickness measuring method according to the present invention, the above-described extraction may be performed based on a frequency distribution of the plurality of measured values.
[0016]
Since the occurrence of noise is irregular and the frequency of noise does not affect the measurement at all, the frequency distribution of the plurality of measured values with the highest frequency is at least affected by noise contamination. It can be considered that the measurement value is an appropriate measurement value that has not been received, and that the measurement value in the vicinity of the measurement having the highest frequency is also an appropriate measurement value. Therefore, by extracting such a measured value and using it for calculating the measurement result of the thickness of the object to be measured, the thickness of the object to be measured can be accurately measured even if the object has only a minute reflected wave. Become like
[0017]
Further, in the ultrasonic thickness measuring method according to the present invention described above, the above-mentioned presentation is a ratio of the number of measurement values extracted as being not affected by the noise to the number of the plurality of measurement values. May be performed when it is determined that is equal to or more than the predetermined ratio.
[0018]
By doing so, when a large number of acquired measurement values are affected by noise contamination, the measurement results of the thickness of the object to be measured are not presented. There is no significant reduction due to the influence of noise mixing.
[0019]
In the above-described ultrasonic thickness measuring method according to the present invention, the above-mentioned presentation may be performed when it is determined that there is no fluctuation in the plurality of measured values.
For example, if the frequency of the largest frequency in the frequency distribution of the plurality of measured values is remarkably larger than the frequency of the measured value in the vicinity, the frequency can be regarded as an appropriate measured value. It can be determined that there is no fluctuation in the plurality of measured values. By performing this determination, a decrease in the accuracy of the thickness measurement result is suppressed.
[0020]
In the above-described ultrasonic thickness measurement method according to the present invention, in the calculation performed for the above-described presentation, a weighted average is calculated based on the number of acquired measurement values for the extracted measurement values. You can do so.
By doing so, the accuracy of the measurement result of the thickness of the measured object can be improved.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a method for measuring the thickness of an object using ultrasonic waves according to the present invention will be described with reference to the drawings.
In this embodiment, when an ultrasonic wave is incident on the object to be measured from a direction perpendicular to the surface of the object, the ultrasonic wave is reflected by the front and back surfaces of the object to be measured. A method of detecting the wave and the backside wave and calculating the difference between the arrival times of the surface wave and the backside wave by the speed of sound to obtain the thickness of the measured object as the value of the measurement result will be described with reference to FIG. The method used shall be used as it is.
[0022]
First, FIG. 1 will be described. FIG. 5 is a flowchart showing a procedure of a method of processing a thickness measurement result according to the present invention.
First, in the step of S30, a measurement value as a measurement result of the thickness of the object to be measured obtained by the method shown in FIG. 3 is obtained, and in the subsequent step of S31, data indicating the measurement value is stored in a semiconductor memory or the like. To a storage device. The number of stored data can be set arbitrarily, and in the present embodiment, the number of stored data is set to i. In the present embodiment, it is assumed that the measured value of the thickness of the object to be measured is obtained on the order of micrometers (μm).
[0023]
In the step of S32, it is determined whether or not the number n of acquisitions of the measured values performed in the step of S30 is equal to or larger than the set number i of stored data. If the determination result is Yes, the procedure proceeds to S33. . On the other hand, if the determination result is No, the procedure returns to S30, and the above-described steps S30 and S31 are repeated.
[0024]
In the step S33, the measured value stored in the above-described step S31 is subjected to a measured value processing described later, and in the subsequent step S34, the result of the measured value processing is a measurement result of the thickness of the measured object. Is output and presented to the measurer, and the procedure shown in FIG. 1 ends.
[0025]
Next, the processing content of the measurement value processing performed in the step S33 in FIG. 1 will be described with reference to the flowchart shown in FIG.
First, in the step of S40, the frequency distribution of the measured values stored in the step of S31 of FIG. 1 is examined, and among these, the measured value having the largest number of appearances (frequency) (hereinafter, referred to as “mode”) Is extracted, and in the subsequent step S41, the number of appearances of the mode in the stored measured values is obtained. The number of appearances of this mode is stored.
[0026]
In the step S42, the number of times that a value larger by 1 [μm] than the mode value described above appears as a measured value in the measured values stored in the step S31 of FIG. 1 is obtained.
In the step S43, the number of times that a value smaller by 1 [μm] from the mode value described above as a measured value in the measured values stored in the step S31 of FIG. 1 is obtained.
[0027]
In step S44, the total of the number of appearances determined in each of the above-described steps S41 to S43 is calculated, and the ratio of the total number to the number of stored measurement values stored in step S31 in FIG. Is calculated, and it is determined whether or not this ratio is equal to or greater than a predetermined ratio. This predetermined ratio can be set arbitrarily, and is set to, for example, 90%. If the ratio of the “mode ± 1 [μm]” is equal to or more than a predetermined ratio, the measurement result of the thickness measurement of the object to be measured performed a plurality of times may not have an influence on the measurement due to the inclusion of the noise component. It can be considered as something that can be done.
[0028]
When it is determined in the step S44 that the ratio of “mode ± 1 [μm]” is equal to or more than the predetermined ratio, in the subsequent step S45, the mode does not fluctuate and the thickness of the object to be measured is not changed. It is determined whether or not this mode value is stably obtained as a measurement result of the measurement. As a method of determining the stability, for example, the following inequality (the number of appearances of the mode)> the number of appearances of [｛(mode + 1 [μm])） + ｛(mode-1 [μm]) Number of occurrences of]
Is determined by determining whether or not.
[0029]
When it is determined in the step S45 that the mode is obtained stably without fluctuation as a measurement result of the thickness measurement of the measured object, the measured value presented to the measurer is determined in the step S46. The measurement result of the object is calculated from the data of the measurement result stored in step S31 in FIG. 1 according to the following equation.
(Measurement result) = [(mode number of appearance) × (mode) + ｛(mode + 1 [μm]) appearance｝ × (mode + 1 [μm]) + ｛(mode Number of occurrences of value-1 [μm])） × (Mode-1 [μm])] ÷ [(Number of appearances of mode) + ｛Number of occurrences of (mode + 1 [μm])｝ + ｛ (Mode of occurrence of mode-1 [μm])｝]
Note that the above equation calculates the weighted average, that is, the mode and the mode ± 1 [μm] with respect to the mode and the mode ± 1 [μm] The average is calculated after weighting is performed based on the weight. That is, based on the mode value and the mode value ± 1 [μm] which can be regarded as having no influence on the measurement due to the mixing of the noise component among the plurality of measurement values stored in the step S31 described above. Calculation of the measurement result of the thickness of the measured object is performed.
[0030]
The equation used to calculate the weighted average is not limited to the above-described equation, and another equation may be used.
The measurement results obtained by the above steps are output as the measurement results of the thickness of the object to be measured in the step of S34 in FIG. 1 and presented to the measurer.
[0031]
As described above, even in the thickness measurement performed using the method described with reference to FIG. 3 as it is, the measurement value obtained by performing the measurement of the thickness of the object to be measured a plurality of times is processed. This suppresses the influence of noise components on the measurement, which makes it possible to accurately obtain the thickness of the measured object.
[0032]
If it is determined in any of the above-described steps S44 and S45 that the stored measurement value is not appropriate, the thickness measurement of the measured object is performed again.
In addition, the present invention is not limited to the above-described embodiment, and various improvements and modifications can be made without departing from the gist of the present invention.
[0033]
【The invention's effect】
As described in detail above, the present invention provides a method of arriving between reflected waves of an emitted ultrasonic wave that arrive from a surface of an object to be measured and those that arrive from a back surface of the object to be measured. Observe the time difference, when measuring the thickness of the object to be measured by calculating the distance between the front surface and the back surface from the arrival time difference, by performing the measurement a plurality of times Obtain a plurality of measurement values indicating the thickness of the measured object obtained at each measurement, and assume that the plurality of measurement values are not affected by noise that may be erroneously observed as the reflected wave. The value calculated based on the measurement value extracted from the measurement target is presented as the measurement result of the thickness of the measured object.
[0034]
By doing so, there is an effect that the thickness of the object to be measured can be measured with high accuracy even when the object to be reflected can only obtain a very small reflected wave.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a procedure of a measuring method according to the present invention.
FIG. 2 is a diagram showing a processing content of a measurement value processing in a flowchart.
FIG. 3 is a diagram showing a method of measuring thickness using ultrasonic waves.
FIG. 4 is a diagram showing an example of a measurement waveform of an ultrasonic wave.
FIG. 5 is a flowchart showing a method for handling measured values in a conventional method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Transmission wave waveform 11 Surface wave waveform 12 Back surface waveform 20 Threshold value 21 Base line 30 Noise waveform 101 Handling device 102 DUT 103 Ultrasonic probe 104 Elastic body 105 Press adjustment means

Claims (5)

Of the reflected waves of the emitted ultrasonic waves, the difference in the arrival time between the one arriving from the front surface of the object to be measured and the one arriving from the rear surface of the object to be measured is observed, and the time of arrival is measured. In an ultrasonic thickness measurement method for measuring the thickness of the object to be measured by calculating the distance between the front surface and the back surface from the difference,
Obtain a plurality of measurement values indicating the thickness of the measured object obtained at each measurement by performing the measurement a plurality of times,
The measurement result of the thickness of the object to be measured is a value calculated based on the measurement value extracted from the plurality of measurement values assuming that it is not affected by noise that may be erroneously observed as the reflected wave. Present as
An ultrasonic thickness measuring method, characterized in that: The method according to claim 1, wherein the extraction is performed based on a frequency distribution of the plurality of measured values. The presentation is performed when it is determined that the ratio of the number of measured values extracted as being not affected by the noise to the number of the plurality of measured values is equal to or greater than a predetermined ratio. The ultrasonic thickness measuring method according to claim 1, wherein: The ultrasonic thickness measuring method according to claim 1, wherein the presentation is performed when it is determined that there is no fluctuation in the plurality of measured values. The ultrasonic thickness measurement method according to claim 1, wherein the calculation performed for the presentation includes calculating a weighted average of the extracted measurement values based on the number of acquired measurement values. .

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