Cobalt Gate Fill with Glue Layer for Void-Resistant Threshold Control
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Solution Overview
Problem
As semiconductor integrated circuits scale down, reducing threshold voltage becomes challenging without adversely affecting other transistor aspects, particularly due to difficulties in increasing the thickness of the work function metal layer.
Innovation Solution
A gate structure using a cobalt fill instead of a tungsten fill, formed through a process involving Physical Vapor Deposition, Chemical Vapor Deposition, and Electro-Chemical Plating, with a glue layer for better adhesion, allows for a lower threshold voltage without increasing the work-function metal layer size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the work function metal layer is increased to reduce threshold voltage, then the threshold voltage is reduced, but the manufacturing complexity and difficulty increase due to scaling constraints
Solution Approach 1:
The patent changes the material parameter from traditional work function metals (titanium nitride, tungsten) to cobalt, which has different physical and chemical properties including lower contact resistance and better adhesion characteristics. This material substitution allows achieving the same electrical function with different structural requirements, resolving the contradiction between threshold voltage control and manufacturing complexity
Solution Approach 2:
The patent employs a multi-layer structure where a thin cobalt layer is deposited and then selectively removed in non-active areas through wet etching. This approach uses a temporary, easily removable material that simplifies the overall manufacturing process by enabling simple wet etch release rather than requiring complex patterning of the work function layer itself
2Reliability
If traditional work function metals are used in scaled-down transistors, then manufacturing processes are established, but void formation and high contact resistance occur
Solution Approach 1:
The patent changes the material properties by substituting cobalt for traditional work function metals. Cobalt exhibits superior adhesion to high-k dielectric materials and lower contact resistance, eliminating the void formation and high resistance issues associated with titanium nitride and tungsten in scaled devices
Solution Approach 2:
The patent creates a composite gate structure combining cobalt work function layer with high-k dielectric materials. This composite approach leverages the complementary properties of cobalt (low contact resistance, good adhesion) and high-k dielectrics (high breakdown voltage, electrical isolation) to achieve superior overall device performance without the harmful effects of traditional materials
3Reliability
If the work function metal layer size is increased to lower threshold voltage, then threshold voltage is reduced, but the device geometry and scaling are adversely affected
Solution Approach 1:
The patent changes the material composition to cobalt, which provides equivalent or superior electrical function at reduced thickness. This allows maintaining the required threshold voltage control while reducing the physical dimensions of the work function layer, thereby preserving device scaling and geometry
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 a lower threshold voltage with improved gate quality, reduced void formation, and lower contact resistance, effectively addressing the scaling challenges in transistor design.
Implementation Method 1
performing a first cobalt deposition process to form a cobalt layer within the trench
Implementation Method 2
performing a second cobalt deposition process to increase a thickness of the cobalt layer within the trench
Implementation Method 3
performing an electrochemical plating (ECP) process to fill the trench with cobalt
Data Source
AI summary
A method for forming a gate structure includes forming a trench within an interlayer dielectric layer (ILD) that is disposed on a semiconductor substrate, the trench exposing a top surface of the semiconductor substrate, forming an interfacial layer at a bottom of the trench, forming a dielectric layer within the trench, forming a work function metal layer on the dielectric layer, forming an in-situ nitride layer on the work function metal layer in the trench, performing a first cobalt deposition process to form a cobalt layer within the trench, performing a second cobalt deposition process to increase a thickness of the cobalt layer within the trench, and performing an electrochemical plating (ECP) process to fill the trench with cobalt.