JPS60235345A - Ion beam generating apparatus - Google Patents

Abstract

PURPOSE:To steeply improve ionization efficiency and ion selectivity by exciting a substance to be ionized to a comparatively lower excitation condition from the basic condition of energy level through gas discharge and moreover to automatic electrolytic dissociation condition through irradiation of laser beam. CONSTITUTION:The beryllium vapor 10 is supplied to a vessel 1 from a gas supply port 1a. A voltage is applied to electrodes 5 and 6 and thereby electrons generated by gas discharge collide with the beryllium vapor 10 and as a result the beryllium vapor 10 is resonant-excited to the quasi stable condition from the basic condition. At the laser beam generating part, a trigger pulse is applied to the lasers from a pulse generating circuit in synchronization with application of voltage, each laser oscillates, both laser beams B3, B4 cross at the ion producing space 4 in the vessel 1. Thereby, the beryllium vapor 10 under the quasi stable condition is resonant-excited step by step to the automatic electrolytic dissociation condition and the excited vapor is ionized with a predetermined transition probability.

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. It is related to.

[Summary of the invention]

The present invention provides an ion beam generator using resonant light excitation and ionization, in which an autoionization level of a substance is set as a state immediately before the substance is ionized by resonant light excitation.
By using conventional resonant optical excitation.

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.

This is a method of irradiating beryllium vapor to be ionized with two laser beams Bl and B2 of 3,000 people. In other words, beryllium atoms in the ground state 2s (IS) are first ionized into 23
Excited state 2p (IPO
), then 3000 laser beams B2
ionization.

The ionization method in the device of the present invention differs from the conventional ionization method described above in that only resonance excitation is used, and beryllium vapor is resonantly excited to a relatively lower level, for example, metastable fi2p (3PG), by gas discharge. Then, the automatic ionization state 1s22p3p is created by laser beam irradiation.
(3S) is resonantly excited. In this excited state, the excited vapor is automatically ionized with a predetermined transition probability.

In the case of the ionization method in the device of this invention, the collision cross section for ionization is several orders of magnitude higher than that in the conventional ionization method, which directly ionizes from energy level 2p (IPO). Therefore, the output energy of the laser beam is small, and since only resonance is used, the energy level of the laser beam can be reduced.

By selecting wavelengths that do not match those of impurity atoms, it is possible to ionize only the substance to be ionized, and moreover, it is possible to ionize the substance with high purity.

Furthermore, by changing the wavelength of the laser beam, ion beams of other types of substances can be easily generated, and in this case, various types of substances to be ionized may be introduced into the ion beam generation container in advance. . The method of the present invention, which allows the M class of the generated ion beam to be easily changed, is unlike any conventional method. There are advantages to being able to do 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,】
1a is a container into which the substance to be ionized is introduced; 1a is a gas introduction hole for introducing the substance into the container 1; 1b is a gas introduction hole for introducing the substance into the container 1;
3a and 3b are gas exhaust holes, and 3a and 3b are laser beams B3. and 3.B from a laser beam generator (not shown). B4 is a window for introducing the beam into the container 1, and the beam inside the container 1 is the window B3. B4
The space where these intersect is the ion generation space 4. Although not shown, the laser beam generating section includes two
There are provided two lasers and a pulse generation circuit that generates an electric signal pulse that serves as an oscillation trigger for each of the lasers.

Note that various lasers such as an excimer, a gas laser such as a nitrogen laser, a solid laser such as an alexandrite laser, a dye laser excited by these, a wavelength tunable laser, or a free electron laser can be used as the laser.

Reference numerals 5 and 6 are electrodes arranged with the ion generation space 4 in between; 5a and 6a are terminals for applying an RF power supply voltage to the electrodes 5 and 6; ) Gas discharge generating section 1 that generates gas discharge
5.

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. 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. Then, a voltage is applied from terminals 5a and 5a to each of the electrodes 5 and 6, and as a result, electrons due to gas discharge collide with the beryllium vapor 10, and as a result, the helium vapor 10 changes from its ground state. It is resonantly excited to the metastable state 2p (3PO). In addition, in time synchronization with the voltage application, in the laser beam generating section, a trigger pulse is applied from the pulse generating circuit to each laser, causing each laser to oscillate.
The laser beam B3 of 51 people enters the above container through the window 3a]
3,865 laser beams B4 were introduced into window 3.
b and both beams B3. B4 intersect in the ion production space 4 in the container 1, so that the beryllium vapor 10 in the metastable state 2p ("PO) is resonantly excited to the excited state 2p (3D) by the 2651 laser beam B3. , and is further resonantly excited stepwise from the excited state 2p (3D) to the autoionization state 1 s22p 3p (3S) by the laser beam B4 of 3865 people, and the excited vapor becomes an ionic state with a predetermined transition probability. A DC voltage is applied between the electrode 6 and the sample stage 8a, whereby the ionized beryllium vapor 1o is extracted as an ion beam 9 consisting only of beryllium ions, and the ion beam 9 is 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, Even if it contains impurities other than beryllium, such as oxygen, nitrogen, carbon, hydrogen, etc., and even if the amount is larger than beryllium, the energy level and wavelength of the laser beam should not match those of the above impurities, etc. The result is a pure beryllium ion beam in which only the desired 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 just need to change the wavelength of the laser beam and the discharge conditions.
There is no need to open or close the container to take out such a sample or replace the ion source, 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, 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. 10 is a magnet for focusing on the axis of the container 1, and 4 is an extraction electrode for extracting the focused beryllium vapor IO 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 by vaporization, and this vapor 10 is introduced into the container 1 through the gas introduction holes 1a-t-il. Then, a voltage is applied to the electrode 5.6, and the vapor 10 is bombarded with electrons from the gas discharge.
A laser beam B3 for 651 people and a laser beam B4 for 3865 people are introduced into the container 1 through the windows 3a and 3b, respectively, and irradiate the steam 10. This causes the steam 10 to change from the metastable state 2p (3PO) to the excited state fi2p
(3D) to autoionization state 1 s22p 3p (3
S) is excited in a stepwise manner, and the excited vapor becomes an ion state with a predetermined transition probability, thereby generating beryllium ions in the ion generation space 4. After the beryllium ions are focused on the axis by the magnet 11, , is 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 a 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 simultaneously generating a trigger pulse from the trigger generator 21 and applying a voltage 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.
5 to 27 are laser beams of solid-state lasers, 28 is a flash lamp 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 oscillating each laser head 25 to 27 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 material to be ionized is resonantly excited from the ground state of its energy level to a relatively lower excited state by gas discharge, and further the material is Since the excited state is changed to an automatic ionization state by irradiation with the laser beam, the ionization efficiency and ion selectivity can be greatly improved.

[Brief explanation of drawings]

FIG. 1 is an energy phase diagram of a singlet system 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. A schematic configuration diagram of a focused ion beam generator according to an embodiment, 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,
FIG. 5 is a block diagram of a laser beam generator of an ion beam generator according to a fourth embodiment of the present invention. 1.13... Container, 15... Gas discharge generating part, 20
. . . Laser beam generator, 21.30 . . . Trigger means, B1 to B4 . . . Laser beam. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Masuo Oiwa Figure 3

Claims (1)

[Scope of Claims] (11) A container containing a substance to be ionized, a laser beam generating section for irradiating the substance in the container with a laser beam, and generating a gas discharge in the atmosphere of the substance in the container. and a gas discharge generating section for generating an ion beam of the substance, wherein the gas discharge generating section excites the substance from a ground state of an energy level to a relatively lower excited state by gas discharge. The laser beam generating section includes a trigger means for generating an electric signal to trigger laser oscillation, and a laser for generating a laser beam having a wavelength that resonantly excites the substance from the excited state to the auto-ionization state. (2) The laser beam generating section resonantly excites the substance stepwise from the relatively lower excited state to the autoionization state via an intermediate state. 2. The ion beam generator according to claim 1, wherein the ion beam generator generates a plurality of laser beams having different wavelengths. (3) The relatively lower excited state is at the energy level of the substance. The ion beam generator according to claim 1 or 2, characterized in that the ion beam is in a quasi-stable state. (4) As the laser of the laser beam generating section, an excimer, a gas laser such as nitrogen, or The ion beam generator according to any one of claims 1 to 3, characterized in that one or both of dye lasers excited by harmonics from the gas laser are used. 5) The ion beam generation device according to any one of claims 1 to 3, characterized in that a dye laser is used as a laser in the laser beam generation section. (6) The laser beam generation device Claims 1 to 3 are characterized in that either one or both of a solid-state laser such as an alexandrite laser or a dye laser excited by harmonics from the solid-state laser is used as the laser in the part. The ion beam generation device according to any one of (7) Claim 1, characterized in that a wavelength tunable laser is used as the laser of the laser beam generation section.
The ion beam generator according to any one of Items 1 to 3. (8) 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. (9) The ion beam generator according to any one of claims 1 to 8, wherein the laser beam and the gas discharge are temporally synchronized in phase. 00) The substance according to any one of claims 1 to 9 is introduced into the container as a vapor generated by heating and vaporizing a solid or liquid substance. Ion beam generator.