WO2006046385A1 - 固体撮像素子 - Google Patents
固体撮像素子 Download PDFInfo
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- WO2006046385A1 WO2006046385A1 PCT/JP2005/018151 JP2005018151W WO2006046385A1 WO 2006046385 A1 WO2006046385 A1 WO 2006046385A1 JP 2005018151 W JP2005018151 W JP 2005018151W WO 2006046385 A1 WO2006046385 A1 WO 2006046385A1
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- 238000005247 gettering Methods 0.000 claims abstract description 95
- 239000012535 impurity Substances 0.000 claims abstract description 76
- 239000000758 substrate Substances 0.000 claims abstract description 25
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 24
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Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/322—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to modify their internal properties, e.g. to produce internal imperfections
- H01L21/3221—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to modify their internal properties, e.g. to produce internal imperfections of silicon bodies, e.g. for gettering
-
- 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
- H01L27/14603—Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
-
- 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
- H01L27/14683—Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
- H01L27/14698—Post-treatment for the devices, e.g. annealing, impurity-gettering, shor-circuit elimination, recrystallisation
-
- 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
- H01L27/148—Charge coupled imagers
- H01L27/14806—Structural or functional details thereof
Definitions
- the present invention relates to a technique for improving an SZN ratio by reducing dark current in a solid-state imaging device.
- Solid-state imaging devices are classified into several types.
- CCD Charge Coupled Device
- CMOS Complementary Metal-Oxide Semiconductor
- a CCD solid-state image sensor converts light into electric charge with a photodiode, and transfers the electric charge in a bucket relay system at a transfer section that is arranged horizontally.
- the CMOS solid-state image sensor does not transfer charge, but immediately changes the voltage to read.
- the CMOS type is also called an amplification type because it amplifies during voltage conversion, and is superior to the CCD type in terms of low power consumption!
- Such an amplification type solid-state imaging device guides the signal charges accumulated in the light receiving portion of each pixel to the control electrode of the amplifying transistor formed in each pixel, and sends the amplified pixel signal to the main electrode Is configured to output from.
- a transistor using a MOS transistor is known, and is described in Patent Document 1, Patent Document 2, and the like.
- An amplification type solid-state imaging device using a junction field effect transistor (hereinafter abbreviated as an amplification transistor is also known and described in Patent Document 3 and the like.
- an impurity diffusion region which is a main part of a pixel, or a shallow trench (for example, electrically separating pixels) is formed in an epitaxial layer or a hole on a semiconductor substrate.
- Patent Document 4 Since such a manufacturing process involves cleaning, etching, etc., some metal impurities are mixed in the wafer.
- the metal impurities here are different from the intentionally introduced N-type or P-type impurities, such as metals in the material gas for epitaxial growth, metals used in process equipment (gas piping, etc.), etc. Is mentioned.
- Patent Document 1 Japanese Patent Laid-Open No. 2003-17677
- Patent Document 2 Japanese Patent Laid-Open No. 11-195776
- Patent Document 3 Japanese Patent Laid-Open No. 2000-77642
- Patent Document 4 Japanese Patent Laid-Open No. 11-102960
- Patent Document 5 Japanese Patent Application Laid-Open No. 2004-31677
- Patent Document 5 Although the invention of Patent Document 5 has excellent operational effects as described above, it is desirable that the dark current be as small as possible.
- the amplifying solid-state imaging device that uses a JFET or MOS transistor as an amplifying transistor as described above is superior in that it can be integrated on-chip with peripheral circuits that match the CMOS process, and there is a demand for reducing dark current. Is particularly strong o
- An object of the present invention is to form a gettering region in a solid-state image sensor, thereby It is possible to reduce the size, especially in the amplification type solid-state imaging device, to reduce the dark current and improve the SZN ratio.
- the average impurity concentration of boron or the like in the gettering region be 1 ⁇ 10 2 ° [cm ” 3 ] or more in order to reduce dark current (paragraph [0013]
- the gettering capability will be insufficient if the volume (area X thickness) of the gettering region is not sufficiently large.
- the inventor has focused his attention.
- a predetermined number or more of metal impurities per unit area viewed in the thickness direction of the wafer are mixed in the element formation surface side in the wafer due to the manufacturing process.
- the number of acceptor-type impurity atoms in proportion to the number of metal impurity atoms is considered necessary. Therefore, even if a gettering region in which an acceptor type impurity is diffused at a high concentration satisfying the above conditions is formed, if the volume of the gettering region is not sufficiently large, a sufficient number of ions to capture all metal impurities is obtained. There is no acceptor-type impurity atom.
- the SZN ratio is determined by the ratio between the number of signal charges and the number of noise charges. As the dark current value increases, the number of noise charges also increases. Here, both the number of signal charges and the dark current value increase as the pixel area increases. This is because the number of signal charges is substantially proportional to the area of the photodiode, and the dark current value is the number of metal impurities per unit pixel, that is, the force that increases as the pixel area increases. Therefore, in order to improve the S / N ratio, the number of gettering type impurity atoms in proportion to the pixel area may be included in each pixel to reduce the ratio of the dark current value to the pixel area.
- the main factor for improving the S / N ratio by reducing dark current is that the number of acceptor-type impurity atoms contained in each pixel per unit area is rather than the acceptor-type impurity concentration in the gettering region.
- the inventor has figured out.
- depth is defined as the length in the thickness direction of the semiconductor substrate, and “area” is considered as a plane in a direction perpendicular to the depth. That is, when expressed as “per unit area”, the unit area as viewed in the thickness direction of the semiconductor substrate is considered. Therefore, the volume V [ ⁇ m 3 ] is given by the product of area A [ ⁇ m 2 ] and depth D [m], and the acceptor-type impurity concentration in the region RE is C [m 3 ], the region RE “The number of acceptor-type impurity atoms per unit area is C [ ⁇ m” 3 ] XD [m].
- the present inventor conducted the following experiment in order to investigate how much the number of acceptor-type impurity atoms per unit area should be increased to reduce the dark current.
- a plurality of amplification type solid-state imaging devices each having a gettering region formed for each pixel were prepared. These amplifying solid-state imaging devices have the same structure except for the number of acceptor-type impurity atoms (boron in this example) in the gettering region. And the dark current value of these amplification type solid-state image sensors was measured on the same conditions.
- FIG. 1 is a graph showing the experimental results.
- the horizontal axis represents the value obtained by multiplying the “number of acceptor-type impurity atoms per 1 ⁇ m square in the gettering region” by the “area ratio of the gettering region in the unit pixel”. Accordingly, the horizontal axis corresponds to the number of acceptor-type impurity atoms per unit area averaged over the entire pixel region.
- the vertical axis is the dark current value and is an arbitrary unit. As shown in FIG, Akuseputa type number impurity atoms in the near-side of the 3 10 6 111-2], which appeared inflection point reduction curve of the dark current value. And even if the number of acceptor-type impurity atoms is increased from 5 ⁇ 10 6 m 2 ], the dark current value is not greatly reduced.
- the number of acceptor-type impurity atoms per unit area is 3 X More preferably mu m 2] or more der Rukoto is desirable instrument may If it is 4 X 10 6 [m 2] or more. More preferably, in consideration of slight variations in the impurity concentration due to the manufacturing process, it should be manufactured to be 5 X 10 6 [m " 2 ] or more.
- the high-concentration P-type region formed for element isolation Alternatively, if a P-type region to which a constant voltage is applied in the pixel is formed with the above impurity concentration, The present inventor noticed that these regions also serve as a gettering function. In this case, the dark current can be reliably reduced without increasing the pixel area.
- the present invention is based on the epoch-making technical idea as described above, and is configured as follows.
- a plurality of pixels each including a photoelectric conversion unit that converts incident light into an electric signal and a discharge unit that outputs the electric signal converted by the photoelectric conversion unit are formed on a silicon substrate.
- Solid-state imaging device Solid-state imaging device.
- the invention of this claim is characterized by the following points. First, in the semiconductor element region formed on the surface of the silicon substrate, gettering regions are formed for the respective pixels. Second, the product of the area ratio occupied by a gettering region in one pixel (an anonymous number of 0 to 1) and the number of acceptor-type impurity atoms contained in the gettering region per unit area is 3 ⁇ 10 6 [ / ⁇ ⁇ 2 ] or more.
- the invention of claim 2 is the solid-state imaging device according to claim 1, wherein the discharge unit includes a charge detection region to which the charge accumulated in the photoelectric conversion unit is transferred, and the charge It is characterized by comprising an amplification unit that outputs a pixel signal corresponding to the amount of charge in the detection region.
- the invention according to claim 3 is the solid-state imaging device according to any one of claims 1 and 2, wherein “the area ratio occupied by the gettering region in one pixel and the acceptor-type impurity included in the gettering region per unit area”. The product force with the number of atoms is 4 X 10 6 [m 2 ] or more.
- the invention of claim 4 is a solid-state imaging device in which a plurality of pixels each including a photoelectric conversion unit, an amplification unit, and an insulating element isolation region are formed on a silicon substrate.
- the photoelectric conversion unit generates and accumulates an amount of charge corresponding to incident light.
- the amplifying unit includes a charge detection region to which charges accumulated in the photoelectric conversion unit are transferred, and outputs a pixel signal corresponding to the amount of charge in the charge detection region.
- the invention of this claim is characterized in that a P-type impurity diffusion region for gettering adjacent to the photoelectric conversion portions of both pixels is formed as an active region at the boundary between adjacent pixels.
- the invention of claim 5 is the solid-state image pickup device according to claim 4, wherein "the ratio of the area occupied by the P-type impurity diffusion region in one pixel and the acceptor included in the P-type impurity diffusion region per unit area".
- the product force with the number of type impurity atoms is 3 ⁇ 10 6 [ ⁇ m 2 ] or more ”.
- the invention according to claim 6 is the solid-state imaging device according to claim 4, wherein the ratio of the area occupied by the P-type impurity diffusion region in one pixel and the acceptor-type impurity atoms included in the unit area by the P-type impurity diffusion region.
- Product with number is 4 X 10 6 [m 2 ] or more ”.
- the invention of claim 7 is characterized in the following points in the solid-state imaging device of any one of claims 4 to 6.
- the photoelectric conversion unit is a photodiode having an N-type charge storage region.
- the amplifying unit is composed of an N-channel MOS transistor and a charge detection region, and the charge detection region is a floating diffusion region connected to the gate of the MOS transistor.
- the invention of claim 8 is a solid-state imaging device in which a plurality of pixels each including a photoelectric conversion unit, a JFET, and a reset unit are formed on a silicon substrate.
- the photoelectric conversion unit generates and accumulates an amount of charge corresponding to incident light.
- the JFET has a gate to which the charge accumulated in the photoelectric conversion unit is transferred, and outputs a pixel signal corresponding to the amount of charge in the gate from the source.
- the reset unit has a reset region to which a predetermined voltage is applied and electrically connects the reset region to the gate of the JFET to reset the gate voltage of the JFET to the predetermined voltage.
- the product of the area ratio occupied in one pixel and the number of acceptor-type impurity atoms included in the reset area per unit area is 3 ⁇ 10 6 [m 2 ] or more. It is characterized by that.
- the invention of claim 9 is a solid-state imaging device in which a plurality of pixels each including a photoelectric conversion unit and an amplification unit are formed on a silicon substrate.
- the photoelectric conversion unit generates and accumulates an amount of charge corresponding to incident light.
- the amplifying unit includes a charge detection region to which charges accumulated in the photoelectric conversion unit are transferred, and outputs a pixel signal corresponding to the amount of charge in the charge detection region.
- the invention of this claim is characterized in that “each pixel includes 3 ⁇ 10 6 [m 2 ] or more of acceptor-type impurity atoms per unit area”.
- the region included in the “pixel” in this claim is only the region on the element formation surface side of the silicon substrate. Therefore, when a pixel is formed on an epitaxial layer or a well layer on a silicon substrate, the thickness of the epitaxial layer or the well layer is defined as the pixel depth.
- the acceptor-type impurity diffused for gettering is preferably boron.
- the gettering region is formed as a P-type impurity diffusion region in silicon. Therefore, get
- the upper limit of the number of acceptor-type impurity atoms per unit area in the trench region is the upper limit at which the gettering region can be electrically P-type, and is represented by the following equation, for example.
- the upper limit of the acceptor-type impurity concentration when forming the P-type region in the silicon substrate is 1 X 10 21 [cm- 3 ].
- a gettering region is formed for each pixel on the surface of the silicon substrate.
- the product of the area ratio occupied by the gettering region in one pixel and the number of acceptor-type impurity atoms in the unit area in the gettering region is 3 ⁇ 10 6 [/ zm 2 ] or more. This value corresponds to the inflection point of the dark current decreasing curve in FIG. Therefore, the dark current can be reliably reduced.
- a P-type impurity diffusion region for gettering adjacent to both photoelectric conversion portions is formed at the boundary between adjacent pixels. It is possible to reliably getter metal impurities present in and near the portion.
- This P-type impurity diffusion region is formed in the active region, and there is no thick insulating layer above it! Therefore, by ion implantation with the same acceleration energy as when forming a normal impurity diffusion region, Easy to form.
- the signal charge accumulated in the photoelectric conversion unit is an electron and the amplification unit is formed as an N-channel MOS transistor.
- the P-type impurity diffusion region having a conductivity type opposite to that of the signal charge can also be used as an inter-element isolation function, and has a gettering effect without increasing the pixel area and decreasing the aperture ratio. can get.
- each pixel has a photoelectric conversion unit, a JFET, and a reset region to which a predetermined voltage is applied for resetting the gate voltage of the JFET.
- the product of the area ratio occupied by the reset region in one pixel and the number of acceptor-type impurity atoms contained in the reset region per unit area is 3 ⁇ 10 6 [/ ⁇ ⁇ 2 ] or more.
- the reset region also functions as a force gettering function, which is a constant voltage region for resetting the gate voltage of the JFET, and dark current can be reduced as described above.
- FIG. 1 is a graph of experimental results showing the relationship between the number of acceptor-type impurity atoms per unit area on the surface of a silicon substrate and the dark current value in an amplification type solid-state imaging device.
- FIG. 2 is an equivalent circuit diagram of the amplification type solid-state imaging device according to the first embodiment of the present invention.
- FIG. 3 is a schematic plan view of a pixel in the amplification type solid-state imaging device of the first embodiment.
- FIG. 4 is a schematic cross-sectional view taken along the line XI-X2 in FIG.
- FIG. 5 is a schematic plan view of two pixels showing another example of the planar arrangement of gettering regions in the first embodiment.
- FIG. 6 is a schematic plan view of four elements showing another example of the planar arrangement of gettering regions in the first embodiment.
- FIG. 7 (a) is a schematic plan view of two pixels showing another example of a planar arrangement of gettering regions in the first embodiment, and (b) is an X3 of (a). — A cross-sectional schematic view taken along X4.
- FIG. 8 is an equivalent circuit diagram of an amplification type solid-state imaging device according to a second embodiment of the present invention.
- FIG. 9 is a schematic plan view of pixels in an amplification type solid-state imaging device according to a second embodiment.
- FIG. 10 is a schematic cross-sectional view between Y1 and Y2 in FIG.
- FIG. 11 is a schematic cross-sectional view taken along the line X5-X6 in FIG.
- FIG. 2 is an equivalent circuit diagram of the amplification type solid-state imaging device according to the first embodiment.
- the symbol that starts with ⁇ indicates the drive voltage
- GND in the figure indicates the ground wire.
- 1, m, n, etc. are added to indicate the arranged pixel rows or pixel columns, but are omitted as appropriate when it is not necessary to distinguish between rows and columns. This will be explained. The above notation is the same for the second embodiment described later.
- the circuit configuration will be described first, the main features of the first embodiment are the arrangement of gettering regions, which will be described later, and the number of acceptor-type impurity atoms in the gettering region.
- the amplifying solid-state imaging device 2 drives a large number of pixels PXL1—l to PXLm—n (hereinafter abbreviated as pixels) having m rows and n columns, and drives each pixel for each row.
- Vertical scanning circuit 4 Vertical signal line VSL, B sound signal output line 8, notch amplifier 10, dark signal output terminal VDout, optical signal output line 12, buffer amplifier 14 and optical signal connected to each pixel for each column
- a signal output terminal VSout and a horizontal scanning circuit 16 are provided.
- the pixel described in the present invention means a minimum repeating unit necessary for obtaining an image, and each pixel is adjacent to each other and there is no inter-pixel.
- a pixel amplifier is also used as a plurality of photodiodes
- a plurality of photodiodes and a pixel amplifier which are the minimum units necessary for obtaining an image, are collectively handled as a unit pixel.
- each pixel includes a photodiode 18 that generates and stores an amount of signal charge corresponding to the amount of received light, an N-channel transfer MOS transistor 20, and a floating state. It has a diffusion (floating diffusion region) FD, an N-channel amplification MOS transistor 22 whose gate is connected to the floating diffusion FD, a selection transistor 24, and a reset MOS transistor 26.
- the photoelectric conversion unit described in the claims corresponds to the photodiode 18, and the amplification unit described in the claims corresponds to the amplification MOS transistor 22 and the floating diffusion FD.
- the gate of the reset MOS transistor 26 is connected to the vertical scanning circuit 4 for each row via a reset gate wiring RESL.
- the reset MOS transistor 26 receives the drive voltage ⁇ RES at its gate, and becomes conductive in response to this, and resets the voltage of the floating diffusion FD to the power supply voltage VDD.
- each transfer MOS transistor 20 is connected to the vertical scanning circuit 4 for each row via a transfer gate wiring TXL.
- the transfer MOS transistor 20 receives the drive voltage ⁇ from the vertical scanning circuit 4 at its gate, and becomes conductive according to this, and the signal charge (electrons in this example) accumulated in the photodiode 18 is floating diffusion. Transfer to FD.
- the amplification MOS transistor 22 outputs a voltage corresponding to the amount of signal charge transferred to the floating diffusion FD from the source to the vertical signal line VSL.
- the gate of the selection transistor 24 is connected to the vertical scanning circuit 4 for each row via a selection gate wiring SELL.
- the selection transistor 24 receives the drive voltage ⁇ SEL from the vertical scanning circuit 4 at its gate and becomes conductive in response to this, and the amplification MOS transistor 22
- the power supply voltage VDD is supplied to the drain of. That is, the selection MOS transistor 24 selects an output pixel.
- each vertical signal line VSL is connected to a MOS type vertical reset transistor TRV and a constant current source PS.
- the vertical reset transistor TRV receives the reset pulse voltage at the gate and becomes conductive in response to this, and resets the vertical signal line VSL to the constant voltage VRES.
- the power supply voltage VCS is supplied to one terminal of the constant current source PS.
- each vertical signal line VSL is branched into two, one of which is a MOS type optical signal transfer transistor TS and a MOS type optical signal. It is connected to the optical signal output line 12 via the readout transistor TSR.
- the other branched side is connected to the B sound signal output line 8 via a dark signal transfer transistor TD and a dark signal read transistor TDR.
- a connection node between the optical signal transfer transistor TS and the optical signal readout transistor TSR is connected to the ground line GND through the optical signal storage capacitor CS.
- the optical signal transfer transistor TS receives the drive pulse voltage at the gate and becomes conductive in response to this, and the pixel signal from each pixel (the sum of the signal component and the fixed pattern noise component) is stored in the optical signal storage capacitor CS. To accumulate.
- a connection node between the B sound signal transfer transistor TD and the dark signal readout transistor TDR is connected to the ground line GND via the dark signal storage capacitor CD.
- the dark signal transfer transistor TD receives the drive pulse voltage ⁇ at its gate and becomes conductive in response to this, and accumulates a dark signal (fixed pattern noise component) of each pixel power in the dark signal storage capacitor CD.
- Driving pulse voltages ⁇ 1 to ⁇ Hn from the horizontal scanning circuit 16 are applied to the gates of the optical signal readout transistor TSR and the dark signal readout transistor TDR for each column.
- the driving pulse voltages ⁇ 1 to ⁇ Hn the pixel signal described above is read out to the optical signal output line 12 and the dark signal is read out to the dark signal output line 8.
- the pixel signal strength / darkness signal is subtracted, and the fixed pattern noise component contained in the pixel signal is eliminated.
- a drive pulse voltage () RH is applied to the gate of the optical signal output line reset transistor TRS and the gate of the dark signal output line reset transistor TRD.
- the optical signal output line reset transistor TRS and the ⁇ signal reset transistor TRD become conductive by this drive pulse voltage () RH, and reset the voltage of the optical signal output line 12 and dark signal output line 8 to the voltage of the ground line GND. .
- Details of the circuit operation of the amplification type solid-state imaging device 2 are well-known and will not be described.
- FIG. 3 is a schematic plan view of four pixels of the amplification type solid-state imaging device 2.
- the vertical signal line VSL extends in the direction perpendicular to the alternate long and short dash line between XI and X2 in the figure.
- a gettering region 30 that is a feature of the first embodiment is formed between pixels adjacent to each other in the horizontal direction so as to be adjacent to the photodiodes 18 of both pixels. It should be noted that the gettering region 30 is indicated by oblique lines including FIG. 5, FIG. 6, and FIG.
- the thick lines (photodiode 18 and the like) and the gettering region 30 in FIG. 3 are active regions.
- an active region is a region where a thick insulating layer such as LOCOS is not formed, and the surface is covered with a thin insulating layer (silicon oxide film or silicon nitride film)! /.
- LOCOS is formed as an element isolation region in a region other than the active region.
- the element isolation region may be formed by, for example, a shallow trench (see Patent Document 4) other than LOCOS.
- FIG. 4 is a schematic cross-sectional view taken along the line XI-X2 in FIG.
- a P-type well 34 is formed on the front surface side of the N-type silicon substrate 32, and an impurity diffusion region of each part of the pixel is formed in the P-type well 34.
- An insulating layer (silicon oxide film in this example) 36 is formed on the P-type well 34.
- the photodiode 18 includes a high-concentration P-type P-type surface region 38 that prevents depletion of the surface thereof, and an N-type charge storage region 40. That is, the electrons accumulated in the N-type charge accumulation region 40 are transferred as signal charges.
- the area ratio of the gettering region 30 in the unit pixel is about 0.08 (the unit pixel area is 1.0).
- the gettering region 30 is a high-concentration n-type region having a number of boron atoms of 6.3 ⁇ 10 m 2 or more. This 6.3 10 7 [111- 2], be multiplied the area ratio gettering region 30 is accounted in the unit pixel, a 5 X 10 6 m 2] or more. That is, each pixel in Ri per unit area having a 5 10 6 [111- 2] or more boron atoms for gettering. Therefore, for the reason described in FIG. 1, in the amplification type solid-state imaging device 2 of the first embodiment, the dark current is reduced as compared with the conventional case, and the SZN ratio is improved.
- the gettering region 30 has a conductivity type opposite to that of the N-type storage region 40 and is disposed between the photodiodes 18 of adjacent pixels, so that it also functions as an element isolation. That is, in the first embodiment, since the area between adjacent pixels, which is a simple element isolation area in the conventional structure, is also used as the gettering function, it is not necessary to secure a new gettering area. Therefore, the gettering effect can be increased without increasing the pixel area and decreasing the aperture ratio.
- the gettering region 30 is adjacent to the photodiode 18, metal impurities existing in the depleted region of the photodiode 18 can be reliably gettered, and the dark current can be significantly reduced. Further, since the gettering region 30 is formed in the active region, a thick insulating layer is not formed thereon. Therefore, the gettering region 30 can be easily formed by ion implantation with the same acceleration energy as that for forming a normal impurity diffusion region such as the photodiode 18.
- the formation depth of the gettering region 30 is not limited to the center depth of the N-type accumulation region 40 as shown in FIG.
- the gettering region 30 may be deeper than the N-type storage region 40 or shallower than the boundary between the N-type storage region 40 and the P-type surface region 38.
- the gettering region 30 may be formed as a buried P-type region directly below the insulating layer 36.
- gettering 30 is formed in a region where no circuit element such as a transistor is disposed, it is desirable because the layout is easy. This is because transistors are concentrated between the photodiodes 18 of adjacent pixels in the vertical direction, so when a gettering region is formed in that region, it is necessary to specify the position and concentration that do not affect the characteristics of the transistor. This is because.
- the planar arrangement of the force gettering region in which all of the regions where the photodiodes 18 face each other in the horizontal direction is the gettering region 30 is not limited to that form.
- the schematic plan view for two pixels shown in FIG. 5 only a part of the region where the photodiodes 18 face each other may be a gettering region.
- the schematic plan view of four pixels shown in FIG. 6 only the boundary on one side of all the photodiodes 18 may be adjacent to the gettering region. In this case as well, if the boundary of the pixel is considered to be at the center between the two photodiodes 18 (the one-dot chain line in the figure), a gettering region is formed for each pixel.
- the area ratio of the gettering region in the unit pixel is about 0.04, for example. In that case, if the number of boron atoms per unit area in the gettering region and 1. 3 X 10 8 [m 2] or more, 1. 3 10 8 [111- 2], 0 product of. 04 is about 5 X 10 6 [; zm 2 ], and the same effect as in FIG. 3 is obtained. 5 and 6, the arrangement other than the gettering region is the same as that in FIG.
- the gettering region is not adjacent to either photodiode 18 between the photodiodes 18 of adjacent pixels. May be formed.
- Fig. 7 (a) only the area inside the bold line and the gettering area is the active area, and the others are the inactive areas. That is, an element isolation region (LOCOS in this example) is formed between the gettering region and the photodiode 18.
- Fig. 7 (b) is a schematic cross-sectional view taken along the line X3-X4 in Fig. 7 (a).
- the area ratio of the gettering grayed region occupied by one pixel, the product of the boron atoms per unit area in the gettering region is 5 ⁇ 10 6 [/ ⁇ ⁇ 2] or more.
- the amplification type solid-state imaging device of the second embodiment uses a JFET as an amplification transistor.
- Second implementation The main feature of this state is that the constant voltage region (reset drain) for resetting the JFET gate voltage also functions as a gettering function.
- the circuit configuration and pixel structure are the same as in the prior art, but for convenience, they will be described first.
- FIG. 8 is an equivalent circuit diagram of the amplification type solid-state imaging device of the second embodiment.
- the amplifying solid-state imaging device 50 includes m rows and n columns of pixels Pxl—l to Pxm—n (hereinafter abbreviated as pixels), a vertical scanning circuit 54, a vertical signal line VL, A signal line 58, a horizontal scanning circuit 60, a notch amplifier 74, and an optical signal output terminal Vout are provided.
- Each pixel has a photodiode PD, a transfer gate 64, a reset gate 66, a reset drain 70 (corresponding to the reset region described in the claims), and a JFET 72, as indicated by a symbol in the pixel Pxl-n.
- the reset drain 70 is connected to a common power source (voltage VG) via a reset drain wiring RDL for each row.
- the reset gate 66 is connected to the vertical scanning circuit 54 via reset gate lines RGL1 to RGLm for each row, and is driven for each row receiving the pulse voltages ⁇ RG1 to ⁇ RGm. That is, when the reset gate 66 becomes conductive, the JF ET 72 is reset to the gate voltage force and becomes inactive. When reset gate 66 becomes non-conductive, JFET 72 is in an operating state with its gate floating.
- the transfer gate 64 is connected to the vertical scanning circuit 54 via transfer gate wirings TGLl to TGLm for each row.
- the transfer gate 64 receives the pulse voltages 0 TG1 to () TGm from the vertical scanning circuit 54 and is driven for each row, and transfers the accumulated charge (holes in this example) of the photodiode PD to the gate of the JFET 72.
- the source of JFET 72 is connected to the vertical signal line VL for each column, and the drain of JFET 72 is connected to a common drain power supply (voltage VD). During operation, the JFET 72 outputs a signal voltage corresponding to the amount of charge transferred to the gate, as well as the photodiode PD force.
- a constant current source PS and a vertical reset transistor TRV are connected to one end side (lower side in the figure) of the vertical signal line VL.
- the vertical reset transistor TRV receives the reset pulse voltage at the gate and becomes conductive in response to the reset pulse voltage, and resets the vertical signal line VL to a constant voltage VRV.
- the power supply voltage VCS is supplied to one terminal of the constant current source PS.
- the other end of the vertical signal line VL (horizontal scanning circuit 60 side) is a vertical line that limits the operating band of JFET72.
- the direct load capacitance Cv, the column buffer amplifier AP, the CDS capacitor Cc, the CDS transistor Tc, and the column selection transistors Thl to Thn are connected.
- the column selection transistors Thl to Thn receive the driving pulse voltages ⁇ Hl to ⁇ from the horizontal scanning circuit 60 at their gates, respectively, and connect the vertical signal lines VLl to VLn to the horizontal signal line 58, respectively.
- the CDS transistor Tc receives a drive pulse voltage at its gate.
- the CDS transistor Tc and the CDS capacitor Cc perform correlated double sampling processing on the output voltage of the JFET 72 before and after signal charge transfer.
- a horizontal reset transistor TRH and an output buffer amplifier 74 are connected to the horizontal signal line 58.
- the horizontal reset transistor TRH receives the drive noise voltage () RH at the gate and resets the horizontal signal line 58 to a constant voltage (in this example, the potential of the ground line GND).
- the pixel signal readout operation of the amplification type solid-state imaging device 50 is the same as that shown in FIG.
- FIG. 9 is a schematic plan view of the unit pixel of the amplification type solid-state imaging device 50
- FIG. 10 is a schematic cross-sectional view between Y1 and Y2 in FIG. 9, and
- FIG. 11 is X5-X6 in FIG. FIG.
- the pixel includes a photodiode PD, JFET 72, and a reset drain 70, and a reset gate wiring RGL, a transfer gate wiring TGL, and a vertical signal line VL are formed across a plurality of pixels.
- the reset drain wiring RDL is formed so as to be connected to all the pixels so that only the upper part of the photodiode PD is opened.
- the reset drain wiring RDL also functions as a light shielding film.
- an N-type epitaxial layer 84 is formed on the front surface side of the high-concentration N-type silicon substrate 80, and the impurity diffusion regions in each part of the pixel are It is formed in the N-type epitaxy layer 84.
- An insulating layer (silicon dioxide) 88 is formed on the N-type epitaxial layer 84, and wiring such as a reset drain wiring RDL and a reset gate wiring RGL is formed in the insulating layer 88.
- the photodiode PD includes a surface N-type region 98 and a P-type charge storage region 100, and stores holes in the P-type charge storage region 100 as signal charges. Further, adjacent to the photodiode PD and the reset drain 70, a channel stop 93 (inter-element isolation region) which is a high concentration N-type impurity diffusion region is formed. The cross section is not shown in the figure. However, an inversion layer is formed according to the voltage of the transfer gate 64, and the signal charge is transferred from the P-type charge storage region 100 to the gate of the JFET 72.
- the JFET 72 is an N-channel type having a P-type gate.
- the drain of the JFET receives the voltage VD of the drain power through the N-type epitaxial layer 84 and the high-concentration N-type silicon substrate 80.
- the reset drain 70 is formed as a P-type, and is connected to the reset drain wiring RDL via the relay wiring 92.
- a P-channel type MOSFET having the gate of the JFET 72 and the reset drain 70 as a source or drain and the reset gate 66 as a gate is formed (corresponding to the reset unit described in the claims). Therefore, an inversion layer is formed according to the voltage of the reset gate 66, and the amount of charge in the gate of the JFET 72 is reset.
- the main feature of the second embodiment is that the product of the area ratio of the reset drain 70 occupying in one pixel and the number of boron atoms per unit area in the reset drain 70 is 5 ⁇ 10 6 [m 2 That's it.
- the area ratio of the reset drain 70 in the unit pixel is about 0.05 (shown larger in FIGS. 9 to 11), and the number of boron atoms per unit area in the reset drain 70 is 1. OX 10 8 [m 2 ] or more.
- the reset drain 70 is originally a constant voltage region for resetting the gate voltage of the JFET 72, but also functions as a gettering region.
- the second embodiment is that in which the gettering function is also used in the P-type constant voltage region. Therefore, also in the second embodiment, the same effect as in the first embodiment can be obtained.
- the present invention can be used in a solid-state imaging device.
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JP2009212248A (ja) * | 2008-03-03 | 2009-09-17 | Sharp Corp | 固体撮像装置および電子情報機器 |
Citations (5)
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JPH05110053A (ja) * | 1991-10-14 | 1993-04-30 | Matsushita Electron Corp | 固体撮像装置およびその製造方法 |
JPH0982933A (ja) * | 1995-09-12 | 1997-03-28 | Toshiba Corp | 固体撮像装置およびその製造方法 |
JP2000077642A (ja) * | 1998-08-27 | 2000-03-14 | Nikon Corp | 固体撮像素子 |
JP2001135816A (ja) * | 1999-11-10 | 2001-05-18 | Nec Corp | 半導体装置及びその製造方法 |
JP2004235609A (ja) * | 2003-01-06 | 2004-08-19 | Canon Inc | 光電変換装置及び光電変換装置の製造方法及び同光電変換装置を用いたカメラ |
-
2005
- 2005-09-30 WO PCT/JP2005/018151 patent/WO2006046385A1/ja active Application Filing
- 2005-10-28 TW TW094137786A patent/TW200629533A/zh unknown
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
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JPH05110053A (ja) * | 1991-10-14 | 1993-04-30 | Matsushita Electron Corp | 固体撮像装置およびその製造方法 |
JPH0982933A (ja) * | 1995-09-12 | 1997-03-28 | Toshiba Corp | 固体撮像装置およびその製造方法 |
JP2000077642A (ja) * | 1998-08-27 | 2000-03-14 | Nikon Corp | 固体撮像素子 |
JP2001135816A (ja) * | 1999-11-10 | 2001-05-18 | Nec Corp | 半導体装置及びその製造方法 |
JP2004235609A (ja) * | 2003-01-06 | 2004-08-19 | Canon Inc | 光電変換装置及び光電変換装置の製造方法及び同光電変換装置を用いたカメラ |
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
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JP2009212248A (ja) * | 2008-03-03 | 2009-09-17 | Sharp Corp | 固体撮像装置および電子情報機器 |
US8106984B2 (en) * | 2008-03-03 | 2012-01-31 | Sharp Kabushiki Kaisha | Image capturing apparatus and electronic information device |
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