Imprint Tool Research Articles

Nano-scale patterning using the roll typed UV-nanoimprint lithography tool

Nanoimprint lithography is a promising technology to produce sub-100nm half-pitch features on silicon wafers. To achieve nano-imprinting process, nano-imprinting lithography equipment must have required some multi-functional units which are imprinting head, self-alignment wafer stage, overlay and alignment system for multi-layer process, stamp with sub-100nm half-pitch patterns, and anti-vibration unit, etc. Although imprinting process has many advantages in terms of low cost, high throughput and reproducibility, these imprinting technologies have a limitation to increase imprinting area and imprinting tool sizes. Also, air entrap phenomenon which is generated between the stamp and the resist surfaces during imprinting process is getting important parameter in the press type imprinting process. In order to get over these limitations and the air entrap and to fabricate large area product, such as above 8in. wafer, display unit and multi-functional device, roll typed UV-nanoimprint lithography tool are certainly necessary. In this study, the roll typed UV-nanoimprint lithography tool which is can be loaded PDMS (polydimethylsiloxane), polycarbonate and PET film as soft stamp, is proposed.

UV nanoimprint materials: Surface energies, residual layers, and imprint quality

UV nanoimprint lithography is attracting more and more interest, because it has the potential of becoming a high-resolution, low-cost patterning technique. The availability of suitable UV curing materials is mandatory for successful imprinting. Within this work, a systematic investigation of commercially available photocuring materials was conducted to provide an overview of the properties of these materials. Their wetting behavior with respect to different substrate surfaces was characterized and their surface tensions were determined from their contact angles against two specifically selected solid surfaces: This method is presented here for the first time. The adhesion properties of the UV curing materials to different substrate surfaces and to the mold were investigated and necessary curing times were estimated. Additionally, the dependence of the residual layer thickness on the viscosity and the initial dispensed volume of UV curing materials was analyzed. It was found that the resist formulation of the UV curing materials strongly influences the surface tension as well as the adhesion to different substrate surfaces. Furthermore, the experiments verified that the thickness of the residual layer for UV curing materials increases with the square root of their viscosity which is predicted by theory. To demonstrate the suitability of the UV curing materials, first imprints with the prototype imprint tool, Nano Patterning Stepper 300 from Süss MicroTec, with pattern sizes down to 50nm are shown.

Distortion and overlay performance of UV step and repeat imprint lithography

High-resolution overlay is considered to be an important challenge for imprint lithography processes. A key advantage of Step and Flash™ Imprint Lithography (S-FIL™) is that it uses low-pressures (<1/40th of an atmosphere) at room temperature during the imprint processes. This makes it specifically suited for overlay as compared to other thermal or high pressure processes. To obtain high resolution overlay, it is critical to minimize in-plane distortions in both the template and substrate. This article presents a detailed budget of the various distortions that affect the S-FIL process. These distortions include: (i) 1X template e-beam pattern distortions; (ii) template distortions due to post-processing steps; and (iii) wafer processing distortions. Distortions associated with template patterning were measured prior to Cr removal using a Leica LMS tool. Field-to-field distortion variations were measured using 27 imprints on three wafers from a step and repeat imprint tool without control of thermal environment. Thermal effects on the imprint tool showed up as uniform magnification errors. Using the field-to-field distortion data, a first order correction scheme was implemented numerically to significantly lower the imprint-related distortion. Related issues such as XY– Θ alignment is also discussed briefly.

Fabrication of hybrid organic–inorganic vertical microcavities through imprint technology

We report on the fabrication of hybrid organic–inorganic vertical microcavities by using imprint lithography tools. The device consists of an organic active layer (rubrene-PMMA blend) embedded between two dielectric distributed Bragg reflectors (DBR). The active organic layer was spin coated on the first DBR, whereas a SU8 lithographic pattern was realized on the second DBR, which was used as the imprint mold. The two parts were then assembled together in an imprint process in order to create a vertical microcavity constituted by the rubrene active layer between two high-reflectivity mirrors. The effectiveness of this technology is demonstrated by the room temperature photoluminescence spectra, recorded on the fabricated microcavity, which show a sharp emission peak at the microcavity resonance wavelength.

Reproducibility and homogeneity in step and repeat UV-nanoimprint lithography

A new approach to step and repeat UV-based nanoimprint lithography (UV-NIL) using sequential imprints on a large-area spin-coated surface is presented. A detailed study has been performed in order to assess the reproducibility and homogeneity of the process. The imprint tool features a movable wafer stage for 4 in. wafers, allowing the high precision vertical and lateral positioning necessary for a step and repeat imprint technique. More than 1000 imprints with a single mold were performed without any cleaning of the mold. This demonstrates the high asymmetry between the detachment from the mold and the adhesion to the substrate achieved, an essential issue for reproducibility. Furthermore, the uniformity of the residual resist thickness was analyzed. The measured thicknesses, 57 ± 12.5 nm and 118 ± 12.5 nm for initial film thicknesses of 210 and 275 nm, respectively, revealed the uniformity to be sufficient for accurate pattern transfer.

Wafer scale patterning by soft UV-Nanoimprint Lithography

We present first results on wafer scale patterning within one imprint step only, using Soft UV-Nanoimprint Lithography (UV-NIL). In this process, flexible transparent stamps, fabricated by cast moulding ensure a conformal contact, whereas the usage of low viscosity UV-curable resists allows three-dimensional pattern generation at low pressure (<1 bar) and room temperature. Technical aspects that will be covered in this paper include the master and stamp fabrication and a new imprint tool, developed by EV Group, Austria. To demonstrate the applicability of this technique, imprints on 100 mm silicon wafers have been analysed with special emphasis to the residual resist thickness h r. In addition, data on the dimensional stability of the imprint process are presented.

Reproducibility and homogeneity in step and repeat UV-nanoimprint lithography

A new approach to step and repeat UV-based nanoimprint lithography (UV-NIL) using sequential imprints on a large-area spin-coated surface is presented. A detailed study has been performed in order to assess the reproducibility and homogeneity of the process. The imprint tool features a movable wafer stage for 4 in. wafers, allowing the high precision vertical and lateral positioning necessary for a step and repeat imprint technique. More than 1000 imprints with a single mold were performed without any cleaning of the mold. This demonstrates the high asymmetry between the detachment from the mold and the adhesion to the substrate achieved, an essential issue for reproducibility. Furthermore, the uniformity of the residual resist thickness was analyzed. The measured thicknesses, 57 ± 12.5 nm and 118 ± 12.5 nm for initial film thicknesses of 210 and 275 nm, respectively, revealed the uniformity to be sufficient for accurate pattern transfer.

Liposomes as signal amplification reagents for bioassays in microfluidic channels.

Liposomes with encapsulated carboxyfluorescein were used in an affinity-based assay to provide signal amplification for small-volume fluorescence measurements. Microfluidic channels were fabricated by imprinting in a plastic substrate material, poly(ethylene terephthalate glycol) (PETG), using a silicon template imprinting tool. Streptavidin was linked to the surface through biotinylated-protein for effective immobilization with minimal nonspecific adsorption of the liposome reagent. Lipids derivatized with biotin were incorporated into the liposome membrane to make the liposomes reactive for affinity assays. Specific binding of the liposomes to microchannel walls, dependence of binding on incubation time, and nonspecific adsorption of the liposome reagent were evaluated. The results of a competitive assay employing liposomes in the microchannels are presented.