Anodic bonding is a common process used in microelectromechanical systems ͑MEMS͒ device fabrication and packaging. Polycrystalline chemical vapor deposited ͑CVD͒ silicon carbide ͑SiC͒ is emerging as a new MEMS device and packaging material because of its excellent material properties including high strength, hardness, and thermal conductivity. A novel process recipe, requiring a SiC RMS surface roughness of 45 nm, was developed for anodically bonding CVD SiC to bulk Pyrex and Hoya SD-2 glass substrates. Transmission electron microscopy ͑TEM͒ and scanning transmission electron microscopy ͑STEM͒ and elemental analysis presented distinct differences in elemental depletion band͑s͒ of bulk Pyrex and Hoya SD-2 glasses bonded to Si, and in interfacial bonding between Pyrex and CVD SiC compared to Pyrex and Si. This study indicates that magnesium in the Pyrex glass network also participates in the depletion layer process compared to previous studies where only potassium, calcium, aluminum, and sodium were identified. For the first time, this study identifies aluminum, magnesium, sodium, and zinc participating in the depletion layer process in Hoya SD-2glass.Since the invention of anodic bonding in 1969, 1 several studies have been conducted to further the understanding of the physical mechanisms involved. The following published results summarize these mechanisms, particularly in the context of the current vs. time models, and the microscopy and chemical analysis.Anodic bonding is performed with an application of a temperature and a direct current ͑dc͒ voltage to a glass and metal alloy, or semiconductor material. A typical bonding application is glass to p-type silicon ͑Si͒. The cathode is attached to the glass and the anode to the Si. The Si is at a positive potential with respect to the glass. Figure 1 shows a schematic of this electrochemical process. 2 The glass and silicon remain relatively stiff during the bonding process because temperatures below the melting point and glass transition point are used. 2 This irreversible bonding process produces a permanent, SiO 2 chemical bond at the glass/Si interface. [3][4][5] With the application of temperature and voltage, two types of reactions occur to form this SiO 2 bond: ion dissociation/association reactions and interfacial bonding reactions. 6 The elevated temperature permits ionic conduction within the glass, while the imposed potential drives the migrating ions of opposite charge towards the interface or towards the cathode. The glass behaves as an electrolyte at elevated temperatures due to the mobile ion species. The cations, principally Na, move through the glass toward the negatively charged cathode. Because the cations move toward the cathode, a depletion layer is formed, and the glass network reconstructs. This reconstruction allows for the excess anionic oxygen species, under the influence of the electrostatic potential, to move towards the interface. The space charging of the depletion layer generates an interfacial electrostatic field. These electrostatic ...
