A dry etch fabrication process for microelectromechanical devices using silicon nitride sacrificial layers

摘要

The fabrication of a wide variety of microelectromechanical devices requires the use of sacrificial layers, We have developed a process using plasma enhanced chemical vapor deposited silicon nitride as the sacrificial layer. This PECVD nitrideetches more than an order of magnitude more quickly than sputtered nitride or thermal silicon dioxide and is etched in a dry etch process using Poly-Etch 907. Typical etch rates for PECVD nitride are about 3μm/min compared to less than 200 A/mm forsputter-deposited nitride or thermal oxide. This allows us to avoid stiction problems typically associated with wet etching and thus allows for the fabrication of devices with very small air gaps and large area. ln addition we believe that this difference in etch rates can be further improved by refinement of the deposition process. We have also investigated the residual stress in sputter-deposited silicon nitride and how it can be controlled by the choice of sputtering conditions. This has allowed us toproduce structures including multilayer membranes and cantilevered beams in which the total residual stress is con trolled, Simple analytic calculations as well as 3-D finite element modelling have allowed us to verify the behavior of these structures.The use of these process technologies in the fabrication of optical devices will be discussed.