JPH09250993A - Secondary ion mass spectrograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary ion mass spectrograph which can microanalyze light element. SOLUTION: The secondary ion mass spectrograph comprises ion generating means 10 for emitting a primary ion beam to the part of a sample, analyzing means 24 for analyzing secondary ion sputter excited from the surface with the primary ion beam, and electron generating means 14 for generating electron for neutralizing charge generated on the surface of the sample by the generation of the secondary ion beam, wherein infrared beam generated from heating means 34 is emitted to the sample S, mass analysis is made in the state of no background due to the residual element by emitting the primary ion beam after the remaining element adhered to the surface of the sample S is previously vaporized by the primary ion beam, and hence the light element can be microanalyzed.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a secondary ion mass spectrometer for analyzing a secondary ion beam generated by irradiating a sample with a primary ion beam.

[0002]

2. Description of the Related Art A secondary ion mass spectrometer is known as one of the apparatuses for surface analysis of substances. The secondary ion mass spectrometer is a sample by irradiating the sample surface, which is usually placed in a depressurized closed container, with primary ions, and performing mass spectrometry of secondary ions generated by exciting the sample surface by sputtering. The element existing on the surface is analyzed.

However, even if the depressurized state in the closed container is set to a high vacuum, light elements such as oxygen, hydrogen, carbon, or nitrogen remain in the closed container, although they are slightly. Since these residual elements are adsorbed on the sample surface to be analyzed in the form of a simple substance or a compound, even if an attempt is made to analyze light elements on the sample surface using a secondary ion mass spectrometer, they remain adsorbed on the sample surface. Since the mass was measured including the elements, it was not possible to carry out microanalysis.

This becomes a serious problem especially when the sample to be analyzed is an insulating material. When the sample is an insulator, the sample surface is charged when the sample is irradiated with the primary ion beam. Therefore, the sample surface is charged by irradiating the sample with the electron beam, and the secondary ion mass spectrometry is performed.

However, when the sample is irradiated with an electron beam, the residual elements adsorbed on the surface of the sample are ionized, so that the influence of the residual elements is extremely large, and a small amount of sample analysis is performed using a secondary ion mass spectrometer. It was impossible.

[0006]

As described above, the conventional secondary ion mass spectrometry apparatus analyzes a trace amount of light element contained in the sample due to the effect of the residual element remaining in the closed container. I couldn't. The present invention has been made in view of such problems, and an object thereof is to provide a secondary ion mass spectrometer capable of measuring light elements in a measurement sample.

[0007]

According to a first aspect of the present invention, there is provided a hermetically sealed container on which a sample can be placed, an ion generating means for irradiating a part of the sample with a primary ion beam, and the above-mentioned primary ion beam. A secondary ion mass spectrometer having an analyzing means for analyzing secondary ions excited by sputtering from a sample surface, and a heating means for heating the vicinity of the primary ion beam irradiation part.

The second invention of the present application is the secondary ion according to the first invention, which has an electron generating means for generating an electron for neutralizing an electric charge generated on the sample surface by the generation of the secondary ion beam. It is a mass spectrometer. In the third invention of the present application, the heating means has an output of 0.1 to 100 W / cm ^2.
2. The secondary ion mass spectrometer according to claim 1, which is infrared light.

[0009]

DETAILED DESCRIPTION OF THE INVENTION A secondary ion mass spectrometer according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of a secondary ion mass spectrometer of the present invention. In the figure, a secondary ion mass spectrometer 1 includes a sample chamber 3 in which a sample S can be installed, an ion generator 5, and a primary ion introduction path 7 for introducing primary ions generated from the ion generator 5 into the sample chamber 3.
Ion generating means 10 including an electron lens 9 for converging the introduced primary ions on the sample surface, and a mass spectrometric section 21 and a mass analyzer 21 for mass-separating secondary ions generated by irradiating the sample with the primary ion beam. A mass analyzer 20 including a secondary ion detector 23 for detecting the amount of secondary ions, an electrostatic lens 19 for taking the secondary ions into the mass analyzer 20, and an introduction path of the secondary ions to the mass analyzer. And an analyzing means comprising a secondary ion introduction path 17
4. There is a closed container including an electron gun 11 that generates a charge for canceling the charge when the surface of the sample S is charged and an electron generation means 14 that includes a charge introduction path 13, and a vacuum pump is provided in the closed container. The pressure is reduced by 15. Further, as the heating means 34, an infrared light laser generator 25 and a reflecting mirror 33 for aligning a laser generated from the infrared light laser generator so as to irradiate the vicinity of the position where the primary ion beam of the sample S is irradiated. Become. Further, the generated laser passes through the laser-transmitting optical window 29 provided in the closed container and enters the closed container.

The inner wall surface of the closed container is inert,
It is desirable to select a material that does not easily adsorb residual gas, and it is desirable to use, for example, stainless steel, aluminum alloy, or the like.

As the ion generating means, the analyzing means and the electron generating means, the same secondary ion mass spectrometer can be used. The ion generating means may be any means as long as it can irradiate the surface of the sample S with an ion beam to excite it by sputtering to sputter the element to be analyzed. For example, Cs, oxygen, Ar, Xe, or the like can be used as the ions generated from the ion generator. Further, in FIG. 1, the ions generated from the ion generator are converged by an electron lens to form an ion beam. It is desirable to set the primary ion introduction path, particularly the connection position between the primary ion introduction path and the sample container, to be as narrow as the width of the ion beam passing therethrough. This is because the ion generator may reduce the degree of vacuum in the sample container.

The analyzing means comprises a mass spectrometric section and a secondary ion detecting section. In the mass spectrometric section, a specific secondary ion to be analyzed is subjected to mass separation, and only the specific secondary ion is allowed to pass through and introduced into the secondary ion detecting section. The secondary ion detector measures the number of secondary ions that have passed through the mass spectrometer,
As a result, the amount of secondary ions of the substance to be measured can be measured. Generally, a double focusing mass analyzer or a quadrupole mass analyzer is used for the mass analysis unit, and a Faraday cup or an electron multiplier tube is used for the secondary ion detection unit.

In the electron generating means, the sample S is made of SiO ₂ , Si.
_{This is} especially necessary in the case of insulators such as ₃ N ₄ and Al ₂ O ₃ . When the sample is an insulator, it is charged when the surface of the sample is excited by sputtering. Therefore, it is possible to neutralize the charge by irradiating electrons with the electron generating means. The charged region is a range wider than the irradiation part centering on the primary ion irradiation part of the sample. Therefore, the irradiation range of neutralizing electrons is usually 100 to 100 nm with respect to the primary ion irradiation part centering on the sample irradiation position.
It is desired to set it in the range of 1000%, more preferably 100 to 400%.

The secondary ion mass spectrometer of the present invention is used under a reduced pressure of usually 10 ^-5 Pa or less, more preferably 10 ^-7 Pa in order to reduce the background. Such a reduced pressure state can be created by connecting a vacuum pump to the closed container.

Such a secondary ion mass spectrometer is capable of storing H, O, C or N in a closed container despite the reduced pressure environment.
Light elements such as remain, and adhere to the sample surface as a simple substance or compound.

The heating means of the present invention is for removing the residual element attached to the sample surface from the sample surface. That is, residual elements adhering to the sample surface are vaporized, and the residual ions in the secondary ions are reduced by irradiating the primary ions with the residual elements removed from the sample surface, and there is no background (such as residual elements). (State in which substances other than the object to be measured are not included in the measured value) It becomes possible to measure the light elements contained in the sample.

Therefore, the heating means in the present invention is
Any material can be used without particular limitation as long as it can heat at least the measured portion (primary ion beam irradiation portion or neutralization electron irradiation portion) of the sample. Further, the heating means in the present invention is preferably one that can selectively heat only a part of the sample. That is, the heating position is sufficient if the primary ion beam irradiation part, or the residual element of the neutralization electron irradiation part can be vaporized, and if a wider range than necessary is heated, the vaporized residual element concentration in the closed container increases, A background resulting from the residual element is generated in the analysis result. Therefore, in the vicinity of the primary ion beam irradiation unit, that is, the primary ion irradiation unit or the neutralizing electron irradiation unit, 100 to 1000% of these irradiation units,
It is desirable to heat within the range of preferably 100 to 200%. As a method for heating only a part of the sample, a heating means is preferably used by using energy such as infrared light as a laser beam.

The heating temperature of the sample is 60 ° C. or higher and 300.
C. or lower, more preferably 80.degree. C. or higher and 300.degree. C. or lower. This is because if the heating temperature is too low, the residual elements adhering to the sample surface cannot be vaporized and removed sufficiently, and if the heating temperature is too high, the sample itself may deteriorate. When a laser beam is used as the heating means, a wavelength having a high absorption efficiency of the sample may be usually used. For example, infrared light (wavelength ² to 40 μm) having a wavelength of 0.1 to 100 W / cm ² , more preferably, 0.2 ~
Heating may be performed with energy of 40 W / cm ² . Specifically, when the sample is SiO ₂ , laser light having a wavelength of 10 to 11 μm is selected.

Further, in the present invention, the effect can be obtained even when the electron generating means is not used.
However, when the charge of the sample surface is neutralized by the electron generating means, the residual element is ionized by the electron.
The ionized residual element has a larger background to the measured value of the element to be measured than the residual element alone or the compound. Therefore, when the sample is an insulating material and an electron generator is used, mass spectrometry of secondary ions is performed in a state where the sample is heated by the heating means and the residual elements on the sample surface are vaporized, as in the present invention. It is especially effective to do.

Further, although the above-mentioned effect can be obtained by heating the sample only when the sample is irradiated with the primary ion beam, the sample is heated in advance and the residual elements on the sample surface are vaporized, and then the primary ion beam is evaporated. By irradiating with an ion beam, it becomes possible to obtain analysis results with less background.

As described above, the sample analyzed by the secondary ion mass spectrometer of the present invention is, for example, SiO.
Insulating materials such as ₂ , Si ₃ N ₄ or glass
A conductive material such as i, GaAs or metal is also possible.

The present invention also etches the sample surface,
Since it is a method of analyzing the etched portion, it is suitable for measuring the vicinity of the surface from the sample surface to a depth of about 10 μm.

[0023]

EXAMPLE This example was carried out using an apparatus as shown in FIG. The sample was placed in the stainless steel sample chamber 3. This sample is a 7 mm square 630 μm thick Si substrate on which a 1 μm thick SiO ₂ film is formed by the CVD method.

FIG. 2 is a view showing irradiation positions of the primary ion beam, neutralizing electrons and infrared light. Primary ion beam,
The positions of irradiation of neutralizing electrons and infrared light will be described with reference to FIG.

The ion generating means is approximately in the center of the position where the sample is placed, in the range of 250 μm square (inside the innermost frame in the figure).
Primary ion energy 8 keV, primary ion current 1 ×
It was set so that the primary ion beam was irradiated under the condition of 10 −7 A. The electron generating means has the same center position as the center position of the primary ion beam, and has an electron energy of 1.2 keV within a 500 μm square range (inside the second frame in the figure).
The electron irradiation was set under the condition of 1 × 10 ⁻⁶ A. Further, the center position of the infrared light is the same as the center position of the primary ion beam, and the laser wavelength is set to 10.6 μm within the range of 400 μm radius (inside the circle in the figure)
The laser was set to oscillate at 0 W / cm ² .

The sample was placed in the sample container of the secondary ion mass spectrometer thus set, and H and C in the sample were measured under the following conditions. The result is shown in FIG. Next, a comparative example was performed in the same manner as the example except that the laser irradiation was not performed. FIG. 4 shows the results.

Comparing FIGS. 3 and 4, it is recognized that a large amount of both carbon and hydrogen is contained at the depth of 1 μm from the surface of the sample, that is, at the interface between the SiO ₂ film and the Si substrate. , The analysis results of the amount of hydrogen and the amount of carbon in the SiO ₂ film or the Si substrate are very different.

Despite the same material, the amount of hydrogen in the SiO ₂ film and Si substrate in FIG.
The large amount of carbon and the uniform distribution are due to the fact that residual carbon or residual hydrogen adhering to the sample surface was detected as the background. This is because the detection limit of hydrogen in a true sample is 10 ¹⁹ atoms / cm ³ and carbon is 9
It is shown that it is about × 10 ¹⁷ atoms / cm ³ , which means that it is impossible to detect a trace amount less than this.

As compared with the comparative example, as shown in FIG. 3, in the secondary ion mass spectrometer of the present invention, the detection of hydrogen was 10 ¹⁸ a.
It is shown that up to about 10 toms / cm ³ and 10 ¹⁷ atoms / cm ^{3 of} carbon are shown, and it can be seen that at least the detection limit is increased by about one digit as compared with the comparative example.

[0030]

As described above, according to the present invention, a secondary ion mass spectrometer capable of measuring a trace amount of a light element contained in a sample even in an environment where a light element to be measured remains. Can be provided.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an example of a secondary ion mass spectrometer of the present invention.

FIG. 2 is a schematic diagram showing irradiation ranges of a primary ion beam, a neutralizing electron, and an infrared light laser with which a sample is irradiated in the present invention.

FIG. 3 is a diagram showing detection results using the secondary ion mass spectrometer of the present invention.

FIG. 4 is a diagram showing a detection result using a conventional secondary ion mass spectrometer.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Secondary ion mass spectrometer 3 ... Sample chamber 5 ... Ion generator 7 ... Primary ion introduction path 9 ... Electron lens 10 ... Ion generating means 11 ... Electron gun 13 ... Electron introduction path 14 ... Electron generation means 15 ... Vacuum pump 17 ... Secondary ion introduction path 19 ... Electrostatic lens 20 ... Mass analyzer 21 ... Mass analysis unit 23 ... Secondary ion detection unit 24 ... Analyzing means 25 ... Infrared laser generator 29 ... Optical window 33 ... Reflecting mirror 34 ... Heating means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiko Yoshiki, No. 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Inside the Corporate Research and Development Center, Toshiba Corporation (72) Inventor Mamoru Takahashi Komukai-Toshiba, Kawasaki-shi, Kanagawa Town No. 1 Incorporated company Toshiba Research and Development Center (72) Inventor Ken Ken Suzuki 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Incorporated company Toshiba Yokohama Works (72) Inventor Akira Tanaka Komukai, Saiwai-ku, Kawasaki-shi, Kanagawa Toshiba Town No. 1 Inside Toshiba Research and Development Center

Claims (3)

[Claims] 1. A closed container on which a sample can be placed, an ion generating means for irradiating a part of the sample with a primary ion beam, and secondary ions which are excited by sputtering from the surface of the sample by the primary ion beam. And a heating means for heating the vicinity of the primary ion beam irradiation part. 2. The secondary ion mass spectrometer according to claim 1, further comprising electron generating means for generating electrons for neutralizing charges generated on the sample surface by the generation of the secondary ion beam. . 3. The heating means has an output of 0.1 to 100 W.
The secondary ion mass spectrometer according to claim 1, which is infrared light of / cm ² .