Fabrication of blazed diffractive optics by through-mask oxidation
A method for manufacturing a low-angle blazed grating on a semiconductor or silicon substrate, includes spin-coating the substrate with resist layer or hydrogen or polysilsesquioxane, being 100-1000 nm or few hundred nanometers thick, applying grayscale irradiation lithography exposure to the resist layer, generating a dose modulated pattern therein, varying in response to absorbed energy density from irradiation lithography exposure. The coated, irradiated substrate is developed in solution, such as TMAH or NaOH, enabling a blazed profile having structures of thickness-dependent diffusion barriers or SiO 2 , with 0-1000 nm height to emerge. Thermal oxidation in oxygen atmosphere at elevated temperature with the developed substrate, converts the upper silicon substrate layer into SiO 2 to a depth depending on the thickness of the pattern in the resist layer above. Hydrofluoric acid fluid removes the SiO 2 , creating low-angle low-roughness blazed grating structure on silicon substrate.
1. A method for manufacturing low-roughness, low-angle blazed profiles or lines of blazed gratings, on a silicon substrate, the method comprising:
a) spin-coating the silicon substrate with a layer of resist having a thickness of between 100 nm and 1000 nm;
b) applying gray-scale lithography exposure to the spin-coated silicon substrate to generate a dose modulated pattern into the resist layer, the dose varying locally in response to a density of absorbed energy from the irradiation of the lithography exposure;
c) developing the dose modulated pattern of the resist layer in a solution, enabling a profile including structures of thickness-dependent diffusion barriers with a positive height up to 1000 nm to emerge;
d) performing thermal oxidation in an oxygen atmosphere at elevated temperature to thereby convert an upper layer of the silicon substrate into silicon dioxide, wherein the upper layer of the silicon substrate is varyingly converted into the silicon dioxide depending on a thickness of the pattern in the resist layer above; and
e) removing the resist layer, which was developed, and removing the silicon dioxide, which was converted from the silicon substrate, in a hydrofluoric acid fluid, creating the low-roughness, low-angle blazed grating structure on the silicon substrate.
2. The method according to claim 1 , which further comprises using hydrogen silsesquioxane (HSQ) or poly-silsesquioxane having a thickness of a few hundred nanometers for the layer of resist.
3. The method according to claim 1 , wherein the solution is TMAH or NaOH.
4. The method according to claim 1 , which further comprises using silicon dioxide (SiO 2 ) for the diffusion barriers.
5. The method according to claim 1 , which further comprises initially using a flat or curved polished silicon substrate as the semiconductor substrate.
6. The method according to claim 1 , which further comprises using an e-beam or a direct laser writer in the gray-scale irradiation lithography exposure.
7. The method according to claim 1 , which further comprises replacing steps b) and c) with nanoimprint lithography (NIL), and subsequently coating resulting structures with a single layer coating or a multilayer coating, producing devices with optimized reflectivity usable with multi-keV x-rays or with EUV radiation.
8. The method according to claim 1 , which further comprises using the method to produce masters for manufacturing blazed gratings by replication techniques or nanoimprint lithography.
9. The method according to claim 1 , wherein the blazed grating structure is formed by portions of the upper layer of the silicon substrate that are not converted into silicon dioxide in step d).