JPS60120204A - Thickness measuring method - Google Patents

Abstract

PURPOSE:To measure the thickness in a sample in submicrons, by measuring the degree of attenuation in reflected wave, which is leaked and yielded from an elastic surface wave, which is propagated on the surface of the sample. CONSTITUTION:The ultrasonic wave generated by a piezoelectric transducer 2 is converged and projected on a sample 5 through a liquid coupler 4, which is filled between an acoustic lens 3 and the sample 5. The reflected wave from the sample 5 is returned to the piezoelectric transducer 2 and converted into an electric signal proportional to the amplitude of the reflected wave. The signal is sent to a receiver 8 through a circulator 1. The signal, which is sent to the receiver 8, is imparted to a gate circuit 9, where only the desired leaked elastic surface wave is extracted and sent to a computer 13 through a peak detector 10, an A/D converter 11, and an interface 12. The thickness of the sample 5 is computer by the computer 13.

Description

Detailed Description of the Invention: A piezoelectric transducer converts reflected waves that are incident near a critical angle and leak from the surface acoustic wave propagating on the sample surface due to its energy into electrical signals, and the electrical signals are used to determine the thickness of the sample. This invention relates to a thickness measurement method using focused ultrasound that takes advantage of this relationship.

When ultrasonic waves generated from a piezoelectric transducer are focused and irradiated onto a sample using an acoustic lens, the energy of the incident waves excites surface acoustic waves on the surface of the sample when the incident angle of the ultrasonic waves is near Rayleigh's critical angle (θC). be done. The excited surface acoustic waves leak, generate reflected waves that are secondary radiated into the coupler (medium), are refracted by the acoustic lens at Rayleigh's critical angle, and return to the piezoelectric transducer as reflected electrical signals. Zeng is output.

That is, the reflected wave of this leaky surface acoustic wave is converted by the piezoelectric transducer into an electric signal proportional to the amplitude of the reflector. This electric signal is sent to a signal processing system, and in the signal processing, a gate circuit is provided only in that part in order to obtain a reflected signal of only the leaky surface acoustic waves. The peak value of the obtained surface acoustic wave signal is held and output as an output voltage.

The output voltage is digitized by an A-D converter and input into a co/beater via a parallel interface, which is a repeater.

Conventional thickness measurement methods using ultrasonic waves include the resonance method, in which ultrasonic waves are irradiated onto the sample to cause resonance in the sample, and this is detected, and the thickness of the sample is measured. There was a pulse reflection method that measures the thickness of a sample using the time difference between the signal of the reflected wave from the surface of the sample and the signal of the reflected wave from the surface of the substrate on which the sample is placed. However, both measurement methods have the disadvantage that they can only be used with thick samples. In addition, there is a method for measuring the film thickness of thin metal plating with a sample thickness of several microns, which uses fluorescent X-rays.
This method is difficult from a practical point of view because there is a risk that the X-rays may have an adverse effect on the human body during measurement, and the sample part must be sealed during measurement. The present invention takes the above-mentioned background into consideration and is a measuring method that allows the thickness of a sample to be measured in submicron units.

The measurement principle of the present invention will be explained in detail using figures.

An electric pulse signal with a frequency of about 10 to 500 MHz, for example, generated by the high-frequency pulse generator (7) is applied to the piezoelectric transducer (2) above the acoustic lens (3) via the circulator fi+. The piezoelectric transducer (2) is made of polyvinylidene fluoride (PV), for example.
This is a polymer piezoelectric element vibrator using F2). Since this vibrator easily generates longitudinal waves and hardly generates transverse waves, multiple reflections at the acoustic lens are less likely to occur, making it easier to obtain the desired leaky surface acoustic waves. This vibrator converts the high-frequency electric pulse momme signal into a super loud sound. Piezoelectric transducer (2
) is a plane wave within the acoustic lens (3) made of sapphire (A1203) or the like, but the ultrasonic wave is converted into a spherical wave in the spherical recess (3a) of the acoustic lens (3). Ultrasonic waves are transmitted between the acoustic lens (3) and the sample (
5) a liquid coupler (medium e.g. water) filled between
4), the sample (5) is focused and irradiated. In addition,
In the figure, (6) is a substrate on which the sample (5) is laminated.

The reflected wave from the sample +51 passes through the same path in the opposite direction and returns to the piezoelectric transducer (2), where it is converted into an electrical signal proportional to the amplitude of the 00 reflected wave, and is converted into an electrical signal proportional to the amplitude of the 00 reflected wave.
The signal is then sent to a receiver (8) having a high frequency band. The signal sent to the receiver (8) is sent to the gate circuit (9)
Only the target leaky surface acoustic wave is extracted, and the peak value of the signal is held by the peak detector α, and a signal with a peak value is output. peak detector 0
The signal of the peak value of the leaky surface acoustic wave outputted by Q0) goes up the A/D converter α, where the analog signal is converted into a digital signal, and the signal is then transferred to the computer via the interface Q2), which is a repeater. α3).

To further explain the reflected waves according to Figure 2 showing the measurement state, when the focal point of the incident focused ultrasonic wave is located below the sample (5), the reflected waves are incident perpendicularly to the surface of the sample (5). Two types of reflected waves are generated: a direct reflected wave of the ultrasonic wave (81) and a reflected wave generated from a leaky surface acoustic wave (g) excited by the incident energy.Reflected signals of these two types of reflected waves is obtained as an output voltage and sent to a receiver (8) having a wide band.Among the reflected signals that have passed through the receiver (8), only leaked surface acoustic waves are extracted by the filtering action of a gate circuit (91), and a peak detector The peak-held reflected signal is converted from an analog signal to a digital signal by a converter aυ, and then sent to an interface (12+
is sent to the computer α3 via the medium and processed.

Leaky surface acoustic wave (L) excited by incident energy
The sample (5) is propagated through the substrate (6) on which the sample is loaded.
), it passes through the liquid coupler (4), becomes a plane wave through the acoustic lens (3), and is transmitted to the piezoelectric transducer (2).
is converted into an electrical signal by This leaky surface acoustic wave (
g) is the sample (5) and the substrate (6) on which the sample is laminated.
Attenuates as it propagates. −Leaky elastic surface wave peak)
As the sample (5) becomes thicker, the propagation distance becomes longer, the energy decreases, and the attenuation increases. Therefore, the intensity of the reflected signal of the leaky surface acoustic wave (L+) changes as the thickness of the sample (5) changes.

In other words, the reflected signal of the leaky elastic surface wave peak) is
) is correlated with the thickness of the

Next, actual thickness measurement will be explained. A reference sample piece with a known thickness is prepared, and the reference sample piece is measured according to the method described above. The peak value of the output voltage of the leaky surface acoustic wave is measured for each thickness of the reference sample piece, input into the computer, data processed, and stored as a calibration value.

As already clear, a sample of unknown thickness can be similarly measured and the thickness of the sample can be determined according to the calibrated value.

The thickness measuring method using ultrasound according to the present invention is as described above, and according to the present invention, unlike X-rays, ultrasound
It is practical because it does not have any adverse effects on the human body. Furthermore, since there is no need to seal the sample part during measurement, thickness measurement using focused ultrasound allows automated online measurement, is efficient in terms of operability, and is easy to measure. It's a method.

Furthermore, by scanning the sample surface using a scan converter and sending the data to a computer via the GP-IB interface for data processing, thickness can be measured over a wide range. In this way, the thickness measurement method using focused ultrasound enables measurements that cannot be made with conventional measurement methods, is a safe measurement method, and has good operability (
This is an industrially significant method.

A specific example of the thickness measuring method of the present invention will be described below.

〔Concrete example〕

An electric signal with a frequency of 50 MHz generated by a pulse generator is transmitted through a circulator to an ultrasonic wave with a frequency of 50 MHz by a piezoelectric transducer whose vibrator is made of polyfluorinated vinyl IJ and has gold foil electrodes on both sides. converted into vibration. A focused ultrasonic wave with a focal length of about 5 words was emitted into the medium (water) using an acoustic lens made of sapphire. A sample on which a gold-plated layer was formed on a substrate (42% alloy, 42% Sokel, balance iron) was placed at a position 4 points from the lower end of the acoustic lens.

Under these measurement conditions, only the reflected signal of the surface acoustic wave is extracted by an ultrasonic analyzer equipped with a receiver, a gate circuit, and a peak detector shown in Fig. 2, and converted into a digital signal by a 12-bit non-Φ converter. The information was input to a computer via a GP-IB type interface.

The thickness of the gold-plated layer of the sample was measured by comparing it with a calibration value stored in the Bonpieux beforehand.

Measurements were well within the range of 0.6 to 10 microns in this example.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an apparatus used in the thickness measuring method using focused ultrasound according to the present invention, and FIG. 2 is a schematic explanatory diagram showing a measurement state. (11...Circulator (21...Piezoelectric transducer (3)...Acoustic lens (4)...Coupler (5)...Sample (6)...Substrate (7)... Pulse generator +81...Receiver (9)
...Gate circuit 00] ...Peak detector Ql
)...A/Di converter (12+...Interface 03)...Computer patent applicant Toppan Printing Co., Ltd. Figure 1

Claims (1)

[Claims] +I+ Ultrasonic elastic waves generated from a piezoelectric transducer are focused and irradiated onto a sample using an acoustic lens, and are incident on the sample at a critical angle. The degree of attenuation of reflected waves that leak from the surface acoustic waves that propagate on the sample surface due to the incident energy. A thickness measuring method characterized in that the thickness of the sample is determined based on the fact that the thickness of the sample has a correlation with the thickness of the sample.