JPH0441461B2 - - 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.

[Conventional technology]

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 and emits the energy of the substance to be ionized at a single wavelength into a laser beam, etc. This method ionizes the substance by making it resonate with the level (see Japanese Patent Application Laid-Open No. 50-22999). The present invention relates to the latter, and uses syncorotron radiation rather than laser light as a light source.

(Summary of the Invention) The present invention uses the autoionization state of the substance to be ionized as the state immediately before the substance is ionized by resonant photoexcitation in the above-mentioned resonant photoexcitation and ionization type ion beam generator. 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 more than two orders of magnitude compared to conventional resonant optical excitation and ionization methods, 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 the case of inventing a boron ion beam as an example. FIG. 1 is an energy level diagram of a boron neutral atom.

Conventional ionization methods, for example, have a wavelength of 2497A,
This is a method of irradiating the boron vapor to be ionized with three laser beams B1 to B3 of 1.17μ and 8668A. In other words, boron atoms in the ground state 2s ² 2p ( ² p ⁰ ) are first excited by laser beam B1 of 2497A. situation
It is resonantly excited at 3s ( ² S), then excited at 3p ( ² p ⁰ ) and 5s ( ² S) by 1.17μ, 8668A laser beams B2 and B3, and further ionized by the above laser beam B3.

The ionization method in the apparatus of the present invention differs from the conventional ionization method described above in that synchrotron radiation, particularly relativistic synchrotron radiation, is used as an excitation light source. Like laser light, synchrotron synchrotron radiation has directionality, and is much more intense and high-energy photons than laser light.
Therefore, as shown in FIG. 1, one photon B4 can excite a relatively lower excited state to a higher excited state. The fundamental difference between the method of the present invention and the conventional method is that the final excited state is an auto-ionization state, and in this excited state, the excited vapor is exactly auto-ionized with a predetermined transition probability. Note that excitation from the ground state to the lower excited state is performed by glow discharge or the like.

In the case of the ionization method in this invention device, the photoexcitation cross section from the metastable state 2 _S 2 _P ² ( ⁴ P) to the autoionization state 2 _S 2 _P 3 _S ² ( ⁴ P ⁰ ) by synchrotron radiation light with a wavelength of 2067 Å is σ _i =1.0×10 ⁻¹⁵ cm ² , and therefore its excitation rate is W=1.04×10 ³ I (W/cm ² ) sec ⁻¹ where I is the synchrotron radiation intensity. Such an autoionization state spontaneously separates into ions and electrons at a fast rate of 10 ¹² sec ^-1 or more, so
This excitation rate W is the wavelength of metastable 2 _S 2 _P ² ( ⁴ P) 2067 Å
Automatic ionization state 2 _S 2 _P by synchrotron radiation of
The ionization rate can be expressed as 3 _S ( ⁴ P ⁰ ). On the other hand, when directly photoionizing from the metastable state 2 _S 2 _P ² ( ⁴ P), which is an example of following the conventional ionization method, the photoionization cross section is σ _i =7.52×10 ^-28
[λ ₂ (Å)] ³ cm ² and therefore its ionization rate is W=
3.78×10 ^-13 [λ ₂ (Å)] ⁴ I (W/cm ² ) ses ^-1 .
Here, the synchrotron radiation wavelength λ ₂ must satisfy λ ₂ <2623 Å in order to exceed the ionization limit. Fifth
The figure shows the ionization rate W and synchrotron radiation wavelength λ ₂
Various synchrotron radiation intensities I as a function of
shown against. As shown in the figure, when the wavelength λ ₂ is changed at a certain synchrotron radiation light intensity, the ionization rate W changes continuously, but λ ₂ changes between the metastable state 2 _S 2 _P ² ( ⁴ P) and the auto-ionization state. 2 _S 2 _P 3 _S ² ( ⁴ P ⁰ ), where the resonance wavelength is 2067 Å, it becomes discontinuously higher by more than two orders of magnitude. Therefore, in the case of the ionization method according to the present invention, the ionization efficiency with respect to the input light energy is 2 times higher than that of the conventional resonance optical excitation and ionization method.
Moreover, since it uses only resonance, if the wavelength of the synchrotron radiation light is selected so that it does not match the energy level of the impurity atoms, only the substance that is desired to be ionized can be ionized, and it can be made with high purity.

In addition, by changing the wavelength of the spectroscopic single-wavelength synchrotron radiation, it is possible to easily generate ion beams of other types of substances. It may be introduced into the generation container. The method of the present invention, which allows the type of ion beam to be generated to be easily changed, is unlike conventional methods, and it is possible to easily change the type of ion beam generated by the method of the present invention. 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, and 1b is a hole for differentially pumping the container 1 into a vacuum. Exhaust passage connected to a vacuum exhaust device (not shown), 1c is a slit, 3 is 2067
This is a synchrotron radiation light generating section that generates synchrotron radiation light B4 having a narrow wavelength width of Å.

Further, 5 and 6 are electrodes arranged across the synchrotron radiation B4 in the ion generation space 4;
5a and 6a are terminals for applying voltage to the electrodes 5 and 6. These constitute a gas discharge generating section 15 that generates RF discharge within the container 1. 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 atomic state. It's okay.

8 is a sample, and 8a is a sample stage that holds the sample material. A DC voltage is applied between the sample stage 8a and the electrode 6, thereby creating an extraction electric field for extracting the ionized substance as an ion beam. is generated.

Next, the operation will be explained.

Let us consider a case where a boron ion beam is generated by the apparatus of this embodiment. First, gas introduction hole 1 in container 1.
Boron vapor 10 is introduced from a. Then, a voltage is applied to each of the electrodes 5 and 6 from the terminals 5a and 6a, and as a result, electrons due to glow discharge or gas discharge collide with the boron vapor 10, and as a result, the boron vapor 10 returns to its ground state 2 _S ² It is resonantly excited from 2 _P (2Po) to the metastable state 2 _S 2 _P ² ( ⁴ P). In addition, in time synchronization with the voltage application, synchrotron radiation B4 with a wavelength of 2067 Å is transmitted from the synchrotron radiation generating section 3 to the container 1 through the slit 1c.
As a result, the boron vapor 10 in the above 2 _S 2 _P ² ( ⁴ P) becomes synchtron radiation B of 2067 Å.
4 to the autoionization state 2 _S 2 _P 3 _S ( ⁴ P ⁰ ), and the excited vapor becomes an ionic state with a predetermined transition probability. Further, a DC voltage is applied between the electrode 6 and the sample stage 8a, whereby the ionized boron vapor 10 is extracted as an ion beam 9 consisting only of boron ions.
The ion beam 9 is irradiated onto the sample 8 .

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, Even if impurities other than boron, such as oxygen, nitrogen, carbon, hydrogen, etc., are contained and the amount is greater than boron, the wavelength of the synchrotron radiation light should not be made to match the energy level of the impurity atoms. A pure boron ion beam is obtained in which only the desired element, in this case boron, is ionized. Second, as mentioned above, this embodiment performs selective ionization and ionization by resonant optical excitation, so there is no possibility that the temperature will rise due to excitation of electrons or other elements or 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.

Thirdly, when changing the type and characteristics of the ion beam, it is better to change the wavelength and discharge conditions of the spectroscopic single-wavelength synchrotron radiation, and it is necessary to remove the sample or replace the ion source as in the case of conventional methods. There is no need to open and close the container, and 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, 11 is a magnet coil that focuses the ionized beryllium vapor 10 on the axis of the container 1, and 14 is the ion beam 9 that focuses the focused boron vapor 10.
This is an extraction electrode that can be extracted as a.

Next, the operation will be explained.

First, boron vapor 10 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, synchrotron radiation B4 of 2067 Å enters the container 1 through the slit 1c. is introduced and irradiated to the evaporator 10. As a result, the steam 10 enters the metastable state 2 _S
2 _P ² ( ⁴ P), the excited vapor is excited to the auto-ionization state 2 _S 2 _P 3 _S ( ⁴ P ⁰ ), and furthermore, the excited vapor becomes an ionic state with a predetermined transition probability, and as a result, boron ions are generated in the ion generation space 4. are generated, and the boron ions are focused on the axis by the magnet coil 11 and then emitted as an ion beam 9 by the extraction electrode 14.

FIG. 4 shows an example of the configuration of a synchrotron radiation generator used in the present invention. In the figure, 21 is a linear accelerator, 22 is an electron storage ring, and 24 is a spectroscopic system, which constitute a synchrotron radiation light generating device 20. 33 is the generator 2
This is a container that is irradiated with synchrotron radiation light from 0.

In the synchrotron radiation introduced into the container 33, electrons are first accelerated by the linear accelerator 21 and are driven into the electron storage ring 22.
2, synchrotron radiation is emitted from the electrons that have reached relativistic speed, and the synchrotron radiation is further introduced into the spectroscopic system 24, where it is made into a single wavelength.

〔Effect of the invention〕

As described above, according to the ion beam generator of the present invention, the substance to be ionized is resonantly excited from the ground state of its energy level to a relatively lower excited state by gas discharge, and the substance is further excited by the synchrotron Since the excited state is automatically ionized by synchrotron radiation 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 resonant light excitation and ionization methods. be.

[Brief explanation of drawings]

FIG. 1 is an energy state diagram of a boron neutral atom, FIG. 2 is a schematic diagram of a shower type ion beam generator according to a first embodiment of the present invention, and FIG. 3 is a diagram of a shower type ion beam generator according to a second embodiment of the present invention. FIG. 4 is a schematic diagram of a focused ion beam generator; FIG. 4 is a schematic diagram of a synchrotron radiation generator used in the present invention; FIG.
The figure is a phase diagram showing the wavelength dependence of the photoionization rate in the metastable state 2 _S 2 _P ² ( ⁴ P) of neutral boron atoms. 1, 33... Container, 3, 20... Synchrotron radiation generating section, 15... Gas discharge generating section, B4
... Synchrotron radiation. 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 synchrotron radiation generating unit that irradiates the substance in the container with synchrotron radiation light, and a gas discharge generating unit that generates a gas discharge in the atmosphere of the substance in the container, and generates an ion beam of the substance. In the generating device, the gas discharge generating unit excites the substance from the ground state of the energy level to a relatively lower excited state by gas discharge, and the synchrotron radiation generating unit excites the substance to the excited state. An ion beam generation device characterized in that it generates synchrotron radiation light having a wavelength that causes resonant optical excitation from a state to an auto-ionization state. 2. The synchrotron radiation light generating section generates a plurality of synchrotron radiation lights having different wavelengths to resonantly excite the substance stepwise from the relatively lower excited state to the autoionization state via an intermediate state. An ion beam generator according to claim 1, wherein the ion beam generator is an ion beam generator. 3 The synchrotron radiation light generating section has an accelerator and a spectroscope or spectroscopic system, and generates light that is made from the output from the accelerator and has a narrow line spectrum after passing through the spectroscope or spectroscopic system. An ion beam generator according to claim 1 or 2, characterized in that: 4. The ion beam generation device according to claim 3, wherein either or both of an electron storage ring and an electron cyclotron are used as the accelerator. 5. The ion beam generator according to claim 1, wherein the relatively lower excited state is a metastable state of the energy level of the substance. 6. The ion beam generating device according to any one of claims 1 to 5, wherein the gas discharge generating section generates radio frequency (RF) discharge. 7. 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 atomic state. An ion beam generator according to any one of claims 1 to 6. 8. The ion beam generator according to claim 1, wherein the synchrotron radiation light and the gas discharge are temporally synchronized in phase. 9. The ion according to any one of claims 1 to 8, wherein the substance is introduced into the container as a vapor generated by heating and vaporizing a solid or liquid substance. Beam generator.