Pixel sensor including a layer stack

Abstract

A pixel sensor may include a layer stack to reduce and/or block the effects of plasma and etching on a photodiode and/or other lower-level layers. The layer stack may include a first oxide layer, a layer having a band gap that is approximately less than 8.8 electron-Volts (eV), and a second oxide layer. The layer stack may reduce and/or prevent the penetration and absorption of ultraviolet photons resulting from the plasma and etching processes, which may otherwise cause the formation of electron-hole pairs in the substrate in which the photodiode is included.

What is claimed is: 
     
         1 . A pixel sensor, comprising:
 a photodiode in a substrate of the pixel sensor; and   an oxide-nitride-oxide layer stack, over the photodiode in the substrate, configured to protect the photodiode from radiation damage.   
     
     
         2 . The pixel sensor of  claim 1 , further comprising:
 a grid structure over the oxide-nitride-oxide layer stack.   
     
     
         3 . The pixel sensor of  claim 2 , wherein the grid structure comprises:
 a titanium nitride layer on the oxide-nitride-oxide layer stack;   a tungsten layer on the titanium nitride layer;   a silicon oxide layer on the tungsten layer; and   a silicon oxynitride layer on the silicon oxide layer.   
     
     
         4 . The pixel sensor of  claim 2 , wherein the grid structure comprises:
 a silicon oxide layer on the oxide-nitride-oxide layer stack; and   a silicon oxynitride layer on the silicon oxide layer.   
     
     
         5 . The pixel sensor of  claim 1 , wherein the oxide-nitride-oxide layer stack comprises:
 a first silicon oxide layer;   a silicon nitride layer on the first silicon oxide layer; and   a second silicon oxide layer on the silicon nitride layer.   
     
     
         6 . The pixel sensor of  claim 5 , wherein the silicon nitride layer is configured to absorb ultraviolet radiation having a wavelength equal to or less than approximately 250 nanometers; and
 wherein the first silicon oxide layer is configured to prevent migration of electron-hole pairs, resulting from absorption of the ultraviolet radiation, toward the photodiode.   
     
     
         7 . The pixel sensor of  claim 6 , wherein the second silicon oxide layer is configured to absorb ultraviolet radiation having a wavelength equal to or less than approximately 140 nanometers. 
     
     
         8 . A pixel sensor, comprising:
 a photodiode in a substrate of the pixel sensor; and   a layer stack, over the photodiode in the substrate, comprising:
 a first layer comprising a first oxide material, 
 a second layer on the first layer,
 wherein a band gap of the second layer is less than approximately 8.8 electron-volts, and 
 
 a third layer, on the second layer, comprising a second oxide material. 
   
     
     
         9 . The pixel sensor of  claim 8 , wherein a band gap of the first layer is greater than the band gap of the second layer. 
     
     
         10 . The pixel sensor of  claim 8 , wherein the second layer is configured to absorb ultraviolet radiation having a wavelength equal to or less than approximately 250 nanometers;
 wherein absorption of the ultraviolet radiation having the wavelength equal to or less than approximately 250 nanometers results in formation of electron-hole pairs in the second layer; and   wherein the first layer is configured to block migration of the electron-hole pairs from the second layer to the photodiode.   
     
     
         11 . The pixel sensor of  claim 8 , further comprising:
 a high dielectric constant (high-k) dielectric layer over the photodiode in the substrate,
 wherein the layer stack is located on the high-k dielectric layer. 
   
     
     
         12 . The pixel sensor of  claim 8 , wherein a thickness of the first layer is in a range of approximately 300 angstroms to approximately 1000 angstroms. 
     
     
         13 . The pixel sensor of  claim 8 , wherein a thickness of the second layer is equal to or greater than approximately 250 angstroms. 
     
     
         14 . The pixel sensor of  claim 8 , wherein the second layer comprises at least one of:
 a silicon nitride,   an aluminum oxide,   a lanthanum oxide,   a titanium oxide,   a zirconium oxide,   a hafnium silicon oxide,   a yttrium oxide,   a barium oxide,   a strontium oxide,   a hafnium oxide, or   a tantalum oxide.   
     
     
         15 . A pixel array, comprising:
 a plurality of photodiodes in a substrate of the pixel array,
 wherein each of the plurality of photodiodes is associated with a respective pixel sensor included in the pixel array; 
   a first layer formed over the plurality of photodiodes;   a second layer formed on the first layer,
 wherein a band gap of the second layer is lower than a band gap of the first layer; 
   a third layer formed on the second layer;   a grid structure formed over the third layer and comprising:
 a plurality of layers comprising openings that extend through the plurality of layers; and 
   a plurality of color filter regions formed in the openings and directly on a surface of the third layer.   
     
     
         16 . The pixel array of  claim 15 , wherein the openings extend into a portion of the third layer. 
     
     
         17 . The pixel array of  claim 15 , further comprising:
 a passivation liner between a sidewall of the grid structure and a color filter region of the plurality of color filter regions.   
     
     
         18 . The pixel array of  claim 15 , further comprising:
 a micro-lens layer above the plurality of color filter regions.   
     
     
         19 . The pixel array of  claim 15 , wherein the plurality of layers includes a tungsten layer. 
     
     
         20 . The pixel array of  claim 15 , wherein a band gap of the third layer is greater than the band gap of the second layer.