Multiwave Electroplating for Void-Free Copper Fill
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Solution Overview
Problem
In semiconductor wafer electroplating, the thin copper seed layer in high aspect ratio features often results in marginal coverage and void formation due to corrosion and uneven nucleation, especially in advanced technology nodes where feature sizes are small and seed layer thickness is minimal.
Innovation Solution
A multiwave electroplating process is employed, involving initial cathodic protection, a high current pulse to prevent corrosion and enhance nucleation, and a micropulse waveform for uniform fill, controlling current densities and pulse durations to ensure void-free fill across features.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin copper seed layer is used in high aspect ratio features, then pinch-off problems are prevented, but marginal coverage and void formation occur due to corrosion and uneven nucleation
Solution Approach 1:
The patent applies preliminary cathodic protection during immersion to prevent seed layer corrosion before plating begins. A high current pulse is applied immediately after immersion to enhance nucleation and establish uniform copper coverage on the thin seed layer, preventing void formation in high aspect ratio features while maintaining the thin seed thickness to avoid pinch-off.
2Productivity
If a high current density is applied during plating, then plating speed increases, but seed layer corrosion and non-uniform fill occur
Solution Approach 1:
The patent employs periodic pulsed current application instead of continuous high current. A high current pulse is applied for a short duration (10-1000 ms) to enhance nucleation and prevent corrosion, then a lower baseline current is applied during bottom-up fill. This periodic action allows the seed layer to be protected and nucleation to be enhanced without causing excessive corrosion or non-uniform fill that would result from continuous high current application.
3Reliability
If a low current density is applied during plating, then seed layer corrosion is prevented, but fill rate decreases and void formation occurs
Solution Approach 1:
The patent uses periodic pulsed current to overcome the limitations of low continuous current. During the pulse phase, high current density (≥20 mA/cm²) is applied to enhance nucleation and prevent corrosion. During the baseline phase, lower current density (1-20 mA/cm²) is applied to maintain controlled fill. This periodic switching allows the system to benefit from both high current nucleation enhancement and low current corrosion prevention, achieving uniform fill without sacrificing productivity.
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 process effectively prevents seed layer corrosion, enhances nucleation, and achieves uniform copper fill in features with minimal seed layer coverage, reducing void formation and improving fill rates across dense feature arrays.
Implementation Method 1
a plating bath to which a wafer is immersed. The plating bath may include a copper salt, a suppressor, and water
Implementation Method 2
Initially, the protocol employs cathodic protection as the wafer is immersed in the plating solution
Implementation Method 3
This process may protect the seed from corrosion while enhancing nucleation during the initial stages of plating
Data Source
AI summary
A plating protocol is employed to control plating of metal onto a wafer comprising a conductive seed layer. Initially, the protocol employs cathodic protection as the wafer is immersed in the plating solution. In certain embodiments, the current density of the wafer is constant during immersion. In a specific example, potentiostatic control is employed to produce a current density in the range of about 1.5 to 20 mA/cm2. The immersion step is followed by a high current pulse step. During bottom up fill inside the features of the wafer, a constant current or a current with a micropulse may be used. This protocol may protect the seed from corrosion while enhancing nucleation during the initial stages of plating.