JPS60235342A - 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 excitation condition by gas discharge, exciting thereafter the substance by resonant light excitation to Rydberg condition through irradiation of laser beam and then ionizing it with application of electric field. CONSTITUTION:The beryllium vapor 10 is supplied to a vessel 1 from a gas supply port 1a. The RF discharge is generated by an induction coil 16, simultaneously a trigger pulse is applied to respective lasers from a pulse generating circuit in the laser beam generating part, thereby each laser oscillates and a voltage is applied and a voltage is applied to electrodes 5 and 6 in synchronization with laser oscillation. The electrons generated by RF discharge collide with the beryllium vapor 10, the laser beams B3-B5 cross at the ion producing space 4 within the vessel 1. Thereby, the beryllium vapor 10 is resonant-excited step by step to Rydberg condition and finally the vapor is ionized by the pulse field generated from the field 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
573 people's two laser beams B1. This is a method of irradiating beryllium vapor to be ionized with B2, that is, beryllium atoms in the ground state 2S (Is) are first ionized into 2349
The first excited state 2p (i
po), then resonantly excited to energy level 3d (1D) by the laser beam B2 of 4573 people, and further ionized by the laser beam B2 of 4573 people.

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.
Beryllium vapor is transformed into a metastable state 2p (3P) by gas discharge.
O) is resonantly excited to a dominant state, and the laser beam, the first
In the example shown, the wavelength is 3321 people, 1.46μ, 6449
Resonantly exciting the excited vapor from this excited state to the Rydberg state using three human laser beams B3 to B5,
Furthermore, unlike conventional ionization methods, beryllium vapor is not brought into a free electronic state, that is, an ion state, by a laser beam, B2 in the example shown in Figure 1, but is changed from the excited state to an ionic state by an electric field expressed by the following equation. do.

E (V/cm)-〇, 3125x109 n-4 where n is the effective quantum number of the Rydberg state.

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 B2 with a wavelength of 4573. . 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.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 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. Although not shown, the laser beam generation section is provided with three lasers and a pulse generation circuit that generates an electric signal pulse that triggers the oscillation of each laser, and the lasers include: A solid laser such as a wavelength tunable laser, a dye laser, a free electron laser, an alexandrite laser, or a gas laser such as an excimer or nitrogen 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 serves as an RF discharge generating section that generates electric 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. First, 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, a trigger pulse is given to each laser from the pulse generation circuit in the laser beam generation section, which causes each laser to oscillate, and is further synchronized in time with the laser oscillation. A voltage is applied to each of the electrodes 5 and 6 from terminals 5a and 6a.

As a result, electrons caused by the RF discharge collide with the beryllium vapor 10 in the ground state 2s (IS), and as a result, the helium vapor 10 enters the metastable state 2p (3PO).
is excited. Also, due to the emission of one of the above lasers, 3321
Laser beams B3, B5 of 6449 people are introduced into the container l through window 3a, and laser beam B4 of 1,46μ is similarly introduced through window 3b, each beam B
3 to B5 intersect in the ion generation space 4 in the container 1, whereby the helium vapor 10 is resonantly excited from the metastable state 2p (3PO) to the excited state tm3s (3S) by the 3321 laser beam B3, Another 1.46
The excited state 33 ("S) is
is excited to the excited state 3p (3PO), and further 644
The vapor is resonantly excited stepwise to the Rydberg state 12d (3D) by the beam B5 of 9 A, and finally the excited vapor is ionized by the pulsed electric field from the electric field generator 15. 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.
is irradiated onto the sample 8.

The characteristics of this embodiment in the above explanation of operation 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, impurities other than beryllium, such as oxygen, nitrogen, carbon, and hydrogen, are included, and even if the amount is greater than helium, the energy level and wavelength of the laser beam will not match those of the above impurities, etc. In this way, 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 is performed by resonant optical excitation. 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, for example, 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 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.

Beryllium vapor 10 is generated by vaporization, and this vapor 10 is introduced into the container 1 through the gas introduction hole 1a. Then, an RF discharge is generated by the induction coil 1G, 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 an electrode 5.6
A voltage is applied to generate a pulsed electric field 4, which causes the vapor 10 to change from the ground state 2s (Is) to the excited state 2p (
3PO), 3s (3S), and 3p (3PO), the electrons of the beryllium vapor 10 in the Rydberg state 12d (3D) become free electrons, and the electrons in the Rydberg state 12d (3D) become free electrons. Beryllium ions are generated in the ion generation space 4, and the beryllium ions are transferred to the ion beam 9 by 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 order to temporally synchronize the laser beam, electric field, and RF discharge for ion generation in the present invention, a plurality of laser beams each having a specific frequency are required, and the plurality of laser beams also need to be synchronized. For some reason,
FIG. 4 shows an example of the 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 trigger for laser oscillation. In this way, each laser 2
2 to 24 are configured to be oscillated by a trigger pulse from one trigger generator 21, the oscillating laser beam ω1. ω2. ω3 becomes temporally synchronized. By simultaneously generating pulses from the trigger generator 21 and applying voltage to the electrodes 5.6 and induction coil 16, the laser beam, electric field, and R
This means that the F discharge can be temporally synchronized.

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 solid-state laser heads, 28 is a flash lamp power supply, and 29 is a Q-switch Bockel cell power supply, and both types of sources 28 and 29 serve as trigger means 30 for triggering each laser 25 to 27. There is. In this example,
Each laser head 25 to 27 is connected to one set of power supplies 28 and 29.
Since the oscillating laser beams ω1 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 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 generator according to an embodiment, FIG. 4 is a block diagram of a loser beam generating section of an ion beam generator according to a third embodiment of the present invention, and FIG. FIG. 2 is a block diagram of a laser beam generation section of an ion beam generation device according to an embodiment. 1.13... Container, 15... Electric field generating section, 16...
- Gas discharge generating section, 20...Laser beam generating section, 2
2-27...Laser, B1-B5...Laser beam. Note that the same reference numerals in the figures indicate the same or equivalent parts. Agent Masuo Oiwa＋＋＋＋２彎〜LS＋I）Iut-guritsu ``呵〜I、Machi V
Conflict mail~----De Osoi HML master-V-1 is also a thing-
Ichicho-41--1-Shukuichi Figure 3

Claims (1)

[Scope of Claims] (11-f) A container containing a substance to be turned on, a laser beam generating section 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 an electric field generating unit that generates a gas discharge in an atmosphere of the substance in the container, and the gas discharge generating unit generates an ion beam of the substance by gas discharge. 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 trigger means for exciting the substance from the ground state of the energy level to a relatively lower excited state. The electric field generator generates an electric field that changes the substance from the Rydberg state to the ionic state by the Stark effect. (2) The laser beam generating section resonantly excites the substance from the relatively lower excited state to the Rydberg state via an intermediate state in a stepwise manner. The ion beam generator according to claim 1, wherein the ion beam generator generates a plurality of laser beams having different wavelengths. (3) As the laser of the laser beam generator, excimer, nitrogen, etc. The ion beam generator according to claim 1 or 2, characterized in that the ion beam generator uses either one or both of a gas laser and a dye laser excited by harmonics from the gas laser. 4) 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 item 1 or 2. (5) The ion beam generating device according to claim 1 or 2, 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 item 1 or 2. (7) The ion beam generating device according to claim 1 or 2, wherein a free electron laser is used as a laser in the laser beam generating section. (8) The ion beam generator according to any one of claims 1 to 7, wherein the relatively lower excited state is a metastable state. (9) The ion beam according to any one of claims 1 to 8, characterized in that 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. Ql The ion beam generating device 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) Claims 1 to 11 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. (13) The substance is introduced into the container as a vapor generated by heating and vaporizing a solid or liquid substance. ion beam generator.