Silicon-based resonant cavity photodiode for image sensors

Abstract

An imager with pixels having a resonant-cavity photodiode. The resonant cavity photodiode increases absorption of light having long wavelengths. A trench is formed for the photodiode and reflective film is grown on the bottom of the trench. The reflective film reflects light that is not initially absorbed back to the active region of the photodiode.

1 - 41 . (canceled)  
     
     
         42 . A method of forming an image sensor comprising the acts of: 
 forming a trench within a substrate of the image sensor;    forming a reflective layer on at least one surface of the trench; and    forming a photoconversion device within the trench over the reflective layer.    
     
     
         43 . The method according to  claim 42 , wherein the trench is formed to a depth in the range of about 0.5 μm to about 10 μm.  
     
     
         44 . The method according to  claim 42 , wherein the trench comprises sidewalls.  
     
     
         45 . The method according to  claim 44 , wherein the sidewalls comprise nitride.  
     
     
         46 . The method according to  claim 44 , wherein the sidewalls comprise an oxide layer.  
     
     
         47 . The method according to  claim 42 , wherein the reflective layer is an oxide layer.  
     
     
         48 . The method according to  claim 47 , wherein the oxide layer is formed to a thickness in the range of about 100 Å to about 300 Å.  
     
     
         49 . The method according to  claim 42 , wherein the photoconversion device comprises polysilicon.  
     
     
         50 . The method according to  claim 49 , wherein the photoconversion device comprises doped polysilicon having a p-n junction.  
     
     
         51 . The method according to  claim 49 , wherein the photoconversion device comprises hydrogenated amorphous polysilicon.  
     
     
         52 . The method according to  claim 49 , wherein the photoconversion device comprises deuteriated amorphous polysilicon.  
     
     
         53 . The method according to  claim 49 , wherein the photoconversion device comprises fluorinated polysilicon.  
     
     
         54 . The method according to  claim 42 , wherein the trench is formed with carrier multiplication layers.  
     
     
         55 . The method according to  claim 54 , wherein said carrier multiplication layers comprise alternating layers of semiconducting films.  
     
     
         56 . The method according to  claim 55 , wherein said carrier multiplication layers comprise alternating layers of Si x Ge 1-x , where x is a mole fraction, from about 0 to about 10.  
     
     
         57 . The method according to  claim 42 , further comprising the act of forming an insulator layer beneath said substrate.  
     
     
         58 . The method according to  claim 57 , wherein said insulator layer comprises an oxide.  
     
     
         59 . The method according to  claim 57 , wherein said insulator layer comprises sapphire.  
     
     
         60 . The method according to  claim 42 , further comprising the act of forming a second reflective layer, the second reflective layer having an index of refraction such that at least a portion of incident light striking the photoconversion device is reflected back toward the active region of the photoconversion device.  
     
     
         61 . The method according to  claim 60 , wherein said second reflective layer comprises dielectric materials.  
     
     
         62 . The method according to  claim 61 , wherein said dielectric materials are selected from the group consisting of silicon dioxide, plasma enhanced chemical vapor deposited oxide, fluorinated silica glass oxide, silicon nitride, high density plasma oxide, spin-on-dielectric oxide, and carbon doped silicon dioxides.  
     
     
         63 . The method according to  claim 60 , wherein said first refractive index is greater than said second refractive index.  
     
     
         64 . The method according to  claim 60 , wherein said first reflective layer comprises an alternating pattern of material having said first refractive index and material having said second refractive index material.  
     
     
         65 . The method according to  claim 60 , wherein said first reflective layer comprises a pattern of material having said first refractive index layered over material having said second refractive index.  
     
     
         66 . The method according to  claim 65 , wherein said first refractive index material layer is layered in a continuous layer across the top of said second refractive index material.  
     
     
         67 . The method according to  claim 65 , wherein said first refractive index material layer has openings and is not continuous across the top of said second refractive index material layer.  
     
     
         68 . A method of forming an image sensor comprising: 
 forming a trench for a photoconversion device within a substrate of the image sensor;    depositing a spacer layer on sidewalls of the trench;    etching the spacer layer such that the bottom surface of the trench is exposed;    growing an oxide layer on the exposed bottom surface of the trench; and    forming a photconversion device within the trench, wherein the oxide layer on the bottom surface of the trench has an index of refraction that reflects at least a portion of incident light.    
     
     
         69 . The method according to  claim 68 , wherein said trench is formed to a depth in the range of about 0.5 μm to about 10 μm.  
     
     
         70 . The method according to  claim 68 , wherein said spacer comprises nitride.  
     
     
         71 . The method according to  claim 68 , wherein said spacer comprises an oxide layer.  
     
     
         72 . The method according to  claim 71 , wherein the oxide layer has a thickness in the range of about 100 Å to about 300 Å.  
     
     
         73 . The method according to  claim 68 , wherein the photoconversion device comprises polysilicon.  
     
     
         74 . The method according to  claim 73 , wherein the photoconversion device comprises doped polysilicon having a p-n junction.  
     
     
         75 . The method according to  claim 68 , further comprising the act of forming a second reflective layer, the second reflective layer having an index of refraction such that at least a portion of incident light striking the photoconversion device is reflected back toward the active region of the photoconversion device.  
     
     
         76 . The method according to  claim 75 , wherein said second reflective layer comprises dielectric materials.  
     
     
         77 . The method according to  claim 76 , wherein said dielectric materials are selected from the group consisting of silicon dioxide, plasma enhanced chemical vapor deposited oxide, fluorinated silica glass oxide, silicon nitride, high density plasma oxide, spin-on-dielectric oxide, and carbon doped silicon dioxides.  
     
     
         78 . The method according to  claim 75 , wherein said first refractive index is greater than said second refractive index.  
     
     
         79 . The method according to  claim 75 , wherein said first reflective layer comprises an alternating pattern of material having said first refractive index and material having said second refractive index material.  
     
     
         80 . The method according to  claim 75 , wherein said first reflective layer comprises a pattern of material having said first refractive index layered over material having said second refractive index.  
     
     
         81 . The method according to  claim 80 , wherein said first refractive index material layer is layered in a continuous layer across the top of said second refractive index material.  
     
     
         82 . The method according to  claim 80 , wherein said first refractive index material layer has openings and is not continuous layer across the top of said second refractive index material layer.