Ultra-precision alignment technique based on modified Moiré signals

A novel method for automatic ultra-precision alignment is presented.This method relies on the modified Moiré technique,and alignment marks are used in the form of gratings.The modified Moiré technique can effectively improve detecting sensitivity of signals and simplify the control system by using only one pair of laser-Moiré sensors.We present the mathematical model and simulation results of diffracting two gratings.The effect of various parameters on Moiré signals is studied theoretically and experimentally,and the results are found to be consistent.A computer controlled alignment device using one pair of Moiré sensors is designed.The device can achieve a fully automatic precision alignment by the modified Moiré signal.The experimental result shows that the alignment device can obtain the resolution of 5 nm and the positioning accuracy of ±0 5 μm.

Ultra-precision positioning control technique based on neural network

Due to the non-linearity behavior of the precision positioning system, an accurate mathematical control model is difficult to set up, a novel control method for ultra-precision alignment is presented. This method relies on neural network and alignment marks that are in the form of 100μm pitch gratings. The 0-th order Moire signals＇ intensity and its intensity rate are chosen as input variables of the neural network. The characteristics of the neural network make it possible to perform self-training and self-adjusting so as to achieve automatic precision alignment. A neural network model for precision positioning is set up. The model is composed of three neural layers, i.e. input layer, hidden layer and output layer. Driving signal is obtained by mapping Moire signals＇ intensity and its intensity rate. The experimental results show that neural network control for precision positioning can effectively improve positioning speed with high accuracy. It has the advantages of fast, stable response and good robustness. The device based on neural network can achieve the positioning accuracy of ± 0. 5μm.

NANOIMPRINT LITHOGRAPHY TECHNOLOGY WITH AUTOMATIC ALIGNMENT

Nanoimprint lithography （NIL） is recognized as one of the most promising candidates for the next generation lithography （NGL） to obtain sub-100 nm patterns because of its simplicity, high-throughput and low-cost. While substantial effort has been expending on NIL for producing smaller and smaller feature sizes, considerably less effort has been devoted to the equally important issue—alignment between template and substrate. A homemade prototype nanoimprint lithography tool with a high precision automatic alignment system based on Moiré signals is presented. Coarse and fine pitch gratings are adopted to produce Moiré signals to control macro and micro actuators and enable the substrate to move towards the desired position automatically. Linear motors with 300 mm travel range and 1 μm step resolution are used as macro actuators, and piezoelectric translators with 50 μm travel range and 1 nm step resolution are used as micro actuators. In addition, the prototype provides one translation （z displacement） and two tilting motion（α and β ） to automatically bring uniform intact contact between the template and substrate surfaces by using a flexure stage. As a result, 10 μm coarse alignment accuracy and 20 nm fine alignment accuracy can be achieved. Finally, some results of nanostructures and micro devices such as nanoscale trenches and holes, gratings and microlens array fabricated using the prototype tool are presented, and hot embossing lithography, one typical NIL technology, are depicted by taking nanoscale gratings fabrication as an example.

Novel Nano-scale Overlay Alignment Method for Room-temperature Imprint Lithography

A novel nano-scale alignment technique based on Moiré signal for room-temperature imprint lithography in the submicron realm is proposed. The Moiré signals generated by a pair of quadruple gratings on two templates respectively are optically projected onto a photodetector array, then the detected Moiré signals are used to estimate the alignment errors in x and y directions. The experiment result indicates that complex differential Moiré signal is sensitive to relative displacement of the pair of marks than each single Moiré signal, and the alignment resolutions obtained in x and y directions are ±20nm(3σ) and ±24nm(3σ). They can meet the requirement of alignment accuracy for submicron imprint lithography.