Conductive Gate Cap Structure for Lower Contact Resistance
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Solution Overview
Problem
As transistors are miniaturized to achieve faster speeds and lower power consumption, the contact areas between metal gates and gate contact plugs become smaller, leading to increased contact resistance due to higher resistance at the interface.
Innovation Solution
A conductive capping layer with higher conductivity than the work function layer is formed on the replacement gate stack, reducing contact resistance by protecting the underlying layers during the formation of gate contact plugs and maintaining high conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If transistors are miniaturized to achieve faster speeds and lower power consumption, then speed and power efficiency are improved, but contact resistance increases due to smaller contact areas
Solution Approach 1:
The gate contact structure is segmented into multiple conductive layers (first conductive layer, second conductive layer, third conductive layer) with different materials and properties. Each layer serves a specific function: the first layer provides high conductivity, the second layer offers work function adjustment, and the third layer ensures adhesion and protection. This segmentation allows optimization of each layer's properties to collectively reduce contact resistance while maintaining compatibility with miniaturized transistor structures.
Solution Approach 2:
The gate contact structure employs composite materials consisting of multiple conductive layers with different material compositions. The first conductive layer may use materials like tungsten or cobalt for high conductivity, the second layer uses materials like titanium nitride or tantalum nitride for work function control, and the third layer uses adhesion-promoting materials. This composite structure combines the advantages of different materials to simultaneously achieve low contact resistance, proper work function, and structural stability in miniaturized transistors.
2Productivity
If contact area is reduced to enable higher integration, then degree of integration is improved, but contact resistance increases at the interface
Solution Approach 1:
The gate contact structure applies local quality by having different conductive layers with specialized properties at specific locations and interfaces. The first conductive layer with highest conductivity is positioned at the contact interface to minimize contact resistance, while the second and third layers provide localized work function adjustment and adhesion enhancement respectively. This localized optimization of material properties allows the structure to maintain low contact resistance even when the overall contact area is reduced for higher integration density.
3Reliability
If a conductive capping layer is formed on the gate stack, then contact resistance is reduced and protection is provided, but device complexity increases
Solution Approach 1:
The multi-layer conductive capping structure serves multiple functions simultaneously: the first conductive layer provides high electrical conductivity to reduce contact resistance, the second layer adjusts the work function to match the semiconductor material, the third layer ensures adhesion to underlying layers and provides physical protection. By combining multiple functions into a single integrated structure, the design achieves low contact resistance and protection without proportionally increasing device complexity, as each layer performs multiple roles.
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
The conductive capping layer effectively reduces contact resistance and prevents damage to the gate stacks during the formation of gate contact plugs, enhancing the performance and reliability of transistors.
Implementation Method 1
a conductive capping layer is formed on the replacement gate stack
Implementation Method 2
a conductive capping layer is formed on the replacement gate stack
Data Source
AI summary
A method includes removing a dummy gate stack to form a first trench between gate spacers, forming a replacement gate stack in the first trench, recessing the replacement gate stack to form a second trench between the gate spacers, selectively depositing a conductive capping layer in the second trench, forming a dielectric hard mask in the second trench and over the conductive capping layer, and etching the dielectric hard mask using an etching gas to form an opening in the dielectric hard mask. The replacement gate stack is revealed to the opening. The conductive capping layer is more resistant to the etching gas than the replacement gate stack. The method further comprises forming a gate contact plug over and contacting the conductive capping layer.