JP2001235436A - Observation/analysis method for sample surface by oblique emission proton beam induced characteristic x- ray analysis and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an analytic method by a PIXE spectrum that allows observation and analysis of the sample surface at a higher S/N ratio. SOLUTION: In the sample surface observation/analytic method by oblique emission measurement proton beam irradiation induced characteristic X rays, characteristic X rays which are induced from a sample surface by the irradiation of a proton beam are observed through a member having a slit with the width thereof of below 1 mm while the angle of the sample surface to the irradiation proton beam is adjusted so that the characteristic X rays taken into a detector are at an angle of 2 deg. or less to the sample surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for observing and analyzing a sample surface using characteristic X-rays induced from the surface of the sample by irradiation of a proton beam, and a method for observing and analyzing a sample surface for implementing the method for observing and analyzing the sample surface. -It relates to an analyzer. In this specification, the sample surface means the surface of the substrate on which the observed / analyzed fine particles are present or the surface of the substrate on which the observed / analyzed thin film is present. Fine particles or thin film to be observed / analyzed (several nm to several μ
m) means X-rays induced by irradiation of protons.

[0002]

2. Description of the Related Art It is well known that elemental analysis of a minute area is important in terms of material development and product quality control. This is because the macroscopic properties of the material are greatly affected by the presence of inclusions in the minute portions, and the characteristics of the device are often influenced by the impurity fine particles as the semiconductor device is miniaturized. The effects of aerosols (particulate matter in the atmosphere) on global weather and the human body are gradually being recognized. For this reason, trace element analysis in aerosols is also an important measurement target for maintaining a healthy natural environment. An electron beam or ion beam having a fine probe diameter is used for elemental analysis of a minute region and a trace component. Consider a single micron-sized particle collected on a substrate. An electron beam or ion beam having a relatively large energy penetrates the fine particles and penetrates into the substrate. Therefore, the observed characteristic X-rays include not only those generated from the fine particles but also the characteristic X-rays of the elements constituting the substrate. When the element constituting the fine particles is included in the element constituting the substrate, it is no longer possible to distinguish between characteristic X-rays from the fine particles and characteristic X-rays from the substrate. In this case, it is conceivable to control the energy of the probe for measurement, but it is possible if the measurement target has some degree of discrimination, but difficult if it is not. Therefore, if the surface layer (several nm)
Such a problem can be solved if X-ray analysis of only particles or only particles can be performed.

[0003] The emission of charged particle-induced characteristic X-rays (PIXE) generally occurs when a solid sample is irradiated with a proton beam having an energy of several MeV to excite electrons in the inner shell of atoms. The characteristic X-ray is emitted from the sample at the time of the transition of the electrons in the excited state. Proton beam induced characteristic X-rays are generally said to be able to be performed in a very low background by using an energy dispersive X-ray detector (EDX). Further, PIXE enables highly sensitive nondestructive analysis. Further, micro-PIXE (micro-PIXE) enables analysis at a spatial resolution of the order of 1 μm.
PIXE is recognized as a method for analyzing fine and trace components. PIXE has been applied in many fields such as biology, environmental chemistry, earth science and archeology. For example, in the case of excitation with an electron beam in EPMA (Electron Beam Probe Micro Analysis), the large background caused by the bremsstrahlung induced by the primary electron beam is a serious disadvantage limiting the detection limit. In contrast, only a low background is observed in the PIXE spectrum. Thus, the limit of detection in PIXE is about 100 times lower than in EPMA. However, even in PIXE analysis, the detection limit for light elements is not so low,
This is because the background in the low energy region (4.0 keV or less) increases due to secondary electrons. This limits the application of PIXE because light elements such as Na, Al, Si, and Ca, which have characteristic X-ray peaks in the low energy range, are important for aerosols or biological samples. This is because it is a constituent. The present inventor has found that the background can be reduced by reducing the emission angle of characteristic X-rays. In addition, the PIXE spectrum measurement to which the oblique emission measurement technique is applied has a great effect of improving the detection characteristics particularly in the detection of light elements such as Na, Al, Si, and Ca having characteristic X-ray peaks in a low energy region. Was an unexpected and surprising discovery.

[0004] Oblique emission technology is based on X-ray fluorescence analysis and EPM.
A, each of which is GE-XRF [Grazin
g-exit (emission) X-ray fluorescence analysis) and GE-EPMA [Grazing-exit (emission) Electron
probe microanalysis]. This method
It is also closely related to the oblique irradiation measurement technique. In a technique for detecting and measuring obliquely emitted X-rays emitted from a sample to be detected, the X-rays are usually emitted at a small angle of several mrad (milliradian) (the angle between the sample surface and the emission characteristic X-rays is small). Characteristic X-rays are used. Therefore, according to this method, X-rays emitted from the inside of the sample due to reflection at the interface (characteristic X-rays of the surface sample) and refraction effect (characteristic X-rays from inside the sample) are not detected. Due to the synergistic effect of the selection of the observation X-rays depending on the arrangement of the members held and the arrangement position of the characteristic X-ray detector, the observation characteristics (on the order of nanometers) of the surface are remarkably improved. Therefore, for example, the aforementioned GE-EPMA
Thus, the decrease in detection accuracy in elemental analysis due to overlapping of characteristic X-rays from constituent elements in a deep portion of the substrate is improved. In other words, the characteristics of the signal / noise (S / N) ratio are improved. The present inventor has found that the background can be significantly reduced by applying the oblique emission measurement technique to the PIXE spectrum measurement. And the effect is that Na, Al, S having a characteristic X-ray peak in a low energy region.
It was particularly remarkable in the detection of light elements such as i and Ca.

Although the above-mentioned GE-PIXE improves the accuracy of elemental analysis due to the overlap of characteristic X-rays from constituent elements in a deep part of the substrate, the overlap from constituent elements in the shallow inner part of the substrate still exists. I do.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an improved GE-PIXE analysis method which eliminates the above disadvantages of the improved PIXE, GE-PIXE, and an apparatus therefor. For this purpose, the surface of the sample to be analyzed for proton-induced characteristic X-rays (thin film or a laminated structure thereof) and impurities on the surface, such as single particles,
In examining the characteristics emitted from airborne particles on the surface, airborne particles, biochemical samples, etc. (these are sometimes collectively referred to as fine particles), the X-ray oblique angle (extraction angle)
It is important to consider the dependence of the angle and to limit the take-out angle to a smaller value (2 ° or less). Under such conditions, characteristic X-rays generated from inside the sample to be analyzed (the surface of the sample to be detected, the carrier of the substance to be detected, etc. are sometimes collectively referred to as the surface of the sample to be detected). Is refracted on the surface, but it has been found that X-rays from foreign substances present on the surface have characteristics that generate isotropically. The inventor thought of incorporating it in the detection device and solved the above-mentioned problem.

[0007]

A first aspect of the present invention is that a characteristic X-ray induced from a sample surface by irradiation of a proton beam is passed through a member provided with a slit having a width of 1 mm or less, and
Oblique emission measurement characterized by adjusting the angle between the sample surface and the proton beam so that the angle between the characteristic X-rays introduced into the X-ray detector and the sample surface is 2 ° or less, and observing the sample. This is a method for observing and analyzing a sample surface by using a type-proton beam irradiation induced characteristic X-ray. Preferably, in order to realize the irradiation of the sample surface with the proton beam such that the angle (oblique emission angle) from the surface of the characteristic X-ray induced from the sample surface by the irradiation of the proton beam is 2 ° or less. , The angle of the irradiated proton beam is the characteristic X
The method for observing and analyzing a sample surface using the obliquely emitted proton beam-induced characteristic X-rays, wherein the sample is held by changing the inclination of the sample surface so as to have a line emission angle. According to a second aspect of the present invention, a proton beam is applied to the sample surface so that the characteristic X-ray induced from the sample surface introduced into the X-ray detector makes an angle of 2 ° or less with the sample surface. A sample holding stage for holding the sample so that the inclination of the sample surface can be adjusted; and a slit having a width of 1 mm or less and being arranged in front of the characteristic X-ray inlet of the X-ray detector and being parallel to the sample surface. Is an oblique emission measurement type-proton beam irradiation-induced characteristic X-ray sample surface observation / analysis apparatus characterized by having a member provided with.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail. A. FIG. 1 illustrates an outline of a sample surface observation / analysis device using a proton beam. The inside of the vacuum chamber (VC) is maintained at a degree of vacuum of 1.0 × 10 ⁻⁵ Torr or less. In the chamber, the inclination of the surface of the sample to be analyzed can be changed so that the angle θ formed between the characteristic X-ray induced by irradiation with the proton beam (PB) and the sample surface is 2 ° or less. A rotatable sample stage (SS) to be held is arranged. If fine particles (aerosol or the like) exist on the surface irradiated with the proton beam, characteristic X-rays specific to the elements constituting the fine particles are emitted. The emitted characteristic X-rays (CX) are transmitted through an X-ray window material [Kapton foil (CF) or the like] through which the X-rays can be transmitted, and an X-ray detector [XD: energy dispersive X-ray detector (EDX)] The presence of fine particles and the elements of the fine particles are observed and analyzed.
The feature of the present invention is the characteristic X-ray intake side of the detector,
A member (S) provided with a slit (SL: width 1 mm or less)
F) is provided to limit the characteristic X-rays to be taken, thereby improving the noise / signal ratio characteristic over the conventional GE-PIXE analysis method. The feature of the present invention is the discovery that the operation and effect when the slit is provided are remarkable in oblique emission characteristic X-ray observation. B. The member (SF) provided with the slit (SL: 1 mm or less in width) is made of a metal plate material such as polymer-coated molybdenum. The upper limit of the slit width is limited to about 1 mm in terms of the noise / signal ratio characteristic, but the lower limit can be appropriately determined in relation to the observation characteristic X-ray.

C. The observation / analysis method of the present invention can be applied to various material samples attached to the surface of various materials. In particular, it can be used for observation and analysis of the surface of a silicon semiconductor material, and analysis of airborne fine particles that cause various pathologies. That is, it exerts a remarkable action and effect on observation and analysis of a trace component in a minute region. D. The characteristic X-ray detector is arranged at a position separated from the sample by 50 mm or more. Therefore, the member provided with the slit is also arranged with its position changed accordingly. This amplifies the selectivity between the characteristic X-rays generated from inside the sample and refracted at the interface and the characteristic X-rays reflected at the sample surface.

[0010]

EXAMPLE 1 A sample was made of gold (50 nm) -copper prepared on a silicon wafer.
(500 nm), the outermost surface of which is a gold layer. The sample was set at the center of a rotary stage (sample holding stage) in a chamber with a degree of vacuum of 10 ⁻⁵ Torr. The sample was irradiated with a proton beam of 2.5 MeV-100 nA at an incident angle of 90 degrees. The characteristic X-rays induced by the proton beam were measured with a semiconductor X-ray detector placed in the atmosphere through a Kapton foil. A member provided with a slit having a width of 1 mm is attached to the tip of the semiconductor X-ray detector, and the distance between the sample and the X-ray detector is 100 mm.
FIG. 2A is a PIXE spectrum measured at an emission angle of 45 degrees. Characteristic X-ray AuL line from gold and copper thin film, CuK
Although α rays are observed, the characteristic X-ray intensity of copper is observed to be stronger than that of gold due to the large thickness of copper. FIG.
FIG. 2B is an enlarged view of the vertical axis (intensity axis) of FIG. The PIXE spectrum is characterized in that the background is small because the bremsstrahlung by the charged particles is small, but it is clear that the background is large in the low energy region as shown in FIG. . FIG. 2C is a PIXE spectrum obtained by measuring the same sample at an emission angle of 0.5 degrees. The intensity scales on the vertical axis in FIG. 2B and FIG. 2C are almost the same, but in FIG. 2C it is clear that the background on the low energy side is smaller. That is, it has been clarified that the background in the PIXE spectrum is reduced by oblique emission measurement. Further, the intensity of the CuK wire is A
The intensity is reduced as compared with the uL line intensity. This indicates that element analysis of the outermost surface can be performed by reducing the emission angle.

Example 2 A sample is a two-layer thin film of copper (10 nm) -bismuth (6 nm) formed on flat glass, and the outermost surface is a copper layer. The sample was placed at the center of a rotating stage in a chamber with a degree of vacuum of 10 ^-5 Torr. 2.5MeV-100nA for sample
Was irradiated at an incident angle of 90 degrees. The characteristic X-rays induced by the proton beam were measured with a semiconductor X-ray detector placed in the atmosphere through a Kapton foil.
A member provided with a slit having a width of 1 mm is attached to the tip of the semiconductor X-ray detector, and the distance between the sample and the X-ray detector is 100 mm. FIG. 3A is a PIXE spectrum at an emission angle of 0.4 degrees. Only the characteristic X-ray CuKα of copper existing on the outermost surface is measured. FIG. 3B shows a spectrum at an emission angle of 1 degree. In addition to CuKα rays, characteristic X-rays BiLa rays of bismuth are also observed.
Further, when the emission angle is set to 4.4 degrees, as shown in FIG. 3C, CaKα rays and FeKα rays, which are characteristic X-rays, from the glass substrate are also observed. Thus, it was shown that by increasing the emission angle from 0.4 degrees to 1 degree and further to 4.4 degrees, elemental analysis from a deeper place is possible. That is, it was found that the elemental analysis in the depth direction can be performed nondestructively by changing the emission angle.

Example 3 The sample is an aerosol (particulate matter suspended in the air) collected on a silicon wafer. The sample was in a vacuum of 10 ^-5 Torr
r at the center of the rotating stage in the chamber.
The sample was irradiated with a proton beam of 2.5 MeV-100 nA at an incident angle of 90 degrees. The characteristic X-rays induced by the proton beam were measured with a semiconductor X-ray detector placed in the atmosphere through a Kapton foil. A member provided with a slit having a width of 1 mm is attached to the tip of the semiconductor X-ray detector, and the distance between the sample and the X-ray detector is 100 mm.
It is. FIG. 4A is a PIXE spectrum at an emission angle of 4.4 degrees. Since a large background of continuous X-rays is observed on the low energy side, it is difficult to analyze trace elements such as calcium contained in the aerosol sample. On the other hand, FIG. 4B shows the result of measuring the same aerosol sample at an emission angle of 0.4 degrees. The measurement time in FIGS. 4A and 4B is also 180 seconds. At the oblique emission angle, the background level generated by the silicon substrate is not detected, and the background level is clearly lower than that in FIG. 4A. As a result, CaKα and Ti
Characteristic X-rays such as Kα and ZnKα are observed with high sensitivity. Eventually, the detection limit of calcium was improved more than 7 times. Given the history of how many aerosol samples have been analyzed by PIXE analysis, reducing background and improving detection limits by oblique emission PIXE are important advances.

[0013]

As described above, in the oblique emission PIXE method, an aperture having a diameter of 1.0 mm or less or a slit having a width of 1.0 mm or less is provided at the tip of the X-ray detector, and the surface of the substrate, particularly a flat surface, is provided. When observing the particulate impurities on the substrate surface, not only does the characteristic X-ray of the oblique emission angle not appear from the substrate, but also the beam directly observed by the X-ray detector and once on the silicon wafer After reflection, as a result of the phenomenon of interference with the detected beam, there is an effect of increasing the intensity of characteristic X-rays, so that an excellent effect is obtained that is extremely effective for analyzing a minute sample. It is clear that such an observation method can be applied to the analysis of the presence of unknown impurities on the surface of a silicon wafer or the like and the impurities present, and has a great effect on the process control in semiconductor production.

[Brief description of the drawings]

FIG. 1 shows an example of a sample surface observation / analysis apparatus according to the oblique emission proton beam induced characteristic X-ray analysis of the present invention.

FIG. 2: Gold (50 nm) -copper (5) on a silicon wafer
The sample surface provided with the two-layer thin film of
(A), (a) Enlarged view of vertical axis (intensity axis) (b), Measurement result at emission angle 0.5 degree (c)

FIG. 3. Copper (10 nm) -bismuth (6
PIXE spectrum obtained by measuring the surface of the sample provided with the two-layer thin film of (nm) at an emission angle of 0.4 degree (a), an emission angle of 1 degree (b), and an emission angle of 4.4 degree (c).

FIG. 4 shows a PIXE spectrum measured at an emission angle of 4.4 degrees (a) and an emission angle of 0.4 degrees (b) using an aerosol collected on a silicon wafer as a sample surface.

[Explanation of symbols]

XD X-ray detector SF Member with slit SL Slit CX Characteristic X-ray CF Kapton foil SS Sample stage VC Vacuum chamber PB
Proton beam

Claims (3)

[Claims] 1. A characteristic X-ray induced from a sample surface by irradiation with a proton beam through a member provided with a slit having a width of 1 mm or less and taken into a detector.
Oblique emission measurement type-proton beam irradiation-induced characteristic X-ray, wherein an angle of the sample surface with respect to the irradiated proton beam is adjusted and observed so that an angle between the line and the sample surface is 2 ° or less. Surface observation and analysis method using 2. A sample beam is irradiated with a proton beam such that an angle (oblique emission angle) from the surface of characteristic X-rays induced from the sample surface by irradiation with the proton beam is 2 ° or less. 2. The apparatus according to claim 1, wherein the sample is held by changing an inclination of the sample surface so that an angle of the irradiated proton beam becomes an emission angle of the characteristic X-ray. Observation / analysis method of sample surface by oblique emission proton beam induced characteristic X-ray. 3. The sample surface is irradiated with a proton beam so that the characteristic X-ray induced from the sample surface introduced into the X-ray detector makes an angle of 2 ° or less with the sample surface. A sample holding stage for holding the sample so that the inclination of the sample surface can be adjusted, and a slit parallel to the sample surface with a width of 1 mm or less and arranged in front of the characteristic X-ray inlet of the X-ray detector are provided. Emission measurement type-proton beam irradiation induced characteristic X characterized by having a bent member
A sample surface observation and analysis device using X-rays.