Piezoelectric constant measuring device

Abstract

A piezoelectric constant measuring device capable of measuring a piezoelectric constant (d33) with high precision even if a load applied to a piezoelectric film on a wafer is small is provided. The piezoelectric constant measuring device (1) measures a piezoelectric constant (d33) of a piezoelectric film (W3) formed on a wafer (WA) and includes a wafer stage (2), a first electrode (3) capable of contacting a given portion of the wafer (WA), a second electrode (4), a second electrode load unit (5) capable of applying a periodic load to the piezoelectric film (W3) via the second electrode controlled by a reference frequency signal, a load measuring unit (6) outputting an amplitude value of the periodic load or a value proportional thereto, a reference frequency signal generator (7) outputting the reference frequency signal, a lock-in amplifier (8) outputting an amplitude value of a measured signal or a value proportional thereto with the measured signal being a current caused by an electric charge generated in the piezoelectric film (W3) input through the second electrode (4) and the reference signal being the reference frequency signal input, and a piezoelectric constant measuring control unit (9) calculating the piezoelectric constant (d33).

Description

Technical Field

[0001] The present invention relates to a piezoelectric constant measuring device for measuring the piezoelectric constant d33 of a piezoelectric thin film formed on a lower electrode layer on a substrate of a wafer. Background Technology

[0002] Piezoelectric devices are used in a wide range of fields, from various sensors to actuators. By measuring the piezoelectric constant, the piezoelectric properties of piezoelectric devices can be quantitatively evaluated. The piezoelectric constant has d31, d33, etc., corresponding to the direction of the applied load and the amount of charge generated therefrom. The piezoelectric constant can be measured using various piezoelectric constant measuring devices. For example, Patent Document 1 discloses a piezoelectric constant measuring device that can measure d31 by mounting a clamp on a piezoelectric constant measuring device for piezoelectric constant d33. Patent Document 2 discloses a piezoelectric constant measuring device that measures the change in the amount of multiple pulse-shaped charges generated by multiple pulse loads, and can calculate the piezoelectric constant d33 (and d31) based on this change and the measured pulse load.

[0003] In recent years, driven by the trend towards miniaturization and low power consumption of piezoelectric devices, the development and commercialization of piezoelectric devices using piezoelectric thin films (thin films of piezoelectric materials) such as PVDF and PZT films have become prevalent. Piezoelectric thin films are formed on the lower electrode layer of a silicon wafer substrate using methods such as sputtering in the production line. After subsequent processes such as the formation of the upper electrode layer, the wafer is diced into a given shape, thus becoming a piezoelectric device product.

[0004] Whether a piezoelectric film is suitable is typically determined by cutting a wafer into a given shape from a sample taken during the production line and measuring its piezoelectric constant using a piezoelectric constant measuring device. Such a sample take-up inspection is a destructive inspection that renders the sampled wafer unusable later. To address this, for example, a non-destructive inspection method, as shown in Patent Document 3, has been proposed to measure the piezoelectric constant d33 in the wafer's current state.

[0005] Prior art literature

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2014-081339

[0008] Patent Document 2: Japanese Patent No. 6241975

[0009] Patent Document 3: Japanese Patent Application Publication No. 2022-128529 Summary of the Invention

[0010] -The problem the invention aims to solve-

[0011] However, if the piezoelectric constant d33 is to be measured without the formation of the upper electrode layer, the load applied to the piezoelectric film must be reduced. In addition, the piezoelectric film is in an unpolarized state, which presents unique challenges for piezoelectric films on wafers.

[0012] The present invention was made in view of the above-mentioned reasons, and its object is to provide a piezoelectric constant measuring device that can measure the piezoelectric constant d33 with high accuracy even when the load applied to the piezoelectric thin film on the wafer is small, when measuring the piezoelectric constant d33 without the formation of the upper electrode layer. Furthermore, the present invention provides a piezoelectric constant measuring device that can measure the piezoelectric constant d33 with high accuracy even when the piezoelectric thin film is in an unpolarized state.

[0013] -Methods for solving problems-

[0014] To achieve the above objectives, the piezoelectric constant measuring apparatus according to embodiments of the present invention measures the piezoelectric constant d33 of a piezoelectric thin film deposited on a lower electrode layer on a substrate of a wafer. The piezoelectric constant measuring apparatus includes: a wafer stage for supporting the substrate; a first electrode that can be connected to a given portion of the wafer and is grounded; a second electrode; a second electrode load unit controlled by a reference frequency signal, capable of applying a periodic load of the reference frequency signal to the piezoelectric thin film via the second electrode; and a load measuring unit that converts the periodic load into an AC signal and outputs the amplitude value of the periodic load or its equivalent. A proportional value; a reference frequency signal generator that generates and outputs the reference frequency signal; a lock-in amplifier that takes the current generated by the charge in the piezoelectric film through the applied periodic load as the measured signal, input through the second electrode, and takes the reference frequency signal or the AC signal as the reference signal, and outputs the amplitude value of the measured signal or a value proportional to it; and a piezoelectric constant measurement and control unit that calculates the piezoelectric constant d33 based on the amplitude value of the measured signal or a value proportional to it, and the amplitude value of the periodic load or a value proportional to it.

[0015] The piezoelectric constant measuring device further comprises: a pulse generator capable of generating a pulse of given polarity, height, and width; and a relay for switching the passage of the current caused by the charge generated in the piezoelectric film and the passage of the pulse, wherein if the pulse passes through the relay, it is applied to the piezoelectric film via the second electrode.

[0016] The second electrode enables metal to adhere to at least the lower surface of the synthetic resin base.

[0017] -Invention Effects-

[0018] According to the piezoelectric constant measuring apparatus of the present invention, when measuring the piezoelectric constant d33 in the state where the upper electrode layer has not been formed, the piezoelectric constant d33 can be measured with good accuracy even when the load applied to the piezoelectric thin film on the wafer is small. Furthermore, by also including a pulse generator and a relay, the piezoelectric constant d33 can be measured with good accuracy even when the piezoelectric thin film is in an unpolarized state. Attached Figure Description

[0019] Figure 1 This refers to the piezoelectric constant measuring device according to an embodiment of the present invention. The wafer stage, the first electrode, the second electrode, the second electrode load unit, and a portion of the load measuring unit are shown in cross-sectional view. Other portions of the load measuring unit, the reference frequency signal generator, the lock-in amplifier, and the piezoelectric constant measuring control unit are shown in block diagram (or schematic diagram).

[0020] Figure 2 This is a top view showing an example of the configuration of the first electrode in the aforementioned piezoelectric constant measuring device.

[0021] Figure 3 It means in Figure 1 The diagram shows examples of different configurations of the first electrode in the piezoelectric constant measuring device.

[0022] Figure 4 The above is an enlarged cross-sectional view of the second electrode of the piezoelectric constant measuring device. (a) shows a structure in which the entire base is made of the same material, and (b) shows a structure in which the base is composed of a lower ball-shaped part and a cage part made of different materials.

[0023] Figure 5 This is a waveform diagram of an example of a load applied to a piezoelectric film in the aforementioned piezoelectric constant measuring device.

[0024] Figure 6 This is a schematic diagram illustrating the structure of the lock-in amplifier in the aforementioned piezoelectric constant measuring device.

[0025] Figure 7 This is a schematic diagram illustrating an example of the structure of the piezoelectric constant measuring control unit of the aforementioned piezoelectric constant measuring device.

[0026] Figure 8 It means to use Figure 1 The diagram shows the crystal stage, first electrode, second electrode, second electrode load unit, load measurement unit, reference frequency signal generator and lock-in amplifier of the piezoelectric constant measuring device, and the experimental results of measuring the piezoelectric constant d33 by changing the reference frequency.

[0027] Figure 9 It means in Figure 1 The diagram shows the structure of the piezoelectric constant measuring device, which incorporates a pulse generator and a relay.

[0028] Figure 10 It means to use Figure 9 The figure shows the experimental results of measuring the piezoelectric constant d33 after applying pulses with varying pulse voltages using the piezoelectric constant measuring device shown. Detailed Implementation

[0029] The following describes the configuration used to implement the present invention. The piezoelectric constant measuring apparatus 1 according to the embodiments of the present invention measures the piezoelectric constant d33 (refer to) of the piezoelectric thin film W3 (e.g., thickness 1 μm to 200 μm) formed on the lower electrode layer W2 of the substrate W1 of the wafer WA on which the piezoelectric film W3 is deposited. Figure 1 In the production line, after a lower electrode layer W2 of noble metal or other metal is formed on a substrate W1 of a wafer WA (such as silicon or metal, e.g., SUS, Ni alloy, etc.), a piezoelectric thin film W3 is formed on it by sputtering or other methods. After the piezoelectric constant d33 of the wafer WA is measured by the piezoelectric constant measuring device 1, it is divided into a given shape after subsequent processes such as the formation of the upper electrode layer, thereby becoming a piezoelectric device product.

[0030] The piezoelectric constant d33 can be calculated (measured) by the amount of charge generated when a load is applied in the thickness direction of the piezoelectric film W3 and the applied load. Here, without the upper electrode layer formed, when the second electrode 4 is brought into contact with a part of the piezoelectric film W3 and a load is applied as described later, the applied load must be reduced to prevent changes in the piezoelectric properties and physical deformation of the contact portion or its surrounding portion. Therefore, the amount of charge generated in the piezoelectric film W3 is reduced, and the noise component is relatively increased, so the S / N ratio in the charge-based signal (specifically, current) tends to become very small. In addition, the noise is generated by the piezoelectric constant measuring device 1 itself or transmitted from other devices, etc. For example, even if vibration damping members, shielding members, etc. are installed on each component or each wire is made into a coaxial cable to implement various countermeasures, some noise will still remain.

[0031] like Figure 1 As shown, the piezoelectric constant measuring apparatus 1 for measuring the piezoelectric constant d33 of the piezoelectric thin film W3 in the state of wafer WA includes a wafer stage 2, a first electrode 3, a second electrode 4, a second electrode load unit 5, a load measuring unit 6, a reference frequency signal generator 7, a lock-in amplifier 8, and a piezoelectric constant measuring control unit 9. Furthermore, in Figure 1 In the illustration, for ease of understanding, the thickness direction of each part of the wafer WA is enlarged.

[0032] The wafer stage 2 holds and supports the wafer WA. In order to measure the piezoelectric constant d33 of the piezoelectric thin film W3 at multiple locations on the wafer WA, the wafer stage 2 can move in a two-dimensional horizontal direction.

[0033] Furthermore, the wafer stage 2 (specifically, the wafer stage body 20 described later) is capable of vertical movement so that a fixed static load (initial load) is applied to the piezoelectric thin film W3 (see below). Figure 5 When the wafer stage 2 rises (as indicated by reference numeral a), it can rise. When the wafer stage 2 rises, the second electrode 4 contacts the piezoelectric film W3. At this time, the second electrode 4 is brought to a standstill. In this way, the load can be measured using the load detector 61 of the load measurement unit 6 (described later). Furthermore, when the wafer stage 2 rises, a static load is applied to the piezoelectric film W3. Thus, a periodic load (alternating force) (described later) can be applied to the piezoelectric film W3 via the second electrode 4 (see reference numeral a). Figure 5 (See reference numeral b) in the attached figure. Alternatively, instead of raising the wafer stage 2, the second electrode 4 can be lowered to contact the piezoelectric thin film W3, and then the second electrode 4 can be lowered further to apply a static load.

[0034] In detail, the wafer stage 2 can be configured to have a wafer stage body 20 and a first direct-drive motor 21 for moving the wafer stage body 20 up and down. The first direct-drive motor 21 is a motor in which the direct-drive part 21a moves directly with respect to the position of the support part 21b. The upper end of the direct-drive part 21a is fixed to the wafer stage body 20, and the support part 21b is fixed to the frame (not shown) of the piezoelectric constant measuring device 1. The first direct-drive motor 21 is not particularly limited, and a servo motor or the like can be used. The first direct-drive motor 21 can be controlled by the piezoelectric constant measuring control unit 9.

[0035] The first electrode 3 can contact a given portion of the wafer WA, grounding it to a ground potential, thereby setting the lower electrode layer W2 to a ground potential. Specifically, when measuring the piezoelectric constant d33 of the piezoelectric thin film W3, the first electrode 3 can be connected to the vicinity of the periphery of the lower electrode layer W2 manually or under the control of the piezoelectric constant measurement control unit 9. Here, as... Figure 2 As shown, the periphery of the lower electrode layer W2, to which the first electrode 3 is connected, can be a portion obtained by chemically or mechanically removing a portion of the piezoelectric thin film W3 near the periphery of the wafer WA. In this case, the portion where the piezoelectric thin film W3 has been removed is preferably a portion not used as a piezoelectric device. Furthermore, if the first electrode 3 is connected to the periphery of the lower electrode layer W2 in this way, even if an insulating layer is provided between the substrate W1 and the lower electrode layer W2 in the wafer WA, the lower electrode layer W2 can be easily set to a ground potential via the first electrode 3.

[0036] In the absence of an insulating layer between the substrate W1 and the lower electrode layer W2 in the wafer WA, or even if such an insulating layer is present, but the wafer WA is large and has a sufficiently large capacitance between the substrate W1 and the lower electrode layer W2, the first electrode 3 can be connected to the periphery of the lower electrode layer W2 instead. Figure 3 As shown, the back side of substrate W1 (on) Figure 3 The lower side (the middle side) is in contact with the substrate W1. This is because, when no insulating layer is provided between the substrate W1 and the lower electrode layer W2 in the wafer WA, conductivity is maintained from the lower electrode layer W2 to the first electrode 3. Furthermore, this is because, even if an insulating layer is provided between the substrate W1 and the lower electrode layer W2, when the wafer WA is large and has a sufficiently large capacitance between the substrate W1 and the lower electrode layer W2, the potential of the lower electrode layer W2 can be approximately stable at the frequency and amplitude of the periodic load described later. With the first electrode 3 in contact with the back side of the substrate W1, the first electrode 3 can be positioned directly above the wafer stage 2 with approximately the same area as it.

[0037] The second electrode 4 is connected to the piezoelectric film W3 from above when measuring the piezoelectric constant d33. A conductor 4A is connected to the second electrode 4 (or another location at the same potential). The shape of the second electrode 4 is not particularly limited; for example, [example image would be inserted here]. Figure 4 As shown in (a) and (b), its lower end face can be formed into a generally hemispherical shape. In order to facilitate stable contact with the piezoelectric film W3, the second electrode 4 can be made of brass or stainless steel, etc. In addition, it can also be obtained by attaching a metal (e.g., gold or silver) to at least the lower surface of the base made of synthetic resin (e.g., nylon). Figure 4 (a) indicates the second electrode 4, which has a base made entirely of the same material (e.g., brass or stainless steel). Figure 4 (b) indicates a second electrode 4 consisting of two bases made of different materials: a base (lower ball-shaped portion) 4l with metal attached to not only its lower surface but also its entire surface, made of synthetic resin and a base (cage portion) 4h made of, for example, brass or stainless steel, which is held in contact with and held therein. Compared to brass or stainless steel, the synthetic resin base 4l with metal attached to its surface is more elastic, which improves the adhesion between it and the piezoelectric film W3, and allows for more stable and easier contact with the piezoelectric film W3.

[0038] The second electrode loading unit 5 applies a fixed-period periodic load (alternating force) to the piezoelectric film W3 via the second electrode 4. The second electrode loading unit 5 is controlled by a reference frequency signal output from the reference frequency signal generator 7. The periodic load varies with the frequency of this reference frequency signal, such as... Figure 5As shown by reference numeral b in the attached figure, when a static load (initial load) is applied (refer to...), Figure 5 The load is applied for a period of time (e.g., approximately 2 seconds to approximately 20 seconds) as indicated by reference numeral a). For example, the static load value can be set to approximately 0.5 N, and the cyclic load can have an amplitude value of approximately 0.25 N. Additionally, in Figure 5 The figure shows the periodic load when the reference frequency signal has a frequency of 100 Hz.

[0039] By applying a periodic load with such a fixed period, a charge that changes with a fixed period in sync with the periodic load is generated on the piezoelectric film W3.

[0040] In detail, the second electrode load unit 5 can be configured to include a second linear motor 51, a load detector mounting plate 52, and a second electrode mounting plate 53. The second linear motor 51 can cause the second electrode 4 to move linearly via the load detector mounting plate 52 and the load detector 61 (described later in the load measurement unit 6). The second linear motor 51 is controlled by a reference frequency signal output from the reference frequency signal generator 7.

[0041] The second direct-acting motor 51 is a motor in which the direct-acting part 51a moves directly relative to the position of the support part 51b. The lower end of the direct-acting part 51a is fixed to the load detector mounting plate 52, and the support part 51b is fixed to the frame of the piezoelectric constant measuring device 1 (not shown). The second direct-acting motor 51 is not particularly limited, and a VCM, servo motor, etc. can be used.

[0042] The load detector mounting plate 52 mounts the load detector 61 so that it can detect forces from below.

[0043] The second electrode mounting plate 53 mounts the end of the second electrode 4 (the end that can contact the piezoelectric film W3) downwards. Specifically, a fixing part 4a is provided on the upper part of the second electrode 4, which is fixed to the second electrode mounting plate 53 by screwing or the like. The upper end face of the fixing part 4a protrudes from the second electrode mounting plate 53. Load detector mounting plate sliding rods 52A and 52A are mounted on the upper surface of the peripheral portion of the second electrode mounting plate 53. Furthermore, the load detector mounting plate 52 is positioned upwards via load detector holding springs 52B and 52B. The load detector mounting plate 52 and the second electrode mounting plate 53 are guided by the load detector mounting plate sliding rods 52A and 52A, and are cushioned by the load detector holding springs 52B and 52B, allowing them to move up and down relative to each other. Additionally, heads 52Aa and 52Aa are provided on the upper part of the load detector mounting plate sliding rods 52A and 52A, determining the maximum separation between the load detector mounting plate 52 and the second electrode mounting plate 53.

[0044] The load measurement unit 6 measures the load (static load and periodic load) applied to the piezoelectric film W3. In this embodiment, the load measurement unit 6 includes a load detector (load sensor) 61 for detecting the load and a load measurement processor 62 for digitizing and outputting an electrical signal (e.g., current) corresponding to the detected load. When measuring a periodic load, the load measurement unit 6 can convert the periodic load into an AC signal (e.g., AC current) in the load detector 61 and output it to the load measurement processor 62, and output data of the amplitude value of the periodic load (or data of a value proportional to the amplitude value of the periodic load) from the load measurement processor 62. Furthermore, the value proportional to the amplitude value of the periodic load is, for example, the effective value (RMS) of the periodic load. If N0 represents the amplitude value of the periodic load, N... RMS The effective value of the periodic load is then called N. RMS =N0 / (√2) relationship.

[0045] The load detector 61 of the load measurement unit 6 is assembled in the mechanism of the second electrode load unit 5. Figure 1 In the accompanying drawing, reference numeral 61A indicates the electrical wire connecting the load detector 61 to the load measurement processor 62. The load measurement processor 62 can also be integrated with the load detector 61.

[0046] The reference frequency signal generator 7 is capable of generating and outputting a reference frequency signal with a reference frequency f (e.g., 1Hz to 500Hz). This reference frequency signal is typically a sine wave. The reference frequency signal generator 7 can have its output switched on and off via the piezoelectric constant measurement and control unit 9.

[0047] The lock-in amplifier 8 receives the current induced by the charge generated in the piezoelectric film W3 via the second electrode 4 as the measured signal, and receives the aforementioned reference frequency signal as the reference signal. It outputs data of the amplitude value of the measured signal (i.e., the amplitude value of the current induced by the charge generated in the piezoelectric film W3) (or data of a value proportional to the amplitude value of the measured signal). Furthermore, the value proportional to the amplitude value of the measured signal is, for example, the effective value (RMS) of the measured signal. If I0 represents the amplitude value of the measured signal, and I... RMS When representing the effective value of the measured signal, it becomes I. RMS =I0 / (√2) relationship.

[0048] Lock-in amplifiers (LIAs) are well-known and can be configured in various circuit structures, but as a basic structure, such as... Figure 6As shown, the device includes a first mixer 81, a first low-pass filter 82, a phase shifter 83, a second mixer 84, a second low-pass filter 85, and a polar coordinate converter 86. It has two input terminals (first input terminal 8a and second input terminal 8b) and two output terminals (first output terminal 8c and second output terminal 8d). An electrical wire 4A is connected to the first input terminal 8a, and the current caused by the charge generated in the piezoelectric film W3 is input as the measured signal. Furthermore, a reference frequency signal output from the reference frequency signal generator 7 is input to the second input terminal 8b as a reference signal. The amplitude value of the measured signal (i.e., data on the amplitude value of the current caused by the charge generated in the piezoelectric film W3 (or data on a value proportional to the amplitude value of the measured signal)) is output from the first output terminal 8c. Furthermore, data on the phase difference between the measured signal (i.e., the current caused by the charge generated in the piezoelectric film W3) and the reference signal (i.e., the reference frequency signal) is output from the second output terminal 8d.

[0049] The operation of the lock-in amplifier 8 is roughly as follows. Since the second electrode load unit 5 is controlled by a reference frequency signal, the charge generated in the piezoelectric film W3 is synchronized with the reference frequency f of the reference frequency signal. The current caused by the charge generated in the piezoelectric film W3 and the reference frequency signal are input to the first mixer 81 for mixing (multiplication), essentially outputting a high frequency of 2f and DC (0Hz). They pass through the first low-pass filter 82, thus becoming a DC-only output. Furthermore, the reference frequency signal is phase-shifted by 90° by the phase shifter 83. The current caused by the charge generated in the piezoelectric film W3 and the 90° phase-shifted reference frequency signal are input to the second mixer 84 for mixing (multiplication), essentially outputting a high frequency of 2f and DC (0Hz). They pass through the second low-pass filter 85, thus becoming a DC-only output. When the outputs of the first low-pass filter 82 and the second low-pass filter 85 are converted by the polar coordinate converter 86, an output representing the amplitude value (or a value proportional to its amplitude) of the current caused by the charge generated in the piezoelectric film W3 and an output representing the phase difference of the current caused by the charge generated in the piezoelectric film W3 relative to a reference frequency signal are obtained. Furthermore, generally, if the piezoelectric film W3 is not in an unpolarized state, the phase difference is approximately +90° or approximately -90° depending on its polarity.

[0050] Here, the noise component of the charge generated in the piezoelectric film W3 can be removed by the first low-pass filter 82 and the second low-pass filter 85. Therefore, even if the amount of charge generated in the piezoelectric film W3 is small and the S / N ratio in the current based on that charge is very small, the data on the amplitude value (or the value proportional to its amplitude value) and the phase difference data of the current caused by the charge generated in the piezoelectric film W3 output by the lock-in amplifier 8 become highly accurate data reflecting the amount of charge generated in the piezoelectric film W3. In addition, the lock-in amplifier 8 can also use a structure integrated with the reference frequency signal generator 7. Furthermore, the lock-in amplifier 8 can also replace the aforementioned reference frequency signal output from the reference frequency signal generator 7 with the AC signal output from the load detector 61 as the reference signal. This is because the AC signal output by the load detector 61 is synchronized with the aforementioned reference frequency signal.

[0051] As described above, the piezoelectric constant measurement and control unit 9 controls the vertical movement of the wafer stage 2, and can raise the wafer stage 2 when a static load is applied to the piezoelectric film W3. Furthermore, as described above, the piezoelectric constant measurement and control unit 9 can control the on / off state of the output of the reference frequency signal generator 7, and sets the output of the reference frequency signal generator 7 to be on when a periodic load is applied to the piezoelectric film W3.

[0052] Furthermore, the piezoelectric constant measurement and control unit 9 calculates the piezoelectric constant d33 based on the amplitude value of the measured signal output by the lock-in amplifier 8 (i.e., the amplitude value of the current caused by the charge generated in the piezoelectric film W3) (or, the data of the value proportional to the amplitude value of the measured signal) and the amplitude value of the periodic load measured by the load measurement unit 6 (or, the data of the value proportional to the amplitude value of the periodic load).

[0053] Specifically, as described above, if N0 represents the amplitude of the periodic load and I0 represents the amplitude of the current caused by the charge generated in the piezoelectric film W3, then the piezoelectric constant d33 can be calculated using the following formula.

[0054] d33=(I0 / 2πf) / N0

[0055] Here, f is the reference frequency.

[0056] Furthermore, as mentioned above, if N is used RMS The effective value of the periodic load is represented by I. RMS When representing the effective value of the current caused by the charge generated in the piezoelectric thin film W3, the piezoelectric constant d33 can be calculated using the following formula.

[0057] d33=(I RMS / 2πf) / N RMS

[0058] In addition, the piezoelectric constant measurement and control unit 9 can also input the phase difference data of the current caused by the charge generated in the piezoelectric film W3 relative to the reference frequency signal, which is measured by the lock-in amplifier 8, and use this phase difference to determine the polarity of the piezoelectric film W3.

[0059] The piezoelectric constant measurement and control unit 9 is typically implemented by a computer (personal computer). For example, such as Figure 7 As shown, the CPU 92 calculates program 91a according to the piezoelectric constant stored in the program storage unit 91, and outputs a signal controlling the up-and-down movement of the chip stage 2 from the output terminal 9a via the output unit 93. Furthermore, it outputs a signal controlling the on / off state of the output of the reference frequency signal generator 7 from the output terminal 9b. In addition, the CPU 92 receives data from the input terminals 9c and 9d via the input unit 94, including data on the amplitude of the periodic load measured by the load measurement unit 6 (or data proportional to the amplitude of the periodic load) and data on the amplitude of the current caused by the charge generated in the piezoelectric film W3 measured by the lock-in amplifier 8 (or data proportional to its amplitude). Then, the CPU 92 calculates the piezoelectric constant d33 using the working memory unit 95 and the above-described calculation method, and outputs it to the outside via the output unit 93 from the output terminal 9e. The data on the piezoelectric constant d33 output from the output terminal 9e is displayed, for example, on a display device (not shown).

[0060] In the piezoelectric constant measuring device 1 described above, when measuring the piezoelectric constant d33 without forming the upper electrode layer, the noise component of the charge generated in the piezoelectric film W3 can be removed by the lock-in amplifier 8. Therefore, the charge generated in the piezoelectric film W3 can be measured with high accuracy, and the piezoelectric constant d33 can be measured with good accuracy even if the load applied to the piezoelectric film W3 is small.

[0061] Figure 8The results show the determination (calculation) of the piezoelectric constant d33 by applying a periodic load of 0.3 N to the piezoelectric film W3 of the experimental wafer WA (without the upper electrode layer) through the second electrode 4, changing the frequency of the reference frequency signal (reference frequency f). The piezoelectric film W3 is a PVDF film. Each measurement was performed 100 times. The results show that the value of the piezoelectric constant d33 converges within ±0.1% for each measurement. Even with a small load applied to the piezoelectric film W3, the piezoelectric constant d33 can be measured with good accuracy when the upper electrode layer is not formed. Furthermore, for convenience, in this experiment, an AC signal output from the load detector 61, synchronized with the reference frequency signal output from the reference frequency signal generator 7, is input to the second input terminal 8b of the lock-in amplifier 8 as a reference signal.

[0062] Next, the piezoelectric constant measuring device 1' will be described. For example... Figure 9 As shown, the piezoelectric constant measuring device 1′ adds a pulse generator 10 and a relay 11 to the structure of the piezoelectric constant measuring device 1.

[0063] The pulse generator 10 is capable of generating and outputting pulses of a given polarity, height, and width. As described later, the polarity, height, and width of the pulse are sufficient to control the polarization of the piezoelectric film W3; for example, the pulse polarity can be set to positive or negative, the pulse height can be set to 150V to 300V, and the pulse width can be set to 10 microseconds to 200 microseconds. The pulse generator 10 can be controlled to switch on and off by the piezoelectric constant measurement and control unit 9.

[0064] Relay 11 switches between the passage of current caused by the charge generated in the piezoelectric film W3 and the passage of pulses output by pulse generator 10. If a pulse passes through relay 11, it is applied to the piezoelectric film W3 via the second electrode 4.

[0065] Specifically, relay 11 has three input / output terminals (first input / output terminal 11a, second input / output terminal 11b, and third input / output terminal 11c) and one control terminal 11d (see reference). Figure 9When the switching control signal input to control terminal 11d is in one state, the first input / output terminal 11a and the second input / output terminal 11b are connected, and the first input / output terminal 11a and the third input / output terminal 11c are disconnected. When the switching control signal input to control terminal 11d is in another state, the first input / output terminal 11a and the second input / output terminal 11b are disconnected, and the first input / output terminal 11a and the third input / output terminal 11c are connected. The electrical wire 4A of the second electrode 4 is disconnected, the first input / output terminal 11a is connected to the disconnected second electrode 4 side, and the second input / output terminal 11b is connected to the disconnected lock-in amplifier 8 side. In addition, the third input / output terminal 11c is connected to the output of the pulse generator 10. The relay 11 can be controlled by the piezoelectric constant measurement and control unit 9 (i.e., the switching control signal is input from the piezoelectric constant measurement and control unit 9 to the control terminal 11d).

[0066] When the switching control signal of relay 11 is in one state, the current caused by the charge generated in the piezoelectric film W3 is input to the lock-in amplifier 8, thus enabling it to operate in the same way as the piezoelectric constant measuring device 1 described above. When the switching control signal of relay 11 is in another state, if the pulse generator 10 is in the on state, a pulse output from the pulse generator 10 is applied to the piezoelectric film W3 through the second electrode 4.

[0067] The polarization of the piezoelectric film W3 is controlled when a pulse of given polarity, height, and width is applied. Figure 10 This indicates the result of measuring (calculating) the piezoelectric constant d33 by applying pulses (pulse voltage) with positive (curve c) or negative (curve d) polarity to the piezoelectric film W3 on the experimental wafer WA (in its state before the upper electrode layer is formed), passing through the second electrode 4, and applying periodic loads after each pulse application. The pulse width is 100 microseconds. The piezoelectric film W3 is a PZT film. Based on this result, it can be seen that if the pulse height, in absolute value, is approximately 75V or higher, the polarization of the piezoelectric film W3 can be appropriately controlled.

[0068] In this way, in addition to the functions of the piezoelectric constant measuring device 1, the piezoelectric constant measuring device 1′ can also easily control the polarization of the piezoelectric thin film W3. Furthermore, generally speaking, the piezoelectric thin film W3 is in an unpolarized state immediately after film formation, and its state is not fixed and unclear among multiple locations on the wafer WA. However, even so, the piezoelectric constant d33 can be measured with good accuracy by controlling the polarization of the piezoelectric thin film W3.

[0069] The piezoelectric constant measuring device according to the embodiments of the present invention has been described above. However, the piezoelectric constant measuring device of the present invention is not limited to the device described in the embodiments, and various design changes can be made within the scope of the claims.

[0070] For example, to measure the piezoelectric constant d33 of the piezoelectric film W3 using the piezoelectric constant measuring device 1 (or 1'), as described above, in addition to applying a load to the piezoelectric film W3 by having the second electrode 4 contact it from above, the piezoelectric film W3 can also be measured by having the second electrode 4 contact it from above with a layer formed above the piezoelectric film W3. For example, in the state where the upper electrode layer has been formed and patterned, the second electrode 4 can also apply a load to the piezoelectric film W3 by contacting it from above with the upper electrode layer or an insulating layer to its side (or above), thereby measuring the piezoelectric constant d33. In this case, compared to checking the suitability of the piezoelectric film in the state where the upper electrode layer has not been formed, checking the suitability of the piezoelectric film after subsequent processes is useful for checking the suitability of the piezoelectric film in the state where the wafer WA is in place. Furthermore, this is particularly useful when the piezoelectric film W3 is very flexible.

[0071] -Explanation of Figure Markers-

[0072] 1.1′ Piezoelectric constant measuring device

[0073] 2. Chip station

[0074] 20. Main body of the chip stage

[0075] 21 First direct drive motor

[0076] 21a The direct-acting part of the first direct-acting motor

[0077] 21b Support part of the first direct-drive motor

[0078] 3 First Electrode

[0079] 4 Second electrode

[0080] 4a Fixing part of the second electrode

[0081] 4h Base of the second electrode (cage part)

[0082] 4l Base of the second electrode (lower ball-shaped part)

[0083] 4A Second electrode wire

[0084] 5 Second Electrode Loading Unit

[0085] 51 Second direct-drive motor

[0086] 51a The direct drive section of the second direct drive motor

[0087] 51b Support part of the second direct-drive motor

[0088] 52 Load Detector Mounting Plate

[0089] 52A Load Detector Mounting Plate Sliding Rod

[0090] 52Aa Load detector mounting plate sliding rod head

[0091] 52B Load Detector Holding Spring

[0092] 53 Second electrode mounting plate

[0093] 6 Load Measurement Unit

[0094] 61 Load Detector

[0095] 61A Load Detector Conductor

[0096] 62 Load Measurement Processor

[0097] 7. Reference Frequency Signal Generator

[0098] 8 Lock-in Amplifier

[0099] The first input terminal of the 8a lock-in amplifier

[0100] 8b Second input terminal of the lock-in amplifier

[0101] The first output terminal of the 8c lock-in amplifier

[0102] The second output terminal of the 8d lock-in amplifier

[0103] 81 Lock-in amplifier's first mixer

[0104] 82. First low-pass filter of lock-in amplifier

[0105] 83. Phase shifter of a lock-in amplifier

[0106] 84. Second mixer of lock-in amplifier

[0107] 85 Second low-pass filter of lock-in amplifier

[0108] 86. Polar coordinate converter of lock-in amplifier

[0109] 9. Piezoelectric constant measurement and control unit

[0110] Output terminals of the piezoelectric constant measurement and control unit (9a, 9b, 9e)

[0111] Input terminals of the piezoelectric constant measurement and control unit (9c, 9d)

[0112] 91. Program storage unit of the piezoelectric constant measurement and control unit

[0113] 91a Piezoelectric constant measurement and control unit piezoelectric constant calculation program

[0114] 92. CPU of the piezoelectric constant measurement and control unit

[0115] 93 Output section of the piezoelectric constant measurement and control unit

[0116] 94 Input section of the piezoelectric constant measurement and control unit

[0117] 95. Working memory section of the piezoelectric constant measurement and control unit

[0118] 10 Pulse Generator

[0119] 11 Relay

[0120] 11a The first input / output terminal of the relay

[0121] 11b The second input / output terminal of the relay

[0122] The third input / output terminal of the 11c relay

[0123] 11d Relay control terminal

[0124] WA wafer

[0125] W1 base board

[0126] W2 lower electrode layer

[0127] W3 piezoelectric film.

Claims

1. A piezoelectric constant measuring device for measuring the piezoelectric constant d33 of a piezoelectric thin film deposited on a lower electrode layer of a wafer substrate. The piezoelectric constant measuring device is characterized by having: A wafer stage that supports the substrate; The first electrode can be connected to a given portion of the wafer and grounded; Second electrode; The second electrode load unit is controlled by a reference frequency signal and is able to apply a periodic load of the frequency of the reference frequency signal to the piezoelectric film via the second electrode. The load measurement unit converts the periodic load into an AC signal and outputs the amplitude value of the periodic load or a value proportional to it. A reference frequency signal generator generates and outputs the reference frequency signal; The lock-in amplifier takes the current generated by the charge in the piezoelectric film through the applied periodic load as the measured signal, input through the second electrode, and takes the reference frequency signal or the AC signal as the reference signal, and outputs the amplitude value of the measured signal or a value proportional to it. as well as The piezoelectric constant measurement and control unit calculates the piezoelectric constant d33 based on the amplitude value of the measured signal or a value proportional to it, and the amplitude value of the periodic load or a value proportional to it.

2. The piezoelectric constant measuring device according to claim 1, wherein, The piezoelectric constant measuring device also includes: A pulse generator capable of producing pulses of given polarity, height, and width; and The relay switches between the passage of the current caused by the charge generated in the piezoelectric film and the passage of the pulse. If the pulse passes through the relay, it is applied to the piezoelectric film via the second electrode.

3. The piezoelectric constant measuring device according to claim 1 or 2, wherein, The second electrode has metal attached to at least the lower surface of the base made of synthetic resin.

Images