Ferroelectric Capacitor Integration in Replacement Gate Structure
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Solution Overview
Problem
The integration of a ferroelectric capacitor in a replacement gate process flow is challenging due to limited space and shorting issues, hindering the further improvement of metal oxide semiconductor transistors (MOSFETs) performance beyond traditional scaling limits.
Innovation Solution
A semiconductor structure is formed with a recessed functional gate structure to create a capacitor cavity, where a ferroelectric capacitor is integrated, comprising a bottom electrode structure, a U-shaped ferroelectric material liner, and a top electrode structure, with the bottom electrode entirely beneath the ferroelectric liner, allowing for effective integration without space or shorting issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ferroelectric capacitor is integrated in a replacement gate process flow using existing technology, then the capacitance and threshold voltage swings of MOSFETs can be enhanced, but limited space and shorting issues arise that hinder device formation
Solution Approach 1:
The device is segmented into distinct functional regions: the ferroelectric capacitor is separated from the MOSFET channel by isolating it within a trench structure. This segmentation allows the capacitor to be formed independently above the gate electrode without interfering with the underlying transistor formation, thus resolving the shorting issue while maintaining enhanced electrical performance
Solution Approach 2:
The ferroelectric capacitor is positioned in the vertical dimension above the gate electrode rather than in the lateral plane alongside other devices. By utilizing the vertical space above the gate structure, the design accommodates the capacitor without consuming additional lateral device formation space, thereby resolving the limited space constraint
2Productivity
If device scaling is continued to improve MOSFET performance, then transistor density increases, but traditional scaling limits are reached that prevent further performance improvement
Solution Approach 1:
The gate electrode structure serves multiple functions: it acts as the control electrode for the MOSFET channel below while simultaneously serving as the bottom electrode for the ferroelectric capacitor above. This multi-functionality allows the same structural element to contribute to both transistor operation and capacitor function, enabling performance enhancement without additional scaling complexity
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 the integration of a ferroelectric capacitor in a replacement gate process flow, enhancing the capacitance and threshold voltage swings of MOSFETs, thus overcoming the limitations of traditional scaling and improving performance beyond current CMOS technology.
Implementation Method 1
Use of ferroelectric materials with negative capacitance such as, for example, HfZrO, in series with the gate stack of a MOSFET can dramatically increase the total capacitance of the MOSFET and can achieve steep threshold voltage swings.
Data Source
AI summary
A replacement gate structure (i.e., functional gate structure) is formed and recessed to provide a capacitor cavity located above the recessed functional gate structure. A ferroelectric capacitor is formed in the capacitor cavity and includes a bottom electrode structure, a U-shaped ferroelectric material liner and a top electrode structure. The bottom electrode structure has a topmost surface that does not extend above the U-shaped ferroelectric material liner. A contact structure is formed above and in contact with the U-shaped ferroelectric material liner and the top electrode structure of the ferroelectric capacitor.