Patterning of silicon surfaces is essential for the design of opto and microelectronic devices. Creating microstructures like trenches, macropores or rods are essentials for the development of several component families in many research fields and commercial applications. Silicon etching is carried out either chemically or by using reactive-ion etching, usually involving one or more lithography steps. This is accompanied by some important constraints. The fabrication of complex structures involves a large number of technological steps that represent eventually a significant cost in the final device cost (and lithography/dry etching equipment also requires considerable investments). Moreover, one is often restricted in the design of perfectly suited surface structures because of limitations due for instance to the influence of the crystallography or to insufficiently high aspect ratios. In addition, in some industries (e.g. photovoltaic), lithography is incompatible with the cost issues and technical constraints of production lines, which strongly limit the surface structures that can be realized and therefore their effectiveness. Recently, a new method to etch silicon has emerged. It is based on the contact at the nanoscale of silicon with a noble metal in the presence of HF and an oxidizing agent (e.g. H2O2, anodic current). The metal acts as a catalyst allowing for a localized dissolution with a resolution of a few nm only. More recently, a Japanese group has shown that it is also possible with this method to use micrometer-sized electrodes made of Pt to etch large structures in silicon. Based on this principle, the PATTERN project aims at the development of a new silicon etching process using metal electrodes that perform "nano-imprints" by direct contact with silicon in a single electrochemical step. The goal is to be able to replicate a large variety of forms such as pores and trenches of high aspect ratio, inverted pyramids, micro-pillars, etc., cumulating high accuracy (~ 10 nm), multi-level etching profile and large surface area processing capabilities (> cm2). The biggest technological issue is the necessity to provide a nanostructured interface with a triple contact Silicon/Electrolyte/Metal. The innovative aspect is the development and use of volumetric nanoporous metal electrodes that can ensure this triple contact whatever the considered dimensions are, and be used several times in industrial processes. PATTERN is intended to provide the basis for this new contact etching process, including a demonstrator in the field of surface treatments for solar cells. PATTERN is divided into three tasks according to a multidisciplinary approach combining microelectronics, optics, powder metallurgy, electrochemistry of semiconductors and modeling of electronic interfaces: T1- Development of nanoporous metal electrodes with defined patterns (IEMN). Production of molds with basic and advanced periodic structures; Elaboration of nanoporous metal imprints by sintering metal powders in the molds. T2 - Contact etching of silicon (ICMPE). Study of the etching process and the transfer of the imprint electrodes surface pattern to the silicon substrate, with different oxidizing agents and metals; Optimization of the operating conditions. T3- 2D modeling of the Silicon/Electrolyte/Metal electronic interface (LGEP). Localization of the anodic currents around metal dots ~10x10 nm2 in size, as a function of the metal work function, the metal polarization, the inter-dot spacing. To conduct the project, three research teams specialized in microelectronics (IEMN), silicon (electro)chemical etching (ICMPE), and modeling of semiconductor electronic properties (LGEP) gathered together. They are acknowledged of a high level expertize in microelectronics, optoelectronics and photovoltaics applications, with several international patents taken in these fields.