US20200052013A1 - Pixel structure and electric device - Google Patents
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- US20200052013A1 US20200052013A1 US16/101,540 US201816101540A US2020052013A1 US 20200052013 A1 US20200052013 A1 US 20200052013A1 US 201816101540 A US201816101540 A US 201816101540A US 2020052013 A1 US2020052013 A1 US 2020052013A1
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- 239000000758 substrate Substances 0.000 claims abstract description 8
- 238000002955 isolation Methods 0.000 claims description 29
- 239000007943 implant Substances 0.000 description 9
- 230000004888 barrier function Effects 0.000 description 4
- 238000009413 insulation Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000005286 illumination Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
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- 239000000969 carrier Substances 0.000 description 1
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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
- H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
- H01L27/1461—Pixel-elements with integrated switching, control, storage or amplification elements characterised by the photosensitive area
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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
- H01L27/14603—Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
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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
- H01L27/14609—Pixel-elements with integrated switching, control, storage or amplification elements
- H01L27/14612—Pixel-elements with integrated switching, control, storage or amplification elements involving a transistor
-
- 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
- H01L27/1463—Pixel isolation structures
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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
- H01L27/14643—Photodiode arrays; MOS imagers
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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
- H01L27/14643—Photodiode arrays; MOS imagers
- H01L27/14654—Blooming suppression
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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
- H01L27/14643—Photodiode arrays; MOS imagers
- H01L27/14654—Blooming suppression
- H01L27/14656—Overflow drain structures
Definitions
- the present invention relates to a pixel structure having an anti-blooming path.
- CMOS image sensor has been widely applied to mobile applications.
- the CMOS image sensor may be applied to other applications such as automotive and security.
- Requirements for the automotive and security applications are quite different from that for the mobile applications.
- blooming is highly undesirable in automotive and surveillance application. Blooming happens when a pixel is filled up with photo carriers and can no longer collect more electron/hole pairs during pixel exposure. A bright pixel will spreads to several other pixels in the neighboring region.
- the road scene especially at night, has a high dynamic range.
- the CMOS image sensor is thus required to have a good blooming control at ultra-bright region in order to ensure that the neighboring dimly lit regions are not washed out by the blooming charges. Otherwise, many details get lost and it is difficult to extract the information from the scene.
- a hot pixel could be filled up by dark current even in the dark. The adjacent good pixels will become hot by receiving the blooming charges.
- Embodiments of the invention provide a pixel structure including following units.
- a crystalline layer of a first doping type is formed on a substrate.
- a photodiode region is formed in the crystalline layer.
- a gate of a source follower transistor is formed on a top surface of the crystalline layer.
- a reset gate is formed on the top surface of the crystalline layer.
- a doped region of a second doping type is formed in the crystalline layer and formed between the reset gate and the gate of the source follower.
- the first doping type is different from the second doping type, and the photodiode region is connected to the doped region under the top surface of the crystalline layer as an anti-blooming path.
- the pixel structure further includes an isolation structure extending from the top surface of the crystalline layer and formed between the photodiode region and the doped region.
- the photodiode region is connected to the doped region under the isolation structure.
- the photodiode region has a first portion of the second doping type that extends toward the doped region under the isolation structure.
- the doped region has a second portion of the second doping type that extends toward the photodiode region under the isolation structure, and the first portion is connected to the second portion.
- the doped region includes a highly doped region of the second doping type, a lightly doped drain of the second doping type located under the highly doped region, and the second portion which extends toward the photodiode region.
- a doping concentration of the second portion is less than a doping concentration of the highly doped drain.
- the pixel structure further includes a well region of the first doping type formed in the crystalline layer.
- the well region has a notch to at least partially surround the first portion and the second portion.
- the well region is vertically spaced from a connection interface between the first portion and the second portion by a distance.
- the width of the notch is shorter than a distance between the reset gate and the gate of the source follower.
- the first doping type is P-type
- the second doping type is N-type
- the doped region is connected to a power supply.
- an electrical device including the aforementioned pixel structure is provided.
- FIG. 1 is a schematic pixel circuit diagram of an image sensor in accordance with an embodiment.
- FIG. 2A is a top view of the pixel structure of the image sensor in accordance with an embodiment.
- FIG. 2B is a cross-sectional view along a section line AA′ of FIG. 2A .
- FIG. 3A is a cross-sectional view of the partial pixel structure in accordance with an embodiment.
- FIG. 3B is a schematic top view of the partial pixel structure along a section line BB′ of FIG. 3A .
- FIG. 3C is a schematic top view of the partial pixel structure along a section line CC′ of FIG. 3A .
- FIG. 3D is a schematic top view of the partial pixel structure along a section line DD′ of FIG. 3A .
- FIG. 4 is a top view of the pixel structure of image sensor in accordance with an embodiment.
- FIGS. 5A, 5B, and 5C are cross-sectional view of the partial pixel structure in accordance with some embodiments.
- FIG. 1 is a schematic pixel circuit diagram of an image sensor in accordance with an embodiment.
- an image sensor 100 may be applied to a front side illumination (FSI) image sensor or a back side illumination (BSI) image sensor.
- the image sensor 100 includes multiple pixels, and each of the pixels includes a photodiode 110 , a transfer transistor TX, a reset transistor RES, a source follower SF, and a select transistor SEL.
- the photodiode 110 has an anode electrically connected to the ground, and a cathode electrically connected to a first terminal of the transfer transistor TX.
- a second terminal of the transfer transistor TX is electrically connected to a first terminal of the reset transistor RES and a gate of the source follower SF.
- a second terminal of the reset transistor RES is electrically connected to a power supply VDD.
- the source follower SF has a first terminal electrically connected to the power supply VDD, and a second terminal electrically connected to a first terminal of the select transistor SEL.
- a second terminal of the select transistor SEL is electrically connected to a bias 130 and outputs to a sensing circuit 140 .
- an anti-blooming path 120 is provided from the photodiode 110 to the power supply VDD.
- FIG. 2A is a top view of the pixel structure of the image sensor in accordance with an embodiment.
- FIG. 2B is a cross-sectional view along a section line AA′ of FIG. 2A .
- the image sensor 100 includes a substrate 201 of a first doping type (e.g. P-type).
- a crystalline layer 202 of the first doping type such as P-type epitaxial layer or P-epi, is formed on the substrate 201 .
- Photodiode regions 203 , 214 and a well region PW of the first doping type are formed in the crystalline layer 202 .
- the photodiode region 203 belongs to one of the pixels of the image sensor 100 , and the photodiode region 214 belongs to an adjacent pixel.
- a surface pinning layer 210 and a gate insulation layer 211 are formed on a top surface 202 a of the crystalline layer 202 .
- the gate insulation layer 211 includes oxide.
- Isolation structures 212 , 213 are formed in the crystalline layer 202 , in which the isolation structure 212 is formed between the photodiode region 203 and the photodiode region 214 .
- the isolation structures 212 , 213 are shallow trench isolations (STI).
- the isolation structure 212 further includes a deep well 215 of the first doping type.
- a gate TX_G (also referred to a transfer gate) of the transfer transistor TX, a gate RES_G (also referred to a reset gate) of the reset transistor RES, a gate SF_G of the source follower SF, and a gate SEL_G (also referred to a select gate) of the select transistor SEL are formed on the gate insulation layer 211 (these gates are not shown in FIG. 2B ).
- the gate TX_G covers a portion of the photodiode region 203 .
- Doped region 204 , 206 , and 207 are formed in the crystalline layer 202 .
- the doped region 204 is formed between the transfer gate TX_G and the reset gate RES_G as source/drain of the transfer transistor TX and the reset transistor RES.
- the doped region 204 is also electrically connected to the gate SF_G through a conductive structure 205 .
- the doped region 206 is formed between the reset gate RES_G and the gate SF_G as source/drain of the reset transistor RES and the source follower SF.
- the doped region 207 is formed between the gate SF_G and the select gate SEL_G as source/drain of the source follower SF and the select transistor SEL.
- the doped regions 204 , 206 , and 207 have a second doping type (e.g. N-type) which is different from the first doping type.
- the photodiode region 203 is connected to the doped region 206 under the top surface 202 a of the crystalline layer 202 so as to provide the anti-blooming path 120 .
- the isolation structure 213 extends from the top surface 202 a of the crystalline layer 202 , and is formed between the photodiode region 203 and the doped region 206 .
- the photodiode region 203 has a first portion 221 of the second doping type (e.g. N-type) that extends toward the doped region 206 under the isolation structure 213 .
- the doped region 206 has a second portion 222 of the second doping type that extends toward the photodiode region 203 under the isolation structure 213 .
- the first portion 221 is connected to the second portion 222 under the isolation structure 213 . That is, the photodiode region 203 is connected to the doped region 206 under the isolation structure 213 . Note that the first portion 221 and the second portion 222 are illustrated by dotted line in FIG. 2A because they are covered by the isolation structure 213 .
- the doped region 206 includes a highly doped region 224 , a lightly doped drain 223 under the highly doped region 224 , and the second portion 222 in which all of these 222 / 223 / 224 have the second doping type.
- the second portion 222 is formed by thermal diffusion so that the doping concentration of the second portion 222 is less than that of the highly doped region 224 , and the doping concentration of the second portion 222 progressively decreases toward the photodiode region 203 . Therefore, it should be appreciated that there is no clear boundary between the lightly doped drain 223 and the second portion 222 in some embodiments.
- the barrier between the photodiode region 203 and doped region 206 is lower than that between the photodiode region 203 and the photodiode region 214 .
- the doped region 206 is connected to the power supply VDD.
- the depth of the highly doped region 224 may be adjusted in which deeper depth leads to lower barrier between the first portion 221 and the second portion 222 .
- the depth of the isolation structure 213 may be adjusted in which deeper depth leads to higher barrier between the first portion 221 and the second portion 222 .
- FIG. 3A is a cross-sectional view of the partial pixel structure in accordance with an embodiment.
- FIG. 3A is identical to FIG. 2B with different references for illustration.
- FIG. 3B is a schematic top view of the partial pixel structure along a section line BB′ of FIG. 3A .
- FIG. 3C is a schematic top view of the partial pixel structure along a section line CC′ of FIG. 3A .
- FIG. 3D is a schematic top view of the partial pixel structure along a section line DD′ of FIG. 3A .
- the well region PW has a notch for at least partially surrounding the first portion 221 and the second portion 222 .
- the space under the isolation structure 213 is occupied by the well region PW, similar to the deep well 215 , in the prior art.
- the well region PW has a notch 320 with height H.
- the well region PW is vertically spaced from a connection interface 310 between the first portion 221 and the second portion 222 by a distance D 1 .
- the notch 320 of the well region PW partially surrounds the first portion 221 and second portion 222 from three sides.
- the notch 320 has a width W and a length L.
- the notch 320 of the well region PW is filled with the crystalline layer 202 .
- the notch 320 is not seen in FIG. 3D .
- the height H, width W, and length L of the notch 320 , and the distance D 1 may be adjusted based on requirements. In general, when the height H, the width W, the length L, and the distance D 1 get larger, the barrier formed by the first portion 221 and the second portion 222 gets lower so as to generate more efficient anti-blooming path 120 .
- FIG. 4 is a top view of the pixel structure of the image sensor in accordance with an embodiment.
- FIG. 4 is basically equal to FIG. 2A , but the well region PW is shown in FIG. 4 for illustration. Note that the well region PW is embedded in the crystalline layer 202 , and therefore the well region PW cannot be “seen” from the top view.
- the notch 320 of the well region PW has the width W and the length L. The width W is shorter than a distance D 2 between the reset gate RES_G and the gate SF_G.
- the notch 320 may extend into a channel region between the reset gate RES_G and the gate SF_G if more anti-blooming strength is needed, as long as the operation of the reset gate RES_G and the gate SF_G is not disturbed.
- an implant region of second doping type may be formed in the crystalline layer 202 for adjusting the anti-blooming strength.
- an implant region 510 is formed under the isolation structure 213 , and formed between the photodiode region 203 and the doped region 206 .
- the implant region 510 is also connected to the photodiode region 203 and the doped region 206 to provide an anti-blooming path.
- an implant region 520 is formed under the isolation structure 213 , but what is different from FIG.
- an implant region 530 is partially formed in the notch 320 , and connected to the doped region 206 and the well region PW.
- the implant region 530 may be an additional element of the doped region 206 . Note that the lengths, widths, heights, and the locations of the implant regions 510 , 520 , and 530 may be adjusted based on requirement, which is not limited in the invention.
- the electrical device includes the aforementioned image sensor 100 with the aforementioned pixel structure.
- the electrical device may be a smart phone, any type of computer, digital camera, etc. that is not limited in the invention.
- the first doping type may be N-type
- the second doping type may be P-type
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Abstract
Description
- The present invention relates to a pixel structure having an anti-blooming path.
- A complementary metal-oxide-semiconductor (CMOS) image sensor has been widely applied to mobile applications. The CMOS image sensor may be applied to other applications such as automotive and security. Requirements for the automotive and security applications are quite different from that for the mobile applications. For example, blooming is highly undesirable in automotive and surveillance application. Blooming happens when a pixel is filled up with photo carriers and can no longer collect more electron/hole pairs during pixel exposure. A bright pixel will spreads to several other pixels in the neighboring region.
- The road scene, especially at night, has a high dynamic range. The CMOS image sensor is thus required to have a good blooming control at ultra-bright region in order to ensure that the neighboring dimly lit regions are not washed out by the blooming charges. Otherwise, many details get lost and it is difficult to extract the information from the scene. Moreover, at high temperature operation such as in a car, a hot pixel could be filled up by dark current even in the dark. The adjacent good pixels will become hot by receiving the blooming charges.
- For the reason that conventional CMOS image sensors could not effectively solve blooming problem, a need has thus arisen to propose a novel CMOS image sensor with improved anti-blooming.
- Embodiments of the invention provide a pixel structure including following units. A crystalline layer of a first doping type is formed on a substrate. A photodiode region is formed in the crystalline layer. A gate of a source follower transistor is formed on a top surface of the crystalline layer. A reset gate is formed on the top surface of the crystalline layer. A doped region of a second doping type is formed in the crystalline layer and formed between the reset gate and the gate of the source follower. The first doping type is different from the second doping type, and the photodiode region is connected to the doped region under the top surface of the crystalline layer as an anti-blooming path.
- In some embodiments, the pixel structure further includes an isolation structure extending from the top surface of the crystalline layer and formed between the photodiode region and the doped region. The photodiode region is connected to the doped region under the isolation structure.
- In some embodiments, the photodiode region has a first portion of the second doping type that extends toward the doped region under the isolation structure. The doped region has a second portion of the second doping type that extends toward the photodiode region under the isolation structure, and the first portion is connected to the second portion.
- In some embodiments, the doped region includes a highly doped region of the second doping type, a lightly doped drain of the second doping type located under the highly doped region, and the second portion which extends toward the photodiode region.
- In some embodiments, a doping concentration of the second portion is less than a doping concentration of the highly doped drain.
- In some embodiments, the pixel structure further includes a well region of the first doping type formed in the crystalline layer. The well region has a notch to at least partially surround the first portion and the second portion.
- In some embodiments, the well region is vertically spaced from a connection interface between the first portion and the second portion by a distance.
- In some embodiments, the width of the notch is shorter than a distance between the reset gate and the gate of the source follower.
- In some embodiments, the first doping type is P-type, and the second doping type is N-type.
- In some embodiments, the doped region is connected to a power supply.
- From another aspect, an electrical device including the aforementioned pixel structure is provided.
- The invention can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows.
-
FIG. 1 is a schematic pixel circuit diagram of an image sensor in accordance with an embodiment. -
FIG. 2A is a top view of the pixel structure of the image sensor in accordance with an embodiment. -
FIG. 2B is a cross-sectional view along a section line AA′ ofFIG. 2A . -
FIG. 3A is a cross-sectional view of the partial pixel structure in accordance with an embodiment. -
FIG. 3B is a schematic top view of the partial pixel structure along a section line BB′ ofFIG. 3A . -
FIG. 3C is a schematic top view of the partial pixel structure along a section line CC′ ofFIG. 3A . -
FIG. 3D is a schematic top view of the partial pixel structure along a section line DD′ ofFIG. 3A . -
FIG. 4 is a top view of the pixel structure of image sensor in accordance with an embodiment. -
FIGS. 5A, 5B, and 5C are cross-sectional view of the partial pixel structure in accordance with some embodiments. - Specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings, however, the embodiments described are not intended to limit the present invention and it is not intended for the description of operation to limit the order of implementation. Moreover, any device with equivalent functions that is produced from a structure formed by a recombination of elements shall fall within the scope of the present invention. Additionally, the drawings are only illustrative and are not drawn to actual size.
-
FIG. 1 is a schematic pixel circuit diagram of an image sensor in accordance with an embodiment. Referring toFIG. 1 , animage sensor 100 may be applied to a front side illumination (FSI) image sensor or a back side illumination (BSI) image sensor. Theimage sensor 100 includes multiple pixels, and each of the pixels includes aphotodiode 110, a transfer transistor TX, a reset transistor RES, a source follower SF, and a select transistor SEL. Thephotodiode 110 has an anode electrically connected to the ground, and a cathode electrically connected to a first terminal of the transfer transistor TX. A second terminal of the transfer transistor TX is electrically connected to a first terminal of the reset transistor RES and a gate of the source follower SF. A second terminal of the reset transistor RES is electrically connected to a power supply VDD. The source follower SF has a first terminal electrically connected to the power supply VDD, and a second terminal electrically connected to a first terminal of the select transistor SEL. A second terminal of the select transistor SEL is electrically connected to abias 130 and outputs to asensing circuit 140. In the embodiment, ananti-blooming path 120 is provided from thephotodiode 110 to the power supply VDD. One pixel structure will be described in detail below. -
FIG. 2A is a top view of the pixel structure of the image sensor in accordance with an embodiment.FIG. 2B is a cross-sectional view along a section line AA′ ofFIG. 2A . Referring toFIG. 2A andFIG. 2B , theimage sensor 100 includes asubstrate 201 of a first doping type (e.g. P-type). Acrystalline layer 202 of the first doping type, such as P-type epitaxial layer or P-epi, is formed on thesubstrate 201.Photodiode regions crystalline layer 202. Thephotodiode region 203 belongs to one of the pixels of theimage sensor 100, and thephotodiode region 214 belongs to an adjacent pixel. Asurface pinning layer 210 and agate insulation layer 211 are formed on atop surface 202 a of thecrystalline layer 202. For example, thegate insulation layer 211 includes oxide.Isolation structures crystalline layer 202, in which theisolation structure 212 is formed between thephotodiode region 203 and thephotodiode region 214. For example, theisolation structures isolation structure 212 further includes a deep well 215 of the first doping type. - A gate TX_G (also referred to a transfer gate) of the transfer transistor TX, a gate RES_G (also referred to a reset gate) of the reset transistor RES, a gate SF_G of the source follower SF, and a gate SEL_G (also referred to a select gate) of the select transistor SEL are formed on the gate insulation layer 211 (these gates are not shown in
FIG. 2B ). The gate TX_G covers a portion of thephotodiode region 203.Doped region crystalline layer 202. The dopedregion 204 is formed between the transfer gate TX_G and the reset gate RES_G as source/drain of the transfer transistor TX and the reset transistor RES. The dopedregion 204 is also electrically connected to the gate SF_G through aconductive structure 205. The dopedregion 206 is formed between the reset gate RES_G and the gate SF_G as source/drain of the reset transistor RES and the source follower SF. The dopedregion 207 is formed between the gate SF_G and the select gate SEL_G as source/drain of the source follower SF and the select transistor SEL. The dopedregions - The
photodiode region 203 is connected to the dopedregion 206 under thetop surface 202 a of thecrystalline layer 202 so as to provide theanti-blooming path 120. In detail, theisolation structure 213 extends from thetop surface 202 a of thecrystalline layer 202, and is formed between thephotodiode region 203 and the dopedregion 206. Thephotodiode region 203 has afirst portion 221 of the second doping type (e.g. N-type) that extends toward the dopedregion 206 under theisolation structure 213. In addition, the dopedregion 206 has asecond portion 222 of the second doping type that extends toward thephotodiode region 203 under theisolation structure 213. Thefirst portion 221 is connected to thesecond portion 222 under theisolation structure 213. That is, thephotodiode region 203 is connected to the dopedregion 206 under theisolation structure 213. Note that thefirst portion 221 and thesecond portion 222 are illustrated by dotted line inFIG. 2A because they are covered by theisolation structure 213. - In some embodiments, the doped
region 206 includes a highly dopedregion 224, a lightly dopeddrain 223 under the highly dopedregion 224, and thesecond portion 222 in which all of these 222/223/224 have the second doping type. In some embodiments, thesecond portion 222 is formed by thermal diffusion so that the doping concentration of thesecond portion 222 is less than that of the highly dopedregion 224, and the doping concentration of thesecond portion 222 progressively decreases toward thephotodiode region 203. Therefore, it should be appreciated that there is no clear boundary between the lightly dopeddrain 223 and thesecond portion 222 in some embodiments. Because thefirst portion 221 and thesecond portion 222 have the same doping type and are connected to the each other, the barrier between thephotodiode region 203 and dopedregion 206 is lower than that between thephotodiode region 203 and thephotodiode region 214. Referring toFIG. 1 andFIG. 2B , the dopedregion 206 is connected to the power supply VDD. When thephotodiode region 203 is overexposed, extra photo electrons flow into the power supply VDD through theanti-blooming path 120 instead of flowing into theadjacent photodiode region 214. In some embodiments, the depth of the highly dopedregion 224 may be adjusted in which deeper depth leads to lower barrier between thefirst portion 221 and thesecond portion 222. In some embodiments, the depth of theisolation structure 213 may be adjusted in which deeper depth leads to higher barrier between thefirst portion 221 and thesecond portion 222. -
FIG. 3A is a cross-sectional view of the partial pixel structure in accordance with an embodiment.FIG. 3A is identical toFIG. 2B with different references for illustration.FIG. 3B is a schematic top view of the partial pixel structure along a section line BB′ ofFIG. 3A .FIG. 3C is a schematic top view of the partial pixel structure along a section line CC′ ofFIG. 3A .FIG. 3D is a schematic top view of the partial pixel structure along a section line DD′ ofFIG. 3A . Referring toFIG. 3A , in some embodiments, the well region PW has a notch for at least partially surrounding thefirst portion 221 and thesecond portion 222. In detail, the space under theisolation structure 213 is occupied by the well region PW, similar to thedeep well 215, in the prior art. However, in the embodiment, the well region PW has anotch 320 with height H. The well region PW is vertically spaced from aconnection interface 310 between thefirst portion 221 and thesecond portion 222 by a distance D1. Referring toFIG. 3B , thenotch 320 of the well region PW partially surrounds thefirst portion 221 andsecond portion 222 from three sides. Thenotch 320 has a width W and a length L. Referring toFIG. 3C , thenotch 320 of the well region PW is filled with thecrystalline layer 202. Referring toFIG. 3D , thenotch 320 is not seen inFIG. 3D . - Note that the height H, width W, and length L of the
notch 320, and the distance D1 may be adjusted based on requirements. In general, when the height H, the width W, the length L, and the distance D1 get larger, the barrier formed by thefirst portion 221 and thesecond portion 222 gets lower so as to generate more efficientanti-blooming path 120. -
FIG. 4 is a top view of the pixel structure of the image sensor in accordance with an embodiment.FIG. 4 is basically equal toFIG. 2A , but the well region PW is shown inFIG. 4 for illustration. Note that the well region PW is embedded in thecrystalline layer 202, and therefore the well region PW cannot be “seen” from the top view. InFIG. 4 , thenotch 320 of the well region PW has the width W and the length L. The width W is shorter than a distance D2 between the reset gate RES_G and the gate SF_G. However, thenotch 320 may extend into a channel region between the reset gate RES_G and the gate SF_G if more anti-blooming strength is needed, as long as the operation of the reset gate RES_G and the gate SF_G is not disturbed. - In some embodiments, in addition to the
first portion 221 and thesecond portion 222 created mainly by thermal diffusions from thephotodiode region 203 and the dopedregion 206, an implant region of second doping type may be formed in thecrystalline layer 202 for adjusting the anti-blooming strength. For example, referring toFIG. 5A , animplant region 510 is formed under theisolation structure 213, and formed between thephotodiode region 203 and the dopedregion 206. Theimplant region 510 is also connected to thephotodiode region 203 and the dopedregion 206 to provide an anti-blooming path. Referring toFIG. 5B , animplant region 520 is formed under theisolation structure 213, but what is different fromFIG. 5A is that theimplant region 520 extends toward thephotodiode region 203 so could be shared with onephotodiode region 203 implant. Referring toFIG. 5C , an implant region 530 is partially formed in thenotch 320, and connected to the dopedregion 206 and the well region PW. The implant region 530 may be an additional element of the dopedregion 206. Note that the lengths, widths, heights, and the locations of theimplant regions - From another aspect, an electrical device is provided in some embodiments. The electrical device includes the
aforementioned image sensor 100 with the aforementioned pixel structure. The electrical device may be a smart phone, any type of computer, digital camera, etc. that is not limited in the invention. - In some embodiments, the first doping type may be N-type, and the second doping type may be P-type.
- Although the present invention has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims.
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US7719026B2 (en) | 2007-04-11 | 2010-05-18 | Fairchild Semiconductor Corporation | Un-assisted, low-trigger and high-holding voltage SCR |
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US8487350B2 (en) * | 2010-08-20 | 2013-07-16 | Omnivision Technologies, Inc. | Entrenched transfer gate |
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US9070802B2 (en) * | 2013-08-16 | 2015-06-30 | Himax Imaging, Inc. | Image sensor and fabricating method of image sensor |
US9443900B2 (en) * | 2014-08-25 | 2016-09-13 | Taiwan Semiconductor Manufacturing Co., Ltd. | Pixel with multigate structure for charge storage or charge transfer |
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