JP2008004678A - Method and device for inspecting ferroelectric material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for easily and precisely inspecting polarization characteristic distribution and a failure of a ferroelectric material in a wafer size. <P>SOLUTION: In the method of inspecting a ferroelectric substance, polarization reversal occurs by first polarization reversal voltage and second polarization reversal voltage whose pole is different from first polarization reversal voltage. The method includes: a first step of applying voltage which has the same pole as first polarization reversal voltage and whose absolute value is not less than that of first polarization reversal voltage to the ferroelectric substance, and polarizing the ferroelectric substance; a second step of applying voltage between voltage which has the same pole as first polarization reversal voltage and is smaller than the absolute value of first polarization reversal voltage, and voltage which has the same pole as second polarization reversal voltage and is smaller than the absolute value of second polarization reversal voltage to the ferroelectric substance; and a third step of applying voltage which has the same pole as second polarization reversal voltage, and whose absolute value is not less than that of second polarization reversal voltage to the ferroelectric substance. A polarization measuring step of heating the ferroelectric substance and measuring the polarization characteristic by pyroelectricity of the ferroelectric substance is performed after the first to third steps. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for inspecting a polarization voltage distribution and a defect of a ferroelectric material, and an inspection apparatus therefor.

  There has been a saw device using a piezoelectric element as a conventional device using a ferroelectric material. In recent years, actuators using piezoelectric elements and semiconductor memory devices (semiconductor ferroelectric memory elements) using ferroelectrics have been developed. In the case of a semiconductor memory device using a ferroelectric material, in manufacturing quality control, it is important to manage the in-plane distribution of the polarization characteristics of the ferroelectric material by the wafer size in order to keep the device characteristics constant. Therefore, it is necessary to measure and inspect the surface distribution of the polarization characteristics of the ferroelectric material simply and accurately in the device manufacturing process.

  Conventionally, there has been a scanning nonlinear permittivity microscopic method for accurately inspecting the polarization state of a minute region of about 20 μm square for measuring the surface distribution of the polarization characteristics of a ferroelectric material. On the other hand, when a ferroelectric material is used for a semiconductor memory device, it is necessary to simply inspect the in-plane distribution of polarization characteristics in a large area such as a substrate size of 5 or 6 inches in diameter. There was no way to measure the in-plane distribution. For this reason, the polarization depends on the electric field, and the electric field depends on the film thickness of the ferroelectric material. Therefore, using the property that the variation in film thickness leads to the variation in polarization characteristics, the ferroelectric material can be obtained using X-rays. It was substituted by inspecting the surface distribution of the film thickness.

  As a method for inspecting the surface distribution of the polarization characteristics of the ferroelectric material, there is a scanning nonlinear permittivity microscopic method, which can inspect a very small area of about 20 μm square, but has a large area of 5 or 6 inches. It is very difficult to examine the surface distribution of the polarization characteristics. On the other hand, the method of estimating the surface distribution of the polarization characteristics from the surface distribution of the film thickness of the ferroelectric material is simple, but there is no guarantee that the properties are constant, so there is a problem in accuracy.

  Further, when a ferroelectric dielectric material is used as a device, the electrode is laminated on the ferroelectric material. In conventional scanning nonlinear permittivity microscopy and film thickness measurement, it has not been possible to inspect electrode defects simultaneously.

  An object of the present invention is to solve the above problems and provide a method for simply and accurately inspecting the polarization characteristic distribution and defects of a ferroelectric material at a wafer size.

  In order to achieve the above object, the present invention provides a second polarization inversion voltage corresponding to a first coercive electric field and a second polarity corresponding to a second coercive electric field and different from the first polarization inversion voltage. And the polarization inversion voltage of the ferroelectric that causes polarization reversal at the same polarity as the first polarization reversal voltage and having an absolute value equal to or greater than the absolute value of the first polarization reversal voltage. A first step of applying the polarization to the ferroelectric to polarize the ferroelectric, a voltage having the same polarity as the first polarization inversion voltage and smaller than an absolute value of the first polarization inversion voltage, and the second A second step of applying to the ferroelectric a voltage having the same polarity as that of the polarization inversion voltage and a voltage smaller than the absolute value of the second polarization inversion voltage, and the same as the second polarization inversion voltage. A third step of applying a voltage having an absolute value equal to or greater than the absolute value of the second polarization inversion voltage to the ferroelectric; Has, heating the ferroelectric, polarization measurement step of measuring the polarization characteristics of the pyroelectric of the ferroelectric, and performing after each step of the first to third steps.

  According to the present invention, the in-plane distribution of polarization characteristics of a ferroelectric material having a large area can be easily and accurately inspected.

  A ferroelectric exhibits polarization without applying an electric field (spontaneous polarization), and the direction of spontaneous polarization can be reversed by an electric field. When the value of the electric flux density (the amount of polarization of the ferroelectric material) proportional to the polarization with respect to the change of the electric field E is measured, it is as shown in FIG. A positive electric field (positive voltage) is applied to the ferroelectric material so as to maximize the amount of polarization, and then the voltage is lowered.

  When the amount of polarization when the voltage is 0 V is Pr, and then the voltage is further lowered (a negative voltage is applied), the amount of polarization becomes 0 at the second coercive electric field −Ec (second polarization inversion voltage). When a negative voltage is further applied beyond the second coercive electric field -Ec, polarization inversion occurs, and the electric field -Emax shows the minimum amount of polarization. Thereafter, when the voltage is increased, the polarization amount -Pr is shown at a voltage of 0 V (electric field is 0). When the voltage is further increased (a positive voltage is applied), the first coercive electric field Ec (first polarization inversion voltage) in which the polarization amount becomes 0 is obtained. When a positive voltage is further applied beyond the first coercive electric field Ec, polarization inversion occurs, and the electric field Emax has the maximum amount of polarization.

  Furthermore, the ferroelectric has the property of pyroelectricity that generates charges in the polarization direction according to the magnitude of polarization when heated and the temperature rises. In the present invention, the in-plane distribution of polarization of a ferroelectric is measured using the pyroelectric property of the ferroelectric. Hereinafter, the measurement principle of the polarization state distribution in the substrate surface will be described with reference to the drawings.

[apparatus]
The inspection apparatus used in the present invention will be described.

  The configuration of the inspection apparatus will be described with reference to FIG. The inspection device includes a polarization voltage application device 23, a polarization measurement device 24, and a temperature control device 25. The sample to be inspected has a laminated structure in which the ferroelectric material 20 is sandwiched between the upper electrode 22 and the lower electrode 21. The polarization voltage application device 23 is a device that applies a voltage between the upper electrode 22 and the lower electrode 21 of the ferroelectric material 20. The polarization measuring device 22 is a device that measures the polarization state of the ferroelectric material 20. The temperature control device 25 is a device that controls the temperature of the ferroelectric material 20 to be constant. By making the temperature of the ferroelectric material 20 constant, the polarization state can be measured with good reproducibility.

  In this example, a Phemos 1000 manufactured by Hamamatsu Photonics Co., Ltd. was used as the polarization measuring device 24. In the Chemos 1000, the polarization state was measured using an OBIRCH (Optical Beam Induced Resistance Change) analysis function that measures current change in synchronization with laser scanning. The configuration of the Chemos 1000 will be described. The Chemos 1000 includes a laser scanning device, an OBIRCH amplifier that is a current amplifier, and a display device that displays a laser scanning position and a current value in synchronization.

[Principle of measurement of polarization state]
Ferroelectrics have the property of pyroelectricity that generates charges in the polarization direction according to the temperature rise and the magnitude of polarization when heated. Therefore, as shown in FIG. 3, when the region 32 polarized in the polarization direction 36 of the ferroelectric 30 is locally heated, a charge Q is generated on the surface 33 in the region 32. When the surface 33 and the surface 37 are electrically connected, a pyroelectric current 34 flows. On the other hand, when the region 35 polarized in the polarization direction 36 is locally heated, the charge Q is generated on the surface 37 and the pyroelectric current 38 flows. That is, since the polarization directions of the region 32 and the region 35 are opposite, the pyroelectric current also flows in the opposite direction. In this embodiment, the charge Q is detected as a pyroelectric current, but it may be detected as a voltage change.

  Therefore, even if the polarization directions of the regions 32 and 35 are unknown, the polarization states of the regions 32 and 35 can be determined by measuring the directions and magnitudes of the pyroelectric current 34 and the pyroelectric current 38 generated by local heating. Can be measured. Similarly, the surface distribution of the polarization state of the wafer can be measured by sequentially repeating local heating and pyroelectric current measurement within the wafer surface.

  From this principle, the measurement of the polarization state can be applied to pyroelectric materials including ferroelectrics among dielectric materials. There are other materials that exhibit pyroelectricity besides ferroelectricity, but crystals that exhibit ferroelectricity always exhibit pyroelectricity. For example, applicable materials are quartz, lithium niobate, potassium niobate, lithium tantalate, langasite, barium titanate, lead titanate, lead metaniobate, polyvinylidene fluoride, zinc oxide, lead zirconate titanate (PZT). ), Lead magnesium niobate-PZT, lead nickel niobate-PZT, lead magnesium niobate-PT, lead nickel niobate-PT, oxide of strontium / bismuth / tantalum, barium strontium titanate, and the like. In this example, PZT, which is a ferroelectric material, was used. As a method of moving the portion to be locally heated, there are a method of scanning a laser, a method of using electromagnetic induction, a method of scanning condensed light, a method of scanning an ion beam, and a method of scanning an electron beam. In this embodiment, a method of scanning a laser with a Chemos 1000 was used. Since laser scanning can be performed from a wide region to a narrow region, the polarization state of a wide region such as a wafer size can be measured.

[sample]
The structure of the inspected ferroelectric sample 40 is shown in FIG. A lower electrode 42 made of Pt (film thickness of 300 nm) / Ti (film thickness of 30 nm), a ferroelectric material 43 of PZT (film thickness of 3 μm), and a Pt ( In this structure, the upper electrode 44 made of (film thickness 300 nm) / Ti (film thickness 30 nm) is laminated. Such a laminated structure is a structure widely used for ferroelectric devices such as ferroelectric memories and ferroelectric piezoelectric elements. Therefore, it can be applied to a general inspection process of a ferroelectric device. The upper electrode 44 and the lower electrode 42 may be formed on the entire surface of the ferroelectric material 43 or may be patterned. When a voltage is applied to the upper electrode 44 and the lower electrode 42, the polarization direction of the ferroelectric material 43 can be made uniform. When a certain voltage is applied, the polarization direction of the ferroelectric material 43 can be reversed. The voltage at this time is called a polarization inversion voltage. As viewed from the lower electrode, when a positive polarization inversion voltage (first polarization inversion voltage) is applied to the upper electrode, polarization is caused in the polarization direction 45, and when a negative polarization inversion voltage (second polarization inversion voltage) is applied, the polarization direction is applied. 46 is polarized.

[Measurement method of polarization state]
This will be described with reference to FIG. First, the connection and arrangement of the polarization measuring device and the ferroelectric sample will be described. The upper electrode 44 and the lower electrode 42 were connected to the OBIRCH amplifier 53. The ferroelectric sample was placed on the sample stage so that the laser 51 was irradiated from the upper electrode 44 direction. If an infrared laser such as a YLF laser is used, it passes through the Si substrate 41 and may be installed so that the infrared laser is irradiated from the direction of the lower electrode 42. In this case, the polarization state can be measured with respect to the sample in which the upper electrode 44 cannot be irradiated with the laser.

  Next, the operation of the polarization measuring device will be described. The laser 51 scans the ferroelectric sample with the laser scanning device, and simultaneously, the OBIRCH amplifier 53 measures the pyroelectric current 52 generated in the ferroelectric sample by local heating of the laser. Next, the scanning position 54 of the laser 51 and the change of the pyroelectric current 52 are imaged in synchronization and displayed on the display device. This image is called a pyroelectric current image 55. An image is formed by associating a negative pyroelectric current with black and a positive pyroelectric current with white. In this embodiment, the image is formed with black and white contrast. However, the image may be formed with color for each pyroelectric current value. In addition, it is possible to display such as storing the irradiation position of the laser beam and the pyroelectric current value and drawing a contour line of the current value.

  Finally, the measurement conditions of a common polarization measuring device will be described in the following examples. The laser used was a YLF laser. The spot diameter was about 1.3 μm. The scan speed value was set to 1 second. The higher the scan speed, the better the SN ratio. Therefore, it was set to the fastest setting that can be set by the polarization measuring device. This is because the pyroelectric reaction time is very short. For example, it has been reported to have a reaction time of 2 μs or less. It is desirable to scan at a speed close to the pyroelectric reaction speed.

  After scanning the entire irradiation region with the laser about 5 times, pyroelectric current was detected. This has the effect that the pyroelectric current can be measured with good reproducibility by making the temperature of the ferroelectric sample surface uniform. Since the temperature of the ferroelectric sample is controlled to be constant by the temperature control device, reproducibility can be improved. The laser intensity was 150 mW. By setting the power to 150 mW, it was possible to obtain a pyroelectric current large enough for measurement. If the laser intensity is excessively increased, the ferroelectric material is damaged. Therefore, it is desirable to set the laser intensity to a minimum level at which the pyroelectric current is large enough to be measured by a current amplifier. Setting the applied voltage during laser scanning to 0 [V] makes it easy to detect the pyroelectric current with an OBIRCH amplifier, and has an effect of acquiring a pyroelectric current image with a good S / N ratio regardless of the polarization state. This is because, as indicated by the pyroelectric current 34 and the pyroelectric current 38 in FIG. 3, the direction in which the pyroelectric current flows is reversed depending on the polarization state, and thus there is no voltage that intensifies either pyroelectric current. . Of course, if the polarization state is known, if a voltage whose absolute value is equal to or less than the polarization inversion voltage is applied in a direction in which the pyroelectric current easily flows, the pyroelectric current can be increased and a pyroelectric current image can be acquired with a high SN ratio. Further, since the applied voltage is 0 [V], there is an effect that a pyroelectric current image can be acquired without affecting the polarization state of the ferroelectric sample.

  In the above example, an example in which a ferroelectric material having upper and lower electrodes is pinpointly heated with a laser is shown. However, for example, the ferroelectric material is entirely heated and partially focused by a pair of electrodes. It can also be applied to a method for measuring electric current.

  Examples of the inspection of the polarization characteristic distribution of the ferroelectric according to the present invention, peeling of electrodes, leakage between electrodes, foreign matter, and polarization lowering are shown below. The voltage having the same polarity as the polarization inversion voltage means a voltage of + when the polarization inversion voltage is +, and a voltage of-when the polarization inversion voltage is −. Further, the polarization inversion voltage and the voltage of a different polarity mean-when the polarization inversion voltage is +, and + when-.

(First embodiment)
The inspection of the polarization characteristic distribution using the present invention will be described.

  The inspection process of the polarization characteristic distribution will be described with reference to FIG. 1, FIG. 6, and FIG. FIG. 1 is a process flow chart of polarization distribution inspection. FIG. 6 shows the time change of the voltage applied to the ferroelectric material by the polarization voltage application device in the polarization treatment step 2 and the polarization inversion step 3 in FIG. FIG. 7 shows the result of polarization measurement. An optical reflection image from the upper electrode direction of the measured sample is shown in FIG.

  The inspection process of the polarization characteristic distribution will be described according to the steps of the flowchart of FIG.

  First, in the pretreatment step 1, the polarization inversion voltage of the ferroelectric sample is measured. The relationship between the polarization amount of the ferroelectric and the electric field as shown in FIG. 8 was obtained using a ferroelectric property measuring apparatus, and the polarization inversion voltage was measured (step 5). As a result, it was found that the polarization was inverted in the direction of the lower electrode around 20 [V] with respect to the upper electrode, and the polarization was inverted in the direction of the upper electrode near −9 [V]. Therefore, in this case, the first polarization inversion voltage is 20 [V], and the second polarization inversion voltage is −9 [V].

  Second, in the polarization treatment step 2, the polarization direction of the ferroelectric sample is aligned. First, as shown in FIG. 6, 25 [V], which is a voltage equal to or higher than the first polarization inversion voltage, was applied to the upper electrode, and the polarization process was performed so that the polarization direction was uniform at the lower electrode (step). 6). It is desirable that the voltage applied in the polarization process has a sufficiently larger absolute value than the first polarization inversion voltage. By performing the polarization process, the pyroelectric current increases, and there is an effect of improving the SN ratio of the pyroelectric current image. Thereafter, the polarization state was measured with a polarization measuring device (step 7). As a result, a uniform pyroelectric current image as shown in FIG. 7B was obtained, and it was confirmed that it was uniformly polarized (step 8).

  Third, in the polarization reversal step 3, a voltage is gradually applied in the direction opposite to the voltage applied in the polarization treatment step 2, the polarization state during the polarization reversal is measured, and unevenness of the polarization reversal voltage is detected. . First, as shown in FIG. 6, polarization inversion was performed by applying −7.5 [V] to the upper electrode whose absolute value is smaller than the second polarization inversion voltage (step 9). After polarization reversal, the polarization state was measured with a polarization measuring device, and a pyroelectric current image as shown in FIG. 7C was obtained (step 10). In FIG.7 (c), the area | region A and the area | region B where the positive / negative of a pyroelectric current are reversed exist.

  This is because the region A and the region B have different polarization inversion voltages, so that the region A has already undergone polarization inversion, while the region B has not yet undergone polarization inversion. This uneven polarization inversion voltage appears as an uneven pyroelectric current image.

  Since there is a region where the polarization inversion is not present in the pyroelectric current image (step 11), the absolute value of the applied voltage is increased by 0.5 [V] steps (step 12), and as shown in FIG. And the polarization state was measured (step 9), and then the polarization state was measured (step 10). When a voltage of −10 [V], which is a voltage whose absolute value is larger than the second polarization reversal voltage, is applied, the polarization state is measured with a polarization measuring device, and as shown in FIG. A pyroelectric current image was acquired (step 10). Since it was confirmed that the pyroelectric current image was uniformly reversed in polarization, the polarization inversion step 3 was completed (step 11). In this manner, by sequentially applying a voltage smaller than the polarization inversion voltage measured in the pretreatment and detecting a region where the polarization is partially inverted, partial polarization such as regions A and B in FIG. It is possible to detect inversion voltage unevenness. By making this increase in voltage fine in the vicinity of the polarization inversion voltage, a more detailed inspection can be performed.

  Fourth, in the inspection process 4, the acquired pyroelectric current image was inspected. FIG. 7C shows that the negative inversion voltage in the region A is −7.5 [V] or more. On the other hand, it can be seen from FIG. 7D that the negative inversion voltage in the region B is smaller than −7.5 [V] and equal to or higher than −10 [V]. Therefore, it was found that the inversion voltage is not uniform in the ferroelectric sample.

  When the positive and negative of the applied voltage are all reversed and the first to fourth steps are performed in the same manner, the positive inversion voltage in the region A is larger than 20 [V]. Thus, it was found that the positive inversion voltage in the region B was 25 [V] or less and 20 [V] or less. From the above, it can be seen that in the region B as compared with the region A, the inversion voltage is shifted in the negative direction. As a result of investigating the manufacturing process of the ferroelectric film, it was found that in the region B, the inversion voltage was shifted in the negative direction due to the damage of the ferroelectric material by the X-ray irradiation.

  Such unevenness of the polarization inversion voltage greatly affects the characteristics of the device. Since there is no difference in film thickness between the region A and the region B, such unevenness in polarization characteristics cannot be found by the conventional method of measuring the film thickness. On the other hand, in the present invention, even if the film thickness is uneven, the polarization inversion voltage changes in the uneven area, so that it can still be detected as a pyroelectric current image unevenness as in the conventional case. As described above, defects in the polarization characteristic distribution can be detected.

(Second Embodiment)
The present invention can also be applied to inspection of peeling between a ferroelectric material and upper and lower electrodes.

  The electrode peeling inspection process will be described with reference to FIG. First, the polarization inversion voltage is acquired in the preprocessing step 1 (step 5). Secondly, in the polarization process step 2, a voltage equal to or higher than the polarization inversion voltage is applied to the ferroelectric sample to perform the polarization process (step 6). At this time, it is desirable that the applied voltage is sufficiently larger than the polarization inversion voltage. By performing the polarization process, the pyroelectric current increases, and there is an effect of improving the SN ratio of the pyroelectric current image. After the polarization process, the polarization state is measured and a pyroelectric current image is acquired (step 7). Next, this pyroelectric current image is inspected (step 8).

  Details of the inspection of the pyroelectric current image will be described. If the electrode is peeled off, the electrical connection between the upper and lower electrodes becomes poor at the peeled portion, so that the pyroelectric current value changes. Therefore, in the pyroelectric current image, a region where the pyroelectric current value is changed can be detected as a defect in the peeled portion.

  Even if the area of the peeled portion is as small as about 500 × 500 nm, a pyroelectric current image can be easily measured due to the difference in luminance.

(Third embodiment)
The present invention can also be applied to inspection of leakage of upper and lower electrodes of a ferroelectric sample.

  An inspection process for leaks in the upper and lower electrodes will be described with reference to FIG. First, the polarization inversion voltage is acquired in the preprocessing step 1 (step 5). Secondly, in the polarization process step 2, a voltage equal to or higher than the polarization inversion voltage is applied to the ferroelectric sample to perform the polarization process (step 6). At this time, it is desirable that the applied voltage is sufficiently larger than the polarization inversion voltage. By performing the polarization process, the pyroelectric current increases, and there is an effect of improving the SN ratio of the pyroelectric current image. After the polarization process, the polarization state is measured and a pyroelectric current image is acquired (step 7). Next, this pyroelectric current image is inspected (step 8).

  Details of the inspection of the pyroelectric current image will be described. Since the electrical connection between the upper and lower electrodes is improved at the leak location, the pyroelectric current value changes. Therefore, in the pyroelectric current image, a region where the pyroelectric current value changes can be detected as a defect at the leak location. Even in the case of a leak, a leak of a very small area can be detected by using a pyroelectric current image in the same manner as the above-described electrode peeling.

(Fourth embodiment)
The present invention can also be applied to inspection of foreign matter in a ferroelectric sample.

  The foreign substance inspection process will be described with reference to FIG. First, the polarization inversion voltage is acquired in the preprocessing step 1 (step 5). Secondly, in the polarization process step 2, a voltage equal to or higher than the polarization inversion voltage is applied to the ferroelectric sample to perform the polarization process (step 6). At this time, it is desirable that the applied voltage is sufficiently larger than the polarization inversion voltage. By performing the polarization process, the pyroelectric current increases, and there is an effect of improving the SN ratio of the pyroelectric current image. After the polarization process, the polarization state is measured and a pyroelectric current image is acquired (step 7). Next, this pyroelectric current image is inspected (step 8).

  Details of the inspection of the pyroelectric current image will be described. Since the foreign matter has a thermal conductivity different from that of the ferroelectric sample, when the local heating is performed, the heating state is different from the ferroelectric sample and the foreign matter. Therefore, the pyroelectric current value changes in a region where there is a foreign object. Therefore, in the pyroelectric current image, a portion where the pyroelectric current value is changed can be detected as a defect in the foreign material portion. Even in the case of a foreign substance, a foreign substance having a very small area can be detected by using a pyroelectric current image in the same manner as the above-described electrode peeling.

(Fifth embodiment)
The present invention can also be applied to inspection of a portion where the polarization of a ferroelectric sample is lowered.
The inspection process for the portion where the polarization is reduced will be described with reference to FIG. First, the polarization inversion voltage is acquired in the preprocessing step 1 (step 5). Secondly, in the polarization process step 2, a voltage equal to or higher than the polarization inversion voltage is applied to the ferroelectric sample to perform the polarization process (step 6). At this time, it is desirable that the applied voltage is sufficiently larger than the polarization inversion voltage. By performing the polarization process, the pyroelectric current increases, and there is an effect of improving the SN ratio of the pyroelectric current image. After the polarization process, the polarization state is measured and a pyroelectric current image is acquired (step 7). Next, this pyroelectric current image is inspected (step 8).

  Details of the inspection of the pyroelectric current image will be described. When the polarization of the ferroelectric sample decreases, the pyroelectric current value also decreases. Therefore, in the pyroelectric current image, a region where the pyroelectric current value is changed can be detected as a defect at a location where the polarization is reduced. Even in the case of a decrease in polarization, a decrease in polarization in a small area can be detected by using a pyroelectric current image in the same manner as the above-described electrode peeling.

(Sixth embodiment)
The present invention can simultaneously carry out the inspection of the polarization characteristic distribution, the electrode separation, the leakage between the electrodes, the foreign matter, a part of the decrease in polarization, and all of the first to fifth embodiments. .

  When a part or all of the pyroelectric current image acquired in the inspection process flow of FIG. 1 is uneven, it can be seen that any of the defects shown in Examples 1 to 5 are present in the ferroelectric sample. On the other hand, if there is no unevenness in all pyroelectric current images, it can be seen that there is no defect in the ferroelectric sample. In this case, image processing may be performed to make unevenness stand out. By doing so, it is possible to easily determine the defect. In addition, it is possible to collectively determine unevenness by superimposing the respective pyroelectric current images and inspecting the superimposed pyroelectric current images. For example, it is conceivable to add or multiply the pyroelectric current images. In this way, the defect can be determined at high speed.

It is a flowchart of the inspection process of this embodiment. It is an inspection apparatus of this embodiment. It is a figure which shows the principle of the measurement of the polarization state of this embodiment. It is a figure which shows the ferroelectric sample test | inspected by this embodiment. It is a figure which shows the structure of the polarization measuring apparatus of this embodiment. It is a figure which shows the time change of the applied voltage of the polarization voltage application apparatus of this embodiment. It is a result of the measurement of the polarization state of this embodiment. It is the figure which showed the polarization characteristic of the ferroelectric substance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 Ferroelectric material 21 Lower electrode 22 Upper electrode 23 Polarization voltage application apparatus 24 Polarization measuring apparatus 25 Temperature control apparatus 30 Ferroelectric substance 31, 36 Polarization direction 32, 35 Polarized area 33, 37 Surface 34, 38 Pyroelectric Current 41 Single crystal Si substrate 42 Lower electrode 43 Ferroelectric material 44 Upper electrode 51 Laser 52 Pyroelectric current 53 OBIRC amplifier

Claims (8)

Ferroelectricity in which polarization reversal occurs between a first polarization reversal voltage corresponding to a first coercive electric field and a second polarization reversal voltage corresponding to a second coercive electric field and having a different polarity from the first polarization reversal voltage A body inspection method,
Applying a voltage having the same polarity as the first polarization inversion voltage and having an absolute value equal to or greater than the absolute value of the first polarization inversion voltage to the ferroelectric to polarize the ferroelectric;
A voltage having the same polarity as the first polarization inversion voltage and smaller than the absolute value of the first polarization inversion voltage, and a voltage having the same polarity as the second polarization inversion voltage and less than the absolute value of the second polarization inversion voltage A second step of applying a voltage between and to the ferroelectric;
A third step of applying a voltage having the same polarity as the second polarization reversal voltage and an absolute value equal to or greater than the absolute value of the second polarization reversal voltage to the ferroelectric;
The ferroelectric inspection, wherein a polarization measurement step of heating the ferroelectric and measuring a polarization characteristic due to pyroelectric property of the ferroelectric is performed after each of the first to third steps. Method.   The ferroelectric inspection method according to claim 1, wherein the second step is performed a plurality of times by changing a voltage to be applied.   3. The ferroelectric of claim 1, wherein the application of a voltage to the ferroelectric and the measurement of the polarization property are performed via a pair of electrodes provided on the ferroelectric. Inspection method.   4. The ferroelectric inspection method according to claim 1, wherein no voltage is applied to the ferroelectric in the polarization measurement step. 5.   5. The ferroelectric inspection method according to claim 1, wherein the ferroelectric is heated using a laser. Measurement of the polarization characteristics
6. The ferroelectric inspection method according to claim 1, wherein a polarization inversion voltage is measured from a pyroelectric current of the ferroelectric.   The ferroelectric inspection method according to claim 6, wherein a defect of the electrode and a film thickness of the ferroelectric are inspected from the pyroelectric current. A ferroelectric inspection apparatus in which electrodes are formed on opposite surfaces,
Control means for controlling the temperature of the ferroelectric;
Means for applying a voltage to the electrode of the ferroelectric;
Means for detecting a current connected to the electrode of the ferroelectric;
A laser light source for irradiating the surface of the ferroelectric with laser light; and
Scanning means for scanning the laser light source and scanning the ferroelectric surface with laser light;
Display means for displaying the current value detected by the detection means,
The means for detecting the current detects a pyroelectric current generated from the ferroelectric in a region heated by the laser beam,
The ferroelectric inspection apparatus characterized in that the display means displays a pyroelectric current image that is imaged by synchronizing the pyroelectric current with a position scanned by the scanning means.

Images