# US 7,608,367 B1 · Vitreous carbon mask substrate for X-ray lithography > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,608,367 B1 - Document ID: US7608367B1 - Status: Granted - Kind: B1 - Application number: 11/192,797 - Filed: 2005-07-28 - Granted: 2009-10-27 - Earliest claimed: 2005-04-22 - Assignees: Sandia Corporation - Inventors: Georg Aigeldinger; Dawn M. Skala; Stewart K. Griffiths; Albert Alec Talin; Matthew W. Losey; Chu-Yeu Peter Yang - Web page: https://patentgrep.com/patent/US7608367B1 ## CPC - G03F 1/22: Masks or mask blanks for imaging by radiation of 100nm or shorter wavelength, e.g. X-ray masks, extreme ultraviolet [EUV] masks; Preparation thereof - G03F: PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR; (phototypographic composing devices B41B; photosensitive materials or processes for photographic purposes G03C; electrophotography, sensitive layers or processes therefor G03G) ## Abstract The present invention is directed to the use of vitreous carbon as a substrate material for providing masks for X-ray lithography. The new substrate also enables a small thickness of the mask absorber used to pattern the resist, and this enables improved mask accuracy. An alternative embodiment comprised the use of vitreous carbon as a LIGA substrate wherein the VC wafer blank is etched in a reactive ion plasma after which an X-ray resist is bonded. This surface treatment provides a surface enabling good adhesion of the X-ray photoresist and subsequent nucleation and adhesion of the electrodeposited metal for LIGA mold-making while the VC substrate practically eliminates secondary radiation effects that lead to delamination of the X-ray resist form the substrate, the loss of isolated resist features, and the formation of a resist layer adjacent to the substrate that is insoluble in the developer. ## Claims ### Claim 1 A lithographic mask comprising a vitreous carbon substrate, wherein a surface of the vitreous carbon substrate comprises a microscopically roughened surface and a patterned metal X-ray absorber layer adhering to the microscopically roughened surface. ### Claim 2 (depends on 1) The lithographic mask of claim 1, wherein the metal absorber layer comprises a metal strike layer. ### Claim 3 (depends on 1) The lithographic mask of claim 1, wherein the metal absorber layer may comprise one or more layers comprising the same or different metals. ### Claim 4 (depends on 2) The lithographic mask of claim 2, wherein the metal absorber layer is deposited by a process selected from the list consisting of electrodeposition, sputtering, particle vapor deposition, and combinations thereof. ### Claim 5 (depends on 2) The lithographic mask of claim 2, wherein the metal absorber layer is deposited over the metal strike layer. ### Claim 6 (depends on 1) The lithographic mask of claim 1, wherein the metal absorber layer is gold. ### Claim 7 (depends on 2) The lithographic mask of claim 2, wherein the metal strike layer is selected from the list consisting of chromium, copper, gold and combinations thereof. ### Claim 8 (depends on 1) The lithographic mask of claim 1, wherein the metal absorber layer is about 10 microns thick. ### Claim 9 A lithographic mask comprising a vitreous carbon substrate, wherein a surface of the vitreous carbon substrate is etched in a reactive ion oxygen plasma to provide a microscopically roughened surface, and wherein an X-ray resist material is affixed to the microscopically roughened surface. ### Claim 10 (depends on 9) The lithographic mask of claim 9, wherein the X-ray resist material comprises a polymer. ### Claim 11 (depends on 10) The lithographic mask of claim 10, wherein the polymer is selected from the list consisting of PMMA and SU-8. ### Claim 12 (depends on 9) The lithographic mask of claim 9, wherein the resist is affixed to the substrate by casting a polymer resin onto the surface of the substrate and curing the resin to produce a suitable resist layer. ### Claim 13 (depends on 10) The lithographic mask of claim 10, wherein the X-ray resist material comprises a sheet. ### Claim 14 (depends on 13) The lithographic mask of claim 13, wherein the sheet is affixed to the substrate by gluing the sheet to the surface of the substrate with a suitable adhesive. ### Claim 15 (depends on 13) The lithographic mask of claim 13, wherein the sheet is affixed to the substrate by applying a thin spin-cast layer to the surface of the substrate and subsequently solvent bonding the sheet to the spin-cast layer. ### Claim 16 (depends on 9) The lithographic mask of claim 9, wherein the X-ray resist material is exposed to a source of patterned X-ray radiation for a period of time, and wherein the exposed resist material is developed to remove portions of the resist material, thereby providing a plurality of areas open to the microscopically roughened surface. ### Claim 17 (depends on 16) The lithographic mask of claim 16, wherein the open areas of the microscopically roughened surface are coated with a thin metal coating. ### Claim 18 (depends on 17) The lithographic mask of claim 17, wherein the thin metal coating comprises one or more layers comprising the same or different metals. ### Claim 19 (depends on 18) The lithographic mask of claim 18, wherein the thin metal coating is selected from the list consisting of chromium, nickel, copper, gold and combinations thereof. ### Claim 20 (depends on 19) The lithographic mask of claim 19, wherein the thin metal coating is provided by a process selected from the list consisting of electrodeposition, sputtering, particle vapor deposition, and combinations thereof. ### Claim 21 (depends on 17) The lithographic mask of claim 17, wherein the plurality of areas are filled with a thick metal layer deposited onto the thin metal coating. ### Claim 22 (depends on 21) The lithographic mask of claim 21, wherein the thick metal layer is gold. ### Claim 23 A method for preparing a microfabricated device, comprising the steps of. providing a lithographic mask comprising a vitreous carbon substrate, wherein a surface of the vitreous carbon substrate is etched in a reactive ion oxygen plasma to provide a microscopically roughened surface, and wherein an X-ray resist material is affixed to the microscopically roughened surface; exposing the lithographic mask to X-ray radiation through a patterned mask; developing the exposed substrate to remove portions of the resist, thereby providing a plurality of areas open to the microscopically roughened surface of the vitreous carbon substrate; and filling the plurality of areas open to the surface of the vitreous carbon substrate with a metal deposit. ### Claim 24 (depends on 23) The method of claim 23, wherein the step of filling further includes a preliminary step of coating the plurality of areas open to the surface of the substrate with a thin metal coating. ### Claim 25 (depends on 24) The method of claim 24, wherein the step of filling comprises electrodepositing the metal deposit onto the thin metal coating.