Method for graded anti-reflective coatings by physical vapor deposition

Abstract

A method for forming an anti-reflective coating (ARC) includes positioning a substrate below a target and flowing a first gas to deposit a first portion of the graded ARC onto the substrate. The method includes gradually flowing a second gas to deposit a second portion of the graded ARC, and gradually flowing a third gas while simultaneously gradually decreasing the flow of the second gas to deposit a third portion of the graded ARC. The method also includes flowing the third gas after stopping the flow of the second gas to form a fourth portion of the graded ARC. In another embodiment a film stack having a substrate having a graded ARC disposed thereon is provided. The graded ARC includes a first portion, a second portion disposed on the first portion, a third portion disposed on the second portion, and a fourth portion disposed on the third portion.

What is claimed is: 
     
         1 . A filmstack comprising:
 a substrate having a graded anti-reflective coating disposed thereon, wherein the graded anti-reflective coating comprises:
 a first portion having first refractive index; 
 a second portion disposed on the first portion, the second portion having a second refractive index less than the first refractive index; 
 a third portion disposed on the second portion, the third portion having a third refractive index less than the second refractive index; and 
 a fourth portion disposed on the third portion, the fourth portion having a fourth refractive index less than third refractive index. 
   
     
     
         2 . The filmstack of  claim 1 , wherein the first portion comprises silicon, the second portion comprises silicon and nitrogen, the third portion comprises silicon, nitrogen and oxygen, and the fourth portion comprises silicon and oxygen. 
     
     
         3 . The filmstack of  claim 2 , wherein the graded anti-reflective coating has a graded refractive index ranging from about 1.46 to about 2.00. 
     
     
         4 . The filmstack  claim 1 , wherein the substrate includes a photodiode disposed thereon. 
     
     
         5 . The filmstack of  claim 1 , wherein the substrate includes a buffer layer comprising oxide or nitride disposed over the graded anti-reflective coating. 
     
     
         6 . The film stack of  claim 2 , wherein the filmstack is configured for use in a complementary metal-oxide-semiconductor image sensor device. 
     
     
         7 . A graded anti-reflective coating comprising:
 a substrate;   a first portion of the graded anti-reflective coating disposed on the substrate, the first portion having a first refractive index;   a second portion of the graded anti-reflective coating disposed on the first portion, the second portion having a second refractive index that is less than the first refractive index;   a third portion of the graded anti-reflective coating disposed on the second portion, the third portion having a third refractive index that is less than the second refractive index; and   a fourth portion of the graded anti-reflective coating disposed on the third portion, the fourth portion having a fourth refractive index that is less than the third refractive index,   wherein the anti-reflective coating has a tuned stress level.   
     
     
         8 . The graded anti-reflective coating of  claim 7 , wherein the stress level is tuned to between −v119 MPa and −599 MPa. 
     
     
         9 . The graded anti-reflective coating of  claim 7 , wherein there are no distinct transitions of refractive index between the first portion and the fourth portion of the graded anti-reflective coating. 
     
     
         10 . The graded anti-reflective coating of  claim 7 , wherein the first portion comprises silicon, the second portion comprises silicon and nitrogen, the third portion comprises silicon, nitrogen and oxygen, and the fourth portion comprises silicon and oxygen. 
     
     
         11 . The graded anti-reflective coating of  claim 10 , wherein the graded anti-reflective coating has a graded refractive index ranging from about 1.46 to about 2.00. 
     
     
         12 . The graded anti-reflective coating of  claim 7 , wherein the substrate includes a photodiode disposed thereon. 
     
     
         13 . The graded anti-reflective coating of  claim 7 , wherein the substrate includes a buffer layer comprising oxide or nitride disposed over the graded anti-reflective coating. 
     
     
         14 . The graded anti-reflective coating of  claim 10 , wherein the graded anti-reflective coating is configured for use in a complementary metal-oxide-semiconductor image sensor device.