JPH0612320B2 - Device and method for evaluating mechanical properties of thin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to an apparatus and an evaluation method for evaluating mechanical properties of a thin film formed on a substrate in terms of structure and functionality.

(Prior Art) Conventionally, when the characteristics of a thin film formed on a substrate are numerically processed, only the adhesion between the substrate and the thin film has been measured. In such a case, the substrate is moved while applying a load-bearing indenter on the thin film formed on the substrate, and the load is sequentially increased during this process until the thin film is peeled off, which occurs when the thin film is peeled off. AE sensor detects acoustic emission (hereinafter referred to as AE). Then, the load value of the indenter when AE started to be generated was detected as a critical load value by the load cell, and at the same time, the scratch relationship was recorded by the XY recorder using the scratch tester that records the load relationship between the detected load and the AE strength. The critical force of the thin film is detected to measure the adhesion between the substrate and the thin film.

Here, AE refers to the phenomenon that elastic waves are generated when strain energy is momentarily released due to structural changes in the solid, and the AE sensor is a conversion element that converts elastic waves of 100 KHz to 5 MHz into electric signals. Say.

Since the mechanical properties of a thin film are greatly affected by the internal stress of the thin film, the internal stress in the thin film must be determined separately by measuring the lattice strain by the X-ray diffraction method or measuring the amount of deformation of the deposited substrate. Was also done.

(Problems to be solved by the invention) Recently, in various fields including electronic devices, for example, by using means such as ion plating, vapor deposition, and sputtering, a different material is formed on a material such as metal, ceramics, and plastics. Has been taken to further improve the electrical, mechanical and chemical properties of the material.

However, as a means to know the characteristics of the thin film formed on the substrate, the critical load by detecting thin film damage under load by a scratch tester as a means for evaluating the adhesion between the substrate and the thin film I only relied on the value.

For this reason, several factors such as the crystal morphology of the thin film, the distribution state of the internal stress of the thin film, and the strength are detected until they overlap,
It is known that the shape of the AE curve, that is, the size and the number of peaks of the AE curve fluctuate greatly depending on the change of the thin film to be measured.However, we wondered how the shape of this AE curve relates to the characteristics of the thin film material. It is impossible to know, and in view of the mechanical properties possessed by the thin film, the emergence of means for numerically clarifying this has been strongly desired by the industry.

Further, the measurement of the internal stress by X-ray has a huge time required for the measurement and the man-hour, and the measured value itself has a high degree of variability.

The internal stress measurement by X-ray diffraction is basically to obtain the internal stress by measuring the lattice strain of the crystal. For example, in the case of a polycrystal, four X-ray incident angles are taken and After the change of the lattice constant in the direction is obtained, the stress parallel to the substrate is obtained.

In addition, in the case of a film having a strong orientation, the plane distance between planes parallel to the substrate is obtained by X-rays, and the stress parallel to the substrate is obtained by the following formula: σ = E / 2ν × (d ₀ −d) / d ₀ .

However, E: Young's modulus, ν: Poisson's ratio, d: Measured interplanar spacing, d ₀ : Interplanar spacing in the absence of stress. It has been said that the above-mentioned problems and the lack of quickness of work are problems, and that the reproducibility of data is poor.

In addition, when measuring the internal stress of a material, there is a method to obtain these from the amount of deformation of the substrate, but in the case of a thin film, the amount of deformation is extremely small, and even if a special device is used, a high degree of skill of the measurer is required. However, the solution of these problems was required.

(Means for Solving the Problems) The present invention analyzes an AE signal obtained by a scratch tester for measuring a critical load value by a spectrum analyzer connected to the scratch tester via an AD converter. Then, the analyzed data is transferred to a computer through an interface, and the calculation, aggregation, search, and collation tasks are performed inside the computer so that the mechanical characteristics of the thin film can be grasped to solve the problem. It is something that is measured.

In order to investigate the AE waveform, the inventors observed the signal obtained from the AE sensor with an oscilloscope, and it was detected that elastic waves frequently occurred when the load of the indenter exceeded the critical load value of the adhesion force of the thin film. While proceeding with the experiment focusing on that, as shown in FIGS. 2 (a) and 2 (b), the AE curves of (a)
It was found that the magnitude of the elastic wave shown in the graph of (b) and the number of occurrences of the elastic wave are drawn. Moreover, since the elastic wave is generated by the strain energy released when the thin film is peeled off and the film is broken, it can be known that the shape of the AE curve greatly depends on the characteristics of the thin film.
In the figure, Lc is the load at which the AE signal rises sharply, and Vb is the bias voltage.

Next, use an optical microscope to examine the peeled portion of the thin film that generated the elastic wave.
As a result of observing at 100 times and measuring the length of the crack, as a result of finding that the relationship between the amplitude of the elastic wave and the size of the crack is proportional as shown in FIG. Is.

Next, an example of a schematic view of the device of the present invention is shown in FIG. In the figure, a resonance type or broadband type AE sensor 6 is attached to the upper part of the indenter 3. The AE sensor 6 is a BNC code AE.
The AE signal connected to the amplifier 9 and detected by the AE sensor 6 is
It is amplified by the AE amplifier 9. This amplified AE signal is sent to a waveform analyzer such as a spectrum analyzer 11, and the number of generated elastic wave amplitudes is measured and analyzed. Spectrum analyzer
The AE signal analyzed in 11 is transferred to the computer 13 as binarized data via the interface 12, and the number of elastic waves generated, the amplitude distribution state of the elastic waves, and the sum of the elastic wave amplitudes generated during the measurement. Is calculated by calculation by the computer 13 and stored in some cases.

Next, the operation example will be described. After fixing the thin film sample 2 to the stage 1, loosen the scratch head height fixing lever 4 so that the tip of the indenter 3 is about 2 mm above the sample surface. Adjust with the adjuster 5, and tighten the scratch head height fixing lever 4 firmly again.

Then, when the measurement is started, the indenter 3 descends until it comes into contact with the sample surface. Thereafter, a load is sequentially applied to the indenter 3 at a rate of 100 N / min, the stage 1 to which the sample 2 is fixed is also slid laterally at a speed of 10 mm / min, and the thin film sample 2 is scratched by the indenter 3.

An AE sensor 6 is connected to the indenter 3 and detects an elastic wave generated when the thin film is separated from the substrate. AE sensor 6
The AE signal detected by is amplified by the AE amplifier 9 and
The intensity is recorded on the Y axis of the XY recorder 10.

On the other hand, the load applied to the indenter 3 is detected by the load cell 7 and is also passed through the load cell amplifier 8 to the XY recorder.
It is sent in 10 and recorded as the load value of the indenter 3 in the X-axis direction.

In this way, it is conventional that the change in the situation on the thin film is drawn by the XY recorder 10 with the AE curve as shown in FIG.

Further, a spectrum analyzer in which the AE signal amplified by the AE amplifier 9 is connected via an AD converter (not shown)
After being analyzed as the amplitude of the elastic method generated in the thin film sample 2 by 11 and transferred to the computer 13 via the interface 12, the number of elastic waves generated, the elastic wave amplitude distribution state, the measured elastic wave amplitude Calculation, totalization, etc.
Jobs such as recording, searching, and collation are performed. The AD converter may be provided in the spectrum analyzer 11 or separately.

Now, when the sum of the amplitudes of elastic waves generated in the thin film by the operation of the scratch tester is defined as the AE intensity, the propagation of cracks that occur in the thin film is suppressed when compressive internal stress is present in the thin film, and the AE intensity Is detected as a small value, it is possible to detect the internal stress possessed by the thin film by comparing the amplitudes of elastic waves.

In addition, the measurement time was Lc when the load increase rate was 100 N / min.
Since the value is almost within 100N, the actual measurement time is within 1 minute, which enables measurement in an extremely short time.

Conventionally, as a tester for evaluating the characteristics of a thin film formed on a substrate, a compressive load is increased with time by an indenter 3, and an elasticity generated when the thin film is separated from the substrate by a scratch tester that moves on the thin film. While only the means for detecting the wave and measuring the critical load value of the thin film from the XY recorder 10 was used as the thin film characteristic evaluation method, the fact that the spectrum analyzer 11 was connected in the present invention was detected by the AE sensor 6. The AE signal is processed computationally, and not only the rising part of the curve is estimated from the conventionally drawn AE curve (see Fig. 4), but also the number and intensity of AE signals are calculated. It is for detecting as a clear numerical value.

Further, the AD converter provided in front of the spectrum analyzer 11 is provided for binarizing the AE signal obtained by the scratch tester, and the interface 12 is provided in connection with the spectrum analyzer 11. Is for transferring data to the computer 13, and
By providing a binarized AE signal, it is possible to quickly perform operations such as calculation, tabulation, search, and collation based on the material stored in the computer 13 in advance.
This is for numerically displaying the strength of the thin film.

(Example) Using a thin film characteristic testing apparatus according to the present invention, a thin film having a thickness of 3 μm formed on a SUS 304 substrate by an ion plating method was used.
The procedure for measuring the characteristics of the TiN film and the results are described below.

After fixing the sample 2 to the stage 1, loosen the scratch head height fixing lever 4 and adjust the head height adjuster 5 so that the tip of the indenter 3 is about 2 mm above the surface of the sample 2, and scratch again. Firmly tighten the head height fixing lever 4. Then, when the measurement is started, the indenter 3 descends until it contacts the surface of the sample 2. In this case, the indenter 3 has 100N
The load is intermittently applied at a rate of / min and sample 2
The stage 1, which is fixed to the stage, is also moved laterally at a speed of 10 mm / min, leaving scratches on the thin film. When the load of the indenter 3 exceeds the critical load value that indicates the adhesion force of the thin film, the thin film peels. And elastic waves are generated.

These elastic waves are detected by the AE sensor 6 and
The AE signal is amplified by the AE amplifier 9 and recorded in the XY recorder 10 as the AE intensity in the Y-axis direction. In addition, the load applied to the indenter 3 is detected by the load cell 7 and then sent to the XY recorder 10 through the load cell amplifier 8 and recorded as the load value of the indenter 3 in the X-axis direction. A relational diagram of the AE intensity detected at is drawn as shown in Fig. 4.

The signal amplified by the AE amplifier 9 is analyzed by the spectrum analyzer 11 and then sent to the computer 13 via the data transfer interface 12.

The generation state of the elastic wave detected by the AE sensor 6 is finally subjected to calculation, tabulation, retrieval and verification by the computer 13 so that the required mechanical characteristics for the thin film sample 2 can be displayed.

That is, for the TiN thin film formed on the SUS 304 substrate by changing the bias voltage to 100, 200, 300, and 400 V, the AE intensity measured by the apparatus according to the present invention and the ordinary X-ray diffraction were obtained. The measured values of the obtained internal stress are shown in FIG.

In this case, ○ indicates the AE intensity, which is the sum of elastic amplitudes, and ●
The mark indicates the internal stress value of the thin film obtained by X-ray diffraction, and it has been clarified that the AE intensity and the internal stress have an inverse ratio relationship.

Similar results are also shown for the ZrN film formed on the SUS 304 substrate as shown in FIG.

As described above, it becomes possible to detect the toughness of the thin film from the magnitude of the elastic wave detected in one inspection, and the internal stress of the thin film from the AE intensity, respectively. Also for measurement, quick and accurate numerical data can be obtained with high reproducibility as compared with the case of using conventional X-rays.

(Effects of the Invention) As described in detail above, according to the present invention, it becomes possible to obtain a measurement value that is simple and highly reproducible with respect to the mechanical properties of a thin film that could not be easily grasped conventionally. The great effect on the improvement of the thin film production technology is extremely great as it contributes to many thin film utilization industries including the electronic device industry.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of an apparatus for evaluating mechanical properties of the present invention, and FIGS. 2 (a) and 2 (b) are relations with the magnitude and generation of elastic wave of AE intensity of thin film, respectively. Curve and graph showing
Fig. 3 shows the relationship between the elastic wave amplitude of the thin film and the crack length, Fig. 4 shows the relationship between the same AE intensity and load, and Fig. 5 shows Ti.
Fig. 6 shows the measurement results of bias voltage versus AE intensity in N / SUS 304 and internal stress obtained by normal X-ray diffraction. Fig. 6 shows the measurement results of AE intensity and internal stress in ZrN / SUS 304. FIG. 1 ... Stage, 2 ... Sample, 3 ... Indenter, 4 ... Fixed lever, 5 ... Adjuster, 6 ... AE sensor, 7 ... Load cell, 8 ... Load cell amplifier, 9 ... AE amplifier, Ten…
… XY recorder, 11 …… Spectrum analyzer, 12 ……
Interface, 13 ... Computer

Claims (2)

[Claims] 1. An indenter for making a polishing mark on a thin film, an AE sensor for detecting an elastic wave generated when the thin film is broken, a load cell for detecting a load applied to the thin film, and an AE
An AE amplifier for amplifying the AE signal detected by the sensor, a load cell amplifier for amplifying the load of the indenter detected by the load cell, and the AE signal and the load of the indenter in the X-axis direction and Y direction, respectively.
A scratch tester equipped with an XY recorder that records in the axial direction, and an AE detected and amplified by this scratch tester
An AD converter that binarizes the signal, a spectrum analyzer that analyzes the binarized AE signal, an interface that transfers the analyzed AE signal, and a calculated, aggregated, and searched AE signal that has been transferred. An apparatus for evaluating the mechanical properties of a thin film, which comprises a matching computer. 2. When measuring the mechanical properties of a thin film formed on a substrate, the load applied is increased while moving the substrate on which the thin film is formed by pressing an indenter on the thin film, The AE sensor detects the Accortech emission generated when the thin film is peeled from the substrate, the load cell of the indenter is detected by the load cell, and both are amplified by the amplifier and recorded by the XY recorder. AD the output data
After binarization by the converter, send it to the spectrum analyzer section, analyze this data with the spectrum analyzer, send the analyzed data to the computer through the interface, the number of elastic waves generated by the rear AE sensor, An evaluation method for evaluating the mechanical properties of a thin film, characterized in that the mechanical properties of the thin film formed on the substrate are evaluated by obtaining the amplitude degree and the total value of the amplitudes.