Copper Interconnect Reflow via Segmented Alloy Seed Layer
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Solution Overview
Problem
In semiconductor manufacturing, high aspect ratio trenches and vias are difficult to fill with copper due to copper migration and agglomeration issues, leading to voids and poor electroplating adherence, especially at low temperatures.
Innovation Solution
A method involving a copper alloy seed layer and a pure copper film layer is formed, where the pure copper migrates to the bottom of the structure while the alloy layer prevents exposure of the barrier layer, allowing for complete filling with electroplated copper and capping with a dielectric material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If ultra thin copper films are deposited and heated at low temperatures to utilize copper migration, then small trenches and vias are filled from the bottom side, but copper atoms migrate at the interface of underlying materials causing exposure of barrier metals and making subsequent electroplating difficult
Solution Approach 1:
The copper film is segmented into multiple layers with different compositions: a pure copper layer for capillary migration and filling, and a copper alloy seed layer for maintaining adhesion during reflow. This segmentation allows each layer to perform its specific function without interfering with the other's performance.
Solution Approach 2:
The copper alloy seed layer acts as an intermediary between the pure copper layer and the barrier metal. It prevents direct contact between the pure copper and barrier metal interface, thereby preventing exposure of the barrier layer during reflow while still allowing the pure copper to migrate effectively.
2Productivity
If copper is heated for reflow, then copper migration occurs to fill trenches, but copper islands are formed due to dewetting of the liner surface causing voids and early pinch off
Solution Approach 1:
Different regions of the copper structure have different compositions and properties: the pure copper layer provides capillary action for uniform migration, while the copper alloy seed layer provides adhesion and prevents dewetting. This local differentiation of material properties solves the contradiction between migration efficiency and uniformity.
Solution Approach 2:
The copper interconnect structure uses a composite material system consisting of pure copper and copper alloy in distinct layers. This composite structure combines the beneficial properties of each material: pure copper for migration and filling, and copper alloy for adhesion and dewetting prevention.
3Temperature
If the copper film thickness is reduced to enable migration, then low temperature filling is achieved, but agglomeration of copper at sidewalls occurs forming isolated islands that do not migrate to the bottom
Solution Approach 1:
The copper film is segmented into functional layers: pure copper for migration and copper alloy for stability. This segmentation allows the system to achieve both low-temperature migration and uniform distribution by assigning different functions to different layers.
Solution Approach 2:
The invention changes the compositional parameter of the copper film by introducing a copper alloy layer with different physical and chemical properties. This parameter change prevents agglomeration while maintaining the migration capability of the pure copper layer at low temperatures.
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 prevents void formation and agglomeration, improving copper interconnect reliability and electromigration performance by maintaining a wet liner surface and ensuring adhesion during reflow and deposition processes.
Implementation Method 1
copper can be used to fill a high aspect ratio trench/via through a migration process. That is, it is known that copper migrates at a much lower temperature than its melting point when the copper film has a thickness less than a few nanometers. This copper migration tends to accumulate at the bottom of the trench and/or via due to the so-called capillary phenomenon.
Implementation Method 2
the alloy metal prevents exposure of the barrier layer
Implementation Method 3
filling the structure with an electroplated copper, directly on the reflowed pure copper
Data Source
AI summary
Interconnect structures and methods of manufacturing the same are disclosed herein. The method includes forming a barrier layer within a structure and forming an alloy metal on the barrier layer. The method further includes forming a pure metal on the alloy metal, and reflowing the pure metal such that the pure metal migrates to a bottom of the structure, while the alloy metal prevents exposure of the barrier layer. The method further includes completely filling in the structure with additional metal.