US20100276778A1 - Image sensor - Google Patents
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- US20100276778A1 US20100276778A1 US12/803,844 US80384410A US2010276778A1 US 20100276778 A1 US20100276778 A1 US 20100276778A1 US 80384410 A US80384410 A US 80384410A US 2010276778 A1 US2010276778 A1 US 2010276778A1
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- photodiode
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
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- E—FIXED CONSTRUCTIONS
- E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
- E01C—CONSTRUCTION OF, OR SURFACES FOR, ROADS, SPORTS GROUNDS, OR THE LIKE; MACHINES OR AUXILIARY TOOLS FOR CONSTRUCTION OR REPAIR
- E01C9/00—Special pavings; Pavings for special parts of roads or airfields
- E01C9/007—Vehicle decelerating or arresting surfacings or surface arrangements, e.g. arrester beds ; Escape roads, e.g. for steep descents, for sharp bends
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L27/00—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
- H01L27/14—Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate including semiconductor components sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation
- H01L27/144—Devices controlled by radiation
- H01L27/146—Imager structures
- H01L27/14601—Structural or functional details thereof
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
- H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by at least one potential-jump barrier or surface barrier, e.g. phototransistors
- H01L31/101—Devices sensitive to infrared, visible or ultraviolet radiation
- H01L31/102—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier or surface barrier
- H01L31/103—Devices sensitive to infrared, visible or ultraviolet radiation characterised by only one potential barrier or surface barrier the potential barrier being of the PN homojunction type
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/547—Monocrystalline silicon PV cells
Definitions
- the present invention relates to a photodiode to be employed in an image sensor, and more particularly, to a photodiode to be employed in a CCD, a close contact type image sensor, or the like.
- a photodetector employed in, for example, a charge-coupled device (CCD) using a reduction optical system, which is used in a digital camera, a video camera, or the like and a close contact type image sensor of a one-to-one optical system.
- CCD charge-coupled device
- a photodiode is a photodetector for converting light irradiated thereon into an electrical signal.
- an image projected on a photo-detecting surface thereof can be converted into an electrical signal.
- SN ratio signal to noise ratio Improvement of signal to noise ratio (SN ratio) in a photodiode is important for increase in sensitivity, and can be realized by reducing a total junction capacitance of the photodiode as will be described below.
- FIG. 5A is a schematic view for explaining a structure of a conventional photodiode and shows a section of the photodiode in a direction perpendicular to a photo-detecting surface.
- the conventional photodiode includes a cathode 2 , an auxiliary cathode 3 , a substrate 4 , and an anode 5 .
- the cathode 2 and the auxiliary cathode 3 are each formed of an n-type semiconductor, and the substrate 4 and the anode 5 are each formed of a p-type semiconductor.
- Higher impurity concentration is set in the cathode 2 than in the auxiliary cathode 3 to give higher carrier (electron) concentration.
- higher impurity concentration is set in the anode 5 has than in the substrate 4 to give higher carrier (hole) concentration.
- the higher impurity concentration in the cathode 2 and in the anode 5 is for obtaining sufficient contact with a wiring made of a metal.
- a depletion layer 10 is indicated as a region defined by dotted lines.
- a capacitor capacitor (capacitance) is formed since both carriers don't exist, leaving positive and negative impurity ions held in a crystal lattice.
- FIG. 5B is a schematic view showing a capacitor formed by the depletion layer 10 .
- the capacitor formed by the depletion layer 10 covers an entire junction region of the p-type semiconductor and the n-type semiconductor.
- the entire junction region can be separated as a bottom capacitor region, which is the bottom portion of the auxiliary cathode 3 , and a side capacitor region, which is the side portion of the auxiliary cathode 3 .
- a capacitor 21 corresponds to the bottom capacitor region and a capacitor 22 (capacitance Cg) corresponds to the side capacitor region.
- the (total) junction capacitance of the p-type semiconductor and the n-type semiconductor is equal to the composite of the capacitances of the capacitor 21 and the capacitor 22 .
- the capacitor 21 and the capacitor 22 are connected in parallel to each other, so the junction capacitance Cs is expressed by the following equation (1).
- a total diode capacitance Ct of the photodiode is the sum of the junction capacitance Cs and a cathode wiring capacitance Ch, and is therefore expressed by the following equation (2).
- a photo-detection voltage Vs of the photodiode is determined by an amount of photocharge Qp induced by light and the total diode capacitance Ct, and is therefore expressed by the following equation (3).
- JP 11-112006 A discloses a technique that reduction in the total junction capacitance Cs reduces the total diode capacitance Ct.
- This document discloses a technique that a cathode is enclosed with an auxiliary cathode having a lower impurity concentration to reduce the total junction capacitance Cs.
- the cathode and the auxiliary cathode correspond to the cathode 2 and the auxiliary cathode 3 of FIGS. 5A and 5B , respectively.
- the present invention has been made in view of the above, and therefore has an object to increase a detection voltage of a photodiode for the purpose of improving an SN ratio.
- an image sensor including: a semiconductor substrate of a first conductivity type on which a photo-detecting surface is formed; a semiconductor region of a second conductivity type which is joined to the semiconductor substrate; and a dielectric provided in the semiconductor substrate and polarized owing to a charge forming a depletion layer region which is generated by joining the semiconductor substrate and the semiconductor region together.
- the dielectric may include an oxide of a semiconductor constituting the semiconductor substrate.
- the dielectric in the first or second aspect, may be in one of a state where the dielectric is in contact with the depletion layer region and a state where at least a part of the dielectric is provided in the depletion layer region.
- the detection voltage of the photodiode can be increased.
- FIG. 1 is a schematic view showing a section of a photodiode in a direction perpendicular to a photo-detecting surface according to an embodiment of the present invention
- FIG. 2A is a view for explaining a shape and an operation of a buried oxide
- FIG. 2B shows a cathode viewed from a photo-detecting surface side
- FIGS. 3A to 3C are views for explaining modified examples of a position where a buried oxide is formed
- FIG. 4 is a circuit diagram as an example.
- FIGS. 5A and 5B are views for explaining conventional art.
- a buried oxide which is opposed to a cathode and is in contact with a lower end of a depletion layer.
- the buried oxide is polarized owing to a charge forming the depletion layer, and thus works as a capacitor.
- FIG. 1 is a schematic view for explaining a structure of a photodiode according to this embodiment and shows a section of a photodiode in a direction perpendicular to a photo-detecting surface.
- a photodiode 1 includes a cathode 2 , an auxiliary cathode 3 , a substrate 4 , an anode 5 , and a buried oxide 6 .
- the substrate 4 and the anode 5 are each formed of a p-type semiconductor.
- the cathode and the auxiliary cathode 3 are each formed of an n-type semiconductor.
- the buried oxide 6 is formed of the oxide of the semiconductor (for example, silicon or germanium) forming the substrate 4 .
- the anode 5 has a higher impurity concentration than the substrate 4 and the cathode 2 has a higher impurity concentration than the auxiliary cathode 3 .
- the differences in impurity concentration provide the low impurity concentration at the junction region, reducing the total junction capacitance.
- the photodiode 1 is not limited to the above-mentioned structure.
- the anode 5 and the substrate 4 , and the cathode 2 and the auxiliary cathode 3 may have the same impurity concentration, respectively, and thus the photodiode 1 may include junction between a p-type semiconductor and an n-type semiconductor having a uniform impurity concentration, respectively.
- a photo-detecting surface 7 is formed on the substrate 4 in a plane shape, being exposed to space.
- the anode 5 is formed in the photo-detecting surface 7 and is provided with a terminal for detecting a photo-detection voltage Vs.
- the cathode 2 is formed separately from the anode 5 and the auxiliary cathode 3 is formed so as to enclose the cathode 2 .
- the cathode 2 is provided with a terminal for detecting the photo-detection voltage Vs.
- a depletion layer 10 (depletion layer region), which is indicated by a region between two dotted lines in the drawing.
- the buried oxide 6 is composed of the oxide of the semiconductor constituting the substrate 4 and is provided on the bottom surface of the depletion layer 10 in a contact state.
- the buried oxide 6 constitutes a dielectric body which is polarized by the charge in the depletion layer 10 .
- the buried oxide 6 needs only to be a dielectric body polarized by the charge in the depletion layer 10 and may not necessarily be the oxide of the semiconductor constituting the substrate 4 .
- the buried oxide 6 is composed of the oxide of the semiconductor constituting the substrate 4 , it is sufficient that a process step of forming a thin film serving as the buried oxide 6 through oxidation of the semiconductor is added to a manufacturing process of the photodiode 1 (for example, ion implantation of an oxygen atom), suppressing an increase in cost due to forming the buried oxide 6 .
- the substrate 4 and the anode 5 constitute a first conductivity type (p-type) semiconductor substrate on which the photo-detecting surface 7 is formed.
- the cathode 2 and the auxiliary cathode 3 constitute a second conductivity type (n-type) semiconductor region provided in the semiconductor substrate (substrate 4 ).
- FIG. 2A is a view for explaining a shape and an operation of the buried oxide 6 .
- the depletion layer 10 is formed over the entire junction surface of the auxiliary cathode 3 and the substrate 4 .
- the auxiliary cathode 3 is enclosed by the substrate 4 except a portion of the photo-detecting surface 7 , the auxiliary cathode 3 is also enclosed by the depletion layer 10 .
- the thickness of the depletion layer 10 is substantially uniform and about 0.1 to 2 or 3 ⁇ m.
- the thickness of the buried oxide 6 is set to approximately equal to that (Al) of the depletion layer 10
- the size of the buried oxide 6 in a direction parallel to the photo-detecting surface 7 is set to approximately equal to the size of the inner surface (A 2 ) of the depletion layer 10 .
- the shape of the buried oxide 6 is an example and maybe larger (or smaller) than the A 2 or may enclose the auxiliary cathode 3 .
- the thickness of the buried oxide 6 can be appropriately selected such that the sum of the capacitances of a capacitor 23 and a capacitor 24 described below is smaller.
- the depletion layer 10 forms capacitors, which can be considered as a capacitor 22 (capacitance Cg) and a capacitor 21 (capacitance Ci) that are connected in parallel.
- the capacitor 22 is formed in the auxiliary cathode 3 in the side surface direction of the auxiliary cathode 3 (in a direction perpendicular to the photo-detecting surface 7 ).
- the capacitor 23 is formed in the auxiliary cathode 3 in the bottom surface direction of the auxiliary cathode 3 (in a direction parallel to the photo-detecting surface 7 ).
- the buried oxide 6 is a dielectric body and in contact with the depletion layer 10 on the surface opposed to the auxiliary cathode 3 , which yields polarization in the buried oxide 6 by a field formed by negative charges generated in the depletion layer 10 . Accordingly, positive charges are induced on the surface side of the buried oxide 6 which is opposed to the auxiliary cathode 3 , while negative charges are induced on the other surface side thereof. Thus, the buried oxide 6 forms the capacitor 24 (capacitance C 3 ).
- FIG. 2B shows the cathode 2 viewed from the side of the photo-detecting surface 7 .
- the cathode 2 is formed in a rectangular shape and the auxiliary cathode 3 is formed in a substantially similar shape around the cathode 2 .
- the buried oxide 6 is also formed in a rectangular shape, the periphery of which is larger than that of the cathode 2 and is smaller than that of the auxiliary cathode 3 .
- the cathode 2 , the auxiliary cathode 3 , and the buried oxide 6 are not limited to have the rectangular shape and can have any shape, for example, circular or elliptical shape. Further, any size of the cathode 2 can be adopted as long as a sufficient junction with a metal wiring can be obtained.
- the total junction capacitance Cs is the composite of: the capacitances of the capacitor 21 (capacitance Ci) and the capacitor 24 (capacitance C 3 ), which are connected in series; and the capacitance of the capacitor 22 (capacitance Cg), which is connected in parallel to the capacitors 21 and 24 .
- the following equation (4) thus can be obtained.
- the total junction capacitance Cs of the photodiode 1 is smaller than that of the conventional art.
- providing the buried oxide 6 in the photodiode 1 can increase the photo-detection voltage Vs of the photodiode 1 and can improve the SN ratio.
- FIG. 3A shows an example in which a part of the buried oxide 6 is formed in the depletion layer 10 .
- a part of the buried oxide 6 which includes a surface opposed to the depletion layer 10 , is formed in the depletion layer 10 , while the other part of the buried oxide 6 , which includes a surface opposed to the above-mentioned surface, is formed outside the depletion layer 10 .
- FIG. 3B shows an example in which the buried oxide 6 is entirely formed in the depletion layer 10 .
- FIG. 3C shows an example in which the buried oxide 6 is formed outside the depletion layer 10 .
- FIG. 4 is a circuit diagram showing a general applied circuit using the photodiode 1 .
- the anode 5 of the photodiode 1 is grounded, and the cathode 2 is connected to an amplifier 33 .
- the amplifier 33 amplifies the output (photo-detection voltage Vs) from the photodiode 1 and sends it as a photo-signal through an output terminal 34 .
- the photodiode 1 and a battery for initialization 32 constitute a closed circuit through an on/off switch 31 for initialization.
- the cathode 2 and the auxiliary cathode 3 are n-type semiconductors and the substrate 4 and the anode 5 are p-type semiconductors.
- the polarities of the semiconductors can be exchanged. That is, regions corresponding to the cathode 2 and the auxiliary cathode 3 can be formed by p-type semiconductors to function as anodes and regions corresponding to the substrate 4 and the anode 5 can be formed by n-type semiconductors to function as cathodes.
Abstract
A buried oxide is provided in a substrate of a photodiode so as to be opposed to a cathode and is in contact with a lower end of a depletion layer. The buried oxide is polarized owing to charges forming the depletion layer and thus works as a capacitor. A capacitor formed in the depletion layer and the additional capacitor made by the buried oxide are, therefore, connected in series, which reduces a total junction capacitance Cs. Increase in photo-detection voltage Vs results in according to an equation, Vs=Qp/Ct, since an amount of photocharge Qp is constant. The increase in the photo-detection voltage Vs allows an improvement in the SN ratio of the photodiode. Further, easy formation of the buried oxide, for example, by implanting oxygen ions, permits low-cost manufacturing of the photodiode.
Description
- 1. Field of the Invention
- The present invention relates to a photodiode to be employed in an image sensor, and more particularly, to a photodiode to be employed in a CCD, a close contact type image sensor, or the like.
- 2. Description of the Related Art
- In recent years, vigorous development is being made on a photodetector employed in, for example, a charge-coupled device (CCD) using a reduction optical system, which is used in a digital camera, a video camera, or the like and a close contact type image sensor of a one-to-one optical system.
- In particular, a photodiode is a photodetector for converting light irradiated thereon into an electrical signal. By using the photodiode, an image projected on a photo-detecting surface thereof can be converted into an electrical signal.
- Improvement of signal to noise ratio (SN ratio) in a photodiode is important for increase in sensitivity, and can be realized by reducing a total junction capacitance of the photodiode as will be described below.
-
FIG. 5A is a schematic view for explaining a structure of a conventional photodiode and shows a section of the photodiode in a direction perpendicular to a photo-detecting surface. - The conventional photodiode includes a
cathode 2, anauxiliary cathode 3, a substrate 4, and ananode 5. - Of those constituents, the
cathode 2 and theauxiliary cathode 3 are each formed of an n-type semiconductor, and the substrate 4 and theanode 5 are each formed of a p-type semiconductor. - Higher impurity concentration is set in the
cathode 2 than in theauxiliary cathode 3 to give higher carrier (electron) concentration. And higher impurity concentration is set in theanode 5 has than in the substrate 4 to give higher carrier (hole) concentration. The higher impurity concentration in thecathode 2 and in theanode 5 is for obtaining sufficient contact with a wiring made of a metal. - In general, when a junction between an n-type semiconductor and a p-type semiconductor is made, holes diffuse from the p-type region to the n-type region on a junction surface and simultaneously electrons diffuse from the n-type region to the p-type region, generating a region containing no carrier (depletion layer). In
FIG. 5A , adepletion layer 10 is indicated as a region defined by dotted lines. In the depletion layer 10 a capacitor (capacitance) is formed since both carriers don't exist, leaving positive and negative impurity ions held in a crystal lattice. -
FIG. 5B is a schematic view showing a capacitor formed by thedepletion layer 10. - The capacitor formed by the
depletion layer 10 covers an entire junction region of the p-type semiconductor and the n-type semiconductor. The entire junction region can be separated as a bottom capacitor region, which is the bottom portion of theauxiliary cathode 3, and a side capacitor region, which is the side portion of theauxiliary cathode 3. - A capacitor 21 (capacitance Ci) corresponds to the bottom capacitor region and a capacitor 22 (capacitance Cg) corresponds to the side capacitor region.
- The (total) junction capacitance of the p-type semiconductor and the n-type semiconductor (total junction capacitance of the
auxiliary cathode 3 and the substrate 4) is equal to the composite of the capacitances of thecapacitor 21 and thecapacitor 22. - The
capacitor 21 and thecapacitor 22 are connected in parallel to each other, so the junction capacitance Cs is expressed by the following equation (1). -
Cs=Cg+Ci (1) - Further, a total diode capacitance Ct of the photodiode is the sum of the junction capacitance Cs and a cathode wiring capacitance Ch, and is therefore expressed by the following equation (2).
-
Ct=Cs+Ch (2) - Further, a photo-detection voltage Vs of the photodiode is determined by an amount of photocharge Qp induced by light and the total diode capacitance Ct, and is therefore expressed by the following equation (3).
-
Vs=Qp/Ct (3) - As is apparent from the equation (3), a large photocharge Qp or a small capacitance Ct is needed to have an increased photo-detection voltage Vs to improve the SN ratio.
- JP 11-112006 A discloses a technique that reduction in the total junction capacitance Cs reduces the total diode capacitance Ct. This document discloses a technique that a cathode is enclosed with an auxiliary cathode having a lower impurity concentration to reduce the total junction capacitance Cs. The cathode and the auxiliary cathode correspond to the
cathode 2 and theauxiliary cathode 3 ofFIGS. 5A and 5B , respectively. - However, further improvement of SN ratio in the photodiode has been still demanded in the conventional technique. In particular, downsizing (area reduction) of the photodiode has been in progress, raising a need for technique of achieving a sufficient SN ratio, which can be applied to even such a downsized photodiode.
- The present invention has been made in view of the above, and therefore has an object to increase a detection voltage of a photodiode for the purpose of improving an SN ratio.
- To achieve the above-described object, according to a first aspect of the present invention, there is provided an image sensor, including: a semiconductor substrate of a first conductivity type on which a photo-detecting surface is formed; a semiconductor region of a second conductivity type which is joined to the semiconductor substrate; and a dielectric provided in the semiconductor substrate and polarized owing to a charge forming a depletion layer region which is generated by joining the semiconductor substrate and the semiconductor region together.
- According to a second aspect of the present invention, in the first aspect, the dielectric may include an oxide of a semiconductor constituting the semiconductor substrate.
- According to a third aspect of the present invention, in the first or second aspect, the dielectric may be in one of a state where the dielectric is in contact with the depletion layer region and a state where at least a part of the dielectric is provided in the depletion layer region.
- According to the present invention, the detection voltage of the photodiode can be increased.
- In the accompanying drawings:
-
FIG. 1 is a schematic view showing a section of a photodiode in a direction perpendicular to a photo-detecting surface according to an embodiment of the present invention; -
FIG. 2A is a view for explaining a shape and an operation of a buried oxide; -
FIG. 2B shows a cathode viewed from a photo-detecting surface side; -
FIGS. 3A to 3C are views for explaining modified examples of a position where a buried oxide is formed; -
FIG. 4 is a circuit diagram as an example; and -
FIGS. 5A and 5B are views for explaining conventional art. - (1) Outline of Embodiment
- Provided in a substrate of a photodiode is a buried oxide which is opposed to a cathode and is in contact with a lower end of a depletion layer.
- The buried oxide is polarized owing to a charge forming the depletion layer, and thus works as a capacitor.
- Thus, a capacitor formed in the depletion layer and the capacitor of the buried oxide are connected in series to each other, which reduces a total junction capacitance Cs. This increases the light detection voltage Vs according to the equation (3) since the amount of photocharge Qp is constant. As a result, an improved SN ratio is achieved.
- (2) Details of Embodiment
-
FIG. 1 is a schematic view for explaining a structure of a photodiode according to this embodiment and shows a section of a photodiode in a direction perpendicular to a photo-detecting surface. - A
photodiode 1 includes acathode 2, anauxiliary cathode 3, a substrate 4, ananode 5, and a buriedoxide 6. The substrate 4 and theanode 5 are each formed of a p-type semiconductor. The cathode and theauxiliary cathode 3 are each formed of an n-type semiconductor. The buriedoxide 6 is formed of the oxide of the semiconductor (for example, silicon or germanium) forming the substrate 4. - The
anode 5 has a higher impurity concentration than the substrate 4 and thecathode 2 has a higher impurity concentration than theauxiliary cathode 3. - The differences in impurity concentration provide the low impurity concentration at the junction region, reducing the total junction capacitance.
- Note that the
photodiode 1 is not limited to the above-mentioned structure. Theanode 5 and the substrate 4, and thecathode 2 and theauxiliary cathode 3 may have the same impurity concentration, respectively, and thus thephotodiode 1 may include junction between a p-type semiconductor and an n-type semiconductor having a uniform impurity concentration, respectively. - A photo-detecting
surface 7 is formed on the substrate 4 in a plane shape, being exposed to space. Theanode 5 is formed in the photo-detectingsurface 7 and is provided with a terminal for detecting a photo-detection voltage Vs. - Further, in the photo-detecting
surface 7, thecathode 2 is formed separately from theanode 5 and theauxiliary cathode 3 is formed so as to enclose thecathode 2. Thecathode 2 is provided with a terminal for detecting the photo-detection voltage Vs. - In a junction surface between the
auxiliary cathode 3 and the substrate 4, holes diffuse from theauxiliary cathode 3 to the substrate 4 and electrons diffuse from the substrate 4 to theauxiliary cathode 3, forming a depletion layer 10 (depletion layer region), which is indicated by a region between two dotted lines in the drawing. - The buried
oxide 6 is composed of the oxide of the semiconductor constituting the substrate 4 and is provided on the bottom surface of thedepletion layer 10 in a contact state. The buriedoxide 6 constitutes a dielectric body which is polarized by the charge in thedepletion layer 10. - Note that the buried
oxide 6 needs only to be a dielectric body polarized by the charge in thedepletion layer 10 and may not necessarily be the oxide of the semiconductor constituting the substrate 4. - When the buried
oxide 6 is composed of the oxide of the semiconductor constituting the substrate 4, it is sufficient that a process step of forming a thin film serving as the buriedoxide 6 through oxidation of the semiconductor is added to a manufacturing process of the photodiode 1 (for example, ion implantation of an oxygen atom), suppressing an increase in cost due to forming the buriedoxide 6. - When light irradiates the photo-detecting
surface 7 of thephotodiode 1 constituted as described above, an electron-hole pair is generated at a junction between theauxiliary cathode 3 and the substrate 4 and accumulated in thedepletion layer 10. Therefore, the light having irradiated the photo-detectingsurface 7 can be detected as a voltage between theanode 5 and thecathode 2. - As described above, the substrate 4 and the
anode 5 constitute a first conductivity type (p-type) semiconductor substrate on which the photo-detectingsurface 7 is formed. - In addition, the
cathode 2 and theauxiliary cathode 3 constitute a second conductivity type (n-type) semiconductor region provided in the semiconductor substrate (substrate 4). -
FIG. 2A is a view for explaining a shape and an operation of the buriedoxide 6. - As indicated by dotted lines of
FIG. 2A , thedepletion layer 10 is formed over the entire junction surface of theauxiliary cathode 3 and the substrate 4. - Since the
auxiliary cathode 3 is enclosed by the substrate 4 except a portion of the photo-detectingsurface 7, theauxiliary cathode 3 is also enclosed by thedepletion layer 10. The thickness of thedepletion layer 10 is substantially uniform and about 0.1 to 2 or 3 μm. - In this embodiment, the thickness of the buried
oxide 6 is set to approximately equal to that (Al) of thedepletion layer 10, and the size of the buriedoxide 6 in a direction parallel to the photo-detectingsurface 7 is set to approximately equal to the size of the inner surface (A2) of thedepletion layer 10. - Note that the shape of the buried
oxide 6 is an example and maybe larger (or smaller) than the A2 or may enclose theauxiliary cathode 3. - The thickness of the buried
oxide 6 can be appropriately selected such that the sum of the capacitances of a capacitor 23 and acapacitor 24 described below is smaller. - The
depletion layer 10 forms capacitors, which can be considered as a capacitor 22 (capacitance Cg) and a capacitor 21 (capacitance Ci) that are connected in parallel. - Here, the
capacitor 22 is formed in theauxiliary cathode 3 in the side surface direction of the auxiliary cathode 3 (in a direction perpendicular to the photo-detecting surface 7). The capacitor 23 is formed in theauxiliary cathode 3 in the bottom surface direction of the auxiliary cathode 3 (in a direction parallel to the photo-detecting surface 7). - Therefore, a positive charge due to a positive ion is generated in the
depletion layer 10 on the side of theauxiliary cathode 3, and a negative charge due to a negative ion is generated in thedepletion layer 10 on the side of the substrate 4. - On the other hand, the buried
oxide 6 is a dielectric body and in contact with thedepletion layer 10 on the surface opposed to theauxiliary cathode 3, which yields polarization in the buriedoxide 6 by a field formed by negative charges generated in thedepletion layer 10. Accordingly, positive charges are induced on the surface side of the buriedoxide 6 which is opposed to theauxiliary cathode 3, while negative charges are induced on the other surface side thereof. Thus, the buriedoxide 6 forms the capacitor 24 (capacitance C3). -
FIG. 2B shows thecathode 2 viewed from the side of the photo-detectingsurface 7. - The
cathode 2 is formed in a rectangular shape and theauxiliary cathode 3 is formed in a substantially similar shape around thecathode 2. - The buried
oxide 6 is also formed in a rectangular shape, the periphery of which is larger than that of thecathode 2 and is smaller than that of theauxiliary cathode 3. - Note that the
cathode 2, theauxiliary cathode 3, and the buriedoxide 6 are not limited to have the rectangular shape and can have any shape, for example, circular or elliptical shape. Further, any size of thecathode 2 can be adopted as long as a sufficient junction with a metal wiring can be obtained. - Referring to
FIG. 2A again, description of the total junction capacitance Cs in a case in which the buriedoxide 6 is provided will be made. - When the buried
oxide 6 is provided, the total junction capacitance Cs is the composite of: the capacitances of the capacitor 21 (capacitance Ci) and the capacitor 24 (capacitance C3), which are connected in series; and the capacitance of the capacitor 22 (capacitance Cg), which is connected in parallel to thecapacitors -
Cs=Cg+Ci×C3/(Ci+C3) (4) - Comparing the equation (4) with the equation (1) of the conventional art, it is found that the second term of the right side of the equation (4) is smaller than that (Ci) of the equation (1).
- Accordingly, the total junction capacitance Cs of the
photodiode 1 is smaller than that of the conventional art. - As a result, it is found from the expression (3) that the total diode capacitance Ct of the
photodiode 1 is smaller than that of the conventional art, and the photo-detection voltage Vs of thephotodiode 1 is larger than that of the conventional example. - Thus, providing the buried
oxide 6 in thephotodiode 1 can increase the photo-detection voltage Vs of thephotodiode 1 and can improve the SN ratio. - Next, modified examples of the position where the buried
oxide 6 is formed will be described. -
FIG. 3A shows an example in which a part of the buriedoxide 6 is formed in thedepletion layer 10. - A part of the buried
oxide 6, which includes a surface opposed to thedepletion layer 10, is formed in thedepletion layer 10, while the other part of the buriedoxide 6, which includes a surface opposed to the above-mentioned surface, is formed outside thedepletion layer 10. -
FIG. 3B shows an example in which the buriedoxide 6 is entirely formed in thedepletion layer 10. - This corresponds to a case in which the buried
oxide 6 is inserted into a capacitor formed in thedepletion layer 10 as a dielectric material. -
FIG. 3C shows an example in which the buriedoxide 6 is formed outside thedepletion layer 10. In this case, it is advantageous to form the buriedoxide 6 to be as close to thedepletion layer 10 as possible because the polarization of the buriedoxide 6 becomes smaller as the buriedoxide 6 is separated from thedepletion layer 10. -
FIG. 4 is a circuit diagram showing a general applied circuit using thephotodiode 1. - As shown in
FIG. 4 , theanode 5 of thephotodiode 1 is grounded, and thecathode 2 is connected to anamplifier 33. Theamplifier 33 amplifies the output (photo-detection voltage Vs) from thephotodiode 1 and sends it as a photo-signal through anoutput terminal 34. - In addition, the
photodiode 1 and a battery forinitialization 32 constitute a closed circuit through an on/offswitch 31 for initialization. - Application of reverse voltage to the
photodiode 1 by closing theinitialization switch 31 can initialize the accumulated charges, which are photocharge Qp, in thedepletion layer 10 of thephotodiode 1. - According to the embodiment described above, following effects can be obtained.
- (1) Arrangement of the buried
oxide 6 can yield the smaller total junction capacitance Cs and the higher photo-detection voltage Vs. - (2) Increase in the photo-detection voltage Vs can improve the SN ratio of the
photodiode 1. - (3) Easy formation of the buried
oxide 6, for example, by implanting oxygen ions, permits low-cost manufacturing of thephotodiode 1. - In this embodiment, the
cathode 2 and theauxiliary cathode 3 are n-type semiconductors and the substrate 4 and theanode 5 are p-type semiconductors. However, the polarities of the semiconductors can be exchanged. That is, regions corresponding to thecathode 2 and theauxiliary cathode 3 can be formed by p-type semiconductors to function as anodes and regions corresponding to the substrate 4 and theanode 5 can be formed by n-type semiconductors to function as cathodes.
Claims (6)
1. An image sensor, comprising:
a semiconductor substrate of a first conductivity type having a photo-detecting surface on one side;
a semiconductor region of a second conductivity type disposed under the photo-detecting surface, and making a junction with the semiconductor substrate; and
a dielectric body disposed in the semiconductor substrate, and polarized owing to charges forming a depletion layer region, the depletion layer region being generated by the semiconductor substrate and the semiconductor region.
2. An image sensor according to claim 1 , wherein the dielectric body comprises an oxide of a semiconductor constituting the semiconductor substrate.
3. An image sensor according to claim 1 , wherein the dielectric body is in contact with the depletion layer region.
4. An image sensor according to claim 1 , wherein at least a part of the dielectric body is provided in the depletion layer region.
5. An image sensor according to claim 2 , wherein the dielectric body is in contact with the depletion layer region.
6. An image sensor according to claim 2 , wherein at least a part of the dielectric body is provided in the depletion layer region.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
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US12/803,844 US20100276778A1 (en) | 2005-03-15 | 2010-07-08 | Image sensor |
Applications Claiming Priority (4)
Application Number | Priority Date | Filing Date | Title |
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JP2005072261A JP4369885B2 (en) | 2005-03-15 | 2005-03-15 | Image sensor |
JP2005-072261 | 2005-03-15 | ||
US11/375,295 US7768046B2 (en) | 2005-03-15 | 2006-03-14 | Image sensor |
US12/803,844 US20100276778A1 (en) | 2005-03-15 | 2010-07-08 | Image sensor |
Related Parent Applications (1)
Application Number | Title | Priority Date | Filing Date |
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US11/375,295 Division US7768046B2 (en) | 2005-03-15 | 2006-03-14 | Image sensor |
Publications (1)
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US20100276778A1 true US20100276778A1 (en) | 2010-11-04 |
Family
ID=37009427
Family Applications (2)
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US11/375,295 Expired - Fee Related US7768046B2 (en) | 2005-03-15 | 2006-03-14 | Image sensor |
US12/803,844 Abandoned US20100276778A1 (en) | 2005-03-15 | 2010-07-08 | Image sensor |
Family Applications Before (1)
Application Number | Title | Priority Date | Filing Date |
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US11/375,295 Expired - Fee Related US7768046B2 (en) | 2005-03-15 | 2006-03-14 | Image sensor |
Country Status (5)
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US (2) | US7768046B2 (en) |
JP (1) | JP4369885B2 (en) |
KR (1) | KR101256227B1 (en) |
CN (1) | CN100573924C (en) |
TW (1) | TWI390720B (en) |
Families Citing this family (7)
Publication number | Priority date | Publication date | Assignee | Title |
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US7755117B2 (en) * | 2006-12-12 | 2010-07-13 | Intersil Americas Inc. | Light sensors with infrared suppression |
US8456410B2 (en) * | 2006-12-12 | 2013-06-04 | Intersil Americas Inc. | Backlight control using light sensors with infrared suppression |
DE112007003037B4 (en) * | 2006-12-12 | 2016-04-28 | Intersil Americas Inc. | Infrared suppression light sensors and backlight control system having such a light sensor |
JP5089159B2 (en) * | 2006-12-20 | 2012-12-05 | セイコーインスツル株式会社 | Manufacturing method of image sensor IC |
EP2254159A4 (en) * | 2007-12-25 | 2012-06-20 | Seiko Instr Inc | Optical detection device, and image display device |
US8492699B2 (en) * | 2009-09-22 | 2013-07-23 | Intersil Americas Inc. | Photodetectors useful as ambient light sensors having an optical filter rejecting a portion of infrared light |
US8778717B2 (en) * | 2010-03-17 | 2014-07-15 | Taiwan Semiconductor Manufacturing Company, Ltd. | Local oxidation of silicon processes with reduced lateral oxidation |
Family Cites Families (5)
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US4961097A (en) * | 1985-03-11 | 1990-10-02 | Motorola Inc. | High frequency photo detector and method for the manufacture thereof |
US5360987A (en) * | 1993-11-17 | 1994-11-01 | At&T Bell Laboratories | Semiconductor photodiode device with isolation region |
US5671914A (en) * | 1995-11-06 | 1997-09-30 | Spire Corporation | Multi-band spectroscopic photodetector array |
US6027956A (en) * | 1998-02-05 | 2000-02-22 | Integration Associates, Inc. | Process for producing planar dielectrically isolated high speed pin photodiode |
TW381345B (en) * | 1998-06-15 | 2000-02-01 | United Microelectronics Corp | CMOS semiconductor sensor structure and the manufacturing method thereof |
-
2005
- 2005-03-15 JP JP2005072261A patent/JP4369885B2/en not_active Expired - Fee Related
-
2006
- 2006-03-14 KR KR1020060023504A patent/KR101256227B1/en active IP Right Grant
- 2006-03-14 US US11/375,295 patent/US7768046B2/en not_active Expired - Fee Related
- 2006-03-15 CN CNB2006100591596A patent/CN100573924C/en not_active Expired - Fee Related
- 2006-03-15 TW TW095108789A patent/TWI390720B/en not_active IP Right Cessation
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2010
- 2010-07-08 US US12/803,844 patent/US20100276778A1/en not_active Abandoned
Also Published As
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JP2006261153A (en) | 2006-09-28 |
TWI390720B (en) | 2013-03-21 |
CN1841790A (en) | 2006-10-04 |
CN100573924C (en) | 2009-12-23 |
US7768046B2 (en) | 2010-08-03 |
JP4369885B2 (en) | 2009-11-25 |
KR20060100215A (en) | 2006-09-20 |
TW200705653A (en) | 2007-02-01 |
US20060208333A1 (en) | 2006-09-21 |
KR101256227B1 (en) | 2013-04-17 |
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