Protective Work-Function Layer for 3D Transistor Interconnects
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Solution Overview
Problem
In 3D integrated circuits, forming conductive interconnects between stacked transistors is challenging due to issues with protecting sensitive materials like high-k gate dielectrics and source/drain regions during vertical etching, which can lead to integrity loss and performance degradation.
Innovation Solution
A protective layer is deposited over sensitive areas to shield them during vertical etching, and this layer is transformed into a work function metal, remaining intact to provide both protection and performance tuning, allowing for efficient conductive interconnect formation between upper and lower transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective layer is deposited over sensitive areas to shield them during vertical etching, then the integrity of sensitive materials is maintained, but the process complexity increases
Solution Approach 1:
The protective layer is designed to serve dual functions: protecting sensitive materials during etching and acting as a work function metal for transistor operation. This multi-functionality reduces the need for separate protective and functional layers, thereby managing process complexity while maintaining material integrity
Solution Approach 2:
The protective layer undergoes transformation through annealing or other thermal processes that change its physical and chemical properties, converting it from a protective coating to a functional work function metal with appropriate electrical characteristics
2Device complexity
If the protective layer is removed after etching, then the structure is simplified, but the sensitive materials lose their protection and integrity deteriorates
Solution Approach 1:
The protective layer remains in the final structure to serve as work function metal, eliminating the need for removal and subsequent re-protection steps. This maintains both structural simplicity and continuous protection of sensitive materials
Solution Approach 2:
The protective layer serves itself by transitioning from a protective role to a functional electronic role, eliminating the need for separate protective and functional components and their associated processing steps
3Ease of manufacture
If conventional protective layers are used without secondary function, then the manufacturing process is straightforward, but additional materials and steps are required for work function
Solution Approach 1:
A single material layer performs both protection during manufacturing and provides work function in the operational device, reducing the total number of material layers from two (protective + work function) to one (dual-function), thereby simplifying manufacturing
Solution Approach 2:
The protective layer and work function layer are merged into a single component that performs both functions sequentially, reducing material quantity and simplifying the manufacturing process while maintaining all necessary 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 protects sensitive materials during interconnect formation, maintaining their integrity and enhancing transistor performance by using a multifunctional protective layer that also serves as a work function metal.
Implementation Method 1
the protective layer is formed by deposition of reactive semiconductor and metal material layers which are subsequently transformed into a work function metal or work function metal-containing compound
Data Source
AI summary
Stacked transistor structures having a conductive interconnect between upper and lower transistors. In an embodiment, the interconnect is formed by first provisioning a protective layer over an area to be protected (gate dielectric or other sensitive material) of upper transistor, and then etching material adjacent and below the protected area to expose an underlying contact point of lower transistor. A metal is deposited into the void created by the etch to provide the interconnect. The protective layer is resistant to the etch process and is preserved in the structure, and in some cases may be utilized as a work-function metal. In an embodiment, the protective layer is formed by deposition of reactive semiconductor and metal material layers which are subsequently transformed into a work function metal or work function metal-containing compound. A remnant of unreacted reactive semiconductor material may be left in structure and collinear with protective layer.