Graded Copper Seed Layer for Self-Aligned Metal Cap Formation
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Solution Overview
Problem
In the manufacturing of integrated circuits, existing seed layer deposition processes struggle to effectively segregate dopant species to the interface between the dielectric cap layer and the electroplated copper metal, leading to increased copper line resistance and reduced electromigration lifetime due to trapped dopants and inadequate migration.
Innovation Solution
A non-uniformly doped metal seed layer is formed with a vertical doping gradient, achieved through a sputtering process using a copper sputter target with low dopant concentration and an RF coil with higher dopant concentration, ensuring dopant species migrate efficiently to the interface during high-temperature processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a uniformly doped metal seed layer is formed using conventional sputtering processes, then the deposition process is simple and straightforward, but dopant species cannot effectively segregate to the interface, resulting in increased copper line resistance and reduced electromigration lifetime
Solution Approach 1:
The patent applies local quality by creating a vertically graded doping concentration within the seed layer, where the dopant concentration varies from the bottom interface to the top surface. This non-uniform doping profile enables effective dopant segregation to the interface region, improving electromigration lifetime while maintaining a single-step sputtering process
Solution Approach 2:
The patent changes the doping concentration parameter throughout the seed layer thickness, creating a gradient from lower concentration at the bottom to higher concentration at the top. This parameter variation enables controlled dopant diffusion and segregation to the interface, resolving the contradiction between reliability improvement and process complexity
2Reliability
If dopant concentration is increased uniformly throughout the seed layer to ensure adequate dopant availability, then dopant supply is sufficient, but dopant species become trapped in the bulk and cannot migrate to the interface, leading to poor adhesion and increased resistance
Solution Approach 1:
The patent concentrates dopant species in specific regions (higher concentration at the top, lower at the bottom) rather than uniform distribution. This localized doping strategy ensures adequate dopant supply at the interface for adhesion while preventing bulk trapping, as dopants naturally diffuse downward during thermal processing
Solution Approach 2:
The patent pre-distributes dopant species in a graded concentration profile before thermal processing occurs. This preliminary non-uniform distribution ensures that during subsequent annealing, dopants will naturally segregate to the interface region, achieving good adhesion without excessive bulk concentration that would cause trapping
3Reliability
If conventional sputtering with uniform doping is used, then the manufacturing process is simple, but copper line resistance increases due to inadequate dopant segregation
Solution Approach 1:
The patent modifies the doping concentration parameter during the sputtering deposition process, creating a vertical gradient from lower to higher concentration. This parameter change is achieved through controlled doping during deposition, maintaining ease of manufacture while achieving the required dopant segregation for low resistance
Solution Approach 2:
The patent creates a seed layer with spatially varying doping quality, where the local dopant concentration is optimized for its position in the layer. This local quality optimization enables effective dopant segregation to reduce copper line resistance while using a straightforward sputtering process
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 dopant segregation, reducing copper line resistance and improving reliability by forming a self-aligned metal cap with better adhesion, thus extending electromigration lifetime and ensuring consistent performance in finer geometries.
Implementation Method 1
a copper sputter target with low dopant concentration
Implementation Method 2
dopant species migrate efficiently to the interface during high-temperature processing
Data Source
AI summary
A trench is opened in a dielectric layer. The trench is then lined with a barrier layer and a metal seed layer. The metal seed layer is non-uniformly doped and exhibits a vertical doping gradient varying as a function of trench depth. The lined trench is then filled with a metal fill material. A dielectric cap layer is then deposited over the metal filled trench. Dopant from the non-uniformly doped metal seed layer is then migrated to an interface between the metal filled trench and the dielectric cap layer to form a self-aligned metal cap.