Proton beam writing of three-dimensional semiconductor microstructures

半导体中微米和亚微米范围内最小的三维结构的制造代表着一个快速增长的高科技领域。通常，这些结构将底层半导体衬底的机械和电子特性结合到所谓的微电子机械系统(MEMS)中。这类系统的突出应用是加速器传感器、高频过滤器、麦克风和最近所谓的能量收集器，这些收集已经提供机械和电磁能量的部件，将这些能量形式转换为电能，然后可用于小型设备的操作。为了制造这种MEMS系统，通常应用传统的光刻技术。在过去的几年中，这些工艺被扩展为所谓的质子束写入(PBW)工艺，该工艺属于无掩模直接写入工艺。这意味着，PBW工艺仅由辐照和结构形成组成，不需要掩模。在PBW中，高能质子束直接聚焦到必须构造的衬底上，这允许在微米范围内对衬底的物理性质进行局部修改，甚至在非常先进的设置的情况下，甚至在纳米范围内。除了可以通过这种方式曝光的传统光刻胶外，PBW也直接适用于半导体。潜在的过程包括缺陷的产生，这些缺陷影响到后来的蚀刻过程。一个例子是通过在半导体衬底中产生缺陷来降低电化学刻蚀速率，这显然允许产生三维悬臂结构。利用聚焦的高能质子创造三维MEMS结构需要了解衬底辐照对其局部电子和结构性质的影响以及随后的电化学刻蚀过程的基础知识。尤其令人感兴趣的是，能够对蚀刻过程进行定量建模，以尽可能精确地预测可生产的结构。因此，在本项目的范围内，我们的目标是通过PBW结合后续刻蚀过程的有限元模拟来进行半导体局部缺陷产生的基础实验。此外，我们还希望优化现有的用于3D结构的离子辐照装置。衬底的选择包括半导体气体和InP，这在我们的初步实验中已经进行了一定程度的研究，但也包括作为参照系的硅以及日益重要的化合物半导体AlGaN。

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.