A team from the Graphene Flagship has reported a new way of solving the notoriously difficult issue of successfully integrating 2D materials into semiconductor manufacturing lines.
As published in Nature Communications, the integration of 2D materials into semiconductor manufacturing lines, which is necessary if we wish to exploit the potential of 2D materials, presents a number of challenges. Arne Quellmalz, researcher at Graphene Flagship Associate Member KTH and lead author of the paper, said: “There’s always this critical step of transferring from a special growth substrate to the final substrate on which you build sensors or components. 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.”
Current methods for transferring 2D materials from their growth substrate to the desired electronics are either non compatible with high-volume manufacturing or lead to a significant degradation of the material. The solution proposed by Quellmalz relies on toolkits of semiconductor manufacturing: to use a standard dielectric material called bisbenzocyclobutene (BCB), along with conventional wafer bonding equipment.
Quellmalz explained: “We basically glue the two wafers together with a resin made of BCB. 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. 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.”
Practical demonstrations of this technology
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 and featured uniform coverage over up to 100-millimetre sized silicon wafers and exhibited little strain in the transferred 2D materials.
Professor Max Lemme, from Graphene Flagship partners AMO GmbH and RWTH Aachen University, said: “Our transfer method is in principle applicable to any 2D material, independent of the size and the type of growth substrate. 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 microsystems.”
The European Commission has recently launched a €20m project to bridge the gap between lab-scale semiconductor manufacturing and large volume production of electronic devices based on two-dimensional materials, the Graphene Flagship 2D Experimental Pilot Line (2D-EPL).
Cedric Huyghebaert, the technical leader of the 2D-EPL project, said: “One of our urgent tasks at the moment is to develop tool kits and design manuals for manufacturing devices based on 2D materials that are compatible with the standards of semiconductor industry. The next step will be to demonstrate the potential of these processes for producing innovative sensors and optoelectronic devices on a pilot line.”