Nanoimprint lithography (NIL) is one of the most promising technology platforms for replication of nanometer and micrometer scale 3D topographies with extremely high resolution and throughput, as needed for e.g. photonic or optical applications. One of the remaining challenges of 3D NIL, however, is the fabrication of high quality 3D master originals – the initial patterns that are replicated multiple times in the NIL process. Here, we demonstrate a joint solution for 3D NIL where NanoFrazor thermal scanning probe lithography (t-SPL) is used to pattern the master templates with singlenanometer accurate 3D topographies. 3D topographies from polymer resist master templates are replicated using a HERCULES NIL system with SmartNIL technology. Furthermore, 3D patterns are transferred from the resist into a silicon substrate via reactive ion etching (RIE) and the resulting silicon master template is used for producing polymeric working stamps into OrmoStamp and, finally, replicas into optical grade OrmoClearFX material. Both replication strategies result in very high-quality replicas of the original patterns.
In the presented work solvent-free film preparation from molecular glass resists, the evaluation of the patterning performance using thermal scanning probe lithography (tSPL) and an efficient etch transfer process are demonstrated. As the presented materials have a high tendency to crystallize and thus form crystalline films of bad quality when processed by solution casting, two component mixtures prepared by coevaporation were investigated. Stable amorphous films were obtained by selecting compatible material pairs for the coevaporation. One optimized material pair is based on trissubstituted, twisted resist materials with a distinct difference in molecular design. Here a high resolution tSPL prepared pattern of 18 nm half pitch in a 10 nm thick film is demonstrated.
A further optimization is reported for “small” cubic silsequioxane molecules. Again single component films show independent to applied film preparation techniques bad film forming properties due to the high crystallinity of the symmetric cubic silsequioxane molecules. But coevaporation of the phenyl substituted octaphenylsilsequioxane combined with the fully aromatic 2,2',7,7'-tetraphenyl-9,9'-spirobi[fluorene] results in stable amorphous thin films. tSPL investigations demonstrate the patternability by writing high resolution line features of 20 nm half pitch. An important advantage of such a silicon rich resist material is that it can be directly converted to SiO2, yielding to a patterned hardmask of SiO2. This proof of principle is demonstrated and an efficient pattern transfer of 60 nm half pitch line into the underlying HM8006 is reported.
Thermal Scanning Probe Lithography (tSPL) is an AFM based patterning technique, which uses heated tips to locally evaporate organic resists such as molecular glasses  or thermally sensitive polymers. Organic resists offer the versatility of the lithography process known from the CMOS environment and simultaneously ensure a highly stable and low wear tip-sample contact due to the soft nature of the resists. Patterning quality is excellent up to a resolution of sub 15 nm, at linear speeds of up to 20 mm/s and pixel rates of up to 500 kHz. The patterning depth is proportional to the applied force which allows for the creation of 3-D profiles in a single patterning run. In addition, non-destructive imaging can be done at pixel rates of more than 500 kHz. If the thermal stimulus for writing the pattern is switched off the same tip can be used to record the written topography with Angstrom depth resolution. We utilize this unique feature of SPL to implement an efficient control system for reliable patterning at high speed and high resolution. We combine the writing and imaging process in a single raster scan of the surface. In this closed loop lithography (CLL) approach, we use the acquired data to optimize the writing parameters on the fly. Excellent control is in particular important for an accurate reproduction of complex 3D patterns. These novel patterning capabilities are equally important for a high quality transfer of two-dimensional patterns into the underlying substrate. We utilize an only 3-4 nm thick SiOx hardmask to amplify the 8±0.5 nm deep patterns created by tSPL into a 50 nm thick transfer polymer. The structures in the transfer polymer can be used to create metallic lines by a lift-off process or to further process the pattern into the substrate. Here we demonstrate the fabrication of 27 nm wide lines and trenches 60 nm deep into the Silicon substrate. In addition, the combined read and write approach ensures that the lateral offset between read and write field is minimized. Thus we achieve high precision in marker-less stitching of patterning fields. A 2D cross-correlation technique is used to determine the offset of a neighboring patterning field relative to a previously written field with an accuracy of about 1 nm. We demonstrate stitching of 1 μm2 fields with ~5 nm accuracy and stitching of larger 10x10 μm2 fields with 10 nm accuracy.
Heated tips offer the possibility to create arbitrary high-resolution nanostructures by local decomposition and
evaporation of resist materials. Turnaround times of minutes are achieved with this patterning method due to the high-speed
direct-write process and an in-situ imaging capability. Dense features with 10 nm half-pitch can be written into
thin films of organic resists such as self-amplified depolymerization (SAD) polymers or molecular glasses. The
patterning speed of tSPL has been increased far beyond usual scanning probe lithography (SPL) technologies and
approaches the speed of Gaussian shaped electron beam lithography (EBL) for <30 nm resolution. A single tip can write
complex patterns with a pixel rate of 500 kHz and a linear scan speed of 20 mm/s. Moreover, a novel scheme for
stitching was developed to extend the patterning area beyond the ≤100 μm range of the piezo stages. A stitching
accuracy of 10 nm is obtained without the use of markers. Furthermore, the patterning depth can be controlled
independently and accurately (~1 nm) at each position. Thereby, arbitrary 3D structures can be written in a single step.
Finally, we demonstrated an all-dry tri-layer pattern transfer concept to create high aspect ratio structures in silicon.
Dense fins and trenches with 27 nm half-pitch and a line edge roughness (LER) below 3nm (3σ) have been fabricated.