Batch-processing method for super-high aspect ratio diffractive optics

A method of fabrication, by batch-processing, of a plurality of device structures each comprising a high aspect-ratio diffractive optic having a specified diffractive line pattern for photons or particle beams of a prescribed wavelength or energy, comprising:

• providing a first substrate having a planar front surface and back surface;
• performing an anisotropic etch process comprising patterning of the front surface of the substrate and removal of material of the substrate to define a precursor structure comprising an array of a plurality of precursor forms comprising one of:
• a) mesas having sidewalls of predetermined vertical and lateral dimensions and sidewall angle;
• b) mesas within holes or trenches, the mesas having sidewalls of predetermined vertical and lateral dimensions and sidewall angle;
• and
• c) a combination thereof;
• smoothing sidewalls of the mesas to a predetermined sidewall surface roughness;
• depositing thereon a sequence of layers defining the specified diffractive line pattern comprising a plurality of m layer stacks, each layer stack comprising at least a pair of layers comprising a layer of a first material (M1) and a layer of a second material (M2), said layer stacks being deposited by an isotropic deposition process providing conformal layers of controlled layer thicknesses on sidewalls of each mesa in sequence (M1, M2)1, (M1, M2)2. . . (M1, M2)m,
• each of said first and second materials having a different selected complex refractive index at the prescribed wavelength or energy,
• wherein each mesa forms a core of one of the diffractive optics and said step of depositing comprises controlling the layer thickness of each pair of layers (M1, M2) of the sequence (M1, M2)1, (M1, M2)2. . . (M1, M2)m to define diffractive lines of the specified diffractive line pattern around each mesa;
• after forming the sequence of layers, providing a planarization layer thereon filling remaining surface voids;
• performing a first planarization to remove parts of the planarization layer and the sequence of layers and exposing a planarized front-side surface comprising a first surface of each mesa, of the diffractive lines around each mesa and surrounding parts of the planarization layer and the first substrate;
• performing a second planarization to thin the backside of first substrate and remove part of the first substrate and the sequence of layers to provide a planarized back-side surface exposing a second surface each mesa, of the diffractive lines around each mesa and first substrate;
• wherein, for photons or particles of the prescribed wavelength or energy, an axial height h between the first surface and second surface of each of the diffractive lines of each diffractive optic, in a propagation direction, provides at least one of:
• a required absorption difference between adjacent diffractive lines,
• a phase shift difference of π between adjacent diffractive lines, and
• a phase shift difference of a designed fraction of π between adjacent diffractive lines;
• and wherein the aspect ratio of the axial height h and the layer thickness of a thinnest layer of the sequence of layers of the diffractive line pattern is greater than 10:1;
• and
• performing device singulation comprising at least one of substrate dicing and cleaving, to form a plurality of individual device structures, each comprising one or a plurality of said diffractive optics.

A method of fabrication, by batch-processing, of a plurality of device structures each comprising a high aspect-ratio Fresnel zone plate having a specified Fresnel zone pattern for photons or particle beams of a prescribed wavelength or energy, comprising:

• providing a first substrate having a planar front surface and back surface;
• performing an anisotropic etch process comprising patterning of the front surface of the substrate and removal of material of the substrate to define a precursor structure comprising an array of a plurality of mesas comprising cylindrical columns, each formed within a surrounding hole or recess, said mesas having sidewalls of predetermined vertical and lateral dimensions and sidewall angle;
• smoothing sidewalls of the mesas to a predetermined sidewall surface roughness;
• depositing thereon a sequence of layers comprising a plurality of m layer stacks, each layer stack comprising at least a pair of layers comprising a layer of a first material (M1) and a layer of a second material (M2),
• each of said first and second materials having a different selected complex refractive index at the prescribed wavelength or energy,
• said layer stacks being deposited by an isotropic deposition process providing conformal layers of controlled layer thicknesses on sidewalls of each mesa in sequence (M1, M2)1, (M1, M2)2. . . (M1, M2)m
• wherein each mesa forms a central non-diffractive area of one of the Fresnel zone plates and said step of depositing comprising controlling the layer thickness of each pair of layers (M1, M2) of the sequence (M1, M2)1, (M1, M2)2. . . (M1, M2)m to define diffractive zones of said specified Fresnel zone pattern around each mesa;
• after forming the sequence of layers, providing a planarization layer thereon filling remaining surface voids;
• performing a first planarization to remove parts of the planarization layer and the sequence of layers and exposing a planarized front-side surface comprising a first surface of each mesa, of the diffractive zones around each mesa and surrounding parts of the planarization layer and the first substrate;
• attaching a carrier substrate to the planarized front-side surface;
• performing a second planarization to thin the backside of first substrate and remove part of the first substrate and the sequence of layers to provide a planarized back-side surface exposing a second surface each mesa, of the diffractive zones around each mesa and first substrate;
• and
• removing part of the carrier substrate to expose the first surface the Fresnel zones around each mesa, thereby producing an array of a plurality of Fresnel zone plates supported by remaining parts of the first substrate and the carrier substrate;
• wherein, for photons or particles of the prescribed wavelength or energy, an axial height h between the first surface and second surface of each of the diffractive lines of each diffractive optic, in a propagation direction, provides at least one of:
• a required absorption difference between adjacent diffractive lines,
• a phase shift difference of π between adjacent diffractive lines, and
• a phase shift difference of a designed fraction of π between adjacent diffractive lines;
• and wherein the aspect ratio of the axial height h and the layer thickness of a thinnest layer of the sequence of layers of the diffractive line pattern is greater than 10:1.