This study presents thermal design of a large-area hot plate for thermal nanoimprint lithography process. The aim is to develop a thermal device which guarantees the capability of rapid heating and cooling, the high temperature uniformity, and the strength to endure high stamping pressure. A conceptual hot plate model is suggested such that a series of cartridge heaters and cooling holes are installed in parallel, which permits a planar extensibility to a large area. Examined are the two types of hot plates having different cooling mechanisms, direct cooling by the coolant flows in the cooling holes and indirect cooling through the heat pipes installed in the cooling holes. In order to analyze the thermal behavior of the proposed hot plates, a numerical model based on ANSYS Fluent is constructed. A particular feature of this tool is that the PID control logic are incorporated to simulate feedback control of the heaters.
A combined experimental and numerical study is conducted on thermal behavior of a small hot plate of a dimension 120 mm x 120 mm x 20 mm made of aluminum and its conceptual feasibility is tested. The results indicate that the proposed design gives reasonably good heating and cooling performance and an acceptable temperature uniformity in the heating mode. However, a technical issue is also raised that the coolant flows could cause large temperature difference on the hot plate surface. As The numerical simulate proposes an alternative that the use of heat pipes in the hot plate could enhance the temperature uniformity in the hot plate.
For practical verification, a comptutational thermal design is performed for a large-area hot plate of a dimension 240 mm x 240 mm x 20 mm made of stainless steel. The numerical results state that the employment of cartridge heaters of 300 W capacity provides an acceptable heating performance and the indirect cooling though heat pipes also gives a reasonable cooling capacity. The installation of heat pipes turns out to be a useful solution to reduce the temperature difference on the hot plate surface both in transient heating and transient cooling modes. Based on the present design, a hot plate is facbricated for a roll-to-palte TH-NIL process which requires only heating mode. The field test demonstrates that the hot plate with cartridge heaters and heat pipes satisfies high temperature uniformity.