JP2022128529A - Piezoelectric constant measuring device - Google Patents

Abstract

To provide a piezoelectric constant measuring device capable of easily measuring the piezoelectric constant d33 of a piezoelectric thin film at a plurality of locations in a wafer state.SOLUTION: The piezoelectric constant measuring device is a piezoelectric constant measuring device 1 that measures a piezoelectric constant d33 of a piezoelectric thin film W3 formed on a lower electrode layer W2 on a substrate W1 of a wafer WA, and includes: a wafer table 2 supporting the substrate W1; a first electrode 3 that can be in contact with a back surface of the substrate W1 or near a periphery of the lower electrode layer W2; a second electrode 4 that can be in contact with the piezoelectric thin film W3 from above; loading means 5 capable of vertically moving the second electrode 4 and applying a load to the piezoelectric thin film W3 via the second electrode 4; load measuring means 6 for measuring the load; charge amount measuring means 7 for measuring an amount of charge generated in the piezoelectric thin film W3 due to an application of the load, by inputting the charge through the first electrode 3 and/or the second electrode 4; and piezoelectric constant measurement control means 8 for calculating the piezoelectric constant d33 from the measured amount of charge and the measured load.SELECTED DRAWING: Figure 1

Description

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.

Piezoelectric devices are used in a wide range of fields, from various sensors to actuators. A piezoelectric device can be quantitatively evaluated for piezoelectric properties by measuring the piezoelectric constant. Piezoelectric constants include d31, d33, etc., depending on the direction of the applied load and the amount of charge generated thereby. The piezoelectric constant can be measured by various piezoelectric constant measuring devices. For example, Patent Literature 1 discloses a piezoelectric constant measuring device that enables measurement of d31 by attaching a jig to the piezoelectric constant measuring device for piezoelectric constant d33. In Patent Document 2, the amount of change in the amount of a plurality of pulse-like charges generated by a plurality of pulse loads is measured, and the piezoelectric constant d33 (and d31) can be calculated from the amount of change and the measured pulse load. A piezoelectric constant measuring device is disclosed.

2. Description of the Related Art In recent years, the development and commercialization of piezoelectric devices using a piezoelectric thin film (thin film of piezoelectric material) has become popular due to the trend toward smaller size and lower power consumption of piezoelectric devices. A piezoelectric thin film is formed on a lower electrode layer on a substrate such as a silicon wafer by a sputtering method or the like in a manufacturing line. After that, the wafer is subjected to subsequent processes such as formation of an upper electrode layer, and then divided into predetermined shapes to produce piezoelectric device products.

Whether the piezoelectric thin film is appropriate or not is generally determined by cutting out a predetermined shape from a wafer sampled in a sampling inspection in the production line and measuring the piezoelectric constant with a piezoelectric constant measuring device. Such a sampling inspection is a destructive inspection in which the wafers that are sampled cannot be used thereafter. On the other hand, for example, a non-destructive inspection for measuring the piezoelectric constant in the state of a wafer as shown in Patent Document 3 has also been proposed.

JP 2014-081339 A Japanese Patent No. 6241975 Japanese Unexamined Patent Application Publication No. 2013-210305

However, the method disclosed in Patent Document 3 cannot measure the variation of the piezoelectric constant within the wafer, and measures the piezoelectric constant d31.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object thereof is to provide a piezoelectric constant measuring apparatus capable of easily measuring the piezoelectric constant d33 of a piezoelectric thin film at a plurality of locations in a wafer state.

In order to achieve the above object, a piezoelectric constant measuring apparatus according to claim 1 is a piezoelectric constant measuring apparatus for measuring a piezoelectric constant d33 of a piezoelectric thin film formed on a lower electrode layer on a substrate of a wafer. a wafer table that supports the substrate; a first electrode that can be in contact with the back surface of the substrate or near the periphery of the lower electrode layer; a second electrode that can be in contact with the piezoelectric thin film from above; and load means for applying a load to the piezoelectric thin film via the second electrode; load measuring means for measuring the load; A charge amount measuring means for inputting through the first electrode and/or the second electrode and measuring the amount of the charge, and a piezoelectric constant for calculating a piezoelectric constant d33 from the measured charge amount and the measured load. and measurement control means.

A piezoelectric constant measuring apparatus according to claim 2 is the piezoelectric constant measuring apparatus according to claim 1, wherein the piezoelectric constant measurement control means generates a tensile stress in the piezoelectric thin film according to the measured amount of charge. Then, the piezoelectric constant d33 is calculated by subtracting the amount of electric charge applied.

According to a third aspect of the present invention, there is provided a piezoelectric constant measuring device according to the first or second aspect, wherein the lower end surface of the second electrode is flat and circular.

According to the piezoelectric constant measuring apparatus of the present invention, it is possible to easily measure the piezoelectric constant d33 of the piezoelectric thin film at a plurality of points in the state of the wafer.

1 shows a piezoelectric constant measuring apparatus according to an embodiment of the present invention, in which a wafer table, a first electrode, a second electrode, load means, and part of a load measuring means are shown in a sectional view, and the rest of the load measuring means is shown. A part, the charge amount measuring means, and the piezoelectric constant measurement control means are shown in block diagrams (or schematic diagrams). FIG. 2 is a plan view showing an example (an example different from FIG. 1) of the arrangement of first electrodes of the piezoelectric constant measuring device; FIG. 4 is a cross-sectional view showing an enlarged state of a piezoelectric thin film in the piezoelectric constant measuring device; Fig. 2 shows an example of waveforms in the piezoelectric constant measuring device, where (a) is a waveform diagram of a load applied to a piezoelectric thin film, and (b) is a waveform diagram of the amount of charge generated by the load. 4 is a schematic diagram showing a configuration example of a charge amount measuring means of the piezoelectric constant measuring device; FIG. There is a graph for explaining the processing by the piezoelectric constant measurement control means of the same piezoelectric constant measuring device, showing the relationship between the amount of charge generated in response to tensile stress and the total amount of charge generated in the piezoelectric thin film. be. FIG. 2 is a schematic diagram showing a configuration example of a piezoelectric constant measurement control means of the piezoelectric constant measuring device;

A mode for carrying out the present invention will be described below. The piezoelectric constant measuring device 1 according to the embodiment of the present invention measures the piezoelectric constant d33 of the piezoelectric thin film W3 (for example, thickness 1 μm to 200 μm) formed on the lower electrode layer W2 on the substrate W1 of the wafer WA. (See Figure 1). In the production line, the piezoelectric thin film W3 is formed by forming a lower electrode layer W2 made of noble metal or metal on a substrate W1 of a wafer WA made of silicon or metal (for example, SUS, Ni alloy, etc.), and then applying a sputtering method thereon. A film is formed by, for example, After the piezoelectric constant d33 is measured by the piezoelectric constant measuring apparatus 1, the wafer WA is divided into predetermined shapes through subsequent steps such as formation of an upper electrode layer, thereby making it possible to produce piezoelectric device products. be.

The piezoelectric constant d33 can indicate the amount of charge generated when stress is applied in the thickness direction of the piezoelectric thin film W3. A piezoelectric constant d31, which will be described later, can indicate the amount of charge generated when stress is applied in the direction along the surface of the piezoelectric thin film W3 (that is, the direction perpendicular to the thickness direction).

As shown in FIG. 1, the piezoelectric constant measuring device 1 for measuring the piezoelectric constant d33 of the piezoelectric thin film W3 in the state of the wafer WA includes a wafer table 2, a first electrode 3, a second electrode 4, a load means 5, and a load measuring means. 6 , charge amount measuring means 7 and piezoelectric constant measurement control means 8 . In FIG. 1, each part of the wafer WA, the first electrode 3, and the like are shown by enlarging the thickness direction for convenience of illustration.

The wafer table 2 supports the wafer WA on which it is placed. The wafer table 2 can be horizontally moved in two dimensions to measure the piezoelectric constant d33 of the piezoelectric thin film W3 at a plurality of locations on the wafer WA.

The first electrode 3 is in contact with the rear surface of the substrate W1 or the vicinity of the periphery of the lower electrode layer W2 when measuring the piezoelectric constant d33 of the piezoelectric thin film W3. An electrical lead 3A is connected to the first electrode 3 or to other locations having the same potential as it. When the first electrode 3 is in contact with the back surface of the substrate W1, the conductivity from the lower electrode layer W2 to the first electrode 3 of the wafer WA is not provided between the substrate W1 and the lower electrode layer W2 in the wafer WA. is preserved. In that case, the first electrode 3 can be provided directly above the wafer table 2 with almost the same area as it (see FIG. 1).

The case where the first electrode 3 is in contact with the vicinity of the periphery of the lower electrode layer W2 is effective especially when the wafer WA has an insulating layer between the substrate W1 and the lower electrode layer W2. As shown in FIG. 2, the first electrode 3 is provided apart from the wafer table 2 so as to be in contact with a portion of the piezoelectric thin film W3 in the vicinity of the peripheral edge of the wafer WA which is chemically or mechanically removed. can be made available. In this case, the portion from which the piezoelectric thin film W3 has been removed is normally not used as a piezoelectric device product.

The second electrode 4 is in contact with the piezoelectric thin film W3 from above when measuring the piezoelectric constant d33 of the piezoelectric thin film W3. An electrical lead 4A is connected to the second electrode 4 (or to another point having the same potential as it). The shape of the second electrode 4 is not particularly limited, but in order to stably contact the piezoelectric thin film W3, the lower end surface thereof is preferably flat, particularly preferably in a flat circular shape. In addition, the second electrode 4 has a small area on the lower end surface so that d33 can be measured at a plurality of locations on the wafer WA.

The load means 5 moves the second electrode 4 up and down and applies a load to the piezoelectric thin film W3 via the second electrode 4 . As shown in FIG. 3, when a load is applied to the piezoelectric thin film W3 by the second electrode 4 in a direction in which the piezoelectric thin film W3 is compressed (indicated by a dashed line with an arrow in the figure), the thickness of the piezoelectric thin film W3 is reduced. A compressive stress (indicated by a solid line with an arrow in the drawing) is generated, and a tensile stress (indicated by a broken line with an arrow in the drawing) is generated in the vicinity of the outer circumference of the second electrode 4 . Then, in the piezoelectric thin film W3, an amount of electric charge corresponding to the compressive stress is generated, and an amount of electric charge corresponding to the tensile stress is generated. The amount of charge corresponding to this tensile stress can be processed by the piezoelectric constant measurement control means 8, which will be described in detail later.

The load means 5 can take various specific forms. pulse load is applied. It should be noted that the piezoelectric constant is measured by applying a static load and a plurality of pulse loads, which is the same as that disclosed in Patent Document 2 above.

A pulse load (indicated by line b in the waveform of FIG. 4(a)) is a pulse-like load. A static load (indicated by line a in the waveform of FIG. 4(a)) is a load that is kept constant as a reference when multiple pulse loads are applied to the piezoelectric thin film W3. The static load can be, for example, about 0.01N to 1N when a plurality of pulse loads are applied to the piezoelectric thin film W3, and the pulse load can also be, for example, about 0.01N to 1N. can be done. The static and pulse loads are typically not too stressful so as not to change the piezoelectric properties of the piezoelectric film W3. Also, the pulse load can have a width of, for example, about 0.5 seconds to 1.5 seconds.

In this embodiment, by applying a plurality of pulse loads, as shown in FIG. 4B, a plurality of pulse-like changes in the amount of charge occur. A plurality of pulse loads are, for example, three or more pulse loads. In order to prevent the amount of generated electric charge from being greatly affected by mechanical vibration and electrical noise from the load means 5 and other members, for example, the second electrode 4 is coated with a conductive resin material or the like. The contact with the piezoelectric thin film W3 can be stabilized, and a vibration isolation member, a shield member, or the like can be attached to the load means 5 or the like.

Specifically, the load means 5 can be configured to have a direct-acting motor 51 , a load detector mounting plate 52 and a second electrode mounting plate 53 .

The linear motion motor 51 can linearly move (linearly move) the second electrode 4 via a load detector mounting plate 52 and a load detector 61 which will be described in detail after the load measuring means 6 . The linear motion motor 51 is a motor in which the linear motion portion 51a moves linearly with the support portion 51b as a reference position. not shown). The direct acting portion 51 a is fixed to the load detector mounting plate 52 at its lower end. The direct-acting motor 51 is not particularly limited, but a position control servomotor or the like can be used.

The load detector mounting plate 52 is mounted so that the load detector 61 can detect force from below.

The second electrode mounting plate 53 is mounted so that the end of the second electrode 4 (the end that can contact the piezoelectric thin film W3) faces downward. Specifically, a fixing portion 4a is provided on the upper portion of the second electrode 4, and is fixed to the second electrode mounting plate 53 by screwing or the like. The upper end surface of the fixing portion 4 a is exposed from the second electrode mounting plate 53 . The second electrode mounting plate 53 has load detector mounting plate slide rods 52A, 52A mounted on the upper surface of the peripheral portion, and the load detector holding springs 52B, 52B above the load detector mounting springs 52B, 52B. A detector mounting plate 52 is located. 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 buffered by the load detector holding springs 52B and 52B so that they can relatively move up and down. It has become. Heads 52Aa and 52Aa for determining 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 rods 52A and 52A.

Until the second electrode 4 contacts the piezoelectric thin film W3, the load detector mounting plate 52 and the second electrode mounting plate 53 maintain the maximum distance therebetween so that the load detector 61 is positioned on the second electrode 4 (fixed). It descends without touching the part 4a). After the second electrode 4 comes into contact with the piezoelectric thin film W3, the space between the load detector mounting plate 52 and the second electrode mounting plate 53 shrinks, and the load detector 61 moves toward the second electrode 4 (fixed portion 4a). come into contact (see Figure 1). Then, a load is applied to the piezoelectric thin film W3 via the second electrode 4, and the load can be measured by the load detector 61 of the load measuring means 6. FIG.

The load measuring means 6 measures the load applied to the piezoelectric thin film W3. In this embodiment, the load measuring means 6 measures a static load and a plurality of pulse loads applied to the piezoelectric thin film W3. In the present embodiment, the load measuring means 6 includes a load detector (load cell) 61 for detecting a load, converts an electric signal corresponding to the detected load into digital data, and outputs the data to the piezoelectric constant measurement control means 8. It has a load measurement processor 62 . The load detector 61 is incorporated in the mechanism of the load means 5, and reference numeral 61A in FIG. The load measurement processor 62 can also be integrated with the load detector 61 .

The charge amount measuring means 7 inputs the charge generated in the piezoelectric thin film W3 by applying a load through the first electrode 3 and/or the second electrode 4 and measures the amount of charge. For example, it is possible to measure the amount of charge by inputting the charge generated in the piezoelectric thin film W3 through the second electrode 4 with the first electrode 3 set to the ground potential. In this case, as shown in FIG. 5, the charge amount measuring means 7 includes a charge amplifier configured by connecting a capacitor 72 and a high resistance 73 in parallel between the inverting input terminal and the output terminal of an operational amplifier 71, and an AD converter 74. and Here, the input terminals 7a and 7b of the charge amount measuring means 7 are connected to the non-inverting input terminal and the inverting input terminal of the operational amplifier 71, respectively, and the output terminal of the operational amplifier 71 and the charge amount are connected to the input terminal and the output terminal of the AD converter 74, respectively. An output terminal 7c of the measuring means 7 is connected. An electric wire 3A (ground potential) and an electric wire 4A are connected to the input terminals 7a and 7b, respectively. The charge amount measuring means 7 converts the charge input through the input terminal 7b into a voltage by a charge amplifier using an operational amplifier 71, a capacitor 72, and a high resistance 73, and converts the voltage into digital data by an AD converter 74. Thus, the amount of charge is measured, and the measured value is output from the output terminal 7c. The charge amplifier is not limited to the illustrated one, and various circuits are possible.

5, the connection switch 75 is provided in parallel with the capacitor 72 and the high resistance 73 between the inverting input terminal and the output terminal of the operational amplifier 71, and the opening and closing of the connection switch 75 is controlled by the control terminal 7d. is controlled via When the connection switch 75 is turned on, the potential difference between the non-inverting input terminal and the inverting input terminal of the operational amplifier 71 becomes zero, and therefore the amount of charge generated in the piezoelectric thin film W3 connected thereto becomes zero. The control terminal 7 d can be controlled by the piezoelectric constant measurement control means 8 . By doing so, the amount of charge generated in the piezoelectric thin film W3 can be reduced to zero before a load is applied to the piezoelectric thin film W3.

The piezoelectric constant measurement control means 8 calculates the piezoelectric constant d33 from the amount of charge measured by the charge amount measuring means 7 and the measured load. The charge measured by the charge amount measuring means 7 includes the charge generated in the piezoelectric thin film W3 in response to the compressive stress as described above, as well as the charge generated in the piezoelectric thin film W3 in response to the tensile stress. . The charge generated in the piezoelectric thin film W3 in response to the compressive stress is the charge to be measured for the piezoelectric constant d33. Therefore, it is extremely preferable to calculate the piezoelectric constant d33 by subtracting the amount of charge generated in the piezoelectric thin film W3 according to the tensile stress from the amount of charge measured by the charge amount measuring means 7. FIG. The charge generated in the piezoelectric thin film W3 according to the tensile stress is the charge for which the piezoelectric constant d31 is to be measured.

In this embodiment, for example, among a plurality of pulse-like charge amount variations and a plurality of pulse loads, the variation ΔQ _1u and the pulse load ΔF _1u at the first rise are measured (FIG. 4 (a) and (b)), and the piezoelectric constant _d33-1u is calculated. Similarly, the amount of change ΔQ _1d and pulse load ΔF _1d at the first falling edge, the amount of change ΔQ _2u and pulse load ΔF _2u at the second rising edge, and the amount of change ΔQ at the second falling edge _2d and the pulse load ΔF _2d , the amount of change ΔQ _3u and the pulse load ΔF _3u at the third rise, and the amount of change ΔQ _3d and the pulse load ΔF _3d at the third fall were measured (Fig. 4 (a ), see (b)), and the piezoelectric constants d33 _1d , d33 _2u , d33 _2d , d33 _3u and d33 _3d are calculated. Then, d33 _1u , d33 _1d , d33 _2u , d33 _2d , d33 _3u and d33 _3d are averaged.

Representing each amount of change ΔQ _1u to ΔQ _3d as ΔQ, each pulse load ΔF _1u to ΔF _3d as ΔF, and each piezoelectric constant d33 _1u to d33 _3d as d33, each piezoelectric constant d33 is given by the following equation (1): Calculated.
d33=(ΔQ−ΔQ ^* )/ΔF (1)
Here, ΔQ ^* is the amount of charge generated in the piezoelectric thin film W3 in response to tensile stress. The relationship between the value of ΔQ ^* and the value of ΔQ is, for example, as shown in FIG. . Note that FIG. 6 shows a case where ΔQ ^* is approximately proportional to ΔQ.

Alternatively, d33 of each piezoelectric constant may be calculated by the following formula (1') by modifying (1).
d33=(1−ΔQ ^* /ΔQ)(ΔQ/ΔF)
=A ^* (ΔQ/ΔF) (1')
Here, A ^* will denote the proportion of the amount of charge that depends on the compressive stress.

In addition, each change amount ΔQ _1u to ΔQ _3d is averaged to obtain ΔQ, each pulse load ΔF _1u to ΔF _3d is averaged to obtain ΔF, and using the ΔQ and ΔF, formula (1) or formula (1′) An averaged piezoelectric constant d33 may be calculated.

Thus, the piezoelectric constant d33 can be calculated by subtracting the amount of charge generated in the piezoelectric thin film W3 according to the tensile stress from the amount of charge measured by the charge amount measuring means 7. FIG.

The piezoelectric constant measurement control means 8 is usually realized by a computer (personal computer). For example, as shown in FIG. 7, according to the piezoelectric constant calculation program 81a in the program storage unit 81, the CPU 82 stores the digital data of the load measured by the load measuring means 6 and the charge measured by the charge amount measuring means 7. is inputted from the input terminals 8a and 8b through the input section 83. Then, the piezoelectric constant d33 is calculated by the above-described calculation method using the data storage unit 84 or the like, and is output to the outside from the output terminal 8c via the output unit 85. FIG. Further, the piezoelectric constant measurement control means 8 can control the direct-acting motor 51 of the load means 5 and the like.

The piezoelectric constant measuring device according to the embodiment of the present invention has been described above. Various design changes are possible.

1 Piezoelectric constant measuring device 2 Wafer table 3 First electrode 3A Electric wire of first electrode 4 Second electrode 4a Fixing part of second electrode 4A Electric wire of second electrode 5 Loading means 51 Linear motor 51a Linear motor 51a Moving part 51b Support part of linear motion motor 52 Load detector mounting plate 52A Load detector mounting plate sliding rod 52Aa Head of load detector mounting plate sliding rod 52B Load detector holding spring 53 Second electrode mounting plate 6 Load Measurement Means 61 Load Detector 61A Electric Wire of Load Detector 62 Load Measurement Processor 7 Charge Amount Measurement Means 7a, 7b Input Terminal of Charge Amount Measurement Means 7c Output Terminal of Charge Amount Measurement Means 7d Control Terminal of Charge Amount Measurement Means Operational amplifier of charge amount measuring means 72 Capacitor of charge amount measuring means 73 High resistance of charge amount measuring means 74 AD converter of charge amount measuring means 75 Connection switch of charge amount measuring means 8 Piezoelectric constant measurement control means 8a, 8b Piezoelectric constant measurement control Input terminal of means 8c Output terminal of piezoelectric constant measurement control means 81 Program storage unit of piezoelectric constant measurement control means 81a Piezoelectric constant calculation program of piezoelectric constant measurement control means 82 CPU of piezoelectric constant measurement control means
83 Input section of piezoelectric constant measurement control means 84 Data storage section of piezoelectric constant measurement control means 85 Output section of piezoelectric constant measurement control means WA Wafer W1 Substrate W2 Lower electrode layer W3 Piezoelectric thin film

Claims (3)

A piezoelectric constant measuring device for measuring a piezoelectric constant d33 of a piezoelectric thin film formed on a lower electrode layer on a substrate of a wafer,
a wafer table that supports the substrate;
a first electrode that can be in contact with the back surface of the substrate or near the periphery of the lower electrode layer;
a second electrode that can be in contact with the piezoelectric thin film from above;
load means capable of vertically moving the second electrode and applying a load to the piezoelectric thin film via the second electrode;
load measuring means for measuring the load;
a charge amount measuring means for inputting the charge generated in the piezoelectric thin film by the application of the load through the first electrode and/or the second electrode and measuring the amount of the charge;
piezoelectric constant measurement control means for calculating a piezoelectric constant d33 from the measured amount of charge and the measured load;
A piezoelectric constant measuring device comprising: In the piezoelectric constant measuring device according to claim 1,
The piezoelectric constant measurement control means calculates the piezoelectric constant d33 by subtracting the amount of charge generated in the piezoelectric thin film according to the tensile stress from the measured amount of charge. In the piezoelectric constant measuring device according to claim 1 or 2,
A piezoelectric constant measuring device, wherein the lower end surface of the second electrode is flat and circular.

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