A novel loading and demoulding process control in UV nanoimprint lithography Hongzhong Liu, Weitao Jiang * , Yucheng Ding, Yiping Tang, Bingheng Lu, Hongbo Lan, Yongsheng Shi, Lei Yin The State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an 710049, China article info Article history: Received 13 July 2008 Accepted 22 August 2008 Available online 12 September 2008 Keywords: Micro/nanostructure Loading Demoulding Nanoimprint lithography (NIL) process abstract In UV nanoimprint lithography (NIL) with elastic mould, a novel multi-step loading and demoulding pro- cess, called distortion reduction by pressure releasing (DRPR) and two-step curing method for demoul- ding, is developed. This novel imprint process is continuous, the pressure releasing method, used to optimize the loading process, can reduce the distortions of imprint mould and wafer stage, while obtain better cavity filling and thin and uniform residual layer; through two-step curing method instead of tra- ditional simple demoulding, the curing degree of resist can be controlled, which is helpful to decrease the demoulding force and avoid residual layer pulled-up while ensure replicated protrusions not collapse. It is a novel and robust process with high fidelity of pattern replication in micro/nano structures fabrication, and the replication error caused by distortions and ‘‘blind” demoulding can be reduced effectively. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Due to recent advancements in micro-electro mechanical sys- tems (MEMS), many studies have focused on the fabrication of 3D functional micro-structures and components (such as micro- hole, micro-tunnel, micro-nozzle, micro-actuator, micro-sensors and so on) [1,2], and nanoimprint lithography (NIL) is considered as a high efficiency, low-cost method, and the critical dimension (CD) of the replication structures can be in the range of 10 nm to several hundred microns [3–10]. Although NIL has many advanta- ges over traditional micro fabrication method, the mechanical mi- cro-replication process involves mechanical force, including loading and demoulding forces, which can induce distortions and some pattern transferring defects. In this paper, based on UV NIL process using elastic imprint mould, two questions are demon- strated. Firstly, in the loading process, the process of cavity filling needs a certain loading pressure, but the experimental results show that this pressure can cause unignorable distortion of the elastic mould, additionally, thinner residual layer needs larger loading pressure, which can also cause distortions, this is the ‘‘loading but distortion” question, simple loading process can not solve this question; secondly, in the demoulding process, because of different resist thicknesses in recess and protruding regions when mould embedded into resist film, through UV curing, the curing degree of resist in recess region is obvious higher than that in protruding region, and when demoulding, too high curing de- gree in recess region will cause residual film pulled-up, while too low curing degree in protruding region will cause protrusions col- lapse. In our experiments, the two defects of pattern transferring results, residual film pulled-up and protrusions collapse, are both found, and the pattern transferring result, in which the two defects appear simultaneously, is also found when the residual film is too thin. So there is a ‘‘match question of curing degree” in the recess and protruding regions. In following paragraphs, through analysis of the loading and demoulding process in UV NIL using elastic mould, a novel preci- sion multi-step process is proposed, which can effectively reduce distortion of elastic mould while obtain better resist filling results, and by this new process, the match problem of curing degree in re- cess and protrusion regions will be solved to avoid the two defects. 2. Experiments devices 2.1. Imprint tools Fig. 1a is the UV NIL tool fabricated by Xi’an Jiaotong University. It can perform UV NIL process on 6-in. wafer and automatic process control, and is composed of following: (1) an precision positioning system, the positioning accuracy in X and Y directions reaches 8 nm with three PZTs [11]; (2) an precision loading system, it can provide a 30 mm range of motion, with the position accuracy of 1 nm in Z direction by the matching of DC motor and PZT, and a 0–2000 N loading force which is monitored during the whole loading process by a force sensor with accuracy of 1 N; (3) an align- ment system, the alignment resolutions in X and Y directions are ±20 nm(3r) and ±25 nm(3r), respectively; Fig. 1b is the imprint mould, which is made of poly- dimethylsiloxane (PDMS) as pattern layer to meet the self-adapt- able and transparent requirements, and quartz plate as hard support. The dimension of the hard quartz support is 40 Â 27 Â 6 mm, and the PDMS pattern layer is 20 Â 20 Â 0.5 mm. 0167-9317/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.mee.2008.08.012 * Corresponding author. Tel.: +86 29 82663198; fax: +86 29 82660114. E-mail address: jwt515@163.com (W. Jiang). Microelectronic Engineering 86 (2009) 4–9 Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee