Dual Work Function Buried Gate Transistor for GIDL Reduction
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Solution Overview
Problem
Buried gate-type transistors face challenges in reducing gate-induced drain leakage (GIDL) due to the large overlap area of metal gate electrodes with impurity regions, leading to increased leakage current and difficulty in improving performance.
Innovation Solution
A dual work function buried gate transistor design is implemented, featuring a high work-function barrier layer made of aluminum-containing titanium nitride and a low work-function barrier layer made of fluorine-free tungsten or titanium-based materials, with the low work-function layer overlapping with the source and drain regions to reduce GIDL, while maintaining low channel impurity dose and resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal gate electrode with high work function is used, then channel impurity dose decreases and leakage current reduces, but gate-induced drain leakage (GIDL) increases due to large overlap area with impurity regions
Solution Approach 1:
The gate electrode is divided into two regions with different work functions: a first gate region with high work function (4.5-5.5 eV) positioned away from impurity regions to reduce leakage current, and a second gate region with low work function (3.5-4.5 eV) positioned overlapping with impurity regions to reduce GIDL. This local differentiation of material properties resolves the contradiction by optimizing each region's function independently.
Solution Approach 2:
The gate electrode is segmented into multiple regions with different work functions, achieved through multi-layer structures (e.g., TiN/W/TiN, TiAlN/TiN/W) where different material layers provide different work function characteristics. This segmentation allows simultaneous optimization of leakage current and GIDL by assigning different functional properties to different parts of the gate.
2Ease of manufacture
If a single work function barrier layer is used, then manufacturing is simplified, but inability to simultaneously reduce leakage current and GIDL occurs
Solution Approach 1:
The gate electrode employs composite material structures combining multiple layers with different work functions (e.g., TiAlN/TiN/W, TiN/W/TiN). These composite structures integrate materials with complementary properties to simultaneously achieve low leakage current and low GIDL, resolving the limitation of single-material gates while maintaining compatibility with existing manufacturing processes.
Solution Approach 2:
The multi-layer gate structure serves multiple functions simultaneously: the high work function layers reduce leakage current, the low work function layers reduce GIDL, and the overall structure maintains compatibility with standard semiconductor fabrication processes. This multi-functionality resolves the contradiction between manufacturing simplicity and performance optimization.
Data Source
AI summary
A transistor includes: a source region and a drain region that are formed in a substrate to be spaced apart from each other; a trench formed in the substrate between the source region and the drain region; and a buried gate electrode inside the trench, wherein the buried gate electrode includes: a lower buried portion which includes a high work-function barrier layer including an aluminum-containing titanium nitride, and a first low-resistivity layer disposed over the high work-function barrier layer; and an upper buried portion which includes a low work-function barrier layer disposed over the lower buried portion and overlapping with the source region and the drain region, and a second low-resistivity layer disposed over the low work-function barrier layer.