Proton beam writing of three-dimensional semiconductor microstructures

在半导体中制造微米和亚微米范围内的最小三维结构是一个快速发展的高科技领域。通常，这些结构将下面的半导体衬底的联合收割机机械以及电子性质组合到所谓的微机电系统（MEMS）中。这种系统的突出应用是加速器传感器，高频滤波器，麦克风和最近所谓的能量采集器，这些组件采集已经存在的机械能和电磁能，将这些能量形式转化为电力，然后可用于小型设备的操作。为了生产这种MEMS系统，通常应用常规的光刻。在过去的几年里，这些过程被扩展为所谓的质子束写入（PBW）过程，它属于无掩模直接写入过程。这意味着，PBW工艺仅由辐照和结构显影组成，并且不需要掩模。在PBW中，高能质子束直接聚焦到必须结构化的衬底上，这允许在微米范围内局部修改衬底的物理性质，并且在非常先进的设置的情况下甚至在纳米范围内。除了可以以这种方式曝光的传统光致抗蚀剂之外，PBW还可以直接应用于半导体。底层工艺包括影响后续蚀刻工艺的缺陷的产生。一个例子是通过在半导体衬底中产生缺陷来降低电化学蚀刻速率，这显然允许产生三维悬臂结构。在聚焦高能质子的帮助下创建3D MEMS结构需要衬底辐照对其局部电子和结构特性以及随后的电化学蚀刻过程的影响的基本知识。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特别令人感兴趣。因此，在本项目的范围内，我们的目标是通过PBW结合随后的蚀刻过程的有限元模拟，在半导体中进行局部缺陷创建的基础实验。此外，我们希望优化现有的离子辐照装置，用于3D结构化。衬底的选择涵盖了半导体气体和InP，这在我们的初步实验中已经在一定程度上进行了研究，但也包括硅作为参考系统，以及越来越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.