Size Reduction of Silicon Nanopillars by Photo-Electrochemical Etching
- PDF / 2,428,795 Bytes
- 5 Pages / 595 x 842 pts (A4) Page_size
- 32 Downloads / 241 Views
Size Reduction of Silicon Nanopillars by Photo-Electrochemical Etching Robert Juhasz, Jan Linnros and Pascal Kleimann1 Royal Institute of Technology, Department of Electronics, Stockholm, SWEDEN; 1 LENAC, Université Claude Bernard Lyon I, Villeurbanne, FRANCE.
ABSTRACT Silicon nanopillars, formed by electron beam lithography, were electrochemically etched to provide controlled size reduction. The smallest dimensions achieved were pillars of 15 nm in diameter, restricted mainly by the scanning electron microscope used for characterization. The etch rate was mainly determined by the photogeneration of carriers, by the HF concentration and by the applied voltage bias. The applied bias also controlled the resulting shape of the pillars such that a high bias resulted in etching of the pillar top whereas a negative bias caused etching only at the pillar base. For 0 V, a relatively conform etching of the pillar was observed. We discuss these phenomena in terms of electropolishing or pore formation effects on a local scale.
INTRODUCTION Precise fabrication control on a nanometer scale has become increasingly important as silicon devices are scaled down. The silicon 'roadmap' forecasts that smallest features will approach 30 - 50 nm ten years from now. Even more stringent are the requirements from single-electron devices based on the Coulomb blockade where dimensions on a few nm scale are needed. Since today's lithographic techniques cannot match these requirements one may explore alternative routes. One such fabrication method would be a controlled shrinking of larger structures, formed by conventional lithography or by electron beam lithography. In this work we explore the possibilities of using electrochemical etching for size reduction of silicon nanopillars, formed by electron beam lithography. Indeed, electrochemical etching is a wellknown technique to form porous silicon [1-2] which microstructure can be scaled down such that the remaining silicon skeleton approaches sizes of only a few nm. On the other hand, the electrochemistry can be tuned into a regime where electropolishing occurs resulting in planar etching of the Si surface. In an intermediate regime, the electrochemical etching can be used to form macro pores [3-4] of extremely high aspect ratio or even free-standing pillars [5]. In this case, ntype Si is normally used and holes, which are consumed in the dissolution reaction, are provided by light generation of excess carriers. The rate of carrier generation is then an additional parameter to carefully control the electrochemical reaction besides parameters such as the hydroflouric acid concentration, current density etc. Here we report experiments on photochemical etching as well as photo-electrochemical etching of Si nanopillars where the objective is a uniform and controlled reduction of the pillar diameter. We demonstrate that the bias voltage provides an additional parameter for control of the pillar shape.
EXPERIMENTAL In the experiments, an electron beam lithography (EBL) process was developed utili
Data Loading...
