JPH04343050A - Non-destructive analysis method below the sample surface - Google Patents

Abstract

PURPOSE:To perform nondestructive analysis of the inside of an object by irradiating an excitation wire from each direction so that it passes one point at a specific depth from a specimen surface, collecting a secondary radiation detection data for each direction, and then screening a common data from those data. CONSTITUTION:A specimen S is retained on a specimen holder 5, its inclination can be changed, and a height position of a surface of the specimen S for its rotary center (horizontal) can be changed. Namely, since a center line 0 of the rotation crosses an electron beam center line of an electron gun 1 and a height (h) from the center line 0 to the surface of the specimen S can be adjusted, thus enabling the electron beam to observe a point 0 which is located at the height (h) under the surface of the specimen when an inclination of the sample S is changed when the inclination of the sample S is changed. Thus, an analysis data at a specific depth can be seen commonly from any direction but a point at the other depth differs depending on the direction, thus enabling a data which is detected with a same value from every direction to be determined as an analysis data of a point at a specified depth.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention provides a method for applying charged particle beams or X-rays to a sample.
The present invention relates to a method of selectively analyzing a portion at a certain depth below the surface of a sample using a device that analyzes the surface of the sample by irradiating it with a beam or the like and detecting secondary radiation emitted from the sample.

0002

[Prior Art] When performing analysis at a certain depth from the sample surface using an analyzer that irradiates the sample with excitation radiation and detects secondary radiation from the sample, the sample surface is removed by ion etching or the like. The analysis was carried out by cutting the material to a desired depth and then performing surface analysis.

However, the above-mentioned conventional method has the following problems. First, the sample surface is etched and scraped, so it is a type of destructive analysis, and it is not applicable when you want to non-destructively inspect products such as semiconductor products in which certain elements are implanted from the surface into the interior. There are limitations to the analyzer, such as the fact that the device must be equipped with an ion source for ion etching in addition to the excitation ray irradiation device, and the excitation rays themselves penetrate to a certain depth from the sample surface, causing damage to the sample. Secondary radiation is emitted not only from the surface of the sample but also from layers up to a certain depth, and conventionally, secondary radiation generated distributed in the depth direction was detected without discrimination, so the analysis results The method itself had an ambiguity in that it was an average result from the sample surface to a certain depth.

0004

[Problems to be Solved by the Invention] The present invention provides a method for non-destructively analyzing the sample surface in the depth direction using an analyzer that irradiates the sample with excitation radiation and detects secondary radiation from the sample. It is something to do.

[0005]

[Means for solving the problem] The beam center line of the sample excitation line passes through a point at a predetermined depth from the sample surface, and the sample is irradiated with the excitation line by changing the irradiation direction, and each irradiation of the excitation line Collect detection data of secondary radiation from the sample in each direction, select data that exists in common and data that does not exist in each irradiation direction from these data, and use the data that appears in common to detect the above from the sample surface. This is analysis data at a point at a predetermined depth.

[0006]

[Operation] According to the above configuration, a point at a predetermined depth below the surface of the sample is viewed with the excitation line while changing the direction. In this way, the analysis data at a given depth looks the same no matter what direction you look at, but at other depths, including the sample surface, the viewpoints differ depending on the direction, so the analysis data looks different in each direction. becomes. Therefore, analysis data detected with the same value when viewed from any direction can be regarded as analysis data at a point at a predetermined depth from the sample surface.

[0007]

Embodiment FIG. 1 shows an embodiment of the present invention. In this embodiment, the present invention is applied to an electron beam microanalyzer (EPMA). In the figure, 1 is an electron gun, 2 is an objective lens, S is a sample, 3 is a spectroscopic crystal that separates the X-rays emitted from the sample, and 4 is an X-ray detector. The wavelength scanning of the X-ray spectrometer is performed by moving the spectroscopic crystal and the X-ray detector so that the electron beam irradiation point on the sample and the electron beam irradiation point on the sample are located on one Rowland circle.

In this apparatus, the sample is held on a sample holder 5 so that its inclination can be changed, and the height position of the sample surface with respect to the rotation center (horizontal) of the rotation that changes the inclination can be changed. It is now possible to That is, as shown in Figure 2, the center line 0 of the rotation that changes the sample's inclination is perpendicular to the center line of the electron beam that irradiates the sample, and the height h from the center line 0 to the sample surface can be adjusted. By changing the inclination of , the electron beam will view the zero point h below the surface of the sample from different directions.

[0009] Electrons that have entered the sample collide with atoms constituting the sample within the sample, travel within the sample in an irregular trajectory, lose energy, and stop, during which time they emit X-rays. The electrons that have entered the sample in this manner are diffused within a certain range within the sample, and the spread area varies depending on the electron accelerating voltage, but is on the order of μm. If a coil 6 is placed around the sample and a magnetic field H is formed in the sample in the same direction as the electron beam, the lateral spread of the electrons entering the sample is suppressed, and the spread of the electrons in the sample is reduced. As shown in FIG. 2, the region is a long and narrow region extending in the depth direction of the sample, and its depth is on the order of μm. Therefore, by adjusting h, it becomes possible to analyze points at arbitrary depths up to about 1 μm from the sample surface. That is, when the inclination of the sample is changed, the elongated electron diffusion regions intersect around the zero point, as shown in FIG. 3, and analytical data near the zero point is obtained.

By changing the inclination of the sample surface, the zero point is determined from each X-ray spectrum when the zero point of the sample is irradiated with an electron beam from two directions A and B as shown in FIG. Obtain neighborhood analysis data. The elements detected in the X-ray spectra in the A direction are a, b, c,
d, and the same elements a, b, c, and d are also detected in the B direction. At this time, the characteristic X-ray peak intensity of each element is set as Pa, Pb, Pc, Pd in direction A, and Qa, Qb, Qc, Qd in direction B, and for element b, Pb=
Qb, and directions A and B for other elements a, c, and d
Suppose that the peak intensities were different between and. In this case, the element at point 0 is determined to be element b. This is because in directions A and B, element b is detected with the same intensity in both directions because the electron beam irradiation conditions and the conditions under which characteristic X-rays reach the sample surface and are detected are the same. Even if more electrons exist in the electron diffusion region in the A direction, fewer exist in the electron diffusion region in the B direction, or vice versa.
, B is unlikely to be distributed at the same concentration in the electron diffusion regions in both directions, so they are detected with different intensities in both directions.

[0011] In this way, even if the exact same combination of elements is detected in two directions, the elements present at a predetermined depth can be specified. An element detected in the A direction but not detected in the B direction is, of course, an element that does not exist at the 0 point. When this method is applied to the detection of impurities in Si wafers, the characteristic X-rays of Si, the main element, are detected with the same intensity from any direction;
Since it is known that i, the characteristic X-ray peak of Si is excluded and the above-mentioned procedure is applied.

The data processing of the above-mentioned measurement results can also be carried out as follows. The spectrum when irradiated in the A direction is A(λ), the spectrum when irradiated in the B direction is B(λ), and F(λ) is F(λ)={A(λ)+B(λ)}/|A
(λ)+B(λ)| is calculated, and it is assumed that an element with a characteristic X-ray wavelength λ for which F(λ) is a predetermined value, for example, 5 or more is in a region near the 0 point. If a certain element is detected in the A direction but not in the B direction, the above F(λ) becomes 1 at the characteristic X-ray wavelength of that element. For an element that is detected with the same intensity in both directions A and B, F(λ) becomes infinite at its characteristic X-ray wavelength. Although it is not actually infinite, at this wavelength the numerator of the formula for F(λ) is twice that of A(λ), and the difference between both denominators is close to 0, so it exists at the 0 point. For elements, the value of F(λ) becomes very large.

[0013] In the above example, the excitation line is irradiated from two symmetrical directions with respect to the perpendicular to the sample surface, but the irradiation direction is not limited to these two directions, and it is possible to irradiate from various directions. However, the data processing method is not limited to the above-mentioned method. Furthermore, although the above example uses an electron beam as the excitation line, it goes without saying that the present invention is also applicable to the case of spectroscopy of fluorescent X-rays using X-rays as the excitation line. In this case, the excitation X-ray must be narrower than the analysis depth, but it is possible to analyze deeper than using an electron beam.

FIG. 4 shows details of the sample holder 5. Reference numeral 51 denotes the base of the sample holder, and a rotating shaft 52 is horizontally attached thereto, and can be rotated by hand. A main body 53 of the sample holder is fixed to the end face of the rotating shaft. The main body 53 is a cylinder, and a cap 55 is screwed onto a threaded portion 54 at the upper end, and the cap 55 has an annular edge 56 projecting inward. The upper surface is brought into contact with the lower surface of this projecting edge 56. The bottom screw 58 is screwed into the screw 57 inside the lower part of the main body 53, and the sample S is brought into contact with the edge 56 of the cap 55 via the spring 59. A micrometer scale is carved on the outer periphery of the cap 55, and when the scale is set to zero, the lower surface of the edge 56 is at the height of the center line of the rotating shaft 52. Therefore, the reading on this scale indicates how far down from the sample surface the centerline of axis 52 coincides. Since the shaft 52 can be manually rotated, the sample can be tilted about its rotation center line, and the angle of tilt can be read from the angle scale of a knob 59 attached to the shaft 52. The lower surface of the platform 51 is provided with a protrusion that fits into a dovetail groove on the upper surface of the sample stage of the EPMA, so that it can be attached to the sample stage.

[0015]

[Effects of the Invention] According to the present invention, it is possible to analyze the portion below the sample surface without etching the sample surface, and the method involves simply changing the inclination of the sample with respect to the excitation line, so an ion etching device is not required. Therefore, conventional analysis equipment can be used as is, and the inside of the sample can be analyzed non-destructively and at low cost.

[Brief explanation of the drawing]

[Figure 1] Side view of an apparatus for carrying out the method of the present invention

[Figure 2
】 Explanatory diagram of the action of the present invention

[Figure 3] Diagram explaining the effect when irradiated with an electron beam

[
Figure 4: Side view of an example of a sample holder 1 Electron gun 2 Objective lens 3 Spectroscopic crystal 4 X-ray detector 5 Sample holder S Sample

Claims (1)

[Claims] Claim 1: Using an analyzer that irradiates a sample with an excitation line and detects secondary radiation emitted from the sample, the direction of the excitation line irradiation is changed around a point at a predetermined depth below the sample surface. ,
A non-destructive analysis method below the surface of a sample, characterized by finding components that give the same detection intensity in secondary radiation detection data in each direction.