JPH03235046A - Total reflection x-ray fluorescence analyzer - Google Patents

Abstract

PURPOSE:To obtain an apparatus for measuring in-plane distribution of a very small amount of impurities on a specimen surface with high sensitivity by a method wherein X-ray applied to the specimen and totally reflected from the surface are reversed into a direction of 180 deg. and made incident again at the same position on the specimen surface. CONSTITUTION:Primary X-rays 12 generated from an X-ray source 11 are applied to a surface of a specimen, for example a silicon semiconductor wafer 13. An incident angle theta to the surface of the wafer 13 at this time is set to an angle such that the primary X-ray 12 are totally reflected from the surface. Reflected X-rays 14 from the wafer 13 are incident on a reflecting crystal body 15 composed of Si for example at incident angles theta1 and theta2, where they are reversed in a direction by 180 deg. to be applied to the same position on the wafer 13 surface again. Thus intensity of the incident primary X-rays is increased so that a level of secondary X-rays generated from the specimen surface, that is fluorescent X-rays, is raised to enable highly sensitive measurement.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a total internal reflection fluorescent X-ray analyzer used for elemental analysis of trace impurities on the surface of a sample such as a silicon wafer.

(Prior Art) Until now, methods based on chemical analysis have mainly been used to analyze impurities on the surface of a sample such as a silicon wafer. This chemical analysis method dissolves the natural oxide film or thermal oxide film on the surface of a silicon wafer with a hydrofluoric acid solution (HF), and determines the types and concentrations of impurity elements contained in this solution using a flameless atomic absorption spectrometer. It is. Conventionally, a method has also been used to obtain information on elements within a range of several micrometers to several tens of micrometers from the surface in a non-destructive and non-contact manner using a fluorescent X-ray analyzer.

However, with the above chemical analysis method, although the average concentration of impurities on the entire wafer surface can be determined, it is not possible to know the impurity concentration in specific parts, such as only the center or the peripheral part of the wafer 1. In other words, it is not possible to obtain an impurity concentration map on the wafer.

In addition, in the method using a fluorescent X-ray analyzer, the measurement region is deep, from several μm to several tens of μm from the surface, so information from the bulk occupies most of the information, and signals from the surface are hidden by signals from the bulk. I can't put it away.

In order to eliminate such drawbacks, a total internal reflection fluorescent X-ray analyzer using total internal reflection of X-rays has been developed. According to this apparatus, an impurity concentration map on the wafer surface can be obtained.

(Problems to be Solved by the Invention) However, with conventional fluorescent X-ray analyzers, the actual detection limit for elements is 10'' to 1012 (atoms/C).
2) is as low as 10, which is actually a problem in device processes.
Detection of levels of 10 (atOIIS/Cll2) or lower is not possible due to the low intensity of the incident X-rays. In addition, the fluorescence emission efficiency of elements close to the atomic number of the incident X-ray is high, but the emission efficiency decreases when the atomic number is far apart.
This has the disadvantage that detection sensitivity decreases.

This invention was made in consideration of the above circumstances, and its purpose is to provide a total internal reflection fluorescent X-ray analyzer that can measure the in-plane distribution of trace impurities on the surface of a sample with higher sensitivity than before. Our goal is to provide the following.

[Structure of the invention]

(Means for Solving the Problems) The total internal reflection fluorescent X-ray spectrometer of the present invention is a total internal reflection fluorescent X-ray spectrometer that analyzes trace impurities on the surface of an optically polished sample. The present invention is characterized by comprising a reflecting means for reversing the totally reflected X-rays in the direction of 180° and making them enter the same position on the sample surface again.

In the total internal reflection X-ray fluorescence analyzer of the present invention, the reflecting means is constituted by a crystal having lattice planes orthogonal to each other, and the incident angles of the X-ray after total reflection to each orthogonal lattice plane are set as θ1 and θ2. Sometimes, θ, +02-90
The crystal body is characterized in that it is constructed so as to satisfy the relationship: °.

Further, as the crystal body, S1SGe, GaP5GaA
ss GaSb, In5bS InAs.

Any one of Cd55CdTe%L i F, a perfect crystal of graphite, or a mixed crystal thereof is used.

(Function) In a total internal reflection fluorescent X-ray analyzer that analyzes trace impurities on a sample surface, X-rays that have been totally reflected on the sample surface are collected using reflective crystals with a special shape and arrangement.
It is reversed by 0° and is incident again on the same position on the sample surface. This increases the intensity of the incident X-rays and increases the level of the secondary X-rays emitted from the sample surface, that is, the fluorescent X-rays, making it possible to perform highly sensitive measurements.

(Examples) Hereinafter, the present invention will be explained by examples with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the total internal reflection fluorescent X-ray analyzer of the present invention. In the figure, 11 is an X-ray source. As this X-ray source 11, for example, SOR light is used. The primary X-rays 12 emitted from this X-ray source II are
For example, the surface of the silicon semiconductor chip 13 is irradiated. At this time, the incident angle θ with respect to the surface of the wafer 13 is set to an angle at which the -order X-rays 12 are totally reflected on the surface. The reflected X-rays 14 from the above-mentioned structure 13 are e.g.
The light is incident on the reflective crystal body 15 constructed by the above at incident angles of θ1 and θ2, the direction of which is reversed to 180°, and the same position on the surface of the wafer 13 is irradiated again.

Further, the wafer 13 is placed and fixed on a vacuum chuck 16 for the purpose of flattening, and the wafer 13 placed on the vacuum chuck 16 is sucked by a bayum bomb (not shown). It has become. Further, above the way /X13, there is a secondary X-ray detector, for example, a solid state detector.
A controller (hereinafter referred to as SSD) 17 is installed, and fluorescent X-rays emitted from the surface of the wafer 113 are detected by this 5SD 17.

Although not shown in the figure, the output from the 5SD17 is supplied to the amplifier, main amplifier, A/D converter, and multi-channel amplifier.
It is supplied to a processing circuit consisting of a channel analyzer (MCA), etc., and the output of this processing circuit is further supplied to a computer, which calculates the in-plane distribution of trace impurities on the surface of the wafer 13.

Although not shown, the vacuum chuck 16, 5SD 17, etc. are housed in a vacuum chamber.

FIG. 2 is a perspective view showing the external shape of the reflective crystal body 15 in FIG. 1. FIG. This reflective crystal body 15 is constructed using a rectangular parallelepiped block made of a perfect Si crystal, for example, and has a shape in which two (100) planes that intersect with each other are cut out from this block, and (800) reflection is used. The SOR light emitted from the X-ray source 11, that is, the incident-order X-ray 12 and the reflected X-ray 14, is white light, and the incident angle θ7. Between θ2, θ, -θ2-45° (θ!
By installing this reflective crystal 15 at a position that satisfies the relationship: +θ2−90°, the wavelength λ can be set to 0.96
Only the X-rays of the person 0 are diffracted and irradiated onto the same position on the surface of the tube 13.

In this way, by inverting the reflected X-rays 14 from the wafer 13 using the reflective crystal 15 and irradiating the same position on the surface of the wafer 13 again, the intensity of the fluorescent X-rays emitted from the surface of the wafer 13 is increased compared to the conventional method. become stronger, 5S
The detection sensitivity at D17 can be improved.

FIGS. 3(a) to 3(d) show that the concentration of each impurity element Fe, Cr, Ni, and Cu adsorbed on a Si wafer was measured using a conventional device from No. 1 to No.
10 is a characteristic diagram showing the results of analysis on 10 wafers, and each broken line in the diagram indicates the detection limit of each impurity.

On the other hand, FIGS. 4(a) to 4(d) are characteristic diagrams showing the results of analyzing each impurity concentration of the same wafer using the apparatus of the above embodiment. Information on impurity concentration, which was limited by the detection limit in the case of conventional devices, was able to be obtained with high sensitivity by using the device of the above embodiment.

That is, the detection limit, which was conventionally on the order of 1010, is lower than that in this embodiment. As is clear from the figure, especially No. 9 and No.
It can be seen that the concentrations of each element of Fe, Cr, Ni, and Cu are particularly low in the wafers of No. , 10.

In the above embodiment, a case where a perfect crystal of Si was used as the reflective crystal was explained;
Not only, but also Ge.

GaP, GaAs, GaSb, Ink, In5bsI
It can be constructed using any one of perfect crystals of nAs, CdS, CdTe%L i F, and graphite, or a mixed crystal thereof.

FIG. 5 is a diagram summarizing the effective wavelengths for the main reflective crystal planes when various perfect crystals are used as the reflective crystal body when θ is -02-45''. In the embodiment of FIG. 1, the reflective crystal body 15
When constructed using various perfect crystals, X-rays of the wavelengths shown in the figure can be obtained by diffraction.

FIG. 6 is a block diagram of another embodiment of the present invention. In the case of this embodiment device, the primary X-rays 12 emitted from the X-ray source 11 are made to enter the spectroscopic crystal 18 made of the same material as the reflective crystal 15 at an incident angle of 45°. As a result, the primary X-rays 12 are diffracted and made monochromatic, and then irradiated onto the surface of the silicon semiconductor wafer 13.

In this embodiment, when both the spectroscopic crystal 18 and the reflective crystal I5 are constructed using perfect crystals of Ge, the spectroscopic crystal 18 uses a (100) reflective surface. Further, when SOR light is used as the -order X-ray 12, the wavelength λ of the monochromatic X-ray diffracted by the spectroscopic crystal 18 is 0.997.

In the case of this embodiment as well, the X-rays diffracted by the spectroscopic crystal 18 are incident on the surface of the wafer 13 at an incident angle θ smaller than the critical angle, and total reflection from the wafer 13 is achieved. By making the light incident on the reflective crystal 15 at an angle of 45'', the same position on the surface of the wafer 13 can be irradiated with X-rays again, as in the case of the embodiment apparatus shown in FIG.

FIG. 7(a) is a diagram showing the arrangement of the embodiment apparatus of FIG. 6 as viewed from above, and FIG. 7(b) is a diagram showing an extracted portion of the reflective crystal body 15. Let us now assume that the direction (vector) of the X-ray incident on the reflective crystal 15 is 1. In addition, in the reflective crystal body 15, two (110)
Assuming that the direction in which the planes intersect is b, the reflective crystal 15 is arranged so that a and b are perpendicular to each other.

[Effects of the Invention] As described above, the present invention provides a total internal reflection fluorescent X-ray spectrometer capable of determining the in-plane distribution aj of wI impurities on the surface of a sample with higher sensitivity than before. be able to.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the total internal reflection fluorescent X-ray analyzer of the present invention, FIG. 2 is a perspective view showing the configuration of the reflective crystal in FIG. 1, and FIGS. 3 and 4. are characteristic diagrams showing the results of sample analysis using the above-mentioned example device and conventional device, respectively, and Figure 5 shows the effective effects on the main reflective crystal planes when various materials are used as reflective crystals. FIG. 6 is a diagram showing the configuration of another embodiment of the present invention; FIG. 7(a) is a diagram showing the arrangement of the apparatus of the embodiment shown in FIG. (b) is a diagram showing an extracted portion of the reflective crystal. 11... X-ray source, 12... -th order X-ray, 13... To silicon semiconductor wafer 14... Reflected X-ray, 15...
- Reflection crystal, 16... Vacuum chuck, 17... Solid state detector (SSD), 18... Spectroscopic crystal.

Claims (3)

[Claims] (1) In a total internal reflection fluorescence X-ray analyzer that analyzes trace impurities on the surface of an optically polished sample, the X-rays that are irradiated onto the sample and totally reflected by the surface are reversed in the direction of 180° and re-applied to the sample. 1. A total internal reflection fluorescent X-ray analyzer, characterized in that it is equipped with a reflection means that causes the light to be incident on the same position on the surface. (2) The reflecting means is composed of a crystal body having lattice planes that are orthogonal to each other, and when the incident angles of the X-rays after total reflection on each orthogonal lattice plane are θ_1 and θ_2, θ_1+θ_2=90°. 2. The total internal reflection X-ray fluorescence spectrometer according to claim 1, wherein the crystal is configured to satisfy the following relationship. (3) The crystal body is Si, Ge, GaP, GaAs,
The total internal reflection fluorescence according to claim 2, characterized in that it is constructed using any one of perfect crystals of GaSb, InSb, InP, InAs, CdS, CdTe, LiF, and graphite, or a mixed crystal thereof. X-ray analyzer.