Backside illuminated image sensor and method of manufacturing the same

Abstract

The application provides a manufacturing method of a back-illumination image sensor, and is applied to the technical field of semiconductors. Specifically, the thickness of the oxide layer formed on the surface of the silicon substrate (semiconductor substrate) is thinned by reducing the deposition time of the decoupling plasma oxidation process (DPO) of the oxide layer formed on the surface of the silicon substrate, so that the silicon damage caused by the impact and damage of the plasma of the DPO process to the silicon surface is reduced, and the dark current caused by the damage of the silicon surface is further reduced. Therefore, the manufacturing method provided by the application can avoid the dark current and white pixel problem caused by the damage of the silicon surface, and finally realizes the purpose of improving the performance of the back-illumination image sensor device.

Description

Technical Field

[0001] This invention relates to CMOS image sensors in the field of semiconductor technology, and particularly to a back-illuminated image sensor and its manufacturing method. Background Technology

[0002] With the booming development of emerging fields such as artificial intelligence, the Internet of Things, and Industry 4.0, the market demand for CMOS image sensors is increasing daily, and the performance requirements are becoming increasingly stringent. Specifically, in the manufacturing process of back-illuminated image sensors (BSI), the dark current (DC) is one of the important optical performance parameters, directly affecting the optical performance (white pixel, WP). DC is the current generated by the thermal excitation of the photodiode in the pixel area under zero illumination. When the current accumulates to a sufficiently high level, it will produce a visible bright white spot in the local imaging area, while the rest of the pixel area is completely dark. Therefore, the white spot is called a white pixel. The formation of dark current is mainly due to defects at the interface and metal ion contamination. These factors create intermediate energy levels in the original bandgap, providing a channel for electron transitions. This causes leakage current to occur in devices that would normally only generate leakage current under illumination, even in the absence of light.

[0003] Improving the quality of thin film growth at the interface and reducing defects while ensuring the absence of metal ion contamination becomes an important direction for improving the DC (Distribution Capacitor) of BSI (Body Separation Injection) products. Current BSI products involve oxidizing the silicon interface at room temperature and low pressure in a continuous mode (CW) plasma environment, followed by the deposition of alumina, tantalum oxide, etc., to separate different color pixel regions. This film deposition method has a low rate and suffers from significant plasma damage. Summary of the Invention

[0004] The purpose of this invention is to provide a back-illuminated image sensor and its manufacturing method, so as to prevent damage to the silicon substrate surface of the photodiode area during the manufacturing process of the back-illuminated image sensor, thereby effectively reducing dark current and further improving the image performance of the product.

[0005] In a first aspect, to achieve the above objectives, the present invention provides a method for manufacturing a back-illuminated image sensor, specifically comprising the following steps:

[0006] Provide a semiconductor substrate;

[0007] Obtain standard parameter values ​​for the decoupled plasma oxidation process, and adjust the standard process parameter values ​​for the decoupled plasma oxidation process so that the thickness of the oxide layer formed on the surface of the semiconductor substrate using the adjusted decoupled plasma oxidation process is reduced by a preset target thickness compared to the thickness formed using the standard parameter values.

[0008] Subsequent processes are performed on the semiconductor substrate containing the oxide layer to form the electrical structure of the back-illuminated image sensor, which includes at least a photodiode region.

[0009] Furthermore, the step of adjusting the standard process parameter values ​​of the decoupled plasma oxidation process may include reducing the process duration in the decoupled plasma oxidation process.

[0010] Furthermore, the process duration in the decoupled plasma oxidation process, which reduces process deposition time, can range from 1 minute to 30 minutes.

[0011] Furthermore, the temperature range of the decoupled plasma oxidation process can be 200℃~500℃.

[0012] Furthermore, the range of the preset target thickness reduction between the thickness of the oxide layer formed on the surface of the semiconductor substrate using the adjusted decoupled plasma oxidation process and the thickness formed using standard parameter values ​​can be:

[0013] Furthermore, at least one natural oxide layer may be formed on the surface of the provided semiconductor substrate.

[0014] Furthermore, before forming the oxide layer on the surface of the semiconductor substrate, the manufacturing method may also include etching away the natural oxide layer.

[0015] Furthermore, the reaction gas in the decoupled plasma oxidation process may include oxygen.

[0016] Furthermore, the semiconductor substrate used to form the back-illuminated image sensor in the manufacturing method provided by the present invention can be a silicon substrate.

[0017] Secondly, based on the manufacturing method of the back-illuminated image sensor described above, the present invention also provides a back-illuminated image sensor. Specifically, the back-illuminated image sensor can be prepared using the manufacturing method of the back-illuminated image sensor described above.

[0018] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0019] The back-illuminated image sensor is manufactured using a method that reduces the deposition time of the decoupled plasma oxidation (DPO) process on the surface of a silicon substrate (semiconductor substrate), thereby thinning the oxide layer formed on the silicon substrate surface. This reduces silicon damage caused by the impact of plasma on the silicon surface during the DPO process, and consequently, dark current caused by silicon surface damage. In other words, the manufacturing method provided by this invention can avoid dark current and white pixel problems caused by silicon surface damage, ultimately achieving the goal of improving the performance of the back-illuminated image sensor device. Attached Figure Description

[0020] Figure 1 A cross-sectional schematic diagram of the WP problem caused by damage to the surface of the silicon substrate during the formation of an oxide layer on the surface of the silicon substrate using the standard parameter values ​​of the decoupled plasma oxidation process determined in the existing process.

[0021] Figure 2 This is a schematic flowchart of a method for manufacturing a back-illuminated image sensor according to an embodiment of the present invention.

[0022] Figure 3 To utilize the invention provided Figure 2 A schematic cross-sectional view of the silicon substrate formed by the manufacturing method of the back-illuminated image sensor. Detailed Implementation

[0023] As described in the background section, in the manufacturing process of back-illuminated image sensors (BSI), the dark current (DC) is one of the important optical performance parameters, directly affecting the optical performance (white pixel, WP). DC is the current generated by the thermal excitation of the photodiode in the pixel area under zero illumination. When the current accumulates to a sufficiently high level, it produces a visible bright white spot in the local imaging area, while the rest of the pixel area is completely dark. Therefore, the white spot is called a white pixel. The formation of dark current is mainly due to defects at the interface and metal ion contamination. These introduce intermediate energy levels in the original bandgap, providing a channel for electron transitions. This causes leakage current to occur even in the absence of light, whereas previously it only occurred under illumination. Figure 1 As shown.

[0024] Improving the quality of thin film growth at the interface and reducing defects while ensuring the absence of metal ion contamination becomes an important direction for improving the DC (Distribution Capacitor) of BSI (Body Separation Injection) products. Current BSI products involve oxidizing the silicon interface at room temperature and low pressure in a continuous mode (CW) plasma environment, followed by the deposition of alumina, tantalum oxide, etc., to separate different color pixel regions. This film deposition method has a low rate and suffers from significant plasma damage.

[0025] Therefore, the present invention provides a back-illuminated image sensor and its manufacturing method to prevent damage to the silicon substrate surface of the photodiode region during the manufacturing process of the back-illuminated image sensor, thereby effectively reducing dark current and further improving the image performance of the product.

[0026] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of a back-illuminated image sensor and its manufacturing method according to the present invention. The advantages and features of the present invention will become clearer from the following description. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the present invention. Many specific details are set forth in the following description to provide a thorough understanding of the present invention; however, the present invention may be implemented in other ways different from those described herein, and therefore the present invention is not limited to the specific embodiments disclosed below.

[0027] As shown in this application and claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements. In detailing the embodiments of the present invention, for ease of explanation, the cross-sectional views showing the device structure may be partially enlarged without adhering to the general scale, and the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. Furthermore, in actual manufacturing, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0028] The manufacturing method of the back-illuminated image sensor provided in the embodiments of the present invention will be described below, for details please refer to Figure 2 and Figure 3 ,in, Figure 2 This is a schematic flowchart of a method for manufacturing a back-illuminated image sensor according to an embodiment of the present invention. Figure 3 To utilize the invention provided Figure 2 A schematic cross-sectional view of the silicon substrate formed by the manufacturing method of the back-illuminated image sensor. From... Figure 2 As can be seen, the manufacturing method of the back-illuminated image sensor provided by the present invention may specifically include the following steps:

[0029] Step S100: A semiconductor substrate is provided, which serves as a process platform for forming a back-illuminated image sensor in subsequent steps. Specifically, the semiconductor substrate can be any suitable substrate known in the art, such as at least one of the following materials: silicon (Si), germanium (Ge), silicon germanium (SiGe), silicon carbide (SiC), silicon carbide (SiGeC), indium arsenide (InAs), gallium arsenide (GaAs), indium phosphide (InP), or other III / V compound semiconductors, including multilayer structures composed of these semiconductors, or silicon-on-insulator (SOI), silicon-on-insulator stacked (SSOI), silicon-on-insulator stacked (S-SiGeOI), silicon-on-insulator (SiGeOI), and germanium-on-insulator (GeOI), or it can be a double-side polished wafer (DSP), or a ceramic substrate such as alumina, a quartz, or a glass substrate. Exemplarily, in this embodiment, the semiconductor substrate is, for example, a silicon substrate (silicon wafer).

[0030] In this embodiment, since the material used to form the semiconductor substrate is a silicon substrate, there is a risk that if the decoupling plasma oxidation (DPO) process takes too long, the surface of the silicon substrate will be exposed to the plasma environment for an extended period. Combined with the temperature effect, this can cause damage to the surface of the silicon substrate. Consequently, when other components constituting the back-illuminated image sensor, such as photodiodes, are formed within or on the surface of the silicon substrate, issues such as… Figure 1 As shown, there are problems with dark current and white noise (WP).

[0031] To address this issue, the researchers of this invention discovered that by altering the process duration of the decoupled plasma oxidation (DPO) process (shortening the process duration), the time the silicon substrate surface is exposed to the plasma environment can be changed. This reduces the thickness of the oxide layer formed on the silicon substrate surface, thereby reducing silicon damage caused by the impact of plasma on the silicon surface during the DPO process. Consequently, the dark current caused by silicon surface damage can be avoided. In other words, the manufacturing method provided by this invention can avoid dark current caused by silicon surface damage and white pixel problems, ultimately achieving the goal of improving the performance of back-illuminated image sensor devices.

[0032] Step S200: Obtain the standard parameter values ​​of the decoupled plasma oxidation process, and adjust the standard process parameter values ​​of the decoupled plasma oxidation process so that the thickness of the oxide layer formed on the surface of the semiconductor substrate using the adjusted decoupled plasma oxidation process is less than the thickness formed using the standard parameter values ​​by a preset target thickness.

[0033] In this embodiment, the process parameters of the decoupled plasma oxidation (DPO) process in the prior art for forming a back-illuminated image sensor can be obtained first. These parameters may include, for example, temperature parameters, process duration parameters, process gas type, and other parameters. In this embodiment, the process parameters of the decoupled plasma oxidation (DPO) process in the prior art are referred to as standard parameter values. The innovation of this invention lies in adjusting the standard process parameter values ​​of the decoupled plasma oxidation process. This allows for a reduction in the thickness of the oxide layer formed on the silicon substrate surface, reducing silicon damage caused by the impact of plasma on the silicon surface during the DPO process, and consequently, reducing dark current caused by silicon surface damage. In other words, the manufacturing method provided by this invention can avoid dark current and white pixel problems caused by silicon surface damage, ultimately achieving the goal of improving the performance of the back-illuminated image sensor device.

[0034] Specifically, this embodiment of the invention provides a specific step for adjusting the standard process parameter values ​​of the decoupled plasma oxidation process, including: reducing the process duration in the decoupled plasma oxidation process. The specific reduction amount depends on the target thickness value of the oxide layer covering the silicon substrate surface formed using the decoupled plasma oxidation process, which is designed based on the actual situation.

[0035] As an example, in this embodiment of the invention, the specific value for reducing or shortening the standard process parameter value of the decoupled plasma oxidation process is based on the target thickness value of the oxide layer covering the silicon substrate surface formed using the decoupled plasma oxidation process. The thickness of the oxide layer formed on the surface of the semiconductor substrate (silicon substrate) using the adjusted decoupled plasma oxidation process (DPO) varies depending on the specific conditions. Specifically, in this embodiment of the invention, the range of values ​​for the predetermined target thickness by which the thickness formed using standard parameter values ​​is reduced compared to the thickness formed using standard parameter values ​​is [range missing]. Specifically, the target thickness can be

[0036] and Furthermore, the range of values ​​formed by any two of the aforementioned specific parameter values ​​is within the protection scope of this application. In this embodiment, it is preferable to set the target thickness value to... In other words, the thickness of the oxide layer formed on the surface of the silicon substrate using the process parameters provided by this invention is smaller than the thickness of the oxide layer formed using process parameters selected using the prior art.

[0037] Furthermore, based on the determined range of the predetermined target thickness reduction between the thickness of the oxide layer formed on the surface of the semiconductor substrate (silicon substrate) using the adjusted decoupled plasma oxidation process DPO and the thickness formed using standard parameter values, the process duration of the adjusted decoupled plasma oxidation process DPO in this invention can be determined. That is, compared to the prior art, the shortening range of the process duration of the decoupled plasma oxidation process DPO provided by this invention relative to the prior art can, for example, be 1 minute to 30 minutes, i.e., any one of 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, 11 minutes, 12 minutes, 13 minutes, 14 minutes, 15 minutes, 16 minutes, 17 minutes, 18 minutes, 19 minutes, 20 minutes, 21 minutes, 22 minutes, 23 minutes, 24 minutes, 25 minutes, 26 minutes, 27 minutes, 28 minutes, 29 minutes, and 30 minutes. Preferably, in this embodiment of the invention, the range for shortening the process duration is such that the value used to form the target thickness value is set to... The time range.

[0038] Furthermore, in the manufacturing method of the back-illuminated image sensor provided by the present invention, the temperature range of the decoupled plasma oxidation process can be 200℃~500℃, specifically 200℃, 250℃, 300℃, 350℃, 400℃, 450℃ and 500℃.

[0039] It is understood that the surface of the semiconductor substrate provided in the embodiments of the present invention may also form one or two layers of natural oxide (silicon dioxide) on its silicon surface due to exposure to the outside. Therefore, when performing step S200, the natural oxide layer may be removed first by a wet etching process or a dry etching process, and then the etching contaminants remaining on the film surface may be removed by a wet cleaning process.

[0040] Step S300: Perform subsequent processes on the semiconductor substrate containing the oxide layer to form the electrical structure of the back-illuminated image sensor, which includes at least a photodiode region.

[0041] In this embodiment of the invention, after the oxide layer (silicon dioxide) is formed, semiconductor processes such as deposition, etching, and ion implantation can be used to form the various devices constituting the back-illuminated image sensor on or inside the semiconductor substrate. Since the semiconductor silicon substrate provided by this invention is a silicon substrate treated with a decoupled plasma oxidation (DPO) process with a shortened duration as described in step S200 above, the silicon surface of this substrate is effectively protected from silicon damage caused by the impact and destruction of the silicon surface by plasma during the DPO process, and consequently, from the dark current caused by silicon surface damage. That is, the manufacturing method provided by this invention can avoid dark current caused by silicon surface damage. Figure 3 As shown, and addressing the white pixel issue, the goal of improving the performance of back-illuminated image sensor devices was ultimately achieved.

[0042] Furthermore, based on the above Figure 2 The present invention also provides a back-illuminated image sensor, specifically, the back-illuminated image sensor can be prepared using the back-illuminated image sensor manufacturing method described above.

[0043] In summary, the manufacturing method of a back-illuminated image sensor provided by this invention reduces the thickness of the oxide layer formed on the silicon substrate surface by decreasing the deposition time of the decoupled plasma oxidation (DPO) process. This reduces silicon damage caused by the impact of plasma on the silicon surface during the DPO process, and consequently, dark current caused by silicon surface damage. In other words, the manufacturing method provided by this invention can avoid dark current and white pixel problems caused by silicon surface damage, ultimately achieving the goal of improving the performance of the back-illuminated image sensor device.

[0044] It should be noted that although the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the present invention. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of the present invention based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention shall still fall within the scope of protection of the present invention.

[0045] It should also be understood that, unless otherwise specified or indicated, the terms “first,” “second,” “third,” etc., in the specification are used only to distinguish the various components, elements, and steps in the specification, and not to indicate the logical or sequential relationships between the various components, elements, and steps.

[0046] Furthermore, it should be recognized that the terminology described herein is used only to describe particular embodiments and not to limit the scope of the invention. It must be noted that the singular forms “a” and “an” used herein and in the appended claims include plural bases unless the context clearly indicates otherwise. For example, a reference to “a step” or “an apparatus” means a reference to one or more steps or apparatuses, and may include secondary steps and secondary apparatuses. All conjunctions used should be understood in the broadest sense. Also, the word “or” should be understood to have the definition of logical “or” rather than logical “exclusive OR”, unless the context clearly indicates otherwise. Furthermore, implementation of the methods and / or devices in embodiments of the invention may include performing selected tasks manually, automatically, or in combination.

Claims

1. A method for manufacturing a back-illuminated image sensor, characterized in that, It should include at least the following steps: Provide a semiconductor substrate; Obtain the standard parameter values ​​of the decoupled plasma oxidation process, and adjust the standard process parameter values ​​of the decoupled plasma oxidation process so that the thickness of the oxide layer formed on the surface of the semiconductor substrate using the adjusted decoupled plasma oxidation process is reduced by a preset target thickness compared with the thickness formed using the standard parameter values. Subsequent processes are performed on the semiconductor substrate containing the oxide layer to form the electrical structure of the back-illuminated image sensor, which includes at least a photodiode region. The step of adjusting the standard process parameter values ​​of the decoupled plasma oxidation process includes: reducing the process duration in the decoupled plasma oxidation process; The process duration in the decoupled plasma oxidation process that reduces process deposition time ranges from 1 minute to 30 minutes.

2. The method for manufacturing a back-illuminated image sensor as described in claim 1, characterized in that, The temperature range for the decoupled plasma oxidation process is 200℃~500℃.

3. The method for manufacturing a back-illuminated image sensor as described in claim 1, characterized in that, The range of the preset target thickness, in which the thickness of the oxide layer formed on the surface of the semiconductor substrate using the adjusted decoupled plasma oxidation process is reduced by the thickness formed using standard parameter values, is 1 μm to 100 μm.

4. The method for manufacturing a back-illuminated image sensor as described in claim 1, characterized in that, At least one natural oxide layer is also formed on the surface of the provided semiconductor substrate.

5. The method for manufacturing a back-illuminated image sensor as described in claim 4, characterized in that, Before forming the oxide layer on the surface of the semiconductor substrate, the manufacturing method further includes etching away the natural oxide layer.

6. The method for manufacturing a back-illuminated image sensor as described in claim 1, characterized in that, The reaction gas in the decoupled plasma oxidation process includes oxygen.

7. The method for manufacturing a back-illuminated image sensor as described in claim 1, characterized in that, The semiconductor substrate is a silicon substrate.

8. A back-illuminated image sensor, characterized in that, It is manufactured using the back-illuminated image sensor manufacturing method according to any one of claims 1 to 7.

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