JPH03245498A - Ion beam deceleration device - Google Patents

Abstract

PURPOSE:To realize a large current of ion beams at less than 100eV by applying a high-frequency voltage to quadrupole electrodes which have a specific waving pitch, and at the same time, leading in the ion beams in a specific direction. CONSTITUTION:A specific ion passing through a mass spectrograph 4 is decelerated by high-frequency quadrupole electrodes 1b and 1b' (1a and 1a'). The quadrupole electrodes are formed in a waving pitch making in a rough pitch at the incident side of beam along the axial direction, and in a minute pitch at the output side. The beams flow in the axial direction of the quadrupole electrodes. As a result, the beams are decelerated reversely to the acceleration, and radiated by maintaining the potential of a sample 8 at the earthing potential. The ion beams are injected when the high-frequency power of the quadrupole electrodes is in a specific phase scope. The energy of the decelerated beams can be regulated freely by converting the frequency of the high-frequency voltage applied to the quadrupole electrodes.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ion beam deceleration device, and more particularly to an ion beam deceleration device that decelerates an ion beam and irradiates a sample substrate with the ion beam.

[Conventional technology]

A conventional device for obtaining a low-velocity ion beam of 100 eV or less is described in the text of the document "'88 Special Symposium on Ion Engineering", page D-1 "Ion Beam Deposition and Related Topics", Fj, g, 6. Several kV~
An ion beam is extracted from an ion source maintained at a potential of several tens of kV, and after mass separation by a mass separator, the beam is irradiated onto a sample substrate placed at a slightly lower potential than the ion source.

At this time, the irradiation energy of the beam is equal to the difference between the ion source potential and the sample substrate potential. That is, as the ion beam approaches the sample substrate, it is subjected to a decelerating electric field, and the speed of the ion beam is reduced to irradiate the substrate. In order to suppress beam divergence due to deceleration, Fig. 3 + Fig. 4 in the same document is used.
As seen in Figure 7, appropriate voltages are applied to a number of electrodes. in this case.

These deceleration electrodes and sample voltages are all DC voltages.

[Problem to be solved by the invention]

As a means to suppress beam divergence during ion beam deceleration,
The combination of flat plate electrodes as in the conventional example utilizes a so-called weak convergence effect in which the convergence effect decreases as the distance from the central axis increases, so the divergence suppression effect is small. Therefore, when decelerating to 100 eV or less, the low-energy beam current reaching the sample substrate was on the order of several μA to several tens of μA at most. In particular, the beam current of an extremely low energy beam of 50 eV or less is 1 μ8 or less, making it impossible to obtain a practical deposition rate when depositing a film using an ion beam.

Furthermore, in the conventional technique, it is necessary to maintain the sample substrate at a voltage almost as high as that of the ion source, which has the disadvantage of making electrical insulation from other parts and handling (replacement, etc.) of the sample complicated.

An object of the present invention is to provide an ion beam deceleration device that can obtain an ion beam of 100 eV or less and a large current (mA level) by using a high frequency quadrupole electrode as an ion beam deceleration device.

Another object of the present invention is to provide an ion beam deceleration device that makes it possible to perform irradiation while keeping the sample potential at ground potential.

[Means to solve the problem]

In order to decelerate the mA class ion beam to an energy of 100 eV or less, the present invention employs a method of applying a high frequency (several MHz to several 100 MHz) high voltage to a quadrupole electrode having a wavy shape in the axial direction.

This allows the strong ion beam focusing effect of the high-frequency quadrupole electrode to work, making it possible to achieve deceleration with little beam loss. Furthermore, in order to carry out this invention effectively, the following invention is adopted as an accompanying technical means.

In other words, the only beams that undergo deceleration are the incident beams that fall within a specific phase range of the high-frequency quadrupole, and the incident beams that deviate from that phase range hit the undulating quadrupole electrodes during deceleration, causing a discharge between the electrodes. provoke. In order to avoid this, the beam is made incident only in a specific phase range.

Specifically, the ion accelerating voltage may be controlled or the ion source plasma generation time may be controlled only within a specific phase range of the high frequency quadrupole. Additionally, there are improvements that add another beam focusing device.

As another accompanying improvement, by varying the frequency of the voltage applied to the high-frequency quadrupole electrodes, the energy of the desired deceleration beam can be freely adjusted and controlled.

[Effect]

Radio Frequency Quadrupole (Radio Frequency Quadrupole, Radi.

A conventional example of a frequency quadrupole is shown in FIG.

In a high-frequency quadrupole, the waving shapes of the two opposing electrodes are the same: lb, lb' in the horizontal direction, 1a in the vertical direction,
The two sets of electrodes la' are out of phase by 180°. That is, when one side is a mountain, the other side is a valley. Furthermore, a high frequency quadrupole with the same voltage and 180° phase shift is applied to the two sets of electrodes. In the figure, V is the maximum amplitude of the high frequency voltage, ω is the angular frequency of the high frequency, β is the ratio of the speed of ions to the speed of light dust, and λ is the wavelength of the high frequency.

A normal high-frequency quadrupole is mainly used for accelerating ion beams, and is expressed by the formula 1. Ok e V ion beam about IM s
It is used when accelerating to about V. The length of the quadruple contact electrode is usually 1 to 2 m, and the frequency of the applied high frequency is several MHz to several 1.
The frequency is usually fixed in the digits of 00 MHz. When the ion beam passes through the quadrupole electrode, it is accelerated by an accelerating electric field generated in the axial direction, and its speed gradually increases. Therefore, βλ in FIG. 2 gradually becomes longer. That is, the wave shape is processed so that when acceleration is performed, the wave pitch (βλ) is fine on the incident side and gradually becomes coarser.

The shape of the wave can be determined by calculation based on the type of ion, incident energy, applied frequency, high frequency voltage amplitude, etc.

The acceleration of the ion beam by the high-frequency quadrupole is several 100 e
Acceleration from V to several keV to several tens of keV is also efficiently performed. In particular, in high-frequency quadruple transverse acceleration, the strong beam convergence effect in the radial direction created by the quadrupole electric field is maintained throughout the entire acceleration process, which has the advantage that beam loss is small and acceleration can be performed with nearly 100% transmittance. be.

By the way, according to ion optics, the ion beam is subjected to controllers (for example, an electric field lens that focuses the beam, a deflector that bends the trajectory, an acceleration,
A deceleration electrode, etc.) can be treated as having the same function as a lens in the case of light for ions passing on a paraxial trajectory near the center of the controller.

Therefore, as in the case of light, the same conditions (
If the ions are reversed (energy, ion position, gradient), the ions will reach the ion source via the same trajectory.

From the above considerations, the incidence is below 100 eV, and several keV ~
Conversely, if you use a high-frequency quadrupole configured to accelerate at several tens of keV and reverse the ion beam extracted from the ion source with an energy of several keV to several 1° keV, ions can be generated with high transmittance. The beam will be efficiently decelerated to less than <100 eV.

Next, in acceleration using a high-frequency quadrupole, the ion beam is made to enter in a direct current manner. However, as the ion beam progresses with axial acceleration, it becomes concentrated in the axial direction and becomes clumpy. The ion beam emitted from the high-frequency quadrupole is fired like a machine gun ball.

If we look at the state after clustering with respect to the phase of the high-frequency electric field, the third
As shown in the figure, the ion beam usually forms a lump centered around -30". Therefore, when reversing, if the ion beam is incident as a DC beam, the ion beam that has not entered the cluster phase will not be decelerated and will diverge. Corresponds to electrodes, etc.

Since a high voltage of several tens of keV is applied between the electrodes, discharge between the electrodes is induced by beam electrode irradiation, making stable deceleration operation difficult. For stable operation, a pulsed ion beam can be introduced into a high-frequency quadrupole.

Next, when decelerating an ion beam using a high-frequency quadrupole, the deceleration energy is fixed when the frequency of the high-frequency voltage is constant. In practice, it is required to change the energy. In order to make the deceleration energy variable for an electrode with a specific wavy shape, it is necessary to make the frequency variable. For this purpose, a voltage from a frequency-variable high-frequency quadrupole generating circuit may be supplied to the electrodes.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This figure is also a diagram of the principle configuration of the present invention as well as an embodiment. The ion source used was a microwave ion source that generates high-temperature, high-density plasma by microwave discharge in a magnetic field and extracts an ion beam using an extraction electrode 5. The beam extracted from the ion source is mass-separated by a magnetic field deflection type mass separator 4,
Specific ions are transferred to high-frequency quadrupole 1 b, 1 b' (1a
, 1a') was introduced into a container 9 containing the following. The high-frequency quadrupole used was one designed so that a Si 2 ion beam incident at 100 eV or less was accelerated at several tens of keV. Electrode length is 60 (1 m, high frequency power is 10 MHz ~
Experiments were conducted at 30 MHz. The experiment was conducted at a high frequency voltage of 1 to 6 kV. The input power is less than 10KW. To make the frequency variable, a one-turn copper coil (length 20
~45aa) and a high voltage generated by an electric resonant circuit consisting of a vacuum capacitor with variable capacity is supplied to the electrodes. The frequency was changed by changing the capacitance value of the capacitor. 1st
In the embodiment shown, the incident beam current is direct current and 1
mA or less. As a result of the experiment, a beam current of 100 eV or less reached the sample 8 in the sample chamber 10 at a little less than 1 mA, and a Si film was deposited on the surface.

FIG. 4 is a diagram illustrating another embodiment based on the present invention. In the figure, the ion beam is introduced into the radio-frequency quadrupole only when it is in the cluster phase of the radio-frequency voltage.

For this reason, an accelerating voltage controller 12 is provided which receives the phase signal from the high frequency power source 11 and sets the ion source accelerating voltage to a predetermined value only within a predetermined time. FIG. 5 shows the temporal change in the accelerating voltage applied to the ion source in this example.

When the accelerating voltage is lower than the set voltage, the ions are significantly bent by the mass separator and do not enter the center of the quadrupole electrode. In FIG. 5, the waveform is such that the acceleration voltage rises in a pulsed manner, but any waveform may be used as long as a part of the waveform is constant at the set voltage. Furthermore, it is clear that the accelerating voltage pulse in FIG. 5 may be a highly repeated rectangular pulse with a smaller pulse width.

Furthermore, it is clear that the beam can be introduced in a pulsed manner by keeping the ion source acceleration voltage at a value higher than the set voltage value except when the ion source is in the cluster phase.

FIG. 6 is a diagram illustrating another embodiment based on the present invention. In the figure, in order to introduce the incident beam in a pulsed manner, the microwave oscillator 7 is operated only during the time in the collective phase.
The ion source generates plasma in the plasma chamber 16 and extracts an ion beam. At this time, the acceleration voltage is kept at a constant set voltage. In the embodiment, a magnetron was used as the oscillator 7. Therefore, magnetron power supply 1
A control circuit 14 is provided in which the magnetron anode voltage from -5 is applied to the magnetron only during the time that it is in the cluster phase.

If the anode voltage is above a certain value.

Microwave oscillation and if microwaves are introduced.

The plasma is ignited and the ion beam is extracted.

Therefore, the anode voltage waveform does not need to have a flat portion as shown in FIG. The magnitude of the anode voltage affects the magnitude of the plasma density and therefore the extracted ion beam current value, but does not affect the beam trajectory in the mass separator 4. In actual ion beam evaporation, the film thickness is monitored using a different method, so slight fluctuations in the ion beam current to the sample substrate do not pose a practical problem.

Based on another embodiment shown in FIGS. 4 and 6, Ga vapor is introduced into the microwave ion source to generate Ga ions at 100 e
The beam was decelerated below V, and Ga was deposited on the sample with a decelerated beam current at the mA level. Next.

As H3 gas was introduced into the ion source, As ions were ion beam-deposited onto the sample substrate, and these steps were repeated to form a multilayer film of Ga and As at high speed.

Although the present invention has been described for the purpose of decelerating an ion beam to below LOOeV, it is obvious from the content of the invention that it is also effective when decelerating an ion beam of several keV to several 100 keV to an energy of 100 eV or more. . In addition, in order to make the deceleration energy variable, as shown in FIG. 1, a voltage generated by an electric circuit with a variable resonance frequency was supplied.

As a result, the ion energy could be efficiently changed even in the region of 100 eV or less. In this example, Si, Ga, A
Although an example of ion beam deceleration for s is shown, it is clear that similar effects can be obtained for other ion types.

Next, FIG. 7 is a diagram illustrating another embodiment based on the present invention. In the figure, in order to separately collect the DC beams extracted from the ion source, a single-gap cavity 17 excited by another high-frequency power source 18 is provided, and the DC beams are collected in a lump. In order to make the focused beam enter the stable phase of the decelerator high frequency quadrupole, the phase controller 1
9 to adjust the mutual phase difference between the two excitation power sources 11 and 18. In the case of this example, although the entire device is a little larger and the operation is a little more complicated, it has been confirmed that it has the advantage of decelerating the DC beam current without waste, and is advantageous for increasing the current.

〔Effect of the invention〕

According to the present invention, it is possible to realize a large current beam exceeding 100 μA for an ultra-low energy ion beam of 100 eV or less, which conventionally could only obtain beam current values of the order of several μA to several 1° μA. This makes it possible to perform high-speed ion beam evaporation, making it possible to produce multilayer films and single crystal films with new functions.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the ion beam deceleration device of the present invention, Fig. 2 is a perspective view illustrating the shape and voltage application state of a conventional high-frequency quadrupole, and Fig. 3 is a diagram showing a conventional high-frequency quadrupole. FIG. 4 is a diagram explaining the clustering phase of the beam during acceleration at the pole, FIG. 4 is a diagram explaining another embodiment of the present invention, and FIG. 5 is a diagram explaining the temporal change of the ion source acceleration voltage in the embodiment of FIG. 4. , FIG. 6, and FIG. 7 are diagrams each explaining another embodiment based on the present invention. la, la', lb, lb' - high frequency quadrupole electrodes,
2. Capacity variable vacuum condenser, 3. Copper wonton coil, 4. Mass separator, 5. Ion extraction electrode,
6...Air core coil, 7...Microwave oscillator, 8.
...sample substrate, 9..decelerator vacuum container, 1o..sample chamber vacuum container, 11..high frequency power supply, 12..acceleration voltage controller, 13..power supply for extraction electrode, 14..magnetron anode voltage Controller, 15... Magnetron power supply, 16...
...Plasma chamber, 17...Single gap type cavity, 18...High frequency for cavity excitation Fig. 10 Fig. 1 Fig. Fig.

Claims (1)

[Claims] 1. An ion source that generates an ion beam, an ion decelerator that decelerates the energy of the ion beam from the ion source, and a sample that irradiates a substrate with the ion beam decelerated by the ion decelerator. an ion beam deceleration device comprising a chamber, the ion decelerator having four electrodes having a wavy shape arranged in a quadrupole along the axial direction, and having a coarse pitch of the undulations on the beam incidence side; An ion beam characterized in that an electrode shape is formed so that the pitch becomes finer as it advances toward the emission side, a high frequency and high voltage is applied to this electrode, and the ion beam is introduced in the axial direction of the central portion of the quadrupole. Reduction device. 2. The device according to claim 1, wherein the application time of the ion accelerating DC voltage for ion extraction applied to the ion source is controlled, and when the high frequency voltage applied to the quadrupole is in a specific phase range, the ion An ion beam deceleration device characterized by causing a beam to enter. 3. The ion deceleration device according to claim 1, wherein the ion source is a microwave ion source that generates high-temperature, high-density plasma by microwave discharge in a magnetic field and extracts a large current ion beam, and that the ion source has a microwave oscillation time of , an ion beam deceleration device characterized in that a specific phase range of a high-frequency quadrupole applied voltage is limited. 4. The ion beam deceleration device according to claim 1, wherein the frequency of the high-frequency voltage applied to the high-frequency quadrupole is made variable, and the deceleration energy is made variable. 5. In the ion deceleration device according to claim 1, a single-gap type cavity for generating a high-frequency electric field is provided in front of the decelerator, and the phase of the high-frequency electric field applied to the decelerator and the high-frequency electric field applied to the single gap is adjusted. An ion beam deceleration device characterized by comprising a phase adjuster for adjusting the ion beam deceleration device.