JPH10221279A - Measuring method and device for thermal diffusivity using alternate current calorimetry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the thermal diffusivity of a multi-layer film, electric conductor film, and semiconductor film in the direction across the thickness. SOLUTION: A laminate thin film specimen LA prepared by pinching a thin film specimen 1 whose thermal diffisivity of the layer 3 is unknown by at least one of the first and second insulative thin film specimens 21 and 22 (layers 2 and 4) where the thermal diffusivities a2 and a4 , thermal conductivity, and thicknesses 12 and 14 are known, is pinched by a pair of specimen holders 31 and 32 (layers 1 and 5), and different AC powers of constant frequency (f) are given one after another to a thin metal film 4 pinched in tight attachment by the first insulative thin film specimen 21 and the specimen holder 31 . The phase difference ΔΦt of the thermal wave transmitted to the laminate specimen LA is measured by an electric resistance thermometer and lock-in amplifier using thin metal film 5 pinched by the second insulative thin film specimen 22 and specimen holder 32 , and using the obtained phase difference, the thermal diffusivity a3 of the unknown thin film specimen is calculated from ΔΦt=ΔΦ2 +ΔΦ3 +ΔΦ4 and ΔΦi =-1i (πf/ai )<1/2> where layer i is 2, 3, 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for measuring a thermal diffusivity in a thickness direction of a thin film sample.

[0002]

Conventionally, various attempts have been made to measure the thermal diffusivity in the thickness direction of a thin film sample. For example, a thin film sample whose thermal diffusivity is unknown is sandwiched between known first and second thin film samples. An AC power is applied to the metal film resistance attached to one surface of the unknown thin film sample to heat the thin film sample, and from an AC temperature signal obtained from a resistance change of the metal film resistance for the thermometer attached to the other surface. A measurement method using AC calorimetry for calculating the thermal diffusivity of an unknown thin film sample has been proposed (JP-A-6-2).
No. 73361).

[0003]

In the above prior art,
The first or second thin film sample thermal diffusivity is known, the same lambda · k with the unknown thin film sample [lambda: thermal conductivity, k (AC Temperature attenuation ^{coefficient) :( πf / a) 1/} 2] of Must be a value.
Therefore, it cannot be measured in the case of two layers, three layers, and
There is a problem that only a single layer can be measured, and a sample is limited to an electrically defective conductor, and there is a problem that a thin film sample of metal or semiconductor cannot be measured. The present invention solves the above-mentioned problems of the conventional method for measuring the thermal diffusivity, and a method for measuring the thermal diffusivity by AC calorimetry capable of measuring the thermal diffusivity of a multilayer film, an electric conductor film, and a semiconductor film. It is an object to provide a device.

[0004]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a thin film sample whose thermal diffusivity is unknown, comprising the steps of: A layered thin film sample sandwiched between at least one first and second insulating thin film samples, each of which is known, is sandwiched between a pair of sample holders, and closely adhered between the first insulating thin film sample and the sample holder. A constant AC power of various frequencies f is sequentially applied to the sandwiched metal thin film, and the phase difference ΔΦ _T of the temperature wave propagating to the layered thin film sample is sandwiched between the second insulating thin film sample and the sample holder. Measured with an electric resistance thermometer and a lock-in amplifier using a thin metal film. _{= ΔΦ 2 + ΔΦ 3 + ΔΦ} 4 (6) ΔΦ i = -l i (πf / a i) 1/2 (i = 2,3,4) (7) where, .DELTA..PHI ₂ is the first insulating thin film sample The phase difference of the temperature wave ΔΦ ₃ is the phase difference of the temperature wave of the unknown thin film sample ΔΦ ₄ is the phase difference of the temperature wave of the second insulating thin film sample l _i is the first and second insulating thin film sample and the unknown the thickness a _i of the thin film sample, the first and second insulating thin film sample and the thermal diffusivity of the phase difference of the unknown film sample ΔΦt _{3. A} method for measuring the thermal diffusivity by AC calorimetry, wherein the thermal diffusivity a ₃ of an unknown thin film sample is calculated from the above equations (6) and (7). The thermal diffusivity, thermal conductivity, and thickness of the thin film sample are known, and the thermal diffusivity of the thin film sample is unknown in the layered thin film sample sandwiched between at least one first and second insulating thin film samples. A thermal diffusivity measuring device, an AC oscillator, an electric resistance thermometer using a metal thin film,
Phase difference ΔΦt of temperature wave of the layered thin film sample composed of DC amplifier and lock-in amplifier Measuring device for measuring Δt _{= ΔΦ 2 + ΔΦ 3 + ΔΦ} 4 (6) ΔΦ i = -l i (πf / a i) 1/2 (i = 2,3,4) (7) The retardation ΔΦt And a means for calculating the thermal diffusivity of the thin film sample whose thermal diffusivity is unknown from the above equations (6) and (7), using a thermal diffusivity measuring apparatus based on AC calorimetry.

In FIG. 1, layers 2, 3 and 4 are a first insulating thin film sample and a thermal diffusivity [a = λ / (C · ρ), respectively.
ρ: density] of the unknown thin film sample and the second insulating thin film sample, the thickness, thermal diffusivity, thermal conductivity and AC temperature decay coefficient of l ₂ , a ₂ , λ ₂ and k ₂ , l ₃ ,
a _3, lambda ₃ and k ₃ and l _4, a _4, and lambda ₄ and k _4. In a state where the layered thin film sample composed of the three layers 2, 3, and 4 is sandwiched between the sample holders of the layers 1 and 5, the surface (x = 0) of the layered thin film sample composed of the three layers has a frequency f, The temperature response and the phase difference on the back surface (x = d ₄ ) of the layered thin film sample when the layered thin film sample is periodically heated by the heat quantity Q (maximum value) per unit area are measured. The layers 1 and 5 of the sample holder are sufficiently thicker than the three-layered thin film sample, and the thickness, thermal diffusivity, thermal conductivity and AC temperature decay coefficient of the layers 1 and 5 are respectively l ₁ , a
_1, lambda ₁ and k ₁ and l _5, a _5, a lambda ₅ and k _5. If the one-dimensional heat conduction equation is solved on the assumption that there is no contact thermal resistance between the layers, the temperature response at x = d ₄ is given by equation (1).

[0006]

(Equation 1)

Here, the suffix is a layer number, and Y, W,
V is represented by the following equation.

[0008]

(Equation 2)

If λ ₁ k ₁ = λ ₂ k ₂ , the phase difference between the layers 2 and 3 (the phase difference between the surface temperature and the back surface temperature of each of the layers 2 and 3, and above and below) is Equations (2) and (3) respectively.

ΔΦ ₂ = −k ₂ l ₂ (2)

[0011]

(Equation 3)

The second term in equation (3) is very small and negligible compared to the first term. That is, it can be approximated as ΔΦ ₃ = −k ₃ l ₃ (4). FIG. 2 shows an error caused by approximation by the equation (4) while changing various parameters. It can be seen that the error is within ± 1% in a practical range [In FIG. 2, Fo ₃ is the Fourier number (at
/ L ² ), Λ is the thermal effusivity, and α is, for example, the ratio of Λ of layer 4 to 層 of layer 3 Λ _4/3 . Λ = (λ ・ C ・
ρ) ^1/2 = (λ · λ / a) ^1/2 = λ / (a) ^1/2 ]. Layer 4
The phase difference of ΔΦ ₄ = −k ₄ l ₄ (5) is assuming that λ ₄ k ₄ = λ ₅ k ₅ . Equation (2) is derived assuming that the physical properties (thermal conductivity and thermal diffusivity) of the layer 2 are the same as those of the layer 1.
Even if the physical property values of the two are different, it is understood that Expression (2) is approximately established by applying the same method as the analysis for the layer 3. Equation (5) is applied to the layer 4 and the layer 5 from the same viewpoint.
Are approximately established even if the physical property values of are different.

After all, the phase difference (heating surface and temperature measurement point) ΔΦ _t of the whole layered thin film sample is expressed by the following equation.
ΔΦ _t = ΔΦ ₂ + ΔΦ ₃ + ΔΦ ₄
(6) _{where, ΔΦ i = -l i (πf} / a i) 1/2 (i =
2,3,4) (7) Equation (7) is obtained by applying AC heat to one surface of the thin film sample, and calculating the phase difference of the temperature wave between the temperature of one surface and the temperature of the other surface. The fact that the above condition is satisfied when is generated is described in detail in, for example, the above-mentioned JP-A-6-273361.

By measuring the phase difference ΔΦ _{t of the} entire layered thin film sample and using equations (6) and (7), the effective thermal diffusivity of the entire layered thin film sample can be calculated. Layer 3
In a physical property value of the thin film sample is unknown, if the known physical properties and thickness of the insulating thin film sample which is another layer, the thermal diffusivity of a ₃ unknown film samples, the entire layered thin film sample position Phase difference Δ
By measuring Φ _t , it can be easily obtained from equations (6) and (7). In the above description, the insulating thin film samples above and below the thin film sample are each one layer, and a total of three layers have been described as an example. However, even if there are three or more layers, the approximation represented by the sum of the respective phase differences is practical. It is established in the range.

[0015] The measuring apparatus according to claim 2, AC generator, the electric resistance thermometer using a metal thin film, measurement for measuring the phase difference [Phi _t temperature wave of said layered film sample consisting of the DC amplifier and the lock-in amplifier The apparatus for heating the layered thin film sample with an alternating current output from an AC oscillator to measure the phase difference of the temperature wave of the layered thin film sample, and the means is configured to measure the phase difference of the measured temperature wave of the layered thin film sample. From the equations (6) and (7), the thermal diffusivity of the thin film sample whose thermal diffusivity is unknown is calculated.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a schematic diagram of a sample system when measuring the thermal diffusivity of a sample thin film.

[0018] In the figure, 1 is corresponding to the layer 3, for example, stainless steel (SUS304) thermal diffusivity unknown lamella is, 2 ₁ and 2 ₂ correspond to the layer 2 and layer 4 for example, an insulating thin film sample a polyimide film, 3 ₁ and 3 ₂ are sample holder such as a polyimide film corresponding to the layer 1 and the layer 5, the sample holder 3 _1, a gold film 4 (the resistance value of the heating 2～3Omu) are deposited by sputtering, a gold film 5 (the resistance value used as an electric resistance thermometer 10 to the sample holder 3 ₂
20Ω) is deposited. These thin film samples 1, 2 ₁
And layered lamella LA and specimen holder 3 ₁ consists of two ₂
And 3 _2, etc., for example, mounted on the base 6 of the glass plate is firmly pressed from above by the pressing plate 7, for example a glass plate in order to reduce the thermal contact resistance between the layers.

FIG. 4 is a block diagram schematically showing a thermal diffusivity measuring apparatus.

In FIG. 1, reference numeral 10 denotes the gold film 4 for heating.
An AC oscillator, for example, a function generator, connected to the gold film 5 via a variable resistor 13 is connected to the gold film 5 via a variable resistor 13; The DC amplifier 16 connected via the compensator 15 is a lock-in amplifier connected to the DC amplifier 14, and the AC oscillator 10, the power amplifier 11, the DC power supply 12 for the resistance thermometer, the DC amplifier 14, and the lock. The in-amplifier 16 and the like constitute a measuring device for measuring the phase difference of the temperature wave of the layered thin film sample LA. Although not shown, this apparatus has means such as a computer which is connected to the lock-in amplifier 16 and calculates the thermal diffusivity of the unknown sample thin film 1 from the equations (6) and (7).

[0021] To explain the thermal diffusivity measurement method of an unknown sample thin film 1 by using the above apparatus, the alternating current from the AC oscillator 10 to the gold film 4 deposited on the sample holder 3 _first surface (x = 0) And periodically heats the layered thin film sample. The maximum heating amount was about 3 W, and the heating frequency was changed in the range of 0.5 to 5.0 Hz. The first insulating thin film sample 3 ₁ which is the layer 2
The phase difference of the temperature wave between the heating surface of the layer 4 and the temperature response surface of the _second insulating thin film sample 32 as the layer 4 is compensated for by the output of the electric resistance thermometer using the gold film 5 and the DC amplifier. 14 by input to a lock-in amplifier 16 via 14 and this output is input to said means, for example a computer,
Using a computer, the thermal diffusivity of the thin film sample 1 was calculated according to the equations (6) and (7).

First, as the unknown thin film sample 1, a thin plate of stainless steel (SUS304) was used, and thin film samples (100, 200, and 300 μm) having different thicknesses were measured. Figure 5 shows the results of the phase difference .DELTA..PHI _t measured when the change in the range of 0.5 to 5.0 Hz frequency. Phase difference .DELTA..PHI _t is linearly changed with respect to the square root of the frequency f, it can be seen that the equation (7) is satisfied.

Table 1 shows the thermal diffusivity of stainless steel obtained from the inclination.

[0024] The measured thermal diffusivity of stainless steel is
Properties Handbook [Jpn. Soc. Thermophys. Prop., Tok
yo.Yokendo, (1990) 26], which is within 4% of the reference data.

As an application example of this measurement method, the thermal diffusivity of a liquid crystal sheet for surface temperature measurement, which is extremely important for knowing how much unsteady temperature response a liquid crystal thermometer has, was measured.

The liquid crystal sheet for temperature measurement is often in the form of a layer. As shown in FIG. 6, for example, a cholesterol-derived liquid crystal sheet is a transparent PET having a thickness of 102 μm.
A liquid crystal (LC) layer 18 (having a thickness of 64 μm including the undercoat layer and the black layer) is provided on the base material of (polyethylene terephthalate) 17 via an undercoat layer. The adhesive layer 19 having a thickness of 100 μm is formed in approximately three layers. This liquid crystal sheet was measured. Table 2 shows the measurement results.

[0027] NO. 1 is a measured value for the entire liquid crystal sheet, N
O. 2 is a measured value for a sample from which the adhesive layer was dissolved and removed with a solvent. As a thermal diffusivity of PET17 as a base material, Polymer Handbook (J. Brandrup, EHImmergut, J
Using the data (a ₂ = 0.929 × 10 ⁻⁷ m ² / s) published in Ohn Wilery & Son (1989), V104), the thermal diffusivity of the liquid crystal layer 18 becomes a ₃ = 0.72 × 10 ^-7
m ² / s. NO. The data of the adhesive layer 19 of No. 4 is a value obtained from the above data and the entire phase difference.

[0028]

According to the present invention, a multi-layer thin film, an electric conductor film,
This has the effect that the thermal diffusivity of the semiconductor film can be measured.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a layered thin film sample.

FIGS. 2A and 2B respectively show an error caused by approximation when the Fourier number is used as a variable and the efficiency ratio as a parameter, and an error caused by approximation when the Fourier number is used as a parameter and the efficiency ratio is used as a parameter. FIG.

FIG. 3 is a schematic diagram of a sample system when measuring the thermal diffusivity of a sample thin film.

FIG. 4 is a block diagram schematically showing a thermal diffusivity measuring apparatus.

FIG. 5 is a view showing a result of measuring the phase difference when a frequency is changed in a range of 0.5 to 5.0 Hz.

FIG. 6 is a schematic diagram showing a configuration of a liquid crystal sheet for temperature measurement.

[Explanation of symbols]

1 ... thin film sample 2 _1, 2 ₂ ... insulating film sample 3 _1, 3 ₂ ... specimen holder 4 ... metal film 5 ... metal film 6 ... base 7 ... push plate 10 ... AC oscillator 11 ... power amplifier 12 ... resistance temperature Meter power supply 14 DC amplifier 16 Lock-in amplifier

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Taro Dai, 1-23-2, Hirosawa, Hamamatsu-shi, Shizuoka Pref. Joint Dormitory 5-33 Hirosawa Residence

Claims (2)

[Claims] 1. A thin film sample whose thermal diffusivity is unknown is made of at least one thin film sample whose thermal diffusivity, thermal conductivity and thickness are each known.
The layered thin film sample sandwiched between the first and second insulating thin film samples is sandwiched between a pair of sample holders, and various types of metal thin films are tightly sandwiched between the first insulating thin film sample and the sample holder. Of the temperature wave propagating to the layered thin film sample by sequentially applying a constant AC power having a frequency f of Is measured by an electric resistance thermometer and a lock-in amplifier using a metal thin film sandwiched between the second insulating thin film sample and the sample holder, and ΔΦt _{= ΔΦ 2 + ΔΦ 3 + ΔΦ} 4 (6) ΔΦ i = -l i (πf / a i) 1/2 (i = 2,3,4) (7) where, .DELTA..PHI ₂ is the first insulating thin film sample The phase difference of the temperature wave ΔΦ ₃ is the phase difference of the temperature wave of the unknown thin film sample ΔΦ ₄ is the phase difference of the temperature wave of the second insulating thin film sample l _i is the first and second insulating thin film samples and the unknown the thickness a _i of the thin film sample, the first and second insulating thin film sample and the thermal diffusivity of the phase difference of the unknown film sample ΔΦt Calculating the thermal diffusivity a ₃ of the unknown thin film sample from the above equations (6) and (7) using the above method. 2. A thin film sample whose thermal diffusivity is unknown has a thermal diffusivity of
An apparatus for measuring the thermal diffusivity of a thin film sample in a layered thin film sample sandwiched between at least one first and second insulating thin film samples, each having a known thermal conductivity and a known thickness, comprising an AC oscillator, a metal thin film A measuring device for measuring the phase difference ΔΦt of the temperature wave of the layered thin film sample comprising an electric resistance thermometer, a DC amplifier and a lock-in amplifier using _{= ΔΦ 2 + ΔΦ 3 + ΔΦ} 4 (6) ΔΦ i = -l i (πf / a i) 1/2 (i = 2,3,4) (7) The retardation ΔΦt And means for calculating the thermal diffusivity of the thin film sample whose thermal diffusivity is unknown from the above equations (6) and (7).