Santos, Jorge Manuel dos
The Dependence of Plasma Parameters on the Plasma Induced Damage in Thick SiO2
Supervisor: Nick Wright
In microelectromechanical system (MEMS) devices, a multi-layer structure is formed, where the surface layer requires physically releasing from the underlying virtual substrate. In this example, a free standing aluminum structure is to be released from a thick silicon dioxide layer, used to protect underlying active devices. The aluminum is patterned and then used as an etch mask for the isotropic etch process. The key process step in the device fabrication is Reactive Ion Etching (RIE) of the dielectric layer. However, it is known that RIE causes damage and contamination effects in exposed semiconductor and dielectric materials leading degradation of the performance, reliability and yields of the final devices. Hence, the motivation to study the SiO2 etch damage is real, due to the processing requirement of the RIE technique for the removal of SiO2 from beneath metal structures for the formation of free standing metal structures for microelectromechanical (MEMS) devices. Wet etch technology is not suitable for this process step for two main reasons. The etchant routinely used for the etching of SiO2, hydrofluoric acid (HF) also reacts with metals with a low selectivity. The use of wet chemistry to release micron scale clearance to the substrate mechanical devices also raises the issue of stiction. Here the mechanical strength of the structure being released is insufficient to overcome the surface tension of the water and the structure adheres to the surface of the substrate as the water is evaporated.