Researchers at the University of Southampton, UK, have developed a technique that will allow silicon wafers to be stacked accurately and inexpensively in 3-D structures.
According to Dr Michael Kraft at the University's School of Electronics and Computer Science (ECS), the major challenge when stacking silicon wafers is aligning one wafer with another, matching all the features.
He states: The alignment needs to be accurate. At the momentbig chunky machines are being used and the process is being carried out optically. The optical path is long and this introduces errors."
Dr Kraft and his colleagueProfessor Mark Spearing at the School of Engineering Sciencesworked with Dr Liudi Jiangwho is now a Roberts Fellow in the School of Engineering Sciencesto develop what they describe as 'an effective passive alignment technique for the achievement of nanoprecision alignment'. The approach 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 200nm has been achieved.
Dr Kraft says: "We have demonstrated that we do not need expensive machines to create alignment. Our system will automatically fit the wafers together like Lego."
The researchers are in the process of submitting a proposal to the Engineering and Physical Sciences Research Council (EPSRC) to enable them to develop their work in this field further.
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