Metal Gate Capping Layers for Stable FinFET Work Function
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Solution Overview
Problem
MOS devices with polysilicon gate electrodes suffer from carrier depletion effects, leading to increased effective gate dielectric thickness and difficulty in creating an inversion layer, which can be mitigated by using metal gate electrodes with appropriate work functions.
Innovation Solution
Forming metal gate electrodes with a silicon-containing soaking process after the work-function layer to prevent metal diffusion and oxygen penetration, followed by the deposition of a metal capping layer to stabilize the work function and enhance the gate stack's integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal gate electrodes are formed with multiple layers to achieve appropriate work functions, then the carrier depletion effect is mitigated and inversion layer creation is improved, but the device complexity and manufacturing process complexity increase
Solution Approach 1:
The gate electrode is divided into multiple functional layers: a first metal layer providing mechanical support and conductivity, a work function layer (5-10 nm thick) controlling the electrical characteristics, and an optional capping layer for protection. This segmentation allows each layer to be optimized independently for its specific function while collectively solving the carrier depletion problem.
Solution Approach 2:
The patent employs composite material structures combining different metal layers with distinct properties. The first metal layer (e.g., tungsten, cobalt) provides structural integrity and baseline conductivity, while the work function layer (e.g., titanium nitride, tantalum nitride) contributes specific electrical characteristics. This composite approach achieves the desired work function without requiring excessive metal thickness, thereby mitigating carrier depletion.
2Manufacturing precision
If metal layers are deposited and CMP is performed to form metal gates, then the gate structure is formed with controlled dimensions, but metal diffusion and oxygen penetration occur affecting work function stability
Solution Approach 1:
A capping layer is deposited over the work function layer before subsequent processing steps. This preliminary protective action prevents oxygen penetration and metal diffusion during high-temperature annealing and other thermal processes, thereby maintaining work function stability and preventing threshold voltage drift throughout the manufacturing sequence.
Solution Approach 2:
The capping layer serves as an intermediary barrier between the work function layer and the external environment. It physically isolates the work function layer from oxygen and other reactive species, preventing unwanted chemical reactions and diffusion processes that would otherwise alter the work function characteristics and compromise device performance.
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 silicon-containing treatment and metal capping layer effectively prevent metal diffusion and oxygen penetration, maintaining the work function stability and reducing threshold voltage drift in FinFETs, thereby improving transistor performance.
Implementation Method 1
performing a first treatment on the wafer, wherein the first treatment is performed by soaking the wafer using a silicon-containing gas... effectively prevent metal diffusion and oxygen penetration
Data Source
AI summary
A method of forming a semiconductor device includes forming a gate electrode in a wafer. The formation of the gate electrode includes depositing a work-function layer, after the work-function layer is deposited, performing a treatment on the wafer, wherein the treatment is performed by soaking the wafer using a silicon-containing gas; after the treatment, forming a metal capping layer over the work-function layer; and depositing a filling metal over the metal capping layer.