Metal Gate Electrode Sacrificial Layer Process
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Parasitic gate capacitance between a gate electrode and a contact in semiconductor devices decreases device speed, and reducing the polysilicon thickness too much results in silicide contacting the underlying gate dielectric, leading to undesirable threshold voltage.
Innovation Solution
A process involving sacrificial layers, such as a nitride and polysilicon layers, is used to protect the metal electrode during patterning and silicidation, allowing for reduced parasitic gate capacitance without silicide contact with the gate dielectric, by forming spacers with a height greater than the metal electrode and removing these layers before forming contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the polysilicon thickness is reduced to decrease parasitic gate capacitance, then the device speed is improved, but the polysilicon is consumed during silicidation and silicide contacts the underlying gate dielectric causing undesirable threshold voltage
Solution Approach 1:
A sacrificial layer is formed over the gate electrode before the silicidation process. This preliminary protective layer prevents the silicide from contacting the gate dielectric during subsequent processing steps, allowing the polysilicon to be reduced in thickness without causing threshold voltage shifts.
Solution Approach 2:
The sacrificial layer acts as an intermediary between the silicide and the gate dielectric. It temporarily occupies the space that would otherwise be occupied by thin polysilicon, preventing harmful contact while allowing the desired thin gate structure to be formed. The sacrificial layer is later removed after serving its protective function.
2Object-generated harmful factors
If the polysilicon thickness is reduced to decrease parasitic gate capacitance, then the parasitic gate capacitance is decreased, but the gate electrode structure becomes unstable and may become silicide only
Solution Approach 1:
The sacrificial layer is deposited in advance over the gate electrode structure. This preliminary action provides a protective barrier that maintains the structural integrity of the gate electrode during the silicidation process, preventing complete consumption of the polysilicon and maintaining compositional stability.
Solution Approach 2:
The sacrificial layer is a temporary, disposable structure used only during the fabrication process. It is intentionally designed to be removed after serving its protective function, allowing the gate electrode to maintain its desired thin composition without the long-term presence of additional material layers.
3Reliability
If a common gate electrode structure with polysilicon and silicide is used, then the gate electrode provides good electrical properties, but the silicide contacts the underlying gate dielectric causing undesirable threshold voltage
Solution Approach 1:
The sacrificial layer serves as an intermediary barrier between the silicide and the gate dielectric. It allows the silicide to be formed over the gate electrode for good electrical properties while preventing direct contact with the gate dielectric that would cause threshold voltage shifts. The sacrificial layer is later removed after contact formation.
Solution Approach 2:
The sacrificial layer is formed in advance to establish a protective barrier before silicidation. This preliminary protective structure enables the formation of a stable gate electrode with silicide for improved electrical properties while preventing the harmful side effect of threshold voltage shift during the process.
Data Source
AI summary
A method for forming a semiconductor device includes forming a gate dielectric over a substrate, forming a metal electrode over the gate dielectric, forming a first sacrificial layer which includes polysilicon or a metal over the metal electrode, removing the first sacrificial layer, and forming a gate electrode contact over and coupled to the metal electrode.