JPH0441459B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to semiconductor processing equipment, material modification,
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 of using 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, and the other is to focus laser light to release gas or liquid. The other method uses a wavelength-tunable light source, which targets the energy of the substance to be ionized with a single wavelength such as a laser beam, and uses it as an ion source. The substance is ionized by resonance with the level, and the present invention relates to the latter.

[Summary of the invention]

The present invention uses the autoionization level of a substance to be ionized as the state immediately before ionizing the substance by resonant light excitation in the above-mentioned resonant light excitation and ionization type ion beam generation apparatus. It is an object of the present invention to provide an ion beam generator that can improve the ionization efficiency with respect to input light energy by two orders of magnitude or more compared to the ionization method, and has excellent selectivity in selective ionization.

[Embodiments of the invention]

First, the ionization method used in the apparatus of the present invention will be explained, taking as an example the case of generating a beryllium ion beam, and comparing it with a conventional method. FIG. 1 is an energy level diagram of beryllium neutral atoms.

Conventional ionization methods, for example, have a wavelength of 2349 Å,
This is a method of irradiating the beryllium vapor to be ionized with two 3000 Å laser beams B1 and B2. In other words, beryllium atoms in the ground state 2s ( ¹ S) are first brought to an excited state by the 2349 Å laser beam B1.
2p ( ¹ P ⁰ ) is resonantly excited and then ionized by a 3000 Å laser beam B2.

The ionization method in the device of the present invention differs from the conventional ionization method described above in that beryllium vapor is brought to a relatively low level, for example, a metastable state, by gas discharge.
2p ( ³ P ⁰ ), further resonantly excited to an auto-ionization state 1s ² 2p3p ( ³ S) by laser beam irradiation, and auto-ionizing in this excited state with a predetermined transition probability; The point is that all of the above excitation processes are performed by resonance.

In the case of the ionization method in this inventive device, a two-electron excited state 1 _S ² 2 _P 2 _P is generated by laser light with a wavelength of 3865 Å.
( ^3D ) to the autoionized state _1S22P3P ( _3S ) is _σi = 1.0× ^10-15 _cm2 ^, and therefore the excitation ^rate is determined by changing ^the laser light intensity to I. Then W=1.95×
10 ³ I (W/cm ² ) sec ^-1 . Since such an autoionization state spontaneously separates into ions and electrons at a fast rate of 10 ¹² sec ^-1 or more, this excitation rate W can be reduced to a two-electron excited state 1 _S ² 2 _P 2 _P ( ³ D) The ionization rate can be achieved via the automatic ionization state 1 _S ² 2 _P 3 _P ( ³ S) by laser light with a wavelength of 3865 Å. On the other hand, the two-electron excited state 1 _S is an example of following the conventional ionization method.
When photoionizing directly from ² 2 _P 2 _P ( ^3D ), the photoionization cross section is σ _i =7.92×10 ^-29 [λ ₂ (Å)] ³ cm ²
Therefore, the ionization rate is W=3.99×10 ^-14 [λ ₂
(Å)] ⁴ I (W/cm ² )sec ^-1 . Here, since the laser light wavelength λ ₂ exceeds the ionization limit, it is necessary that λ ₂ <6453 Å. FIG. 5 shows this ionization rate W as a function of the laser light wavelength λ ₂ for various laser light intensities I. As shown in the figure, when the wavelength λ ₂ is changed at a certain laser light intensity, the ionization rate W changes continuously, but λ ₂ is in the two-electron excited state 1 _S ² 2 _P 2 _P
( ³ D) and the autoionization state 1 _S ² 2 _P 3 _P ( ³ S), at the resonance wavelength of 3865 Å, it becomes discontinuously higher by more than two orders of magnitude. Therefore, in the case of the ionization method of the present invention, the ionization efficiency with respect to the input light energy is more than two orders of magnitude higher than that of the conventional resonant optical excitation and ionization method.Moreover, since only resonance is used, the wavelength of the laser beam is adjusted to the wavelength of the impurity atoms. If the energy level is selected so that it does not match the energy level, only the desired substance can be ionized, and the substance can be highly purified.

In addition, by changing the wavelength 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. Also good. 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 are advantages to doing so.

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 is a container into which a substance to be ionized is introduced, 1a is a gas introduction hole for introducing the substance into the container 1, 1b is a gas discharge hole, 3a, 3b
is a window through which laser beams B3 and B4 from a laser beam generating section (not shown) are introduced into the container 1, and the space in the container 1 where the laser beams B3 and B4 intersect is an ion generation space 4. Note that as the laser beam generating section, a laser such as a wavelength tunable laser or a free electron laser is used.

Reference numerals 5 and 6 are electrodes placed across the ion generation space 4, and 5a and 6a are terminals for applying voltage to the electrodes 5 and 6, which generate excitation high-frequency gas discharge in the ion generation space 4. This constitutes a gas discharge generating section 15 that closes the gap. Note that 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 also serves as a gas discharge to bring the substance into a neutral element state. Good too.

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. and terminals 5a and 6a of the electrodes 5 and 6, respectively.
, which causes electrons to collide with the beryllium vapor 10 due to the gas discharge, so that the beryllium vapor 10 is resonantly excited from its ground state to the metastable state 2p ( ³ P ⁰ ). In addition, the laser beam generating section oscillates in time synchronization with the voltage application, thereby causing a laser beam B with a wavelength of 2651 Å.
3 is introduced into the container 1 through the window 3a, and
A laser beam B4 of 3865 Å is similarly introduced through the window 3b, and both beams B3 and B4 intersect in the ion production space 4 in the container 1, thereby causing the beryllium vapor in the above-mentioned metastable state 2p ( ³ P ⁰ ) 10
is excited by the 2651 Å laser beam B3.
It is resonantly excited to 1s ² 2p ² ( ^3D ), and further resonantly excited stepwise from the excited state 2p ( ^3D ) to the autoionization state 1s ² 2p3p ( ^3S ) by laser beam B4 of 3865 Å, and the excited vapor is becomes an ionic state even with a predetermined transition probability. Further, a DC voltage is applied between the electrode 6 and the sample stage 8a, whereby the ionized beryllium vapor 10 is extracted as an ion beam 9 consisting only of beryllium ions. The sample 8 is irradiated.

The features of this embodiment in the above operation description are as follows: First of all, this embodiment performs selective ionization completely using only resonance, so the substance to be ionized and this In the case that impurities other than beryllium, such as oxygen, nitrogen, carbon, and hydrogen, are included, and even if the amount is larger than beryllium, the desired wavelength can be avoided by making the wavelength of the laser beam do not match the energy level of the impurity atoms. 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 can simply change the wavelength of the laser beam, and there is no need to take out the sample or open and close the container to replace the ion source, as in the case of conventional methods. 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 11 is ionized beryllium vapor. A magnet 10 focuses the focused beryllium vapor 1 on the axis of the container 1, and 14 the focused beryllium vapor 1.
This is an extraction electrode that extracts 0 as an ion beam 9.

Next, the operation will be explained.

When beryllium 12, which is an ionized substance, is placed in the oven 13 and the oven 13 is heated by the heater 13a, the beryllium 12 melts.
The vaporization generates beryllium vapor 10, and the vapor 1
0 is introduced into the container 1 through the gas introduction hole 1a. Then, a voltage is applied to the electrodes 5 and 6, and the vapor 10 is bombarded with electrons from the gas discharge, and in time synchronization with this, a laser beam B3 of 2651 Å is generated.
A laser beam B4 of 3865 Å is introduced into the container 1 through the windows 3a and 3b, and irradiates the vapor 10. As a result, the vapor 10 is excited stepwise from the metastable state 2p ( ³ P ⁰ ) to the excited state 2p ( ³ D) to the autoionization state 1s ² 2p 3p ( ³ S), and furthermore, the excited vapor undergoes a predetermined transition. It becomes an ion state with probability, and as a result, beryllium ions are generated in the ion generation space 4, and after being focused to the axis by the magnet 11, the beryllium ions are emitted as an ion beam 9 by the extraction electrode 14.

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, and 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 wavelength-tunable dye lasers 22, 23, and 24, and each dye laser 2.
an excitation source laser 21 for exciting 2 to 24;
It is composed of half mirrors 25 and 26 and a total reflection mirror 27. By configuring the excitation source with one laser 21 in this manner, the oscillated laser beams ω1, ω2, and ω3 are temporally synchronized. By simultaneously oscillating the vapor excitation source laser 21 and applying voltage to the electrodes 5 and 6, the laser beam and the gas discharge can be synchronized in time.

〔Effect of the invention〕

As described above, according to the ion beam generator of the present invention, the substance to be ionized is raised from the ground state of its energy level to a relatively lower excited state by gas discharge, and the substance is further ionized by the laser beam. Since the excited state is changed to an auto-ionization state by irradiation, it has excellent ion selectivity and has the effect of improving ionization efficiency with respect to input energy by more than two orders of magnitude compared to conventional resonance optical excitation and ionization methods.

[Brief explanation of drawings]

FIG. 1 is an energy phase diagram of beryllium neutral atoms, FIG. 2 is a schematic diagram of the shower type ion beam generator according to the first embodiment of the present invention, and FIG. 3 is a diagram according to the second embodiment of the present invention. A schematic configuration diagram of a focused ion beam generator, FIG. 4 is the third embodiment of the present invention.
A block diagram of a laser beam oscillator of an ion beam generator according to an embodiment of the present invention, and FIG. 5 is a phase diagram showing the wavelength dependence of the photoionization rate in the excited state 1 _S ² 2 _P 2 _P ( ^3D ) of beryllium neutral atoms. It is. DESCRIPTION OF SYMBOLS 1... Container, 15... Gas discharge generating part, 20...
...Laser beam generating section, B1 to B4...Laser beam. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A container containing a substance to be ionized;
A laser beam generating section that irradiates the substance in the container with a laser beam, and a gas discharge generating section that generates a gas discharge that intersects with the laser beam in the atmosphere of the substance in the container, the ion beam of the substance In the device for generating , the gas discharge generating section excites the substance from the ground state of the energy level to a relatively lower excited state by gas discharge, and the laser beam generating section excites the substance from the ground state of the energy level to the excited state. An ion beam generator, characterized in that it generates a laser beam having a wavelength that causes resonant optical excitation from an ion beam to an auto-ionization state. 2. The laser beam generating unit generates a plurality of laser beams with different wavelengths to resonantly excite the substance in a stepwise manner from the relatively lower excited state to the intermediate state and then to the autoionization state. 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 of the energy level of the substance. 4. The ion beam generator according to any one of claims 1 to 3, characterized in that a wavelength tunable laser is used as the laser beam generator. 5. The ion beam generator according to any one of claims 1 to 3, characterized in that a free electron laser is used as the laser beam generator. 6. Claim 6, characterized in that the laser beam generating section comprises one excitation source laser and a plurality of dye lasers that are excited by the laser beam from the excitation source laser and can be alternately time-synchronized. 2
The ion beam generator according to item 1 or 3. 7. The ion beam generator according to any one of claims 1 to 6, wherein the gas discharge generating section generates a high-frequency discharge. 8. The substance is introduced into the container as a gas in a compound or molecular state, and the gas discharge also serves as a gas discharge to bring the substance introduced into the container into a neutral element state. An ion beam generator according to any one of claims 1 to 7.