Appl Phys A (2011) 103:1111–1116 DOI 10.1007/s00339-010-6051-z Selective ablation-assisted two-photon stereolithography for effective nano- and microfabrication Tae Woo Lim · Yong Son · Dong-Yol Yang · Hong-Jin Kong · Kwang-Sup Lee Received: 14 May 2010 / Accepted: 8 September 2010 / Published online: 9 October 2010 © Springer-Verlag 2010 Abstract The two-photon stereolithography (TPS) process has strong merits for the direct fabrication of 2-D and 3-D microstructures with sub-100-nm resolution. In this paper, we report an effective fabrication process in which selec- tive ablation-assisted TPS (SA-TPS) was used to amelio- rate some of the limitations of the TPS process. In SA-TPS, two processes (namely, an additive process of two-photon induced photocuring and a subtractive process of selective laser ablation) were performed sequentially using a single femtosecond laser optical scanning system. The effective- ness of the proposed process was demonstrated in several applications, including precise high-resolution patterning at resolution levels higher than those achievable using the TPS process, and the fabrication of structures with high mechan- ical sensitivity. 1 Introduction The process of direct writing is maskless, simple and cost effective for the fabrication of 2-D and 3-D microstructures [1–4]. It has been widely used in fundamental laboratory- scale investigations of nanoscale and microscale structures. T.W. Lim · Y. Son · D.-Y. Yang ( ) Department of Mechanical Engineering, Korea Advanced Institute of Science & Technology, Science Town, Daejeon 305-701, Korea e-mail: dyyang@kaist.ac.kr Fax: +82-42-3503210 H.-J. Kong Department of Physics, Korea Advanced Institute of Science & Technology, Science Town, Daejeon 305-701, Korea K.-S. Lee Department of Advanced Materials, Hannam University, Daejeon 305-811, Korea Recently, two-photon stereolithography (TPS), which is an additive process based on two-photon absorptive photocur- ing with a femtosecond laser, has proven to be an effi- cient direct writing process [5–9]. The TPS process has several advantages. In particular, it achieves a resolution that is higher than the diffraction limit, and it can be ap- plied to diverse materials such as polymers, metals and ce- ramics [10–13]. In recent years, numerous studies have at- tempted to overcome some of the limitations of the TPS process. One limitation is that the resolution achieved by the TPS process is on the 100-nm scale, which is insuffi- cient for some nanoscale applications [14–17]. Another lim- itation is the prolonged processing time; speed is essential for processes that use pin-point scanning [18–20]. A third limitation is that structures occasionally collapse because the surface tension imposed during rinsing limits the precise fabrication of delicate structures [21, 22]. In addition to the TPS technique, femtosecond lasers are efficient tools for precise micromachining because they in- troduce a small, weak, heat-affected zone; a femtosecond laser has a sharp intensity distribution and an ultra-short pulse width that significantly reduce the threshold energy for material modification and ablation [23–26]. The fem- tosecond pulse energy may be adjusted to the appropriate threshold using a Gaussian beam profile, and the laser can machine features that are smaller than the size of the beam spot on diverse materials, such as metals, ceramics and poly- mers. A tightly focused femtosecond laser pulse deposits en- ergy onto transparent materials via higher-order nonlinear absorption. This characteristic enables 3-D localized mater- ial ablation and has been used in some applications for the fabrication of 3-D microchannels [27]. Here, we propose a novel effective fabrication technique, selective ablation-assisted TPS (SA-TPS). First, TPS was used to fabricate 2-D and 3-D structures. After removing the