Work Function Modulating Layer via Plasma Nitridation
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Solution Overview
Problem
Current methods for forming work function modulating layers in microelectronic devices, such as those used in CMOS FETs and DRAMs, result in high effective work functions and increased flat band voltage, leading to leakage issues and degraded performance.
Innovation Solution
A method involving the deposition of a molybdenum nucleation layer on a gate oxide layer, followed by a molybdenum layer and a plasma nitridation process using a radical-rich plasma containing N2 or NH3 to form a molybdenum nitride work function modulating layer with an effective work function ≤ 4.5 eV, accompanied by an optional annealing step.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nitrogen implantation processes are used to reduce effective work function, then effective work function is reduced, but flat band voltage increases and leakage issues occur
Solution Approach 1:
The patent changes the method of nitrogen introduction from implantation to in-situ formation during atomic layer deposition. By controlling deposition temperature (200-400°C) and using ammonia-containing precursors, nitrogen is incorporated into the tungsten nitride layer in-situ, achieving the desired work function (3.8-4.5 eV) without the harmful side effects of implantation such as increased flat band voltage and leakage currents.
Solution Approach 2:
The patent replaces the mechanical implantation process with a chemical deposition process. Instead of physically implanting nitrogen ions into the metal layer, nitrogen is introduced through chemical reactions during ALD using ammonia-containing precursors, resulting in cleaner interface formation and避免了 implantation-induced damage.
2Object-affected harmful factors
If molybdenum is used as metal fill material to reduce word line resistance, then word line resistance is reduced, but effective work function becomes too high
Solution Approach 1:
The patent creates a composite structure by forming tungsten nitride within the molybdenum metal fill material. The tungsten nitride phase (formed by in-situ nitrogen incorporation during ALD) provides the lower work function (3.8-4.5 eV) needed for proper device operation, while the molybdenum matrix maintains the low electrical resistivity for word line applications.
Solution Approach 2:
The patent applies local quality by creating regions of tungsten nitride within the molybdenum metal fill. The nitrogen incorporation is controlled to occur at specific locations and concentrations during the ALD process, allowing the metal fill to simultaneously exhibit low resistance properties from the molybdenum matrix and appropriate work function properties from the tungsten nitride regions.
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 reduces the effective work function, decreases flat band voltage, and improves device performance without degrading electronic properties, thereby enhancing the functional density and reducing leakage currents in microelectronic devices.
Implementation Method 1
performing a plasma nitridation process to insert nitrogen atoms into the molybdenum layer to form a work function modulating layer. The plasma nitridation process comprises exposing the molybdenum layer to a radical-rich plasma comprising one or more of N2 or NH3.
Implementation Method 2
The method further comprises annealing the work function modulating layer.
Data Source
AI summary
Method of forming film stacks and film stacks for electronic devices are described herein. The methods comprise depositing a molybdenum nucleation layer on a gate oxide layer; depositing a molybdenum layer on the molybdenum nucleation layer; and performing a plasma nitridation process to insert nitrogen atoms into the molybdenum layer to form a work function modulating layer having an effective work function ≤ 4.5 eV. The plasma nitridation process comprises exposing the molybdenum layer to a radical-rich plasma comprising one or more of N2 or NH3. Some methods further comprise one or more of annealing the work function modulating layer, depositing a conductive layer on the work function modulating layer, or performing an etch process.