In 2020 there will be 7 billion people each surrounded by a thousand wireless devices – that is the prediction of the Wireless World Research Forum. In the next few years an incredible number of smart, miniaturised electronics will have to introduced. Stacking chips and Through Silicon Vias (TSVs) connections will save a lot of space. TNO is creating solutions to help make conducting TSVs cheaper and better.
In conventional devices the chips are adjacent to each other on a printed circuit board (PCB). Stacking saves a lot of space and boost performance at the same time. Stacking requires vertical connections, so-called TSVs. The solution may not be today's news and nor is it as simple as it sounds. First, the passages have to be etched in the silicon, normally through Deep Reactive Ion Etching (DRIE). This process, developed by Bosch, is particularly time-consuming and, therefore, expensive. Think of a speed of micrometres per minute – a factor of 5 to 10 too slow to make the process substantially cheaper. Second, the method tends not to result in smooth sidewalls, which poses a problem for the next step of the process, finishing off the connections with functional materials, such as the barrier layer, the insulation layer and conductive material.
If the world wants 3D integration, TSVs are essential. With a view to reducing the production costs an innovative laser technology is being developed to enable holes to be drilled into the silicon. This method is suitable for passages of 10 to 50 micrometres, with a density of 50 to 60 units per chip. The technology works faster than DRIE and can save up to 80 per cent in costs. Modifying the existing DRIE process offers possibilities for more efficiency, so TNO is developing a way of raising the etching speed using innovative microplasma sources. To improve the quality TNO is working on Atomic Layer Deposition (ALD), an existing method that sees a uniform layer of material built up to the required thickness atomic layer for atomic layer. Combining ALD and the improved DRIE process in a single tool brings down costs even further.
The efficiency boost can be attributed to the breadth and depth of process knowledge among TNO's experts, from acoustic mechanics and flow dynamics to plasma technology and laser beam interaction with materials. But more than this, the success is down to the broadly available system knowledge to merge application and underlying technologies. Good relationships with universities, as a supplier of fundamental knowledge, and industry are indispensable. We have joined forces with the University of Twente and Advanced Laser Separation International N.V. (ALSI) to get laser technology in the market. Along with Eindhoven University of Technology and several industrial partners steps are being taken to perfect the new DRIE process. With a focus on applicability, TNO helps manufacturers of chip production machines to make their production technologies affordable and, in turn, enjoy success in business.