PECVD makes 2D heterostructures over 100mm wafer

Researchers at the Korea Institute of Machinery and Materials have developed a way to grow 2d transition metal dichalcogenides heterostructures across 100mm wafers using plasma-enhanced chemical vapour deposition (PECVD), claiming this to be a first.

“Transition metal dichalcogenides [are] candidates for next-generation semiconductors, with atomic-level 2d structures offering silicon-like performance, low power operation, and fast switching speeds,” according to the Institute. They are “particularly suitable for neuromorphic systems and used in machine learning, deep learning, and cognitive computing.”

Such dichalcogenides include molybdenum disulfide (MoS₂), tungsten disulfide (WS₂) and molybdenum selenide (MoSe₂).

Two heterostructures were grown:

• WS₂ and graphene, fabricated by depositing 1nm of tungsten onto a graphene-transferred wafer, followed by H₂S plasma sulfurisation.
• Orthorhombic 1T phase (metallic) molybdenum disulfide (MoS₂) on hexagonal 2H phase MoS₂ ,and vice versa.

The orthorhombic structure is prone to decay compared with the stable hexagonal phase, making large-area wafer production of it challenging, according to the Institute, whose technology allowed the team to stack entirely 1T phase layers on wafers, as well as the stacking alternate 1T-2H phases to build heterostructures.

“This technology not only allows experimental validation previously restricted to academic research, but fulfills wafer-size and reproducibility requirements. Using PECVD, widely employed in the semiconductor industry, offers high potential for mass production,” said KIMM scientist Hyeong-U Kim (left in photo), who developed the necessary custom plasma synthesis equipment (photo).

The Korea Institute of Machinery and Materials worked with Sungkyunkwan University

Patents for the fabrication technology have been registrations in South Korea and the US.

The work is described in two papers: ‘Electron release via internal polarization fields for optimal S-H bonding states‘ in Advanced Materials, and ‘Unlocking of Schottky barrier near the junction of MoS₂ heterostructure under electrochemical potential‘ in Energy & Environmental Materials.

Photo: Hyeong-U Kim (left) from the Korea Institute of Machinery and Materials, holding a heterostructure semiconductor sample.