Preparation of thin GaAs suspended membranes for gas micro-sensors using plasma etching

The GaAs/AlGaAs heterostructure layer system grown by MBE on GaAs substrate was designed to be used for micro-mechanical structure fabrication. In the first step, double-side aligned photolithography is carried out to define the etching masks on both sides of the substrate. After this, highly selective reactive ion etching (SRIE) of GaAs from the front side is used to determine the lateral dimensions of the membrane structure. The vertical dimension is defined by deep backside SRIE through a 300 μm thick GaAs substrate to the AlGaAs etch stop layer, hence the structure thickness is precisely determined by the thickness of MBE-grown GaAs layer over this etch stop layer. The last step is selective etching of the AlGaAs etch stop layer. The thermal resistance value of the membrane structure as high as 21 K/mW is achieved.