Transistor Gate Work Function Control via Width-Selective Metal Diffusion
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Solution Overview
Problem
Existing methods for forming transistor gates with different work functions are limited in achieving precise control over threshold voltages and power consumption, as they often rely on varying materials or dopants, which can be inefficient and costly.
Innovation Solution
A method involving the formation of first and second transistor gates with different widths, where a material is deposited and etched to expose the conductive material of the narrower gate while leaving the wider gate covered, followed by in-situ plasma exposure to diffuse metal into the narrower gate, modifying its work function relative to the wider gate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If different gate materials or dopants are used to achieve different work functions, then transistor threshold voltages can be controlled, but manufacturing complexity and cost increase
Solution Approach 1:
The patent applies local quality by selectively modifying the work function of specific gate regions through targeted metal implantation. Different areas of the gate structure receive different metal treatments (e.g., tungsten, molybdenum, titanium) to create locally distinct work functions, enabling threshold voltage control without requiring entirely different gate materials across the device
Solution Approach 2:
The patent changes the work function parameter of existing gate structures through metal implantation and silicide formation processes. By controlling the type, concentration, and distribution of implanted metals, the work function can be precisely adjusted to achieve desired threshold voltages while maintaining the same base gate material composition
2Manufacturing precision
If metal implantation is used to modify work function, then precise threshold voltage control is achieved, but process steps and manufacturing complexity increase
Solution Approach 1:
The patent merges multiple process functions into integrated steps. The metal implantation process simultaneously achieves work function modification, threshold voltage control, and gate contact formation. Subsequent annealing steps combine silicide formation with stress engineering, reducing the total number of discrete process modules required
Solution Approach 2:
The patent uses intermediate metal layers (such as tungsten, molybdenum, or titanium) as mediators between the gate structure and the silicon substrate. These intermediate metals serve dual purposes: they modify the work function through controlled implantation and diffusion, and they form stable silicide compounds during annealing that provide both electrical contact and mechanical stress control
3Adaptability or versatility
If different metals or metal alloys are used in gate electrodes, then different work functions are achieved, but material selection and process control complexity increase
Solution Approach 1:
The patent employs universal metal implantation processes that can accommodate multiple metal types (tungsten, molybdenum, titanium, nickel, cobalt) using the same fundamental implantation and annealing equipment and methodology. This multi-functional approach allows a single process module to achieve work function control across a wide range of threshold voltage requirements without requiring dedicated process lines for each metal type
Solution Approach 2:
The patent creates composite gate structures by combining base gate materials with implanted metal atoms. The resulting composite structure exhibits tailored work function properties that differ from either component alone, enabling precise threshold voltage control. The composite nature also provides beneficial secondary effects such as stress engineering and diffusion barrier functionality
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 effectively creates transistor gates with distinct work functions, optimizing threshold voltages and reducing power consumption by allowing for tailored gate material modifications within the same processing chamber.
Implementation Method 1
subjecting the substrate to a plasma comprising a metal at a substrate temperature of at least 300°C to diffuse said metal into the conductive region of the transistor gate
Implementation Method 2
subjecting the substrate to a plasma comprising a metal
Data Source
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AI summary
A method of forming a plurality of transistor gates having at least two different work functions includes forming first and second transistor gates over a substrate having different widths, with the first width being narrower than the second width. A material is deposited over the substrate including over the first and second gates. Within an etch chamber, the material is etched from over both the first and second gates to expose conductive material of the first gate and to reduce thickness of the material received over the second gate yet leave the second gate covered by the material. In situ within the etch chamber after the etching, the substrate is subjected to a plasma comprising a metal at a substrate temperature of at least 300°C to diffuse said metal into the first gate to modify work function of the first gate as compared to work function of the second gate.