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nanotimes News in Brief
11-05 :: May/June 2011
Production Systems // Solution for the Production of Long-range Infrared Microsensors
R
esearchers of the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in
Duisburg, Germany, are now offering a solution for the production of long-range infrared microsen- sors. On June 22, they will be opening a new facility in which the production of such micro-system tech- nology (MST) is possible. MST involves minute sen- sors, valves or other mechanical components that are integrated into semiconductor chips. For instance, in airbags they serve as motion sensors, and they are no thicker than a human hair. If MST is to be applied on semiconductors and integrated, one has to master the art of etching – which is where the researchers at IMS come in.
“Traditional etching methods allow us only to etch vertically into the layers,“ explains Dr. Marco Russ, project manager at IMS. “However, unsupported structures are decisive for the mechanical functions of many items of MST.“ In other words: the etching must work not only vertically but evenly in all direc- tions. Experts call this process “isotropic etching.“
This ensures that the etching substance not only eats vertically to the substrate but also digs itself under the function layer, like a tunnel. What remains is an unsupported structure of the function layer that is only one hundred nanometers thin and connected
to the substrate only at certain suspension points. “A conventional technique is etching with liquids“, says Russ. However, capillary forces can occur when the etching fluid dries. The result: the filigree membra- nes are glued to the substrate or are even destroyed. In addition, most etching liquids do not permit the choice of just any combination of materials for the function and sacrificial layers.
“We bypass these problems with our new facility,“ says Russ. The highlight: “We can use two different gases in the processing chambers of the machine instead of fluids.“ They are highly selective: hydrogen fluoride (HF) has strong etching properties on silicon dioxide but does not affect silicon. The exact reverse is the case with xenon difluoride gas (XeF2
).
“This way, we can select which material is better suited to be the function layer,“ says Russ. The new facility could revolutionize MST production, since the process works in a highly precise manner on an industrial scale. And: whether thermal detectors, acceleration sensors and pressure sensors or micro machines – a multitude of MST structures can be produced in this way.