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Surface Micro-Machined Encapsulation on Wafer Level


The goal of this proposal made by IMEC, Bosch and STS is to develop a technique for wafer-level encapsulation of large micro-electromechanical devices having high aspect ratio trenches by the fabrication and sealing of surface micro-machined membranes. This integrated packaging technique would replace controlled atmosphere encapsulation by wafer bonding and would have the advantage of reduced thickness and area consumption and the promise of being a low-cost batch process. After a concept phase, all technology steps needed for success are developed aided by extensive simulations. After studying the systems aspects, the results will then be applied to a specific demonstrator (a wafer level encapsulated accelerometer). This demonstrator will be thoroughly tested to see if the project objectives are met.

Many micro-electomechanical systems require a vacuum or controlled atmosphere operation in order to ensure a good performance and/or an acceptable lifetime of operation. Currently wafer bonding is used to provide the hermetic seal of an accelerometer. This is an expensive and area consuming process. A possible alternative for vacuum encapsulation is the fabrication and sealing of surface micro-machined membranes over the device that needs to be encapsulated. The advantage of this integrated packaging technique would be the reduced thickness and area consumption and the promise of being a low-cost batch process. The objective of this project is to develop a wafer encapsulation technique that is capable of covering up to 1 mm² large devices having high aspect ratio trenches (1:5), that can survive plastic packaging and that is cheaper and uses less chip area than the current process. The goal set for this project is a 50% reduction of the total chip cost

Work description:
The project starts with a concept phase in which the possible process flow(s) are laid out, the development requirements are identified and the demonstrator specifications are determined. Then all technology steps needed to come to a successful surface micro-machined encapsulation on wafer level are developed. During this development often several options are evaluated for a certain process module, but milestones are foreseen at which only one option is withheld for the final demonstrator. The process development is aided by extensive simulations to decide on the required thickness and stress of membrane and sealing layer, the number of supports and the optimal sensor design. After studying the system aspects, the results can then be applied to a specific demonstrator (an accelerometer). This demonstrator will be completely made, including the final plastic packaging, and will be thoroughly tested to see if the project objectives are met. The technology development work is shared by all three partners. STS is involved in all workpackages where layers are deposited for which they already have equipment on the market. By being involved in the development phase from the beginning, STS can immediately implement any process and/or hardware changes in their equipment and thus be ready to produce production equipment by the end of the project. The design and simulations are done by Bosch, Bosch also handles solely the system aspects and the demonstrator manufacturing and testing. This implies that any necessary technology transfer from the other partners to Bosch is already done during stage and that the transition to produce will be very smooth. The whole project is managed by IMEC, with very close help of Bosch and STS concerning the exploitation of the results.

The final result is a plastic packaged demonstrator made and tested against the specifications.
In between milestones are:
M6: Demonstrator specifications fixed and concept(s) laid out;
M18: Sacrificial layer and membrane material chosen and membrane geometry including substructure and stress decided;
M24: Sacrificial etching technique and sealing technique for demonstrators chosen;
M31: Design rules for demonstrator fabrication available and decision on system concept.
The SUMICAP project has been successfully ended and fully functioning plastic molded demonstrators were made. Demonstrator chips for two different process alternatives were processed and developed. All measures of success have been reached. A stable "SUMICAP" process flow has been developed allowing the processing of wafers within the sensor production facility at BOSCH in Reutlingen. The 100g acceleration sensors obtained a good performance within the expected specification and could be powered with standard evaluation circuits and ASICs from commercial BOSCH devices. The area shrink enabled by the "SUMICAP" process leads to more than 10000 chips per 6''-wafer resulting in the potential for a significant cost reduction.

Call for proposal

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Kapeldreef 75
3001 Leuven

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EU contribution
€ 0,00

Participants (2)