Lateral Expansion of Polysilicon Gate Spacer for Metal Stack Gap Fill
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Solution Overview
Problem
Conventional replacement metal gate (RMG) processes face difficulties in completely filling the metal gate stack as gate sizes decrease, limiting their effectiveness with increasing device scaling.
Innovation Solution
The method involves forming a replacement gate structure with a polysilicon layer, implanting atoms to expand the upper portion laterally, removing the polysilicon layer to create a gate cavity, and forming a metal gate stack within the cavity, ensuring the upper portion of the metal gate stack is wider than the lower portion, which facilitates better gap fill.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional replacement metal gate processes are used, then the process is simple and easy to manufacture, but the metal gate stack cannot be completely filled as gate sizes decrease
Solution Approach 1:
A polysilicon layer is deposited and patterned before the metal gate stack formation to create a preliminary structure that defines the gate region. This preliminary polysilicon layer serves as a template that ensures complete metal stack filling by pre-establishing the gate footprint and preventing void formation during subsequent metal deposition processes.
Solution Approach 2:
The polysilicon layer acts as an intermediary material between the semiconductor substrate and the metal gate stack. It facilitates complete metal stack filling by providing a stable, patterned interface that guides metal deposition and prevents voids, while being selectively removable afterward to complete the gate structure formation.
2Productivity
If gate sizes are decreased for scaling, then device density increases, but conventional processes become even more limited in filling the metal gate stack
Solution Approach 1:
The polysilicon layer is formed in advance with precise patterning that accounts for scaled dimensions. This preliminary structure ensures that even at reduced gate sizes, the metal stack will be completely filled by providing a pre-defined template that prevents void formation during metal deposition, thereby maintaining manufacturing precision while enabling higher device density.
Solution Approach 2:
The process utilizes controlled deposition parameters and selective removal conditions for the polysilicon layer. By adjusting deposition thickness, pattern dimensions, and removal selectivity, the process maintains complete metal stack filling even as gate size parameters are reduced for scaling, thereby preserving manufacturing precision across different device densities.
3Manufacturing precision
If the upper portion of the polysilicon layer is expanded laterally, then gap fill of the metal stack is improved, but the process requires additional implantation steps
Solution Approach 1:
The polysilicon layer is deposited with intentionally extended lateral dimensions beyond the final gate boundaries. This preliminary over-extension ensures that when the metal stack is deposited, the polysilicon provides sufficient lateral coverage to guide complete filling and prevent voids at the gate edges, thereby improving gap fill quality through advance preparation.
Solution Approach 2:
The laterally expanded polysilicon layer serves as an intermediary structure that temporarily provides extended coverage during metal deposition. It mediates the gap fill process by ensuring continuous material presence at critical regions, preventing void formation, and then is selectively removed to achieve the final gate structure with improved fill quality.
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 enhances the ability to fill the metal gate stack effectively, preventing voids and improving the reliability of the semiconductor device by expanding the upper portion of the polysilicon layer and corresponding gate spacer, allowing for better metal deposition and contact with the sidewalls.
Implementation Method 1
Atoms are implanted in an upper portion of the polysilicon layer. The implanting expands the upper portion of the polysilicon layer and a corresponding upper portion of the gate spacer in at least a lateral direction
Data Source
AI summary
A method for fabricating a semiconductor device comprises forming a replacement gate structure on a semiconductor layer of a substrate. The replacement gate structure at least including a polysilicon layer. After forming the replacement gate structure, a gate spacer is formed on the replacement gate structure. Atoms are implanted in an upper portion of the polysilicon layer. The implanting expands the upper portion of the polysilicon layer and a corresponding upper portion of the gate spacer in at least a lateral direction beyond a lower portion of the polysilicon layer and a lower portion of the spacer, respectively. After the atoms have been implanted, the polysilicon layer is removed to form a gate cavity. A metal gate stack is formed within the gate cavity. The metal gate stack includes an upper portion having a width that is greater than a width of a lower portion of the metal gate stack.