Image sensor and method of forming the same

Abstract

Embodiments of the present disclosure describe a method for forming a mirror microstructure on a radiation sensing region of an image sensor device. The method includes forming an opening in a front side surface of a substrate; forming a conformal implantation layer on the bottom and sidewall surfaces of the opening; growing a first epitaxial layer on the bottom and sidewall surfaces of the opening; depositing a second epitaxial layer on the first epitaxial layer to fill the opening, wherein the second epitaxial layer forms a radiation sensing region. The method also includes depositing a stack on an exposed surface of the second epitaxial layer, wherein the stack includes alternating pairs of high refractive index material layers and low refractive index material layers. Embodiments of the present application provide image sensors and methods for forming the same.

Description

Technical Field

[0001] Embodiments of the present application relate to image sensors and methods of forming the same. Background Art

[0002] Semiconductor image sensors are used to sense incident visible or invisible radiation, such as visible light, infrared light, etc. Complementary metal oxide semiconductor (CMOS) image sensors (CIS) and charge coupled device (CCD) sensors are used in various applications, such as computers, digital cameras, mobile phones, tablets, goggles, scientific instruments, etc. These image sensors utilize an array of pixels to absorb (e.g., sense) incident radiation and convert it into an electrical signal. An example of an image sensor is a backside illuminated (BSI) image sensor device, which detects radiation from the "back side" of a substrate. Summary of the invention

[0003] In some embodiments, a method includes: forming an opening in a front side surface of a substrate; forming a conformal implant layer on a bottom and sidewall surfaces of the opening; growing a first epitaxial layer on the bottom and sidewall surfaces of the opening; depositing a second epitaxial layer on the first epitaxial layer to fill the opening, wherein the second epitaxial layer forms a radiation sensing region; and depositing a stack on an exposed surface of the second epitaxial layer, wherein the stack includes alternating pairs of high refractive index material layers and low refractive index material layers.

[0004] In some embodiments, an image sensor includes: a substrate having a front surface and an opposite back surface; a microlens formed on the back surface of the substrate; a color filter disposed between the microlens and the back surface of the substrate; a radiation sensing region formed in a groove in the front surface of the substrate, wherein the radiation sensing region includes an epitaxial semiconductor material; a mirror structure disposed on the surface of the epitaxial semiconductor material and including alternating layers of a first material layer having a first refractive index value and a second material layer having a second refractive index value different from the first refractive index value; and a metallization layer formed on the front surface of the substrate above the radiation sensing region and the mirror structure.

[0005] In some embodiments, an image sensor includes: a substrate having a front side surface and an opposite back side surface; a groove formed in the front side surface of the substrate, wherein the bottom of the groove has a tapered profile; a radiation sensing region located in the groove and including an epitaxial semiconductor material layer having a cut surface; an oxide layer disposed between the surface of the groove and the cut surface of the epitaxial semiconductor material layer; and a stack of alternating layers disposed on the cut surface of the epitaxial semiconductor material layer, wherein the alternating layers include a first material layer having a first refractive index and a second material layer having a second refractive index.

[0006] Embodiments of the present application provide image sensors with improved light conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] When read in conjunction with the accompanying drawings, various aspects of the present invention can be best understood from the following detailed description. It should be noted that, according to standard practice in the industry, the various components are not drawn to scale. In fact, for the sake of clarity of discussion, the size of the various components can be arbitrarily increased or reduced.

[0008] Figure 1 is a cross-sectional view of a stack having a backside illuminated (BSI) image sensor device attached to an application specific integrated circuit (ASIC) according to some embodiments.

[0009] Figure 2 is an enlarged cross-sectional view of a radiation sensing region with a Bragg mirror according to some embodiments.

[0010] Figure 3 is a flow chart describing a method of fabricating a process for forming a Bragg mirror on a radiation sensing region in a backside illuminated (BSI) image sensor device according to some embodiments.

[0011] According to some embodiments, Figures 4 to 11 is a cross-sectional view of an intermediate structure during fabrication of a Bragg mirror on a radiation sensing region in a backside illuminated (BSI) image sensor device.

[0012] Fig.12a is a cross-sectional view of Bragg mirrors formed on multiple surfaces of a radiation sensing region in a backside illuminated (BSI) image sensor device, according to some embodiments.

[0013] Figure 12b to Figure 12e is a cross-sectional view of an intermediate structure during fabrication of a radiation sensing region having multiple exposed surfaces in a backside illuminated (BSI) image sensor device in accordance with some embodiments.

[0014] Fig.13is a cross-sectional view of a Bragg mirror formed on an octahedron-shaped radiation sensing region in a backside illuminated (BSI) image sensor device in accordance with some embodiments.

[0015] Fig.14 is a cross-sectional view of a Bragg mirror formed on a diamond-shaped radiation sensing region in a backside illuminated (BSI) image sensor device in accordance with some embodiments. DETAILED DESCRIPTION

[0016] The following disclosure provides many different embodiments or examples for realizing different features of the present invention. Specific examples of components and arrangements are described below to simplify the present invention. Of course, these are merely examples and are not intended to limit the present invention. For example, in the following description, forming a first component above or on a second component may include an embodiment in which the first component and the second component are directly contacted, and may also include an embodiment in which an additional component may be formed between the first component and the second component so that the first component and the second component may not be in direct contact. Forming a first component on a second component as used herein means that the first component is formed to be in direct contact with the second component. In addition, the present invention may repeat reference numbers and / or letters in various examples. This repetition itself does not indicate the relationship between the various embodiments and / or structures discussed.

[0017] For ease of description, spatially relative terms such as "under," "beneath," "lower," "over," "upper," etc. may be used herein to easily describe the relationship of one element or component to another (or additional) elements or components as shown 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 should be interpreted accordingly.

[0018] As used herein, the term "nominal" refers to the desired or target value of a characteristic or parameter of a component or process operation, as set during the design phase of a product or process, and values ​​above and / or below the desired value. The range of values ​​may be due to minor variations in the manufacturing process and / or tolerances.

[0019] In some embodiments, the terms "about" and "substantially" may indicate a value of a given quantity that varies within 5% of the value (e.g., ±1%, ±2%, ±3%, ±4%, ±5% of the value). These values ​​are examples only and are not intended to be limiting. It should be understood that the terms "approximately" and "substantially" may refer to a percentage of a value of a given quantity as interpreted by a person skilled in the relevant (some) art(s) in accordance with the teachings herein.

[0020] A backside illumination (BSI) image sensor device includes a semiconductor substrate (e.g., a silicon substrate) in which an array of pixels or radiation sensing regions is formed. As disclosed herein, the terms "radiation sensing region" and "pixel" may be used interchangeably throughout the text. The radiation sensing region (pixel) is configured to convert photons from incident radiation into electrical signals. The electrical signals are then distributed to processing components connected to the BSI image sensor device. Therefore, the pixel array is covered with a multi-layer metallization layer, which is configured to distribute the electrical signals generated in the radiation sensing region to the appropriate processing components. The multi-layer metallization layer is formed on a first surface of the semiconductor substrate, referred to herein as the "front side" surface of the semiconductor substrate. In addition, the pixel array extends into the semiconductor substrate and is configured to receive radiation from a second surface of the semiconductor substrate opposite to the front side surface of the semiconductor substrate. The second surface of the semiconductor substrate that receives radiation (opposite to the front surface of the semiconductor substrate) is referred to herein as the "back side" surface of the semiconductor substrate.

[0021] Adjacent radiation sensing regions (pixels) in the semiconductor substrate are electrically isolated by isolation structures, such as deep trench isolation (DTI) structures, to minimize crosstalk and signal loss between the radiation sensing regions. Aligned with the above isolation structures (and formed on the back surface of the semiconductor substrate) are individual grid structures that provide optical isolation between adjacent pixels or radiation sensing regions. Adjacent grid structures together form cells that together form a composite grid structure configured to receive a color filter material.

[0022] The color filter material can be selected so that light having a desired wavelength passes through the color filter material, while light having other wavelengths is absorbed by the color filter material. For example, a color filter material that receives green light from unfiltered natural light will allow the green portion (wavelengths between about 495 nm and about 570 nm) to pass through the color filter, but will absorb all other wavelengths. The color filter is aligned with each pixel or radiation sensing area to provide filtered light to the corresponding radiation sensing area.

[0023] By way of example and not limitation, a substrate having a radiation sensing region (pixel), a plurality of metallization layers, and a grid structure formed thereon may be connected to an application specific integrated circuit (ASIC) formed on a different substrate via a wafer bonding structure. The ASIC may be, for example, a complementary metal oxide semiconductor (CMOS) wafer (fabricated separately from the BSI image sensor device) configured to perform the above-described signal processing operations.

[0024] A challenge for BSI image sensor devices is the efficiency of converting photons into electrical signals. This is because not all impinging photons from incident radiation are converted into electrical signals, and photons that escape into the radiation sensing area cannot be "recaptured." Therefore, BSI image sensor devices may require long radiation exposure times, large footprints, large amounts of signal enhancement, or a combination thereof, to operate in low radiation conditions.

[0025] In order to address the above shortcomings, the embodiments described herein are directed to a method for forming a reflector microstructure on a radiation sensing region at the exit path of the incident radiation. In some embodiments, the reflector microstructure is a Bragg reflector, which increases the optical path of the incident radiation in the radiation sensing region, thereby improving the capture of photons. In some embodiments, the mirror microstructure increases the optical path of the incident radiation in the radiation sensing region and improves the capture of photons. According to some embodiments, each reflector microstructure is a Bragg reflector (or Bragg reflector) comprising a stack of pairs of layers alternating with high refractive index (high index) and low refractive index (low index) materials plus one high refractive index material layer (2m+1); where 2m is the number of pairs of high and low rates. The terms "high rate" and "low rate" as used herein are relative and reflect the relationship between the refractive indices of the layers in the stack. For example, a "high rate" material has a higher refractive index than a "low rate" material. As an example and not a limitation, the stack may include 3 to 21 layers of high and low rate materials formed during or after the manufacture of the radiation sensing region. In some embodiments, the thickness and number of layers in a Bragg reflector can be tailored based on the target wavelength of incident radiation and the desired reflectivity.

[0026] Figure 1 1 is a cross-sectional view of a stack 100 according to some embodiments, the stack 100 including a BSI image sensor device 105 attached to an ASIC 110. As an example and not limitation, the ASIC 110 may be configured to process electrical signals generated by the BSI image sensor device 105. In the stack 100, an incident radiation beam 115 enters the BSI image sensor device 105 through a microlens 120 and a color filter 125 to a radiation sensing region or pixel 130. As described above, the radiation sensing region 130 is separated by an isolation structure 135. In some embodiments, the radiation sensing region 130 includes a semiconductor material such as silicon (Si), germanium (Ge), or silicon germanium (SiGe) depending on the wavelength of radiation of interest. For example, Si can be used for visible light applications (e.g., between about 380nm and 740nm), while Ge can be used for infrared applications (e.g., for wavelengths between about 940nm and about 1550nm). SiGe can be used for wavelengths between visible light and infrared. Without departing from the spirit and scope of the present disclosure, the radiation sensing region 130 will be described in the context of Ge.

[0027] Within the radiation sensing region 130, the incident radiation beam 115 is converted into an electrical signal, which in turn is dispersed onto the ASIC 110 by the multiple metallization layers 140 and the bonding structure 145. In some embodiments, the ASIC 110 is a manufactured CMOS wafer. By way of example and not limitation, the ASIC 110 may include active devices (e.g., transistor structures) 150 formed on a doped region 155 of a semiconductor (e.g., silicon) substrate 160. By way of example and not limitation, the ASIC 110 may include active devices (e.g., transistor structures) 150. In addition, the active devices 150 are physically and electrically isolated by isolation structures (e.g., shallow trench isolation structures) 165. By way of example and not limitation, an array of active devices 150 may be used to form logic and memory circuits in the ASIC 110. As Figure 1 As shown, electrical connections between the active device 150 and the BSI image sensor device 105 are provided by a multi-layer metallization layer 170 formed above the active device 150. By way of example and not limitation, the multi-layer metallization layer 170 of the ASIC 110 may be similar to the multi-layer metallization layer 140 of the BSI image sensor device 105. However, this is not limiting, and the multi-layer metallization layer 170 may be different from the multi-layer metallization layer 140. For example, the multi-layer metallization layer 170 may be more complex than the multi-layer metallization layer 140 with multiple additional wiring layers and tighter spacing (e.g., shorter distances between wirings). The multi-layer metallization layers 140 and 170 are coupled by a bonding structure 145 made of a metal or metal alloy such as copper, aluminum-copper, aluminum-germanium, or copper-tin.

[0028] The stack 100 may be physically and electrically connected to an external device or circuit through the pad structures 175 and the solder bumps 180. As an example and not limitation, the pad structures 175 may be disposed around the radiation sensing region 130 around the BSI image sensor device 105.

[0029] Without departing from the spirit and scope of the present disclosure, the stack 100 may include Figure 1 For ease of illustration, these additional components are Figure 1 100 and may include metal wiring, active and / or passive devices, insulating layers, etch stop layers, doped regions, and other components. Figure 1 The illustrated approach may be arranged differently and may include additional ASCIs or ASCIs different from ASCI 110 .

[0030] like Figure 1As shown, all elements of the BSI image sensor device 105 are formed in or around a substrate 185. For example, a radiation sensing region 130 and an isolation structure 135 are formed in the substrate 185, and a microlens 120 is formed on a side of the substrate 185 opposite to the multi-layer metallization layer 140. As referred to herein, the side of the substrate 185 on which the microlens 120 is formed is also referred to as a "backside surface," and the side of the substrate 185 on which the multi-layer metallization layer is formed is also referred to as a "backside surface."

[0031] According to some embodiments, each radiation sensing region 130 of the BSI image sensor device 105 has a Bragg mirror 190 that reflects the transmitted radiation beam 115 back to the radiation sensing region 130 to be recaptured. In some embodiments, the Bragg mirror includes a stack of alternating layers of high-rate and low-rate materials having an even number (2m+1). Where "m" is the required number of high-rate layers or low-rate layers, and 2m is the number of pairs of high-rate and low-rate. For example, if the required number of high-rate material layers is 3, the Bragg reflector stack will have a total of 7 layers. More specifically, the Bragg reflector stack will have 6 pairs of high-rate and low-rate layers and one additional high-rate layer, so that the top and bottom layers of the Bragg reflector stack are high-rate material layers. In some embodiments, the first (e.g., bottom layer) and last (e.g., top layer) layers of the Bragg reflector stack are high-rate material layers.

[0032] According to some embodiments, Figure 2 yes Figure 1 FIG. 1 is an enlarged view of the radiation sensing region 130 and the Bragg mirror 190. Figure 2 As shown, the Bragg mirror 190 includes alternating layers of high-rate material 200. Due to the construction of the Bragg reflector 190, when the incident radiation beam 115 travels through the stack to form the reflected radiation beam 115', the incident radiation beam 115 is partially reflected from the interface of each high-rate material 200 and the low-rate material 205. The reflected radiation beam 115' enters the radiation sensing region 130 for photon capture. Due to the photon recapture process, a portion of the reflected radiation beam 115' will be converted into an electrical signal in the radiation sensing region 130, and a portion of any uncaptured radiation beam 115' will escape from the radiation sensing region 130. A second portion of the incident radiation beam 115 may be absorbed by the stack (not shown), and a third portion of the incident radiation beam 115 may be transmitted into the substrate 185 as shown by arrow 115".

[0033] In some embodiments, the amount of high-rate material 200 and low-rate material 205 and their respective thicknesses are selected so that the intensity of the incident radiation beam 115 decreases as it passes through the stack. At the same time, if the absorptivity of the stack is negligible, the intensity of the reflected radiation beam 115' increases. This is possible if the reflected radiation beams 115' are in phase [or have a phase difference of a multiple of 360° (2π)] to promote constructive interference. If the thicknesses 200t and 205t of the high-rate material 200 and the low-rate material 205 are respectively equal to λ / (4n H ) and λ / (4n L ), then this can be achieved. Where n H is the refractive index of the high-index material 200, n L is the refractive index of the low index material 205, and λ is the wavelength of the incident radiation beam 115. Therefore, the Bragg mirror stack may be referred to as a "quarter wave" stack. Based on the above, the high index material 200 is formed thinner than the low index material 205 (eg, 200t<205t).

[0034] In some embodiments, the reflectivity obtained in the Bragg reflector 190 is determined by the number of layer pairs (2m) of the high-index material 200 and the low-index material 205 and their refractive index contrast (e.g., the difference in refractive index between the high-index material 200 and the low-index material 205). For example, between two Bragg reflectors with substantially similar refractive index contrast and different numbers of pairs of layers, the Bragg reflector with the larger number of pairs of layers can achieve the highest reflectivity value. In addition, between two Bragg reflectors with the same number of pairs of layers and different refractive indexes, the Bragg reflector with the highest refractive index contrast layers can achieve the highest reflectivity value. Therefore, if a high-index material 200 and a low-index material 205 with a high refractive index contrast are selected, a thinner Bragg reflector (e.g., with fewer layers) can be manufactured. In addition, when the refractive index contrast between the high-index material 200 and the low-index material 205 is larger, the reflection bandwidth (e.g., the number of wavelengths that can be reflected around the average wavelength value λ of the incident radiation beam 115) increases.

[0035] By way of example and not limitation, the Bragg reflector 190 may include (i) titanium oxide (TiO2) as the high-rate material 200 and silicon oxide (SiO2) or magnesium fluoride (MgF2) as the low-rate material 205, (ii) gallium arsenide (GaAs) as the high-rate material 200 and aluminum arsenide (AlAs) as the low-rate material 205, or (iii) gallium nitride (GaN) as the high-rate material 200 and aluminum nitride (AlN) as the low-rate material 205. This list is not exhaustive, and other suitable material combinations may be used based on the desired reflective properties of the Bragg mirror 190 and the desired operating wavelength or wavelength range.

[0036] In some embodiments, the reflectivity R of the Bragg mirror 190 having an even number (2m+1) of layers is provided by the formula (1) shown below:

[0037]

[0038] Where n0 is the refractive index of the radiation sensing region 130, and Y is the optical admittance provided by the following equation (2):

[0039]

[0040] where n H is the refractive index of the high-index material 200, n L is the refractive index of the low-index material 205, n S is the refractive index of the layer formed directly on the stack and 2m is the logarithm 190 of the layer in the Bragg mirror.

[0041] For example, if the radiation sensing region 130 includes Ge with n0=4 and the Bragg reflector 190 includes 7 layers (eg, m=3) and the high efficiency material 200 is n H = 2.45 TiO2, then the low rate material 205 is n L =1.45SiO2, and n S n S =1.46 for silicon suboxide (SiOx) 210 (eg, the cover layer on the Bragg mirror 190), the reflectivity R is approximately 84.6% and the admittance Y is approximately 97.7.

[0042] Figure 3 Is a description Figure 1 and Figure 2 190 . Other manufacturing operations may be performed between various operations of method 300, and other manufacturing operations may be omitted for purposes of clarity and ease of description only. These various operations are within the spirit and scope of the present disclosure. In addition, not all operations may be required to perform the disclosure provided herein. In addition, some operations may be performed simultaneously, or in parallel. Figure 3 In some embodiments, one or more other operations may be performed in addition to or in place of the operations currently described.

[0043] For illustrative purposes and ease of description, the method 300 will be described with reference to the formation of a single Bragg mirror stack; however, to avoid repetition, it will not be described again. However, it should be understood that the method 300 can be used to simultaneously form an array of Bragg mirror stacks. Figures 4 to 11Method 300 is described. The drawings provided for describing method 300 are for illustrative purposes only and are not drawn to scale. In addition, these drawings may not reflect the actual geometry of real structures, components or films. For the purpose of illustration, some structures, films or geometries may be intentionally exaggerated or omitted.

[0044] refer to Figure 3 , method 300 begins with operation 305 and the process of forming a trench opening in the front side surface of the semiconductor substrate. By way of example and not limitation, Figure 4 305 is a partial cross-sectional view of the substrate 185 after forming the trench opening 400 according to operation 305 of the method 300. In some embodiments, the isolation structure 135 (formed before the trench opening 400 is formed) is used as an alignment mark for aligning the trench opening 400. As described above, an array of trench openings, such as the trench opening 400, can be formed in the front side surface of the substrate 185 during operation 305. In the method 300, the radiation sensing region and the Bragg mirror will be formed in the corresponding trench openings, such as the trench opening 400. In some embodiments, the formation of the trench opening 400 requires the use of photolithography and etching operations. For example, a hard mask or photoresist (not shown) can be deposited on the front side surface of the substrate 185 and patterned. The patterned hard mask or photoresist is then used as an etching mask to form the trench opening 400 in the front side surface of the substrate 185.

[0045] In some embodiments, substrate 185 is a photonic wafer, for example, a wafer made of a material suitable for photonic applications. By way of example and not limitation, substrate 185 may include Si or another elemental semiconductor, for example, (i) Ge; (ii) a compound semiconductor including SiGe, silicon carbide (SiC), GaAs, gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), and / or indium antimonide (InSb); (iii) an alloy semiconductor including gallium arsenide phosphide (GaAsP), aluminum indium arsenide (AlInAs), aluminum gallium arsenide (AlGaAs), gallium indium arsenide (GaInAs), gallium indium phosphide (GaInP), and / or gallium indium arsenide phosphide (GaInAsP); or (iv) a combination thereof.

[0046] For example purposes, substrate 185 will be described in the context of Si (eg, single crystal). Based on the disclosure herein, other materials as described above may be used. These materials are within the spirit and scope of the present disclosure.

[0047] As described above, the isolation structure 135 is configured to minimize crosstalk and signal loss between radiation sensing regions, and can be formed, for example, by etching the substrate 185 to form a trench opening, which can then be filled with a dielectric material (e.g., silicon oxide). In some embodiments, the isolation structure 135 is taller than the height H of the trench opening 400 in the z direction and narrower than the width W of the trench opening 400 in the x direction. By way of example and not limitation, the height H of the trench opening 400 can be between about 50 nm and about 700 μm, and the width W can be between about 50 nm and about 700 μm. Larger or smaller trench openings 400 are possible. By way of example and not limitation, the depth of the trench opening 400 in the y direction can be about 5 μm.

[0048] Notice, Figure 4 The substrate 185 is shown relative to Figure 1 The orientation of the substrate 185 is shown rotated 180°. In other words, Figure 1 The substrate 185 in the embodiment is “turned upside down.” In some embodiments, the formation of the radiation sensing region as described herein is performed from the front side surface of the substrate 185 .

[0049] refer to Figure 3 , method 300 continues with operation 310 and the process of forming a common implant layer on the bottom and sidewall surfaces of the trench opening 400. In some embodiments, this can be achieved by depositing and patterning undoped silicon glass (USG) with a thickness of about 75 nm. USG has a high deposition rate at low temperatures and has similar properties to silicon oxide. By way of example and not limitation, USG can be deposited by plasma enhanced chemical vapor deposition (PECVD), high density plasma CVD (HDP-CVD), or sub-atmospheric pressure CVD (SACVD). The USG is then patterned and used as an implant mask in a subsequent implant process. Figure 5 The resulting structure after operation 310 is shown, wherein the patterned USG layer 500 is disposed on the front side surface of the substrate 185, and the implant layer 505 is formed on the sidewall and bottom surface of the trench opening 400. In some embodiments, during the rapid thermal annealing (RTA) process, the implant layer 505 is formed due to the increase in dopant mobility. t The thickness of 505t will increase.

[0050] Because the patterned USG layer 500 is used as an implantation mask, the sidewalls of the patterned USG layer 500 are not aligned with the sidewalls of the trench opening 400. More specifically, the width 500w (the width of the opening formed in the USG layer by the patterning process) is greater than the width W of the trench opening 400 by an amount approximately equal to the thickness of the implantation layer 505. In other words, 500 w-W≈505t. In some embodiments, the thickness of the implantation layer 505 is about 100 nm, and the dopant used to form the implantation layer 505 is boron. In some embodiments, the implantation layer 505 isolates the radiation sensing region from the substrate 185 and prevents the signal from being lost by leaking to the substrate 185. Therefore, the thickness of 505 can be adjusted. t and dopant concentrations to achieve adequate electrical isolation.

[0051] refer to Figure 3 , the method 300 continues with operation 315 and a process of epitaxially growing a crystalline Si (c-Si) layer on the bottom and sidewall surfaces of the trench opening 400. In some embodiments, the c-Si epitaxial layer is a "buffer layer" that facilitates the formation of the radiation sensing region and prevents the formation of defects. By way of example and not limitation, the c-Si epitaxial layer can be grown using silane (SiH4) by a CVD epitaxial process. Figure 6 A c-Si epitaxial layer 600 is shown grown on the implant layer 505 according to operation 315 of the method 300. In some embodiments, the c-Si epitaxial layer 600 is selectively grown on the exposed surface of the substrate 185, which is also crystalline as described above. In other words, the c-Si epitaxial layer 600 is not grown on the patterned USG layer 500. In some embodiments, the thickness of the c-Si epitaxial layer is about 45 nm. A thinner c-Si epitaxial layer (e.g., less than about 45 nm) may not prevent defects from occurring in the radiation sensing region grown thereon, while a thicker c-Si epitaxial layer (e.g., greater than about 45 nm) may occupy additional space in the trench opening 400 without providing additional benefits to the radiation sensing region.

[0052] refer to Figure 3 , the method 300 continues with operation 320 and the process of filling the trench opening 400 with an epitaxial layer to form the radiation sensing region 130. By way of example and not limitation, the radiation sensing region 130 includes epitaxially grown Ge. As described above, the material for the radiation sensing region 130 may be selected based on the wavelength range that the BSI image sensor device is configured to detect. By way of example and not limitation, additional materials that may be used for the radiation sensing region 130 include semiconductor materials of the III-V group, such as GaAs, InP, GaP, and GaN. In some embodiments, if a material other than Ge is used for the radiation sensing region 130, the c-Si epitaxial layer 600 may be replaced with another more suitable epitaxial layer. Therefore, different combinations of epitaxial layers in operations 315 and 320 may be used to achieve a substantially defect-free radiation sensing region 130. In some embodiments, defects in the radiation sensing region 130 may affect the photon conversion performance of the radiation sensing region 130.

[0053] In some embodiments, the radiation sensing region 130 may be grown by a CVD process using an appropriate precursor gas [e.g., germanium (GeH4)]. After the material of the radiation sensing region 130 is grown, a chemical mechanical polishing (CMP) process is used to flatten the surface of the radiation sensing region 130 so that the top surface of the radiation sensing region 130 and the patterned USG layer 500 are substantially coplanar. Figure 7 During the above-described CMP process, the patterned USG layer 500 is polished (eg, thinned), but is not removed from the front side surface of the substrate 185 .

[0054] In reference Figure 3 When the method 300 continues with operation 325 and the process of depositing alternating layers of high rate layers and low rate layers to form a Bragg mirror stack, such as Figure 1 and Figure 2 The Bragg mirror 190 is shown. Figure 1 and 2 As shown, the high-index and low-index layers can be selected from materials such as TiO2, SiO2, GaAs, AlAs, AlN, etc. In some embodiments, the thickness of these layers is adjusted to about λ / (4n); where n is the respective refractive index of each layer, and λ is the desired wavelength to be detected (e.g., the wavelength of the incident radiation beam 115). As described above, the reflectivity obtained by the Bragg mirror is determined by the number of pairs (2m) of layers of high-index material and low-index material and their refractive index contrast. Therefore, if high-index and low-index materials with high refractive index contrast (e.g., the maximum possible refractive index difference) are selected, thinner Bragg mirrors can be manufactured. In addition, when the index contrast between the high-index material and the low-index material is large, the reflection bandwidth (e.g., the number of wavelengths that can be reflected near the average wavelength value λ of the incident radiation beam) increases. Therefore, the higher the refractive index contrast, the wider the reflection bandwidth and the number of wavelengths near the average wavelength value that can be reflected by the Bragg reflector structure.

[0055] Therefore, radiation sensing regions made of different materials and configured to respond to different wavelengths require Bragg reflectors with different types of layers, different numbers of layers, different layer thicknesses, or a combination thereof. In some embodiments, the BSI image sensor device can be divided into regions with different radiation sensing materials in each region to enable the BSI image sensor to detect a larger spectrum of wavelengths. Therefore, a Bragg reflector with appropriate layer characteristics (e.g., number of layers, type of layer, thickness of layer, or a combination thereof) can be formed for each radiation sensing region using a combination of lithography, etching, and deposition operations.

[0056] In some embodiments, the high refractive index material and the low refractive index material may be deposited using a CVD-based method, an atomic layer deposition (ALD)-based method, or any suitable method that can achieve suitable layer thickness control and thickness uniformity. Thickness control (e.g., at the sub-nanometer level), thickness uniformity (e.g., at the sub-nanometer level), and surface roughness control (e.g., at the Level) ensures that the reflected radiation beams are not out of phase.

[0057] In some embodiments, Figure 1 and Figure 8 As shown, after depositing the stack, the layers of high rate material and low rate material are patterned to form individual Bragg mirrors 190 on corresponding radiation sensing regions 130. Furthermore, as described above, the top and bottom layers of the Bragg reflector 190 are high rate materials.

[0058] Subsequently, a protective capping layer 800 (eg, a silicon epitaxial layer) is selectively deposited on the Bragg mirror 190 with a thickness of about 40 nm, followed by a dielectric layer 805 deposition and a CMP process to planarize the dielectric layer 805, as shown in FIG. Figure 8 As shown, the remaining thickness of the dielectric layer 805 on the protective cover layer 800 is about 15 nm. By way of example and not limitation, the dielectric layer 805 can be USG, silicon oxide, or any other suitable dielectric material that is transparent to the wavelength of the incident radiation. In some embodiments, the protective cover layer 800 surrounds the Bragg mirror 190 and is not grown on the patterned USG layer 500.

[0059] refer to Figure 3 , method 300 continues with operation 330, and in the case Fig. 9 The process of forming a multi-layer metallization layer 140 on the front side surface of the substrate 184 coupled to the radiation sensing region 130 is shown. The multi-layer metallization layer 140 may include any number of metallization layers (e.g., between about 1 and about 9) for effective signal propagation from the radiation sensing region 130 to the ASCI. In some embodiments, each layer of the multi-layer metallization layer 140 includes a metal wiring network in the form of vias and lines. The vias ( Fig. 9 185) is electrically coupled to radiation sensing region 130 to propagate electrical signals generated in the photon conversion process when incident radiation enters the BSI image sensor from the backside surface of substrate 185.

[0060] Bonding structures 145 are formed in dielectric layer 900 formed on top of the multi-layer metallization layer 140. Bonding structures 145 align with respective bonding structures of the ASCI when the two devices are physically and electrically bonded together. Figure 1 The stack 100 shown. In some embodiments, as Fig. 9As shown, the bonding structure 145 is electrically coupled to the top layer of the multi-layer metallization layer 140 .

[0061] In some embodiments, to form Figure 1 The BSI image sensor device 105 shown has additional components (e.g., forming the color filter 125, the microlens 120, and the pad structure 175), and the partially fabricated BSI image sensor device 105 is shown in FIG. Fig.10 As shown, Fig. 9 The sensor device is rotated 180° so that the back surface of the substrate 185 faces upward. Fig.11 As shown, once these components are formed, the bonded structures of the BSI image sensor device 105 and the ASCI 110 are aligned and aligned. By way of example and not limitation, the bonding process may be followed by forming Figure 1 Solder bumps 180 are shown.

[0062] In some embodiments, the formation of the Bragg reflector 190 may not be limited to a single surface of the radiation sensing region 130 (e.g., Figure 8 For example, Fig.12a As shown, the radiation sensing region 130 can be made to have multiple facets, which are then covered by a layer of Bragg reflector 190. The benefit of this structure is that the additional surface area of ​​the radiation sensing region 130 can be increased. The Bragg reflector 190 uses a "reflector" to reflect the transmitted incident radiation beam back to the radiation sensing region 130. In some embodiments, the growth of the facets is promoted by forming spacers 1200 on the sidewalls of the trench opening before forming the radiation sensing region 130.

[0063] Reference Figure 12b to Figure 12e For example, the spacer 1200 may be formed as follows. Figure 12b As shown, after forming the trench opening 400 and the patterned USG layer 500, a thermal oxidation process grows a silicon oxide layer 1200' on the exposed surface of the trench opening 400. Since the front side surface of the substrate 185 is covered by the patterned USG layer 500, no silicon oxide is formed on the surface outside the trench opening 400. Subsequently, an anisotropic etching process removes a portion of the silicon oxide layer 1200' from the bottom of the trench opening 400 to form a spacer 1200. After the above-mentioned etching operation, the remaining thickness of the spacer 1200 is less than about 10nm. In some embodiments, thicker spacers are possible; however, thicker spacers deprive the radiation sensing area 130 of valuable space. Subsequently, the method 300 ( Fig.12c As shown in FIG. 5 ), an implantation layer 505 and a c-Si epitaxial layer are formed, and then as shown in FIG. Fig.12e The radiation sensing region 130 is shown as being grown. In some embodiments, the presence of the spacer 1200 promotes the formation of a cut surface in the radiation sensing region 130, such as Fig.12e shown, and in Fig.12e An isometric view of the radiation sensing area 130 is shown in the inset of FIG.

[0064] The aforementioned formation process of the multi-faceted radiation sensing region 130 is not limiting, and similar operations performed in a different order or alternative manufacturing operations are possible and within the spirit and scope of the present disclosure. For example, the spacer 1200 may be formed before forming the patterned USG layer 500 or after forming the implant layer 505 and the c-Si epitaxial layer 600.

[0065] In some embodiments, the combination of the shapes of the spacer 1200 and the trench opening 400 can produce a variety of radiation sensing area shapes with different numbers of facets, for example, Fig.13 and Fig.14 As shown in FIG. 1 , the Bragg mirror 190 formed thereon will follow the edge contour of the underlying radiation sensing region 130. In some embodiments, as shown in FIG. Fig.13 and Fig.14 As shown, the sidewall angle θ and the bottom width W of the trench opening 400 are controlled. b The shape of the radiation sensing region 130 is generated. In some embodiments, the sidewall angle θ is in the range of about 30° to about 60°, and the bottom width W b Than the top width W t By way of example and not limitation, a large sidewall angle (e.g., close to 60°) and a wide bottom width Wb (closer to the top width W t ) to generate a radiation sensing area with more sections, such as Fig.13 The octahedral radiation sensing area 130 is shown in an isometric view. Fig.13 On the other hand, a smaller sidewall angle (e.g., close to 30°) and a narrower bottom width W b (For example, equal to or less than the top width W t half of the total area) produces a radiation sensing area with fewer cut surfaces, such as Fig.14 The diamond-shaped radiation sensing area 130 is shown in an isometric view. Fig.14 Note that the bottom width W b It cannot be smaller than about 100 nm, which is undesirable because the amount of radiation entering the radiation sensing region 130 is reduced.

[0066] Note that any combination of radiation sensing devices and corresponding Bragg mirrors described herein may be used within a single BSI image sensor device.

[0067] According to various embodiments of the present disclosure, the formation of a mirror microstructure on a radiation sensing region at the exit path of incident radiation is described. In some embodiments, the reflector microstructure is a Bragg reflector, which increases the optical path of the incident radiation in the radiation sensing region, thereby improving the capture of photons. According to some embodiments, each Bragg mirror includes a stack of alternating pairs of layers, the pairs of layers having high-index and low-index materials, and an additional layer of high-index material (2m+1); wherein 2m is the number of pairs of high refractive index layers and low refractive index layers. In some embodiments, the thickness of these layers is adjusted to about λ / (4n); preferably, the thickness is adjusted to about λ / (4n). Where n is the corresponding refractive index of each layer, and λ is the desired wavelength to be detected (e.g., the wavelength of the incident radiation). The reflectivity obtained by the Bragg mirror depends on the number of pairs of layers of high refractive index material and low refractive index material (2m) and their refractive index contrast. Therefore, if the high refractive index material and the low refractive index material are selected with a high refractive index contrast, a thinner Bragg mirror can be manufactured. In addition, when the refractive index contrast between the high refractive index material and the low refractive index material is large, the reflection bandwidth (e.g., the number of wavelengths that can be reflected around the average wavelength value λ of the incident radiation beam) increases. By way of example and not limitation, the stack may include any of 3 to 21 layers of high and low refractive index materials formed during or after fabrication of the radiation sensing region. In some embodiments, a pair of high and low index layers include TiO2 and SiO2, GaAs and AlAs, or GaN and AlN, respectively. In some embodiments, a reflectivity of 84.6% or more may be achieved. In some embodiments, the Bragg mirror covers more than one surface (e.g., a facet) of the radiation sensing region. In some embodiments, the radiation sensing region includes Si, Ge, SiGe, or III-V. In some embodiments, a Ge radiation sensing region with a facet may be formed by implementing a silicon oxide spacer.

[0068] In some embodiments, a method includes forming an opening in a front side surface of a substrate; and forming a conformal implant layer on a bottom and sidewall surface of the opening; growing a first epitaxial layer on the bottom and sidewall surface of the opening; depositing a second epitaxial layer on the first epitaxial layer to fill the opening, wherein the second epitaxial layer forms a radiation sensing region. The method also includes depositing a stack on an exposed surface of the second epitaxial layer, wherein the stack includes alternating pairs of high refractive index material layers and low refractive index material layers.

[0069] In some embodiments, an image sensor includes a substrate having a front side surface and an opposite back side surface; and a micro lens formed on the back side surface of the substrate. A color filter is disposed between the micro lens and the back side surface of the substrate; a radiation sensing region formed in a groove in the front side surface of the substrate, wherein the radiation sensing region includes an epitaxial semiconductor material. The image sensor also includes a mirror structure disposed on the surface of the epitaxial semiconductor material, the mirror structure having alternating layers of a first material layer having a first refractive index value and a second material layer having a second refractive index value different from the first refractive index value. The metallization layer is formed on the front side surface of the substrate above the radiation sensing region and the mirror structure.

[0070] In some embodiments, an image sensor includes a substrate having a front side surface and an opposite back side surface; a groove formed in the front side surface of the substrate, wherein the bottom of the groove has a tapered profile. The image sensor also includes a radiation sensing region in the groove, wherein the radiation sensing region includes an epitaxial semiconductor material layer having a cut surface. In addition, the image sensor includes an oxide layer disposed between a surface of the groove and the cut surface of the epitaxial semiconductor material layer; a stack of alternating layers disposed on the cut surface of the epitaxial semiconductor material layer, wherein the alternating layers include a first material layer having a first refractive index and a second material layer having a second refractive index.

[0071] In some embodiments, a method includes: forming an opening in a front side surface of a substrate; forming a conformal implant layer on a bottom and sidewall surfaces of the opening; growing a first epitaxial layer on the bottom and sidewall surfaces of the opening; depositing a second epitaxial layer on the first epitaxial layer to fill the opening, wherein the second epitaxial layer forms a radiation sensing region; and depositing a stack on an exposed surface of the second epitaxial layer, wherein the stack includes alternating pairs of high refractive index material layers and low refractive index material layers.

[0072] In some embodiments, the method further includes: depositing a capping layer on the stack; and forming a metallization layer on the capping layer, wherein the metallization layer is electrically coupled to the radiation sensing region and is configured to propagate an electrical signal from the radiation sensing region to a signal processing device. In some embodiments, the method further includes forming a microlens on a backside surface of the substrate opposite to the frontside surface, wherein the microlens is configured to directly incident radiation onto the backside surface of the substrate toward the radiation sensing region. In some embodiments, depositing the stack includes: depositing a high refractive index material layer, the thickness of the high refractive index material layer being substantially equal to the wavelength of the incident radiation divided by four times the refractive index value of the high refractive index material layer; and depositing a low refractive index material layer, the thickness of the low refractive index material layer being substantially equal to the wavelength of the incident radiation divided by four times the refractive index value of the low refractive index material layer. In some embodiments, the high refractive index material layer includes titanium oxide (TiO2), gallium arsenide (GaAs), or gallium nitride (GaN), and the low refractive index material layer includes silicon oxide (SiO2), aluminum arsenide (AlAs), or aluminum nitride (AlN). In some embodiments, depositing the second epitaxial layer comprises depositing a germanium epitaxial layer. In some embodiments, depositing the stack comprises forming an additional high refractive index material layer on the alternating pairs of the high refractive index material layers and the low refractive index material layers. In some embodiments, depositing the stack comprises forming each of a top layer and a bottom layer of the stack with the high refractive index material layer.

[0073] In some embodiments, an image sensor includes: a substrate having a front surface and an opposite back surface; a microlens formed on the back surface of the substrate; a color filter disposed between the microlens and the back surface of the substrate; a radiation sensing region formed in a groove in the front surface of the substrate, wherein the radiation sensing region includes an epitaxial semiconductor material; a mirror structure disposed on the surface of the epitaxial semiconductor material and including alternating layers of a first material layer having a first refractive index value and a second material layer having a second refractive index value different from the first refractive index value; and a metallization layer formed on the front surface of the substrate above the radiation sensing region and the mirror structure.

[0074] In some embodiments, the epitaxial semiconductor material comprises germanium having three or more facets, and wherein an oxide layer is interposed between the epitaxial semiconductor material and a surface of the trench. In some embodiments, the thickness of the first material layer is substantially equal to the ratio provided by the wavelength of radiation incident to the radiation sensing region divided by four times the first refractive index value. In some embodiments, the thickness of the second material layer is substantially equal to the ratio provided by the wavelength of radiation incident to the radiation sensing region divided by four times the second refractive index value. In some embodiments, the first refractive index value is greater than the second refractive index value. In some embodiments, a capping layer is further included, the capping layer covering the top surface and sidewall surfaces of the mirror structure.

[0075] In some embodiments, an image sensor includes: a substrate having a front side surface and an opposite back side surface; a groove formed in the front side surface of the substrate, wherein the bottom of the groove has a tapered profile; a radiation sensing region located in the groove and including an epitaxial semiconductor material layer having a cut surface; an oxide layer disposed between the surface of the groove and the cut surface of the epitaxial semiconductor material layer; and a stack of alternating layers disposed on the cut surface of the epitaxial semiconductor material layer, wherein the alternating layers include a first material layer having a first refractive index and a second material layer having a second refractive index.

[0076] In some embodiments, the first material layer is thinner than the second material layer. In some embodiments, the tapered profile comprises a sidewall angle between about 30° and about 60° measured from an axis parallel to the front side surface and the back side surface. In some embodiments, the first material layer comprises titanium oxide (TiO2), gallium arsenide (GaAs), or gallium nitride (GaN). In some embodiments, the second material layer comprises silicon oxide (SiO2), aluminum arsenide (AlAs), or aluminum nitride (AlN). In some embodiments, the epitaxial semiconductor material layer comprises silicon, germanium, silicon germanium, or a III-V material.

[0077] It should be understood that the detailed description section, rather than the abstract, is intended to be used to interpret the claims. The abstract of the disclosure section may set forth one or more but not all contemplated exemplary embodiments and, thus, is not intended to limit the dependent claims.

[0078] The features of several embodiments are summarized above so that those skilled in the art can better understand the various aspects of the present disclosure. Those skilled in the art should understand that they can easily use the present disclosure as a basis for designing or modifying other processes and structures for performing the same or similar purposes and / or achieving the same or similar advantages as the present disclosure. Those skilled in the art should also be aware that such equivalent structures do not depart from the spirit and scope of the present disclosure, and various changes, substitutions and modifications can be made without departing from the spirit and scope of the present disclosure.

Claims

1. A method of forming an image sensor, comprising: forming an opening in the front side surface of the substrate; forming a conformal implant layer on the bottom and sidewall surfaces of the opening by using the patterned silicon glass layer as an implant mask; growing a first epitaxial layer on the bottom and the sidewall surfaces of the opening; depositing a second epitaxial layer on the first epitaxial layer to fill the opening, wherein the second epitaxial layer forms a radiation sensing region, wherein the second epitaxial layer is coplanar with a top surface of the patterned silicon glass layer; and depositing a stack on the exposed surface of the second epitaxial layer, wherein the stack includes alternating pairs of layers of high refractive index material and layers of low refractive index material; and A capping layer is deposited on the stack, wherein the capping layer surrounds the stack and does not grow on the patterned silicon glass layer.

2. The method of forming an image sensor according to claim 1, further comprising: A metallization layer is formed on the cover layer, wherein the metallization layer is electrically coupled to the radiation sensing region and is configured to propagate an electrical signal from the radiation sensing region to a signal processing device.

3. The method of forming an image sensor according to claim 1, further comprising forming a microlens on a backside surface of the substrate opposite to the frontside surface, wherein The microlens is configured to direct radiation incident on the backside surface of the substrate toward the radiation sensing region.

4. The method of forming an image sensor according to claim 1, wherein depositing the stack comprises: depositing a layer of high refractive index material having a thickness substantially equal to the wavelength of incident radiation divided by four times the refractive index value of the layer of high refractive index material; as well as A layer of low refractive index material is deposited having a thickness substantially equal to the wavelength of the incident radiation divided by four times the refractive index value of the layer of low refractive index material.

5. The method of forming an image sensor according to claim 1, wherein: The high refractive index material layer includes titanium oxide (TiO2), gallium arsenide (GaAs) or gallium nitride (GaN), and the low refractive index material layer includes silicon oxide (SiO2), aluminum arsenide (AlAs), or aluminum nitride (AlN). 6 . The method of forming an image sensor of claim 1 , wherein depositing the second epitaxial layer comprises depositing a germanium epitaxial layer. 7 . The method of forming an image sensor of claim 1 , wherein depositing the stack comprises forming additional layers of high refractive index material on the alternating pairs of the layers of high refractive index material and low refractive index material.

8. The method of forming an image sensor according to claim 1, wherein: Depositing the stack includes forming each of a top layer and a bottom layer of the stack with the high refractive index material layer.

9. An image sensor, comprising: a substrate having a front side surface and an opposite back side surface; a microlens formed on the backside surface of the substrate; a color filter disposed between the microlens and the backside surface of the substrate; a radiation sensing region formed in a trench in the front surface of the substrate, wherein the radiation sensing region comprises epitaxial semiconductor material; a mirror structure disposed on a surface of the epitaxial semiconductor material and comprising alternating layers of a first material layer having a first refractive index value and a second material layer having a second refractive index value different from the first refractive index value; and a metallization layer formed on the front side surface of the substrate above the radiation sensing region and the mirror structure, The epitaxial semiconductor material has a cut surface and a flat bottom surface, and the mirror structure extends along the cut surface of the epitaxial semiconductor material to the flat bottom surface of the epitaxial semiconductor material.

10. The image sensor according to claim 9, wherein: The epitaxial semiconductor material includes germanium having three or more facets, and wherein an oxide layer is interposed between the epitaxial semiconductor material and a surface of the trench.

11. The image sensor according to claim 9, wherein: The thickness of the first material layer is substantially equal to a ratio provided by a wavelength of radiation incident on the radiation sensing region divided by four times the first refractive index value.

12. The image sensor according to claim 9, wherein: The thickness of the second material layer is substantially equal to a ratio provided by a wavelength of radiation incident on the radiation sensing region divided by four times the second refractive index value.

13. The image sensor according to claim 9, wherein: The first refractive index value is greater than the second refractive index value. 14 . The image sensor according to claim 9 , further comprising a cover layer covering a top surface and sidewall surfaces of the mirror structure.

15. An image sensor, comprising: a substrate having a front side surface and an opposite back side surface; a groove formed in the front side surface of the substrate, wherein a bottom of the groove has a tapered profile; a radiation sensing region located in the trench and comprising an epitaxial semiconductor material layer having a cut surface and a flat bottom surface; an oxide layer disposed between a surface of the trench and the cut surface of the epitaxial semiconductor material layer; as well as A stack of alternating layers is arranged on the cut surface of the epitaxial semiconductor material layer, wherein the alternating layers include a first material layer with a first refractive index and a second material layer with a second refractive index, wherein the stack of alternating layers extends along the cut surface of the epitaxial semiconductor material layer to the flat bottom surface of the epitaxial semiconductor material layer.

16. The image sensor according to claim 15, wherein: The first material layer is thinner than the second material layer.

17. The image sensor according to claim 15, wherein: The tapered profile includes a side wall angle between 30° (1±5%) and 60° (1±5%) measured from an axis parallel to the anterior and dorsal surfaces.

18. The image sensor according to claim 15, wherein: The first material layer includes titanium oxide (TiO2), gallium arsenide (GaAs) or gallium nitride (GaN).

19. The image sensor according to claim 15, wherein: The second material layer includes silicon oxide (SiO2), aluminum arsenide (AlAs) or aluminum nitride (AlN).

20. The image sensor according to claim 15, wherein: The epitaxial semiconductor material layer includes silicon, germanium, silicon germanium or III-V group materials.

Images