US20180040651A1 - Image sensor and related fabrication method - Google Patents

Image sensor and related fabrication method Download PDF

Info

Publication number
US20180040651A1
US20180040651A1 US15/334,309 US201615334309A US2018040651A1 US 20180040651 A1 US20180040651 A1 US 20180040651A1 US 201615334309 A US201615334309 A US 201615334309A US 2018040651 A1 US2018040651 A1 US 2018040651A1
Authority
US
United States
Prior art keywords
conductivity
type doped
recess
semiconductor substrate
image sensor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
US15/334,309
Other versions
US9899436B1 (en
Inventor
Shih-Ping Lee
Yu-An Chen
Hsiu-Wen Huang
Chuan-Hua Chang
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Powerchip Semiconductor Manufacturing Corp
Original Assignee
Powerchip Technology Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Powerchip Technology Corp filed Critical Powerchip Technology Corp
Assigned to POWERCHIP TECHNOLOGY CORPORATION reassignment POWERCHIP TECHNOLOGY CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: CHANG, CHUAN-HUA, CHEN, YU-AN, HUANG, HSIU-WEN, LEE, SHIH-PING
Publication of US20180040651A1 publication Critical patent/US20180040651A1/en
Application granted granted Critical
Publication of US9899436B1 publication Critical patent/US9899436B1/en
Assigned to POWERCHIP SEMICONDUCTOR MANUFACTURING CORPORATION reassignment POWERCHIP SEMICONDUCTOR MANUFACTURING CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: POWERCHIP TECHNOLOGY CORPORATION
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices 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
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14601Structural or functional details thereof
    • H01L27/14603Special geometry or disposition of pixel-elements, address-lines or gate-electrodes
    • H01L27/14607Geometry of the photosensitive area
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices 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
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14601Structural or functional details thereof
    • H01L27/14609Pixel-elements with integrated switching, control, storage or amplification elements
    • H01L27/1461Pixel-elements with integrated switching, control, storage or amplification elements characterised by the photosensitive area
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices 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
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14601Structural or functional details thereof
    • H01L27/14625Optical elements or arrangements associated with the device
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices 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
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14601Structural or functional details thereof
    • H01L27/14625Optical elements or arrangements associated with the device
    • H01L27/14629Reflectors
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices 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
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14643Photodiode arrays; MOS imagers
    • H01L27/14645Colour imagers
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices 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
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14683Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices 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
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14683Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
    • H01L27/14685Process for coatings or optical elements
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01LSEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L27/00Devices consisting of a plurality of semiconductor or other solid-state components formed in or on a common substrate
    • H01L27/14Devices 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
    • H01L27/144Devices controlled by radiation
    • H01L27/146Imager structures
    • H01L27/14683Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof
    • H01L27/14689MOS based technologies

Definitions

  • the present invention relates to an image sensor and related fabrication method, more particularly, to an image sensor and related fabrication method capable of improving quantum efficiency and reducing crosstalk issue.
  • CMOS image sensors have certain advantages of low operating voltage, low power consumption, high operating efficiency, and the ability for random access.
  • CMOS image sensors are currently capable of integration with the semiconductor fabrication process. Based on those benefits, the application of CMOS image sensors has increased significantly.
  • the incident light is separated into a combination of light of different wavelengths.
  • the incident light can be separated into a combination of red, blue, and green light.
  • the light of different wavelengths is received by respective optical sensors such as photodiodes and is subsequently transformed into digital signals of different intensities.
  • respective optical sensors such as photodiodes and is subsequently transformed into digital signals of different intensities.
  • the size of the photodiode is reduced together. Accordingly, the crosstalk between the pixels is increased, and the optical sensitivity is decreased.
  • CMOS image sensor is usually disposed in a semiconductor substrate with high reflectivity, the light is easy to be reflected by the semiconductor substrate when the light propagates to the semiconductor substrate.
  • an image sensor includes a semiconductor substrate, a first-conductivity-type doped region, a second-conductivity-type doped region, a gate, a gate oxide layer and a doped diffusion region.
  • a photosensitive area is defined on a surface of the semiconductor substrate, and the surface of the semiconductor substrate has at least one recess in the photosensitive area.
  • the first-conductivity-type doped region is disposed in the semiconductor substrate and in the photosensitive area.
  • the second-conductivity-type doped region is disposed on a surface of the first-conductivity-type doped region and on a surface of the recess, wherein the first-conductivity-type doped region and the second-conductivity-type doped region have different conductivity types, and the first-conductivity-type doped region and the second-conductivity-type doped region form a photosensitive device.
  • the gate is disposed on the semiconductor substrate.
  • the gate oxide layer is disposed between the gate and the semiconductor substrate.
  • the doped diffusion region is disposed in the semiconductor substrate, and the gate is disposed between the first-conductivity-type doped region and the doped diffusion region.
  • a fabrication method of an image sensor including following steps is provided. First, a semiconductor substrate is provided, wherein a photosensitive area is defined on a surface of the semiconductor substrate. Next, a first-conductivity-type doped region is formed near the surface of the semiconductor substrate and in the photosensitive area. An etching process is then performed to remove a portion of the first-conductivity-type doped region of the semiconductor substrate so as to form at least one recess, wherein the recess is disposed in the photosensitive area.
  • an ion implantation process is performed to form a second-conductivity-type doped region on a surface of the first-conductivity-type doped region in the photosensitive area, wherein the first-conductivity-type doped region and the second-conductivity-type doped region have different conductivity types, and the first-conductivity-type doped region and the second-conductivity-type doped region form a photosensitive device.
  • FIGS. 1-7 are schematic diagrams illustrating a fabrication method of an image sensor of a first embodiment of the present invention, wherein:
  • FIG. 1 is a schematic diagram illustrating the step of forming a first-conductive-type doped region in a semiconductor substrate
  • FIG. 2 is a schematic diagram illustrating the fabrication method subsequent to FIG. 1 ;
  • FIG. 3 is a schematic diagram illustrating the fabrication method subsequent to FIG. 2 ;
  • FIG. 4 is a schematic diagram illustrating the fabrication method subsequent to FIG. 3 ;
  • FIG. 5 is a schematic diagram illustrating the fabrication method subsequent to FIG. 4 ;
  • FIG. 6 is a schematic diagram illustrating the fabrication method subsequent to FIG. 5 ;
  • FIG. 7 is a schematic diagram illustrating the fabrication method subsequent to FIG. 6 , and also illustrating the structure of an image sensor according to a first embodiment of the present invention the present invention.
  • FIG. 8 is a schematic diagram illustrating a process flow of the fabrication method of the image sensor of the present invention.
  • FIG. 9 is a schematic diagram illustrating a cross-sectional view of an image sensor of a first variant embodiment of the first embodiment of the present invention.
  • FIG. 10 is a schematic diagram illustrating a cross-sectional view of an image sensor of a second variant embodiment of the first embodiment of the present invention.
  • FIGS. 11-12 are schematic diagrams illustrating a fabrication method of an image sensor of a second embodiment of the present invention, wherein:
  • FIG. 11 is a schematic diagram illustrating the step of forming a first-conductive-type doped region in a semiconductor substrate.
  • FIG. 12 is a schematic diagram illustrating the fabrication method subsequent to FIG. 11 .
  • FIG. 13 is a schematic diagram illustrating a cross-sectional view of an image sensor of a first variant embodiment of the second embodiment of the present invention.
  • FIGS. 1-7 are schematic diagrams illustrating a fabrication method of an image sensor 1 A according to a first embodiment of the present invention
  • FIG. 8 is a schematic diagram illustrating a process flow of the fabrication method of the image sensor 1 A according to the first embodiment of the present invention
  • the image sensor 1 A of this embodiment is a front side illumination (FSI) image sensor.
  • FSI front side illumination
  • a semiconductor substrate 100 is provided first, and a photosensitive area 10 is defined on the surface of the semiconductor substrate 100 .
  • the semiconductor substrate 100 of this embodiment is, but not limited to, a p-type semiconductor substrate, such as a silicon substrate including p-type dopants.
  • the semiconductor substrate 100 may be a silicon substrate, an epitaxial silicon substrate, a silicon-germanium (SiGe) substrate, a silicon carbide (SiC) substrate or a silicon-on-insulator (SOI) substrate, but not limited thereto.
  • a first-conductivity-type doped region 102 , a second-conductivity-type sacrificial layer 104 and a doped diffusion region 106 are formed in the surface of the semiconductor substrate 100 .
  • the first-conductivity-type doped region 102 is formed near the surface of the semiconductor substrate 100 and in the photosensitive area 10 .
  • the depth D 2 of the first-conductivity-type doped region 102 is less than or equal to 0.2 micrometers approximately, but not limited thereto.
  • the dopants of the first-conductivity-type doped region 102 have a conductivity type opposite to the dopants of the semiconductor substrate 100 .
  • the first-conductivity-type doped region 102 may be an n-type doped region.
  • the first-conductivity-type doped region 102 may be formed through an ion implantation process by implanting n-type dopants into the semiconductor substrate 100 .
  • the second-conductivity-type sacrificial layer 104 is formed in the photosensitive area 10 and covers the surface of the first-conductivity-type doped region 102 .
  • the second-conductivity-type sacrificial layer 104 includes dopants having the same conductivity type as the semiconductor substrate 100 , but having a higher doping concentration.
  • the second-conductivity-type sacrificial layer 104 may be a p-type doped region, and may be formed through an ion implantation process by implanting p-type dopants into the semiconductor substrate 100 .
  • the second-conductivity-type sacrificial layer 104 can be formed close to the surface of the semiconductor substrate 100 , and the first-conductivity-type doped region 102 can be formed deeper in the semiconductor substrate 100 .
  • the doped diffusion region 106 is formed out of the photosensitive area 10 , and includes the dopants having the conductivity type opposite to the semiconductor substrate 100 .
  • the doped diffusion region 106 may be an n-type doped region for instance, and may be formed through the same method as the first-conductivity-type doped region 102 .
  • the doped diffusion region 106 serves as a floating diffusion (FD) region of the image sensor 1 A.
  • FD floating diffusion
  • the semiconductor substrate 100 may be an n-type semiconductor substrate
  • the first-conductivity-type doped region 102 and the doped diffusion region 106 may be p-type doped regions respectively
  • the second-conductivity-type sacrificial layer 104 may be an n-type doped region.
  • a gate oxide layer 110 and a gate 108 are formed on the semiconductor substrate 100 sequentially, wherein the gate oxide layer 110 is disposed between the gate 108 and the semiconductor substrate 100 .
  • the gate 108 is approximately disposed between the first-conductivity-type doped region 102 and the doped diffusion region 106 , and the first-conductivity-type doped region 102 extends to a portion of the semiconductor substrate 100 below the gate 108 such that a part of the first-conductivity-type doped region 102 is covered by a portion of the gate 108 .
  • the gate oxide layer 110 may include silicon oxide
  • the gate 108 may include polysilicon, but not limited thereto.
  • the gate 108 serves as a transfer gate (Tx) of the image sensor 1 A.
  • the gate oxide layer 110 and the gate 108 may be formed before forming the first-conductivity-type doped region 102 , the second-conductivity-type sacrificial layer 104 and the doped diffusion region 106 .
  • the gate oxide layer 110 and the gate 108 may be formed after forming the first-conductivity-type doped region 102 but before forming the second-conductivity-type sacrificial layer 104 .
  • the present invention does not limit when to form the gate oxide layer 110 and the gate 108 .
  • an isolation structure 112 may be selectively formed in the semiconductor substrate 100 before forming the first-conductivity-type doped region 102 , the second-conductivity-type sacrificial layer 104 and the doped diffusion region 106 .
  • the isolation structure 112 may be a shallow trench isolation (STI), a local oxidation of silicon isolation layer (LOCOS), or a junction isolation, for preventing the image sensor 1 A from being coupled to other devices and resulting in short-circuit issue.
  • the method of forming the isolation structure 112 may include forming a mask on the semiconductor substrate 100 first, performing an etching process to form a trench in the semiconductor substrate 100 , then filling an insulating material (such as silicon oxide) into the trench, and removing the mask.
  • a screen oxide layer (not shown) and other pad layers or liners (not shown) maybe selectively formed on the semiconductor substrate 100 in this embodiment of the present invention.
  • a patterned mask layer 114 is formed on the surface of the semiconductor substrate 100 for defining the pattern of one or more recesses in the photosensitive area 10 .
  • the patterned mask layer 114 of this embodiment defines the patterns of a plurality of recesses, and therefore the patterned mask layer 114 includes a plurality of openings 114 a, wherein the width W 1 of each opening 114 a is about 0.15 micrometers for example.
  • the width W 2 of the patterned mask layer 114 disposed between the adjoining openings 114 a is about 60 nanometers for example. It should be noted that the above mentioned width W 1 and width W 2 are examples only, not used for limiting the present invention.
  • the patterned mask layer 114 disposed out of the photosensitive area 10 covers the isolation structure 112 , the gate oxide layer 110 and the gate 108 , such that the isolation structure 112 , the gate oxide layer 110 and the gate 108 will not be influenced by the following processes.
  • the method of forming the patterned mask layer 114 may include fully coating a photoresist layer first, exposing the photoresist layer with a mask, and then developing the exposed photoresist layer to form the patterned mask layer 114 .
  • an etching process 115 is performed by taking the patterned mask layer 114 as an etching mask, so as to remove a portion of the first-conductivity-type doped region 102 of the semiconductor substrate 100 and form at least one recess 116 in the semiconductor substrate 100 . Since the number of the recesses 116 is determined by the number of the openings 114 a of the patterned mask layer 114 , a plurality of recesses 116 are formed in the semiconductor substrate 100 in this embodiment.
  • the remaining second-conductivity-type sacrificial layer 104 in the photosensitive area 10 has the width W 2 of about 60 nanometers, which also means that the distance between the adjoining recesses 116 is about 60 nanometers, but not limited thereto.
  • the etching process 115 of this embodiment is an anisotropic etching process, such as an anisotropic wet etching process, an anisotropic dry etching process, or a combination of the anisotropic wet etching process and the anisotropic dry etching process.
  • the etchant of the anisotropic wet etching process may include tetramethylammonium hydroxide (TMAH), ethylene diamine, ethylene diamine and pyrocatechol (EDP), alkali-based etching solution, diluted hydrofluoric (DHF), hydrogen fluoride (HF), buffered oxide etching (BOE) solution, SC-1 cleaning liquid, or a combination of the aforementioned etchants.
  • the etchant of this embodiment includes TMAH and DHF, wherein the DHF is used for removing the screen oxide layer on the surface of the semiconductor substrate 100 , and the TMAH is used for removing the material of the semiconductor substrate 100 .
  • the etching process may include dipping the semiconductor substrate 100 into the TMAH solution with a concentration of about 25 wt % for 12 seconds, so as to form the recesses 116 having a depth D 1 that is about 0.1 micrometers.
  • the width of the recesses 116 is substantially equal to the width W 1 of the openings 114 a of the patterned mask layer 114 .
  • the depth D 1 of the recesses 116 may reach to about 1 micrometer, and the width W 1 of the openings 114 a may reach to about 1.5 micrometers, but not limited thereto.
  • the etching process 115 of this embodiment is an anisotropic etching process
  • the depths and the cross-sectional profiles of the recesses 116 formed through the etching process 115 are related to the selected etchant, the process duration, and the size and the shape of the openings 114 a of the patterned mask layer 114 .
  • the cross-sectional profile and the depth of the recess 116 may be controlled by adjusting the duration of the etching process 115 .
  • each of the recesses 116 formed in this embodiment is gradually reduced from the opening of the recess 116 to the bottom of the recess 116 .
  • the recesses 116 are cone-shaped recesses, but not limited thereto.
  • the recesses may be hemispherical-shaped recesses, or have inverted trapezoid cross-sectional profiles.
  • the shapes of the opening of the recesses 116 in the top-view may include circle, square, rectangle, rhombus, elongated rectangle, hexagon, cross, or any other suitable shapes.
  • an ion implantation process 118 is performed by taking the patterned mask layer 114 as a mask to implant the second-conductivity-type dopants into the semiconductor substrate 100 , so as to form a second-conductivity-type doped layer 120 on the surface of the first-conductivity-type doped region 102 in the photosensitive area 10 .
  • the second-conductivity-type doped layer 120 includes the dopants having the same conductivity type as the second-conductivity-type sacrificial layer 104 , and the second-conductivity-type doped layer 120 is a p-type doped region for example.
  • the ion implantation process 118 of this embodiment may be a plasma doping process for instance.
  • the ion implantation process 118 is not limited to implanting the dopants only along the direction perpendicular to the surface of the semiconductor substrate 100 (such as the direction Z shown in FIG. 3 ), and the dopants may be implanted along various oblique directions.
  • the patterned mask layer 114 is removed, and an annealing process 121 may be selectively performed after the ion implantation process 118 to activate the dopants in the second-conductivity-type sacrificial layer 104 and the second-conductivity-type doped layer 120 .
  • the annealing process 121 of this embodiment may be a laser annealing process for example, but not limited thereto.
  • the remaining portion of the second-conductivity-type sacrificial layer 104 after the etching process 115 is connected to the second-conductivity-type doped layer 120 , so as to form a second-conductivity-type doped region 122 on the surface of the first-conductivity-type doped region 102 .
  • the second-conductivity-type doped region 122 in this embodiment is a p-type doped region.
  • the first-conductivity-type doped region 102 and the second-conductivity-type doped region 122 form a photosensitive device 124 of this embodiment, and the photosensitive device 124 is a pinned photodiode for example.
  • a dielectric layer 126 and a conductive line 128 disposed in the dielectric layer 126 are formed on the surface of the semiconductor substrate 100 .
  • the dielectric layer 126 covers the photosensitive device 124 and is filled in the recesses 116 .
  • the conductive line 128 may be connected to the gate 108 .
  • the dielectric layer 126 may include a plurality of inter-layer dielectric layers, and the material of the dielectric layer 126 may include a low-K dielectric material, such as silicon oxide, borophosphosilicate glass (BPSG), phosphosilicate glass (PSG), fluorinated silicate glass (FSG), carbon-doped silicon oxide or the like.
  • the method of forming the dielectric layer 126 may include the chemical vapor deposition (CVD) technique for example, but not limited thereto.
  • the conductive line 128 may be a multilayer-interconnect (MLI) structure for example, and the dielectric layer 126 can be used for isolating and separating the MLI structure from other conductive devices on the semiconductor substrate 100 .
  • the method of patterning the conductive line 128 may include a plasma etching or a damascene process, and the material of the conductive line 128 may include aluminum, copper, doped polysilicon or the like.
  • the dielectric layer 126 and the conductive line 128 may be fabricated by sequentially forming multiple inter-layer dielectric layers, interconnects, and contacts or vias.
  • a light pipe opening 130 is formed in the dielectric layer 126 .
  • the method of forming the light pipe opening 130 may include forming a patterned mask layer (not shown in figures) on the dielectric layer 126 to define the pattern of the light pipe opening 130 first, and performing an etching process next, so as to form the light pipe opening 130 in the dielectric layer 126 .
  • the cross-sectional profile of the light pipe opening 130 may have a vertical sidewall as shown in FIG. 6 , but may have an inclined sidewall in another embodiment such that the area of the bottom of the light pipe opening 130 is less than the area of the top of the light pipe opening 130 .
  • a barrier layer 132 can be selectively formed on the dielectric layer 126 and the sidewall and the bottom surface of the light pipe opening 130 .
  • the material of the barrier layer 132 may include silicon nitride (SiN) or silicon oxynitride (SiON).
  • SiN silicon nitride
  • SiON silicon oxynitride
  • the barrier layer 132 can prevent the devices underneath from being damaged by oxygen and moisture, but not limited thereto.
  • a material having a high refractive index is filled in the light pipe opening 130 to form a light pipe 134 above the photosensitive device 124 .
  • a chemical mechanical polishing (CMP) process may be performed to enable the light pipe 134 to have a flat surface.
  • a color filter layer 136 and a micro lens 138 are sequentially formed on the surface of the light pipe 134 .
  • the color filter layer 136 includes a colored photoresist pattern for example, and may be formed through a photolithography and etching process.
  • the color filter layer 136 is disposed between the micro lens 138 and the light pipe 134 , and the light pipe 134 and the conductive line 128 are disposed between the color filter layer 136 and the recesses 116 of the photosensitive device 124 . According to the above mentioned processes, the fabrication of the image sensor 1 A of the first embodiment of the present invention is finished.
  • the fabrication method of the image sensor 1 A of the present invention mainly includes the steps shown in FIG. 8 :
  • Step S 10 Providing a semiconductor substrate, wherein a photosensitive area is defined on the surface of the semiconductor substrate;
  • Step S 12 Forming a first-conductivity-type doped region near the surface of the semiconductor substrate and in the photosensitive area;
  • Step S 14 Performing an etching process to remove a portion of the surface of the semiconductor substrate for forming at least one recess in the semiconductor substrate and in the photosensitive area;
  • Step S 16 Performing an ion implantation process to form a second-conductivity-type doped layer on the surface of the recess in the photosensitive area, wherein the first-conductivity-type doped region and the second-conductivity-type doped layer have different conductivity types, and the first-conductivity-type doped region and the second-conductivity-type doped layer form a photosensitive device.
  • the image sensor 1 A includes the semiconductor substrate 100 , the first-conductivity-type doped region 102 , the second-conductivity-type doped region 122 , the gate 108 , the gate oxide layer 110 and the doped diffusion region 106 .
  • the photosensitive area 10 is defined on the surface of the semiconductor substrate 100 , and the surface of the semiconductor substrate 100 has a plurality of recesses 116 distributed in the photosensitive area 10 . The size of the recesses 116 is gradually reduced from the openings of the recesses 116 to the bottoms of the recesses 116 .
  • the recesses 116 of this embodiment are cone-shaped recesses, but not limited thereto.
  • the recesses may be hemispheric recesses, or may have inverted trapezoid cross-sectional profiles.
  • the shapes of the openings of the recesses 116 in the top-view may include circle, square, rectangle, rhombus, elongated rectangle, hexagon, or other suitable shapes.
  • the first-conductivity-type doped region 102 is disposed in the semiconductor substrate 100 and in the photosensitive area 10
  • the second-conductivity-type doped region 122 is disposed on the surface of the first-conductivity-type doped region 102 and the surface of the recesses 116 .
  • the first-conductivity-type doped region 102 is an n-type doped region
  • the second-conductivity-type doped region 122 is a p-type doped region
  • the first-conductivity-type doped region 102 and the second-conductivity-type doped region 122 form the photosensitive device 124 .
  • the photosensitive device 124 of this embodiment is a pinned photodiode.
  • a barrier layer of SiN, an anti-reflection coating (ARC), or a contact etch stop layer, CESL may be disposed on the photosensitive device 124 .
  • ARC anti-reflection coating
  • CESL contact etch stop layer
  • the gate 108 is disposed on the semiconductor substrate 100 , and the first-conductivity-type doped region 102 extends to a portion of the semiconductor substrate 100 below the gate 108 such that apart of the first-conductivity-type doped region 102 is covered by the portion of the gate 108 .
  • the gate 108 is a transfer gate of the image sensor 1 A
  • the gate oxide layer 110 is disposed between the gate 108 and the semiconductor substrate 100
  • the doped diffusion region 106 is disposed in the semiconductor substrate 100 and at one side of the gate 108
  • the gate 108 is approximately disposed between the first-conductivity-type doped region 102 and the doped diffusion region 106 .
  • the doped diffusion region 106 of this embodiment serves as a floating diffusion (FD) region of the image sensor 1 A, and it is an n-type doped region.
  • the photosensitive device 124 generates photo electrons under illumination, and the photo electrons can be transmitted to the FD region, i.e. the doped diffusion region 106 , through providing a voltage to the gate 108 and will be further transformed into electric signals for output.
  • the image sensor 1 A may further include a reset transistor, a source follower transistor, or a read select transistor, and may include a pixel circuit having three transistors (3 T) or four transistors (4 T). For emphasizing the characteristic features of the image sensor 1 A of this embodiment, the aforementioned devices are not shown in the figures.
  • the image sensor 1 A of this embodiment includes the dielectric layer 126 , the conductive line 128 , the color filter layer 136 and the micro lens 138 disposed on the surface of the semiconductor substrate 100 .
  • the dielectric layer 126 is filled in the recesses 116
  • the conductive line 128 is electrically connected to the gate 108
  • the conductive line 128 is disposed in the dielectric layer 126 but does not cover the photosensitive area 10 .
  • the color filter layer 136 and the micro lens 138 are disposed on the surface of the dielectric layer 126 and cover the photosensitive area 10 .
  • the color of the color filter layer 136 may include red, blue, or green, so that the photosensitive device 124 can detect the light with a specific color.
  • the image sensor 1 A may selectively include the light pipe 134 disposed in the dielectric layer 126 and between the color filter layer 136 and the recesses 116 .
  • the light pipe 134 may extend downward to the top of the recesses 116 and is in contact with the second-conductivity-type doped region 122 . Since the light pipe 134 includes the material having high refractive index, its refractive index is greater than the refractive index of the dielectric layer 126 , such that total reflection easily occurs in the light pipe 134 when light entering the light pipe 134 . Therefore, the light pipe 134 assists in guiding light to the photosensitive device 124 , and further improves the quantum efficiency of the image sensor 1 A.
  • the surface of the photosensitive device 124 has recesses 116 , and the profile of each recess 116 is gradually reduced from the opening to the bottom of the recess 116 .
  • the specific profile of each recess 116 helps to keep on reflecting light in the recess 116 and also guide the light to the bottom of the recess 116 .
  • the recesses 116 can significantly enhance the sensing area of the photosensitive device 124 in the photosensitive area 10 , so as to effectively increase the percentage of the light absorbed by the photosensitive device 124 . As a result, the quantum efficiency of the image sensor 1 A can be improved.
  • the recesses 116 prevent the light from being reflected to the photosensitive devices of other adjoining pixels and thus reduce the crosstalk issue.
  • the image sensor and the related fabrication method of the present invention are not limited to the aforementioned embodiment.
  • the following description continues to detail other embodiments or variant embodiments. To simplify the description and show the difference between other embodiments, variant embodiments and the above-mentioned embodiment, identical components in each of the following embodiments are marked with identical symbols, and the identical features will not be redundantly described.
  • FIG. 9 is a schematic diagram illustrating a cross-sectional view of an image sensor 1 B of a first variant embodiment of the first embodiment of the present invention.
  • the difference between this variant embodiment and the first embodiment is that the number of the recesses 116 of the image sensor 1 B is less than the image sensor 1 A.
  • the recesses 116 of the image sensor 1 B are respectively disposed adjacent to the outer edge of the photosensitive area 10 , thus the portion of the second-conductivity-type doped region 122 around the central region of the photosensitive area 10 has a flat surface.
  • FIG. 10 is a schematic diagram illustrating a cross-sectional view of an image sensor 1 C of a second variant embodiment of the first embodiment of the present invention.
  • the difference between this variant embodiment and the first embodiment is that the photosensitive device 124 of the image sensor 1 C has only one recess 116 , and the area of the opening of the recess 116 is approximate to the area of the photosensitive area 10 .
  • the recess 116 of this variant embodiment has an inverted trapezoid cross-sectional profile, but not limited thereto. Since the sidewall of the recess 116 inclines from the edge of the photosensitive area 10 to the center of the photosensitive area 10 , the light propagates to the outer edge of the photosensitive device 124 is prevented from being reflected to other adjoining image sensors, and the crosstalk issue can further be avoided.
  • FIG. 11 and FIG. 12 are schematic diagrams illustrating a fabrication method of an image sensor 2 A of a second embodiment of the present invention.
  • the image sensor 2 A of the second embodiment of the present invention is a back side illumination (BSI) image sensor.
  • BSI back side illumination
  • a semiconductor substrate 100 is provided first.
  • the semiconductor substrate 100 of this embodiment selectively includes an epitaxial layer 142 disposed at one side of the semiconductor substrate 100 .
  • the thickness of the epitaxial layer 142 is about 4 micrometers, but not limited thereto.
  • a doped diffusion region 106 , a first-conductivity-type doped region 102 , and one or more selective isolation structures 112 are formed in the epitaxial layer 142 of the semiconductor substrate 100 .
  • a gate oxide layer 110 and a gate 108 are formed on the epitaxial layer 142 .
  • a second-conductivity-type doped layer 146 is formed near the surface of the epitaxial layer 142 .
  • the second-conductivity-type doped layer 146 is disposed at one side of the gate 108 .
  • the second-conductivity-type doped layer 146 of this embodiment is not covered by the gate 108 , but not limited thereto.
  • the second-conductivity-type doped layer 146 includes dopants having the same conductivity type as the semiconductor substrate 100 (or the epitaxial layer 142 ), but having a higher doping concentration.
  • a conductive line 128 and a dielectric layer 126 are formed on the semiconductor substrate 100 , wherein the dielectric layer 126 covers the gate 108 and the second-conductivity-type doped layer 146 .
  • the conductive line 128 may be a MLI structure and is electrically connected to the gate 108 .
  • a carrier substrate may be adhered to the side of the semiconductor substrate 100 having the conductive line 128 and the dielectric layer 126 , and a buffer layer may be selectively disposed between the carrier substrate and the semiconductor substrate 100 .
  • the material of the carrier substrate may include silicon material similar to the material of the semiconductor substrate 100 or be a glass substrate.
  • the material of the buffer layer may include silicon oxide, silicon nitride, or other dielectric materials. In order to emphasize the characteristic features of the image sensor 2 A of this embodiment, the carrier substrate and the buffer layer are not shown in the figures. Then, a thinning process 144 is performed to remove most of the semiconductor substrate 100 , but the epitaxial layer 142 is remained.
  • the recesses 116 and the second-conductivity-type doped layer 120 are formed at another side of the epitaxial layer 142 of the semiconductor substrate 100 , which means the recesses 116 and the conductive line 128 are disposed at the opposite sides of the epitaxial layer 142 respectively.
  • An annealing process may be performed to the second-conductivity-type doped layer 120 after the second-conductivity-type doped layer 120 is formed, thus the dopants in the second-conductivity-type doped layer 120 can be activated to form the second-conductivity-type doped region 122 .
  • the doping concentration of the second-conductivity-type doped region 122 is higher than the doping concentration of the epitaxial layer 142 .
  • the annealing process may be a laser annealing process for example, but not limited thereto.
  • a barrier layer (not shown) maybe selectively formed on the surfaces of the recesses 116 and the epitaxial layer 142 .
  • the barrier layer may fully covers the surfaces of the recesses 116 and the epitaxial layer 142 .
  • the material of the barrier layer may be silicon nitride or silicon oxide for example, but not limited thereto.
  • an ARC (not shown) may also be selectively formed on the surfaces of the recesses 116 and the epitaxial layer 142 .
  • a filling layer 140 is formed on the surface of the epitaxial layer 142 , at the side of the epitaxial layer 142 having the recesses 116 .
  • the filling layer 140 may include silicon oxide or other dielectric materials having high light transmittances.
  • the filling layer 140 can be formed through CVD process, physical vapor deposition (PVD) process, or other suitable techniques.
  • the portion of the filling layer 140 out of the recesses 116 can be removed by performing chemical mechanical polishing or other processes, such that the filling layer 140 has a flat surface.
  • a color filter layer 136 and a micro lens 138 are formed on the filling layer 140 .
  • the material and the fabrication method of each device in the image sensor 2 A of this embodiment may be the same as the first embodiment, and will not be redundantly described.
  • the image sensor 2 A is a BSI image sensor.
  • the photosensitive device 124 is disposed between the conductive line 128 and the color filter layer 136 .
  • the semiconductor substrate 100 (or the epitaxial layer 142 ) includes a front side 12 and a back side 14 , and the isolation structure 112 and the doped diffusion region 106 are disposed in the portion of the semiconductor substrate 100 near the front side 12 .
  • the image sensor 2 A further includes the second-conductivity-type doped layer 146 disposed in the portion of the semiconductor substrate 100 near the front side 12 , adjoining to the gate 108 .
  • the gate 108 , the gate oxide layer 110 , the conductive line 128 and the dielectric layer 126 are all disposed on the surface of the front side 12 of the semiconductor substrate 100 .
  • the recesses 116 are disposed in the portion of the semiconductor substrate 100 near the back side 14 , and therefore the second-conductivity-type doped layer 146 and the conductive line 128 are disposed at one side of the semiconductor substrate 100 , and the recesses 116 are disposed at another side of the semiconductor substrate 100 .
  • the first-conductivity-type doped region 102 is disposed between the second-conductivity-type doped layer 146 and the recesses 116 , and also between the conductive line 128 and the recesses 116 .
  • the p-n junction between the first-conductivity-type doped region 102 and the second-conductivity-type doped region 122 is disposed at the back side 14 of the semiconductor substrate 100 .
  • the image sensor 2 A further includes the color filter layer 136 and the micro lens 138 disposed on the surface of the back side 14 of the semiconductor substrate 100 , covering the photosensitive area 10 .
  • the image sensor 2 A also includes the filling layer 140 filled in the recesses 116 , which is disposed between the photosensitive device 124 and the color filter layer 136 .
  • FIG. 13 is a schematic diagram illustrating a cross-sectional view of an image sensor 2 B of a first variant embodiment of the second embodiment of the present invention.
  • the difference between this variant embodiment and the second embodiment is that the color filter layer 136 of the image sensor 2 B is directly filled in the recesses 116 , and therefore the filling layer 140 shown FIG. 12 is not required.
  • the material and the fabrication method of each device in the image sensor 2 B may be the same as the second embodiment, and will not be redundantly described.
  • the first-conductivity-type doped region is formed in the semiconductor substrate first, and the recesses are formed on the surface of the first-conductivity-type doped region. Then, the second-conductivity-type doped region is formed on the surface of the first-conductivity-type doped region. Specifically, the second-conductivity-type doped region is formed on the surfaces of the recesses, such that the p-n junction of the photosensitive device existed between the first-conductivity-type doped region and the second-conductivity-type doped region is formed along the surfaces of the recesses.
  • the structure of the recess of the image sensor according to the present invention keeps the light being reflected in the recess and guides the light to the bottom of the recesses, so as to increase the amount of the light absorbed by the photosensitive device.
  • the area of the p-n junction of the photosensitive device is increased due to the existence of the recesses, which means the light-sensing area is increased and the quantum efficiency of the image sensor is then improved.
  • the propagating direction of the light can be adjusted by the recesses, so as to prevent the light propagating to the outer edge of the photosensitive device from being reflected to other adjoining image sensors. As a result, the crosstalk issue can be effectively improved. In short, the efficiency and the accuracy of the image sensor are effectively improved according to the present invention.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Electromagnetism (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Solid State Image Pick-Up Elements (AREA)
  • Light Receiving Elements (AREA)

Abstract

An image sensor includes a semiconductor substrate with at least one recess disposed on its surface and in the photosensitive area defined on the surface of the semiconductor substrate, a first-conductivity-type doped region disposed in the semiconductor substrate and in the photosensitive area, and a second-conductivity-type doped region disposed on the surface of the first-conductivity-type doped region and on the surface of the recess. A photosensitive device of the image sensor is formed of the first-conductivity-type doped region and the second-conductivity-type doped region.

Description

    BACKGROUND OF THE INVENTION 1. Field of the Invention
  • The present invention relates to an image sensor and related fabrication method, more particularly, to an image sensor and related fabrication method capable of improving quantum efficiency and reducing crosstalk issue.
  • 2. Description of the Prior Art
  • As the development of electronic products such as digital cameras and scanners progresses, the demand for image sensors increases accordingly. In general, image sensors in common usage nowadays are divided into two main categories: charge coupled device (CCD) sensors and complementary metal-oxide-semiconductor (CMOS) image sensors, CIS. Primarily, CMOS image sensors have certain advantages of low operating voltage, low power consumption, high operating efficiency, and the ability for random access. Furthermore, CMOS image sensors are currently capable of integration with the semiconductor fabrication process. Based on those benefits, the application of CMOS image sensors has increased significantly.
  • In the operation theory of CMOS image sensor, the incident light is separated into a combination of light of different wavelengths. For example, the incident light can be separated into a combination of red, blue, and green light. The light of different wavelengths is received by respective optical sensors such as photodiodes and is subsequently transformed into digital signals of different intensities. However, as the dimensions of the pixel are reduced, the size of the photodiode is reduced together. Accordingly, the crosstalk between the pixels is increased, and the optical sensitivity is decreased. Furthermore, since CMOS image sensor is usually disposed in a semiconductor substrate with high reflectivity, the light is easy to be reflected by the semiconductor substrate when the light propagates to the semiconductor substrate. Accordingly, the light cannot enter the optical sensors effectively, which leads to the problem of low quantum efficiency in the conventional CMOS image sensor. Thus, in order to solve the above-mentioned shortcomings, there is still a need in the industry to provide a CMOS image sensor having high quantum efficiency and less crosstalk.
  • SUMMARY OF THE INVENTION
  • It is therefore one of the objectives of the present invention to provide an image sensor and related fabrication method for improving quantum efficiency and reducing crosstalk of the image sensor.
  • According to an embodiment of the present invention, an image sensor is provided. The image sensor includes a semiconductor substrate, a first-conductivity-type doped region, a second-conductivity-type doped region, a gate, a gate oxide layer and a doped diffusion region. A photosensitive area is defined on a surface of the semiconductor substrate, and the surface of the semiconductor substrate has at least one recess in the photosensitive area. The first-conductivity-type doped region is disposed in the semiconductor substrate and in the photosensitive area. The second-conductivity-type doped region is disposed on a surface of the first-conductivity-type doped region and on a surface of the recess, wherein the first-conductivity-type doped region and the second-conductivity-type doped region have different conductivity types, and the first-conductivity-type doped region and the second-conductivity-type doped region form a photosensitive device. The gate is disposed on the semiconductor substrate. The gate oxide layer is disposed between the gate and the semiconductor substrate. The doped diffusion region is disposed in the semiconductor substrate, and the gate is disposed between the first-conductivity-type doped region and the doped diffusion region.
  • According to another embodiment of the present invention, a fabrication method of an image sensor including following steps is provided. First, a semiconductor substrate is provided, wherein a photosensitive area is defined on a surface of the semiconductor substrate. Next, a first-conductivity-type doped region is formed near the surface of the semiconductor substrate and in the photosensitive area. An etching process is then performed to remove a portion of the first-conductivity-type doped region of the semiconductor substrate so as to form at least one recess, wherein the recess is disposed in the photosensitive area. Next, an ion implantation process is performed to form a second-conductivity-type doped region on a surface of the first-conductivity-type doped region in the photosensitive area, wherein the first-conductivity-type doped region and the second-conductivity-type doped region have different conductivity types, and the first-conductivity-type doped region and the second-conductivity-type doped region form a photosensitive device.
  • These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
  • BRIEF DESCRIPTION OF THE DRAWINGS
  • FIGS. 1-7 are schematic diagrams illustrating a fabrication method of an image sensor of a first embodiment of the present invention, wherein:
  • FIG. 1 is a schematic diagram illustrating the step of forming a first-conductive-type doped region in a semiconductor substrate;
  • FIG. 2 is a schematic diagram illustrating the fabrication method subsequent to FIG. 1;
  • FIG. 3 is a schematic diagram illustrating the fabrication method subsequent to FIG. 2;
  • FIG. 4 is a schematic diagram illustrating the fabrication method subsequent to FIG. 3;
  • FIG. 5 is a schematic diagram illustrating the fabrication method subsequent to FIG. 4;
  • FIG. 6 is a schematic diagram illustrating the fabrication method subsequent to FIG. 5; and
  • FIG. 7 is a schematic diagram illustrating the fabrication method subsequent to FIG. 6, and also illustrating the structure of an image sensor according to a first embodiment of the present invention the present invention.
  • FIG. 8 is a schematic diagram illustrating a process flow of the fabrication method of the image sensor of the present invention.
  • FIG. 9 is a schematic diagram illustrating a cross-sectional view of an image sensor of a first variant embodiment of the first embodiment of the present invention.
  • FIG. 10 is a schematic diagram illustrating a cross-sectional view of an image sensor of a second variant embodiment of the first embodiment of the present invention.
  • FIGS. 11-12 are schematic diagrams illustrating a fabrication method of an image sensor of a second embodiment of the present invention, wherein:
  • FIG. 11 is a schematic diagram illustrating the step of forming a first-conductive-type doped region in a semiconductor substrate; and
  • FIG. 12 is a schematic diagram illustrating the fabrication method subsequent to FIG. 11.
  • FIG. 13 is a schematic diagram illustrating a cross-sectional view of an image sensor of a first variant embodiment of the second embodiment of the present invention.
  • DETAILED DESCRIPTION
  • To provide a better understanding of the present invention, preferred embodiments will be detailed as follows. The preferred embodiments of the present invention are illustrated in the accompanying drawings with numbered elements to elaborate the contents and effects to be achieved.
  • Referring to FIG. 1 to FIG. 8, FIGS. 1-7 are schematic diagrams illustrating a fabrication method of an image sensor 1A according to a first embodiment of the present invention, and FIG. 8 is a schematic diagram illustrating a process flow of the fabrication method of the image sensor 1A according to the first embodiment of the present invention. The image sensor 1A of this embodiment is a front side illumination (FSI) image sensor. As shown in FIG. 1, a semiconductor substrate 100 is provided first, and a photosensitive area 10 is defined on the surface of the semiconductor substrate 100. The semiconductor substrate 100 of this embodiment is, but not limited to, a p-type semiconductor substrate, such as a silicon substrate including p-type dopants. The semiconductor substrate 100 may be a silicon substrate, an epitaxial silicon substrate, a silicon-germanium (SiGe) substrate, a silicon carbide (SiC) substrate or a silicon-on-insulator (SOI) substrate, but not limited thereto. Next, a first-conductivity-type doped region 102, a second-conductivity-type sacrificial layer 104 and a doped diffusion region 106 are formed in the surface of the semiconductor substrate 100. The first-conductivity-type doped region 102 is formed near the surface of the semiconductor substrate 100 and in the photosensitive area 10. For example, the depth D2 of the first-conductivity-type doped region 102 is less than or equal to 0.2 micrometers approximately, but not limited thereto. In this embodiment, the dopants of the first-conductivity-type doped region 102 have a conductivity type opposite to the dopants of the semiconductor substrate 100. For example, the first-conductivity-type doped region 102 may be an n-type doped region. The first-conductivity-type doped region 102 may be formed through an ion implantation process by implanting n-type dopants into the semiconductor substrate 100. The second-conductivity-type sacrificial layer 104 is formed in the photosensitive area 10 and covers the surface of the first-conductivity-type doped region 102. The second-conductivity-type sacrificial layer 104 includes dopants having the same conductivity type as the semiconductor substrate 100, but having a higher doping concentration. For example, the second-conductivity-type sacrificial layer 104 may be a p-type doped region, and may be formed through an ion implantation process by implanting p-type dopants into the semiconductor substrate 100. Specifically, by the way of adjusting the doping energy of dopant-implantation, the second-conductivity-type sacrificial layer 104 can be formed close to the surface of the semiconductor substrate 100, and the first-conductivity-type doped region 102 can be formed deeper in the semiconductor substrate 100. The doped diffusion region 106 is formed out of the photosensitive area 10, and includes the dopants having the conductivity type opposite to the semiconductor substrate 100. The doped diffusion region 106 may be an n-type doped region for instance, and may be formed through the same method as the first-conductivity-type doped region 102. In this embodiment, the doped diffusion region 106 serves as a floating diffusion (FD) region of the image sensor 1A. In a variant embodiment, the semiconductor substrate 100 may be an n-type semiconductor substrate, the first-conductivity-type doped region 102 and the doped diffusion region 106 may be p-type doped regions respectively, and the second-conductivity-type sacrificial layer 104 may be an n-type doped region.
  • Next, a gate oxide layer 110 and a gate 108 are formed on the semiconductor substrate 100 sequentially, wherein the gate oxide layer 110 is disposed between the gate 108 and the semiconductor substrate 100. The gate 108 is approximately disposed between the first-conductivity-type doped region 102 and the doped diffusion region 106, and the first-conductivity-type doped region 102 extends to a portion of the semiconductor substrate 100 below the gate 108 such that a part of the first-conductivity-type doped region 102 is covered by a portion of the gate 108. In this embodiment, the gate oxide layer 110 may include silicon oxide, and the gate 108 may include polysilicon, but not limited thereto. Furthermore, the gate 108 serves as a transfer gate (Tx) of the image sensor 1A. In another embodiment, the gate oxide layer 110 and the gate 108 may be formed before forming the first-conductivity-type doped region 102, the second-conductivity-type sacrificial layer 104 and the doped diffusion region 106. In still another embodiment, the gate oxide layer 110 and the gate 108 may be formed after forming the first-conductivity-type doped region 102 but before forming the second-conductivity-type sacrificial layer 104. Briefly speaking, the present invention does not limit when to form the gate oxide layer 110 and the gate 108. In addition, an isolation structure 112 may be selectively formed in the semiconductor substrate 100 before forming the first-conductivity-type doped region 102, the second-conductivity-type sacrificial layer 104 and the doped diffusion region 106. The isolation structure 112 may be a shallow trench isolation (STI), a local oxidation of silicon isolation layer (LOCOS), or a junction isolation, for preventing the image sensor 1A from being coupled to other devices and resulting in short-circuit issue. As an example, the method of forming the isolation structure 112 may include forming a mask on the semiconductor substrate 100 first, performing an etching process to form a trench in the semiconductor substrate 100, then filling an insulating material (such as silicon oxide) into the trench, and removing the mask. Furthermore, a screen oxide layer (not shown) and other pad layers or liners (not shown) maybe selectively formed on the semiconductor substrate 100 in this embodiment of the present invention.
  • Next, a patterned mask layer 114 is formed on the surface of the semiconductor substrate 100 for defining the pattern of one or more recesses in the photosensitive area 10. The patterned mask layer 114 of this embodiment defines the patterns of a plurality of recesses, and therefore the patterned mask layer 114 includes a plurality of openings 114 a, wherein the width W1 of each opening 114 a is about 0.15 micrometers for example. In the photosensitive area 10, the width W2 of the patterned mask layer 114 disposed between the adjoining openings 114 a is about 60 nanometers for example. It should be noted that the above mentioned width W1 and width W2 are examples only, not used for limiting the present invention. Furthermore, another portion of the patterned mask layer 114 disposed out of the photosensitive area 10 covers the isolation structure 112, the gate oxide layer 110 and the gate 108, such that the isolation structure 112, the gate oxide layer 110 and the gate 108 will not be influenced by the following processes. The method of forming the patterned mask layer 114 may include fully coating a photoresist layer first, exposing the photoresist layer with a mask, and then developing the exposed photoresist layer to form the patterned mask layer 114.
  • Next, as shown in FIG. 2, an etching process 115 is performed by taking the patterned mask layer 114 as an etching mask, so as to remove a portion of the first-conductivity-type doped region 102 of the semiconductor substrate 100 and form at least one recess 116 in the semiconductor substrate 100. Since the number of the recesses 116 is determined by the number of the openings 114 a of the patterned mask layer 114, a plurality of recesses 116 are formed in the semiconductor substrate 100 in this embodiment. In addition, a portion of the second-conductivity-type sacrificial layer 104 is also removed through the etching process 115, and another portion of the second-conductivity-type sacrificial layer 104 covered by the patterned mask layer 114 is left after the etching process 115. As an example, the remaining second-conductivity-type sacrificial layer 104 in the photosensitive area 10 has the width W2 of about 60 nanometers, which also means that the distance between the adjoining recesses 116 is about 60 nanometers, but not limited thereto. The etching process 115 of this embodiment is an anisotropic etching process, such as an anisotropic wet etching process, an anisotropic dry etching process, or a combination of the anisotropic wet etching process and the anisotropic dry etching process. For instance, the etchant of the anisotropic wet etching process may include tetramethylammonium hydroxide (TMAH), ethylene diamine, ethylene diamine and pyrocatechol (EDP), alkali-based etching solution, diluted hydrofluoric (DHF), hydrogen fluoride (HF), buffered oxide etching (BOE) solution, SC-1 cleaning liquid, or a combination of the aforementioned etchants. As an example, the etchant of this embodiment includes TMAH and DHF, wherein the DHF is used for removing the screen oxide layer on the surface of the semiconductor substrate 100, and the TMAH is used for removing the material of the semiconductor substrate 100. The etching process may include dipping the semiconductor substrate 100 into the TMAH solution with a concentration of about 25 wt % for 12 seconds, so as to form the recesses 116 having a depth D1 that is about 0.1 micrometers. The width of the recesses 116 is substantially equal to the width W1 of the openings 114 a of the patterned mask layer 114. According to the present invention, in various embodiments, the depth D1 of the recesses 116 may reach to about 1 micrometer, and the width W1 of the openings 114 a may reach to about 1.5 micrometers, but not limited thereto. Since the etching process 115 of this embodiment is an anisotropic etching process, the depths and the cross-sectional profiles of the recesses 116 formed through the etching process 115 are related to the selected etchant, the process duration, and the size and the shape of the openings 114 a of the patterned mask layer 114. Especially, the cross-sectional profile and the depth of the recess 116 may be controlled by adjusting the duration of the etching process 115. For example, since the etching rates are different in different crystalline directions, the size of each of the recesses 116 formed in this embodiment is gradually reduced from the opening of the recess 116 to the bottom of the recess 116. In this embodiment, the recesses 116 are cone-shaped recesses, but not limited thereto. In other embodiments, the recesses may be hemispherical-shaped recesses, or have inverted trapezoid cross-sectional profiles. In addition, the shapes of the opening of the recesses 116 in the top-view may include circle, square, rectangle, rhombus, elongated rectangle, hexagon, cross, or any other suitable shapes.
  • Next, as shown in FIG. 3, an ion implantation process 118 is performed by taking the patterned mask layer 114 as a mask to implant the second-conductivity-type dopants into the semiconductor substrate 100, so as to form a second-conductivity-type doped layer 120 on the surface of the first-conductivity-type doped region 102 in the photosensitive area 10. The second-conductivity-type doped layer 120 includes the dopants having the same conductivity type as the second-conductivity-type sacrificial layer 104, and the second-conductivity-type doped layer 120 is a p-type doped region for example. The ion implantation process 118 of this embodiment may be a plasma doping process for instance. The ion implantation process 118 is not limited to implanting the dopants only along the direction perpendicular to the surface of the semiconductor substrate 100 (such as the direction Z shown in FIG. 3), and the dopants may be implanted along various oblique directions. Sequentially, as shown in FIG. 4, the patterned mask layer 114 is removed, and an annealing process 121 may be selectively performed after the ion implantation process 118 to activate the dopants in the second-conductivity-type sacrificial layer 104 and the second-conductivity-type doped layer 120. The annealing process 121 of this embodiment may be a laser annealing process for example, but not limited thereto. The remaining portion of the second-conductivity-type sacrificial layer 104 after the etching process 115 is connected to the second-conductivity-type doped layer 120, so as to form a second-conductivity-type doped region 122 on the surface of the first-conductivity-type doped region 102. The second-conductivity-type doped region 122 in this embodiment is a p-type doped region. The first-conductivity-type doped region 102 and the second-conductivity-type doped region 122 form a photosensitive device 124 of this embodiment, and the photosensitive device 124 is a pinned photodiode for example.
  • Sequentially, referring to FIG. 5, a dielectric layer 126 and a conductive line 128 disposed in the dielectric layer 126 are formed on the surface of the semiconductor substrate 100. The dielectric layer 126 covers the photosensitive device 124 and is filled in the recesses 116. The conductive line 128 may be connected to the gate 108. The dielectric layer 126 may include a plurality of inter-layer dielectric layers, and the material of the dielectric layer 126 may include a low-K dielectric material, such as silicon oxide, borophosphosilicate glass (BPSG), phosphosilicate glass (PSG), fluorinated silicate glass (FSG), carbon-doped silicon oxide or the like. The method of forming the dielectric layer 126 may include the chemical vapor deposition (CVD) technique for example, but not limited thereto. The conductive line 128 may be a multilayer-interconnect (MLI) structure for example, and the dielectric layer 126 can be used for isolating and separating the MLI structure from other conductive devices on the semiconductor substrate 100. For example, the method of patterning the conductive line 128 may include a plasma etching or a damascene process, and the material of the conductive line 128 may include aluminum, copper, doped polysilicon or the like. In this embodiment, the dielectric layer 126 and the conductive line 128 may be fabricated by sequentially forming multiple inter-layer dielectric layers, interconnects, and contacts or vias.
  • Next, as shown in FIG. 6, a light pipe opening 130 is formed in the dielectric layer 126. The method of forming the light pipe opening 130 may include forming a patterned mask layer (not shown in figures) on the dielectric layer 126 to define the pattern of the light pipe opening 130 first, and performing an etching process next, so as to form the light pipe opening 130 in the dielectric layer 126. The cross-sectional profile of the light pipe opening 130 may have a vertical sidewall as shown in FIG. 6, but may have an inclined sidewall in another embodiment such that the area of the bottom of the light pipe opening 130 is less than the area of the top of the light pipe opening 130. Next, a barrier layer 132 can be selectively formed on the dielectric layer 126 and the sidewall and the bottom surface of the light pipe opening 130. The material of the barrier layer 132 may include silicon nitride (SiN) or silicon oxynitride (SiON). For example, the barrier layer 132 can prevent the devices underneath from being damaged by oxygen and moisture, but not limited thereto. Then, as shown in FIG. 7, a material having a high refractive index is filled in the light pipe opening 130 to form a light pipe 134 above the photosensitive device 124. A chemical mechanical polishing (CMP) process may be performed to enable the light pipe 134 to have a flat surface. Next, a color filter layer 136 and a micro lens 138 are sequentially formed on the surface of the light pipe 134. The color filter layer 136 includes a colored photoresist pattern for example, and may be formed through a photolithography and etching process. In this embodiment, the color filter layer 136 is disposed between the micro lens 138 and the light pipe 134, and the light pipe 134 and the conductive line 128 are disposed between the color filter layer 136 and the recesses 116 of the photosensitive device 124. According to the above mentioned processes, the fabrication of the image sensor 1A of the first embodiment of the present invention is finished.
  • In short, the fabrication method of the image sensor 1A of the present invention mainly includes the steps shown in FIG. 8:
  • Step S10: Providing a semiconductor substrate, wherein a photosensitive area is defined on the surface of the semiconductor substrate;
  • Step S12: Forming a first-conductivity-type doped region near the surface of the semiconductor substrate and in the photosensitive area;
  • Step S14: Performing an etching process to remove a portion of the surface of the semiconductor substrate for forming at least one recess in the semiconductor substrate and in the photosensitive area; and
  • Step S16: Performing an ion implantation process to form a second-conductivity-type doped layer on the surface of the recess in the photosensitive area, wherein the first-conductivity-type doped region and the second-conductivity-type doped layer have different conductivity types, and the first-conductivity-type doped region and the second-conductivity-type doped layer form a photosensitive device.
  • Referring back to FIG. 7, the structure of the image sensor 1A of this embodiment is described below. The image sensor 1A includes the semiconductor substrate 100, the first-conductivity-type doped region 102, the second-conductivity-type doped region 122, the gate 108, the gate oxide layer 110 and the doped diffusion region 106. In this embodiment, the photosensitive area 10 is defined on the surface of the semiconductor substrate 100, and the surface of the semiconductor substrate 100 has a plurality of recesses 116 distributed in the photosensitive area 10. The size of the recesses 116 is gradually reduced from the openings of the recesses 116 to the bottoms of the recesses 116. The recesses 116 of this embodiment are cone-shaped recesses, but not limited thereto. In other embodiments, the recesses may be hemispheric recesses, or may have inverted trapezoid cross-sectional profiles. In addition, the shapes of the openings of the recesses 116 in the top-view may include circle, square, rectangle, rhombus, elongated rectangle, hexagon, or other suitable shapes.
  • Furthermore, the first-conductivity-type doped region 102 is disposed in the semiconductor substrate 100 and in the photosensitive area 10, and the second-conductivity-type doped region 122 is disposed on the surface of the first-conductivity-type doped region 102 and the surface of the recesses 116. In this embodiment, the first-conductivity-type doped region 102 is an n-type doped region, the second-conductivity-type doped region 122 is a p-type doped region, and the first-conductivity-type doped region 102 and the second-conductivity-type doped region 122 form the photosensitive device 124. The photosensitive device 124 of this embodiment is a pinned photodiode. In other embodiments, a barrier layer of SiN, an anti-reflection coating (ARC), or a contact etch stop layer, CESL (not shown) may be disposed on the photosensitive device 124. The aforementioned layers are not shown in figures of the present application.
  • Moreover, the gate 108 is disposed on the semiconductor substrate 100, and the first-conductivity-type doped region 102 extends to a portion of the semiconductor substrate 100 below the gate 108 such that apart of the first-conductivity-type doped region 102 is covered by the portion of the gate 108. In this embodiment, the gate 108 is a transfer gate of the image sensor 1A, the gate oxide layer 110 is disposed between the gate 108 and the semiconductor substrate 100, the doped diffusion region 106 is disposed in the semiconductor substrate 100 and at one side of the gate 108, and the gate 108 is approximately disposed between the first-conductivity-type doped region 102 and the doped diffusion region 106. The doped diffusion region 106 of this embodiment serves as a floating diffusion (FD) region of the image sensor 1A, and it is an n-type doped region. The photosensitive device 124 generates photo electrons under illumination, and the photo electrons can be transmitted to the FD region, i.e. the doped diffusion region 106, through providing a voltage to the gate 108 and will be further transformed into electric signals for output. The image sensor 1A may further include a reset transistor, a source follower transistor, or a read select transistor, and may include a pixel circuit having three transistors (3 T) or four transistors (4 T). For emphasizing the characteristic features of the image sensor 1A of this embodiment, the aforementioned devices are not shown in the figures.
  • In addition, the image sensor 1A of this embodiment includes the dielectric layer 126, the conductive line 128, the color filter layer 136 and the micro lens 138 disposed on the surface of the semiconductor substrate 100. The dielectric layer 126 is filled in the recesses 116, the conductive line 128 is electrically connected to the gate 108, and the conductive line 128 is disposed in the dielectric layer 126 but does not cover the photosensitive area 10. The color filter layer 136 and the micro lens 138 are disposed on the surface of the dielectric layer 126 and cover the photosensitive area 10. The color of the color filter layer 136 may include red, blue, or green, so that the photosensitive device 124 can detect the light with a specific color. The image sensor 1A may selectively include the light pipe 134 disposed in the dielectric layer 126 and between the color filter layer 136 and the recesses 116. In another embodiment, the light pipe 134 may extend downward to the top of the recesses 116 and is in contact with the second-conductivity-type doped region 122. Since the light pipe 134 includes the material having high refractive index, its refractive index is greater than the refractive index of the dielectric layer 126, such that total reflection easily occurs in the light pipe 134 when light entering the light pipe 134. Therefore, the light pipe 134 assists in guiding light to the photosensitive device 124, and further improves the quantum efficiency of the image sensor 1A.
  • According to this embodiment, the surface of the photosensitive device 124 has recesses 116, and the profile of each recess 116 is gradually reduced from the opening to the bottom of the recess 116. The specific profile of each recess 116 helps to keep on reflecting light in the recess 116 and also guide the light to the bottom of the recess 116. In addition, the recesses 116 can significantly enhance the sensing area of the photosensitive device 124 in the photosensitive area 10, so as to effectively increase the percentage of the light absorbed by the photosensitive device 124. As a result, the quantum efficiency of the image sensor 1A can be improved. Moreover, the recesses 116 prevent the light from being reflected to the photosensitive devices of other adjoining pixels and thus reduce the crosstalk issue.
  • The image sensor and the related fabrication method of the present invention are not limited to the aforementioned embodiment. The following description continues to detail other embodiments or variant embodiments. To simplify the description and show the difference between other embodiments, variant embodiments and the above-mentioned embodiment, identical components in each of the following embodiments are marked with identical symbols, and the identical features will not be redundantly described.
  • Referring to FIG. 9, FIG. 9 is a schematic diagram illustrating a cross-sectional view of an image sensor 1B of a first variant embodiment of the first embodiment of the present invention. As shown in FIG. 9, the difference between this variant embodiment and the first embodiment is that the number of the recesses 116 of the image sensor 1B is less than the image sensor 1A. In addition, the recesses 116 of the image sensor 1B are respectively disposed adjacent to the outer edge of the photosensitive area 10, thus the portion of the second-conductivity-type doped region 122 around the central region of the photosensitive area 10 has a flat surface. Owing to the design of disposing the recesses 116 adjacent to the outer edge of photosensitive area 10, the light propagates to the outer edge of the photosensitive device 124 is prevented from being reflected to the photosensitive devices of other adjoining pixels, and the crosstalk issue can further be avoided. Referring to FIG. 10, FIG. 10 is a schematic diagram illustrating a cross-sectional view of an image sensor 1C of a second variant embodiment of the first embodiment of the present invention. As shown in FIG. 10, the difference between this variant embodiment and the first embodiment is that the photosensitive device 124 of the image sensor 1C has only one recess 116, and the area of the opening of the recess 116 is approximate to the area of the photosensitive area 10. The recess 116 of this variant embodiment has an inverted trapezoid cross-sectional profile, but not limited thereto. Since the sidewall of the recess 116 inclines from the edge of the photosensitive area 10 to the center of the photosensitive area 10, the light propagates to the outer edge of the photosensitive device 124 is prevented from being reflected to other adjoining image sensors, and the crosstalk issue can further be avoided.
  • Referring to FIG. 11 and FIG. 12, FIG. 11 and FIG. 12 are schematic diagrams illustrating a fabrication method of an image sensor 2A of a second embodiment of the present invention. The image sensor 2A of the second embodiment of the present invention is a back side illumination (BSI) image sensor. As shown in FIG. 11, a semiconductor substrate 100 is provided first. The semiconductor substrate 100 of this embodiment selectively includes an epitaxial layer 142 disposed at one side of the semiconductor substrate 100. For example, the thickness of the epitaxial layer 142 is about 4 micrometers, but not limited thereto. Next, a doped diffusion region 106, a first-conductivity-type doped region 102, and one or more selective isolation structures 112 are formed in the epitaxial layer 142 of the semiconductor substrate 100. Then, a gate oxide layer 110 and a gate 108 are formed on the epitaxial layer 142. Next, a second-conductivity-type doped layer 146 is formed near the surface of the epitaxial layer 142. The second-conductivity-type doped layer 146 is disposed at one side of the gate 108. The second-conductivity-type doped layer 146 of this embodiment is not covered by the gate 108, but not limited thereto. The second-conductivity-type doped layer 146 includes dopants having the same conductivity type as the semiconductor substrate 100 (or the epitaxial layer 142), but having a higher doping concentration. Sequentially, a conductive line 128 and a dielectric layer 126 are formed on the semiconductor substrate 100, wherein the dielectric layer 126 covers the gate 108 and the second-conductivity-type doped layer 146. The conductive line 128 may be a MLI structure and is electrically connected to the gate 108. Next, a carrier substrate may be adhered to the side of the semiconductor substrate 100 having the conductive line 128 and the dielectric layer 126, and a buffer layer may be selectively disposed between the carrier substrate and the semiconductor substrate 100. The material of the carrier substrate may include silicon material similar to the material of the semiconductor substrate 100 or be a glass substrate. The material of the buffer layer may include silicon oxide, silicon nitride, or other dielectric materials. In order to emphasize the characteristic features of the image sensor 2A of this embodiment, the carrier substrate and the buffer layer are not shown in the figures. Then, a thinning process 144 is performed to remove most of the semiconductor substrate 100, but the epitaxial layer 142 is remained.
  • Next, as shown in FIG. 12, the recesses 116 and the second-conductivity-type doped layer 120 are formed at another side of the epitaxial layer 142 of the semiconductor substrate 100, which means the recesses 116 and the conductive line 128 are disposed at the opposite sides of the epitaxial layer 142 respectively. An annealing process may be performed to the second-conductivity-type doped layer 120 after the second-conductivity-type doped layer 120 is formed, thus the dopants in the second-conductivity-type doped layer 120 can be activated to form the second-conductivity-type doped region 122. The doping concentration of the second-conductivity-type doped region 122 is higher than the doping concentration of the epitaxial layer 142. The annealing process may be a laser annealing process for example, but not limited thereto. Next, a barrier layer (not shown) maybe selectively formed on the surfaces of the recesses 116 and the epitaxial layer 142. The barrier layer may fully covers the surfaces of the recesses 116 and the epitaxial layer 142. The material of the barrier layer may be silicon nitride or silicon oxide for example, but not limited thereto. In addition, an ARC (not shown) may also be selectively formed on the surfaces of the recesses 116 and the epitaxial layer 142. Then, a filling layer 140 is formed on the surface of the epitaxial layer 142, at the side of the epitaxial layer 142 having the recesses 116. The filling layer 140 may include silicon oxide or other dielectric materials having high light transmittances. The filling layer 140 can be formed through CVD process, physical vapor deposition (PVD) process, or other suitable techniques. The portion of the filling layer 140 out of the recesses 116 can be removed by performing chemical mechanical polishing or other processes, such that the filling layer 140 has a flat surface. After that, a color filter layer 136 and a micro lens 138 are formed on the filling layer 140. The material and the fabrication method of each device in the image sensor 2A of this embodiment may be the same as the first embodiment, and will not be redundantly described.
  • The difference between this embodiment and the first embodiment is that the image sensor 2A is a BSI image sensor. Thus, the photosensitive device 124 is disposed between the conductive line 128 and the color filter layer 136. The semiconductor substrate 100 (or the epitaxial layer 142) includes a front side 12 and a back side 14, and the isolation structure 112 and the doped diffusion region 106 are disposed in the portion of the semiconductor substrate 100 near the front side 12. The image sensor 2A further includes the second-conductivity-type doped layer 146 disposed in the portion of the semiconductor substrate 100 near the front side 12, adjoining to the gate 108. The gate 108, the gate oxide layer 110, the conductive line 128 and the dielectric layer 126 are all disposed on the surface of the front side 12 of the semiconductor substrate 100. The recesses 116 are disposed in the portion of the semiconductor substrate 100 near the back side 14, and therefore the second-conductivity-type doped layer 146 and the conductive line 128 are disposed at one side of the semiconductor substrate 100, and the recesses 116 are disposed at another side of the semiconductor substrate 100. Accordingly, the first-conductivity-type doped region 102 is disposed between the second-conductivity-type doped layer 146 and the recesses 116, and also between the conductive line 128 and the recesses 116. In addition, the p-n junction between the first-conductivity-type doped region 102 and the second-conductivity-type doped region 122 is disposed at the back side 14 of the semiconductor substrate 100. The image sensor 2A further includes the color filter layer 136 and the micro lens 138 disposed on the surface of the back side 14 of the semiconductor substrate 100, covering the photosensitive area 10. The image sensor 2A also includes the filling layer 140 filled in the recesses 116, which is disposed between the photosensitive device 124 and the color filter layer 136.
  • Referring to FIG. 13, FIG. 13 is a schematic diagram illustrating a cross-sectional view of an image sensor 2B of a first variant embodiment of the second embodiment of the present invention. As shown in FIG. 13, the difference between this variant embodiment and the second embodiment is that the color filter layer 136 of the image sensor 2B is directly filled in the recesses 116, and therefore the filling layer 140 shown FIG. 12 is not required. The material and the fabrication method of each device in the image sensor 2B may be the same as the second embodiment, and will not be redundantly described.
  • To sum up, in the fabrication method of the image sensor of the present invention, the first-conductivity-type doped region is formed in the semiconductor substrate first, and the recesses are formed on the surface of the first-conductivity-type doped region. Then, the second-conductivity-type doped region is formed on the surface of the first-conductivity-type doped region. Specifically, the second-conductivity-type doped region is formed on the surfaces of the recesses, such that the p-n junction of the photosensitive device existed between the first-conductivity-type doped region and the second-conductivity-type doped region is formed along the surfaces of the recesses. The structure of the recess of the image sensor according to the present invention keeps the light being reflected in the recess and guides the light to the bottom of the recesses, so as to increase the amount of the light absorbed by the photosensitive device. At the same time, the area of the p-n junction of the photosensitive device is increased due to the existence of the recesses, which means the light-sensing area is increased and the quantum efficiency of the image sensor is then improved. In addition, the propagating direction of the light can be adjusted by the recesses, so as to prevent the light propagating to the outer edge of the photosensitive device from being reflected to other adjoining image sensors. As a result, the crosstalk issue can be effectively improved. In short, the efficiency and the accuracy of the image sensor are effectively improved according to the present invention.
  • Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.

Claims (22)

1. An image sensor, comprising:
a semiconductor substrate, wherein a photosensitive area is defined on a surface of the semiconductor substrate, and the surface of the semiconductor substrate has at least one recess in the photosensitive area;
a first-conductivity-type doped region disposed in the semiconductor substrate and in the photosensitive area;
a second-conductivity-type doped region disposed on a surface of the first-conductivity-type doped region and on a surface of the recess, wherein the first-conductivity-type doped region and the second-conductivity-type doped region have different conductivity types, and the first-conductivity-type doped region and the second-conductivity-type doped region form a photosensitive device;
a gate disposed on the semiconductor substrate;
a gate oxide layer disposed between the gate and the semiconductor substrate; and
a doped diffusion region disposed in the semiconductor substrate, wherein the gate is disposed between the first-conductivity-type doped region and the doped diffusion region.
2. The image sensor according to claim 1, wherein a size of the recess is gradually reduced from an opening of the recess to a bottom of the recess.
3. The image sensor according to claim 2, wherein the recess is a cone-shaped recess or the recess has a trapezoid cross-sectional profile.
4. The image sensor according to claim 1, wherein the recess is disposed adjacent to an edge of the photosensitive area.
5. The image sensor according to claim 1, wherein an area of the opening of the recess is approximate to an area of the photosensitive area.
6. The image sensor according to claim 1, further comprising a dielectric layer filled in the recess.
7. The image sensor according to claim 6, further comprising:
a color filter layer and a micro lens sequentially disposed on the surface of the semiconductor substrate and covering the photosensitive area; and
a conductive line electrically connected to the gate, wherein the conductive line is disposed in the dielectric layer and does not cover the photosensitive area.
8. The image sensor according to claim 7, further comprising a light pipe disposed between the color filter layer and the recess.
9. The image sensor according to claim 1, further comprising:
a second-conductivity-type doped layer disposed on another surface of the first-conductivity-type doped region and adjacent to the gate, wherein the second-conductivity-type doped layer is disposed at one side of the semiconductor substrate, the recess and the second-conductivity-type doped region are disposed at the other side of the semiconductor substrate, and the first-conductivity-type doped region is disposed between the second-conductivity-type doped layer and the recess and between the second-conductivity-type doped layer and the second-conductivity-type doped region;
a color filter layer and a micro lens sequentially disposed on the surface of the semiconductor substrate and covering the photosensitive area; and
a conductive line electrically connected to the gate, wherein the photosensitive device is disposed between the conductive line and the color filter layer.
10. The image sensor according to claim 9, wherein the color filter layer is filled in the recess.
11. The image sensor according to claim 9, further comprising a filling layer disposed between the recess and the color filter layer, wherein the filling layer is filled in the recess.
12. A fabrication method of an image sensor, comprising:
providing a semiconductor substrate, wherein a photosensitive area is defined on a surface of the semiconductor substrate;
forming a first-conductivity-type doped region near the surface of the semiconductor substrate and in the photosensitive area;
performing an etching process to remove a portion of the first-conductivity-type doped region of the semiconductor substrate to form at least one recess in the photosensitive area; and
performing an ion implantation process to form a second-conductivity-type doped region on a surface of the first-conductivity-type doped region in the photosensitive area, wherein the first-conductivity-type doped region and the second-conductivity-type doped region have different conductivity types, and the first-conductivity-type doped region and the second-conductivity-type doped region form a photosensitive device.
13. The fabrication method of the image sensor according to claim 12, further comprising forming a second-conductivity-type sacrificial layer in the photosensitive area before forming the recess, wherein the second-conductivity-type sacrificial layer covers the surface of the first-conductivity-type doped region, and an annealing process is performed after the ion implantation process.
14. The fabrication method of the image sensor according to claim 12, wherein a size of the recess is gradually reduced from an opening of the recess to a bottom of the recess.
15. The fabrication method of the image sensor according to claim 12, wherein the recess is a cone-shaped recess or the recess has a trapezoid cross-sectional profile.
16. The fabrication method of the image sensor according to claim 12, wherein the recess is disposed adjacent to an edge of the photosensitive area.
17. The fabrication method of the image sensor according to claim 12, wherein an area of the opening of the recess is approximate to an area of the photosensitive area.
18. The fabrication method of the image sensor according to claim 12, wherein the etching process is an anisotropic wet etching process or an anisotropic dry etching process.
19. The fabrication method of the image sensor according to claim 18, wherein the semiconductor substrate is a silicon-based substrate, and an etchant of the anisotropic wet etching process comprises tetramethylammonium hydroxide (TMAH), ethylene diamine and pyrocatechol (EDP), alkali-based etching solution, diluted hydrofluoric (DHF), hydrogen fluoride (HF), buffered oxide etching (BOE) solution or SC-1 cleaning liquid.
20. The fabrication method of the image sensor according to claim 12, further comprising:
forming a dielectric layer on the surface of the semiconductor substrate, wherein the dielectric layer covers the photosensitive device and is filled in the recess;
forming a conductive line on the surface of the semiconductor substrate;
removing a portion of the dielectric layer to form a light pipe opening in the dielectric layer on the photosensitive device;
filling a material with a high refractive index in the light pipe opening to form a light pipe above the photosensitive device; and
sequentially forming a color filter layer and a micro lens on a surface of the light pipe.
21. The fabrication method of the image sensor according to claim 12, further comprising:
forming a second-conductivity-type doped layer and a conductive line on another surface of the semiconductor substrate before forming the recess, wherein the second-conductivity-type doped layer and the conductive line are disposed at one side of the semiconductor substrate, the recess is disposed at the other side of the semiconductor substrate, and the first-conductivity-type doped region is disposed between the second-conductivity-type doped layer and the recess and between the conductive line and the recess; and
sequentially forming a color filter layer and a micro lens on a surface of the second-conductivity-type doped region.
22. The fabrication method of the image sensor according to claim 21, further forming a filling layer filled in the recess before forming the color filter layer and the micro lens.
US15/334,309 2016-08-04 2016-10-26 Image sensor and related fabrication method Active US9899436B1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
TW105124710 2016-08-04
TW105124710A 2016-08-04
TW105124710A TWI608600B (en) 2016-08-04 2016-08-04 Image sensor and related fabrication method

Publications (2)

Publication Number Publication Date
US20180040651A1 true US20180040651A1 (en) 2018-02-08
US9899436B1 US9899436B1 (en) 2018-02-20

Family

ID=61069975

Family Applications (1)

Application Number Title Priority Date Filing Date
US15/334,309 Active US9899436B1 (en) 2016-08-04 2016-10-26 Image sensor and related fabrication method

Country Status (3)

Country Link
US (1) US9899436B1 (en)
CN (1) CN107689381A (en)
TW (1) TWI608600B (en)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110235251A (en) * 2016-12-27 2019-09-13 夏普株式会社 Image panel and its manufacturing method
US10475828B2 (en) * 2017-11-21 2019-11-12 Taiwan Semiconductor Manufacturing Co., Ltd. Image sensor device structure with doping layer in light-sensing region
TWI717795B (en) * 2019-05-07 2021-02-01 台灣積體電路製造股份有限公司 Image sensor and method for forming the same
US11340398B2 (en) * 2018-10-25 2022-05-24 Artilux, Inc. Waveguide structure and optoelectronic device comprising the same
TWI771875B (en) * 2020-01-21 2022-07-21 台灣積體電路製造股份有限公司 Image sensor device and fabrication method thereof
CN114784033A (en) * 2022-06-20 2022-07-22 西安中科立德红外科技有限公司 Hybrid imaging chip based on semiconductor process and preparation method thereof
WO2023080000A1 (en) * 2021-11-05 2023-05-11 ソニーセミコンダクタソリューションズ株式会社 Imaging element and electronic device

Families Citing this family (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10205037B2 (en) * 2017-06-09 2019-02-12 Taiwan Semiconductor Manufacturing Company Ltd. Photodiode device and manufacturing method thereof
US10515989B2 (en) * 2017-08-30 2019-12-24 Taiwan Semiconductor Manufacturing Co., Ltd. Device comprising photodiode and method of making the same
CN110224038A (en) * 2018-03-02 2019-09-10 中芯国际集成电路制造(上海)有限公司 Photodiode and forming method thereof
CN108649044A (en) * 2018-05-09 2018-10-12 德淮半导体有限公司 Imaging sensor and the method for forming imaging sensor
JP2021168316A (en) * 2018-07-13 2021-10-21 ソニーセミコンダクタソリューションズ株式会社 Sensor element and electronic apparatus
TWI675467B (en) * 2018-08-29 2019-10-21 力晶積成電子製造股份有限公司 Image sensor and manufacturing method therefore
CN109585484A (en) * 2018-12-04 2019-04-05 德淮半导体有限公司 Imaging sensor and forming method thereof
US10991667B2 (en) * 2019-08-06 2021-04-27 Taiwan Semiconductor Manufacturing Co., Ltd. Isolation structure for bond pad structure
TW202332072A (en) * 2022-01-19 2023-08-01 友達光電股份有限公司 Sensing device
CN114725147B (en) * 2022-05-16 2022-08-26 晶芯成(北京)科技有限公司 Image sensor and manufacturing method thereof

Family Cites Families (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7038232B2 (en) 2003-09-24 2006-05-02 Taiwan Semiconductor Manufacturing Co., Ltd. Quantum efficiency enhancement for CMOS imaging sensor with borderless contact
KR100694470B1 (en) * 2005-07-11 2007-03-12 매그나칩 반도체 유한회사 Method for fabricating image sensor
US7355222B2 (en) * 2005-05-19 2008-04-08 Micron Technology, Inc. Imaging device having a pixel cell with a transparent conductive interconnect line and the method of making the pixel cell
US7358583B2 (en) 2006-02-24 2008-04-15 Tower Semiconductor Ltd. Via wave guide with curved light concentrator for image sensing devices
KR100792342B1 (en) * 2006-08-23 2008-01-07 동부일렉트로닉스 주식회사 Image sensor fabricating method
US7822300B2 (en) 2007-11-20 2010-10-26 Aptina Imaging Corporation Anti-resonant reflecting optical waveguide for imager light pipe
TWI553844B (en) * 2009-07-02 2016-10-11 邰祐南 An image sensor and a method for forming an image sensor
KR101790164B1 (en) 2010-02-05 2017-10-26 삼성전자 주식회사 Back-side illumination CMOS image sensor including photo diode that the surface shape of receiving light has a curvature and the generating method for the CMOS image sensor
JP5682174B2 (en) * 2010-08-09 2015-03-11 ソニー株式会社 Solid-state imaging device, manufacturing method thereof, and electronic apparatus
CN104952966A (en) * 2014-03-31 2015-09-30 中芯国际集成电路制造(上海)有限公司 Photodiode, production method thereof and image sensor with photodiode
JP6235412B2 (en) * 2014-05-27 2017-11-22 ルネサスエレクトロニクス株式会社 Semiconductor device and manufacturing method thereof
KR102354420B1 (en) * 2014-12-24 2022-01-24 삼성전자주식회사 Image Sensor

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN110235251A (en) * 2016-12-27 2019-09-13 夏普株式会社 Image panel and its manufacturing method
US10992884B2 (en) * 2016-12-27 2021-04-27 Sharp Kabushiki Kaisha Imaging panel and method for producing same
US10475828B2 (en) * 2017-11-21 2019-11-12 Taiwan Semiconductor Manufacturing Co., Ltd. Image sensor device structure with doping layer in light-sensing region
US10777590B2 (en) 2017-11-21 2020-09-15 Taiwan Semiconductor Manufacturing Co., Ltd Method for forming image sensor device structure with doping layer in light-sensing region
US11340398B2 (en) * 2018-10-25 2022-05-24 Artilux, Inc. Waveguide structure and optoelectronic device comprising the same
TWI717795B (en) * 2019-05-07 2021-02-01 台灣積體電路製造股份有限公司 Image sensor and method for forming the same
TWI771875B (en) * 2020-01-21 2022-07-21 台灣積體電路製造股份有限公司 Image sensor device and fabrication method thereof
WO2023080000A1 (en) * 2021-11-05 2023-05-11 ソニーセミコンダクタソリューションズ株式会社 Imaging element and electronic device
CN114784033A (en) * 2022-06-20 2022-07-22 西安中科立德红外科技有限公司 Hybrid imaging chip based on semiconductor process and preparation method thereof

Also Published As

Publication number Publication date
TWI608600B (en) 2017-12-11
US9899436B1 (en) 2018-02-20
CN107689381A (en) 2018-02-13
TW201806137A (en) 2018-02-16

Similar Documents

Publication Publication Date Title
US9899436B1 (en) Image sensor and related fabrication method
CN109585466B (en) CMOS image sensor and method for forming the same
KR101864481B1 (en) Image sensor and method of forming the same
KR102674895B1 (en) Image sensor and method of fabricating the same
US9473753B2 (en) Apparatus and method for reducing optical cross-talk in image sensors
US8748945B2 (en) Image sensors including a gate electrode surrounding a floating diffusion region
KR20190062241A (en) Multiple deep trench isolation (mdti) structure for cmos image sensor
US9818782B2 (en) Image sensor and method for fabricating the same
TWI525804B (en) Image sensor device and method of fabricating the same
TWI593290B (en) Image sensor device
US9484376B2 (en) Semiconductor isolation structure and manufacturing method thereof
US9030587B2 (en) Solid-state image sensor with light-guiding portion
KR102699394B1 (en) Backside structure for image sensor
KR20200045327A (en) Image sensor and method of manufacturing the same
KR102587498B1 (en) Image sensor
US20190181167A1 (en) Backside illuminated image sensor and method of manufacturing the same
US11764248B2 (en) Band-pass filter for stacked sensor
US10497736B2 (en) Backside illuminated image sensor
KR102551483B1 (en) Image sensor and method for fabricating the same
TWI717795B (en) Image sensor and method for forming the same
KR101380311B1 (en) An image sensor and a method of manufacturing the same
JP2008182076A (en) Solid-state imaging device and its manufacturing method
CN107785383B (en) Image sensor and manufacturing method thereof
US20220377266A1 (en) Solid-state imaging device and method of manufacturing solid-state imaging device
KR20090025933A (en) Image sensor and method of fabricating the same

Legal Events

Date Code Title Description
AS Assignment

Owner name: POWERCHIP TECHNOLOGY CORPORATION, TAIWAN

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:LEE, SHIH-PING;CHEN, YU-AN;HUANG, HSIU-WEN;AND OTHERS;REEL/FRAME:040124/0960

Effective date: 20161012

STCF Information on status: patent grant

Free format text: PATENTED CASE

AS Assignment

Owner name: POWERCHIP SEMICONDUCTOR MANUFACTURING CORPORATION,

Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:POWERCHIP TECHNOLOGY CORPORATION;REEL/FRAME:049770/0199

Effective date: 20190628

MAFP Maintenance fee payment

Free format text: PAYMENT OF MAINTENANCE FEE, 4TH YEAR, LARGE ENTITY (ORIGINAL EVENT CODE: M1551); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY

Year of fee payment: 4