The laser-supported selective bonding of glass/ silicon combinations and glass/glass combinations

摘要

The technique of anodic bonding for glass/silicon or glass/ glass combinations (with an electrically conductive interlayer) has developed into the most important bonding technique for either pre-structured wafers or single components. It requires the use of alkali-containing, expansion-adapted glass materials, and the elements lying on top of each other need to be heated to temperatures between 350 and 450 deg C while an electric DC-voltage is simultaneously applied. Depending on the individual configuration of electrodes, the bond is spreading out from centrally located points in the form of a proceeding front until the entire bonding area has been affected. The technique of anodic bonding, in other words, can be applied to whole areas and surfaces which can be joined with high degrees of mechanical strength and hermeticity [1]. If it is not possible to use alkali-containing glass or to apply a bonding voltage, processes must be selected which do not require any support by electric forces. Such processes include eutectic alloying, soldering, welding and diffusion bonding. The latter is also well suited for the direct mutual bonding of glass and quartz glass elements [2] and the bonding of glass with silicon [3] at temperatures in excess of 500 deg C. Process engineering and equipment technology of the above-mentioned techniques (with the exception of welding) are usually developed under the generalised assumption that the entire assembly or wafer staple will be subjected to the maximum processing temperature. This severely restricts the potential application range of these techniques, for instance with a view to the packaging of microsystems (MEMS), since certain structural elements and functional layers cannot be exposed to such high levels of thermal stress. It would also be beneficial if bonding zones could be generated which are independent from the geometrical contact surface. This would ensure the spatial manoeuvrability of actor elements and help to keep the spread of the bonding fronts from being disrupted during the process of conventional anodic bonding in narrowly structured wafers [4, 5]. Also, and in response to the continuous demand for further minaturisation of electronic assemblies, additive-free bonding techniques with high temperature resistance levels and short bonding times need to be developed as an alternative to adhesive techniques. This will serve a number of purposes and will, for instance, allow the process engineers to adjust optical components on silicon substrates.