JPH0517653B2 - - 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 light and use the resulting plasma as an ion source, and the other is to focus the light and irradiate it onto a gas or liquid. to create plasma,
This is used as an ion source, and other 1
One is to use a variable wavelength light source to make a single wavelength of light resonate with the energy level of the substance to be ionized, and ionize the substance. It concerns something that uses synchrotron radiation instead of light.

[Summary of the invention]

The present invention resonantly excites a substance to be ionized from its ground state to a Ryudberg state by irradiating it with synchrotron radiation, and then brings the substance to a Ryudberg state close to its ionization limit by applying a pulsed electric field synchronized with the synchrotron radiation. A compact low-energy ion beam generator with excellent selectivity in selective ionization, which improves ionization efficiency for input light energy by more than four orders of magnitude compared to conventional resonant optical excitation and ionization methods by changing the state from Rydberg level to ionization. is intended to provide.

[Embodiments of the invention]

First, the ionization method in the apparatus of the present invention will be explained using an example of generating a magnesium ion beam and comparing it with a conventional method. FIG. 1 is an energy level diagram of a neutral magnesium atom.

Conventional ionization methods, for example, have a wavelength of 2853 Å,
This is a method of irradiating the magnesium vapor to be ionized with two 5528 Å laser beams B1 and B2. In other words, magnesium atoms in the ground state 3s ( ¹ S) are first transformed into the first excited state 3p (1 S) by the 2853 Å laser beam ^B1 . P ⁰ ), then resonantly excited to energy level 3d ( ¹ D) by a laser beam B2 of 5528 Å, and further ionized by a laser beam B1 of 3853 Å.

The ionization method in the device of the present invention differs from the conventional ionization method described above in that the final excited state is the Ryudberg state and that synchrotron radiation, particularly relativistic synchrotron radiation, is used as the excitation light source. . Synchrotron synchrotron radiation has directionality similar to laser light, and is much more intense and high-energy photons than laser light.
Therefore, as shown in FIG. 1, a single photon can excite magnesium vapor from the gas state to the Lyudberg state. Furthermore, in order to ionize the excited vapor, for example, an electric field expressed by the following formula is applied to the vapor together with synchrotron radiation light, and ionization is carried out from this excited state by the electric field, which is also different from the conventional ionization method. different from.

E (V/cm)≧0.13125×10 ⁹ ·n* ^-4 where n* is the effective principal quantum number of the Rydberg state, and this relationship is shown in FIG. The Ryudberg state generally refers to a highly excited state of an atom that has a principal quantum number n that is about 10 or more larger than the ground state. In the case of a neutral magnesium atom, the ground state is 3s ( ¹ S), n=3, and the Ryudberg state is a highly excited state with n≧13.

For the 13p ( ¹ P ⁰ ) level of the neutral magnesium atom, n * = 12.40, and therefore the electric field strength required for ionization of the Ryudberg state 13p ( ¹ P ⁰ ) is E ≥ 1.321 × 10 ⁴ V/ cm. Furthermore, if a higher Ryudberg state, that is, closer to the ionization limit is selected, for example, the 29p ( ¹ P ⁰ ) level, the electric field strength required for ionization is E≧4.418×10 ² V/cm.
becomes smaller. On the other hand, the first excited state 3p ( ¹ P ⁰ )
For n*=2.03, if this 3p ( ¹ P ⁰ )
If a level is directly ionized by an electric field, an extremely large electric field strength of E≧1.840×10 ⁷ V/cm is required for the ionization.

By the way, the radiative lifetime of a Ryudberg state with effective principal quantum number n* is τr∝n* ³ , and under gas pressure so low that collisions can be ignored, n
The larger the * is in the highly excited state, the longer the radiation lifetime τr becomes. Figure 6 shows the relationship of the radiative lifetime τr (ns) = 1.38 x (n * - 0.0144) ³ for the p-state of a neutral magnesium atom. For the Ryudberg state 13p ( ¹ P ⁰ ) of a neutral magnesium atom, τr ~ 2.6 us is sufficient, but for a higher Ryudberg state, that is, closer to the ionization limit, such as the 29p ( ¹ P ⁰ ) level, τr ~ 34 us. becomes longer. On the other hand, the first excited state 3p
( ¹ P ⁰ ) is about τr ~ 10 ns, and the radiative lifetime is extremely short compared to the Ryudberg state.

Therefore, the ground state 3p of the magnesium neutral atom
(1S) is excited to the Lyudberg state 29p ( ¹ P ⁰ ) by synchrotron radiation with wavelength λ ₁ = 1625 Å,
This 29p ( ¹ P ⁰ ) level is applied to the electric field E＞4.418×10 ² V/cm
In the case of an example of the ionization method in the device of the present invention in which magnesium vapor is ionized by synchrotron radiation λ ₁ , the radiative lifetime of Rydberg state 29p ( ¹ P ⁰ ) is approximately τr ~ 34 us. All you have to do is apply an electric field to ionize the level, and apply a voltage of >400V with a rise/fall time <
An ordinary pulse voltage generator capable of generating pulse voltage in about 10 us can be used.

Ground state, an example of following traditional ionization methods
When photoionizing directly from 3s (1S), its photoionization cross section is σi = 2.50 × 10 ^-27 [λ ₁ (Å)] ³ cm ² ,
Therefore, the ionization rate is W=1.25×10 ^-12 [λ ₁ (Å)] ⁴
I(W/cm ² )sec ^-1 . Here, since the synchrotron radiation wavelength λ ₁ exceeds the ionization limit, λ ₁ <
Must be 1621Å. FIG. 7 shows this ionization rate W as a function of the radiation wavelength λ ₁ for various radiation intensities I. As shown in the figure, when the wavelength λ ₁ is changed at a certain radiation light intensity, the ionization rate W
changes continuously.

In addition, as a conventional ionization method, the wavelength λ ₁ =
ground state by synchrotron radiation of 2853 Å
A method of directly photoionizing the neutral magnesium atoms photoexcited from 3s ( ¹ S) to the first excited state 3p ( ¹ P ⁰ ) is also considered. In this case, its photoionization cross section is σi
= 3.06×10 ^-28 [λ ₂ (Å)] ³ cm ² , so its ionization rate is W = 1.54×10 ^-13 [λ ₂ (Å)] ⁴ I (W/cm ² )
sec ^-1 . Here, since the synchrotron radiation wavelength λ ₂ exceeds the ionization limit, it is necessary that λ ₂ <3756 Å. FIG. 8 shows this ionization rate W as a function of the radiation wavelength λ ₂ for various radiation intensities I. As shown in the figure, in this case as well, if the wavelength λ ₂ is changed at a certain radiation intensity, the ionization rate W
changes continuously.

On the other hand, in the case of the ionization method in this inventive device, synchrotron radiation with a wavelength λ ₁ = 1625 Å is used to convert the ground state 3s (1S) to the Lyudberg state 29p.
Photoexcitation cross section to ( ¹ P ⁰ ) σ _ex = 9.91×10 ^-23 [λ ₁
(Å)] ³ cm ² , and therefore its excitation rate is W=4.98×10 ^-8 [λ ₁ (Å)] ⁴ I(W/
cm ² ) sec ^-1 . However, the above values are for the ground state
The optical absorption spectrum from 3s (1S) to Ryudberg state 29p ( ¹ P ⁰ ) has a Doppler broadening at room temperature, and was calculated assuming that the spectral width of the emitted light is about 10 times the Doppler broadening. When such Ryudberg state 29p ( ¹ P ⁰ ) is ionized by an electric field, the electric field strength is changed to the electric field threshold required for ionization E _cr = 0.3125×10 ⁹・n ^-4 = 4.418×
When the voltage is about 10% higher than 10 ² V/cm, it separates into ions and electrons at a high speed of 10 ¹² sec ^-1 or more. Therefore, this excitation speed W is the wavelength of the ground state 3s ( ¹ S)
Lyudberg state 29p due to 1625Å synchrotron radiation
( ¹ P ⁰ ) can be defined as the field ionization rate via (1 P 0 ).

FIG. 9 shows this ionization rate W for various emitted light intensities I for several Ryudberg states np ( ¹ P ⁰ ) (n=13-15, 21, 29). When the radiation wavelength λ ₁ is changed at a certain radiation intensity, the state changes from the ground state 3s ( ¹ S) to the Lyudberg state np
The ionization rate W exhibits a finite value only at the wavelength λ ₁ that resonates with the transition 3s ( ¹ S)−np ( ¹ P ⁰ ) to ( ¹ P ⁰ ), and W=0 at other wavelengths.

Comparing Figures 7, 8, and 9, the ionization rate W of ionization via the Ryudberg state
It can be seen that this is more than four orders of magnitude larger than that of conventional photoionization.

By the way, as a conventional ionization method, the wavelength λ ₁
Another possible ionization method is to directly ionize neutral magnesium atoms excited from the ground state 3s ( ¹ S) to the first excited state 3p ( ¹ P ⁰ ) by an electric field using synchrotron radiation of = 2853 Å. In this case,
As mentioned above, an extremely large electric field strength of E≧1.840×10 ⁷ V/cm is required. In addition, since the radiative lifetime of the 3p ( ¹ P ⁰ ) level is extremely short at ~10 ns, it is necessary to apply an electric field for ionization for an extremely short time of ~10 ns after irradiation with synchrotron radiation λ ₁ . . Therefore, this ionization method requires a special high-voltage short pulse generator capable of generating an ultra-high voltage of about >10 MV in an ultra-short time of ~10 ns. In comparison, voltage generation for field ionization of the Ryudberg state according to the ionization method of the apparatus of the present invention can be achieved with an extremely compact and inexpensive ordinary apparatus.

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 four orders of magnitude higher than that of the conventional resonance optical excitation and ionization method, and since only resonance is used completely, the energy level of the synchrotron radiation is By selecting the wavelength so that it does not match that of the impurity atoms, it is possible to ionize only the substance that is desired to be ionized, and moreover, it is possible to ionize the substance with high purity.

Furthermore, in the case of the ionization method in this invention,
Even compared to the method of ionizing the excited state, which is much lower than the Ryudberg state, by field ionization,
There are advantages that can be achieved using conventional compact and inexpensive voltage generators without the need for specialized and expensive high voltage short pulse generators.

In addition, by changing the wavelength and electric field strength of the synchrotron radiation, it is possible to easily generate ion beams of other types of substances. You can also introduce it. The method of the present invention, which allows the type of ion beam generated to be easily changed, is different from conventional methods, and has the advantage of being able to perform two or more processing steps using an ion beam in succession. be.

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 an evacuation device for evacuating the container 1 (see FIG. (not shown), 3 is a synchrotron radiation generating unit that generates synchrotron radiation B3 with a narrow wavelength width of 1625 Å, and 5 and 6 are electrodes placed on both sides of the synchrotron radiation B3. , 5a and 6a are terminals for applying voltage to the electrodes 5 and 6, and these constitute an electric field generating section 15 that applies an ionizing electric field for ionizing the substance in the container 1. 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. Note that the ionization electric field may also serve as the extraction electric field.

Next, the operation will be explained.

Let us consider the case where a magnesium ion beam is generated by the apparatus of this embodiment. First, magnesium vapor 10 is introduced into the container 1 through the gas introduction hole 1a. Synchrotron radiation B3 with a wavelength of 1625 Å is introduced into the container 1 from the synchrotron radiation generating section 3, and the magnesium vapor 10 is brought into the ground state 3s by the synchrotron radiation B3.
( ¹ S) to the Lyudberg state 29p ( ¹ P ⁰ ).

In addition, terminals 5a and 6 are connected to electrodes 5 and 6, respectively, in synchronization with the introduction of vapor synchrotron radiation light.
A voltage is applied from a, thereby applying an electric field to the magnesium vapor 10 in the Lyudberg state 29p ( ¹ P ⁰ ), and as a result, the magnesium vapor 10 is ionized. Here, as described above, the electric field strength required for ionization of the Ryudberg state 29p ( ¹ P ⁰ ) is E>4.418×10 ² V/cm.
Therefore, if the distance between electrode 5 and electrode 6 is d (cm), the voltage applied between these electrodes is Vr>4.418
×10 ² dV. Further, a DC voltage is applied between the electrode 6 and the sample stage 8a, so that the ionized magnesium vapor 10 is extracted as an ion beam 9 consisting only of magnesium ions. The sample 8 is irradiated.

The energy Vi of the ion beam 9 is determined by the voltage Vr applied between the electrodes 5 and 6 and the voltage Va applied between the electrodes 6 and the sample 8a. For example, the synchrotron radiation irradiation area between electrode 5 and electrode 6 is
Assuming that d/ ₂ ^is in the middle ^of
It becomes 2.209×10 ² +VaV. Therefore, if no voltage is applied between the electrode 6 and the sample stage 8a (Va
= 0), it is possible to obtain an ion beam with a low energy of about 200V.

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 magnesium, such as oxygen, nitrogen, carbon, and hydrogen, are contained, and the amount is greater than that of magnesium, the energy level and wavelength of synchrotron radiation light should not match those of the impurities mentioned above. The result is a pure magnesium ion beam in which only the desired element, in this case magnesium, 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.

Thirdly, as described above, in this embodiment, the energy of the ion beam can be controlled by the applied voltage when the Ryudberg state is ionized by an electric field, and an ion beam with low energy can be obtained. Therefore, the surface of the target sample 8 to be irradiated with the ion beam, such as a semiconductor substrate, can be treated without damaging it. Further, such a low energy ion beam can be used as a high energy ion beam by further accelerating the beam after extraction. Therefore, the ion beam in this example ranges from low energy of 100V or less to high energy of 1MV or more.
This is an ion source that can handle ion beams with a wide energy range.

Fourth, if you want to change the type or characteristics of the ion beam, you can simply change the wavelength of the synchrotron radiation light and the applied voltage.
There is no need to open or close the container to 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 a container containing the substance 12 to be ionized, 13a is a heater provided on the outer periphery of the container 13, and the container 13 is thereby It serves as an oven in which the substance 12 is evaporated.
11 is a magnet that focuses the ionized magnesium vapor 10 on the axis of the container 1, and 14 is an extraction electrode that extracts the focused magnesium vapor 10 as an ion beam 9.

Next, the operation will be explained.

Magnesium 12, which is a substance to be ionized, is placed in the container 13, and the container 13 is heated by the heater 13a.
When heated, the magnesium 12 is melted and vaporized to generate magnesium vapor 10. Then, synchrotron radiation B3 having a wavelength of 1625 Å is introduced into the container 13 and irradiated onto the vapor 10, and at the same time, a voltage is applied to the electrodes 5 and 6 to apply an electric field to the vapor 10. As a result, steam 10 changes from the ground state 3s (1S) to the Lyudberg state.
29p ( ¹ P ⁰ ), and due to an external electric field, the electrons of the magnesium vapor 10 in the Ryudberg state 29p ( ¹ P ⁰ ) become free electrons, thereby producing magnesium ions, which are axially moved by the magnet 11. After being focused on the heart, the ions are emitted as an ion beam 9 by an extraction electrode 14.

Here, as mentioned above, the Lyudberg state
The electric field strength required for ionization of 29p ( ¹ P ⁰ ) is E>
It becomes 4.418×10 ² V/cm. Therefore, assuming that the distance between electrode 5 and electrode 6 is d (cm), the voltage applied between the electrodes needs to be Vr>4.418×10 ² dV.

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, 23 is a wiggler, 24 is a spectroscopic system, and 33 is a container.

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.
Synchrotron radiation light is emitted from the electrons that have reached relativistic speed in step 2, and is further introduced into the spectroscopic system 24, where the light is made into a single wavelength. In this embodiment, since the wiggler 23 is provided, the wavelength tunability range can be expanded in addition to the wavelength tunability of the spectroscopic system 24, and ion beams of various materials can be generated.

〔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 its ground state to the Lyudberg state by irradiation with the synchrotron radiation light, and the substance is further excited by the synchrotron radiation light. By applying a synchronized pulsed electric field, the Ryudberg state is transformed into an ion state, resulting in excellent ion selectivity, and compared to conventional resonant optical excitation and ionization methods, the ionization efficiency for input light energy can be improved by more than four orders of magnitude. Moreover, there is an effect that a compact low-energy ion beam generator can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an energy phase diagram of a singlet system of magnesium 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. Schematic configuration diagram of focused ion beam generation according to the embodiment, No. 4
The figure is a schematic diagram of the synchrotron radiation generation section used in the present invention. Figure 6 is a phase diagram showing the radiative lifetime of an excited state with effective principal quantum number n* in the p state of a neutral magnesium atom, and Figure 7 is a diagram showing the photoionization rate in the ground state 3s ( ¹ S) of a neutral magnesium atom. Figure 8 is a phase diagram showing the wavelength dependence of the photoionization rate in the first excited state 3p ( ¹ P ⁰ ) of a neutral magnesium atom. Figure 9 is a phase diagram showing the wavelength dependence of a neutral magnesium atom. Ryudberg state np ( ¹ P ⁰ ) in state 3s ( ¹ S ⁰ ) (n = 13 ~ 15,
21, 29) is a phase diagram showing the wavelength dependence of field ionization rate. 1, 13, 33... Container, 15... Electric field generating section, 20... Synchrotron radiation generating section, B3
... 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 section that irradiates the substance in the container with synchrotron radiation light to excite resonance light from the ground state of the energy level to the Ryudberg state; An ion beam generator comprising: an electric field generator that applies a pulsed electric field synchronized with synchrotron radiation to change the Ryudberg state to the ion state. 2. The ion beam generation device according to claim 1, wherein the synchrotron radiation light generation section includes an accelerator. 3. The ion beam generator according to claim 2, wherein an electron storage ring or an electron cyclotron is used as the accelerator. 4. The synchrotron radiation light generating section is characterized by having an accelerator and a spectrometer or spectroscopic system, and generating light of a single wavelength by passing the output from the accelerator through the spectrometer or spectroscopic system. An ion beam generator according to claim 2 or 3. 5 The synchrotron radiation light generating unit has a spectrometer or a spectroscopic system, and generates synchronized plural single wavelength lights that resonantly excite a substance in a stepwise manner from a ground state to an intermediate state to a Rydberg state. The first claim characterized in that
The ion beam generator described in Section 1.