JPH09145344A - Measuring method for film thickness - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a measuring method which can deal with a measuring area in a wide range and in which a measurement can be performed in a short time by a method wherein characteristic X-rays are grasped in advance by using a material having a known film thickness and they are compared with characteristic X-rays in a material having an unknown film thickness. SOLUTION: First, secondary electrons which are emitted at a time when an electron beam is radiated from an electron gun 3 at an SEM (scanning electron microcope) 1 are detected by a secondary-electron detector 7, characteristic X-rays are detected by an X-ray detector 8 and the kind and the amount of every component are measured. In the SEM 1, the electron beam penetrates down to a depth of several μm from the surface of a material. As a result, the characteristic X-rays which are detected by the detector 8 contain information on a part down to the depth of several μm from the surface. Then, a material whose plated thickness is known in advance is used as a standard material, the detection result of the secondary electrons from the SEM 1 and that of the characteristic X-rays are analyzed quantitatively, and a working curve is created on the basis of them. When a material, to be measured, whose plated thickness is unknown is analyzed qualitatively and quantitatively on the basis of them, the plated thickness of the material to be measured can be computed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film thickness measuring method for measuring the thickness of a film such as plating.

[0002]

2. Description of the Related Art The following four methods and devices are known for measuring the film thickness, for example, the plating thickness. (1) The cross section of the plated material is observed with a microscope or an electron microscope, and after taking a photograph, the plating thickness is measured using a scale or the like (or, it is measured using the length measuring scale of the eyepiece lens). (2) The plating thickness is measured using a fluorescent X-ray film thickness meter. (3) Using a plating device, set the polarity opposite to that used during plating,
The plating thickness is calculated from the amount of electricity per unit area until the plating is electrically peeled (electrolysis) and completely peeled. (4) The plating thickness is measured by using an emission spectroscopy analyzer (spark discharge, glow discharge, etc.).

[0003]

However, in the above-mentioned prior art, in the case of the method (1), it is necessary to clarify the boundary between the plating material and the base material in the cross section, and therefore the following is enumerated. It has such a problem. Precise polishing and etching are required, and it takes time to prepare for measurement. In order to accurately measure the plating thickness, it is necessary to cut at 90 ° to the plating surface and further polish, but this is a very difficult work in reality. Since the plating thickness measurement from the cross section is a measurement of a very small part of the material, it is not possible to evaluate the entire material. Also, if the number of cut surfaces is increased in order to evaluate the entire material, a huge amount of time is required.

Further, the method (2) has the following problems. Since the fluorescent X-ray film thickness meter uses an X-ray tube, it causes leakage of X-rays and the like, and there is a problem in safety. Since the area for measuring the plating thickness is fixed, it is difficult to measure with a minute plating material.

The method (3) has the following problems. It is difficult to accurately determine the total amount of electricity required to completely electrolyze only the plated material. There are many fluctuation factors such as the temperature, component concentration, and current of the electrolyte, and it is difficult to keep these conditions constant.
Poor reproducibility. In order to perform good measurement, a sufficient area (usually several cm × several cm or more) is required, and the plating thickness of a minute material or a minute portion cannot be measured. Since the electrolytic solution contains chemicals, the problem is how to treat it. It takes time to completely electrolyze the plated material,
Can't measure quickly.

Further, the method (4) has the following problems. It is difficult to emit light with a flat material. The plating thickness is calculated based on the time when the light emission intensity of the plating material becomes zero, but when the plating thickness is thin, the intensity becomes zero in a very short time, and sufficient accuracy cannot be obtained. Since the area of the light emitting surface is fixed, minute objects cannot be measured. It is necessary to maintain the airtightness of the light emitting part, and only flat objects can be measured.

As described above, each of the conventional film thickness measuring methods has a plurality of problems to be solved, and in particular, the problems remain in terms of quickness and measurement area. Therefore, an object of the present invention is to provide a film thickness measuring method capable of supporting a wide range of measurement areas and capable of measuring in a short time.

[0008]

In order to achieve the above-mentioned object, the present invention uses a SEM and a component analyzer to grasp a characteristic X-ray by using a material whose film thickness is known in advance. The film thickness of the unknown material is calculated by comparing with the characteristic X-ray of the material of which the film thickness is unknown.

As described above, since the measurement is performed by comparing the measured data which is grasped in advance and the data when the material to be measured is measured, there is no need for the prior processing as in the prior art, and the cross section is not used for the measurement. Because there is no restriction on the measurement area,
Measurement time does not increase. Conventionally, in the electrolysis method, it is necessary to accurately determine the total amount of electricity, and a sufficient measurement area is also required.
Although it was easily affected by the surrounding environment, it is reproducible because it is compared with the reference value in the present invention. As described above, according to the present invention, the measurement can be performed in a short time, the measurement area can be applied from a minute area to a relatively wide area, and the measurement target of the material can be widened.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a reference material having a known film thickness value is observed with a scanning electron microscope, and characteristic X-rays generated from the material at that time are analyzed by a component analyzer, and The result is used as a reference, and this reference is compared with the result of analyzing the characteristic X-rays for another material to be measured by the component analyzer to calculate the film thickness of the material to be measured.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. The present invention uses an SEM (scanning electron microscope) for observing the surface of a plated material. The SEM detects secondary electrons emitted when a material is irradiated with an electron beam and displays it as an image on a monitor, and can be used in a magnification range of several tens to several tens of thousands. Further, in the present invention, EDX and WDX are used in combination with SEM,
We conduct component analysis (qualitative and quantitative) of materials. SEM
Includes, for example, a model “JSM-5” manufactured by JEOL Ltd.
300 ", and a model" JED-2001 "manufactured by JEOL Ltd. can be used for EDX.

FIG. 1 shows a schematic configuration of a measuring system for realizing the method of the present invention. A sample (material to be measured) 2 is installed at a measuring position of an SEM 1, and the sample 2 is set at an arbitrary angle by a table (not shown). Can be set. SEM1
Is provided with an electron gun 3, a focusing lens 4, a deflection coil 5, an objective lens 6 and the like, a secondary electron detector 7, a sample fine movement mechanism (not shown), a diaphragm mechanism and the like. Furthermore,
An X-ray detector 8 is provided for detecting characteristic X-rays (X-rays having an energy and a wavelength peculiar to each element) emitted together with the secondary electrons. An analyzer 9 (EDX, WDX, etc.) is connected to the X-ray detector 8.

The SEM 1 includes an electron gun 3 as shown in FIG.
An electron (secondary electron) different from the incident electron can be repelled from the portion hit by the electron from. Then, the size of the secondary electrons is detected while scanning the incident electrons at a constant speed, and the signal is displayed as bright and dark on the cathode ray tube. The proportion of secondary electrons emitted varies depending on the incident angle of the substance and the electron beam with respect to the substance, if the energy of the incident electrons is constant. As shown in FIG. 2, the larger the angle θ,
The distance (r cos θ) until the secondary electrons generated inside escape from the surface of the substance becomes short.

Therefore, the proportion of secondary electrons emitted is 1 /
Since it increases in proportion to cos θ, that is, the larger θ, the unevenness on the surface of the sample 2 can be observed as a change in brightness. In particular, when the inclined surface 2a of the sample 2 faces the secondary electron detector 7, the secondary electron collection efficiency is highest, and the sample 2 is irradiated with light from the position of the secondary electron detector 7.
You can get the same stereoscopic image as you see. Therefore, it is favorably used for evaluating the shape and crystallinity of semiconductors.

In the present invention, when a substance is irradiated with an electron beam, X-rays emitted together with secondary electrons are used. The emitted X-rays are characteristic X-rays peculiar to the elements contained in the substance, and have the energy and quantity. The method of the present invention utilizing this characteristic X-ray will be described below.

First, secondary electrons emitted when an electron beam is emitted from the electron gun 3 of the SEM 1 are detected by the secondary electron detector 7, and characteristic X-rays are detected by the X-ray detector 8. Determine the type and amount of each component. In the SEM 1, an electron beam generally penetrates from the surface of the material to a depth (thickness direction) of several μm. Therefore, the characteristic X-ray detected by the X-ray detector 8 must include information up to a depth of several μm from the surface. become. When the alloy material is quantitatively analyzed by the analyzer 9, the amount of each component is always a constant value if the alloy material is uniform. However, when quantitatively analyzing a material obtained by plating a certain base material with a different element, it is found that the amount of the plating material is large in proportion to the plating thickness in the range where the plating thickness is thinner than the penetration depth of the electron beam. I mean.

In the present invention, attention is paid to this point, and a material having a known plating thickness is used as a standard material. The detection results of the secondary electrons and the characteristic X-rays from the SEM 1 are quantitatively analyzed by the analyzer 9, and a calibration curve is created based on this. Based on this, if the qualitative analysis and the quantitative analysis of the material of which the plating thickness is unknown (the material to be measured) are performed, the plating thickness of the material to be measured can be calculated. That is, it is possible to know the plating thickness of the material to be measured with reference to the standard material for comparison.

FIG. 3 is a characteristic diagram showing the relationship between the quantitative analysis value and the film thickness by the film thickness measuring method of the present invention. The material to be measured is
The surface of the copper material was plated with chromium, and an electron beam with an accelerating voltage of 20 KV was irradiated from the SEM.
As a result, a proportional relationship with the quantitative value was confirmed up to a plating thickness of about 1.5 μm. Since the penetration depth of the electron beam from the material surface is proportional to the acceleration voltage, the measurable range of the plating thickness can be expanded by further increasing the acceleration voltage.
However, in a normal SEM, the maximum voltage is about 50 KV, so the upper limit is about 5 μm in plating thickness.

According to the present invention, by using the SEM, it is possible to measure almost any area within a range of several μm square to several mm square, and it is possible to measure with an extremely small area. On the other hand, in the conventional technique using the fluorescent X-ray film thickness meter, several steps in the range of about 0.1 mmφ to 3 × 4 mm square, and in the range of several cm square to tens of cm square in the electrolysis method. Yes, some area is required.

In the case of the method of the present invention, the measuring time can be about 1 minute. On the other hand, in the conventional technique of observing the cross section of the material with a microscope or an electron microscope, it is about 1
It takes time and about 20 minutes by the electrolysis method. Thus, according to the present invention, the film thickness can be measured in an extremely short time.

(Second Embodiment) The method according to the present invention is SE
Instead of M, a sputtering device can also be used. That is, by combining a sputter device and an analyzer (EDX or WDX), component analysis is performed while sputtering the material to be measured at high speed, and when the type of the detected element changes (the plating material is completely sputtered on the material to be measured). At the point of time), the sputtering depth is set to the plating thickness. As a result, the film thickness measurement in sputtering can be performed in the process of forming the sputter without a separate process, and the productivity can be improved. In the above description, plating was used as an example of the film, but the present invention is not limited to plating and can be applied to any film.

[0022]

As described above, according to the present invention, a reference material having a known film thickness value is observed by a scanning electron microscope,
At that time, the characteristic X-ray generated from the material is analyzed by a component analyzer, and this result is used as a reference, and this reference is compared with the result of analyzing the characteristic X-ray for another material to be measured by the component analyzer. Since the film thickness of the material to be measured is calculated, the measurement can be performed in a short time, the measurement area can be applied from a very small area to a relatively wide area, and the measurement object of the material can be widened.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a measurement system that realizes the method of the present invention.

2 is an explanatory diagram showing a state of secondary electron emission by the SEM of FIG. 1. FIG.

FIG. 3 is a characteristic diagram showing a relationship between a quantitative analysis value and a film thickness by the film thickness measuring method of the present invention.

[Explanation of symbols]

 1 SEM 2 sample 7 secondary electron detector 8 X-ray detector 10 analyzer

Claims (1)

[Claims] 1. A reference material having a known film thickness value is observed by a scanning electron microscope, characteristic X-rays generated from the material at that time are analyzed by a component analyzer, and the result is used as a reference. A method of measuring a film thickness, which comprises calculating a film thickness of the material to be measured by comparing a standard X-ray with respect to another material to be measured with a component analyzer.