Residual Layer Thickness Uniformity Research Articles

Chip-scale pattern modification method for equalizing residual layer thickness in nanoimprint lithography

A software program for modifying a mold design to obtain a uniform residual layer thickness (RLT) distribution has been developed and its validity was verified by UV-nanoimprint lithography (UV-NIL) simulation. First, the effects of granularity (G) on both residual layer uniformity and filling characteristics were characterized. For a constant complementary pattern depth and a granularity that was sufficiently larger than the minimum pattern width, filling time decreased with the decrease in granularity. For a pattern design with a wide density range and an irregular distribution, the choice of a small granularity was not always a good strategy since the etching depth required for a complementary pattern occasionally exceptionally increased with the decrease in granularity. On basis of the results obtained, the automated method was applied to a chip-scale pattern modification. Simulation results showed a marked improvement in residual layer thickness uniformity for a capacity-equalized (CE) mold. For the given conditions, the standard deviation of RLT decreased in the range from 1/3 to 1/5 in accordance with pattern designs.

Influence of discrete drop locations on film thickness uniformity in UV- nanoimprint lithography

Multi-nozzle inkjetting is the material deposition approach for a variant of UV-nanoimprint lithography called Jet-and-Flash Imprint Lithography (J-FIL). J-FIL has several advantages with respect to addressing pattern density variations in the template as well as achieving low material waste when compared with spin-coating. In this work, the influence of discrete drop placement in J-FIL on residual layer thickness uniformity has been investigated with the help of a novel nonlinear lubrication theory model, which takes into account the compliant nature of the template in the presence of a moving contact line. This work is directed at thin residual layers (sub-20nm), where a correlation exists between minimum drop resolution, inkjet nozzle pitch and residual layer thickness uniformity. Numerical simulations reveal that the non-uniformity resulting from discrete drop placement can exceed desired process tolerances when low film thicknesses are desired with relatively larger drop volumes. The results have been verified experimentally to reveal the same trend. This work can be useful in determining the correlation of inkjet drop resolution with inkjet nozzle pitch to meet process tolerances in the J-FIL process.

Hard disk drive thin film head manufactured using nanoimprint lithography

The lithographic requirements for the thin film head (TFH) industry are comparable to the semiconductor industry for certain parameters such as resolution and pattern repeatability. In other aspects such as throughput and defectivity, the requirements tend to be more relaxed. These requirements match well with the strengths and weaknesses reported concerning nanoimprint lithography (NIL) and suggest an alternative approach to optical lithography. We demonstrate the proof of concept of using NIL patterning, in particular Jet and Flash™ Imprint Lithography (J-FIL™) (Imprio, Jet and Flash Imprint Lithography, and J-FIL trademarks are the property of Molecular Imprints, Inc.), to build functional TFH devices with performance comparable to standard wafer processing. An Imprio™ 300 tool from Molecular Imprints, Inc. (MII) was modified to process the AlTiC ceramic wafers commonly used in the TFH industry. Templates were produced using commercially viable photomask manufacturing processes and the AlTiC wafer process flow was successfully modified to support NIL processing. Future work is identified to further improve lithographic performance including residual layer thickness uniformity, wafer topography, NIL→NIL overlay, and development of a large imprint field that exceeds what is available in optical lithography.

Simulation and Experimental Study of the Effects of Process Factors on the Uniformity of the Residual Layer Thickness in Hot Embossing

Hot embossing replica are characterized by the quality of the molded structures and the uniformity of the residual layer. In particular, the even distribution of the residual layer thickness (RLT) is an important issue in hot embossing and the related process of thermal nanoimprint lithography, as variations in the RLT may affect the functionality or further processing of replicated parts. In this context, the paper presents an experimental and simulation study on the influence of three process factors, namely the molding temperature, the embossing force, and the holding time, on the residual layer homogeneity achieved when processing 2 mm thick PMMA sheets with hot embossing. The uniformity of the RLT was assessed for different experimental conditions by calculating the standard deviation of thickness measurements at different set locations over the surface of each embossed sample. It was observed that the selected values of the studied parameters have an effect on the resulting RLT of the PMMA replica. In particular, the difference between the largest and lowest RLT standard deviation between samples was 18 μm, which was higher than the accuracy of the instrument used to carry out the thickness measurements. In addition, the comparison between the obtained experimental and simulation results suggests that approximately 12% of the RLT uniformity was affected by the local deflections of the mold. Besides, polymer expansion after release of the embossing load was estimated to contribute to 8% of the RLT nonuniformity. It is essential to understand the effects of the process parameters on the resulting homogeneity of the residual layer in hot embossing. In this research, the best RLT uniformity could be reached by using the highest considered settings for the temperature and holding time and the lowest studied value of embossing force. Finally, the analysis of the obtained results also shows that, across the range of processing values studied, the considered three parameters have a relatively equal influence on the RLT distribution. However, when examining narrower ranges of processing values, it is apparent that the most influential process parameter depends on the levels considered. In particular, the holding time had the most effect on the RLT uniformity when embossing with the lower values of process parameters while, with higher processing settings, the molding temperature became the most influential factor.

Development of a large area plate-to-plate type UV imprinting tool

A UV imprint lithography tool has been developed for micro/nano-scale patterning in an extremely large area, i.e., ∼300×400mm2. To achieve high pattern fidelity, residual-layer thickness uniformity, and an air bubble-free layer in a large area, the UV imprint tool has several main components including a silicon rubber uniform pressurizer, a large area UV-LED module, a vacuum pump, a chuck module, etc. Contact and structural analyses have been performed using commercial FEM packages such as LS-DYNA and ANSYS. The developed tool has been tested, and its performance indices including pattern fidelity and residual-layer thickness uniformity have been measured to be ∼97% and ∼90%, respectively.

Modeling and simulation of stamp deflections in nanoimprint lithography: Exploiting backside grooves to enhance residual layer thickness uniformity

We describe a model for the compliance of a nanoimprint stamp etched with a grid of backside grooves. We integrate the model with a fast simulation technique that we have previously demonstrated, to show how etched grooves help reduce the systematic residual layer thickness (RLT) variations that occur when different patterns lie in close proximity on the stamp.

Homogeneity of Residual Layer thickness in UV Nanoimprint Lithography

In nanoimprint lithography, control of residual layer thickness is a very important issue. Pattern density variation is inconvenient for nanoimprint lithography but UV nanoimprint is considered more adaptive to pattern density variation thanks to the higher fluidity of UV-curable resin. Despite this consideration, methods to overcome pattern density problems have been developed and adopted in UV nanoimprint lithography. These methods work well; however, it is still remains there a question of whether residual layer thickness uniformity is improved without such methods. In this study, UV nanoimprint is carried out using a conformable contact mechanism, and the impact of pattern density variation and pressing time of nanoimprint on the residual layer profile is investigated for an initially thin UV-curable resin. After recess filling, UV-curable resin moves very locally so as to make the residual layer smoothly change, but does not move sufficiently for the residual layer to be modified across the entire imprint field. For a longer pressing time, the residual layer thickness is decreased only at the edges. A small amount of the UV-curable resin was expelled from the mold, but most was retained between the mold and wafer, and the UV-curable resin moved inward. For realization of a thin and uniform residual layer, the residual layer must be thin throughout the imprint field from the beginning of the pressing process; otherwise the resulting residual layer that is thick only at peripheral regions must be thinned by a long pressing time.