Thin film layers having non-uniform thicknesses

A method for generating a diffractive optical element, the method comprising:

• depositing a thin film stack on a substrate, the thin film stack including a first layer and a second layer, the first layer being disposed between the substrate and the second layer, the first layer having a non-uniform thickness, the second layer having a non-uniform thickness;
• forming a first pattern on the second layer to define first areas;
• etching the second layer in the first areas to form first holes;
• forming a second pattern on the first layer in the first holes, the second pattern defining second areas, each second area being smaller than a corresponding first area;
• etching the first layer in the second areas to form second holes, the second holes extending fully through the first layer to depths that correspond to the non-uniform thickness of the first layer;
• and
• forming an imprint of the etched thin film stack such that the first holes and the second holes form a plurality of diffractive elements on the imprint.

A method for generating a diffractive optical element, the method comprising:

• depositing, via sputtering, a first layer of silicon dioxide (SiO2) on a substrate, the first layer having a uniform thickness;
• depositing, via graded sputtering, a second layer of amorphous silicon (Si) on the first layer, the second layer having a non-uniform thickness;
• depositing, via sputtering, a third layer of silicon dioxide on the second layer, the third layer having a uniform thickness;
• depositing, via graded sputtering, a fourth layer of amorphous silicon on the third layer, the fourth layer having a non-uniform thickness;
• forming, with electron-beam lithography, a first pattern on the fourth layer to define first areas;
• etching, using sulfur hexafluoride (SF6), the fourth layer in the first areas to form first holes;
• etching, using trifluoromethane (CHF3), the third layer in the first areas to deepen the first holes to form deepened first holes, the deepened first holes having depths that correspond to the non-uniform thickness of the fourth layer plus the uniform thickness of the third layer;
• forming, with electron-beam lithography, a second pattern on the second layer within the deepened first holes to define second areas within respective deepened first holes;
• etching, using sulfur hexafluoride, the second layer in the second areas to form second holes;
• and
• etching, using trifluoromethane, the first layer in the second areas to deepen the second holes to form deepened second holes, the deepened second holes having depths that correspond to the non-uniform thickness of the second layer plus the uniform thickness of the first layer.