Image sensor with infrared enhancement structure

Abstract

The invention discloses an image sensor with infrared enhancement structures and a preparation method thereof, and the method comprises the steps: arranging a plurality of crossed infrared enhancement structures and / or incompletely surrounded infrared enhancement structures in a plurality of pixel regions of a CMOS image sensor, and enabling incident light to be better limited and retained in a photodiode region; therefore, the infrared light absorption efficiency of different wave bands is enhanced.

Description

Technical Field

[0001] The present invention relates to the field of image sensors, and in particular to an image sensor with an infrared enhancement structure. Background Art

[0002] CMOS (Complementary Metal-Oxide-Semiconductor) image sensors have the advantages of simple process, easy integration with other devices, small size, light weight, low power consumption, and low cost. Therefore, with the development of technology, CMOS image sensors are increasingly replacing CCD (Charge-coupled Device) image sensors in various electronic products. At present, CMOS image sensors have been widely used in static digital cameras, camera phones, digital video cameras, medical cameras (such as gastroscopes), automotive cameras, etc. CMOS image sensors can be divided into FSI (Front Side Illumination) and BSI (Back Side Illumination).

[0003] The image sensor operates in response to image light from an external scene being irradiated on the image sensor. The image sensor includes a pixel array having a portion that absorbs incident light and a photosensitive element (e.g., a photodiode) that generates image charge after absorbing the image light, and the pixel array is composed of a plurality of pixel units arranged in an array. The photosensitive element within the pixel unit changes according to changes in the incident image light, thereby generating different images according to the incident light.

[0004] The image quality and light sensitivity of image sensors are particularly important indicators, especially in the NIR (Near Infrared) band. The level of QE (Quantum Efficiency) has a great influence on the imaging quality of image sensors. Improving the QE of image sensors in the NIR band is of great significance to improving the imaging quality of image sensors. Summary of the invention

[0005] The purpose of the present invention is to provide an image sensor with an infrared enhancement structure and a preparation method thereof, wherein at least one groove with a polygonal cross-section is formed on the light incident surface of a pixel unit of a back-illuminated image sensor to increase the number of reflections, scatterings or refractions of incident light in the pixel unit, thereby increasing the optical path of the incident light in the pixel area, enhancing the image sensor's ability to capture incident light, reducing light energy reflection losses, and improving the device's light absorption and conversion efficiency.

[0006] To achieve the above objectives, the present invention provides an image sensor with an infrared enhancement structure, comprising a plurality of pixel units, wherein at least one pixel unit has at least one group of grooves; the grooves include at least one group of cross structures and / or at least one group of incomplete surrounding structures to improve the infrared absorption quantum efficiency of the image sensor.

[0007] Furthermore, the incomplete surrounding structures are all located around the crossing structure to reduce crosstalk between pixels through reflection and refraction.

[0008] Furthermore, the projection of the intersection on the substrate surface is a regular polygon or a circle, usually a circle.

[0009] Furthermore, the groove is formed by dry etching, and the groove has a rectangular or trapezoidal cross-sectional shape along the incident light direction.

[0010] Furthermore, the incomplete surrounding structure is composed of a plurality of discrete grooves to reduce optical crosstalk and etching damage to the substrate.

[0011] Furthermore, the present invention provides a method for enhancing the infrared absorption of an image sensor, which specifically includes providing a substrate having a plurality of pixel units, forming at least one group of grooves on the surface of at least one pixel unit, wherein the grooves include at least one group of cross structures and / or at least one group of incompletely enclosed structures formed by etching, and incident light is reflected, refracted or scattered between the cross structures and / or the incompletely enclosed structures to improve the infrared absorption quantum efficiency of the image sensor.

[0012] Furthermore, the incomplete surrounding structure is formed around the cross structure, and the incomplete surrounding structure and the cross structure are formed by synchronous etching or step-by-step etching.

[0013] Furthermore, the projection of the intersection on the substrate surface is a square or a circle.

[0014] Furthermore, the groove is formed by dry etching, and the groove has a rectangular or trapezoidal cross-sectional shape along the incident light direction.

[0015] Furthermore, the incomplete surrounding structure is composed of a plurality of discrete grooves.

[0016] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: the present invention increases the number of reflections, scatterings or refractions of incident light in the pixel unit by arranging one or more grooves with an infrared enhancement function of an incompletely enclosed structure in multiple pixel areas to improve the effective absorption of incident light by the substrate, thereby improving the quantum efficiency of the image sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings of the present invention constitute a part of this specification and are used to further understand the present invention. The drawings illustrate embodiments of the present invention and together with the description are used to explain the principle of the present invention.

[0018] Figure 1-4 Schematic diagram of the structure of the infrared enhancement structure on the light incident surface.

[0019] Figure 5-6 It is a schematic cross-sectional view along the optical axis. DETAILED DESCRIPTION

[0020] The following detailed descriptions are all illustrative and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0021] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention.

[0022] In a first aspect, the present invention provides an image sensor with an infrared enhancement structure; in a second aspect, the present invention provides a method for preparing an image sensor with an infrared enhancement structure.

[0023] The following is explained based on some examples. It should be noted that the examples of the cross structure and the incompletely enclosed infrared enhancement structure involved in the present invention are only for illustrative purposes and are not intended to limit the scope. In particular, the description of situations other than the cross structure and the surrounding incompletely enclosed structure (for example, the cross structure can be two bars crossing or multiple bars, can cross at one point or multiple points, and the incompletely enclosed structure can be four discrete bars or multiple straight or curved discrete structures, etc.) is not limited in any way, because they are all for the purpose of explaining some optional examples of the cross structure combined with the incompletely enclosed infrared enhancement structure and the preparation method.

[0024] The infrared enhancement structure of the present invention can be used in a back-illuminated image sensor. As a preferred example, Figure 1As shown, it is a top view of the light incident surface of the pixel unit of the image sensor, including a substrate 100, in which a pixel unit with a light absorption layer is arranged, wherein an incomplete surrounding structure 101 and a cross structure 102 are arranged in a plurality of pixel units, and the incomplete surrounding structure 101 and the cross structure 102 are formed by extending from one side of the substrate into the substrate to form a groove, and one or more dielectric layers are filled in the groove. The dielectric constant of the dielectric layer is smaller than the dielectric constant of the substrate, so that when the incident light is irradiated to the side wall of the incomplete surrounding structure 101, it is redirected to the side wall of the cross structure 102 of the same pixel unit, or the opposite light path mentioned above, and further scattering, refraction or reflection occurs. That is to say, the cross structure 102 and the incomplete surrounding structure 101 cooperate to make the optical path of the incident light in the pixel unit longer, while reducing the crosstalk between adjacent pixels, thereby improving the quantum efficiency of the incident light.

[0025] like Figure 2 Another embodiment is illustrated, including a substrate 100, in which a pixel unit having a light absorption layer is arranged, wherein an incomplete surrounding structure 101 and a cross structure 102 are arranged in a plurality of pixel units, wherein the incomplete surrounding structure 101 and the cross structure 102 are formed by extending from one side of the substrate into the substrate to form a groove, and one or more dielectric layers are filled in the groove. Different from the first embodiment, the cross structure in the second embodiment is two horizontal lines and two vertical lines perpendicular to each other with four different intersections, which can be applied to pixel units of larger size. By arranging multiple grooves in the cross structure, the incident light can be reflected back and forth multiple times in the pixel unit, thereby increasing the optical path of the incident light, and further improving the quantum efficiency.

[0026] like Figure 3 As shown, another embodiment of the present invention is different from the first embodiment in that the grooves in the cross structure 102 and the incompletely enclosed structure 101 may not be parallel to the pixel unit along the surface of the substrate 100, and may be 0-90°, and 45° is preferred in this embodiment.

[0027] like Figure 4 As shown, it is another embodiment of the present invention. Different from the first embodiment, the intersection area of ​​the intersection structure 102 may include a centrally symmetrical figure, such as a circle, a square, a regular hexagon, etc. The present embodiment preferably uses a square. In some other embodiments, it may also be at a certain angle, such as an angle between 0-90°.

[0028] In some embodiments, the crossing structure 102 may also be a plurality of grooves that intersect at the same point in the pixel unit region, thereby combining with the incomplete surrounding structure 101 around the crossing structure 102 to jointly increase the optical path of the incident light in the pixel unit.

[0029] like Figure 5, which is a side cross-sectional view of an embodiment of the present invention, a CMOS image sensor includes a substrate 100, a pixel unit structure is provided in the substrate 100, and some pixel unit structures include a cross structure 102, an incomplete surrounding structure 101, and a deep trench isolation structure 103 between adjacent pixel units. The cross structure 102 is located in the middle of the incomplete surrounding structure 101, and in some embodiments, the depth of the cross structure 102 is less than that of the incomplete surrounding structure 101, so as to reduce the lateral crosstalk of the incident light. The grooves of the two structures are obtained through multiple etching processes.

[0030] like Figure 6 FIG. 1 is a side cross-sectional view of another embodiment of the present invention, wherein the CMOS image sensor includes a substrate 100, wherein the substrate 100 has a pixel unit structure, wherein some pixel unit structures include a cross structure 102, an incomplete surrounding structure 101, and a deep trench isolation structure 103 between adjacent pixel units. The cross structure 102 is located in the middle of the incomplete surrounding structure 101, and in some embodiments, the depth of the cross structure 102 is less than that of the incomplete surrounding structure 101, thereby reducing the lateral crosstalk of the incident light. The grooves of the two structures are obtained through multiple etching processes. In addition, Figure 5 The difference is that the side cross-section shape of the incompletely enclosed structure is an inverted trapezoid, and in some other embodiments it can also be a triangle, a vase shape, etc.

[0031] The present invention also provides a method for preparing an image sensor with an infrared enhancement structure, by performing synchronous or distributed etching on the light incident surface of the pixel unit of the CMOS image sensor to obtain grooves projected on the substrate in a cross shape and an incompletely surrounded shape, and then filling the grooves with dielectric materials to obtain a cross structure 102 and an incompletely surrounded structure 101, thereby improving the absorption efficiency of the image sensor for infrared light.

[0032] The present invention arranges a plurality of cross structures and a plurality of incomplete surrounding structures in the light incident surface substrate of the pixel unit of the CMOS image sensor so as to reduce the refraction, scattering or reflection of the incident light when it irradiates the side walls of the cross structures and the incomplete surrounding structures, thereby increasing the optical path of the incident light in the pixel unit, so as to achieve a higher quantum efficiency for the incident light, especially infrared light.

[0033] The basic concepts have been described above. Obviously, for those skilled in the art, the above detailed disclosure is only for example and does not constitute a limitation of the present invention. Although not explicitly stated herein, those skilled in the art may make various modifications, improvements and corrections to the present invention. Such modifications, improvements and corrections are suggested in the present invention, so such modifications, improvements and corrections still belong to the spirit and scope of the exemplary embodiments of the present invention.

[0034] It should be understood that the embodiments described in the present invention are only used to illustrate the principles of the embodiments of the present invention. Other variations may also fall within the scope of the present invention. Therefore, as examples and not limitations, alternative configurations of the embodiments of the present invention may be considered consistent with the teachings of the present invention. Accordingly, the embodiments of the present invention are not limited to the embodiments explicitly introduced and described in the present invention.

Claims

1. An image sensor with infrared absorption enhancement function, characterized in that: include: A plurality of pixel units, wherein at least one pixel unit has at least one group of grooves therein; The groove includes at least one group of cross structures and / or at least one group of incomplete surrounding structures to improve the infrared absorption quantum efficiency of the image sensor.

2. The image sensor according to claim 1, wherein: The incomplete surrounding structures are all located around the crossing structure to reduce crosstalk between pixels through reflection and refraction.

3. The image sensor according to claim 1, wherein: The projection of the intersection on the substrate surface is a square or a circle.

4. The image sensor according to claim 1, wherein: The groove is formed by dry etching, and has a rectangular or trapezoidal cross-sectional shape along the incident light direction.

5. The image sensor according to claim 1, wherein: The incomplete surrounding structure is composed of a plurality of discrete grooves to reduce optical crosstalk and etching damage to the substrate.

6. A method for enhancing infrared absorption of an image sensor, characterized in that: providing a substrate having a plurality of pixel units, At least one group of grooves is formed on the light incident surface of at least one pixel unit, and the grooves include at least one group of cross structures and / or at least one group of incomplete surrounding structures formed by etching, and the incident light is reflected, refracted or scattered between the cross structures and / or the incomplete surrounding structures to improve the infrared absorption quantum efficiency of the image sensor.

7. The method according to claim 6, characterized in that The incomplete surrounding structure is formed at the periphery of the intersection structure, and the incomplete surrounding structure and the intersection structure are formed by simultaneous etching or step-by-step etching.

8. The image sensor according to claim 6, wherein: The projection of the intersection on the substrate surface is a square or a circle.

9. The method according to claim 6, characterized in that The groove is formed by dry etching, and has a rectangular or trapezoidal cross-sectional shape along the incident light direction.

10. The method according to claim 6, characterized in that The incomplete surrounding structure is composed of a plurality of discrete or continuous grooves to reduce optical crosstalk and etching damage to the substrate.

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