Piezoelectric constant measuring device

Abstract

Provided is a piezoelectric constant measuring device capable of accurately measuring a piezoelectric constant d33 even when a load applied to a piezoelectric thin film on a wafer is small. A piezoelectric constant measuring device 1 measures a piezoelectric constant d33 of a piezoelectric thin film W3 formed on a wafer WA, and comprises: a wafer table 2; a first electrode 3 which can be in contact with a predetermined portion of the wafer WA; a second electrode 4; a second electrode load means 5 which is controlled by a reference frequency signal and can apply a periodic load to the piezoelectric thin film W3 via the second electrode 4; a load measuring means 6 that outputs the amplitude value of the periodic load or a value proportional to the amplitude value; a reference frequency signal generator 7 that outputs the reference frequency signal; a lock-in amplifier 8 to which is input through the second electrode 4, as a signal to be measured, a current due to an electric charge generated in the piezoelectric thin film W3, and to which is input the reference frequency signal as a reference signal, and which outputs the amplitude value of the signal to be measured or a value proportional thereto; and a piezoelectric constant measurement control means 9 that calculates the piezoelectric constant d33.

Description

Piezoelectric constant measuring device

[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 wafer substrate.

[0002] Piezoelectric devices are used in a wide range of applications, from various sensors to actuators. The piezoelectric characteristics of piezoelectric devices can be quantitatively evaluated by measuring their piezoelectric constants. Piezoelectric constants include d31 and d33, which depend on the direction of the applied load and the amount of charge generated by it. Piezoelectric constants can be measured using various piezoelectric constant measurement devices. For example, Patent Document 1 discloses a piezoelectric constant measurement device that can measure d31 by attaching a jig to a piezoelectric constant measurement device for d33. Patent Document 2 discloses a piezoelectric constant measurement device that can measure the amount of change in the amount of multiple pulse-like charges generated by multiple pulse loads and calculate the piezoelectric constant d33 (and d31) from the amount of change and the measured pulse loads.

[0003] In recent years, the trend toward miniaturization and reduced power consumption of piezoelectric devices has led to the active development and commercialization of piezoelectric devices using piezoelectric thin films (thin films of piezoelectric materials) such as PVDF and PZT films. In manufacturing lines, piezoelectric thin films are deposited by sputtering or other methods on the bottom electrode layer of a wafer substrate, such as silicon. The wafer then undergoes subsequent processes, such as the formation of the top electrode layer, before being divided into the desired shape to produce the piezoelectric device.

[0004] To determine whether a piezoelectric thin film is suitable, a predetermined shape is cut out from a wafer sampled in a sampling test on the production line, and the piezoelectric constant is measured using a piezoelectric constant measuring device. This sampling test is a destructive test in which the sampled wafer cannot be used thereafter. In contrast, a non-destructive test has been proposed in which the piezoelectric constant d33 is measured in the wafer state, as shown in Patent Document 3, for example.

[0005] JP 2014-081339 A Japanese Patent No. 6241975 A Japanese Patent No. 2022-128529 A

[0006] However, if one attempts to measure the piezoelectric constant d33 without forming the upper electrode layer, it is necessary to reduce the load applied to the piezoelectric thin film, and the piezoelectric thin film may be in an unpolarized state, which presents challenges specific to piezoelectric thin films on wafers.

[0007] The present invention has been made in consideration of the above circumstances, and its purpose is to provide a piezoelectric constant measuring device that can accurately measure the piezoelectric constant d33 even when a small load is applied to a piezoelectric thin film on a wafer when measuring the piezoelectric constant d33 in a state where an upper electrode layer is not formed, and further to provide a piezoelectric constant measuring device that can accurately measure the piezoelectric constant d33 even when the piezoelectric thin film is in an unpolarized state.

[0008] In order to achieve the above object, a piezoelectric constant measurement device according to an embodiment of the present invention is a piezoelectric constant measurement device for measuring the piezoelectric constant d33 of a piezoelectric thin film formed on a lower electrode layer on a wafer substrate, and comprises: a wafer stage for supporting the substrate; a first electrode that is capable of contacting a predetermined portion of the wafer and is grounded; a second electrode; second electrode load means that is controlled by a reference frequency signal and that is capable of applying a periodic load of the frequency of the reference frequency signal to the piezoelectric thin film via the second electrode; load measurement means that converts the periodic load into an AC signal and outputs the amplitude value of the periodic load or a value proportional thereto; a reference frequency signal generator that generates and outputs the reference frequency signal; a lock-in amplifier that receives as input, via the second electrode, a current due to charges generated in the piezoelectric thin film when the periodic load is applied as a signal to be measured, receives as input the reference frequency signal or the AC signal as a reference signal, and outputs the amplitude value of the signal to be measured or a value proportional thereto; and piezoelectric constant measurement control means that calculates the piezoelectric constant d33 from the amplitude value of the signal to be measured and the amplitude value of the periodic load or a value proportional thereto.

[0009] The piezoelectric constant measuring device further includes a pulse generator capable of generating a pulse of a predetermined polarity, height, and width, and a relay that switches between passing the current caused by the charge generated in the piezoelectric thin film and passing the pulse, and the pulse can be applied to the piezoelectric thin film through the second electrode when it passes through the relay.

[0010] The second electrode may have a base made of synthetic resin with metal attached to at least the lower surface thereof.

[0011] According to the piezoelectric constant measuring device of the present invention, when measuring the piezoelectric constant d33 without forming an upper electrode layer, it is possible to measure the piezoelectric constant d33 with high accuracy even if the load applied to the piezoelectric thin film on the wafer is small.Furthermore, by further providing a pulse generator and a relay, it is possible to measure the piezoelectric constant d33 with high accuracy even if the piezoelectric thin film is in an unpolarized state.

[0012] 1 shows a piezoelectric constant measurement device according to an embodiment of the present invention, in which the wafer stage, first electrode, second electrode, second electrode load means, and part of the load measurement means are shown in cross-section, and other parts of the load measurement means, the reference frequency signal generator, the lock-in amplifier, and the piezoelectric constant measurement control means are shown in block diagrams (or schematic diagrams).

[0023] FIG. 1 is a plan view showing an example of the arrangement of the first electrode of the piezoelectric constant measurement device.

[0024] FIG. 2 is a diagram showing an example of a different arrangement of the first electrode in the piezoelectric constant measurement device shown in FIG. 1.

[0025] FIG. 3 is an enlarged cross-sectional view showing a second electrode of the piezoelectric constant measurement device, in which (a) all of the bases are made of the same material, and (b) the base is composed of a lower ball-shaped portion and a holder portion made of different materials.

[0026] FIG. 4 is a waveform diagram of an example of a load applied to a piezoelectric thin film in the piezoelectric constant measurement device.

[0027] FIG. 5 is a schematic diagram showing an example of the configuration of a lock-in amplifier of the piezoelectric constant measurement device.

[0028] FIG. 6 is a schematic diagram showing an example of the configuration of the piezoelectric constant measurement control means of the piezoelectric constant measurement device. Fig. 9 is a diagram showing experimental results in which the piezoelectric constant d33 was measured by changing the reference frequency using the wafer stage, first electrode, second electrode, second electrode load means, load measuring means, reference frequency signal generator, and lock-in amplifier of the piezoelectric constant measurement apparatus shown in Fig. 1. Fig. 10 is a diagram showing a configuration in which a pulse generator and a relay are added to the piezoelectric constant measurement apparatus shown in Fig. 1. Fig. 9 is a diagram showing experimental results in which the piezoelectric constant d33 was measured after applying pulses with different pulse voltages using the piezoelectric constant measurement apparatus shown in Fig. 9.

[0013] An embodiment of the present invention will be described below. A piezoelectric constant measuring apparatus 1 according to an embodiment of the present invention measures the piezoelectric constant d33 of a piezoelectric thin film W3 (e.g., 1 μm to 200 μm thick) formed on a lower electrode layer W2 on a substrate W1 of a wafer WA (see FIG. 1 ). The piezoelectric thin film W3 is formed on the lower electrode layer W2, such as a noble metal or metal, by sputtering or other methods, after the lower electrode layer W2, such as a silicon or metal (e.g., SUS, Ni alloy, etc.), is formed on the substrate W1 of the wafer WA in a manufacturing line. After measuring the piezoelectric constant d33 using the piezoelectric constant measuring apparatus 1, the wafer WA undergoes subsequent processes, such as the formation of an upper electrode layer, and is then divided into predetermined shapes to produce piezoelectric devices.

[0014] The piezoelectric constant d33 can be calculated (measured) from the amount of charge generated when a load is applied in the thickness direction of the piezoelectric thin film W3 and the applied load. When a load is applied by contacting a portion of the piezoelectric thin film W3 with the second electrode 4 (described later) without the upper electrode layer formed, the applied load must be small to prevent changes in the piezoelectric properties and physical deformation at the contact point or its surrounding area. This reduces the amount of charge generated in the piezoelectric thin film W3, increasing the noise component relatively, which tends to result in a very small S / N ratio in the signal (specifically, current) generated by the charge. Note that noise may be generated by the piezoelectric constant measurement device 1 itself or transmitted from other devices, and remains even when various countermeasures are taken, such as attaching vibration-isolating members or shielding members to each component or using coaxial cables for each conductor.

[0015] 1, a piezoelectric constant measuring device 1 for measuring the piezoelectric constant d33 of a piezoelectric thin film W3 in the state of a wafer WA comprises a wafer stage 2, a first electrode 3, a second electrode 4, a second electrode load means 5, a load measuring means 6, a reference frequency signal generator 7, a lock-in amplifier 8, and a piezoelectric constant measurement control means 9. Note that in FIG. 1, the various parts of the wafer WA are shown enlarged in the thickness direction for convenience of illustration.

[0016] The wafer WA is placed on and supported by the wafer stage 2. The wafer stage 2 can be moved in two-dimensional horizontal directions in order to measure the piezoelectric constant d33 of the piezoelectric thin film W3 at multiple locations on the wafer WA.

[0017] Furthermore, the wafer stage 2 (more specifically, the wafer stage main body 20, described later) can be made movable up and down so that it can be raised when a fixed static load (initial load) (see symbol a in FIG. 5, described later) is applied to the piezoelectric thin film W3. When the wafer stage 2 is raised, the second electrode 4 comes into contact with the piezoelectric thin film W3. At this time, the second electrode 4 is kept stationary. This allows the load to be measured by a load detector 61, described later, of the load measurement means 6. Furthermore, when the wafer stage 2 is raised, a static load is applied to the piezoelectric thin film W3. This allows a periodic load (alternating force) (see symbol b in FIG. 5, described later) to be applied to the piezoelectric thin film W3 via the second electrode 4. It is also possible to lower the second electrode 4 to contact the piezoelectric thin film W3 without raising the wafer stage 2, and then further lower the second electrode 4 to apply a static load.

[0018] Specifically, the wafer stage 2 can be configured to include a wafer stage main body 20 and a first linear motor 21 that moves it up and down. The first linear motor 21 is a motor in which a linear moving portion 21a moves linearly with a support portion 21b as a reference position. The linear moving portion 21a has an upper end fixed to the wafer stage main body 20, and the support portion 21b is fixed to a frame (not shown) of the piezoelectric constant measurement device 1. The first linear motor 21 is not particularly limited, but a servo motor or the like can be used. The first linear motor 21 can be controlled by the piezoelectric constant measurement control means 9.

[0019] The first electrode 3 can be in contact with a predetermined portion of the wafer WA so as to ground the lower electrode layer W2. Specifically, when measuring the piezoelectric constant d33 of the piezoelectric thin film W3, the first electrode 3 can be brought into contact with the vicinity of the periphery of the lower electrode layer W2 manually or by control of the piezoelectric constant measurement control means 9. Here, the vicinity of the periphery of the lower electrode layer W2 to which the first electrode 3 is in contact can be a portion of the wafer WA where a portion of the piezoelectric thin film W3 has been chemically or mechanically removed, as shown in FIG. 2 . In this case, the portion from which the piezoelectric thin film W3 has been removed is preferably a portion that will not be used in a piezoelectric device product. By bringing the first electrode 3 into contact with the vicinity of the periphery of the lower electrode layer W2 in this manner, the lower electrode layer W2 can be easily brought to ground potential via the first electrode 3, even if an insulating layer is provided between the substrate W1 and the lower electrode layer W2 in the wafer WA.

[0020] When an insulating layer is not provided between the substrate W1 and the lower electrode layer W2 in the wafer WA, or when an insulating layer is provided 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 configured to contact the back surface of the substrate W1 (the lower surface in FIG. 3 ) as shown in FIG. 3 instead of contacting the vicinity of the periphery of the lower electrode layer W2. This is because, when an insulating layer is not provided between the substrate W1 and the lower electrode layer W2 in the wafer WA, conductivity is maintained from the lower electrode layer W2 of the wafer WA to the first electrode 3. Furthermore, when an insulating layer is provided between the substrate W1 and the lower electrode layer W2 but 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 made substantially stable at the frequency and amplitude of the periodic load described below. When the first electrode 3 is in contact with the rear surface of the substrate W1 in this way, the first electrode 3 can be provided directly above the wafer stage 2 with approximately the same area as the wafer stage 2.

[0021] The second electrode 4 contacts the piezoelectric thin film W3 from above when measuring the piezoelectric constant d33 of the piezoelectric thin film W3. An electrical 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, but its lower end surface can be approximately hemispherical, as shown in Figures 4(a) and 4(b). The second electrode 4 can be made of brass or stainless steel to facilitate stable contact with the piezoelectric thin film W3. Alternatively, the second electrode 4 can have a synthetic resin (e.g., nylon) base with a metal (e.g., gold or silver) attached to at least the lower surface. Figure 4(a) shows a second electrode 4 whose base is made entirely of the same material (e.g., brass or stainless steel). 4(b) shows the second electrode 4, which is composed of two bases made of different materials: a ball-shaped synthetic resin base 4l (lower ball-shaped portion) with metal attached not only to the lower surface but also to the entire surface, and a base (holder portion) 4h that contacts and holds the base 4l and is made of, for example, brass or stainless steel. Such a synthetic resin base 4l with a metal attached to its surface is more elastic than a base made of brass or stainless steel, and can thereby improve adhesion with the piezoelectric thin film W3 and make it easier to contact the piezoelectric thin film W3 more stably.

[0022] The second electrode load means 5 applies a periodic load (alternating force) with a constant period to the piezoelectric thin film W3 via the second electrode 4. The second electrode load means 5 is controlled by a reference frequency signal output by a reference frequency signal generator 7. The periodic load varies with the frequency of this reference frequency signal, and is applied while the static load (initial load) (see reference symbol a in FIG. 5) is being applied (e.g., approximately 2 to 20 seconds), as indicated by symbol b in FIG. 5. For example, the static load value can be approximately 0.5 N, and the periodic load can have an amplitude value of approximately 0.25 N. Note that FIG. 5 shows the periodic load when the frequency of the reference frequency signal is 100 Hz.

[0023] By applying such a periodic load at a constant period, an electric charge is generated in the piezoelectric thin film W3, which changes at a constant period in synchronization with the periodic load.

[0024] More specifically, the second electrode loading means 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 linearly move the second electrode 4 via the load detector mounting plate 52 and a load detector 61, which will be described in detail after the load measuring means 6. The second linear motor 51 is controlled by a reference frequency signal output by a reference frequency signal generator 7.

[0025] The second linear motor 51 is a motor in which a linear motion portion 51a moves linearly with a support portion 51b as a reference position. The lower end of the linear motion portion 51a is fixed to a load detector mounting plate 52, and the support portion 51b is fixed to a frame (not shown) of the piezoelectric constant measuring device 1. The second linear motion motor 51 is not particularly limited, but a VCM, a servo motor, or the like can be used.

[0026] The load detector mounting plate 52 is mounted on the load detector 61 so that the load detector 61 can detect a force from below.

[0027] The second electrode 4 is attached to the second electrode mounting plate 53 so that its end (the end that can contact the piezoelectric thin film W3) faces downward. Specifically, a fixed portion 4a is provided on the top of the second electrode 4, and this fixed portion 4a is fixed to the second electrode mounting plate 53 by screwing or the like. The upper end surface of the fixed portion 4a is exposed from the second electrode mounting plate 53. Load detector mounting plate sliding rods 52A, 52A are attached to the upper surface of the periphery of the second electrode mounting plate 53, and the load detector mounting plate 52 is positioned above via load detector holding springs 52B, 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, 52A and cushioned by the load detector holding springs 52B, 52B, allowing them to move up and down relative to each other. In addition, heads 52Aa, 52Aa that determine the maximum distance between the load detector mounting plate 52 and the second electrode mounting plate 53 are provided on the upper portions of the load detector mounting plate sliding bars 52A, 52A.

[0028] The load measuring means 6 measures the load (static load and periodic load) applied to the piezoelectric thin film W3. In this embodiment, the load measuring means 6 has a load detector (load cell) 61 that detects the load, and a load measurement processor 62 that converts an electric signal (e.g., current) corresponding to the detected load into data and outputs it. When measuring the periodic load, the load measuring means 6 can convert the periodic load in the load detector 61 into an AC signal (e.g., AC current) and output it to the load measurement processor 62, and output data on the amplitude value of the periodic load (or data on a value proportional to the amplitude value of the periodic load) from the load measurement processor 62. The value proportional to the amplitude value of the periodic load is, for example, the root mean square (RMS) value of the periodic load. The amplitude value of the periodic load is expressed as N ０ The effective value of the periodic load is expressed as N ＲＭＳ Expressed as N ＲＭＳ = N ０ The relationship is / (√2).

[0029] The load detector 61 of the load measuring means 6 is incorporated into the mechanism of the second electrode load means 5, and in Fig. 1, reference numeral 61A denotes an electric lead that connects the load detector 61 and the load measurement processor 62. The load measurement processor 62 can also be integrated with the load detector 61.

[0030] The reference frequency signal generator 7 can generate and output a reference frequency signal having a reference frequency f (for example, 1 Hz to 500 Hz). This reference frequency signal is usually a sine wave. The on / off state of the output of the reference frequency signal generator 7 can be controlled by the piezoelectric constant measurement control means 9.

[0031] The lock-in amplifier 8 receives the current due to the charge generated in the piezoelectric thin film W3 as the signal to be measured through the second electrode 4, receives the standard frequency signal as the reference signal, and outputs data on the amplitude value of the signal to be measured (i.e., the amplitude value of the current due to the charge generated in the piezoelectric thin film W3) (or data on a value proportional to the amplitude value of the signal to be measured). The value proportional to the amplitude value of the signal to be measured is, for example, the root mean square (RMS) value of the signal to be measured. The amplitude value of the signal to be measured is expressed as I ０ and the effective value of the signal under test is expressed as I ＲＭＳ Expressed as I ＲＭＳ=I ０ The relationship is / (√2).

[0032] The lock-in amplifier 8 is well known and can have various circuit configurations. However, as a basic configuration, as shown in FIG. 6 , it has 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, as well as two input terminals (a first input terminal 8a and a second input terminal 8b) and two output terminals (a first output terminal 8c and a second output terminal 8d). The first input terminal 8a is connected to the electrical conductor 4A, and a current due to charges generated in the piezoelectric thin film W3 is input as the signal under measurement. The second input terminal 8b receives a reference signal, a reference frequency signal output from the reference frequency signal generator 7. The first output terminal 8c outputs the amplitude value of the signal under measurement (i.e., data on the amplitude value of the current due to charges generated in the piezoelectric thin film W3 (or data on a value proportional to the amplitude value of the signal under measurement)). The second output terminal 8d outputs data on the phase difference of the signal under measurement (that is, the current due to the charges generated in the piezoelectric thin film W3) relative to the reference signal (that is, the reference frequency signal).

[0033] The operation of the lock-in amplifier 8 is outlined as follows. The electric charge generated in the piezoelectric thin film W3 is synchronized with the reference frequency f of the reference frequency signal because the second electrode load means 5 is controlled by the reference frequency signal. The current due to the electric charge generated in the piezoelectric thin film W3 and the reference frequency signal are input to the first mixer 81 and mixed (multiplied), which basically outputs a high frequency of 2f and DC (0 Hz). These pass through the first low-pass filter 82, resulting in only DC output. The reference frequency signal is also phase-shifted by 90° by the phase shifter 83. The electric current due to the electric charge generated in the piezoelectric thin film W3 and the 90° phase-shifted reference frequency signal are input to the second mixer 84 and mixed (multiplied), which basically outputs a high frequency of 2f and DC (0 Hz). These pass through the second low-pass filter 85, resulting in only DC output. When the outputs of the first low-pass filter 82 and the second low-pass filter 85 are converted by a polar coordinate converter 86, an output indicating the amplitude value (or a value proportional to that amplitude value) of the current due to the charge generated in the piezoelectric thin film W3 and an output indicating the phase difference between the reference frequency signal and the current due to the charge generated in the piezoelectric thin film W3 are obtained. Note that, unless the piezoelectric thin film W3 is in an unpolarized state, the phase difference is generally about +90° or about −90° depending on its polarity.

[0034] Here, noise components added to the charge generated in the piezoelectric thin 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 thin film W3 is small and the S / N ratio of the current due to that charge is very small, the amplitude value data (or data proportional to that amplitude value) and phase difference data of the current due to the charge generated in the piezoelectric thin film W3 output by the lock-in amplifier 8 will be highly accurate and reflect the amount of charge generated in the piezoelectric thin film W3. Note that the lock-in amplifier 8 may also be integrated with the reference frequency signal generator 7. Alternatively, the lock-in amplifier 8 may receive the AC signal output by the load detector 61 as a reference signal instead of the reference frequency signal output from the reference frequency signal generator 7. This is because the AC signal output by the load detector 61 is synchronized with the reference frequency signal.

[0035] As described above, the piezoelectric constant measurement control means 9 controls the up and down movement of the wafer stage 2, and can raise the wafer stage 2 when applying a static load to the piezoelectric thin film W3. Also, as described above, the piezoelectric constant measurement control means 9 controls the on / off of the output of the reference frequency signal generator 7, and can turn on the output of the reference frequency signal generator 7 when applying a periodic load to the piezoelectric thin film W3.

[0036] Furthermore, the piezoelectric constant measurement control means 9 calculates the piezoelectric constant d33 from data on the amplitude value of the signal to be measured output by the lock-in amplifier 8 (i.e., the amplitude value of the current due to the charge generated in the piezoelectric thin film W3) (or data on a value proportional to the amplitude value of the signal to be measured) and data on the amplitude value of the periodic load measured by the load measurement means 6 (or data on a value proportional to the amplitude value of the periodic load).

[0037] Specifically, the piezoelectric constant d33 is determined by the amplitude value of the periodic load N ０ and the amplitude value of the current due to the charge generated in the piezoelectric thin film W3 is I ０ can be calculated using the following formula: d33 = (I ０ / 2πf) / N ０ Here, f is the reference frequency. As described above, the piezoelectric constant d33 is determined by dividing the effective value of the periodic load by N.ＲＭＳ and the effective value of the current due to the charge generated in the piezoelectric thin film W3 is I ＲＭＳ can be calculated using the following formula: d33 = (I ＲＭＳ / 2πf) / N ＲＭＳ

[0038] In addition, the piezoelectric constant measurement control means 9 can input data on the phase difference between the current due to the charge generated in the piezoelectric thin film W3 measured by the lock-in amplifier 8 and a reference frequency signal, and determine the polarity of the piezoelectric thin film W3 based on this phase difference.

[0039] The piezoelectric constant measurement control means 9 is typically implemented by a computer (personal computer). For example, as shown in FIG. 7 , in accordance with a piezoelectric constant calculation program 91 a stored in a program storage unit 91, a CPU 92 outputs a signal for controlling the vertical movement of the wafer stage 2 from an output terminal 9 a via an output unit 93, and outputs a signal for controlling the on / off state of the output of the reference frequency signal generator 7 from an output terminal 9 b. The CPU 92 also receives, via an input unit 94, input terminals 9 c and 9 d, data on the amplitude of the periodic load measured by the load measurement means 6 (or data on a value proportional to the amplitude of the periodic load) and data on the amplitude of the current due to the charge generated in the piezoelectric thin film W3 measured by the lock-in amplifier 8 (or data on a value proportional to the amplitude). The CPU 92 then calculates the piezoelectric constant d33 using the working memory unit 95 and other components according to the above-described calculation method, and outputs the calculated value from an output terminal 9 e via an output unit 93 to the outside. The data on the piezoelectric constant d33 output from the output terminal 9 e is displayed, for example, on a display device (not shown).

[0040] In the piezoelectric constant measuring device 1 described above, when measuring the piezoelectric constant d33 without forming the upper electrode layer, the noise components added to the charge generated in the piezoelectric thin film W3 can be removed by the lock-in amplifier 8, so that the charge generated in the piezoelectric thin film W3 can be measured with high accuracy, and the piezoelectric constant d33 can be measured with high accuracy even if the load applied to the piezoelectric thin film W3 is small.

[0041] FIG. 8 shows the results of measuring (calculating) the piezoelectric constant d33 by applying a periodic load to the piezoelectric thin film W3 of an experimental wafer WA (without an upper electrode layer) through the second electrode 4 while varying the frequency (reference frequency f) of the reference frequency signal, with an effective periodic load of 0.3 N. The piezoelectric thin film W3 is a PVDF film. Each measurement was performed 100 times. The results show that the piezoelectric constant d33 for each measurement is within ±0.1%, demonstrating that accurate measurement of the piezoelectric constant d33 is possible even with a small load applied to the piezoelectric thin film W3 when the upper electrode layer is not formed. For convenience, in this experiment, the second input terminal 8b of the lock-in amplifier 8 was supplied with an AC signal output by the load detector 61 synchronized with the reference frequency signal output from the reference frequency signal generator 7 as a reference signal.

[0042] Next, a piezoelectric constant measuring device 1' will be described. As shown in Fig. 9, the piezoelectric constant measuring device 1' has a pulse generator 10 and a relay 11 added to the configuration of the piezoelectric constant measuring device 1.

[0043] The pulse generator 10 can generate and output pulses of predetermined polarity, height, and width. The polarity, height, and width of the pulse are sufficient to control the polarization of the piezoelectric thin film W3 as described below, and for example, the pulse polarity can be positive or negative, the pulse height can be 150 V to 300 V, and the pulse width can be 10 microseconds to 200 microseconds. The on / off of the pulse generator 10 can be controlled by the piezoelectric constant measurement control means 9.

[0044] The relay 11 switches between passing a current due to charges generated in the piezoelectric thin film W3 and passing a pulse output from the pulse generator 10. When the pulse passes through the relay 11, it is applied to the piezoelectric thin film W3 through the second electrode 4.

[0045] Specifically, the 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 FIG. 9 ). When a switching control signal input to the control terminal 11d is in a first state, the first input / output terminal 11a and the second input / output terminal 11b are electrically connected and the first input / output terminal 11a and the third input / output terminal 11c are electrically disconnected. When the switching control signal input to the control terminal 11d is in a second state, the first input / output terminal 11a and the second input / output terminal 11b are electrically disconnected and the first input / output terminal 11a and the third input / output terminal 11c are electrically connected. The electrical conductor 4A of the second electrode 4 is divided, with the first input / output terminal 11a connected to the divided second electrode 4 side and the second input / output terminal 11b connected to the divided lock-in amplifier 8 side. 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 control means 9 (that is, a switching control signal is input from the piezoelectric constant measurement control means 9 to the control terminal 11d).

[0046] When the switching control signal of the relay 11 is in one state, a current due to charges generated in the piezoelectric thin film W3 is input to the lock-in amplifier 8, and therefore it is possible to operate in the same manner as the above-described piezoelectric constant measuring device 1. When the switching control signal of the 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 thin film W3 through the second electrode 4.

[0047] When pulses of a predetermined polarity, height, and width are applied, the polarization of the piezoelectric thin film W3 is controlled. Figure 10 shows the results of applying pulses of positive (curve c) or negative (curve d) polarity and varying pulse heights (pulse voltages) to the piezoelectric thin film W3 of an experimental wafer WA (without an upper electrode layer) through the second electrode 4, and measuring (calculating) the piezoelectric constant d33 by applying a periodic load after each pulse application. The pulse width is 100 microseconds. The piezoelectric thin film W3 is a PZT film. The results show that the polarization of the piezoelectric thin film W3 is properly controlled when the pulse height is approximately 75 V or higher in absolute value.

[0048] In this way, the piezoelectric constant measuring apparatus 1' makes it possible to easily control the polarization of the piezoelectric thin film W3, in addition to the effects of the piezoelectric constant measuring apparatus 1. Generally, the piezoelectric thin film W3 immediately after deposition is in an unpolarized state, and the state is not consistent and unknown among multiple locations on the wafer WA. Nevertheless, by controlling the polarization of the piezoelectric thin film W3, it is possible to accurately measure the piezoelectric constant d33.

[0049] The above describes a piezoelectric constant measuring device according to an embodiment of the present invention, but the piezoelectric constant measuring device of the present invention is not limited to the embodiment described, and various design modifications are possible within the scope of the matters described in the claims.

[0050] For example, when measuring the piezoelectric constant d33 of the piezoelectric thin film W3 using the piezoelectric constant measuring device 1 (or 1'), in addition to measuring the piezoelectric constant d33 by having the second electrode 4 contact the piezoelectric thin film W3 from above and applying a load to the piezoelectric thin film W3 as described above, it is also possible to measure the piezoelectric constant d33 by having the second electrode 4 contact a layer formed above the piezoelectric thin film W3 from above and applying a load to the piezoelectric thin film W3. For example, after an upper electrode layer has been formed and patterned, it is also possible to measure the piezoelectric constant d33 by having the second electrode 4 contact the upper electrode layer or an insulating layer on its side (or above) from above and applying a load to the piezoelectric thin film W3. In this case, the piezoelectric thin film is inspected for suitability through a subsequent process, as opposed to inspecting the piezoelectric thin film for suitability before the upper electrode layer is formed. However, being able to inspect the piezoelectric thin film for suitability in the wafer WA state is useful, and is particularly useful when the piezoelectric thin film W3 is very soft.

[0051] 1, 1' Piezoelectric constant measuring device 2 Wafer stage 20 Wafer stage main body 21 First linear motor 21a Linear motion part of first linear motor 21b Support part of first linear motor 3 First electrode 4 Second electrode 4a Fixing part of second electrode 4h Base part (holder part) of second electrode 4l Base part (lower ball-shaped part) of second electrode 4A Electrical conductor of second electrode 5 Second electrode loading means 51 Second linear motor 51a Linear motion part of second linear motor 51b Support part of second linear motor 52 Load detector mounting plate 52A Load detector mounting plate sliding rod 52Aa Head part of load detector mounting plate sliding rod 52B Load detector holding spring 53 Second electrode mounting plate 6 Load measuring means 61 Load detector 61A Electrical conductor of load detector 62 Load measurement processor 7 Reference frequency signal generator 8 Lock-in amplifier 8a First input terminal of lock-in amplifier 8b Second input terminal of lock-in amplifier 8c First output terminal of lock-in amplifier 8d Second output terminal of lock-in amplifier 81 First mixer of lock-in amplifier 82 First low-pass filter of lock-in amplifier 83 Phase shifter of lock-in amplifier 84 Second mixer of lock-in amplifier 85 Second low-pass filter of lock-in amplifier 86 Polar coordinate converter of lock-in amplifier 9 Piezoelectric constant measurement control means 9a, 9b, 9e Output terminal of piezoelectric constant measurement control means 9c, 9d Input terminal of piezoelectric constant measurement control means 91 Program storage unit of piezoelectric constant measurement control means 91a Piezoelectric constant calculation program of piezoelectric constant measurement control means 92 CPU of piezoelectric constant measurement control means 93 Output unit of piezoelectric constant measurement control means 94 Input unit of piezoelectric constant measurement control means 95 Working memory unit of piezoelectric constant measurement control means 10 Pulse generator 11 Relay 11a First input / output terminal of relay 11b Second input / output terminal of relay 11c Third input / output terminal of relay 11d Control terminal of relay WA Wafer W1 Substrate W2 Lower electrode layer W3 Piezoelectric thin film

Claims

1. A piezoelectric constant measurement device for measuring the piezoelectric constant d33 of a piezoelectric thin film formed on a lower electrode layer on a wafer substrate, comprising: a wafer stage for supporting the substrate; a grounded first electrode capable of contacting a predetermined portion of the wafer; a second electrode; second electrode load means controlled by a reference frequency signal and capable of applying a periodic load of the frequency of the reference frequency signal to the piezoelectric thin film via the second electrode; load measurement means for converting the periodic load into an AC signal and outputting the amplitude value of the periodic load or a value proportional thereto; a reference frequency signal generator for generating and outputting the reference frequency signal; a lock-in amplifier to which a current due to charges generated in the piezoelectric thin film when the periodic load is applied is input via the second electrode as a signal to be measured, and to which the reference frequency signal or the AC signal is input as a reference signal and which outputs the amplitude value of the signal to be measured or a value proportional thereto; and piezoelectric constant measurement control means for calculating the piezoelectric constant d33 from the amplitude value of the signal to be measured or a value proportional thereto and the amplitude value of the periodic load or a value proportional thereto.

2. A piezoelectric constant measuring device as defined in claim 1, further comprising: a pulse generator capable of generating pulses of a predetermined polarity, height, and width; and a relay for switching between passing the current caused by the charge generated in the piezoelectric thin film and passing the pulse, wherein the pulse is applied to the piezoelectric thin film through the second electrode when it passes through the relay.

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

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