Researchers at Germany’s Fraunhofer Institute for Microelectronic Circuits and Systems (IMS) have developed a new way to produce long range infrared microsensors, which could be used in thermal imaging cameras for automotive safety systems.
At present, thermal imaging cameras for traffic safety are rarely seen because these micro sensors are produced with great difficulty. However, the Fraunhofer Institute is planning to inaugurate a new facility on June 22nd 2011 for producing such microsystem technology (MST).
The MST includes a number of components such as valves, minute sensors and other parts into semiconductor chips. To apply and integrate the MST on semiconductors, the researchers at IMS use etching methods. Three layers are placed on top of each other when the MST is applied to a semiconductor. First is the function layer, followed by the sacrificial layer in the centre, which acts as a spacer, and finally the bottom is the substrate layer. Ultimately, the sacrificial layer is etched away leaving behind only the proper sensor structure.
Marco Russ, IMS’ Project Manager, revealed that traditional etching methods would allow only vertical etching into the layers and what was needed was not just vertically etching but uniform etching in all directions i.e. isotopic etching, which would ensure that the etching material would consume vertically the substrate and leave behind an unsupported structure of the function layer, 100 nm thin, and connected to the substrate at some suspension points only.
Russ stated that the normal etching technique makes use of liquids where the disadvantage was mainly due to the capillary forces, which occur when the etching fluid dries up. This results in the filigree membranes getting glued on to the substrate or sometimes even getting destroyed. Furthermore, etching liquids also would not allow the selection of any combination of materials for the sacrificial and function layers. Russ further mentioned that all these problems are overcome in the new facility where two different gases are used in the processing chambers of the machine. These liquids are highly selective. For instance, xenon difluoride gas (XeF) has strong etching properties on Silicon but does not affect silicon dioxide, while hydrogen fluoride (HF) acts in the reverse way. The new facility could thus revolutionize and transform MST structure production.