Asymmetric Work Function Metal Gate for Trench Filling
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Solution Overview
Problem
Conventional polysilicon gates in semiconductor devices face issues such as boron penetration and depletion, leading to reduced gate capacitance and performance, while work function metal layers struggle to fill trenches with smaller pitches, affecting device performance.
Innovation Solution
A semiconductor device with a metal gate featuring asymmetrical work function metal layers, including vertical and horizontal portions of different heights or U-shapes, formed through a process involving selective etching and deposition to ensure proper filling and performance in both larger and smaller transistor regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional polysilicon gates are used, then gate electrode fabrication is simplified, but boron penetration and depletion effects reduce gate capacitance and device performance
Solution Approach 1:
The patent changes the material parameter from polysilicon to work function metal (such as titanium nitride, tantalum nitride, or tungsten), fundamentally altering the electrical and physical properties of the gate electrode to eliminate boron penetration and depletion effects, thereby maintaining high gate capacitance and device performance
Solution Approach 2:
The patent employs a composite structure combining high-k dielectric material (such as hafnium oxide, silicon oxide, or silicon nitride) with work function metal layers, creating a metal-oxide-semiconductor (MOS) gate that integrates the advantages of both materials to achieve superior electrical characteristics
2Reliability
If multiple layers of work function metal layers are used, then gate performance is improved, but the layers cannot fill trenches with smaller pitches
Solution Approach 1:
The patent transitions from planar (2D) work function metal layers to three-dimensional (3D) conformal coating techniques, allowing the metal layers to uniformly cover trench walls and bottom surfaces, ensuring complete filling of narrow trenches while maintaining precise thickness control through atomic layer deposition or chemical vapor deposition processes
Solution Approach 2:
The patent implements a nested multi-layer structure where different work function metal layers are sequentially deposited within the same trench, with each layer conformally coating the previous layer and trench surfaces, enabling precise control of gate work function while ensuring complete trench filling even at small pitches
Data Source
AI summary
A semiconductor device includes a metal gate on a substrate, in which the metal gate includes a first work function metal (WFM) layer and the first WFM layer further includes a first vertical portion, a second vertical portion, wherein the first vertical portion and the second vertical portion comprise different heights, and a first horizontal portion connecting the first vertical portion and the second vertical portion.