Patent Publication Number: US-2019170884-A1

Title: Imaging panel and method for producing same

Description:
TECHNICAL FIELD 
     The present invention relates to an imaging panel and a method for producing the same. 
     BACKGROUND ART 
     An X-ray imaging device that picks up an X-ray image with an imaging panel that includes a plurality of pixel portions is known. In such an X-ray imaging device, irradiated X-rays are converted into charges by, for example, p-intrinsic-n (PIN) photodiodes. Converted charges are read out by thin film transistors (hereinafter also referred to as TFTs) that are caused to operate, the TFTs being provided in the pixel portions. With the charges being read out in this way, an X-ray image is obtained. 
     JP-A-2014-78651 discloses a photoelectric conversion device that is such an X-ray imaging device. In this photoelectric conversion device, a photoelectric conversion layer is provided on the lower electrodes, upper electrodes are provided on the photoelectric conversion layer, and a protection film covering side surfaces of the photoelectric conversion layer is provided on the upper electrodes. 
     SUMMARY OF THE INVENTION 
     Problem to be Solved by the Invention 
     The photodiode of the X-ray imaging device as described above can be formed by forming semiconductor films of an n-layer, an i-layer, and a p-layer that compose the photoelectric conversion layer, sequentially on the lower electrodes, forming the upper electrodes on the p-layer, applying a resist so that the resist covers the upper electrodes, and etching the semiconductor films. After etching, in order to suppress leakage current in the photoelectric conversion layer, the side surfaces of the photoelectric conversion layer are subjected to a reduction treatment with hydrogen fluoride in some cases, in a case where this reduction treatment is carried out after the resist is removed, the upper electrodes are dissolved by the reduction treatment, and metal ions adhere to the side surfaces of the photoelectric conversion layer. In a case where the reduction treatment is carried out before the resist is removed, organic substances adhere to the side surfaces of the photoelectric conversion layer due to a removing liquid that is used when the resist is removed. If metal ions or organic substances adhere to the side surfaces of the photoelectric conversion layer in this way, it is impossible to achieve an effect of suppressing leakage current even if the reduction treatment using hydrogen fluoride is carried out with respect to the side surfaces of the photoelectric conversion layer. 
     It is an object of the present invention to provide an X-ray imaging panel in which leakage current in the photoelectric conversion layer can be suppressed, and to provide a method for producing the same. 
     An imaging panel of the present invention with which the above-described problem is solved is an imaging panel that generates an image based on scintillation light that is obtained from X-rays transmitted through an object, and the imaging panel includes: a substrate; a thin film transistor that is formed on the substrate; an insulating film that covers the thin film transistor; a photoelectric conversion layer that is provided on the insulating film, and converts the scintillation light into charges; an upper electrode that is provided on the photoelectric conversion layer; a lower electrode that is provided under the photoelectric conversion layer, and is connected with the thin film transistor; and an upper electrode protection film that covers the upper electrode, above the photoelectric conversion layer, wherein ends of the upper electrode are arranged in such a manner that each end thereof is arranged on an inner side of the photoelectric conversion layer with respect to a corresponding end of the photoelectric conversion layer, and ends of the upper electrode protection film are arranged in such a manner that each end thereof is arranged between a corresponding end of the upper electrode and a corresponding end of the photoelectric conversion layer. 
     With the present invention, leakage current in the photoelectric conversion layer can be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  schematically illustrates a schematic configuration of an X-ray imaging device in an embodiment. 
         FIG. 2  schematically illustrates a schematic configuration of an imaging panel illustrated in  FIG. 1 . 
         FIG. 3  is an enlarged plan view illustrating one pixel portion of an imaging panel  1  illustrated in  FIG. 2 . 
         FIG. 4A  is a cross-sectional view of the pixel illustrated in  FIG. 3 , taken along the line A-A. 
         FIG. 4B  is an enlarged cross-sectional view of a part including an upper electrode protection film illustrated in  FIG. 4A . 
         FIG. 5A  is a cross-sectional view illustrating a step of forming a first insulating film on a gate insulating film and a TFT formed on a substrate. 
         FIG. 5B  is a cross-sectional view illustrating a step of forming a contact hole CH 1  in the first insulating film illustrated in  FIG. 5A . 
         FIG. 5C  is a cross-sectional view illustrating a step of forming a second insulating film on the first insulating film illustrated in  FIG. 5B . 
         FIG. 5D  is a cross-sectional view illustrating a step of forming an opening in the second insulating film, on the contact hole CH 1  illustrated in  FIG. 5C . 
         FIG. 5E  is a cross-sectional view illustrating a step of forming a metal film on the second insulating film illustrated in  FIG. 5D . 
         FIG. 5F  is a cross-sectional view illustrating a step of patterning the metal film illustrated in  FIG. 5E  so as to form a lower electrode connected with a drain electrode via the contact hole CH 1 . 
         FIG. 5G  is a cross-sectional view illustrating a step of forming n-type amorphous semiconductor layer, an intrinsic amorphous semiconductor layer, and a p-type amorphous semiconductor layer so that these layers cover the lower electrode illustrated in  FIG. 5F , and forming a transparent conductive film on the p-type amorphous semiconductor layer. 
         FIG. 5H  is a cross-sectional view illustrating a step of patterning the transparent conductive film illustrated in  FIG. 5G  so as to form an upper electrode. 
         FIG. 5I  is a cross-sectional view illustrating a step of forming an insulating film so that the insulating film covers the upper electrode illustrated in  FIG. 5H . 
         FIG. 5J  is a cross-sectional view illustrating a step of patterning the insulating film, the n-type amorphous semiconductor layer, the intrinsic amorphous semiconductor layer, and the p-type amorphous semiconductor layer illustrated in  FIG. 5I  so as to form a photoelectric conversion layer and an upper electrode protection film. 
         FIG. 5K  is a cross-sectional view illustrating a state after removing a resist used in the step of  FIG. 5J  and carrying out a reduction treatment in which hydrogen fluoride is applied to the surface of the photoelectric conversion layer. 
         FIG. 5L  is a cross-sectional view illustrating a step of forming a third insulating film on the upper electrode protection film illustrated in  FIG. 5K . 
         FIG. 5M  is a cross-sectional view illustrating a step of forming a contact hole CH 2  that passes through the third insulating film and the upper electrode protection film illustrated in  FIG. 5L . 
         FIG. 5N  is a cross-sectional view illustrating a step of forming a fourth insulating film on the third insulating film illustrated in  FIG. 5M , and forming an opening in the fourth insulating film, on the contact hole CH 2 . 
         FIG. 5O  is a cross-sectional view illustrating a step of forming a metal film on the fourth insulating film illustrated in  FIG. 5N . 
         FIG. 5P  is a cross-sectional view illustrating a step of forming a bias line by patterning the metal film illustrated in  FIG. 5O . 
         FIG. 5O  is a cross-sectional view illustrating a step of forming a transparent conductive film so that the transparent conductive film covers the bias line illustrated in  FIG. 5P . 
         FIG. 5R  is a cross-sectional view illustrating a step of patterning the transparent conductive film illustrated in  FIG. 5Q . 
         FIG. 5S  is a cross-sectional view illustrating a step of forming a fifth insulating film so that the fifth insulating film covers the transparent conductive film illustrated in  FIG. 5R . 
         FIG. 5T  is a cross-sectional view illustrating a step of forming a sixth insulating film on the fifth insulating film illustrated in  FIG. 5S . 
         FIG. 6  is a cross-sectional view illustrating an imaging panel after a reduction treatment in Embodiment 3 is carried out. 
     
    
    
     MODE FOR CARRYING OUT THE INVENTION 
     An imaging panel according to one embodiment of the present invention is an imaging panel that generates an image based on scintillation light that is obtained from X-rays transmitted through an object, and the imaging panel includes: a substrate; a thin film transistor that is formed on the substrate; an insulating film that covers the thin film transistor; a photoelectric conversion layer that is provided on the insulating film, and converts the scintillation light into charges; an upper electrode that is provided on the photoelectric conversion layer; a lower electrode that is provided under the photoelectric conversion layer, and is connected with the thin film transistor; and an upper electrode protection film that covers the upper electrode, above the photoelectric conversion layer, wherein ends of the upper electrode are arranged in such a manner that each end thereof is arranged on an inner side of the photoelectric conversion layer with respect to a corresponding end of the photoelectric conversion layer, and ends of the upper electrode protection film are arranged in such a manner that each end thereof is arranged between a corresponding end of the upper electrode and a corresponding end of the photoelectric conversion layer (the first configuration). 
     According to the first configuration, the upper electrode protection film is formed on the upper electrode. Ends of the upper electrode are arranged in such a manner that each end thereof is arranged on an inner side of the photoelectric conversion layer with respect to a corresponding end of the photoelectric conversion layer, and ends of the upper electrode protection film are arranged in such a manner that each end thereof is arranged between a corresponding end of the upper electrode and a corresponding end of the photoelectric conversion layer. In other words, the upper electrode is covered with the upper electrode protection film, on the photoelectric conversion layer. As compared with a case where the upper electrode protection film is not provided, it is therefore less likely that the photoelectric conversion layer would be affected by a reduction treatment using hydrogen fluoride, which is intended to suppress leakage current in the photoelectric conversion layer, or by a resist removing liquid that is used when the photoelectric conversion layer is formed. It is therefore unlikely that organic substances or metal ions would adhere to the surface of the photoelectric conversion layer, which results in that leakage current in the photoelectric conversion layer can be suppressed. 
     The first configuration may be such that the upper electrode protection film is made of silicon nitride (the second configuration). 
     With the second configuration, leakage current in the photoelectric conversion layer can be suppressed, and at the same time, the adhesiveness with the upper electrode can be improved. 
     The first configuration may be such that the upper electrode protection film is made of silicon oxide (the third configuration). 
     With the third configuration, leakage current in the photoelectric conversion layer can be suppressed. 
     The first configuration may be such that the upper electrode protection film is made of silicon oxide nitride (the fourth configuration). 
     With the fourth configuration, leakage current in the photoelectric conversion layer can be suppressed. 
     A method for producing an imaging panel according to one embodiment of the present invention is a method for producing an imaging panel that generates an image based on scintillation light that is obtained from X-rays transmitted through an object, and the producing method includes: forming a thin film transistor on a substrate; forming a first insulating film and a second insulating film on the thin film transistor; forming a first contact hole on a drain electrode of the thin film transistor so that the first contact hole passes through the first insulating film and the second insulating film; forming, on the second insulating film, a first transparent electrode film as a lower electrode that is connected with the drain electrode through the first contact hole; forming, on the first transparent electrode film, a first semiconductor layer of a first conductive type as a photoelectric conversion layer, an intrinsic amorphous semiconductor layer, and a second semiconductor layer of a second conductive type that is opposite to the first conductive type of the first semiconductor layer, in the stated order; forming an upper electrode on the second semiconductor layer; forming an insulating film as an upper electrode protection film, on the upper electrode; applying a resist on the insulating film, and etching the insulating film, the first semiconductor layer, the intrinsic amorphous semiconductor layer, and the second semiconductor layer, so as to form the photoelectric conversion layer and the upper electrode protection film; removing the resist, and thereafter, carrying out a reduction treatment with respect to a surface of the photoelectric conversion layer; forming a third insulating film that covers the upper electrode protection film, after the reduction treatment; forming a second contact hole on the upper electrode so that the second contact hole passes through the third insulating film and the upper electrode protection film; forming a fourth insulating film on the third insulating film except for a portion of the second contact hole; forming a signal line for supplying a bias voltage, on the fourth insulating film; forming, on the fourth insulating film, a transparent conductive film that connects the signal line and the upper electrode with each other through the second contact hole; and forming a fifth insulating film that covers the transparent conductive film (the fifth configuration). 
     According to the fifth configuration, after the photoelectric conversion layer is formed and the resist is removed, the surface of the photoelectric conversion layer is subjected to the reduction treatment. As compared with a case where the reduction treatment is applied before the resist is removed, it is therefore unlikely that the surface of the photoelectric conversion layer would be contaminated with organic substances. Further, since the upper electrode protection film is formed on the upper electrode, even if the reduction treatment is carried out after the resist is removed, such a phenomenon does not occur that metal ions generated as a result of dissolution of the upper electrode would adhere to a surface of the photoelectric conversion layer. This consequently makes it possible to produce an imaging panel in which leakage current in the photoelectric conversion layer is suppressed. 
     The fifth configuration may be such that, as the reduction treatment, a reduction treatment using hydrogen fluoride is carried out (the sixth configuration). 
     With the sixth configuration, leakage current in the photoelectric conversion layer can be suppressed. 
     The sixth configuration may be such that, after the reduction treatment using hydrogen fluoride is carried out, before the third insulating film is formed, a hydrogen-gas-containing plasma treatment is carried out (the seventh configuration). 
     With the seventh configuration, even if a hydrogen-gas-containing plasma treatment is carried out before the third insulating film is formed, the upper electrode therefore is not affected by the plasma treatment since it is covered with the upper electrode protection film, and the transmittance of the upper electrode therefore does not decrease. As a result, without decreasing the light receiving sensitivity of the photoelectric conversion layer, the effect of suppressing leakage current in the photoelectric conversion layer can be improved. 
     The fifth configuration may be such that, as the reduction treatment, a reduction treatment using hydrogen gas is carried out (the eighth configuration). 
     With the eighth configuration, even if a hydrogen-gas-containing plasma treatment is carried out after the resist is removed, the upper electrode therefore is not affected by the plasma treatment since it is covered with the upper electrode protection film, and the transmittance of the upper electrode therefore does not decrease. As a result, without decreasing the light receiving sensitivity of the photoelectric conversion layer, leakage current in the photoelectric conversion layer can be suppressed. 
     The following description describes embodiments of the present invention in detail while referring to the drawings. Identical or equivalent parts in the drawings are denoted by the same reference numerals and descriptions of the same are not repeated. 
     Embodiment 1 
     (Configuration) 
       FIG. 1  is a schematic diagram illustrating an X-ray imaging device in the present embodiment. The X-ray imaging device  100  includes an imaging panel  1  and a control unit  2 . The control unit  2  includes a gate control unit  2 A and a signal reading unit  2 B. X-rays are projected from the X-ray source  3  to an object S, and X-rays transmitted through the object S are converted into fluorescence (hereinafter referred to as scintillation light) by a scintillator  1 A provided above the imaging panel  1 . The X-ray imaging device  100  acquires an X-ray image by picking up the scintillation light with the imaging panel  1  and the control unit  2 . 
       FIG. 2  is a schematic diagram illustrating a schematic configuration of the imaging panel  1 . As illustrated in  FIG. 2 , a plurality of source lines  10 , and a plurality of gate lines  11  intersecting with the source lines  10  are formed in the imaging panel  1 . The gate lines  11  are connected with the gate control unit  2 A, and the source lines  10  are connected with the signal reading unit  2 B. 
     The imaging panel  1  includes TFTs  13  connected to the source lines  10  and the gate lines  11 , at positions at which the source lines  10  and the gate lines  11  intersect. Further, photodiodes  12  are provided in areas surrounded by the source lines  10  and the gate lines  11  (hereinafter referred to as pixels). In each pixel, scintillation light obtained by converting X-rays transmitted through the object S is converted by the photodiode  12  into charges according to the amount of the light. 
     The gate lines  11  in the imaging panel  1  are sequentially switched by the gate control unit  2 A into a selected state, and the TFT  13  connected to the gate line  11  in the selected state is turned ON. When the TFT  13  is turned ON, a signal according to the charges obtained by the conversion by the photodiode  12  is output through the source line  10  to the signal reading unit  2 B. 
       FIG. 3  is an enlarged plan view of one pixel portion of the imaging panel  1  illustrated in  FIG. 2 . As illustrated in  FIG. 3 , in the pixel surrounded by the gate line  11  and the source line  10 , a lower electrode  14   a , a photoelectric conversion layer  15 , and an upper electrode  14   b  that compose the photodiode  12  are arranged so as to overlap with one another. Further, a bias line  16  is arranged so as to overlap with the gate line  11  and the source line  10  when viewed in a plan view. The bias line  16  supplies a bias voltage to the photodiode  12 . The TFT  13  includes a gate electrode  13   a  integrated with the gate line  11  a semiconductor activity layer  13   b , a source electrode  13   c  integrated with the source line  10 , and a drain electrode  13   d . In the pixel, a contact hole CH 1  for connecting the drain electrode  13   d  and the lower electrode  14   a  with each other is provided. Further, in the pixel, a transparent conductive film  17  is provided so as to overlap with the bias line  16 , and a contact hole CH 2  for connecting the transparent conductive film  17  and the upper electrode  14   b  with each other is provided. 
     Here,  FIG. 4A  illustrates a cross-sectional view of the pixel illustrated in  FIG. 3  taken along line A-A. As illustrated in  FIG. 4A , the TFT  13  is formed on the substrate  101 . The substrate  101  is a substrate having insulating properties, such as a glass substrate, a silicon substrate, a plastic substrate having heat-resisting properties, or a resin substrate. 
     On the substrate  101 , the gate electrode  13   a  integrated with the gate line  11  is formed. The gate electrode  13   a  and the gate line  11  are made of, for example, a metal such as aluminum (Al), tungsten (W), molybdenum (Mo), molybdenum nitride (MoN), tantalum (Ta), chromium (Cr), titanium (Ti), or copper (Cu), an alloy of any of these metals, or a metal nitride of these metals. In the present embodiment, the gate electrode  13   a  and the gate line  11  have a laminate structure in which a metal film made of molybdenum nitride and a metal film made of aluminum are laminated in this order. Regarding thicknesses of these metal films, for example, the metal film made of molybdenum nitride has a thickness of 100 nm, and the metal film made of aluminum has a thickness of 300 nm. 
     The gate insulating film  102  is formed on the substrate  101 , and covers the gate electrode  13   a . The gate insulating film  102  may be formed with, for example, silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxide nitride (SiO x N y )(x&gt;y), or silicon nitride oxide (SiN x O y )(x&gt;y). In the present embodiment, the gate insulating film  102  is formed with a laminate film obtained by laminating silicon oxide (SiO x ) and silicon nitride (SiN x ) in the order, and regarding the thicknesses of these films, the film of silicon oxide (SiO x ) has a thickness of 50 nm, and the film of silicon nitride (SiN x ) has a thickness of 400 nm. 
     The semiconductor activity layer  13   b , as well as the source electrode  13   c  and the drain electrode  13   d  connected with the semiconductor activity layer  13   b  are formed on the gate electrode  13   a  with the gate insulating film  102  being interposed therebetween. 
     The semiconductor activity layer  13   b  is formed in contact with the gate insulating film  102 . The semiconductor activity layer  13   b  is made of an oxide semiconductor. For forming the oxide semiconductor, for example, the following material may be used: InGaO 3 (ZnO) 5 ; magnesium zinc oxide (Mg x Zn 1-x O); cadmium zinc oxide (Cd x Zn 1-x O); cadmium oxide (CdO); or an amorphous oxide semiconductor containing indium (In), gallium (Ga), and zinc (Zn) at a predetermined ratio. In the present embodiment, the semiconductor activity layer  13   b  is made of an amorphous oxide semiconductor containing indium (In), gallium (Ga), and zinc (Zn) at a predetermined ratio, and has a thickness of, for example, 70 nm. 
     The source electrode  13   c  and the drain electrode  13   d  are formed in contact with the semiconductor activity layer  13   b  and the gate insulating film  102 . The source electrode  13   c  is integrated with the source line  10 . The drain electrode  13   d  is connected with the lower electrode  14   a  through the contact hole CH 1 . 
     The source electrode  13   c  and the drain electrode  13   d  are formed in the same layer, and are made of, for example, a metal such as aluminum (Al), tungsten (W), molybdenum (Mo), tantalum (Ta), chromium (Cr), titanium (Ti), or copper (Cu), or alternatively, an alloy of any of these, or a metal nitride of any of these. Further, as the material for the source electrode  13   c  and the drain electrode  13   d , the following material may be used: a material having translucency such as indium tin oxide (ITO), indium zinc oxide (IZO), indium tin oxide (ITSO) containing silicon oxide, indium oxide (In 2 O 3 ), tin oxide (SnO 2 ), zinc oxide (ZnO), or titanium nitride; or a material obtained by appropriately combining any of these. 
     The source electrode  13   c  and the drain electrode  13   d  may be, for example, a laminate of a plurality of metal films. More specifically, the source electrode  13   c , the source line  10 , and the drain electrode  13   d  have a laminate structure in which a metal film made of molybdenum nitride (MoN), a metal film made of aluminum (Al), and a metal film made of molybdenum nitride (MoN) are laminated in this order. Regarding the thicknesses of the films, the metal film in the lower layer, which is made of molybdenum nitride (MoN), has a thickness of 100 nm, the metal film made of aluminum (Al) has a thickness of 500 nm, and the metal film in the upper layer, which is made of molybdenum nitride (MoN), has a thickness of 50 nm. 
     A first insulating film  103  is provided so as to cover the source electrode  13   c  and the drain electrode  13   d . The first insulating film  103  may have a single layer structure made of silicon oxide (SiO 2 ) or silicon nitride (SiN), or a laminate structure obtained by laminating silicon nitride (SiN) and silicon oxide (SiO 2 ) in this order. 
     On the first insulating film  103 , a second insulating film  104  is formed. The second insulating film  104  is made of an organic transparent resin, for example, acrylic resin or siloxane-based resin, has a thickness of, for example, 2.5 μm. 
     On the drain electrode  13   d , the contact hole CH 1  is formed, which passes through the second insulating film  104  and the first insulating film  103 . 
     On the second insulating film  104 , the lower electrode  14   a , which is connected with the drain electrode  13   d  through the contact hole CH 1 , is formed. The lower electrode  14   a  is formed with, for example, a metal film containing molybdenum nitride (MoN), and has a thickness of, for example, 200 nm. 
     On the lower electrode  14   a , the photoelectric conversion layer  15  is formed. The photoelectric conversion layer  15  is composed of the n-type amorphous semiconductor layer  151 , the intrinsic amorphous semiconductor layer  152 , and the p-type amorphous semiconductor layer  153 , which are laminated in the order. 
     The n-type amorphous semiconductor layer  151  is made of amorphous silicon doped with an n-type impurity (for example, phosphorus). The n-type amorphous semiconductor layer  151  has a thickness of, for example, 30 nm. 
     The intrinsic amorphous semiconductor layer  152  is made of intrinsic amorphous silicon. The intrinsic amorphous semiconductor layer  152  is formed in contact with the n-type amorphous semiconductor layer  151 . The intrinsic amorphous semiconductor layer has a thickness of, for example, 1000 nm. 
     The p-type amorphous semiconductor layer  153  is made of amorphous silicon doped with a p-type impurity (for example, boron). The p-type amorphous semiconductor layer  153  is formed in contact with the intrinsic amorphous semiconductor layer  152 . The p-type amorphous semiconductor layer  153  has a thickness of, for example, 5 nm. 
     On the p-type amorphous semiconductor layer  153 , the upper electrode  14   b  is formed. The upper electrode  14   b  is made of, for example, indium tin oxide (ITO), and has a thickness of, for example, 70 nm. 
     On the p-type amorphous semiconductor layer  153 , an insulating film  18  (hereinafter referred to as an upper electrode protection film) is formed so as to cover the upper electrode  14   b . The upper electrode protection film  18  is, for example, an inorganic insulating film made of silicon oxide (SiO 2 ), and has a thickness of, for example, 100 nm. 
       FIG. 4B  is an enlarged view illustrating a part of the photoelectric conversion layer  15 , the upper electrode  14   b , and the upper electrode protection film  18  illustrated in  FIG. 4A . An X-axis direction end  18   a  of the upper electrode protection film  18  in the present embodiment is arranged between an X-axis direction end  141  of the upper electrode  14   b , and an X-axis direction end  15   a  of the photoelectric conversion layer  15 . 
     Referring back to  FIG. 4A , a third insulating film  105  is formed on the second insulating film  104  so as to cover the photodiode  12  and the upper electrode protection film  18 . The third insulating film  105  is, for example, an inorganic insulating film made of silicon nitride (SiN), and has a thickness of, for example, 300 nm. 
     In the third insulating film  105  and the upper electrode protection film  18 , a contact hole CH 2  is formed at a position that overlaps with the upper electrode  14   b.    
     On the third insulating film  105 , in an area thereof except for the contact hole CH 2 , a fourth insulating film  106  is formed. The fourth insulating film  106  is formed with an organic transparent resin made of, for example, acrylic resin or siloxane-based resin, and has a thickness of, for example, 2.5 μm. 
     On the fourth insulating film  106 , the bias line  16  is formed. Further, on the fourth insulating film  106 , the transparent conductive film  17  is formed so as to overlap with the bias line  16 . The transparent conductive film  17  is in contact with the upper electrode  14   b  at the contact hole CH 2 . The bias line  16  is connected to the control unit  2  (see  FIG. 1 ). The bias line  16  applies a bias voltage through the contact hole CH 2  to the upper electrode  14   b , the bias voltage being input from the control unit  2 . The bias line  16  has a laminate structure that is obtained by laminating, for example, a metal film made of molybdenum nitride (MoN), a metal film made of aluminum (Al), and a metal film made of titanium (Ti) in this order. The films of molybdenum nitride (MoN), aluminum (Al), and titanium (Ti) have thicknesses of, for example, 100 nm, 300 nm, and 50 nm, respectively. 
     On the fourth insulating film  106 , a fifth insulating film  107  is formed so as to cover the transparent conductive film  17 . The fifth insulating film  107  is an inorganic insulating film made of, for example, silicon nitride (SiN), and has a thickness of, for example, 200 nm. 
     On the fifth insulating film  107 , a sixth insulating film  108  is formed. The sixth insulating film  108  is made of, for example, an organic transparent resin such as acrylic resin or siloxane-based resin, and has a thickness of, for example, 2.0 μm. 
     (Method for Producing Imaging Panel  1 ) 
     Next, the following description describes a method for producing the imaging panel  1 .  FIGS. 5A to 5T  are cross-sectional views of the pixel taken along line A-A in respective steps of the method for producing the imaging panel  1  (see  FIG. 3 ). 
     As illustrated hi  FIG. 5A , the gate insulating film  102  and the TFT  13  are formed on the substrate  101  by a known method, and the first insulating film  103  made of silicon nitride (SiN) is formed by, for example, plasma CVD, so as to cover the TFT  13 . 
     Subsequently, a heat treatment at about 350° C. is applied to an entire surface of the substrate  101 , and photolithography and wet etching are carried out so that the first insulating film  103  is patterned, whereby the contact hole CH 1  is formed on the drain electrode  13   d  (see  FIG. 5B ). 
     Next, the second insulating film  104  made of acrylic resin or siloxane-based resin is formed on the first insulating film  103  by, for example, slit coating (see  FIG. 5C ). 
     An opening  104   a  of the second insulating film  104  is formed by photolithography on the contact hole CH 1  (see  FIG. 5D ). 
     Subsequently, a metal film  210  made of molybdenum nitride (MoN) is formed on the second insulating film  104  by, for example, sputtering (see  FIG. 5E ). 
     Then, photolithography and wet etching are carried out, whereby the metal film  210  is patterned. Through these steps, the lower electrode  14   a , which is connected with the drain electrode  13   d  through the contact hole CH 1 , is formed on the second insulating film  104  (see  FIG. 5F ). 
     Next, the n-type amorphous semiconductor layer  151 , the intrinsic amorphous semiconductor layer  152 , and the p-type amorphous semiconductor layer  153  are formed in this order on the second insulating film  104  by, for example, plasma CVD, so as to cover the lower electrode  14   a . Then, a transparent conductive film  220  made of, for example, ITO is formed on the p-type amorphous semiconductor layer  153  (see  FIG. 5G ). 
     Thereafter, photolithography and dry etching are carried out so that the transparent conductive film  220  is patterned, whereby the upper electrode  14   b  is formed on the p-type amorphous semiconductor layer  153  (see  FIG. 5H ). 
     Subsequently, an insulating film  180  made of silicon nitride (SiN) is formed on the p-type amorphous semiconductor layer  153  by, for example, plasma CVD, so as to cover the upper electrode  14   b . Then, a resist  200  is applied on the insulating film  180  (see  FIG. 5I ). 
     Then, photolithography and dry etching are carried out, whereby the insulating film  180 , the n-type amorphous semiconductor layer  151 , the intrinsic amorphous semiconductor layer  152 , and the p-type amorphous semiconductor layer  153  are patterned. Through these steps, the photoelectric conversion layer  15  and the upper electrode protection film  18 , having smaller widths in the X-axis direction than the width of the lower electrode  14   a , are formed (see  FIG. 5J ). 
     Next, the resist  200  is removed, and thereafter, in order to suppress leakage current in the photoelectric conversion layer  15 , a reduction treatment using hydrogen fluoride is applied to the surfaces of the upper electrode protection film  18  and the photoelectric conversion layer  15 . The upper electrode protection film  18  is partially etched in the X-axis direction by the reduction treatment. As a result, each end  18   a  of the upper electrode protection film  18  is arranged between the X-axis direction end  141  of the upper electrode  14   b  and the end  15   a  of the photoelectric conversion layer  15  (see  FIG. 5K ). 
     In this way, the upper electrode protection film  18  is partially etched in the X-axis direction by the reduction treatment using hydrogen fluoride, but the upper electrode  14   b  is not exposed to hydrogen fluoride since it is covered with the upper electrode protection film  18 . The reduction treatment using hydrogen fluoride does not lead to a phenomenon that metal ions generated as a result of dissolution of the upper electrode  14   b  would adhere to side surfaces of the photoelectric conversion layer  15 . 
     Next, the third insulating film  105  made of silicon nitride (SiN) is formed on the upper electrode protection film  18  by, for example, plasma CVD (see  FIG. 5L ). 
     Then, photolithography and wet etching are carried out so that the contact hole CH 2  passing through the third insulating film  105  and the upper electrode protection film  18  is formed (see  FIG. 5M ). 
     Subsequently, the fourth insulating film  106  made of acrylic resin or siloxane-based resin is formed on the third insulating film  105  by, for example, slit coating. Then, an opening  106   a  in the fourth insulating film  106  is formed by photolithography on the contact hole CH 2  (see  FIG. 5N ). 
     Next, a metal film  160  is formed by laminating molybdenum nitride (MoN), aluminum (Al), and titanium (Ti) in this order on the fourth insulating film  106  by, for example, sputtering (see  FIG. 5O ). 
     Then, photolithography and wet etching are carried out so that the metal film  160  is patterned, whereby the bias line  16  is formed (see  FIG. 5P ). 
     Subsequently, a transparent conductive film  170  made of ITO is formed by, for example, sputtering on the fourth insulating film  106  so as to cover the bias line  16  (see  FIG. 5Q ). 
     Then, photolithography and dry etching are carried out so that the transparent conductive film  170  is patterned, whereby the transparent conductive film  17  is formed that is connected with the bias line  16  and is connected with the upper electrode  14   b  through the contact hole CH 2  (see  FIG. 5R ). 
     Next, the fifth insulating film  107  made of silicon nitride (SiN) is formed by, for example, plasma CVD on the fourth insulating film  106  so as to cover the transparent conductive film  17  (see  FIG. 5S ). 
     Subsequently, the sixth insulating film  108  made of acrylic resin or siloxane-based resin is formed on the fifth insulating film  107  by, for example, slit coating (see  FIG. 5T ). 
     What is described above is the method for producing the imaging panel  1  in the present embodiment. As described above, the upper electrode protection film  18  is formed on the upper electrode  14   b  of the photodiode  12 . In this configuration, the upper electrode  14   b  is thus covered with the upper electrode protection film  18 , which results in the following: even if a reduction treatment using hydrogen fluoride is carried out after the resist  200  used for forming the photodiode  12  (see  FIG. 5J ) is removed, the upper electrode  14   b  is not exposed to hydrogen fluoride, and metal ions of the upper electrode  14   b  do not adhere to the side surfaces of the photoelectric conversion layer  15 . Further, since a reduction treatment using hydrogen fluoride is carried out after the resist  200  is removed, it is less likely that organic substances would adhere to the side surfaces of the photoelectric conversion layer  15 , as compared with the case where the resist  200  is removed after a reduction treatment using hydrogen fluoride. This makes it possible to prevent the side surfaces of the photoelectric conversion layer  15  from being contaminated with metals or organic substances, thereby to suppress leakage current in the photodiode  12 . 
     (Operation of X-Ray Imaging Device  100 ) 
     Here, operations of the X-ray imaging device  100  illustrated in  FIG. 1  are described. First, X-rays are emitted from the X-ray source  3 . Here, the control unit  2  applies a predetermined voltage (bias voltage) to the bias line  16  (see  FIG. 3  and the like). X-rays emitted from the X-ray source  3  are transmitted through an object S, and are incident on the scintillator  1 A. The X-rays incident on the scintillator  1 A are converted into fluorescence (scintillation light), and the scintillation light is incident on the imaging panel  1 . When the scintillation light is incident on the photodiode  12  provided in each pixel in the imaging panel  1 , the scintillation light is changed to charges by the photodiode  12  in accordance with the amount of the light. A signal according to the charges obtained by conversion by the photodiode  12  is read out through the source line  10  to the signal reading unit  2 B (see  FIG. 2  and the like) when the TFT  13  (see  FIG. 3  and the like) is in the ON state according to a gate voltage (positive voltage) that is output from the gate control unit  2 A through the gate line  11 . Then, an X-ray image in accordance with the signal thus read out is generated in the control unit  2 . 
     Embodiment 2 
     Embodiment 1 is described above with reference to an exemplary case where in the step illustrated in  FIG. 5K , after the resist  200  (see  FIG. 5J ) is removed, a reduction treatment using hydrogen fluoride is carried out, and thereafter, in the step illustrated in  FIG. 5L , the third insulating film  105  is formed. The process, however, may be as follows. 
     In the above-described step illustrated in  FIG. 5K , after a reduction treatment using hydrogen fluoride is carried out, before the third insulating film  105  is formed, the surfaces of the upper electrode protection film  18  and the photoelectric conversion layer  15  are subjected to a hydrogen-gas-containing plasma treatment. 
     By performing a hydrogen-gas-containing plasma treatment subsequently to a reduction treatment using hydrogen fluoride in this way, the effect of suppressing leakage current in the photodiode  12  can be further improved as compared with Embodiment 1. 
     Besides, in a case where the upper electrode protection film  18  is not provided, when a hydrogen-gas-containing plasma treatment is applied to the surface of the photodiode  12 , metals contained in the upper electrode  14   b  are reduced by the plasma treatment, whereby the transmittance of the upper electrode  14   b  decreases. In the present embodiment, the upper electrode  14   b  is covered with the upper electrode protection film  18 . Even if a hydrogen-gas-containing plasma treatment is carried out before the third insulating film  105  is formed, the upper electrode  14   b  therefore is not affected by the plasma treatment, and the transmittance is not caused to decrease, which results in that it is unlikely that the light receiving sensitivity of the photodiode  12  would decrease. 
     Embodiment 3 
     Embodiment 1 and Embodiment 2 are described above with reference to an exemplary case where a reduction treatment using hydrogen fluoride is carried out in the step illustrated in  FIG. 5K . In the present embodiment, a hydrogen-gas-containing plasma treatment is carried out in place of the reduction treatment using hydrogen fluoride. 
     In other words, after the step illustrated in  FIG. 5J , the resist  200  is removed, and a hydrogen-gas-containing plasma treatment is carried out. Thereafter, by the step illustrated in  FIG. 5L , the third insulating film  105  is formed on the upper electrode protection film  18 . By carrying out the hydrogen-gas-containing plasma treatment in this way, leakage current on the surface of the photoelectric conversion layer  15  can be suppressed. Besides, in the present embodiment as well, the upper electrode  14   b  is covered with the upper electrode protection film  18 . Even if a hydrogen-gas-containing plasma treatment is carried out before the third insulating film  105  is formed, the upper electrode  14   b  therefore is not affected by the plasma treatment, and the transmittance is not caused to decrease, which results in that it is unlikely that the light receiving sensitivity of the photodiode  12  would decrease. 
     Incidentally, in a case where a reduction treatment using hydrogen fluoride is carried out in the step illustrated in  FIG. 5K , as described above, a part of the upper electrode protection film  18  is etched in the X-axis direction, and the position of the end  18   a  of the upper electrode protection film  18  is arranged on an inner side with respect to the end  15   a  of the photoelectric conversion layer  15 . On the other hand, in a case where the resist  200  is removed after the step illustrated in  FIG. 5J  and a hydrogen-gas-containing plasma treatment is carried out, the ends of the upper electrode protection film  18  are not etched. As a result, in this case, as illustrated in  FIG. 6 , each end  18   a  of the upper electrode protection film  18  is arranged at approximately the same position as the position of the end  15   a  of the photoelectric conversion layer  15 . 
     The embodiments of the present invention, described above, are merely examples for implementing the present invention. The present invention, therefore, is not limited to the above-described embodiments, but can be appropriately modified without deviating from the scope of the invention and be implemented. The following description describes modifications of the present invention. 
     (1) Embodiments 1 to 3 are described above with reference to an exemplary case where silicon nitride (SiN) is used as a material for the upper electrode protection film  18 , but silicon oxide (SiO 2 ) may be replaced with silicon nitride (SiN), or alternatively, silicon oxide nitride (SiON) may be used. 
     Silicon nitride (SiN), silicon oxide (SiO 2 ), and silicon oxide nitride (SiON) provide different adhesivenesses with the upper electrode  14   b , respectively, when they are used for forming the upper electrode protection film  18 . More specifically, the respective adhesivenesses with the upper electrode  14   b  of silicon nitride (SiN), silicon oxide (SiO 2 ), and silicon oxide nitride (SiON) descend in this order. In a case where the adhesiveness with the upper electrode  14   b  is taken into consideration, therefore, it is preferable to use silicon nitride (SiN) as a material for the upper electrode protection film  18 . 
     Further, silicon nitride (SiN), silicon oxide (SiO 2 ), and silicon oxide nitride (SiON) are etched to different levels by a reduction treatment using hydrogen fluoride, respectively. In other words, the relationship of the etched amounts of silicon nitride (SiN), silicon oxide (SiO 2 ), and silicon oxide nitride (SiON) in a reduction treatment using hydrogen fluoride is as follows: silicon nitride (SiN)&lt;silicon oxide (SiO 2 )&lt;silicon oxide nitride (SiON). The upper electrode protection film  18  after a reduction treatment using hydrogen fluoride is carried out preferably has a thickness of 70 μm or more. The thickness of the film when the film is formed is therefore set according to the material used for forming the upper electrode protection film  18 . For example, the films of silicon nitride (SiN), silicon oxide (SiO 2 ), and silicon oxide nitride (SiON) are formed so as to have thicknesses of 100 nm, 150 nm, and 200 nm, respectively when the films are just formed.