JPS59155701A - Method and device for thickness measurement of specimen - Google Patents

Abstract

PURPOSE:To measure the thickness of a very thin specimen accurately by a method wherein a specimen is placed at the center of a pair of parallel plates and two pairs of facing electrodes are provided to the plates at the positions symmetrical about the center of the plates and the thickness of the specimen is measured as the summation of reciprocals of the capacitances of the two pairs of electrodes. CONSTITUTION:Two pairs of electrodes 1, 2 and 3, 4 each of which has the same area, are provided to a pair of parallel plates 5, 6 at their both ends and a specimen is held between these plates at their center. The parallel plates 5, 6 are so arranged as to have the two electrodes face each other. The 1st arithmetic circuit 9 includes the capacitance C1 of the electrodes 1, 2 in its feedback components and the 2nd arithmetic circuit 10 includes the capacitance C2 of the electrodes 3, 4 in its feedback components. These two arithmetic circuits 9, 10 are connected to an oscillation circuit 8. A summing operational circuit 11 is connected to the output of the 1st and 2nd arithmetic circuits 9, 10 and the summation of the output voltages of the 1st and 2nd arithmetic circuits is calculated. A phase detection circuit 12 is connected to the output of the summing operational circuit 11. A reference signal, whose phase is shifted by 90 deg. against the oscillation signal of the oscillation circuit 8, is given to the phase detection circuit 12 through a phase shifting circuit 21. With this procedure, the summation of the output voltages of the 1st and 2nd arithmetic circuits 9, 10 is subjected to the phase detection at the point where the phase is shifted by 90 deg. against the oscillation signal. The thickness (d) of the specimen 7 is obtained by proportional division.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for measuring the thickness of thin samples.

Accurately measuring the thickness of very thin samples is required in many technical fields, but until now it has not been possible to fully meet this demand. For example, it has not been possible to accurately measure the thickness of a piezoelectric film with a wall thickness of 700 μm to 70 μm. Therefore, it has been difficult to determine the properties of piezoelectric films by measuring changes in thickness.

An object of the present invention is to provide a method and apparatus for accurately measuring the thickness of very thin samples.

The purpose of this is to arrange the sample at the center of a parallel plate according to the present invention, and calculate the thickness of the sample as the sum of the reciprocals of the capacitance of two sets of electrodes placed symmetrically to the center of the parallel plate and facing each other. This is achieved by measuring the

Reference is made to FIG. 7, which provides a detailed description of the invention with reference to the accompanying drawings. The sample 7 is sandwiched between two parallel plates 5.6 having electrodes 1.2.8.4 of the same area on both ends, and the parallel plates 5.6 are arranged one above the other with the electrodes facing each other. The distance between electrodes 1.2 is dl, and the distance between electrodes 8.4 is d2.
Letting the thickness of the electrode 8.4 be d, the capacitance C2 of the electrode 8.4 can be calculated as follows.

See Figure 2. Electrostatic capacitance ic of electrodes 1 and 2.

A first arithmetic circuit 9 whose feedback element includes the capacitance C2 of the electrode 8.4 and a first arithmetic circuit 10 whose feedback element includes the capacitance C2 of the electrode 8.4 are connected to the oscillation circuit 8. First and first arithmetic circuits 9, l
An adder circuit 11 is connected to the output of O, and the sum of the output voltages of the first and first arithmetic circuits is calculated. A phase detection circuit 12 is connected to the output of the adder circuit 1, and a reference signal whose phase is shifted by q0 degrees from the oscillation signal of the oscillation circuit 8 is applied to the phase detection circuit 12 via the phase shift circuit 21, thereby detecting the oscillation. signal and 90
The sum of the output voltages of the first and first arithmetic circuits is phase-detected at a point where the phase is shifted by a degree. This is because the feedback element of each arithmetic circuit is a capacitor, and detection is performed with a phase that matches the measurement phase of the oscillation signal.

By configuring the circuit in this way, the output voltage V of the first arithmetic circuit 9 is: v,=vo-yuπ1zuR
,C.

(Here, ■o is the output voltage of the oscillation circuit 8, f is the frequency, and R4 is the input resistance.) The output voltage ■2 of the first arithmetic circuit 10 is also proportional to A signal representing the thickness d is obtained at the output terminal 1B.

See Figure 3. Components that are the same as those in the circuit of FIG. 2 are designated by the same reference numerals, and since the portions consisting of these components operate in the same manner as the circuit of FIG. 2, their explanation will be omitted. While the circuit shown in Figure Ω is for measuring the thickness of the sample, the circuit shown in Figure 3 is for measuring the change in thickness of the sample and the thickness of the sample. As shown in the figure, an integrating circuit 14 and a sample/hold circuit 15 are connected to the output of the phase detection circuit 12. A third arithmetic circuit 1 having the same configuration as the seventh or first arithmetic circuit is provided between the oscillation circuit 8 and the addition circuit 11.
8 is also connected to the inverting multiplier circuit 19, and the output of the sample-and-hold circuit 15 is connected to the inverting circuit 19 to adjust the gain of the inverting multiplier circuit 19.

With this configuration, in order to apply, for example, a sinusoidal stress to the sample and measure its thickness change, the sample/hold circuit 15 causes the integration circuit 14 to integrate the output of the phase detection circuit 12 at the period of the stress change. . A signal representing the integral value of .

This results in a value obtained by subtracting a signal corresponding to the sample thickness (average thickness) from the output signals of the first and first arithmetic circuits corresponding to the instantaneous value of the sample thickness, that is, a signal representing the change in the sample thickness. is obtained at the first output terminal 20. Further, a signal corresponding to the thickness of the sample is obtained at the a-th output terminal 16.

That is, the integrating circuit 14 and the sample/hold circuit 15
, the third arithmetic circuit 18 and the inverting multiplier circuit 19 constitute a negative feedback system, and due to the negative feedback effect, in a steady state, the sample/hold circuit continues to send a signal corresponding to the sample thickness to the inverting multiplier circuit 19. In addition, as a result, the output of the phase detection circuit 12 only corresponds to the change in the thickness of the sample.

To measure the characteristics of a piezoelectric element as a sample, a sample electrode (not shown) is provided at the center of two parallel plates 5 and 6, the piezoelectric element is sandwiched between the two, and a sinusoidal voltage is applied to this to measure the thickness. What is necessary is to apply a stress that changes sinusoidally in the direction.

[Brief explanation of the drawing]

Claims (1)

[Claims] ■ A sample is placed at the center of two parallel plates, and the above value is calculated as the sum of the reciprocals of the capacitances of two sets of electrodes placed opposite each other at symmetrical positions about the center of the parallel plates. A method for measuring the thickness of a sample that uses the measurement of the thickness of the sample as a percentage. (Seventh and first arithmetic circuits each including two sets of electrodes placed symmetrically to the left of the center of 21 parallel plates in the feedback element and connected to the oscillation circuit; first and second arithmetic circuits) An adder circuit connected to the output of the circuit and calculates the sum of the output voltages of these arithmetic circuits; connected to the output of this adder circuit, the output signal of the adder circuit is connected to the oscillation signal from the oscillation circuit and has a phase difference of 9θ degrees. A sample thickness measuring device comprising a circuit for phase detection using different reference signals and generating a signal proportional to the thickness of the sample at the center of the parallel plates at the output of the phase detection circuit. First and first arithmetic circuits each including two sets of electrodes arranged symmetrically around the center of the parallel plate in the feedback element and connected to the oscillation circuit; connected to the outputs of the first and first arithmetic circuits; An adder circuit that calculates the sum of the output voltages of these arithmetic circuits; connected to the output of this adder circuit, the output signal of the adder circuit is phased with a reference signal that has a phase difference of 9θ degrees from the oscillation signal from the oscillation circuit. a detection circuit; and a negative feedback circuit connected between the output of this phase detection circuit and the input of the addition circuit, and this negative feedback circuit includes an integration circuit connected to the phase detection circuit; A sample and hold circuit connected to the circuit, a third arithmetic circuit including a capacitor as a feedback element and connected to the oscillation circuit, and an inverting circuit connected to the third arithmetic circuit and the input of the adder circuit. a type multiplier circuit, the inverting type multiplier circuit being connected to the sample and hold circuit, and generating a signal proportional to the thickness change of the sample at the center of the parallel plate at the output of the phase detection circuit. A sample thickness measuring device that uses this as a percentage.