Self-Aligned Contact Stop Layer for Replacement Metal Gate Isolation
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Solution Overview
Problem
The integration of metal gate electrodes in semiconductor devices poses challenges, such as degradation during high-temperature annealing and compatibility issues with self-aligned contact formation, particularly at small gate pitches, leading to poor electrical isolation and increased leakage current.
Innovation Solution
A method integrating self-aligned contacts with replacement metal gate electrodes, involving the formation of a removable polysilicon gate, a dielectric SAC stop layer, and transforming the metal gate into a dielectric layer, while using spacers and a hardmask to enable precise contact formation without degrading the gate dielectric.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If metal gate electrodes are used to improve drive current, then drive current increases, but the metal gate degrades during high-temperature annealing and interacts with gate dielectric
Solution Approach 1:
The gate electrode is segmented into two parts: a removable polysilicon gate used during high-temperature processing, and a metal replacement gate inserted afterward. This segmentation allows the polysilicon to withstand annealing temperatures while the metal gate provides superior electrical performance in the final device.
Solution Approach 2:
A polysilicon gate is formed preliminarily to enable high-temperature annealing processes. After the annealing is complete, the polysilicon gate is removed and replaced with a metal gate, which then provides the desired high drive current without exposure to degrading temperatures.
2Ease of manufacture
If conventional self-aligned contact methodology is used with metal gates, then contact formation is simplified, but electrical isolation between gate line and contact deteriorates
Solution Approach 1:
A dielectric layer is introduced as an intermediary between the metal gate electrode and the contact. This dielectric layer acts as a mediator that provides the necessary electrical isolation, preventing direct contact between the conductive gate and contact while maintaining the self-aligned fabrication advantage.
3Productivity
If gate pitch is reduced to increase integration density, then number of circuit elements increases, but sufficient isolation between gate and contact cannot be maintained
Solution Approach 1:
The introduction of the dielectric layer changes the electrical parameters of the gate-contact interface. By adding this intermediate layer with different dielectric properties, sufficient electrical isolation is achieved even when the physical dimensions are scaled down to maintain high integration density.
4Reliability
If polysilicon gate is used during high-temperature annealing, then source/drain implants are activated properly, but subsequent metal gate formation requires additional processing steps
Solution Approach 1:
The polysilicon gate is discarded after serving its temporary purpose of enabling high-temperature annealing. It is then recovered or replaced by inserting a metal gate in the same location, allowing the process to benefit from both polysilicon's thermal stability and metal's electrical performance.
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 drive current and maintains low leakage by ensuring good electrical isolation between gate lines and contacts, even at small pitches, without degrading the gate dielectric, thus improving transistor performance.
Implementation Method 1
transforming the upper portion of the metal into a dielectric layer by oxidation or nitridation, or fluorination
Implementation Method 2
transforming the upper portion of the metal into a dielectric layer by oxidation or nitridation, or fluorination
Implementation Method 3
transforming the upper portion of the metal into a dielectric layer by oxidation or nitridation, or fluorination
Implementation Method 4
anodizing an upper portion of the metal, which comprises aluminum, to form aluminum oxide (Al2O3)
Data Source
AI summary
Semiconductor devices with replacement gate electrodes and integrated self aligned contacts are formed with enhanced gate dielectric layers and improved electrical isolation properties between the gate line and a contact. Embodiments include forming a removable gate electrode on a substrate, forming a self aligned contact stop layer over the removable gate electrode and the substrate, removing a portion of the self aligned contact stop layer over the removable gate electrode and the electrode itself leaving an opening, forming a replacement gate electrode of metal, in the opening, transforming an upper portion of the metal into a dielectric layer, and forming a self aligned contact. Embodiments include forming the contact stop layer of a dielectric material, e.g., a hafnium oxide, an aluminum oxide, or a silicon carbide and transforming the upper portion of the metal into a dielectric layer by oxidation, fluorination, or nitridation. Embodiments also include forming a hardmask layer over the removable gate electrode to protect the electrode during silicidation in source/drain regions of the semiconductor device.