Hermetically-sealed MEMS device and its fabrication

Abstract

A hermetic package comprising a substrate (110) having a surface with a MEMS structure (101) of a first height (101a), the substrate hermetically sealed to a cap (120) forming a cavity over the MEMS structure; the cap attached to the substrate surface by a vertical stack (130) of metal layers adhering to the substrate surface and to the cap, the stack having a continuous outline surrounding the MEMS structure while spaced from the MEMS structure by a distance (140); the stack having a bottom first metal seed film (131a) adhering to the substrate and a bottom second metal seed film (131b) adhering to the bottom first seed film, both seed films of a first width (131c) and a common sidewall (138); further a top first metal seed film (132a) adhering to the cap and a top second metal seed film (132b) adhering to the top first seed film, both seed films with a second width (132c) smaller than the first width and a common sidewall (139); the bottom and top metal seed films tied to a metal layer (135) including gold-indium intermetallic compounds, layer (135) having a second height (133a) greater than the first height and encasing the seed films and common sidewalls.

Description

FIELD OF THE INVENTION[0001]The present invention relates to semiconductor devices and processes, and more specifically to the structure and fabrication of hermetically sealed microelectromechanical system (MEMS) devices.DESCRIPTION OF RELATED ART[0002]The wide variety of products collectively called Micro-Electro-Mechanical devices (MEMS) are small, low weight devices on the micrometer to millimeter scale, which may have mechanically moving parts and often movable electrical power supplies and controls, or they may have parts sensitive to thermal, acoustic, or optical energy. MEMS have been developed to sense mechanical, thermal, chemical, radiant, magnetic, and biological quantities and inputs, and produce signals as outputs. Because of the moving and sensitive parts, MEMS have a need for physical and atmospheric protection. Consequently, MEMS are placed on or in a substrate and have to be surrounded by a housing or package, which has to shield the MEMS against ambient and electri...

AI Technical Summary

Benefits of technology

This patent describes a method for making a hermetically sealed MEMS device with sidewall encapsulation of seed layers. A first layer of metal is deposited over a substrate with a MEMS structure, followed by a second mask layer with a different pattern. A first vertical stack of metal layers is plated over the first pile of metal, and a sacrificial polymer and getter and passivation material are dispensed. A cap material element is then aligned with the substrate and a second vertical stack of metal layers is plated over the second pile of metal. Thermal energy is applied to create intermetallic compounds between the metal layers. The method ensures good protection and lateral spacing between the metal layers. The use of metal from the IVA or VA group of metals can be employed. The technical effect of this method is improved protection and reliability of the MEMS device.

Problems solved by technology

Such movement or deflection of the reflector causes deformation of its supporting hinge which stores potential energy that mechanically biases the reflector for movement back to its normal position when the attracting voltage is removed.

It has been found, though, that there is a risk that a deflected reflector may stick to or adhere to its associated landing electrode.

MEMS hermetic packaging is expensive not only because the package often includes a ceramic material, or a metallic or glass lid, but also because the package must be configured to avoid contact with moving and other sensitive parts of the MEMS device and to further allow a controlled or reduced atmosphere inside the package.

The high package cost is, however, in conflict with market requirements for many applications of MEMS devices, which put a premium at low device cost and, therefore, low package cost.

Further, the conventional fabrication of hermetic MEMS packages also encounters many technical challenges, such as those caused by potentially high temperatures in connection with welding of a hermetic lid to the package base.

These temperature ranges are a risk for the reliability of silicon integrated circuits and for proper functioning of many MEMS device components, and inhibit passivation and lubrication methods.

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