Polysilicon Gate Stack With Metal Layers for Low-Resistance SiC Switching
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Solution Overview
Problem
Semiconductor devices using silicon carbide face issues with high gate wiring resistance and threshold shift due to polysilicon electrodes, leading to delays in signal transmission and increased costs, especially during high-speed switching.
Innovation Solution
Incorporating a first and second metal layer, made of materials like Ti silicide and TiN, on the polysilicon gate electrode to reduce resistance and suppress movable ion movement, thereby stabilizing the threshold voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polysilicon gate electrode is used, then the gate electrode is easy to form in a wafer process, but the polysilicon electrode has lower conductivity than a metal layer, resulting in high wiring resistance and signal transmission delay
Solution Approach 1:
The gate electrode structure uses a composite material system combining polysilicon with metal layers (tungsten, tungsten silicide, or titanium nitride). This composite structure leverages the ease of polysilicon formation while adding metal layers to provide low resistance pathways, thereby reducing overall wiring resistance and signal transmission delay.
Solution Approach 2:
The gate electrode is segmented into multiple functional layers: the polysilicon base layer for ease of formation and the additional metal layers (first and second metal layers) for conductivity enhancement. This segmentation allows each layer to perform its specialized function - polysilicon for structural integrity and ease of fabrication, metal layers for electrical conductivity.
2Ease of manufacture
If a polysilicon gate electrode is used, then the gate electrode is easy to form in a wafer process, but the high polysilicon wiring resistance interferes with speed-up in switching
Solution Approach 1:
The composite gate electrode structure combines polysilicon with highly conductive metal layers to create a hybrid material system that maintains the ease of polysilicon fabrication while achieving metal-level conductivity. This enables high-speed switching by reducing the RC time constant associated with gate wiring resistance.
Solution Approach 2:
The solution adds a vertical dimension to the gate electrode structure by stacking metal layers above the polysilicon layer. This vertical stacking creates multiple parallel conduction pathways, effectively reducing the overall resistance and enabling faster signal transmission for high-speed switching applications.
3Reliability
If barrier metal layers are added to prevent threshold shift, then threshold voltage stability is improved, but the number of manufacturing steps increases
Solution Approach 1:
The barrier metal layer is merged with the existing metal layer structure, serving dual purposes: as a diffusion barrier to prevent threshold voltage shifts and as part of the conductive pathway. By integrating the barrier function into the metal layer stack rather than adding a completely separate layer, the design reduces the net increase in manufacturing complexity while achieving the desired reliability improvement.
Data Source
AI summary
A semiconductor device according to the present disclosure, includes a semiconductor substrate; a gate electrode which is provided above the semiconductor substrate with a gate insulating film intervening between the gate electrode and the semiconductor substrate and is made with polysilicon; a first metal layer which is provided on the gate electrode; a second metal layer which is provided on the first metal layer; a first electrode which is provided above the second metal layer with an interlayer insulating film intervening between the first electrode and the second metal layer; and a second electrode which is provided on an opposite side of the semiconductor substrate from the first electrode, wherein at least one of the first metal layer and the second metal layer contains a metal which suppresses movement of a movable ion.