High aspect ratio fine pattern transfer using a novel mold by nanoimprint lithography

Abstract

To conduct our research, a Si mold with a high aspect nano trench pattern was fabricated using a new edge lithography process, and the pattern was replicated into PMMA films on Si wafer by thermal nanoimprint lithography. By using edge lithography, a SiO2 circular line pattern of 35 nm width and 3.5 μm height was obtained and the aspect ratio became 100. The Cr patterns were fabricated by a lift-off process by using the high aspect SiO2 nano patterns, and the Si substrate was etched by the advanced plasma etching of the gas switching process. A Si trench pattern of 25 nm width and 1.0 μm depth was obtained, and these Si trench patterns were used for nanoimprint molds. The aspect ratios of the nano trench patterns were about 10. The nano trench patterns were replicated into PMMA films with various molecular weights by thermal nanoimprint lithography. The pattern replication failed when the PMMA resins of 50 and 120 k molecular weights were used. It is found that the PMMA pattern was often broken during the demolding process and its strength was very important for the successful pattern replication of the high aspect pattern. A PMMA line pattern of 30 nm width and 230 nm height was successfully fabricated when the PMMA resin of 996 k molecular weight was used.

Fabrication of nanochannels using underexposed nanoimprint method

“…For gratings with a too low molecular weight and a too high aspect ratio, the gratings may collapse unordered and the pattern damage is easily induced. In Sakamoto's study [14], the pattern replication failed when the poly(methyl methacrylate) (PMMA) resins of 50 and 120 k molecular weights were used, and a PMMA line pattern of 30 nm width and 230 nm height was successfully fabricated when the PMMA resin of 996 k molecular weight was used. So, the molecular weight of the resist should be large enough to ensure sufficient modulus and strength.…”

“…The collapse of the nanotrenches is a common defect in NIL [13][14][15]. Low molecular weight, high aspect ratio, insufficient curing dose and high surface energy may cause the collapse of the nanotrenches.…”

Guiding Chart for Initial Layer Choice with Nanoimprint Lithography

“…With optical lithography, these windows result in a straightforward way by complete removal of the photoresist in exposed regions during development. However, with NIL, this is not naturally the case due to the residual layer, typically remaining with T-NIL (thermal NIL [ 1 , 10 , 20 , 21 , 22 , 23 ]) and with UV-NIL (ultraviolet-assisted NIL [ 2 , 3 , 24 , 25 , 26 , 27 ]) as well. Without specific precautions, a certain amount of imprint material always remains below the elevated stamp structures (see Figure 1 a).…”

Fabrication of polydimethylsiloxane nanofluidic chips under AFM tip-based nanomilling process

“…Interference lithography (IL) is suitable for fabricating simple periodical structures over a large area; however, it is not suitable to machine a single nanochannel [24, 25]. The processing resolution of nanoimprinting depends on template properties, the crucial issue for this approach is how to fabricate the template with high-precision nanostructures [26]. In addition, sacrificial molding and creak-based method are also adopted to fabricate micro/nanoscale devices [27, 28]; however, the accurate control of nanochannel size is very difficult in these approaches.…”