SEM images of the silicon grating templates fabricated by electron beam lithography with different periods of (a) , (b) 500 nm, and (c) 300 nm.
(Color online) Schematic of the pattern transfer process based on SU8//PMMA trilayer NIL. (a) The silicon substrate is coated by the trilayer system; (b) imprinting the trilayer system; (c) after imprint, there is a very thin residual SU8; (d) RIE is used to remove the residual SU8; (e) and PMMA are etched away by and RIEs, respectively, after which the undercut is formed; (f) Cr is deposited onto the structure; (g) Cr structures after metal lift-off; (h) deep etching the silicon substrate and removing the Cr.
SEM images of the grating with 300 nm period after each step of the replication process. (a) After trilayer imprint; (b) removing the residual SU8; (c) etching the PMMA, an undercut is formed.
SEM images of the replication patterns for gratings with different periods of (a) , (b) 500 nm, and (c) 300 nm. The inset shows the enlarged images of the replicated patterns.
(a) SEM images of the trilayer system after removing the residual SU8 with a long etching time and (b) its corresponding replication pattern.
(Color online) SEM images of the samples after removing the PMMA with RIE at 20 SCCM, 40 W, 3 Pa after different etching times: (a) 45 s RIE, the structure is still stable with a thick residual PMMA; (b) 55 s RIE, the structure is about to collapse with a thin residual PMMA; (c) 65 s RIE, the structure completely collapsed with no residual PMMA. (d) The RIE result after reducing the chamber pressure. The sidewall of PMMA becomes more vertical.
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