JPS60235338A - Ion beam generating apparatus - Google Patents

Abstract

PURPOSE:To sharply improve ionization efficiency and ion selectivity by exciting a substance to be ionized to a comparatively lower exciting condition with gas discharge, resonant-exciting to the Rydberg condition through irradiation of laser beam and then to the ion condition through application of electric field. CONSTITUTION:The beryllium vapor 10 is supplied to a vessel 1 from a gas supply port 1a. An RF discharge is generated by an induction coil 16 and simultaneously a laser beam generator oscillates and a voltage is applied respectively to the electrodes 5 and 6 in synchronization with laser oscillation. Electrons generated by RF discharge collide with the beryllium vapor 10, the laser beams B3, B5 are supplied to the vessel 1 through a window 3a, the laser beam B4 is also introduced in the same way through a window 3b. The beryllium vapor 10 is resonant-excited step by step to the Reydberg condition. Finally, the excited vapor is ionized by the pulse field generated from the final generating part 15.

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 as described above, in which the substance to be ionized is set in the Rydberg state (R
The purpose of this project is to provide an ion beam generator that can improve the ionization efficiency for input light energy by several orders of magnitude compared to conventional resonant optical excitation and ionization methods, and has excellent selectivity in selective ionization. There is.

[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.

Conventional ionization methods, for example, have wavelengths of 2349 and 4
This is a method of irradiating beryllium vapor to be ionized with two laser beams Bl and B2 of 573 people, that is, helium atoms in the ground state 2s (1s) are first ionized into 2349
The first excited state 2p (IPO
), and then 4573 people's laser beam B2
The beam is resonantly excited to energy level 3d (ID) by 4573 laser beams B2 and ionized.

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.
Does beryllium vapor become metastable by gas discharge? , 2p
'(3PO) is resonantly excited to a dominant state, and the laser beam, in the example shown in Figure 1, has a wavelength of 3321, , 1.46μ,
The above-mentioned excited vapor is resonantly excited from this excited state to the Rydherg state by three laser beams B3 to B5 of 6449 people, and then, as in the conventional ionization method, the beryllium vapor is irradiated with a laser beam, B2 in the example shown in FIG. Instead of changing the state into a free electronic state, that is, into an ionic state, the excited state is changed into an ionic state by an electric field represented by the following equation.

E (V'/cm) -〇, 3125X109 n-4
Here n is the effective quantum number of the Rydberg state.

In the case of the ionization method in this invention device, the collision cross section for ionization is several orders of magnitude higher than that in the conventional ionization method, in which the helium vapor is directly ionized from the energy level 3d (ID) by the laser beam B2 of wavelength 4573. More expensive than that. Therefore, the output energy of the laser beam is small, and since the excitation is from a metastable state rather than the ground state, the wavelength of the photon is short, and since only resonance is used, the energy level of the laser beam 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 and electric field strength of the laser beam, ion beams of other types of substances can be easily generated. 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 present invention, in which 1
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 or 3b is a gas exhaust hole, and 3a or 3b is a laser beam B3. from a laser beam generator (not shown). This is a window through which B5 or B4 is introduced into the container 1, and the space in the container 1 where the laser beams B3 to B5 intersect is an ion generation space 4. The laser beam generating section includes a flash lamp for an excitation source and three lasers that are excited by the flash lamp and generate the laser beams B3 to B5,
As this laser, a solid laser such as a wavelength tunable laser, a dye laser, or an alexandrite laser is used.

Reference numerals 5.6 and 5.6 are electrodes placed across the ion generation space 4; 5a and 6a are terminals that apply voltage to the electrodes 5.6; 15. Reference numeral 16 designates an induction coil which is also placed across the ion generation space 4, and which generates high frequency (RF) waves in the ion generation space 4.
) It is an RF discharge generating part that generates a discharge. 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. Beryllium vapor 10 is introduced into the container 1 through the gas introduction hole 1a. and the above induction coil 1
6 generates an RF discharge, and at the same time, the laser beam generating section oscillates, and voltage is applied to each of the electrodes 5 and 6 from the terminals 5a and 5a in temporal synchronization with the laser oscillation. Then, due to this, the above ground state p ”l
Electrons from the RF discharge collide with beryllium vapor 10 in S (IS), and as a result, beryllium vapor 10 is excited to a metastable state 2p (3PO). In addition, the above laser oscillation produces laser beams B3 for 3,321 people and 6,449 people. A BS is introduced into the container l through the window 3a, and a 1,46μ laser beam B4 is likewise introduced through the window 3b, with each beam B3-B5 intersecting in the ion production space 4 within the container 1. , As a result, the beryllium vapor 10 is resonantly excited from the metastable state 2p (3PO) to the excited state 3s (3S) by the 3321 laser beam B3, and further changed to the excited state 3s (3S) by the 1°46μ laser beam B4. is excited to the excited state 3p (3PO), and further resonantly excited stepwise to the Rydberg state 12d (3D) by the laser beam B5 of 6449 people.Finally, the excited vapor is excited by the pulsed electric field from the electric field generator 15. Ionized. 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 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 it contains impurities other than beryllium, such as oxygen, nitrogen, carbon, hydrogen, etc., and the amount thereof tends to be greater than beryllium, the energy level and wavelength of the laser beam should not be made to match those of the above impurities, etc. A pure beryllium ion beam is obtained 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 can simply change the wavelength of the laser beam and the applied voltage, 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 14 is ionized beryllium. This is an extraction electrode that extracts the 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 helillium 12 is melted.

The beryllium vapor 10 is vaporized and is introduced into the container 1 through the gas introduction hole 1a. Then, an RF discharge is generated by the induction coil 16, and at the same time 33
21 people, 6449 people laser beams B3 and B5 are window 3
Through a, a laser beam B4 of 1,46μ is also applied to the window 3.
b into the container 1, and further electrodes 5, 6.
A voltage is applied to generate a pulsed electric field, which causes the vapor IO to change from the ground state 2s (1S) to the excited state 2+) (3
Ryu through PO), 3s (3S), 3p (3PO)
The electrons of the beryllium vapor 10 in the Rydberg state 12d (3D) are excited stepwise into the Rydberg state 12d (3D) and become free electrons, thereby generating beryllium ions in the ion generation space 4. 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, and FIG. 5 shows a part of the dye cell.

In the present invention, in order to excite elements stepwise, a plurality of laser beams each having a specific frequency are required, and the plurality of laser beams must be synchronized. An example of the synchronization method is shown below.

In the figure, 21 is a reflector cell of the laser oscillation device 20;
22 is two dye cells, 23 is one Franche lamp, 24 is a mirror, 25 is a plane mirror, 26 is a diffraction grating, ω1. ω
2 is a laser beam.

In this laser oscillation device 20, one Franche lamp 2
3, the two dye cells 22 are excited, whereby dye laser beams ω1°ω2 having different wavelengths are synchronously oscillated. In this example device, two laser beams ω
1. Due to ω2, the substance to be ionized is resonantly excited stepwise from a metastable state to an intermediate state to the Rydberg state.

The above laser beam ω1. In order to make the wavelength of ω2 different, the wavelength can be changed by using different dyes as the dye cell 22 of 2 (Ili!), or the same dye can be used as the two dye cells 22. The wavelengths can be mutually changed by adjusting the coordination angles θ1 and θ2 between the plane mirror 25 and the diffraction grating 26. In this way, the wavelength that resonates with the substance to be ionized can be selected, and the time of each laser beam can be changed. It can be synchronized and, as a result, matter can be excited in a stepwise manner.

In addition, the above-mentioned flash lamp 23 is started, and the above-mentioned electrode 5,
6 or the induction coil 16 at the same time, the laser beam and the electric field or RF discharge can be 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 photoexcited and then brought from the excited state to the ion state by applying an electric field, 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 generation device according to an embodiment, FIG. 4 is a schematic configuration diagram of a laser beam generation section of an ion beam generation device according to a third embodiment of the present invention,
Figure 5 shows the Franche lamp and dye cell part.
FIG. 5 (a cross-sectional side view of the same, shown in FIG. 5) is a cross-sectional front view thereof. 1.13... Container, 15... Electric field ordering section, 16...
- Gas discharge generating section, 20...Laser beam generating section, 2
2... Dye laser, 23... Franche lamp, B
1-B5...Laser beam. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Masuo Oiwa

Claims (1)

[Claims] (1) A container containing a substance to be ionized, a laser beam generator that irradiates the substance in the container with a laser beam, and an electric field that applies an electric field to the substance in the container. In an apparatus for generating an ion beam of the substance, the gas discharge generating unit includes a gas discharge generating unit that generates a gas discharge in an atmosphere of the substance in the container, and the gas discharge generating unit generates the substance by gas discharge. It excites the energy level from the ground state to a relatively lower excited state, and the laser beam generating section is excited by a flash lamp and causes the substance to resonate from the relatively lower excited state to the Lyudhelg state. and a laser that generates a laser beam having a wavelength that causes optical excitation, and the electric field generating section generates an electric field that changes the substance from the Rydberg state to the ionic state by the Stark effect. Ion beam generator. (2) The laser beam generating section generates a plurality of laser beams having different wavelengths to resonantly excite the substance stepwise from the relatively lower excited state to the Ludherg state via an intermediate state. An ion beam generator according to claim 1, characterized in that: (3) The laser beam generating section is comprised of one flash lamp and a plurality of mutually time-synchronizable laser oscillation cells excited by light from the Franche lamp. The ion beam generator according to item 1 or 2. (4) The ion beam generating device according to any one of claims 1 to 3, characterized in that a variable eL length laser is used as a laser in the laser beam generating section. (5) The ion beam generating 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 generating section. (6) A claim characterized in that the laser of the laser beam generating section is one or both of a solid-state laser such as an alexandrite laser and a dye laser excited by harmonics from the solid-state laser. The ion beam generator according to any one of Items 1 to 3. (7) The ion beam generator according to any one of claims 1 to 6, wherein the relatively lower excited state is a metastable state. (8) The ion beam according to any one of claims 1 to 7, wherein the electric field for ionization due to the Stark effect of the electric field generating section also serves as an extraction electric field for extracting ions as a beam. Generator. (9) The ion beam generating device according to any one of claims 1 to 8, wherein the gas discharge generating section generates radio frequency (RF) discharge. αΦ 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 9. (11) Claims 1 to 10 are characterized in that the phases of at least any two of the laser beams, gas discharges, and electric fields can be temporally synchronized. 2. The ion beam generator according to any one of paragraphs. (12) The substance is introduced into the container as a vapor generated by heating and vaporizing a solid or liquid substance. ion beam generator.