JP2752626B2 - Field ionization gas ionization method and its ion source - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a field ionization gas ionization method and apparatus for forming a focused ion beam for use in microfabrication, and to forming a focused ion beam with a large current. Can be.

(Conventional technology) Focused ion beam technology formed using an ion source and an ion optical system is easy to perform pattern formation because of its fine workability, processing in a clean atmosphere, and electrical deflection of the beam. For this reason, it is attracting attention as one of the future fine processing technologies. 0.01 as an ion source for this purpose
As an ion source capable of forming a focused ion beam having a diameter of μm, there is an electric field ionization gas ion source having high luminance.

The field ionization gas ion source supplies a gas to be ionized around a sharply pointed conductive needle electrode (mainly metal), applies a high electric field of about 10 V / nm to the tip of the needle electrode, and generates a gas near the tip. It is to ionize molecules by electric field. According to this principle, elements that cannot be ionized by a liquid metal ion source, such as H, He, and Ar, can be ionized. In this ion source, in order to obtain a large ion current, the needle electrode and the gas to be supplied are cooled to extremely low temperature, the density of gas molecules at the tip of the needle electrode is increased, and the supply amount is increased. The kinetic energy is lowered, the residence time of gas molecules in the ionization region at about 0.4 nm in front of the needle tip is extended, the ionization efficiency is increased, and the ion current is increased. Normally, this ion source has a total emission ion current of 100 nA or less. Further, since the ionization region of this ion source is as narrow as 0.02 nm, the kinetic energies of gas molecules are uniform, and the energy width of emitted ions is as narrow as about 1 eV, which is advantageous for forming a focused ion beam.

(Problems to be Solved by the Invention) However, in this method, since the ionized substance is supplied in a gaseous state, there is a limit to an increase in the density of gas molecules even when cooled to a very low temperature, and the supply amount is not sufficient. Absent. Therefore, the total emission ion current is small and not practical.

An object of the present invention is to increase the ion current of a field ionized gas ion source that emits a high-intensity ion beam necessary to form a focused ion beam having a diameter of the order of 0.01 μm, and to increase the ion current for practical use for fine processing technology. It is to provide an ion source.

(Means for Solving the Problem) According to the field ionization gas ionization method of the first invention, a gas field is applied to a needle-shaped metal electrode in which a high electric field is applied and the electrode is set at a temperature at which the gas inserted into the chamber does not liquefy. Or, by supplying atoms, in the field ionization gas ionization method in which gas molecules or atoms are field-ionized, surface diffusion energy is given to the gas molecules or atoms adsorbed on the needle-shaped metal electrode, and the gas molecules or atoms are surface-diffused. The gas is supplied to the tip of the needle-shaped metal electrode to ionize gas molecules or atoms diffused or adsorbed on the surface at the tip of the needle-shaped metal electrode.

A field ionization gas ion source according to a second aspect of the present invention includes a needle-shaped metal electrode having an electrode set at a temperature at which a gas inserted into a chamber is not liquefied, means for applying an electric field to the electrode, and gas molecules or atoms around the electrode. In an electric field ionization gas source composed of a device for supplying and the electrode and a means for cooling gas molecules or atoms, a light source for irradiating light to diffuse the surface of the gas molecules or atoms adsorbed on the surface of the electrode is provided. It is characterized by having been provided.

A field ionization gas ion source according to a third aspect of the present invention comprises a needle-shaped metal electrode having an electrode set at a temperature at which a gas inserted into a chamber is not liquefied, means for applying an electric field to the electrode, and gas molecules or atoms around the electrode. An electron gun for irradiating electrons to diffuse the surface of gas molecules or atoms adsorbed on the surface of an electrode in an electric field ionization gas source composed of a device for supplying a gas and the electrode and a means for cooling gas molecules or atoms. Is provided.

(Operation) In the present invention, in addition to the cooling mechanism normally provided in the field ionization gas ion source, energy necessary for surface diffusion of the adsorbed gas molecules (atoms) on the needle surface is supplied to the surface adsorbed molecules (atoms). . The adsorption energy is typically 0.2 eV or less for physical adsorption, and 0.4 to 1.
It is about 2 eV. This is about 10 to 1 μm in terms of light wavelength, and surface diffusion can be controlled by selecting and irradiating an appropriate value in this wavelength region. The surface adsorbed molecules (atoms) are subjected to a high electric field (10
⁸ V / cm) and receive the force toward the needle tip.
The adsorbed molecule (atomic) layer becomes equivalent to the atomic spacing of the solid when adsorbed by one atomic layer, has a higher density than gas, and can supply more molecules (atoms) by diffusion of the adsorbed molecules (atoms). Further, in the supply by diffusion, gas molecules adsorbed on a wide area are directed to the needle tip which is an ionization region, so that more gas molecules (atoms) can be supplied. The adsorbed molecules (atoms) supplied to the tip of the needle desorb from the needle and reach the ionization region about 0.4 nm in front of the needle tip. Does not spread. After that, it is ionized in the ionization region, is attracted by a high electric field, and is emitted.
Thereby, 1 μm, which is higher than that of the conventional field ionized gas ion source, is obtained.
An ion beam having a current of A or more can be emitted. This ion beam has the same brightness (10 ⁸ A / cm ² · sr) and low energy width (about
1eV), and it is possible to form a focused ion beam having a diameter of 0.01 μm or less by an ion optical system. As described above, a focused ion beam for ultra-fine processing, which cannot be formed by the liquid metal ion source, is obtained, and the current amount is large, so that a practical focused ion beam can be used.

(Embodiment) (Embodiment 1) An embodiment of a field ionization gas ionization method provided with a surface diffusion-enhancing energy supply device according to the first invention will be described. He is used as the ionized gas for electric field ionization. In the field ionization gas ion source, a supply device of He gas, a tungsten needle whose tip radius is about 50 to 200 nm for ionization, an extraction electrode to give an electric field required for ionization, and a cooling mechanism of He and tungsten needle It has. Further, the present invention is provided with a surface diffusion-enhancing energy supply device for diffusing the adsorbed gas molecules onto the surface, which is a feature of the present invention. The cooling mechanism is usually provided to increase the ionization efficiency, cools the conductive needle and the gas to be ionized, and lowers the kinetic energy of gas molecules (atoms).
As a result, the width of 0.02 nm at about 0.4 nm from the tip of the needle
Therefore, the time spent in the ionization region becomes longer, and the ionization efficiency is increased. In the present invention, the cooling mechanism also serves to cool He and the needle-shaped electrode, and to adsorb He on the surface of the conductive needle. The cooled gas is maintained at 10 ^-5 to 10 ^-3 Torr released between the conductive needle and the extraction electrode. When He is used as the ionized gas, the cooling temperature is 4.2 K, which is the boiling point of He.
Up to. He is the gas with the lowest boiling point, but when cooled to 4.2K, the gas readily adsorbs on conductive surfaces. In the present invention, the adsorbed gas is supplied by surface diffusion to the tip of the conductive needle which is an ionization region. In order to introduce a large amount of the adsorbed gas molecules (atoms) to the tip of the needle electrode by surface diffusion, light or electrons are irradiated to give surface diffusion energy and increase the surface diffusion speed. This increases the supply of gas molecules (atoms) to the tip of the needle. The gas molecules (atoms) supplied to the tip of the needle are desorbed and ionized near the tip. Since gas molecules (atoms) supplied to the tip of the needle by surface diffusion are sufficiently cooled and have low energy, the density of gas at the tip of the needle is increased, the ionization efficiency is increased, and a large current ion beam is obtained.

Light is used as a surface diffusion energy-enhancing device.
The activation energy of He diffusion to the tungsten surface is about 0.17 eV. The activation energy for desorption is 0.
It is about 39 eV. Therefore, the energy of the irradiated light is 0.17
Light having a wavelength of about 0.39 eV, that is, about 10 to 5 μm is used. On the other hand, at the tip of the needle electrode, 10 V / nm
A high electric field is applied, and the adsorbed He atoms are polarized and are attracted toward the needle tip. When irradiated with light, He, which has been strongly adsorbed by cooling, absorbs energy and accelerates the diffusion speed, and diffuses toward the tip of the needle due to the attractive force of the high electric field. As a result, He diffuses to the tip of the needle, then desorbs and immediately ionizes into the ionization region. Since He to be ionized is sufficiently cooled and has a low movement speed, most of He in the ionization region is ionized and the efficiency is high.
After that, it is accelerated and released by the high electric field. The ion beam obtained in this way is ionized by electric field ionization, so it has high brightness and a small energy width like a normal field ionized gas ion source. Has favorable properties.

Gases that can be ionized include reactive substances, and all elements are possible. In the case of a reactive gas, in order to adsorb the gas itself on the surface of the needle, it is necessary that the material does not react with the gas or is difficult to react with the gas.

In this way, high current, high brightness and low energy width ions of all gaseous species can be obtained. By combining with the optical system shown in FIG. 3, it is possible to form a focused ion beam of less than 0.01 μm diameter at several μA. Can be. Thereby, maskless ultrafine processing on the order of 0.01 μm using an extremely fine focused ion beam can be performed.

(Example 2) Regarding the second invention, an electric field ionization gas ion device provided with an optical surface diffusion acceleration energy supply device will be described. FIG. 1 is a schematic view of the field ionization gas ion source of the present invention.
The field ionization gas ion source consists of an ionized gas supply device, a conductive needle with a small tip radius (50 to 200 nm) for ionization, an extraction electrode for applying an electric field required for ionization, and a needle and a cooling mechanism for the ionized gas. Become. According to the present invention, a surface diffusion-enhancing energy supply device using light to diffuse the adsorbed gas molecules on the surface is provided. The conductive needle is usually polished with an electric field so that the tip radius is about 0.1 μm. For this reason, tungsten, which is easy to polish and is durable, is often used as a needle material. The cooling mechanism is usually provided to increase the ionization efficiency, cools the conductive needle and the gas to be ionized, and lowers the kinetic energy of gas molecules (atoms). In the present invention, the cooling also serves to adsorb gas molecules to the needle surface. The cooled gas is released between the conductive needle and the extraction electrode, usually 10
^-5 to 10 ^-3 Torr. The cooling temperature is 4.2K or more, which is the boiling point of He, from the performance of the cooler and the ease of handling. He, X
Gases such as e and H are often used in the field ionization gas ion source.

As shown in FIG. 1, light is used as a surface diffusion-enhancing energy supply device. As the wavelength, an energy causing appropriate diffusion is selected in consideration of the adsorption energy, surface diffusion energy and absorption wavelength of each gas. Although a part of the needle may be irradiated, it is conceivable to adopt a configuration using a light-collecting reflector as shown in FIG. 1 to irradiate the entire surface of the needle in order to increase the efficiency. It is useful to use, as a light source, a mercury lamp having a wide wavelength range, a high-intensity laser, particularly a dye laser capable of changing the wavelength.

(Embodiment 3) An electric field ionization gas ion apparatus provided with an electron surface diffusion acceleration energy supply apparatus according to the third invention will be described.
FIG. 2 is a schematic view of the field ionization gas ion source of the present invention. The field ionization gas ion source is an ionized gas supply device,
Small tip radius for ionization (50-200nm)
It comprises a conductive needle, an extraction electrode for applying an electric field necessary for ionization, and a needle and a cooling mechanism for ionized gas for increasing ionization efficiency in an ionization region near the needle tip. In the present invention, gas molecules (atoms) are added to the surface of the conductive needle.
For the purpose of adsorbing the gas molecules, and an electron surface diffusion-enhancing energy supply device for cooling and diffusing the adsorbed gas molecules to the surface. Conductive needles usually have a tip radius of 0.1μ
The electric field is polished in order to make it about m. The cooled gas is released between the conductive needle and the extraction electrode, usually 10 ^-5 to 10 ^-3 To
kept at rr. As shown in FIG. 2, electrons are used as a surface diffusion energy-enhancing device. An electron gun for generating electrons includes an electron gun main body in a vacuum container and a power supply placed outside the container. As the electron gun, a general one such as a tungsten filament can be used. By adjusting the acceleration energy of the electron beam and the current density (current amount), optimal irradiation conditions can be selected for the combination of the ionized gas and the needle material so that the adsorbed gas molecules (atoms) can be sufficiently diffused.

FIG. 3 shows an example of an ion optical system for forming a focused ion beam using the electric field ionization gas source. In this example, a two-stage electrostatic lens is provided for focusing. In addition, 2 emitted from a field ionization gas ion source using a compound gas is used.
An ExB mass spectrometer is provided to select only necessary ions from ions of more than one kind. Thereby, ultrafine processing of semiconductors and other substances can be easily performed by the focused ion beam.

(Effects of the Invention) As described above, the present invention is a method and an apparatus capable of ionizing various gases and obtaining an ion beam with high current, high brightness, and low energy width. This ion beam can be used to form a focused ion beam with a practical ultra-fine diameter (0.01 μm or less). Maskless etching of semiconductors and other materials, maskless ion implantation, maskless ion beam modification, etc. This has the effect that it can be performed in a clean atmosphere without contamination of the material.

[Brief description of the drawings]

FIG. 1 is a schematic view of an electric field ionization gas ion source equipped with an optical surface diffusion acceleration energy supply device according to the present invention, and FIG. 2 is an electric field ionization gas ion source equipped with an electron beam surface diffusion acceleration energy supply device. FIG. 3 schematically shows a focused ion beam apparatus using an electric field ionization gas ion source. DESCRIPTION OF SYMBOLS 1 ... Surface diffusion acceleration energy supply device (light source) 2 ... Light beam 3 ... Conductive needle 4 ... Extraction electrode 5 ... Cooling device 6 ... Ionized gas supply device 9 ... Reflector 16 ... Surface diffusion Accelerated energy supply device (electrons) 18 Electron beam 19 Ex-B mass spectrometer 20 Objective lens 21 Sample to be processed

Claims (3)

(57) [Claims] 1. A high electric field is applied to supply gas molecules or atoms to a needle-shaped metal electrode whose electrodes are set to a temperature at which the gas inserted into the chamber is not liquefied, thereby causing the gas molecules or atoms to be field-ionized. In the field ionization gas ionization method, surface diffusion energy is given to gas molecules or atoms adsorbed on the needle-shaped metal electrode, and the gas molecules or atoms are surface-diffused and supplied to the needle-shaped metal electrode tip, and the needle-shaped metal A field ionization gas ionization method, comprising ionizing gas molecules or atoms that have been surface-diffused or adsorbed at an electrode tip. 2. A needle-shaped metal electrode having an electrode set at a temperature at which a gas inserted into a chamber does not liquefy, means for applying an electric field to said electrode, a device for supplying gas molecules or atoms around said electrode, and said electrode And a means for cooling gas molecules or atoms, wherein a light source for irradiating light to diffuse the surface of the gas molecules or atoms adsorbed on the surface of the electrode is provided. Field ionization gas ion source. 3. A needle-shaped metal electrode having an electrode set at a temperature at which a gas inserted into a chamber does not liquefy, means for applying an electric field to the electrode, a device for supplying gas molecules or atoms around the electrode, and the electrode And an electron gun for irradiating electrons to diffuse the surface of the gas molecules or atoms adsorbed on the surface of the electrode, in an electric field ionization gas source constituted by and a means for cooling gas molecules or atoms. Field ionizing gas ion source.