Pixel sensor including a transfer finfet

Abstract

A pixel sensor includes a transfer fin field effect transistor (finFET) to transfer a photocurrent from a photodiode to a drain region. The transfer finFET includes at least a portion of the photodiode, an extension region associated with the drain region, a plurality of channel fins, and a transfer gate at least partially surrounding the channel fins to control the operation of the transfer finFET. In the transfer finFET, the transfer gate is wrapped around (e.g., at least three sides) of each of the channel fins, which provides a greater surface area over which the transfer gate is enabled to control the transfer of electrons. The greater surface area results in greater control over operation of the finFET, which may reduce switching times of the pixel sensor (which enables faster pixel sensor performance) and may reduce leakage current of the pixel sensor relative to a planar transfer transistor.

What is claimed is: 
     
         1 . A pixel sensor, comprising:
 a photodiode comprising an n-type region; and   a transfer fin field effect transistor (finFET), configured to transfer a photocurrent from the photodiode to a drain region of the pixel sensor, comprising:
 at least a portion of the n-type region, 
 a drain extension region coupled to the drain region, 
 a plurality of channel fins coupling the n-type region and the drain extension region, and 
 a transfer gate at least partially surrounding the plurality of channel fins. 
   
     
     
         2 . The pixel sensor of  claim 1 , further comprising:
 a first p-type region included in the photodiode above the n-type region; and   a second p-type region, below the transfer gate, configured to provide electrical isolation for the transfer gate.   
     
     
         3 . The pixel sensor of  claim 1 , further comprising:
 a first buffer oxide region between the transfer gate and the n-type region; and   a second buffer oxide region between the transfer gate and the drain extension region.   
     
     
         4 . The pixel sensor of  claim 1 , wherein the photodiode is spaced away from a top surface of a silicon substrate. 
     
     
         5 . The pixel sensor of  claim 1 , wherein the drain extension region is spaced away from a top surface of a silicon substrate. 
     
     
         6 . The pixel sensor of  claim 1 , wherein the photodiode further comprises:
 a plurality of deep n-type regions below the n-type region.   
     
     
         7 . The pixel sensor of  claim 1 , further comprising:
 an extension implant over the plurality of channel fins; and   an oxide layer over the extension implant.   
     
     
         8 . A pixel sensor, comprising:
 a substrate;   a plurality of channel fins in the substrate;   an n-type region coupled to the plurality of channel fins at a first side of the plurality of channel fins;   a drain extension region coupled to the plurality of channel fins at a second side of the plurality of channel fins opposing the first side;   a drain region coupled to the drain extension region;   a p-type region below the plurality of channel fins; and   a transfer gate above the p-type region and surrounding at least three sides of the plurality of channel fins.   
     
     
         9 . The pixel sensor of  claim 8 , wherein the transfer gate comprises:
 a first titanium nitride layer;   a tantalum nitride layer over the first titanium nitride layer;   a second titanium nitride layer over the tantalum nitride layer;   a titanium aluminum layer over the second titanium nitride layer; and   a tungsten layer over the titanium aluminum layer.   
     
     
         10 . The pixel sensor of  claim 8 , further comprising:
 a first buffer oxide region above the p-type region and between the transfer gate and the n-type region; and   a second buffer oxide region above the p-type region and between the transfer gate and the drain extension region.   
     
     
         11 . The pixel sensor of  claim 8 , further comprising:
 a transfer gate electrode coupled to the transfer gate; and   an n-doped upper transfer gate electrode region over the transfer gate electrode.   
     
     
         12 . The pixel sensor of  claim 8 , further comprising:
 a photodiode comprising:
 a first deep n-type region; 
 a second deep n-type region over the first deep n-type region; 
 the n-type region over the second deep n-type region; and 
 another p-type region over the n-type region,
 wherein the other p-type region is spaced away from a top surface of the substrate. 
 
   
     
     
         13 . The pixel sensor of  claim 12 , wherein the drain extension region is spaced away from the top surface of the substrate. 
     
     
         14 . The pixel sensor of  claim 8 , wherein the transfer gate is coupled to a gate electrode stack. 
     
     
         15 . A pixel sensor, comprising:
 an n-type region;   a drain extension region;   a plurality of channel fins coupling the n-type region and the drain extension region;   a transfer gate at least partially surrounding the plurality of channel fins; and   a p-type region below the transfer gate.   
     
     
         16 . The pixel sensor of  claim 15 , further comprising:
 a deep p-well region (DPW); and   a cell p-well region (CPW) over the DPW.   
     
     
         17 . The pixel sensor of  claim 16 , wherein the CPW further comprises:
 an isolation structure that comprises one or more trenches.   
     
     
         18 . The pixel sensor of  claim 17 , wherein the isolation structure further comprises a field implant layer (FIL) on sidewalls and a bottom surface of the isolation structure. 
     
     
         19 . The pixel sensor of  claim 18 , wherein the isolation structure further comprises an oxide layer over the FIL. 
     
     
         20 . The pixel sensor of  claim 15 , further comprising:
 a plurality of isolation regions in between the plurality of channel fins.