Film thickness measurement system

Abstract

This invention provides a film thickness measurement system that can accurately measure the thickness of a conductive film, even when the conductive film is thin. [Solution] The film thickness measurement system 1 includes an eddy current type displacement sensor 2 equipped with a sensor coil 21 and a Z / V conversion unit 22 that converts the impedance of the sensor coil 21 into a voltage, and a film thickness calculation device 3 equipped with a storage unit 32 and a calculation unit 33. The Z / V conversion unit 22 is configured to convert the impedance of the sensor coil 21 into a voltage based on the following equations (1) and (2). V(x,t)=a·tan{Z0(x,t)α}+b ···(1) Z0(x,t)=Z(x,t)-Z(0,0) ···(2)

Description

[Technical Field]

[0001] This invention relates to a film thickness measurement system. [Background technology]

[0002] Eddy current film thickness measurement systems have been known for some time, which are configured to measure the thickness of a conductive film formed on a substrate using eddy currents. For example, Patent Document 1 describes an eddy current sample measurement method in which an alternating magnetic field is applied to a sample to generate eddy currents, and various measurements such as resistivity, sheet resistance, and film thickness are performed by detecting the power absorption due to the eddy currents. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2009-204342 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, the eddy current sample measurement method described in Patent Document 1 tends to have a decrease in measurement accuracy as the thickness of the conductive film decreases, and in particular, it is difficult to accurately measure the thickness of very thin conductive films, such as those with a thickness of 1 μm or less.

[0005] This invention was made in view of the above background, and aims to provide a film thickness measurement system that can accurately measure the thickness of a conductive film even when the thickness of the conductive film is thin. [Means for solving the problem]

[0006] One aspect of the present invention is a film thickness measuring system for measuring the thickness of a conductive film formed on a metal substrate, the conductive film being made of a conductive material having an electrical conductivity different from that of the metal constituting the metal substrate, the system comprising a metal substrate and a conductive film formed on the metal substrate. An eddy current type displacement sensor comprising a sensor coil and a Z / V conversion unit that converts the impedance of the sensor coil into a voltage, A film thickness calculation device comprising a memory unit and a calculation unit, The Z / V conversion unit is configured to convert the impedance of the sensor coil into a voltage based on the following equations (1) and (2): The aforementioned film thickness calculation device is, A calibration data acquisition step involves using the eddy current displacement sensor to measure a plurality of calibration samples in which the thickness t of the conductive film is known, and storing the thickness t of the conductive film, the distance x from the sensor coil to the calibration sample, and the corresponding voltage V(x,t) in each calibration sample as calibration data in the storage unit. A calibration step in which the calibration data is input to the calculation unit and a conversion function is determined to convert the voltage V(x,t) to the thickness t of the conductive film, A measurement data acquisition step involves measuring the object to be measured using the eddy current type displacement sensor and storing the voltage V(x,t) corresponding to the thickness t of the conductive film on the object to be measured and the distance x from the sensor coil to the object to be measured as measurement data in the storage unit. The film thickness measurement system is configured to perform a film thickness calculation step in which the measurement data is input to the calculation unit and the voltage V(x,t) is converted to the thickness t of the conductive film on the object to be measured using the conversion function. V(x,t)=a·tan{Z0(x,t)α}+b ···(1) Z0(x,t)=Z(x,t)-Z(0,0) ···(2)

[0007] However, a, b, and α in the formula (1) are correction coefficients, and Z(x, t) in the formula (2) is the impedance of the sensor coil corresponding to the distance x from the sensor coil to the measurement object and the thickness t of the conductive film. Z(x, t) is the impedance of the eddy current displacement sensor corresponding to the distance x from the sensor coil to the measurement object and the thickness t of the conductive film.

Advantages of the Invention

[0008] The eddy current displacement sensor (hereinafter referred to as "EC sensor") of the film thickness measurement system has a Z / V conversion unit that converts the impedance Z0(x, t) of the sensor coil into a voltage V(x, t) using the formulas (1) and (2). The impedance Z0(x, t) of the sensor coil in the EC sensor changes to a value corresponding to the distance x from the sensor coil to the measurement object according to the thickness t of the conductive film by being arranged near the measurement object. Also, by using the specific formula for the conversion between impedance and voltage, the EC sensor can output a voltage V(x, t) corresponding to the thickness t of the conductive film and the distance x from the sensor coil to the measurement object even when measuring a measurement object having a relatively thin conductive film. Therefore, the thickness t of the conductive film can be calculated by converting the voltage V(x, t) output from the EC sensor into the thickness t of the conductive film in the film thickness calculation device.

[0009] As described above, according to the above aspect, it is possible to provide a film thickness measurement system that can accurately measure the thickness of a conductive film even when the thickness of the conductive film is thin.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is an explanatory diagram showing a schematic configuration of a film thickness measurement system in an embodiment. [Figure 2] FIG. 2 is a block diagram of a film thickness measurement system in an embodiment. [Figure 3]Figure 3 is an explanatory diagram showing the equivalent circuit of the high-frequency section of the eddy current type displacement sensor in the embodiment. [Figure 4] Figure 4 is a graph showing the measurement results of the conductive film thickness in the experimental example. [Modes for carrying out the invention]

[0011] (Embodiment) An embodiment of the aforementioned film thickness measurement system will be described with reference to Figures 1 to 3. As shown in Figure 1, the film thickness measurement system 1 of this embodiment includes an EC sensor 2 and a film thickness calculation device 3. The film thickness measurement system 1 is used to measure the thickness of a conductive film 82 in an object to be measured 8, which consists of a metal substrate 81 and a conductive material having an electrical conductivity different from that of the metal constituting the metal substrate 81, and which is formed on the metal substrate 81.

[0012] The metal constituting the metal substrate 81 is not particularly limited. For example, the metal substrate 81 may be composed of various metals or alloys thereof, such as iron, iron alloys, copper, copper alloys, aluminum, aluminum alloys, titanium, and titanium alloys.

[0013] The conductive material constituting the conductive film 82 has an electrical conductivity different from that of the metal constituting the metal substrate 81. The conductive film 82 may be composed of a metal different from that of the metal substrate 81. For example, if the metal substrate 81 is made of iron or an iron alloy, it is preferable that the conductive film 82 be made of aluminum or an aluminum alloy. Alternatively, the conductive film 82 may be composed of a nonmetallic material having an electrical conductivity sufficient to generate eddy currents due to the magnetic flux generated from the EC sensor 2. Examples of such nonmetallic materials include conductive metal oxides and conductive resins.

[0014] The sheet resistance of the conductive film 82 is preferably 3Ω / □ or less. In this case, eddy currents can be reliably generated in the conductive film 82 by the magnetic flux generated from the EC sensor 2. As a result, the thickness of the conductive film 82 can be measured more easily, and the accuracy of thickness measurement can be further improved even when the thickness of the conductive film 82 is thin.

[0015] The thickness of the conductive film 82 on the object to be measured 8 is preferably 1 μm or less. The film thickness measurement system 1 is configured to convert the impedance of the sensor coil 21 into a voltage based on the above equations (1) and (2). This makes it possible to accurately measure the thickness of a thin conductive film 82, which was difficult to measure with conventional EC sensors 2, such as one with a thickness of 1 μm or less.

[0016] The film thickness measurement system 1 is configured to measure the thickness of the conductive film 82 by converting the voltage output from the EC sensor 2 into a film thickness in the film thickness calculation device 3.

[0017] The EC sensor 2 includes a sensor coil 21, a Z / V conversion unit 22 that converts the impedance of the sensor coil 21 into a voltage, and a coaxial cable 23 that electrically connects the sensor coil 21 and the Z / V conversion unit 22. The sensor coil 21 is positioned facing the conductive film 82 on the object to be measured 8. The sensor coil 21 may be in contact with the conductive film 82, or it may be positioned at a distance from the conductive film 82.

[0018] The specific configuration of the Z / V conversion unit 22 is not particularly limited, and the configuration of the Z / V conversion unit 22 in a known eddy current displacement sensor can be appropriately adopted. For example, as shown in FIG. 2, the Z / V conversion unit 22 of this embodiment includes an oscillation / resonance circuit 221 that generates a high frequency for exciting the sensor coil 21, a detection circuit 222 connected to the oscillation / resonance circuit 221, a linearizer 223 connected to the detection circuit 222, an amplifier 224 connected to the linearizer 223, and a power supply circuit 225 that supplies power to the oscillation / resonance circuit 221, the detection circuit 222, the linearizer 223, and the amplifier 224.

[0019] The EC sensor 2 of this embodiment adopts a Colpitts parallel resonance type self-excitation method as the excitation method. Therefore, in the EC sensor 2 of this embodiment, the excitation frequency f is determined by the entire measurement system including the measurement object 8.

[0020] In the oscillation / resonance circuit 221, an alternating current i of frequency f i is generated and supplied to the sensor coil 21 as the alternating current i i . Then, a magnetic flux Φ i is generated around the sensor coil 21. When this magnetic flux Φ i links with the measurement object 8, an eddy current i e is generated in the measurement object 8. And when an eddy current i e is generated in the measurement object 8, a magnetic flux Φ e caused by the eddy current i e is generated in the measurement object 8. When this magnetic flux Φ e links with the sensor coil 21, an induced electromotive force E i that obstructs the alternating current i e is generated in the sensor coil 21, and the impedance of the sensor coil 21 changes. Also, the amount of change in the impedance of the sensor coil 21 varies according to the distance x from the sensor coil 21 to the surface of the measurement object 8 and the thickness t of the conductive film ⑧2. Therefore, the distance x from the sensor coil 21 to the measurement object 8 and the thickness t of the conductive film 82 are reflected in the impedance of the sensor coil 21.

[0021] As a result of diligent research, the inventors experimentally discovered that in the linearizer 223 of the EC sensor 2, by converting the impedance Z0(x,t) of the sensor coil to a voltage V(x,t) using a tangent function, a voltage V(x,t) corresponding to the distance x from the sensor coil 21 to the surface of the object to be measured 8 and the thickness t of the conductive film 82 can be obtained, thus completing the present invention. That is, the Z / V conversion unit 22 of the EC sensor 2 is configured to convert the impedance of the sensor coil to a voltage based on the following equations (1) and (2). V(x,t)=a·tan{Z0(x,t)α}+b ···(1) Z0(x,t)=Z(x,t)-Z(0,0) ···(2)

[0022] Here, Z0(x,t) in equations (1) and (2) above is the impedance of the sensor coil 21 corresponding to the distance x from the sensor coil 21 to the object to be measured 8 and the thickness t of the conductive film 82. In the equivalent circuit of the high-frequency flow portion of the EC sensor 2 shown in Figure 3, the sensor coil 21 has a resistive component R0(x,t), an inductive component L0(x,t), and a capacitive component C0. Therefore, the impedance Z0(x,t) of the sensor coil 21 is expressed by the following equation (3), using the resistive component R0(x,t), the inductive component L0(x,t), and the capacitive component C0 of the sensor coil 21.

[0023]

number

[0024] Furthermore, in equation (2), Z(x,t) is the impedance of the EC sensor 2, corresponding to the distance x from the sensor coil 21 to the object to be measured 8 and the thickness t of the conductive film 82. The impedance Z(x,t) of the EC sensor 2 is equal to the impedance Z of the oscillation / resonance circuit 221. C2 The combined impedance Z of the sensor coil 21 and the coaxial cable 23. s Using (x,t), it can be expressed by the following equation (4).

[0025]

number

[0026] Here, the impedance Z of the oscillator / resonant circuit 221 C2 This is expressed by the following equation (5), using the capacitance component C2 of the oscillator / resonant circuit 221.

number

[0027] Furthermore, the combined impedance Z of the sensor coil 21 and the coaxial cable 23. s (x,t) is the combined impedance Z0(x,t) of the sensor coil 21 and the combined impedance Z of the resistive component R1 and inductive component L1 in the coaxial cable 23. LR And the impedance Z of the capacitive component C1 in the coaxial cable 23 C1 Using and , it can be expressed by the following equation (6).

[0028]

number

[0029] Here, the combined impedance Z of the resistive component R1 and the inductive component L1 in the coaxial cable 23. LR It can be expressed by the following equation (7).

[0030]

number

[0031] Furthermore, the impedance Z of the capacitive component C1 in the coaxial cable 23 C1 It can be expressed by the following equation (8).

[0032]

number

[0033] The correction coefficients a and b in equation (1) are coefficients used in the amplifier 224 to adjust the voltage V(x,t) to a desired range, and can be set appropriately according to, for example, the range of voltages that can be input to the film thickness calculation device 3. In addition, the correction coefficient α in equation (1) sets the upper limit of the distance from the sensor coil 21 to the object to be measured 8 to x max When expressed as such, you can set it appropriately from within the range that satisfies the following equation (9). -π / 2<[Z(x max ,0)-Z(0,0)]·α<π / 2 ···(9)

[0034] Note that Z(x) in equation (9) above max ,0) is measured on an object 8 that does not have a conductive film 82, and the distance from the object 8 is x max The impedance of the EC sensor 2 when the sensor coil 21 is placed at the position where Z(0,0) is the impedance of the EC sensor 2 when the sensor coil 21 is in contact with the object to be measured 8 which does not have a conductive film 82. The distance x in equation (9) max The value of is the voltage V(x) corresponding to the thickness t of the conductive film 82 when the object 8 is measured using the EC sensor 2. max You can set it appropriately within the range where ,t) is output.

[0035] The correction coefficients a, b, and α in equation (1) can be set at any time before measuring the thickness of the conductive film 82. For example, the correction coefficients a, b, and α can be determined when the film thickness measurement system 1 is used for the first time, and these values ​​can be used continuously in subsequent measurements. Alternatively, different correction coefficients a, b, and α can be prepared depending on the combination of the metal constituting the metal substrate 81 and the conductive material constituting the conductive film 82 in the object to be measured 8, and the thickness of the conductive film 82 can be measured using the correction coefficients corresponding to the configuration of the object to be measured 8.

[0036] As shown in Figure 2, the film thickness calculation device 3 has a storage unit 32 and a calculation unit 33, and is configured to calculate the thickness of the conductive film 82 based on the voltage output from the EC sensor 2. The film thickness calculation device 3 is also configured to perform a calibration data acquisition step, a calibration step, a measurement data acquisition step, and a film thickness calculation step. These steps may be performed, for example, by an electronic circuit, or based on a program stored in the storage unit 32 for the film thickness calculation step. The film thickness calculation device 3 may also be configured to perform these steps in order, or to perform a step selected by the user.

[0037] The specific configuration of the film thickness calculation device 3 is not particularly limited and can take various forms. For example, the film thickness calculation device 3 in this embodiment is a general-purpose electronic computer equipped with an input unit 31, a storage unit 32, a calculation unit 33, and an output unit 34, and is configured to execute each of the above steps according to a program stored in the storage unit 32 based on the user's operation.

[0038] The input unit 31 is configured to input data such as the voltage V(x,t) output from the EC sensor 2 to the film thickness calculation device 3. The specific configuration of the input unit 31 is not particularly limited. For example, the input unit 31 in the film thickness calculation device 3 of this embodiment has a human interface such as a mouse, keyboard, and touch panel, and a communication interface connected to the EC sensor 2. The human interface is configured to input user instructions and data to the film thickness calculation device 3. The communication interface is configured to input the voltage V(x,t) value output from the EC sensor 2 to the film thickness calculation device 3.

[0039] The storage unit 32 stores, for example, a program for executing each of the steps described above, calibration data acquired in the calibration data acquisition step, measurement data acquired in the measurement data acquisition step, and a conversion function used in the film thickness calculation step. The specific form of the storage unit 32 is not particularly limited. For example, the storage unit 32 may be the main memory of a computer or an auxiliary memory device.

[0040] The calculation unit 33 is configured to execute each of the above steps according to the program stored in the storage unit 32. Specifically, the calculation unit 33 in the film thickness calculation apparatus 3 of this embodiment is the central processing unit of an electronic computer.

[0041] The output unit 34 is configured to output the thickness t of the conductive film 82 calculated by the film thickness calculation device 3. Specifically, the output unit 34 in the film thickness calculation device 3 of this embodiment includes a display.

[0042] The film thickness calculation device 3 in this embodiment is configured to execute a step selected by the user from among the calibration data acquisition step, calibration step, measurement data acquisition step, and film thickness calculation step, based on the user's instructions input from the input unit 31.

[0043] In the calibration data acquisition step, the thickness t of the conductive film in each calibration sample, the distance x from the sensor coil 21 to the calibration sample, and the corresponding voltage V(x,t) are stored in the storage unit 32 as calibration data obtained by measuring multiple calibration samples with known conductive film thickness t using the EC sensor 2. As calibration samples, metal members having the same type of metal substrate and conductive film as the metal substrate 81 and conductive film 82 in the object to be measured 8 can be used. Preferably, the thickness of the conductive film in the calibration sample is measured in advance by a film thickness measuring device other than the EC sensor 2, such as an X-ray fluorescence analyzer.

[0044] The specific form of calibration data can take various forms. For example, by preparing multiple calibration samples with different conductive film thicknesses t, and measuring these calibration samples while keeping the distance x from the sensor coil 21 to the calibration sample constant during the calibration data acquisition step, a set of a specific distance x, the conductive film thickness t of each calibration sample, and the corresponding voltage V(x,t) can be obtained as calibration data. In this case, in the subsequent measurement data acquisition step, by setting the distance x from the sensor coil 21 to the object to be measured 8 to the same value as the calibration data and acquiring measurement data, it is possible to calculate the thickness t of the conductive film 82 to be closer to the true value.

[0045] The distance x from the sensor coil 21 to the calibration sample in the calibration data is 0 or greater, and the distance x from the sensor coil 21 to the object to be measured in equation (9) is 0. max The following is preferable: The distance x from the sensor coil 21 to the object to be measured 8 is 0 or greater x max By obtaining calibration data under the following conditions, a more accurate conversion function can be determined in subsequent calibration steps.

[0046] In the calibration step, calibration data is input to the calculation unit 33, and a conversion function is determined to convert the voltage V(x,t) to the thickness t of the conductive film 82. More specifically, in the calibration step, the calculation unit 33 determines a function that best approximates multiple pairs of the thickness t of the conductive film 82 and the voltage V(x,t) included in the calibration data, and stores this function as a conversion function in the storage unit 32. The specific functional form of the conversion function is not particularly limited. For example, various functions such as a linear function that expresses the voltage V(x,t) as a linear expression of the thickness t of the conductive film 82, or a quadratic function that expresses the voltage V(x,t) as a quadratic expression of the thickness t of the conductive film 82 can be used as the conversion function. Furthermore, the method for determining the conversion function from the calibration data is not particularly limited, and various approximation methods can be used. For example, in the calibration step, the least squares method can be used to determine the conversion function from the calibration data.

[0047] In the measurement data acquisition step, the thickness t of the conductive film 82 on the object to be measured 8 and the voltage V(x,t) corresponding to the distance x from the sensor coil 21 to the object to be measured 8, obtained by measuring the object to be measured 8 using the EC sensor 2, are stored as measurement data in the storage unit 32.

[0048] In the film thickness calculation step, the measurement data is input to the calculation unit 33, and the voltage V(x,t) is converted to the thickness t of the conductive film 82 of the object to be measured 8 using a conversion function. In the film thickness calculation step, it is preferable to use a conversion function determined based on calibration data obtained by using a calibration sample having the same configuration as the object to be measured 8 and performing measurements at the same distance x from the sensor coil 21 to the object to be measured 8 in the measurement data. In this way, by using a conversion function based on calibration data measured under conditions close to the measurement conditions of the measurement data, it is possible to calculate the thickness t of the conductive film 82 that is closer to the true value.

[0049] The timing of the calibration data acquisition step and the calibration step is not particularly limited. For example, before performing the measurement data acquisition step and the film thickness calculation step, multiple types of calibration data may be acquired by changing various conditions such as the type of metal substrate 81 and conductive film 82 in the calibration sample, the thickness t of the conductive film 82, and the distance x from the sensor coil 21 to the object to be measured 8, and multiple conversion functions may be determined based on this calibration data. In this case, in the film thickness calculation step, a conversion function determined using calibration data with measurement conditions close to the measurement conditions of the measurement data is selected from the multiple conversion functions stored in the storage unit 32, and the voltage V(x,t) is converted to the thickness t of the conductive film 82 using this conversion function, thereby calculating the thickness t of the conductive film 82 which is closer to the true value.

[0050] Alternatively, for example, the calibration data acquisition step, calibration step, and measurement data acquisition step can be performed in this order, and the film thickness calculation step can be performed using the conversion function determined in the calibration step.

[0051] In the film thickness measurement system 1 of this embodiment, the EC sensor 2 has a Z / V conversion unit 22 that converts the impedance Z0(x,t) of the sensor coil 21 to a voltage V(x,t) using equations (1) and (2). The impedance Z0(x,t) of the sensor coil 21 in the EC sensor 2 changes to a value corresponding to the distance x from the sensor coil 21 to the object to be measured 8, which corresponds to the thickness t of the conductive film 82, by being placed near the object to be measured 8. Furthermore, by using the above specific equations for the conversion between impedance and voltage, the EC sensor 2 can output a voltage V(x,t) corresponding to the thickness t of the conductive film 82 and the distance x from the sensor coil 21 to the object to be measured 8, even when measuring an object 8 having a thin conductive film 82. Therefore, the thickness t of the conductive film 82 can be calculated by converting the voltage V(x,t) output from the EC sensor 2 to the thickness t of the conductive film 82 in the film thickness calculation device 3.

[0052] As described above, the film thickness measurement system 1 of this embodiment can accurately measure the thickness of a conductive film even when the conductive film is thin.

[0053] (Example of experiment) This example shows how the thickness t of a conductive film 82 attached to the surface of a metal substrate 81 is measured using the film thickness measurement system 1. In this experimental example, unless otherwise specified, the same reference numerals used in the previously described embodiments represent the same components as those in the previously described embodiments.

[0054] The EC sensor 2 used in this example is specifically the "Quick RIVERNEW®" RX series manufactured by Shinkawa Sensor Technology Co., Ltd. The film thickness calculation device 3 used in this example is an electronic computer equipped with an input unit 31, a storage unit 32, a calculation unit 33, and an output unit 34, and is configured to execute the calibration data acquisition step, calibration step, measurement data acquisition step, and film thickness calculation step.

[0055] In the calibration data acquisition step of this example, a calibration sample consisting only of a metal substrate (Table 1, Sample S1) and three types of calibration samples (Table 1, Samples S2-S4) comprising a metal substrate and a conductive film formed on the metal substrate, with the thickness t of the conductive film differing from each other, are used. The specific structure of the calibration samples is shown in Table 1. The thickness of the conductive film shown in Table 1 is a value measured using an X-ray fluorescence analyzer.

[0056] [Table 1]

[0057] Furthermore, the object to be measured in this example, 8, has a metal substrate 81 made of chromium steel and a conductive film 82 made of aluminum that is formed on the surface of the metal substrate 81.

[0058] The method for calculating the thickness of the conductive film 82 in this example is as follows. First, using sample S1 from the calibration samples mentioned above, the correction coefficients a, b, and α of equation (1) that convert the impedance of the sensor coil 21 to voltage in the Z / V conversion unit 22 of the EC sensor 2 are determined. In determining the value of α among these correction coefficients, first, the impedance Z(0,0) of the EC sensor 2 when the sensor coil 21 is in contact with sample S1 and the distance x from sample S1 to the sensor coil 21 are determined. max The impedance Z(x) of EC sensor 2 when it is positioned as follows: max Measure (0). Then, determine the value of α from within the range where these values ​​satisfy the following equation (9). -π / 2<[Z(x max ,0)-Z(0,0)]·α<π / 2 ···(9)

[0059] Furthermore, in determining the correction coefficients a and b, appropriate correction coefficients a and b are set in advance, and the output voltage V(0,0) of the EC sensor 2 when the sensor coil 21 is in contact with the sample S1 and the distance of the sensor coil 21 from the sample S1 is x max The output voltage V(x) of EC sensor 2 when it is positioned as follows: maxMeasure (0). Then, adjust the values ​​of a and b as appropriate so that these values ​​fall within a suitable range for measurement.

[0060] Next, using the EC sensor 2, the thickness t of the conductive film in each sample, the distance x from the sensor coil 21 to each sample, and the corresponding voltage V(x,t) are obtained. These data are then input via the input unit 31 of the film thickness calculation device 3 and stored in the storage unit 32 as calibration data (calibration data acquisition step). In this example, the distance x from the sensor coil 21 to each calibration sample is constant in the calibration data.

[0061] After performing the calibration data acquisition step, the calibration data is input to the calculation unit 33 to determine a conversion function that converts the voltage V(x,t) to the thickness t of the conductive film (calibration step). Specifically, the conversion function in this example is a quadratic function that expresses the voltage V(x,t) as a quadratic expression of the thickness t of the conductive film, and is obtained by determining the quadratic function that best approximates the calibration data using the least squares method.

[0062] After performing the calibration data acquisition step, the EC sensor 2 is used to measure various positions on the surface of the object to be measured 8, thereby acquiring the voltage V(x,t) corresponding to the thickness t of the conductive film 82 and the distance x from the sensor coil 21 to the metal substrate 81 at each measurement position. The voltage V(x,t) is then input via the input unit 31 of the film thickness calculation device 3 and stored as measurement data in the storage unit 32 (measurement data acquisition step). In this example, the distance x from the sensor coil 21 to the metal substrate 81 in the measurement data is the same as the distance x from the sensor coil 21 to the metal substrate 81 in the calibration data.

[0063] After performing the measurement data acquisition step, the measurement data is input to the calculation unit 33, and the voltage V(x,t) is converted to the thickness t of the conductive film 82 using the conversion function determined in the calibration step (film thickness calculation step). Table 2 shows the output voltage of the EC sensor 2 at each measurement position, the thickness t of the conductive film 82 converted from the output voltage, and the thickness of the conductive film 82 at each measurement position measured using an X-ray fluorescence analyzer.

[0064] Furthermore, Figure 4 shows the measured thickness t of the conductive film 82 using an X-ray fluorescence analyzer. X The graph shows the thickness t of the conductive film 82 measured by the EC sensor 2 plotted on the x-axis (unit: μm) and the thickness t of the conductive film 82 measured by the EC sensor 2 plotted on the y-axis. X By performing regression calculations assuming that the regression can be expressed as a linear equation, the regression equation shown in equation (10) below is obtained. The coefficient of determination of the regression equation is R 2 It is 0.84. Figure 4 shows the line L corresponding to the following equation (10). t = 1.2661 × t X -0.0159 ···(10)

[0065] [Table 2]

[0066] As shown in Table 2 and Figure 4, the measured thickness t of the conductive film 82 by the EC sensor 2 is the same as the measured thickness t of the conductive film 82 by the X-ray fluorescence analyzer. X It is roughly proportional to this. Therefore, these results show that the measurement value t of the thickness of the conductive film 82 by the EC sensor 2 reflects the true thickness of the conductive film 82, and that the thickness of the conductive film 82 can be measured by the film thickness measurement system 1 using the EC sensor 2.

[0067] Although the embodiments of the film thickness measurement system have been described above based on the embodiments and experimental examples, the specific embodiments of the film thickness measurement system according to the present invention are not limited to those of the embodiments and experimental examples, and the configuration can be modified as appropriate without impairing the spirit of the present invention.

[0068] For example, the film thickness measurement system may be incorporated into a machining apparatus such as a cutting apparatus or a plastic deformation apparatus, which is configured to process a workpiece by bringing a tool into contact with the workpiece. In these machining apparatuses, when the tool comes into contact with the workpiece, material constituting the workpiece may adhere to the surface of the tool, and a film may be formed on the surface of the tool. Since the thickness of the film formed on the surface of the tool may affect the machining accuracy, it is desirable to measure the thickness of the film formed on the surface of the tool during machining and adjust the film thickness according to the measurement result, from the viewpoint of machining the workpiece with high accuracy.

[0069] In contrast, the sensor coil in the aforementioned film thickness measurement system exhibits excellent durability against contaminants such as water, oil, and fumes generated during processing. On the other hand, the film thickness measurement system can calculate the thickness of the conductive film based on the impedance of the sensor coil, even when the Z / V conversion unit and film thickness calculation device are located at a distance from the sensor coil. Therefore, by placing the sensor coil near the tool, the film thickness measurement system can measure the thickness of the film attached to the surface of the tool.

[0070] Furthermore, the voltage V(x,t) output from the EC sensor is less likely to fluctuate even when the aforementioned contamination is present. Moreover, as mentioned above, the film thickness measurement system can accurately measure the thickness of the conductive film even when the conductive film is thin. Therefore, by incorporating the film thickness measurement system into a processing device, for example, the thickness of the film formed on the surface of the tool while processing a workpiece can be accurately measured, and the film thickness can be adjusted according to the measurement results.

[0071] In addition, the film thickness measurement system may take the following forms, for example: [1] to [3].

[0072] [1] A film thickness measuring system for measuring the thickness of a conductive film in an object to be measured, which comprises a metal substrate and a conductive material having an electrical conductivity different from that of the metal constituting the metal substrate, wherein the conductive film is formed on the metal substrate, An eddy current type displacement sensor comprising a sensor coil and a Z / V conversion unit that converts the impedance of the sensor coil into a voltage, A film thickness calculation device comprising a memory unit and a calculation unit, The Z / V conversion unit is configured to convert the impedance of the sensor coil into a voltage based on the following equations (1) and (2): The aforementioned film thickness calculation device is, A calibration data acquisition step involves using the eddy current displacement sensor to measure a plurality of calibration samples in which the thickness t of the conductive film is known, and storing the thickness t of the conductive film, the distance x from the sensor coil to the calibration sample, and the corresponding voltage V(x,t) in each calibration sample as calibration data in the storage unit. A calibration step in which the calibration data is input to the calculation unit and a conversion function is determined to convert the voltage V(x,t) to the thickness t of the conductive film, A measurement data acquisition step involves measuring the object to be measured using the eddy current type displacement sensor and storing the voltage V(x,t) corresponding to the thickness t of the conductive film on the object to be measured and the distance x from the sensor coil to the object to be measured as measurement data in the storage unit. A film thickness measurement system configured to perform a film thickness calculation step of inputting the measurement data into the calculation unit and converting the voltage V(x,t) into the thickness t of the conductive film on the object to be measured using the conversion function. V(x,t)=a·tan{Z0(x,t)α}+b ···(1) Z0(x,t)=Z(x,t)-Z(0,0) ···(2) (However, in equation (1), a, b, and α are correction coefficients, and in equation (2), Z0(x,t) is the impedance of the sensor coil corresponding to the distance x from the sensor coil to the object to be measured and the thickness t of the conductive film, and Z(x,t) is the impedance of the eddy current type displacement sensor corresponding to the distance x from the sensor coil to the object to be measured and the thickness t of the conductive film.)

[0073] [2] The film thickness measurement system according to [1], wherein the metal substrate is made of iron or an iron alloy, and the conductive film is made of aluminum or an aluminum alloy. [3] The film thickness measurement system according to [1] or [2], wherein the thickness of the conductive film is 1 μm or less. [Explanation of symbols]

[0074] 1. Film Thickness Measurement System 2. Eddy current type displacement sensor 21 Sensor coil 22 Z / V conversion section 3. Film Thickness Calculation Device 32 Storage section 33 Arithmetic section 8. Object to be measured 81 Metal base material 82 Conductive film

Claims

1. A film thickness measuring system for measuring the thickness of a conductive film in an object to be measured, which comprises a metal substrate and a conductive material having an electrical conductivity different from that of the metal constituting the metal substrate, wherein the conductive film is formed on the metal substrate, the system comprises a metal substrate and a conductive film formed on the metal substrate. An eddy current type displacement sensor comprising a sensor coil and a Z / V conversion unit that converts the impedance of the sensor coil into a voltage, A film thickness calculation device comprising a memory unit and a calculation unit, The Z / V conversion unit is configured to convert the impedance of the sensor coil into a voltage based on the following equations (1) and (2): The aforementioned film thickness calculation device is, A calibration data acquisition step involves using the eddy current displacement sensor to measure a plurality of calibration samples in which the thickness t of the conductive film is known, and storing the thickness t of the conductive film, the distance x from the sensor coil to the calibration sample, and the corresponding voltage V(x,t) in each calibration sample as calibration data in the storage unit. A calibration step in which the calibration data is input to the calculation unit and a conversion function is determined for converting the voltage V(x, t) to the thickness t of the conductive film, A measurement data acquisition step involves measuring the object to be measured using the eddy current displacement sensor and storing the voltage V(x, t) corresponding to the thickness t of the conductive film on the object to be measured and the distance x from the sensor coil to the object to be measured as measurement data in the storage unit. A film thickness measurement system configured to perform a film thickness calculation step of inputting the measurement data into the calculation unit and converting the voltage V(x, t) to the thickness t of the conductive film on the object to be measured using the conversion function. |(##,#)##|・| 0 ・・・() Z 0 (x,t)=Z(x,t)-Z(0,0) ・・・(2) (However, a, b and α in equation (1) are correction coefficients, and Z in equation (2) 0 (x, t) is the impedance of the sensor coil corresponding to the distance x from the sensor coil to the object to be measured and the thickness t of the conductive film, and Z(x, t) is the impedance of the eddy current type displacement sensor corresponding to the distance x from the sensor coil to the object to be measured and the thickness t of the conductive film.

2. The film thickness measurement system according to claim 1, wherein the metal substrate is made of iron or an iron alloy, and the conductive film is made of aluminum or an aluminum alloy.

3. The film thickness measurement system according to claim 1 or 2, wherein the thickness of the conductive film is 1 μm or less.

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