Image sensor

Abstract

The invention discloses an image sensor, which relates to the technical field of semiconductors. The periphery of a medium layer on the surface of a photosensitive area adopts alternate laminations which have medium materials with different refractive indexes such as ABAB and the like as a side wall reflecting layer to form a light path, and light is confined to a corresponding pixel photosensitive area and is prevented from going into adjacent pixel photosensitive areas, so that the cross interference is reduced, and the effective photosensitive efficiency of the photosensitive area is improved. The side wall reflecting layer achieves reflection of incident light in different ranges by selecting proper medium materials and periods, so that the incident light of corresponding wave bands is limited to the light path, the cross interference is further avoided, and the transmission efficiency and the absorption efficiency of the incident light are improved. Dielectric constants of inter layer medium layers are increased from top to bottom, that is, refractive indexes are increased progressively, good condensation effect is achieved, light which goes into the side wall reflecting layer is reduced, and the absorption efficiency of the incident light is further improved.

Description

technical field [0001] The invention relates to the technical field of semiconductors, in particular to an image sensor with a light path. Background technique [0002] As we all know, an image sensor is a semiconductor device that converts an optical image into an electrical signal. Image sensors can be generally classified into two types: Charge-Coupled Device (CCD for short) and Complementary Metal Oxide Semiconductor (CMOS for short) image sensors. [0003] According to its readout method, existing CMOS image sensors can be roughly divided into passive pixel sensor (Passive Pixel Sensor, referred to as "PPS"), active pixel sensor (Active Pixel Sensor, referred to as "APS") and digital pixel sensor. There are three types of sensors (Digital Pixel Sensor, referred to as "DPS"). [0004] figure 1 and figure 2 are the photosensitive conditions in the image sensor structure under ideal conditions and actual conditions, respectively. [0005] like figure 1 As shown, in ...

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Problems solved by technology

[0006] However, in actual work, due to the extremely small size of the pixel unit compared to the external environment to be detected, the light-gathering effect of the microlens is limited. After a large amount of light enters the interlayer dielectric layer, it will not only enter the photosensitive area of ​​the corresponding pixel, It also enters the photosensitive area of ​​​​the adjacent pixel, such as figure 2 As shown, thereby causing crosstalk and reducing the effective photosensitive efficiency of the photosensitive area

[0007] In the prior art, it has been proposed that an air hole is formed by etching around the dielectric layer above the photosensitive area, thereby forming a waveguide-like optical path above the photosensitive area, and confining most of the incident light to be transmitted in this path, but This method has limited restrictions on light, especially the dielectric layer above the photosensitive area is usually a low dielectric constant material, and the refractive index is usually low (generally about 1.5); in addition, it has also been proposed that the dielectric layer above the photosensitive area Around, a continuous metal layer is used as a reflective layer to prevent the impact of incident light on adjacent pixels, but metal has a certain absorption effect on electromagnetic waves. With the further shrinking of the size of CMOS image sensors, for certain limit wavelengths of light, It can be regarded as an electromagnetic wave approximately, and the absorption effect of metal cannot be ignored

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