Advanced transistors (FinFET and GAA)
For transistors with channels made of 2D materials such as MoS2, what is the main reason it is hard to deposit a uniform high-k gate dielectric by atomic layer deposition (ALD)?
- A2D materials are metals and react with the dielectric
- BTheir surfaces have almost no dangling bonds, so there are few sites where ALD precursors can adsorb and start film growth
- CThe surfaces of 2D materials are very rough, so ALD precursors cannot reach deep areas
Show answer and explanation
Answer: B. Their surfaces have almost no dangling bonds, so there are few sites where ALD precursors can adsorb and start film growth
Because 2D materials have no dangling bonds on their layer surfaces, they keep their mobility even below 1 nm thickness. The same property means ALD precursors hardly adsorb chemically on the surface, so films nucleate as islands at defects and grain boundaries and do not form thin, uniform dielectrics. Plasma-based methods tend to damage the layer, so approaches such as first forming a thin nucleation layer are being studied.
- A. MoS2 and similar materials are semiconductors, not metals.
- B. Correct. The chemically inert surface is the cause.
- C. The surface is atomically flat; roughness is not the cause.
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