RoW Transistor Stack Vt Tuning with Selective Dipole Shifters
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Solution Overview
Problem
Stacked gate-all-around (GAA) transistor structures, such as ribbon or wire (RoW) structures, face challenges in setting and tuning the transistor threshold voltage (Vt) due to limitations in work function metal thickness and the inability to use multiple work function metals within a single transistor stack.
Innovation Solution
The introduction of a dipole Vt shifter, a metallic compound formed around the channels of a transistor stack, which can be diffused to alter the dipole properties of the gate insulator material, allowing for selective tuning of Vt across different channels within a stack.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If work function metal thickness is varied to tune Vt, then Vt can be adjusted, but the small spaces between stacked channel regions limit the metal thickness to insufficient levels
Solution Approach 1:
An intermediary dipole layer is introduced between the gate insulator and the channel regions. This dipole layer acts as a mediator that provides strong Vt tuning capability without requiring thick work function metals. The dipole layer creates an electric field that shifts the threshold voltage, enabling effective Vt control in the limited space between stacked channels.
Solution Approach 2:
The invention changes the physical parameter used for Vt tuning from metal thickness to dipole moment density. By varying the concentration, composition, or thickness of the dipole layer, strong Vt shifts can be achieved without increasing the physical thickness of the gate electrode, thus resolving the contradiction between tuning capability and space constraints.
2Adaptability or versatility
If multiple work function metals are used to achieve multiple threshold voltages, then diverse Vt values can be obtained, but the fabrication process becomes more complex
Solution Approach 1:
A single gate electrode structure is designed to perform multiple functions by incorporating a dipole layer that can provide various Vt values. The dipole layer can be engineered with different compositions or concentrations to achieve multiple threshold voltages, eliminating the need for multiple different work function metals and simplifying the fabrication process.
Solution Approach 2:
Instead of using multiple materials (different work function metals) to achieve multiple Vt values, the invention uses parameter changes within a single material system - specifically, varying the dipole layer's composition, concentration, or thickness to tune Vt across a range of values, thereby reducing fabrication complexity.
3Reliability
If work function metal thickness is increased to strongly set Vt, then Vt control is improved, but the device geometry and small spaces between stacked channels preclude such thickness
Solution Approach 1:
The dipole layer serves as an intermediary that provides strong Vt setting capability without requiring thick gate electrodes. The dipole moments in this layer create a significant electric field that strongly influences the channel, enabling reliable Vt control within the thin geometry constraints of stacked channel devices.
Solution Approach 2:
The invention transitions from controlling Vt through geometric parameter (metal thickness) to controlling Vt through material parameter (dipole moment density). This allows strong Vt setting to be achieved through high dipole moment density in a thin layer, rather than requiring thick metals that are incompatible with the device geometry.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables effective Vt tuning for transistors within a stack, even in aggressively scaled devices, by allowing different channels to be exposed to varying amounts or types of the metallic dipole species, thereby achieving a range of Vt values.
Implementation Method 1
a dipole Vt shifter, a metallic compound formed around the channels of a transistor stack, which can be diffused to alter the dipole properties of the gate insulator material
Data Source
AI summary
Integrated circuitry comprising a ribbon or wire (RoW) transistor stack within which the transistors have different threshold voltages (Vt). In some examples, a gate electrode of the transistor stack may include only one workfunction metal. A metal oxide may be deposited around one or more channels of the transistor stack as a solid-state source of a metal oxide species that will diffuse toward the channel region(s). As diffused, the metal oxide may remain (e.g., as a silicate, or hafnate) in close proximity to the channel region, thereby altering the dipole properties of the gate insulator material. Different channels of a transistor stack may be exposed to differing amounts or types of the metal oxide species to provide a range of Vt within the stack. After diffusion, the metal oxide may be stripped as sacrificial, or retained.