Excimer lamp

A excimer lamp comprises an electric discharge container in which a sealing member is provided between a lid member and an arc tube which does not contain silica, and a pair of external electrodes which are separately provided on an outer surface of the arc tube, wherein rare gas and a fluoride is enclosed in the electric discharge container, and the fluoride is sulfur hexafluoride, carbon tetrafluoride, or nitrogen trifluoride.

CROSS-REFERENCES TO RELATED APPLICATION

The disclosure of Japanese Patent Application No. 2007-226551, filed Aug. 31, 2007 including its specification, claims and drawings, are incorporated herein by reference in its entirety.

TECHNICAL FIELD

Described herein is an excimer lamp, and in particular, an excimer lamp in which an electrode is provided in an outer surface of an arc tube.

BACKGROUND

Conventionally, an excimer lamp is used as a light source of ultraviolet rays for photochemical reaction. For example, such an excimer lamp is disclosed in Japanese Patent No. 3178162.

FIGS. 11,12A and12B are diagrams for explaining the conventional excimer lamp1disclosed in Japanese Patent No. 3178162.FIG. 11is a perspective view of the excimer lamp1.FIG. 12Ais a cross sectional view of an arc tube21of the excimer lamp1shown inFIG. 11, taken along a direction of a tube axis thereof.FIG. 12Bis a cross sectional view thereof, taken along a direction perpendicular to the tube axis of the arc tube21shown inFIG. 12A(a cross sectional view thereof taken along a line F-F ofFIG. 12A). InFIGS. 12A and 12B, the same reference numerals as those ofFIG. 11are assigned to the same structural parts as those shown inFIG. 11.

Lid portion members221and222are arranged so as to cover both ends of the straight tube shaped arc tube21of the excimer lamp1, which are free ends. Sealing members231and232are filled up between the arc tube21and the respective lid portion members221and222, so that the arc tube21and the respective lid portion members221and222are connected to each other. Thereby, an electric discharge container2which is made up of the arc tube21, the lid portion members221and222, and the sealing members231and232is formed.

A gas pipe2221is provided in the second lid portion member222. After air in an inner space24of the electric discharge container2is discharged from the gas pipe2221, krypton (Kr) and fluorine (F2) gas is enclosed as light emitting gas. A sealing portion2222is formed by welding the gas pipe2221with pressure after the enclosure of the light emitting gas.

A pair of external electrodes31and32which are electrically separated from each other is provided on the outer surface of the arc tube21. Leads41and42are electrically connected to the respective end portions of the external electrodes31and32in the longitudinal direction thereof by, for example, solders51and52.

The leads41and42are connected to a power supply (not shown). Electric discharge occurs in the arc tube21, between the pair of external electrodes31and32to which electric power is supplied from the leads41and42, when a lamp1is lit. The light emitting gas enclosed in the inner space24of the electric discharge container2is ionized, so that, for example, krypton ions and fluorine ions are formed in the inner space24of the electric discharge container2, whereby excimer molecules which consist of krypton-fluorine are formed, and, for example, light with a wavelength of approximately 248 nm is generated.

SUMMARY

When the lamp1is lit, the ionized fluorine ions are diffused throughout the inner space24of the electric discharge container2, so that the inner space is filled up with fluorine ions. Even if, for example, fluorine resin which is hard to absorb fluorine is formed on the sealing members231and232, the fluorine is absorbed as lighting time of the lamp1passes. Since the ionized fluorine ions contribute to emission of light, when the ionized fluorine ions decrease with passage of lighting time of the lamp1, the illuminance thereof decreases. That is, in the conventional excimer lamp1, there is a problem of a life span, in that an illuminance cannot be maintained for a long time.

Hereinafter, an excimer lamp capable of controlling absorption of fluorine ions into sealing members when a lamp is lit will be offered below.

The present excimer lamp comprises an electric discharge container in which a sealing member is provided between a lid member and an arc tube which does not contain silica, and a pair of external electrodes which are separately provided on an outer surface of the arc tube, wherein rare gas and a fluoride is enclosed in the electric discharge container, and the fluoride is sulfur hexafluoride, carbon tetrafluoride, or nitrogen trifluoride.

The excimer lamp may further include an insulator or grooves which are formed between the external electrodes which face each other on an outer surface of the arc tube.

In the excimer lamp, the external electrodes may be covered with an insulator.

In the excimer lamp according to a first embodiment, since the chemical stability of the fluoride enclosed in the electric discharge container is high, even at time the lamp is lit, the ionized fluorine ions can return to fluoride, in a range from the end portions in which the external electrodes face each other in the electric discharge container, to the respective sealing members which are located near there. Since contacts of the sealing members with fluorine ions can be suppressed, it is possible to suppress absorption of the fluorine ions into the sealing members. That is, in the excimer lamp according to the first embodiment, the illuminance deterioration due to absorption of the fluorine ions in sealing members can be suppressed, so that the illuminance thereof can be maintained for a long time.

In the excimer lamp according to a second embodiment, creeping discharge between the electrodes provided on the outer surface of the electric discharge container can be suppressed.

Since, in the excimer lamp according to a third embodiment, the outer surface of the external electrodes can be electrically insulated, the creeping discharge between the electrodes on the outer surface of the arc tube can be prevented. Furthermore, it is possible to electrically insulate the external electrodes from the outside.

DESCRIPTION

The descriptions in the specification are provided for illustrative purposes only, and are not limiting thereto. An appreciation of various aspects of the present excimer lamp is best gained through a discussion of various examples thereof. The meaning of these terms will be apparent to persons skilled in the relevant arts based on the entirety of the teachings provided herein.

The present excimer lamp1comprises an electric discharge container2having an arc tube21which does not contain silica (Si), and which is sealed with sealing members231and232, and at least a pair of external electrodes31and32provided on the outer surface of the arc tube21, wherein light emitting gas is enclosed in the electric discharge container2. The light emitting gas is, for example, rare gas and a fluoride with high chemical stability. The light emitting gas forms rare-gas ions and fluorine ions at time the lamp1is lit.

Description of a first embodiment of the excimer lamp1will be given below, referring toFIGS. 1 and 2Aand2B.

FIGS. 1,2A and2B are explanatory diagrams of the excimer lamp1according to the embodiment.FIG. 1is a perspective view of the excimer lamp1.FIG. 2Ais a cross sectional view of the excimer lamp1, taken along a direction of the tube axis of the arc tube21.FIG. 2Bis a cross sectional view thereof, taken along a direction perpendicular to the tube axis direction of the arc tube21ofFIG. 2A(a cross sectional view thereof, taken along a line A-A ofFIG. 2A). InFIGS. 1,2A and2B, the same reference numerals as those ofFIGS. 12A and 12B are assigned to the same structural parts as those shown inFIGS. 12A and 12B.

The arc tube21of the excimer lamp1according to the embodiment is in the shape of a straight pipe. The arc tube21has optical permeability to wavelengths of 150-400 nm, and is formed of material with little absorption of fluorine ions. As the material of the arc tube21, for example, metal oxides such as sapphire (single crystal alumina) or alumina (polycrystal alumina), whose principal component is aluminum oxide (Al2O3), may be used. In addition, a fluoride such as magnesium difluoride (MgF2), lithium fluoride (LiF), calcium difluoride (CaF2), barium difluoride (BaF2), or YAG (yttrium aluminum garnet) may be used as the material of the arc tube21. Although quartz glass (SiO2) may be selected as the material which has the optical permeability, since silica (Si) contained in the quartz glass (SiO2) has the high reactivity with fluorine ions, the quartz glass (SiO2) might not be used as the material of the arc tube21which comes into contact with fluorine ions while the lamp1is lit. For this reason, material which does not contain silica (Si) is used suitably, for the arc tube21which consists of material with little absorption of fluorine ions.

The arc tube21in the longitudinal direction has openings at both ends thereof respectively, and cup-like lid portion members221and222are arranged on the both ends. The lid portion members221and222are made of the so-called kovar which is an alloy in which nickel (Ni) and cobalt (Co) are blended with iron (Fe). The material of the lid portion members221and222is not limited to such a metal. Since material having ultraviolet light resistance can be used for the lid portion members221and222, for example, sapphire (single crystal alumina) whose principal component is aluminum oxide (Al2O3) which is the same material as that of the arc tube21may be used therefor.

The sealing members231and232are filled up between the arc tube21and the lid portion members221and222, respectively, whereby the arc tube21and the lid portion members221and222are connected to each other, so that the electric discharge container2which is made up of the arc tube21, the lid portion members221and222, and the sealing members231and232is formed. Also, wax material which consists of, for example, an alloy (Ag—Cu alloy) of silver and copper can be used as the material of the sealing members231and232in order to seal the spaces between the arc tube21and the lid portion members231and232. Since, at the time the lamp1is lit, not only ultraviolet rays are irradiated to the sealing members231and232, but the sealing members231and232are also heated by lighting of the lamp1, material having ultraviolet light resistance and thermal resistance can be used. Especially, material such as an alloy (Ag—Cu alloy) of silver and copper, which absorbs little fluorine ions can be suitably used.

The gas pipe2221is provided to the second lid portion member222. After air in the inner space24of the electric discharge container2is exhausted from the gas pipe2221so that the pressure thereof is reduced, rare gas and a fluoride having high chemical stability is filled in as the light emitting gas. After filling the light emitting gas therein, an electric discharge container2is formed as a sealed structure by forming a sealing portion2222to the gas pipe2221by a pressure welding etc. Rare gas which is argon (Ar), krypton (Kr), or xenon (Xe), and a fluoride which is sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), or nitrogen trifluoride (NF3) may be used as a light emitting gas filled in the inner space24of the electric discharge container2.

As shown inFIG. 2B, a pair of external electrodes31and32is arranged on the outer surface of the arc tube21, so as to be electrically separated from each other. As shown inFIG. 2A, the pair of the electrodes is provided, so as to extend along the tube axis direction of the arc tube21. Furthermore, the external electrodes31and32are provided so as to be separately placed from the sealing members231and232and the lid portion members221and222. The external electrodes31and32can be formed by applying, for example, copper in paste form, to the outer surface of the arc tube21. Moreover, for example, plate-like aluminum can also be pasted on the outer surface of the arc tube21with an adhesive agent etc. Each of the leads41and42is electrically connected to one end of the external electrode with solder51or52etc. in a longitudinal direction of the external electrode31or32. A power supply (not shown) is connected to the leads41and42, and electric power is supplied at time the lamp1is lit.

Electric discharge occurs between the pair of external electrodes31and32through the arc tube21by impressing voltage between the external electrodes31and32when the lamp1is lit. When the rare gas used as the light emitting gas is argon (Ar), and the fluoride is, for example, sulfur hexafluoride (SF6), they are ionized so that argon ions and fluorine ions are formed, whereby excimer molecules which consist of argon-fluorine are formed, and light with wavelengths of approximately 193 nm is emitted from the arc tube21.

As shown inFIG. 2B, electric discharge occurs between the external electrode31and32at time the lamp1is lit, in a range L1in the tube axis direction of the arc tube21in which the external electrodes31and32face each other. When the arc tube21is made of material which does not contain silica (Si), as material with little absorption of fluorine ions, it is possible to prevent the arc tube21from absorbing the ionized fluorine ions.

Since, in the inner space24of the electric discharge container2, the external electrodes31and32are provided in a position where they are separated from the sealing members231and232and the lid portion members221and222in the tube axis direction of the arc tube21, no electric discharge occur in a range L2extending from the end portions of the range L1where the external electrodes31and32in the tube axis direction of the arc tube21face each other, to the respective sealing members231and232which are located near there. For this reason, when material such as sulfur hexafluoride (SF6), with high chemical stability, is filled, as the light emitting gas, in the inner space24of the electric discharge container2, since no electric discharge occurs in the range L2from the end portions of the range L1where the external electrodes31and32in the direction of the tube axis of the arc tube21face each other, to the respective sealing members231and232which are located near there, the fluorine ions ionized by electric discharge returns to, for example, sulfur hexafluoride which was before the ionization. Thereby, in the inner space24of the electric discharge container2, as compared with the range L1where the external electrodes31and32in the tube axis direction of the arc tube21face each other, the fluorine ions decrease extremely in the range L2from the end portions of the range L1where the external electrodes31and32in the tube axis direction of the arc tube21face each other, to the respective sealing members231and232which are located near there. That is, since it is possible to suppress contacts of fluorine ions with the sealing members231and232, it is possible to prevent decrease of the fluorine ions in the inner space24of the electric discharge container2when the lamp1is lit, and the illuminance reduction of the lamp1due to the fluorine ion reduction can be prevented.

The excimer lamp1according to this embodiment comprises the electric discharge container2having the sealing members231and232in the arc tube21which does not contain silica, and at least a pair of external electrodes31and32provided on the outer surface of the arc tube21, wherein rare gas and a fluoride are enclosed in the electric discharge container2, and further the fluoride consisting of sulfur hexafluoride, carbon tetrafluoride, or nitrogen trifluoride. Since the chemical stability of the fluoride enclosed in the electric discharge container2is high, even when the lamp1is lit, in the range L2from the end portions of the range L1where the external electrodes31and32face each other in the inner space24of the electric discharge container2, to the respective sealing members which are located near there, the ionized fluorine ions can return to a fluoride. Since it is possible to suppress contacts of the sealing members231and232with fluorine ions, absorption of the fluorine ions by the sealing members231and232can be suppressed. That is, the excimer lamp1according to this embodiment can control illuminance reduction due to absorption of the fluorine ions in the sealing members231and232, so that an illuminance can be maintained for a long time.

Description of a second embodiment of an excimer lamp1will be given below, referring toFIGS. 3,4A and4B.

FIGS. 3,4A and4B are diagrams for explaining the excimer lamp1according to the embodiment.FIG. 3is a perspective view of the excimer lamp1.FIG. 4Ais a cross sectional view of the excimer lamp1, taken along a direction of the tube axis of an arc tube21of the excimer lamp1.FIG. 4Bis a cross sectional view thereof, taken along a direction perpendicular to the tube axis direction of the arc tube21ofFIG. 4A(a cross sectional view thereof taken along a line B-B ofFIG. 4A). InFIGS. 3,4A and4B, the same reference numerals as those ofFIG. 2are assigned to the same structural parts as those shown inFIG. 2.

The excimer lamp1shown inFIGS. 3,4A and4B is different from that shown inFIGS. 1,2A and2B, in that external electrodes31and32are covered with an insulator6. Description ofFIGS. 3 and 4will be given below in view of the difference between the excimer lamp shown inFIGS. 3,4A and4B and that shown inFIGS. 1,2A and2B.

The arc tube21of the excimer lamp1according to the embodiment, is in the shape of a straight pipe. The arc tube21has optical permeability to wavelengths of 150-400 nm, and is formed of material with little absorption of fluorine ions. As the material of the arc tube21, for example, metal oxides such as sapphire (single crystal alumina) or alumina (polycrystal alumina), whose principal component is aluminum oxide (Al2O3), may be used. In addition, a fluoride such as magnesium difluoride (MgF2), lithium fluoride (LiF), calcium difluoride (CaF2), barium difluoride (BaF2), or YAG (yttrium aluminum garnet) may be used as the material of the arc tube21. Although quartz glass (SiO2) may be selected as the material which has the optical permeability, since silica (Si) contained in the quartz glass (SiO2) has the high reactivity with fluorine ions, the quartz glass (SiO2) might not be used as the material of the arc tube21which comes into contact with fluorine ions while the lamp1is lit. For this reason, material which does not contain silica (Si) is used suitably, for the arc tube21which consists of material with little absorption of fluorine ions.

The arc tube21in the longitudinal direction has openings at both ends thereof, respectively, and cup-like lid portion members221and222are arranged on the both ends. The lid portion members221and222are made of the so-called kovar which is an alloy in which nickel (Ni) and cobalt (Co) are blended with iron (Fe). The material of the lid portion members221and222is not limited to such a metal. Since material having ultraviolet light resistance can be used for the lid portion members221and222, for example, sapphire (single crystal alumina) whose principal component is aluminum oxide (Al2O3) which is the same material as that of the arc tube21may be used therefor.

Sealing members231and232are filled up between the arc tube21and the respective lid portion members221and222, whereby the arc tube21and the lid portion members221and222are connected to each other, so that an electric discharge container2which is made up of the arc tube21, the lid portion members221and222, and the sealing members231and232is formed. Also, wax material which is, for example, an alloy (Ag—Cu alloy) of silver and copper can be used as the material of the sealing members231and232in order to seal the spaces between the arc tube21and the respective lid portion members231and232. Since, at the time the lamp1is lit, not only ultraviolet rays are irradiated to the sealing members231and232, but the sealing members231and232are also heated by lighting of the lamp1, material having ultraviolet light resistance and thermal resistance can be used. Especially, material such as an alloy (Ag—Cu alloy) of silver and copper, which absorbs little fluorine ions can be suitably used.

A gas pipe2221is provided to the second lid portion member222. After air in the inner space24of the electric discharge container2is discharged from the gas pipe2221so that the pressure thereof is reduced, rare gas and a fluoride having high chemical stability is filled therein as light emitting gas. After filling the light emitting gas therein, an electric discharge container2is formed as a sealed structure by forming a sealing portion2222to the gas pipe2221by a pressure welding etc. The rare gas which is, for example, argon (Ar), krypton (Kr), or xenon (Xe), and a fluoride which is, for example, sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), or nitrogen trifluoride (NF3) may be used as a light emitting gas filled in the inner space24of the electric discharge container2.

As shown inFIG. 4B, a pair of external electrodes31and32is arranged on the outer surface of the arc tube21, so as to be electrically separated from each other. As shown inFIG. 2A, the pair of the electrodes is provided, so as to extend along the tube axis direction of the arc tube21. Furthermore, the external electrodes31and32are provided so as to be separately placed from the sealing members231and232and the lid portion members221and222. The pair of external electrodes31and32is provided so as to have portions L6and L7where the electrodes31and32do not respectively face the other electrode at end portions in a longitudinal direction thereof. As shown inFIG. 4A, the first external electrode31has the portion L6which does not face the second external electrode32, in the first lid portion member221side in the longitudinal direction. Moreover, the second external electrode32has the portion L7which does not face the first external electrode31, in the second lid portion member222side in the longitudinal direction.

The external electrodes31and32can be formed by applying, for example, copper in paste form, to the outer surface of the arc tube21. Moreover, for example, plate-like aluminum can also be pasted on the outer surface of the arc tube21with an adhesive agent etc.

An insulator6is formed so as to cover the outer face of the external electrodes31and32provided on the outer surface of the arc tube21. As shown inFIG. 4A, the insulator6is formed in the tube axis direction of the arc tube21, so as to extend over the range L1in the tube axis direction of the arc tube21where the external electrodes31and32face each other. Moreover, as shown inFIG. 4B, the insulator6is formed in the circumferential direction of an arc tube21, so as to cover portions L4which are located (in portions L3) between the external electrodes31and32which face each other on the outer circumferential surface of the arc tube21but which are located outside the external electrodes31and32in a circumferential direction of the outer circumferential surface of the arc tube21, and portions L5which are located outside the external electrodes31and32in the diameter direction of the arc tube21. The insulator6is formed by applying, for example, paste in which silica particles are dispersed in organic solvent, so as to cover the outside portions of the external electrodes31and32, and sintering the applied paste. Moreover, material having a dielectric constant lower than that of material of the external electrodes31and32is used as material of the insulator6. In particular, when the dielectric constant of the material of the insulator6is lower than that of the material of the arc tube21, the material of the insulator6may suitably function as an insulator between the electrodes31and32when the lamp1is lit.

A first lead41is electrically connected, by a first solder51etc., to a portion L61of the first external electrode31which does not face the second external electrode32and which is not covered with the insulator6so as to be exposed to the outside of the first external electrode31. A first lead42is electrically connected, by a first solder52etc., to a portion L71of the second external electrode32which does not face the first external electrode31and which is not covered with the insulator6so as to be exposed to the outside of the first external electrode32. A power supply (not shown) is connected to the leads41and42, and electric power is supplied when the lamp1is lit.

An electric discharge occurs between the pair of external electrode31and32through the arc tube21by impressing voltage between the external electrodes31, and32at time the lamp1is lit. When, for example, the rare gas used as the light emitting gas is argon (Ar), and the fluoride is sulfur hexafluoride (SF6), they are ionized so that argon ions and fluorine ions are formed, whereby excimer molecules which consist of argon-fluorine are formed, and light with wavelengths of approximately 193 nm is emitted from the arc tube21.

As shown inFIG. 4B, electric discharge which occurs between the external electrodes31and32at time of lighting of the lamp1occurs through the arc tube21in a range L1in the tube axis direction of the arc tube21, where the external electrode31and the32face each other. When the arc tube21is made of material which does not contain silica (Si) as material with little absorption of fluorine ions, it possible to prevent the arc tube21from absorbing the ionized fluorine ions.

Since, in the inner space24of the electric discharge container2, the external electrodes31and32are provided in positions where they are separately placed from the sealing members231and232and the lid portion members221and222in the tube axis direction of the arc tube21, no electric discharge occurs in a range L2extending from the end portions of the range L1where the external electrodes31and32in the tube axis direction of the arc tube21face each other, to the respective sealing members231and232which are located near there. For this reason, when material such as sulfur hexafluoride (SF6), with high chemical stability, is filled as the light emitting gas, since in the inner space24of the electric discharge container2, no electric discharge occurs in the range L2from the end portions of the range L1where the external electrodes31and32in the direction of the tube axis of the arc tube21face each other, to the respective sealing members231and232which are located near there, the fluorine ions ionized by the electric discharge return to, for example, sulfur hexafluoride which was before the ionization. Thereby, in the inner space24of the electric discharge container2, as compared with the range L1where the external electrodes31and32in the tube axis direction of the arc tube21face each other, the fluorine ions decrease extremely in the range L2from the end portions of the range L1where the external electrodes31and32in the tube axis direction of the arc tube21face each other, to the respective sealing members231and232which are located near there. That is, since it is possible to suppress contacts of fluorine ions with the sealing members231and232, it is possible to prevent decrease of the fluorine ions in the inner space24of the electric discharge container2when the lamp1is lit, whereby the illuminance reduction of the lamp1due to the fluorine ion reduction can be prevented.

In order to use the excimer lamp1according to the embodiment as an ultraviolet rays light source for photochemical reaction, it is necessary to stably start electric discharge. Furthermore, generation of electrons which have high energy required to generate excimer molecules in the excimer lamp1is required. However, the chemical stability of the fluoride contained in the inner space24of the electric discharge container2is high. That is, a fluoride with the high chemical stability, which is sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), or nitrogen trifluoride (NF3) is gas having high electron attachment nature (in other words, it exhibits the property of capturing electrons, largely). For this reason, since electrons produced by ionization are captured with high probability, breakdown voltage thereof becomes higher than that of the conventional lamp1in which fluorine (F2) gas is enclosed. Furthermore, in order to generate electrons with high energy, applied voltage needs to be high. Moreover, in the case of the excimer lamp1according to the embodiment, in order to obtain sufficient illuminance, 100 Torr or more of light emitting gas needs to be enclosed in the electric discharge container2. As in the excimer lamp1according to the first embodiment shown inFIGS. 1,2A and2B, in case where it has the structure in which the external electrodes31and32are provided on the outer surface of the arc tube21, when high voltage is impressed to the external electrodes31and32, the so-called creeping discharge in which discharge occurs along a surface of the arc tube21between the external electrodes31and32, is generated.

Then, as in the excimer lamp1according to this embodiment, creeping discharge can be suppressed by forming the insulator6, in the circumferential direction of the arc tube21and along the external electrodes31and32, at least in the portion L3between the external electrodes31and32which face each other on the outer circumferential surface of the arc tube21, but in portions L4of outsides of the external electrodes31and32in the circumferential direction of the outer circumferential surface of the arc tube21.

Furthermore, in case electric conductive material (for example, a work piece to which ultraviolet rays is irradiated) which is not shown, is arranged, for example, near the excimer lamp1, if high voltage is inputted at a high frequency to the external electrodes31and32, electric discharge occurs toward the electric conductive material (not shown) from the external electrode31(or/and,32), so that the electric discharge between the external electrodes31and32may be disturbed. For this reason, since the insulator6is formed on the portions L5which are located outside the external electrodes31and32in the diameter direction of the arc tube21, it is possible to electrically insulate the portions L4and L5from the outside of the external electrodes31and32.

The excimer lamp1according to this embodiment, comprises the electric discharge container2in which the sealing members231and232are provided in the arc tube21which does not contain silica, and at least the pair of the external electrodes31and32which are separately provided on the outer surface of the arc tube21, wherein rare gas and a fluoride are enclosed in the electric discharge container2, and the fluoride is sulfur hexafluoride, carbon tetrafluoride, or nitrogen trifluoride. Since the chemical stability of the fluoride enclosed in the electric discharge container2is high, the ionized fluorine ion can return to a fluoride even when the lamp1is lit, in the range L2from the end portions of the range L1where the external electrodes31and32face each other in the inner space24of the electric discharge container2, to the respective sealing members which are located near there. Since it is possible to suppress contacts of the sealing members231and232and the fluorine ions, absorption of the fluorine ions in the sealing members231and232can be controlled. That is, according to the feature, in the excimer lamp1according to this embodiment, the illuminance fall due to the absorption of the fluorine ions in the sealing members231and232can be suppressed, and an illuminance thereof can be maintained for a long time.

Furthermore, the external electrodes31and32are covered with the insulator, so that the insulator6is formed on the portion L3between the external electrodes31and32which face each other on the outer surface of the arc tube21. For this reason, the creeping discharge in the portion L3between the electrodes31and32on the outer surface of the electric discharge container2can be suppressed.

Moreover since the external electrodes31and32are covered with the insulator6, the insulator6is formed in the outer portions L5which are located outside the external electrodes31and32in the diameter direction of the arc tube21. For this reason, in the excimer lamp1according to this embodiment, the outer portions L4and L5which are located outside the external electrodes31and32can be insulated to the outside thereof.

Another form of the second embodiment of the excimer lamp1will be described below referring toFIGS. 5A and 5B.FIGS. 5A and 5Bare diagrams of the excimer lamp1according to the embodiment.FIG. 5Ais a side elevational view thereof which is seen from a direction perpendicular to the tube axis of the arc tube21of the excimer lamp1(a side elevational view seen from the second external electrode32side).FIG. 5Bis a cross sectional view thereof taken along a direction perpendicular to the tube axis of the arc tube21ofFIG. 5A(a cross sectional view thereof taken along a line C-C ofFIG. 5A). InFIGS. 5A and 5B, the same numerals as those ofFIGS. 4A and 4Bare assigned to the same structural elements as those ofFIGS. 4A and 4B.

The excimer lamp1shown inFIGS. 5A and 5Bis different from that shown inFIGS. 3,4A and4B, in that the excimer lamp1shown inFIGS. 5A and 5Bhas three external electrodes.FIGS. 5A and 5Bwill be described in terms of differences between the excimer lamp ofFIGS. 3,4A and4B and that ofFIGS. 5A and 5B.

The arc tube21of the excimer lamp1according to this embodiment is in a shape of a straight pipe, which is made of material having optical permeability with respect to 150-400 nm, and having little absorption of fluorine ions. The material of the arc tube21, is, for example, a metal oxide such as sapphire (single crystal alumina), or alumina (polycrystal alumina), whose principal component is an aluminum oxide (A2O3). In addition, a fluoride such as magnesium difluoride (MgF2), lithium fluoride (LiF), calcium difluoride (CaF2), barium difluoride (BaF2), or YAG (yttrium aluminum garnet) can be used as the material of the arc tube21. In addition, although quartz glass (SiO2) may be selected as the material having the optical permeability, since silica (Si) contained in quartz glass (SiO2) has high reactivity with fluorine ions, the quartz glass (SiO2) might not be used as the material of the arc tube21which is brought into contact with fluorine ions when the lamp1is lit. For this reason, material which does not contain silica (Si) is suitably used for the arc tube21which is made of material with little absorption of fluorine ions.

The arc tube21is opened at both ends in the longitudinal direction thereof, and cup-like lid portion members221and222are arranged at the both ends. The lid portion members221and222are formed of the so-called kovar, an alloy in which nickel (Ni) and cobalt (Co) is blended with iron (Fe). The material of the lid portion members221and222is not limited to such a metal. Since all that is required is that the material has ultraviolet light resistance, the lid portion member221and222may be made of material which is the same as that of the arc tube21, that is, for example, sapphire (single crystal alumina) whose main component is aluminum oxide (A2O3) etc.

Since sealing members231and232are filled up between the arc tube21and the respective lid portion members221and222, the arc tube21and the lid portion members221and222are respectively connected to each other, so that the electric discharge container2which is made up of the arc tube21, the lid portion members221and222, and the sealing members231and232is formed. Wax material for sealing which is an alloy of, for example, silver and copper (Ag—Cu alloy) may be used as the material of the sealing members231and232. Since the sealing members231and232are heated by lighting heat from the lamp1while ultraviolet rays are irradiated to the sealing members231and232when the lamp1is lit, material which has ultraviolet light resistance and thermal resistance may be used as that of the sealing members231and232. In particular, material with little absorption of fluorine ions, such as an alloy of silver and copper (Ag—Cu alloy), can suitably used.

A gas pipe2221is provided in the second lid portion member222. After air is discharged from an inner space24of an electric discharge container2via the gas pipe2221so that the pressure thereof is decreased, rare gas and a fluoride with high chemical stability is filled in as a light emitting gas. After the enclosure of the light emitting gas, the sealing portion2222is formed by performing, for example, a pressure welding etc. to a gas pipe2221, so that the electric discharge container2is formed as a sealed structure. The light emitting gas enclosed in the inner space24of the electric discharge container2may be rare gas which is, for example, argon (Ar), krypton (Kr), or xenon (Xe), and a fluoride which is, for example, sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), or nitrogen trifluoride (NF3).

While, as shown inFIG. 5B, three external electrodes31,32, and33are arranged on the outer surface of the arc tube21so as to be electrically separated from one another, as shown inFIG. 5A, they are provides so as to extend along the tube axis direction of the arc tube21. Furthermore, the external electrodes31,32, and33are provided so as to be separated from the sealing members231and232and the lid portion members221and222. As shown inFIG. 5A, in the first external electrode31, a portion L6where the first external electrode31does not face the second external electrode32is formed in a side of the first lid portion member221in the longitudinal direction of the arc tube. Moreover, in the second external electrode32, a portion L7where the second external electrode32does not face the first external electrode31is formed in a side of the second lid portion member222in the longitudinal direction of the arc tube. As described below, in order to electrically connect the first external electrode31and leads41and43to each other, in the third external electrode33, a portion L6where the third external electrode33does not face the second external electrode32, is formed in a side of the first lid portion member221in the longitudinal direction of the arc tube. That is, the third external electrode33is formed so as to face the first external electrode31in the longitudinal direction.

The external electrodes31,32, and33can be formed by applying material, such as copper in form of paste, to the outer surface of the arc tube21. Moreover, strip-shaped aluminum can also be pasted on the outer surface of the arc tube21with an adhesive agent etc.

An insulator6is formed so as to respectively cover the outside of the external electrodes31,32, and33provided on the outer surface of the arc tube21. As shown inFIG. 5A, the insulator6is formed in the tube axis direction of the arc tube21, so as to extend over a portions L1where the external electrodes31,32, and33face one another in the tube axis direction of the arc tube21. Moreover, as shown inFIG. 5B, in the circumferential direction of the arc tube21, the insulator6is formed so as to cover outer portions L41, each of which is located within portions L31extending between two of the external electrodes31,32, and33which face one another on the outer circumferential surface of the arc tube21but each of which is located outside the external electrodes31,32, and33in the circumferential direction of the outer circumferential surface of the arc tube21, and outer portions L5, each of which is located outside the external electrodes31,32, and33in a diameter direction of the arc tube21. The insulator6is formed by applying paste in which, for example, silica particles are dispersed in organic solvent, so as to cover the outside portions of the external electrodes31,32, and33, and then sintering it. Moreover, material having a dielectric constant lower than that of the external electrodes31,32, and33is used for the insulator6. In particular, if the dielectric constant of the material of the insulator6is lower than the material of the arc tube21, it is suitably used as means for insulating the electrodes3132and33among one another when the lamp1is lit.

The first lead41is electrically connected, by a first solder51etc., to a portion L61of the first external electrode31which does not face the second external electrode32, which is not covered with the insulator6, and which is exposed to the outside. Moreover, as to the second external electrode32, the second lead42is electrically connected, by the second solder52etc., to a portion L71of the second external electrode32, which does not face the first external electrode31, which is not covered with the insulator6, and which is exposed to the outside. As to the third external electrode33, the third lead43is electrically connected, by a third solder53etc., to a portion L61of the third external electrode33, which does not face the second external electrode32, which is not covered with the insulator6, and which is exposed to the outside.

When voltage is impressed between the first and third external electrodes31and33to which the first and third leads41and43are connected electrically, and the second external electrode32, at time of lighting of the lamp1, electric discharge occurs between the second external electrode32and the first and third external electrodes31and33to which the first and third leads41and43are electrically connected, through the arc tube21. When the rare gas of the light emitting gas is, for example, argon (Ar), and the fluoride is, for example, sulfur hexafluoride (SF6), they are ionized so that argon ions and fluorine ions are formed, whereby excimer molecules which are made up of argon-fluorine are formed, and light having approximately 193 nm wavelength is emitted from the arc tube21. Although not illustrated, the first lead41and the third lead43are connected electrically to each other. A power supply (not shown) is connected to the second lead42and the first and third leads41and43which are connected electrically to each other, so that electric power is supplied thereto when the lamp1is lit.

As shown inFIG. 5B, when the lamp1is lit, electric discharge which occurs between the second external electrode32and the first and third external electrodes31and33, is generated through the arc tube21in a range L1in the tube axis direction of the arc tube21, in which the external electrodes31,32and33face one another. When the arc tube21is made of material which does not contain silica (Si), as material with little absorption of fluorine ions, it is possible to prevent the arc tube21from absorbing the ionized fluorine ions.

When the external electrodes31,32and33are provided so as to be separately placed from the sealing members231and232and the lid portion members221and222in the tube axis direction of the arc tube21, in the inner space24of the electric discharge container2, no electric discharge occurs in a range L2extending from the end portions of the range L1where the external electrodes31,32and33in the tube axis direction of the arc tube21face one another, to the respective sealing members231and232which are located near there. For this reason, when material such as sulfur hexafluoride (SF6), with high chemical stability, is filled as the light emitting gas, in the inner space24of the electric discharge container2, since no electric discharge occurs in the range L2from the end portions of the range L1where the external electrodes31,32and33in the direction of the tube axis of the arc tube21face one another, to the respective sealing members231and232which are located near there, the fluorine ions ionized by the electric discharge return to, for example, sulfur hexafluoride which was before the ionization. Thereby, in the inner space24of the electric discharge container2, as compared with the range L1where the external electrodes31,32and33in the tube axis direction of the arc tube21face one another, the fluorine ions decrease extremely in the range L2from the end portions of the range L1where the external electrodes31,32and33in the tube axis direction of the arc tube21face one another, to the respective sealing members231and232which are located near there. That is, since it is possible to suppress contacts of fluorine ions with the sealing members231and232, it is possible to prevent decrease of the fluorine ions in the inner space24of the electric discharge container2when the lamp1is lit, and the illuminance reduction of the lamp1due to decrease of the fluorine ions can be prevented.

In order to use the excimer lamp1according to the embodiment as an ultraviolet rays light source for photochemical reaction, it is necessary to stably start electric discharge. Furthermore, generation of electrons which have high energy required for generating excimer molecules is required for the excimer lamp1. However, the chemical stability of the fluoride enclosed in the inner space24of the electric discharge container2is high. That is, a fluoride with the high chemical stability, which is sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), or nitrogen trifluoride (NF3) is gas having high electron attachment nature (in other words, it exhibits the property of capturing electrons, largely). For this reason, since electrons produced by ionization are captured with high probability, breakdown voltage thereof becomes higher than that of the conventional lamp1in which fluorine (F2) gas is enclosed. Furthermore, in order to generate electrons with high energy, applied voltage needs to be high. Moreover, in the case of the excimer lamp1according to the embodiment, in order to obtain sufficient illuminance, 100 Torr or more of light emitting gas needs to be enclosed in the electric discharge container2. As in the excimer lamp1according to the first embodiment shown inFIGS. 1 and 2, in case where it has the structure in which the external electrodes31and32are provided on the outer surface of the arc tube21, when high voltage is impressed to the external electrodes31and32, the so-called creeping discharge in which discharge occurs along a surface of the arc tube21between the external electrodes31and32, is generated.

Then, as in the excimer lamp1according to this embodiment, creeping discharge can be suppressed by forming the insulator6along the external electrodes31,32and33, in at least the portion L31between the external electrodes31and33and the second external electrode32on the outer circumferential surface of the arc tube21, but in the portions L41of outsides of the external electrodes31,32and33in the circumferential direction of the outer circumferential surface of the arc tube21, between which potential difference is generated when the lamp1is let.

Furthermore, in case electric conductive material (for example, a work piece to which ultraviolet rays are irradiated) which is not shown, is arranged, for example, near the excimer lamp1, when high voltage is inputted at a high frequency to the external electrodes31,32and33, electric discharge occurs toward the electric conductive material (not shown) from the external electrode31(32, or/and33), so that the electric discharge between the external electrodes31and33and the second external electrode32may be disturbed through the arc tube21. For this reason, since the insulator6is formed on the portions L5which are located outside the external electrodes31,32and33in the diameter direction of the arc tube21. Furthermore, the insulator6is formed in a portion L32between the first external electrode31and the third external electrode33on the outer circumferential surface of the arc tube21, but in portions L42which are located outside the first and third external electrodes31and33in the circumferential direction of the outer circumferential surface of the arc tube21, between which the potential difference is not generated when the lamp1is lit. That is, the portions L41, L42, and L5which are located outside the external electrodes31,32, and33respectively, can be electrically insulated by covering the external electrodes31,32, and33with the insulator6. The excimer lamp1according to this embodiment, comprises the electric discharge container2in which the sealing members231and232are provided in the arc tube21which does not contain silica, and at least the pair of the external electrodes (31,32and33) which are separately provided on the outer surface of the arc tube21, wherein rare gas and a fluoride are enclosed in the electric discharge container2, and further the fluoride is sulfur hexafluoride, carbon tetrafluoride, or nitrogen trifluoride. Since the chemical stability of the fluoride enclosed in the electric discharge container2is high, the ionized fluorine ions can return to a fluoride even at time of lighting of the lamp1, in the range L2from the end portions of the range L1where the external electrodes31,32and33face one another in the inner space24of the electric discharge container2, to the respective sealing members which are located near there. Since it is possible to suppress contacts of the sealing members231and232and the fluorine ions, absorption of the fluorine ions in the sealing members231and232can be controlled. That is, according to the feature, in the excimer lamp1according to this embodiment, the illuminance fall due to the absorption of the fluorine ions in the sealing members231and232can be controlled, so that an illuminance thereof can be maintained for a long time.

Further, the external electrodes31,32, and33are covered with the insulator6, and the insulator6is formed in the portions L31between the second external electrode32and the first external electrodes31and33, on the outer circumferential surface of the arc tube21, but in the portions L41which are located outside the external electrodes31,32and33in the circumferential direction of the outer circumferential surface of the arc tube21, between which the potential difference is not generated when the lamp1is lit. For this reason, in the excimer lamp1according to this embodiment, it is possible to suppress creeping discharge between the second external electrode32and the first and third external electrodes31and33, on the outer surface of the electric discharge container2.

In addition, the external electrodes31,32, and33are covered with the insulator6, and the insulator6is formed on the portions L5which are located outside the external electrodes31,32and33in the diameter direction of the arc tube21. Furthermore, the insulator6is formed in the portion L32between the first external electrode31and the third external electrode33on the outer circumferential surface of the arc tube21, but in the portions L42which are located outside the first and third external electrodes31and33in the circumferential direction of the outer circumferential surface of the arc tube21, between which the potential difference is not generated at the time of lighting of the lamp1. For this reason, in the excimer lamp1according to this embodiment, it is possible to electrically insulate the external electrodes31,32, and33in the outside portions L41, L42, and L5.

A third embodiment of the excimer lamp1is described, referring toFIGS. 6,7A and7B.

FIGS. 6,7A and7B are explanatory diagrams of an excimer lamp1according to the embodiment.FIG. 6is a perspective view of the excimer lamp1.FIG. 7Ais a side elevational view of the excimer lamp1(a side elevational diagram, viewing a portion L3between a first external electrode31and a second external electrodes32) which is viewed perpendicularly to the tube axis direction of an arc tube21.FIG. 7Bis a cross sectional view thereof (taken along a line D-D ofFIG. 7A), taken along a direction perpendicular to the tube axis direction of the arc tube21ofFIG. 7A. InFIGS. 6,7A and7B, the same reference numerals as those ofFIG. 2are assigned to structural parts which are the same as those shown inFIG. 2.

The excimer lamps1shown inFIGS. 6,7A and7B is different from the excimer lamp1shown inFIGS. 1,2A and2B, in that grooves7are formed in portions L3between the external electrodes31and32.FIGS. 6,7A and7B will be described in terms of differences between the excimer lamp ofFIGS. 1 and 2and that ofFIGS. 6,7A and7B.

The arc tube21of the excimer lamp1according to this embodiment is in a shape of a straight pipe, which is made of material having optical permeability with respect to 150-400 nm, and having little absorption of fluorine ions. The material of the arc tube21, is, for example, a metal oxide such as sapphire (single crystal alumina), or alumina (polycrystal alumina), whose principal component is an aluminum oxide (A2O3). In addition, a fluoride such as magnesium difluoride (MgF2), lithium fluoride (LiF), calcium difluoride (CaF2), barium difluoride (BaF2), or YAG (yttrium aluminum garnet) can be used as the material of the arc tube21. In addition, although quartz glass (SiO2) may be selected as the material having the optical permeability, since silica (Si) contained in quartz glass (SiO2) has high reactivity with fluorine ions, the quartz glass (SiO2) might not be used as the material of the arc tube21which is brought into contact with fluorine ions when the lamp1is lit. For this reason, material which does not contain silica (Si) is suitably used for the arc tube21which is made of material having little absorption of fluorine ions.

The arc tube21is opened at both ends in the longitudinal direction thereof, and cup-like lid portion members221and222are arranged at the both ends. The lid portion members221and222are formed of the so-called kovar, an alloy in which nickel (Ni) and cobalt (Co) is blended with iron (Fe). The material of the lid portion members221and222is not limited to such a metal. Since all that is required is that the material has ultraviolet light resistance, the lid portion members221and222may be made of material which is the same as that of the arc tube21, that is, for example, sapphire (single crystal alumina) whose main component is aluminum oxide (A2O3) etc.

Since sealing members231and232are filled up between the arc tube21and the respective lid portion members221and222, the arc tube21and the lid portion members221and222are respectively connected to each other, so that the electric discharge container2which is made up of the arc tube21, the lid portion members221and222, and the sealing members231and232is formed. Wax material for sealing which is made up of an alloy of, for example, silver and copper (Ag—Cu alloy) may be used as the material of the sealing members231and232. Since the sealing members231and232are heated by lighting heat from the lamp1while ultraviolet rays are irradiated to the sealing members231and232when the lamp1is lit, material which has ultraviolet light resistance and thermal resistance may be used as that of the sealing members231and232. In particular, material with little absorption of fluorine ions, such as an alloy of silver and copper (Ag—Cu alloy), can suitably used.

A gas pipe2221is provided to the second lid portion member222. After air is discharged from the inner space24of the electric discharge container2via the gas pipe2221so that the pressure thereof is decreased, rare gas and a fluoride with high chemical stability is enclosed as a light emitting gas. After the enclosure of the light emitting gas, the sealing portion2222is formed by performing, for example, a pressure welding etc. to a gas pipe2221, so that the electric discharge container2is formed as a sealed structure. The light emitting gas enclosed in the inner space24of the electric discharge container2may be rare gas which is, for example, argon (Ar), krypton (Kr), or xenon (Xe), and a fluoride which is, for example, sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), or nitrogen trifluoride (NF3).

While, as shown inFIG. 7B, a pair of external electrodes31and32are arranged on the outer surface of the arc tube21so as to be electrically separated from each other, as shown inFIG. 7A, they are provides so as to extend along the tube axis direction of the arc tube21. Furthermore, the external electrodes31and32are provided so as to be separated from the sealing members231and232and the lid portion members221and222.

The external electrodes31and32can be formed by applying material, such as copper in form of paste, to the outer surface of the arc tube21. Moreover, for example, strip-shaped aluminum can also be pasted on the outer surface of the arc tube21with an adhesive agent etc. Each of the leads41and42is electrically connected to one end of the external electrode with solder51or52etc. in a longitudinal direction of the external electrodes31and32. A power supply (not shown) is connected to the leads41and42, and electric power is supplied when the lamp1is lit.

On the outer surface of the arc tube21, the grooves7are provided between the external electrodes31and32. In the tube axis direction of the arc tube21, as shown inFIG. 7A, the grooves7are formed so as to extend over a range L1where the external electrodes31and32face each other in the tube axis direction of the arc tube21. Moreover, as shown inFIG. 7B, in the circumferential direction of the arc tube21, the grooves7are provided in the portions L3between the external electrodes31and32which face each other on the outer circumferential surface of the arc tube21. The grooves7can be formed by irradiating laser to the outer surface of the arc tube21made up of, for example, sapphire (single crystal alumina) whose principal component is aluminum oxide (A2O3).

Electric discharge occurs between the pair of external electrodes31and32through the arc tube21by impressing voltage between the external electrodes31and32when the lamp1is lit. When the rare gas of the light emitting gas is, for example, argon (Ar), and the fluoride is, for example, sulfur hexafluoride (SF6), they are ionized so that argon ions and fluorine ions are formed, whereby excimer molecules which are made up of argon-fluorine is formed, and light having approximately 193 nm wavelength is emitted from the arc tube21.

As shown inFIG. 7B, when the lamp1is lit, electric discharge which occurs between the external electrodes31and32is generated through the arc tube21in a range L1in the tube axis direction of the arc tube21, in which the external electrodes31and32face each other. When the arc tube21is made of material which does not contain silica (Si), as material with little absorption of fluorine ions, it is possible to prevent the arc tube21from absorbing the ionized fluorine ions.

When the external electrodes31and32are provided so as to be separately placed from the sealing members231and232and the lid portion members221and222in the tube axis direction of the arc tube21, no electric discharge occurs, in a range L2extending from the end portions of the range L1where the external electrodes31and32in the tube axis direction of the arc tube21face each other, to the sealing members231and232which are located near there, in the inner space24of the electric discharge container2. For this reason, when material such as sulfur hexafluoride (SF6), with high chemical stability, is filled as the light emitting gas, in the inner space24of the electric discharge container2, since no electric discharge occurs in the range L2from the end portions of the range L1where the external electrodes31and32in the direction of the tube axis of the arc tube21face each other, to the sealing members231and232which are located near there, the fluorine ions ionized by the electric discharge return to, for example, sulfur hexafluoride which was before the ionization. Thereby, in the inner space24of the electric discharge container2, as compared with the range L1where the external electrodes31and32in the tube axis direction of the arc tube21, face each other, the fluorine ions decrease extremely in the range L2from the end portions of the range L1where the external electrodes31and32in the tube axis direction of the arc tube21face each other, to the sealing members231and232which are located near there. That is, since it is possible to suppress contacts of fluorine ions with the sealing members231and232, it is possible to prevent decrease of the fluorine ions in the inner space24of the electric discharge container2when the lamp1is lit, and the illuminance reduction of the lamp1due to decrease of the fluorine ions can be prevented.

In order to use the excimer lamp1according to the embodiment as an ultraviolet rays light source for photochemical reaction, it is necessary to stably start electric discharge. Furthermore, generation of electrons which have high energy required for generating excimer molecules is required for the excimer lamp1. However, the chemical stability of the fluoride enclosed in the inner space24of the electric discharge container2is high. That is, a fluoride with the high chemical stability, which is sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), or nitrogen trifluoride (NF3) is gas having high electron attachment nature (in other words, it exhibits the property of capturing electrons, largely). For this reason, since electrons produced by ionization are captured with high probability, breakdown voltage thereof becomes higher than that of the conventional lamp1in which fluorine (F2) gas is enclosed. Furthermore, in order to generate electrons with high energy, applied voltage needs to be high. Moreover, in the case of the excimer lamp1according to the embodiment, in order to obtain sufficient illuminance, 100 Torr or more of light emitting gas needs to be enclosed in the electric discharge container2. As in the excimer lamp1according to the first embodiment shown inFIGS. 1,2A and2B, in case where it has the structure in which the external electrodes31and32are provided on the outer surface of the arc tube21, when high voltage is impressed to the external electrodes31and32, the so-called creeping discharge in which discharge occurs along a surface of the arc tube21between the external electrodes31and32, is generated.

Further, as shown in the excimer lamp1according to this embodiment, in the circumferential direction of the arc tube21, since the grooves7are formed along the longitudinal direction of the external electrodes31and32on at least the portions L3between the external electrodes31and32which face each other on the outer circumferential surface of the arc tube21, it is possible to suppress the creeping discharge. That is, when the grooves7are formed, since the creeping distance between the external electrodes31and32in the outer circumferential surface of the arc tube21which face each other is extended, the creeping discharge can be suppressed.

The excimer lamp1according to this embodiment, comprises the electric discharge container2in which the sealing members231and232are provided in the arc tube21which does not contain silica, and at least a pair of the external electrodes31and32which are separately provided on the outer surface of the arc tube21, wherein rare gas and a fluoride are enclosed in the electric discharge container2, and the fluoride is sulfur hexafluoride, carbon tetrafluoride, or nitrogen trifluoride. Since the chemical stability of the fluoride enclosed in the electric discharge container2is high, the ionized fluorine ion can return to a fluoride even at time of lighting of the lamp1, in the range L2from the end portions of the range L1where the external electrodes31and32face each other in the inner space24of the electric discharge container2, to the respective sealing members which are located near there. Since it is possible to control contacts of the sealing members231and232and the fluorine ions, absorption of the fluorine ions in the sealing members231and232can be suppressed. That is, according to the feature, in the excimer lamp1according to this embodiment, the illuminance fall due to the absorption of the fluorine ions in the sealing members231and232can be suppressed, so that an illuminance thereof can be maintained for a long time.

When the grooves7are formed between the external electrodes31and32which face each other on the outer surface of the arc table21, the creeping distance between the external electrodes31and32on the outer surface of the arc tube21can be extended. For this reason, the creeping discharge between the electrodes31and32on the outer surface of the electric discharge container2can be suppressed.

Another form of the third embodiment of an excimer lamp1is described, referring toFIGS. 8A and 8B.

FIGS. 8A and 8Bare explanatory diagrams of the excimer lamp1according to the embodiment.FIG. 8Ais a side elevational view of the excimer lamp1(a side elevational diagram, viewing from a side of the second external electrode32) which is viewed perpendicularly to a direction of the tube axis of the arc tube21.FIG. 8Bis a cross sectional view thereof (taken along a line E-E ofFIG. 8A), taken along a direction perpendicular to the tube axis direction of the arc tube21ofFIG. 8A. InFIGS. 8A and 8B, the same reference numerals as those ofFIGS. 7A and 7Bare assigned to structural parts which are the same as those shown inFIGS. 7A and 7B.

The excimer lamp1shown inFIGS. 8A and 8Bis different from that shown inFIGS. 6,7A and7B, in that inFIGS. 8A and 8B, three external electrodes31,32, and33are provided.FIGS. 8A and 8Bwill be described in terms of differences between the excimer lamp ofFIGS. 6,7A and7B and that ofFIGS. 8A and 8B.

The arc tube21of the excimer lamp1according to this embodiment is in a shape of a straight pipe, which is made of material having optical permeability with respect to 150-400 nm, and having little absorption of fluorine ions. The material of the arc tube21, is, for example, a metal oxide such as sapphire (single crystal alumina), or alumina (polycrystal alumina), whose principal component is an aluminum oxide (A2O3). In addition, a fluoride such as magnesium difluoride (MgF2), lithium fluoride (LiF), calcium difluoride (CaF2), barium difluoride (BaF2), or YAG (yttrium aluminum garnet) can be used as the material of the arc tube21. In addition, although quartz glass (SiO2) may be selected as the material having the optical permeability, since silica (Si) contained in quartz glass (SiO2) has high reactivity with fluorine ions, the quartz glass (SiO2) might not be used as the material of the arc tube21which is brought into contact with fluorine ions when the lamp1is lit. For this reason, material which does not contain silica (Si) is suitably used for the arc tube21which is made of material having little absorption of fluorine ions.

The arc tube21is opened at both ends in the longitudinal direction thereof, and cup-like lid portion members221and222are arranged at the both ends. The lid portion members221and222are formed of the so-called kovar, an alloy in which nickel (Ni) and cobalt (Co) is blended with iron (Fe). The material of the lid portion members221and222is not limited to such a metal. Since all that is required is that the material has ultraviolet light resistance, the lid portion member221and222may be made of material which is the same as that of the arc tube21, that is, for example, sapphire (single crystal alumina) whose main component is aluminum oxide (A2O3) etc.

Since sealing members231and232are filled up between the arc tube21and the lid portion members221and222, respectively, the arc tube21and the lid portion members221and222are respectively connected to each other, so that the electric discharge container2which is made up of the arc tube21, the lid portion members221and222, and the sealing members231and232is formed. Wax material for sealing which consists of an alloy of, for example, silver and copper (Ag—Cu alloy) may be used as the material of the sealing members231and232. Since the sealing members231and232are heated by lighting heat from the lamp1while ultraviolet rays are irradiated to the sealing members231and232when the lamp1is lit, material which has ultraviolet light resistance and thermal resistance may be used as that of the sealing members231and232. In particular, material with little absorption of fluorine ions, such as an alloy of silver and copper (Ag—Cu alloy), can suitably used.

A gas pipe2221is provided to the second lid portion member222. After air is discharged from an inner space24of the electric discharge container2via the gas pipe2221so that the pressure thereof is decreased, rare gas and a fluoride with high chemical stability is enclosed as a light emitting gas. After the enclosure of the light emitting gas, the sealing portion2222is formed by performing, for example, a pressure welding etc. to a gas pipe2221, so that the electric discharge container2is formed as a sealed structure. The light emitting gas enclosed in the inner space24of the electric discharge container2may be rare gas which is, for example, argon (Ar), krypton (Kr), or xenon (Xe), and a fluoride which is, for example, sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), or nitrogen trifluoride (NF3)

While, as shown inFIG. 8B, three external electrodes31,32, and33arranged on the outer surface of the arc tube21, so as to be electrically separated from one another, as shown inFIG. 8A, they are provided so as to extend along a direction of the tube axis of the arc tube21. Furthermore, the external electrodes31,32, and33are provided so as to be separated from the sealing members231and232and the lid portion members221and222.

The external electrodes31,32and33can be formed by applying material, such as copper in form of paste, to the outer surface of the arc tube21. Moreover, for example, strip-shaped aluminum can also be pasted on the outer surface of the arc tube21with an adhesive agent etc. Each of the leads41,42and43is electrically connected to one end of the external electrode with solder51,52or53etc. in a longitudinal direction of the external electrodes3132and33. Although not illustrated, the first lead41connected to the first external electrode31and the third lead43connected to the third external electrode33are connected electrically to each other. A power supply (not shown) is connected to the first and third leads41and43electrically connected to each other and the second lead42, and electric power is supplied when the lamp1is lit.

On the outer surface of the arc tube21, the grooves7are provided between the first and second external electrodes31and32, and the second and third external electrodes32and33. In the tube axis direction of the arc tube21, as shown inFIG. 8A, the grooves7are formed so as to extend over a range L1where the external electrodes31,32and33face each other, in the tube axis direction of the arc tube21. Moreover, as shown inFIG. 8B, in the circumferential direction of the arc tube21, the grooves7are respectively provided in portions L31between the first and second external electrodes31and32, and the second and third external electrodes32and33on the outer circumferential surface of the arc tube21. The grooves7can be formed by irradiating laser to the outer surface of the arc tube21made up of, for example, sapphire (single crystal alumina) whose principal component is aluminum oxide (A2O3).

Voltage is impressed between and the second external electrode32and the first and third external electrodes31and33to which the first and third leads41and43are connected electrically when the lamp1is lit, whereby electric discharge occurs, through the arc tube21, between the second external electrode32and the first and third external electrodes31and33to which the first and third leads41and43are electrically connected. When the rare gas of the light emitting gas is, for example, argon (Ar), and the fluoride is, for example, sulfur hexafluoride (SF6), they are ionized so that argon ions and fluorine ions are formed, whereby excimer molecules which are made up of argon-fluorine is formed, and light having approximately 193 nm wavelength is emitted from the arc tube21.

As shown inFIG. 8B, when the lamp1is lit, electric discharge which occurs between the second external electrodes32and the first and third external electrodes31and33is generated through the arc tube21in the range L1in the tube axis direction of the arc tube21, in which the external electrodes31,32and33face one another. When the arc tube21is made of material which does not contain silica (Si), as material with little absorption of fluorine ions, it is possible to prevent the arc tube21from absorbing the ionized fluorine ions.

When the external electrodes31,32and33are provided so as to be separately placed from the sealing members231and232and the lid portion members221and222in the tube axis direction of the arc tube21, in the inner space24of the electric discharge container2, no electric discharge occurs in a range L2extending from the end portions of the range L1where the external electrodes31,32and33in the tube axis direction of the arc tube21face one another, to the sealing members231and232which are located near there. For this reason, when material such as sulfur hexafluoride (SF6), with high chemical stability, is filled as the light emitting gas, in the inner space24of the electric discharge container2, since no electric discharge occurs in the range L2from the end portions of the range L1where the external electrodes31,32and33in the direction of the tube axis of the arc tube21face one another, to the respective sealing members231and232which are located near there, the fluorine ions ionized by the electric discharge return to, for example, sulfur hexafluoride which was before the ionization. Thereby, in the inner space24of the electric discharge container2, as compared with the range L1where the external electrodes31,32and33in the tube axis direction of the arc tube21, face one another, the fluorine ions decrease extremely in the range L2from the end portions of the range L1where the external electrodes31,32and33in the tube axis direction of the arc tube21face one another, to the sealing members231and232which are located near there. That is, since it is possible to suppress contacts of fluorine ions with the sealing members231and232, it is possible to prevent decrease of the fluorine ions in the inner space24of the electric discharge container2when the lamp1is lit, and the illuminance reduction of the lamp1due to decrease of the fluorine ions can be prevented.

In order to use the excimer lamp1according to the embodiment as an ultraviolet rays light source for photochemical reaction, it is necessary to stably start electric discharge. Furthermore, generation of electrons which have high energy required for generating excimer molecules is required for the excimer lamp1. However, the chemical stability of the fluoride enclosed in the inner space24of the electric discharge container2is high. That is, a fluoride with the high chemical stability, which is sulfur hexafluoride (SF6), carbon tetrafluoride (CF4), or nitrogen trifluoride (NF3) is gas having high electron attachment nature (in other words, it exhibits the property of capturing electrons, largely). For this reason, since electrons produced by ionization are captured with high probability, breakdown voltage thereof becomes higher than that of the conventional lamp1in which fluorine (F2) gas is enclosed. Furthermore, in order to generate electrons with high energy, applied voltage needs to be high. Moreover, in the case of the excimer lamp1according to the embodiment, in order to obtain sufficient illuminance, 100 Torr or more of light emitting gas needs to be enclosed in the electric discharge container2. As in the excimer lamp1according to the first embodiment shown inFIGS. 1,2A and2B, in case where it has the structure in which the external electrodes31and32are provided on the outer surface of the arc tube21, when high voltage is impressed to the external electrodes31and32, the so-called creeping discharge in which discharge occurs along a surface of the arc tube21between the external electrodes31and32, is generated.

As in the excimer lamp1according to this embodiment, at least on the outer surface of the arc tube21, the grooves7are provided in the circumferential direction of the arc tube21and extends along the longitudinal direction of the external electrodes31,32and33, in the portion31L between the second external electrode32and the first and third external electrodes31and33, so that it is possible to suppress creeping discharge. That is, when the grooves7are formed between the first and second external electrodes31and32and between the second and third external electrodes32and33where potential difference is generated when the lamp1is lit, creeping distances between the first and second external electrodes31and32, and between the second and third external electrodes32and33are extended, so that it is possible to suppress the creeping discharge.

In addition, it is not necessary to form grooves in the portion L32between the first external electrode31and the third external electrode33on the outer circumferential surface of the arc tube21, since potential difference is not generated there when the lamp1is lit.

The excimer lamp1according to this embodiment, comprises the electric discharge container2in which the sealing members231and232are provided in the arc tube21which does not contain silica, and at least external electrodes31,32and33which are separately provided from one another on the outer surface of the arc tube21, wherein rare gas and a fluoride are enclosed in the electric discharge container2, and further the fluoride is sulfur hexafluoride, carbon tetrafluoride, or nitrogen trifluoride. Since the chemical stability of the fluoride enclosed in the electric discharge container2is high, the ionized fluorine ions can return to a fluoride even at time of lighting of the lamp1, in the range L2from the end portions of the range L1where the external electrodes31,32and33face one another in the inner space24of the electric discharge container2, to the respective sealing members which are located near there. Since it is possible to control contacts of the sealing members231and232and the fluorine ions, absorption of the fluorine ions in the sealing members231and232can be suppressed. That is, according to the feature, in the excimer lamp1according to this embodiment, the illuminance fall due to the absorption of the fluorine ions in the sealing members231and232can be suppressed, so that an illuminance thereof can be maintained for a long time.

When on the outer surface of the arc tube21, the grooves7are provided between the first and second external electrodes31and32, and the second and third external electrodes32and33, creeping distance between the first and second external electrodes31and32, and between the second and third external electrodes32and33can be extended. Therefore, it is possible to suppress the creeping discharge between the second external electrodes and the first and third electrodes31and33on the outer surface of electric discharge container2.

In order to check the effects of the excimer lamp1according to the embodiments, the following Experiments 1 and 2 were conducted.

In the Experiment 1, the effects of the excimer lamp1according to the first embodiment were checked.

As Comparative Example 1, an excimer lamp1of the prior art shown inFIGS. 11,12A and12B was prepared, in which 100 Torr of argon (Ar) and a fluorine (F2) was enclosed in the inner space24of the electric discharge container2. The amount (99.9%) of argon (Ar) and that (0.1%) of the fluorine (F2) was enclosed. The wax material which was made up of an alloy (Ag—Cu alloy) of silver and copper was used for the sealing members231and232.

The excimer lamp1according to the first embodiment, shown inFIGS. 1,2A and2B, was prepared, in which 100 Torr of argon (Ar) and a sulfur hexafluoride (SF6) was enclosed in the inner space24of the electric discharge container2. The amount (99.9%) of the argon (Ar) and that of (0.1%) the sulfur hexafluoride (SF6) was enclosed. The wax material which was made up of an alloy (Ag—Cu alloy) of silver and copper was used for the sealing members231and232.

While impressing voltage of 3 kV to the external electrodes31and32of the excimer lamp1of the Comparative Example 1 and that of the first embodiment, each illuminance was measured, and further a period (life span) in which the illuminance could be maintained was measured.

FIG. 9shows a table of the experimental result. The optical intensity shown inFIG. 9represents the relative value when the illuminance of the Comparative Example 1 is set to a reference value.

As shown inFIG. 9, in the Comparative Example 1, the illuminance could not be maintained in 10 hours. This is considered to be due to absorption of the ionized fluorine ions by the sealing members231and232.

On the other hand, since in the excimer lamp1according to the first embodiment, energy is required to ionize the sulfur hexafluoride (SF6), the illuminance was decreased. However, the illuminance could be maintained for 1,000 hours or more. It is considered that since the chemical stability of the sulfur hexafluoride (SF6) is high, the ionized fluorine ions could return to sulfur hexafluoride (SF6), whereby absorption thereof in the sealing members231and232could be suppressed. Therefore, in the excimer lamp1according to the first embodiment, since a fluoride having high chemical stability was used as the light emitting gas, it was possible to suppress absorption of fluorine ions in the sealing members231and232so that the illuminance could be maintained for a long time.

In Experiment 2, it was checked whether even if the excimer lamp1according to the second and third embodiments was operated with the illuminance of the excimer lamp1of the prior art, creeping discharge would be prevented and the illuminance would be maintained.

As Comparative Example 1, the excimer lamp1of the prior art shown inFIGS. 11,12A and12B was prepared, and 100 Torr of argon (Ar) and fluorine (F2) was filled in the inner space24of the electric discharge container2. The amount (99.9%) of the argon (Ar) and that of (0.1%) the fluorine (F2) was enclosed. Wax material which was made up of an alloy (Ag—Cu alloy) of silver and copper was used for the sealing members231and232. This lamp1was the same as that of the Comparative Example 1 used for Experiment 1. The outer diameter of the arc tube21was 10 mm, and the voltage impressed to the external electrodes31and32was 5 kV when the lamp1is lit.

Moreover, an excimer lamp1according to the first embodiment shown inFIGS. 1,2A and2B was prepared as Comparative Example 2, in which 100 Torr of argon (Ar) and sulfur hexafluoride (SF6) was filled in the inner space24of the electric discharge container2. The amount of (99.9%) argon (Ar) and that (0.1%) of the sulfur fluoride (SF6) was enclosed therein. Wax material which was made up of an alloy (Ag—Cu alloy) of silver and copper was used for the sealing members231and232. The outer diameter of the arc tube21was 10 mm, and the voltage impressed to the external electrodes31and32was 3 kV when the lamp1was lit.

An excimer lamp1according to the second embodiment shown inFIGS. 3,4A and4B was prepared. Three kinds of excimer lamps A, B and C as the excimer lamp1were prepared. In the inner space24of the electric discharge container2of the lamp A, 100 Torr of argon (Ar) and sulfur hexafluoride (SF6) was filled. In the inner space24of the electric discharge container2of the lamp B, 100 Torr of argon (Ar) and carbon tetrafluoride (CF4) was filled. In the inner space24of the electric discharge container2of the lamp C, 100 Torr of argon (Ar) and nitrogen trifluoride (NF3) was filled. In the Lamp A, the amount (99.9%) of the argon (Ar) and that (0.1%) of the sulfur hexafluoride (SF6) was enclosed therein. In the Lamp B, the amount (99.9%) of the argon (Ar) and that (0.1%) of the carbon tetrafluoride (CF4) was enclosed therein. In the Lamp C, the amount (99.9%) of the argon (Ar) and that (0.1%) of the nitrogen trifluoride (NF3) was enclosed therein. Wax material which was made up of an alloy (Ag—Cu alloy) of silver and copper was used for the sealing members231and232of the lamps A, B, and C, respectively. The insulator6was formed by applying, for example, paste in which silica particles are dispersed in organic solvent, so as to cover the outside portions of the external electrodes31and32, and sintering the applied paste. The outer diameter of the arc tube21was 10 mm, and the voltage impressed to the external electrodes31and32was 7 kV when the lamp1was lit.

Moreover, the excimer lamp1according to the third embodiment shown inFIGS. 6,7A and7B was prepared as an example. Three kinds of excimer lamps D, E and F as the excimer lamp1were prepared. In the inner space24of the electric discharge container2of the lamp D, 100 Torr of argon (Ar) and sulfur hexafluoride (SF6) was filled. In the inner space24of the electric discharge container2of the lamp E, 100 Torr of argon (Ar) and carbon tetrafluoride (CF4) was filled. In the inner space24of the electric discharge container2of the lamp F, 100 Torr of argon (Ar) and nitrogen trifluoride (NF3) was filled. In the Lamp D, the amount (99.9%) of the argon (Ar) and that (0.1%) of the sulfur hexafluoride (SF6) was enclosed therein. In the Lamp E, the amount (99.9%) of the argon (Ar) and that (0.1%) of the carbon tetrafluoride (CF4) was enclosed therein. In the Lamp C, the amount (99.9%) of the argon (Ar) and that (0.1%) of the nitrogen trifluoride (NF3) was enclosed therein. Wax material which was made up of an alloy (Ag—Cu alloy) of silver and copper was used for the sealing members231and232of the lamps D, E, and F, respectively. The outer diameter of the arc tube21was 10 mm, and the voltage impressed to the external electrodes31and32was 8 kV when the lamp1was lit. The depth of the grooves7of the respective lamps D, E, and F was 0.3 mm and the width of the grooves in the circumferential direction of the arc tube21was 0.3 mm. The grooves7whose number was twelve were formed on the outer circumferential surface of the arc tube21. In the lamps A, B, and C according to the third embodiment, a creeping distance between the electrodes31and32was from 7 mm to 10.6 mm.

When voltage was impressed to each lamp1, the illuminance of each lamp1was measured, and further a period (life span) in which the illuminance could be maintained was measured.FIG. 10shows a table the experimental result. The optical intensity shown inFIG. 10represents the relative value when the illuminance of Comparative Example 1 is set to a reference value.

In Comparative Example 2, when applied voltage was 5 kV, the optical intensity was 0.7. However, creeping discharge occurred so that voltage of 5 kV or more could not be impressed. It is considered that since sulfur hexafluoride (SF6) with high chemical stability were hard to be ionized, electric discharge did not occur in the inner space24of the discharge tube2, so that the electric discharge (creeping discharge) occurred on the side face.

In the lamps A, B, and C according to the second embodiment, the optical intensity was 1.1 when the applied voltage was 7 kV, so that the illuminance which was higher than that of the lamp1of the prior art was obtained. Furthermore, the life span hours was one thousand hours (1,000) or more, during which creeping discharge was not generated. This is considered that it was possible to prevent the creeping discharge by the formation of the insulator6on the external electrodes31and32. In connection with this, the voltage impressed to the external electrodes could also be raised to 7 kV, so that the higher illuminance than that of the prior art could be obtained. Moreover, in the excimer lamp1according to the second embodiment, compared with the excimer lamp1of the prior art, absorption of the fluorine ions in the sealing members231and232could be suppressed by using a fluoride with high chemical stability as the light emitting gas, so that the illuminance could be maintained for a long time.

In the lamps A, B, and C according to the third embodiment, the optical intensity was 1.2 when the applied voltage was 8 kV, so that the illuminance which was higher than that of the lamp1of the prior art was obtained. Furthermore, the life span hours was one thousand (1,000) or more, during which creeping discharge was not generated. This is considered that it was possible to prevent the creeping discharge by the formation of the grooves7on the external electrodes31and32. In connection with this, the voltage impressed to the external electrodes could also be raised to 8 kV, so that the higher illuminance than that of the prior art could be obtained. Moreover, in the excimer lamp1according to the third embodiment, compared with the excimer lamp1of the prior art, absorption of the fluorine ions in the sealing members231and232could be suppressed by using a fluoride with high chemical stability as the light emitting gas, so that the illuminance could be maintained for a long time.

Therefore, since in the excimer lamp1according the second and third embodiments, in the circumferential direction of the arc tube21, the insulator6was formed so as to cover the external electrodes31and32or the grooves7were formed between the external electrodes31, and32, it was possible to prevent creeping discharge so that voltage applied thereto could be raised. Therefore, in the excimer lamp according to the second and third embodiments, as compared with the excimer lamp1of the prior art, it was possible to achieve longer life span and and to obtain higher illuminance.