Method for fabricating a blazed grating

A method for fabricating a blazed grating comprising a ridge having a blaze facet facing a blaze facet direction and an anti-blaze facet facing an anti-blaze facet direction, the blaze facet direction and the anti-blaze facet direction extending along a grating cross-sectional plane, the method comprising:

• providing a substrate and a patterned mask layer on the substrate,
• performing primary dry etching of the substrate such that primary ions are accelerated towards a primary etch direction to impinge on the substrate, and
• performing secondary dry etching of the substrate such that secondary ions are accelerated towards a secondary etch direction to impinge on the substrate;
• wherein a primary projection of the primary etch direction onto the grating cross-sectional plane extends perpendicular to the anti-blaze facet direction and a secondary projection of the secondary etch direction onto the grating cross-sectional plane extends perpendicular to the blaze facet direction and ions accelerated towards a direction with a projection onto the grating cross-sectional plane perpendicular to the blaze facet direction are collimated to form a collimated ion beam for etching the substrate;
• wherein the method comprises not revealing a ridge portion of the substrate prior to the process of performing secondary dry etching and the mask layer comprises an inorganic material.