JP3440300B2 - Time-of-flight velocity measuring device for gas atoms or gas molecules - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention of this application relates to a high-efficiency velocity measuring device for gas atoms or gas molecules. More particularly, it relates to a gas atom or gas molecule high-efficiency velocimetry device useful for measuring the translational velocity and rotational or vibrational state of a gas atom or gas molecule in a gas phase synthesis reaction.

[0002]

2. Description of the Related Art In gas phase synthesis reactions such as thin film formation on semiconductors, the translational velocity, vibrational state, and rotational state of gas atoms or gas molecules influence the structure and electrical properties of the product. It has been known. Therefore, it can be said that measuring and controlling the translational velocity, the vibration state, and the rotation state of the reactants and products are indispensable for efficiently proceeding the gas phase synthesis reaction.

Traditionally, time-of-flight analysis methods have been widely used to measure the translational velocity of gas atoms or molecules. In this measurement method, the velocity is analyzed by measuring the time required for gas atoms and gas molecules to fly a certain distance. Depending on how to set a trigger for time measurement, (1) a method of pulsing a beam of gas atoms or gas molecules using a chopper, flying in a vacuum, and then detecting with a mass detector (2) gas atoms or gas molecules Is ionized with a pulsed laser, then it is flown in a tube without an electric field gradient (drift tube) and is detected using a multi-channel plate. In the above method (1), since it is premised that the gas is made into a beam, it is applicable to the velocity analysis of the reaction product.
On the other hand, it is not applicable to rate analysis of products. In addition, the method (1) requires a large-scale vacuum system that is differentially evacuated over a length of about 1 m.

On the other hand, the above method (2) can be realized with a small-scale configuration as compared with the above method (1), and analysis of gas which has not been converted into a beam is also possible. Further, by utilizing the resonance ionization by laser light, there is an advantage that the vibrational and rotational states of gas molecules can be selectively subjected to velocity analysis.

Unlike the time-of-flight analyzer for the purpose of mass spectrometry, in the time-of-flight analyzer for the purpose of velocity analysis, between the ionization section (focusing point of laser) and the drift tube, No voltage is applied, or a low voltage of 10 V or less is applied.
This is to prevent the translational energy distribution (translational velocity distribution) of atoms or molecules much smaller than 1 eV from being disturbed by a strong accelerating electric field.

When no voltage is applied, only a small portion of the ionized atoms or molecules can enter the drift tube and reach the detection portion, and therefore the detection efficiency is low. . In particular, it is known that low-energy (low-velocity) atoms / molecules of 0.05 eV or less have a high probability of colliding with the tube side wall before arriving at the detection unit, so that the detection efficiency in the low-velocity region is significantly reduced. ing.

In order to solve this problem, a method has been devised in which a weak attracting electric field is created between the ionization section and the drift tube to attract ions into the drift tube. In this method, an electrode with a hole made of metal is installed in front of the ionization section (the side farther from the drift tube), this is grounded, and a negative voltage of 10 V or less is applied to the drift tube.

As described above, the detection efficiency of the time-of-flight velocity analyzer can be improved by applying a voltage of 10 V or less between the ionization section and the drift tube. In the prior art, a metal electrode is provided outside the drift tube, which complicates the structure of the analyzer. In addition, the electrode has a hole so that gas atoms or gas molecules to be measured can pass therethrough, which causes a distortion in the distribution of the electric field generated between the electrode and the drift tube. In the velocity analysis of reaction products and desorbed species on the solid surface, which is an applied technology of velocity analysis of gas atoms or gas molecules, the electric field leaked from the electrode affects the reaction on the solid surface and is the object of measurement. This may disturb the production process of reaction products and the velocity distribution, which hinders accurate measurement.

Therefore, the invention of this application has been made in view of the circumstances as described above, and minimizes the adverse effect on the object to be measured due to the leakage of the electric field, and the velocity distribution is reduced to the low velocity region. An object of the present invention is to provide a velocity measuring device for gas atoms or gas molecules that realizes highly efficient velocity analysis without distortion.

[0010]

Means for Solving the Problems The invention of this application is to solve the above-mentioned problems. Firstly, an ionization part for ionizing gas atoms or gas molecules by pulse laser irradiation, and an ionization part A drift tube for introducing velocity ions to perform velocity separation, a two-stage acceleration / focusing unit for accelerating ions that have passed through the drift tube and at the same time focusing them spatially, and ions emitted from this two-stage acceleration / focusing unit. A time-of-flight velocity measuring device comprising an ion detection unit for detecting the two-stage acceleration and convergence unit, the first grid installed on the drift tube side and the second grid installed on the ion detection unit side. And a distance d between the first grid and the ion emission port of the drift tube and, if it has a pull-in portion, a drift tube length L including this. But it provides a time-of-flight velocity measuring device, characterized in that L / d is set to be in the range of 10 to 50.

Secondly, the invention of this application is
Applied to the drift tube for the device
Negative voltage V_dIs -10≤V_dIn the range of ≦ −1V, the second
Negative voltage V applied to the grid₂Is -2k≤V₂
Marked in the range ≤ -1 kV and for the first grid
Negative voltage V applied₁Is | V_d| <| V₁| <| V₂Range of |
The flight time type speed is characterized by
The third is the drift tube
Electrically insulated from the drift tube at the on-inlet
It is equipped with a pull-in part, and the negative
Voltage V_gIs 0 <| V _g| ≦ | V_dTo be set in the range of |
Providing a characteristic time-of-flight velocity measuring device,
Fourth, the tip has an opening with a diameter of 5 mm or less for introducing gas.
Made entirely of highly magnetically permeable metal electrically grounded
Inside the shield, the ionization part, drift tube, and
A stage acceleration / focusing unit and an ion detection unit are installed.
A time-of-flight velocity measuring device is provided.

Fifthly, the invention of this application provides a method for measuring the velocity of a gas atom or a gas molecule by any one of the above devices.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of this application has the characteristics as described above, and the embodiments thereof will be described below.

The time-of-flight velocity measuring apparatus according to the invention of this application has an ionization section, a drift tube, a two-stage acceleration convergence section, and an ion detection section as basic components. In order to prevent external electric and magnetic fields from disturbing ions in flight and to shield external leakage of the electric field applied to the two-stage acceleration focusing unit and ion detection unit, these ionization units, drift tubes, two-stage acceleration The converging unit and the ion detecting unit are installed while being covered with a metal shield. As a material for the shield, a highly magnetically transparent metal material is appropriately selected, and it is particularly preferable to use mu metal. Also,
The entire shield is electrically grounded.

A gas introduction hole is opened at the tip of the shield, and gas atoms or gas molecules are introduced into the ionization section through the hole.

In the ionization section, the pulsed laser is applied to the gas atoms or gas molecules, thereby ionizing the gas atoms or gas molecules.

Next, the ions generated in the ionization section are introduced into the drift tube and subjected to velocity separation. The inlet to the drift tube is provided with a lead-in section that is electrically insulated from the drift tube. A negative voltage is applied to this attracting portion, and the ions are attracted to the drift tube without distorting the velocity distribution. In addition to the efficient drawing from the ionization part, the drawing part also has a function of converging the spatial spread of the ions in the stage before entering the drift tube. Ions fly through the drift tube in which there is no electric field gradient, then are ejected from the ion exit of the drift tube, and are accelerated by the two-stage acceleration converging unit. Further, the two-stage acceleration converging unit also has a function of converging the spatial spread of the ions simultaneously with acceleration.

The two-stage acceleration converging unit is composed of a first grid installed on the drift tube side and a second grid installed on the ion detection unit side. Since a negative voltage is applied to each of the two grids, the acceleration and spread of the ions are converged. Regarding the distance d between the first grid and the ion emission port of the drift tube and the drift tube length L including the pull-in portion, L / d, which is the ratio thereof, may be set in a range of 10 to 50. preferable.

Ions whose acceleration and spread are converged by the two-stage acceleration converging unit are detected by the ion detecting unit.
A multi-channel plate, for example, is used for the ion detector, and the detection signal is amplified through a preamplifier or the like, and is further input to a measuring instrument to analyze the velocity distribution of ions.

Negative applied to the drift tube
Voltage V_dIs −10 ≦ V_dSet within the range indicated by ≤-1V
Is preferably performed. Also, for the second grid
Negative voltage V applied₂Is −2k ≦ V₂≤-1kV
It is preferable that the range is set. Also,
Negative voltage V applied to one grid₁Is | V _d|
<| V₁| <| V₂It is set within the range indicated by |. further,
Negative voltage V applied to the pull-in part_gIs 0 <| V
_g| ≦ | V_dIt is set in the range of |.

By applying a voltage to the pull-in portion as described above, ion lenses are formed between the ionization portion and the pull-in portion, and between the pull-in portion and the drift tube, respectively. The spatial spread of can be suppressed.

Further, by applying a voltage to the first grid and the second grid as described above, it becomes possible to generate an accelerating electric field without distortion, and gas atoms or gas incident from the drift tube can be generated. The molecule can be guided to the detection section with high efficiency.

As described above, for the first time in this application, it is possible to reduce the disturbance of the velocity distribution of gas atoms or gas molecules due to the drawing electric field, and to realize velocity measurement with high accuracy even in the low velocity region near zero velocity. It

Further, since the leakage of the drawing electric field to the outside of the shield can be made minute, it is possible to prevent the adverse effect on the surface of the reaction sample placed outside the shield.

Furthermore, since the time-of-flight velocity measuring device of the invention of this application does not require external electrodes,
It has a compact and easy-to-use structure.

The invention of this application has the above-mentioned features, but the following examples will be given to explain it more specifically.

[0027]

Embodiment 1 FIG. 1 is a schematic diagram illustrating the configuration of a time-of-flight velocity measuring device according to the invention of this application.

In the time-of-flight velocity measuring apparatus according to the invention of this application, the gas atom or gas molecule to be measured is introduced into the conical metal shield (1) with a diameter of about 3 mm provided at the tip of the shield. It passes through the hole (2) and is introduced into the ionization section (3) inside the shield. Gas atoms or gas molecules introduced into the shield are generated by laser light (5) incident on the ionization section (3) from a laser introduction hole (4) having a diameter of about 1 mm provided on the side surface of the shield (1). Ionized.

The shield (1) is electrically grounded, and the entrance (7) of the entrance of the drift tube (6).
To the drift tube (6) by applying a voltage of −1.4 V to the drift tube (6) and a voltage of −5 V to the drift tube (6) without distorting its velocity distribution.
It is drawn inside. In the time-of-flight velocity measuring device of the invention of this application, unlike the prior art, since the shield (1) is grounded, it acts as an electrode and does not require an external acceleration electrode.

The ions taken into the drift tube (6) fly about 10 cm inside the drift tube (6) where there is no electric field gradient, and enter the two-stage acceleration converging section (8). The two-stage acceleration converging unit (8) has a first grid (9) installed at a position of about 5 mm from the exit of the drift tube (6) and a second grid (9) installed at a position of about 11 mm ( 10).
The ions accelerated and focused by these two grids are detected by the multi-channel plate (11). The detection signal is amplified through a preamplifier and input to measurement equipment such as an oscilloscope.

FIG. 2 shows the results of numerical simulation for the potential distribution that appears when the voltage is applied as described above to each part constituting the time-of-flight velocity measuring device having the structure described above. A straight line penetrating the central portion of FIG. 2 represents a track of ions. As shown in FIG. 2, according to the invention of this application, it is possible to obtain an equipotential surface having no distortion in the same radial direction in the two-stage acceleration convergence part. Further, as shown in FIG. 2, the negative potential V _g of the lead-in portion is lower than the negative potential V _d of the drift tube (| V _g | <| V _d |).
By setting, it becomes possible to generate an ion lens between the pulling-in part and the drift tube, and it is possible to dramatically improve the convergence of ions in the drift tube. Embodiment 2 FIG. 3 shows one application example of the time-of-flight velocity measuring device according to the invention of this application.

In the evacuated vacuum chamber (31),
The time-of-flight velocity measuring device (32) of the invention of this application is installed, and a laser beam is incident through a window (33) attached to the upper part of the vacuum chamber (31). A lens (34) is installed above the window (33) and is designed so that laser light is focused on the ionization part of the time-of-flight velocity measuring device (32).

Gas atoms or gas molecules are introduced into the vacuum chamber (31) from the inlet (35), and further the time-of-flight velocity measuring device (3) is passed through the gas inlet hole.
2) It is introduced inside. As described above, the detection of ions is performed by the multi-channel plate, and the detection signal is the preamplifier (36) directly connected to the multi-channel plate.
After being amplified by, it is input to the digital oscilloscope,
The accumulated values are further input to a computer for speed analysis.

FIG. 4 is a graph showing the results of the velocity analysis of hydrogen molecules performed in this example. The hydrogen gas pressure outside the shield was 4 × 10 ⁻⁶ Torr, the gas cell temperature was 500 ° C., and the vibration and rotation states of the selectively ionized hydrogen molecules were v = 0 and J = 5, respectively. In FIG. 4, the solid line represents the measured value and the broken line represents the theoretical value. By comparing the measured value with the theoretical value, the time-of-flight velocity measuring device of the invention of this application shows 0.05 eV.
It is apparent that the velocity analysis is possible even at the low energy below, that is, at the low velocity of 3000 m / s or less. Third Embodiment Furthermore, FIG. 5 shows one application example of the time-of-flight velocity measuring device according to the invention of this application.

In the structure similar to that shown in FIG. 3, the sample (58) is placed immediately before the gas introduction hole (57) of the time-of-flight velocity measuring device (52). By irradiating the sample (58) with a molecular beam (59) or the like, a reaction product (60) is produced, and the reaction product (60) is further subjected to a time-of-flight velocity measuring device (52). By introducing into the inside, it becomes possible to carry out velocity analysis of gas atoms or gas molecules involved in the reaction on the sample surface.

[0036]

As described above in detail, according to the invention of this application, it is possible to minimize the adverse effect on the object to be measured due to the leakage of the electric field, and to distort the velocity distribution up to the low velocity region and to achieve high efficiency. An apparatus for measuring a velocity of a gas atom or a gas molecule is provided that realizes a simple velocity analysis.

According to the invention of this application, a time-of-flight velocity measuring device having a small structure which does not require an external electrode is technically realized for the first time.

According to the invention of this application, it is possible to measure with high accuracy the velocity of gas atoms or gas molecules produced and desorbed in the surface reaction of a solid such as thin film formation by molecular beam. Therefore, the invention of this application is strongly expected to be put into practical use as a technique for realizing reaction control on the solid surface at the atomic or molecular level, such as oxide film formation on the semiconductor surface and hydrogen termination reaction.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of a time-of-flight velocity measuring device according to the invention of this application.

FIG. 2 is a contour diagram showing the result of a numerical simulation for the potential distribution that appears when a voltage is applied to each part of the time-of-flight velocity measuring device of the invention of this application.

FIG. 3 is a schematic diagram showing one application example of the time-of-flight velocity measuring device according to the invention of this application.

FIG. 4 is a graph showing the results of velocity analysis of hydrogen molecules in the example of the invention of this application.

FIG. 5 is a schematic diagram showing one application example of the time-of-flight velocity measuring device according to the invention of this application.

[Explanation of symbols] 1 shield 2 gas introduction holes 3 Ionization part 4 Laser introduction hole 5 laser light 6 drift tubes 7 Retractor 8 Two-step acceleration convergence unit 9 First grid 10 Second grid 11 multi-channel plate 31 vacuum chamber 32 Time-of-flight velocity measuring device 33 windows 34 lens 35 inlet 36 preamplifier 51 vacuum chamber 52 Time-of-flight velocity measuring device 53 windows 54 lens 56 preamp 57 Gas introduction hole 58 samples 59 molecular beam 60 reaction products

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masanori Yada 1-2-1 Sengen, Tsukuba, Ibaraki Prefectural Government, Science and Technology Agency, Institute for Materials Research (56) References A. T. J. B. Eppink, D.H. Parker, "Velocity map of ions and electrons using electrostatic lenses," Rev. Sci. Instrum. , September 1997, vol. 68, no. 9, p. 3477-3484 A. Kubo and 3 others, "An Intense Pulsed Atomic Hydrogen Beam Source", Jpn. J. Appl. Phys. , October 2000, vol. 39, pp. 6101-6104 (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 27/62-27/70 JISST file (JOIS) IEEE Xplore Web of Science

Claims (5)

(57) [Claims] 1. An ionization part for ionizing a gas atom or a gas molecule by pulse laser irradiation, a drift tube for introducing ions generated in the ionization part to perform velocity separation, and accelerating ions passing through the drift tube. A time-of-flight velocity measuring device comprising a two-stage acceleration / focusing unit for simultaneously spatially focusing and an ion detector for detecting ions emitted from the two-stage acceleration / focusing unit, The part is composed of a first grid installed on the drift tube side and a second grid installed on the ion detection part side, and the distance d between the first grid and the ion emission port of the drift tube and the retracting part are set. When having, the drift tube length L including this is L
The time-of-flight velocity measuring device is characterized in that / d is set in a range of 10 to 50. 2. The negative voltage V _d applied to the drift tube is within a range of −10 ≦ V _d ≦ −1 V, and the negative voltage V ₂ applied to the second grid is −2 k. ≤V ₂ ≤
In the range of −1 kV, and the negative voltage V ₁ applied to the first grid is in the range of | V _d | <| V ₁ | <| V ₂ |
The time-of-flight velocity measuring device according to claim 1, wherein each of them is set. 3. A drift tube having an ion inlet is provided with a door.
Equipped with lift tube and electrically insulated retractor
The negative voltage V applied to the pull-in portion. _gIs 0 <| V
_g| ≦ | V_dThe range is set to |
2 time-of-flight velocity measuring device. 4. An ionization part, a drift tube, a two-stage acceleration converging part, and a highly magnetically permeable metal shield, which is electrically grounded as a whole and has an opening with a diameter of 5 mm or less for introducing a gas at its tip. The time-of-flight velocity measuring device according to any one of claims 1 to 3, further comprising an ion detector. 5. A high-efficiency velocity measuring method for gas atoms or gas molecules, wherein velocity measurement is performed by the apparatus according to any one of claims 1 to 4.