JPH10221047A - Fluorescent x-ray film thickness analyzer and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a thickness over a wide range to be measured highly accurately. SOLUTION: In the fluorescent X-ray film thickness analyzer for placing a standard sample plate 10 whose thickness and composition ratio are known on a rear of a film 9 to be measured and radiating X-rays from an X-ray bulb 1 to detect fluorpscent X-rays generated from the standard sample plate 10 for measuring a thickness of the film 9 when an infinite thickness can be determined or cannot be determined, a mixture standard sample plate comprising a plurality of elements generating, characteristic X-rays of different energy is used as the standard sample plate 10. Among the fluorescent X-rays generated from the mixture standard sample plate, a ray whose intensity drops into a predetermined range due to absorption by the film 9 is selected as an analysis ray, and the thickness of the film 9 is obtained based on intensity of the analysis ray.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating X-rays by placing a standard sample plate having a known thickness and composition ratio on the back side of a film to be measured, if the thickness can be regarded as infinite or not. And a method for detecting a fluorescent X-ray generated from a standard sample plate and a film to be measured to measure the film thickness.

[0002]

2. Description of the Related Art Film thickness analysis using fluorescent X-rays is widely used for film thickness measurement and composition analysis of plating, evaporated films, sputtered films, CVD films, and the like. In recent years, an energy dispersive X-ray fluorescence spectrometer (EDXRF) that can analyze from carbon has been marketed, but the analysis elements used for calculating the film thickness are mainly relatively heavy elements and have a light composition. It is rarely used for a film to be measured (sample) such as a polymer film made of an element or paper.

In order to measure the film thickness, a method of comparing the characteristic line intensity generated from a standard sample plate having a known film thickness and composition with the characteristic line intensity of the elements constituting the sample is described. There are a method of obtaining from a transmission loss of a line, a method of obtaining from a scattered radiation intensity from a sample, and the like. When measuring the film thickness from the excitation line intensity ratio of the elements that make up the sample, the absorption loss of the excitation line is large, so the sample must be extremely thin to be considered a thin film. And irradiation X
The film thickness of a sample whose composition is made of a light element because it was difficult to respond to a wide range of sample thicknesses because the interaction with the line was small and accuracy was not achieved unless the sample was extremely thick. X-ray fluorescence analysis was not employed for the measurement. Therefore, transmission loss has conventionally been measured using β-rays from a radiation source, but a measurement method that does not use radiation has been required due to management problems.

FIG. 5 is a view for explaining a conventional fluorescent X-ray film thickness analyzer, and FIG. 6 is a view showing the relationship between the intensity of fluorine K-rays and the film thickness in tetrafluoroethylene-ethylene copolymer (ETFE). It is.

[0005] In the fluorescent X-ray film thickness analyzer, as shown in FIG. 5, X-rays (primary X-rays) are emitted from an X-ray tube 21 and applied to a film 22 to be measured on a base 23 having an infinite thickness. , Measured film 2
2 and fluorescent X-rays a and b generated from the base 23 are detected by the detector 2
4 and is converted into an electric signal. Then, the fluorescent X-rays are amplified by a filter amplifier, the S / N ratio is improved, AD-converted, and taken into a computer. The composition and thickness of the film 22 to be measured can be known by measuring the energy and the amount of the fluorescent X-rays detected here. For example, FIG. 6 shows the relationship between the K-line intensity and the film thickness when the film 22 to be measured is a fluororesin, and the vertical axis indicates FP (Fu
It is the intensity ratio between the theoretical intensity obtained by the ndamental parameter) method calculation and the standard sample fluorine which can be regarded as infinite thickness. From this relationship, it can be seen that conventionally, only a film thickness of 3 μm or less can be measured, and the range of the film thickness that can be measured is not wide.

[0006]

As is clear from the relationship shown in FIG. 6, the relationship between the X-ray intensity generated from the film to be measured and the film thickness is such that the linearity becomes worse as the film thickness increases, The calculation cannot be performed in the portion where the curve is curved due to the statistical fluctuation of the line intensity. In the case of a method in which a metal plate or the like is placed on the back surface of the film to be measured and the film thickness is determined from the amount of X-ray fluorescence generated from the metal plate, the amount of X-ray absorption decreases as the film thickness decreases. Worsens. Therefore, the width over which the film thickness can be accurately measured is narrow in any of the methods. As described above, when the characteristic X-ray of the element contained in the film to be measured is used as the decomposition line, the measurable film thickness is determined by the characteristic line energy, and the range is narrow.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is intended to measure a wide range of film thickness with high accuracy.

Therefore, the present invention can be regarded as an infinite thickness,
Alternatively, if the thickness cannot be regarded as infinite, place a standard sample plate with a known thickness and composition ratio on the back side of the film to be measured, irradiate X-rays, detect fluorescent X-rays generated from the standard sample plate, and perform measurement. In the fluorescent X-ray film thickness analyzer for measuring the film thickness, a mixed standard sample plate made of a plurality of elements that generate characteristic X-rays having different energies is used as the standard sample plate, and the mixed standard sample plate is generated from the mixed standard sample plate. Of the fluorescent X-rays to be analyzed, a line whose intensity is reduced to a predetermined range by absorption by the film to be measured is selected as an analysis line, and the film thickness of the film to be measured is obtained based on the intensity of the analysis line. It is assumed that.

The predetermined range is 80 to 20%, and among the lines falling to the predetermined range, a line used for analysis is a line having the highest energy of 70% or less. If there are multiple lines that fall in the range
It is characterized in that an average value of the film thickness obtained by each line is obtained.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing an embodiment of a fluorescent X-ray film thickness analyzer according to the present invention, wherein 1 is an X-ray tube, 2 is a shutter, 3 is a filter, 4 is a primary collimator, 5 is a secondary collimator, 6 is a detector, 7 is a filter amplifier & AD converter, 8 is a computer system, 9 is a film to be measured, 10 is a mixed standard sample plate, 11 is a sample room, 12
Indicates an exhaust port.

In FIG. 1, an X-ray tube 1 generates irradiation X-rays. The X-rays are applied to a film to be measured (sample film) 9 through a shutter 2, a filter 3, and a primary collimator 4. You. On the back side of the film 9 to be measured, a mixed standard sample plate 10 whose thickness and composition ratio are known can be regarded as an infinite thickness, or when it cannot be regarded as an infinite thickness, and the film 9 and the mixed standard are mixed by X-ray irradiation. The fluorescent X-rays excited from the sample plate 10 are detected by the detector 6 through the secondary collimator 5. The fluorescent X-ray is converted into an electric signal by the detector 6, amplified by the filter amplifier & AD converter 7, and S / N is improved, and then AD-converted to the computer system 8.
It is taken in. Here, the X-ray fluorescence film thickness analyzer according to the present invention uses the mixed standard sample plate 10 that generates a spectrum dispersed in the entire measurement energy range. A line whose intensity falls within a predetermined range due to absorption by the measurement film 9 is selected, and the line is used as an analysis line to determine the film thickness.

FIG. 2 is a view showing the absorption attenuation characteristics of the film to be measured when the measurement is performed with the mixed standard sample plate placed on the back side of the film to be measured. FIG. 3 is included in the mixed standard sample plate. It is a figure showing an example of a spectrum of an element.

The mixed standard sample plate 10 is shown in FIGS.
A characteristic X-ray as shown in (E) is generated, and the amount by which the characteristic line is absorbed and attenuated by the film to be measured 9 is measured. From this characteristic, a film thickness of about 1 μm can be measured using an aluminum K line, and a film thickness of around 100 μm can be measured for a copper K line.
It can be seen that the film thickness is suitable for about the same. (F)
Indicates the relationship between the characteristic X-ray intensity of the element and fluorine in the film 9 to be measured and the film thickness. Therefore, among the characteristic X-rays generated from the mixed standard sample plate 10 placed on the back side of the film to be measured 9, the measured intensity is in a region where the linearity in the relationship between the film thickness and the X-ray intensity is good, for example, By selecting characteristic X-rays having an energy such that the intensity becomes 40% or more and 70% or less as compared to when there is no film to be measured due to absorption of the characteristic line by the film to be measured 9, the optimum according to the film thickness By selecting an appropriate analytical line, the film thickness can be calculated.

FIG. 3 shows an example of the spectrum of the elements contained in the mixed standard sample plate. The usable characteristic X-ray energy is, for example, AlKα 1.5 KeV MoKα 3.5 KeV Lα 2.3 KeV GeKα 9 9.9 KeV Lα 1.2 KeV MnKα 5.9 KeV TiKα 4.5 KeV FeKα 6.4 KeV CuKα 8.0 KeV. If the energy of the characteristic X-ray is low, such as an AlK line, it is absorbed at a small film thickness and greatly attenuated.
If the energy of the characteristic X-rays is high, it is hardly absorbed at a thin film thickness and the attenuation is small, and the attenuation occurs in a thick film region. In other words, the higher the characteristic X-ray energy, the higher the film thickness can be accommodated. By mixing these, the mixed standard sample plate 10 that generates a spectrum dispersed in the entire measurement energy range as shown in FIG. It can be applied to the film to be measured 9 having a wide range of film thickness.

FIG. 4 is a view for explaining a film thickness measuring process by the fluorescent X-ray film thickness analyzer according to the present invention. When measuring the film thickness by the fluorescent X-ray film thickness analyzer according to the present invention, the composition and density of the film are determined in advance as pretreatment. Further, the specifications of the fluorescent X-ray film thickness analyzer, ie, X
The target of the tube, the acceleration voltage, the thickness of the beryllium window,
The characteristic line shown in FIG. 2 is obtained based on the length of the path, the window material of the detector, the type of the detector, and the like. Then, the following film thickness measurement processing is executed.

First, a sample (film to be measured) is set on a mixed standard sample plate of the apparatus, and a spectrum is measured (step S11). Next, among the peaks exceeding a preset threshold value in the measured spectrum, the peak having the highest energy is designated as an analysis line (step S12).
Then, the ratio of the spectrum designated as the analysis line to the intensity of the mixed standard sample plate whose concentration is known and measured and recorded in advance is calculated (step S13). Subsequently, it is checked whether the analysis line is a characteristic X-ray from an element contained in the film to be measured or a characteristic X-ray from an element contained in the mixed standard sample plate (step S14).

In the case where the analysis line is a characteristic X-ray from an element contained in the film to be measured, the ratio between the measured spectrum intensity, the composition ratio of the film to be measured, and the spectrum intensity expected from the film thickness is set in advance. It is checked whether it is in a range, for example, 70% or less and 30% or more (step S15). If it is in the set range, the film thickness is calculated using the characteristic line, and the display is terminated (step S16).

When the analysis line is a characteristic X-ray from an element contained in the mixed standard sample plate, the ratio between the measured spectrum intensity, the composition ratio of the film to be measured, and the spectrum intensity expected from the film thickness is preset. (Step S).
17) If it is within the set range, the film thickness is calculated using the characteristic line, and the display is terminated (step S18).

In the judgment processing of steps S15 and S17, if the ratio of the measured spectrum intensity to the composition ratio of the film to be measured and the spectrum intensity expected from the film thickness is not within the preset range, the threshold value in the measured spectrum is determined. The peak having the next highest energy is designated as the analysis line among the peaks exceeding, and the process returns to step S13 (step S19).

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above-described embodiment, the example in which the mixed standard sample plate in which the composition of the elements is adjusted is placed on the back of the film to be measured is shown, but the mixed standard sample plate is generated from the substrate like a sample (film to be measured) deposited on a compound semiconductor. The same processing can be performed even when a plurality of characteristic lines are obtained as X-rays. Also, of the characteristic X-rays generated from a substance placed on the back side of the film to be measured, from the measured intensity,
The characteristic X having an energy such that the intensity is 70% or less as compared to when there is no film to be measured due to absorption of the characteristic line by the film to be measured is in a region where the linearity in the relationship between the film thickness and the X-ray intensity is good. The line was selected as the analysis line and the film thickness was calculated.
The characteristic X-rays in the range of 0% may be selected as the analysis lines, or all the characteristic X-rays in the range may be selected, and the film thickness may be obtained from the average value thereof. Further, the above range may be set for each characteristic X-ray.

[0021]

As is apparent from the above description, according to the present invention, the measured spectral intensity of the characteristic X-rays generated from the mixed standard sample plate placed on the back side of the film to be measured (sample) is measured. Since the film thickness is calculated using a characteristic line in which the ratio of the spectrum intensity expected from the composition ratio of the film to be measured and the film thickness is within a preset range, a region having good linearity in the relationship between the film thickness and the X-ray intensity is obtained. Can be used to calculate the film thickness, and the measurement accuracy of the film thickness can be improved. In addition, since a mixed standard sample plate that generates a spectrum dispersed in the entire measurement energy range is used, it is possible to cope with a film to be measured having a wide range of film thickness.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a fluorescent X-ray film thickness analyzer according to the present invention.

FIG. 2 is a diagram showing each characteristic line when a mixed standard sample plate is placed on the back side of a film to be measured and the absorption characteristic of the film to be measured is measured.

FIG. 3 is a diagram showing an example of a spectrum of an element contained in a mixed standard sample plate.

FIG. 4 is a view for explaining a film thickness measuring process by the fluorescent X-ray film thickness analyzer according to the present invention.

FIG. 5 is a view for explaining a conventional fluorescent X-ray film thickness analyzer.

FIG. 6 is a diagram showing the relationship between the fluorine K-ray intensity and the film thickness in a tetrafluoroethylene-ethylene copolymer (ETFE).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 2 ... Shutter, 3 ... Filter, 4 ... Primary collimator, 5 ... Secondary collimator, 6 ... Detector, 7 ... Filter amplifier & AD converter, 8 ... Computer system, 9 ... Film to be measured, 10: mixed standard sample plate, 11: sample chamber, 12: exhaust port

Claims (5)

[Claims] 1. If the thickness can be regarded as infinite or cannot be regarded as infinite, a standard sample plate having a known thickness and composition ratio is placed on the back side of the film to be measured, and X-rays are applied to generate a standard sample plate. X-ray film thickness analyzer for measuring the film thickness of a film to be measured by detecting fluorescent X-rays to be emitted, wherein the standard sample plate is a mixed standard sample plate comprising a plurality of elements generating characteristic X-rays having different energies Of the fluorescent X-rays generated from the mixed standard sample plate, a line whose intensity is reduced to a predetermined range due to absorption by the film to be measured is selected as an analysis line, and based on the intensity of the analysis line, An X-ray fluorescence film thickness analyzer for determining the thickness of a measurement film. 2. The X-ray fluorescence film thickness analyzer according to claim 1, wherein the predetermined range is 80 to 20%. 3. The X-ray fluorescence film thickness analysis according to claim 1, wherein a line used for analysis among the lines falling into the predetermined range is a line having the highest energy at 70% or less. apparatus. 4. The fluorescent X-ray film thickness analyzer according to claim 1, wherein when there are a plurality of lines falling in the predetermined range, an average value of the film thickness obtained by each line is obtained. 5. If the thickness can be regarded as infinite, or if it cannot be regarded as infinite, a standard sample plate having a known thickness and composition ratio is placed on the back side of the film to be measured and irradiated from the standard sample plate by X-ray irradiation. X-ray film thickness analysis method for measuring the film thickness of a film to be measured by detecting fluorescent X-rays to be applied, wherein the standard sample plate is a mixed standard sample plate comprising a plurality of elements generating characteristic X-rays having different energies. Of the fluorescent X-rays generated from the mixed standard sample plate, a line whose intensity is reduced to a predetermined range due to absorption by the film to be measured is selected as an analysis line, and based on the intensity of the analysis line, A fluorescent X-ray film thickness analysis method characterized by determining a film thickness of a measurement film.