Method of fabricating an X-ray detector array element

[0002] 1. Field of the Invention

[0003] The present invention relates to a method of fabricating an image sensor. More particularly, the present invention relates to a method of fabricating an X-ray detector array including a plurality of pixels, each including a storage capacitor and a thin film transistor (TFT).

[0004] 2. Description of the Background Art

[0005] Electronic matrix arrays find considerable application in X-ray image sensors. Such devices generally include X and Y (or row and column) address lines transversely and longitudinally spaced apart and across at an angle to one another, thereby forming a plurality of crossover points. Associated with each crossover point is an element (e.g. a pixel) to be selectively addressed. These elements in many instances are memory cells or pixels of an electronically adjustable memory array or X-ray imaging array.

[0006] Typically, at least one switching or isolation device such as a diode or thin film transistor (TFT) is associated with each array element or pixel. The isolation devices permit the individual pixels to be selectively addressed by the application of suitable potentials between respective pairs of the X and Y address lines. Thus, the TFTs and diodes act as switching elements for energizing or otherwise addressing corresponding memory cells or storage capacitors.

[0007] In FIG. 1, a background X-ray detector for capturing digital radiographic images is illustrated. The X-ray detector includes a plurality of pixels 3, each including a thin film transistor (TFT) 5 and a storage capacitor 7. The storage capacitor 7 in each pixel includes a charge collector electrode 4 that functions as a top plate of the storage capacitor, and a pixel electrode 11 that functions as a bottom electrode of the capacitor.

[0008] FIG. 2 is a top view of a background X-ray detector pixel. FIG. 2B is a sectional view taken along line C-C′ of FIG. 2A. As shown in FIGS. 2A and 2B, each pixel of the background art includes a substrate 200, a gate electrode 205, a gate line 206, a first gate insulation layer 210, an a-Si layer 215, an α-Si (amorphous silicon) layer 215, an n⁺ α-Si layer 220, a common line 225, a source electrode 230, a drain electrode 235, a data line 240, a planarization layer 245, a first via hole 250, a second via hole 255, a bottom electrode (a pixel electrode) 260, a dielectric layer 265, and a top electrode (a charge collector electrode) 270. In addition, symbol Cs indicates a storage capacitor.

[0009] The method for fabricating the above X-ray detector includes seven steps of photolithography and etching. That is, the background method requires seven masks. The processing steps are concisely described as follows.

[0010] The first photolithography step defines the gate electrode 205 and the gate line 206.

[0011] The second photolithography step defines the α-Si layer 215 and the n⁺ α-Si layer 220 to obtain a semiconductor island structure.

[0012] The third photolithography step defines the common line 225, the source electrode 230, the drain electrode 235, and the data line 240.

[0013] The fourth photolithography step defines the first via hole 250.

[0014] The fifth photolithography step defines the bottom electrode (the pixel electrode) 260.

[0015] The sixth photolithography step defines the second via hole 255.

[0016] The seventh photolithography step defines the top electrode (the charge collector electrode) 270.

[0017] The inventors of the present invention have recognized that to decrease manufacturing costs, a method that requires utilizing fewer masks than in the background method would be beneficial.

[0018] Thereby, an object of the present invention is to provide a novel method of fabricating an X-ray detector array element.

[0019] Another object of the present invention is to provide a novel method of fabricating an X-ray detector array element, requiring only six masks during photolithography.

[0020] In order to achieve these objects, the present invention provides a novel method of fabricating an X-ray detector array element. A substrate having a capacitor area and a transistor area is provided. A transversely extending gate line is formed on the substrate, wherein the gate line includes a gate electrode in the transistor area. A gate insulation layer is formed on the gate line, the gate electrode, and the substrate. A semiconducting island is formed on the gate insulation layer in the transistor area. A longitudinally extending common line and a longitudinally extending data line are formed on the gate insulation layer, and simultaneously, a source electrode and a drain electrode are formed on the semiconducting island to form a thin film transistor (TFT) structure, wherein the drain electrode electrically connects to the data line. A planarization layer is formed on the gate insulation layer, the common line, the TFT structure, the data line, and the gate line. A first conductive layer is formed on the planarization layer in the capacitor area. A dielectric layer is formed on the first conductive layer and the planarization layer. A first via hole and a second via hole penetrating the dielectric layer and the planarization layer are formed, wherein the first via hole exposes the surface of the source electrode, and the second via hole exposes part of the surface of the first conductive layer and part of the surface of the common line. A conformal second conductive layer is formed on the dielectric layer, the interior surrounding surface of the first via hole, and the interior surrounding surface of the first via hole. Part of the second conductive layer is removed to form a third conductive layer, a fourth conductive layer, and a first opening. The third conductive layer is isolated from the fourth conductive layer by the first opening, the third conductive layer electrically connects to the source electrode, and the first conductive layer electrically connects to the common line by the fourth conductive layer. Thus, a storage capacitor structure composed of the first conductive layer, the dielectric layer, and the third conductive layer in the capacitor area is obtained.

[0021] The present invention also provides another method of fabricating an X-ray detector array element. A substrate having a capacitor area and a transistor area is provided. A transversely extending gate line is formed on the substrate, wherein the gate line includes a gate electrode in the transistor area. A gate insulation layer is formed on the gate line, the gate electrode, and the substrate. A semiconducting island is formed on the gate insulation layer in the transistor area. A longitudinally extending common line and a longitudinally extending data line are formed on the gate insulation layer, and simultaneously, a source electrode and a drain electrode are formed on the semiconducting island to form a thin film transistor (TFT) structure, wherein the drain electrode electrically connects the data line. A planarization layer is formed on the gate insulation layer, the common line, the TFT structure, the data line, and the gate line. A first conductive layer having a first opening is formed on the planarization layer in the capacitor area, wherein the first opening exposes the planarization layer above the common line. A dielectric layer is formed on the first conductive layer and the planarization layer. A first via hole and a second via hole penetrating the dielectric layer and the planarization layer are formed. The first via hole exposes the surface of the source electrode, the second via hole exposes part of the surface of the first conductive layer and part of the surface of the common line, and the second via hole and the first opening overlap. A conformal second conductive layer is formed on the dielectric layer, the interior surrounding surface of the first via hole, and the interior surrounding surface of the second via hole. Part of the second conductive layer is removed to form a third conductive layer, a fourth conductive layer, and a second opening. The third conductive layer is isolated from the fourth conductive layer by the second opening, the third conductive layer electrically connects to the source electrode, and the first conductive layer electrically connects to the common line by the fourth conductive layer. Thus, a storage capacitor structure composed of the first conductive layer, the dielectric layer, and the third conductive layer in the capacitor area is obtained.

[0022] A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

[0023] FIG. 1 is a schematic of a background art imager array in which each pixel includes a TFT and a storage capacitor;

[0024] FIG. 2A is a perspective top view of an X-ray detector pixel of the background art;

[0025] FIG. 2B is a sectional view taken along line C-C′ of FIG. 2A;

[0026] FIGS. 3A-8A are perspective top views of an X-ray detector array element according to the first embodiment of the present invention;

[0027] FIGS. 3B-8B are sectional views taken along line c-c′ of FIGS. 3A-8A;

[0028] FIGS. 3C-8C are sectional views taken along line d-d′ of FIGS. 3A-8A;

[0029] FIG. 8D is a perspective top view, according to a modification of the first embodiment of the present invention;

[0030] FIG. 8E is a sectional view taken along line f—f of FIG. 8D;

[0031] FIGS. 9A-14A are perspective top views of an X-ray detector array element according to the second embodiment of the present invention;

[0032] FIGS. 9B-14B are sectional views taken along line c-c′ of FIGS. 9A-14A; and

[0033] FIGS. 9C-14C are sectional views taken along line e-e′ of FIGS. 9A-14A.

[0034] First Embodiment

[0035] FIGS. 3A-8A are perspective top views of an X-ray detector ray element according to the first embodiment of the present invention. FIGS. 3B-8B are sectional views taken along line c-c′ of FIGS. 3A-8A. FIGS. 3C-8C are sectional views taken along line d-d′ of FIGS. 3A-8A. In order to simplify the illustration, the accompanying drawings show a substrate in only one sample pixel region. That is, although only one pixel region is shown, the actual number of pixel regions may be very large.

[0036] In FIGS. 3A, 3B, and 3C, a substrate 300, such as a glass substrate, having a capacitor area 301 and a transistor area 302 is provided. Then, deposition and a first photolithography procedure using a first mask (also referred to as a first photo engraving process, PEP I) are performed, and a transversely extending gate line 310 is formed on the substrate 300. The gate line 310 includes a gate electrode 320 in the transistor area 302.

[0037] It should be noted that FIG. 3A shows the gate line 310 having a protruding portion 320 in the transistor area 302, serving as the gate electrode 320. Nevertheless, the present invention is not intended to limit the position of the gate electrode. For example, the gate line 310 located in the transistor area 302 can also serve as the gate electrode 320, as shown in FIGS. 8D and 8E. The illustration of the FIGS. 8D and 8E will be described as a modification of the first embodiment.

[0038] In FIGS. 3A, 3B, and 3C, a gate insulation layer 330 is formed on the gate line 310, the gate electrode 320, and the substrate 300. The gate line 310 and the gate electrode 320 may be metal formed by deposition. The gate insulation layer 330 maybe SiO₂, SiN_x, or SiON formed by deposition.

[0039] In FIGS. 4A, 4B, and 4C, an amorphous silicon layer (α-Si layer, not shown) is deposited on the gate insulation layer 330, and then a doped amorphous silicon layer (e.g. n⁺ α-Si, not shown) is deposited on the amorphous silicon layer. Next, a second photolithography procedure using a second mask (PEP II) is performed, and part of the doped amorphous silicon layer and the amorphous silicon layer are etched to form a semiconducting island on the gate insulation layer 330 in the transistor area 302. The semiconducting island is composed of a patterned amorphous silicon layer 410 and a patterned doped amorphous silicon layer 420.

[0040] In FIGS. 5A, 5B, and 5C, a conductive layer (not shown) is deposited on the gate insulation layer 330 and the semiconducting island. Then, a third photolithography procedure using a third mask (PEP III) is performed to remove part of the conductive layer (not shown), and a longitudinally extending common line 510 and a longitudinally extending data line 520 are formed on the gate insulation layer 330, and simultaneously, a source electrode 530 and a drain electrode 540 are formed on the doped amorphous silicon layer 420. Then, using the source electrode 530 and the drain electrode 540 as a mask, part of the doped amorphous silicon layer 420 is etched to expose part of the surface of the amorphous silicon layer 410. Thus, a thin film transistor (TFT) structure is obtained in the transistor area 302. Also, the drain electrode 540 electrically connects to the data line 520.

[0041] In FIGS. 6A, 6B, and 6C, a planarization layer 610 is formed on the gate insulation layer 330, the common line 510, the TFT structure, the data line 520, and the gate line 310. The planarization layer 610 may be a spin-on-glass (SOG) or organic layer formed by spin coating. Then, deposition and a fourth photolithography procedure using a fifth mask (PEP IV) are performed, and a first conductive layer 620 is formed on the planarization layer 610 in the capacitor area 301. The first conductive layer 620 may be indium tin oxide (ITO) or indium zinc oxide (IZO) formed by deposition, serving as a bottom electrode or a pixel electrode.

[0042] In FIGS. 7A, 7B, and 7C, a dielectric layer 710 is formed on the first conductive layer 620 and the planarization layer 610. The dielectric layer 710 can be SiN_x, SiON, or SiO_xformed by deposition, serving as a dielectric layer of a capacitor. Then, a fifth photolithography procedure using a fifth mask (PEP V) is performed, and a first via hole 720 and a second via hole 730 penetrating the dielectric layer 710 and the planarization layer 610 are formed. The first via 720 exposes the surface of the source electrode 530, and the second via 730 exposes part of the surface of the first conductive layer 620 and part of the surface of the common line 510.

[0043] In FIGS. 8A, 8B, and 8C, a conformal second conductive layer (not shown) is formed on the dielectric layer 710, the interior surrounding surface of the first via hole 720, and the interior surrounding surface of the second via hole 730. The second conductive layer may be indium tin oxide (ITO) or indium zinc oxide (IZO) formed by deposition. Then, a sixth photolithography procedure using a sixth mask (PEP VI) is performed, and part of the second conductive layer is removed to form a third conductive layer 810, a fourth conductive layer 820, and an opening 830. The third conductive layer 810 is isolated from the fourth conductive layer 820 by the opening 830. The third conductive layer 810 electrically connects to the source electrode 530, and the first conductive layer 620 electrically connects to the common line 510 by the fourth conductive layer 820. The third conductive layer 810 serves as a top electrode or a charge collector electrode. Thus, a storage capacitor structure Cs composed of the first conductive layer 620, the dielectric layer 710, and the third conductive layer 810 in the capacitor area 301 is obtained.

[0044] Modification of the First Embodiment

[0045] FIG. 8D is a perspective top view according to a modification of the first embodiment of the present invention. FIG. 8E is a sectional view taken along line f-f′ of FIG. 8D. Elements in FIGS. 8D and 8E repeated from FIGS. 8A-8C use the same reference numbers. Additionally, because the materials of the parts in the modification is the same as in the above first embodiment, the description of the materials is omitted.

[0046] In FIGS. 8D and 8E, a substrate 300 having a capacitor area 301 and a transistor area 302 is provided. Then, a transversely extending gate line 310 is formed on the substrate 300. The gate line 310 includes a gate electrode 320 in the transistor area 302.

[0047] Next, a gate insulation layer 330 is formed on the gate line 310, the gate electrode 320, and the substrate 300. Then, an amorphous silicon layer 410 and a doped amorphous silicon layer 420 are formed on part of the gate insulation layer 330. Thus, a semiconducting island composed of the amorphous silicon layer 410 and the doped amorphous silicon layer 420 is obtained.

[0048] Next, a longitudinally extending common line 510 and a longitudinally extending data line 520 are formed on the gate insulation layer 330, and simultaneously, a source electrode 530 and a drain electrode 540 are formed on the doped amorphous silicon layer 420. Then, using the source electrode 530 and the drain electrode 540 as a mask, part of the doped amorphous silicon layer 420 is etched to expose part of the surface of the amorphous silicon 410. Thus, a thin film transistor (TFT) structure is obtained on the gate line 310. Also, the drain electrode 540 electrically connects to the data line 520.

[0049] Next, a planarization layer 610 is formed on the gate insulation layer 330, the common line 510, the TFT structure, the data line 520, and the gate line 310. Then, a first conductive layer 620 is formed on the planarization layer 610 in the capacitor area 301. The first conductive layer 620 serves as a bottom electrode or a pixel electrode.

[0050] Next, a dielectric layer 710 is formed on the first conductive layer 620 and the planarization layer 610. The dielectric layer 710 serves as a dielectric layer of a capacitor. Then, a first via hole 720′ and a second via hole 730 (shown in FIG. 8C) penetrating the dielectric layer 710 and the planarization layer 610 are formed. The first via hole 720′ exposes the TFT structure including the surface of the source electrode 530, and the second via hole 730 (shown in FIG. 8C) exposes part of the surface of the first conductive layer 620 and part of the surface of the common line 510.

[0051] Next, a conformal second conductive layer (not shown) is formed on the dielectric layer 710, the interior surrounding surface of the first via hole 720′, and the interior surrounding surface of the second via hole 730 (shown in FIG. 8C). Then, referring to FIGS. 8C and 8E, part of the second conductive layer is removed to form a third conductive layer 810, a fourth conductive layer 820, and an opening 830. The third conductive layer 810 is isolated from the fourth conductive layer 820 by the opening 830. The third conductive layer 810 electrically connects to the source electrode 53, and the first conductive layer 620 electrically connects to the common line 510 by the fourth conductive layer 820. The third conductive layer 810 serves as top electrode or a charge collector electrode. Thus, a storage capacitor or a charge collector electrode. Thus, a storage capacitor structure Cs composed of the first conductive layer 620, the dielectric layer 710, and the third conductive layer 810 in the capacitor area 301 is obtained.

[0052] Second Embodiment

[0053] FIGS. 9A-14A are perspective top views of an X-ray detector array element according to the second embodiment of the present invention. FIGS. 9B-14B are sectional views taken along line c-c′ of FIGS. 9A-14A. FIGS. 9C-14C are sectional views taken along line e-e′ of FIGS. 9A-14A. In order to simplify the illustrations, the accompanying drawings show a substrate in only one sample pixel region. That is, although only one pixel region is shown, the actual number of pixel regions may be very large.

[0054] In FIGS. 9A, 9B, and 9C, a substrate 900, such as a glass substrate, having a capacitor area 901 and a transistor area 902 is provided. Then, deposition and a first photolithography procedure using a first mask (also referred to as a first photo engraving process, PEP I) are performed, and a transversely extending gate line 910 is formed on the substrate 900. The gate line 910 includes a gate electrode 920 in the transistor area 902.

[0055] It should be noted that FIG. 9A shows the gate line 910 having a protruding portion 920 in the transistor area 902, serving as the gate electrode 920. Nevertheless, the present invention is not intended to limit the position of the gate electrode. For example, the gate line 910 located in the transistor area 902 can serve as the gate electrode 920, whose illustration is similar to the modification of the first embodiment and thus is not described again here.

[0056] In FIGS. 9A, 9B, and 9C, a gate insulation layer 930 is formed on the gate line 910, the gate electrode 920, and the substrate 900. The gate line 910 and the gate electrode 920 may be metal formed by deposition. The gate insulation layer 930 may be SiO₂, SiN_x, or SiON formed by deposition.

[0057] In FIGS. 10A, 10B, and 10C, an amorphous silicon layer (α-Si layer, not shown) is deposited on the gate insulation layer 930, and then a doped amorphous silicon layer (e.g. n⁺ α-Si, not shown) is deposited on the amorphous silicon layer. Next, a second photolithography procedure using a second mask (PEP II) is performed, and part of the doped amorphous silicon layer and the amorphous silicon layer are etched to form a semiconducting island on the gate insulation layer 930 in the transistor area 902. The semiconducting island is composed of a patterned amorphous silicon layer 1010 and a patterned doped amorphous silicon layer 1020.

[0058] In FIGS. 11A, 11B, and 11C, a conductive layer (not shown) is deposited on the gate insulation layer 930 and the semiconducting island. Then, a third photolithography procedure using a third mask (PEP III) is performed to remove part of the conductive layer (not shown), and a longitudinally extending common line 1110 and a longitudinally extending data line 1120 are formed on the gate insulation layer 930, and simultaneously, a source electrode 1130 and a drain electrode 1140 are formed on the doped amorphous silicon layer 1020. Then, using the source electrode 1130 and the drain electrode 1140 as a mask, part of the doped amorphous silicon layer 1020 is etched to expose part of the surface of the amorphous silicon layer 1010. Thus, a thin film transistor (TFT) structure in the transistor area 902 is obtained. Also, the drain electrode 1140 electrically connects to the data line 1120.

[0059] In FIGS. 12A, 12B, and 12C, a planarization layer 1210 is formed on the gate insulation layer 930, the common line 1110, the TFT structure, the data line 1120, and the gate line 910. The planarization layer 1210 may be a spin-on-glass (SOG) or organic layer by spin coating. Then, deposition and a fourth photolithography procedure using a fourth mask (PEP IV) are performed, and a first conductive layer 1220 having a first opening 1230 is formed on the planarization layer 1210 in the capacitor area 901. The first conductive layer 1220 may be indium tin oxide (ITO) or indium zinc oxide (IZO) formed by deposition, serving as a bottom electrode or a pixel electrode. The first opening 1230 exposes part of the planarization layer 1210 above the common line 1110.

[0060] In FIGS. 13A, 13B, and 13C, a dielectric layer 1310 is formed on the first conductive layer 1220 and the planarization layer 1210. The dielectric layer 1310 can be SiN_x, SiON, or SiO_xformed by deposition, serving as a dielectric layer of a capacitor. Then, a fourth photolithography procedure using a fourth mask (PEP IV) is performed, and a first via hole 1320 and a second via hole 1330 penetrating the dielectric layer 1310 and the planarization layer 1210 are formed. The first via hole 1320 exposes the surface of the source electrode 1130, and the second via hole 1330 exposes part of the surface of the first conductive layer 1220 and part of the surface of the common line 1110. Also, the second via hole 1330 and the first opening 1230 overlap (regarding the opening area).

[0061] In FIGS. 14A, 14B, and 14C, a conformal second conductive layer (not shown) is formed on the dielectric layer 1310, the interior surrounding surface of the first via hole 1320, and the interior surrounding surface of the second via hole 1330. The second conductive layer may be indium tin oxide (ITO) or indium zinc oxide (IZO) formed by deposition. Then, a sixth photolithography procedure using a sixth reticle (PEP VI) is performed, and part of the second conductive layer is removed to form a third conductive layer 1410, a fourth conductive layer 1420, and a second opening 1430. The third conductive layer 1410 is isolated from the fourth conductive layer 1420 by the second opening 1430. The third conductive layer 1410 electrically connects to the source electrode 1130, and the first conductive layer 1220 electrically connects to the common line 1110 by the fourth conductive layer 1420. The third conductive layer 1410 serves as a top electrode or a charge collector electrode. Thus, a storage capacitor structure Cs composed of the first conductive layer 1220, the dielectric layer 1310, and the third conductive layer 1410 in the capacitor area 901 is obtained.

[0062] In comparison with the background art, the present invention only uses six masks to form the X-ray detector array, thereby decreasing costs.

[0063] Finally, while the present invention has been described by way of example and in terms of the above, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the present invention covers various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation to encompass all such modifications and similar arrangements.