JP2018018889A - Electric characteristic evaluation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric characteristic evaluation device capable of evaluating the electric characteristic of a ferroelectric or a pyroelectric before formation of upper electrode, without touching the ferroelectric or pyroelectric.SOLUTION: An electric characteristic evaluation device for evaluating the electric characteristic of a ferroelectric or pyroelectric (thin film material 13) formed on a substrate 11, has temperature variable means (23) for varying the temperature of the substrate 11 to vary the temperature of the thin film material 13, temperature measurement means (22) for measuring the temperature of the thin film material 13 in non-contact, and surface potential measurement means (21) for measuring the surface potential of the thin film material 13 in non-contact. The electric characteristic evaluation device varies the temperature of the thin film material 13, and evaluates the electric characteristic of the thin film material 13, from temperature variation of the thin film material 13 and variation of the surface potential.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electrical property evaluation apparatus.

  Conventionally, devices using unique physical properties (piezoelectricity, ferroelectricity, pyroelectricity, photovoltaic power, nonlinear optical effect) possessed by ferroelectrics and pyroelectrics have been actively researched and developed. A method for evaluating the electrical properties of a ferroelectric or pyroelectric material (sometimes called a thin film material) generally forms a capacitor structure in which a thin film material is sandwiched between upper and lower electrodes, and is used for electrical, mechanical, thermal, and optical This is done by signal input and output.

  However, in the conventional evaluation methods, it is necessary to form a capacitor structure in which a thin film material is sandwiched between upper and lower electrodes. Therefore, the evaluation results include the physical properties of the electrode material and the influence of the electrode formation process. There has been a problem that the electrical characteristics of the pyroelectric thin film immediately after deposition cannot be evaluated.

  Also, when evaluating with a capacitor structure sandwiched between upper and lower electrodes, it takes man-hours to form a structure sandwiched between upper and lower electrodes, or when outsourcing a ferroelectric or pyroelectric thin film, On the other hand, there is a problem that non-contact and non-invasive acceptance inspection cannot be performed (in contrast, the pre-shipment inspection cannot be performed on the supply side).

  For example, Patent Document 1 is disclosed as an element evaluation method. Patent Document 1 relates to an element evaluation method, and allows the polarization distribution of a ferroelectric thin film itself to be easily obtained even during the manufacturing process of an element such as a ferroelectric capacitor. Proposals have been made for the purpose of making these determinations and enabling the results to be fed back to the manufacturing process. As its contents, an atomic force microscope equipped with a conductive cantilever is used to measure the nonlinear dielectric constant of the surface of the ferroelectric thin film to obtain the polarization distribution state of the surface, and this polarization distribution state is determined according to a predetermined standard. In comparison, the quality of the ferroelectric thin film is judged.

However, although Patent Document 1 aims to evaluate the physical properties of the thin film material during the manufacturing process of the element, the problem that the thin film material is damaged by the contact of the probe of the atomic force microscope with the thin film material has been solved. Absent. Further, the scanning speed and scanning range of the atomic force microscope are not appropriate as a wafer inspection method.
Therefore, there is a demand for a technique capable of evaluating physical properties without using a capacitor structure and without touching a thin film material.

  An object of the present invention is to provide an electrical property evaluation apparatus that can evaluate electrical properties of a ferroelectric or pyroelectric material before forming an upper electrode without touching the ferroelectric or pyroelectric material.

  In order to solve the above problems, the present invention provides an electrical property evaluation apparatus for evaluating electrical properties of a ferroelectric material or pyroelectric material formed on a substrate, wherein the ferroelectric material is made variable by changing the temperature of the substrate. Temperature varying means for varying the temperature of the body or pyroelectric material, temperature measuring means for measuring the temperature of the ferroelectric or pyroelectric material in a non-contact manner, and the surface potential of the ferroelectric or pyroelectric material in a non-contact manner A surface potential measuring means for measuring the ferroelectric or pyroelectric material, and varying the temperature of the ferroelectric or pyroelectric material and the amount of change in the surface potential from the amount of change in the surface potential. The electrical characteristics of the dielectric or pyroelectric material are evaluated.

  ADVANTAGE OF THE INVENTION According to this invention, the electrical property evaluation apparatus which can evaluate the electrical property of the ferroelectric or pyroelectric body before upper electrode formation without touching a ferroelectric or pyroelectric material can be provided.

It is a schematic diagram for demonstrating an example of the electrical property evaluation apparatus which concerns on this invention. It is a schematic diagram for demonstrating the other example of the electrical property evaluation apparatus which concerns on this invention. Graphs (a) to (c) showing changes in surface potential when the temperature of the PVDF sheet (a), PZT ceramics (b), and PZT thin film (c) is changed, and the polarization state due to the pyroelectric effect are schematically shown. It is figure (d) to explain. It is a figure which shows the change of the surface potential normalized by the thickness when PZT ceramics and a PZT thin film are temperature-changed. It is a figure which shows a temperature change when a 2.0, 6.5, 10, 20 W / mm < ² > laser is irradiated from the back surface with respect to a PZT thin film. It is a figure which shows the relationship between the laser energy density in FIG. 5, and temperature. The figure (a) which showed the relationship between the temperature change amount required in order to obtain the pyroelectric response of + 1V, and the thickness of a measurement sample, and the energy density required in order to obtain the pyroelectric response of + 1V, and the thickness of a measurement sample It is the figure (b) which showed the relationship. Diagram showing changes in temperature and surface potential when the ON / OFF the laser irradiation of 20W / mm ² with respect to small sample pyrochlore phase (a) and the laser irradiation of 20W / mm ² with respect to many samples pyrochlore phase It is a figure (b) which shows change of temperature and surface potential when turning on / off. It is the STEM-HAADF image (a) obtained about the cross section of the PZT thin film containing a pyrochlore phase, and its schematic diagram (b). It is a schematic diagram for demonstrating the other example of the electrical property evaluation apparatus which concerns on this invention. It is a schematic diagram for demonstrating the other example of the electrical property evaluation apparatus which concerns on this invention. It is a schematic diagram for demonstrating the other example of the electrical property evaluation apparatus which concerns on this invention. It is a schematic diagram for demonstrating the other example of the electrical property evaluation apparatus which concerns on this invention.

  Hereinafter, an electrical property evaluation apparatus according to the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and other embodiments, additions, modifications, deletions, and the like can be changed within a range that can be conceived by those skilled in the art, and any aspect is possible. As long as the functions and effects of the present invention are exhibited, the scope of the present invention is included.

  The present invention relates to an electrical property evaluation apparatus for evaluating electrical properties of a ferroelectric or pyroelectric material formed on a substrate, wherein the temperature of the ferroelectric or pyroelectric material is varied by varying the temperature of the substrate. Variable temperature means, variable temperature measuring means for measuring the temperature of the ferroelectric or pyroelectric material in a non-contact manner, and surface potential measuring means for measuring the surface potential of the ferroelectric or pyroelectric material in a non-contact manner; The temperature of the ferroelectric material or pyroelectric material is varied, and the temperature of the ferroelectric material or pyroelectric material and the amount of change in the surface potential are used to determine the electrical properties of the ferroelectric material or pyroelectric material. It is characterized by evaluating characteristics.

The present invention also relates to an electrical property evaluation method for evaluating electrical properties of a ferroelectric or pyroelectric material formed on a substrate, wherein the temperature of the substrate is changed to change the temperature of the ferroelectric or pyroelectric material. A temperature variable step for varying the temperature, a temperature measurement step for measuring the temperature of the ferroelectric or pyroelectric material in a non-contact manner, and a surface potential measurement for measuring the surface potential of the ferroelectric or pyroelectric material in a non-contact manner. A step of varying the temperature of the ferroelectric or pyroelectric material from the amount of change in temperature of the ferroelectric or pyroelectric material and the amount of change in the surface potential. It is characterized by evaluating the electrical characteristics of.
Details will be described below.

(First embodiment)
The electrical property evaluation apparatus of this embodiment is shown in FIG. FIG. 1 is a schematic diagram for explaining the electrical property evaluation apparatus of the present embodiment.
In FIG. 1, a substrate 11, a lower electrode 12, a thin film material 13 (ferroelectric material or pyroelectric material) are illustrated, a surface potential meter 21 (surface potential measuring means), a heating light source 23 (temperature variable means), A radiation thermometer 22 (temperature measuring means) is shown. The substrate 11 of this embodiment is a Si wafer. Moreover, although the electrical property evaluation apparatus of this embodiment is installed in the shield box 20, the present invention is not limited to this.
Hereinafter, the ferroelectric or pyroelectric material may be referred to as the thin film material 13 or the sample.

  In this embodiment, the evaluation target of the electrical characteristics is that the lower electrode 12 and the thin film material 13 are formed on the substrate 11 (Si wafer), and the upper electrode is not formed on the thin film material 13. In this embodiment, since the electrical characteristics immediately after the thin film material 13 is formed can be evaluated at the stage before the upper electrode is formed, the evaluation result can be reflected in the manufacturing process, and the yield of the final device is improved. Can be made. In addition, when the production of the thin film material is outsourced, it is possible to make a pass / fail determination at the time of the acceptance inspection of the outsourced thin film material, so that the yield of the final device can be improved and the risk of delivering defective products can be reduced.

The heating light source 23 can apply uniform light energy to the irradiation position by top-hat condensing. In this embodiment, the ferroelectric or pyroelectric material is heated by irradiating a laser from the back surface (substrate 11 side) and absorbing light energy by Si of the substrate 11. By making the heating source light, heating can be performed without contacting the ferroelectric or pyroelectric material. Since it is non-contact, the influence of the heat capacity of the heating source on the rate at which the temperature of the sample changes is suppressed. Further, since the light irradiation spot becomes a heated portion, the spatial resolution can be increased by reducing the irradiation spot in the measurement of the in-wafer distribution of the pyroelectric response.
In addition, since light has no heat capacity, it is possible to quickly heat and cool the sample by turning on and off the light irradiation, and the stability of the polarization of the sample from the difference between the surface potential during heating and the surface potential during cooling The advantage that can be evaluated is also obtained.

  As described above, the heating light source 23 varies the temperature of the ferroelectric material or pyroelectric material by varying the temperature of the substrate 11. Since the light from the light irradiation means of this embodiment is absorbed by the Si wafer, the wavelength is preferably 900 nm or less. In the case of a MEMS (Micro Electro Mechanical Systems) device, a Si wafer is often used, but the optical characteristics of the Si wafer are known and stable. On the other hand, the ferroelectric material, pyroelectric material, and lower electrode have different optical characteristics depending on the material and form. Therefore, it is necessary to absorb light in the Si wafer in order to heat the sample with different material and form in the same way. There is. If the wavelength of the light is 900 nm or less, the Si wafer can absorb the light, and the temperature of the ferroelectric / pyroelectric body can be varied through the Si wafer.

  The temperature of the sample is measured using a radiation thermometer 22. The radiation thermometer 22 measures the temperature by measuring infrared rays emitted from a location that is a target of temperature measurement. In FIG. 1 of the present embodiment, the temperature of the substrate 11 is measured by the radiation thermometer 22, but the thin film material 13 is thinner than the substrate 11, and the substrate 11 and the thin film material 13 have the same temperature. Measuring the temperature means measuring the temperature of the thin film material 13.

  When performing temperature measurement using a radiation thermometer, since the emissivity of the thin film material 13 is unknown, accurate temperature measurement is difficult, but the emissivity of the Si substrate is known (depending on the surface morphology). The accuracy of temperature measurement can be made relatively high. Note that the temperature of the thin film material 13 instead of the substrate 11 may be measured.

  The potential generated by the pyroelectric effect is measured using a surface electrometer 21. As shown in the figure, the surface potential meter 21 and the radiation thermometer 22 are not in contact with the thin film material 13, and the electric characteristics of the ferroelectric or pyroelectric body before the formation of the upper electrode are changed to the ferroelectric or pyroelectric body. Can be evaluated without touching

Details of the electrical property evaluation apparatus according to the present embodiment are shown below.
Surface potential meter 21: made by TREK, model 323, manufacturer demo machine Radiation thermometer 22: made by MICRO-EPSILON, CT-SF22-C3, without measuring instrument heating source 23: made by Hamamatsu Photonics, L12333-411, wavelength 940nm, maximum output 40W, spot diameter 1.6mmΦ, manufacturer demonstration machine

Next, details of the evaluation of electrical characteristics in the present embodiment will be described. In this embodiment, the pyroelectric effect (temperature dependence of the amount of spontaneous polarization) is used. When the temperature of a ferroelectric or pyroelectric material is changed, the amount of polarization changes and the surface potential changes accordingly. Is used. The amount of change in surface potential (ΔV) is expressed by the following formula (1).
The following formula (1) is based on MJ Johnson, J. Linczer, and DB Go, Plasma Sources Sci. Technol. 23, 065018 (2014).

    ΔV = dpΔT / ε (1)

  In formula (1), d, p, T, and ε are the thickness, pyroelectric coefficient, temperature, and dielectric constant of the sample (thin film material 13), respectively. By using the above formula (1), the electrical characteristics such as pyroelectric coefficient and dielectric constant of the sample can be obtained.

As the ferroelectric or pyroelectric material to be evaluated, for example, PVDF sheet (Poly Vinylidene Fluoride sheet), barium titanate (BaTiO ₃ ), lead titanate (PbTiO ₃ ), lead zirconate titanate (zirconate- Lead titanate, PZT), potassium niobate (KNbO ₃ ), lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), zinc oxide (ZnO), aluminum nitride (AlN), Ba ₂ NaNb ₅ O ₅ , Sodium potassium niobate ((K, Na) NbO ₃ ), bismuth ferrite (BiFeO ₃ ), sodium niobate (NaNbO ₃ ), bismuth titanate (Bi ₄ Ti ₃ O ₁₂ ), bismuth sodium titanate (Na _0.5 Bi _0.5 TiO ₃ ) and the like.

  According to the electrical property evaluation apparatus of the present embodiment, the temperature change of the thin film material can be caused without touching the thin film material by heating from the Si substrate side with a hot plate, light or the like. The generated potential can be measured in a non-contact manner with the thin film material using a surface potentiometer. Thus, since it is possible to measure without the measurement member coming into contact with the surface of the thin film material, it is possible to suppress the thin film material from being damaged by the measurement device member coming into contact with the thin film material.

(Second Embodiment)
Next, another embodiment of the electrical property evaluation apparatus according to the present invention will be described. A description of the same components as those in the above embodiment may be omitted. The electrical property evaluation apparatus of this embodiment is shown in FIG. FIG. 2 is a diagram for schematically explaining the electrical property evaluation apparatus of the present embodiment.

  In the electrical property evaluation apparatus of this embodiment, the hot plate 24 is used as the temperature variable means. By using the hot plate 24, the entire thin film material 13 can be heated. By changing the temperature of the substrate 11 and the thin film material 13 as a whole, the in-plane average of the electrical characteristics of the thin film material 13 can be evaluated.

  Further, the radiation thermometer 22 measures the temperature of the thin film material 13 by measuring the infrared rays emitted from the thin film material 13 from the thin film material 13 side.

Details of the electrical property evaluation apparatus according to the present embodiment are shown below.
Surface electrometer 21: Made by TREK, Model 323, manufacturer demo machine Radiation thermometer 22: Made by MICRO-EPSILON, CT-SF22-C3, without S / N Hot plate 24: Made by AS ONE, HP-2SA, S / N None

  Thus, also in the electrical property evaluation of this embodiment, the electrical property of the ferroelectric or pyroelectric body before the upper electrode is formed can be evaluated without touching the ferroelectric or pyroelectric material.

(Verification of electrical property evaluation)
Next, the electrical property evaluation apparatus of the present invention is verified for electrical property evaluation.
First, in the second embodiment, a case where a PVDF sheet, PZT ceramics, or PZT thin film is selected as the thin film material 13 and the temperature is changed will be described with reference to FIG.
FIGS. 3A to 3C are graphs when the temperature of the PVDF sheet, PZT ceramics, and PZT thin film is changed, with the horizontal axis representing time and the vertical axis representing surface potential and temperature. FIG. 3D schematically shows a steady state and a polarization state at the time of temperature rise. The arrows in FIGS. 3A to 3C indicate which corresponding vertical axis is.

As shown in the figure, the PVDF sheet generates a potential of −100 V with a temperature change of about 3 ° C. (FIG. 3A), and the PZT ceramics generates a potential of −100 V with a temperature change of about 10 ° C. (Fig. 3 (b)). On the other hand, in the PZT thin film, it can be seen that a potential of about −0.4 V is generated with a temperature change of about 10 ° C. (0 s to about 60 s in FIG. 3C).
Therefore, it is possible to evaluate the change in surface potential (the above formula (1)) related to the physical properties and thickness of the thin film material 13 from these.

In addition, although the negative electric potential generate | occur | produced in FIG. 3, in the PVDF sheet | seat and the PZT ceramics, it has confirmed that a positive electric potential generate | occur | produced if the same experiment was carried out by inverting upside down (back and front).
Also, as shown in FIG. 3 (d), since the amount of polarization decreases as the temperature of the sample increases, if the sample is placed with the polarization direction as the upward direction of the sample, the polarization of the sample must be changed before the temperature rises. The compensated negative surface charge appears to have appeared as a negative surface potential.
For these reasons, the electrical property evaluation apparatus according to the present invention can measure the potential of the polarity due to the polarization direction.

  Next, in the data of FIG. 3B and FIG. 3C, the result of normalizing the potential change amount with the thickness of the sample (thin film material) and plotting the relationship with the temperature change amount is shown in FIG. In FIG. 4, the amount of change in surface potential is shown with the horizontal axis normalized by temperature and the vertical axis normalized by thickness.

Here, the quantitative validity of the evaluation result obtained by the evaluation apparatus of the present embodiment is examined. In the examination, the actual measurement results are compared with the literature values.
In the actual measurement results, as shown in FIG. 4, the slopes of the PZT ceramics and the PZT thin film are approximately the same. Since the change amount of the surface potential caused by the pyroelectric effect can be expressed by the above formula (1), when the pyroelectric coefficient is calculated from this slope and the above formula (1), 1.5 × 10 ⁻⁴ C / m ² ° C.
This is comparable to the values reported for PZT ceramics and PZT thin films (1.0 to 5.3 × 10 ⁻⁴ C / m ² ° C., the following references (A) to (D)). all right. Therefore, it can be said that the electrical property evaluation apparatus according to the present invention is appropriate for quantitative discussion of the pyroelectric effect.

[References]
(A) G. Sebald, E. Lefeuvre, and D. Guyomar, IEEE transactions on ultrasonics, 55, 538 (2008)
(B) MT Kesim, J. Zhang, S. Trolier-McKinstry, JV Mantese, RW Whatmore and SP Alpay, J. Appl. Phys. 114, 204101 (2013).
(C) RVK Mangalam, JC Agar, AR Damodaran, J. Karthik, and LW Martin, Appl. Mater. Interfaces, 5, 13235 (2013).
(D) G. Sebald, E. Lefeuvre, and D. Guyomar, IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 55, 3, (2008)

Next, in the first embodiment, the thin film material 13 is a PZT thin film, and the PZT thin film is irradiated with 2.0, 6.5, 10, 20 W / mm ² laser from the back surface (from the substrate 11 side). The change in temperature is shown in FIG. Note that, as described above, the temperature in FIG. 5 is obtained by measuring the infrared rays emitted from the substrate 11 with the radiation thermometer 22, and this corresponds to the temperature of the sample (thin film material 13).

As shown in FIG. 5, after the laser irradiation, the temperature of the sample rises and is saturated at a certain temperature. The temperature at the time of saturation shows a high temperature corresponding to the increase in the energy of the laser, the largest at 20 W / mm ² , and a temperature increase of 250 ° C. or more can be confirmed.

  Next, in FIG. 5, the relationship between the energy density of the laser and the temperature of the sample is shown in FIG. The temperature in FIG. 6 indicates the temperature when the temperature rise is saturated by laser irradiation in FIG. As shown, the temperature on the vertical axis increases linearly with the energy density of the laser. It can be seen that the temperature can be controlled by adjusting the energy density of the laser, and therefore the temperature of the sample can be easily controlled in the electrical property evaluation apparatus of the present invention.

  Next, in the first embodiment, considering the development to various evaluation objects, it is examined how much temperature change and light energy are required for various ferroelectric / pyroelectric materials. Since the measurement sensitivity of a commercially available surface electrometer is about 10 mV, it is desirable to obtain a pyroelectric response of about +1 V for quantitative discussion. Therefore, in the materials shown in Table 1, the relationship between the temperature change amount / energy density necessary for obtaining a pyroelectric response of +1 V and the thickness of the measurement sample is calculated from the above formula (1) and the physical property values shown in Table 1. did. The result is shown in FIG.

In Table 1, p represents a pyroelectric coefficient, and ε _r represents a relative dielectric constant. PMNPT represents lead magnesium niobate / lead titanate. In Table 1, the pyroelectric coefficient of PZT is based on the above reference (D).

  FIG. 7A shows the relationship between the amount of temperature change necessary to obtain a + 1V pyroelectric response and the thickness of the measurement sample, and FIG. 7B shows the relationship between the + 1V pyroelectric response. The relationship between a required energy density and the thickness of a measurement sample is shown. Regarding the thickness of FIG. 7, the thickness range shown in FIG. 7 was examined in consideration of the general film thickness of a piezoelectric thin film material used in piezoelectric MEMS (Micro Electro Mechanical Systems) being about 1 μm.

In FIG. 7A, when the film thickness is 1 μm, the required temperature change is 1.8 ° C. for LiTaO ₃ (first graph in the figure), and 19 ° C. for PZT (first graph in the figure). Can be estimated.

Further, from the relationship between the temperature change amount and the laser energy density shown in FIG. 6, the vertical axis (required temperature change amount) in FIG. 7A is recalculated to the required laser energy density, and the result is shown in FIG. 7 (b).
In FIG. 7B, when the film thickness is 1 μm, the required energy density is 0.13 W / mm ^{2 for} LiTaO ₃ (the bottom graph in the figure) and PZT (the top graph in the figure). It can be estimated as 1.4 W / mm ² .
As described above, it is possible to estimate the temperature change amount and the energy density necessary for obtaining a predetermined pyroelectric response for a sample having a predetermined thickness.

Next, in the first embodiment, FIG. 8 shows changes in temperature and surface potential when 20 W / mm ² laser irradiation is turned on / off for a sample having a small pyrochlore phase and a sample having a large pyrochlore phase. FIG. 8A is for a sample with a small pyrochlore phase, and FIG. 8B is for a sample with a large pyrochlore phase. In addition, the sample in FIG. 8 is a thing measured about the PZT thin film.

  In FIG. 8A, when the laser irradiation is turned on / off for a sample having a small pyrochlore phase, the surface potential is generated as the temperature rises and approaches about 300 ° C. in the laser irradiation ON region− You can see it approaching 4V. When the laser irradiation is turned off, the surface temperature approaches the original value (about 20 ° C.) with time, and the surface potential approaches the original value (about 0 V).

On the other hand, when FIG. 8B shows a case where laser irradiation is turned on / off for a sample having a large pyrochlore phase, the surface potential increases in the laser irradiation ON region as the temperature increases and approaches 280 ° C. Occurrence is approaching -4V.
Here, in the laser irradiation ON region of FIG. 8B, the surface potential increases with increasing temperature from 0 s to about 50 s, but the surface potential decreases from about 50 s to about 120 s. (It changes in a direction approaching 0V). After about 120 seconds, the surface potential increases again until the laser irradiation is turned off. When the laser irradiation is turned off, the surface temperature approaches the original temperature (about 20 ° C.) with time, and the surface potential decreases with this.

First, the validity of the measurement system is examined using the results of FIG. For each of FIGS. 8A and 8B, from the response around room temperature (from 0 s to about 50 s), the thickness of the sample is 1 μm, the amount of change in temperature and surface potential, and the relative dielectric constant (ε _r ) 1600 Substituting into (1), the pyroelectric coefficient of the sample was calculated. As a result, both samples are about 3 × 10 ⁻⁴ C / m ² ° C., which is about the same as the values reported for PZT ceramics and PZT thin films (1 to 5.3 × 10 ⁻⁴ C / m ² ° C.). I found out.
From this, it can be said that the electrical property evaluation apparatus in the embodiment is appropriate for quantitative discussion of the pyroelectric effect.

  Next, the influence of the pyrochlore phase on the pyroelectric response of FIG. It is known that the surface charge generated by the pyroelectric effect decreases exponentially by conducting through the crystal of the pyroelectric material. This appears as a decrease in the surface potential in the range of about 50 s to about 120 s in FIG.

  The relaxation time at this time can be expressed by the following formula (2).

τ = ε _r ε ₀ / σ Equation (2)

In equation (2), ε _r is the relative permittivity of the sample, ε ₀ is the permittivity of vacuum, and σ is the electrical conductivity of the sample.

  The above equation (2) can be said to be τ = ερ (ε is the dielectric constant of the sample, and ρ is the electrical resistivity of the sample). The lower the dielectric constant and electrical resistivity of the sample, the surface generated by the pyroelectric effect. The time for the electric charge to disappear as a relaxation current is shortened.

  Thus, since the time constant of the relaxation time of the surface potential is represented by the product of the dielectric constant and the electrical resistivity, information on the dielectric constant and the electrical resistivity can be obtained from the charge retention characteristics. In other words, the charge retention characteristics of the thin film material can be evaluated by measuring the time change of the surface potential when the temperature is raised and then kept constant.

Further, it is generally known that the dielectric constant of the pyrochlore phase is several orders of magnitude lower than that of Pb (Zr, Ti) O ₃ .
Here, the STEM-HAADF image obtained about the cross section of the PZT thin film containing a pyrochlore phase is shown to Fig.9 (a). Moreover, the schematic diagram of Fig.9 (a) is shown in FIG.9 (b). In FIG. 9B, reference numeral 31 denotes an electric charge, reference numeral 32 denotes Pb (Zr, Ti) O ₃ , reference numeral 33 denotes a pyrochlore phase, reference numeral 34 denotes a lower electrode, and reference numeral 35 denotes an adhesion layer and a substrate.

As shown in FIGS. 9A and 9B, it can be seen that the pyrochlore phase exists in parallel with Pb (Zr, Ti) O _{3 in the} thin film. These, especially by the examination of FIG. 9B, are generated by a pyroelectric effect from a microscopic region such as a lattice defect generated at the interface between the pyrochlore phase or the pyrochlore phase and Pb (Zr, Ti) O ₃ . It is suggested that the charge flows as a relaxation current.

The above is briefly summarized below.
Since the pyroelectric coefficient calculated from the evaluation result is approximately the same as the literature value, it can be said that the electrical property evaluation apparatus of the present invention is appropriate for quantitative discussion of the pyroelectric effect. In addition, the charge retention characteristics of the thin film material can be evaluated by measuring the temporal change of the surface potential when the temperature is raised to a constant temperature. Further, in the Pb (Zr, Ti) O ₃ thin film having different pyrochlore phase contents, a clear difference can be confirmed in the charge retention characteristics of each thin film.
From the above, the electrical property evaluation apparatus of the present invention evaluates the electrical properties of the ferroelectric or pyroelectric material without the upper electrode without the measurement member coming into contact with the surface of the ferroelectric or pyroelectric material. Can do. Even when the production of the thin film material is outsourced, effective evaluation can be performed in the acceptance inspection of the ferroelectric or pyroelectric thin film material outsourced. By performing such evaluation, an improvement in yield can be expected.

(Third embodiment)
Next, another embodiment of the electrical property evaluation apparatus according to the present invention will be described. A description of the same components as those in the above embodiment may be omitted. A schematic diagram of the electrical property evaluation apparatus of this embodiment is shown in FIG.

  The electrical property evaluation apparatus of this embodiment is almost the same as that of the first embodiment, but in this embodiment, the substrate 11 fixing means (XY stage) capable of moving the substrate 11 in the surface direction of the substrate 11. 25). By having the XY stage 25, the substrate 11 can be moved in the X direction and the Y direction (the surface direction of the substrate 11), the location where the temperature is varied, the location where the temperature is measured, or the surface of the thin film material 13 is changed. The location where the potential is measured can be changed. As a result, the distribution of electrical characteristics in the sample plane can be evaluated.

(Fourth embodiment)
Next, another embodiment of the electrical property evaluation apparatus according to the present invention will be described. A description of the same components as those in the above embodiment may be omitted. A schematic diagram of the electrical property evaluation apparatus of this embodiment is shown in FIG.

  The electrical property evaluation apparatus of this embodiment is almost the same as that of the second embodiment, but a plurality of surface potential measuring means of this embodiment are arranged in an array, and a plurality of locations of ferroelectric or pyroelectric materials. The surface potential meter 21 is arranged in an array in FIG. In the present embodiment, the thin film material 13 is heated as a whole by the hot plate 24, and the surface potential at a plurality of locations is measured by the array-type surface potential meter 21, so that the distribution of electrical characteristics in the sample surface can be achieved in a short time. Can be evaluated.

  In FIG. 11, only one radiation thermometer 22 is illustrated, but the invention is not limited to this, and the radiation thermometer 22 may be changed as appropriate, and the location where the radiation thermometer 22 measures temperature may be changed. Then, the number of radiation thermometers 22 may be increased so that a plurality of locations can be measured simultaneously.

(Fifth embodiment)
Next, another embodiment of the electrical property evaluation apparatus according to the present invention will be described. A description of the same components as those in the above embodiment may be omitted. A schematic diagram of the electrical property evaluation apparatus of the present embodiment is shown in FIG.

  The electrical property evaluation apparatus of the present embodiment is almost the same as that of the second embodiment, but the surface potential measuring means of the present embodiment measures the surface potential of the entire ferroelectric or pyroelectric body. In the present embodiment, the thin film material 13 is entirely heated by the hot plate 24, and the average electrical characteristics of the sample can be evaluated by measuring with the surface potentiometer 21 that can measure the entire surface of the thin film material 13. it can.

  Although only one radiation thermometer 22 is shown in FIG. 12, the present invention is not limited to this, and can be changed as appropriate, and the location where the radiation thermometer 22 measures temperature may be changed. Then, the number of radiation thermometers 22 may be increased so that a plurality of locations can be measured simultaneously.

(Sixth embodiment)
Next, another embodiment of the electrical property evaluation apparatus according to the present invention will be described. A description of the same components as those in the above embodiment may be omitted. A schematic diagram of the electrical property evaluation apparatus of this embodiment is shown in FIG.

The electrical property evaluation apparatus of this embodiment is substantially the same as that of the second embodiment, but the temperature variable means of this embodiment has means for heating and cooling the ferroelectric or pyroelectric material. In FIG. 13, a Peltier element 26 is shown as a temperature variable means. In the Peltier element 26, heating and cooling can be switched by changing the direction of the current flowing through the element.
According to this embodiment, the stability of polarization of a sample can be evaluated from the difference between the surface potential during heating and the surface potential during cooling.

  In addition, in this embodiment, it is not restricted to a Peltier device, If it can heat and cool, it can change suitably. Further, the heating means and the cooling means may be separated.

DESCRIPTION OF SYMBOLS 11 Substrate 12 Lower electrode 13 Thin film material 20 Shield box 21 Surface potential meter 22 Radiation thermometer 23 Heating light source 24 Hot plate 25 XY stage 26 Peltier element 31 Charge 32 Pb (Zr, Ti) O ₃
33 Pyrochlore phase 34 Lower electrode 35 Adhesion layer and substrate

JP 2004-221411 A

Claims (11)

An electrical property evaluation apparatus for evaluating electrical properties of a ferroelectric or pyroelectric material formed on a substrate,
Temperature varying means for varying the temperature of the ferroelectric or pyroelectric material by varying the temperature of the substrate;
Temperature measuring means for measuring the temperature of the ferroelectric or pyroelectric material in a non-contact manner;
Surface potential measuring means for measuring the surface potential of the ferroelectric or pyroelectric material in a non-contact manner,
Varying the temperature of the ferroelectric or pyroelectric material, and evaluating the electrical characteristics of the ferroelectric or pyroelectric material from the amount of change in temperature of the ferroelectric or pyroelectric material and the amount of change in the surface potential. A device for evaluating electrical characteristics. The electrical property evaluation apparatus according to claim 1, wherein a pyroelectric coefficient of the ferroelectric material or pyroelectric material is obtained by the following formula (1).
ΔV = dpΔT / ε (1)
(In the formula (1), ΔV, d, p, ΔT, and ε represent the amount of change in surface potential, the thickness, the pyroelectric coefficient, the amount of temperature change, and the dielectric constant of the ferroelectric or pyroelectric material, respectively.)   The electrical property evaluation apparatus according to claim 1, further comprising a fixing unit for fixing the substrate capable of moving the substrate in a surface direction of the substrate.   The electrical temperature evaluation apparatus according to any one of claims 1 to 3, wherein the temperature measuring means is a radiation thermometer that measures a temperature with emitted infrared rays.   By increasing the temperature of the ferroelectric or pyroelectric material by the temperature variable means and measuring the time change of the surface potential when the temperature is constant, the charge retention characteristics of the ferroelectric or pyroelectric material can be obtained. The electrical property evaluation apparatus according to claim 1, wherein evaluation is performed.   6. The electrical property evaluation apparatus according to claim 1, wherein the temperature varying means is a hot plate that heats the substrate. The temperature variable means varies the temperature of the entire ferroelectric or pyroelectric material,
The electrical characteristics according to any one of claims 1 to 6, wherein a plurality of the surface potential measuring means are arranged in an array and measure surface potentials at a plurality of locations of the ferroelectric or pyroelectric body. Evaluation device. The temperature variable means varies the temperature of the entire ferroelectric or pyroelectric material,
The electrical property evaluation apparatus according to claim 1, wherein the surface potential measuring unit measures a surface potential of the ferroelectric body or the pyroelectric body as a whole.   6. The electrical property evaluation apparatus according to claim 1, wherein the temperature variable means is light irradiation means for irradiating the substrate with light.   6. The electrical property evaluation apparatus according to claim 1, wherein the temperature variable means includes means for heating and cooling the ferroelectric material or pyroelectric material. An electrical property evaluation method for evaluating electrical properties of a ferroelectric or pyroelectric material formed on a substrate,
A temperature variable step of varying the temperature of the ferroelectric or pyroelectric material by varying the temperature of the substrate;
A temperature measurement step for measuring the temperature of the ferroelectric or pyroelectric material in a non-contact manner;
A surface potential measurement step of measuring the surface potential of the ferroelectric or pyroelectric material in a non-contact manner,
Varying the temperature of the ferroelectric or pyroelectric material, and evaluating the electrical characteristics of the ferroelectric or pyroelectric material from the amount of change in temperature of the ferroelectric or pyroelectric material and the amount of change in the surface potential. A method for evaluating electrical characteristics.