Tomi Haatainen

Continuous Double-Sided Roll-to-Roll Imprinting of Polymer Film

Roll-to-roll imprinting of two-sided structures on thermoplastic polymer film have been studied. Two continuous roll-to-roll approaches to producing structures on both sides of a web have been developed. In the sequential method, two separate printing units are used to the pattern upper and bottom surfaces of the film. In simultaneous roll-to-roll imprinting, two patterned rolls are used in one imprinting unit to pattern both sides simultaneously. In both experiments, flexible Ni-masters with submicron patterns wrapped on supporting metal rolls are used as stamps. The cellulose acetate film 95 µm thick and 50 mm wide has been used as the imprint material in the experiments. Patterned films were studied with an optical microscope and an atomic force microscope (AFM). The results indicate that both methods can be used for double-sided imprinting. However, in sequential imprinting, the first printed pattern is slightly damaged during the second printing phase.

Step and stamp imprint lithography using a commercial flip chip bonder

In this work we describe a new method suitable for large area nanoimprint lithography. In step&stamp process the pattern on a stamp is transferred into a polymer layer on the substrate by repeating a step&stamp cycle. The method is demonstrated by imprinting matrices of test structures on polymer-coated 100 mm silicon wafers. A new polymer, PPM, is used as resist in the experiments. The polymer has been developed to fulfill the demands of imprint lithography. Patterns with sizes down to 400 nm were imprinted into either 100 nm or 340 nm thick PPM resist. After thinning in oxygen plasma, the resist layer is used as etching mask or for fabrication of interdigitated aluminum fingers by lift-off.

Imprinted electrically conductive patterns from a polyaniline blend

Imprinting three-dimensional patterns directly into electrically conductive polymer blends is investigated. Silicon substrates are spin-coated by a polymethylmethacrylate/polyaniline-camphor sulfonic acid mixture dissolved in m-cresol. The patterns are imprinted using a silicon stamp having a 500 nm deep grating with 5 μm wide lines and spaces. The imprinting temperature was 140 °C, pressure 150 bar, and time 10 min. The conductivity of the blend was 1 S/cm prior to imprinting and decreased by a factor of about 2 in the process. Removing the residual film from the grooves by etching in argon/oxygen plasma results in resistance anisotropy larger than 104 perpendicular and parallel to the imprinted polymer ridges.

Benchmarking of 50 nm features in thermal nanoimprint

The objective of this benchmarking is to establish a comparison of several tools and processes used in thermal NIL with Si stamps at the nanoscale among the authors’ laboratories. The Si stamps have large arrays of 50nm dense lines and were imprinted in all these laboratories in a ∼100nm thick mr-18010E film. Other materials, such as mr-17010E, were also tested. Good patterns were obtained and some limitations were identified. Reducing the pressure to 15bars enables the printing of 50nm structures without pulling them off. At higher pressures, some bending effects resulting in pattern deformation were observed. It was proven that a pressure of 1.5bars is sufficient to imprint perfect 50nm lines. The influence of the antiadhesive layer and mold design has been characterized by the demonstration of pulled off lines in some cases. Moreover, it has been shown that the scatterometry method is particularly useful for the characterization of 50nm lines and that the residual layer thickness corresponds to the the...

Fabrication of mesas with micro- and nanopatterned surface relief used as working stamps for step and stamp imprint lithography

A manufacturing concept to fabricate working stamps with defined mesa structures using combined nanoimprint and photolithography is presented. OrmoStamp, an UV-curable organic-inorganic hybrid polymer, was used as mold material. 30 μm high large mesa structures (4×4 mm2) with sharp borders and almost vertical sidewalls were manufactured. On top they featured nanograting patterns with 200 nm height and lateral size as a surface relief. The good thermal decoupling of stamp body and imprinted substrate and the high planarity (divergence <50 nm) make the stamp very suitable for thermal step and repeat nanoimprint lithography of confined patterns with low stitching errors. Up to 210 imprints were performed with a single mesa into a 325 nm thin layer of mr-I 7030E.

Imprinted 50 nm Features Fabricated by Step and Stamp UV Imprinting

We fabricated features down to 50 nm by UV step and stamp imprint lithography (UV-SSIL). This method enables fast sequential imprinting for large areas operating at room temperature with a low-viscosity material. This allows the patterning of both large micron-scale and submicron-scale structures simultaneously. A low-viscosity polymer allows pattern transfer at moderate pressures, thereby reducing mechanical stress on the stamp and substrate. Processing at room temperature helps to maintain the alignment and to prevent the distortion of the features caused by the thermal expansion of the mold and substrate. A UV-SSIL experiment with a novel photosensitive polymer was performed using a prototype of currently commercially available machines used for both thermal and UV step and stamp imprintings. As a master, we used a transparent quartz stamp (with features down to 50 nm) patterned by electron-beam lithography. The polymer was dispensed on a 100 mm silicon substrate using a syringe-type dispensing system. The results were analyzed by atomic force microscopy and a scanning electron microscopy. The fabricated structures exhibited good lateral and vertical feature replication fidelities.

Electrostatic MEMS tunable split-ring resonators for THz filter applications

We propose a new use of an RF-MEMS (radio frequency - micro electro mechanical systems) capacitive switch to construct a tunable terahertz filter. The built-in capacitor within a split-ring resonator is electrostatically actuated to shift the resonant frequency, providing a behavior as an ON/OFF switch for a particular frequency in the terahertz band. The device is compatible with the surface micromachining process of metals as well as with the roll-to-roll printing patterning for large and flexible sheet filters.

Step and Stamp Imprint Lithography

As the semiconductor industry continues to push to smaller device geometries, lithography becomes more and more a crucial process step. Traditionally, the semiconductor industry has relied on optical lithography and new generations of optical steppers are being developed for shorter wavelengths. Anyhow, in order to produce sub-50 nm lithography researches have started to look for new solutions, such as X-ray lithography, fast electron beam (e-beam) lithography and nanoimprint lithography (NIL).

Flexible stamp for nanoimprint lithography

The design, fabrication and performance of a flexible silicon stamp for homogenous large area nanoimprint lithography (NIL) are presented. The flexible stamp is fabricated by bulk semiconductor micro machining of a 4-inch silicon wafer and consists of thick anchor like imprint areas connected by membranes. The bending stiffness difference between the imprint areas and the membranes ensures that the deformation of the stamp during the imprint process mainly takes place in the membranes, leaving the imprint structures unaffected. By this design the strong demand to the parallelism between stamp and substrate in the imprint situation is decoupled from the pressing tool and the wafer quality. The stamp consist of 1562 imprint areas (1 mm /spl times/ 1 mm) containing the patterns to be replicated. The imprinted patterns are characterized with respect to the imprint depth and the polymer residual layer thickness. It is found that within a 50 mm diameter the polymer residual layer thickness is 18.8 nm with a standard deviation of 6.6 nm.