Method using block copolymers for making a master mold for nanoimprinting patterned magnetic recording disks with chevron servo patterns
A method for making a master mold used to nanoimprint patterned magnetic recording disks that have chevron servo patterns with minimal defects uses directed self-assembly of block copolymers. A pattern of chemically modified polymer brush material is formed on the master mold substrate. The pattern includes sets of slanted stripes and interface strips between the sets of slanted stripes. A block copolymer material is deposited on the pattern, which results in directed self-assembly of the block copolymer as lamellae perpendicular to the substrate that are formed into alternating slanted stripes of alternating first and second components of the block copolymer. This component also forms on the interface strips, but as a lamella parallel to the substrate. One of the components is then removed, leaving the remaining component as a grid that acts as a mask for etching the substrate to form the master mold. The disks nanoimprinted by the master mold have reduced defective areas in the transition regions of the chevron servo patterns.
1. A method for making an imprinting master mold using directed self-assembly of a block copolymer having polymeric block components, the method comprising:
providing a substrate;
depositing on the substrate a layer of neutral material having no strong affinity for any component of said block copolymer;
forming over the neutral material a resist pattern comprising a first set of parallel bands and a second set of parallel bands non-parallel to and spaced from said first set of bands;
modifying the neutral material unprotected by the resist;
removing the resist, leaving a pattern of modified neutral material comprising a first set of parallel bars, a second set of parallel bars non-parallel to and spaced from said first set of bars, and an interface strip between said first and second sets of bars, wherein the block copolymer has a bulk period L 0 and the interface strip has a width greater than 0.5L 0 and less than 5L 0 ;
depositing a layer of said block copolymer material and annealing the deposited block copolymer material to cause phase separation into a first set of parallel stripes of alternating first and second components and a second set of parallel stripes of alternating first and second components non-parallel to and spaced from said first set of stripes, the first component forming on said first and second sets of parallel bars as lamella perpendicular to the substrate surface and on said interface strip of modified neutral material as a lamella oriented parallel to the substrate surface; and
removing one of said first and second components, leaving a first set of parallel stripes of the non-removed component and a second set of parallel stripes of the non-removed component non-parallel to and spaced from said first set of stripes of non-removed component.
2. The method of claim 1 wherein the interface strip is connected to the ends of the bars in the first and second sets of parallel bars.
3. The method of claim 1 wherein the interface strip is discontinuous with discrete segments.
4. The method of claim 1 wherein the block copolymer has a bulk period L 0 and wherein the parallel bars in said first set are spaced apart a distance nL o where n is an integer greater than or equal to 2.
5. The method of claim 4 wherein the parallel bars in said second set are spaced apart a distance equal to the spacing of the parallel bars in said first set.
6. The method of claim 1 wherein providing a substrate comprises providing a substrate formed of a material selected from single-crystal Si, amorphous Si, silica, quartz, silicon nitride, carbon, tantalum, molybdenum, chromium, alumina and sapphire.
7. The method of claim 1 wherein providing a substrate comprises providing a rigid substrate base having a transfer layer formed on it.
8. The method of claim 1 wherein the transfer layer is formed of a material selected from silicon oxide, chromium, germanium, aluminum oxide, silicon nitride, tungsten, diamond-like carbon (DLC), molybdenum and tantalum.
9. The method of claim 1 wherein the substrate has a center, and wherein the first set of parallel stripes of the non-removed component are slanted at an acute angle relative to a radius, the second set of parallel stripes of the non-removed component are slanted at said acute angle relative to a radius, and said first and second sets of stripes are slanted in different directions.
10. The method of claim 1 wherein the substrate has a center, and wherein the first set of parallel stripes of the non-removed component are slanted at an acute angle relative to a radius and the second set of parallel stripes of the non-removed component are generally concentric rings about said center.
11. The method of claim 10 further comprising:
forming a pattern of radial lines on the substrate;
etching the substrate, using said first set of stripes, said concentric rings and said radial lines as an etch mask; and
removing said first set of stripes, said concentric rings and said radial lines, leaving a substrate with a pattern of substrate material.
12. The method of claim 11 wherein the pattern of radial lines is formed on the substrate and said first set of stripes and said concentric rings are formed on the pattern of radial lines.
13. The method of claim 11 further comprising forming a protective layer on the radial lines and wherein depositing a layer of neutral material comprises depositing the neutral material directly on the protective layer.
14. The method of claim 1 wherein the block copolymer material is a copolymer of polystyrene (PS) and poly(methyl methacrylate) (PMMA).
15. A method for making a master mold for use in imprinting magnetic recording disks having chevron servo patterns using directed self-assembly of a block copolymer having polymeric block components, the method comprising:
providing a rigid substrate having a generally planar surface with a center;
depositing on the substrate surface a layer of neutral polymer brush material having no strong affinity for any component of said block copolymer;
forming over the neutral material a resist pattern comprising a first set of parallel bands slanted at an acute angle relative to a radial line from said substrate center and a second set of parallel bands, said second set of bands being non-parallel to and spaced from said first set of bands and slanted at said acute angle relative to a radial line from said substrate center;
modifying the neutral material unprotected by the resist;
removing the resist, leaving a pattern of modified neutral material comprising a first set of parallel bars, a second set of parallel bars non-parallel to and spaced from said first set of bars, and an interface strip between said first and second sets of bars;
depositing a layer of said block copolymer material and annealing the deposited block copolymer material to cause phase separation into a first set of parallel stripes of alternating first and second components and a second set of parallel stripes of alternating first and second components non-parallel to and spaced from said first set of stripes, the first component forming on said first and second sets of parallel bars of modified neutral material as lamellae perpendicular to the substrate surface and on said interface strip of modified neutral material as a lamella parallel to the substrate surface; and
removing the parallel stripes of second component, leaving a first set of parallel stripes of the first component, a second set of parallel stripes of the first component non-parallel to and spaced from said first set of stripes of first component, and the lamella of first component parallel to the substrate surface on said interface strip.
16. The method of claim 15 wherein the block copolymer has a bulk period L 0 and wherein the interface strip has a width greater than 0.5L 0 and less than 5L 0 .
17. The method of claim 15 wherein the block copolymer has a bulk period L 0 and wherein the parallel bars in said first and second sets are spaced apart a distance nL 0 where n is an integer greater than or equal to 2.
18. The method of claim 15 further comprising etching the substrate, using as an etch mask said first and second sets of parallel stripes of the non-removed component and the lamella of first component parallel to the substrate surface on said interface strip.
19. The method of claim 15 wherein providing a substrate comprises providing a rigid substrate base having a transfer layer formed on it.
20. The method of claim 19 wherein the transfer layer is formed of a material selected from silicon oxide, chromium, germanium, aluminum oxide, silicon nitride, tungsten, diamond-like carbon (DLC), molybdenum and tantalum.