JPH0682049B2 - Thin film thickness measurement method - Google Patents

Description

The present invention relates to a thin film thickness measuring apparatus using Compton scattering of X-rays.

(Prior Art) There is a method of utilizing Compton scattering of X-rays to measure the thickness of a thin film. This method is different from the film thickness measurement by X-ray absorption.
It has an advantage that it can be applied to organic materials such as those having a small line absorption. When the sample is irradiated with X-rays of a certain wavelength, X-rays of different wavelengths from the sample-irradiated X-rays are observed depending on the scattering angle.
This is Compton scattering, and since Compton scattering is based on the interaction between X-rays and electrons, the intensity of Compton scattered rays is determined by the area density of the sample, regardless of the type of atoms constituting the sample. If the materials are the same, the area density of the sample is proportional to the thickness. Desired. This is the conventional method for measuring the film thickness by the Compton scattering method.

(Problems to be Solved by the Invention) In the above-mentioned conventional method, it is necessary to prepare a thin-film standard sample of the same substance as the sample to be measured and having a known thickness. Is often difficult to obtain. Therefore, the present invention does not need to be a thin film as a standard sample, and may provide a lump sample or a lump sample of a substance which is not the same as the sample to be measured, and provides a film thickness measuring method using Compton scattering. It is a thing.

(Means for solving the problem) Arbitrary thickness of arbitrary substance (bulk is acceptable, in this case the thickness is ∞)
Calculate the Compton scattering intensity for the standard sample, measure the Compton scattering intensity for the above standard sample and the sample to be measured, and calculate the ratio of the Compton scattering intensity of the standard sample to the measured value for the Compton scattering intensity of the sample to be measured. Multiply the measured value, calculate the area density of the sample to be measured from the ratio of the value and the Compton scattering intensity of the standard sample, and divide the calculated area density by the volume density of the sample to be measured Calculate the thickness of.

(Action) Compton scattering is an interaction between an X-ray and an electron and is not directly related to the atomic structure. Therefore, the wavelength difference between the scattered ray and the incident X-ray is determined only by the scattering angle, and the intensity of the observed Compton scattered ray. Is the same regardless of the type of substance if the area density of the sample is the same. The present invention takes advantage of this property of Compton scattering. Such Compton scattering intensity can be theoretically calculated, and the method is, for example, “Internal Tables fo
r X ray Christallography ”and the like.
In this calculation, as shown in FIG. 2, the area density σ of the sample is σ = ATρ / Compton scattering intensity is calculated as a function of A.

The ratio between the calculated value of Compton scattering intensity and the actual measured value for the above-mentioned standard sample is calculated by the irradiation X-ray intensity and the measured X-ray intensity.
It is determined by the difference in the line intensity, that is, the sensitivity of the X-ray detector, etc., and it is a conversion factor between the calculated value and the measured value. Is. Therefore, the calculated Compton scattering intensity of the sample to be measured can be obtained by multiplying the measured Compton scattering intensity of the sample to be measured by this ratio. Since the calculated Compton scattering intensity is a function of the area density, the area density is obtained from the calculated Compton scattering intensity of the measured sample obtained above, and the volume density of the measured sample is the material of the measured sample. If it is known, it is known from various handbooks, so the thickness is calculated from the area density.

(Example) FIG. 1 is a flowchart for obtaining an outline of the method of the present invention. First, the Compton scattering intensity of a standard sample of an arbitrary substance is calculated. The Compton scattering intensity is obtained as a function of the area density of the sample (a). Next, the Compton scattering intensity is measured for a standard sample of known thickness (b). Similarly, the Compton scattering intensity is measured for the sample to be measured (C). Using the measured Compton scattering intensity of the standard sample in step (b) as the denominator, the conversion coefficient is calculated with the Compton scattering intensity of the step (a) for the standard sample having the same thickness as the measured standard sample as the numerator (d).
The measured Compton scattering intensity of the sample to be measured measured in the step (c) is multiplied by the conversion coefficient (e). The area density of the sample to be measured is known by comparing the value obtained in the step (e) with the calculated Compton scattering intensity obtained in the step (b) (f). The area density is divided by the volume density of the sample to be measured to obtain the thickness of the sample to be measured (g).

There are two methods for handling the above-mentioned actually measured Compton scattering intensity. Before the description, a method of measuring Compton scattered X-rays will be described. As shown in FIG. 2, sample S
X-ray spectroscope M
Are arranged and wavelength scanning is performed, an X-ray spectrum as shown in FIG. 3 is obtained. The horizontal axis of this X-ray spectrum is the rotation angle of the X-ray detector D of the spectroscope M. In this spectrum, the peak P1 is the Compton scattered ray, and P2 is the Rayleigh scattering of the irradiated X-ray itself, and has the same wavelength as the irradiated X-ray. As the irradiation X-ray, one characteristic X-ray such as Kα ray of an appropriate target material is used, but P3 and P4 in the spectrum of the figure are Compton and Rayleigh scattering rays of Kβ ray of the same target material. Since the irradiation X-rays include continuous X-rays, the Compton scattering and Rayleigh scattering form the background B, and the peak of the Compton scattering line is on the background. The measured Compton line intensity in FIG. 1 should use this net peak intensity. There are two ways to find the net intensity of this Compton scattering.

(Part 1) In the scattered X-ray spectrum of Fig. 3, the scattered X-ray intensity was measured at the center position p0 of the Compton scattered ray peak and the background level positions p1 and p2 on both sides of it, and the background level was measured. By connecting the measured values at the two positions p1 and p2 with a straight line, the background level at the Compton scattering peak center position p0 is calculated by interpolation, and this is calculated from the X-ray intensity at the Compton scattering peak center position. Subtract the Compton scattering intensity. The table below shows an example of this method. In the examples, polyester films of three different thicknesses were used as samples. A brass lump sample was used as a standard sample, and Rh Kα ray was used as an irradiation X-ray. Table 1 shows the values obtained by performing the above background correction on the measured Compton scattering intensities of the standard sample and the above-described three types of polyester films (Samples A, B, and C).

Table 1 Sample brass ABC strength KCPS 2.81651 2.10186 0.97320 0.43136 The conversion factor using the measured Compton scattering intensity of the above standard sample as the denominator and the actual calculated value as the numerator was calculated as 421,565. The coefficient was 421,565 / 2.81651 = 149.7. Table 2 shows the values obtained by multiplying the measured Compton scattering intensities of Samples A, B and C by the above conversion coefficient. Table 2 ABC C 314.599 145.665 64.565 From these results, the area density of each sample and its volume density 1.
Table 3 shows the thickness values divided by 39 g / cm ² and the direct thickness measurements of each sample.

From this result, it can be seen that the measured value by the method of the present invention substantially coincides with the true thickness.

(Part 2) In this, the background at the center position of the Compton scattered ray peak is also calculated. In the method of the above-mentioned 1), the background is obtained by the linear interpolation method, but since the actual background distribution has a complicated bend, the accuracy is not sufficient with the linear interpolation method. Therefore, it is more accurate if the background is calculated and corrected. The background is the overlap of Compton scattering and Rayleigh scattering of the continuous X-ray component because the continuous X-rays of the irradiation X-rays and the characteristic X-rays of the target material of the X-ray tube overlap. . This Rayleigh scattering can also be theoretically calculated and is described in the above-mentioned literature. The conversion factor between the calculated value and the actual measured value is the Compton scattering peak center with the background of the standard sample calculated by calculating the Compton scattering intensity and background intensity at the characteristic X-ray wavelength used for the arbitrary standard sample. It is calculated by dividing by the strength of. On the other hand, for the sample to be measured, the measured intensity including the background at the center of the peak of Compton scattered rays is multiplied by the above conversion coefficient, and the area density of the sample is obtained from it. According to this method, it is not necessary to measure the background on both sides of the peak of Compton scattered rays, and the measurement operation is rather simple. The table below shows examples of this method. In this embodiment, the standard sample, the sample to be measured, and the X-ray tube used are all the same as in the previous example. Calculated background of standard sample is 38.6
It becomes 3, and when the calculated value of Compton scattering intensity of 421.565 (same as the previous example) is added and divided by the measured X-ray intensity of 4.42439 at the peak center of Compton scattering line, the conversion factor = (421.565 + 38.63) /4.42439 = 104.01. Table 4 shows the measured values of the X-ray intensity (including the background) at the peak center of the Compton scattered rays of Samples A, B, and C, the value obtained by multiplying it by the conversion coefficient, the areal density,
Indicates the thickness.

This result shows that the value is closer to the true value and the accuracy is higher than in the previous example.

(Effect of the invention) According to the present invention, a standard sample of the same kind as the sample is not required,
Since the actually measured value of the substance to be measured can be calibrated using an appropriate substance in any available form as a standard sample, the applicable range of the measurement using Compton scattering is significantly expanded.

[Brief description of drawings]

FIG. 1 is a flow chart for explaining the outline of the present invention, and FIG.
FIG. 3 is a plan view of the Compton scattering measuring device, and FIG. 3 is a view of Compton scattering spectrum. S: sample, M: X-ray spectroscope.

Claims (1)

[Claims] 1. Compton scattering intensity is calculated for a standard sample having an arbitrary thickness of an arbitrary substance, Compton scattering intensity is measured for the standard sample and the sample to be measured, and a calculated value and measured value of Compton scattering intensity for the standard sample are calculated. The thickness of the thin film is measured by multiplying the measured Compton scattering intensity of the sample to be measured by the ratio with the calculated value of the Compton scattering intensity of the standard sample. Method.