Generation and characterization of polymeric tridimensional microstructures for micromachine application A.P. Mousinho a, * , R.D. Mansano a,b , A.C.S. de Arruda a a Laborato ´rio de Sistemas Integra ´veis da Escola Polite ´cnica da Universidade de Sa ˜o Paulo, Av. Prof. Luciano Gualberto 158, trav.3 CEP: 05508-900, Sa ˜o Paulo, SP, Brazil b Faculdade SENAC de Cie ˆncias Exatas e Tecnologia Rua Galva ˜o Bueno, 430 CEP: 01506-000, Sa ˜o Paulo, SP, Brazil Abstract In this work, we use the thick layer of polymethylmethacrylate polymer, for micromachining development. In the development of the structures, a three layer process is used. In a silicon wafer is deposited the thick layer spin coating. Over this layer is deposited a thin layer of silicon. The third layer is 1.5 mm of e-beam resist deposited by spin coating. After the deposition of the layers, we perform the e-beam lithography in the top layer resist. This pattern is transferred by plasma etching for the silicon layer. The resolution limits of this process is the resolution of the electron resist and is increased to 0.25 mm (nanometric resolution), using an electron beam spot size of 50 nm and dry development. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Micromachine; Tridimensional structures; Polymer micromachine 1. Introduction Lithography was first developed for the quasi two- dimensional process of microelectronics [1]. With the emergence of the micromechanics, more interest was generated for the three-dimensional process. For example, thick layers were used as mould for electrochemical growth [2,3]. Recently in micromachine development, a new interesting area is the polymer utilization as structural materials [4]. In these studies, several process technologies were utilized, as in the pattern generation, as in the development of the structures. In this case, the development of polymeric structures use a lithography process and plasma etching, these techniques reduce the cost and process time of prototype fabrication [5]. In this work, we use an electron bean lithography and plasma etching for the fabrication of three-dimensional structures with high aspect ratio, in special microchannels and gears. 2. Experimental The polymer used in this work is the polymethylmetha- crylate (PMMA) (2041 Evalcite). In the development of structures, a three layer process is used. In a silicon wafer, 3 in. p-type bare silicon wafers with (100) orientation is deposited on the thick layer (80 mm) of PMMA by spin coating (1000 rpm at 40 s) baking at 200 8C, [6]. Before the polymer deposition, we cleaned the samples in a ‘Piranha’ clean followed by HF solution dip. Over this layer is deposited 500 nm of silicon by reactive sputtering. This process use a 6 in. pure silicon (99.999%) target and argon plasma. the wafer is positioned at 10 cm of this target and the process pressure is 5 mTorr and the RF (13.56 MHz) power is 150 W. The third layer is 1.5 mm layer of e-beam resist (PMMA type) deposited by spin coating (2000 rpm at 40 s). After the deposition of the layers, we perform the e-beam lithography in the top layer of PMMA resist and the pattern is generated. This pattern is transferred by plasma etching for the silicon layer. In this process, we used SF 6 RF plasma with 100 W RF power (13.56 MHz) and 50 mTorr for process pressure, during 1 min. After the plasma etching, the silicon layer is used how hard mask for the plasma etching of the thick polymer layer. This process is showed in Fig. 1. The polymer plasma etching is performed in a planar reactive ion etching (RIA) system with 50 W (13.56 MHz) RF power, 30 mTorr process pressure, in oxygen plasma. The characterization of the polymeric structures is performed in a scanning electron microscopy (SEM). 0026-2692/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0026-2692(03)00085-5 Microelectronics Journal 34 (2003) 651–653 www.elsevier.com/locate/mejo * Corresponding author. Tel.: þ 55-11-30915660; fax: þ 55-11- 30915665. E-mail address: mousinho@lsi.usp.br (A.P. Mousinho).