Multi-Workfunction Gate Sections for Threshold Voltage Tuning

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Solution Overview

Problem

Current semiconductor devices face challenges in scaling and optimizing threshold voltage levels due to limitations in multi-level work function configurations, which affect the performance and efficiency of integrated circuits.

Innovation Solution

The implementation of semiconductor devices with multiple gate sections having different workfunction levels, achieved through the deposition of metal gate layers with varying workfunction levels and thicknesses, allows for the tuning of threshold voltage levels by configuring the percentage of gate length occupied by each workfunction level.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a single metal gate layer with uniform workfunction is used, then the device structure is simple and easy to manufacture, but the threshold voltage cannot be tuned to multiple levels

Engineering Contradiction:

Improvethreshold voltage tuning capabilityVSAvoidgate structure complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The gate is divided into multiple sections along the channel length, with each section having a different metal layer and workfunction level. This segmentation enables different threshold voltage regions within a single device, allowing tuning of overall threshold voltage by adjusting the proportion of each gate section while maintaining a manageable structured complexity through modular design

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the gate are assigned different metal materials with specific workfunction levels (e.g., tungsten for higher workfunction, molybdenum for lower workfunction) to create local variations in electrical characteristics. This local quality differentiation enables precise control over threshold voltage by optimizing the spatial distribution of workfunction levels across the gate length

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

If multiple metal gate layers with different workfunction levels are deposited, then threshold voltage can be tuned precisely, but the manufacturing process becomes more complex

Engineering Contradiction:

Improvethreshold voltage control precisionVSAvoidfabrication process simplicity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

Metal layers with different workfunction levels are deposited in a predetermined sequence before final gate formation, with each metal layer's thickness and position pre-configured to achieve the desired threshold voltage. This preliminary action allows threshold voltage tuning to be built into the structure during fabrication rather than requiring post-processing adjustment, improving manufacturing precision while managing process complexity through planned deposition sequences

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The gate structure employs composite metal layers combining different materials (e.g., tungsten, molybdenum, tungsten silicide) with distinct workfunction properties. These composite materials enable precise threshold voltage control by leveraging the complementary electrical characteristics of different metals, achieving high manufacturing precision through material composition optimization

Inventive Principle:

Principle #40Composite materials

3Power

If the gate length is increased to improve device performance, then the drive current increases, but the device area and scaling are adversely affected

Engineering Contradiction:

Improvedrive currentVSAvoiddevice area

Core Design Contradiction:

PowerVSArea of stationary object

Solution Approach 1:

Different gate sections are assigned different workfunction levels to create local variations in carrier inversion and current flow. By optimizing the workfunction distribution across gate sections, the device achieves enhanced drive current through improved carrier control in critical regions without requiring a proportional increase in overall gate length, thus maintaining compact device area while improving power characteristics

Inventive Principle:

Principle #3Local 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

This approach enables the fabrication of semiconductor devices with tailored threshold voltage levels, improving the performance and efficiency of integrated circuits by allowing for precise control over the drive current and voltage characteristics.

Implementation Method 1

The metal gate has a first gate section with a first workfunction and a first thickness and a second gate section with a second workfunction and a second thickness

Methodology Applied

Scientific EffectPhysical Vapour Deposition: Physical Vapour Deposition

Data Source

PatentUS9929245B2Semiconductor structures and methods for multi-level work function

Publication Date: 2018.03.27 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Semiconductor devices and methods for forming semiconductor devices are provided. A vertical channel structure extends from a substrate and is formed as a channel between a source region and a drain region. A first metal gate surrounds a portion of the vertical channel structure and has a gate length. The first metal gate has a first gate section with a first workfunction and a first thickness. The first metal gate also has a second gate section with a second workfunction and a second thickness. The first thickness is different from the second thickness, and the sum of the first thickness and the second thickness is equal to the gate length. A ratio of the first thickness to the second thickness is chosen to achieve a desired threshold voltage level for the semiconductor device.