Design And Optfmization Of CMOS Image Sensor Pixel

As the resolution of the CMOS image sensor increases,the pixel size and pixel pitch continue to shrinkage,which causes two serious problems:quantum efficiency degradation of the pixel and the crosstalk increase between pixels.In response to these problems;,this paper studies the factors that affect quantum efficiency and crosstalk,and designs and optimizes the pixel structure.The main research contents and results are as follows:1.In order to increase the quantum efficiency of the pixel,A "Stepped" pinned photodiodes applied to the pixel structure is studied.The structure first uses phosphorus to form a lightly doped N2 buried layer directly below the N buried layer of the traditional pinned photodiodes,which expands the N buried layer and helps to improve the quantum efficiency and full well capacity of the pixel;Then insert a high-concentration N3 buried layer at the position where the clamped photodiode is connected to the transmission tube,to eliminate the problem of reduced charge transfer efficiency caused by the longitudinal expansion of the N buried layer.The results show that,compared with the traditional pixel,the full well capacity has increased from the original 1208e-to 4097e-,an increase of 239.16%;when the incident light wavelength is 420nm,560nm,780nm and 900nm the quantum efficiency is increased by 1.1%,1.8%,5.6%and 11.2%.And in this process,the charge transfer efficiency did not decrease.2,In order to reduce crosstalk between pixels,the effect of epitaxial layer thickness and substrate concentration on quantum efficiency and crosstalk characteristics was studied.The results show that when the thickness of the epitaxial layer is greater than 5?m,the quantum efficiency increases as the thickness of the epitaxial layer decreases,and crosstalk decreases as the thickness of the epitaxial layer decreases.When the thickness of the epitaxial layer is less than 5?m,quantum efficiency and crosstalk both decrease as the thickness of the epitaxial layer decreases.When the substrate concentration increases from 1.0×10-14cm-3 to 10×1017cm-3,the quantum efficiency is significantly enhanced,and the crosstalk is significantly reduced.However,when the substrate concentration is greater than 1.0×1016cm-3,the increase in quantum efficiency gain is negligible,and the decreasing trend of crosstalk decreases with increasing substrate concentration.Finally,the thickness of the epitaxial layer was determined to be 5?m,and the substrate concentration was 1.0×1016cm-3.Compared with before optimization,when the incident light wavelength is 700nm,the quantum efficiency is increased by 6.53%,and the crosstalk is reduced by 31.47%3.Finally,combined with the 0.11?m CMOS image sensor manufacturing process of front-side illuminated,the main structure and process flow of the stepped pinned photodiodes pixel are detailed.Furthermore,the structure of the stepped pinned photodiodes pixel is realized through process simulation,and the feasibility of the stepped pinned photodiodes pixel is explained.