Research Papers

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

[+] Author and Article Information
F. Omar, H. Hirshy

Institute of Mechanical and
Manufacturing Engineering,
Cardiff School of Engineering,
Cardiff University,
Cardiff CF24 3AA, UK

A. Kolew

Institute of Microstructure Technology,
Karlsruhe Institute of Technology,
Karlsruhe 76131, Germany

E. B. Brousseau

e-mail: BrousseauE@cf.ac.uk

1Corresponding author.

Contributed by the Manufacturing Engineering Division of ASME for publication in the JOURNAL OF MICRO- AND NANO-MANUFACTURING. Manuscript received July 31, 2012; final manuscript received March 21, 2013; published online April 22, 2013. Assoc. Editor: Liwei Lin.

J. Micro Nano-Manuf 1(2), 021002 (Apr 22, 2013) (10 pages) Paper No: JMNM-12-1042; doi: 10.1115/1.4024097 History: Received July 31, 2012; Revised March 21, 2013

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.

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Saile, V., 2009, “Introduction: LIGA and its Applications,” Adv. Micro Nanosyst., 7, pp. 1–10.
Dornfeld, D., Min, S., and Takeuchi, Y., 2006, “Recent Advances in Mechanical Micro Machining,” CIRP Ann., 55(2), pp. 745–768. [CrossRef]
Rizvi, N. H., and Apte, P., 2002, “Developments in Laser Micro-Machining Techniques,” J. Mater. Process. Technol., 127(2), pp. 206–210. [CrossRef]
Griffiths, C., Dimov, S., Scholz, S., Hirshy, H., and Tosello, G., 2011, “Process Factors Influence on Cavity Pressure Behaviour in Microinjection Moulding,” ASME J. Manuf. Sci. Eng., 133(3), p. 0310071. [CrossRef]
Worgull, M., 2009, Hot Embossing: Theory and Technology of Microreplication, Elsevier, New York.
Chou, S. Y., Krauss, P. R., and Renstrom, P. J., 1995, “Imprint of Sub 25 nm Vias and Trenches in Polymers,” Appl. Phys. Lett., 67(21), pp. 3114–3116. [CrossRef]
Heckele, M., and Schomburg, W. K., 2004, “Review on Micro Molding of Thermoplastic Polymers,” J. Micromech. Microeng., 14, pp. R1–R14. [CrossRef]
Yong, H., Jian-Zhong, F., and Zi-Chen, C., 2007, “Research on Optimization of the Hot Embossing Process,” J. Micromech. Microeng., 17(12), pp. 2420–2425. [CrossRef]
Becker, H., and Heim, U., 2000, “Hot Embossing as a Method for the Fabrication of Polymer High Aspect Ratio Structures,” Sens. Actuators, A, 83(1–3), pp. 130–135. [CrossRef]
Cui, B., and Veres, T., 2006, “Pattern Replication of 100 nm to Millimeter-Scale Features by Thermal Nanoimprint Lithography,” Microelectron. Eng., 83(4–9), pp. 902–905. [CrossRef]
Heckele, M., Gerlach, A., Guber, A., and Schaller, T., 2001, “Large Area Polymer Replication for Microstructured Fluidic Devices,” Proc. SPIE, 4408, pp. 469–476. [CrossRef]
McGeough, J., 2002, Micromachining of Engineering Materials, Marcel Dekker, New York, Chap. 4.
Chang, J.-H., and Yang, S.-Y., 2003, “Gas Pressurized Hot Embossing for Transcription of Micro-Features,” Microsyst. Technol., 10(1), pp. 76–80. [CrossRef]
Hocheng, H., and Wen, T. T., 2008, “Innovative Approach to Uniform Imprint of Micron and Submicron Features,” J. Achiev. Mater. Manuf. Eng., 28(1), pp. 79–82.
Gao, H., Tan, H., Zhang, W., Morton, K., and Chou, S. Y., 2006, “Air Cushion Press for Excellent Uniformity, High Yield, and Fast Nanoimprint Across a 100 mm Field,” Nano Lett., 6(11), pp. 2438–2441. [CrossRef] [PubMed]
Lazzarino, F., Gourgon, C., Schiavone, P., and Perret, C., 2004, “Mold Deformation in Nano Imprint Lithography,” J. Vac. Sci. Technol. B, 22(6), pp. 3318–3323. [CrossRef]
Sirotkin, V., Svintsov, A., Schift, H., and Zaitsev, S., 2007, “Coarse-Grain Method for Modelling of Stamp and Substrate Deformation in Nanoimprint,” Microelectron. Eng., 84(5–8), pp. 868–871. [CrossRef]
Merino, S., Retolaza, A., Juarros, A., and Schift, H., 2008, “The Influence of Stamp Deformation on Residual Layer Homogeneity in Thermal Nanoimprint Lithography,” Microelectron. Eng., 85(9), pp. 1892–1896. [CrossRef]
He, Y., Fu, J.-Z., and Chen, Z.-C., 2008, “Optimization of Control Parameters in Micro Hot Embossing,” Microsyst. Technol., 14(3), pp. 325–329. [CrossRef]
Mehne, Ch., 2007, “Großformatige Abformung mikrostrukturierter Formeinsätze durch Heißpräqen,” Ph.D. thesis, University of Karlsruhe, Institute for Microstructure Technology, Karlsruhe, Germany.
Shan, X. C., Liu, Y. C., and Lam, Y. C., 2008, “Studies of Polymer Deformation and Recovery in Micro Hot Embossing,” Microsyst. Technol., 14(7), pp. 1055–1060. [CrossRef]
Lin, C.-R., Chen, R.-H., and Hung, C., 2003, “Preventing Non-Uniform Shrinkage in Open-Die Hot Embossing of PMMA Microstructures,” J. Mater. Process. Technol., 140(1), pp. 173–178. [CrossRef]
Jenoptik Mikrotechnik, 2002, “Datasheet of HEX03 Hot Embossing System,” Jenoptik Mikrotechnik, Jena, Germany.
Simprint Nanotechnologies Ltd., 2012, “Simprint Nanotechnologies,” Bristol, http://simprintnanotech.com
Velkova, V., Lalev, G., Hirshy, H., Scholz, S., Hiitola-Keinänen, J., Gold, H., Haase, A., Hast, J., Stadlober, B., and Dimov, S., 2010, “Design and Validation of a Novel Master-Making Process Chain for Organic and Large Area Electronics on Flexible Substrates,” Microelectron. Eng., 87(11), pp. 2139–2145. [CrossRef]
Hirshy, H., Lalev, G., Velkova, V. L., Popov, K., Scholz, S., and Dimov, S. S., 2011, “Master Tool Fabrication for the Replication of Micro and Nano Features,” Proceedings of the 8th International Conference on Multi-Material Micro Manufacture, 4M2011, Stuttgart, Germany, Nov. 8–10, pp. 317–320.
Lalev, G., Petkov, P., Sykes, N., Hirshy, H., Velkova, V., Dimov, S. S., and Barrow, D. A., 2009, “Fabrication and Validation of Fused Silica NIL Templates Incorporating Different Length Scale Features,” Micorelectron. Eng., 86(4–6), pp. 705–708. [CrossRef]
Li, W., Dimov, S., and Lalev, G., 2007, “Focused-Ion Beam Direct Structuring of Fused Silica for Fabrication of Nano-Imprinting Templates,” Microelectron. Eng., 84(5–8), pp. 829–832. [CrossRef]
McGeough, J. A., Leu, M. C., Rajurkar, K. P., De Silva, A. K. M., and Liu, Q., 2001, “Electroforming Process and Application to Micro/Macro Manufacturing,” CIRP Ann., 50(2), pp. 499–514. [CrossRef]
Ng., S. H., Tjeung, R. T., and Wang, Z., 2006, “Hot Embossing on Polymethyl Methacrylate,” Proceedings of the 8th IEEE Electronics Packaging Technology Conference, EPTC’06, Singapore, Dec. 6–8, pp. 615–621.
Toh, A. G., Wang, Z. F., and Wang, Z. P., 2009, “Ambient Hot Embossing of Polycarbonate, Poly-Methyl Methacrylate and Cyclic Olefin Copolymer for Microfluidic Applications,” Proceedings of the IEEE Symposium on Design, Test, Integration & Packaging of MEMS/MOEMS, Singapore, Apr. 1–3, pp. 359–362.
Matbase VOF, 2003, “Material Properties Database,” Matbase VOF, Delft, http://www.matbase.com/material/polymers/commodity/pmma/properties
Ng, S. H., Wang, Z. F., Tjeung, R. T., and de Rooij, N. F., 2006, “Process Issues for a Multi-Layer Microelectrofluidic Platform,” Proceedings of the Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS, DTIP 2006, Stresa, Italy, Apr. 26–28.
Scheer, H.-C., and Schulz, H., 2001, “A Contribution to the Flow Behaviour of Thin Polymer Films During Hot Embossing Lithography,” Microelectron. Eng., 56(3–4), pp. 311–332. [CrossRef]
Schelb, M., Vannahme, C., Kolew, A., and Mappes, T., 2011, “Hot Embossing of Photonic Crystal Polymer Structures with a High Aspect Ratio,” J. Micromech. Microeng., 21(2), pp. 1–5. [CrossRef]
Luo, Y., Xu, M., Wang, X. D., and Liu, C., 2006, “Finite Element Analysis of PMMA Microfluidic Chip Based on Hot Embossing Technique,” J. Phys.: Conf. Ser., 48, pp. 1102–1106. [CrossRef]
Taylor, H., Lam, Y. C., and Boning, D., 2009, “A Computationally Simple Method for Simulating the Micro-Embossing of Thermoplastic Layers,” J. Micromech. Microeng., 19(7), 075007. [CrossRef]
Mitutoyo, 2004, “Quick Vision Accel – CNC Vision Measuring System,” http://www.mitutoyo.com/pdf/QV%20Accel%201759.pdf
Spetzler, H. A., and Meyer, M. D., 1974, “Precise Length Measurement Technique under Hydrostatic Pressure: Isothermal Bulk Modulus of PMMA,” Rev. Sci. Instrum., 45(7), pp. 911–915. [CrossRef]


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Fig. 5

Process chain used to manufacture the hot embossing Ni mold

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Fig. 4

Additional structures for preventing the formation high contact stress at the boundary of the mold. (a) Circular cavities in the substrate plate and (b) circular structures in the mold insert [5]. Reprinted from Ref. [5], page 303, with permission from Elsevier.

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Fig. 3

Schematics of possible issues affecting the parallelism of the hot plates: (a) imperfect plate surface, and (b) uneven mold backside, and (c) nonparallel plates

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Fig. 2

Schematic view of the main elements of a typical hot embossing machine [5]. Reprinted from Ref. [5], page 231, with permission from Elsevier.

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Fig. 1

Schematic view of the hot embossing and the thermal nanoimprinting processes

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Fig. 6

Microstructures produced by photolithography

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Fig. 7

Sub-micrometer structures produced by FIB

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Fig. 8

Structures replicated by UV-NIL

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Fig. 9

Replication of structures in Ni by electroforming

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Fig. 10

Viscosity model of PMMA [5]. Reprinted from Ref. [5], page 193, with permission from Elsevier.

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Fig. 11

Selected measurement points

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Fig. 12

Example area on a hot embossed PMMA replica

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Fig. 13

RLT uniformity plot for different values of temperature and holding time

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Fig. 14

Cross sectional views of the simulated pressure distribution at applied embossing forces of 5 kN, 10 kN, and 15 kN

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Fig. 15

(a) Pressure distribution, (b) RLT distribution under load, and (c) RLT distribution after the release of the embossing force

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Fig. 16

Main effect plots for the RLT standard deviation



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