Ag-Al Clad Metallization for Semiconductor Interconnect Adhesion
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Solution Overview
Problem
In ultra-large-scale-integration technologies, interconnects face premature failure due to high current densities and thermal stresses, primarily attributed to electromigration and poor adhesion of pure silver (Ag) metallization with dielectrics, which leads to agglomeration and increased resistivity.
Innovation Solution
A cladded silver (Ag) metallization structure is developed, where a thin layer of Ag is sandwiched between two layers of Ag-Al alloy, with the Ag-Al alloy acting as an adhesion layer and a cladding layer to prevent agglomeration and enhance electromigration resistance, reducing the need for additional diffusion barrier layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If pure silver (Ag) metallization is used, then lower resistivity is achieved, but poor adhesion to dielectrics and agglomeration at high temperatures occur
Solution Approach 1:
The patent uses a composite metallization structure consisting of a pure Ag layer combined with an Ag-Al alloy layer. The pure Ag provides low resistivity while the Ag-Al alloy layer provides strong adhesion to the dielectric substrate and prevents agglomeration at high temperatures. This composite structure resolves the contradiction by combining materials with complementary properties.
Solution Approach 2:
The Ag-Al alloy layer acts as an intermediary between the pure Ag metallization and the dielectric substrate. It provides the adhesion function that pure Ag lacks, while allowing the pure Ag layer to maintain its low resistivity. The intermediary layer prevents direct contact between pure Ag and the dielectric, eliminating both adhesion problems and agglomeration issues.
2Loss of energy
If pure silver (Ag) metallization is used, then lower resistivity is achieved, but electromigration resistance deteriorates under high current densities
Solution Approach 1:
The composite structure combines pure Ag (low resistivity) with Ag-Al alloy (high electromigration resistance). The Ag-Al alloy layer protects the pure Ag from electromigration effects while maintaining the overall low resistivity of the interconnect structure.
Solution Approach 2:
The Ag-Al alloy layer serves as a protective intermediary that shields the pure Ag metallization from high current density effects. It absorbs and mitigates electromigration stress, preventing failure in the low-resistivity pure Ag layer.
3Reliability
If aluminum (Al) metallization is used, then good adhesion to dielectrics is achieved, but higher resistivity and poor electromigration resistance occur
Solution Approach 1:
The patent creates a composite where the Ag-Al alloy layer provides the adhesion benefits of Al while the pure Ag layer provides the low resistivity. The alloy composition (Ag with small Al content) ensures good adhesion without the high resistivity penalty of pure Al metallization.
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 Ag-Al clad structure significantly improves adhesion, prevents agglomeration, and enhances electromigration resistance, resulting in a 38-fold increase in failure time compared to pure Ag, while maintaining lower resistivity and compatibility with existing fabrication processes.
Implementation Method 1
The alloy film on the oxide is also of a thickness so as to prevent diffusion of the silver into the oxide
Implementation Method 2
an Ag (Al) alloy is deposited on a semiconductor oxide layer... A layer of substantially pure Ag is then deposited on the thin alloy film
Data Source
AI summary
In semiconductor integrated circuit and device fabrication interconnect metallization is accomplished by a clad Ag deposited on a SiO2 level on a Si surface. The clad Ag has a layer of an alloy of Ag and Al (5 atomic %) contacting the SiO2, a layer of substantially pure Ag and an outer layer of the Ag and Al alloy. The alloy improves adhesion to the SiO2, avoids agglomeration of the Ag, reduces or eliminates diffusion at the SiO2 surface, reduces electromigration and presents a passive exterior surface.