Silicon Intermixing Layer for Metal Gate Diffusion Blocking
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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 NMOS and PMOS devices.
Innovation Solution
Formation of a silicon-containing intermixing layer after the deposition of a metal gate electrode, using a silicon-containing gas soaking process to prevent diffusion of oxygen into the work function layer and metal from the work function layer, thereby stabilizing the work function and reducing threshold voltage drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a polysilicon gate electrode is used, then the device structure is simple and manufacturing is easier, but carrier depletion effect occurs leading to increased effective gate dielectric thickness and difficulty in creating inversion layer
Solution Approach 1:
The patent uses a composite gate structure combining metal layers (tungsten, titanium nitride, tantalum nitride) with a silicon-containing intermixing layer. This composite approach eliminates the carrier depletion effect inherent in polysilicon while maintaining manufacturability through established metal deposition and CMP processes.
Solution Approach 2:
The patent extracts the problematic polysilicon material from the gate electrode and replaces it with metal materials that do not exhibit carrier depletion. The silicon-containing intermixing layer is retained as a separate functional component to provide diffusion blocking without the electrical issues of polysilicon.
2Reliability
If metal gate electrodes are formed to solve poly depletion, then carrier depletion effect is eliminated, but the gate structure becomes more complex requiring multiple layers and CMP processing
Solution Approach 1:
The silicon-containing intermixing layer serves multiple functions: it acts as a diffusion barrier for oxygen and metal atoms, provides a blocking layer for the metal gate, and contributes to work function tuning. This multi-functionality reduces the need for separate dedicated layers, simplifying the overall gate structure.
Solution Approach 2:
The patent merges the diffusion barrier function and the gate electrode function into an integrated structure. The silicon-containing intermixing layer is formed in-situ during the metal gate deposition process, combining what would otherwise be separate process steps into one unified operation.
3Stability of the object's composition
If oxygen diffusion into the work function layer is prevented, then work function stability is improved, but additional blocking layers and processes are required
Solution Approach 1:
The silicon-containing intermixing layer acts as an intermediary barrier between the metal gate electrode and the work function layer. It selectively blocks oxygen diffusion into the work function layer while allowing the metal gate to maintain electrical contact, thus stabilizing the work function without requiring additional complex blocking structures.
4Stability of the object's composition
If the silicon-containing intermixing layer is formed by soaking in silicon-containing gas, then diffusion blocking is achieved, but the process time and temperature requirements increase
Solution Approach 1:
The silicon-containing intermixing layer is formed in-situ during the metal gate deposition process, before subsequent high-temperature processing steps. This preliminary formation of the diffusion barrier prevents oxygen and metal diffusion during later fabrication steps, eliminating the need for separate prolonged soaking 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 intermixing layer effectively blocks the diffusion of oxygen and metal, maintaining the stability of the work function layer and reducing threshold voltage variations between transistor-dense and transistor-sparse regions.
Implementation Method 1
The remaining portions of the metal layers form metal gates. A silicon-containing intermixing layer is formed after the deposition of the metal gate electrode. The silicon-containing intermixing layer blocks diffusion of oxygen into the work function layer and metal from the work function layer.
Data Source
AI summary
A method of forming an integrated circuit structure includes forming a gate dielectric on a wafer, forming a work function layer over the gate dielectric, depositing a capping layer over the work function layer, soaking the capping layer in a silicon-containing gas to form a silicon-containing layer, forming a blocking layer after the silicon-containing layer is formed, and forming a metal-filling region over the blocking layer.