JP3287069B2 - Measurement method and apparatus for total reflection X-ray fluorescence analysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is based on total reflection X-Ray Fluorescence.
The present invention relates to a total reflection X-ray fluorescence measurement method and apparatus for performing measurement.

[0002]

2. Description of the Related Art First, a total reflection X-ray fluorescence analysis method will be briefly described. Optical Flat Surfa X-ray
When ce) is illuminated at a low incident angle, the X-rays are reflected equiangularly with the incident angle without being absorbed by the irradiated material. That is, X-rays are totally reflected. At this time, if the sample is placed on the optical plane where the X-rays are totally reflected, the X-rays other than the X-rays hitting the sample are totally reflected, and the scattered X-rays exit from the sample in a state that can be apparently ignored. X-ray fluorescence can be detected. Therefore, spectrum measurement with a good S / N ratio can be performed (Journal of the Japan Institute of Metals, Vol. 24, No. 11 (1985)
Year), pp. 956-961). Such an analysis method is called total reflection X-ray fluorescence analysis.

A qualitative analysis and a quantitative analysis of a sample are performed from the result of the spectrum measurement. As an example of this analysis, a qualitative / quantitative analysis of a sample placed on a wafer surface is described.
Advances in X-ray analysis 19 (Agne Technology Center), P.217-
226 and Osaka Electro-Communication University Research Papers “Natural Science” 2
2 (1986), p. 87-. Also,
For the qualitative and quantitative analysis of the aqueous solution dropped on the wafer surface, see X-ray Analysis Advance 19 (Agne Technology Center), p.23
7 to 249.

A conventional typical total reflection X-ray fluorescence analyzer used for such total reflection X-ray fluorescence analysis has a configuration as shown in FIG. 2 and so on. A sample positioning device 3 is provided in the measurement chamber 2, and the sample positioning device 3 has a sample support 5 for supporting a sample. The surface of the sample 4 on the sample support 5 is an optical plane, and the X-rays radiated from the X-ray generator 1 and totally reflected on the optical plane are applied to the scintillation mounted in the measurement chamber 2. The sample 4 detected by the counter 6 and on the sample support 5
X-rays emitted from the detector 7 are detected by the detector 7.

The sample positioning device 3 has a four-axis adjustment mechanism for X, Y, Z, and θ, adjusts the total reflection angle and sets the measurement position, and places the sample on the detector. 7 and also has a function of transporting it to a position directly below 7 and incorporates a transmission mechanism including gears and shafts and various electric wires.

[0006]

In such a conventional apparatus, the detector 7 has a structure in which the detector 7 is fixed just above the X-ray irradiation surface of the sample 4 so as to face each other. In the case of a single crystal sample such as a silicon wafer or a gallium arsenide wafer used for a semiconductor element or the like, since the surface has a high degree of smoothness as shown in FIG. . Therefore, if the detector 7 is arranged immediately above the irradiation surface, the scattered X-rays do not enter the detector 7.

However, in the case of a sample 4 or an organic thin film which cannot be precisely polished due to insufficient surface polishing or material properties, as shown in FIG. In addition to being reflected at an angle, the surface is also reflected upward due to unevenness, and this scattered X-ray sometimes enters the detector 7. When this scattered X-ray enters the detector 7,
Forming a background that lowers the S / N ratio,
There is a problem in that the material is secondarily excited until it enters the detector 7 and information from the sample 4 cannot be accurately detected.

The present invention has been made in order to solve such a problem, and an object of the present invention is to reduce scattered X-rays incident on a detector and accurately detect fluorescent X-rays emitted from a sample. And total reflection fluorescence X that can obtain highly reliable analysis results
It is an object of the present invention to provide a method and a device for measuring a line analysis.

[0009]

Therefore, in the measuring method of the total reflection X-ray fluorescence analysis according to the present invention, the light emitted from the sample is used.
The X-ray detector on which the sample is placed
It is tilted in any direction and angle with respect to the Z axis perpendicular to the Y plane, and the fluorescent X-ray intensity and the scattered X-ray intensity incident on this detector are detected while changing the tilt direction and the tilt angle. . The fluorescent X-ray intensity incident on the detector is maintained at a predetermined level, and the tilt direction and tilt angle of the detection unit at which the incident scattered X-ray intensity is reduced are individually adjusted according to the measurement site of the sample. Select.

In order to realize this method, the total reflection X-ray fluorescence spectrometer according to the present invention uses the X-ray
An X-ray irradiating unit for irradiating a line, a detecting unit for detecting fluorescent X-rays emitted from the surface of the sample, and a movable supporting unit for movably supporting the detecting unit are provided.
The movable supporting means supports the detecting means so as to be movable in three directions of X-axis, Y-axis and Z-axis with reference to the XY plane on which the sample is mounted, and The detecting means is configured to be rotatable about the Y axis and the Z axis.

[0011]

As a result of the research, by inclining the detector in a predetermined direction and at an angle with respect to the Z axis, the intensity of the fluorescent X-rays incident on the detector is sufficiently maintained and incident on the detector. It has been found that the proportion of scattered X-rays decreases. Therefore, in the actual measurement, the detector is positioned above the X-ray irradiation site, and the tilt direction and the tilt angle of the detector are determined.
Alternatively, while slightly changing the height etc. along the Z axis,
The fluorescent X-ray intensity and the scattered X-ray intensity incident on the detector are monitored. In this manner, the optimum tilt direction and tilt angle are selected such that the intensity of the incident scattered X-ray is reduced and the intensity of the fluorescent X-ray is not reduced. This selection process is repeatedly performed for each measurement site of the sample.

In the total reflection X-ray fluorescence spectrometer, the detecting means is moved in three directions of X-axis, Y-axis and Z-axis by movable supporting means, and is rotated about Y-axis and Z-axis. By doing so, the detecting means can be displaced in a total of five axial directions, and the above-described measuring method is realized.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 schematically shows the configuration of a total reflection X-ray fluorescence spectrometer. The apparatus includes an X-ray generation unit 1 for generating X-rays, a measurement chamber 2 having a closed structure, and the like.

The X-ray generator 1 has an X-ray source 12 that emits tungsten (W) as X-rays.
X-rays radiated from are converted into a thin X-ray flux by the slits 13, and an X-ray spectroscope 14 made of lithium fluoride (LiF), an artificial multilayer film, or the like crystallizes tungsten (W).
Is the measurement chamber 2 are the Spectroscopy in the L? ₁ line includes a sample support 5 mounted with the sample 4, X-rays which are dispersed by X-ray spectrometer 14 through the slit 15, at low illumination angle , Sample 4
It is arranged to irradiate the light. The sample support 5 is provided with an electrostatic chuck so that warpage of the surface of the sample support 4 can be corrected.

The sample support 5 constitutes a moving stage of the sample positioning device 3. The sample positioning device 3 is of a general type which has been widely used in the past. The position of the body 5 can be adjusted by a four-axis adjustment mechanism of X, Y, Z , and θ. Also, 4
The axis adjustment mechanism is controlled by a controller 1 outside the measurement chamber 2.
6. A scintillation counter 6 is provided in the measurement chamber 2 and is used for adjusting the parallelism between the sample surface and the X-ray.

On the other hand, above the sample support 5, a semiconductor X-ray detector (hereinafter referred to as a detector) 7 for detecting fluorescent X-rays and the like emitted from the sample 4 is provided. As shown in FIG. 2, the detector 7 includes a sample 4
X-axis and Y-axis directions parallel to the surface of (sample support 5), Z-axis direction perpendicular to the surface of sample 4, θ _XZ- axis direction for rotation in the _XZ plane, and X The mechanism is movable and rotatable in a total of five directions in the θ _XY axis direction, which is a rotation in the −Y plane.

FIG. 3 schematically shows the structure of the detector 7.
As a detection element used in the detector 7 for total reflection X-ray fluorescence analysis, a Si (Li) detection element or the like is generally used.
It is used, using the detector of same configuration in the present embodiment. The structure of the detector 7 has a so-called double structure with an outer container 21 and an inner container 23 of a Dewar bottle, and liquid nitrogen 10 is sealed inside the inner container 23. A detection element 8 and a preamplifier 9 are fixed to the tip of a tubular portion 22 extending from the bottom of the inner container 23, and the detection element 8 and the preamplifier 9 are fixed by liquid nitrogen 10 sealed in the inner container 23.
It has a structure to cool. The lower end of the outer container 21 is closed by an incident window 11 formed of an extremely thin film of beryllium or the like. Fluorescent X-rays enter through the incident window 11 and are detected by the detecting element 8. The reason why the detection element 8 and the preamplifier 9 are cooled and the vacuum insulation structure is employed is to prevent generation of thermal noise and to diffuse Li (lithium) of the detection element 8 into Si (silicon). This is in order to prevent that.

At the time of measurement, fluorescent X-rays and the like emitted from the sample are detected by the detector 7. The detection output from the detector 7 is amplified by the preamplifier 9 and the linear amplifier 18, and is extracted as a pulse output having a wave height proportional to the energy of the fluorescent X-ray. Further, this pulse output is converted into a digital output by the A / D converter 19, integrated by a multi-channel analyzer for each energy, and subjected to data processing in the central processing control unit 20.

A measuring method using the thus configured total reflection X-ray fluorescence analyzer will be described.

First, the sample support 5 is displaced in the four axes of X, Y, Z , and θ by the sample positioning device 3 to irradiate a predetermined measurement site with X-rays and reflect the X-rays.
Positioning is performed so that the line enters the scintillation counter 6.

Next, X-rays are emitted from the X-ray generation unit 1 to the measurement site of the sample 4, and the detector 7 is set to XY.
-The detector 7 is driven in three Z-axis directions, and the detector 7 is positioned immediately above the X-ray irradiation site of the sample to detect the fluorescent X-ray emitted from the sample. At this time, if the surface of the sample 4 has irregularities, scattered X-rays also enter the detector 7, so that both the fluorescent X-rays and the scattered X-rays are detected by the detector 7. ((1)-(a)), (2)-
(A)).

Next, the detector 7 is tilted in a predetermined direction and angle with respect to the Z axis, and while changing the tilt direction and the tilt angle, the fluorescent X-ray intensity and the scattered X-ray detected at each position are changed. Measure strength.

Here, the operation of tilting the detector (7) with respect to the Z axis will be described in detail. In the case of a sample having an uneven surface, the detector 7 is set to θ which is in the opposite direction to the incident X-ray.
By tilting in the _XZ- axis direction, the intensity of scattered X-rays incident on this detector can be reduced (FIG. 4 (1)-).
(B)). However, at this time, the intensity of the fluorescent X-rays which are originally to be measured and which are incident on the detector also slightly decreases (FIG. 4 (2)-(b)). When the detector is tilted in the opposite direction, the fluorescent X-rays incident on the detector are:
Although the incident light has almost the same intensity as in the case of FIG. 4 (2)-(b) (FIG. 4 (2)-(c)), the intensity of the scattered X-ray tends to increase (FIG. 4 (1)-). (C)). Therefore, based on these results, if the detector is tilted in the optimum direction and angle with respect to the Z axis, the intensity of the scattered X-rays incident on the detector is reduced, and the incident fluorescent X-rays are reduced. It is understood that the strength of the wire can be sufficiently maintained. The tilt direction and the tilt angle vary depending on the shape of the sample surface, and the optimum direction and angle may be selected individually according to the measurement site.

FIG. 5 shows the result of using a glass substrate (SiO ₂ ) as a sample as a specific example. This sample is mirror-polished, but has a lower smoothness than a silicon wafer. The scattered X-ray intensity can be detected as an Lβ1 ray of W (tungsten) as an excitation source.
In addition, the intensity of the fluorescent X-rays from the sample surface can be detected as Fe (iron) or Cl (chlorine), which are contaminants on the sample surface. The detected Ni (nickel) is an impurity element in the beryllium film that is a material of the entrance window 11 in front of the detector. If the intensity of the scattered X-rays is high, the Ni intensity is also strong due to the secondary excitation, and it is difficult to determine whether the information is from the sample surface. From the results shown in FIG. 5, it is understood that the scattered X intensity can be reduced by one digit by giving the detector a tilt of only about 1 degree. In addition, the fluorescent X-ray intensity hardly decreased, but rather the effect of improving the S / N ratio and the sensitivity by reducing the background component due to scattered X-rays was recognized.

FIG. 6 shows changes in the intensity of the fluorescent X-rays and the scattered X-rays when the detector 7 is moved along the Z-axis direction. From this result, as compared with the above-described θ _XZ axis direction, the change is slight, but as the detector moves away from the sample, the scattered X-ray (W-Lβ1 line) shows an increasing tendency, and the fluorescent X-ray ( Fe, Cl) shows a decreasing tendency.

Similarly, the other three axes (X, Y, θ _XY ) and 5
By installing the detector at the position where the axes are combined,
It is possible to select the optimum tilt direction and tilt angle at which scattered X-rays can be reduced as much as possible and many fluorescent X-rays can be detected. These are particularly effective for samples whose surface smoothness is not high.

The movable range of the detector 7 is related to the region where the sample is irradiated with X-rays and the size of the detector. In the X, Y and Z axes, the movable range is 20 mm wider than the irradiation area. The Z axis ranges from 0 to 50 mm from the surface of the sample 4, and
It is desirable that the θ _XZ axis can move within ± 60 degrees and the θ _XY axis can move 360 degrees. Outside of these variable regions, both the scattered X-rays and the fluorescent X-rays are not significantly reduced.

[0029]

As described above, according to the measuring method of the total reflection X-ray fluorescence analysis according to the present invention, the fluorescent X-rays incident on the detector are changed while changing the tilt direction and the tilt angle of the detector. By detecting the intensity and the scattered X-ray intensity, the intensity of the scattered X-ray incident on this detector is reduced, and the optimum tilt direction and tilt angle that can sufficiently obtain the fluorescent X-ray intensity to be measured are selected. And

Therefore, the conventional total reflection X-ray fluorescence analysis is also applied to the analysis of the sample surface such as a sample whose surface is not sufficiently polished or an organic thin film, and the fluorescent X-ray emitted from the sample is accurately detected. And a highly reliable analysis result can be obtained.

Further, in the total reflection X-ray fluorescence spectrometer according to the present invention, the detection means is provided by the movable support means.
Since it is configured to be able to move in three axis directions of axis, Y axis, and Z axis and to rotate around the Y axis and Z axis, the above-described measurement method can be realized, and the fluorescent X-ray can be accurately detected. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a total reflection X-ray fluorescence spectrometer according to the present embodiment.

FIG. 2 is an explanatory diagram schematically showing a movable direction of a detector.

FIG. 3 is a schematic sectional view showing a detector.

4 (1) and (2), a) is a position of a conventional detector, b) is a state where it is inclined in the direction opposite to the incident X-ray on the θ _XZ axis, and c) is X in the θ _XZ axis. It is explanatory drawing which shows the state inclined in the incident direction of the line, respectively.

FIG. 5 is a chart showing the results of analysis using a glass substrate as a sample (θ _XZ axis rotation effect).

FIG. 6 is a chart showing the results of analysis using a glass substrate as a sample (Z-axis variable effect).

FIG. 7 is a schematic configuration diagram showing a conventional total reflection X-ray fluorescence analysis.

FIGS. 8A and 8B are explanatory diagrams showing scattering directions of scattered X-rays due to differences in unevenness on a sample surface.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... X-ray generation part, 2 ... Measurement room, 4 ... Sample, 5 ... Sample support, 7 ... Detector.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-196583 (JP, A) JP-A-5-99865 (JP, A) JP-A-4-1433642 (JP, A) JP-A-1- 97843 (JP, A) JP-A-3-246452 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 23/00-23/227

Claims (2)

(57) [Claims] An X-ray is radiated onto a surface of a sample at a predetermined incident angle, and a fluorescent X-ray emitted from the sample is detected by a detection unit disposed above the sample. In the measurement method for analysis, the detection unit is tilted in an arbitrary direction and an angle with respect to a Z axis perpendicular to an XY plane on which the sample is mounted, and while changing the tilt direction and the tilt angle, By detecting the intensity of the fluorescent X-rays and the intensity of the scattered X-rays incident on the detector, the intensity of the fluorescent X-rays incident on the detector is maintained at a predetermined level, and the intensity of the scattered X-rays incident on the detector is reduced. Wherein the tilt direction and the tilt angle of the detection unit are individually selected according to the measurement site of the sample.
Line analysis measurement method. 2. An X-ray irradiating means for irradiating an X-ray toward a surface of a sample, a detecting means for detecting fluorescent X-rays emitted from the surface of the sample, and a movable means for supporting the detecting means movably. The movable support means movably supports the detection means in three directions of X-axis, Y-axis, and Z-axis with reference to the XY plane on which the sample is placed. A total reflection X-ray fluorescence spectrometer, wherein the detection means is rotatably supported around the Y axis and the Z axis.