Dummy Metal Feature Mitigates Galvanic Corrosion in Integrated Circuit Metallization
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Solution Overview
Problem
Integrated circuits face galvanic corrosion and metal void formation during fabrication, particularly in vias connecting to higher metal layers, due to electrical charge trapping and the limitations of tie-down diodes in handling high voltages in non-volatile memory devices.
Innovation Solution
Incorporating a dummy metal feature in the metallization stack, which is in electrical communication with functional vias but isolated from electrical current flow, effectively spreading the impact of galvanic corrosion over a larger area and mitigating metal void formation without the need for tie-down diodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a tie-down diode is used to release trapped electrical charges from isolated wells, then electrical charge accumulation is prevented, but the maximum voltage that can be introduced into the isolated well is limited to the voltage threshold of the diode, making programming of NVM devices impossible
Solution Approach 1:
The patent removes the tie-down diode from the isolated well structure entirely. Instead of using a diode to release trapped charges, the invention employs a dummy metal feature connected to a functional via that provides an alternative path for charge dissipation without imposing voltage threshold limitations, thereby enabling high-voltage NVM programming while preventing charge accumulation.
Solution Approach 2:
The dummy metal feature acts as an intermediary element between the isolated well and the ground. It provides a controlled interface for charge dissipation through the functional via, mediating the charge release process without the voltage threshold constraints of a diode, thus allowing both charge prevention and high-voltage operation.
2Ease of manufacture
If metal features are formed in electrical connection with isolated p-wells during BEOL fabrication, then interconnect functionality is achieved, but galvanic corrosion occurs through solvent circuits during cleaning, leading to metal void formation in affected metal features
Solution Approach 1:
The patent converts the harmful effect of galvanic corrosion by introducing a dummy metal feature that deliberately provides a preferred corrosion path. This dummy feature acts as a sacrificial element that absorbs the corrosive effects through the solvent circuit, protecting the functional metal features from metal void formation while maintaining interconnect functionality.
Solution Approach 2:
The dummy metal feature serves as an intermediary that intercepts the galvanic corrosion process. By being in electrical connection with the isolated well through the functional via, it provides an alternative path for the solvent circuit, mediating the corrosive effects away from critical functional metal features and preventing metal void formation.
3Device complexity
If the number of vias connecting to higher metal layers is reduced, then device complexity is lowered, but galvanic corrosion becomes more prevalent in these fewer vias, increasing metal void formation risk
Solution Approach 1:
The dummy metal feature connected through the functional via converts the risk of galvanic corrosion in the reduced via count into a protected scenario. By providing an additional dummy via path, the system creates a sacrificial corrosion path that protects the fewer functional vias, allowing device complexity to be reduced while maintaining via integrity through the protective dummy structure.
Solution Approach 2:
The patent changes the parameter distribution of via connectivity by introducing a dummy metal feature with different electrical connection characteristics. This alters the galvanic corrosion parameters by providing an additional path with different corrosion susceptibility, thereby protecting the functional vias even when their number is reduced, maintaining reliability despite lower via count.
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
The dummy metal feature minimizes metal void formation and prevents galvanic corrosion in integrated circuits during fabrication, allowing for reliable operation without the constraints of tie-down diodes, especially in high-voltage applications.
Implementation Method 1
galvanic corrosion may occur in various metal features, especially in vias connecting to higher levels of metal layers
Data Source
AI summary
Integrated circuits and methods of forming the same are provided herein. In an embodiment, an integrated circuit includes a semiconductor substrate that has an isolated well. A multilayer metallization stack overlies the semiconductor substrate. The multilayer metallization stack includes a metal layer, a functional via, and a dummy metal feature. The metal layer includes a first line in electrical communication with the isolated well through a contact. The functional via is in electrical communication with the first line and the contact. The dummy metal feature is in electrical communication with the functional via.