Pixel array including air gap reflection structures

Abstract

A pixel array may include air gap reflection structures under a photodiode of a pixel sensor to reflect photons that would otherwise partially refract or scatter through a bottom surface of a photodiode. The air gap reflection structures may reflect photons upward toward the photodiode so that the photons may be absorbed by the photodiode. This may increase the quantity of photons absorbed by the photodiode, which may increase the quantum efficiency of the pixel sensor and the pixel array.

What is claimed is: 
     
         1 . A pixel array, comprising:
 a plurality of pixel sensors, a pixel sensor of the plurality of pixel sensors comprising:
 a photodiode in a silicon layer of the pixel array; 
 one or more first air gap reflection structures below the photodiode and in an interlayer dielectric (ILD) layer that is below the silicon layer; and 
 one or more second air gap reflection structures under the one or more first air gap reflection structures. 
   
     
     
         2 . The pixel array of  claim 1 , wherein the one or more first air gap reflection structures are configured to reflect incident light upward toward the photodiode. 
     
     
         3 . The pixel array of  claim 1 , wherein an aspect ratio, between a depth of an air gap reflection structure of the one or more first air gap reflection structures and a width of the air gap reflection structure, is greater than approximately 2. 
     
     
         4 . The pixel array of  claim 1 , wherein the one or more first air gap reflection structures include a plurality of holes that are arranged in an asymmetric configuration. 
     
     
         5 . The pixel array of  claim 1 , wherein the one or more first air gap reflection structures include a plurality of holes that are arranged in a substantially symmetrical grid. 
     
     
         6 . The pixel array of  claim 1 , wherein the one or more first air gap reflection structures include a plurality of trenches. 
     
     
         7 . The pixel array of  claim 1 , wherein the one or more first air gap reflection structures include:
 a first plurality of trenches; and   a second plurality of trenches that are perpendicular to and intersect the first plurality of trenches.   
     
     
         8 . A pixel array, comprising:
 a first pixel sensor comprising:
 a first photodiode in a silicon layer of the pixel array; and 
 a first plurality of air gap reflection structures under the first photodiode and in:
 an interlayer dielectric (ILD) layer that is below the silicon layer, or 
 an inter-metal dielectric (IMD) layer that is below the ILD layer; and 
 
   a second pixel sensor comprising:
 a second photodiode in the silicon layer; 
 a second plurality of air gap reflection structures under the second photodiode and in:
 the ILD layer, or 
 the IMD layer; and 
 
 a third plurality of air gap reflection structures under the second plurality of air gap reflection structures. 
   
     
     
         9 . The pixel array of  claim 8 , wherein the first plurality of air gap reflection structures and the second plurality of air gap reflection structures are in the ILD layer. 
     
     
         10 . The pixel array of  claim 9 , further comprising:
 a fourth plurality of air gap reflection structures in the IMD layer and under the first plurality of air gap reflection structures.   
     
     
         11 . The pixel array of  claim 10 , wherein the third plurality of air gap reflection structures are in the IMD layer. 
     
     
         12 . The pixel array of  claim 8 , wherein the first plurality of air gap reflection structures and the second plurality of air gap reflection structures are in the ILD layer. 
     
     
         13 . The pixel array of  claim 12 , wherein the third plurality air gap reflection structures are adjacent to a metallization layer in the IMD layer. 
     
     
         14 . The pixel array of  claim 8 , wherein the second plurality of air gap reflection structures are in the ILD layer; and
 wherein the third plurality of air gap reflection structures are in the IMD layer.   
     
     
         15 . A pixel array, comprising:
 a first pixel sensor comprising:
 a first photodiode in a silicon layer of the pixel array; and 
 a first plurality of air gap reflection structures under the first photodiode and in an interlayer dielectric (ILD) layer; and 
   a second pixel sensor comprising:
 a second photodiode in the silicon layer; and 
 a second plurality of air gap reflection structures under the second photodiode and in an inter-metal dielectric (IMD) layer. 
   
     
     
         16 . The pixel array of  claim 15 , wherein the IMD layer is below the ILD layer. 
     
     
         17 . The pixel array of  claim 15 , wherein the first pixel sensor further comprises:
 a third plurality of air gap reflection structures in the IMD layer.   
     
     
         18 . The pixel array of  claim 15 , wherein the second pixel sensor further comprises:
 a third plurality of air gap reflection structures in the ILD layer.   
     
     
         19 . The pixel array of  claim 15 , wherein the IMD layer includes a plurality of layers; and
 wherein the second plurality of air gap reflection structures are in an intermediate layer of the plurality of layers.   
     
     
         20 . The pixel array of  claim 15 , wherein the IMD layer includes a metallization layer.