Acid Generating Surface for Electroplating Bath pH Control
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Solution Overview
Problem
Nickel sulfamate electroplating baths in semiconductor manufacturing face challenges in maintaining constant pH levels over time, leading to inferior electroplating performance and potential defects due to pH drift and excess nickel ion accumulation, which existing methods like sulfamic acid dosing struggle to address effectively.
Innovation Solution
The introduction of an acid generating surface (AGS) that generates free hydrogen ions through electrolysis to lower bath pH and reduce metal ion concentration, using an inert anode to balance metal and acid levels, and employing a metal-to-acid process to control pH and ion concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional sulfamic acid dosing is used to control pH, then pH can be adjusted, but the process is inefficient and does not effectively address excess nickel ion accumulation
Solution Approach 1:
The patent replaces the chemical dosing system (sulfamic acid addition) with an electrochemical system (electrolytic cell with anode and cathode). The electrolytic cell generates acid in-situ through water electrolysis, eliminating the need for external chemical dosing. This substitution provides more reliable pH control and simultaneously addresses nickel ion accumulation through electrochemical reduction at the cathode.
Solution Approach 2:
The electrolytic cell performs self-service by generating the acid needed for pH control through water electrolysis. The system produces its own hydrogen ions at the anode, eliminating dependence on external acid dosing. Simultaneously, the cathode reduces excess nickel ions, making the system self-regulating for both pH and metal ion concentration control.
2Ease of operation
If pH is not controlled, then the system is simpler to operate, but electroplating quality deteriorates due to pH drift and metal ion accumulation
Solution Approach 1:
The electrolytic cell automatically maintains pH within the target range through continuous or periodic electrolysis operations. The system self-regulates by generating acid when pH rises, eliminating the need for manual pH monitoring and adjustment while ensuring consistent plating quality. The cathode simultaneously manages nickel ion concentration, providing dual control functionality.
Solution Approach 2:
The system incorporates pH sensing and control logic that monitors bath pH and activates the electrolytic cell when pH exceeds the target range. This feedback mechanism ensures pH remains within 3.0-5.0 while maintaining operational simplicity through automated control rather than manual intervention.
3Stability of the object's composition
If frequent acid dosing is performed to maintain pH, then pH stability is achieved, but operational complexity and chemical consumption increase
Solution Approach 1:
The patent replaces the complex chemical dosing system with a simpler electrochemical system. Instead of managing chemical storage, handling, and dosing equipment, the system uses an electrolytic cell that generates acid on-demand through electricity. This substitution reduces operational complexity while achieving superior pH stability and simultaneous metal ion control.
Solution Approach 2:
The electrolytic cell serves the dual function of pH control and metal ion management through a single integrated system. By generating acid in-situ and reducing nickel ions simultaneously, the system eliminates the need for separate chemical dosing operations, reducing both operational complexity and chemical consumption while maintaining stable pH.
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 effectively stabilizes the pH and metal ion concentrations in the electroplating bath, reducing the need for frequent sulfamic acid dosing and extending bath life by maintaining optimal electroplating conditions, thereby improving the quality and consistency of nickel plating.
Implementation Method 1
free hydrogen ions are generated at the acid generating surface by electrolysis of water molecules in the bath
Implementation Method 2
biasing the substrate surface sufficiently negative relative to the counterelectrode such that metal ions from the bath are reduced and plated onto the substrate surface
Data Source
AI summary
Disclosed are methods of electroplating a metal onto a substrate surface in an electroplating bath and adjusting the pH of the bath. The methods may include exposing the substrate surface, a counter-electrode, and an acid generating surface to the bath, biasing the substrate surface sufficiently negative relative to the counterelectrode such that metal ions from the bath are reduced and plated onto the substrate surface, and biasing the acid generating surface sufficiently positive relative to the counterelectrode such that free hydrogen ions are generated at the acid generating surface thereby decreasing the pH of the bath. Also disclosed are apparatuses for electroplating metal onto a substrate surface in an electroplating bath, and for adjusting the pH of the electroplating bath. The apparatuses may include an acid generating surface configured to generate free hydrogen ions in the bath upon supply of sufficient positive voltage bias relative to a counterelectrode electrical contact.