JP4568183B2 - Ultraviolet light source device - Google Patents

Description

  The present invention relates to an ultraviolet light source device that generates ultraviolet light that can be used industrially by utilizing a photochemical reaction.

Conventionally, as means for generating ultraviolet light, there is an ultraviolet light irradiation device using discharge called an excimer lamp.
As shown in FIG. 8, this excimer lamp is made of synthetic quartz glass having a double structure of an inner tube 30 and an outer tube 31 arranged coaxially, and an inner electrode 32 is disposed inside the inner tube 30, and the outer tube 31. External electrodes 33 are provided on the outer sides of the electrodes, and a discharge space 34 formed between the inner tube 30 and the outer tube 31 is filled with a xenon (Xe) gas 35 as a rare gas for discharge.

  Then, by applying a low voltage from the high frequency power source 36 between the electrodes 32 and 33, a plasma discharge is generated between the inner tube 30 and the outer tube 31 of the quartz tube, and the discharge rare gas 35 is generated by the discharge plasma. Exciter state is instantaneously excited. When returning from the excimer state to the original state (ground state), a spectrum unique to the excimer is generated.

  The emission spectrum can be set by the composition of the discharge gas to be filled, and ultraviolet light or vacuum ultraviolet light can be generated by selecting the composition of the discharge gas (see, for example, Patent Document 1).

This ultraviolet light, especially vacuum ultraviolet light, has features such as low power, high output and low temperature irradiation. For example, industries such as synthesis of useful chemical substances, decomposition of toxic substances, surface treatment, creation of new materials, sterilization, sterilization, etc. Many uses are expected.
JP 2002-352774 A

  However, in order to actually use ultraviolet light (hereinafter, described with vacuum ultraviolet light as an example) in the industry, a more powerful light source is required, so conventional excimer lamps lack energy and are practical. Not suitable for.

In addition, the luminous efficiency (energy conversion efficiency from electric energy to vacuum ultraviolet light) is low, which is economically problematic.
In addition, when producing a useful chemical substance by controlling a chemical reaction, a vacuum ultraviolet light having a narrow pulse width of 100 nanoseconds or less may be required. With an excimer lamp, it is almost impossible to produce a pulse with a pulse width of less than several tens of microseconds, which is not practical.

  The present invention has been made in order to solve the above-described problems, and is required for industrial application of vacuum ultraviolet light. It is powerful, has high luminous efficiency, and has a pulse width of 100 nanoseconds as required. An object of the present invention is to provide an ultraviolet light source device capable of generating vacuum ultraviolet light having a narrow width as follows.

In order to achieve the above object, an invention according to claim 1 is directed to an electron beam generator that generates an electron beam and a discharge gas, and the electron beam generated in the electron beam generator is incident on the discharge gas. In this way, the light generating part for generating ultraviolet light and the electron beam generating part and the light generating part are isolated and kept airtight, and the electron beam generated by the electron beam generating part is transmitted into the light generating part. In an ultraviolet light source device comprising an electron beam transmission window made of a diamond thin film and a light transmission window for extracting ultraviolet light generated by the light generating portion, the diamond thin film is formed on a silicon substrate, It is attached to the anode .

  According to the ultraviolet light source device of the present invention, it is possible to generate ultraviolet light that is powerful, has high luminous efficiency, and has a pulse width of 100 nanoseconds or less, which has not been realized with conventional excimer lamps. It becomes possible to use vacuum ultraviolet light in various industrial fields.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a sectional view showing an ultraviolet light source device according to a first embodiment of the present invention.
In FIG. 1, reference numeral 1 denotes an electron beam generator, and a cathode 3 which is a thermionic cathode is provided as an electron emission source inside a container 2 kept in a vacuum.

The cathode 3 is connected to an electron beam accelerating power source 4 provided outside the container 2 so as to have a negative potential with respect to the ground potential.
A heater 5 provided in the container 2 for heating the cathode 3 is connected to a heater power source 6 provided outside the container 2.

Reference numeral 7 denotes a grid plate made of a metal plate, which is provided on the front surface of the cathode 3 and forms slits 9 for shaping the shape of the accelerated electron beam 8 emitted from the cathode 3.
An electron beam control power source 10 is provided outside the container 2 and connected to the cathode 3 so that a positive or negative voltage can be applied to the cathode 3.

Reference numeral 11 denotes an anode, which is attached to the inner surface of the container 2 of the electron beam generator 1 so as to face the electron beam 8 emitted from the cathode 3 and is grounded to form a slit-shaped opening 12.
Although not shown, the anode 11 is cooled by water or other means.

  Reference numeral 13 denotes an electron beam transmission window. For example, a thin film of diamond is formed on a silicon substrate, and is attached to the anode 11 so as to close the slit-like opening 12 of the anode 11. Further, the container 2 is integrated with the anode 11. It is attached to the inner surface of the container 2 so as to close the opening 14 formed in the container 2.

Reference numeral 15 denotes a light generator, and a container 16 is attached to the container 2 of the electron beam generator 1, and an opening 17 is formed at a position facing the opening 14 of the container 2.
At least the inner surface of the container 16 of the light generating unit 15 is made of a material that easily reflects light in order to efficiently extract the generated vacuum ultraviolet light to the outside, for example, a material such as aluminum, or a material that easily reflects light. It is coated.

  A light transmission window 18 is formed on a surface opposite to the opening 17 of the container 16 of the light generation unit 15 and is formed of a material that transmits vacuum ultraviolet light, such as magnesium fluoride. .

A discharge gas 19 containing a rare gas such as xenon (Xe) gas having a pressure of 1 to several atmospheres is sealed inside the container 16 of the light generating unit 15.
Airtightness between the electron beam generator 1 kept in a vacuum and the light generator 15 filled with a high-pressure discharge gas is maintained by the electron beam transmission window 12.

Next, the operation of this embodiment will be described.
The heater 5 to which a voltage is applied by the heater power supply 6 generates heat and heats the adjacent cathode 3.

The cathode 6 heated by the heater 5 emits a high energy electron beam by thermionic emission.
On the other hand, a positive or negative voltage is applied to the grid plate 7 provided on the front surface of the cathode 6 by an electron beam control power source 10.
When a negative voltage is applied to the grid plate 7, the emission of the electron beam from the cathode 3 is suppressed.

Conversely, when 0 or a positive voltage is applied to the grid plate 7, an electron beam is emitted from the cathode 3.
The electron beam 8 emitted from the cathode 3 is accelerated by the electron beam acceleration power source 4 in the container 2 of the electron beam generator 1 and further accelerated toward the anode 11 at the ground potential.
The voltage of the electron beam accelerating power source 4 is preferably about several tens Kv to 100 Kv, for example.

When the voltage of the electron beam accelerating power source 4 is lowered, the number and energy of electron beams that pass through the electron beam transmission window 13 are reduced.
On the contrary, if the voltage of the electron beam acceleration power source 4 becomes too high, insulation becomes difficult, and the apparatus becomes large and expensive. In particular, when the voltage exceeds 100 Kv, measures against insulation become extremely difficult.

The accelerated electron beam 8 passes through the slit-shaped opening 12 of the anode 11, passes through the electron beam transmission window 13, and enters the light generation unit 15.
Since the discharge gas 19 containing xenon gas is enclosed in the container 16 of the light generation unit 15, the high energy electron beam 8 collides with the xenon gas atoms and generates ions or excited atoms.

Thereafter, excimers are generated through collision reaction processes such as excited molecule generation and electron-ion recombination.
Excimer dissociates in a very short time and returns to the ground state, and excimer-specific vacuum ultraviolet light is generated in the process.
For example, light emitted from a xenon excimer is vacuum ultraviolet light 20 having a wavelength of 173 nm.

The energy conversion efficiency from the electron beam 8 to the vacuum ultraviolet light 20 can be expected to be as high as about 60% according to computer simulation.
The vacuum ultraviolet light 20 generated by the light generator 15 passes through the light transmission window 18 and is extracted outside.

  The vacuum ultraviolet light 20 thus generated is used in many industrial fields such as synthesis of useful chemical substances, decomposition of toxic substances such as chlorofluorocarbon, PCB, and dioxin, surface treatment, creation of new materials, sterilization, and sterilization. Used.

  According to the present embodiment, the high energy electron beam 8 generated from the electron beam generator 1 is incident on the high-pressure discharge gas 19 to generate excimer in the light generator 15 and generate the vacuum ultraviolet light 20. Therefore, the energy conversion efficiency from the electron beam 8 to the light via excimer generation can be close to 60%.

Further, since the generation efficiency of the high energy electron beam 8 can be as high as 100%, conversion from electric energy to vacuum ultraviolet light can be performed with a very high efficiency of several tens of percent.
The light generated from the excimer is ultraviolet light, and particularly, the light generated from the single gas of the rare gas or the excimer of the mixed gas is vacuum ultraviolet light having a wavelength of 200 nm or less.

FIG. 2 shows values obtained by converting bond energies of various chemical bonds into light wavelengths, and at the same time, the wavelength of light 173 nm generated from the xenon excimer.
In the figure, the shorter the wavelength, the higher the energy.

As can be seen from FIG. 2, since xenon excimer light has energy higher than most chemical bond energies except N≡N, C≡C, and C═O, a chemical bond having a wavelength longer than this wavelength has a wavelength of 173 nm. It can be seen that the bonds can be cut directly with vacuum ultraviolet light, and most bonds can be cut.
Further, by increasing the power density of the electron beam 8, in principle, more powerful (higher luminance) vacuum ultraviolet light 20 can be generated.

  The biggest problem in increasing the power density of the electron beam 8 is the destruction of the electron beam transmission window 13 due to heat generation. In this embodiment, the use of a diamond thin film for the electron beam transmission window 13 reduces the electron density. The power density of the line 8 can be increased.

  The diamond used as the material for the electron beam transmission window 13 has characteristics such as high strength, small atomic number, and very high thermal conductivity, and has very excellent properties as the electron beam transmission window 13. .

  When the electron beam 8 passes through the electron beam transmission window 13, it collides with the electrons in the constituent atoms of the electron beam transmission window 13 and is scattered and loses energy. Therefore, the thickness of the electron beam transmission window 13 is reduced. Moreover, the transmittance of the electron beam 8 can be increased by using a substance having a small atomic number.

Since diamond has high strength, the thickness of the film can be reduced, and since the atomic number is as small as 6, the transmittance of the electron beam 8 can be increased.
Further, the shape of the electron beam transmission window 13 is made slit by the slit-shaped opening 12 of the anode 11 so that the thickness is reduced compared to a circular (pinhole) electron beam transmission window or the like of the same area. It becomes possible to do.

  For example, if the slit width is about 1 mm, a diamond film thickness of several μm is sufficient. When the energy of the electron beam 8 is several tens Kv with respect to the diamond film having this thickness, the transmittance of the electron beam 8 is 98% or more.

Further, the density of the electron beam 8 that passes through the electron beam transmission window 13 is determined by the balance between the heat generation in the electron beam transmission window 13 and its cooling ability.
That is, if the cooling capability of the electron beam transmission window 13 is high, more electron beams 8 can be passed, and the output as the ultraviolet light source device increases.

  Since diamond has a thermal conductivity that is about an order of magnitude higher than that of a metal having good thermal conductivity, if the anode 11 is sufficiently cooled, the electron beam transmission window 13 can be efficiently cooled by thermal conduction. Can do.

Therefore, a current density of one digit or more can be passed as compared with a normal metal thin film or silicon thin film.
On the other hand, the material for forming the light transmission window 18 may be any material that allows the vacuum ultraviolet light 20 to pass through. In addition to the magnesium fluoride described in the above embodiment, calcium fluoride, barium fluoride, lithium fluoride, Materials such as sodium fluoride, potassium fluoride, quartz, and sapphire can also be used.

Aluminum or the like is suitable as a material that is formed or coated on at least the inner surface of the container 16 of the light generating unit 15 and easily reflects vacuum ultraviolet light.
For example, aluminum has a reflectance of 92% or more with respect to vacuum ultraviolet light of 173 nm.

  Furthermore, the inner surface of the container 16 of the light generating unit 15 or the inner surface of the container 16 is coated with a material that reflects vacuum ultraviolet light, and then coated with a material that transmits vacuum ultraviolet light, thereby preventing corrosion of the inner wall of the container 16. can do.

In particular, when a mixed gas of a rare gas and a halogen gas is used as a discharge gas sealed in the light generating portion 15, aluminum as a reflective material is easily corroded, and thus a coating for preventing corrosion is necessary.
As a coating material for preventing corrosion, magnesium fluoride, calcium fluoride, barium fluoride, lithium fluoride, sodium fluoride, potassium fluoride and the like can be considered.

The discharge gas sealed in the light generating unit 15 may be a single rare gas such as xenon, krypton, argon, or helium, or may be a mixed gas of two or more kinds of rare gases, or a rare gas and a halogen gas (fluorine, A mixed gas of chlorine, bromine, etc.).
If xenon simple substance gas is used, vacuum ultraviolet light with a wavelength of 173 nm can be obtained, and any gas is basically the same.

  As the grid plate 7, a metal plate provided with slits 9 for forming an electron beam shape so that all the accelerated electron beams 8 pass through the electron beam transmission window 13 is used in the description of the above embodiment. Although the case has been described, a mesh-like one can also be used.

  Further, an electron beam incident on the light generation unit 15 is provided by installing a grid plate 7 on the front surface of the cathode 3 as an electron emission source and controlling on / off of emission of the electron beam from the cathode 3 by the electron beam control power source 10. The pulse width of the generated vacuum ultraviolet light 20 can be narrowed to 100 nanoseconds or less.

  FIG. 3 shows a state of the grid plate applied voltage V to the cathode in the case of performing pulse control for generating vacuum ultraviolet light generated from the light generating unit in a pulse manner by controlling the electron beam output.

  In FIG. 3, when the voltage is applied to the grid plate 7 at the timing A, the vacuum ultraviolet light can be emitted in a pulse manner only at the timing A when the voltage is not applied to the grid plate 7 at the timing B.

In addition to the means using thermionic generation described in the above embodiment, many means are conceivable for the configuration of the electron beam generator.
For example, a plasma electron source that generates electrons using plasma is one of the means. Any other means may be used as long as it can generate and accelerate electrons.

FIG. 4 is a diagram showing an example of how to attach the electron beam transmission window to the anode.
In FIG. 4, 11 is an anode, 12 is a slit-like opening formed at substantially the central part of the anode 11, 21 is a silicon substrate, and etching is performed corresponding to the slit-like opening 12 of the anode 11 at almost the central part. A slit hole 22 having a width of about 1 mm is formed.

On the surface of the silicon substrate 21 facing the anode 11, a metal (for example, copper, silver, gold, etc.) 23 that is compatible with a material such as copper constituting the anode 11 is deposited, and the silicon substrate is interposed through the metal 23. 21 is brazed to the anode 11.
Reference numeral 24 denotes a diamond film constituting the electron beam transmission window 13 and has a thickness of about several μm.

Further, a water cooling part 25 is formed on the anode 11 and cooled.
As a method of attaching the silicon substrate 21 to the anode 11, as shown in FIG. 5, it may be mechanically fixed with a presser fitting 27 and a screw 28 with a soft metal thin film 26 such as gold interposed therebetween.

By doing in this way, the diamond thin film 24 can be easily attached to the anode 11, and the electron beam transmission window 13 can be comprised.
Further, since the thickness of the silicon substrate 21 is sufficiently thick (several tens of times) as compared with the diamond thin film 24, it hardly hinders heat conduction.

FIG. 6 is a view showing a modification of the present invention, and the shape of the container 16 of the light generating unit 15 is changed from the rectangular box shape shown in the first embodiment to a conical box shape.
By doing in this way, the vacuum ultraviolet light 20 generated in the container 16 can be taken out to the outside with less reflection. Of course, a polygonal pyramid such as a triangular pyramid or a quadrangular pyramid may be used instead of the conical shape.

  Further, as shown in FIG. 7, the tip of the container 2 of the electron beam generator 1 may be opened, and the anode 11 with the electron beam transmission window 13 attached may be attached to the outer surface of the container 16 of the light generator 15. In some cases, it may be attached to the inner surface of the container 16.

Sectional drawing of the ultraviolet light source device by the 1st Embodiment of this invention. Explanatory drawing which converted and expressed the bond energy of various chemical bonds into the wavelength of light. Explanatory drawing which shows an example of the pulse voltage applied to a grid board with respect to the cathode of the electron beam generation part in this invention. Sectional drawing which shows an example of the attachment method of the electron beam transmission window to the anode in this invention. Sectional drawing which shows another example of the attachment method of the electron beam transmission window to the anode in this invention. Sectional drawing which shows the modification of this invention. Sectional drawing which shows another modification of this invention. Sectional drawing which shows the conventional excimer lamp.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Electron beam generating part, 2 ... Electron beam generating part container, 3 ... Cathode, 4 ... Electron beam acceleration power source, 5 ... Heater, 6 ... Heater power source, 7 ... Grid plate, 8 ... Electron beam, 9 ... Slit DESCRIPTION OF SYMBOLS 10 ... Electron beam control power supply, 11 ... Anode, 12 ... Slit-shaped opening part, 13 ... Electron beam transmission window, 14 ... Opening part, 15 ... Light generating part, 16 ... Container of light generating part, 17 ... Opening part , 18 ... light transmission window, 19 ... discharge gas, 20 ... vacuum ultraviolet light, 21 ... silicon substrate, 22 ... slit hole, 23 ... metal, 24 ... diamond film, 25 ... water-cooled part, 26 ... metal film, 27 ... presser Metal fitting, 28 ... screw.

Claims (5)

An electron beam generating unit that generates an electron beam; a light generating unit that encloses a discharge gas and generates ultraviolet light by causing the electron beam generated by the electron beam generating unit to enter the discharge gas; and the electron beam An electron beam transmission window made of a diamond thin film that isolates the generation unit and the light generation unit to keep each airtight and transmits the electron beam generated in the electron beam generation unit into the light generation unit, and the light generation unit In the ultraviolet light source device consisting of a light transmission window that takes out the ultraviolet light generated in
An ultraviolet light source device, wherein the diamond thin film is formed on a silicon substrate, and the silicon substrate is attached to an anode .   2. The ultraviolet light source device according to claim 1, wherein the electron beam transmitting window has a slit shape. 3. The ultraviolet light source device according to claim 1, wherein an inner surface of the light generating portion is made of a material that reflects ultraviolet light, or a material that reflects ultraviolet light is coated on the inner surface. 4. The ultraviolet light source device according to claim 3, wherein an inner surface of the light generating portion is coated with a material that transmits ultraviolet light for preventing corrosion. 5. The ultraviolet light source device according to claim 4 , wherein any one of magnesium fluoride, calcium fluoride, barium fluoride, lithium fluoride, sodium fluoride, and potassium fluoride is used as the coating material for preventing corrosion. .

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