Image sensor forming method and image sensor

Abstract

The invention provides an image sensor forming method, which comprises the following steps of: arranging a plurality of pixel unit groups comprising first pixel units and second pixel units, and forming first photosensitive areas and second photosensitive areas corresponding to the first pixel units and the second pixel units in a semiconductor substrate; forming a plurality of first absorption enhancement structures and second absorption enhancement structures on the semiconductor substrate at the upper part of the first photosensitive region and the upper part of the second photosensitive region respectively, the two side faces of the first absorption enhancement structure and the two side faces of the second absorption enhancement structure respectively form included angles with different sizes with the surface of the semiconductor substrate, and the first absorption enhancement structure and the second absorption enhancement structure are in central symmetry relative to the midpoint of the first pixel unit and the midpoint of the second pixel unit.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to an image sensor forming method and an image sensor. Background Technology

[0002] Phase detection autofocus (PDAF) is a common method for achieving fast focusing functionality in image sensors.

[0003] Currently, the main methods for implementing PDAF are: ① Half-Shield structure, which can quickly determine the focusing distance and achieve fast focusing by detecting the phase difference of the light received by the left and right shielded pixels; ② Super PD structure, which is a PDAF structure with one microlens corresponding to 1×2 dual pixels; ③ Qual PD structure, in which the entire pixel array uses one microlens corresponding to 2×2 quad pixel PDAF units; ④ Dual PD structure, which divides the pixel into two parts to obtain information from the global photodiode.

[0004] However, in the above methods, the metal shielding method such as semi-shielding can easily affect the response sensitivity of the pixel unit. Qual PD and Super PD structures are prone to large crosstalk and are severely affected by process fluctuations. Dual PD structure pixel design is more difficult. Summary of the Invention

[0005] The purpose of this invention is to provide an image sensor forming method, comprising: A plurality of pixel unit groups including a first pixel unit and a second pixel unit are provided, and a first photosensitive area and a second photosensitive area corresponding to each first pixel unit and the second pixel unit are formed in a semiconductor substrate; A plurality of first absorption enhancement structures and second absorption enhancement structures are formed on the semiconductor substrate above the first photosensitive area and the second photosensitive area, respectively. The two sides of the first absorption enhancement structure and the second absorption enhancement structure form angles of different sizes with the surface of the semiconductor substrate, and the first absorption enhancement structure and the second absorption enhancement structure are centrally symmetrical with respect to the midpoint of the first pixel unit and the second pixel unit.

[0006] Furthermore, the first side and the second side of the first absorption enhancement structure form a first angle and a second angle of different sizes with the surface of the semiconductor substrate, respectively. The third side and the fourth side of the second absorption enhancement structure form a third angle and a fourth angle of different sizes with the surface of the semiconductor substrate, respectively. The first angle and the fourth angle are equal, and the second angle and the third angle are equal.

[0007] Furthermore, after forming the first absorption-enhancing structure and the second absorption-enhancing structure, the method further includes: A dielectric layer is formed on the first absorption enhancement structure and the second absorption enhancement structure by a deposition process.

[0008] Furthermore, the refractive index of the dielectric layer is less than that of the semiconductor substrate.

[0009] Furthermore, after forming the dielectric layer, the process further includes: This forms color filters and microlens structures.

[0010] Furthermore, forming the first absorption-enhancing structure and the second absorption-enhancing structure includes: A mask layer having the shapes of the first absorption enhancement structure and the second absorption enhancement structure is formed above the surface of the semiconductor substrate; The semiconductor substrate is etched using the mask layer to form the first absorption enhancement structure and the second absorption enhancement structure that undulate along the surface of the semiconductor substrate.

[0011] Further, forming the first absorption-enhancing structure and the second absorption-enhancing structure includes: The first absorption enhancement structure and the second absorption enhancement structure are respectively formed in an array on the semiconductor substrate above the first photosensitive region and the second photosensitive region.

[0012] The present invention also provides an image sensor formed using the image sensor forming method described above.

[0013] This invention proposes a novel image sensor fabrication method using the aforementioned scheme, which leverages an absorption enhancement structure with a centrally symmetric pattern to achieve phase detection autofocus. The absorption enhancement structure in this invention not only provides the phase information required for phase autofocus but also reduces the reflectivity of the semiconductor substrate, increasing the effective absorption of light by the semiconductor substrate, thereby improving the quantum efficiency of the image sensor.

[0014] The phase focusing method proposed in this invention will not affect the response sensitivity of pixels due to metal obstruction or other reasons, nor will it have the problems of large crosstalk and susceptibility to process fluctuations in the four-pixel structure. It can also increase the quantum efficiency of the image sensor and can be applied to all pixel units of the image sensor pixel array. Attached Figure Description

[0015] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments, taken in conjunction with the accompanying drawings.

[0016] Figure 1This is a schematic diagram of the structure of an image sensor in one embodiment of the present invention; Figure 2 This is a schematic diagram of the image sensor structure in another embodiment of the present invention; Figure 3 These are top cross-sectional schematic diagrams of the image sensor in different embodiments of the present invention; Figure 4 This is a schematic diagram of the image sensor formation process in another embodiment of the present invention.

[0017] Throughout the figures, the same or similar reference numerals denote the same or similar devices (modules) or steps. Detailed Implementation

[0018] In image sensors with PDAF, the PDAF function is implemented through pixel unit groups. In an optional embodiment of the present invention, a pair of PDAF pixels is also provided, which can be achieved through the following steps: Step S100: During the formation of the image sensor, a plurality of pixel unit groups including a first pixel unit P1 and a second pixel unit P2 are set, and a first photosensitive area 110 and a second photosensitive area 120 corresponding to each of the first pixel unit P1 and the second pixel unit P2 are formed in the semiconductor substrate 100. Step S200: A plurality of first absorption enhancement structures 111 and second absorption enhancement structures 121 are formed on the semiconductor substrate 100 on the upper part of the first photosensitive region 110 and the upper part of the second photosensitive region 120, respectively, as follows: Figure 1 As shown. During formation, the two sides of the first absorption enhancement structure 111 and the second absorption enhancement structure 121 are respectively arranged to form angles of different sizes with the surface of the semiconductor substrate 100, such as... Figure 2 As shown. Furthermore, the first absorption enhancement structure 111 and the second absorption enhancement structure 121 are centrally symmetrical with respect to the midpoint of the first pixel unit P1 and the second pixel unit P2.

[0019] In an optional embodiment, the first side surface 111a and the second side surface 111b of the first absorption enhancement structure 111 form a first angle A1 and a second angle A2 of different sizes with the surface of the semiconductor substrate 100, respectively. The third side surface 121a and the fourth side surface 121b of the second absorption enhancement structure 121 form a third angle B1 and a fourth angle B2 of different sizes with the surface of the semiconductor substrate 100, respectively. To achieve phase detection autofocus, the first angle A1 is equal to the fourth angle B2, and the second angle A2 is equal to the third angle B1, i.e., it presents a centrally symmetrical structure, such as... Figure 2 As shown.

[0020] In an optional embodiment, the arrangement of the absorption enhancement structures within a pixel unit is centrally symmetrical with respect to the midpoint between two pixel units. For example, to better achieve phase focusing functionality, when forming the first absorption enhancement structure 111 and the second absorption enhancement structure 121 in step S200, the first absorption enhancement structure 111 and the second absorption enhancement structure 121 can be arrayed on the semiconductor substrate 100 above the first photosensitive region 110 and the second photosensitive region 120, respectively. Figure 3 As shown, except Figure 3 Besides the 3×3 arrangement, other array methods can also be used.

[0021] In another embodiment, one side of the absorption enhancement structure of the present invention may be perpendicular to the surface of the semiconductor substrate 100, such as... Figure 1 As shown, the shapes of the first absorption enhancement structure 111 and the second absorption enhancement structure 121 are centrally symmetrical with respect to the midpoint of the two pixel units.

[0022] The absorption enhancement structure with a centrally symmetric pattern proposed in this invention can not only provide the phase information required for PDAF, but also reduce the reflectivity of the semiconductor substrate in the image sensor and increase the effective absorption of light by the substrate, thereby improving the quantum efficiency of the image sensor.

[0023] Compared to traditional methods, the design in this invention effectively avoids the impact of factors such as metal obstruction on the response sensitivity of pixels. It also avoids the problems of large crosstalk and susceptibility to process fluctuations in existing four-pixel structures, and can increase the quantum efficiency of image sensors. It can be applied to all pixel units of image sensor pixel arrays.

[0024] In one optional embodiment, when forming the first absorption enhancement structure 111 and the second absorption enhancement structure 121 in step S200, the following steps can be taken: Step S210: A mask layer 200 having the shapes of the first absorption enhancement structure 111 and the second absorption enhancement structure 121 is formed above the surface of the semiconductor substrate 100, such as... Figure 4 As shown; Step S220: The semiconductor substrate 100 is etched using the mask layer 200 to form the first absorption enhancement structure 111 and the second absorption enhancement structure 121 undulating along the surface of the semiconductor substrate 100.

[0025] Optionally, after the first absorption enhancement structure 111 and the second absorption enhancement structure 121 are formed, a dielectric layer 130 can be formed on the first absorption enhancement structure 111 and the second absorption enhancement structure 121 by a deposition process, such as... Figure 1 As shown. Specifically, the refractive index of the dielectric layer 130 is less than that of the semiconductor substrate 100.

[0026] In an optional embodiment, after forming the dielectric layer 130, a color filter 300 and a microlens structure 400 can be formed, such as... Figure 1 As shown, the structure of the image sensor is further completed.

[0027] The present invention also provides an image sensor formed using the image sensor forming method described above.

[0028] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and not restrictive in any way. Furthermore, it is clear that the word "comprising" does not exclude other elements and steps, and the word "a" does not exclude a plural. Multiple elements recited in the apparatus claims may also be implemented by a single element. The terms "first," "second," etc., are used to denote names and do not indicate any particular order.

Claims

1. A method for forming an image sensor, characterized in that, include: A plurality of pixel unit groups including a first pixel unit and a second pixel unit are provided, and a first photosensitive area and a second photosensitive area corresponding to each first pixel unit and the second pixel unit are formed in a semiconductor substrate; A plurality of first absorption enhancement structures and second absorption enhancement structures are formed on the semiconductor substrate above the first photosensitive area and the second photosensitive area, respectively. The two sides of the first absorption enhancement structure and the second absorption enhancement structure form angles of different sizes with the surface of the semiconductor substrate, and the first absorption enhancement structure and the second absorption enhancement structure are centrally symmetrical with respect to the midpoint of the first pixel unit and the second pixel unit.

2. The image sensor forming method as described in claim 1, characterized in that, The first side and the second side of the first absorption enhancement structure form a first angle and a second angle of different sizes with the surface of the semiconductor substrate, respectively. The third side and the fourth side of the second absorption enhancement structure form a third angle and a fourth angle of different sizes with the surface of the semiconductor substrate, respectively. The first angle and the fourth angle are equal, and the second angle and the third angle are equal.

3. The image sensor forming method as described in claim 1, characterized in that, After forming the first absorption enhancement structure and the second absorption enhancement structure, the method further includes: A dielectric layer is formed on the first absorption enhancement structure and the second absorption enhancement structure by a deposition process.

4. The image sensor forming method as described in claim 3, characterized in that, The refractive index of the dielectric layer is less than that of the semiconductor substrate.

5. The image sensor forming method as described in claim 3, characterized in that, After forming the dielectric layer, the method further includes: This forms color filters and microlens structures.

6. The image sensor forming method as described in claim 1, characterized in that, The formation of the first absorption enhancement structure and the second absorption enhancement structure includes: A mask layer having the shapes of the first absorption enhancement structure and the second absorption enhancement structure is formed above the surface of the semiconductor substrate; The semiconductor substrate is etched using the mask layer to form the first absorption enhancement structure and the second absorption enhancement structure that undulate along the surface of the semiconductor substrate.

7. The image sensor forming method as described in claim 1, characterized in that, Forming the first absorption-enhancing structure and the second absorption-enhancing structure includes: The first absorption enhancement structure and the second absorption enhancement structure are respectively formed in an array on the semiconductor substrate above the first photosensitive region and the second photosensitive region.

8. An image sensor, characterized in that, It is formed using the image sensor forming method as described in claims 1 to 7.

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