Metal Gate Capping Layers for Stable Work-Function Control
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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 affects the performance of transistors.
Innovation Solution
Formation of metal gate electrodes with a silicon-containing layer to prevent carrier depletion, using a silicon-containing gas soaking process to form a silicon oxide layer that blocks oxygen diffusion and maintains the stability of the work-function layer, and a metal capping layer to prevent metal diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal gate electrodes are formed to eliminate carrier depletion effect, then transistor performance is improved, but oxygen diffusion and metal diffusion occur causing instability
Solution Approach 1:
A silicon-containing layer is introduced as an intermediary between the metal gate electrode and the work-function layer. This intermediate layer serves as a diffusion barrier that prevents oxygen from reaching the work-function layer and prevents metal atoms from diffusing downward, thereby stabilizing the work-function layer while maintaining the benefits of the metal gate electrode
Solution Approach 2:
The gate structure is formed as a composite multi-layer system comprising the metal gate electrode, silicon-containing layer, and work-function layer. Each layer provides specific functions: the metal layer eliminates carrier depletion, the silicon-containing layer provides diffusion blocking, and the work-function layer provides appropriate work function. The composite structure combines the advantages of different materials while mitigating their individual drawbacks
2Stability of the object's composition
If silicon-containing layer is added to prevent oxygen diffusion, then work-function layer stability is improved, but device structure becomes more complex
Solution Approach 1:
The silicon-containing layer is formed as a thin film with thickness in the range of 1-10 nanometers. This thin film configuration provides effective diffusion blocking functionality while minimizing the increase in overall device complexity and maintaining compatibility with existing manufacturing processes
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 layer effectively prevents oxygen penetration and metal diffusion, stabilizing the work-function layer and maintaining the threshold voltage of the FinFET, thereby improving transistor performance.
Implementation Method 1
a silicon-containing layer to prevent oxygen penetration and metal diffusion
Implementation Method 2
a metal capping layer to prevent metal diffusion
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.