JP2964284B2 - Field emission type electron gun stabilization method and field emission type electron gun - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stabilizing a radiation current of a field emission type electron gun used for an electron microscope, an electron beam exposure apparatus, an electron beam inspection apparatus, and the like, and an implementation of the method.
The present invention relates to a field emission type electron gun used directly . In particular, the present application
3, 4 and 5 in the specification. The method of stabilizing the emission current of a field emission type electron gun comprising a small cold cathode and the electric field directly used for implementing the method It relates to a radiation type electron gun.

[0002]

2. Description of the Related Art Electron guns for generating electrons are roughly classified into a hot cathode type and a field emission type. The former uses thermoelectrons emitted from a heated cathode, and does not require a high accelerating electric field on the cathode surface, so a space charge is formed near the cathode surface, and a negative feedback action occurs between the current and the electric field. It is established and the emission current is stabilized. Since the latter has a small electron emission area and a small current spread, high brightness can be obtained.Therefore, it is possible to reduce the charge on the sample by lowering the acceleration voltage and use a high-resolution electron microscope. Has begun to be put into practical use. By the way, as one mode of the field emission type electron gun , the configuration is described in FIGS. 3, 4, and 5 of the present specification.
A field emission type electron gun including a small cold cathode as a component has been developed. This is 3, 4 or 5
As can be seen, it is manufactured using semiconductor device manufacturing technology.

However, unlike the hot cathode type, the field emission type electron gun does not form a high-density space charge, has a slight change in work function due to adatoms or molecules on the cathode surface, and has been ionized near the cathode. There is a disadvantage that the emission current becomes unstable due to a change in the surface shape of the cathode due to the impact of ions on the cathode. Therefore, a general field emission electron gun uses a high vacuum (10 ⁻⁹ to 10 ⁻¹⁰⁾ to reduce ion bombardment.
⁻¹⁰ Torr) , and a cleaning process called flushing is performed to release adsorbed atoms and molecules from the cathode surface.

[0004] The flushing is performed by heating the surface of the cathode for a period of several seconds to several minutes by conducting electricity or the like.
In addition, the cathode of the field emission type electron gun is always 1000K to 20K.
An electron gun called a thermal field emission electron gun that maintains the temperature of 00K is known, but in the case of this electron gun, a stable current is obtained.

[0005]

The object of the invention is to be Solved by the above-mentioned minute cold cathode structure
In an electron beam inspection apparatus or the like comprising a plurality of micro electron guns and micro electron optics arranged at minute intervals of about 100 μm, such as a field emission electron gun as a component, all the constituent materials have heat resistance. It is difficult to request,
In addition, since the inspection is performed close to the sample to be inspected (about 1 mm), the temperature of the sample itself increases. Therefore,
Using forced to field emission electron gun of the room temperature as the electron gun, cold field emission type electron gun, in particular micro cold cathode
In the case of the field emission type electron gun as a component, there is a problem that the emission current is unstable as described above.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate this drawback and to provide a method for stabilizing the emission current of a field emission type electron gun at room temperature and a field emission type electron gun used for implementing the method. Is to do. In particular, it is an object of the present invention to provide a method for stabilizing the emission current of a field emission type electron gun composed of micro cold cathodes and a field emission type electron gun used directly for implementing the method.

[0007]

SUMMARY OF THE INVENTION Among the above objects, a method for stabilizing a field emission type electron gun is achieved by the following means.

[0008] That is, a reactive radiation is applied to a field emission type electron gun.
Gas that generates calcium is sealed, and ultraviolet light and laser light
Irradiation of electromagnetic waves such as to generate reactive radicals,
Desorb atoms or molecules adsorbed on the pole surface
Stabilization method of field emission type electron gun which stabilizes radiation current
is there.

Among the above objects, the field emission type electron gun is
This can be achieved by any of the following means.

The first means is an electric field emission device having a micro cold cathode.
In the period when the electron emission operation is stopped in the firing electron gun
A cathode of a field emission electron gun having the micro cold cathode in between
In order to clean, the surface of the cathode constituting the field emission electron gun having the micro-cold cathode, atoms or molecules that are externally adsorbed on the surface of the cathode by irradiating ultraviolet light or laser light This is a field emission type electron gun composed of micro cold cathodes movably mounted with light irradiating means used to remove the electron beam.

The second means is an electromagnetic wave irradiating means having a function of irradiating the surface of the cathode of the field emission type electron gun with electromagnetic waves such as ultraviolet light and laser light, and a reactive means for supplying a gas generating reactive radicals. This is a field emission type electron gun having gas supply means for generating radicals.

[0012]

FIG. 6 shows the relationship between the energy at which atoms and molecules are bonded on the material surface and the distance from the material surface. In the figure, the state indicated by A is called chemisorption,
The state indicated by B is called physical adsorption. The atoms and molecules adsorbed on the cathode surface are
The activation energy indicated by Q ₁ and Q ₂ can be released from the surface.

In the case of a thermal field emission type electron gun and in the case where the field emission type electron gun is heated and flashed, this activation energy is given by thermal energy, and
A temperature between 0K and 2000K corresponds to an activation energy between 0.1 and 0.2 eV.

On the other hand, X-rays and ultraviolet light are several nm to several hundred nanometers.
It has a wavelength of m and corresponds to an activation energy of several KeV to several tens eV. Therefore, irradiation with X-rays or ultraviolet light can provide a high activation energy higher than the heat energy, and can desorb atoms and molecules adsorbed on the surface (see FIG. 7). However, it is necessary to irradiate a sufficient number of photons in consideration of the probability of collision between the photons and the adsorbed atoms or molecules.

Normally, a negative potential is applied to an electron gun, but a positive potential is applied to the electron gun, and several eV to
Irradiating electrons accelerated to several tens of eV can also give activation energy for desorption to an adsorbed atom or molecule, thereby desorbing an atom or molecule adsorbed on the surface (see FIG. 8). . Also, oxygen gas,
Hydrogen gas, chlorine gas, etc. are sealed and irradiated with ultraviolet light, etc., to generate reactive radicals with strong chemical reactivity near the cathode surface, which are chemically bonded or chemically reacted with adsorbed atoms and molecules to be adsorbed. Atoms and molecules can be separated and removed from the cathode surface (see FIG. 9).

[0016]

EXAMPLES Hereinafter, with reference to the drawings, ginseng with embodiments of the present invention
The method of stabilizing the field emission type electron gun and the field emission type electron gun according to the present invention will be described.

First Example FIG. 1 is a sectional view of a field emission type electron gun having an electromagnetic wave irradiation means for irradiating a cathode with an electromagnetic wave such as ultraviolet light. In the figure, 1 is a lens barrel, 2 is a field emission type electron gun composed of a cathode 3 and an electron extraction electrode 4, and a voltage is applied between the cathode 3 and the electron extraction electrode 4. Reference numeral 5 denotes an electromagnetic wave irradiating unit that irradiates the cathode 3 with an electromagnetic wave such as ultraviolet light. The electromagnetic wave irradiating means 5 can be moved left and right in the figure, and at the time of irradiation, the electromagnetic wave guided by the optical fiber 6 is provided at the distal end by being inserted into the lens barrel 1 so that the distal end is on the optical axis of the electron gun 2. The light is irradiated toward the cathode 3 through the mirror 7 and the atoms or molecules adsorbed on the surface of the cathode 3 are separated and removed.

First Reference Example FIG. 2 is a sectional view of a field emission type electron gun having a means for irradiating a particle beam such as an electron beam. In the figure, the same elements as those shown in FIG. 1 are indicated by the same symbols, and 8 is a particle beam irradiation means comprising a ring-shaped hot cathode for generating an electron beam. By setting the cathode 3 of the electron gun 2 to a positive potential and irradiating the cathode 3 with electrons generated by the hot cathode 8, the atoms or molecules adsorbed on the surface of the cathode 3 are desorbed.
Removed.

SECOND REFERENCE EXAMPLE An electron beam inspection apparatus in which a large number of minute electron guns and minute electron optical systems are formed at a pitch of about 100 μm in a chip, as in the case where a field emission type electron gun is a minute cold cathode. The case where the present invention is applied will be described.

FIG. 3 is a plan view of the electron beam inspection apparatus. In the figure, reference numeral 11 denotes an electron beam generating unit (array) which includes a plurality of minute multi-electron beam columns (see FIGS. 4 and 5).
It has become a micro electron gun barrel) 12 having a cross section shown, each of the micro multi-electron beam column 12 10
A large number of microelectron guns and microelectron optical systems (stacks surrounding each microelectron gun) 18 are formed at a pitch of about 0 μm. 13 is a sample to be inspected, and 10 is a chip in the inspection area. Reference numeral 14 denotes an ultraviolet light irradiation means, which is fixed on the stage 15, and guides the ultraviolet light through an optical fiber 16. The stage 15 is moved to move the ultraviolet light irradiating means 14 below the chip 12, and the ultraviolet light is irradiated from the lower surface of the chip 12 so that the atoms or the atoms adsorbed on the cathode of the micro electron gun formed on the chip 12 Detach and remove molecules.

FIG. 4 is a diagram supplementing the first example, and is a cross-sectional view showing a state in which the ultraviolet light irradiation means 14 has been moved directly below the chip 12 of the electron beam generator (array) 11. In the figure, reference numeral 17 denotes a micro electron gun (micro cold cathode) , and 18 denotes a micro electron optical system (electrode layer and insulating layer surrounding each micro electron gun).
Generated electron beam
Electron beam consisting of an electron lens and deflection element that converge and deflect light
An academic system), both formed on the same substrate. 1
9 is an optical lens provided in the ultraviolet light irradiation means 14, the micro electron guns are provided corresponding to the (micro cold cathode) 17, the slits 2 of downward through the optical lens 19
Ultraviolet light guided from 0 is used for micro electron gun (micro cold cathode) 17
Irradiation.

FIG. 5 is a view supplementing the second reference example, and shows a cross-sectional view of a micro electron gun having electron beam irradiation means. In the figure, 21 is a minute cold cathode, 22 is an electron drawer
A use electrode (anode), 23 is a cathode ring-shaped cleaning. The minute cold cathode 21 is set to a positive potential, and the cleaning cathode 2
By irradiating the cathode 21 with the electrons emitted from 3, the atoms or molecules adsorbed on the surface of the cathode 21 are separated and removed.

Second Example If a gas nozzle is provided in the vicinity of an electron gun, oxygen gas, hydrogen gas, chlorine gas or the like is enclosed in a lens barrel and irradiated with electromagnetic waves such as ultraviolet light, reactive radicals are generated and adsorbed. The atoms or molecules react with the reactive radicals and are easily separated and removed. If the temperature of the electron gun and the electron optical system is within the range of heat resistance and the temperature of the sample under test is allowed to rise, the heating of the electron gun is also used to release the adsorbed atoms or molecules. It is possible to promote.

[00024]

As described above, the method for stabilizing the field emission type electron gun and the field emission type electron gun according to the present invention, and in particular, the method for stabilizing the radiation current of the field emission type electron gun comprising a small cold cathode and the electric field In a radiation type electron gun, a light beam is applied to a cathode to give activation energy to atoms or molecules adsorbed externally on the cathode surface, or a gas in which reactive radicals are easily generated. Enclose
Irradiating this with electromagnetic waves such as ultraviolet light to generate reactive radicals and reacting with the atoms or molecules adsorbed on the cathode surface, these atoms or molecules are desorbed from the cathode surface. Since it is necessary to remove the atoms or molecules, it is difficult to heat the atoms or molecules or to keep them at a high temperature. It is possible to stabilize. And, the present invention relates to a micro cold cathode.
Method for stabilizing radiation current of electric field emission type electron gun and electric field
It is particularly useful in a radiation type electron gun.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a field emission type electron gun having an electromagnetic wave irradiation unit.

FIG. 2 is a configuration diagram of a field emission type electron gun having particle beam irradiation means.

FIG. 3 is a configuration diagram of an electron beam inspection apparatus.

FIG. 4 is a sectional view showing a state in which a micro electron gun of the electron beam inspection apparatus is irradiated with ultraviolet light.

FIG. 5 is a cross-sectional view showing a state in which a micro electron gun of the electron beam inspection apparatus is irradiated with an electron beam.

FIG. 6 is a graph showing a relationship between a potential energy at which atoms and molecules are bonded on a material surface and a distance from the surface.

FIG. 7 is an explanatory view of desorbing an adsorbed atom or molecule by irradiation with ultraviolet light.

FIG. 8 is an explanatory view of desorbing an adsorbed atom or molecule by electron beam irradiation.

FIG. 9 is an explanatory diagram of sealing a gas generating a reactive radical and irradiating it with ultraviolet light to desorb adsorbed atoms or molecules.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Column 2 Electron gun 3 Cathode 4 Electron extraction electrode (anode) 5 Electromagnetic wave irradiation means 6 Optical fiber 7 Mirror 8 Particle beam irradiation means 10 Chip in inspection area 11 Electron beam generation part 12 Micro multi electron tube 13 Sample to be inspected 14 Ultraviolet light irradiation means 15 Stage 16 Optical cable 17 Micro electron gun 18 Micro electron optical system 19 Optical lens 20 Slit 21 Cathode (micro cold cathode) 22 Electron extraction electrode 23 Cleaning cathode

Continuation of the front page (56) References JP-A-4-332424 (JP, A) JP-A-51-105761 (JP, A) JP-A-50-62766 (JP, A) JP-A-64-54639 (JP) JP-A-47-11809 (JP, A) JP-A-4-22038 (JP, A) JP-B-53-4387 (JP, B2) (58) Fields investigated (Int. Cl. ⁶ , DB Name) H01J 1 / 30,9 / 02,9 / 44 H01J 3 / 02,37 / 073 JICST file (JOIS)

Claims (3)

(57) [Claims] 1. Reactive radicals are emitted to a field emission type electron gun.
The generated gas is sealed and the surface of the cathode of the electron gun is
To, ultraviolet light, reactive Raj is irradiated with electromagnetic wave such as a laser beam
A method for stabilizing a field emission type electron gun , comprising generating nuclei and desorbing atoms or molecules externally adsorbed on the surface of the cathode to stabilize a radiation current. 2. A field emission type electron gun having a small cold cathode.
In the period in which the electron emission operation is stopped, the minute cold cathode
In order to clean the cathode of the field emission type electron gun having
The surface of the cathode constituting the field emission electron gun having the minute cold cathode, is used to separate the atoms or molecules by irradiating with ultraviolet light or laser light is foreign adsorbed on the surface of the cathode light irradiating means can mounted is moved that
A field emission type electron gun comprising a small cold cathode. 3. An ultraviolet light is applied to the surface of the cathode of the field emission type electron gun.
Electromagnetic waves having the function of irradiating electromagnetic waves such as light and laser light
Supply irradiation means and gas generating reactive radicals
A field emission type electron gun comprising: a reactive radical generating gas supply unit .