JPH0750043B2 - X-ray spectroscopic analysis method for thin layer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for quantifying thin layer thickness and composition by X-ray spectroscopy.

(Prior Art) When performing thickness and quantitative analysis of a thin layer such as a plated layer, conventionally, methods such as emission analysis using glow discharge, fluorescent X-ray spectroscopy, and secondary ion mass spectrometry have been used. The method using glow discharge performs both quantitative analysis and sample surface removal by glow discharge, but it takes several minutes for sample surface removal by discharge and the speed is slow, so it takes a long time for measurement.
The analysis area is as wide as a few mm. Also, the method using fluorescent X-rays is not suitable for analysis of a minute area of about several μm. Secondary ion mass spectrometry is suitable for analysis of a minute region, but since it uses the deletion of the sample surface by ions, it requires a longer time for analysis than the method by glow discharge.

(Problems to be Solved by the Invention) The present invention is intended to provide a method capable of performing thickness measurement and quantitative analysis of a minute region of a thin layer in a short time.

(Means for Solving the Problem) The constituent elements of the sample are known. Thickness and elemental composition ratio Change the accelerating voltage of the excited electron beam into multiple types by using a standard sample of known composition, and for each accelerating voltage, the relationship between the characteristic X-ray intensity of the constituent element and the sample thickness and compositional ratio. A curve is obtained, the characteristic X-ray intensity of the constituent element is measured for the sample to be measured by changing the accelerating voltage of the excited electron beam to a plurality of types, and the above relation is obtained from the relation between the electron accelerating voltage and the characteristic X-ray intensity. The curve is used to find points that give the same sample thickness and composition ratio at any acceleration voltage.

(Operation) When the accelerating voltage of the electron beam for sample excitation is fixed to a (for example, 15 KV) and the sample thickness is changed when the composition of the sample is constant, the characteristic X-ray intensity and the thickness of the component element One relationship curve is obtained. When the composition ratio of the components is changed, another curve is obtained, and a curve group A as shown by the solid line in FIG. 1 is obtained on the graph surface of the sample thickness and the characteristic X-ray intensity. In the present case, since both the thickness and the composition ratio of the sample are unknown and they are to be determined at the same time, neither the thickness nor the composition ratio can be determined only by the curve group A in FIG. When the accelerating voltage of the excited electron beam is increased, the sample transmittance of electrons is increased, and most of the incident electrons penetrate the thin layer, and the characteristic X-ray intensity from the atoms constituting the thin layer depends on the minimum excitation voltage. Generally decreases. Therefore, when the same voltage as the above is made by changing the accelerating voltage of the excited electron beam to b (for example, 20 KV), a curve group B as shown by the dotted line in FIG. 1 is obtained. Therefore, for the sample to be measured, the acceleration voltage a
Assuming that the characteristic X-ray intensities Ia and Ib of the constituent elements are obtained by using b and b, assuming that the sample thickness is t1, the case where the apparent component% is b is more than the case where the acceleration voltage is a (14% in this example). It is read that (16%) is large, and assuming that the thickness is t2, the component% is smaller in case of b (10%) than in case of a (12%). Therefore, between the thicknesses t1 and t2, there is a thickness t3 at which the component% is determined to be the same regardless of the acceleration voltage a or b. This is the sample thickness, and the component% at that time is the quantitative analysis of the sample. It is a value. Simultaneous determination of thickness and composition ratio is possible by measurement with two kinds of accelerating voltage, but in reality, the accelerating voltage region in which the thickness and composition ratio are well reflected in the accelerating voltage differs depending on the thickness and composition ratio. Therefore, it is preferable to measure with two or more kinds of accelerating voltages and select two appropriate accelerating voltages for quantification.

(Example) In this example, Fe15%, Zn85
%, The thickness and composition ratio of the surface layer in the case where the undercoating having a thickness of 5 μm is plated and the surface layer is plated with Fe—Zn are measured. In this case, the effect of iron and zinc in the underlying plating layer appears, so in order to remove this, measurements were also performed on a sample in which the same plating layer as the surface layer was formed on a copper plate as a preliminary experiment. Since the difference in the measured values between the sample with the undercoat on iron (license) and the sample with the plating on the copper plate is the measurement output by the undercoat, the influence of the undercoat can be excluded from this data by calculation. it can.

Creating a calibration curve.

The standard sample is an iron plate with base plating and a surface layer plating on it.

Base plating Fe15%, Zn85%, thickness 5μm Surface layer Fe84%, Zn16%, surface layer thickness 0.95μm (7.4g / m ² ) 0.37μm (2.9g / m ² ) 0.17μm (1.33g / m ² ) A copper plate sample is a copper plate directly coated with the same plating layer as the surface layer in the above three types of thickness.

The acceleration voltage of the excited electron beam is 10.0, 12.
The intensity I of FeKα ray was measured by changing to five kinds of 5,15.0, 20.0 and 30.0 KV. The results are shown in FIG. In this figure, the measured values are normalized by dividing by the Kα ray intensity Io of the pure iron sample.
The solid line is the standard sample and the dotted line is the copper plate sample. I / Io in this figure
The difference between the solid line and the dotted line is the effect of FeKα from the undercoat. The results of FIG. 2 can be rewritten as a graph of the relationship between the surface layer thickness and the characteristic X-ray intensity I / Io using the acceleration voltage as a parameter, as shown in FIG. FIG. 3 is drawn only for the standard sample. In the case of this example, it was difficult to obtain a standard sample in which the composition of the surface layer was arbitrarily changed, so it was decided to create the graph of FIG. 3 when the composition ratio was changed by calculation. For this purpose, the above-mentioned measurement results of the copper plate sample are useful.
Now, for example, in FIG. 3, when the accelerating voltage is 20 KV, the measurement result of the copper plate sample is shown in FIG.
The difference is the effect of FeKα from the undercoat as described above. According to another experiment, the ratio I / Io between the intensity I of FeKα line of the Fe-Zn binary alloy and the intensity Io of Kα line of pure iron is 10 ~
It was confirmed to be proportional to Fe% in the range of 50 KV as shown in FIG. Similar results hold for the Zn side as well. By utilizing this fact, a graph similar to that shown in FIG. 3 can be prepared for standard samples having other Fe--Zn composition ratios by calculation from the results shown in FIG. For example, the dotted line in Fig. 3 is the curve when the surface layer of the copper plate sample is Fe84%, Zn16%. From this, the surface layer is Fe42%, Zn58%.
To find the curve for%, set I / Io to 1 / the height of the dotted line.
You can set it to 2. The above-mentioned effect from the undercoating (difference between solid line and dotted line) is added to the curve for the surface layer of Fe42% and Zn58% in the case of accelerating voltage of 20 KV in the actual sample. In this way, a graph showing the relationship between the thickness of the surface layer and the intensity of the FeKα ray with the composition ratio of Fe-Zn as a parameter can be prepared for each electron beam accelerating voltage.

(Effect) Since the method of the present invention uses X-ray spectroscopy by electron beam excitation of the sample, it is possible to measure a minute area, and the electron penetration characteristic into the sample is utilized, and the sample surface is not etched. Therefore, the time required for measurement is short, and it is an extremely effective method for quality control of the surface treatment layer in the field.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph explaining the principle of the present invention, and FIG. 2 is a graph showing the relationship between accelerating voltage and characteristic X-ray intensity in the example using the thickness of the surface layer as a parameter. FIG. 3 is a graph in which the above graph is rewritten to the relationship between the thickness of the surface layer and the characteristic X-ray intensity with the acceleration voltage as a parameter, and FIG. 4 is the relationship between the Fe% of the Fe-Zn alloy and the FeKα ray intensity. It is a graph.

Claims (1)

[Claims] 1. A sample in which a characteristic X-ray intensity of a sample component element is measured in advance by using a standard sample of a thin layer having a known composition and a thickness, by plural kinds of excited electron beam accelerating voltages in the range of 5.0 KV to 50.0 KV. The relationship between the thickness and the characteristic X-ray intensity is obtained using the component composition and the electron beam accelerating voltage as parameters, and the characteristic X-ray intensities of the plurality of component elements under the electron beam accelerating voltage are measured for the sample to be measured. Of the layer thickness or the component composition ratio, the other value of the layer thickness or the component composition ratio which gives the measured characteristic X-ray intensity at each electron beam accelerating voltage is previously measured. The electron beam accelerating voltage and the component composition ratio obtained as a parameter are used to perform the operation to obtain the relationship between the characteristic X-ray intensity and the thickness by changing the assumed value of one of the above values, and Assuming that the other values above agree with each other And search, X-ray spectroscopy methods of thin layers, characterized in that the measured values of interest with a component composition ratio and layer thickness at that time.