Basic Research On Key Techniques For Microimprint And Nanoimprint

Traditional ultraviolet lithography in microelectronics industry meets expensive lithography tool and complex technical problems, such as optic diffraction and choice of lens material. In the Next Generation Lithography, imprint technique has the advantage of high throughput because one single stamp can replicate many patterned micro/nanostructures in a low cost. However, current imprint technique has drawbacks such as long time needed to fabricate stamp and high temperature demanded to imprint. In this dissertation, novel stamp fabrication method and low Tg (glass transition temperature) polymers were studied in the imprint process with the optimized parameters. Finally, imprinted samples were taken as polymer gratings and substrates for bio experiment.Imprint technique includes three different methods: hot embossing lithography (HEL), ultraviolet nanoimpirnt lithography (UV-NIL) and soft lithography (SL). HEL usually needs a hard stamp, while UV-NIL and SL can use soft imprint stamp, which is outstanding for 3D fabrication and applications. The common feature of SL is that all of techniques need soft PDMS stamps. Conventional method of fabricating PDMS is to cast mixture of PDMS prepolymer and its curing agent directly on a master, which is time-consuming because it occupies the master a long time for curing. Two novel methods have been innovated to manufacture PDMS quickly. One technique is using spin-coating instead of casting on the master. The other is using the master to imprint many polymer molds and then spin-coating or casting PDMS mixture on the polymer molds to produce many PDMS stamps. We call the later method MMS technique (from Master via Mold to Stamp). Because imprint has a short process cycle, the master can imprint may polymer molds in a short time, and then use them to manufacture PDMS stamps.The disadvantage of current HEL technique is that long time is needed to manufacture the imprint stamp because e-beam writing is a slow technique since its low energy. New method of using Focused Ion Beam (FIB) was taken to fabricate all kinds of patterns, such as lines, curves, and emblems of Beijing 2008 Olympic Games and Shanghai 2010 World Expo on different substrates. The advantage of FIB method is that it can form pattern directly on the final substrate without RIE process needed in the common method. The other notable merit is that it can fabricate micron and nano sized patterns on one single substrate at the same time. Another fast method of fabricating imprint stamp is using holographical lithography combined with ICP etching. Using this method, we fabricated quartz gratings with different pitch and depth.The disadvantage of conventional imprint technique is that imprint temperature is high as the conventional imprint materials such as PMMA and PC have a high Tg. Novel imprint polymers PETG (polyethylene terephthalate glycol), SU-8 2000.1 and Hybrane resist were imprinted. All of them have a low Tg and can be imprinted at a lower temperature. PETG is suitable for imprint at micron sized pattern, while SU-8 2000.1 and Hybrane suitable for nanoimprint and Hybrane can be imprinted at room temperature.From theory, we calculated the filling time of polymer into FIB fabricated stamp cavities, analyzed the imprint process and found the concept of effective intensity of pressure, simulated the anti-sticking material by Molecular Dynamics (MD) method. With the help of MD, we investigated the combination energy of CF2 and SiO2 substrate, and indicated that CF2 has the effect of anti-sticking property. In experiment, we used CHF3 and SF6 in RIE machine to produce anti-sticking film on stamps because they can produce CF2. (1,1,2,2 H perfluorooctyl)-trichlorosilane is also a good choice for helping to release stamp from substrate. Orthogonal method was employed to optimize experiment parameters. SU-8 2000.1 with the Tg of which is only 55℃was used for NIL. We also imprint Hybrane resist under room temperature. Mr-I 9020 was also taken for NIL because it is a good mask material for later pattern transfer. Diverse stamps were used to imprint different polymer. SEM and AFM were taken to characterize the stamps and their replicas and the result indicates that the imprint quality is high.Imprint technique can be widely used in manufacturing plastic gratings, soft PDMS gratings, etc. It can also be used in bio experiment and applications, such as protein transfer and cell growth. We cultivated C6 glioma and SD mouse ostoblast cells on the patterned polystyrene samples and vascular smooth muscle cells on patterned PETG substrates, both with uniform grooves replicated from silica master. The results indicated that ordered groove microstructures on substrate can guide cell alignment and oriented growth along definite directions, which has a vital implication for cell biology and biosensor research.