Geometrical and Process Effects on MEMS Dimensional Loss: a Frequency Based Characterization

In this paper we describe a methodology to fully characterize the Deep Reactive Ion Etching (DRIE) of Micro-Electro Mechanical (MEM) structures. One of the key aspects of this manufacturing step is the dimensional loss (CDloss) with respect to nominal geometry. For the sake of simplicity, this parameter is commonly considered uniform in the mechanical element design, leading to a series of approximations. In order to better fashion the local response of the etching process on the mechanical elements, a test pattern of resonating structures was implemented. An in plane resonator using folded springs arranged in a “Tang-like” configuration, shielded with different sets of dummy elements was designed. With an extensive experimental campaign, it has been possible to demonstrate a strong correlation between the first natural frequency of the resonator (i.e. CDloss) with the characteristic dimensions of the shielding elements. Moreover, the effect of different etching equipment was analyzed, showing a significant impact and highlighting the need of different mask design customization for each process tool.