IMAGE SENSING DEVICE

Image sensing devices are disclosed. In some implementations, an image sensing device may include a substrate having an upper surface and a lower surface, a photoelectric conversion device formed in the substrate and structured to convert incident light into an electrical signal carrying information associated with the incident light, and an isolation structure formed in the substrate along at least a side surface and a bottom surface of the photoelectric conversion device. The isolation structure comprises a first isolation region which extends from the upper surface of the substrate to a first depth in the substrate to surround the side surface of the photoelectric conversion device, and a second isolation region which is formed in the substrate below the bottom surface of the photoelectric conversion device, the second isolation region electrically connected with the first isolation region.

CROSS-REFERENCES TO RELATED APPLICATION

This patent document claims the priority and benefits of Korean application number 10-2021-0018444, filed on Feb. 9, 2021, which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The technology and implementations disclosed in this patent document generally relate to an image sensing device, more particularly to an image sensing device including an avalanche diode.

BACKGROUND

Time of flight (TOF) technology is a way of building up an image of a scene based on distance between the sensor and the subject by measuring the round trip time of a light signal provided by a light source.

Single-photon avalanche diode (SPAD) arrays are solid-state detectors that offer imaging capabilities at the level of individual photons. TOF sensors utilizing SPAD allow fast, accurate distance measurements.

SUMMARY

The technology disclosed in this patent document can be implemented in various embodiments to improve operational reliability of image sensing devices.

In some embodiments of the disclosed technology, an image sensing device may include a substrate having an upper surface and a lower surface, a photoelectric conversion device formed in the substrate and structured to convert incident light into an electrical signal carrying information associated with the incident light, and an isolation structure formed in the substrate along at least a side surface and a bottom surface of the photoelectric conversion device. The isolation structure comprises a first isolation region which extends from the upper surface of the substrate to a first depth in the substrate to surround the side surface of the photoelectric conversion device, and a second isolation region which is formed in the substrate below the bottom surface of the photoelectric conversion device, the second isolation region electrically connected with the first isolation region.

In some embodiments of the disclosed technology, an image sensing device may include a substrate having an upper surface and a lower surface, a photoelectric conversion device including a first impurity region having a first conductive type formed in the substrate and a second impurity region having a second conductive type to surround a side surface and a bottom surface of the first impurity region, a first isolation region configured to surround the side surface of the photoelectric conversion device, the first isolation region extending from the upper surface of the substrate to a first depth in the substrate, a third isolation region formed in the substrate, the third isolation region extending from the lower surface of the substrate toward a lower end of the first isolation region in the substrate, and a second isolation region formed in the substrate and aligned with the photoelectric conversion device, the second isolation region being in contact with the first isolation region and the third isolation region at both ends thereof.

In some embodiments of the disclosed technology, an image sensing device may include a substrate, a photoelectric conversion device and an isolation structure. The substrate may have an upper surface and a lower surface. The photoelectric conversion device may be formed at the substrate. The isolation structure may be formed at the substrate to surround a side surface and a bottom surface of the photoelectric conversion device. The isolation structure may include a first isolation region and a second isolation region. The first isolation region may make contact with the upper surface of the substrate to surround the side surface of the photoelectric conversion device. The second isolation region may be formed in the substrate to surround the bottom surface of the photoelectric conversion device. The second isolation region may be electrically connected with the first isolation region. The isolation structure may further include a third isolation region formed at the substrate and overlapped with the first isolation region. The third isolation region may include the other end configured to make contact with the lower surface of the substrate, and one end configured to make contact with the first isolation region and the second isolation region.

In some embodiments of the disclosed technology, an image sensing device may include a substrate, a photoelectric conversion device, a first isolation region, a third isolation region and a second isolation region. The substrate may have an upper surface and a lower surface. The photoelectric conversion device may include a first impurity region having a first conductive type formed at the substrate, and a second impurity region having a second conductive type configured to surround a side surface and a bottom surface of the first impurity region. The first isolation region may be configured to surround a side surface of the photoelectric conversion device. The first isolation region may include one end configured to make contact with the upper surface of the substrate. The third isolation region may be formed at the substrate. The third isolation region may include the other end configured to make contact with the lower surface of the substrate, and one end configured to make contact with the first isolation region. The second isolation region may be formed in the substrate to be overlapped with the photoelectric conversion device. The second isolation region may include both ends configured to make contact with the first isolation region and the third isolation region.

In some embodiments of the disclosed technology, the first isolation region and the second isolation region may be configured to isolate the photoelectric conversion devices including an avalanche diode to prevent an electrical crosstalk and to reduce a dark current rate. Particularly, an isolation voltage may be applied to the first isolation region and the second isolation region to maintain operational characteristics of the photoelectric conversion device, to effectively prevent the electrical crosstalk and to more reduce the dark current rate.

Further, the third isolation region may prevent an optical crosstalk between adjacent unit pixels. The first isolation region and the second isolation region may trap a dark current source, which may be caused by the third isolation region including a trench type isolation layer, to more decrease the dark current ratio.

As a result, the image sensing device may include the first to third isolation regions to have improved operational characteristics.

DETAILED DESCRIPTION

Features of the technology disclosed in this patent document are described by examples of an image sensing device.

The disclosed technology can be implemented in some embodiments to improve operational reliability of image sensing devices by, for example, reducing or minimizing an optical crosstalk and an electrical crosstalk in the image sensing device including an avalanche diode.

FIG. 1is an example configuration of an image sensing device based on some embodiments of the disclosed technology.

Referring toFIG. 1, an image sensing device ISD implemented based on some embodiments of the disclosed technology may measure a distance from an object1using a time of flight (TOF) technique. The image sensing device ISD may include a light source10, a lens module20, a pixel array30and a control circuit module40.

The light source10may emit light toward the object1. The light source10may generate light (or photons) having a specific wavelength such as infrared light or visible light. Examples of the light source10may include a laser diode, a light emitting diode (LED), a near infrared laser (NIR), a point light source, a white light lamp, a monochromatic illuminator, and a combination thereof. For example, the light source10may emit infrared light having a wavelength of about 800 nm to about 1,000 nm. As shown inFIG. 1, the image sensing device ISD may include one light source10. Alternatively, the image sensing device ISD may include a plurality of the light sources10arranged near or around the lens module20.

The lens module20may be used to converge light reflected from the object1onto unit pixels of the pixel array30. For example, the lens module20may include a condensing lens having a glass surface or plastic surface, a cylindrical optical element, or others. The lens module20may include a plurality of lenses arranged along an optical axis.

The pixel array30may include a plurality of unit pixels PX arranged in rows and columns in a two-dimensional matrix array.

Each of the unit pixels PX may convert light incident through the lens module20into an electrical signal corresponding to an intensity of the light. The pixel signal may include information corresponding to the distance between the pixel array30(or the light source10) and the object1, in addition to or instead of information about a color of the object1. Each of the unit pixels PX may include a photoelectric conversion device. The photoelectric conversion device may include an avalanche diode. For example, the photoelectric conversion device may include a single photon avalanche diode (SPAD).

In some implementations, the single photon avalanche diode may be a photosensitive P-N junction that is used as a photoelectric conversion device. The single photon avalanche diode may detect a single photon reflected from an object to generate a current pulse corresponding to the detected single photon. In SPAD, when the reverse bias is so high that an impact ionization occurs to cause an avalanche current to develop. A large avalanche of current carriers grows and can be triggered from as few as a single photon-initiated carrier. More specifically, an avalanche breakdown may be triggered by a single photon in Geiger mode where a reverse bias voltage is applied to generate the current pulse such that a voltage between a cathode and an anode is higher than a breakdown voltage may be applied. The avalanche breakdown may be generated at a depletion region in the single photon avalanche diode. When the reverse bias voltage is applied to the single photon avalanche diode increase an electric field, electrons are generated by the photons incident and create a strong electric field, causing the impact ionization to occur and thereby generating an electron-hole pair. In the single photon avalanche diode operated in the Geiger mode where the reverse bias voltage higher than the breakdown voltage is applied, carriers such as electrons or holes, which may be generated by the incident light, and the electrons and the holes, which may be generated by the impact ionization, collide against each other to generate numerous carriers. Therefore, even with a single photon, the avalanche breakdown may be triggered to generate a measurable current pulse.

The control circuit module40may control the light source10to emit the light toward the object1. The control circuit module40may operate the unit pixels PX of the pixel array30to process the pixel signal corresponding to the reflected light from the object1, thereby measuring the distance between the pixel array30(or the light source10) and a surface of the object1.

The control circuit module40may include a control circuit41, a light source driver42, a timing controller43and a readout circuit44.

The control circuit41may operate the unit pixels PX of the pixel array30in response to a timing signal provided by the timing controller43. For example, the control circuit41may generate a control signal for selecting and controlling at least one row line among a plurality of row lines. The control signal may include a demodulation control signal for generating a hole current in the substrate, a reset signal for controlling a reset transistor, a transmission signal for controlling a transmission of an optical charge accumulated in a detection node, a floating diffusion signal for providing an additional electric capacity in a high irradiance condition, a selection signal for controlling a selection transistor, for example.

The timing controller43may generate the timing signal for controlling the operations of the control circuit41, the light source driver42and the readout circuit44.

The readout circuit44may process pixel signal generated by the pixel array30based on control signals and/or instructions received from the timing controller43to generate pixel data (e.g., digital signals). The readout circuit44may include a correlated double sampler (CDS) for performing a correlated double sampling with respect to the pixel signals outputted from the pixel array30. In some implementations, the readout circuit44may include an analog-digital converter configured to convert output signals from the CDS into digital signals. Furthermore, the readout circuit44may include a buffer circuit configured to temporarily store the pixel data outputted from the analog-digital converter and to output the pixel data based on control signals and/or instructions received from the timing controller43.

As will be discussed below, the unit pixel implemented based on some embodiments of the disclosed technology can include the avalanche diode and an isolation structure configured to isolate the adjacent unit pixels from each other.

FIG. 2is a plan view illustrating a part of a pixel array based on some embodiments of the disclosed technology,FIG. 3is a cross-sectional view taken along a line I-I′ inFIG. 2, andFIG. 4is a cross-sectional view illustrating a unit pixel and movements of charges for generating an electrical crosstalk and a dark current based on some embodiments of the disclosed technology.

InFIG. 2andFIG. 3, a first direction D1, a second direction D2and a third direction D3may be substantially perpendicular to each other. For example, in an XYZ coordinate, the first direction D1may be an X-direction, the second direction D2may be a Y-direction, and a third direction D3may be a Z-direction.

In some implementations, a first conductive type and a second conductive type may be complimentary conductive types. For example, when the first conductive type may be a P type, the second conductive type may be an N type. In contrast, when the first conductive type may be the N type, the second conductive type may be the P type. In example embodiments, the first conductive type may be the P type and the second conductive type may be the N type.

Referring toFIGS. 2 and 3, the pixel array30of example embodiments may include a plurality of unit pixels PX sequentially arranged in a two-dimensional array. Each of the unit pixels PX may be used to measure a distance from an object using a time of flight (TOF) technique.

Each of the unit pixels PX may include a substrate100, a photoelectric conversion device110and an isolation structure120. The substrate100may have an upper surface S1and a lower surface S2. The photoelectric conversion device110may be formed at the substrate100. In some implementations, the photoelectric conversion device110may be formed in the substrate100such that an upper portion of the photoelectric conversion device110is at the upper surface S1of the substrate100. In one example, the upper portion of the photoelectric conversion device110is exposed through the upper surface S1of the substrate100. The isolation structure120may be formed at the substrate100to surround a side surface and a bottom surface of the photoelectric conversion device110.

The substrate100may include a bulk single-crystalline silicon wafer, a silicon-on-insulation (SOI) wafer, a compound semiconductor wafer such as Si—Ge, a wafer including a silicon epitaxial layer or others. For example, the substrate100may include a bulk single-crystalline silicon wafer doped with first conductive type impurities, for example, P type impurities.

Although not depicted in the drawings, the control circuit module40for controlling the photoelectric conversion device110may be formed on the upper surface S1of the substrate100. The lower surface S2of the substrate100may the incident light therethrough. Thus, a micro-lens130may be formed on the lower surface S2of the substrate100. Although not depicted in the drawings, an optical filter and/or a grid pattern may be formed on the lower surface S2of the substrate Sub.

The photoelectric conversion device110may include an avalanche diode. For example, the photoelectric conversion device110may include a single photon avalanche diode (SPAD).

In some implementations, the photoelectric conversion device110may include a first impurity region112having a first conductive type and a second impurity region114having a second conductive type. The first impurity region112may correspond to an anode of the single photon avalanche diode. The second impurity region114may correspond to a cathode of the single photon avalanche diode. The first impurity region112may be formed in the second impurity region114and may extend from the upper surface S1of the substrate100to a certain depth. The first impurity region112may have a plate shape. The second impurity region114may be formed in the substrate100and a portion of the second impurity region114may extend from the upper surface S1of the substrate100to a certain depth in the substrate100. The second impurity region114may be structured to surround a side surface and a bottom surface of the first impurity region112. The second impurity region114may have a cylindrical shape and may be in contact with the bottom surface of the first impurity region. Thus, the second impurity region114may have a planar annular shape when viewed from the upper surface S1of the substrate100. The second impurity region114may have a planar plate shape when viewed from the lower surface S2of the substrate100. The second impurity region114may have a planar U shape.

The photoelectric conversion device110may further include a guard ring116formed in the second impurity region114. The guard ring116may be arranged at the upper surface S1of the substrate100to surround the side surface of the first impurity region112. The guard ring116may be in contact with the side surface of the first impurity region112to surround the first impurity region112. A depth of the guard ring116measured from the upper surface S1of the substrate100may be greater than a depth of the first impurity region112and less than a depth of the second impurity region114. The guard ring116may include an impurity region having the first conductive type. The guard ring116with the impurity region having the first conductive type may have a doping concentration lower than a doping concentration of the first impurity region112. The guard ring116may include a trench type isolation layer. The guard ring116with the trench type isolation layer may include a trench formed at the upper surface S1of the substrate100, and an isolation layer formed in the trench.

In some implementations, each of the first impurity region112and the second impurity region114may include a single impurity region. In other implementations, the first impurity region112may include a plurality of impurity regions that includes the first conductive type impurity and is stacked on top of one another along the third direction D3. In some implementations, the second impurity region114may include a plurality of impurity regions that includes the second conductive type impurity and is stacked on top of one another along the third direction D3. The impurity regions of the first impurity region112stacked in the third direction D3may have different doping concentrations. Likewise, the impurity regions of the second impurity region114stacked in the third direction D3may have different doping concentrations. For example, the doping concentration may decrease from the upper surface S1toward the lower surface S2in the substrate100to prevent or reduce a punch-through effect that would have been caused by an expansion of a depletion region, thereby improving breakdown voltage characteristics.

The isolation structure120may include a first isolation region122, a second isolation region124and a third isolation region126that are structured to isolate the unit pixels PX from each other or reduce an optical and/or electrical crosstalk between adjacent unit pixels PXs. In each of the unit pixels PX, the first isolation region122may be structured to surround the side surface of the photoelectric conversion device110. The second isolation region124may be structured to surround the bottom surface of the photoelectric conversion device110. Thus, the photoelectric conversion device110may be electrically isolated or reduce an optical and/or electrical crosstalk between adjacent unit pixels PXs by the first isolation region122and the second isolation region124.

The first isolation region122and the second isolation region124may prevent or reduce an electrical crosstalk between the adjacent unit pixels PX. In some implementations, the first impurity region122and the second impurity region124may trap electrons that would have caused a dark current, thereby reducing a dark current rate (DCR). The first isolation region122and the second isolation region124may include an impurity region having the second conductive type impurity, which is the same as the second conductive type of the second impurity region114in the photoelectric conversion device110. The first isolation region122may have a doping concentration greater than a doping concentration of the second isolation region124. The second isolation region124may be electrically connected with the first isolation region122.

In order to effectively prevent or reduce the electrical crosstalk and effectively decrease the dark current rate, the first isolation region122and the second isolation region124may be configured to receive an isolation voltage VISOfrom the control circuit module40on the upper surface S1of the substrate100. When the first isolation region122and the second isolation region124include the impurity region having the second conductive type, the isolation voltage VISOmay be a positive voltage. For example, the isolation voltage VISOmay be higher than a ground voltage GND and less than a breakdown voltage of the photoelectric conversion device110. In contrast, when the first isolation region122and the second isolation region124may include the impurity region having the first conductive type, the isolation voltage VISOmay be a negative voltage. For example, the isolation voltage VISOmay have an absolute value higher than the ground voltage GND and less than the breakdown voltage of the photoelectric conversion device110.

The isolation voltage VISOmay be applied to the first isolation region122and the second isolation region124to prevent an avalanche current between the substrate100and the first and second isolation regions122and124. Even if the isolation voltage VISOis applied to the first isolation region122and the second isolation region124, the isolation voltage VISOmay have no influence on operational characteristics of the photoelectric conversion device110adjacent to the first isolation region122and the second isolation region124, i.e., the single photon avalanche diode.

In some implementations, each of the first isolation region122and the second isolation region124may include one impurity region. In other implementations, each of the first isolation region122and the second isolation region124may include a plurality of impurity regions that includes the second conductive type impurity and is stacked on top of one another along the third direction D3.

The first isolation region122may have one end formed at or near the upper surface S1of the substrate100. The first isolation region122may extends from the upper surface S1of the substrate100in the third direction D3to surround the side surface of the photoelectric conversion device110. In one example, the first isolation region122may have a pipe shape. In this case, a horizontal cross-section of the first isolation region122may have a ring shape and a vertical cross-section of the first isolation region122may have a bar shape. Side surfaces of the first isolation region122may be spaced apart from the side surfaces of the photoelectric conversion device110facing the side surfaces of the first isolation region122by a first gap140along the first and second directions D1and D2, thereby preventing or reducing a punch-through effect between the first isolation region122and the photoelectric conversion device110. The first gap140may be sufficiently large such that the depletion region caused by the first isolation region122is not connected with the depletion region caused by the second impurity region114of the photoelectric conversion device110. The first isolation region122may have a depth from the upper surface S1of the substrate100greater than a depth of the photoelectric conversion device110. That is, the depth of the first isolation region122may be greater than the depth of the second impurity region114of the photoelectric conversion device110.

The second isolation region124may be formed in the substrate100and in contact with the first isolation region122at one end and the third isolation region126at the other end. The second isolation region124may be aligned with the photoelectric conversion device110in the third direction D3and may be structured to surround the bottom surface of the photoelectric conversion device110. In one example, the second isolation region124may have a plate shape. The second isolation region124may have an upper surface spaced apart by a second gap150from the bottom surface of the photoelectric conversion device110. The second gap150may prevent or reduce the punch-through effect between the second isolation region124and the photoelectric conversion device110. The second gap150may be sufficiently large such that the depletion region caused by the second isolation region124is not connected with the depletion region caused by the second impurity region114of the photoelectric conversion device110. In order to effectively prevent or reduce the punch-through effect between the second isolation region124and the photoelectric conversion device110, the second gap150may be wider than the first gap140.

The third isolation region126may prevent or reduce an optical crosstalk between the adjacent unit pixels PX. The third isolation region126may include a trench type isolation layer. The trench type isolation layer may include an isolation trench formed at the lower surface S2of the substrate100, and a gap-filling insulation layer formed in the trench. The trench type isolation layer may further include a dielectric layer having a high dielectric constant inserted between the isolation trench and the gap-filling insulation layer to suppress the generation of the dark current caused by the third isolation region126. The dielectric layer having the high dielectric constant may a plurality of dipoles for trapping charges acting as a source of the dark current.

The third isolation region126may have its lower at the lower surface S2of the substrate and may be in contact with the first isolation region122and the second isolation region124at its upper end. The third isolation region126may be overlapped with the first isolation region122in the third direction D3. That is, the third isolation region126may have a pipe shape. A horizontal cross-section of the third isolation region126may have an annular shape and a vertical cross-section of the third isolation region126may have a bar shape. The third isolation region126may have a depth from the lower surface S2of the substrate100that is sufficiently deep to prevent the optical crosstalk between the adjacent unit pixels PX.

In some implementations, the upper end of the third isolation region126may be in contact with the lower end of the first isolation region122. In other implementations, in order to effectively prevent or reduce the optical crosstalk, the upper end of the third isolation region126may be extended into the first isolation region122. In this case, the first isolation region122may be structured to surround a side surface and a top surface of the upper end of the third isolation region126.

In some example embodiments of the disclosed technology, the first isolation region122and the second isolation region124may be configured to isolate the photoelectric conversion devices110including the avalanche diode to prevent or reduce the electrical crosstalk, thereby reducing the dark current rate. In some implementations, the isolation voltage VISOmay be applied to the first isolation region122and the second isolation region124to maintain the operational characteristics of the photoelectric conversion device110, effectively preventing or reducing the electrical crosstalk and decreasing the dark current rate.

Referring toFIG. 4, electrons (A and B inFIG. 4) may be generated by converting light incident upon a first depletion region112A caused by the first impurity region112and a second depletion region114A caused by the second impurity region114in the photoelectric conversion device110. Those electrons may move into the second impurity region114of the adjacent photoelectric conversion device110, generating the electrical crosstalk. In some implementations, electrons may be generated by incident light or a defect in a junction between the first impurity region112and the second impurity region114in the photoelectric conversion device110, i.e., a P-N junction. Those electrons may also move into the second impurity region114of the photoelectric conversion device110, generating the electrical crosstalk. However, the image sensing device based on some embodiments of the disclosed technology may release electric charges that are generated by light incident upon the first depletion region112A and the second depletion region114A and electric charges that are generated at the P-N junction due to the incident light or the internal defects, from the first and second isolation regions122and124to which the isolation voltage VISOis applied, thereby preventing or reducing the electrical crosstalk.

In some implementations, the third isolation region126may prevent or reduce the optical crosstalk between the adjacent unit pixels. The first isolation region122and the second isolation region124may trap electric charges corresponding to the dark current, which may be caused by the third isolation region126including the trench type isolation layer, thereby further decreasing the dark current rate.

ReferringFIG. 4, electrons (C inFIG. 4) may be generated at an interface of the third isolation region126including the trench type isolation layer to prevent the optical crosstalk. Those electrons may move into the photoelectric conversion device110, increasing the dark current rate. However, the image sensing device based on some embodiments of the disclosed technology may release electric charges that are be generated in forming the third isolation region126, from the first and second isolation regions122and124to which the isolation voltage VISOis applied, decreasing the dark current rate.

As a result, the first to third isolation regions122,124and126allow the image sensing device to have improved operational characteristics.