Methods for prevention, reduction, and elimination of outgassing and trapped gases in micromachined devices

Abstract

Unwanted gasses created during bonding within micromachined vacuum cavities are reduced in a manner conducive to mass manufacturing. Two broad approaches may be applied separately or in combination according to the invention. One method is to deposit a barrier layer within the cavity (for example, on an exposed surface of the substrate). Such a layer not only provides a barrier against gases diffusing out of the substrate, but is also chosen so as to not outgas by itself. Another approach is to use a material which, instead of, or in addition to, acting as a barrier layer, acts as a getterer, such that it reacts with and traps unwanted gases. Incorporation of a getterer according to the invention can be as straightforward as depositing a thin metal layer on the substrate, which reacts to remove the impurities, or can be more elaborate through the use of a non-evaporable getter in a separate cavity in gaseous communication with the cavity. The invention is applicable to a wide range of micromachined devices and structures, including micromachined capacitive pressure sensors and other transducers, though the techniques are not limited to such applications. Anodic bonding is used in conjunction with a glass substrate, with the understanding that various types of substrates and bonding/attachment procedures may alternatively be used.