Multipass Copper Plating With Rinse-Dry Steps for Low Hillocks
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Solution Overview
Problem
Electroplated metal layers, especially at high thickness, are prone to protrusion defects known as hillocks, which can cause degradation in manufacturing yield and reliability of electronic devices due to stress relief mechanisms and material migration, leading to shorts and open circuits, and also result in high resistance and current faults in the plating system.
Innovation Solution
A method involving multipass electroplating with intervening rinse and drying steps to deposit metal layers, breaking up the deposition process and reducing hillock defects, and mitigating passivation film growth on the anode, thereby achieving a metal layer with a defect density of less than 700 defects/m² for protrusions of 0.2 μm or more from the upper surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If single-step thick copper plating is performed to achieve high thickness metal layers, then productivity is improved, but hillock defects increase due to stress relief mechanisms
Solution Approach 1:
The plating process is divided into multiple steps with intermediate rinsing and drying. After each plating step, the substrate is rinsed with deionized water and dried, which interrupts continuous stress accumulation and prevents hillock formation while maintaining overall plating efficiency
Solution Approach 2:
The plating process uses periodic cycles of deposition followed by rinsing and drying. This periodic interruption allows stress relief without material migration, maintaining surface integrity while continuing to build thickness over multiple cycles
2Manufacturing precision
If extended plating time is used to achieve high thickness, then manufacturing precision is improved, but passivation film growth on anode increases
Solution Approach 1:
The extended plating time is segmented into multiple shorter plating steps. Each step is followed by rinsing and drying, which prevents continuous passivation film growth on the anode while still achieving the required total thickness over the segmented process
Solution Approach 2:
The intermediate rinsing and drying steps quickly interrupt the plating process, preventing the anode from being exposed to plating conditions for extended continuous periods, thereby limiting passivation film growth while maintaining overall process efficiency
3Productivity
If high current is used to accelerate plating, then productivity is improved, but passivation film growth on anode increases
Solution Approach 1:
High current plating is performed in periodic cycles with intermediate rinsing and drying. This allows high-rate deposition when needed while preventing continuous passivation film growth through periodic interruption, maintaining both productivity and anode health
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 method effectively reduces hillock defects and limits passivation film growth, improving the reliability and yield of electronic devices by maintaining a low defect density in thick metal layers, independent of subsequent thermal processing, and avoiding additional process steps or changes in annealing temperatures.
Implementation Method 1
electroplate depositing a first metal layer to a first thickness on a metal seed layer
Implementation Method 2
performing one or more additional electroplating processes that respectively deposit an additional metal layer
Implementation Method 3
performing an additional rinse process that rinses the additional metal layer with deionized water
Implementation Method 4
performing an additional drying process that dries the wafer
Data Source
AI summary
Methods of forming metal interconnections of an integrated circuit include electroplating two or more metal layers over a metal seed layer, rinsing each of the metal layers with deionized water after the electroplating, and drying each of the metal layers after the rinsing. After forming a last metal layer, the two or more metal layers are annealed thereby forming a final metal layer, resulting in a low defect density of the final metal layer.