Alternating Metal Nitride Gate Stack for Work Function Tuning
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Solution Overview
Problem
As semiconductor devices continue to shrink in feature size, the integration density of electronic components increases, but this leads to challenges in forming effective gate structures that require precise control of work function layers to optimize device performance.
Innovation Solution
The formation of a gate structure with a work function layer composed of alternating layers of different metal nitrides, such as TiN and TaN, allows for tuning the work function by adjusting the ratio of these metals, enabling precise control over the electrical properties of the gate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the minimum feature size is reduced to increase integration density, then more components can be integrated into a given area, but the precision and control of gate structure formation becomes more difficult
Solution Approach 1:
The gate structure is divided into multiple distinct layers including a gate dielectric layer and a work function layer with alternating high-k and low-k metal nitride layers. This segmentation allows each layer to be formed and controlled independently, enabling precise work function tuning even as overall device dimensions shrink and integration density increases.
Solution Approach 2:
The work function layer incorporates alternating layers of different metal nitrides (such as TiN and TaN) with different dielectric constants. By locally varying the material composition and thickness ratios of these alternating layers, the work function can be precisely tuned to specific values needed for different transistor types (nMOS or pMOS), providing local quality control that maintains manufacturing precision despite reduced feature sizes.
2Ease of manufacture
If a single-layer work function layer is used, then the gate structure is simpler to manufacture, but the work function cannot be precisely tuned to meet different device requirements
Solution Approach 1:
The work function layer is constructed as a composite structure with alternating layers of high-k metal nitride (e.g., TaN) and low-k metal nitride (e.g., TiN). This composite material approach enables continuous tuning of the work function by adjusting the thickness ratios of the alternating layers, while still using standard sputtering deposition processes that are compatible with existing manufacturing lines, thus maintaining ease of manufacture while achieving precise work function control.
Solution Approach 2:
The work function is tuned by changing the physical parameters of the alternating layers, specifically the thickness of each layer type. By varying the thickness ratio of high-k to low-k metal nitride layers, the effective work function can be continuously adjusted. This parameter-based control method allows precise tailoring of electrical characteristics without requiring fundamentally different manufacturing processes.
3Manufacturing precision
If alternating layers of different metal nitrides are used to tune work function, then precise electrical property control is achieved, but the manufacturing process becomes more complex
Solution Approach 1:
The work function layer is formed by repeating a periodic deposition sequence of high-k metal nitride and low-k metal nitride layers multiple times. This periodic action creates the alternating layer structure needed for work function tuning. The process uses standard sputtering techniques with alternating target materials, and the repetition of the deposition cycle allows precise control of layer thicknesses and compositions while maintaining process compatibility with existing manufacturing equipment.
Data Source
AI summary
A semiconductor device and a method of forming the same are provided. The semiconductor device includes a gate stack over an active region of a substrate. The gate stack includes a gate dielectric layer and a first work function layer over the gate dielectric layer. The first work function layer includes a plurality of first layers and a plurality of second layers arranged in an alternating manner over the gate dielectric layer. The plurality of first layers include a first material. The plurality of second layers include a second material different from the first material.