Image sensor, integrated chip, and method for forming image sensor

Abstract

Various embodiments of the present invention relate to an image sensor having a substrate including a plurality of sidewalls, the plurality of sidewalls defining a plurality of protrusions along a first side of the substrate. The substrate has a first refractive index. A photodetector is disposed within the substrate and below the plurality of protrusions. A plurality of microlenses overlie the first side of the substrate. The microlenses have a second refractive index that is smaller than the first refractive index. The microlenses are respectively disposed laterally between a pair of adjacent protrusions among the plurality of protrusions and directly contact the pair of adjacent protrusions. In addition, the microlenses each include a convex upper surface.

Description

Technical Field

[0001] The embodiments of the present invention relate to an image sensor, an integrated chip, and a method for forming an image sensor. Background Art

[0002] Many modern electronic devices (e.g., digital cameras, optical imaging devices, etc.) include image sensors. Image sensors convert optical images into digital data that can be represented in the form of digital images. Image sensors include an array of pixel sensors, which are unit devices used to convert optical images into digital data. Some types of pixel sensors include charge-coupled device (CCD) image sensors and complementary metal-oxide-semiconductor (CMOS) image sensors (CIS). Compared with CCD pixel sensors, CIS is favored due to its low power consumption, small size, fast data processing, direct data output, and low manufacturing cost. Summary of the invention

[0003] Some embodiments of the present application provide an image sensor, comprising: a substrate comprising a plurality of sidewalls, the plurality of sidewalls defining a plurality of protrusions along a first side of the substrate, wherein the substrate has a first refractive index; a photodetector disposed within the substrate and below the plurality of protrusions; and a plurality of microlenses overlying the first side of the substrate, wherein the microlenses have a second refractive index smaller than the first refractive index, wherein the microlenses are respectively disposed laterally between and in direct contact with an adjacent pair of protrusions among the plurality of protrusions, and wherein the microlenses respectively include a convex upper surface.

[0004] In addition, other embodiments of the present application provide an integrated chip, comprising: a substrate, comprising a plurality of first protrusions along the back side of the substrate, wherein the substrate comprises a first material having a first refractive index; an internal connection structure, arranged along the front side of the substrate; a photodetector, arranged in the substrate and located under the plurality of first protrusions; a passivation layer, arranged on and between the plurality of first protrusions, wherein the passivation layer comprises a plurality of second protrusions along the upper surface of the passivation layer, wherein the plurality of second protrusions are different from the plurality of first protrusions, wherein the passivation layer comprises a second material having a second refractive index, which is different from the first refractive index; and a filter, overlying the passivation layer.

[0005] In addition, other embodiments of the present application provide a method for forming an image sensor, comprising: performing an ion implantation process to define a photodetector within a substrate; etching a first side of the substrate to define a plurality of protrusions overlying the photodetector; depositing a dielectric layer over the plurality of protrusions, wherein the dielectric layer comprises a first material; depositing an anti-reflective coating layer over the dielectric layer, wherein the anti-reflective coating layer comprises a second material different from the first material; performing a first patterning process on the anti-reflective coating layer; and performing a second patterning process on the dielectric layer and the anti-reflective coating layer to define a plurality of microlenses each having a concave upper surface, wherein the dielectric layer is etched at a first rate during the second patterning process and the anti-reflective coating layer is etched at a second rate during the second patterning process, wherein the first rate is greater than the second rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The various aspects of the present invention will be best understood by reading the following detailed description in conjunction with the accompanying drawings. Note that, in accordance with standard practice in the industry, various features are not drawn to scale. In fact, the size of the various features may be arbitrarily increased or reduced for clarity of discussion.

[0007] Figure 1 Cross-sectional views illustrating some embodiments of an image sensor including a substrate having a plurality of protrusions and a plurality of microlenses disposed over the protrusions and laterally spaced apart between the protrusions.

[0008] Figure 2 illustrate Figure 1 Cross-sectional views of some alternative embodiments of image sensors are shown in which a plurality of semiconductor devices are disposed on a front side surface of a substrate.

[0009] FIG. 3A to FIG. 3B illustrate Figure 2 Cross-sectional views of some alternative embodiments of image sensors are shown in which a filter overlies the plurality of microlenses.

[0010] Figures 4 to 9 Cross-sectional views illustrating some embodiments of a method of forming an image sensor including a substrate having a plurality of protrusions and a plurality of microlenses disposed over the protrusions and laterally spaced apart between the protrusions.

[0011] Fig.10 A method is described in a flow chart format that illustrates some embodiments of forming an image sensor including a substrate having a plurality of protrusions and a plurality of microlenses disposed over the protrusions and laterally spaced apart between the protrusions. DETAILED DESCRIPTION

[0012] The present invention provides many different embodiments or examples to implement different features of the present invention. Specific examples of components and arrangements are described below to make the present invention concise. Of course, these are only examples and are not intended to be limiting. For example, in the following description, a first feature formed on or formed on a second feature may include an embodiment in which the first feature and the second feature are formed in direct contact, and may also include an embodiment in which an additional feature may be formed between the first feature and the second feature so that the first feature and the second feature may not be in direct contact. In addition, the present invention may reuse reference numbers and / or letters in various examples. This repetition is for the purpose of simplicity and clarity, and does not indicate the relationship between the various embodiments and / or configurations discussed by itself.

[0013] Additionally, for ease of description, spatially relative terms, such as "beneath," "below," "lower," "above," "upper," etc., may be used herein to describe the relationship of one element or feature to another element or feature, 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 device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

[0014] A CMOS image sensor (CIS) generally includes an array of pixel regions, each of which has a photodetector arranged in a semiconductor substrate. Filters (e.g., color filters, infrared (IR) filters, etc.) are arranged on the photodetectors and are configured to filter incident light provided to different photodetectors in the CIS. After receiving the light, the photodetector is configured to generate an electrical signal corresponding to the received light. The signal processing unit can process the electrical signal from the photodetector to determine the image captured by the CIS. Quantum efficiency (QE) is the ratio of the number of photons used for the electrical signal generated by the photodetector in the pixel region to the number of photons incident on the pixel region. It should be understood that the QE of the CIS can be improved using an on-chip absorption enhancement structure.

[0015] The absorption enhancement structure may include a plurality of protrusions arranged along the surface of the semiconductor substrate. The absorption enhancement structure may increase absorption by reducing reflection of incident radiation. In addition, a passivation layer overlies the absorption enhancement structure and fills the grooves between the plurality of protrusions. During the formation of the passivation layer on the absorption enhancement structure, an anti-reflective coating (ARC) layer is formed on the passivation layer. Subsequently, the ARC layer and the passivation layer are etched at the same rate until the top surface of the protrusion is reached, so that the passivation layer has a substantially flat top surface. However, when the incident radiation passes through the substantially flat top surface of the passivation layer and reaches the plurality of protrusions, the incident radiation may be reflected away from the sidewalls of the protrusions away from the underlying photodetector. This may be due to the fact that the incident light travels along a path substantially perpendicular to the substantially flat top surface of the passivation layer and cannot be focused toward the underlying photodetector. The reflected radiation may be directed toward an adjacent underlying photodetector, causing crosstalk between the photodetectors, and / or reflected away from the pixel area. Additionally, the reflected radiation can be directed away from the semiconductor substrate, which can reduce the incident radiation disposed on the underlying photodetector. This can partially reduce the QE of the underlying photodetector.

[0016] Therefore, some embodiments of the present invention are directed to an image sensor, comprising: a substrate having a plurality of protrusions; and a plurality of microlenses, each having a convex upper surface, overlying the protrusions and spaced laterally between the protrusions. For example, during the manufacture of the image sensor, a photodetector is formed in the substrate and a plurality of protrusions are formed along the back surface of the substrate. A passivation layer is formed over the plurality of protrusions so that the passivation layer fills a plurality of grooves disposed between the plurality of protrusions. An ARC layer is formed over the passivation layer, and the ARC layer is partially etched until the upper surface of the passivation layer is reached, thereby leaving at least a portion of the ARC layer on the passivation layer. In addition, one or more highly selective etching processes are performed on the ARC layer and the passivation layer so that the passivation layer is etched at a higher rate than etching the ARC layer. This partially defines a plurality of microlenses over the plurality of protrusions so that the microlenses are disposed between each pair of adjacent protrusions and each microlens has a convex upper surface. Since the upper surface is convex, the microlens is configured to focus incident radiation toward a focal point between each pair of adjacent protrusions, thereby reducing reflection of the incident radiation and increasing the incident radiation directed toward the photodetector. This in turn can improve the QE of the image sensor.

[0017] Figure 1 Cross-sectional views illustrating some embodiments of an image sensor 100 that includes a substrate 104 having a plurality of protrusions 110 and a plurality of microlenses 112 disposed over the protrusions 110 and laterally spaced apart between the protrusions 110 .

[0018] The image sensor 100 includes an interconnect structure 102 disposed along a front side 104f of a substrate 104. In some embodiments, the substrate 104 includes any semiconductor body (e.g., bulk silicon, epitaxial silicon, another suitable semiconductor material, etc.) and / or has a first doping type (e.g., p-type doping). A photodetector 108 is disposed within the substrate 104 and is configured to convert incident electromagnetic radiation 114 (e.g., photons) into electrical signals (i.e., generate electron-hole pairs from the incident electromagnetic radiation 114). The photodetector 108 includes a second doping type (e.g., n-type doping) that is opposite to the first doping type. In some embodiments, the first doping type is n-type and the second doping type is p-type, or vice versa. In other embodiments, the photodetector 108 may be configured as and / or may include a photodiode. An isolation structure 106 is disposed within the substrate 104 and extends from the front side 104f of the substrate 104 to a point above the front side 104f. In some embodiments, the isolation structure 106 may include a dielectric material (eg, silicon dioxide, silicon nitride, silicon carbide, etc.) and / or may be configured as a shallow trench isolation (STI) structure, a deep trench isolation (DTI) structure, or another suitable isolation structure.

[0019] The back side 104b of the substrate 104 is disposed opposite to the front side 104f of the substrate 104. The back side 104b of the substrate 104 includes an uneven surface that defines a plurality of protrusions 110 arranged in a periodic pattern. Thus, the protrusions 110 may be or include the same material as the substrate 104 (e.g., silicon). The plurality of protrusions 110 are laterally separated from each other by grooves within the back side 104b of the substrate 104. The plurality of protrusions 110 each include opposing angled sidewalls. For example, the protrusions 110 of the substrate 104 are configured to increase the light receiving surface area for incident electromagnetic radiation 114 disposed on the photodetector 108. This may, in part, improve the sensitivity and / or quantum efficiency (QE) of the image sensor 100.

[0020] In addition, a plurality of microlenses 112 are disposed in grooves located laterally between the protrusions 110, so that one of the microlenses 112 is disposed laterally between a corresponding pair of protrusions 110. In some embodiments, for example, the microlenses 112 may be or include a dielectric material (e.g., silicon dioxide) and / or may have a first refractive index. It should be understood that other materials for the microlenses 112 are also within the scope of the present invention. In other embodiments, the substrate 104 includes a semiconductor material (e.g., silicon) different from the dielectric material of the microlenses 112, and / or has a second refractive index different from the first refractive index. It should be understood that other materials for the substrate 104 are also within the scope of the present invention. In some embodiments, the second refractive index is greater than the first refractive index. In some embodiments, the microlenses 112 respectively include microlens protrusions 112p conformal to the sidewalls of the protrusions 110, and fill the grooves between the protrusions 110. In other embodiments, the microlenses 112 directly contact the protrusions 110. Each of the micro lenses 112 includes a convex upper surface 112us that is curved outwardly in a direction away from the protrusion 110 and / or is rounded. Figure 1 As illustrated in FIG. 1 , incident electromagnetic radiation 114 (as illustrated by the arrow) enters the microlens 112 through the convex upper surface 112us. Due to the convex upper surface 112us of each microlens 112, the incident electromagnetic radiation 114 is significantly bent toward a focal point 119 located below the convex upper surface 112us and / or presents an angle toward the focal point 119. The focal point 119 is disposed along a focal plane 120, which is vertically spaced apart from the top surface 110ts of the protrusion 110 by a first height h1 and vertically spaced apart from the bottom surface 110bs of the protrusion by a second height h2. In some embodiments, the first height h1 is greater than the second height h2. In these embodiments, this mitigates the incident electromagnetic radiation 114 from being reflected off the sidewalls of the protrusion 110 in a direction away from the photodetector 108. In other embodiments, because the second height h2 is less than the first height h1, the incident angle θ1 of the incident electromagnetic radiation 114 on the sidewall of the protrusion 110 is significantly small, so the light is not reflected away from the substrate 104. Other electromagnetic radiation (not shown) that is not parallel to the incident electromagnetic radiation 114 and enters the microlens 112 is refracted as described above and intersects other focal points along the focal plane 120.

[0021] In addition, after the incident electromagnetic radiation 114 presents an angle toward the focal point 119, it may pass over the sidewalls of the protrusion 110. Because the microlens 112 has a first refractive index less than a second refractive index of the underlying protrusion 110 in some embodiments, the incident electromagnetic radiation 114 will be refracted away from the corresponding normal axis 122 and toward the photodetector 108. In other words, the lower refractive index of the microlens 112 relative to the protrusion 110 causes the incident electromagnetic radiation 114 to have a refraction angle θ2 less than the corresponding incident angle θ1, thereby focusing the incident electromagnetic radiation 114 toward the photodetector 108. This may increase the absorption of the incident electromagnetic radiation 114 by the substrate 104 (e.g., by reducing reflection of the incident electromagnetic radiation 114 away from the protrusion 110). Increasing the absorption of the incident electromagnetic radiation 114 increases the QE of the photodetector 108, thereby improving the performance of the image sensor 100.

[0022] Figure 2 Description and Figure 1 Alternative embodiments of image sensor 100 are shown corresponding to cross-sectional views of some embodiments of image sensor 200 .

[0023] In some embodiments, the image sensor 200 includes a substrate 104 overlying an interconnect structure 102. The image sensor 200 may be configured as a back-side illuminated CMOS image sensor (BSI-CIS). A plurality of semiconductor devices 212 are disposed within the interconnect structure 102 and are disposed along a front side 104f of the substrate 104. In some embodiments, the semiconductor device 212 may be configured as a pixel device that may output and / or process an electrical signal generated by the photodetector 108. For example, the semiconductor device 212 may be configured as a transfer transistor, a source follower transistor, a row select transistor, and / or a reset transistor. It should be understood that semiconductor devices 212 configured as other semiconductor devices are also within the scope of the present invention. In addition, the semiconductor devices 212 may each include: a gate structure 216 disposed along the front side 104f of the substrate 104; and a sidewall spacer structure 214 disposed along the sidewall of the gate structure 216. In another embodiment, the gate structure 216 includes a gate dielectric layer and a gate electrode, wherein the gate dielectric layer is disposed between the substrate 104 and the gate electrode.

[0024] The interconnect structure 102 may include an interconnect dielectric structure 206, a plurality of conductive wires 208, and a plurality of conductive vias 210. In some embodiments, the interconnect dielectric structure 206 includes one or more inter-level dielectric (ILD) layers, which may be or include an oxide (e.g., silicon dioxide), fluorosilicate glass, phosphate glass (e.g., borophosphosilicate glass), another suitable dielectric material, or any combination of the foregoing materials. It should be understood that the interconnect dielectric structure 206 including other suitable materials is also within the scope of the present invention. The conductive wires 208 and the conductive vias 210 are disposed within the interconnect dielectric structure 206 and are configured to electrically couple devices disposed within the image sensor 200 to each other and / or to another integrated chip (not shown). In some embodiments, for example, the conductive wires 208 and / or the conductive vias 210 may be or include copper, aluminum, titanium nitride, tantalum nitride, tungsten, another conductive material, or any combination of the foregoing materials. It should be understood that the conductive wires 208 and / or the conductive vias 210 comprising other suitable materials are also within the scope of the present invention.

[0025] In some embodiments, the substrate 104 may be any semiconductor body (e.g., bulk silicon, another suitable semiconductor material, etc.) and / or have a first doping type (e.g., p-type doping). The pixel region 202a and the pixel region 202b are laterally separated from each other by a plurality of isolation structures 106. In some embodiments, the plurality of isolation structures 106 may be configured as an STI structure, a DTI structure, a back-side deep trench isolation (BDTI) structure, another suitable isolation structure, or any combination of the aforementioned isolation structures. In other embodiments, the isolation structure 106 may be or include silicon dioxide, silicon nitride, silicon carbide, etc. In addition, the photodetector 108 is disposed in each of the pixel region 202a and the pixel region 202b. For example, the photodetector 108 may include a second doping type (e.g., n-type doping) that is opposite to the first doping type. It should be understood that a photodetector 108 and / or substrate 104 including another doping type is also within the scope of the present invention.

[0026] In some embodiments, the photodetector 108 may be configured to generate an electrical signal from near infrared (NIR) radiation of electromagnetic radiation included in a first wavelength range. For example, the first wavelength range may be in the range of about 850 nanometers to 940 nanometers. It should be appreciated that other values ​​of the first wavelength range are also within the scope of the present invention. The substrate 104 has a thickness Ts defined between the front side 104f of the substrate 104 and the back side 104b of the substrate 104. In some embodiments, the thickness Ts is in the range of about 4 microns to 6 microns. It should be appreciated that other values ​​of the thickness Ts are also within the scope of the present invention. The thickness Ts of the substrate 104 is selected to ensure high QE for the first wavelength range. For example, if the thickness Ts of the substrate 104 is thin (e.g., less than about 4 microns), the photodetector 108 will have a poor NIR light QE, which may weaken the phase detection capability. Furthermore, if the thickness Ts of the substrate 104 is thick (eg, greater than about 6 microns), the QE of NIR light may not be improved and the placement of pixel devices (eg, contact regions, isolation structures, and / or transfer transistors) may be negatively impacted.

[0027] The back side 104b of the substrate 104 includes a plurality of protrusions 110, and a plurality of microlenses 112 are disposed between pairs of adjacent protrusions 110. The microlenses 112 each have a convex upper surface 112us configured to direct incident radiation toward the underlying photodetector 108, such as Figure 1 This will increase the QE of photodetector 108, thereby improving the performance of image sensor 200.

[0028] In other embodiments, the plurality of microlenses 112 may be configured as and / or referred to as a passivation layer that extends laterally continuously across the back side 104b of the substrate 104. In these embodiments, the passivation layer overlies each protrusion 110 and includes a plurality of upper convex protrusions 112up spaced laterally between pairs of adjacent protrusions 110 and includes a plurality of lower protrusions 112lp disposed below the upper convex protrusions 112up. The lower protrusions 112lp directly contact the sidewalls of the protrusions 110. Furthermore, in some embodiments, the passivation layer may extend laterally continuously across the protrusions 110 along an uninterrupted path.

[0029] Figure 3A Description and Figure 2 Alternative embodiments of image sensor 200 are shown corresponding to cross-sectional views of some embodiments of image sensor 300 a .

[0030] The image sensor 300a includes an upper dielectric layer 302 overlying the microlenses 112 and the back side 104b of the substrate 104. In some embodiments, for example, the upper dielectric layer 302 can be or include a plasma-enhanced oxide (PEOX) layer, silicon dioxide, or another suitable dielectric material. It should be understood that other suitable materials for the upper dielectric layer 302 are also within the scope of the present invention. In addition, a plurality of filters 304 (e.g., color filters, infrared (IR) filters, etc.) overly the upper dielectric layer 302. The plurality of filters 304 are each configured to transmit incident radiation of a specific wavelength. For example, a first filter can transmit radiation having a wavelength within a first range, while a second filter adjacent to the first filter can transmit radiation having a wavelength within a second range different from the first range. In other embodiments, for example, the filters 304 may be configured as color filters, wherein a first filter is configured to transmit a first color (e.g., green light) and an adjacent second filter is configured to transmit a second color different from the first color (e.g., blue light). In addition, a plurality of upper lenses 306 are disposed above the plurality of filters 304. Respective upper lenses of the upper lenses 306 are laterally aligned with the filters 304 and overlie the pixel regions 202a, 202b. The plurality of upper lenses 306 are configured to focus incident electromagnetic radiation toward the photodetector 108, thereby further improving the QE of the photodetector and the performance of the image sensor 300a.

[0031] The photodetector 108 is configured to generate an electrical signal from electromagnetic radiation having a wavelength λ. In some embodiments, the wavelength λ may include near infrared (NIR) radiation, which includes electromagnetic radiation in the range of about 850 nanometers to 940 nanometers. It should be understood that other values ​​of the wavelength λ are also within the scope of the present invention. In other embodiments, the height hp of the protrusion 110 may be greater than about λ / 2.5, thereby increasing the light receiving surface area for incident electromagnetic radiation disposed on the substrate 104. For example, the height hp may be greater than about 340 nanometers. It should be understood that other values ​​of the height hp are also within the scope of the present invention. This partially improves the sensitivity and / or QE of the image sensor 300a. A distance d1 is defined between the top surfaces of two adjacent protrusions 110. In other embodiments, the distance d1 may be greater than about λ / 2, thereby increasing the light receiving surface area for incident electromagnetic radiation disposed on the substrate 104. For example, the distance d1 may be greater than about 425 nanometers. It should be understood that other values ​​of the distance d1 are also within the scope of the present invention. This partially further improves the sensitivity and / or QE of the image sensor 300a. Since height hp is greater than λ / 2.5 and distance d1 is greater than about λ / 2, absorption of incident radiation having wavelength λ by substrate 104 is increased while reflection of incident radiation having wavelength λ away from photodetector 108 is reduced. In some embodiments, distance d1 is greater than height hp.

[0032] Figure 3B Description and Figure 3A Some alternative embodiments of the image sensor 300a are shown as cross-sectional views of some embodiments of the image sensor 300b, in which the upper dielectric layer 302 is omitted. In these embodiments, the plurality of filters 304 directly contacts the plurality of microlenses 112.

[0033] Figures 4 to 9 Cross-sectional views 400 to 900 illustrate some embodiments of a method of forming an image sensor according to the present invention, the image sensor comprising a substrate having a plurality of protrusions and a plurality of microlenses disposed on the protrusions and spaced apart between the protrusions. Figures 4 to 9 400 to 900, but it should be understood that Figures 4 to 9 The structure shown in is not limited to the method, but can exist independently of the method. Figures 4 to 9 It is described as a series of actions, but it should be understood that these actions are not restrictive, but the order of actions can be changed in other embodiments, and the disclosed method is also applicable to other structures. In other embodiments, some actions described and / or described can be omitted in whole or in part.

[0034] like Figure 4As illustrated in the cross-sectional view 400 of , a substrate 104 is provided, and an isolation structure 106 is formed on the front side 104f of the substrate 104. In some embodiments, for example, the substrate 104 can be a bulk substrate (e.g., a bulk silicon substrate), a silicon-on-insulator (SOI) substrate, or another suitable substrate. It should be understood that other materials for the substrate 104 are also within the scope of the present invention. In some embodiments, before forming the isolation structure 106, a first implantation process is performed to dope the substrate 104 with a first doping type (e.g., p-type). In some embodiments, the process of forming the isolation structure 106 may include: selectively etching the substrate 104 to form a trench in the substrate 104 extending from the front side 104 f of the substrate 104 into the substrate 104; and filling the trench with a dielectric material (e.g., chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), thermal oxidation, etc.) (e.g., by chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), thermal oxidation, etc.). In other embodiments, the substrate 104 is selectively etched by forming a masking layer (not shown) on the front side 104 f of the substrate 104 and then exposing the substrate 104 to one or more etchants configured to selectively remove unmasked portions of the substrate 104.

[0035] In addition, if Figure 4 As shown in , a photodetector 108 is formed within a substrate 104. In some embodiments, the photodetector 108 includes a region of the substrate 104 that includes a second doping type (e.g., n-type) that is opposite to the first doping type. In some embodiments, the photodetector 108 can be formed by a selective ion implantation process that selectively implants ions into the substrate using a masking layer (not shown) on the front side 104f of the substrate 104. In other embodiments, the first doping type includes a p-type dopant and the second doping type includes an n-type dopant, or vice versa. The photodetector 108 is configured to generate an electrical signal from electromagnetic radiation having a wavelength λ. In some embodiments, the wavelength λ may include near infrared (NIR) radiation, which includes electromagnetic radiation in the range of approximately 850 nanometers to 940 nanometers. It should be understood that other values ​​of the wavelength λ are also within the scope of the present invention.

[0036] In addition, if Figure 4As described in , after forming the photodetector 108, a thinning process is performed on the back side 104b of the substrate 104 to reduce the initial thickness Ti of the substrate 104 to a thickness Ts. The thickness Ts is defined between the front side 104f of the substrate 104 and the back side 104b of the substrate 104. In some embodiments, the thickness Ts is in the range of about 4 microns to 6 microns. It should be understood that other values ​​of the thickness Ts are also within the scope of the present invention. In some embodiments, the thinning process may include performing a mechanical grinding process, a chemical mechanical planarization (CMP) process, another suitable thinning process, or any combination of the foregoing processes.

[0037] like Figure 5 As shown in the cross-sectional view 500, Figure 4 The structure of the substrate 104 is flipped, and then patterned to define a plurality of protrusions 110 along the back side 104b of the substrate 104. The back side 104b of the substrate 104 is opposite to the front side 104f of the substrate 104. In some embodiments, the plurality of protrusions 110 are formed by performing one or more etching processes according to one or more masking layers (not shown). For example, the one or more etching processes may include a wet etching process, a dry etching process, another suitable etching process, or any combination of the aforementioned etching processes. In addition, in some embodiments, the protrusions 110 are formed so that the height hp of the protrusions 110 may be greater than about λ / 2.5, and the distance d1 may be greater than about λ / 2, thereby increasing the light receiving surface area for incident electromagnetic radiation disposed on the substrate 104. The distance d1 is defined between the top surfaces of two adjacent protrusions 110. In yet another embodiment, the height hp may be greater than about 340 nanometers and / or the distance d1 may be greater than about 425 nanometers. It should be understood that other values ​​of the height hp and / or other values ​​of the distance d1 are also within the scope of the present invention.

[0038] like Figure 6As illustrated in the cross-sectional view 600 of , an upper dielectric layer 602 is deposited over the protrusion 110. The upper surface of the upper dielectric layer 602 may correspond to the shape of the protrusion 110. In some embodiments, the upper dielectric layer 602 may be deposited by, for example, CVD, ALD, PVD, thermal oxidation, a plasma-enhanced deposition process (e.g., plasma-enhanced CVD (PECVD)), or another suitable deposition process or growth process. Thus, for example, the upper dielectric layer 602 may be or include a plasma-enhanced oxide, silicon dioxide, silicon oxycarbide (SiOC), another suitable dielectric material, or any combination of the foregoing materials, and / or may be formed to a thickness in the range of about 3,000 angstroms to 5,000 angstroms. It should be understood that other values ​​of the thickness of the upper dielectric layer 602 are also within the scope of the present invention. In yet another embodiment, a bottom anti-reflective coating (BARC) layer 604 is formed over the upper dielectric layer 602. In some embodiments, the BARC layer 604 may be formed by CVD, ALD, PVD, or another suitable deposition process or growth process, for example. In yet another embodiment, the BARC layer 604 may be or include a high-k dielectric material (e.g., a dielectric material having a dielectric constant greater than 3.9), another suitable dielectric material, or any combination of the foregoing materials, for example, and / or may be formed to a thickness in the range of about 4,000 angstroms to 6,000 angstroms. It should be understood that other values ​​of the thickness of the BARC layer 604 are also within the scope of the present invention. Thus, in some embodiments, the BARC layer 604 has a greater thickness than the upper dielectric layer 602.

[0039] like Figure 7 , a first patterning process is performed on the BARC layer 604 to reduce the initial thickness of the BARC layer 604. In some embodiments, the first patterning process includes performing a dry etching process, a blanket dry etching process, or another suitable etching process. In other embodiments, the first patterning process may include exposing the BARC layer 604 to one or more etchants, such as oxygen (e.g., O2), carbon monoxide (CO), another suitable etchant, or any combination of the foregoing etchants. In yet another embodiment, the first patterning process does not etch the upper dielectric layer 602.

[0040] FIG. 8A to FIG. 8C Cross-sectional views 800a-800c corresponding to some embodiments illustrate performing a second patterning process on the upper dielectric layer 602 and the BARC layer 604 to form microlenses 112. The second patterning process is performed such that the microlenses 112 each have a convex upper surface 112us overlying the protrusions 110. Fig. 8A and Figure 8BCross-sectional views 800a and 800b corresponding to some embodiments of first and second snapshots of a second patterning process are illustrated. Figure 8C A cross-sectional view 800c corresponding to some embodiments of the microlens 112 is illustrated after the second patterning process is completed.

[0041] In some embodiments, the second patterning process includes performing a dry etching process, a blanket dry etching process, or another suitable etching process. In various embodiments, the second patterning process is performed only by a blanket dry etching process. In other embodiments, the second patterning process may include exposing the upper dielectric layer 602 and the BARC layer 604 to one or more etchants, such as a polymer-rich etchant, octafluorocyclobutane (e.g., C4F8), trifluoromethane (e.g., CHF3), another suitable etchant, or any combination of the foregoing etchants. During the second patterning process, the upper dielectric layer 602 is etched at a first etch rate, and the BARC layer 604 is etched at a second etch rate. In some embodiments, the first etch rate is at least 10 times greater than the second etch rate. In these embodiments, the second patterning process has a low selectivity for the BARC layer 604 relative to the upper dielectric layer 602, so that the upper dielectric layer 602 is etched faster (e.g., at least 10 times greater) than the BARC layer 604. This may be due to the one or more etchants removing the upper dielectric layer 602 faster than removing the BARC layer 604. Since the first etch rate is at least 10 times greater than the second etch rate, each of the microlenses 112 has a convex upper surface 112us. Therefore, in some embodiments, the ratio of the first etch rate to the second etch rate is, for example, about 10:1, about 11:1, about 12:1, in the range of about 10:1 to 20:1, or greater than 10:1. It should be understood that other values ​​of the ratio of the first etch rate to the second etch rate are also within the scope of the present invention. The convex upper surfaces 112us of the microlenses 112 are each configured to bend and / or angle incident electromagnetic radiation toward a focal point located below the corresponding convex upper surface 112us. This increases absorption of incident electromagnetic radiation by the substrate 104 (e.g., by reducing reflection of incident electromagnetic radiation away from the substrate 104). Increasing absorption of incident electromagnetic radiation improves the QE of the photodetector 108.

[0042] Fig. 8A Cross-sectional view 800a illustrates some embodiments of a first snapshot of a second patterning process taken at a first time, wherein the upper dielectric layer 602 is removed faster than the BARC layer 604. In addition, Figure 8B The cross-sectional view 800b of FIG. 8 illustrates some embodiments of a second snapshot of a second patterning process taken at a second time, where the second snapshot is taken at a time after the first snapshot. Figure 8BAs illustrated, the remnants of the BARC layer 604 are disposed along the top surface of the upper dielectric layer 602 such that the upper surfaces of the BARC layer 604 and the upper dielectric layer 602 that are laterally spaced apart between a pair of adjacent protrusions 110 are outwardly curved and / or rounded (i.e., convex) in a direction away from the protrusions 110. Figure 8C The cross-sectional view 800c of FIG. 8 illustrates some embodiments of the microlenses 112 after performing a second patterning process on the upper dielectric layer 602 and the BARC layer 604. The convex upper surface 112us of each of the microlenses 112 corresponds to Figure 8B 4 and 5. The curved upper surface of the BARC layer 604 and the curved upper surface of the upper dielectric layer 602 are illustrated in FIG.

[0043] like Fig. 9 As illustrated in the cross-sectional view 900 of , a filter 304 is formed over the microlens 112. The filter 304 is formed of a material that allows transmission of incident electromagnetic radiation (e.g., light) having a specific wavelength range, while blocking incident wavelengths having another wavelength outside the specified range. In other embodiments, the filter 304 may be formed by CVD, PVD, ALD, sputtering, etc., and / or the filter 304 may be planarized after formation (e.g., via a chemical mechanical planarization (CMP) process). In addition, an upper lens 306 is formed over the filter 304. In some embodiments, the upper lens 306 may be formed by depositing (e.g., by CVD, PVD, etc.) a lens material on the filter 304. A lens template (not shown) having a curved upper surface is patterned over the lens material. The upper lens 306 is then formed by selectively etching the lens material according to the lens template.

[0044] Fig.10 A method 1000 of forming an image sensor according to some embodiments of the present invention is described, wherein the image sensor includes a substrate having a plurality of protrusions and a plurality of microlenses disposed on the protrusions and spaced apart between the protrusions. Although method 1000 is described and / or illustrated as a series of actions or events, it should be understood that the method is not limited to the described order or actions. Therefore, in some embodiments, the actions may be implemented in an order different from the described order and / or may be implemented simultaneously. In addition, in some embodiments, the described actions or events may be subdivided into multiple actions or events, which may be implemented at separate times or simultaneously with other actions or sub-actions. In some embodiments, some of the described actions or events may be omitted, and other undescribed actions or events may be included.

[0045] At act 1002, an isolation structure is formed in a front side of a substrate. Figure 4 Cross-sectional view 400 corresponding to some embodiments of act 1002 is illustrated.

[0046] At act 1004, a photodetector is formed within a substrate. Figure 4 Cross-sectional view 400 corresponding to some embodiments of act 1004 is illustrated.

[0047] At act 1006, a plurality of protrusions are formed in the back side of the substrate. The protrusions overlying the photodetectors. Figure 5 Cross-sectional view 500 corresponding to some embodiments of act 1006 is illustrated.

[0048] An upper dielectric layer is deposited over the plurality of protrusions at act 1008. Additionally, a bottom anti-reflective coating (BARC) layer is deposited over the upper dielectric layer. Figure 6 Cross-sectional view 600 corresponding to some embodiments of act 1008 is illustrated.

[0049] At act 1010, a first patterning process is performed on the BARC layer. Figure 7 Cross-sectional view 700 corresponding to some embodiments of act 1010 is illustrated.

[0050] At action 1012, a second patterning process is performed on the upper dielectric layer and the BARC layer. The upper dielectric layer is etched faster than the BARC layer. In addition, the second patterning process defines a plurality of microlenses above the protrusions, such that each microlens has a convex upper surface. FIG. 8A to FIG. 8C Cross-sectional views 800a through 800c corresponding to some embodiments of act 1012 are illustrated.

[0051] At act 1014, a filter is formed over the plurality of microlenses. Fig. 9 Cross-sectional view 900 corresponding to some embodiments of act 1014 is illustrated.

[0052] At act 1016, an upper lens is formed over the filter. Fig. 9 Cross-sectional view 900 corresponding to some embodiments of act 1014 is illustrated.

[0053] Thus, in some embodiments, the present invention relates to an image sensor comprising a substrate having a plurality of protrusions disposed along a back side of the substrate. In addition, a plurality of microlenses are disposed above the protrusions and laterally spaced apart between the protrusions. The microlenses each comprise a convex upper surface configured to direct incident radiation to a focal point located below the convex upper surface.

[0054] In some embodiments, the present application provides an image sensor, comprising: a substrate comprising a plurality of sidewalls, the plurality of sidewalls defining a plurality of protrusions along a first side of the substrate, wherein the substrate has a first refractive index; a photodetector disposed within the substrate and below the plurality of protrusions; and a plurality of microlenses overlying the first side of the substrate, wherein the microlenses have a second refractive index smaller than the first refractive index, wherein the microlenses are respectively disposed laterally between and directly contact an adjacent pair of protrusions among the plurality of protrusions, and wherein the microlenses respectively include a convex upper surface.

[0055] According to some embodiments, the plurality of protrusions are laterally spaced apart from each other by grooves in the first side of the substrate, wherein the plurality of microlenses respectively include lens protrusions that fill corresponding grooves.

[0056] According to some embodiments, the substrate comprises silicon and the microlenses comprise silicon dioxide.

[0057] According to some embodiments, a height of the plurality of microlenses is greater than a height of the plurality of protrusions.

[0058] According to some embodiments, the plurality of protrusions include a first protrusion and a second protrusion disposed adjacent to each other in a laterally direction, wherein the first protrusion includes a first vertex and the second protrusion includes a second vertex, wherein a height of the plurality of protrusions is less than a lateral distance between the first vertex and the second vertex.

[0059] According to some embodiments, the plurality of microlenses includes a first microlens disposed between the first protrusion and the second protrusion, wherein a convex upper surface of the first microlens is laterally spaced apart between the first vertex of the first protrusion and the second vertex of the second protrusion.

[0060] According to some embodiments, the first microlens is configured to direct incident electromagnetic radiation toward a focal point located below the convex upper surface of the first microlens, wherein the focal point is laterally spaced apart between the first protrusion and the second protrusion, and wherein the focal point is vertically spaced apart above the bottom surfaces of the plurality of protrusions.

[0061] In some embodiments, the present application provides an integrated chip, comprising: a substrate comprising a plurality of first protrusions along the back side of the substrate, wherein the substrate comprises a first material having a first refractive index; an internal connection structure arranged along the front side of the substrate; a photodetector arranged in the substrate and located under the plurality of first protrusions; a passivation layer arranged on and between the plurality of first protrusions, wherein the passivation layer comprises a plurality of second protrusions along the upper surface of the passivation layer, wherein the plurality of second protrusions are different from the plurality of first protrusions, wherein the passivation layer comprises a second material having a second refractive index, which is different from the first refractive index; and a filter overlying the passivation layer.

[0062] According to some embodiments, the first protrusions each have a triangular shape and the second protrusions each have a semicircular shape.

[0063] According to some embodiments, the lower surface of the passivation layer includes a plurality of third protrusions that intersect in a meshing manner with a plurality of grooves spaced apart between the plurality of first protrusions of the substrate.

[0064] According to some embodiments, the first refractive index is at least two times greater than the second refractive index.

[0065] According to some embodiments, the photodetector is configured to generate an electrical signal from near infrared radiation.

[0066] According to some embodiments, the thickness of the substrate is in a range of about 4 microns to 6 microns.

[0067] According to some embodiments, the integrated chip further includes: an upper lens overlying the filter, wherein an upper surface of the upper lens is convex.

[0068] According to some embodiments, a bottom surface of the optical filter directly contacts the plurality of second protrusions.

[0069] In some embodiments, the present application provides a method for forming an image sensor, the method comprising: performing an ion implantation process to define a photodetector within a substrate; etching a first side of the substrate to define a plurality of protrusions overlying the photodetector; depositing a dielectric layer over the plurality of protrusions, wherein the dielectric layer comprises a first material; depositing an anti-reflective coating (ARC) layer over the dielectric layer, wherein the ARC layer comprises a second material different from the first material; performing a first patterning process on the ARC layer; and performing a second patterning process on the dielectric layer and the ARC layer to define a plurality of microlenses each having a concave upper surface, wherein the dielectric layer is etched at a first rate during the second patterning process and the ARC layer is etched at a second rate during the second patterning process, wherein the first rate is greater than the second rate.

[0070] According to some embodiments, the second patterning process includes performing a blanket dry etching process.

[0071] According to some embodiments, the method further includes: forming a filter on the plurality of microlenses such that the filter directly contacts the microlenses.

[0072] According to some embodiments, the method further includes: forming an upper lens on the filter, such that the upper lens has a curved upper surface.

[0073] According to some embodiments, the second patterning process includes exposing the dielectric layer and the anti-reflective coating layer to one or more etchants, wherein the one or more etchants include octafluorocyclobutane and / or trifluoromethane.

[0074] The foregoing summarizes the features of several embodiments so that those skilled in the art can better understand the various aspects of the present invention. Those skilled in the art will appreciate that they can easily use the present invention as a basis for designing or modifying other processes and structures to achieve the same purposes and / or achieve the same advantages as the embodiments described herein. Those skilled in the art will also appreciate that these equivalent constructions do not depart from the spirit and scope of the present invention, and that they may make various changes, substitutions, and modifications herein without departing from the spirit and scope of the present invention.

Claims

1. An image sensor, characterized in that: include: a substrate comprising a plurality of sidewalls defining a plurality of protrusions along a first side of the substrate, wherein the substrate has a first refractive index; a photodetector disposed in the substrate and below the plurality of protrusions; as well as a plurality of microlenses overlying the first side of the substrate, wherein the microlenses have a second refractive index smaller than the first refractive index, wherein the microlenses are respectively disposed laterally between and directly contact an adjacent pair of protrusions among the plurality of protrusions, and wherein the microlenses respectively include a convex upper surface, The plurality of protrusions include a first protrusion and a second protrusion disposed adjacent to each other in a lateral direction, wherein the first protrusion includes a first vertex and the second protrusion includes a second vertex, wherein a height of the plurality of protrusions is less than a lateral distance between the first vertex and the second vertex.

2. The image sensor according to claim 1, characterized in that The plurality of protrusions are laterally spaced apart from each other by grooves in the first side of the substrate, wherein the plurality of microlenses respectively include lens protrusions that fill corresponding grooves.

3. The image sensor according to claim 1, characterized in that Wherein the substrate comprises silicon and the microlenses comprise silicon dioxide.

4. The image sensor according to claim 1, characterized in that The height of the plurality of micro lenses is greater than the height of the plurality of protrusions.

5. The image sensor according to claim 1, characterized in that The plurality of microlenses include a first microlens disposed between the first protrusion and the second protrusion, wherein a convex upper surface of the first microlens is laterally spaced apart between the first vertex of the first protrusion and the second vertex of the second protrusion.

6. The image sensor according to claim 5, characterized in that wherein the first microlens is configured to direct incident electromagnetic radiation toward a focal point located below the convex upper surface of the first microlens, wherein the focal point is laterally spaced apart between the first protrusion and the second protrusion, and wherein the focal point is vertically spaced apart above the bottom surfaces of the plurality of protrusions.

7. An integrated chip, characterized in that: include: a substrate including a plurality of first protrusions along a back side of the substrate, wherein the substrate comprises a first material having a first refractive index; an interconnect structure disposed along the front side of the substrate; A photodetector, disposed in the substrate and below the plurality of first protrusions; a passivation layer arranged on and between the plurality of first protrusions, wherein the passivation layer comprises a plurality of second protrusions along an upper surface of the passivation layer, wherein the plurality of second protrusions are different from the plurality of first protrusions, wherein the passivation layer comprises a second material having a second refractive index, the second refractive index being different from the first refractive index; as well as a filter overlying the passivation layer, The plurality of first protrusions include a first first protrusion and a second first protrusion that are arranged adjacent to each other in a laterally direction, wherein the first first protrusion includes a first vertex and the second first protrusion includes a second vertex, and wherein a height of the plurality of first protrusions is less than a lateral distance between the first vertex and the second vertex.

8. The integrated chip according to claim 7, characterized in that: The first protrusions each have a triangular shape and the second protrusions each have a semicircular shape.

9. The integrated chip according to claim 7, characterized in that: The lower surface of the passivation layer includes a plurality of third protrusions that intersect in an engaging manner with a plurality of grooves spaced apart between the plurality of first protrusions of the substrate.

10. The integrated chip according to claim 7, characterized in that: Wherein the first refractive index is at least two times greater than the second refractive index.

11. The integrated chip according to claim 7, characterized in that: Wherein the photodetector is configured to generate an electrical signal from near infrared radiation.

12. The integrated chip according to claim 11, characterized in that: The thickness of the substrate is in the range of 4 microns to 6 microns.

13. The integrated chip according to claim 7, characterized in that: Also includes: An upper lens overlies the optical filter, wherein an upper surface of the upper lens is convex.

14. The integrated chip according to claim 7, characterized in that: wherein a bottom surface of the optical filter directly contacts the plurality of second protrusions.

15. A method of forming an image sensor, characterized in that: include: performing an ion implantation process to define a photodetector within the substrate; etching the first side of the substrate to define a plurality of protrusions overlying the photodetector; depositing a dielectric layer over the plurality of protrusions, wherein the dielectric layer comprises a first material; depositing an anti-reflective coating layer over the dielectric layer, wherein the anti-reflective coating layer comprises a second material different from the first material; performing a first patterning process on the anti-reflective coating layer; as well as A second patterning process is performed on the dielectric layer and the anti-reflective coating layer to define a plurality of microlenses each having a concave upper surface, wherein the dielectric layer is etched at a first rate during the second patterning process and the anti-reflective coating layer is etched at a second rate during the second patterning process, wherein the first rate is greater than the second rate.

16. The method according to claim 15, characterized in that The second patterning process includes performing a blanket dry etching process.

17. The method according to claim 15, characterized in that Also includes: A filter is formed over the plurality of microlenses such that the filter directly contacts the microlenses.

18. The method according to claim 17, characterized in that Also includes: An upper lens is formed over the filter such that the upper lens has a curved upper surface.

19. The method according to claim 15, characterized in that The second patterning process includes exposing the dielectric layer and the anti-reflective coating layer to one or more etchants, wherein the one or more etchants include octafluorocyclobutane and / or trifluoromethane.

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