JPH06265491A - Secondary electron spectroscope - Google Patents

Abstract

PURPOSE:To provide such a secondary electron spectroscope as capable of selectively observating a specific material alone in plural pieces of matter by means of changing an ultraviolet wavelength to be radiated together with X-rays at the time of observing a certain element in a sample in which plural materials including the same element exist. CONSTITUTION:A laser beam out of a YAG laser light source 1 is branched off by a half mirror 30, converting it into a triple higher harmonic wave over an ultraviolet wave length area with a nonlinear crystal 32, and an ultraviolet wavelength is regulated by optical parametric generator 33 according to observation object material, thereby changing an optical path with a mirror 34. Next, it is further converted into a higher harmonic wave by a harmonic generator 35, condensing it on a sample with a condenser lens 36, and intensity in an ultraviolet wave is regulated by a wedge 37, while an ultraviolet optical path, which radiates ultraviolet rays as an exciting radiant light to the sample 11 via an ultraviolet-ray transmitting window 38 installed in a vacuum sample chamber 8, is constituted there, and ultraviolet rays are irradiated to the sample 11 together with X-rays.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention detects a spectral spectrum of secondary electrons emitted from a sample by irradiating the sample with a particle beam of electrons, protons, positrons, ions, neutrons, photons and the like. The present invention relates to a secondary electron spectrometer.

[0002]

2. Description of the Related Art In recent years, in the fields of surface analysis of semiconductors, particularly analysis of organic substances containing carbon, analysis of semiconductor processes such as CVD, evaluation of organic electronic devices, etc., soft X with a long wavelength of several Å or more is used. Evaluation using methods such as ESCA (electron spectrochemical analysis) and Auger spectroscopy using light in the linear region as a probe is required. In particular,
Recently, oxygen (K absorption edge 23.32Å), nitrogen (K absorption edge 30.99Å), carbon (K absorption edge 43.68Å),
Phosphorus (L absorption end 94Å, K absorption end 5.8Å), calcium (L absorption end 35Å), sodium (K absorption end 11.6)
Å), magnesium (K absorption edge 9.5 Å) and other biological materials are actively researched, and analysis using a soft X-ray with a long wavelength of 5 Å or longer as a probe is required.

However, since the X-ray tube is used as the light source in the current commercially available evaluation apparatus, only characteristic X-rays with a short wavelength of several Å or less can be used, and carbon is the main factor. In the evaluation of organic substances that are composed,
There is a problem that the absorption coefficient is small, the production rate of secondary electrons such as photoelectrons and Auger electrons becomes poor, and the analysis sensitivity becomes low. Moreover, since only X-rays having a specific wavelength can be used, multifaceted analysis cannot be performed, which is particularly disadvantageous in elemental identification.

For this reason, evaluation using light in the soft X-ray region having a long wavelength of several Å or more is required. Conventionally, a large-scale facility is required to obtain white soft X-rays. A SOR (synchrotron radiation) light source is required, which is extremely difficult for general users to implement.

In order to solve such a problem, the applicant of the present invention has proposed an electron spectroscopic analyzer using a laser plasma light source in Japanese Patent Laid-Open No. 4-140651.
In this analyzer, in a vacuum of 10 ^-4 Torr or less, 10 ¹²
It irradiates with a laser beam with an intensity of W / cm ² or more, and puts the metal of the target into a plasma state to emit soft X-rays with a wavelength of 5 Å or more. Can be realized.

Light in the soft X-ray region emitted from the laser plasma light source can be dispersed in a wider range by using an oblique incidence type spectroscope than the constant deviation type spectroscope. A specific wavelength can be extracted by providing a slit on the Roland circle of the spectroscope. Therefore, by irradiating the sample surface with monochromatic X-rays passing through this slit, the secondary electrons emitted thereby are detected by an electron spectroscope installed at a specific observation angle, and the energy analysis is performed to obtain the sample. It is possible to identify elements on the surface with high accuracy. That is, by observing the energies of the photoionizing electrons and Auger electrons emitted from the surface of the sample, it is possible to know which element of which energy level and which electron of many energy levels were emitted.

Further, by selecting the wavelength of X-rays to be irradiated, the observed amount of Auger electrons from a specific element can be increased. For example, by irradiating a wavelength in the vicinity of the K absorption edge of carbon, it is possible to preferentially observe the carbon KLL Auger electron with an emission kinetic energy of about 250 eV, and thereby measure the carbon content on the sample surface. You can

As described above, according to the electron spectroscopic analyzer developed by the present applicant, Auger electrons from various elements can be observed by selecting the wavelength of X-rays. Elemental analysis with higher sensitivity can be performed as compared with ESCA using a wire tube. In addition, by scanning the wavelength of X-rays irradiated on the sample and measuring the amount of secondary electrons emitted, EXAFS (Extended
Analysis by X-ray Absorption Fine Structure) is also possible. Further, an X-ray optical system such as an oblique incidence mirror is installed behind the slit provided on the Roland circle of the spectroscope,
By forming a linear microbeam and scanning the sample stage with this, a two-dimensional image of the element distribution to be observed can be obtained. In this case, if a Schwarzschild type optical system or a wavelength dispersive X-ray optical system such as a zone plate is used as the X-ray optical system, the spectroscope can be omitted.

[0009]

When performing observation using the above-mentioned conventional technique, a plurality of substances may exist in the sample to be observed, and the same element may be contained in the plurality of substances. , The observation result does not always represent only the observation target element existing in a specific substance. For example, when the element to be observed is carbon, since carbon is contained in various substances, a plurality of proteins containing carbon are often present in the sample. Therefore, when a sample containing, for example, two kinds of substances containing carbon is irradiated with X-rays and carbon distribution is to be observed, carbon in each protein emits secondary electrons in response to the X-rays. Therefore, it is extremely difficult to obtain the carbon distribution of only one protein.

In view of the above problems, the present invention, when observing an element using a sample containing a plurality of substances containing the same element, selects only a specific substance from among the plurality of substances containing the element. It is an object of the present invention to provide a secondary electron spectroscopic device that can be visually observed.

[0011]

To achieve this object, a secondary electron spectroscopic apparatus according to claim 1 of the present invention is a radiation source for excitation, an X-ray source, the radiation source and the X-ray source. And a detector for detecting secondary electrons emitted from the sample when the sample is irradiated with excitation radiation and an X-ray source. Further, the secondary electron spectroscopic apparatus according to claim 2 of the present invention is characterized in that the wavelength of the excitation radiation is changed according to the substance to be observed in the sample.

[0012]

According to the constitution of claim 1 of the present invention, since the sample is irradiated with the excitation radiation (for example, ultraviolet ray) together with the X-ray, it is possible to obtain the distribution of the element concerned only with respect to the specific substance to be observed. You can In addition, claim 2 of the present invention
According to this configuration, since the wavelength of the excitation radiation irradiated on the sample can be changed, it is possible to easily obtain the distribution of the element concerned for a plurality of substances to be observed.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a diagram showing the configuration of a first embodiment of a secondary electron spectroscopy apparatus of the present invention. In this embodiment, the laser light from the YAG laser light source 1 is condensed by the condenser lens 2 and is incident on the polarizer 31 via the half mirror 30 to adjust the intensity of the laser light, and then provided on the vacuum container 3. The target 5 rotatably provided in the vacuum container 3 is irradiated through the window 4 and a part of the target 5 is turned into plasma to generate soft X-rays. The soft X-rays generated by the target 5 are
The concave diffraction grating 7 provided in the vacuum container 6 communicating with the vacuum container 3 splits the light and guides it to the vacuum sample chamber 8 communicating with the vacuum container 6.

In the vacuum sample chamber 8, a slit 9, an X-ray optical system (Wolter mirror optical system) 10, a sample holder 12 for holding a sample 11, an electron spectroscope 13 and an MC.
A P (microchannel plate) 14 is provided, and the entire vacuum sample chamber 8 is configured to be movable with respect to the vacuum container 6 so that the slit 9 can move on the Rowland circle of the concave diffraction grating 7. As shown in FIG. 3, the electron spectroscope 13 is a coaxial cylindrical electrostatic type having an entrance slit 15 and an exit slit 16, and two cylindrical electrodes 17 and 18 provided between these slits. This is a support 19
Hold on. In addition, the sample holder 12 has a support base 19
On the other hand, it is provided so as to be movable in a two-dimensional direction within a plane orthogonal to the incident direction of soft X-rays.

In this embodiment, a lid 20 is provided between the vacuum container 6 and the vacuum sample chamber 8 so that they communicate with each other through the slit 9. Further, a gas injection device 21 is connected to the vacuum sample chamber 8 so that He gas is enclosed in the vacuum sample chamber 8 prior to the analysis of the secondary electrons of the sample 11. Here, the vacuum state of the vacuum containers 3 and 6 and the vacuum sample chamber 8 is set to 10 ⁻⁴ to 10 ⁻⁶ Torr.

In the first embodiment, the vacuum sample chamber 8 is further added.
An ultraviolet ray optical path for irradiating the sample 11 therein with ultraviolet rays as excitation radiation is provided. That is, in this ultraviolet light path, a part of the laser light from the YAG laser light source 1 is branched by the half mirror 30, and the nonlinear crystal 32 divides the ultraviolet light into 3 in the ultraviolet wavelength range.
Converted to double harmonics, the ultraviolet wavelength is adjusted by the optical parametric oscillator (OPO) 33, the optical path is changed by the mirror 34, the harmonics are further converted by the harmonic generator (SHG) 35, and the condensing lens 36 is used. The light is focused on the sample, the intensity of the ultraviolet light is adjusted by the wedge-shaped glass (wedge) 37, and the sample 11 is obliquely irradiated with the ultraviolet light through the ultraviolet light transmission window 38 provided in the vacuum sample chamber 8.

As shown in FIG. 2, the OPO 33 includes a half-wave plate 40, a polarizer 41, beam expanders 42 and 43, a BBO resonance mirror 44, and a BBO from the incident side.
It comprises a crystal 45 and a BBO resonance mirror 46 (OPO
Are commercially available from BMI, France). Here, optical parametric oscillation (OPO) is a nonlinear optical process that oscillates light that can be tuned in a wide range, and continuous wavelength tuning is performed by adjusting temperature change or angle of a BBO crystal that is a nonlinear optical crystal. The tuning range on the short wavelength side extends to the ultraviolet region (400 nm to). Further, as shown in FIG. 1, by using SHG35 in combination, the tuning range can be further extended to the shorter wavelength side. In this embodiment, a wide wavelength range (200
It is possible to obtain ultraviolet rays having a wavelength of nm to).

The wedge 37 includes a mirror 34 and SH.
Sample 11 of ultraviolet rays from G35 through the condenser lens 36
Is an element that adjusts the intensity of ultraviolet light when irradiating the sample, and changes the optical path length (glass thickness) of the ultraviolet light that passes through the wedge by moving in the direction orthogonal to the optical axis of the ultraviolet light (the direction of the arrow shown in the figure), Adjust the intensity of UV light that is radiated on. As the wedge 37, a substance (for example, BK7; glass) having a sufficiently high absorption rate for ultraviolet rays is used. If the size of the region irradiated with ultraviolet rays does not matter, if the condenser lens 36 is movable in the optical axis direction of the ultraviolet rays, the focus state can be changed to adjust the intensity of the ultraviolet rays. Yes, in that case the wedge 37 is omitted.

Next, the operation of the first embodiment will be described.
6 (a) to 6 (f) respectively show transitions of electronic states when carbon atoms emit Auger electrons in this example with time. In the conventional example, the Auger electron was directly emitted by irradiating with X-ray, but in this practical example, first, as shown in FIG. One electron is excited or ionized to leave a vacancy in the 2P orbit of the carbon atom as shown in FIG. Next, FIG.
As shown in, the soft X-rays are irradiated to excite 1S electrons into the vacant holes of the 2P orbit still open. As a result, the state shown in (d) of the same figure is obtained, but since this state is extremely unstable in terms of energy, the electrons of the 2P orbit are transited to the holes of the 1S orbit, and as shown in (e) of the same figure. It will be in a stable state. At the time of this transition, another electron in the 2P orbit is emitted to the outside, and finally the electronic state as shown in FIG.
The observation of the protein by electron spectroscopy is performed by detecting the electrons emitted at the stage of FIG. At this time, only the carbon in the specific substance can be selected by selecting the wavelength of the ultraviolet light with which the sample is irradiated as follows.

On the other hand, in this embodiment, first, 2P electrons are ionized or excited by the reverse process of the third transition from the ground state shown in FIG. 5 (a) by ultraviolet irradiation to realize the electronic state of FIG. 5 (b). To do. Then, from this state, the 1S electron is excited by the soft X-ray to the still vacant 2P orbit by the reverse process of the second transition as shown in FIG. After this transition process, the state shown in FIG. This state is exactly the same as that in the case of FIG. 6B, and the electrons are ejected by the energy when the outer shell electrons make a transition to the inner shell vacancy. At this time, only the carbon in the specific substance can be selected by selecting the wavelength of the ultraviolet light with which the sample is irradiated as follows.

That is, the wedge 37 is used so that the laser light source for generating soft X-rays can be shared for ultraviolet ray generation.
A wedge drive circuit (not shown) for driving the sample 11 is provided, and this wedge drive circuit is controlled by a wedge drive signal from a host computer (not shown) so that the intensity of the ultraviolet rays with which the sample 11 is irradiated becomes appropriate. Also OP
An OPO control signal is output to the O33 from the host computer to control the wavelength of ultraviolet rays by changing the temperature or angle of the BBO crystal inside the OPO33.

Specifically, first, before starting the observation,
Select the substance name (or code number, etc.) of the carbon-containing substance to be observed from Table 1 and enter it.

[Table 1] With this input, as will be described later, when the ultraviolet light is generated using the laser light from the YAG laser light source 1, the ultraviolet wavelength is automatically adjusted so as to have a suitable ultraviolet wavelength according to the target substance as shown in Table 1. The UV wavelength is adjusted to 205 to 230 nm for observing tryptophan, and to 250 to 300 nm for observing tyrosine. In addition to the above-mentioned automatic adjustment function, it is possible to observe a substance whose suitable UV wavelength is unknown, so a manual adjustment function shall be added.

After the above adjustment is completed, the YAG laser light source 1 is driven to generate laser light. A part of the laser light is converted into ultraviolet rays as described above after being branched by the half mirror 30, but the intensity of the laser light that has proceeded straight through the half mirror 30 is adjusted by the polarizer 31 that can rotate about the optical axis center. It collides with the target 5 and generates soft X-rays. At that time, the intensity of soft X-rays can be controlled independently of the intensity of the ultraviolet rays by the polarizer 31. Regarding this soft X-ray, while the soft X-ray of the above-mentioned conventional example has the energy required to excite 1S electrons to the 2P orbit, the soft X-ray of the present embodiment shows carbon inner shell electrons. Since it is insufficient for direct excitation or ionization, only carbon excited by ultraviolet rays reacts with this soft X-ray.

Therefore, the vacuum sample chamber 8 is moved with respect to the vacuum container 6, and is dispersed by the concave diffraction grating 7 in the vacuum sample chamber 8 to pass through the slit 9 for vacuum sample wet and soft X having a desired wavelength.
A line is selected (when the desired wavelength is changed according to the substance to be observed, the concave diffraction grating 7 is moved and adjusted), and the soft X-ray of the selected wavelength is sampled via the X-ray optical system 10. 11 and irradiate the secondary electrons emitted by the soft X-ray irradiation and the ultraviolet irradiation with the MCP 14 while sweeping the voltage applied to the two cylindrical electrodes 17 and 18 through the electron spectroscope 13. When detecting, by sweeping the voltage applied to the two cylindrical electrodes 17 and 18 in the electron spectroscope 13, a specific kinetic energy according to the applied voltage among the charged particles entering from the entrance slit 15 is obtained. Particles are deflected so as to pass through a circular orbit passing between the electrodes, and are ejected from the ejection slit 16.
4 will be incident. Therefore, the secondary electron of carbon can be emitted only from a specific substance (specific protein) by using X-rays and ultraviolet rays together.

The spectral spectrum of secondary electrons is measured in a state where He gas is sealed in the vacuum sample chamber 8 and the difference between the energy value of the known secondary electron resonance line of this He gas and the actual measured value is measured. Is detected and the difference is subtracted from the measured energy value of the secondary electron emitted from the sample 11, the measured energy value of the secondary electron of the sample 11 can be calibrated to determine the absolute value. .

FIG. 4 shows the energy spectrum of the automatic ionization resonance line of He gas upon electron impact.
The energies of these resonance lines are known, and especially when He gas is bombarded with high-energy electrons, there is little signal due to ionization other than the resonance line, and the automatic ionization resonance line is 40e.
Since it appears only below V, the background noise when analyzing the secondary electrons of the sample 11 can be made extremely small. Therefore, if the difference between the energy value of the known secondary electron resonance line of He gas and the actual measured value is obtained, the amount of energy fluctuation due to the undesired electromagnetic field generated in the electron spectroscope 13 can be known. Therefore, the absolute value of the secondary electron energy of the sample 11 can be accurately determined by subtracting this variation from the measured value of the secondary electron energy of the sample 11.

It should be noted that the present invention is not limited to the above-described embodiments, but many modifications and variations are possible. For example, in the above-described embodiment, the He gas is enclosed in the vacuum sample chamber 8 at the time of measurement, but the type of this gas can be appropriately selected according to the particle beam that impacts the sample 11. . For example, when photons such as X-rays are used, Auger electrons are generated more easily than automatic ionization resonance lines. In this case, therefore, calibration is performed using Kr gas having a known MNN Auger resonance line energy spectrum. Then, the absolute value of the secondary electron energy of the sample 11 can be accurately determined.

Further, the electron spectroscope 13 is not limited to the coaxial cylindrical electrostatic type shown in FIG. 3, but a parallel plane type electrostatic electron spectroscope, a hemispherical type electrostatic electron spectroscope, and a cylindrical mirror. Type electrostatic electron spectroscope or electric field blocking type electrostatic electron spectroscope which deflects charged particles by an electric field may be used, and especially when the kinetic energy of the charged particles to be analyzed is large. Alternatively, a magnetic field deflector may be used.
Although the MCP is used as the detector in FIG. 1, an electron multiplier tube may be used instead.

[0029]

As described above, according to the present invention, in the structure of claim 1, the sample is irradiated with the X-ray from the X-ray source and the radiation source is irradiated with the excitation radiation, and the detector is used. Since the secondary electrons emitted by the sample are detected,
By appropriately selecting the wavelength of the excitation radiation according to the substance to be observed, the distribution of the element or the like can be obtained only for the specific substance to be observed. In the configuration of claim 2 of the present invention, since the wavelength of the excitation radiation is changed according to the observation target substance in the sample, the excitation radiation irradiated to the sample according to the change of the observation target substance. Since the wavelength of is changed, it is possible to easily obtain the distribution of the element concerned only for the specific substance to be observed.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of a first embodiment of a secondary electron spectroscopy apparatus of the present invention.

FIG. 2 is a diagram showing a configuration of an optical parametric oscillator according to a first embodiment.

FIG. 3 is a diagram showing a schematic configuration of the electron spectrometer shown in FIG.

FIG. 4 is a diagram showing a known autoionization resonance energy spectrum of He gas that can be used in the first embodiment.

5 (a) to 5 (f) are diagrams showing transitions of electron states when a carbon atom emits Auger electrons in the above-mentioned example.

[Explanation of symbols]

 1 YAG Laser Light Source 3, 6 Vacuum Container 4 Window 5 Target 7 Concave Diffraction Grating 8 Vacuum Sample Chamber 9 Slit 10 X-ray Optical System 11 Sample 12 Sample Holder 13 Electron Spectrometer 14 MCP 21 Gas Injection Device 30 Half Mirror 31 Polarizer 32 Nonlinear crystal 33 Optical parametric oscillator (OPO) 35 Harmonic generator (SHG) 37 Wedge glass (wedge) 38 Ultraviolet transmission window

Claims (2)

[Claims] 1. A radiation source for excitation, an X-ray source, and radiation and X-rays for excitation from the radiation source and the X-ray source to a sample.
A secondary electron spectroscope comprising a detector for detecting secondary electrons emitted from the sample when irradiated with a radiation source. 2. The secondary electron spectroscopic apparatus according to claim 1, wherein the wavelength of the excitation radiation is changed according to the substance to be observed in the sample.