Researchers from the Graphene Flagship have detailed a new method to integrate graphene and 2D materials into semiconductor manufacturing lines.
The technique, published in Nature Communications, was developed by researchers from RWTH Aachen University, Universität der Bundeswehr München and AMO in Germany along with the KTH Royal Institute of Technology in Sweden and Protemics in Germany. AMO is running one of the multiwafer runs for graphene on large silicon wafers next year as part of the 2D Experimental Production LIne (2D-EPL) for sensors, photnics and electronics applications.
The integration of 2D materials with silicon or with a substrate with integrated electronics presents a number of challenges.
“There’s always this critical step of transferring from a special growth substrate to the final substrate on which you build sensors or components,” said Arne Quellmalz, researcher at KTH. “You might want to combine a graphene photodetector for optical on-chip communication with silicon read-out electronics, but the growth temperatures of those materials is too high, so you cannot do this directly on the device substrate.”
The technique uses a standard dielectric material called bisbenzocyclobutene (BCB), along with conventional wafer bonding equipment, to move the material from a small substrate onto a 100mm silicon wafer.
“We basically glue the two wafers together with a resin made of BCB,” said Quellmalz. “We heat the resin, until it becomes viscous, like honey, and press the 2D material against it.”
At room temperature, the resin becomes solid and forms a stable connection between the 2D material and the wafer, he says. “To stack materials, we repeat the steps of heating and pressing. The resin becomes viscous again and behaves like a cushion, or a waterbed, which supports the layer stack and adapts to the surface of the new 2D material.
The researchers demonstrated the transfer of graphene and molybdenum disulfide (MoS2), as a representative for transition metal dichalcogenides, and stacked graphene with hexagonal boron nitride (hBN) and MoS2 to heterostructures. All transferred layers and heterostructures were reportedly of high quality with they featured uniform coverage over up to 100mm silicon wafers and exhibited little strain in the transferred 2D materials.
Next: Graphene transfer
“Our transfer method is in principle applicable to any 2D material, independent of the size and the type of growth substrate,” said Prof. Max Lemme, from AMO and RWTH Aachen University. “And, since it relies only on tools and methods that are already common in the semiconductor industry, it could substantially accelerate the appearance on the market of a new generation of devices where 2D materials are integrated on top of conventional integrated circuits or microsystem.
“This work is an important step towards this goal and, although many further challenges remain, the range of potential applications is large: from photonics, to sensing, to neuromorphic computing. The integration of 2D materials could be a real game-changer for the European high-tech industry,” he said.
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