JPH08189917A - Mass spectrometry device - Google Patents

Abstract

PURPOSE: To make spacial resolution of a device below wave length of laser beam by introducing sample excitation laser beam with the use of an optical fiber provided with an opening smaller than the wave length of the laser beam, and analyzing with the use of an ion trap type mass spectrometer. CONSTITUTION: Laser beam 7 from a laser beam source 6 is, through a fiber 50, introduced into a sample 2, and converged on the sample 2. Thereby, a sticking material at a converging position of the laser beam on the surface becomes molecular beam 21a, and is made incident to an ion trap mass spectrometer 52. The ion trap mass spectrometer 52, at an ion trap part 53, accumulates ion for a specified period, and then the accumulated ion is sent to a detector 54 in order of mass number, for mass spectrometry. By the operation, chemical species of the sticking material at a specific position is identified. And, with the use of a piezoelectric element 60, the optical fiber 50 is moved two- dimensionally on the surface, so that the converging position of the laser beam is two-dimensionally scanned on the surface of the sample 2, and thus, a distribution of chemical species of the sticking material on the surface is identified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for analyzing the chemical species of minute deposits attached (contaminated) to electronic parts such as semiconductors, and more particularly to an analyzer for carrying out excitation / desorption using a laser for mass spectrometry. .

[0002]

2. Description of the Related Art A conventional mass spectrometer is disclosed in JP-A-4-3065.
As described in Japanese Patent Publication No. 49, it was as shown in FIG. 1 is a mass spectrometer, 2 is a sample, 6 is a laser light source, 8
Is a light source for observation illumination, 18 is a vacuum chamber, 21b is an ion beam, 22 is a condenser lens, 24 is a light reflecting mirror, 26 is a sample stage, 30 is an ion reflector, and 34 is an ion detector. The laser light generated from the laser light source 6 is condensed on the sample 2 by the condenser lens 22 and the light reflection mirror 24. The ions excited by this laser light are subjected to mass analysis in the mass analysis unit 1.

In this conventional apparatus, since the laser light 7a is condensed by the optical lens 22, the laser light can be condensed only in the size of the wavelength. Therefore, the spatial resolution is 7
The wavelength is limited to about a.

[0004]

In the above-mentioned conventional device, since the laser light is condensed by the lens, the laser light cannot be condensed to a size smaller than the wavelength, and the spatial resolution of the device is that of the laser light. It is limited to about the wavelength.

An object of the present invention is to enable the spatial resolution of the device to be less than the wavelength of the laser.

[0006]

In order to achieve the above object, the present invention introduces a sample excitation laser beam through an optical fiber having an opening smaller than the wavelength of the laser beam.

In order to achieve the same object, the present invention uses an ion trap type mass spectrometer as a mass spectrometer so that the deposits excited and desorbed by laser light can be efficiently analyzed.

[0008]

The system diagram of the present invention is shown in FIG. Reference numeral 50 is an optical fiber for introducing laser light, 2 is a sample, and 7a is laser light.
With the conventional laser focusing method using a lens, it is possible to narrow down only to about the wavelength, and it is difficult to make the spatial resolution of the device below the wavelength. In the present invention, by using a method in which the opening at the tip of the optical fiber 50 is made sufficiently smaller than the wavelength and the laser light is introduced into the sample, it is possible to focus the laser light 7a on the surface of the sample considerably smaller than the wavelength. . As a result, the laser beam can be irradiated only to the site smaller than the wavelength, and only the deposits on the site can be selectively vaporized, so that the spatial resolution can be set to the wavelength or less. In order to efficiently analyze the desorbed molecules, an ion trap type mass spectrometer 52 is used as a mass spectrometric unit, and a mechanism for synchronizing the laser irradiation time and the ion trapping time is provided, whereby the desorbed molecules are desorbed. Only ions can be detected efficiently and with extremely high sensitivity. As a result, it is possible to detect even the adhered matter in the extremely small portion with a good S / N ratio.

[0009]

【Example】

(Embodiment 1) In FIG. 1, 2 is a sample, 6a is a laser light source for vaporizing foreign matter, 7a is laser light, 17 is an optical path, 18 is a vacuum chamber, 19 is a vacuum container, and 21a is laser light 7a irradiation. Vaporized deposit, 26 is a sample table, 50
Is an optical fiber for introducing laser light, 51 is a Pockel cell,
52 is an ion trap mass spectrometer, 53 is an ion trap unit, 54 is a detector, 57 is a temperature controller for heating the optical fiber, 58 is a vacuum pump, and 60 is for moving the optical fiber 50 in the XYZ three-axis directions. Of the piezoelectric element.

The outline of the measurement will be briefly described. Laser light source 6
The laser light 7a from a is introduced into the sample by the optical fiber 50 and focused on the sample. As a result, only the deposits on the surface where the laser light is focused are selectively vaporized. The vaporized deposit becomes a molecular beam 21a and enters the ion trap mass spectrometer 52. Then, mass spectrometry is performed. This makes it possible to know the chemical species of the deposit at the specific position. Further, by using the piezoelectric element 60 and moving the optical fiber 50 two-dimensionally on the surface, the focus position of the laser light 7a can be continuously scanned two-dimensionally on the sample surface. The distribution state of chemical species can be known.

Next, the details of each component will be described. Figure 2 shows a diagram near the sample. Reference numeral 56 is the attached matter. The optical fiber 50 has an opening of about 30 nm at its tip. By bringing the tip of the optical fiber 50 closer to the sample surface by about 50 nm or less, it is possible to focus the laser light on the sample surface to about several tens of nm. The distance between the tip of the optical fiber and the sample is controlled by using the piezoelectric element 60 while observing the atomic force between the fiber and the sample surface. As the laser 6a, a continuous wave laser having a low peak output is used so as not to break the tip of the optical fiber.
By irradiating laser light continuously for a certain time,
Realizes the detachment of adhered substances. In this embodiment, an oscillation line of 364 nm of an Ar ion laser which is the shortest wavelength light of a continuous wave laser which is easily available is used. Then, the laser beam 7a from this laser is irradiated for a certain period of time. The irradiation time of the laser light 7a is controlled by the Pockel cell 51. The Pockel cell 51 transmits the laser light 7a only when a voltage is applied. Thus, the laser light irradiation time can be freely controlled by controlling the time for applying the voltage. Thereby, the optimum irradiation time condition can be selected. By combining these methods, only the diameter of several tens of nm is selectively heated to a high temperature, and only the deposit on that portion is selectively desorbed. Then, the desorbed molecules are detected by the ion trap mass spectrometer 52. The ion trap mass spectrometer 52 is a method of performing mass analysis by accumulating ions in the ion trap unit 53 for a certain period of time and sending the accumulated ions to the detector 54 in order of mass number. Therefore, the molecules that are desorbed for a certain period of time can be accumulated and detected, which is optimal for the desorption method by irradiation for a certain period of time using a continuous wave laser as in this embodiment. Further, in order to further improve the efficiency, a vacuum pump 58 is arranged on the opposite side of the sample of the ion trap mass spectrometer, and the sample is put into an operating exhaust state.

An explanatory view of the optical fiber 50 for introducing laser light is shown in FIG. The laser optical fiber 50 is coated with a tantalum vapor deposition film 61 except for the tip. By energizing this vapor deposition film, the optical fiber can be heated. By this mechanism, the fiber is heated during the irradiation of the sample surface with the laser beam 7a so that the detached molecules do not reattach to the fiber. This allowed the desorbed molecules to be efficiently introduced into the mass spectrometer.

In this embodiment, such a device was assembled and the measurement was performed. When the tip of the optical fiber 50 is brought close to the sample,
Molecules desorbing from the sample adhere to the optical fiber 50, the number of molecules entering the mass spectrometer is reduced, and sensitivity is lowered.
On the other hand, when the tip of the optical fiber 50 is moved away from the sample surface, the number of molecules that collide with the optical fiber 50 decreases, and the number of molecules that adhere to the optical fiber decreases, resulting in the mass spectrometer 52.
The number of molecules incident on is increased, but the spatial resolution is greatly reduced. Then, the tantalum vapor deposition film is energized, and the optical fiber 50
The temperature of was set to about 400 ° C. to prevent detached molecules from reattaching to the optical fiber 50. As a result, even if the distance between the tip of the optical fiber 50 and the surface is about 30 nm, reattachment to the fiber can be considerably prevented, and it can be efficiently sent to the ion trap mass spectrometer 52. Also, the laser light could be focused on the surface of the sample at about 50 nm.

A quadrupole type ion trap mass spectrometer 52 was used as the mass spectrometer. The laser irradiation time was set to 20 ms in the Pockel cell, and the ion trap time was set to 20 ms in synchronization with this.

FIG. 4 shows a sample measured by the method of this embodiment. An organic substance is vapor-deposited in a thin film on the surface of Al, and a pattern as shown in FIG. 4 is produced by electron beam exposure. Here, the width of the pattern is 50 nm, the black portion in the figure is the portion where the organic thin film is attached, and the white portion is the portion where the underlying Al is exposed. The spectra measured for both of these sites are shown in FIGS. FIG. 5 is a spectrum of a black portion of FIG. 4, that is, a portion where the organic thin film is attached, and FIG. 6 is a spectrum of a white portion, that is, a portion of a portion where the Al pattern is exposed. In the spectrum of FIG. 6, almost no peak due to the organic thin film is observed, while in FIG.
Since the spectrum of the organic thin film is clearly observed, the method of this embodiment realizes a spatial resolution of 50 nm or more. Spatial resolution is 500 nm with the conventional method
Since the degree was limited, this method improved the spatial resolution more than 10 times.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIG. As shown in this figure, the optical fiber 50 is tilted with respect to the sample. This makes it possible to partially prevent the molecules desorbed from the sample from adhering to the optical fiber 50.

In this embodiment, the tilt angle is 45 degrees.
As a result, the laser spot diameter on the sample surface is 100
Although it could be narrowed down to only about nm, the spatial resolution was lowered, but reattachment to the optical fiber could be considerably prevented without heating the optical fiber.

(Embodiment 3) FIG. 8 shows a system diagram of Embodiment 3 of the present invention. 55 is a time-of-flight mass spectrometer. The procedure up to laser irradiation is the same as that in the first embodiment, but in this embodiment, after trapped by the ion trap unit 53, all trapped molecules are pulsed for about 10 ns, and the time-of-flight mass spectrometer 55 is momentarily supplied. Is injected and mass spectrometry is performed. In this case, the analysis efficiency of the time-of-flight mass spectrometer is high, so the sensitivity is further improved, and it is possible to obtain a smaller mass spectrum of the deposit.

(Embodiment 4) FIG. 9 shows a system diagram in Embodiment 4 of the present invention. It is almost the same as the apparatus of the first embodiment, but here 62 is a liquid nitrogen reservoir, into which liquid nitrogen can be introduced to cool the optical fiber. 63 is a manipulator for moving the optical fiber 50.

In this embodiment, the surface of the sample is irradiated with the laser light as in the case of the first embodiment to remove the adhered substances. Contrary to the first embodiment, the optical fiber is cooled to reattach the detached deposit to the tip of the optical fiber 50. Then, the manipulator 63 is used to carry the tip of the optical fiber to the vicinity of the ion trap mass spectrometer. Then, the optical fiber 50 is heated, and the deposit on the tip of the optical fiber 50 is introduced into the mass spectrometer. As a result, the mass spectrum of the adhered matter that was initially adhered to the sample surface is obtained.

A device having such a mechanism was manufactured and measured. The optical fiber is also brought close to 30 nm and laser light is irradiated. The temperature of the optical fiber 50 is -130 ° C.
The desorbed molecules were attached to the tip of the optical fiber 50. After that, the optical fiber 50 is broken up to the ion trap mass spectrometer 52 by the manipulator 70,
The temperature was raised to about 500 ° C. at the moment of about 20 ms, and the molecules desorbed from the optical fiber 50 were subjected to mass analysis by the ion trap mass spectrometer 52.

As a result, the same effect as in Example 1 was obtained.

(Embodiment 5) This embodiment is almost the same as the embodiment 4, except that a spherical plate like 64 in FIG. 10 is attached to the optical fiber 50. As a result, almost all the molecules desorbed by the laser light can be reattached to the tip end portion of the optical fiber 50 and the plate 64.

A device such as this was manufactured and measured. The plate 64 and the optical fiber 50 were cooled to −130 ° C. to reattach the desorbing molecules. After that, the optical fiber is sunk by the manipulator 63 to the ion trap mass spectrometer 52, and the temperature is raised to about 500 ° C. at a moment of about 20 ms, during which the molecules desorbed from the fiber are mass analyzed by the ion trap mass spectrometer 52. went.

As a result, the detection sensitivity was increased by a factor of 2 as compared with Example 4.

(Embodiment 6) In this embodiment, foreign matter attached to the bottom of the deep groove of the semiconductor element as shown in FIG. 11 was analyzed. As the optical fiber 50, the angle θ of the tapered portion at the tip is used.
Use as small as possible. In this embodiment, an optical fiber with θ of about 30 ° was used. Insert this optical fiber into the groove and use liquid nitrogen to put it in -130
Cooled to ° C. Then, the laser light 7a is fed to the optical fiber 5
At 0, it is introduced at the bottom of the groove. Then, the foreign matter desorbed by the laser light 7a adheres to the cooled optical fiber.
Then, the optical fiber was conveyed to the ion trap mass spectrometer, the temperature of the optical fiber was rapidly raised, and the attached matter adhered to the optical fiber was subjected to mass analysis.

As a result, it has become possible to analyze foreign matters existing at the bottom of the deep groove, which has been difficult in the past.

[0028]

According to the present invention, the laser light is introduced into the sample surface by the optical fiber having the opening sufficiently smaller than the wavelength, so that the laser light is condensed on the surface of the sample much smaller than the wavelength. In addition, the molecules desorbed from the sample are detected by an ion trap mass spectrometer. As a result, it is possible to provide a microscopic laser mass spectrometer having a spatial resolution below the wavelength.

[Brief description of drawings]

FIG. 1 is a systematic diagram of Example 1.

FIG. 2 is an explanatory diagram near a sample of Example 1.

FIG. 3 is an explanatory diagram of the optical fiber 50 according to the first embodiment.

FIG. 4 is an explanatory diagram of a sample measured in Example 1.

5 is a mass spectrum characteristic diagram of an organic thin film adhesion portion measured in Example 1. FIG.

6 is a mass spectrum characteristic diagram of an exposed Al portion measured in Example 1. FIG.

FIG. 7 is an explanatory diagram near the sample of Example 2.

FIG. 8 is a systematic diagram of Example 3.

FIG. 9 is a systematic diagram of Example 4.

FIG. 10 is an explanatory diagram of an optical fiber 50 according to a fifth embodiment.

FIG. 11 is an explanatory diagram of the vicinity of the sample of Example 6.

FIG. 12 is a system diagram of a conventional device.

[Explanation of symbols]

 2 ... Sample, 6 ... Laser light source, 7 ... Laser light, 18 ... Vacuum chamber, 21a ... Molecular beam, 50 ... Optical fiber, 51 ... Pockel cell, 52 ... Mass spectrometer, 53 ... Ion trap part, 54 ... Detector, 57 ... Temperature controller, 58 ... Vacuum pump.

Claims (9)

[Claims] 1. A mass spectrometer for detecting molecules that are excited and desorbed by irradiating a sample with laser light, wherein the laser light is introduced into the sample with an optical fiber having an opening smaller than the wavelength of the laser light at the tip. A mass spectrometer. 2. The mass spectrometer according to claim 1, which uses an ion trap mass spectrometer. 3. The mass spectrometer according to claim 1, wherein a continuous wave laser is used as the laser light. 4. The mass spectrometer according to claim 3, comprising a mechanism for synchronizing a sample heating time by a laser and an ion trapping time. 5. The mass spectrometer according to claim 2, which uses a quadrupole type ion trap mass spectrometer. 6. The mass spectrometer according to claim 2, wherein the ion trap section and the time-of-flight mass spectrometer are used. 7. The mass spectrometer according to claim 1, comprising a mechanism for controlling the temperature of the optical fiber. 8. The mass spectrometer according to claim 1, comprising a mechanism for freely changing the tilt angle of the optical fiber with respect to the sample. 9. The detached molecule according to claim 1, wherein the desorbed molecules are attached to the tip of the optical fiber or another suitable substrate, and then the temperature of the tip of the optical fiber or another suitable substrate is raised. Mass spectrometer.