Silicon Intermixing Layer for Stable MOS Gate 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 affects the performance of NMOS and PMOS devices.
Innovation Solution
Forming a silicon-containing intermixing layer after the capping layer, using a silicon-containing gas soaking process, to prevent the 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
1Reliability
If a polysilicon gate electrode is used with doped impurities to adjust work function, then the work function can be adjusted to the band-edge of silicon, but carrier depletion effect occurs increasing effective gate dielectric thickness
Solution Approach 1:
A silicon-containing intermixing layer is introduced as an intermediary between the gate dielectric and the work function layer. This intermediate layer prevents carrier depletion by providing a buffer zone that reduces the electric field effect on carriers in the gate dielectric, thereby maintaining proper gate control without requiring heavy doping of the polysilicon gate.
Solution Approach 2:
The gate stack is segmented into multiple functional layers: gate dielectric, silicon-containing intermixing layer, work function layer, and capping layer. This segmentation allows each layer to perform its specific function independently, with the silicon-containing layer specifically addressing the carrier depletion issue while the work function layer handles work function adjustment.
2Object-affected harmful factors
If metal gate electrodes are formed to solve poly depletion problem, then carrier depletion is eliminated, but multiple layers are required to meet NMOS and PMOS band-edge work function requirements
Solution Approach 1:
The silicon-containing intermixing layer serves multiple functions simultaneously: it prevents carrier depletion effects, blocks oxygen diffusion into the work function layer, and blocks metal diffusion from the work function layer. This multi-functionality reduces the need for separate dedicated layers for each function, simplifying the overall gate structure compared to conventional metal gates.
3Stability of the object's composition
If work function layer is exposed to oxygen during processing, then oxygen can diffuse into the work function layer causing work function instability, but preventing exposure requires additional blocking layers
Solution Approach 1:
The silicon-containing intermixing layer acts as an oxygen diffusion barrier, serving as an intermediary that protects the work function layer from oxygen exposure during subsequent processing steps. This intermediate blocking layer is more effective than conventional approaches because it is integrated into the gate stack formation process rather than added as a separate subsequent step.
4Object-generated harmful factors
If capping layer is deposited over work function layer, then metal diffusion is partially blocked, but oxygen can still diffuse into the work function layer from the capping layer interface
Solution Approach 1:
Instead of placing the oxygen barrier at the top interface (between capping layer and work function layer), the silicon-containing intermixing layer is positioned at the bottom interface (between gate dielectric and work function layer). This inverted approach effectively blocks oxygen diffusion from the gate dielectric side, complementing the capping layer's metal diffusion blocking function.
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 silicon-containing intermixing layer effectively blocks the diffusion of oxygen and metal
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.