IOP PUBLISHING JOURNAL OF MICROMECHANICS AND MICROENGINEERING J. Micromech. Microeng. 17 (2007) 1387–1393 doi:10.1088/0960-1317/17/7/022 Polymeric mask protection for alternative KOH silicon wet etching G Canavese, S L Marasso, M Quaglio, M Cocuzza, C Ricciardi and C F Pirri LATEMAR Unit Politecnico di Torino, Materials and Microsystems Laboratory (χ -Lab), Via Lungo Piazza D’Armi 6, 10034 Chivasso (Torino), Italy E-mail: giancarlo.canavese@polito.it Received 19 February 2007, in final form 20 April 2007 Published 14 June 2007 Online at stacks.iop.org/JMM/17/1387 Abstract A new cost-effective setup for silicon bulk micromachining is presented which makes use of a polymeric protective coating, ProTEK R  B2 coating, instead of a conventional hardmask. Different concentrations of KOH and bath conditions (pure, with surfactant, with stirrer, with both surfactant and stirrer) have been considered. ProTEK R  B2 coating exhibits good adhesion to Si substrates, no degradation, etching rates and surface roughness comparable to literature data, and etching times greater than 180 min without damaging front side microstructures. Microcantilevers have also been fabricated using two different process flows in order to demonstrate the suitability of such a protective coating in microelectromechanical system (MEMS) technology. (Some figures in this article are in colour only in the electronic version) 1. Introduction Silicon bulk micromachining is traditionally applied in the field of microelectromechanical systems (MEMS) for the fabrication of thin membranes [1, 2], released cantilevers [3–5] and other free-standing structures for mass, acceleration, flow, rotation and pressure sensing [6, 7]. Recently, this process step has become a key point process for micro- and nano-size fluidic chips [8] as well as micro-optical elements [9]. Bulk micromachining often requires the deposition of a hardmask layer, such as silicon nitride or silicon oxide, on the sample front side to prevent undesired etching of the already patterned structures [10, 11]. However, hardmask deposition techniques such as low-pressure chemical vapour deposition (LPCVD) or plasma-enhanced chemical vapour deposition (PECVD) both exhibit some problems. LPCVD requires high temperatures, which can induce unwanted mechanical stress in the layer [12], while PECVD silicon nitride and/or oxide exhibit a fair etch rate in KOH. Alternatives to using a hardmask can be the use of a Teflon R  cell with O-rings or a polymeric protective coating. The first approach requires the development of a more complex experimental setup to mask the sample, while sealing and clamping of the cell can seriously compromise the effectiveness of this method. Furthermore, any possible fracture of a membrane can directly compromise the integrity of the whole wafer surface. In contrast, the use of a polymeric protective coating, directly deposited on a Si surface, has been recently proposed as a very efficient and cost-effective solution to the problem [13, 14]. This configuration does not introduce any mechanical stress and prevents the possible etching of the coated front side surface when a fracture of a membrane occurs. The aim of this work is to investigate the compatibility of a polymeric protective coating, ProTEK R  B2 coating, under different bath conditions during a KOH Si bulk micromachining. For such purpose, three main parameters were identified: the Si etch rate, selectivity of the Si etch rate with respect to the SiO 2 etch rate and the roughness of the etched surface. These three values have been characterized with varying KOH concentration (20%, 30%, 40% by weight) under four different bath conditions: pure, with sodium dihexyl sulfosuccinate (SDSS) surfactant, with mechanical agitation (by stirrer) and with both surfactant and stirrer agitation. In the second part of the paper, two different process flows used for microcantilever fabrication are shown in order to investigate the compatibility of the polymeric coating within an entire MEMS process flow. 0960-1317/07/071387+07$30.00 © 2007 IOP Publishing Ltd Printed in the UK 1387