Nanoimprint Lithography System Design And Process Simulation For Fabrication Of Micro Optical Elements

Micro Optical Element (MOE) is the essential element for fabricating Micro-Optoelectronic System, which can be widely applied in fields such as space technology, ultra-precision fabrication, optical fiber communication, etc. The fabrication problem is the bottleneck for development of MOE industry, and Nanoimprint Lithography (NIL) can be used to replicate continuous relief MOE with high efficiency, high accuracy and low-cost. Nowadays, most of commercial NIL equipments are concentrating on replicating patterns at nano-scale based on Micro-electronics industry. However, to develop a kind of nanoimprint equipment, which specializes in fabricating patterns with large scale area and relative lower aspect ratio, such as MOE, is an inevitable tendency. The equipment needs the following advantages: simple structure, easily to use and low-cost; functional modules are easily to replace and update; uniform stress at large scale and good parallelism between two pressure heads. Based on the requirements discussed above, the mainly innovative works are as follows:(1) Manufacturing techniques of nanoimprint and effects of main parametersA modeling method for filling process in hot embossing is presented in this paper. A finite element software Marc was used to simulate filling process and the effects of different imprinting time on recovery are analyzed. Then the obtained optimized parameters were applied in test of MOE fabrication.(2) Designing and debugging of nanoimprint equipmentMechanical structure: Mechanical structure design of nanoimprint equipment is finished in this paper. For the main object of uniform stress, gantry type and close type machine structure is applied to eliminate errors caused by deformation of machine body. Then two type long and short axle sleeves which are separately fitted with finished axles to decrease the nonparallelism between two pressure heads. Finally, the screw joint between air cylinder and worktable is replaced by a designed structure, and it can guarantee good running in the condition that the axes of cylinder and lead rail are not parallel.Designing pressure and temperature control system: A pressure control system based on high-speed switching valve and air cylinder is designed. Firstly, the characteristic of electro-pneumatic on-off servo system is studied, and pulse width modulation (PWM) was used to control gas-flow rate, the gas which is imported into and exported from the air cylinder. Then a model of pressure servo system controlled by PWM was built to obtain the relationship between output pressure and controlled quantity, which provides theoretical foundation for the following realization of control algorithm. Secondly, hardware of pressure control system based on MSP430F149 was designed, and taking PID as control policy the designed objectives of pressure control system are achieved. Finally, a temperature control system was successfully set up and heat insulation system was designed, they all reached the requirements of system.Control software: The control software of nanoimprint equipment was written using Visual C++, which can be used to setup parameter, to control imprinting process and save and display testing data (pressure data and temperature data).(3) Measurement of essential performances of nanoimprint equipment and Test of MOE fabricationThe tests mainly focused on following parts: parallelism of two pressure heads; stability, linearity and resolution of pressure control system; characteristics and heating rate of temperature control system. Then a sample with continuous relief profile was fabricated in the debugged nanoimprint equipment using optimized imprinting parameters. The experimental results indicate that the designed nanoimprint equipment in this paper can obtain uniform and complete replication effects at a large scale area and on a variety of scales.