Multi-level diffractive optical element thin film coating

A method, comprising:

• depositing a plurality of layers onto a substrate;
• depositing a first mask and a second mask on a top layer of the plurality of layers,
• the first mask having a different pattern than the second mask, and
• the first mask completely covering a top surface of the second mask;
• etching a first subset of layers, of the plurality of layers, at a first location that is not covered by the first mask or the second mask;
• removing the first mask, without removing the second mask, to expose a second location of the first subset of layers and to expose the top surface of the second mask;
• and
• etching the second location of the first subset of layers and the first location of a second subset of layers, of the plurality of layers, that are not covered by the second mask to form a three or more-level relief profile within the plurality of layers,
• the three or more-level relief profile including:
• a first anti-reflectance structure at the first subset of layers;
• a second anti-reflectance structure at the second subset of layers;
• and
• a third anti-reflectance structure.