Metal Gate Contact Structure With Embedded Conductive Layer
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Solution Overview
Problem
The challenge in forming contact features on metal gates during semiconductor device fabrication is the high resistance at the interface between the contact feature and the metal gate, which is difficult to control due to reduced feature sizes and the presence of multiple work-function metal layers.
Innovation Solution
The solution involves forming a conductive layer on the top surface of the metal gate structure, with a portion of the conductive layer embedded below the top surface of the metal gate, to reduce contact resistance. This conductive layer is formed using a cyclic deposition process with multiple gaseous species, ensuring self-alignment with the metal gate layers and improving bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If contact features are formed directly on metal gates with multiple work-function layers, then device scaling is achieved, but contact resistance becomes high and difficult to control
Solution Approach 1:
A conductive layer is introduced as an intermediary between the contact feature and the metal gate structure. This conductive layer replaces the high-resistance work-function metal layers at the contact interface, providing a low-resistance pathway while allowing the metal gate to maintain its original work-function layers for proper transistor operation. The conductive layer acts as a mediator that decouples the conflicting requirements of low contact resistance and proper gate function.
Solution Approach 2:
The gate structure is segmented into two functional parts: the metal gate structure with work-function layers that maintains proper transistor threshold voltage, and the conductive layer that provides low-resistance contact. This segmentation allows each layer to be optimized for its specific function without compromising the other, resolving the contradiction between device scaling and contact resistance control.
2Reliability
If multiple work-function metal layers are used in metal gate structures, then device performance is improved, but interface resistance with contact features increases
Solution Approach 1:
Different regions of the gate structure are assigned different material properties. The bulk metal gate structure retains its multiple work-function metal layers for optimal device performance and threshold voltage control, while the contact interface region is replaced with a highly conductive material to minimize interface resistance. This local differentiation allows simultaneous optimization of both device performance and contact properties.
Solution Approach 2:
The conductive layer serves as an intermediary that interfaces between the contact feature and the metal gate structure. It provides a low-resistance pathway for current flow while allowing the underlying metal gate structure to maintain its complex multi-layer work-function architecture for proper transistor operation.
3Productivity
If feature sizes are reduced for scaling, then production efficiency increases, but control of contact resistance becomes more difficult
Solution Approach 1:
The conductive layer acts as a buffer that decouples the contact resistance from the scaling process. By introducing this intermediate layer with inherently low resistance, the system becomes less sensitive to dimensional variations and material property changes that occur during scaling, thereby maintaining better control over contact resistance despite reduced feature sizes.
Solution Approach 2:
The introduction of the conductive layer changes the electrical parameters at the contact interface. By selecting a material with vastly superior conductivity compared to the work-function metal layers, the system transitions from a high-resistance interface to a low-resistance interface, making the contact resistance less critical and easier to control even as dimensions shrink.
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 reduces the contact resistance at the interface between the metal gate and the contact feature, enhancing the overall performance of the semiconductor device by improving electrical properties and controlling misalignment effects.
Implementation Method 1
The conductive layer is formed using a cyclic deposition process with multiple gaseous species
Data Source
AI summary
A semiconductor structure includes a metal gate structure having a gate dielectric layer and a gate electrode. A topmost surface of the gate dielectric layer is above a topmost surface of the gate electrode. The semiconductor structure further includes a conductive layer disposed on the gate electrode of the metal gate structure, the conductive layer having a bottom portion disposed laterally between sidewalls of the gate dielectric layer and a top portion disposed above the topmost surface of the gate dielectric layer. The semiconductor structure further includes a contact feature in direct contact with the top portion of the conductive layer.