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Trench isolation for micromechanical devices
| Details |
Inventors: Adams, Scott G.; Shaw, Kevin A.; Webb, Russell Y.; Reed, Bryan W.; MacDonald, Noel C.; Davis, Timothy J.;
Assignee: Kionix, Inc. (Ithaca, NY); Cornell Research Foundation Inc. (Ithaca, NY)
Primary Examiner: Jackson, Jr.; Jerome
Assistant Examiner:
Attorney, Agent or Firm: Jones, Tullar & Cooper, P.C.
An isolation process which enhances the performance of silicon micromechanical devices incorporates dielectric isolation segments within the silicon microstructure, which is otherwise composed of an interconnected grid of cantilevered beams. A metal layer on top of the beams provides interconnects and also allows contact to the silicon beams, electrically activating the device for motion or transduction. Multiple conduction paths are incorporated through a metal patterning step prior to structure definition. The invention improves manufacturability of previous processes by performing all lithographic patterning steps on flat topographies, and removing complicated metal sputtering steps required of most high aspect ratio processes. With little modification, the invention can be implemented with integrated circuit fabrication sequences for fully integrated devices. |
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DETAILED DESCRIPTION In order to achieve the foregoing and to overcome the problems inherent in prior electrical isolation schemes, the present invention is directed to a beam-level isolation technique in which insulating segments are incorporated within silicon beam microstructures to provide electrical isolation.
It is therefore an object of the present invention to provide suitably modified trench isolation techniques, utilizing dielectric materials, in conjunction with micromechanical device fabrication processes to achieve electrical isolation within the microstructure.
It is a further object of the invention to eliminate the use of unsuitable and unreliable sidewall metal layers for electrical activation of a MEMS device, and instead to use the silicon cores of microstructure beams for conduction and as capacitor plates.
This is achieved by creating contacts from a metal layer through a dielectric layer to the silicon beams using techniques which are common in the art.
It is a further object of the invention to provide multiple metal interconnections within a MEMS device.
This is achieved by placing metal conductor lines over isolation segments and on top of cantilever beams to provide multiple metal paths.
The conductor lines are separated from the core silicon by an insulating layer which is also present on top of the beams, thus achieving isolation between the metal and the silicon.
It is a further object of the invention to alleviate dielectric-induced stress on silicon beam microstructures by minimizing the amount of sidewall film present on the silicon.
Thermal oxidation of existing beam structures creates a thick sidewall oxide film which dominates device characteristics.
By performing isolation processes before structure formation, sidewall films can be reduced or even eliminated, and hence passivation films can be rendered unimportant to device performance.
It is a further object of the invention to provide a trench isolation process for fabricating microstructures which is scalable to different structure etch depths, while maintaining high manufacturing yield
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MEMS 
