Patent ID: 12211862

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components, materials, values, steps, operations, materials, arrangements, or the like, are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. Other components, values, operations, materials, arrangements, or the like, are contemplated. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

In various embodiments, a transistor structure includes a substrate region having a first doping type and first and second regions having a second doping type opposite the first doping type. A gate conductor of the transistor structure includes a plurality of conductive protrusions extending into the substrate region between the first and second regions. By including the plurality of conductive protrusions, channel area is increased and the transistor structure is capable of improving electron transmission efficiency between the first and second regions compared to approaches that do not include a plurality of conductive protrusions. In pixel transfer gate applications, particularly those in which deep photodiodes are used, the electron transmission efficiency improvement reduces lag times and occurrences of photodiode saturation, also known as white pixel (WP).

FIGS.1A and1Bare diagrams of a transistor structure100, in accordance with some embodiments.FIG.1Adepicts a plan view of transistor structure100, an X direction, and a Y direction perpendicular to the X direction.FIG.1Bdepicts a cross sectional view of transistor structure100along line A-A′, the X direction, and a Z direction perpendicular to the X and Y directions. In various embodiments, transistor structure100is also referred to as transfer transistor structure100or IC structure100.

As depicted inFIGS.1A and1B, transistor structure100includes a gate conductor100G, also referred to as gate structure100G in some embodiments, positioned between regions100R1and100R2along the X direction. Gate conductor100G includes a conductive region100C overlying a plurality of conductive protrusions P1-P6. A dielectric layer100D contacts a lower surface (not labeled) of conductive region100C and surrounds each conductive protrusion P1-P6. As further discussed below, the number and positioning of conductive protrusions P1-P6depicted inFIGS.1A and1Bis a non-limiting example presented for the purpose of illustration.

As illustrated inFIG.1B, regions100R1and100R2are positioned within a substrate100B having an upper surface100S extending in the X and Y directions. Conductive protrusions P1-P6extend into substrate100B in the negative Z direction, perpendicular to upper surface100S, and are also referred to as vertical gate structures P1-P6in some embodiments. Conductive region100C is continuous with each conductive protrusion P1-P6and electrically isolated from substrate100B by dielectric layer100D.

Gate conductor100G, dielectric layer100D, and regions100R1and100R2of transistor structure100are arranged as depicted inFIGS.1A and1Bfor the purpose of illustration. In various embodiments, transistor structure100includes gate conductor100G, dielectric layer100D, and regions100R1and100R2arranged other than as depicted inFIGS.1A and1B, as discussed below.

In the embodiment depicted inFIGS.1A and1B, transistor structure100includes both of regions100R1and100R2. In various embodiments, transistor structure100does not include one or both of regions100R1and100R2, and the one or both of regions100R1and100R2is part of one or more IC structures (not shown) separate from transistor structure100. In various embodiments, one of regions100R1or100R2is a photodiode of a pixel sensor, e.g., a photodiode300PD of a pixel sensor300or300P discussed below with respect toFIGS.3A-3C, and/or the other of regions100R1or100R2is a floating diffusion (FD) region or node of the pixel sensor. A region or node of a circuit is referred to as floating based on a configuration by which the region or node is capable of being simultaneously decoupled from other circuit elements, e.g., through one or more open transistors and/or one or more reverse-biased diodes.

As further discussed below, transistor structure100is thereby usable as some or all of a transfer transistor of a pixel sensor, e.g., pixel sensor300or300P discussed below with respect toFIGS.3A-3C, a pixel sensor circuit, e.g., a pixel sensor circuit200discussed below with respect toFIG.2, and in some embodiments, as one of a plurality of transfer transistors of an image sensor, e.g., a pixel sensor array400discussed below with respect toFIG.4. Transistor structure100is thereby further usable as some or all of a transistor of another type of IC device, e.g., a logic, memory, or other IC device including one or more transistors having the properties discussed below.

Substrate100B, also referred to as substrate region100B in some embodiments, is a portion of a semiconductor wafer suitable for forming one or more IC devices. In various embodiments, substrate100B includes n-type silicon (Si) including one or more donor dopants, e.g., phosphorous (P) or arsenic (As), referred to as having n-type doping in some embodiments, or p-type silicon including one or more acceptor dopants, e.g., boron (B) or aluminum (Al), referred to as having p-type doping in some embodiments. In some embodiments, substrate100B includes a compound semiconductor, e.g., indium phosphide (InP), gallium arsenide (GaAs), silicon germanium (SiGe), indium arsenide (InAs), silicon carbide (SiC), or another suitable compound semiconductor material. In various embodiments, substrate100B includes a bulk silicon layer or a silicon-on-insulator (SOI) substrate, e.g., a silicon layer separated from a bulk silicon layer by a buried oxide (BOX) layer.

Regions100R1and100R2are regions within substrate100B having a doping type opposite that of substrate100B, e.g., by including one or more of the dopants discussed above with respect to substrate100B. In some embodiments, substrate100B has p-type doping and each of regions100R1and100R2has n-type doping.

In some embodiments, one or both of regions100R1or100R2includes one or more epitaxial layers. In various embodiments, one or both of substrate regions100R1or100R2includes one or more of silicon, InP, Ge, GaAs, SiGe, InAs, SiC, or another suitable semiconductor material.

Conductive region100C and conductive protrusions P1-P6include one or more conductive materials capable of distributing charge throughout gate conductor100G. In various embodiments, conductive materials include one or more of polysilicon, copper (Cu), aluminum (Al), tungsten (W), cobalt (Co), ruthenium (Ru), or one or more other metals, and/or one or more other suitable materials.

Dielectric layer100D includes one or more dielectric materials capable of capacitively coupling gate conductor100G to substrate100B by electrically isolating a charge distributed throughout gate conductor100G from substrate100B. In some embodiments, dielectric layer100D includes one or more high-k dielectric materials, i.e., a material having a dielectric constant above 3.9, the dielectric constant of silicon dioxide (SiO2). In various embodiments, dielectric materials include one or more of SiO2, silicon nitride, (Si3N4), aluminum oxide (Al2O3), hafnium oxide (HfO2), tantalum pentoxide (Ta2O5), titanium oxide (TiO2), or another suitable material.

Gate conductor100G and dielectric layer100D are thereby configured to, in operation, form a conductive channel100CH in substrate100B adjacent to dielectric layer100D based on a charge distributed throughout gate conductor100G.

By the arrangement and compositions discussed above, transistor structure100is configured as a transistor including gate conductor100G positioned between regions100R1and100R2configured as source/drain features. At least a portion of each of conductive protrusions P1-P6is positioned between regions100R1and100R2. In some embodiments, region100R1is configured as a source feature of transistor structure100and region100R2is configured as a drain feature of transistor structure100.

In the embodiment depicted inFIGS.1A and1B, region100R2includes a lightly doped region100R2A. In some embodiments, lightly doped region100R2A is an n-type region referred to as a pixel n-type lightly doped drain (PNLD). In some embodiments, region100R2does not include lightly doped region100R2A.

In some embodiments, transistor structure100includes one or more contacts, vias, and/or other conductive features (not shown) in contact with one or more of regions100R1or100R2or gate conductor100G, and transistor structure100is thereby configured to electrically connect the one or more of regions100R1or100R2or gate conductor100G to one or more IC structures and/or devices (not shown) separate from transistor structure100.

In the embodiment depicted inFIGS.1A and1B, gate conductor100G includes a total of six conductive protrusions P1-P6arranged in three rows of two conductive protrusions per row, e.g., conductive protrusions P1and P2depicted inFIG.1B, thereby forming two columns. In various embodiments, gate conductor100G includes conductive protrusions arranged in fewer or greater than three rows and/or fewer or greater than two columns.

In various embodiments, gate conductor100G includes a total number of conductive protrusions less than or greater than six. In some embodiments, gate conductor100G includes a total of two conductive protrusions, e.g., the single row of conductive protrusions P1and P2or a single column of conductive protrusions P1and P3. In some embodiments, gate conductor100G includes a total number of conductive protrusions ranging from three to twelve. Gate conductor100G including conductive protrusions having other total numbers, e.g., those in accordance with ranges other than the ranges discussed above, are within the scope of the present disclosure.

In the embodiment depicted inFIGS.1A and1B, gate conductor100G includes conductive protrusions, e.g., conductive protrusions P1-P6, arranged in an array of rows and columns. In various embodiments, gate conductor100G includes conductive protrusions having one or more arrangements other than or in addition to that of an array, e.g., staggered rows and/or columns, a circular or concentric ring pattern, a triangle pattern, a zigzag pattern, a combination of patterns, and/or one or more predetermined locations independent of a pattern.

In the embodiment depicted inFIGS.1A and1B, conductive protrusions P1-P6have a shape in the X-Y plane of a circle having a diameter given by width W, including dielectric100D. In the embodiment depicted inFIGS.1A and1B, conductive protrusions P1-P6have a tapered shape in the X-Z plane and the Y-Z plane (not shown), narrowing along the negative Z direction, and width W corresponds to a largest diameter of conductive protrusions P1-P6.

In various embodiments, conductive protrusions P1-P6have a shape in the X-Y plane other than that of a circle, e.g., a square or other rectangular shape or an irregular shape, and width W corresponds to a largest dimension in the X-Y plane, e.g., a diagonal of a rectangle.

In some embodiments, conductive protrusions P1-P6have a tapered shape in a single one of the X-Z or Y-Z planes, narrowing along the negative Z direction. In some embodiments, conductive protrusions P1-P6do not have a tapered shape in either of the X-Z and Y-Z planes, and width W does not vary with respect to the Z direction.

A given conductive protrusion, e.g., conductive protrusion P1, is separated from a nearest other conductive protrusion, e.g., conductive protrusion P2, by a distance equal to or greater than a minimum spacing S. In some embodiments, minimum spacing S is greater than or equal to one half of width W.

In the embodiment depicted inFIGS.1A and1B, each conductive protrusion P1-P6is separated from a nearest conductive protrusion along a given X or Y direction by approximately a same distance corresponding to minimum spacing S, and from other conductive protrusions by distances greater than minimum spacing S, thereby being separated from the remainder of the conductive protrusions by one or more distances approximately equal to or greater than minimum spacing S. In various embodiments, gate conductor100G is otherwise configured such that a given conductive protrusion is separated from the remainder of the conductive protrusions by one or more distances approximately equal to or greater than minimum spacing S.

Multiple features are considered to have approximately a same dimension, e.g., width W or minimum spacing S, based on one or more features being within a manufacturing tolerance of a same nominal value of the dimension.

In the embodiment depicted inFIGS.1A and1B, each conductive protrusion P1-P6has approximately a same length L, extending in the negative Z direction away from conductive region100C. In various embodiments, one or more conductive protrusions, e.g., a conductive protrusion P1-P6, has a length L different from a length of one or more other conductive protrusions, e.g., another conductive protrusion P1-P6.

In operation, electrons are transmitted to and/or from conductive protrusions P1-P6from and/or to regions100R1and100R2based on an average electron transmission path length between the conductive protrusions P1-P6and the corresponding region100R1or100R2. As a value of length L increases from zero relative to a size of the corresponding region100R1or100R2, the average transmission path length initially decreases based on increasing overlap in the Z direction, then increases as length L corresponds to conductive protrusions P1-P6extending beyond the corresponding region100R1or100R2in the negative Z direction. In some embodiments, length L has a value ranging from 100 angstroms (Å) to 10,000 Å. In some embodiments, length L has a value ranging from 1000 Å to 4000 Å. Length L having other values, e.g., those in accordance with ranges other than the ranges discussed above, are within the scope of the present disclosure.

In addition to upper surface100S, substrate100B includes a lower surface (not shown) such that a distance between the lower surface and upper surface100S defines a substrate thickness. In some embodiments, length L has a value ranging from 3% to 90% of the substrate thickness. Length L having other values relative to substrate thickness, e.g., those in accordance with ranges other than the ranges discussed above, are within the scope of the present disclosure.

In the embodiment depicted inFIGS.1A and1B, conductive region100C extends above upper surface100S in the positive Z direction, and thereby includes a top surface100CS above upper surface100S. In various embodiments, conductive region100C is coextensive with upper surface100S in the positive Z direction such that top surface100CS is coplanar with upper surface100S, or conductive region100C does not extend to upper surface100S in the positive Z direction such that top surface100CS is below upper surface100S.

In the embodiment depicted inFIGS.1A and1B, an entirety of conductive region100C is positioned above upper surface100S in the positive Z direction. In various embodiments, a portion or an entirety of conductive region100C is positioned at and/or below upper surface100S in the negative Z direction.

In the embodiment depicted inFIGS.1A and1B, conductive region100C extends away from conductive protrusion P1in the negative X direction such that portions of each of conductive region100C and dielectric layer100D overlie, in the positive Z direction, a portion of substrate100B between conductive protrusion P1and region100R1. In some embodiments, conductive region100C does not extend away from conductive protrusion P1in the negative X direction, and conductive region100C and dielectric layer100D do not include portions that overlie, in the positive Z direction, a portion of substrate100B between conductive protrusion P1and region100R1.

In the embodiment depicted inFIGS.1A and1B, conductive region100C extends away from conductive protrusion P2in the positive X direction such that portions of each of conductive region100C and dielectric layer100D overlie, in the positive Z direction, a portion of substrate100B between conductive protrusion P2and region100R2. In some embodiments, conductive region100C does not extend away from conductive protrusion P2in the positive X direction, and conductive region100C and dielectric layer100D do not include portions that overlie, in the positive Z direction, a portion of substrate100B between conductive protrusion P2and region100R2.

In the embodiment depicted inFIGS.1A and1B, region100R1extends in the positive X direction up to an edge of conductive region100C. In various embodiments, region100R1extends in the positive X direction beyond the edge of conductive region100C such that conductive region100C overlies region100R1in the positive Z direction, or region100R1does not extend in the positive X direction up to the edge of conductive region100C such that region100R1and conductive region100C are separated by a gap (not shown).

In the embodiment depicted inFIGS.1A and1B, region100R2extends in the negative X direction up to an edge of conductive region100C. In various embodiments, region100R2extends in the negative X direction beyond the edge of conductive region100C such that conductive region100C overlies region100R2in the positive Z direction, or region100R2does not extend in the negative X direction up to the edge of conductive region100C such that region100R2and conductive region100C are separated by a gap (not shown).

In the embodiment depicted inFIGS.1A and1B, each of regions100R1and100R2is coplanar with upper surface100S. In some embodiments, one or both of region100R1or100R2extends in the positive Z direction above upper surface100S and thereby includes a topmost portion above upper surface100S. In some embodiments, one or both of region100R1or100R2does not extend in the positive Z direction to upper surface100S and thereby includes the topmost portion below upper surface100S.

In the embodiment depicted inFIGS.1A and1B, each of conductive protrusions P1-P6extends in the negative Z direction beyond a bottommost portion of each of regions100R1and100R2. In some embodiments, one or both of region100R1or100R2extends in the negative Z direction beyond a bottommost portion of at least one of conductive protrusions P1-P6. In some embodiments, one or both of region100R1or100R2extends in the negative Z direction beyond the bottommost portions of all of conductive protrusions P1-P6.

By the configuration discussed above, transistor structure100includes gate conductor100G including conductive protrusions P1-P6extending into substrate region100B between regions100R1and100R2. By including conductive protrusions P1-P6, a volume of conductive channel100CH is increased and the transistor is capable of improving electron transmission efficiency between regions100R1and100R2compared to approaches that do not include a plurality of conductive protrusions, e.g., conductive protrusions P1-P6.

The improved transmission efficiency is especially effective in applications in which electrons are transmitted to and/or from one or more adjacent features that extend alongside conductive protrusions, based on reducing the average electron transmission path length between the one or more adjacent features and the conductive protrusions. For example, in the pixel transfer gate applications discussed below, the transmission efficiency improvement reduces lag times and WP occurrences compared to approaches that do not include a plurality of conductive protrusions.

FIG.2is a schematic diagram of a pixel sensor circuit200, in accordance with some embodiments. Pixel sensor circuit200includes a transistor structure100-1, an instance of transistor structure100discussed above with respect toFIGS.1A and1B. Pixel sensor circuit200also includes power supply nodes VDDN and VSSN, an internal node N1, and an output node OUT. A transistor RST is coupled between power supply node VDDN and internal node N1, and transistor structure100-1and a photodiode PD1are coupled in series between internal node N1and power supply node VSSN. The cathode of photodiode PD1is coupled to transistor structure100-1, and the anode of photodiode PD1is coupled to power supply node VSSN. Transistors SF and RS are coupled in series between power supply node VDDN and output node OUT, a gate of transistor SF is coupled to internal node N1, and a current source Ib is coupled between output node OUT and power supply node VSSN.

Two or more circuit elements are considered to be coupled based on a direct electrical connection or an electrical connection that includes one or more additional circuit elements, e.g., one or more logic or transmission gates, and is thereby capable of being controlled, e.g., made resistive or open by a transistor or other switching device.

In some embodiments, pixel sensor circuit200includes one or more additional instances of transistor structure100and corresponding photodiodes coupled in series between internal node N1and power supply node VSSN, represented as an Nth transistor structure100-N and photodiode PDN in the dashed box inFIG.2. In some embodiments, pixel sensor circuit200includes a total number N of transistor structures100-1-100-N and corresponding photodiodes PD1-PDN ranging from two to four. In the discussion below, references to transistor structures100-1-100-N and photodiodes PD1-PDN include the case in which N=1 and pixel sensor circuit200includes the single transistor structure100-1and the single photodiode PD1.

In some embodiments, a single transistor structure100-1coupled in series with photodiode PD1corresponds to pixel sensor300discussed below with respect toFIGS.3A and3B. In some embodiments, a total number N of transistor structures100-1-100-N and corresponding photodiodes PD1-PDN equal to four corresponds to pixel sensor300P discussed below with respect toFIG.3C. In some embodiments, pixel sensor circuit200is one pixel sensor circuit of a pixel sensor array, e.g., pixel sensor array400discussed below with respect toFIG.4.

In some embodiments, pixel sensor circuit200includes one or more circuit elements (not shown) in addition to the elements cited above, e.g., one or more transistors and/or resistive devices coupled between power supply node VDDN and internal node N1.

Power supply node VDDN is a circuit node configured to carry a power supply voltage VDD having a power supply voltage level, e.g., an operating voltage level of a power domain including pixel sensor circuit200. Power supply node VSSN is a circuit node configured to carry a power supply voltage VSS having a power supply reference level, e.g., a ground level, of the power domain including pixel sensor circuit200.

In the embodiment depicted inFIG.2, each of transistors RST, SF, and RS and transistor structures100-1-100-N is an n-type metal-oxide semiconductor (NMOS) transistor. In various embodiments, one or more of transistors RST, SF, or RS or transistor structures100-1-100-N is a p-type metal-oxide semiconductor (PMOS) transistor.

A gate of transistor RST is configured to receive a signal Vrst, gates of transistor structures100-1-100-N are configured to receive respective signals Vtx1-VtxN, a gate of transistor RS is configured to receive a signal Vrs, and a gate of transistor SF is configured to receive a voltage Vn1on internal node N1. Current source Ib is configured to control a current, also referred to as current Ib, through the series of transistors SF and RS.

In operation, one or more of photodiodes PD1-PDN is exposed to electromagnetic radiation, e.g., light, for a predetermined period of time and, in response to one or more intensity levels of the electromagnetic radiation, accumulate one or more charge levels on the corresponding cathode(s) representative of the one or more intensity levels. In some embodiments, the one or more intensity levels is an intensity level of light. In some embodiments, the one or more intensity levels include multiple intensity levels based on corresponding separate frequencies of the electromagnetic radiation.

In various embodiments, pixel sensor circuit200has a back-side illumination (BSI) or front-side illumination (FSI) configuration and, in operation, the electromagnetic radiation is received by the one or more of photodiodes PD1-PDN from a respective back or front direction, e.g., the respective negative or positive Z direction discussed below with respect toFIGS.3A-3C.

In response to one or more of signals Vtx1-VtxN, in operation, the corresponding one or more of transistors100-1-100-N closes, thereby causing a portion of the accumulated charge to be transferred to internal node N1and generating voltage Vn1having a voltage level representative of the one or more intensity levels. In some embodiments, signals Vtx1-VtxN are referred to as transfer or control signals of a pixel sensor array including pixel sensor circuit200. In some embodiments, the pixel sensor array is configured to generate signals Vtx1-VtxN causing one or more of transistor structures100-1-100-N to close corresponding to controlling one or more predetermined exposure periods of the pixel sensor array, e.g., after opening and closing a shutter of the pixel sensor array.

In response to signal Vrs, in operation, transistor RS closes, thereby establishing a current path by which current Ib flows through transistor SF, the gate of which is biased by the voltage level of voltage Vn1on internal node N1. In some embodiments, signal Vrs is referred to as a row select signal of a pixel sensor array including pixel sensor circuit200. In some embodiments, the pixel sensor array is configured to generate signal Vrs causing transistor Rs to close as part of a row selection operation.

By the arrangement discussed above, transistor SF has a source follower configuration by which, in operation, an output voltage Vout is generated on output node OUT having an output voltage level that follows the voltage level of voltage Vn1on internal node N1.

In response to signal Vrst, in operation, transistor RST closes, thereby selectively coupling internal node N1to power supply node VDDN and discharging internal node N1. In some embodiments, signal Vrst is referred to as a reset signal of a pixel sensor array including pixel sensor circuit200. In some embodiments, the pixel sensor array is configured to generate signal Vrst causing transistor RST to close corresponding to controlling one or more predetermined exposure periods of the pixel sensor array, e.g., coordinated with opening and/or closing a shutter of the pixel sensor array.

Pixel sensor circuit200is thereby configured to, in operation, generate output voltage Vout on output node OUT having an output voltage level representative of a voltage level of voltage Vn1on internal node N1, thereby being representative of one or more charge levels transferred to internal node N1through one or more pairs of transistor structures100-1-100-N and photodiodes PD1-PDN, and thereby being representative of one or more intensity levels of the electromagnetic radiation received by photodiodes PD1-PDN.

By the configuration depicted inFIG.2and discussed above, pixel sensor circuit200includes one or more instances of transistor structure100configured as a transfer transistor coupled between a photodiode and an internal node. In various embodiments, pixel sensor circuit200has a configuration other than that depicted inFIG.2such that transistor structure100is otherwise configured as a transfer transistor coupled between a photodiode and an internal node.

Pixel sensor circuit200is thereby capable of realizing the benefits discussed above with respect to transistor structure100. Because each of the one or more instances of transistor structure100includes conductive protrusions, e.g., conductive protrusions P1-P6discussed above with respect toFIGS.1A and1B, compared to approaches that do not include a plurality of conductive protrusions, the efficiency by which charge is transferred to internal node N1is improved such that lag times for charge transfer are reduced and occurrences of photodiode cathode saturation (WP) are avoided.

FIGS.3A-3Care diagrams of pixel sensors300and300P, in accordance with some embodiments.FIG.3Ais a plan view of pixel sensor300in the X-Y plane,FIG.3Bis a cross-sectional view of pixel sensor300in the X-Z plane, andFIG.3Cis a plan view of pixel sensor300P in the X-Y plane. Pixel sensor300is an IC device usable as a combination of one of transistor structures100-1-100-N coupled in series with the corresponding one of photodiodes PD1-PDN, discussed above with respect toFIG.2, and pixel sensor300P is an IC device usable as a combination of transistor structures100-1-100-N collectively coupled in series with corresponding photodiodes PD1-PDN for the case in which N=4.

Pixel sensor300includes transistor structure100including gate conductor100G and regions100R1and100R2within substrate100B, each discussed above with respect toFIGS.1A and1B, a photodiode300PD, and two instances of an isolation structure300S. Pixel sensor300P includes four instances of transistor structure100, four instances of photodiode300PD, and a floating diffusion node (FDN)300F corresponding collectively to the regions100R2of the four instances of transistor structure100.

The depictions of pixel sensors300and300P inFIGS.3A-3Care simplified for the purpose of illustration. In various embodiments, pixel sensors300and300P include elements (not shown), e.g., transistors, conductive features, and/or isolation structures, in addition to the elements depicted inFIGS.3A-3C. In some embodiments, transistor structure100has a configuration other than that depicted inFIG.3B, as discussed above with respect toFIGS.1A and1B.

Isolation structures300S are regions within substrate100B including one or more dielectric materials configured to electrically isolate pixel sensor300from adjacent IC devices, e.g., additional instances of pixel sensor300.

Photodiode300PD is a photodetector structure including an anode300A adjacent to a cathode300C. Anode300A is a p-type region in substrate100B, cathode300C is an n-type region in substrate100B, and pixel sensor300is configured to, in operation, respond to exposure to electromagnetic radiation by accumulating electronic charge in cathode300C, also referred to as a collector in some embodiments. In some embodiments, photodiode300PD is referred to as a deep photodiode.

In some embodiments, pixel sensor300and/or300P is configured such that, in operation, photodiode300PD responds to electromagnetic radiation received from the negative Z direction, thereby corresponding to a BSI configuration. In some embodiments, pixel sensor300and/or300P is configured such that, in operation, photodiode300PD responds to electromagnetic radiation received from the positive Z direction, thereby corresponding to an FSI configuration.

As depicted inFIGS.3A and3B, pixel sensor300includes transistor structure100and photodiode300PD positioned adjacent to each other and between isolation structures300S along the X direction, at least a portion of each of the conductive protrusions of gate conductor100G, e.g., conductive protrusions P1and P2, thereby being positioned between cathode300C and region100R2. In the embodiment depicted inFIGS.3A and3B, substrate100B has p-type doping and each of regions100R1and100R2has n-type doping.

In the embodiment depicted inFIGS.3A and3B, region100R1and cathode300C are separate regions in substrate100B, and region100R1is adjacent to anode300A. In some embodiments, region100R1and cathode300C are a single, continuous region in substrate100B. In some embodiments, region100R1and anode300A are separated within substrate100B by a gap (not shown).

As depicted inFIG.3B, in some embodiments, cathode300C includes a portion300CX extending in the positive X direction, and conductive protrusion P1extends into portion300CX of cathode300C. In various embodiments in which cathode300C includes portion300CX extending in the positive X direction, one or more conductive protrusions of gate conductor100G, e.g., conductive protrusion P2, in addition to conductive protrusion P1extends into portion300CX of cathode300C.

As depicted inFIGS.3A and3Band discussed above, pixel sensor300is configured to, in operation, accumulate a charge on cathode300C in response to electromagnetic radiation and, in response to a voltage on gate conductor100G, transfer at least a portion of the accumulated charge to region100R2through a conduction channel (not shown inFIGS.3A and3B) corresponding to the conductive protrusions of gate conductor100G, e.g., conductive protrusions P1and P2.

Anode300A and cathode300C of photodiode300PD are arranged as depicted inFIG.3Bfor the purpose of illustration. In various embodiments, photodiode300PD includes anode300A and cathode300C arranged other than as depicted inFIG.3B, e.g., by having shapes, sizes, and/or relative positioning other than those depicted inFIG.3B, such that pixel sensor300is configured to operate as discussed above. In some embodiments, photodiode300PD includes one or more elements (not shown) in addition to anode300A and cathode300C such that pixel sensor300is configured to operate as discussed above. In some embodiments, photodiode300PD includes a p-type region (not shown) in addition to anode300A and is thereby configured as a pinned photodiode such that pixel sensor300is configured to operate as discussed above.

As depicted inFIG.3C, pixel sensor300P includes two instances of photodiode300PD, two instances of transistor structure100, and FDN300F aligned in the X direction, and two instances of photodiode300PD, two instances of transistor structure100, and FDN300F aligned in the Y direction. Each instance of transistor structure100is positioned between FDN300F and a corresponding instance of photodiode300PD, thereby having a cross-sectional configuration equivalent to that of pixel sensor300depicted inFIG.3B, but without an instance of isolation structure300S adjacent to FDN300F (region100R2). Additional elements, e.g., one or more isolation structures, of pixel sensor300P are not shown inFIG.3Cfor the purpose of clarity.

Pixel sensor300P is thereby configured such that, in operation, a given instance of photodiode300PD accumulates a charge on cathode300C in response to electromagnetic radiation and, in response to a voltage on gate conductor100G of the corresponding transistor structure100, transfer at least a portion of the accumulated charge to FDN300F through a conduction channel (not shown inFIG.3C) corresponding to the conductive protrusions of gate conductor100G, e.g., conductive protrusions P1and P2, of the corresponding transistor structure100.

Four instances of photodiode300PD, four instances of transistor structure100, and FDN300F of pixel sensor300P are arranged as depicted inFIG.3Cfor the purpose of illustration. In various embodiments, pixel sensor300P includes a total of two or three instances of each of photodiode300PD and transistor structure100aligned accordingly such that pixel sensor300P is configured to operate as discussed above. Numbers of instances of photodiode300PD other than those discussed above are within the scope of the present disclosure.

Because each of pixel sensors300and300P includes at least one instance of transistor structure100configured as discussed above, each of pixel sensors300and300P is thereby capable of realizing the benefits discussed above with respect to transistor structure100and pixel sensor circuit200.

FIG.4is a diagram of pixel sensor array400, in accordance with some embodiments. Pixel sensor array400, also referred to as image sensor400in some embodiments, includes an array of N rows and M columns of pixel sensor circuits200, discussed above with respect toFIG.2, and peripheral circuit400P. In various embodiments, pixel sensor array400has a BSI or FSI configuration as discussed above with respect toFIGS.2-3C. Peripheral circuit400P and pixel sensor circuits200are based on CMOS technology and, in some embodiments, pixel sensor array400is referred to as a CIS.

Peripheral circuit400P is an electronic circuit including a controller and memory, thereby being configured to cause some or all of pixel sensor circuits200to generate a voltage representative of a corresponding electromagnetic radiation intensity such that a collective digital image based on the N rows and M columns of pixel sensor circuits200is generated in operation.

In some embodiments, pixel sensor array400includes a shutter (not shown) configured to cause some or all of pixel sensor circuits to be exposed to electromagnetic radiation for one or more predetermined exposure periods.

In some embodiments, pixel sensor array400includes one or more filters (not shown) configured to limit exposure of one or more subsets of pixel sensor circuits200to one or more electromagnetic radiation frequency ranges. In some embodiments, the one or more electromagnetic radiation frequency ranges correspond to red, green, and blue light.

In various embodiments, peripheral circuit400P is configured to generate signals Vtx1-VtxN, Vrst, and/or Vrs and/or receive signal Vout corresponding to each pixel sensor circuit200, as discussed above with respect toFIG.2.

A digital image generated by pixel sensor array400in operation has a size based on a total pixel number equal to the number N of rows times the number M of columns of pixel sensor circuits200. In some embodiments, pixel sensor array400includes the number N of rows ranging from 1000 to 10,000. In some embodiments, pixel sensor array400includes the number M of columns ranging from 1200 to 12,000. In some embodiments, pixel sensor array400includes the total pixel number ranging from 1 megapixel (MP) to 125 MP. In various embodiments, pixel sensor array400includes the total pixel number of 8 MP, 16 MP, 24 MP, 48 MP, 64 MP, or 128 MP. Pixel sensor array400including other total pixel numbers, e.g., those in accordance with ranges other than the ranges discussed above, are within the scope of the present disclosure.

For a given pixel number, pixel sensor array400has a width and height (not labeled) in the respective X and Y directions, and thereby a resolution, that depends on a size and spacing of pixel sensor circuits200, referred to as a pitch in some embodiments. In some embodiments, pixel sensor circuits200of pixel sensor array400have a pitch ranging from 0.5 micrometers (μm) to 2.0 μm. In some embodiments, pixel sensor circuits200of pixel sensor array400have a pitch ranging from 0.75 μm to 1.0 μm. Pixel sensor array400including other pitch values, e.g., those in accordance with ranges other than the ranges discussed above, are within the scope of the present disclosure.

To accommodate decreasing pitch, a pixel sensor circuit, e.g., pixel sensor circuit200, often includes elements, e.g., photodiode300PD discussed above with respect toFIGS.3A-3C, that extend perpendicular to the X and Y directions. Because pixel sensor circuits200of pixel sensor array400include the conductive protrusions, e.g., conductive protrusions P1-P6, of transistor structure100, pixel sensor array400is thereby capable of realizing the benefits discussed above with respect to transistor structure100and pixel sensor circuit200.

FIG.5is a flowchart of a method500of operating a pixel sensor, in accordance with some embodiments. The operations of method500are capable of being performed as part of a method of operating one or more IC devices including one or more pixel sensors, e.g., pixel sensor array400discussed above with respect toFIG.4, pixel sensor300or300P discussed above with respect toFIGS.3A-3C, and/or pixel sensor circuit200discussed above with respect toFIG.2.

In some embodiments, the operations of method500are performed in the order depicted inFIG.5. In some embodiments, the operations of method500are performed in an order other than the order depicted inFIG.5. In some embodiments, one or more operations are performed before, between, during, and/or after performing one or more operations of method500.

At operation510, in some embodiments, a reset transistor is used to couple an internal node of a pixel sensor to a power supply node. Using the reset transistor to couple the internal node to the power supply node causes the internal node to discharge some or all of a stored charge, thereby setting the internal node to a predetermined voltage level, e.g., a power supply voltage level of the power supply node. In some embodiments, coupling the internal node to the power supply node includes coupling a FDN to the power supply node.

In some embodiments, using the reset transistor to couple the internal node to the power supply node includes using transistor RST to couple internal node N1to power supply node VDDN, discussed above with respect toFIG.2. In some embodiments, using the reset transistor to couple the internal node to the power supply node includes coupling region100R2, discussed above with respect toFIGS.1A,1B,3A, and3B, to the power supply node. In some embodiments, using the reset transistor to couple the internal node to the power supply node includes coupling FDN300F, discussed above with respect toFIG.3C, to the power supply node.

In some embodiments, using the reset transistor to couple the internal node to the power supply node corresponds to controlling one or more predetermined exposure periods of the pixel sensor. In some embodiments, using the reset transistor to couple the internal node to the power supply node corresponds to controlling one or more predetermined exposure periods of a pixel sensor array including the pixel sensor, e.g., pixel sensor array400discussed above with respect toFIG.4.

At operation520, a photodiode of the pixel sensor is illuminated with electromagnetic radiation, e.g., light. In some embodiments, illuminating the photodiode includes opening and closing a shutter for a predetermined period of time. In various embodiments, illuminating the photodiode includes performing a BSI or FSI operation, as discussed above with respect toFIGS.1A-4.

In some embodiments, illuminating the photodiode with electromagnetic radiation includes using a filter to limit the electromagnetic radiation received by the photodiode to one or more electromagnetic radiation frequency ranges. In some embodiments, limiting the electromagnetic radiation to one or more electromagnetic radiation frequency ranges includes limiting the electromagnetic radiation to one of red, green, or blue light.

In some embodiments, illuminating the photodiode with electromagnetic radiation includes causing a charge to accumulate on a cathode of the photodiode, an amount of the charge being representative of an intensity level of the electromagnetic radiation.

In some embodiments, illuminating the photodiode with electromagnetic radiation includes illuminating photodiode300PD discussed above with respect toFIGS.3A-3C.

At operation530, vertical gate structures of a transfer transistor are used to couple a cathode of the photodiode to the internal node, thereby generating an internal node voltage level. Using the vertical gate structures to couple the cathode to the internal node includes biasing the vertical gate structures to a common bias voltage level. In some embodiments, biasing the vertical gate structures to the common bias voltage level includes biasing a conductive region of a gate conductor of the transfer transistor, the conductive region being electrically connected to each of the vertical gate structures.

In some embodiments, biasing the vertical gate structures to the common bias voltage level includes biasing conductive protrusions, e.g., conductive protrusions P1-P6, of gate conductor100G discussed above with respect to transistor structure100andFIGS.1A and1B. In some embodiments, biasing the vertical gate structures to the common bias voltage level includes receiving a signal at a gate of a transistor structure, e.g., receiving one of signals Vtx1-VtxN at a corresponding gate of one of transistor structures100-1-100-N, as discussed above with respect toFIG.2. In some embodiments, biasing the vertical gate structures to the common bias voltage level includes using a circuit to generate a control signal, e.g., using peripheral circuit400P to generate one of signals Vtx1-VtxN, as discussed above with respect toFIG.4.

Using the vertical gate structures to couple the cathode to the internal node includes using at least a portion of each vertical gate structure positioned between the photodiode and the internal node. In some embodiments using the at least a portion of each vertical gate structure includes using at least a portion of each of conductive protrusions, e.g., conductive protrusions P1-P6, of gate conductor100G positioned between photodiode300PD and region100R2or FDN300F, as discussed above with respect toFIGS.3A-3C.

Coupling the cathode of the photodiode to the internal node includes providing a conductive channel between the photodiode and the internal node in response to the bias voltage level. In various embodiments, providing the conductive channel includes establishing the conductive channel or enhancing an existing conductive channel. In some embodiments, providing the conductive channel includes providing conductive channel100CH discussed above with respect toFIGS.1A and1B.

Coupling the cathode of the photodiode to the internal node includes coupling the cathode of the photodiode to the internal node of a pixel sensor. In some embodiments, coupling the cathode of the photodiode to the internal node of the pixel sensor includes coupling the cathode of one of photodiodes PD1-PDN to internal node N1of pixel sensor circuit200discussed above with respect toFIG.2. In various embodiments, coupling the cathode of the photodiode to the internal node of the pixel sensor includes coupling cathode300C to region100R2of pixel sensor300or coupling an instance of cathode300C to FDN300F of pixel sensor300P discussed above with respect toFIGS.3A-3C.

Generating the internal node voltage level includes generating the internal node voltage level representative of the amount of the charge accumulated on the cathode of the photodiode, e.g., the cathode of one of photodiodes PD1-PDN discussed above with respect toFIG.2or cathode300C discussed above with respect toFIGS.3A-3C.

At operation540, in some embodiments, an output voltage level of the pixel sensor is generated based on the internal node voltage level. Generating the output voltage level includes receiving the internal node voltage level at a gate of a transistor configured to generate the output voltage. In some embodiments, receiving the internal node voltage level at the gate of the transistor includes receiving the internal node voltage level at the gate of the transistor configured as a source follower, the output voltage level thereby following the internal node voltage level. In some embodiments, receiving the internal node voltage level at the gate of the transistor includes receiving voltage Vn1at the gate of transistor SF discussed above with respect toFIG.2.

In some embodiments, generating the output voltage level includes using a selection transistor to selectively couple the transistor to an output node of the pixel sensor. In some embodiments, using the selection transistor to selectively couple the transistor to the output node includes using transistor RS to selective couple transistor SF to output node OUT discussed above with respect toFIG.2.

In some embodiments, using the selection transistor to selectively couple the transistor to the output node includes receiving a control signal at a gate of the selection transistor. In some embodiments, receiving the control signal at the gate of the selection transistor includes receiving signal Vrs at the gate of transistor RS discussed above with respect toFIG.2.

In some embodiments, using the selection transistor to selectively couple the transistor to the output node includes using a circuit to generate the control signal provided at the gate of the selection transistor. In some embodiments, using the circuit to generate the control signal includes using peripheral circuit400P discussed above with respect toFIG.4.

At operation550, in some embodiments, the reset transistor is used to couple the internal node to the power supply node after using the transfer transistor to decouple the cathode from the internal node. Using the transfer transistor to decouple the cathode from the internal node includes using the vertical gate structures of the transfer transistor to decouple the cathode from the internal node.

Using the vertical gate structures to decouple the cathode from the internal node includes biasing the vertical gate structures to a common second voltage level different from the common bias voltage level used to couple the cathode to the internal node. Biasing the vertical gate structures to the second voltage level includes reducing or eliminating the conductive channel between the photodiode and the internal node provided in response to the bias voltage level, e.g., conductive channel100CH discussed above with respect toFIGS.1A and1B.

Using the transfer transistor to decouple the cathode from the internal node thereby includes using the vertical gate structures of the transfer transistor in the decoupling operation having features analogous to those of the coupling operation discussed above with respect to operation530.

Using the reset transistor to couple the internal node to the power supply node is performed as discussed above with respect to operation510.

By executing some or all of the operations of method500, electromagnetic radiation is detected using vertical gate structures of a transfer transistor having the properties, and thereby the benefits, discussed above with respect to transistor structure100, pixel sensor circuit200, pixel sensors300and300P, and pixel sensor array400.

FIG.6is a flowchart of a method600of manufacturing a transistor structure, e.g., transistor structure100discussed above with respect toFIGS.1A and1B, in accordance with some embodiments.FIGS.7A-7Fare diagrams of transistor structure100at various manufacturing stages corresponding to the operations of method600, in accordance with some embodiments.

Each ofFIGS.7A-7Fcorresponds to the cross-sectional view of transistor structure100depicted inFIG.1B. To facilitate the illustration of the various features, the cross-sectional views include only relevant portions of transistor structure100. The arrangement of the features depicted inFIGS.7A-7Fis a non-limiting example provided for the purpose of illustration. In various embodiments, the operations of method600correspond to transistor structure100having the various features and arrangements discussed above with respect toFIGS.1A and1B.

The sequence in which the operations of method600are depicted inFIG.6is for illustration only; the operations of method600are capable of being executed simultaneously or in sequences that differ from that depicted inFIG.6. In some embodiments, operations in addition to those depicted inFIG.6are performed before, between, during, and/or after the operations depicted inFIG.6.

In various embodiments, some or all of method600is executed as part of manufacturing a pixel sensor, e.g., pixel sensor300or300P discussed above with respect toFIGS.3A-3C, a pixel sensor circuit, e.g., pixel sensor circuit200discussed above with respect toFIG.2, or a pixel sensor array, e.g., pixel sensor array400discussed above with respect toFIG.4.

At operation610, in some embodiments, a substrate having an upper surface is provided. In various embodiments, providing the substrate includes providing a bulk silicon layer or a SOI substrate, a silicon layer having n-type or p-type doping, or a compound semiconductor material. In some embodiments, providing the substrate includes providing substrate100B having upper surface100S discussed above with respect toFIGS.1A,1B, and3A-3C, and discussed below with respect toFIGS.7A-7F.

In some embodiments, providing the substrate having the upper surface includes providing the upper surface by executing a planarization process, e.g., a chemical-mechanical polishing (CMP).

At operation620, a mask including a plurality of openings is applied at the upper surface of the substrate. In some embodiments, applying the mask includes depositing a photoresist material on the upper surface and using photolithography to form a pattern in the photoresist material corresponding to the plurality of openings and selectively remove the patterned portions of the photoresist material. In some embodiments, applying the mask includes applying mask M1including plurality of openings O1and O2at upper surface100S, as depicted inFIGS.7A and7B.

At operation630, a plurality of substrate trenches corresponding to the plurality of openings is formed. Forming the plurality of trenches includes forming the plurality of trenches configured in accordance with the conductive protrusions, e.g., conductive protrusions P1-P6, of gate conductor100G discussed above with respect toFIGS.1A,1B, and3A-3C.

Forming the plurality of trenches includes removing portions of the substrate exposed by the plurality of openings. In some embodiments, forming the plurality of trenches includes performing an etching process. In various embodiments, using an etching process includes using one or more etch processes such as a wet etch, a dry etch, a sputtering etch or other suitable removal process. In various embodiments, using an etching process includes using one or more etchant materials, e.g., one or more of Cl2, SF6, HBr, HCl, CF4, CHF3, C2F6, C4F8, or other suitable etchant materials.

In some embodiments, forming the plurality of trenches corresponding to the plurality of openings includes forming trenches T1and T2corresponding to respective openings O1and O2, as depicted inFIG.7B.

In some embodiments, forming the plurality of trenches includes removing the mask from the upper surface of the substrate after removing the portions of the substrate exposed by the plurality of openings.

At operation640, the plurality of trenches is lined with a dielectric material. Lining the plurality of trenches with the dielectric material includes lining an entirety of the surface of each trench of the plurality of trenches with the dielectric material. In some embodiments, lining the plurality of trenches with the dielectric material includes lining one or more portions of the upper surface of the substrate between and/or adjacent to the plurality of trenches with the dielectric material. In some embodiments, lining the plurality of trenches with the dielectric material includes forming a dielectric layer D1depicted inFIGS.7C-7E.

In some embodiments, lining the plurality of trenches with the dielectric material includes using a deposition process. In various embodiments, a deposition process includes a chemical vapor deposition (CVD), a plasma enhanced CVD (PECVD), or other process suitable for depositing one or more material layers.

In various embodiments, lining the plurality of trenches with the dielectric material includes depositing one or more of SiO2, silicon nitride, (Si3N4), aluminum oxide (Al2O3), hafnium oxide (HfO2), tantalum pentoxide (Ta2O5), titanium oxide (TiO2), or another suitable material.

At operation650, in some embodiments, substrate regions are formed at opposite sides of the plurality of trenches. Forming the substrate regions includes forming regions having a doping type opposite that of the substrate. In some embodiments, forming the substrate regions includes forming regions100R1and100R2discussed above with respect toFIGS.1A,1B, and3A-3C, and depicted inFIGS.7D-7F.

In various embodiments, forming the substrate regions includes performing an implant and/or deposition process. In some embodiments, forming the substrate regions includes removing portions of the dielectric material, e.g., dielectric layer D1, deposited on the upper surface of the substrate.

In some embodiments, an implant process includes implanting one or more donor dopants, e.g., P or As, and/or one or more acceptor dopants, e.g., B or Al. In some embodiments, performing a deposition process includes depositing one or more of Si or a compound semiconductor, e.g., InP, GaAs, SiGe, InAs, SiC, or another suitable compound semiconductor material. In some embodiments, performing a deposition process includes forming one or more epitaxial layers.

At operation660, the plurality of trenches is filled with a conductive material. Filling the plurality of trenches with a conductive material includes forming conductive protrusions, e.g., conductive protrusions P1-P6, of gate conductor100G discussed above with respect toFIGS.1A,1B, and3A-3C. In some embodiments, filling the plurality of trenches with the conductive material includes performing a deposition process.

In various embodiments, filling the plurality of trenches with the conductive material includes filling the plurality of trenches with one or more of polysilicon, Cu, Al, W, Co, Ru, or one or more other metals, and/or one or more other suitable materials.

In some embodiments, filling the plurality of trenches with the conductive material includes depositing the conductive material on the dielectric material deposited in the plurality of trenches and on the upper surface of the substrate. In some embodiments, filling the plurality of trenches with the conductive material includes depositing a conductive layer C1on dielectric layer D1deposited in trenches T1and T2and on upper surface100S as depicted inFIG.7E.

At operation670, in some embodiments, portions of the conductive material adjacent to the plurality of trenches are removed. In various embodiments, removing the portions of the conductive material adjacent to the plurality of trenches includes removing portions of the conductive material adjacent to the plurality of trenches in the positive and/or negative X direction and/or in the positive Z direction.

In some embodiments, removing the portions of the conductive material adjacent to the plurality of trenches includes removing portions of conductive layer C1adjacent to trenches T1and T2in the positive and negative X directions to form conductive region100C of gate conductor100G, as depicted inFIG.7F. In some embodiments, removing the portions of the conductive material adjacent to the plurality of trenches includes removing portions of conductive layer C1adjacent to trenches T1and T2in the positive Z direction to form top surface100CS of conductive region100C of gate conductor100G, as depicted inFIG.7F.

In some embodiments, removing the portions of the conductive material adjacent to the plurality of trenches includes removing portions of the conductive material overlying one or both of the substrate regions, e.g., substrate region100R1and100R2.

In some embodiments, removing the portions of the conductive material adjacent to the plurality of trenches includes removing portions of the dielectric material on the upper surface of the substrate, e.g., portions of dielectric layer D1on upper surface100S, as depicted inFIG.7F.

At operation680, in some embodiments, a conductive path is formed on the conductive material. Forming the conductive path includes forming a via (not shown) overlying the conductive material, thereby forming an electrical connection between the conductive material and the via.

The operations of method600are usable to form an IC structure, e.g., transistor structure100discussed above with respect toFIGS.1A,1B, and3A-3C, by forming conductive protrusions of a gate conductor between adjacent substrate regions. Compared to methods that do not include forming the conductive protrusions, method600is usable to form transistor structures with improved electron transmission efficiency as discussed above with respect to transistor structure100.

In some embodiments, a method of manufacturing a transistor structure includes forming a plurality of trenches in a substrate, lining the plurality of trenches with a dielectric material, forming first and second substrate regions at opposite sides of the plurality of trenches, and filling the plurality of trenches with a conductive material. The plurality of trenches includes first and second trenches aligned between the first and second substrate regions, and filling the plurality of trenches with the conductive material includes the conductive material extending continuously between the first and second trenches. In some embodiments, forming the plurality of trenches includes forming each trench of the plurality of trenches having a circular cross-section. In some embodiments, forming the plurality of trenches includes forming the plurality of trenches having a same depth in the substrate. In some embodiments, the substrate has a substrate thickness, and forming the plurality of trenches includes forming each trench of the plurality of trenches having a depth in the substrate ranging from 3% to 90% of the substrate thickness. In some embodiments, forming the plurality of trenches includes forming the first and second trenches having a same diameter and separated by a distance equal to or greater than one half of the same diameter. In some embodiments, forming the first trench includes forming the first trench extending into a cathode of a photodiode. In some embodiments, forming the second trench includes forming the second trench extending into the cathode of the photodiode. In some embodiments, forming the plurality of trenches in the substrate includes forming the plurality of trenches in a SOI substrate. In some embodiments, filling the plurality of trenches with the conductive material includes the conductive material extending continuously between the first and second substrate regions. In some embodiments, forming the second substrate region includes forming a floating diffusion region of a pixel sensor.

In some embodiments, a method of manufacturing a transistor structure includes etching a plurality of trenches at an upper surface of a p-type substrate region, depositing a dielectric material on the plurality of trenches and a portion of the upper surface between each trench of the plurality of trenches, forming n-type source and drain regions at the upper surface, wherein first and second trenches of the plurality of trenches are aligned between the source and drain regions, and depositing a conductive material on the dielectric material in the first and second trenches of the plurality of trenches and on the portion of the upper surface. In some embodiments, forming the n-type drain region includes forming a lightly doped drain. In some embodiments, the plurality of trenches is a first plurality of trenches, the n-type source region is a first n-type source region, the portion of the upper surface is a first portion of the upper surface, and the method includes etching a second plurality of trenches at the upper surface of the p-type substrate region, wherein the drain is between the first and second pluralities of trenches, depositing the dielectric material on the second plurality of trenches and a second portion of the upper surface between each trench of the second plurality of trenches, forming a second n-type source region at the upper surface, wherein first and second trenches of the second plurality of trenches are aligned between the second source region and the drain region, and depositing the conductive material on the dielectric material in the first and second trenches of the second plurality of trenches and on the second portion of the upper surface. In some embodiments, the method includes etching third and fourth pluralities of trenches at the upper surface of the p-type substrate region, wherein the drain is between the third and fourth pluralities of trenches, depositing the dielectric material on the third and fourth pluralities of trenches and corresponding third and fourth portions of the upper surface between each trench of the third and fourth pluralities of trenches, forming third and fourth n-type source regions at the upper surface, wherein first and second trenches of the third plurality of trenches are aligned between the third source region and the drain region, and first and second trenches of the fourth plurality of trenches are aligned between the fourth source region and the drain region, and depositing the conductive material on the dielectric material in the first and second trenches of each of the third and fourth pluralities of trenches and on the third and fourth portions of the upper surface. In some embodiments, each of the etching the plurality of trenches, the depositing the dielectric material, the forming n-type source and drain regions, and the depositing the conductive material is part of forming a transfer gate of a pixel sensor of a pixel sensor array, and the method includes forming corresponding transfer gates of each additional pixel sensor of the pixel sensor array.

In some embodiments, a method of manufacturing a transistor structure includes forming an array of trenches in a substrate, wherein the array comprises first and second columns of trenches, lining each trench of the array and an upper surface of the substrate with a dielectric material, forming a first substrate region adjacent to the first column and a second substrate region adjacent to the second column, and depositing a conductive material on the dielectric material, thereby forming conductive protrusions in each trench of the array and a conductive layer overlying and continuous with each conductive protrusion. In some embodiments, depositing the conductive material on the dielectric material includes forming the conductive layer overlying the first and second substrate regions. In some embodiments, the method includes removing a portion of the conductive layer overlying the first substrate region and a portion of the conductive layer overlying the second substrate region. In some embodiments, forming the conductive protrusions in each trench of the array includes forming each conductive protrusion having approximately a same diameter and separated from each nearest conductive protrusion along a row or column direction by approximately a same distance. In some embodiments, the same distance is equal to or greater than one half of the same diameter.

It will be readily seen by one of ordinary skill in the art that one or more of the disclosed embodiments fulfill one or more of the advantages set forth above. After reading the foregoing specification, one of ordinary skill will be able to affect various changes, substitutions of equivalents and various other embodiments as broadly disclosed herein. It is therefore intended that the protection granted hereon be limited only by the definition contained in the appended claims and equivalents thereof.