Gallium Nitride Dipole Layer for Gate Work Function Control
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Solution Overview
Problem
Conventional CMOS devices face challenges with doped polysilicon gate electrodes, such as gate depletion and non-ideal effective work function, which become complex and impractical in advanced node applications, necessitating alternative materials for improved performance.
Innovation Solution
The use of a cyclical deposition process to form a dipole layer comprising gallium nitride over a gate dielectric in semiconductor structures, which can include additional metal-containing layers, to modulate the effective work function and threshold voltage of MOS devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If doped polysilicon is used as gate electrode material, then the device can be manufactured with conventional processes, but gate depletion occurs and effective work function is non-ideal
Solution Approach 1:
The patent uses a composite gate electrode structure consisting of multiple metal layers (e.g., titanium nitride, tungsten, cobalt) combined with dielectric materials. This composite approach allows optimization of both electrical properties (work function, depletion) and manufacturability, replacing the single-material polysilicon gate with a multi-layer structure that addresses the limitations of conventional materials.
2Productivity
If gate oxide thickness is reduced for advanced node applications, then device density and speed improve, but gate depletion region becomes significant
Solution Approach 1:
The patent changes the material parameters of the gate electrode from doped polysilicon to metal-based materials with different electrical characteristics. This parameter change (material composition, work function, carrier concentration) allows maintaining effective gate control even with reduced oxide thickness, preventing the gate depletion region from becoming significant while enabling advanced node scaling.
3Reliability
If threshold voltage adjustment implantation is used to overcome non-ideal effective work function, then work function can be adjusted, but process complexity increases
Solution Approach 1:
The patent performs preliminary action by selecting metal materials with inherently suitable work functions for the desired device type (NMOS or PMOS). Instead of starting with a generic polysilicon gate and adjusting it later through complex implantation processes, the gate material is pre-selected to have the appropriate electrical characteristics, simplifying the overall manufacturing process while maintaining reliable work function control.
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
The gallium nitride dipole layer induces a significant threshold voltage shift, improving the performance of MOS devices by altering the band alignment and providing a more ideal work function, suitable for advanced node applications.
Implementation Method 1
performing one or more cycles of a cyclical deposition process to deposit a dipole layer comprising gallium nitride over a surface of the gate dielectric. The cyclical deposition process can include (e.g., sequentially and separately) providing a gallium precursor to the reaction chamber and providing a nitrogen reactant to the reaction chamber.
Data Source
AI summary
Methods for forming a semiconductor structure including a gallium nitride dipole layer are disclosed. An exemplary method includes using a cyclical deposition process to deposit a dipole layer comprising gallium nitride over a surface of a gate dielectric. The cyclical deposition process can include providing a gallium precursor to the reaction chamber and separately providing a nitrogen reactant to the reaction chamber. The cyclical deposition process may desirably be a thermal cyclical deposition process. Exemplary structures can include field effect transistor structures, such as gate all around structures.