Fabrication of chevron patterns for patterned media with block copolymer directed assembly
Design of chevron structures to extract the position error signal (PES) for magnetic data storage. (a) Schematic of the servo pattern and data pattern on magnetic data storage media. The data are defined by concentric tracks. The dotted box highlights the transition from a data to a servo and back to a data pattern. (b) Zoom-in view of the dotted box in (a). A group of n = 11 tracks with a track pitch (track-to-track distance) of L0 = 27 nm is defined by the circumferential lines and the chevron structures. The cross-track positions of the 11 tracks are at 0, 27, 54,…, 270 nm, respectively. The horizontal track pitch . The group repeats itself starting at a cross-track position of 297 nm. The circumferential lines can be considered as horizontal lines on the nanometer scale, along the direction of which the data tracks run. The imaginary read head (black box) flies across the chevrons along the data track direction. The angle at the apex of the chevrons is 2atan(1/11). (c) One exemplary collection of the signals while the head is flying across the chevrons following the arrow in (b). The abscissa denote the crossing number at which the head crosses the chevrons. The ordinate is the down-track position when the head crosses the chevrons. The dashed lines are extrapolations of the fitting lines to the data, and the intercepts are x 1 and x 2. The PES = x 2 − x 1. (d) The PES as a function of the position of the head across the track direction. The solid circles denote the points where the head is flying on the track. The arrows in (d) illustrate the identification of a cross-track position of 54 nm, or a track number of 3, when the read head flies along the arrow highlighted in (b).
(Color online) (left) Schematics of the directed assembly of block copolymers on chemical patterns with density multiplication and (right) top-down SEM images of the corresponding block copolymer (bcp) patterns after directed assembly with density multiplication. The inset images are the corresponding photoresist patterns that are used to define the chemical patterns. In design I, only every other horizontal line and chevron is patterned using electron beam lithography. In design II, extra vertical stripes at the apex of the chevrons and in the junction areas between the horizontal lines and chevrons are added in order to control the propagation of defective structures. The angle of the apices of the chevrons is 20°. The dotted lines highlight the boundaries between defective areas and nondefective areas. The boundaries in design I are wavier with a higher amplitude than those in design II. For design I, the peak-to-peak widths of the defective areas at the apex of the chevrons and of the junction areas between the chevrons and the periodic horizontal lines are ∼232 nm and ∼118 nm, whereas for design II they are ∼96 nm and 89 nm, respectively. The scale bars represent 200 nm.
Top-down SEM images of the block copolymer patterns at the apices of the chevrons after directed assembly on chemical patterns with density multiplication (design II). The angle of the apices of the chevrons varies from 30° to 70° with a 10° increment, as shown in each image. All defective structures are constrained within a small band of <100 nm. The scale bar applies to all the SEM images.
Top-down SEM images of the block copolymer patterns at the junctions between the chevrons and the horizontal lines after directed assembly on chemical patterns with density multiplication (design II). The angle of the apices of the chevrons varies from 30° to 70° with a 10° increment, as shown in each image.
(Color online) Cross-sectional SEM images and the corresponding schematics of the block copolymer patterns after various etching time in oxygen plasma. The arrows (green online) highlight the corresponding etched domains in the SEM images. The scale bar applies to all the SEM images. The color image is a cross-section profile from molecular simulations. The non-interpolated PMMA domains (yellow online) penetrate through the entire film and are in registration with the oxygen-plasma-treated PS brush (yellow online). Between the interpolated PMMA domains (yellow online) and the PS brush (blue online) is a thin layer of PS domain (blue online).
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