Image sensor and method of manufacturing the same
By forming a lattice structure of aluminum metal layer and SiAlxOy layer in CMOS image sensor, the problems of crosstalk between adjacent pixel units and low light receiving efficiency are solved, achieving high light isolation and good reflectivity.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SMARTSENS TECH (SHANGHAI) CO LTD
- Filing Date
- 2022-05-13
- Publication Date
- 2026-07-24
Smart Images
Figure CN117096164B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of sensor technology, and in particular to an image sensor and its fabrication method. Background Technology
[0002] An image sensor is a functional device that uses the photoelectric conversion function of optoelectronic devices to convert a light image on a photosensitive surface into an electrical signal proportional to the light image. There are generally two types of image sensors: charge-coupled device (CCD) image sensors and CMOS image sensors (CIS). CCDs collect charge through the photoelectric effect; the charge of each row of pixels is sent to an analog shift register with a clock signal and then serially converted into a voltage. CIS is a rapidly developing solid-state image sensor. Because the image sensor and control circuitry are integrated into a single chip, CMOS image sensors are smaller, consume less power, and are less expensive, giving them advantages over traditional CCD image sensors and making them easier to popularize.
[0003] A CMOS image sensor includes a pixel array consisting of multiple pixel units. Each pixel unit senses the intensity of light in a certain area of the image, and the light intensities sensed by each pixel unit are combined to obtain the image.
[0004] As process nodes continue to shrink, it becomes increasingly important to minimize the escape of incident light between adjacent pixel units to prevent crosstalk, and to maximize the amount of incident light received by each pixel unit in order to increase the number of photogenerated carriers generated by each pixel unit.
[0005] Therefore, it is necessary to provide an image sensor and its fabrication method. Summary of the Invention
[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an image sensor and its manufacturing method to solve the problems of crosstalk between adjacent pixel units and low light reception efficiency in the prior art.
[0007] To achieve the above and other related objectives, the present invention provides a method for manufacturing an image sensor, comprising the following steps:
[0008] A semiconductor substrate is provided, wherein a pixel unit array is formed in the semiconductor substrate;
[0009] A silicon oxide layer is formed on the semiconductor substrate;
[0010] The silicon oxide layer is etched to form a groove in the silicon oxide layer. The groove is disposed corresponding to the pixel unit array to define the opening for each pixel unit in the pixel unit array to receive light.
[0011] An aluminum metal layer is formed on the surface of the silicon oxide layer, and a SiAlxOy layer is formed between the formed aluminum metal layer and the silicon oxide layer;
[0012] Etching is performed to remove the aluminum metal layer and the SiAlxOy layer located at the bottom of the groove, and to remove the aluminum metal layer located on the sidewall of the groove to expose the SiAlxOy layer located on the sidewall of the groove, forming a grid structure.
[0013] Optionally, the method for forming the aluminum metal layer on the surface of the silicon oxide layer includes physical vapor deposition; the etching step employs dry etching.
[0014] Optionally, the physical vapor deposition method includes sputtering or ion plating, wherein the process temperature is less than or equal to 400°C during the formation of the aluminum metal layer on the surface of the silicon oxide layer.
[0015] Optionally, after the step of etching the aluminum metal layer, the silicon oxide layer is topped with the aluminum metal layer.
[0016] Optionally, the thickness of the aluminum metal layer located on top of the silicon oxide layer is greater than the thickness of the aluminum metal layer located at the bottom of the groove, which is greater than the thickness of the aluminum metal layer located on the sidewall of the groove.
[0017] Optionally, the step of forming an intermediate layer between the semiconductor substrate and the silicon oxide layer is further included, the intermediate layer comprising one or a combination of a high-k dielectric layer, a silicon oxide, a silicon nitride, a silicon oxynitride, and a transparent metal oxide.
[0018] Optionally, after the step of forming the grid structure, the method further includes the step of forming a filter layer and a microlens in the groove.
[0019] The present invention also provides an image sensor, the image sensor comprising:
[0020] A semiconductor substrate in which a pixel unit array is formed;
[0021] A grid structure, the grid structure comprising:
[0022] A silicon oxide layer is located on the semiconductor substrate, and the silicon oxide layer has a groove, which is correspondingly disposed with respect to the pixel unit array to define the opening for each pixel unit in the pixel unit array to receive light;
[0023] A SiAlxOy layer is formed over the silicon oxide layer and exposes the bottom of the groove.
[0024] Optionally, the surface of the SiAlxOy layer located on top of the silicon oxide layer has an aluminum metal layer.
[0025] Optionally, an intermediate layer may be further included between the semiconductor substrate and the silicon oxide layer, the intermediate layer comprising one or a combination of a high-k dielectric layer, a silicon oxide, a silicon nitride, a silicon oxynitride, and a transparent metal oxide.
[0026] Optionally, the groove may also include a filter layer and a microlens.
[0027] As described above, the image sensor and its fabrication method of the present invention involve forming a silicon oxide layer on a semiconductor substrate having a pixel unit array, forming a groove in the silicon oxide layer corresponding to the pixel unit array to define the opening for each pixel unit in the pixel unit array to receive light, then forming an aluminum metal layer on the surface of the silicon oxide layer, and forming a SiAlxOy layer between the formed aluminum metal layer and the silicon oxide layer, and then performing an etching process to remove the aluminum metal layer and the SiAlxOy layer located at the bottom of the groove, and removing the aluminum metal layer located on the sidewall of the groove to expose the SiAlxOy layer located on the sidewall of the groove to form a grid structure.
[0028] The image sensor of the present invention provides a grating structure with high optical isolation performance through the SiAlxOy layer, which can effectively overcome the problem of poor integrity of aluminum metal layer and provide a high reflectivity layer with good performance, thereby effectively preventing crosstalk between adjacent pixel units in the image sensor and improving the light receiving efficiency of the image sensor. Attached Figure Description
[0029] Figure 1 The diagram shows the process flow for fabricating the image sensor in an embodiment of the present invention.
[0030] Figure 2 The diagram shows a schematic representation of the structure of a semiconductor substrate provided in an embodiment of the present invention.
[0031] Figure 3 The diagram shown is a schematic representation of the structure after the formation of the silicon oxide layer in an embodiment of the present invention.
[0032] Figure 4 The diagram shown is a schematic representation of the structure after a groove is formed in the silicon oxide layer in an embodiment of the present invention.
[0033] Figure 5 The diagram shows the structure after forming a SiAlxOy layer and an aluminum metal layer on the surface of the silicon oxide layer in an embodiment of the present invention.
[0034] Figure 6 This is a schematic diagram showing the structure after etching away the aluminum metal layer, SiAlxOy layer at the bottom of the groove, and the aluminum metal layer on the sidewall of the groove in an embodiment of the present invention.
[0035] Component designation explanation
[0036] 100 Semiconductor substrate
[0037] 101 Semiconductor Substrate
[0038] 102 Metal Wiring Layer
[0039] 103 Isolation Structure
[0040] 104 pixel unit
[0041] 200 intermediate layers
[0042] 300 silicon oxide layer
[0043] 301 Groove
[0044] 400 aluminum metal layer
[0045] 500 SiAlxOy layers Detailed Implementation
[0046] In image sensors, optical isolation between adjacent pixel units is achieved through metal meshes. In existing back-illuminated (BSI) CMOS image sensors, as the process node continues to shrink, tungsten metal is often used as the metal mesh material due to its compatibility with fine-pitch patterning processes. However, aluminum metal has better light reflectivity than tungsten metal. But when applied to fine-pitch products, aluminum metal has poorer coverage integrity than tungsten metal. Therefore, most fine-pitch BSI image sensors currently use tungsten metal as the metal mesh material. However, tungsten metal meshes are difficult to satisfy both good coverage integrity and reflectivity.
[0047] This embodiment addresses the aforementioned problems by providing an image sensor and its fabrication method. This effectively overcomes the issue of poor integrity of the aluminum metal layer and provides a high-reflectivity layer with good performance to effectively prevent crosstalk between adjacent pixel units in the image sensor and improve the light reception efficiency of the image sensor.
[0048] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.
[0049] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.
[0050] For ease of description, spatial relation terms such as "below," "below," "lower than," "below," "above," and "upper" may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being "between" two layers, it may be the only layer between the two layers, or there may be one or more layers in between. Wherein, when an element is referred to as being "fixed to" or "set on" another element, it may be directly on or indirectly on the other element. When an element is referred to as being "connected to" another element, it may be directly connected to or indirectly connected to the other element.
[0051] The text may use expressions such as "between..." to indicate that both endpoints are included, and may also use expressions such as "multiple" to indicate two or more, unless otherwise explicitly specified. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of that feature.
[0052] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.
[0053] like Figure 1 As shown, this embodiment provides a method for fabricating an image sensor, including the following steps:
[0054] S1: A semiconductor substrate is provided, wherein a pixel unit array is formed in the semiconductor substrate;
[0055] S2: A silicon oxide layer is formed on the semiconductor substrate;
[0056] S3: Etch the silicon oxide layer to form a groove in the silicon oxide layer. The groove is disposed corresponding to the pixel unit array to define the opening for each pixel unit in the pixel unit array to receive light.
[0057] S4: An aluminum metal layer is formed on the surface of the silicon oxide layer, and a SiAlxOy layer is formed between the formed aluminum metal layer and the silicon oxide layer;
[0058] S5: Perform etching to remove the aluminum metal layer and the SiAlxOy layer located at the bottom of the groove, and remove the aluminum metal layer located on the sidewall of the groove to expose the SiAlxOy layer located on the sidewall of the groove, forming a grid structure.
[0059] The image sensor fabrication method of this embodiment involves forming a silicon oxide layer on a semiconductor substrate having the pixel unit array, and forming a groove in the silicon oxide layer corresponding to the pixel unit array to define the opening for each pixel unit in the pixel unit array to receive light. Then, an aluminum metal layer is formed on the surface of the silicon oxide layer, and a SiAlxOy layer is formed between the aluminum metal layer and the silicon oxide layer. Then, an etching process is performed to remove the aluminum metal layer and the SiAlxOy layer located at the bottom of the groove, and to remove the aluminum metal layer located on the sidewall of the groove to expose the SiAlxOy layer located on the sidewall of the groove, thereby forming the grid structure.
[0060] The image sensor prepared in this embodiment can provide a grating structure with high optical isolation performance through the SiAlxOy layer, which can effectively overcome the problem of poor integrity of the aluminum metal layer and provide a high reflectivity layer with good performance. This can effectively prevent crosstalk between adjacent pixel units in the image sensor and improve the light receiving efficiency of the image sensor.
[0061] The following is in conjunction with the instruction manual. Figure 2 ~Attached Figure 6 The fabrication of the image sensor described in this embodiment will be further described, specifically including:
[0062] First, refer to Figure 2 Step S1 is executed, in which a semiconductor substrate 100 is provided, wherein a pixel unit array is formed in the semiconductor substrate 100.
[0063] Specifically, the semiconductor substrate 100 includes a semiconductor substrate 101, a metal wiring layer 102 formed in the semiconductor substrate 101, an isolation structure 103, and a pixel unit 104. The semiconductor substrate 101 may include a silicon substrate, a germanium substrate, a silicon carbide substrate, etc., and the specific type can be selected as needed. In this embodiment, the incident light is incident from top to bottom, and the metal wiring layer 102 is located below the pixel unit 104, meaning the image sensor uses a back-illuminated (BSI) image sensor to improve the image sensor's radiation reception. However, the type and structure of the image sensor are not limited to this; a front-illuminated (FSI) image sensor can also be used. No excessive limitation is made here; this embodiment only uses a BSI image sensor as an example. The materials, structures, and fabrication of the metal wiring layer 102, the isolation structure 103, and the pixel unit 104 are not excessively limited here.
[0064] Next, refer to Figure 3 Step S2 is performed to form a silicon oxide layer 300 on the semiconductor substrate 100.
[0065] Furthermore, in this embodiment, before forming the silicon oxide layer 300, a step of forming an intermediate layer 200 on the semiconductor substrate 100 is included. The intermediate layer 200 may include one or a combination of a high-k dielectric layer, silicon oxide, silicon nitride, silicon oxynitride, and transparent metal oxide to protect the pixel unit 104 and reduce or prevent the reflection of incident light on the surface of the semiconductor substrate 100. The type of intermediate layer 200 is not excessively limited here.
[0066] Next, refer to Figure 4 Step S3 is executed, etching the silicon oxide layer 200 to form a groove 301 in the silicon oxide layer 200. The groove 301 is correspondingly disposed with the pixel unit 104 array to define the opening for light reception of each pixel unit 104 in the pixel unit array. The groove 301 can be formed by any suitable etching method known in the art, such as wet etching, dry etching, etc., for patterning processing.
[0067] Next, refer to Figure 5 Step S4 is executed, in which an aluminum metal layer 400 is formed on the surface of the silicon oxide layer 300, and a SiAlxOy layer 500 is formed between the formed aluminum metal layer 400 and the silicon oxide layer 300.
[0068] Specifically, the method for forming the aluminum metal layer 400 may include physical vapor deposition (PVD), chemical vapor deposition (CVD), atomic layer deposition (ALD), metal-organic chemical vapor deposition (MOCVD), or jet vapor deposition (JVD), etc. In this process, after forming the aluminum metal layer 400, aluminum is implanted into the silicon oxide layer 300, thereby forming the SiAlxOy layer 500 with good reflectivity on the surface of the silicon oxide layer 300. This effectively prevents crosstalk between adjacent pixel units 104 in the image sensor and improves the light receiving efficiency of the image sensor.
[0069] Furthermore, the physical vapor deposition method for forming the aluminum metal layer 400 includes sputtering or ion plating. For example, argon discharge generates gas ionization, and the positive ions bombard aluminum at high speed under the influence of an electric field, ejecting aluminum atoms that fly towards the surface of the silicon oxide layer 300, causing the silicon oxide and aluminum to mix and ultimately deposit as a SiAlxOy thin film. Low temperature is extremely important in the process of this invention and must be compatible with BEOL levels. Therefore, during the formation of the aluminum metal layer 400 on the surface of the silicon oxide layer 300, the process temperature must be less than or equal to 400°C.
[0070] As an example, the surface of the SiAlxOy layer 500 located on top of the silicon oxide layer 300 has the aluminum metal layer 400. The aluminum metal layer 400 with a certain thickness is retained on top of the silicon oxide layer 300. While being compatible with fine-pitch patterning processes, the aluminum metal layer 400 is also suitable for optical isolation, thereby improving the reflectivity of the image sensor.
[0071] As an example, in the formed aluminum metal layer 400, the thickness of the aluminum metal layer 400 located on top of the silicon oxide layer 300 is greater than the thickness of the aluminum metal layer 400 located at the bottom of the groove 301 and greater than the thickness of the aluminum metal layer 400 located on the sidewall of the groove 301, so as to facilitate the subsequent etching process.
[0072] Of course, in other embodiments of the present invention, the technical effect of the present invention can also be achieved by not retaining the aluminum metal layer 400 on top of the silicon oxide layer 300 after etching the aluminum metal layer 400.
[0073] Next, refer to Figure 6 Step S5 is executed to perform etching, removing the aluminum metal layer 400 and the SiAlxOy layer 500 located at the bottom of the groove 301, and removing the aluminum metal layer 400 located on the sidewall of the groove 301 to expose the SiAlxOy layer 500 located on the sidewall of the groove 301, so as to form a grid structure.
[0074] Specifically, since the etching rate of the aluminum metal layer 400 is greater than that of the SiAlxOy layer 500, and the aluminum metal layer 400 located on the silicon oxide layer 300 has a different thickness, a highly directional, vertical etching method can be used during the etching process. This makes the etching directional, i.e., the etching amount in the vertical direction is greater than the etching amount in the lateral direction. This removes the aluminum metal layer 400 and the SiAlxOy layer 500 located at the bottom of the groove 301, and removes the aluminum metal layer 400 located on the sidewall of the groove 301, exposing the SiAlxOy layer 500 located on the sidewall of the groove 301 to form the grid structure. Thus, the SiAlxOy layer 500 can provide a high-reflectivity layer with good performance, and can effectively overcome the problem of poor integrity of the aluminum metal layer 400. This can effectively prevent crosstalk between adjacent pixel units 104 in the image sensor and improve the light receiving efficiency of the image sensor.
[0075] Furthermore, after the step of forming the grid structure, the step of forming a filter layer (not shown) and a microlens (not shown) in the groove 301 may also be included.
[0076] Specifically, the filter layer filled in the groove 301 can be used to filter the incident light entering the opening, thereby extracting the filtered wavelength. Generally, the filter materials in adjacent pixel units 104 can correspond to the three primary colors such as R, G, and B, thereby forming a color image sensor. The filter layer may also include a step of forming the microlens to converge and collimate the incident light.
[0077] See Figure 6 This embodiment also provides an image sensor, the image sensor comprising:
[0078] A semiconductor substrate 100, wherein a pixel unit array is formed in the semiconductor substrate 100;
[0079] A grid structure, the grid structure comprising:
[0080] A silicon oxide layer 300 is located on the semiconductor substrate 100, and the silicon oxide layer 300 has a groove 301, which is correspondingly disposed with the pixel unit array to define the opening for each pixel unit 104 in the pixel unit array to receive light.
[0081] A SiAlxOy layer 500 is formed, which covers the silicon oxide layer 300 and exposes the bottom of the groove 301.
[0082] The fabrication of the image sensor can be referred to the above-described fabrication method, but it is not limited thereto. The image sensor in this embodiment is directly fabricated using the above-described fabrication method. Therefore, the fabrication process of the image sensor will not be elaborated here.
[0083] As an example, the surface of the SiAlxOy layer 500 located on top of the silicon oxide layer 300 has an aluminum metal layer 400 to improve the reflectivity of the image sensor through the aluminum metal layer 400.
[0084] As an example, an intermediate layer 200 is further included between the semiconductor substrate 100 and the silicon oxide layer 300. The intermediate layer 200 may include one or a combination of a high-k dielectric layer, silicon oxide, silicon nitride, silicon oxide oxynitride, and transparent metal oxide, thereby protecting the pixel unit 104 and reducing or preventing the reflection of incident light on the surface of the semiconductor substrate 100. The type of intermediate layer 200 is not excessively limited here.
[0085] As an example, the groove 301 also includes a filter layer (not shown) and a microlens (not shown) to provide the image sensor in color through the filter layer, and the microlens located on the filter layer to converge and collimate the incident light.
[0086] In summary, the image sensor and its fabrication method of the present invention involve forming a silicon oxide layer on a semiconductor substrate having a pixel unit array, forming a groove in the silicon oxide layer corresponding to the pixel unit array to define the opening for each pixel unit in the pixel unit array to receive light, then forming an aluminum metal layer on the surface of the silicon oxide layer, and forming a SiAlxOy layer between the formed aluminum metal layer and the silicon oxide layer, and then performing an etching process to remove the aluminum metal layer and the SiAlxOy layer located at the bottom of the groove, and removing the aluminum metal layer located on the sidewall of the groove to expose the SiAlxOy layer located on the sidewall of the groove, thereby forming a grid structure.
[0087] The image sensor of the present invention provides a grating structure with high optical isolation performance through the SiAlxOy layer, which can effectively overcome the problem of poor integrity of aluminum metal layer and provide a high reflectivity layer with good performance, thereby effectively preventing crosstalk between adjacent pixel units in the image sensor and improving the light receiving efficiency of the image sensor.
[0088] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.
Claims
1. A method for fabricating an image sensor, characterized in that, Includes the following steps: A semiconductor substrate is provided, wherein a pixel unit array is formed in the semiconductor substrate; A silicon oxide layer is formed on the semiconductor substrate; The silicon oxide layer is etched to form a groove in the silicon oxide layer. The groove is disposed corresponding to the pixel unit array to define the opening for each pixel unit in the pixel unit array to receive light. An aluminum metal layer is formed on the surface of the silicon oxide layer, and a SiAlxOy layer is formed between the formed aluminum metal layer and the silicon oxide layer; Etching is performed to remove the aluminum metal layer and the SiAlxOy layer located at the bottom of the groove, and to remove the aluminum metal layer located on the sidewall of the groove to expose the SiAlxOy layer located on the sidewall of the groove, forming a grid structure.
2. The method for fabricating an image sensor according to claim 1, characterized in that: The method for forming the aluminum metal layer on the surface of the silicon oxide layer includes physical vapor deposition; the etching step uses dry etching.
3. The method for fabricating an image sensor according to claim 2, characterized in that: The physical vapor deposition method includes sputtering or ion plating, wherein the process temperature is less than or equal to 400°C during the formation of the aluminum metal layer on the surface of the silicon oxide layer.
4. The method for fabricating an image sensor according to claim 1, characterized in that: After the step of etching the aluminum metal layer, the silicon oxide layer is topped with the aluminum metal layer.
5. The method for fabricating an image sensor according to claim 4, characterized in that: The thickness of the aluminum metal layer located on top of the silicon oxide layer is greater than the thickness of the aluminum metal layer located at the bottom of the groove, which is greater than the thickness of the aluminum metal layer located on the sidewall of the groove.
6. The method for fabricating an image sensor according to claim 1, characterized in that: The step of forming an intermediate layer between the semiconductor substrate and the silicon oxide layer is further included, the intermediate layer comprising one or a combination of a high-k dielectric layer, a silicon oxide, a silicon nitride, a silicon oxynitride, and a transparent metal oxide.
7. The method for fabricating an image sensor according to claim 1, characterized in that: Following the step of forming the grid structure, the method further includes the step of forming a filter layer and a microlens in the groove.
8. An image sensor, characterized in that, The image sensor includes: A semiconductor substrate in which a pixel unit array is formed; A grid structure, the grid structure comprising: A silicon oxide layer is located on the semiconductor substrate, and the silicon oxide layer has a groove, which is correspondingly disposed with respect to the pixel unit array to define the opening for each pixel unit in the pixel unit array to receive light; A SiAlxOy layer is formed over the silicon oxide layer and exposes the bottom of the groove.
9. The image sensor according to claim 8, characterized in that: The surface of the SiAlxOy layer located on top of the silicon oxide layer has an aluminum metal layer.
10. The image sensor according to claim 8, characterized in that: An intermediate layer is further included between the semiconductor substrate and the silicon oxide layer, the intermediate layer comprising one or a combination of a high-k dielectric layer, a silicon oxide, a silicon nitride, a silicon oxynitride, and a transparent metal oxide.
11. The image sensor according to claim 8, characterized in that: The groove also contains a filter layer and microlenses.
Citation Information
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