JPH02301940A - Ion source - Google Patents

Abstract

PURPOSE:To make it possible to apply the generation of low energy ion beams and convergent ion beams to ultra high brightness ion beams by extracting ion current from the super-sonic molecule flow of plasma obtained from super- sonic expansion taking a place when plasma generated in a discharge chamber is introduced into a vacuum chamber. CONSTITUTION:Plasma composed of specimen gas B generated in a discharge chamber 1 and of carrier gas A, flows out into the first vacuum chamber 22 through a nozzle 26 so as to be super-sonically expanded so that the super-sonic free jet steam D of plasma is thereby formed. In the second place, a section close to the center axis of the super-sonic free jet stream D of plasma in a region of stillness is extracted out as super-sonic molecule flow E into the second vacuum chamber 23 by means of a skimmer 28 provided for the first bulkhead 27. The super-sonic molecule flow E passes through a collimator 30 provided for the second bulkhead 29 so as to flow in the third vacuum chamber 24. Plasma ions are extracted as ion current F out of an electric hole 8 while being accelerated to the direction of an electrode 7 by means of the electric field applied between the collimator 30 and the electrode 7.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ion source, and particularly to ion implantation, ion beam exposure, ion beam deposition, ion beam etching, ion beam writing, etc. in the field of semiconductor device manufacturing processes. This invention relates to a gas ion source that generates a high-intensity ion beam used in ultra-fine processing.

[Conventional technology]

FIG.
This is a schematic cross-sectional view showing a conventional gas ion source published in Japan (Japanese edition), in which 1 is a discharge chamber, 2 is a cathode installed in this discharge chamber 1, and 3 is a cathode installed in the discharge chamber 1. an anode; 4 is an anode hole that this anode 3 has; 5 is the discharge chamber 1;
An intermediate electrode is installed between the cathode 2 and the anode 3, 6 is an intermediate electrode hole that this intermediate electrode 5 has, 7 is an extraction electrode installed close to the anode 3, and 8 is an intermediate electrode that this extraction electrode 7 has. This is a lead-out electrode hole.

9 is a vacuum chamber that includes the extraction electrode 7 and is adjacent to the discharge chamber 1 via the anode 3; 10 is a vacuum outlet for exhausting the vacuum chamber 9; 11 is the cathode 2 of the discharge chamber 1; A carrier gas introduction port for introducing carrier gas A between the intermediate electrode 5; 12 a sample gas introduction port for introducing the sample gas B between the intermediate electrode 5 and the anode 3 of the discharge chamber 1; C is an ion flow extracted from the extraction electrode 7 through the extraction electrode hole 8. Note that the cathode 2,
The intermediate electrode hole 6, the anode hole 4, and the extraction electrode hole 8 are arranged in a straight line and are coaxial with the central axis of the extracted ion flow C.

Next, the operation will be explained.

First, the vacuum chamber 9 is evacuated through the vacuum puller 10 to bring the discharge chamber 1 and the vacuum chamber 9 to a predetermined degree of vacuum. Next, while evacuation is performed from the vacuum port 10, carrier gas A is introduced into the discharge chamber 1 from the carrier gas introduction port 11, and a DC voltage is applied between the cathode 2 and the intermediate electrode 5. As a result, the carrier gas A is ionized by glow discharge or arc discharge generated between the cathode 2 and the intermediate electrode 5, and plasma is generated.

The generated plasma then passes through the intermediate electrode hole 6 and flows between the intermediate electrode 5 and the anode 3.

Here, the sample gas B is introduced into the discharge chamber 1 from the sample gas inlet 12.
When introduced into the sample gas B, the sample gas B is ionized by interaction with the plasma of the carrier gas A. The plasma of the carrier gas A containing the ionized sample gas passes through the anode hole 4 and flows between the anode 3 and the extraction electrode 7. Here, since a DC voltage is applied between the anode 3 and the extraction electrode 7 to generate an electric field, the ion flow C is extracted from the extraction electrode hole 8 in the direction of the arrow. At this time, non-ionized neutral gas also flows into the vacuum chamber 9 together with the ion flow C.

[Problem to be solved by the invention]

As described above, the conventional gas ion source is configured to extract ions from the high-temperature plasma generated in the discharge chamber 1, so the temperature of the resulting ion flow C is high and the thermal velocity of the ions is low. Due to its large size, it was impossible to generate a low-energy ion beam. In addition, this thermal motion remains even in the ion beam obtained by accelerating the ion flow C, so there is a limit to the diameter that can be focused using an electromagnetic field. There were problems such as the impossibility of applying it to ultra-high-brightness ion beams.

This invention was made to solve the above-mentioned problems, and it uses a cryogenic gas that can generate low-energy ion beams and can be applied to ultra-high-brightness ion beams such as focused ion beams. The aim is to obtain an ion source for

[Means to solve the problem]

The ion source according to the present invention has a generated gas jetting nozzle, and is provided with a discharge chamber for generating ionized gas by ionizing atoms and molecules of the raw material gas, and also includes a discharge chamber for generating ionized gas by ionizing atoms and molecules of the raw material gas, and the ionized gas is supplied through the jetting nozzle. a first vacuum chamber for introducing the ionized gas into the interior and expanding it at supersonic speed to form a supersonic free jet; and a skimmer for extracting a supersonic molecular flow from the supersonic free jet of the ionized gas; A second vacuum chamber is provided for introducing a supersonic molecular flow, and an ion flow is separated and extracted from the molecular flow.

[Effect]

In this invention, plasma generated in a discharge chamber is introduced into a first vacuum chamber through a nozzle and expanded at supersonic speed, and a supersonic molecular flow of the plasma is extracted from a supersonic free jet obtained by the expansion. Since the ion flow is extracted from the supersonic molecular flow of this plasma, it is possible to generate a plasma whose temperature is sufficiently low due to supersonic expansion. It is possible to generate a plasma supersonic molecular flow in which the thermal kinetic velocity of The temperature can be extremely low and the thermal velocity of the ions can be extremely low. As a result, it becomes possible to generate low-energy ion beams and apply to ultra-high-intensity ion beams such as focused ion beams.

〔Example〕

Hereinafter, an exemplary embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of essential parts showing the configuration of an ion source according to an embodiment of the present invention. In the figure, 1 is a discharge chamber, 2 is a cathode installed in this discharge chamber 1, 3 is an anode installed in the discharge chamber 1, and 5 is installed between the cathode 2 and the anode 3 in the discharge chamber 1. An intermediate electrode, 6 is an intermediate electrode hole that this intermediate electrode 5 has, and 22 is a first electrode located adjacent to the discharge chamber 1.
23 is a second vacuum chamber disposed adjacent to the first vacuum chamber 22, and 24 is a third vacuum chamber disposed adjacent to the second vacuum chamber 23. Further, 26 is a nozzle installed on the anode 3, and 27 is the first vacuum chamber 2.
2 and a first partition wall that partitions the second vacuum chamber 23, 28 a skimmer installed on the first partition wall 27, and 29 a skimmer that partitions the second vacuum chamber 23 and the third vacuum chamber 24. 2
The partition wall 30 is a collimator installed on this second partition wall 29.

Further, 31 is a first vacuum port for evacuation of the first vacuum chamber 22, 32 is a second vacuum port for evacuation of the second vacuum chamber 23, and 33 is the third vacuum port. 11 is a third vacuum inlet for exhausting the chamber 24; 11 is a carrier gas inlet for introducing carrier gas A between the cathode 2 and intermediate electrode 5 of the discharge chamber 1; 12 is the discharge chamber 1; D is a sample gas introduction port for introducing sample gas B between the intermediate electrode 5 and the anode 3, where the plasma generated in the discharge chamber 1 passes through the nozzle 26 and enters the first vacuum chamber. E is the supersonic free jet of plasma formed by supersonic expansion into the second vacuum chamber 23, and E is the supersonic velocity of the plasma extracted from this supersonic free jet of plasma through the skimmer 28 into the second vacuum chamber 23. It is a molecular flow.

7 is an extraction electrode installed in the third vacuum chamber 24 in close proximity to the collimator 30, 8 is an extraction electrode hole that this extraction electrode 7 has, and F is the above-mentioned supersonic molecular flow E of the plasma. An ion flow extracted into the third vacuum chamber 24 through the extraction electrode hole 8 of the extraction electrode 7 from the supersonic molecular flow of plasma introduced into the third vacuum chamber 24 through the collimator 30 It is.

Note that the intermediate electrode hole 6, the nozzle 26, the skimmer 28, the collimator 30. and the extraction electrode holes 8 are arranged in a straight line, and the supersonic free jet D of the plasma in the first vacuum chamber 22, the supersonic molecular flow E of the plasma in the second vacuum chamber 23, and the 3 vacuum chamber 2
It is on the same axis as the central axis of the ion flow F extracted into the ion stream F.

Next, the operation will be explained.

First, the first vacuum port 31, the second vacuum port 32, and the third
from the vacuum outlet 33 of the first vacuum chamber 22 and the second vacuum chamber 22, respectively.
The discharge chamber 1, the first vacuum chamber 22, the second vacuum chamber 23 and the third vacuum chamber 24 are evacuated.
The vacuum chamber 24 is brought to a predetermined degree of vacuum.

Next, carrier gas A is introduced into the discharge chamber 1 through the carrier gas inlet 11 while exhausting from the first vacuum outlet 31, second vacuum outlet 32, and third vacuum outlet 33, and the cathode 2 A DC voltage is applied between the intermediate electrode 5 and the intermediate electrode 5. Then,
The carrier gas A is ionized by glow discharge or arc discharge generated between the cathode 2 and the intermediate electrode 5, and plasma is generated. For example, argon gas is used as the carrier gas A, and the gas pressure in the discharge chamber I is 103 to 10'.
The temperature is set at about Torr and about 10'' to 104 degrees.

Then, the generated plasma of carrier gas A passes through the intermediate electrode hole 6 and flows between the intermediate electrode 5 and the anode 3.

Here, the sample gas B is introduced into the discharge chamber 1 from the sample gas inlet 12.
When introduced into the sample gas B, the sample gas B is ionized by interaction with the plasma of the carrier gas A. For example, gallium vapor or the like is used as the sample gas B.

The plasma of the sample gas B and carrier gas A thus generated in the discharge chamber 1 passes through the nozzle 26 and flows out into the first vacuum chamber 22, where it expands at supersonic speed. A supersonic free jet is formed. Here, the opening diameter of the nozzle 26 is set to, for example, about 1 mm, and the pressure within the first vacuum chamber 22 is set to about 10-3 to 10-'' Torr.

As shown in detail in Figure 2, the supersonic free jet has a region of supersonic free expanding flow called a zone of silence, a barrel-shaped shock wave surrounding this zone of silence, and a barrel-shaped shock wave surrounding this zone of silence. It is characterized by a shock wave called a Mach Disk. Note that there is a jet boundary around the barrel-shaped shock wave, and a reflected shock wave downstream of the disk toward Matsuno.
5hock) exists. In supersonic free expansion in a quiet region, as we move downstream along the central axis of the flow,
The supersonic free expansion of the gas, in other words, the adiabatic expansion of the gas, reduces the density and temperature of the plasma, that is, the density and temperature of the neutral atoms, molecules, ions, and electrons that make up the plasma. Therefore, the frequency of collisions between plasma particles decreases, the degree of ionization freezes, but the flow velocity increases. Then, downstream from the nozzle 26 by about 10 times or more the opening diameter of the nozzle 26, the gas temperature of the plasma, that is, the temperature of heavy particles such as neutral atoms and molecules and ions, becomes an extremely low temperature of several degrees or less in absolute terms. The collision frequency between them is almost infinitesimal. However, the electron temperature of the plasma does not decrease as much as the temperature of heavy particles, and remains at about 103 degrees.

In this way, in the supersonic free jet of plasma, supersonic free expansion develops sufficiently along the central axis of the flow, and the gas temperature of the plasma decreases sufficiently, allowing thermal movement of heavy particles such as neutral atoms and molecules and ions. The skimmer 28 is placed at a position where the velocity is extremely low and interactions between heavy particles can be ignored. Specifically, a skimmer 28 is installed on the first partition wall 27, and the opening of the skimmer 28 has a shape that does not cause disturbance to the upstream of the supersonic free jet, and the opening of the skimmer 28 has a diameter that is equal to the opening diameter of the nozzle 26. It should be about 2 to 3 times or less. With such a skimmer 28, a portion near the central axis in the quiet region of the supersonic free jet of plasma formed in the first vacuum chamber 22 is transferred into the second vacuum chamber 23 as a supersonic molecular flow E. Extracted. The pressure inside this second vacuum chamber 23 is 10-6 to 1
It is maintained at about 0-5T o rr.

By the way, the state of the supersonic free jet of plasma, for example, the size of the quiet region and the changes in physical quantities such as the gas density, temperature, and flow velocity of the plasma along the central axis of the flow, are as follows:
It is defined by various conditions such as the shape and opening diameter of the nozzle 26, the gas pressure in the discharge chamber 1, and the pressure in the first vacuum chamber 22. Therefore, the supersonic molecular flow E of plasma from the quiet region of the supersonic free jet of plasma formed in the first vacuum chamber 22 to the second vacuum chamber 23 through the gap 28
In order to maintain optimal extraction in response to changes in various conditions, it is preferable to provide a mechanism that allows the distance between the nozzle 26 and the skimmer 28 to be continuously varied.

Next, an example of such a mechanism for continuously varying the distance between the nozzle 26 and the skimmer 28 will be explained using FIG. As shown in the figure, in this mechanism, the discharge chamber 1 is connected to the first vacuum chamber 22 by, for example, a bellows 35, and this bellows 35
The distance between the nozzle 26 and the skimmer 28 can be changed continuously by expanding and contracting the discharge chamber 1 and moving the discharge chamber 1 in the directions of arrows α and β in the figure. Therefore,
The supersonic molecular flow E of plasma can be optimally extracted from the supersonic free jet of plasma whose state changes in response to changes in various conditions.

Furthermore, in the supersonic molecular flow E of the plasma extracted into the second vacuum chamber 23, the gas temperature of the plasma is extremely low, at a few degrees or less in absolute terms, which means that the thermal velocity of heavy particles such as neutral atoms and molecules and ions is extremely low. The supersonic molecular flow E of the plasma, which has such characteristics that the interaction between heavy particles is extremely small and can be ignored, is produced by the collimator 30 installed on the second partition wall 29.
and flows into the third vacuum chamber 24. The opening diameter of this collimator 30 is about the same or smaller than the opening diameter of the skimmer 28, and the pressure inside the third vacuum chamber 24 is 1O-Il~l.
It is maintained at about O-'T o r r. An extraction electrode 7 is installed in the third vacuum chamber 24 in close proximity to the collimator 30, and a DC voltage is applied between the collimator 30 and the extraction electrode 7 to generate an electric field. As a result, the plasma ions are accelerated in the direction of the extraction electrode 7 and extracted from the extraction electrode hole 8 as an ion stream F.

Since the ion flow F is thus extracted from the supersonic molecular flow of the plasma, the thermal velocity of the extracted ions is extremely small, and the temperature of the ion flow F is extremely low. Note that between the collimator 30 and the extraction electrode 7, plasma electrons are decelerated and move in the opposite direction to the ions, and are captured by the collimator 30. In addition, non-ionized neutral atomic molecules in the plasma do not respond to the electric field between the collimator 30 and the extraction electrode 7, and pass through the extraction electrode hole 8 together with the ion flow F as a supersonic molecular flow of neutral gas. do.

However, when Rbon gas is used as the carrier gas A and gallium vapor is used as the sample gas B as in this embodiment, the ion flow F extracted from the extraction electrode hole 8
contains argon ions and gallium ions, and as mentioned above, there is also a supersonic molecular flow of neutral gas atomic molecules, ie, neutral argon atoms and gallium atoms. Therefore, in order to separate the desired gallium ions from the ion flow F and extract the gallium ion beam, the third
In the vacuum chamber 24, it is necessary to provide means for applying a magnetic field in a direction perpendicular to the extracted ion flow F.

A case where such a magnetic field applying means is provided will be explained using FIG. 4.

Here, as shown in the figure, a DC magnetic field is applied in a direction T perpendicular to the ion flow F by a magnetic field applying means 37 using a permanent magnet or an electromagnetic coil, so that the ions undergo cyclotron movement around the lines of magnetic force of the magnetic field. performs a rotational movement called At this time, the radius of rotation of the heavier gallium ions, the so-called Larmor radius, is larger than the Larmor radius of the lighter argon ions, and the ion flow F is separated into the gallium ion flow H and the argon ion flow G, and the gallium ion flow H is taken out through the slit 38. Note that here, the neutral gas atomic molecules, that is, the neutral argon atoms and the gallium atoms do not respond to the magnetic field from the magnetic field applying means 37, and travel straight as a supersonic molecular flow I of the neutral gas.

In this example, the plasma generated in the discharge chamber was expanded at supersonic speed in a vacuum, so the gas temperature was extremely low, that is, the thermal velocity of heavy particles such as neutral atoms and molecules was extremely low. It is possible to obtain a small plasma jet with negligible interaction between heavy particles. Furthermore, since a supersonic molecular flow is generated from the plasma jet and ions are extracted from the supersonic molecular flow of the plasma, the temperature of the extracted ion flow is extremely low, and the thermal velocity of the ions is extremely low. It becomes small. Therefore,
This gas ion source can generate a low energy ion beam and can be applied to ultra-high brightness ion beams such as focused ion beams.

In addition, as shown in Fig. 3, a mechanism for continuously varying the distance between the nozzle 26 and the skimmer 28 is provided, so that the supersonic free jet of plasma whose state changes in response to changes in various conditions can be optimally adjusted. A sonic molecular flow E can be extracted.

Furthermore, in this embodiment, a means for applying a magnetic field in a direction perpendicular to the extracted ion flow F is provided in the third vacuum chamber 24, so that the ion flow F is provided with a means for applying a magnetic field in a direction perpendicular to the extracted ion flow F. Even if the PLF contains argon ions and gallium ions, and further contains a supersonic molecular flow of neutral gas atoms, that is, neutral argon atoms and gallium atoms, from the ion flow F, the target Gallium ions can be separated and a gallium ion beam can be extracted.

In the above embodiments, the plasma in the discharge chamber 1 is generated by direct current glow discharge or arc discharge. However, the plasma in the discharge chamber 1 can be generated by high frequency glow discharge or arc discharge using RF or microwaves. Alternatively, it may be generated by beam irradiation ionization discharge using an electron beam, ion beam, neutral particle beam, laser beam, or the like.

Furthermore, in the above embodiment, argon gas is used as the carrier gas A, and gallium vapor is used as the sample gas B, but the sample gas B is not limited to this. Various types of vapors and gases including atomic and molecular species can be selected,
Further, as the carrier gas A, helium, neon, nitrogen gas, etc. may be used in addition to argon gas.

Further, in the above embodiment, the case where the opening diameter of the nozzle 26 is about 1 mm has been explained, but the exhaust speed from the first vacuum suction port 31 is increased to make the opening diameter of the nozzle 26 larger than about 1 mm. The opening diameter of the skimmer 28 may be increased in accordance with the opening diameter of the nozzle 26 by increasing the exhaust speed from the second vacuum suction port 32. In that case, skimmer 28
The flux of the supersonic molecular flow E of the plasma extracted through is increased, and the evacuation speed from the third vacuum outlet 33 is further increased to increase the diameter of the collimator 30 and the extraction electrode hole 8 of the extraction electrode 7. By increasing the diameter, the flux of the extracted ion flow F increases.

〔Effect of the invention〕

As described above, according to the present invention, a discharge chamber is provided which has a generated gas jetting nozzle and is used to generate ionized gas by ionizing the atoms and molecules of the raw material gas, and the ionized gas is discharged through the jetting nozzle. a first vacuum chamber for supersonic expansion to form a supersonic free jet;
and a skimmer for extracting a supersonic molecular stream from the supersonic free jet of the ionized gas, a second vacuum chamber for introducing the supersonic molecular stream, and separating an ion stream from the molecular stream. Since the ion beam is extracted at a low temperature, a low-energy ion beam can be generated, and an extremely low temperature gas ion source can be obtained which can be applied to ultra-high-intensity ion beams such as focused ion beams.

[Brief explanation of drawings]

FIG. 1 is a sectional view of essential parts showing the configuration of an ion source according to an embodiment of the present invention, FIG. 2 is a sectional view illustrating details of a supersonic free jet generated in the ion source, and FIG. 3 4 is a sectional view showing an example of a configuration in which the distance between the nozzle and the skimmer in the ion source is continuously variable, and FIG. 4 shows a case in which the ion source is provided with means for applying a magnetic field to the ion extraction portion FIG. 5 is a partial cross-sectional view for explanation, and is a schematic cross-sectional view showing a conventional ion source. In the figure, 1 is a discharge chamber, 7 is an extraction electrode, 22 is a first vacuum chamber, 23 is a second vacuum chamber, 26 is a nozzle, and 28
is a skimmer, 35 is a continuously variable nozzle-skimmer distance mechanism, 37 is a magnetic field applying means, A is a carrier gas, B is a sample gas, D is a supersonic free jet of ionized gas, and E is a supersonic molecular flow of ionized gas. , F is the ion current. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] (1) An ion source for introducing a raw material gas to generate an ion flow of the gas, which has a generated gas jet nozzle, and a discharge for generating ionized gas by ionizing atoms and molecules of the raw material gas. a first vacuum chamber for introducing the ionized gas into the interior through the jet nozzle and expanding it at supersonic speed to form a supersonic free jet; and a first vacuum chamber for forming a supersonic free jet of the ionized gas; It has a skimmer for extracting a supersonic molecular flow, a second vacuum chamber for introducing the supersonic molecular flow, and is configured to separate and extract an ion flow from the molecular flow. ion source.