JPS6127040A - Ion beam generator - Google Patents

Abstract

PURPOSE:To greatly improve the ionization efficiency and the ionic specificity of an ion beam generator by resonantly exciting the ionization substance to a Rydberg state immediately before ionizing the substance. CONSTITUTION:Beryllium vapor 10 is introduced into a case 1 through a gas introduction hole 1a and voltage is applied across electrodes 5 and 6. As the result, electrons produced by gas electric discharge strike the beryllium vapor 10 to excite it to a metastable state. Synchronously with the above voltage application, laser beams (B4) and (B6) are introduced into the case 1 through a window 3a and a laser beam (B5) is introduced into the case 1 through a window 3b to resonantly excite the beryllium vapor 10 to a Rydberg state. After that, the excited beryllium vapor 10 is ionized by electronic impacts caused by gas electric discharge. D.C. voltage is applied across an electrode 6 and a sample base 8a and the ionized beryllium vapor 10 is irradiated upon a sample 8 as an ion beam 9 consisting of beryllium ions alone.

Description

[Detailed description of the invention] [Technical field of invention] The present invention is applicable to material modification including semiconductor processing equipment.

This relates to ion beam generators used for materials synthesis, etc.

[Prior art]

Conventionally, various methods have been considered and put into practical use as ion generation methods using ion beam generators. Most of them used electric discharge, but in recent years ion sources using laser light have been devised. There are two methods that use light such as laser light. One is to irradiate a solid such as a metal with laser light and use the resulting plasma as an ion source, or to focus the laser light and convert it into gas or liquid. irradiation to create plasma, which is used as an ion source.
The other method uses a variable wavelength light source to ionize a substance by resonating a single wavelength such as a laser beam with the energy level of the substance to be ionized (Japanese Unexamined Patent Application Publication No. 1983-1992). 22999), the present invention relates to the latter.

[Summary of the invention]

The present invention uses the Rydberg state of a substance to be ionized as the state immediately before the substance is ionized by resonant light excitation in the above-mentioned resonant light excitation and ionization type ion beam generation apparatus, thereby improving the conventional resonance light excitation and ionization method. .

It is an object of the present invention to provide an ion beam generator that can improve the ionization efficiency for input light energy by several orders of magnitude compared to the ionization method, and has excellent selectivity in selective ionization.

[Embodiments of the invention]

First, the ionization method in the apparatus of the present invention will be explained by comparing it with a conventional method using an example in which a beryllium ion beam is generated. FIG. 1 is an energy level diagram of beryllium neutral atoms.

In the conventional ionization method, for example, the wavelength is 2349.

Three laser beams Bl for 4573 people and 5000 people,
This is a method of irradiating beryllium vapor to be ionized with B2 and B3. In other words, beryllium atoms in the ground state 2s (Is) are first resonantly excited to the first excited state 2p (IPO) by the 2349 laser beam B1, and then 457
Energy level 3d (ID
), and further 5000 laser beam B3
It ionizes it.

The ionization method in the device of the present invention is to bring the beryllium vapor into a state in which the metastable state 2p (3PO) is dominant by gas discharge, and to use a laser beam, in the example shown in Fig. 1, three beams with wavelengths of 3321, 1.46μ, and 6449. Laser beam B
4 to B6 to change the excited vapor from the excited state to the Rydberg state, and then, as in the conventional ionization method, the beryllium vapor is exposed to a laser beam, B3 in the example shown in FIG.
The method of the present invention differs from conventional methods in that it uses only resonance excitation in the photo-excitation process. The point is that there is.

In the case of the ionization method in this inventive device, the collision cross section for ionization is several orders of magnitude higher than in the conventional ionization method, in which beryllium vapor is directly ionized from the energy level 3d (ID) using a laser beam B3 with a wavelength of 5000. . Therefore, the output energy of the laser beam is small and the purity of the generated ions is high. That is, since only resonance is used, if the wavelength of the laser beam is selected so as not to match the energy level of the impurity atoms, only the substance to be ionized can be ionized, and moreover, it can be made with high purity.

In addition, by changing the wavelength and discharge conditions of the laser beam, ion beams of other types of substances can be easily generated.In this case, various types of substances to be ionized can be introduced into the ion beam generation container in advance. It's okay to stay. The method of the present invention, which can easily change the type of ion beam generated in this way, is unlike any conventional method.
There is an advantage that two or more steps of processing with an ion beam can be performed in succession.

Next, embodiments of the invention will be described with reference to the drawings.

FIG. 2 shows a first embodiment of the invention. In the figure, 1
1a is a container into which the substance to be ionized is introduced, and 1a is the container into which the substance is introduced.

1b is a gas exhaust hole, 3a or 3b is a laser beam B from a laser beam generating section (not shown), respectively.
4. A window for introducing B6 or B5 into the container 1,
The space in the container 1 where the laser beams B4 to B6 intersect is an ion generation space 4. Although not shown, the laser beam generating section is provided with three lasers and a pulse generating circuit that generates electric signal pulses that serve as oscillation triggers for each of the lasers. In addition, the above laser is
Various lasers can be used, such as an excimer laser, a gas laser such as a nitrogen laser, a solid laser such as an alexandrite laser, a dye laser excited by these lasers, a wavelength tunable laser, or a free electron laser.

Reference numerals 5.6 and 5.6 denote electrodes arranged across the ion generation space 4; 5a and ia are terminals for applying voltage to the electrodes 5.6; It constitutes a gas discharge generating section 15 that generates a gas discharge.In addition, when the substance to be ionized is introduced into the container 1 as a gas in a compound or molecular state, the excitation gas discharge It may also serve as a gas discharge to bring the substance into a neutral atomic state.

8 is a sample, and 8a is a sample stand that holds the sample 8. A direct current voltage is applied between the sample stand 8a and the electrode 6, and a drawer is used to extract the ionized substance as an ion beam. An electric field is generated.

Next, the operation will be explained.

Let us consider the case where a beryllium ion beam is generated by the apparatus of this embodiment. First, beryllium vapor 10 is introduced into the container 1 through the gas introduction hole 1a. A voltage is applied to each of the electrodes 5 and 6 from terminals 5a and 6a. As a result, electrons due to the gas discharge collide with the beryllium vapor 10 in the ground state 2g (Is), and as a result, the beryllium vapor 10 is excited to the metastable state 2p (3PO). In addition, in time synchronization with the voltage application, in the laser beam generation section, a trigger pulse is applied from the pulse generation circuit to each laser, causing each laser to oscillate, thereby generating laser beams B4.
B6 is introduced into the container 1 through the window 3a, and 1, 4
A laser beam B5 of 6μ is similarly introduced through the window 3b, and each beam B4 to BG enters the ion generation space 4 in the container 1.
This causes the beryllium vapor 10 to enter the metastable state 2p (
3PO) to the excited state 3s (3S), and further excited from the excited state 3s (33) to the excited state 3p (3PO) by a 1.46μ laser beam B5,
Furthermore, the 6449 laser beam B6 resonantly excites the Rydberg state 12d (3D) in a stepwise manner, and finally the excited vapor is ionized by the collision of electrons caused by the gas discharge. Further, a DC voltage is applied between the electrode 6 and the sample stage 8a, so that the ionized beryllium vapor 10 is extracted as an ion beam 9 consisting only of beryllium ions. The sample 8 is irradiated.

The characteristics of this embodiment in the above operation description are as follows: First of all, since this embodiment performs selective ionization completely using only resonance, the substance to be ionized in the container 1, in this case, It contains impurities other than beryllium, such as oxygen, nitrogen, carbon, and hydrogen, and the amount is higher than that of beryllium. A pure beryllium ion beam is obtained in which only the element, in this case beryllium, is ionized.

Second, as mentioned above, this embodiment performs selective ionization and ionization by resonant optical excitation, so there is no possibility that electrons or other elements will be excited or that the temperature will rise due to energy absorption. As a result, low-temperature processing can be performed without increasing the temperature of the target sample 8 to be irradiated with the ion beam, such as a substrate in the case of a semiconductor.

Third, if you want to change the type or characteristics of the ion beam, you only need to change the wavelength of the laser beam and the discharge conditions, and there is no need to open and close the container to take out the sample or replace the ion source as in the past. Therefore, continuous operations such as ion implantation and annealing can be easily performed.

FIG. 3 shows a second embodiment of the invention. In the figure, the same reference numerals as in FIG. 2 indicate the same or equivalent parts, 13 is an oven containing the substance 12 to be ionized, 13a is a heater provided on the outer periphery of the oven 13, and 16 is ionized beryllium vapor. 10 is a magnet that focuses the ion beam on the axis of the container 1, and 14 is an extraction electrode that extracts the focused beryllium vapor 10 as an ion beam 9.

Next, the operation will be explained.

When beryllium 12, which is a substance to be ionized, is placed in the oven 13 and the oven 13 is heated by the heater 13a, the beryllium 12 is melted.

Beryllium vapor 10 is generated through vaporization, and this vapor 10 is introduced into the volume 81 through the gas introduction hole 1a. Then, a voltage is applied to the electrode 5.6, and electrons due to gas discharge collide with the vapor 10, and in synchronization with this, 3321 people
A laser beam B4°B6 of 6,449 people is introduced into the container 1 through the window 3a and a laser beam B5 of 1,46μ is introduced into the container 1 through the window 3b and irradiates the steam 10, so that the steam 10 becomes From the ground state 2S (Is) to the excited states 2p (3PO), 3s (3S), 3p
(3PO), is excited to the Rydberg state 12d (3D) in a stepwise manner, and further the Rydberg state 12d
The electrons in the beryllium vapor 10 in (3D) become free electrons, thereby generating beryllium ions in the ion generation space 4. After the beryllium ions are focused to the axis by the magnet 16, the ion beam 9 is transferred to the extraction electrode 14. released as.

FIG. 4 shows an example of the configuration of a laser oscillation device in an ion beam generator according to a third embodiment of the present invention.

In the present invention, the laser beam and gas discharge for ion generation need to be synchronized in time; - Also, in order to excite the elements in a stepwise manner, a plurality of laser beams each having a specific frequency are required; Of course, it is necessary to synchronize the plurality of laser beams, and FIG. 4 shows an example of a synchronization method.

This laser oscillation device 20 includes three lasers 2 with different wavelengths.
2, 23, and 24, and one trigger generator 21 that provides each of the lasers 22 to 24 with an electric signal pulse serving as a laser oscillation pulse. In this way, each laser 2
2 to 24 are configured to oscillate in response to a trigger pulse from the trigger generator 21, the oscillating laser beams ω1. ω2. ω3 becomes temporally synchronized. By synchronizing the generation of the trigger pulse by the pulse generator 21 and the voltage application to the electrode 5.6, the laser beam and the gas discharge can be synchronized in time.

FIG. 5 shows a configuration example of a laser oscillation device of an ion beam generator according to a fourth embodiment of the present invention.
Reference numerals 5 to 27 are laser heads of solid-state lasers, 28 is a Franschlump power supply, and 29 is a Q-switch Bockel cell power supply, and this set of power supplies serves as a trigger means 30 for causing each laser head 25 to 27 to oscillate in synchronization. There is. In this embodiment, each laser head 25 to 27 is connected to one set of power supplies 2 and 27.
8.29 is shared, so the oscillating laser beam ω
1 to ω3 are temporally synchronized.

〔Effect of the invention〕

As described above, according to the ion beam generator of the present invention, the substance to be ionized is excited to a relatively lower excited state by gas discharge, and the substance to be ionized is resonated from the excited state to the Rydberg state by laser beam irradiation. Since the substance is photo-excited and further changed from the excited state to the ion state by collision with electrons from a gas discharge, the ionization efficiency and ion selectivity can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is an energy phase diagram of beryllium neutral atoms, FIG. 2 is a schematic configuration diagram of a shower-type ion beam generator according to the first embodiment of the present invention, and FIG.
The figure is a schematic configuration diagram of a focused ion beam generator according to a second embodiment of the present invention, FIG. 4 is a block diagram of a laser beam generator of an ion beam generator according to a third embodiment of the present invention, and FIG. FIG. 3 is a block diagram of a laser beam generator of an ion beam generator according to a fourth embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Container, 15... Gas discharge generating part, 2o...
Laser beam generator, 21.30... trigger means, B
i~B6...Laser beam. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (14)

[Claims] (1) A container that contains a substance to be ionized, a laser beam generating unit that irradiates the substance in the container with a laser beam, and generates a gas discharge that intersects with the laser beam in the atmosphere of the substance in the container. In an apparatus for generating an ion beam of the above substance,
The gas discharge generating unit excites the substance from a ground state of energy level to a relatively lower excited state by gas discharge,
The Rydberg state obtained by irradiation with a laser beam, which will be described later, is converted into an ion state, and the laser beam generating section includes a trigger means for generating an electric signal to trigger laser oscillation, and a trigger means for generating an electric signal to trigger laser oscillation, and a means for converting the substance into an ion state. 1. An ion beam generator comprising: a laser that generates a laser beam having a wavelength that causes resonant optical excitation from a lower excited state to a Rydberg state. (2) The laser beam generating section generates a plurality of laser beams with different wavelengths to resonantly excite the substance from the relatively lower excited state to the Rydberg state via an intermediate state in a stepwise manner. An ion beam generator according to claim 1, characterized in that: (3) The ion beam generator according to claim 1 or 2, wherein the relatively lower excited state is a metastable state. (4) As the laser of the laser beam generating section, one or both of an excimer, a gas laser such as nitrogen, or a dye laser excited by harmonics from the gas laser is used. The ion beam generator according to any one of the ranges 1 to 3. (5) The ion beam generating device according to any one of claims 1 to 3, wherein a solid-state laser such as an alexandrite laser is used as a laser in the laser beam generating section. (6) The ion beam generating device according to any one of claims 1 to 3, wherein a dye laser is used as a laser in the laser beam generating section. (7) As the laser of the laser beam generating section, one or both of a solid-state laser and a dye laser excited by harmonics from the solid-state laser is used. The ion beam generator according to any one of Item 3. (8) Claim 1, characterized in that a wavelength tunable laser is used as the laser of the laser beam generating section.
The ion beam generator according to any one of Items 1 to 3. (9) Claim 1, characterized in that a free electron laser is used as the laser of the laser beam generating section.
The ion beam generator according to any one of Items 1 to 3. (10) The ion beam generator according to any one of claims 1 to 9, wherein the gas discharge generating section generates radio frequency (RF) discharge. (11) The substance is introduced into the container as a compound or molecular gas, and the gas discharge also serves as a gas discharge to bring the substance introduced into the container into a neutral atomic state. An ion beam generator according to any one of claims 1 to 10, characterized in that: (12) The ion beam generator according to claim 10, wherein the gas discharge generating section has a high frequency power source that resonates so that the substance changes from its Rydberg state to an ion state. . (13) Claim 1, wherein the laser beam and the gas discharge are temporally synchronized in phase.
The ion beam generator according to any one of Items 1 to 9. (14) The substance is introduced into the container as a vapor generated by heating and vaporizing a solid or liquid substance. ion beam generator.