Multiple-threshold nanosheet transistors via selective layer deactivation
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Solution Overview
Problem
The fabrication of nanowire and nanosheet transistors is limited by the need for complex processes with multiple masking steps to create various devices on a single chip, restricting the tuning of device characteristics and requiring all or none of the nanostructures to be active, which is not suitable for applications needing specific properties.
Innovation Solution
A method of forming a semiconductor device with multiple vertically aligned layers of channel material, where all but one layer are deactivated, allowing for a gate stack and source/drain regions to be formed around the active layer, enabling the creation of field effect transistors with different threshold voltages and properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple masking steps are used to create different device varieties on a single chip, then device variety is improved, but fabrication complexity increases
Solution Approach 1:
The channel structure is segmented into multiple discrete nanosheet layers stacked vertically, where each layer can be independently controlled through selective deactivation. This segmentation allows different threshold voltages to be achieved by activating specific layers without requiring separate fabrication processes for each device type.
Solution Approach 2:
The invention transitions from planar device variation to vertical stacking, utilizing the third dimension to create multiple channel layers. This dimensional change enables device variety to be achieved through vertical integration rather than through multiple masking steps in the planar domain, thereby simplifying the fabrication process.
2Productivity
If all nanosheet layers are kept active, then current per unit area is improved, but stability deteriorates for applications requiring lower current
Solution Approach 1:
The invention introduces dynamic control over channel layer activation through adjustable threshold voltages. By applying different gate voltages, specific nanosheet layers can be selectively activated or deactivated, allowing the device to adapt its current characteristics to match application requirements. This dynamic control enables stable operation at lower current levels when needed while maintaining the capability for high current operation when required.
3Adaptability or versatility
If device characteristics are tuned by setting doping properties and thickness, then device customization is improved, but fabrication complexity increases
Solution Approach 1:
Different nanosheet layers are doped with different doping concentrations and types, creating local quality variations within the stacked structure. Each layer can be tailored with specific doping properties to achieve desired threshold voltages, while the overall fabrication process remains unified and does not require separate processing steps for each device type.
Data Source
AI summary
Semiconductor devices and methods of making the same include forming a stack of alternating layers of channel material and sacrificial material. The sacrificial material is etched away to free the layers of channel material. A gate stack is formed around the layers of channel material. At least one layer of channel material is deactivated. Source and drain regions are formed in contact with the at least one layer of active channel material.