Proton beam writing of three-dimensional semiconductor microstructures

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The manufacturing of smallest three-dimensional structures in the micro- and sub-micrometer range in semiconductors represents a rapid growing high-technology area. Often these structures combine mechanical as well as electronic properties of the underlying semiconductor substrates into so-called Micro-Electro-Mechanical Systems (MEMS). Prominent applications of such systems are accelerator sensors, high frequency filters, microphones and recently so-called energy harvesters, components that harvest already present mechanical as well as electromagnetic energy, transforming these energy forms to electricity which is then made available for operation of small equipment. In order to produce such MEMS systems typically conventional lithography is applied. In the past years these processes were expanded with the so-called proton beam writing (PBW) process, which belongs to the maskless direct writing processes. This means, that the PBW process consists solely of irradiation and structure development and that no masks are necessary. In PBW a high energetic proton beam is focused directly onto the substrate that has to be structured, which allows for a local modification of the physical properties of the substrate in the micrometer range, and in case of very advanced setups even on the nanometer range. Besides conventional photo resists, which can be exposed this way, PBW is also applicable directly to semiconductors. The underlying process consists of the creation of defects which influence the later etching process. An example is the reduction of the electrochemical etching rate by means of the creation of defects in semiconductor substrates, which demonstrably allows for the creation of three dimensional, cantilever structures. The creation of 3D MEMS structures with the help of focused high energetic protons requires fundamental knowledge of the effects of substrate irradiation on its local electronic and structural properties and thus also on the subsequent electrochemical etching process. It is of particular interest to be able to quantitatively model the etching process to predict producible structures as precise as possible. Within the scope of this project we therefore aim at performing fundamental experiments of local defect creation in semiconductors through PBW in combination with finite element simulation of the subsequent etching process. Furthermore we would like to optimize the existing ion irradiation setup for 3D structuring. The choice of substrates covers the semiconductors Gas and InP, which were already investigated to some extend in our preliminary experiments, but also silicon as a reference system together with the increasingly important compound semiconductor AlGaN.