AVS 50th International Symposium
    Microelectromechanical Systems (MEMS) Tuesday Sessions
       Session MM-TuA

Paper MM-TuA9
Integration of Silicon Anisotropic Wet Etching and BCB Processes

Tuesday, November 4, 2003, 4:40 pm, Room 320

Session: Fabrication and Characterization of MEMS Devices
Presenter: N. Ghalichechian, University of Maryland, College Park
Authors: N. Ghalichechian, University of Maryland, College Park
A. Modafe, University of Maryland, College Park
R. Ghodssi, University of Maryland, College Park
Correspondent: Click to Email
We have developed a fabrication process for integration of Benzocyclobutene (BCB) dielectric film and anisotropically etched deep silicon v-grooves in potassium hydroxide (KOH) solution for development of MEMS actuators such as an electrostatic micromotor supported on microball bearings. BCB is a low dielectric constant polymer (k=2.65) with several advantages over silicon dioxide for dielectric insulation such as simple deposition process, low-temperature cure, and low residual stress that are desired in a reliable, efficient electrostatic micromotor. KOH solution is used for fabrication of silicon v-grooves that form a bearing structure to house the micro-balls. We have used gold (Au) film as the etch mask and chromium (Cr) film as the adhesion layer that bonds the Au to the underlying BCB. It was initially observed that the metal films lost adhesion and no longer protected the BCB film during long KOH etching (7 hours in 20 %w solution) process. A fabrication process is developed to improve the adhesion between the BCB and the metal films during the silicon anisotropic bulk micromachining using KOH. This is achieved through several unit process experiments to investigate (a) the effect of cure temperature (210-250 °C), (b) surface treatment of BCB, (c) adhesion improvement at the interface between thin film metals and BCB by applying an adhesion promoter, AP3000, prior to metallization, and (d) the required Cr and Au thickness that results in a robust adhesion to BCB and reliable etch mask for KOH. The optimized experimental results in this work have enabled successful and repeatable fabrication of deep v-grooves (280 µm wide, 220 µm deep) in silicon with BCB (1 µm thick) and Cr/Au (20/500 nm thick) multilayer etch mask. The detailed process parameters and experimental results for this integrative process technology will be presented.