Inverted Trapezoidal Gate Structure for Work Function Metal Deposition
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Solution Overview
Problem
Conventional polysilicon gates in semiconductor devices face issues such as boron penetration and depletion effects, leading to inferior performance and increased equivalent thickness of the gate dielectric layer, which complicates the fabrication of CMOS devices and requires stringent filling materials for work function metals.
Innovation Solution
A semiconductor device with an inverted trapezoidal gate structure is fabricated by forming a polysilicon gate with a dopant concentration gradually increasing from top to bottom, allowing for a larger aperture at the top and smaller aperture at the bottom of the gate trench, enabling stable voltage application and optimized device performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional polysilicon gates are used, then fabrication process is simple, but device performance deteriorates due to boron penetration and depletion effects
Solution Approach 1:
The patent changes the gate structure from conventional trapezoidal to inverted trapezoidal shape, and modifies the dopant concentration profile to be gradually increased from top to bottom. These parameter changes resolve the contradiction by enabling better metal layer deposition (improving manufacturability) while eliminating boron penetration and depletion effects (improving device performance and reliability).
2Reliability
If gate last process is used to replace polysilicon gate with work function metals, then gate capacitance improves, but fabrication complexity increases and filling material requirements become more stringent
Solution Approach 1:
The patent inverts the conventional gate structure geometry and the dopant concentration gradient. The inverted trapezoidal shape with larger top aperture and smaller bottom aperture, combined with reversed dopant profiling, simplifies the gate last process by making metal layer deposition easier while maintaining the required gate capacitance and work function matching for both NMOS and PMOS devices.
3Ease of manufacture
If conventional trapezoidal gate structure is used, then fabrication is straightforward, but metal layer deposition into gate trench is difficult
Solution Approach 1:
The patent employs an asymmetric inverted trapezoidal gate structure where the top aperture is deliberately made larger than the bottom aperture. This asymmetric geometry, combined with the reversed dopant concentration profile (higher at bottom, lower at top), creates favorable deposition conditions that allow metal layers to be uniformly and completely filled into the gate trench, resolving the contradiction between straightforward fabrication and high deposition quality.
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 inverted trapezoidal gate structure facilitates better deposition of work function metal layers, resulting in improved device performance with enhanced reliability and efficiency, capable of forming logic or high-voltage elements with stable currents.
Implementation Method 1
a polysilicon gate structure is formed on the substrate, wherein the polysilicon gate structure includes a dopant having a concentration gradually increased from top to bottom
Data Source
AI summary
The present invention provides a semiconductor device and a method of fabricating the same, which includes a substrate, a gate structure, and a dielectric layer. The gate structure is disposed on the substrate and includes an inverted trapezoidal shape. The dielectric layer is disposed on the substrate, and the gate structure is disposed within the dielectric layer. The gate structure includes a metal gate structure or a polysilicon gate structure.