Stressed Tri-Gate Transistors Using Complementary Gate Fill Materials
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Solution Overview
Problem
As gate lengths decrease, it becomes challenging to fabricate silicon MOSFET devices with low source-to-drain leakage in the off-state, and existing technologies struggle to enhance charge carrier mobility effectively in CMOS devices, which limits the drive current and operating speed of transistors.
Innovation Solution
The use of stressed channels in CMOS devices with complementary gate fill materials, such as copper for tensile stress in N-type devices and tungsten for compressive stress in P-type devices, to improve charge carrier mobility by imparting stress perpendicular to the gate plane and in the current flow direction, combined with a shallow trench isolation layer to prevent leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If gate length is decreased to improve device scaling, then device density and integration are improved, but source-to-drain leakage current increases
Solution Approach 1:
The patent applies different stress conditions to different regions of the transistor channel. N-type devices receive tensile stress while P-type devices receive compressive stress through selective gate fill material placement. This localized differentiation improves carrier mobility in each device type while maintaining low leakage through the tri-gate structure.
Solution Approach 2:
The patent uses composite gate fill materials (copper for tensile stress, tungsten for compressive stress) combined with tri-gate structure and shallow trench isolation to achieve both low leakage and high carrier mobility. The combination of these materials and structures resolves the contradiction between scaling and leakage control.
2Ease of manufacture
If conventional gate structures are used in tri-gate devices, then fabrication is simpler, but carrier mobility and drive current are limited
Solution Approach 1:
The patent changes the stress parameter in the channel by introducing gate fill materials with different intrinsic stress properties. Copper provides tensile stress while tungsten provides compressive stress. This parameter change significantly improves carrier mobility without fundamentally altering the tri-gate fabrication process.
3Productivity
If high drive current is achieved through device scaling, then operating speed improves, but leakage current increases
Solution Approach 1:
The patent applies stress locally to the channel region through gate fill materials, improving carrier mobility and thus drive current. Simultaneously, the tri-gate structure provides effective leakage control. The local stress application achieves high drive current without proportionally increasing leakage.
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 significantly increases carrier mobility and drive current in both N-type and P-type devices, reducing leakage current and power consumption while maintaining a high operating frequency, by strategically applying tensile and compressive stresses through the selection of metallic gate fill materials and deposition processes.
Implementation Method 1
The gate metal fill that expands, i.e., gate metal fill made of copper, exerts the desired tensile stress upon an N-type tri-gate channel. Metal fill that shrinks, i.e. tungsten, imparts the desired compressive stress in the current flow direction to a P-type tri-gate structure.
Data Source
AI summary
Embodiments relate to an improved tri-gate device having gate metal fills, providing compressive or tensile stress upon at least a portion of the tri-gate transistor, thereby increasing the carrier mobility and operating frequency. Embodiments also contemplate method for use of the improved tri-gate device.