In situ ERDA studies of ion drift processes during anodic bonding of alkali-borosilicate glass to metal

Although anodic bonding is widely used to join silicon wafers or metals and glass the underlying ion-drift mechanism and interface bonding process are not yet clarified in detail. In situ ERDA with 35 MeV Cl ions was used to study the ion-drift of sodium, oxygen and hydrogen in glass. Three particle identifying detection techniques were used to separate the scattered ions and target recoils with respect to their energy and atomic number or mass. The thermally activated drift of sodium ions has been characterized quantitatively up to a depth of about 1 mu m by means of a TOF-E telescope. Activation energies. drift rates and depletion layer thicknesses were determined. A Bragg Ionization Chamber with an energy resolution of Delta E/E = 1.1% was used to determine the slight oxygen buildup in the metal layer near the interface to the glass. Hydrogen depth profiles up to a depth of 600 nm were measured by a Si detector with a 17 mu m Al range foil. A considerable drift of hydrogen from the "leached'' glass surface was found which is strongly correlated with the sodium drift. The simultaneous oxygen drift gives rise to the assumption that a (OH)(-)-drift takes place. A reaction path for the anodic oxidation process at the metal-glass interface is proposed. (C) 1998 Elsevier Science B,V.