JP2007227102A - Ion source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ion source requiring no cooling to extremely low temperatures and having a simple structure, capable of obtaining an ion beam having high luminance and high efficiency of beam focusing. <P>SOLUTION: The ion source includes a vessel 4 filled with a material gas, a needle electrode 2 disposed in the vessel 4, and a minute opening 3a provided on the outer wall of the vessel 4. The inside of the vessel 4 is kept at higher pressure compared with the outside of the vessel, and the material gas is injected to the outside of the vessel 4 through the minute opening 3a from the inside of the vessel 4. The surrounding of the minute opening 3a is used as an opening electrode 3, the needle electrode 2 and the opening electrode 3 are made to have the same potential, and a strong electric field is impressed on the tip of the needle electrode by a potential difference between the needle electrode 2 as well as the opening electrode 3 and an external electrode 6 disposed in the outside of the vessel 4, to ionize the material gas by ionization of the electric field and extract the ionized ions. Thereby, an ion beam having a fixed beam emitting angle and high luminance can be obtained with a simple structure requiring no cooling to the extremely low temperature zone of the extraction electrode 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  This invention generates a small-diameter ion beam used for, for example, a surface physical analysis device, a semiconductor manufacturing inspection device, a defect repair device ion probe, ion implantation, ion beam exposure, ion beam deposition, ion beam etching, ion beam drawing, etc. The present invention relates to a high-intensity ion source.

Since the development of the liquid metal ion source, in the fields of the semiconductor industry and the like, in recent years, the application of the ion beam finely focused to submicron or less has been rapidly spreading. However, there are limitations on the types of ions that can be obtained with a liquid metal ion source. In particular, when obtaining a focused ion beam such as an inert gas such as argon or oxygen, a gas phase field ionization ion source is more suitable than a liquid metal ion source. Is suitable. This gas-phase field ion source has a strong force of about 50 to 60 V / nm on a metal needle electrode whose tip radius is sharpened to about 5 to 100 nm in a gas having a pressure of about 10 ⁻¹ Pa. The apparatus is configured to apply an electric field. As a result, gas molecules near the tip of the needle electrode are separated into ions and electrons by the field ionization phenomenon, and the separated ions are extracted as an ion beam.

The ion beam current I generated in such an ion source is proportional to the gas pressure P and temperature T as shown in the equation (1).
I∝P / T ^3/2 --------------- (1)
Usually, in an ion source, in order to minimize the disappearance of ions after ionization, the ions are caused to fly in a high vacuum container of about 10 ⁻³ to 10 ⁻⁶ . Therefore, it is impossible to increase the gas pressure P in the container. For this reason, in the prior art, the device configuration is such that the gas temperature T is lowered to about several tens of K and the ion beam current I is increased to increase the brightness of emitted ions.

  As an ion source for increasing the brightness of the emitted ions, that is, the ion beam, for example, as shown in FIG. 5 of Patent Document 1, an extraction electrode 12 having a needle-like emitter 11 and an opening 13 positioned on the axis thereof is used. Then, the source gas 14 is introduced into the ionization chamber 15 so that ions 16 are emitted from the tip of the emitter 11, and the tip of the emitter 11 is about 2 mm outward from the inner surface of the extraction electrode 12 (not shown). Dimension b) A field ionization ion source of an ion beam exposure apparatus arranged so as to protrude is disclosed. In this ion source, since the tip of the emitter 11 protrudes as described above, the gas pressure around the emitter 11 is low at the tip even if it is high at the base of the tip of the emitter 11, and the ionization chamber 15. Even if the gas pressure inside is increased, the temperature rise at the tip of the emitter 11 due to the impact of gas molecules polarized in a high electric field is reduced, the supply of ionized gas molecules is not hindered, and the brightness of emitted ions can be increased. It is stated that it is possible.

On the other hand, it is also important to increase the brightness of the ion beam and to efficiently focus the ion beam. For this purpose, it is effective to suppress the beam divergence angle at the ion beam generation stage. In order to suppress this beam divergence angle, for example, Non-Patent Document 1 describes a high-intensity ion beam using a method of forming a protrusion (superchip) on the order of several nm on a needle-like electrode on the order of several hundred nm. Has been. Non-Patent Document 2 describes that the ion beam current increases as the radius of the needle-like electrode serving as a base for forming the protrusion increases.
JP-A-64-63247 S. Kalbitzer: Nuclear Instruments and Methods in Physics Research B 158 (1999), p. 53 R. Borret et al: Applied Physics 23 (1990), P. 1271

  In the apparatus configuration in which the gas temperature T is lowered to about several tens of K in order to increase the ion beam current I and the luminance of emitted ions is increased, liquid helium, liquid nitrogen, etc. are usually used to lower the temperature. Or a refrigerator using a compressor or the like. However, in any case, not only an increase in size and complexity of the apparatus is unavoidable, but also the refrigerant replenishment is complicated when the refrigerant is used, and the focused beam system is used when the refrigerator is used. Has a fatal vibration problem.

  In the ion source disclosed in Patent Document 1, the emitter 11 is still cooled to a low temperature range of about 10 to 20 K by a cooler disposed in the ionization chamber 15, and the ion beam is focused efficiently. There is nothing listed about what to do. Further, in the method of increasing the brightness by forming the protrusion (super chip) described in Non-Patent Documents 1 and 2, a high temperature of 1000 K or more is required to generate the protrusion, and the formation of the protrusion (super chip) is large. In addition, not only a simple apparatus is required, but also, in principle, the projections cannot be formed at an arbitrary place, so that the throughput of the needle-shaped electrode, that is, the productivity is unsatisfactory.

  Therefore, an object of the present invention is to provide an ion source that does not require cryogenic cooling, has a simple device structure, has high brightness, has a small beam divergence angle, and has high beam focusing efficiency. is there.

  In order to solve the above problems, the present invention employs the following configuration.

  The ion source according to claim 1 includes a container filled with a source gas, a needle-like electrode disposed in the container, and a minute opening provided in an outer wall of the container, The pressure is higher than the outside of the container, and the raw material gas is injected from the inside of the container to the outside of the container through the minute hole, and the periphery of the minute hole is an opening portion electrode, Applying a strong electric field to the tip of the needle electrode due to a potential difference between the needle electrode and the hole electrode and the external electrode arranged outside the container An ion source characterized in that the source gas is ionized by field ionization and the ions are extracted.

  The ion source according to claim 2 is an ion source in which a tip of the needle electrode protrudes from an outer surface of the aperture electrode.

  An ion source according to a third aspect is an ion source formed in a tapered shape that tapers in an ion extraction direction.

  The ion source according to claim 4 is an ion source in which the container is installed in a vacuum chamber and the outside of the container is a vacuum region.

  In this invention, an external electrode is disposed outside the container filled with the source gas, and the needle electrode and the aperture electrode around the micro-opening provided in the container are set to the same potential, and the needle electrode and the open electrode are opened. The source gas is ionized by applying a strong electric field to the tip of the needle electrode due to a potential difference between the hole electrode and the external electrode, and the ionized source gas is ejected from the minute aperture. Therefore, a sudden pressure gradient is generated on the exit side of the minute aperture. This rapid pressure gradient makes it possible to suppress the probability that the generated ions collide with the atmospheric gas, that is, the probability of ion annihilation, while ionizing the source gas extremely efficiently. As a result, it is possible to obtain an ion source capable of efficiently performing ionization with a simple structure, such as eliminating the need for cooling the needle-like electrode to a cryogenic temperature range.

  In addition, since the tip of the needle electrode protrudes from the outer surface of the aperture electrode, it is possible to apply a very strong local electric field to the tip of the needle electrode, and the beam divergence angle is reduced. A small and constant high-intensity ion beam can be obtained efficiently.

  Embodiments of the present invention will be described below with reference to the accompanying FIGS.

FIG. 1 shows an ion source 1 for generating a minute-diameter ion beam according to an embodiment. This ion source 1 is usually installed in a high vacuum chamber (not shown) of about 10 ⁻³ Pa or less in order to minimize ion annihilation after ionization, and the diameter of the tip 2 b of the tapered portion 2 a is about 100 nm. In the following, a stainless steel or conductive silicon aperture electrode having a needle-like electrode 2 made of axisymmetric tungsten or indium and a micro-aperture 3a whose center coincides with the axis of the needle-like electrode 2 3 is provided. The aperture electrode 3 may be configured by forming a part of the outer wall of the container 4 into which an inert gas such as argon or a source gas such as oxygen is introduced and filled with these source gases. As described above, the opening electrode 3 can also form the container 4. The pressure in the container 4 is set to 1000 Pa to 1 MPa, the inside of the container 4 is set to a pressure higher than that in the vacuum region outside the container 4, and the raw material gas is injected from the inside of the container to the outside of the container through the minute holes. The needle-like electrode 2 is arranged such that the tip 2b protrudes from the minute hole 3a, and the protruding amount a is usually about 2 mm or less. Further, as shown in FIG. 2, the minute opening 3a has a thickness c of about 0.5 mm and is formed in a tapered shape that tapers in the ion extraction direction, and is ionized. However, a more rapid pressure gradient is generated on the outlet side of the container 4 by the throttling effect at the tip of the minute opening 3a. The diameter d1 on the small diameter side of the tapered fine opening 3a is usually 100 μm or less, and in this embodiment is 50 μm. The taper angle θ of the fine opening 3a is about 30 ° to 80 °. In this embodiment, it is about 54.7 °. An external electrode 6 having an ion beam 5 passage 6a is arranged in the ion extraction direction outside the container 4 so that the center of the ion beam passage 6a coincides with the center of the minute aperture 3a. ing. The needle electrode 2 and the aperture electrode 3 are set to the same potential, and the external electrode 6 is applied with a wide positive potential of about 10 V to 30 KV with respect to the needle electrode 2 and the aperture electrode 3. It has become. Due to the positive potential (potential difference) between the needle electrode 2 and the aperture electrode 3 and the external electrode 6, a strong electric field is formed around the tip of the needle electrode 2. Then, the raw material gas injected from the container 4 through the minute opening 3a is ionized and extracted, and the ion beam 5 is formed. In addition, a strong electric field concentrates on the tip 2b of the protruding needle electrode 2 so that the divergence angle of the ion beam 5 can be reduced, and the ion beam 5 is efficiently focused.

  FIG. 3 schematically shows a pressure gradient around the minute aperture 3a, and i1 to i3 indicate isobaric lines. As described above, the needle electrode 2 has the same potential as the aperture electrode 3 having the minute aperture 3a with respect to the external electrode 6, and the tip 2b of the needle electrode 2 is the aperture electrode 3, that is, By adopting a device configuration that protrudes from the outer surface of the minute aperture 3a, a strong electric field is concentrated on the tip 2b of the needle electrode 2 and the divergence angle of the ionized beam is reduced. Further, by ejecting the raw material gas from the minute opening 3a, a sudden pressure gradient region 7 (region from the vicinity of the minute opening 3a to the vicinity of the isobaric line i3 in the figure) is generated on the exit side of the minute opening 3a. To do. The source gas is ionized by field ionization at the periphery of the needle-like electrode 2b inside the isobaric line i1, that is, the portion of the high gas pressure where the source gas is present. In the region extending from the isobaric lines i2 to i3, a high vacuum region in which the extracted ions have a low probability of colliding with the atmospheric gas, that is, the ion annihilation probability is low. The high vacuum region 8 is a high vacuum region sufficient to suppress the probability that generated ions collide with the atmospheric gas, that is, the probability of ion annihilation. In this way, since the ion annihilation probability can be kept low and a large amount of ion beam current can be generated, it is not necessary to cool the needle-like electrode 2 to the cryogenic temperature range, and the divergence angle is further improved with a simple structure. It is possible to obtain a high-intensity ion beam that is small and constant and can perform beam focusing efficiently. The electric field strength can be adjusted by adjusting the protruding amount a of the needle electrode 2 and the positive potential (voltage) of the needle electrode 2 and the aperture electrode 3 with respect to the external electrode 6. Further, the size of the minute opening 3a and the protruding amount a of the needle-like electrode 2 can be appropriately set depending on the pressure inside the container 4, the pressure outside the container 4, and the like. The external electrode 6 is preferably an integrated electrode having a beam passage portion 6a, but may be a non-integral structure electrode having a beam passage portion. The aperture electrode 3 may be provided around the minute aperture 3a as a separate body from the vessel 4 instead of constituting a part of the outer wall of the vessel 4.

It is explanatory drawing which shows the ion source of embodiment of this invention. It is explanatory drawing which shows the principal part of the ion source of FIG. It is explanatory drawing which shows typically the pressure gradient around the micro opening of the opening part electrode of the ion source of FIG. It is explanatory drawing which shows the ion source of a prior art.

Explanation of symbols

1: ion source 2: needle-like electrode 2a: tapered portion 2b: tip 3: aperture electrode 3a: minute aperture 4: container 5: ion beam 6: external electrode 6a: ion beam passage 7: pressure gradient region 8 : High vacuum region i1 to i3: Isobaric lines

Claims (4)

A container filled with source gas, a needle-like electrode disposed in the container, and a minute opening provided in the outer wall of the container, the interior of the container is at a higher pressure than the outside of the container, The source gas is configured to be jetted from the inside of the container to the outside of the container through the minute opening,
The periphery of the minute aperture is an aperture electrode, the needle electrode and the aperture electrode are at the same potential, the needle electrode and the aperture electrode, and an external electrode disposed outside the container; An ion source characterized in that a strong electric field is applied to the tip of the needle-like electrode by the potential difference to ionize the source gas by field ionization and extract the ions.   The ion source according to claim 1, wherein a tip of the needle electrode protrudes from an outer surface of the aperture electrode.   The ion source according to claim 1, wherein the minute aperture is formed in a tapered shape that tapers in a direction in which ions are extracted.   The ion source according to claim 1, wherein the container is installed in a vacuum chamber, and the outside of the container is a vacuum region.

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