Method for graded anti-reflective coatings by physical vapor deposition

A method for forming a graded anti-reflective coating in a physical vapor deposition processing chamber comprising:

• positioning a substrate on a substrate support in the processing chamber below a target;
• flowing a first inert gas into the processing chamber to sputter the target to deposit a first portion of the graded anti-reflective coating onto the substrate, the first portion having a first refractive index;
• gradually flowing a second gas into the processing chamber to deposit a second portion of the graded anti-reflective coating onto the substrate, the second portion having a second refractive index that is less than the first refractive index;
• gradually flowing a third gas into the processing chamber while simultaneously gradually decreasing the flow of the second gas into the processing chamber to deposit a third portion of the graded anti-reflective coating onto the substrate, the third portion having a third refractive index that is less than the second refractive index;
• arriving at a final value of a flow rate of the third gas to tune a stress level of the graded anti-reflective coating;
• and
• flowing the third gas into the processing chamber after stopping the flow of the second gas to form a fourth portion of the graded anti-reflective coating, the fourth portion having a fourth refractive index that is less than the third refractive index.