1. Field of the Invention
The present invention relates to a micro electro mechanical system (MEMS). More particularly, the present invention relates to a method and apparatus for vacuum-mounting at least one MEMS on a substrate.
2. Description of the Related Art
MEMS generally refers to either a micro miniature mechanical device or technology that is fabricated using a semiconductor manufacturing process. MEMS generally involves a micro scale, and thus is sensitive to pollution caused by fine dust particles or peripheral electric signals having extremely low power. In view of this high sensitivity, MEMS fabrication requires special measures so as not to be affected by pollution and the peripheral environment. To satisfy this requirement of special measures, an MEMS manufacturing process includes a process of bonding a cover made of a material, such as glass, to an upper surface of a substrate having an MEMS structure. A vacuum is required between the cover and the substrate to guarantee a stable operation of an MEMS device in view of the properties of the MEMS device.
Conventionally, two vacuum-mounting methods have been primarily utilized to vacuum-mount an MEMS. One method makes use of anodic bonding, and the other method uses a material of getter.
Anodic bonding is a technology for bonding two different structures, such as a glass plate and a silicon substrate, together under high temperature and at a high voltage. In this method, the silicon substrate and the glass plate, which is formed with a cavity, are aligned in a chamber. After the degree of vacuum in the chamber is adjusted using an inert gas, the glass plate is heated to a high temperature while a high voltage is applied to the cover. Thus, glass ions of the cover (i.e., the glass plate) migrate to the silicon substrate, so that the two different structures are bonded. Due to bonding of the two different structures, the cavity is under vacuum conditions.
Alternately, in the vacuum-mounting method using the getter material, a glass plate formed with a cavity is bonded to a silicon substrate, with the getter material attached to a portion of the cavity to enhance the degree of vacuum or the purity of gas contained inside. Thus, the cavity is under vacuum conditions.
However, of the foregoing conventional MEMS vacuum-mounting methods, the vacuum-mounting method using the anodic bonding has a problem in that, as time passes, gas injected into the interior of the cavity exits to the exterior of the cavity, so that a desired degree of vacuum is not maintained. Similarly, the vacuum-mounting method using the getter material has a problem in that, because the cavity is excessively evacuated by the getter material, it is difficult to provide the proper degree of vacuum for either device.