Metal Gate Transistor Threshold Voltage Control via Oxygen Concentration
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Solution Overview
Problem
The challenge in manufacturing replacement metal gate (RMG) transistors is the difficulty in controlling threshold voltage (Vth) and forming different metal gate electrodes for various polarities and threshold voltages, which results in high costs and low yield due to complex fabrication processes and damage to gate dielectrics.
Innovation Solution
The solution involves selectively incorporating oxygen into metal gate electrodes with different oxygen concentrations for N-channel and P-channel transistors, using a work function metal like TiC(Al) and employing selective oxidation to control the effective work function, allowing the same metal to be used for both types of transistors with varying oxygen levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If different metal gate electrodes are formed for different polarities and threshold voltages, then threshold voltage control is achieved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent changes the oxygen concentration parameter in the metal gate electrode to control threshold voltage. By varying oxygen content in the same metal material (e.g., TiN, TaN), different work functions are achieved, enabling threshold voltage control without requiring different metal materials for NMOS and PMOS transistors.
Solution Approach 2:
The patent makes a single metal gate material serve multiple functions by controlling its oxygen concentration. The same metal layer can provide different threshold voltages for both NMOS and PMOS transistors, eliminating the need for separate metal gate formation processes for different transistor types.
2Manufacturing precision
If conventional replacement metal gate processes are used, then metal gate electrodes are formed, but threshold voltage control is difficult and yield is reduced
Solution Approach 1:
The patent introduces oxygen concentration as a controllable parameter in metal gate formation. By adjusting oxygen content during deposition or subsequent annealing, precise threshold voltage control is achieved while maintaining manufacturing reliability through a simplified single-metal gate process.
Solution Approach 2:
The patent replaces the mechanical approach of forming different metal layers with a chemical/compositional approach. Instead of depositing different metals for different threshold voltages, oxygen is incorporated into the metal gate to modify its work function, achieving the same effect through compositional control rather than structural complexity.
3Temperature
If polysilicon gate electrodes are used, then thermal processing is withstandable, but operating speed is reduced due to higher resistivity
Solution Approach 1:
The patent uses metal nitride materials (such as TiN, TaN) that combine the low resistivity of metals with the ability to withstand high temperature processing. These composite-like materials provide both the electrical performance of metals and the thermal stability traditionally associated with polysilicon.
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 precise control of threshold voltage for RMG transistors, simplifying the fabrication process, reducing costs, and increasing yield by stabilizing the threshold voltage without damaging the gate dielectric, thus achieving high-yield, low-cost RMG transistors.
Implementation Method 1
selectively incorporating oxygen into the metal conductive layer on the P-channel transistor
Data Source
AI summary
A method and structure for a semiconductor device includes a semiconductor substrate and an N-channel transistor and a P-channel transistor provided on the semiconductor substrate. Each of the N-channel transistor and the P-channel transistor has a gate dielectric film on the semiconductor substrate, and a gate electrode is formed on the gate dielectric. The gate electrode comprises a metal conductive layer. The oxygen concentration in the metal conductive layer for the N-channel transistor is different from that for the P-channel transistor.