Block Copolymer Master Mold for Chevron Servo Patterns
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Solution Overview
Problem
The existing methods for fabricating master molds for nanoimprinting patterned-media magnetic recording disks with chevron servo patterns often result in defective areas due to sharp transitions and interface regions, limiting the areal bit density and accuracy of the resulting disks.
Innovation Solution
A method using directed self-assembly of block copolymers, where a chemically modified polymer brush material is patterned with interface strips to reduce defects, allowing for the formation of concentric rings and slanted stripes that define the data and servo patterns, respectively, with minimal disruptive areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional lithography or direct nanoimprinting methods are used to fabricate master molds with chevron servo patterns, then the manufacturing process is relatively simple, but defective areas occur due to sharp transitions and interface regions between slanted stripes
Solution Approach 1:
The patent introduces block copolymers as an intermediary material between the master mold substrate and the final nanoimprinted pattern. The block copolymers self-assemble to form intermediate structures that guide the formation of the chevron servo pattern, avoiding direct contact between the mold and the problematic sharp transitions. This intermediary layer enables defect reduction while managing process complexity.
Solution Approach 2:
The patent changes the physical and chemical parameters of the fabrication process by using block copolymer self-assembly instead of conventional lithography. This involves controlling parameters such as polymer composition, molecular weight, solvent conditions, and thermal annealing parameters to achieve desired self-assembly patterns, thereby resolving the contradiction between reliability and complexity.
2Quantity of substance
If higher areal bit densities are achieved through nanoimprinting, then data storage capacity increases, but defective areas in transition regions limit the accuracy and signal-to-noise ratio
Solution Approach 1:
The block copolymers perform self-service by automatically organizing into the required chevron servo pattern through self-assembly. This self-organizing capability ensures high precision in pattern formation without requiring complex external control mechanisms, thereby achieving both high areal bit density and accurate servo pattern registration simultaneously.
Solution Approach 2:
The patent employs curved or slanted stripe patterns in the chevron servo design rather than sharp angular transitions. This curvature approach reduces stress concentration and defect formation at interface regions, enabling higher precision in servo pattern registration while maintaining high areal bit density.
3Shape
If sharp transitions are used in chevron servo patterns to define clear boundaries, then pattern definition is improved, but disruptive areas and defects increase in transition regions
Solution Approach 1:
The patent applies preliminary chemical modification to the master mold substrate surface before the self-assembly process. This preliminary action creates specific surface properties that guide the block copolymers to form well-defined patterns without sharp transitions, thereby achieving good pattern definition while minimizing defects in advance.
Solution Approach 2:
The patent applies different local qualities to different regions of the master mold. The interface regions between slanted stripes have modified surface properties or compositions that differ from the bulk regions, allowing these local areas to accommodate transitions smoothly and reduce defect formation while maintaining overall pattern definition.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces defects in the transition regions of the chevron servo patterns, enabling higher areal bit densities and precise registration of the servo pattern with data tracks, resulting in improved signal-to-noise ratio and reduced defective areas in the nanoimprinted disks.
Implementation Method 1
directed self-assembly of the first block copolymer as lamellae perpendicular to the substrate that are formed into alternating concentric rings and alternating slanted stripes
Implementation Method 2
One of the components of the first block copolymer has an affinity for the chemically-modified polymer brush material, which results in directed self-assembly
Data Source
AI summary
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.