Gas electron multiplier and manufacturing method for gas electron multiplication foil used for same as well as radiation detector using gas electron multiplier

To attain objects to reduce the spread of electrons as compared with a conventional one without degrading the multiplication factor of electrons; to provide a large electron multiplication factor; and to improve positional resolution, there is provided a gas electron multiplier using interaction between radiation and gas through photoelectric effects including: a chamber filled with gas and a single gas electron multiplication foil arranged in the chamber wherein the gas electron multiplication foil is made of a plate-like multilayer body composed by having a plate-like insulation layer made of a macromolecular polymer material having a thickness of around 100 μm to 300 μm and flat metal layers overlaid on both surfaces of the insulation layer, and the plate-like multilayer body is provided with a through-hole structure.

TECHNICAL FIELD

The present invention relates to a gas electron multiplier and a manufacturing method for a gas electron multiplication foil used for the same as well as a radiation detector using a gas electron multiplier, and in particular, to a gas electron multiplier using the interaction between radiation and gas through the photoelectric effect, and a manufacturing method for a gas electron multiplication foil used for the same as well as a radiation detector using a gas electron multiplier.

BACKGROUND ART

Conventional gas electron multipliers (GEM) have been used to detect radiation, such as charged particles, gamma rays, x-rays, neutrons and ultraviolet rays.

When the radiation, which is the detection target, enters such a gas electron multiplier, it uses electron avalanche effects to multiply photoelectrons released from gas atoms as a result of the interaction between radiation and a gas through photoelectric effects and enables to detect the radiation as an electrical signal.

FIG. 1is a cross sectional diagram schematically showing a configuration of a radiation detector using a conventional gas electron multiplier.

The radiation detector100shown inFIG. 1is composed of an outer chamber102filled with a predetermined gas for detection, and detector elements inside the chamber102, which are a drift electrode104and a collecting electrode106, and a first gas electron multiplication foil (GEM foil)108and a second gas electron multiplication foil110placed between the drift electrode104and the collecting electrode106at a predetermined distance TR.

Here, as the gas for detection to be filled in the chamber102, mixed gas of rare gas and quencher gas is generally used. For example, the rare gas may be He, Ne, Ar, Xe or the like and the quencher gas may be CO2, CH4, C2H6, CF4or the like. In addition, the fraction of the quencher gas mixed with the rare gas is appropriate to be 5% to 30%.

Here, the chamber102filled with the predetermined gas for detection, the first gas electron multiplication foil108and the second gas electron multiplication foil110form a gas electron multiplier. The first gas electron multiplication foil108and the second gas electron multiplication foil110, each of which is made of a plate-like multilayer body having the same configuration, are to provide a function to multiply charge using electron avalanche effects.

In further detail, the first gas electron multiplication foil108(the second gas electron multiplication foil110) is composed of a plate-like insulation layer108a(110a) made of resin having a thickness t0of 50 μm, and flat metal layers108band108c(110band110c) overlaid on both surfaces of the insulation layer108a(110a). In addition, a large number of through-holes108d,110dare formed for condensing the electrical field in the first gas electron multiplication foil108and the second gas electron multiplication foil110, respectively.

In addition, the radiation detector100is equipped with a power supply section112for applying voltage to the metal layers108b,108c,110b,110cand the drift electrode104, and a detecting unit114connected to the collecting electrode106.

In the above described configuration, a predetermined voltage is applied from the power supply section112to the metal layers108b,108c,110b,110cand the drift electrode104in the radiation detector100so as to generate an electric field Ed between the drift electrode104and the metal layer108b, an electric field Et between the metal layer108cand the metal layer110b, with which the electric fields inside of the through-hole structures108dand110dare generated, and an electric field Ei between the metal layer110cand the collecting electrode106.

In this situation, the electric field Et is condensed inside the through-hole structures108dand110d, and electrons that have entered are accelerated to cause the electron avalanche effects. Then, the collecting electrode106detects the electrons multiplied through the electron avalanche effects and the detecting section114receives a detection signal to deduce various types of detection data.

Here, in the gas electron multiplier of the above described radiation detector100, gas electron multiplication foils in two stages having the first gas electron multiplication foil108and the second gas electron multiplication foil110are used in order to gain a large multiplication factor of electrons due to the electron avalanche effects.

That is to say, a conventional gas electron multiplier has a structure where multiple layers of gas electron multiplication foils are used in stages in order to increase the multiplication factor of electrons.

Meanwhile, photoelectrons released when interaction between radiation and a gas occurs spread approximately several hundreds of μm.

Spread of electrons increases every time the electrons pass through a gas electron multiplication foil, and therefore, position resolution gets worse and precise position information cannot be attained, and consequently, a problem arises where an image obtained in the detecting section becomes blurred.

Detection is possible using Compton scattering or electron pair generation in addition to the photoelectric effects.

Here, the conventional art known by the present applicant at the time of the filing of the patent application is described in the above and does not relate to an invention that has been documented, and therefore, there is no conventional art information to be described.

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

The present invention is provided in view of the above described problems of the prior art, and an object thereof is to provide a gas electron multiplier which enables to reduce the spread of electrons compared with the conventional one without degrading the multiplication factor of electrons, has a large multiplication factor of electrons, and is excellent in positional resolution, and a manufacturing method for a gas electron multiplication foil used for the same as well as a radiation detector using this gas electron multiplier.

Means for Solving Problem

In order to achieve the above described object, the gas electron multiplier and the manufacturing method for a gas electron multiplication foil used for the same as well as the radiation detector using a gas electron multiplier according to the present invention is configured to use a single electron multiplication foil and the thickness of the insulation layer of the electron multiplication foil is made larger than the conventional electron multiplication foils.

In addition, the gas electron multiplier and the manufacturing method for a gas electron multiplication foil used for the same as well as the radiation detector using a gas electron multiplier according to the present invention is configured to use a single electron multiplication foil and the electron multiplication foil is composed of a multilayer body where insulation layer thereof is made in a multilayer structure and metal layers are provided between the respective insulation layers.

With the gas electron multiplier and the manufacturing method for a gas electron multiplication foil used for the same as well as the radiation detector using a gas electron multiplier according to the present invention, spreading of electrons can be reduced compared with the prior art without lowering the multiplication factor of electrons, and a positional resolution can be improved while keeping a large multiplication factor of electrons.

Specifically, the present invention provides a gas electron multiplier using interaction between radiation and gas through photoelectric effects, which includes a chamber filled with gas, and a single gas electron multiplication foil arranged in the chamber, wherein the gas electron multiplication foil is made of a plate-like multilayer body composed of a plate-like insulation layer made of a macromolecular polymer material having a thickness of around 100 μm to 300 μm and flat metal layers overlaid on both surfaces of the insulation layer, and the plate-like multilayer body is provided with a through-hole structure.

In addition, the present invention provides a gas electron multiplier using interaction between radiation and gas through photoelectric effects, which includes a chamber filled with gas, and a single gas electron multiplication foil arranged in the chamber, wherein the gas electron multiplication foil is made of a plate-like multilayer body which is composed of a multilayer body where multiple plate-like insulation layers made of a macromolecular polymer material are stacked with a flat metal layer sandwiched in between and flat metal layers overlaid on both surfaces of the multilayer body, and the plate-like multilayer is provided with a through-hole structure.

In addition, according to the present invention as described above, the total thickness of the multiple insulation layers is around 100 μm to 600 μm.

In addition, the present invention provides a radiation detector utilizing a gas electron multiplier using interaction between radiation and gas through photoelectric effects, wherein the gas electron multiplier is provided according to invention as described above.

In addition, the present invention provides a manufacturing method for a gas electron multiplication foil used in a gas electron multiplier using interaction between radiation and gas through photoelectric effects. At first, flat metal layers are placed on both surfaces of a plate-like insulation layer made of a macromolecular polymer material having a thickness of around 100 μm to 300 μm. The metal layers are etched according to a predetermined hole pattern, and laser beam is irradiated to remove insulator material perpendicularly to the plane of the metal layers to create a through-hole extending in the direction perpendicular to the plane of the metal layers in accordance with the etched pattern of the metal layers. Finally, a desmear process is performed using plasma and chemicals on a surfaces of the metal layers and a wall surface of the through-hole in the insulation layers.

In addition, the present invention provides a manufacturing method for a gas electron multiplication foil used in a gas electron multiplier using interaction between radiation and gas through photoelectric effects. Flat metal layers are placed on both surfaces of a plate-like insulation layer made of a macromolecular polymer material having a thickness of around 50 μm to 300 μm. The metal layers are etched to a predetermined pattern, and a resultant of overlaying a flat metal layer on one surface of a plate-like insulation layer made of a macromolecular polymer material having a thickness of around 50 μm to 300 μm, on one or both surfaces of the metal layers. Outermost metal layers of the resultant are etched in the stacking step in accordance with the predetermined pattern, and all of the insulating films are laser-etched through irradiation with a laser beam applied perpendicularly to the plane of the outermost metal layers in accordance with the predetermined pattern; creating through-holes extending in the direction perpendicular to the plane of the metal layers on the outermost surfaces. Finally, carried out is a desmear process using plasma and a chemical on surfaces of the metal layers and a wall surface of the through-hole in the insulation layers.

Effects of the Invention

According to the present invention, excellent effects can be attained such that a gas electron multiplier, which allows to reduce the spread of electrons as compared with a conventional one without degrading the multiplication factor of electrons, has a large electron multiplication factor and is excellent in the position resolution, and a manufacturing method for a gas electron multiplication foil used for the same as well as a radiation detector using a gas electron multiplier can be provided.

EXPLANATION OF SYMBOLS

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, a gas electron multiplier and a manufacturing method for a gas electron multiplication foil used for the same as well as a radiation detector using a gas electron multiplier according to an embodiment of the present invention are described in detail in reference to the accompanying drawings.

Here, in the following description, the same reference numerals are designated to components having the same or equivalent configurations as those described before in reference to a figure, such asFIG. 1, and the detailed description of the configurations and working effects will not be repeated.

FIG. 2is a cross sectional diagram schematically showing a configuration of a radiation detector using a gas electron multiplier according to a first embodiment of the present invention.

This radiation detector10is different from the conventional radiation detector100in that the gas electron multiplier is composed by having a chamber102filled with a predetermined gas for detection and a single gas electron multiplication foil12.

Here, the gas electron multiplication foil12is composed by having a plate-like insulation layer12amade of resin, and flat metal layers12band12coverlaid on both surfaces of the insulation layer12a. In addition, multiple through-hole structures12dwhich extend in a direction perpendicular to the plane of the metal layers12band12care formed in the gas electron multiplication foil12as through-hole structures for condensing an electric field.

In addition, the thickness t1of the insulation layer12ais greater than t0of the insulation layer of the conventional gas electron multiplication foil, and is set to 100 μm, for example. The thickness of the insulation layer12amay be set to an appropriate value in a range from approximately 100 μm to 300 μm.

Here, in the case where the thickness t1of the insulation layer12ais 100 μm, a voltage of approximately 700 V to 1000 V can be applied across the metal layers12band12cfrom the power supply section112.

As the material for the insulation layer12a, a macromolecular polymer material, such as polyimide or a liquid crystal polymer, can be used.

Meanwhile, as the material for the metal layers12band12c, which function as electrodes for generating an electric field inside the through-hole structures12d, copper, aluminum, gold or boron, for example, can be used. Here, in order to form the metal layers12band12con the insulation layer12a, such a technique as lamination, sputtering vapor deposition or plating may be used, and the thickness of the metal layers12band12cis set to approximately 5 μm, for example.

In the radiation detector10according to the above described configuration, a predetermined voltage is applied to the metal layers12band12cand the drift electrode104from the power supply section112, and then an electric field Ed is generated between the drift electrode104and the metal layer12b, an electric field Et is generated inside the through-hole structures12d, and an electric field Ei is generated between the metal layer12cand the collecting electrode106.

The electric field Et is condensed inside the through-hole structures12dso that electrons that have entered are accelerated to cause the electron avalanche effects. Then, the collecting electrode106detects the electrons multiplied through the electron avalanche effects and the detecting section114receives a detection signal to deduce various types of detection data.

The radiation detector10has a single gas electron multiplication foil12only, and therefore, the spreading of electrons can be reduced as compared with the case using the multiple conventional gas electron multiplication foils.

In addition, the thickness t1of the insulation layer12ais larger than the thickness t0of the insulation layer of conventional gas electron multiplication foils, and therefore, the value of the voltage applied to the metal layers12band12cand the drift electrode104from the power supply section112can be set higher than the value of the voltage applied to the gas electron multiplication foils and the drift electrode in case of conventional radiation detectors, and therefore, the multiplication factor of electrons is not degraded, as compared with a conventional one.

Next,FIG. 3is a cross sectional diagram schematically showing a configuration of a radiation detector using a gas electron multiplier according to the second embodiment of the present invention.

This radiation detector20is different from the conventional radiation detector100in that the gas electron multiplier is composed of a chamber102filled with a predetermined gas for detection and a single gas electron multiplication foil22.

Here, the gas electron multiplication foil22includes a multilayer structure composed of a multilayer body where multiple plate-like insulation layers made of resin and metal layers are alternately layered.

In further detail, the gas electron multiplication foil22includes a plate-like insulation layer22a-1made of resin and a plate-like insulation layer22a-2made of resin, and a flat metal layer22ebetween the insulation layer22a-1and the insulation layer22a-2. Furthermore, a flat metal layer22bis formed on an opposite side of the insulation layer22a-1to the surface where the metal layer22eis formed, while a flat metal layer22cis formed on an opposite surface of the insulation layer22a-2from the one where the metal layer22eis formed. In addition, multiple through-hole structures22dfor condensing an electrical field are formed in the gas electron multiplication foil22.

The sum of the thickness t2-1of the insulation layer22a-1and the thickness t2-2of the insulation layer22a-2is greater than the thickness t0of the insulation layers in conventional gas electron multiplication foils, and is set to 100 μm, for example. The thickness t2-1of the insulation layer22a-1and the thickness t2-2of the insulation layer22a-2may be set to appropriate values in a range from approximately 50 μm to 300 μm, for example. The sum of the thickness t2-1of the insulation layer22a-1and the thickness t2-2of the insulation layer22a-2may be set to an appropriate value in a range from approximately 100 μm to 600 μm, for example.

Here, in this embodiment, the thickness t2-1of the insulation layer22a-1and the thickness t2-2of the insulation layer22a-2are both 50 μm, so that the sum of the thickness t2-1of the insulation layer22a-1and the thickness t2-2of the insulation layer22a-2is 100 μm.

In the case where the thicknesses t2-1and t2-2of the insulation layer22a-1and22a-2are 50 μm, a voltage of approximately 350 V to 500 V can be applied across the metal layers22band22e, as well as across the metal layers22eand22c, from the power supply section112, while in the case where the thicknesses t2-1and t2-2of the insulation layer22a-1and22a-2are 100 μm, a voltage of approximately 700 V to 1000 V can be applied across the metal layers22band22e, as well as across the metal layers22eand22c, from the power supply section112.

As the material for the insulation layers22a-1and22a-2, a macromolecular polymer material, such as polyimide or a liquid crystal polymer, for example, can be used.

Meanwhile, as the material for the metal layers22b,22cand22ewhich function as electrodes for generating an electric field inside the through-hole structures22d, copper, aluminum, gold or boron, for example, can be used. Here, in order to form the metal layers22b,22cand22eon the insulation layers22a-1and22a-2, such a technique as lamination, sputtering vapor deposition or plating may be used, and the thickness of the metal layers22b,22cand22eis set to approximately 5 μm, for example.

In the radiation detector20according to the above described configuration, a predetermined voltage is applied to the metal layers22b,22cand22eand the drift electrode104from the power supply section112and then an electric field Ed is generated between the drift electrode104and the metal layer22b, an electric field Et is generated inside the through-hole structures22d, and an electric field Ei is generated between the metal layer22cand the collecting electrode106.

The electric field Et is condensed inside the through-hole structures22dso that electrons that have entered are accelerated to cause the electron avalanche effects. Then, the collecting electrode106detects the electrons multiplied through the electron avalanche effects and the detecting section14receives the detection signal to deduce various types of detection data.

The radiation detector20has a single gas electron multiplication foil22only, and therefore, the spreading of electrons can be reduced compared with the case using the multiple conventional gas electron multiplication foils.

In addition, sum of the thickness t2-1of the insulation layer22a-1and the thickness t2-2of the insulation layer22a-2is greater than the thickness t0of the insulation layer of conventional gas electron multiplication foils, and therefore, the value of the voltage applied to the metal layers22b,22cand22eand the drift electrode104from the power supply section112can be set higher than the value of the voltage applied to the gas electron multiplication foils and the drift electrode by conventional radiation detectors, and therefore, the multiplication factor of electrons is not degraded, as compared with a conventional one.

Furthermore, in the radiation detector20, the electrical field Et generated between the metal layer22band the metal layer22cis rectified by applying a voltage to the metal layer22e, thereby causing electron avalanche effects efficiently.

Next, the results of experiments by the present inventors using the above described conventional radiation detector100, the radiation detector10using a gas electron multiplier according to the first embodiment of the present invention and the radiation detector20using a gas electron multiplier according to the second embodiment of the present invention are described.

Here, in the radiation detector100used in the experiments, polyimide having a thickness t0of 50 μm was used as the insulation layers108aand110a, copper having a thickness of 5 μm was used as the metal layers108b,108c,110band110c, and a voltage of 350 V to 450 V was applied across the metal layers108band108c, as well as across the metal layers110band110cfrom the power supply section112.

In case of the radiation detector10used in the experiments, liquid crystal polymer having a thickness t1of 100 μm was used as the insulation layer12a, copper having a thickness of 5 μm was used as the metal layers12band12c, and a voltage of 700 V was applied across the metal layers12band12cfrom the power supply section112.

Furthermore, in the radiation detector20used in the experiments, liquid crystal polymer having a thickness t2-1and t2-2of 50 μm was used as the insulation layers22a-1and22a-2, copper having a thickness of 5 μm was used as the metal layers22b,22cand22e, and a voltage of 700 V was applied across the metal layers22band22cfrom the power supply section112.

Here, in the experiments, a pixel detector for reading a charge was used as the detecting section114. In addition, the drift region DR was 5.5 mm and the induction region IR was 2.7 mm in all of the radiation detectors10,20and100. The distance TR between the first gas electron multiplication foil108and the second gas electron multiplication foil110in the radiation detector100was 2.0 mm.

As for a measuring method, the spread of signals (electrons) was determined by measuring the spread of the reaction points of X-rays (5.9 keV) from a55Fc radiation source.

FIG. 4(a) is a graph showing the results of measurement by the radiation detector10,FIG. 4(b) is a graph showing the results of measurement by the radiation detector20, andFIG. 4(c) is a graph showing the results of measurement by the radiation detector100. Here, in the graphs shown inFIGS. 4(a),4(b) and4(c), the longitudinal axis indicates the number of counts N [count] and the lateral axis indicates the spread of signals [10 μm].

From the graphs inFIGS. 4(a),4(b) and4(c), it can be seen that the measured value for the spread of signals in the radiation detector10was 353 μm (FWHM), the measured value for the spread of signals in the radiation detector20was 344 μm (FWHM), and the measured value for the spread of signals in the radiation detector100was 608 μm (FWHM).

Thus, the spread of electrons was smaller in the radiation detectors10and20than in the radiation detector100.

Next,FIG. 5is a cross sectional diagram showing an example of the configuration of a two-dimensional image detector of X-rays using the gas electron multiplier according to the first embodiment of the present invention.

In this two-dimensional image detector200, a mixed gas where 30% of carbon dioxide (CO2) is mixed with argon (Ar) is filled in a chamber102as a gas for detection. In the chamber102, a single gas electron multiplication foil12is placed between a drift electrode104and a collecting electrode106and a predetermined voltage is applied across the drift electrode104and the metal layers12band12cof the gas electron multiplication foil12from the power supply section112.

In addition, the detecting section114is provided with a thin film transistor202for each pixel and configured to output a detection signal for each pixel.

With the two-dimensional image detector200as such configured, X-rays entered into the chamber102act on the gas for detection to generate electrons. These electrons are accelerated by the gas electron multiplying foil12, so that the electrons are multiplied to approximately 100 times to 100,000 times as a result of electron avalanche effects, and are detected by the detecting section114.

Accordingly, when the two-dimensional image detector200is used, X-rays can be detected with high efficiency and a clear image can be attained.

Such two-dimensional image detector200can be applied to medical X-ray machines, CT machines and detectors mounted in dosage monitors, for example.

Next,FIGS. 6 and 7are cross sectional diagrams showing different examples of the configuration of a photodetector using the gas electron multiplier according to the first embodiment of the present invention.

Here, the photodetector300shown inFIG. 6is different from the two-dimensional image detector200shown inFIG. 5in that a photoelectric layer302is formed on the metal layer12bof the gas electron multiplication foil12.

With the photodetector300as such configured, when light such as ultraviolet rays or visible light enters into the chamber102, photoelectrons are generated by the photoelectrical layer302then electrons are multiplied in the electrical fields inside the through-hole structures12dformed in the gas electron multiplication foil12. The multiplied electrons are detected by the detecting section114, as in the two-dimensional image detector200shown inFIG. 5.

In addition, the photodetector400shown inFIG. 7is different from the two-dimensional image detector200shown inFIG. 5in that a photoelectric layer402is formed on the inner surface of the entrance window.

With the photodetector400as such configured, when light such as ultraviolet light or visible light enters into the chamber102, photoelectrons are generated by the photoelectrical layer402and after that, electrons multiplied according to the same procedure as in the photodetector300are detected by the detecting section114.

Next, with reference toFIGS. 8(a) to8(d), the manufacturing method for a gas electron multiplication foil12in a gas electron amplifier according to the first embodiment of the present invention is described.

That is to say, in order to manufacture the gas electron multiplication foil12, at first flat metal layers12band12care overlaid on both surfaces of the plate-like insulation layer12amade of a liquid crystal polymer having a thickness of 100 μm, for example, and after a pre-process carried out on the surfaces of the metal layers12band12c, a resist layer500is formed (seeFIG. 8(a)). Here, for example, copper can be used for the metal layers12band12c, and a dry film resist (AQ2558, made by Asahi Kasei Corporation) for the resist layer500.

Then, the resist layer500is patterned to have aligned with the locations of the through-hole structures12d, and then openings are created in the metal layers12band12cin accordance with the above described patterning (seeFIG. 8(b)). The patterning described above can be carried out by vacuum contact exposure with an exposure dose of 60 mJ/cm2using a mask for exposure having a predetermined pattern, and then developing using a solution of 1% sodium carbonate. The openings can be created in the metal layers12band12cthrough etching using a solution of ferric chloride, for example, in the case where the metal layers12band12care made of copper.

Next, the resist layer500is removed using a solution of 3% sodium hydroxide, for example (seeFIG. 8(c)), and the portion of the insulation layer12ais removed by irradiating a laser beam such as a CO2laser, thus through-holes are created to form through-hole structures12d(seeFIG. 8(d)).

When portions of the insulation layer12aare removed using a laser beam to create through-holes, the laser beam is directed so that the walls of the through-hole structures12dbecome perpendicular to the plane of the metal layers12band12c.

Here, it is preferable to make smooth the surface of the walls of the through-hole structures12dformed in the step shown inFIG. 8(d) in the surface finishing step. This can prevent the walls of the through-hole structures12dfrom charge deposition during the operation of the gas electron multiplier.

In the surface finishing step, plasma etching is carried out for three minutes each on the front surface and rear surface under the conditions where the gas ratio is SF6:0.05, N2:0.10, O2:1.0 and the RF output is 2.1 kW, so that a soot-like substance attached on the walls of the through-hole structures12dis removed through irradiation of the above described laser beam.

Next, the surface of the walls of the through-hole structures12dis processed with a permanganate-based solution or a solution of sodium hydroxide, so that the smoothness on the surface increases. This makes the roughness of the surface of the walls of the through-hole structures12dto be 4 μm or less. This surface processing using a permanganate-based solution or a solution of sodium hydroxide can be carried out as a hole cleaning process with Emplate MLB made by Meltex Inc., for example.

By carrying out the above described desmear process, the roughness of the surface of the inner walls of the through-hole structures12dcan be made 4 μm or less. In addition, even if protrusions are created on the inner walls of the through-hole structures12d, their height can be 15% or less of the thickness of the insulation layer12a.

Next, with reference toFIGS. 9(a) to9(f), the manufacturing method for a gas electron multiplication foil22in a gas electron amplifier according to the second embodiment of the present invention is described.

That is to say, in order to manufacture the gas electron multiplication foil22, at first flat metal layers22band22eare overlaid on both surfaces of the plate-like insulation layer22a-1made of a liquid crystal polymer having a thickness of 50 μm, for example, and after a pre-process is carried out on the surfaces of metal layers22band22e, a resist layer500is formed (seeFIG. 9(a)). Here, copper can be the metal layers22band22e, and a dry film resist (AQ2558, made by Asahi Kasei Corporation) for the resist layer500, for example.

Then, the resist layer500is patterned on the surface of the metal layer22eso as to align with the location of the through-hole structures22d, and marks are created on the metal layers22band22efor the align exposure after overlay, and then openings are created in the metal layers22band22ein accordance with the above described pattern (seeFIG. 9(b)). The above described patterning can be carried out by vacuum contact exposure with an exposure dose of 60 mJ/cm2using a mask for exposure having a predetermined pattern, and then developing using a solution of 1% sodium carbonate. The openings can be created in the metal layers22band22ethrough etching using a solution of ferric chloride, for example, in the case where the metal layers22band22eare made of copper.

Next, the resist layer500is removed using a solution of 3% sodium hydroxide, for example, and a two-layer material where a flat metal layer22cis overlaid on one side of the plate-like insulation layer22a-2made of a liquid crystal polymer having a thickness of 50 μm is adhered through thermal pressing under a high temperature in a vacuum (seeFIGS. 9(c) and9(d)). Here, technique for stacking is not limited to thermal pressing, and an appropriate adhesive or the like may be used.

Then, the resist layer500is patterned again to align with the location of the through-hole structures22d, and then openings are created in the metal layers22band22cin accordance with the above described pattern (seeFIG. 9(d)). The above described patterning can be carried out by vacuum contact exposure with an exposure dose of 60 mJ/cm2using a mask for exposure having a predetermined pattern, and then developing using a solution of 1% sodium carbonate. The openings can be created in the metal layers22band22cthrough etching using a solution of ferric chloride, for example, in the case where the metal layers22band22dare made of copper.

Next, the resist layer500is removed using a solution of 3% sodium hydroxide, for example, and the portion of the insulation layers22a-1and22a-2is removed by irradiating a laser beam such as a CO2laser, to form through-hole structures22d(seeFIG. 9(f)).

When portions of the insulation layers22a-1and22a-2are removed using a laser beam to create through-holes, the laser beam is directed so that the walls of the through-hole structures22dbecome perpendicular to the plane of the metal layers22b,22eand22c.

Here, it is preferable to make smooth the surface of the walls of the through-hole structures22dformed in the step shown inFIG. 9(f) in the surface finishing step. This can prevent the walls of the through-hole structures22dfrom charging up during the operation of the gas electron multiplier.

In the surface finishing step, plasma etching is carried out for three minutes each on the front surface and rear surface under conditions where the gas ratio is SF6:0.05, N2:0.10, O2:1.0 and the RF output is 2.1 kW, so that a soot-like substance attached on the walls of the through-hole structures22dis removed through irradiation with the above described laser beam.

Next, the surface of the walls of the through-hole structures22dis processed with a permanganate-based solution or a solution of sodium hydroxide, so that the smoothness of the surface increases. This allows the roughness of the surface of the walls of the through-hole structures22dto be 4 μm or less. This surface processing using a permanganate-based solution or a solution of sodium hydroxide can be carried out as a hole cleaning process with Emplate MLB made by Meltex Inc., for example.

By carrying out the above described desmear process, the roughness of the surface of the inner walls of the through-hole structures22dcan be made 4 μm or less. In addition, even if protrusions are created on the inner walls of the through-hole structures22d, their height can be 15% or less of the thickness of the insulation layers22a-1and22a-2.

Here, the above described embodiments can be modified as described in the following (1) to (3).

(1) Though in the above described second embodiment, two insulation layers: insulation layer22a-1and insulation layer22a-2, are provided with a metal layer22esandwiched in between, it is apparent that the present invention is not limited to this configuration, and three or more insulation layers may be provided in such a manner that metal layers and insulation layers are alternately stacked.
(2) Though in the above described second embodiment, the thickness of the insulation layer22a-1and that of the insulation layer22a-2are the same, it is apparent that the present invention is not limited to this configuration, and the two layers may have a different thickness, as long as the total thickness of the insulation layers is greater than the thickness of the insulation layer of the conventional gas electron multiplication foil.
(3) The above described embodiments and the modifications described in the above (1) and (2) may be used in appropriate combinations.

INDUSTRIAL APPLICABILITY

The present invention can be applied in order to reduce the amount of radiation in the field of medical image diagnosis, in order to detect the radiation from space, and in the field of biochemistry, and more specifically, in x-ray dosage monitors, medical x-ray machines (mammography, general x-ray machines), industrial non-destructive inspection machines, charged particle track detectors, space x-ray detectors, photodetection imagers, slow neutron detectors and the like.