LONDON Researchers at the University of Southampton have developed a technique that will allow silicon wafers to be stacked accurately and inexpensively in 3-D structures.
The approach adopted by the researchers means that the alignment features consisting of convex pyramids and concave pits can be fabricated and chip scale specimens can be successfully bonded after the microfabrication process. An alignment precision of 200-nm has been achieved.
The researchers are in the process of submitting a proposal to the U.K.'s Engineering and Physical Sciences Research Council (EPSRC) to enable them to develop their work in this field further.
According to Dr Michael Kraft at the University's School of Electronics & Computer Science (ECS), the major challenge when stacking silicon wafers is to align one wafer to another, matching all the features.
"The alignment needs to be accurate," said Dr Kraft. "At the moment, big chunky machines are being used and the process is being carried out optically. The optical path is long and this introduces errors."
Dr Kraft worked with Professor Mark Spearing at the School of Engineering Sciences, as well as with Dr Liudi Jiang, who is now a Roberts Fellow in the School of Engineering Sciences, to develop what they describe as "an effective passive alignment technique for the achievement of nanoprecision alignment."
Dr Kraft said the team has shown that there is no need for expensive machines to create alignment. "Our system will automatically fit the wafers together like Lego."
Further information about Dr Kraft's work can be downloaded here.