Isolation Transistor Work Function Engineering for Leakage Reduction
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Solution Overview
Problem
In advanced semiconductor technology, the reduced geometry and pitch between devices lead to interference issues, limiting device performance and scalability, as existing isolation methods either rely on non-self-aligned physical disconnection or tie-off devices with similar charge carrier types, resulting in leakage currents.
Innovation Solution
The method involves altering the work function material of isolation transistors to create a difference in threshold voltage, reducing leakage current and providing effective isolation between adjacent devices without physical disconnection, using existing materials and processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If device geometry and pitch are reduced to increase device density, then device integration density is improved, but device interference and performance degradation worsen
Solution Approach 1:
The patent applies local quality by creating distinct work function material configurations in different regions: active transistors have work function materials optimized for low threshold voltage (e.g., titanium nitride), while isolation transistors have work function materials optimized for high threshold voltage (e.g., tungsten). This local differentiation enables adjacent devices to coexist at reduced pitch without interference, as the isolation devices' high threshold voltage prevents leakage currents that would otherwise affect neighboring active devices.
Solution Approach 2:
The patent implements parameter changes by modifying the work function of isolation transistor gate materials. By selecting work function materials with higher work functions (e.g., tungsten at 4.5 eV) for isolation devices compared to active devices (e.g., titanium nitride at 4.7 eV but with different stack configurations), the threshold voltage of isolation transistors is increased to >0.5V, effectively suppressing leakage currents and enabling closer device spacing.
2Reliability
If physical disconnection methods are used to isolate adjacent devices, then device isolation is improved, but manufacturing complexity and process alignment requirements worsen
Solution Approach 1:
The patent applies self-service by designing isolation transistors that automatically provide electrical isolation through their inherent high threshold voltage characteristics. The isolation devices self-regulate leakage currents without requiring external control circuits or complex physical disconnection structures. The work function material configuration inherently creates the isolation effect, eliminating the need for additional alignment-critical fabrication steps.
Solution Approach 2:
The patent replaces mechanical/physical disconnection methods with an electrical field-based isolation mechanism. Instead of using physical barriers or disconnected structures that require precise mechanical alignment, the invention uses work function material engineering to create electrical potential differences that suppress carrier flow. This substitution of physical isolation with electrical isolation simplifies the manufacturing process and reduces alignment requirements.
3Reliability
If tie-off devices with similar charge carrier types are used for isolation, then device isolation is attempted, but leakage currents increase
Solution Approach 1:
The patent resolves this contradiction by changing the threshold voltage parameter of isolation transistors to >0.5V through work function material selection. This parameter change creates a sufficient potential barrier that suppresses leakage currents even when isolation devices have similar charge carrier types to active devices. The high threshold voltage acts as an electrical barrier that prevents unwanted carrier flow while maintaining device structural similarity.
Solution Approach 2:
The patent applies preliminary anti-action by pre-configuring isolation transistors with work function materials that create high threshold voltages before any leakage current can develop. The work function material stack is designed during fabrication to inherently prevent leakage currents by establishing strong electrical barriers at the gate interface, countering the potential harmful effect of leakage before it can occur during device operation.
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
This approach enables reliable operation in reduced device geometries by reducing leakage current and improving electrical isolation between devices, allowing for efficient operation in advanced logic technologies like 7-nanometer logic and beyond.
Implementation Method 1
etching the first-type work function material of the isolation transistor to form a second-type work function material for the isolation transistor within the first-type region
Implementation Method 2
depositing a conductive fill material on the second-type work function material of the isolation transistor
Implementation Method 3
altering the work function material of isolation transistors to create a difference in threshold voltage, reducing leakage current
Data Source
AI summary
An integrated circuit (IC) device may include a first active transistor of a first-type in a first-type region. The first active transistor may have a first-type work function material and a low channel dopant concentration in an active portion of the first active transistor. The IC device may also include a first isolation transistor of the first-type in the first-type region. The second active transistor may have a second-type work function material and the low channel dopant concentration in an active portion of the first isolation transistor. The first isolation transistor may be arranged adjacent to the first active transistor.