Image sensor and method for fabricating the same

A method for fabricating an image sensor in accordance with an embodiment of the inventive concepts may include forming first and second photodiodes within a substrate, forming first and second gate electrodes over the substrate, the first gate electrode vertically partially overlapping the first photodiode and the second gate electrode vertically partially overlapping the second photodiode, forming an impurity injection region comprising first and second type impurities between the first and the second gate electrodes, and performing an annealing process to form a floating diffusion region comprising the first type impurities and a channel region comprising the second type impurities. The channel region surrounds lateral surfaces and a bottom surface of the floating diffusion region.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority under 35 U.S.C. 119(a) to Korean Patent Application No. 10-2016-0034103 filed on Mar. 22, 2016, which is herein incorporated by reference in its entirety.

BACKGROUND

Exemplary embodiments of the present invention present invention provide generally image sensors for converting an optical image into an electric signal and methods for fabricating the same.

2. Description of the Related Art

Recently, as the information communication industry is advancing and electronic devices are digitalized, image sensors having improved performance are being used in various fields, such as digital cameras, camcorders, mobile phones, personal communication systems (PCSs), gaming machines, cameras for surveillance, and micro-cameras for medicine.

Generally, an image sensor includes pixel region including a photodiode and a peripheral region. A unit pixel includes the photodiode and a transfer transistor. The transfer transistor is disposed between the photodiode and a floating diffusion region and transfers charges generated by the photodiode to the floating diffusion region.

SUMMARY

Exemplary embodiments of the present invention provide image sensors.

Exemplary embodiments of the present invention provide methods for fabricating image sensors.

The technical objectives of the present invention are not limited to the above mentioned embodiments, and those skilled in the art to which the present invention pertains will understand other technical objectives related to the embodiments can be derived from the following description.

In accordance with an exemplary embodiment of the inventive concepts, a method for forming an image sensor may include forming first and second photodiodes within a substrate, forming first and second gate electrodes over the substrate, the first gate electrode vertically partially overlapping the first photodiode and the second gate electrode vertically partially overlapping the second photodiode, forming an impurity injection region comprising first and second type impurities between the first and the second gate electrodes, and performing an annealing process to form a floating diffusion region comprising the first type impurities and a channel region comprising the second type impurities. The channel region surrounds lateral surfaces and a bottom surface of the floating diffusion region.

The second type impurities have a greater thermal diffusivity than the first impurities.

The second type impurities have a smaller atom size than the first type impurities.

The method may further include injecting an amorphizing material into the substrate prior to the forming of the impurity injection region.

The method may further include injecting a clustering material into the substrate prior to the forming of the impurity injection region.

The method may further include forming gate spacers between sides of the first and the second gate electrodes.

The channel region partially overlaps corners of regions of the first and the second photodiodes.

The impurity injection region may include a reserved floating diffusion region comprising the first type impurities, and a reserved channel region comprising the second type impurities.

The reserved channel region surrounds lateral surfaces and a bottom surface of the reserved floating diffusion region.

The method may further include forming a pixel field region between the first and the second photodiodes, wherein the pixel field region has a lower second type impurity ion concentration than the channel region.

In accordance with an embodiment of the inventive concepts, a method of forming an image sensor may include forming a first photodiode within a substrate, forming a first gate electrode vertically partially overlapping the first photodiode and a second gate electrode spaced apart from the first gate electrode and not vertically overlapping the first photodiode on the substrate, forming a first impurity injection region by injecting n-type impurities and p-type impurities into the substrate between first sides of the first gate electrode and the second gate electrode, and performing an annealing process to form a floating diffusion region and a channel region surrounding the floating diffusion region by diffusing the n-type impurities and the p-type impurities within the first impurity injection region.

The method may further include forming a second photodiode vertically partially overlapping the second gate electrode within the substrate.

The method may further include forming a device voltage node and a reset channel region within the substrate and adjacent to a second side of the second gate electrode.

The forming of the device voltage node and the reset channel region may include forming a second impurity injection region by injecting n-type impurities and p-type impurities into the substrate adjacent to the second side of the second gate electrode, and performing an annealing process to form the device voltage node and the reset channel region surrounding the device voltage node by diffusing the n-type impurities and the p-type impurities within the second impurity injection region.

The device voltage node and the floating diffusion region may have an identical depth, and the reset channel region and the channel region may have an identical depth.

In accordance with an embodiment of the inventive concepts, a method of forming an image sensor may include forming a first photodiode within a substrate, forming a first transistor having a first side vertically partially overlapping the first photodiode on the substrate, forming an impurity injection region by injecting first and second type impurities into the substrate adjacent to a second side of the first transistor, and performing an annealing process to form a floating diffusion region by diffusing the first type impurities within the impurity injection region and a channel region surrounding lateral surfaces and a bottom surface of the floating diffusion region by diffusing the second type impurities within the impurity injection region.

The method may further include forming a second photodiode spaced apart from the first photodiode within the substrate, and forming a second transistor having a first side vertically partially overlapping the second photodiode on the substrate, wherein the impurity injection region is formed between the first photodiode and the second photodiode.

The floating diffusion region may include a first overlap region vertically overlapping the first transistor and a second overlap region vertically overlapping the second transistor, and a length of the first overlap region is identical to a length of the second overlap region.

The channel region may include a first channel region vertically overlapping the first transistor and a second channel region vertically overlapping the second transistor, and a length of the first channel region may be identical to a length of the second channel region.

A portion of the first photodiode overlapping the channel region may be an inverted region.

In accordance with an embodiment of the inventive concepts, an image sensor may include photodiodes suitable for being formed within a substrate, transfer transistors suitable for partially vertically overlapping the photodiodes on the substrate, and a floating diffusion region and a channel region suitable for being formed within the substrate between the transfer transistors. The channel region surrounds lateral surfaces and a bottom surface of the diffusion region.

The channel region may partially overlap corners of the photodiodes.

The floating diffusion region may partially vertically overlap the transfer transistors.

The floating diffusion region may be electrically insulated from the substrate by the channel region.

The channel region may have a higher p-type impurity concentration than the substrate.

In accordance with an embodiment of the inventive concepts, an image sensor may include a first photodiode suitable for being formed within a substrate, a first transistor suitable for being formed within the substrate and partially vertically overlapping the first photodiode, a second transistor suitable for being spaced apart from the first transistor, and a first n-type impurity region suitable for being formed within the substrate between the first transistor and the second transistor and a first p-type impurity region suitable for surrounding lateral surfaces and a bottom surface of the first n-type impurity region.

The first n-type impurity region and the first p-type impurity region may partially vertically overlap the first and the second transistors.

The first p-type impurity region may partially overlap a corner of the first photodiode.

The image sensor may further include a second n-type impurity region suitable for being formed within the substrate adjacent to a second side of the second transistor, and a second p-type impurity region suitable for surrounding lateral surfaces and a bottom surface of the second n-type impurity region.

The first n-type impurity region and the second n-type impurity region may be spaced apart from each other. The first p-type impurity region and the second p-type impurity region may be contiguous.

In accordance with an embodiment of the inventive concepts, an image sensor may include a first photodiode suitable for being formed within a substrate, a first transistor suitable for being formed on the substrate and having a first side vertically overlapping the first photodiode, and a first n-type impurity region suitable for being formed within the substrate and vertically overlapping a second side of the first transistor and a first p-type impurity region suitable for being formed within the substrate and surrounding lateral surfaces and a bottom surface of the first n-type impurity region.

The image sensor may further includes a second photodiode suitable for being formed within the substrate and spaced apart from the first photodiode, and a second transistor suitable for being formed on the substrate and having a first side vertically overlapping the second photodiode. The first n-type impurity region and the first p-type impurity region may partially overlap a second side of the second transistor.

The first n-type impurity region may include a first n-type overlap region vertically overlapping the first transistor and a second n-type overlap region vertically overlapping the second transistor. A length of the first n-type overlap region may be identical with a length of the second n-type overlap region.

The first p-type impurity region may include a first p-type overlap region vertically overlapping the first transistor and a second p-type overlap region vertically overlapping the second transistor. A length of the first p-type overlap region may be identical with a length of the second p-type overlap region.

The image sensor may further include a pixel field region suitable for being formed between the first photodiode and the second photodiode. The pixel field region may have a lower p-type impurity ion concentration than the first p-type impurity region.

The image sensor may further include a second transistor suitable for being formed on the substrate and spaced apart from the first transistor. The first n-type impurity region and the first p-type impurity region may vertically overlap a first side of the second transistor.

The image sensor may further include a second n-type impurity region suitable for vertically overlapping a second side of the second transistor within the substrate, and a second p-type impurity region suitable for surrounding lateral surfaces and a bottom surface of the second n-type impurity region.

A length of a region in which the first n-type impurity region vertically overlaps the first transistor may be identical with a length of a region in which the second n-type impurity region vertically overlaps the second transistor.

The first p-type impurity region and the second p-type impurity region may be contiguous within the substrate under the second transistor.

The first photodiode and the channel region may partially overlap.

DETAILED DESCRIPTION

The drawings are not necessarily to scale and in some instances, proportions may have been exaggerated to clearly illustrate features of the embodiments.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present invention. As used herein, singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise.

It is also noted, that in some instances, as would be apparent to those skilled in the relevant art, an element also referred to as a feature, described in connection with one embodiment may be used singly or in combination with other elements of another embodiment, unless specifically indicated otherwise.

Referring toFIG. 1, an image sensor in accordance with an embodiment of the present invention may include a pixel array100configured to have a plurality of unit pixel groups110arranged in a matrix for a correlated double sampler (CDS)120, an analog digital converter (ADC)130, a buffer140, a row driver150, a timing generator160, a control register170, and a ramp signal generator180.

The timing generator160may generate one or more control signals CSD, CSC, CSA, and CSR for controlling the operations of the row driver150, the CDS120, the ADC130, and the ramp signal generator180, respectively. The control register170may generate control signals CRSR, CRST, and CRSB for controlling the operations of the ramp signal generator180, the timing generator160, and the buffer140.

The row driver150may drive the pixel array100in a row line unit. For example, the row driver150may generate a selection signal capable of selecting any one of a plurality of row lines RL. Each row line RL may be coupled to a plurality of unit pixel groups110.

Each of the plurality of unit pixel groups110may detect incident light and output an image reset signal RS and an image signal IS to the CDS120through a column line CL. The CDS120may perform sampling on each received image reset signal RS and each received image signal IS. The plurality of unit pixel groups110may be coupled to a plurality of column lines CL, respectively. Furthermore, a plurality of the unit pixel groups110in each column of the pixel array100may be coupled to one column line CL. The ADC130may compare a ramp signal RSG received by the ramp signal generator180, with a sampling signal SS received by the CDS120and output a comparison signal CS to the Buffer. The ADC130may count the level transition time of the comparison signal CS in response to a clock signal CSA also referred to earlier as a control signal, provided by the timing generator160, and may output a count value CV to the buffer140. The ramp signal generator180may operate under the control of the timing generator160.

The buffer140may store a plurality of digital signals output by the ADC130that is, the comparison signals CS and may sense, amplify, and output each of the digital signals. Accordingly, the buffer140may include a memory (not shown) and a sense amplifier (not shown). The memory may store the count values. A count value may mean a count value associated with signals output by the plurality of unit pixel groups110. The sense amplifier may sense and amplify each of the count values output by the memory.

FIGS. 2A to 2Care simplified layout diagrams of pixels of image sensors in accordance with various embodiments of the present invention.

Referring toFIG. 2A, a unit pixel PX1of an image sensor in accordance with an embodiment of the present invention may include photodiodes PD1-PD4, pixel field regions PF, transfer transistors Tt1-Tt4, a floating diffusion region FD, a reset transistor Tr, a drive transistor Td, and a select transistor Ts. In the unit pixel PX1in accordance with the embodiment ofFIG. 2A, at least four photodiodes PD1-PD4and at least four transfer transistors Tt1-Tt4may share a single floating diffusion region FD and may arranged around the floating diffusion region FD to surround the floating diffusion region FD. For example, as illustrated inFIG. 2A, the four photodiodes PD1-PD4and the four transfer transistors Tt1-Tt4may be arranged in an axial-symmetrical or a point-symmetrical form, respectively. The four transfer transistors Tt1-Tt4may be positioned symmetrically around the centrally disposed floating diffusion region FD and the four photodiodes PD1-PD4ray be positioned around the four transfer transistors Tt1-Tt4.

Each of the photodiodes PD1-PD4may receive light and generate photoelectrons. The pixel field regions PF may separate the photodiodes PD1-PD4spatially and/or electrically. In more detail, each pixel field region PF is disposed between two neighboring photodiodes, for example, as illustrated inFIG. 2A, a first pixel field region PF is disposed between photodiodes PD1and PD2, a second pixel field region PF is disposed between photodiodes PD2and PD3, a third pixel field region PF is disposed between photodiodes PD3and PD4, and a fourth pixel field region is disposed between photodiodes PD4and PD1.

The first pixel field region PF also separates the first transfer transistor Tt1from the second transfer transistor Tt2, the second pixel field region PF separates the second transfer transistor Tt2from the third transfer transistor Tt3, the third pixel field region PF separates the third transfer transistor Tt3from the fourth transfer transistor Tt4, and the fourth pixel field region PF separates the fourth transfer transistor Tt4from the first transfer transistor Tt1.

Each transfer transistor Tt1-Tt4may transfer photoelectrons, generated in its respective photodiode PD1-PD4, to the shared floating diffusion region FD in response to respective turn-on signals. InFIG. 2A, the transfer transistors Tt1-Tt4may be interpreted as gate electrodes.

The floating diffusion region FD may temporarily store the photoelectrons that were generated from the photodiodes PD1-PD4transferred by the transfer transistors Tt1-Tt4, and may transfer the photoelectrons to the drive transistor Td.

A gate electrode of the drive transistor Td may be electrically connected to the floating diffusion region FD. Accordingly, the drive transistor Td may be driven in response to the amount of electrons in the floating diffusion region FD, and output various voltages and currents.

The select transistor Ts may transfer a device voltage to a source electrode of the drive transistor Td in response to a selection signal. Accordingly, a voltage output to a drain electrode of the drive transistor Td may be changed depending on the amount of photoelectrons of the floating diffusion region FD. The drain electrode of the drive transistor Td may be electrically connected to an output node. The reset transistor Tr may reset the floating diffusion region FD to the same level as the device voltage or a reset voltage, in response to a reset signal.

Referring toFIG. 2B, a unit pixel PX2of an image sensor in accordance with an embodiment of the present invention may include photodiodes PD1and PD2, transfer transistors Tt1and Tt2, pixel field regions PF, a floating diffusion region FD, a reset transistor Tr, a drive transistor Td, and a select transistor Ts. In the unit pixel PX2two photodiodes PD1and PD2and two transfer transistors Tt1and Tt2may share a single floating diffusion region FD. The two photodiodes PD1and PD2and the two transfer transistors Tt1and Tt2may be arranged in an axial-symmetrical form on either side of a first elongated pixel field region PF. In more detail, the first elongated pixel field region PF separates the first photodiode PD1and the first transfer transistor Tt1from the second photodiode PD2and the second transfer transistor Tt2.

The first and second transfer transistors Tt1and Tt2may be adjacent to a first side of the floating diffusion region and the corresponding first and second photodiodes PD1and PD2may be adjacent to the first and second transfer transistors, respectively.

A first side of the reset transistor Tr may be adjacent to a second side of the floating diffusion region FD. The other side of the reset transistor Tr may be adjacent to a reset voltage node Vr. Thus, when viewed from the top, the first elongated pixel field region PF, the floating diffusion FD, the reset transistor Tr and the reset voltage node Vr are positioned in series in a first direction extending along the elongated axis of symmetry of the first elongated pixel field region PF.

Referring toFIG. 2C, a unit pixel PX3of an image sensor in accordance with an embodiment of the present invention may include a photodiode PD, pixel field regions PF, a transfer transistor Tt, a floating diffusion region FD, a reset transistor Tr, a drive transistor Td, and a select transistor Ts. One electrode of the reset transistor Tr and one electrode of the drive transistor Td may be electrically coupled to a reset voltage node Vr. The transfer transistor Tt, the floating diffusion region FD, the reset transistor Tr, the drive transistor Td, and the select transistor Ts may be sequentially coupled in this order to form a generally L-shaped region with the reset voltage node Vr coupling the reset transistor Tr with the drive transistor at the right angle transition point of the generally L shaped region. The transfer transistor Tt may be coupled to the photodiode PD. The photodiode PD when viewed from the top has a generally rectangular shape and occupies a first part of the unit pixel PX3area. Two pixel field regions PF occupy the rest of the unit pixel PX3area on either side of the L-shaped region.

FIG. 3A to 3Dare simplified longitudinal sectional views of the image sensors taken along line I-I′ ofFIG. 2Aor II-II′ ofFIG. 2Bin accordance with various embodiments of the present invention.

Referring toFIG. 3A, an image sensor in accordance with an embodiment of the present invention may include the photodiodes PD1and PD2and the pixel field region PF formed within a substrate210, the transfer transistors Tt1, and Tt2formed on the substrate210, and the floating diffusion region FD and a channel region CH formed in the substrate210between the transfer transistors Tt1and Tt2. The image sensor may further include an interlayer dielectric layer240configured to cover the transfer transistors Tt1and Tt2on the substrate210.

The substrate210may include at least one of a silicon substrate, a silicon on insulator (SOI) substrate, or a substrate having an epitaxial growth layer. For example, in an embodiment of the present invention, the photodiodes PD1and PD2may be formed within an epitaxial growth layer. The substrate210may include p-type impurities, such as boron (B).

The photodiodes PD1and PD2may include n-type impurities, such as phosphorous (P) or arsenic (As). Some regions of the photodiodes PD1and PD2overlapping the channel region CH may be inversion regions IR1and IR2. For example, the inversion regions IR1and IR2may be regions inverted from an n-type impurity region to a p-type impurity region.

The pixel field region PF may be formed between the photodiodes PD1and PD2. The pixel field region PF may be part of the substrate210including p-type impurities, such as boron (B), or may include an insulating region, such as a shallow trench isolation (STI) or a deep trench isolation (DTI). In various embodiments of the present invention, the pixel field region PF may include a p-type impurity region formed between the photodiodes PD1and PD2and/or an STI or DTI formed between unit pixels PXn. When the pixel field region PF includes a p-type impurity region, the pixel field region PF may have a higher p-type impurity concentration than the substrate210.

The transfer transistors Tt1and Tt2may include gate insulating layers221and222and gate electrodes231and232, respectively. The gate insulating layers221and222may include silicon oxide. For example, the gate insulating layers221and222may include at least one of an oxidized silicon layer which is oxidized from a surface of the substrate210or a silicon oxide layer deposited on a surface of the substrate210. The gate electrodes231and232may include at least one of doped polysilicon, silicide, metal, a metal compound, or combinations thereof.

The floating diffusion region FD may include n-type impurities. For example, the floating diffusion region FD may include at least one of arsenic (As), phosphorous (P), or antimony (Sb). The floating diffusion region FD may vertically partially overlap the gate insulating layers221and222and gate electrodes231and232of the transfer transistors Tt1and Tt2. The floating diffusion region FD may be extended to portions below the transfer transistors Tt1and Tt2. For example, the width, length, or area size of a region E1in which the floating diffusion region FD partially vertically overlaps the first transfer transistor Tt1and the width, length, or area size of a region E2in which the floating diffusion region FD partially vertically overlaps the second transfer transistor Tt2may be the same.

The channel region CH may surround lateral surfaces and a bottom surface of the floating diffusion region FD so that the floating diffusion region FD may be spaced apart from the substrate210. The channel region CH may include p-type impurities. For example, the channel region CH may include at least one of boron (B) or indium (In). The channel region CH may have a higher p-type impurity ion concentration than the substrate210and the pixel field region PF. For example, the channel region CH may have a higher impurity concentration than the photodiodes PD1and PD2. The width or lengths CL1and CL2of the channel region CH overlapping the transfer transistors Tt1and Tt2may be the same.

The transfer transistors Tt1and Tt2, the floating diffusion region FD, and the channel region CH may have a left and right axial-symmetrical shape along an axis of symmetry extending along the elongated axis of symmetry of the pixel field region PF.

The interlayer dielectric layer240may include silicon oxide, such as tetra-ethyl-ortho-silicate (TEOS).

In the image sensor in accordance with an embodiment of the present invention, the leakage current of the floating diffusion region FD can be small due to the channel region CH having a higher p-type impurity ion concentration than the substrate210surrounding the floating diffusion region FD. The channel region CH can provide a short channel length since it inverts the polarity of the photodiode PD. Accordingly, the operating speed of the image sensor can be improved.

The transfer transistors Tt1and Tt2, the floating diffusion region FD, and the channel region CH can have uniform electrical characteristics since they have a left and right line-symmetrical shape. Accordingly, all of pixels can have uniform electrical characteristics, and the distortion of an image of the image sensor can be greatly reduced.

Referring toFIG. 3B, the transfer transistors Tt1and Tt2of an image sensor in accordance with an embodiment of the present invention may further include spacers251and252formed on the sides of the gate insulating layers221and222and the gate electrodes231and232compared to the image sensor ofFIG. 3A. The spacers251and252may include, for example, one of silicon nitride, silicon oxide, or a combination thereof.

Referring toFIG. 3C, in an image sensor in accordance with an embodiment of the present invention, the transfer transistors Tt1and Tt2may further include gate capping layers261and262formed on the gate electrodes231and232compared to the image sensors ofFIGS. 3A and 3B. The gate capping layers261and262may include an insulating material such as silicon nitride or silicon oxide. In some embodiments the gate capping layers261and262may include a conductor, such as metal, metal silicide, or a metal compound.

Referring toFIG. 3D, an image sensor in accordance with an embodiment of the present invention may include the spacers251and252and the gate capping layers261and262compared to the image sensors ofFIGS. 3A to 3C.

FIG. 4is a simplified longitudinal sectional view of the image sensor in accordance with an embodiment of the present invention, which is taken along line III-III′ ofFIG. 2C.

Referring toFIG. 4, the image sensor in accordance with an embodiment of the present invention may include the photodiode PD formed within a substrate210, the transfer transistor Tt and the reset transistor Tr formed on the substrate210, the floating diffusion region FD and the channel region CH formed within the substrate210between one side of the transfer transistor Tt and one side of the reset transistor Tr, and the reset voltage node Vr and a reset channel region CHr adjacent to the other side of the reset transistor Tr and formed within the substrate210. The floating diffusion region FD and the reset voltage node Vr may have the same depth and n-type impurities. The channel region CH and the reset channel region CHr may have the same depth and p-type impurities. The floating diffusion region FD and the reset voltage node Vr may be spaced apart from each other. The channel region CH and the reset channel region CHr may be contiguous within the substrate210under the reset transistor Tr without a boundary. The width, length and/or area size of a region Et in which the floating diffusion region FD vertically overlaps the transfer transistor Tt and the width, length and/or area size of a region Er in which the floating diffusion region FD vertically overlaps the reset transistor Tr may be the same.

FIGS. 5A to 5Dare longitudinal sectional views taken along line I-I′ ofFIG. 2Aor line II-II′ ofFIG. 2Bfor describing a method for forming an image sensor in accordance with an embodiment of the present invention.

Referring toFIG. 5A, the method for forming an image sensor in accordance with an embodiment of the present invention may include forming the photodiodes PD1and PD2and the pixel field region PF within the substrate210and forming the gate insulating layers221and222and gate electrodes231and232of the transfer transistors Tt1and Tt2on a surface of the substrate210.

In an embodiment of the present invention, the substrate210may have an epitaxial growth layer. For example, the method may include growing an epitaxial layer on a silicon wafer by performing an epitaxial growth process and forming the photodiodes PD1and PD2within the epitaxial growth layer. Forming the photodiodes PD1and PD2may include injecting n-type impurities, such as phosphorous (P) or arsenic (As), into the substrate210or the epitaxial growth layer. Forming the pixel field region PF may include injecting p-type impurities, such as boron (B), into the substrate210or the epitaxial growth layer.

Forming the gate insulating layers221and222may include oxidizing the surface of the substrate210by performing an oxidation process or forming silicon oxide on the substrate210by performing a deposition process. Forming the gate electrodes231and232may include forming one or more of doped polysilicon, silicide, metal, and a metal compound by performing a deposition process.

Referring toFIG. 5B, the method may include forming a mask pattern M exposing the region between the photodiodes PD1and PD2and forming an impurity injection region R by injecting both n-type impunities and p-type impurities into the substrate210using the mask pattern M and the gate electrodes231and232as an ion implantation mask. In the embodiment of the present invention, the p-type impurities may have a relatively smaller atom size or greater thermal diffusivity than the n-type impurities. For example, the p-type impurities may include boron (B), and the n-type impurities may include arsenic (As). In some embodiments of the present invention, the p-type impurities may include indium (In), and the n-type impurities may include antimony (Sb). The mask pattern M may include a photoresist. After the impurity injection process is performed, the mask pattern M may be removed.

Referring toFIG. 5C, the method may include diffusing the n-type impurities and p-type impurities of the impurity injection region R into the substrate210by performing an annealing process. The n-type impurities having a smaller thermal diffusivity, for example, arsenic (As) atoms may be diffused into the substrate210relatively shallowly and narrowly, thereby being capable of forming the floating diffusion region FD. The p-type impurities having a greater thermal diffusivity, for example, boron (B) atoms may be diffused into the substrate210relatively deeply and widely, thereby being capable of forming the channel region CH. The channel region CH may fully surround the lateral surfaces and bottom surface of the floating diffusion region FD so that the floating diffusion region FD is electrically insulated from the substrate210. The channel region CH may partially overlap the top corners of the photodiodes PD1and PD2. The regions of the photodiodes PD1and PD2overlapping the channel region CH may be inverted from an n-type conductive layer to a p-type conductive layer.

Thereafter, referring toFIG. 3A, the method may further include forming the interlayer dielectric layer240configured to cover the gate insulating layers221and222and gate electrodes231and232of the transfer transistors Tt1and Tt2on the substrate210. The interlayer dielectric layer240may include silicon oxide.

Referring toFIG. 5D, a method for forming an image sensor in accordance with an embodiment of the present invention may include forming the mask pattern M configured to expose the region between the photodiodes PD1and PD2and forming the impurity injection region R including a reserved floating diffusion region p-FD and a reserved channel region p-CH by injecting both the n-type impurities and the p-type impurities into the substrate210using the mask pattern M and the gate electrodes231and232as an ion implantation mask, compared toFIG. 5B. For example, the method may include injecting the p-type impurities into the substrate210deeper than the n-type impurities. Accordingly, the reserved channel region p-CH including the p-type impurities may be formed under the reserved floating diffusion region p-FD including the n-type impurities. Thereafter, the processes described with reference toFIGS. 5C and 3Amay be performed.

FIGS. 6A to 6Dare longitudinal sectional views taken along line I-I′ ofFIG. 2Aor line II-II′ ofFIG. 2Bfor describing a method for forming an image sensor in accordance with an embodiment of the present invention.

Referring toFIG. 6A, the method for forming an image sensor in accordance with an embodiment of the present invention may include forming the photodiodes PD1and PD2within the substrate210, forming a buffer layer215on the substrate210, and forming a mask pattern M on the buffer layer215. The buffer layer215may include silicon oxide.

Referring toFIG. 6B, the method may include forming an impurity injection region R by performing an ion implantation process using the mask pattern M as an ion implantation mask and using the buffer layer215as an ion implantation buffer layer. The ion implantation process may include injecting both n-type impurities having a relatively larger atom size and smaller thermal diffusivity and p-type impurities having a relatively smaller atom size and greater thermal diffusivity. Thereafter, the mask pattern M may be removed. In another embodiment of the present invention, referring toFIG. 5D, the n-type impurities and the p-type impurities may be injected into the substrate210so that they have different depths. For example, referring toFIG. 5D, the impurity injection region R including the reserved floating diffusion region p-FD adjacent to a surface of the substrate210and the reserved channel region p-CH under the reserved floating diffusion region p-FD may be formed.

Referring toFIG. 6C, the method may include forming the floating diffusion region FD and the channel region CH by diffusing the n-type impurities and p-type impurities of the reserved floating diffusion region p-FD into the substrate210by performing an annealing process. The inversion regions IR1and IR2which overlap the channel region CH and the photodiodes PD1and PD2may be formed. For example, the polarity such as, n type of the photodiodes PD1and PD2may be inverted to the polarity such as, p type of the channel region CH. Thereafter, the buffer layer215may be removed. The buffer layer215may be removed before the annealing process is performed.

Referring toFIG. 6D, the method may include forming the gate insulating layers221and222and gate electrodes231and232of the transfer transistors Tt1and Tt2on the substrate210. The gate insulating layers221and222and the gate electrodes231and232vertically partially overlap the photodiodes PD1and PD2and the pixel field region PF. For example, the gate insulating layer221and the gate electrode231are coextensive and extend partially over the photodiode PD1and the pixel field region PF. Likewise, the gate insulating layer222and the gate electrode232are coextensive and extend partially over the photodiode PD2and the pixel field region PF. Thereafter, referring toFIG. 3A, the method may further include forming the interlayer dielectric layer240configured to cover the gate insulating layers221and222and gate electrodes231and232of the transfer transistors Tt1and Tt2on the substrate210.

FIGS. 7A and 7Bare longitudinal sectional views taken along line I-I′ ofFIG. 2Aor line II-II′ ofFIG. 2Bfor describing methods for forming an image sensor in accordance with various embodiments of the present invention.

Referring toFIG. 7A, a method of forming an image sensor in accordance with an embodiment of the present invention may include forming the photodiodes PD1and PD2within the substrate210, forming an ion implantation mask Mi on the substrate210, and performing a pre-amorphization process of forming an amorphous region Ra within the substrate210by implanting ions. The pre-amorphization process may convert the substrate210of a single crystal state into a polycrystalline and amorphous state, thereby being capable of increasing a thermal diffusivity of impurities injected into the amorphous region Ra in a subsequent annealing process. That is, the annealing process can be enhanced so that the floating diffusion region FD and the channel region CH are formed deeper and wider. Thereafter, the method may include forming the image sensor ofFIG. 3Aby performing the processes described with reference toFIGS. 4A to 5C, orFIGS. 6A to 6D.

Referring toFIG. 7B, a method for forming an image sensor in accordance with an embodiment of the present invention may include forming the photodiodes PD1and PD2within the substrate210, forming the ion implantation mask Mi on the substrate210, and performing an ion implantation process of forming a cluster region Rc within the substrate210by implanting clustering ions. Thermal diffusivity of the impurities injected into the cluster region Rc can be increased. The clustering ions may include carbon (C). Thereafter, the method may include forming the image sensor ofFIG. 3Aby performing the processes described with reference toFIGS. 5A to 5C or 6A to 6D.

FIG. 8Ais a longitudinal sectional view taken along line I-I′ ofFIG. 2Aor line II-II′ ofFIG. 2Bfor describing a method for forming an image sensor in accordance with an embodiment of the present invention, andFIGS. 8B and 8Care longitudinal sectional views taken along line III-III′ ofFIG. 2Cfor describing methods for forming an image sensor in accordance with embodiments of the present invention.

Referring toFIG. 8A, a method for forming an image sensor may include forming the photodiodes PD1and PD2within the substrate210, forming the gate insulating layers221and222, the gate electrodes231and232, and the spacers251and252on the substrate210, forming the mask pattern M, and forming the impurity injection region R by implanting the n-type and p-type impurities into the substrate210between the spacers251and252. Thereafter, the method may include removing the mask pattern M and forming the floating diffusion region FD and channel region CH having the shape ofFIG. 3Bby thermally diffusing the n-type impurities and the p-type impurities within the impurity injection region R by performing an annealing process. In another embodiment of the present invention, referring toFIG. 5B, the impurity injection region R may include the reserved floating diffusion region p-FD and the reserved channel region p-CH under the reserved floating diffusion region p-FD.

Referring toFIG. 8B, a method for forming an image sensor in accordance with an embodiment of the present invention may include forming the photodiode PD within the substrate210, forming the gate insulating layer221and gate electrode231of the transfer transistor Tt and the gate insulating layer223and gate electrode233of the reset transistor Tr on the substrate210, forming the mask pattern and forming first and second impurity injection regions R1and R2by injecting n-type impurities and p-type impurities into the substrate210. The first impurity injection region R1may be formed within the substrate210between one side of the transfer transistor Tt and one side of the reset transistor Tr. The second impurity injection region R2may be formed within the substrate210adjacent to the other side of the reset transistor Tr. Thereafter, the method may include removing the mask pattern M and forming the floating diffusion region FD, channel region CH, reset voltage node Vr, and reset channel region CHr having the shape ofFIG. 4by thermally diffusing the n-type impurities and the p-type impurities within the first and the second impurity injection regions R1and R2by performing an annealing process.

Referring toFIG. 8C, a method for forming an image sensor in accordance with an embodiment of the present invention may include forming a first impurity injection region R1, including a reserved floating diffusion region p-FD and a reserved channel region p-CH under the reserved floating diffusion region p-FD, and a second impurity injection region R2, including a reserved reset voltage node p-Vr and a reserved reset channel region p-CHr under the reserved reset voltage node p-Vr, with reference toFIG. 5D.

FIG. 9is diagram schematically illustrating an electronic device including at least one of the image sensors in accordance with the various embodiments of the present invention.

Referring toFIG. 9, the electronic device including at least one of the image sensors, in accordance with the various embodiments of the present invention, may be or include a camera capable of capturing a still image or a moving image. The electronic device may include an optical system310or an optical lens, a shutter unit311, an image sensor300, a driving unit313and a signal processing unit312configured to control/drive the shutter unit311.

The optical system310guides image light that is, incident light from a subject to the pixel array (refer to100ofFIG. 1) of the image sensor300. The optical system310may include a plurality of optical lenses. The shutter unit311controls the light radiation period and light shield period of the image sensor300. The driving unit313controls the transmission operation of the image sensor300and the shutter operation of the shutter unit311. The signal processing unit312performs various types of signal processing on a signal output by the image sensor300. An image signal Dout after the signal processing is stored in a storage medium, such as memory, or is output to a monitor.

The image sensors in accordance with various embodiments of the present invention can have an excellent arrangement and a short channel length since they employ channel regions surrounding the floating diffusion regions. Accordingly, the image sensors can have faster operating speed without a malfunction.

The methods for forming an image sensor in accordance with various embodiments of the present invention can include forming the floating diffusion region and the channel region by performing one photolithography process and one annealing process. Accordingly, a process can be simplified, and the floating diffusion region and the channel region having a uniform shape can be formed without misalignment.

In the methods for forming an image sensor in accordance with various embodiments of the present invention, a process can be simplified since the size of the floating diffusion region and the channel region can be set through the annealing process.

A short channel can be implemented since the channel region can invert the photodiode.