Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
  • H10F39/10—Integrated devices
  • H10F39/12—Image sensors
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
  • H10F39/80—Constructional details of image sensors
  • H10F39/803—Pixels having integrated switching, control, storage or amplification elements
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
  • H10F39/011—Manufacture or treatment of image sensors covered by group H10F39/12
  • H10F39/014—Manufacture or treatment of image sensors covered by group H10F39/12 of CMOS image sensors
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
  • H10F39/00—Integrated devices, or assemblies of multiple devices, comprising at least one element covered by group H10F30/00, e.g. radiation detectors comprising photodiode arrays
  • H10F39/10—Integrated devices
  • H10F39/12—Image sensors
  • H10F39/18—Complementary metal-oxide-semiconductor [CMOS] image sensors; Photodiode array image sensors

Definitions

• the present invention relates to semiconductor optical image sensors, and particularly, to a novel CMOS (complementary metal oxide semiconductor) image sensor cell structure exhibiting reduced lag, higher capacity and lower dark current.
• CMOS complementary metal oxide semiconductor
• CMOS image sensors are beginning to replace conventional CCD sensors for applications requiring image pick-up such as digital cameras, mobile telephones, cellular telephones, pervasive digital devices such as PDA's (personal digital assistant), personal computers, medical devices, and the like.
• CMOS image sensors are fabricated by applying present CMOS fabricating process for semiconductor devices such as photodiodes or the like, at low costs.
• CMOS image sensors can be operated by a single power supply so that the power consumption for that can be restrained lower than that of CCD sensors, and further, CMOS logic circuits and like logic processing devices are easily integrated in the sensor chip and therefore the CMOS image sensors can be miniaturized.
• CMOS image sensors comprise an array of CMOS Active Pixel Sensor (APS) cells, which are used to collect light energy and convert it into readable electrical signals.
• Each APS cell comprises aphotosensitive element, such as a photodiode, photogate, or photoconductor overlying a doped region of a substrate for accumulating photo-generated charge in an underlying portion thereof.
• a read-out circuit is connected to each pixel cell and often includes a diffusion region for receiving charge from the photosensitive element, when readout. Typically, this is accomplished by a transistor device having a gate electrically connected to the floating diffusion region.
• the imager may also include a transistor, having a transfer gate, for transferring charge from the photosensitive element across a channel to the floating diffusion region, and a transistor for resetting the floating diffusion region to a predetermined charge level prior to charge transfer.
• a typical CMOS APS cell 10 includes a pinned photodiode 20 having a pinning layer 18 doped p -type and, an underlying lightly doped n-type region 17.
• the pinned diode 20 is formed on top of a p-type substrate 15 or a p-type epitaxial layer or p-well surface layer having a lower p-type concentration than the diode pinning layer 18.
• the surface doped p -type pinning layer 18 is in electrical contact with the substrate 15 (or p-type epitaxial layer or p-well surface layer).
• the photodiode 20 thus has two p-type regions 18 and 15 having a same potential so that the n-type doped region
• Vp pinning voltage
• the pinned photodiode is termed "pinned" because the potential in the photodiode is pinned to a constant value, Vp, when the photodiode is fully depleted.
• Vp a constant value
• This pinned photodiode configuration improves the device performance by decreasing dark current (current output by a pixel in a dark environment).
• the pinned photodiode configuration may cause image lag due to the incomplete transfer of charge from the photodiode to the floating node.
• the n-type doped region 17 and p region 18 of the photodiode 20 are spaced between an isolation region, e.g., a shallow trench isolation (STI) region 40, and a charge transfer transistor gate 25 which is surrounded by thin spacer structures 23a,b.
• the shallow trench isolation (STI) region 40 is located proximate the pixel image cell for isolating the cell from an adjacent pixel cell. In operation, light coming from the pixel is focused down onto the photodiode through the diode where electrons collect at the n-type region 17.
• Fig. 2 depicts a further prior art CMOS APS cell 10' having incorporated a gate 25' having a portion that is p-type material 70a and a portion that is n-type 70b.
• the n-type portion 70b of the gate has a lower Vt and the p- type portion 70a of the gate has a higher Vt.
• the transfer gate has a built in field pulling electrons from the photodiode to the floating diffusion.
• Fig. 3 A depicts a CMOS imager 12 having a suicide layer blocked from the photodiode surface since suicide blocks light while a suicide layer 80 formed over the transfer gate polysilicon and floating diffusion remain.
• Fig. 3B illustrates the CMOS imager 12 of Fig. 3 A having suicide layers 80 removed from the gate poly and floating diffusion for even lower leakage behavior.
• Fig. 3 C illustrates a top plan view of the CMOS imager 10' of Fig. 2 having suicide surface layers removed from the photodiode 20, gate poly regions 70a, 70b and floating diffusion node 30.
• each CMOS APS cell gate polysilicon formed with the built-in diode within the gate prevents the entire gate from being contacted. That is, a contact which only connects either the n-type or p-type side of the polysilicon gate will not be adequately connected to the other polarity of the gate poly layer. This results in a time dependent voltage on the uncontacted portion of the gate. That is, if a contact is made to the n-type part of the gate, the p-type part floats; likewise, if contact is made to the p-type side of the gate, the n-type part floats.
• CMOS image sensor array including a novel APS cell structure that exhibits reduced (low) lag and dark current and, that eliminates bright spikes leakage phenomena.
• the invention relates generally to improved semiconductor imaging devices and in particular to an imaging device which can be fabricated using a standard CMOS process.
• the present invention is directed to a CMOS image sensor wherein the sensor comprises a photodetecting region (e.g. photodiode); a floating diffusion; a transfer gate located between the photodetecting region and the floating diffusion, the transfer gate comprising n and p type doped regions to from a diode; and, an interconnect layer (e.g. a suicide structure) electrically coupling the n-type and p-type doped regions of the transfer gate.
• the interconnect layer comprises a suicide and is formed in physical contact with at least a portion of the p-type region and a portion of the n-type region of a polysilicon transfer gate.
• the suicide layer may be over all or just a portion of the poly gate width and suicide is not formed on the diffusions (i.e. photodiode and floating diffusion).
• the CMOS imager of the invention including a transfer gate device having two workfunctions (n-type and p-type gate poly) and a suicide strap cooperatively exhibit a high barrier at the photodiode for dark current while a low barrier is provided at the floating diffusion for low lag performance.
• the suicide strap prevents the diodic behavior from allowing one or the other side of the gate to float to an indeterminate voltage.
• an active pixel sensor (APS) cell structure comprises: a substrate of a first conductivity type material; a transfer gate device comprising a gate dielectric layer formed on the substrate and a dual workfunction gate conductor layer formed on the gate dielectric layer, the dual workfunction gate conductor layer comprising a first doped region of first conductivity type material and a second doped region of a second conductivity type material; a photosensing device formed at or below a substrate surface adjacent the first doped region of the transfer gate device for collecting charge carriers in response to light incident thereto; a diffusion region of a second conductivity type material formed at the substrate surface adjacent the second doped region of the transfer gate device, the transfer gate device forming a channel region enabling charge transfer between the photosensing device and the diffusion region; and, a suicide structure formed atop the dual workfunction gate conductor layer for electrically coupling the first doped region of first conductivity type material of the transfer
• the photosensing device comprises a photodiode comprising: a collection well of a second conductivity type material formed below the substrate surface; and, a pinning layer of the first conductivity type material formed atop the collection well at the substrate surface.
• the substrate, pinning layer of the first conductivity type material, and the first doped region of the dual workfunction gate conductor layer of the transfer gate device includes p-type dopant material, e.g., Boron or Indium.
• the collection well of the second conductivity type material, the floating diffusion region of second conductivity type material, and the second doped region of the dual workfunction gate conductor layer of the transfer gate includes n-type dopant material, e.g., Phosphorus, Arsenic or Antimony.
• the suicide structure comprises a suicide of Ti, Ta, W, Co, Ni, Pt, Pd or alloys thereof.
• the suicide structure formed over the dual workfunction gate conductor layer for electrically coupling the first doped region of first conductivity type material and the second doped region of second conductivity type material of the transfer gate device is smaller in area dimension than an area dimension of the dual workfunction gate conductor layer.
• the suicide structure formed over the dual workfunction gate conductor layer for electrically coupling the first doped region of first conductivity type material and the second doped region of second conductivity type material of the transfer gate device is reduced only in length dimension than a length of the dual workfunction gate conductor layer.
• the transfer gate device defines a conducting channel region where charge transfer is enabled between the collection well and the floating diffusion region underneath the transfer gate device
• the suicide structure is formed atop the dual workfunction gate conductor layer for electrically coupling the first doped region of first conductivity type material and the second doped region of second conductivity type material of the transfer gate device outside of the area defining the conducting channel region.
• teachings of the invention may be applicable for devices of both polarities, i.e., n type photodiodes and p type pinning layers and nFETS, as well as to p type photodiodes, and n type pinning layers with pFETs.
• Fig. 1 depicts a CMOS Active Pixel Sensor (APS) cell 10 for an image sensor according to the prior art
• Fig. 2 illustrates, through a cross-sectional view, a CMOS Active Pixel Sensor (APS) cell 10 for an image sensor according to the prior art
• Fig. 2 illustrates, through a cross-sectional view, a CMOS Active Pixel Sensor (APS) cell 10 for an image sensor according to the prior art
• Fig. 2 illustrates, through a cross-sectional view, a CMOS Active Pixel Sensor (APS) cell 10 for an image sensor according to the prior art
• Fig. 2 illustrates, through a cross-sectional view, a CMOS Active Pixel Sensor (APS) cell 10 for an image sensor according to the prior art
• Fig. 2 illustrates, through a cross-sectional view, a CMOS Active Pixel Sensor (APS) cell 10 for an image sensor according to the prior art
• Fig. 2 illustrates, through a cross-sectional view, a CMOS Active Pixel Sensor
• Pixel Sensor (APS) cell 10' according to the prior art having a gate polysilicon layer with a built in diode, e.g., a pn junction;
• Figs. 3A and 3B illustrate, through cross-sectional views
• CMOS Active Pixel Sensor (APS) cell 12 having suicide contacts regions removed from the photodiode (Fig. 3A) and having suicide surface layer contact regions removed from the gate poly layer and floating diffusion layer in accordance with the prior art (Fig. 3B);
• Fig. 3 C illustrates a top plan view of the CMOS imager 10' of Fig. 2 having suicide surface layers removed from the photodiode 20, gate poly regions 70a, 70b and floating diffusion node 30.
• Fig. 4 illustrates, through a cross-sectional view, a CMOS APS cell 100 having suicide contacts regions removed from the photodiode and floating node diffusion regions and, having a partial conductive strap formed on the gate polysilicon for improved gate barrier ac characteristics according to a first embodiment of the invention
• Fig. 5A illustrates, through a top plan view, the CMOS APS cell 100 formed in accordance with the embodiment of the invention shown in Fig. 4;
• Fig. 5B illustrates, through a top plan view, the CMOS APS cell 100' formed in accordance with a first variation of the embodiment of the invention shown in Fig. 4;
• Fig. 5C illustrates, through a top plan view, the CMOS APS cell 100" formed in accordance with a second variation of the embodiment of the invention shown in Fig. 4;
• Fig. 5D illustrates, through a top plan view, the CMOS APS cell 100"' formed in accordance with a third variation of the embodiment of the invention shown in Fig. 4; and, Fig. 6 is a side view of a camera device implementing an image sensor having the CMOS Active Pixel Sensor (APS) cells formed in accordance with the present invention.
• APS CMOS Active Pixel Sensor
• CMOS active pixel sensor Active pixel sensor (APS) refers to an active electrical element within the pixel, other than transistors functioning as switches.
• APS active pixel sensor
• CMOS complementary metal oxide silicon type electrical components such as transistors which are associated with the pixel, but typically not in the pixel, and which are formed when the source/drain of a transistor is of one dopant type and its mated transistor is of the opposite dopant type.
• CMOS devices include some advantages one of which is it consumes less power.
• Fig. 4 illustrates, through a cross-sectional view, a back end of line CMOS imager APS 100 including photosensing device, e.g., photodiode 200, and silicon-containing, e.g., polysilicon, transfer gate 125 according to a first embodiment of the invention.
• the polysilicon transfer gate 125 includes an anodic (p-type doped) region and abutting cathodic (n-type doped) region forming a diode.
• the polysilicon transfer gate 125 comprises a Schottky diode.
• a conductive structure e.g., a partial suicide "strap" 190, is formed on the surface of the poly gate having p-type 175a and n-type 175b portions for improved gate barrier ac characteristics as will be described in greater detail herein below.
• the partial suicide strap layer 190 electrically connects the p-type doped 175a and n-type doped 175b portions of the polysilicon gate 125. Moreover, as shown in Fig. 4, the partial suicide "strap" layer 190 has edges formed at a distance from the boundary of the gate, i.e., the suicide strap 190 is inset a distance, e.g., distances di and d 2 , from respective edges 171, 172 of the poly gate layer.
• the inset distances di and d 2 of the formed suicide strap are not required to be equal, i.e., the strap is formed to lie over just a portion of the poly width, as long as the suicide strap 190 electrically shorts the p-type portion 175a to the n-type portion 175b.
• the suicide strap 190 is formed atop a portion of the poly width. It is understood that in preferred embodiments, the suicide strap 190 is kept off the diffusion 130.
• CMOS imager APS 100 structure shown in Fig. 4 is now described. It is understood that other techniques may be used for forming the transfer gate having the diode structure, i.e., abutting p-type and n-type gate poly regions, as known in the art.
• the device 100 is formed on a substrate 15 which may be a bulk semiconductor including, for example, Si, SiGe, SiC, SiGeC, GaAs, InP, InAs and other semiconductors, or layered semiconductors such as silicon-on-insulators (SOI), SiC-on-insulator (SiCOI) or silicon germanium-on-insulators (SGOI).
• SOI silicon-on-insulators
• SiCOI SiC-on-insulator
• SGOI silicon germanium-on-insulators
• substrate 15 is a Si-containing semiconductor substrate of a first conductivity type, e.g., lightly doped with p-type dopant material such as boron or indium (beryllium or magnesium for a M-V semiconductor), to a standard concentration ranging between, e.g., IxIO 14 to IxIO 16 cm “3 .
• p-type dopant material such as boron or indium (beryllium or magnesium for a M-V semiconductor
• dielectric material layer 60 is formed by standard deposition/growth techniques atop the substrate 15 that will form the eventual transfer gate dielectric.
• the dielectric layer may be formed to a thickness ranging between 40 A to 100 A, for example, and may comprise suitable gate dielectric materials including but not limited to: an oxide (e.g., SiO 2 ), a nitride (e.g., silicon nitride) an oxynitride (e.g, Si oxynitride), N 2 O, NO, ZrO 2 , or other like materials.
• the gate dielectric 60 is comprised of an oxide such as, for example, SiO 2 , HfO 2 , ZrO 2 , Al 2 O 3 , TiO 2 , La 2 O 3 , SrTiO 3 , LaAlO 3 , and mixtures thereof.
• the dielectric layer 60 is formed on the surface of the Si-containing semiconductor substrate 15 using conventional thermal oxidation or by a suitable deposition process such as chemical vapor deposition, plasma-assisted chemical vapor deposition, atomic layer deposition (ALD), evaporation, reactive sputtering, chemical solution deposition and other like deposition processes.
• the gate dielectric 16 may also be formed utilizing any combination of the above processes. Although it is not shown, it is understood that the dielectric layer may comprise a stack of dielectric materials.
• a Silicon-containing layer e.g., polycrystalline silicon
• CVD chemical vapor deposition
• the transfer gate 125 is then formed by a photolithographic process, e.g., applying a mask, e.g., a photoresist layer, over the polysilicon layer and applying a mask patterned to define the gate region, e.g., length determining an effective channel length of the transfer gate to be formed, and then developing the resist and performing an etch process.
• a photolithographic process e.g., applying a mask, e.g., a photoresist layer, over the polysilicon layer and applying a mask patterned to define the gate region, e.g., length determining an effective channel length of the transfer gate to be formed, and then developing the resist and performing an etch process.
• an etch window is provided in a resist mask, the size and shape of which approximately defining the lateral size and shape of the gate region to be formed.
• etch processes are performed, e.g., a reactive ion etch (RIE) process, that is optimized to ensure proper etching of the polysilicon layer and dielectric layer 60 or dielectric layer stack to result in the transfer gate structure.
• RIE reactive ion etch
• a subsequent mask deposition process that covers a portion of the transfer gate structure and ion implantation process is performed to implant dopant material of a second conductivity type, e.g., n -type dopant material, such as phosphorus, arsenic or antimony, into the polysilicon layer to form n -type doped gate poly portion 175b.
• dopant material of a second conductivity type e.g., n -type dopant material, such as phosphorus, arsenic or antimony
• the n-type dopant material may be implanted to achieve a dosing concentration ranging between IxIO 17 cm “3 to IxIO 20 cm “3 .
• an ion implantation process is performed to implant dopant material of a first conductivity type, e.g., p -type dopant material, such as boron or gallium or indium into the polysilicon layer to form p -type doped gate poly portion 175a as shown in Fig. 4.
• the p-type dopant material may be implanted to achieve a dosing concentration ranging between 1x10 17 cm "3 to 1x10 20 cm "3 in the gate poly.
• the doping of the polysilicon may be achieved using implants already present in the process by appropriate use of those implant masks at the same time those implants are being performed elsewhere in the chip. (One example would be the source drain implants and masks, but others are also possible.) It should be noted that in a variation of the method described, in- situ n-type, p-type doped, or both n-type and p-type polysilicon material may be deposited on top of the gate dielectric layer 60 according to an in-situ doping deposition process or deposition (e.g., CVD, plasma-assisted, etc.).
• the in-situ doping deposition process may be employed when the gate dielectric cannot withstand a subsequent high temperature annealing, whereas ion implantation and annealing can be employed when the gate dielectric is a material that can withstand such high temperature annealing.
• gate sidewall spacers may be formed at either side of the transfer gate by conventional deposition processes well known in the art, and may comprise any conventional oxide or nitride (e.g., Si 3 N 4 ) or oxide/nitride which are then etched by RIE or another like etch process.
• the thickness of spacers may vary, but typically they have a thickness of from about 5 nm to about 150 run.
• a next step is performed to provide the photodiode pinning region 180.
• This step comprises forming a photoresist layer (not shown) patterning, and creating an ion implantation mask according to techniques known in the art to form a mask edge approximately coincident with the gate edge or as close as possible given alignment tolerances, to provide an opening to an area between an edge of the gate and a formed isolation region, e.g., STI region (not shown), where the charge accumulation region of the photodiode is to be formed.
• This opening permits the implantation of ions of p-type dopant material, e.g., such as boron, at a concentration sufficient to form the p -type dopant pinning region 180 as shown in Figure 4.
• This pinning region 180 may be formed up to the edge of a spacer (not shown).
• the active p -type dopant material is then ion implanted at dosing concentrations ranging between 1x10 17 and 1x10 19 cm "3 .
• the p-type pinning photodiode surface layer 180 may be formed by other known techniques.
• the p-type surface layer 180 may be formed by a gas source plasma doping process, or by diffusing a p-type dopant from the in-situ doped layer or a doped oxide layer deposited over the area where photodiode is to be formed.
• a further step is then performed to ion implant the n-type dopant underneath the p -type doped region 180 of the substrate surface of the photodiode element 200.
• the same ion implantation mask could be used as when implanting the p -type material to form pinning region, an ion implantation process is performed to implant dopant material of the second conductivity type, e.g., n -type dopant material, such as phosphorus, arsenic or antimony, to form the charge collection layer beneath the ion implanted p-type pinning layer 180.
• the n-type dopant material is implanted at higher energy levels to form the n-type doped region 170 of the photodiode 190 as shown in Figure 4.
• the active n-type dopant material may be ion implanted at dosing concentrations ranging between IxIO 16 and 1x10 18 cm "3 .
• the photosensitive charge storage region 170 for collecting photo-generated electrons may be formed by multiple implants to tailor the profile of the n-type region 170.
• an additional step of forming an n-type floating diffusion region 130 at the other side of the transfer gate comprises forming a photoresist layer and patterning and etching an ion implantation mask according to techniques known in the art to form a mask edge approximately coincident with the gate edge or as close as possible given alignment tolerances, to provide an opening allowing the implantation of n -type dopant material, such as phosphorus, arsenic or antimony, at a concentration sufficient to form the n+ -type doped floating diffusion region 130 as shown in Figure 4 or, up to the edge of a gate sidewall spacer (not shown).
• n -type dopant material such as phosphorus, arsenic or antimony
• n+-type dopant material is ion implanted at the floating diffusion region at dosing concentrations ranging between 1x10 18 and 1x10 20 .
• n-type dopant materials may be additionally implanted at the doped transfer gate polysilicon layer 175b portion as well.
• a salicide process is then performed to consume the polysilicon gate 125 to form the metal suicide strap 190 according to the invention, as shown in Figs.5A-5D.
• the first step of the salicide process includes first forming on the p- type doped 175a and n-type doped 175b polysilicon gate layer, a blanket insulative cap using well known deposition techniques.
• a dielectric cap layer is formed atop the polysilicon gate layer 175a,b utilizing a deposition process such as, for example, physical vapor deposition or chemical vapor deposition.
• the dielectric cap layer may be an oxide, nitride, oxynitride or any combination thereof.
• a nitride such as, for example, Si 3 N 4 , is employed as the dielectric cap layer.
• the thickness, i.e., height, of the dielectric cap layer may range from about 20 nm to about 180 nm.
• the lithography step includes applying a photoresist to the upper surface of the dielectric cap layer, exposing the photoresist to a desired pattern of radiation and developing the exposed photoresist utilizing a conventional resist developer.
• the pattern in the photoresist is then transferred to the dielectric cap layer utilizing one or more dry etching steps leaving exposed the underlying polysilicon gate layer and, particularly, opening up a window in the dielectric cap layer to expose adjacent portions of both doped regions 175a,b in the exposed underlying polysilicon layer.
• the desired pattern is the area and dimension of the suicide strap to be formed such as shown in Figures 5A-5D.
• the photolithographic mask, develop and etch process applied to the overlying cap dielectric (e.g., nitride) layer will result in the exposure region 195 of the underlying polysilicon layer that is inset a distance dl and d2 from each of the respective gate edges 171, 172 along the length of the gate that will be subject to formation of the suicide contact.
• the patterned photoresist may be removed after the pattern has been transferred into the dielectric cap layer.
• Suitable dry etching processes that can be used in the present invention in forming the patterned gate include, but are not limited to: reactive ion etching, ion beam etching, plasma etching or laser ablation.
• the metal used in forming the suicide strap comprises any metal that is capable of reacting with silicon to form a metal suicide.
• metals include, but are not limited to: Ti, Ta, W, Co, Mo, Ni, Pt, Pd or alloys thereof.
• the metal may be deposited using any conventional deposition process including, for example, sputtering, chemical vapor deposition, a physical vapor deposition (PVD) of the suicide evaporation, chemical solution deposition, plating and the like.
• a thermal anneal process is employed to form a suicide phase in the structure; preferably, the suicide representing the lowest resistivity phase of a metal suicide.
• the anneal is performed utilizing the ambients and temperatures well known in the art that cause the suicide metal to react with the underlying polysilicon to form the metal suicide layer 190 as shown in Fig. 4.
• the suicide metal may comprise Co noting that CoSi 2 forms using a two step annealing process as known in the art.
• the suicide metal is Ni or Pt; NiSi and PtSi being formed using a single annealing step. Then, a selective wet etch step may be employed to remove any non-reactive suicide metal from the structure.
• the wafer is then annealed at approximately 500° C to about 800 ° C for approximately 30 seconds in a nitrogen environment to react with the portions of the polysilicon layer 175a,b to form the conductive suicide strap 190.
• the conventional approach for building an interconnect structure for transistor to transistor and transistor to external contacts can be employed.
• Figure 5B illustrates, through a top plan view, the CMOS APS cell 100' formed in accordance with a first variation of the embodiment of the invention shown in Fig, 5A, where a suicide strap 191 is formed utilizing the process described herein that has edges formed an inset distance di,d 2 from edges of the boundary gate, however, is formed to extend substantially over the whole width of the poly.
• a suicide strap 191 is formed utilizing the process described herein that has edges formed an inset distance di,d 2 from edges of the boundary gate, however, is formed to extend substantially over the whole width of the poly.
• the photolithographic mask, develop and etch process applied to the overlying cap dielectric (e.g., nitride) layer will result in formation of the exposure region 196 of the underlying polysilicon layer that is inset a distance dl and d2 from each of the respective gate edges 171, 172 along the length of the gate, however extends to both edges of the poly layer width a distance, dw, for example.
• the overlying cap dielectric e.g., nitride
• Figure 5C illustrates, through a top plan view, the CMOS APS cell 100" formed in accordance with a second variation of the embodiment of the invention shown in Fig, 5 A, where a suicide strap 192 is formed utilizing the process described herein that has edges formed an inset distance di,d2 from edges of the boundary gate, however, extends a short distance of the poly gate.
• a suicide strap 192 is formed utilizing the process described herein that has edges formed an inset distance di,d2 from edges of the boundary gate, however, extends a short distance of the poly gate.
• the photolithographic mask, develop and etch process applied to the overlying cap dielectric (e.g., nitride) layer will result in formation of the exposure region 197 of the underlying polysilicon layer that is inset a distance dl and d2 from each of the respective gate edges 171, 172 along the length of the gate, however extends for only a short distance of the poly gate, for example.
• the overlying cap dielectric e.g., nitride
• the suicide strap for the CMOS imager APS transfer gate may be made on a portion of the polysilicon gate that is not directly over the conducting channel (i.e., as long as the n and p regions are shorted by the strap somewhere).
• Figure 5D illustrates, through a top plan view, the CMOS APS cell 100"' formed in accordance with a third variation of the embodiment of the invention shown in Fig, 5 A, where a suicide strap 193 is formed utilizing the process described herein that has edges formed an inset distance from edges of the boundary gate, and that extends a short distance of the poly gate. However, the strap 193 is offset from that portion of the gate 175a,b that defines the channel region for the transfer device.
• the suicide strap 193 is formed on a portion of the polysilicon gate that is not directly over the conducting channel.
• the photolithographic mask, develop and etch process applied to the overlying cap dielectric (e.g., nitride) layer will result in formation of the exposure region 198 of the underlying polysilicon layer that is inset a distance from each of the respective gate edges 171, 172 along the length of the gate, and extends for only a short distance of the poly gate, for example, in a region that does not directly overly the device channel region.
• any conductive structure for electrically shorting the anode 175a and cathode 175b portions of the transfer gate poly may be implemented besides the suicide contact structure as described. However, it is imperative that the photodetection region and the floating diffusion regions be silicide-free.
• a high barrier exists at the photodiode for reducing the dark current leakage, and that a low barrier is present at the floating diffusion for lower lag.
• the suicide strap prevents diodic behavior from allowing one or the other side of the gate to float to an indeterminate voltage.
• FIG. 6 there is shown a side view of a camera device 300 implementing an image sensor 302 having the CMOS Active Pixel Sensor (APS) cells 100-100"' formed in accordance with the respective embodiments of the invention depicted in Figs. 5A-5D.
• APS CMOS Active Pixel Sensor

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• 2006
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• 2007
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  • 2007-11-30 TW TW096145709A patent/TWI420659B/zh active
  • 2007-11-30 WO PCT/US2007/024684 patent/WO2008069994A2/en not_active Ceased
  • 2007-11-30 JP JP2009539352A patent/JP5096483B2/ja active Active
• 2010
  • 2010-02-03 US US12/699,419 patent/US8158453B2/en active Active

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