Optical sensor device

Abstract

The optical sensor device includes: a substrate; a first transistor that functions as a light-receiving element and is provided in a pixel region on the substrate, and a second transistor for writing / reading. The first transistor is formed of a transistor using polysilicon, and the second transistor is formed of a transistor using an oxide semiconductor. A light-shielding layer is provided on the back side of the oxide semiconductor of the second transistor. As a result, light can be irradiated onto the optical sensor device for a long time, so that the amount of light received by the first transistor can be increased, and characteristic variations of the second transistor can be suppressed.

Description

Technical Field

[0001] One embodiment of the present invention relates to an optical sensor having a low-temperature polysilicon and an oxide semiconductor. Background Art

[0002] In the case of optical sensors, a type using amorphous silicon that can be formed over a large area or a type using single-crystalline silicon that can be formed with high resolution has become mainstream. In contrast, a type using low-temperature polysilicon has the characteristics of both, and it is expected that an optical sensor with a large area and high resolution can be fabricated.

[0003] However, compared with single-crystalline silicon, low-temperature polysilicon has a large variation in characteristics, resulting in a problem that noise increases when amplifying a signal generated from a photocurrent detected by a photodiode. To solve this problem, it is necessary to increase the photocurrent of the photodiode. For example, thick film formation of low-temperature polysilicon can be considered. However, in the case of low-temperature polysilicon, compared with amorphous silicon, there are problems in that it is difficult to form a thick film and it is difficult to form a uniform p-i-n laminated structure in the film thickness direction.

[0004] Patent Document 1 discloses an optical sensor in which a light-receiving element uses amorphous silicon or microcrystalline silicon, and a peripheral circuit or a pixel transistor uses an oxide semiconductor.

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent No. 5174988 Summary of the Invention

[0008] Problems to be Solved by the Invention

[0009] The optical sensor disclosed in Patent Document 1 is premised on being incorporated into a liquid crystal display. Therefore, its ability as an optical sensor has not been fully considered, and there are deficiencies in terms of performance. In particular, although the photocurrent of amorphous silicon itself can be sufficiently obtained, since a peripheral circuit is formed of an oxide semiconductor, an nMOS circuit with low driving ability is formed. Therefore, there is a problem that the optical sensor cannot have high functionality.

[0010] In view of the above problems, one object of one embodiment of the present invention is to achieve large area and high resolution of an optical sensor device.

[0011] Means for Solving the Problems

[0012] One embodiment of the present invention relates to a photosensor device, comprising: a substrate, a first transistor, a second transistor, and a first light-shielding layer disposed in a pixel region on the substrate; the first transistor includes: a first polysilicon layer disposed on the substrate, a first insulating film disposed on the first polysilicon layer, a first gate electrode disposed on the first insulating film and having a region overlapping with the first polysilicon layer, a second insulating film and a third insulating film disposed on the first gate electrode, and a first source electrode and a first drain electrode electrically connected to the first polysilicon layer through openings provided in the second insulating film and the third insulating film; the second transistor includes: an oxide semiconductor layer disposed on the second insulating film, a third insulating film disposed on the oxide semiconductor layer, a second gate electrode disposed on the third insulating film, a fourth insulating film disposed on the second gate electrode, and a second source electrode and a second drain electrode electrically connected to the oxide semiconductor layer through an opening provided in the fourth insulating film; the first light-shielding layer is disposed between the first insulating film and the second insulating film and has a region overlapping with the first oxide semiconductor layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a layout diagram of the photosensor device according to one embodiment of the present invention.

[0014] Figure 2 is a circuit diagram of a sensor pixel according to one embodiment of the present invention.

[0015] Figure 3 is a timing diagram of a sensor pixel according to one embodiment of the present invention.

[0016] Figure 4 is a planar layout of a sensor pixel according to one embodiment of the present invention.

[0017] Figure 5 is a planar layout of a sensor pixel according to one embodiment of the present invention.

[0018] Figure 6 is a planar layout of a sensor pixel according to one embodiment of the present invention.

[0019] Figure 7 is a cross-sectional view of transistors included in a sensor pixel and a driving circuit.

[0020] Figure 8A is a cross-sectional view for explaining a method of manufacturing a photosensor device according to one embodiment of the present invention.

[0021] Figure 8B is a cross-sectional view for explaining a method of manufacturing a photosensor device according to one embodiment of the present invention.

[0022] Figure 9AThis is a cross-sectional view illustrating a method for manufacturing a photosensor device according to an embodiment of the present invention.

[0023] Figure 9B This is a cross-sectional view illustrating a method for manufacturing a photosensor device according to an embodiment of the present invention.

[0024] Figure 10 This is a cross-sectional view illustrating a method for manufacturing a photosensor device according to an embodiment of the present invention. Detailed Embodiment

[0025] Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. It should be noted that the present invention can be implemented in a variety of different ways and is not limited to the content described in the following exemplary embodiments. In addition, for the sake of clearer explanation, the width, thickness, shape, etc. of each part are schematically shown in the drawings compared to the actual mode, but this is only an example and does not limit the interpretation of the present invention. In addition, in this specification and each figure, for the figures that have appeared, sometimes the same reference numerals are attached to the same elements as those described above, and the detailed description is appropriately omitted.

[0026] (First Embodiment)

[0027] In the present embodiment, for a photosensor device 100 according to an embodiment of the present invention, reference is made to Figures 1 to 10 for description.

[0028] Figure 1 This is a layout diagram of a photosensor device 100 according to an embodiment of the present invention. In a sensor region 102 on a substrate 211, a plurality of sensor pixels 110 are arranged in an array. In addition, a peripheral region 103 is provided so as to surround the sensor region 102. In the peripheral region 103, drive circuits 104_R, 104_L, protection circuits 105_R, 105_L, a terminal region 106, etc. are provided.

[0029] The drive circuits 104_R, 104_L are arranged on the left and right of the sensor region 102. In addition, the protection circuit 105_R is provided between the sensor region 102 and the drive circuit 104_R. The protection circuit 105_L is provided between the sensor region 102 and the drive circuit 104_L.

[0030] The terminal area 106 is a plurality of terminals for inputting signals to the sensor area 102. Various signals are respectively input to the terminals GND_L, Gate_L, VR1_L, RST_L, SVS_L, DCH_L, SVG_L, Sig, GND_R, Gate_R, VR1_R, RST_R, SVS_R, DCH_R, SVG_R. The signal input from the terminal Gate_L is input to the driving circuit 104_L and is input to the sensor area 102 via the protection circuit 105_L. In addition, the signals input from the terminals VR1_L, RST_L, SVS_L, DCH_L, SVG_L, Sig are also input to the sensor area 102. In addition, the signals input from the terminals VR1_R, RST_R, SVS_R, DCH_R, SVG_R are also input to the sensor area 102. Use Figure 2 the pixel circuit shown in Figure 3 and the timing diagram shown in

[0031] [Pixel Circuit]

[0032] Figure 2 is the pixel circuit included in each of the plurality of sensor pixels 110 disposed in the sensor area 102. Each of the plurality of sensor pixels 110 includes at least transistors 201 to 204 and a capacitive element 205. Figure 2 In the sensor pixel 110 shown in Figure 1 Gate, SVS, DCH, RST, Sig, VR1, SVG respectively correspond to the wirings for inputting the signals input to the

[0033] terminal area 106 shown in

[0034] The transistor 201 functions as a light-receiving element. The transistor 201 is formed of polysilicon. The gate of the transistor 201 is electrically connected to the first wiring SVG, and one of the source or drain is electrically connected to one of the source or drain of the transistor 202, electrically connected to one of the source or drain of the transistor 203, and electrically connected to one of the electrodes of the capacitive element 205, and the other of the source or drain is electrically connected to the second wiring SVS.

[0035] The transistor 204 is a reset transistor. The transistor 204 is formed using an oxide semiconductor. The gate of the transistor 204 is electrically connected to the seventh wiring RST, and the other of the source or the drain is electrically connected to the fourth wiring Sig.

[0036] When forming a photodiode and a transistor in the same layer using low-temperature polysilicon, it is impossible to form the p-i-n layer for forming the photodiode into a thick film. Therefore, for the photodiode, a structure that allows current to flow in the planar direction is required. In this case, even if the size of the low-temperature polysilicon is set to a size such as W / L = 3 mm / 3 μm that is easy for current to flow in the planar direction, only a photocurrent of about 1 nA can be obtained. In addition, although the cut-off current of the transistor using low-temperature polysilicon is also related to the conditions of the p-i-n layer, a current of about 1 to 10 pA flows. Therefore, if a large-area photosensor device is to be manufactured, there is a problem that the photocurrent of the selected pixel cannot be detected due to the cut-off current of the transistors connected in parallel to the same signal line.

[0037] Therefore, as in the photosensor device 100 according to an embodiment of the present invention, the transistor 201 that functions as a light-receiving element is formed of polysilicon, and the transistors 202 to 204 for writing / reading are formed of an oxide semiconductor. In addition, the cut-off current of the transistors 202 to 204 using the oxide semiconductor is 1 fA and can be set to be very small. Therefore, it is possible to suppress the leakage of the photocurrent detected by the transistor 201 through the transistors 202 to 204. Thus, even a minute photocurrent detected by a transistor using polysilicon can be detected with high sensitivity. In addition, the influence of the cut-off current of the transistors connected in parallel to the same signal line can be reduced, so that the photosensor device can be made larger in area. In addition, light can be irradiated from the substrate 211 side (the back side of the substrate 211) of the photosensor device 100 for a long time, so that the amount of light received can be increased. Thereby, the characteristic deviation of the transistors 201 in the plurality of sensor pixels 110 can be suppressed. In addition, by irradiating the photosensor device 100 with light for a long time, the amount of light received can be increased, so that the size of the polysilicon can be set to, for example, W / L = 120 / 3.5 μm. In addition, the size of the oxide semiconductor can also be set to, for example, W / L = 240 / 3.5 μm. That is, since the size of each transistor can be reduced, high resolution of the photosensor device 100 can be achieved.

[0038] [Timing diagram of pixel circuit]

[0039] Figure 3 is the timing diagram of the sensor pixel 110. Figure 3 In the shown timing diagram, Gate, SVS, DCH, RST, Sig, VR1, SVG respectively correspond to the inputs toFigure 1 the signals in the terminal region 106 shown, and the signals input to Figure 2 the signals of the first to seventh wirings shown. In addition, Gate1 corresponds to the third wiring Gate1 in the first row, and Gate84 corresponds to the third wiring Gate84 in the 84th row.

[0040] First, during period t1, before resetting the sensor pixel 110, by supplying a high-level potential to the first wiring SVG and the seventh wiring RST, the transistors 201 and 204 are set to the conducting (ON) state. In addition, by supplying a low-level potential to the fifth wiring DCH and the third wiring Gate1, the transistors 202 and 203 are set to the non-conducting (OFF) state. In addition, a low-level potential is supplied to the second wiring SVS.

[0041] Next, during periods t2 and t3, the sensor pixel 110 is reset. During period t2, the transistors 201 and 204 are in the conducting state, and the transistor 203 is in the non-conducting state. By changing the third wiring Gate1 from a low-level potential to a high-level potential, the transistor 202 is changed from the non-conducting state to the conducting state. Thus, by allowing the reset current to flow from the sixth wiring VR1 through the transistors 204 and 202 to the transistor 201, the optical response can be eliminated and the initial state can be achieved. After that, during period t3, by changing the third wiring Gate1 from a high-level potential to a low-level potential, the transistor 202 is changed from the conducting state to the non-conducting state, thus ending the reset of the sensor pixel 110.

[0042] Next, during period t4, before resetting the capacitor element 205, by changing the first wiring SVG from a high-level potential to a low-level potential, the transistor 101 is changed from the conducting state to the non-conducting state.

[0043] Next, during period t5, the capacitor element 205 is reset. During period t5, by changing the fifth wiring DCH from a low-level potential to a high-level potential, the transistor 203 is changed from the non-conducting state to the conducting state. In addition, the low-level potential supplied to the second wiring SVS is changed to a high-level potential. Thus, the charge accumulated in the capacitor element 205 can be changed to a certain level potential by means of the transistor 203. After that, by changing the fifth wiring DCH from a high-level potential to a low-level potential, the transistor 203 is changed from the conducting state to the non-conducting state, thus ending the reset of the capacitor element 205.

[0044] Next, during period t6, light is irradiated to the sensor pixel (exposure period). By irradiating light to the non-conducting transistor 201, charge is accumulated in the capacitor element 205 according to the amount of the irradiated light. Period t6 is, for example, about 1 second.

[0045] Next, during period t7, before reading the charge stored in the capacitor element 205, by changing the seventh wiring RST from a high-level potential to a low-level potential, the transistor 204 is thereby set from the conducting state to the cutoff state.

[0046] Next, during period t8, the charge stored in the capacitor element 205 is read. During period t8, by changing the third wiring Gate1 from a low-level potential to a high-level potential, the transistor 202 is thereby set from the cutoff state to the conducting state. Thus, the charge stored in the capacitor element 205 corresponding to the amount of light can be read from the fourth wiring Sig via the transistor 204.

[0047] Finally, during period t9, by changing the third wiring Gate1 from a high-level potential to a low-level potential, the transistor 202 is thereby set from the conducting state to the cutoff state, thus ending the reading of the charge. In the above driving method, the third wiring Gate1 is taken as an example for explanation, and the same applies to the third wiring Gate84.

[0048] [Planar layout diagram of the optical sensor device]

[0049] Next, regarding the structure of the optical sensor device 100, refer to Figures 4 to 7 for a detailed description. Figure 4 is a planar layout diagram of the optical sensor device 100. Figure 5 is the planar layout of the transistors of the optical sensor device 100 using polysilicon. Figure 6 is the planar layout of the transistors of the optical sensor device 100 using oxide semiconductors. It should be noted that in Figures 4 to 6 only the semiconductor layer and the conductive layer are shown, and the insulating film is omitted from the illustration.

[0050] Figure 4 shows the transistors 201 to 204 and the capacitor element 205. In Figure 4 the four transistors connected in series and in two columns in parallel are regarded as one transistor 201. Similarly, the four transistors connected in series and in two columns in parallel are regarded as one transistor 203.

[0051] As shown in Figure 5As shown, a transistor 201 using polysilicon is configured. A semiconductor layer 213_1 formed of polysilicon that the transistor 201 has is configured. Eight semiconductor layers 213_1 are configured. Conductive layers 215_1 to 215_4 are configured on the semiconductor layer 213_1. The conductive layer 215_1 functions as a gate electrode of the transistor 201, and the conductive layer 215_2 functions as a light-shielding layer of the transistor 202. The conductive layer 215_3 functions as a light-shielding layer of the transistor 203, and the conductive layer 215_4 functions as a light-shielding layer of the transistor 204. Conductive layers 218_1 to 218_7 are configured on the conductive layers 215_1 to 215_4. The conductive layer 218_1 functions as the other of a source electrode or a drain electrode of the transistor 201, and the conductive layers 218_2 and 218_5 function as one of a source electrode or a drain electrode of the transistor 201. The conductive layer 218_3 functions as a gate electrode of the transistor 203, and the conductive layer 218_4 functions as one of electrodes of a capacitor element. The conductive layer 218_6 functions as a gate electrode of the transistor 202, and the conductive layer 218_7 functions as a gate electrode of the transistor 204.

[0052] As Figure 6 shown, transistors 202 to 204 using an oxide semiconductor and a capacitor element 205 are configured. In addition, the conductive layers 215_2 to 215_4 that function as light-shielding layers described previously are configured under the transistors 202 to 204. Semiconductor layers 231_1 to 231_3 formed of an oxide semiconductor that the transistors 202 to 204 have are configured on the conductive layers 215_2 to 215_4. In addition, eight semiconductor layers 231_1 are configured. Conductive layers 218_1 to 218_7 are configured on the semiconductor layers 231_1 to 231_4. Conductive layers 221_1 to 221_5 are configured on the conductive layers 218_1 to 218_7. The conductive layers 221_1 and 221_5 function as one of a source electrode or a drain electrode of the transistor 203. In addition, the conductive layer 221_2 functions as the other of a source electrode or a drain electrode of the transistor 203, as one of a source electrode or a drain electrode of the transistor 202, as one of a source electrode or a drain electrode of the transistor 204, and as the other of electrodes of the capacitor element 205. The conductive layer 221_3 functions as the other of a source electrode or a drain electrode of the transistor 202, and the conductive layer 221_4 functions as the other of a source electrode or a drain electrode of the transistor 204.

[0053] [Cross-sectional view of a photosensor device]

[0054] Figure 7 are shown together in Figure 4The cross-section of the sensor pixel 110 cut along line A1 - A2 and the cross-section cut along line B1 - B2 are shown. Additionally, Figure 7 also shows the cross-section of the drive circuit 104_R not illustrated in Figure 4 . In Figure 7 , as the sensor pixel 110, a cross-sectional view of the transistor 201, the transistor 203, and the capacitor element 205 is shown, and as the peripheral region 103, a cross-sectional view of the transistor 210 in the drive circuit 104_R is shown. It should be noted that the configurations of the transistors constituting the drive circuit 104_L and the protection circuits 105_R and 105_L are the same as that of the transistor 210. For the sensor pixel 110, light is irradiated from the back side of the substrate 211.

[0055] The transistor 201 that functions as a light-receiving element is disposed on the substrate 211 with an intervening base insulating film 212. The transistor 201 is composed of at least a semiconductor layer 213_1, an insulating film 214, and a conductive layer 215_1. The semiconductor layer 213_1 for the transistor 201 is polysilicon. Additionally, in the semiconductor layer 213_1, by adding impurities that impart an n-type, a low-concentration impurity region and a high-concentration impurity region are formed. Here, the insulating film 214 functions as the gate insulating film of the transistor 201. Additionally, insulating films 216 and 217 are provided on the conductive layer 215_1. Conductive layers 218_1 and 218_2 are provided on the insulating film 217. The conductive layers 218_1 and 218_2 are electrically connected to the semiconductor layer 213_1 via openings provided in the insulating films 216 and 217. The insulating films 216 and 217 function as interlayer insulating films.

[0056] An insulating film 219 is provided on the conductive layers 218_1 and 218_2. A conductive layer 221_1 is provided on the insulating film 219. The conductive layer 221_1 is connected to the conductive layer 218_2 via an opening provided in the insulating film 219.

[0057] The transistor 203 is disposed on the insulating film 214. In addition, the transistor 203 is a top-gate type transistor. Further, a conductive layer 215_3 is provided between the insulating film 214 and the insulating film 216. The transistor 203 is composed of at least a semiconductor layer 231_1, an insulating film 217, and a conductive layer 218_3. The semiconductor layer 231_1 for the transistor 203 is an oxide semiconductor. In addition, the insulating film 217 functions as a gate insulating film of the transistor 203. Further, an insulating film 219 is provided on the conductive layer 218_3. Conductive layers 221_1 and 221_2 are provided on the insulating film 219. The conductive layers 221_1 and 221_2 are electrically connected to the semiconductor layer 231_1 via openings provided in the insulating films 217 and 219. In addition, the conductive layer 221_ is connected to the conductive layer 218_2 provided in the insulating film 217. The insulating film 219 functions as an interlayer insulating film. An insulating film 222 is provided on the conductive layers 221_1 and 221_2. An insulating film 224 is provided on the insulating film 222. It should be noted that the transistors 202 and 204 are also transistors that use an oxide semiconductor in the semiconductor layer and have the same structure as the transistor 203. In addition, for the transistors 202 and 204, a conductive layer that functions as a light-shielding layer is also provided.

[0058] The capacitor element 205 is composed of a conductive layer 218_4 on the insulating film 217, a conductive layer 221_2, and an insulating film 219 provided between the conductive layer 218_4 and the conductive layer 221_2. In addition, the capacitor element 205 may further have a conductive layer between the insulating film 214 and the insulating film 216.

[0059] The transistor 210 is provided on a substrate 211. The transistor 210 is a top-gate transistor. In addition, a conductive layer 232 that functions as a light shielding layer is provided between the substrate 211 and the base insulating film 212. The conductive layer 232 that functions as a light shielding layer of the transistor 210 is provided at a lower layer than the conductive layer 215_3 that functions as a light shielding layer of the transistor 203. The semiconductor layer 213_2 used for the transistor 210 is polycrystalline silicon. In addition, in the semiconductor layer 213_2, a low-concentration impurity region and a high-concentration impurity region are formed by adding impurities that impart n-type. Here, the insulating film 214 functions as a gate insulating film of the transistor 210. In addition, a conductive layer 215_5 is provided on the insulating film 214. The conductive layer 215_5 functions as a gate electrode of the transistor 210. Insulating films 214 and 216 are provided on the conductive layer 215_5. Conductive layers 218_8 and 218_9 are provided on the insulating film 216. The conductive layers 218_8 and 218_9 are electrically connected to the semiconductor layer 213_2 via openings provided in the insulating films 214 and 216. That is, the insulating films 214 and 216 function as interlayer insulating films. In addition, as the transistor 210, the configuration of an nch type transistor is illustrated, but one embodiment of the present invention is not limited to this. For example, in the driving circuits 104_R and 104_L, an nch type transistor and a pch type transistor can be combined to form a CMOS device. In addition, an insulating film 219 is provided on the conductive layers 218_8 and 218_9, and an opening is provided in the insulating film 219. The conductive layer 221_5 is connected to the conductive layer 218_8 via the opening, and the conductive layer 221_6 is connected to the conductive layer 218_9 via the opening.

[0060] An insulating film 222 is provided on the conductive layers 221_1 to 221_6. Conductive layers 223_1 and 223_2 are provided on the insulating film 222. The conductive layer 223_1 is connected to the conductive layer 221_1 via an opening provided in the insulating film 222, and the conductive layer 223_2 is connected to the conductive layer 221_5 via an opening provided in the insulating film 222. An insulating film 224 is provided on the conductive layers 223_1 and 223_2. Conductive layers 225_1 and 225_2 are provided on the insulating film 224. The conductive layer 225_1 is connected to the conductive layer 223_1 via an opening provided in the insulating film 224. In addition, the conductive layer 225_2 is connected to the conductive layer 221_5 via an opening provided in the insulating film 224. The conductive layers 223_1, 223_2, 225_1, and 225_2 function as routing wirings.

[0061] As the oxide semiconductor for the semiconductor layers 231_1 to 231_4, it includes Group 13 elements such as indium and gallium. It can contain various different Group 13 elements and can be a compound of indium and gallium (IGO). The semiconductor layers 231_1 to 231_4 can also include Group 12 elements. The semiconductor layer 231 can include other elements, and can include tin as a Group 14 element, titanium, zirconium, etc. as Group 4 elements. As the oxide semiconductor, specifically, for example, indium gallium zinc oxide (IGZO), indium gallium oxide (IGO), indium zinc oxide (IZO), zinc tin oxide (ZnSnO), zinc oxide (ZnO), and transparent amorphous oxide semiconductor (TAOS) can be cited.

[0062] The conductive layers 215_1 to 215_5, the conductive layers 218_1 to 218_9, the conductive layers 221_1 to 221_6, the conductive layers 223_1, 223_2, and the conductive layers 225_1, 225_2 are formed of, for example, molybdenum, chromium, tungsten, aluminum, copper, titanium, nickel, tantalum, silver, or their alloys. The above-mentioned conductive layers are not limited to the metals listed above, and other metals and alloys can also be used. In addition, the conductive materials listed above can be formed into a conductive layer as a single layer or laminated to form a conductive layer.

[0063] The base insulating film 212, the insulating films 214, 216, 217, 219, 222, 224 are formed of an inorganic insulating film such as a silicon oxide film or a silicon nitride film. In addition, not limited to the inorganic insulating film, an organic insulating film using an organic resin can also be used.

[0064] In one embodiment of the present invention, in the sensor pixel 110, polysilicon is used for the semiconductor layer 213_1 of the transistor 201 that functions as a light-receiving element. In addition, oxide semiconductors are used for the semiconductor layers 231_1 to 231_3 of the transistors 202 to 204. The transistor 202 using the oxide semiconductor can make the cut-off current very small compared to the transistor 201 using polysilicon. Therefore, even if the photocurrent detected in the transistor 201 is small and there are characteristic deviations, the sensing time can be increased to accumulate the read charge, and thus the influence of the characteristic deviations of the transistor can be reduced.

[0065] In addition, in the photosensor device 100 according to one embodiment of the present invention, for transistors other than the transistor 201 that functions as a light-receiving element, a conductive layer that functions as a light-shielding layer is provided between the substrate 211 and the semiconductor layer. Therefore, even if light is irradiated from the substrate 211 side for a long time, light irradiation to the semiconductor layers of transistors other than the light-receiving element can be suppressed. Thereby, light irradiation to the semiconductor layers of the transistors 202 to 202, 210 can be suppressed, and the characteristics of the transistors can be prevented from changing.

[0066] In addition, by using CMOS devices to form the drive circuits 104_R and 104_L, the control of current becomes easy, and the through-current can be reduced. As a result, compared with a photosensor using amorphous silicon, driving with reduced noise can be performed.

[0067] [Method for manufacturing a photosensor device]

[0068] Regarding the method for manufacturing the photosensor device 100 according to an embodiment of the present invention, reference is made to FIGS. 8 to Figure 10 for description. FIGS. 8 to Figure 10 The cross-sectional views shown correspond to Figure 7 the cross-sectional views shown.

[0069] Figure 8A FIG. is a diagram for describing the process of forming the conductive layer 232, the base insulating film 212, and the semiconductor layers 213_1 and 213_2 on the substrate 211. As the substrate 211, for example, a glass substrate, a flexible substrate such as polyimide, etc. are used. First, a conductive film is formed on the substrate 211 by sputtering, and the conductive film is processed by a photolithography process to form the conductive layer 232. The conductive layer 232 is formed of a metal material having light-shielding properties. It should be noted that the conductive layer 232 is provided in the regions where the transistors 210 constituting the drive circuits 104_R and 104_L and the protection circuits 105_R and 105_L are to be provided. The conductive layer 232 is preferably provided in each of the transistors constituting the drive circuits 104_R and 104_L and the protection circuits 105_R and 105_L and directly below the semiconductor layer of the transistor.

[0070] Next, the base insulating film 212 is formed on the substrate 211 and the conductive layer 232. The base insulating film 212 is formed by CVD method or sputtering method using, for example, silicon oxide or silicon nitride. As the base insulating film 212, silicon oxide and silicon nitride can be used individually as a single layer, or can be used in a stacked manner. Next, a semiconductor film formed of polysilicon is formed on the base insulating film 212, and the semiconductor film is processed by a photolithography process to form the semiconductor layers 213_1 and 213_2. Here, the semiconductor layer 213_1 is provided in a region that does not overlap with the conductive layer 232, and the semiconductor layer 213_2 is provided in a region that overlaps with the conductive layer 232.

[0071] Figure 8BThis is a diagram for explaining the processes of forming the insulating film 214 and the conductive layers 215_1 to 215_5. First, an insulating film 214 is formed on the semiconductor layers 213_1 and 213_2. The insulating film 214 is formed by CVD method or sputtering method using, for example, silicon oxide or silicon nitride. As the insulating film 214, for example, a silicon nitride film is formed in contact with the semiconductor layers 213_1 and 213_2. The silicon nitride film is a film that contains a relatively high concentration of hydrogen and easily releases hydrogen. By performing a heat treatment in a state where the semiconductor layers 213_1 and 213_2 are in contact with the insulating film 214, the dangling bonds contained in the semiconductor layers 213_1 and 213_2 formed of polysilicon can be capped with hydrogen and become inactive. Next, a conductive film is formed on the insulating film 214 by sputtering method, and the conductive film is processed by a photolithography process, thereby forming the conductive layers 215_1 to 215_5. It should be noted that Figure 8B the conductive layers 215_2 and 215_4 are not shown in the figure, and the conductive layers 215_2 and 215_4 are arranged at Figure 5 the positions shown. The conductive layer 215_1 is formed in a region overlapping with the semiconductor layer 213_1, and then the conductive layers 215_2 to 215_4 are formed in regions overlapping with the semiconductor layers formed of oxide semiconductors, and the conductive layer 215_5 is formed in a region overlapping with the semiconductor layer 213_3.

[0072] Although not shown, doping treatment is performed on the semiconductor layers 213_1 and 213_2 using the conductive layers 215_1 and 215_5 as masks. Thereby, impurity regions are formed in the semiconductor layers 213_1 and 213_2. In the case of forming an nch-type transistor, by adding an impurity that imparts an n-type, a low-concentration impurity region and a high-concentration impurity region are formed in the semiconductor layer. In the case of forming a pch-type transistor, by adding an impurity that imparts a p-type, an impurity region is formed thereby. In the present embodiment, in the drive circuits 104_R and 104_L and the sensor pixel 110, although nch-type transistors are shown, it is not limited thereto. As the transistors constituting the drive circuits 104_R and 104_L, both nch-type transistors and pch-type transistors can be formed.

[0073] Figure 9A This is a diagram for explaining the processes of forming the insulating film 216 and the semiconductor layers 231_1 to 231_4. First, an insulating film 216 is formed on the insulating film 214 and the conductive layers 215_1 to 215_5. The insulating film 216 is formed by CVD method or sputtering method using, for example, silicon oxide or silicon nitride.

[0074] When an oxide semiconductor is used as the semiconductor layer of a transistor, if hydrogen or moisture invades the oxide semiconductor from an adjacent film, the characteristics of the transistor may deteriorate. Specifically, a decrease in the mobility of the transistor and a deviation in the threshold value may occur. Therefore, an insulating film in contact with the semiconductor layers 231_1 to 231_2 preferably uses a film with a reduced hydrogen concentration. Therefore, for the insulating film 216, a silicon oxide film is formed by, for example, CVD method. In addition, for the insulating film 216, it may also be a laminated structure in which a silicon nitride film and a silicon oxide film are laminated from the side of the conductive layers 215_1 to 215_3.

[0075] Next, a semiconductor film using an oxide semiconductor is formed on the insulating film 216 by sputtering, and the semiconductor film is processed by a photolithography process to form semiconductor layers 231_1 to 231_4. The semiconductor layer 231_1 is formed on the conductive layer 215_3 that functions as a light-shielding layer. It should be noted that Figure 9A the semiconductor layers 231_2 to 231_4 are not shown in the figure, and the semiconductor layers 231_2 to 231_4 are arranged at Figure 6 the positions shown.

[0076] When the semiconductor film using an oxide semiconductor is processed into the semiconductor layers 231_1 to 231_4, damage may sometimes occur on the surfaces of the semiconductor layers 231_1 to 231_4. The damaged regions of the semiconductor layers 231_1 to 231_4 include a large number of oxygen defects. Due to the oxygen defects, a problem of an increase in the off-state leakage current of the transistor occurs. In order to reduce the off-state leakage current, it is necessary to introduce sufficient oxygen into the oxide semiconductor through a heat treatment. Therefore, it is preferable to perform the heat treatment in a state where the silicon oxide film is in contact with the semiconductor layers 231_1 to 231_4. The heat treatment is preferably performed, for example, in a nitrogen, dry air, or atmospheric atmosphere. Thereby, oxygen is released from the silicon oxide, and oxygen can be supplied to the damaged regions of the semiconductor layers 231_1 to 231_4. Therefore, the oxygen defects included in the semiconductor layer 231 can be reduced.

[0077] Figure 9BThis is a diagram for explaining the processes of forming the insulating film 217 and the conductive layers 218_1 to 218_9. First, on the insulating film 216 and the semiconductor layer 231, an insulating film 217 is formed by CVD method or sputtering method using, for example, silicon oxide or silicon nitride. For the insulating film 217, for example, it is preferable to form a silicon oxide film from the side of the semiconductor layers 231_1 to 231_4 by CVD method and form a silicon nitride film on the silicon nitride film by sputtering method. Then, a heat treatment can be performed again. The conditions of the heat treatment are the same as those of the heat treatment performed after the formation of the semiconductor layers 231_1 to 231_4. Through this heat treatment, oxygen is released from the silicon oxide film in contact with the semiconductor layers 231_1 to 231_4, and oxygen can be supplied to the damaged regions of the semiconductor layers 231_1 to 231_4. Therefore, the oxygen deficiency contained in the semiconductor layers 231_1 to 231_4 can be reduced. It should be noted that the heat treatment can be performed at any stage after the formation of the semiconductor layers 231_1 to 231_4 or after the formation of the insulating film 217.

[0078] Next, contact holes reaching the semiconductor layers 213_1 and 213_2 are formed in the insulating film 216 and the insulating film 217. Next, a conductive film is formed on the insulating film 217 by sputtering method, and is processed by a photolithography process to form the conductive layers 218_1 to 218_9. It should be noted that Figure 9B the conductive layers 218_5 to 218_7 are not shown in the figure, and the conductive layers 218_5 to 218_7 are arranged at Figure 5 and Figure 6 the positions shown. The conductive layers 218_1 and 218_2 are connected to the semiconductor layer 213_1, and the conductive layer 218_3 is provided in the region overlapping with the semiconductor layer 231. In addition, the conductive layers 218_5 and 218_6 are connected to the semiconductor layer 213_2.

[0079] Although not shown in the figure, hydrogen or argon is added to the semiconductor layer 231 by ion implantation using the conductive layer 218_3 as a mask. Thus, in the semiconductor layer 121, a channel can be formed in the region overlapping with the gate electrode 123, and a low-resistance region can be formed in a manner sandwiching the channel.

[0080] Figure 10This is a diagram for explaining the processes of forming the insulating film 219 and the conductive layers 221_1 to 221_6. First, on the insulating film 217 and the conductive layers 218_1 to 218_9, an insulating film 219 is formed by CVD method or sputtering method using, for example, silicon oxide or silicon nitride. Next, contact holes reaching the conductive layers 218_2, 218_8, 218_9 and the semiconductor layer 231 are formed in the insulating film 219. Next, a conductive film is formed on the insulating film 219 and processed through a photolithography process to form the conductive layers 221_1 to 221_6. The conductive layer 221_1 is connected to the conductive layer 218_2, and the conductive layer 221_2 is connected to the conductive layer 218_2 and the semiconductor layer 231_1. The conductive layer 221_2 is connected to the semiconductor layer 231_1. The conductive layer 221_2 is disposed in a region overlapping with the conductive layer 218_4. The conductive layer 221_5 is connected to the conductive layer 218_8, and the conductive layer 221_6 is connected to the conductive layer 218_9.

[0081] Next, an insulating film 222 is formed on the conductive layers 221_1 to 221_5. Next, openings reaching the conductive layers 221_1 and 221_5 are formed in the insulating film 222, and a conductive film is formed on the insulating film 222. Next, it is processed through a photolithography process to form the conductive layers 223_1_1 and 223_2. Next, an insulating film 224 is formed on the conductive layers 223_1 and 223_2. Next, openings reaching the conductive layers 223_1 and 223_2 are formed in the insulating film 224, and a conductive film is formed on the insulating film 224. Finally, it is processed through a photolithography process to form the conductive layers 225_1_1 and 225_2.

[0082] Through the above processes, the optical sensor device 100 according to one embodiment of the present invention can be manufactured.

[0083] When transistors using polysilicon and transistors using oxide semiconductors are formed on the same substrate, deterioration of the transistors using oxide semiconductors due to hydrogen becomes a problem. In order to improve the characteristics of the transistors using polysilicon, a heat treatment is performed to terminate the defect energy levels at the interface between the polysilicon layer and the gate insulating film. Through this heat treatment, hydrogen is mixed into the oxide semiconductor, and thus the oxide semiconductor becomes degenerate and becomes a conductor.

[0084] In the manufacturing method of the photosensor device 100 according to an embodiment of the present invention, a conductive layer 215_2 that functions as a light-shielding layer of transistors 202 to 204 using an oxide semiconductor is formed using the same conductive film as the conductive layer 215_1 that functions as a gate electrode of the transistor 201 using polysilicon. In addition, a silicon oxide film serving as an insulating film 216 is formed on the conductive layers 215_1 to 215_3, and a silicon oxide film serving as an insulating film 217 is formed. Thus, the hydrogen-absorbing conductive layer 215_2 is provided closer than the drive circuits 104_R and 104_L disposed in the peripheral region 103. Thereby, hydrogen mixing into the semiconductor layers 231_1 to 231_4 of the transistors 202 to 204 can be suppressed. Thus, in the photosensor device 100 according to an embodiment of the present invention, not only the influence of light on the transistors 202 to 204 can be reduced, but also the influence of hydrogen can be suppressed. In addition, the conductive layer 215_2 is disposed at a position higher than the semiconductor layer 213_1 formed of polysilicon. Thereby, light can be reflected by the conductive layer 215_2, and the reflected light can be incident on the semiconductor layer 213_1, so that the light condensing rate can be improved.

[0085] In addition, the photosensor device 100 according to an embodiment of the present invention can be formed not only on a transparent glass substrate but also on a flexible substrate. Therefore, it is possible to cope with various designs and various shapes.

[0086] In the scope of the present invention, those skilled in the art can conceive of various modification examples and alteration examples, and it should be understood that these modification examples and alteration examples also belong to the scope of the present invention. For example, embodiments in which those skilled in the art appropriately add, delete, or design-change constituent elements to the above-described respective embodiments, or embodiments in which processes are added, omitted, or condition-changed, as long as they have the gist of the present invention, are also included in the scope of the present invention.

[0087] Description of Reference Numerals

[0088] 100: Photosensor device, 101: Transistor, 102: Sensor region, 103: Peripheral region, 104: Drive circuit, 105: Protection circuit, 106: Terminal region, 110: Sensor pixel, 121: Semiconductor layer, 123: Gate electrode, 201 to 204: Transistors, 205: Capacitor element, 210: Transistor, 211: Substrate, 212: Base insulating film, 213: Semiconductor layer, 214: Insulating film, 215: Conductive layer, 216: Insulating film, 217: Insulating film, 218: Conductive layer, 219: Insulating film, 221: Conductive layer, 222: Insulating film, 223: Conductive layer, 224: Insulating film, 225: Conductive layer, 231: Semiconductor layer, 232: Conductive layer.

Claims

1. A photosensor device, comprising: a substrate; and a first transistor, a second transistor, and a first light-shielding layer disposed at a pixel region on the substrate, wherein the first transistor includes: a first polysilicon layer disposed on the substrate; a first insulating film disposed on the first polysilicon layer; a first gate electrode disposed on the first insulating film and having a region overlapping with the first polysilicon layer; a second insulating film and a third insulating film disposed on the first gate electrode; and a first source electrode and a first drain electrode electrically connected to the first polysilicon layer through openings provided in the second insulating film and the third insulating film, wherein the second transistor includes: an oxide semiconductor layer disposed on the second insulating film; the third insulating film disposed on the oxide semiconductor layer; a second gate electrode disposed on the third insulating film; a fourth insulating film disposed on the second gate electrode; and a second source electrode and a second drain electrode electrically connected to the oxide semiconductor layer through an opening provided in the fourth insulating film, wherein the first light-shielding layer is disposed between the first insulating film and the second insulating film and has a region overlapping with the oxide semiconductor layer, the photosensor device further includes a capacitor element disposed on the substrate, the capacitor element being composed of a first electrode disposed on the third insulating film, the fourth insulating film, and a second electrode disposed on the fourth insulating film, one of the second source electrode and the second drain electrode being electrically connected to the second electrode, at a driving circuit disposed on the substrate and at the periphery of the pixel region, there is further a third transistor, wherein the third transistor includes: a second light-shielding layer disposed on the substrate; a fifth insulating film disposed on the second light-shielding layer; a second polysilicon layer disposed on the fifth insulating film and having a region overlapping with the second light-shielding layer; the first insulating film disposed on the second polysilicon layer; a third gate electrode disposed on the first insulating film and having a region overlapping with the second polysilicon layer; the second insulating film and the third insulating film disposed on the third gate electrode; and a third source electrode and a third drain electrode electrically connected to the second polysilicon layer through openings provided in the second insulating film and the third insulating film.

2. The photosensor device according to claim 1, wherein one of the first source electrode and the first drain electrode is electrically connected to the other of the second source electrode and the second drain electrode.

3. The optical sensor device according to claim 1, wherein, The first gate electrode is made of the same conductive material as the first light-shielding layer.

4. The optical sensor device according to claim 1, wherein, The first source electrode and the first drain electrode are made of the same conductive material as the second gate electrode.

5. The optical sensor device according to claim 1, wherein, When the first transistor and the second transistor are in the off state, the amount of charge accumulated in the capacitor element is controlled according to the amount of light incident on the first polysilicon layer from the substrate side.

6. The optical sensor device according to claim 5, wherein, When the first transistor is in the off state, by changing the second transistor from the off state to the on state, the charge accumulated in the capacitor element is read.

7. The optical sensor device according to claim 1, wherein, The second light-shielding layer is disposed at a lower layer than the first light-shielding layer.

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