Alkaline Copper Plating Bath Analysis via Titration
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Solution Overview
Problem
The challenge in the Damascene process for semiconductor chip fabrication is the nonuniformity of seed layers deposited by PVD or CVD methods, leading to incomplete filling of fine features due to reduced seed layer thickness and restricted electrolyte flow, which complicates copper electrodeposition in alkaline copper electroplating baths.
Innovation Solution
A two-stage titration method using a single copper ion titrant to determine the concentrations of copper ions and complexing agents in alkaline copper electroplating baths, allowing for precise control and automation, thereby simplifying the analysis and minimizing waste.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If PVD or CVD seed layers are deposited to promote adhesion, then adhesion between barrier layer and copper electrodeposited layer is improved, but nonuniformity of seed layer thickness occurs leading to incomplete filling of fine features
Solution Approach 1:
The patent changes the chemical parameters of the electroplating bath from acidic to alkaline conditions, which fundamentally alters the deposition behavior. In alkaline baths, copper deposits more uniformly on the seed layer without the rapid dissolution that occurs in acidic baths, achieving both good adhesion and uniform thickness distribution across the seed layer surface.
Solution Approach 2:
The patent addresses the local quality issue by using alkaline electroplating conditions that promote uniform copper deposition across the entire seed layer surface, including the sidewalls and bottom of fine features. This local uniformity ensures adequate seed layer thickness everywhere, preventing pinch-off at feature entrances while maintaining good adhesion.
2Strength
If thicker copper seed layer is deposited to provide adequate coverage, then adhesion and coverage are improved, but feature entrance is pinched-off reducing electrolyte flow
Solution Approach 1:
The patent employs alkaline electroplating parameters that enable uniform copper deposition at lower current densities. This allows achieving adequate seed layer thickness (500-1500 Å) without excessive deposition rates that would pinch off feature entrances, thereby maintaining electrolyte flow while ensuring sufficient coverage and adhesion.
3Productivity
If acid copper sulfate electroplating bath is used for rapid filling, then filling speed is improved, but seed layer copper dissolves rapidly causing loss of seed layer thickness
Solution Approach 1:
The patent fundamentally changes the bath chemistry from acidic to alkaline. In alkaline copper electroplating baths, copper does not readily dissolve from the seed layer, eliminating the rapid dissolution problem. The alkaline environment stabilizes the copper seed layer while still enabling adequate copper deposition for complete filling of Damascene features.
Solution Approach 2:
The patent converts the typically harmful effect of copper dissolution in acidic baths into a beneficial process. By using alkaline baths, the copper seed layer is protected from dissolution and remains stable, providing durable adhesion and coverage while enabling complete filling of fine features through controlled deposition.
4Measurement precision
If multiple reagents are used for analysis of copper ion and complexing agent, then measurement accuracy is improved, but device complexity and waste generation increase
Solution Approach 1:
The patent employs a single copper ion-selective electrode that serves multiple functions: it measures copper ion concentration directly and also indirectly measures complexing agent concentration through complexation reactions. This multi-functional approach eliminates the need for separate measurement systems for different analytes, reducing device complexity and waste while maintaining measurement accuracy.
Solution Approach 2:
The patent uses the copper ion-selective electrode to measure both copper ions and complexing agents, allowing the same measurement device to serve multiple analytical purposes. The electrode 'services' both measurement needs simultaneously, reducing the number of reagents and equipment required while maintaining precision for both analytes.
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 method enables accurate measurement of copper ion and complexing agent concentrations, ensuring conformal copper seed layers with adequate thickness and adhesion, improving the quality and yield of high-speed integrated circuit chips by simplifying automation and reducing waste.
Implementation Method 1
a copper ion selective electrode or other means for detecting a copper ion concentration parameter in the analysis solution
Implementation Method 2
a copper complexing agent (preferably ethylene diamine or citric acid, or salts thereof) having a molar ratio in the range from 1 to 4 relative to the copper ion concentration
Implementation Method 3
A two-stage titration method using a single copper ion titrant to determine the concentrations of copper ions and complexing agents in alkaline copper electroplating baths
Implementation Method 4
Copper is ultimately electrodeposited within the trenches and vias to form the circuitry
Data Source
AI summary
A simple titration method involving a single copper ion titrant detected by a copper ion specific electrode provides the concentrations of both copper ions and bath complexing agent (ethylene diamine, for example) in alkaline copper electroplating baths of the type used to deposit or thicken copper seed layers on silicon wafers. Standard addition of an excess of a strong complexing agent (EDTA, for example) and back-titration with the copper ion titrant yields the bath copper ion concentration, and continued titration to a second endpoint, preferably after addition of hydroxide to adjust the pH of the analysis solution, yields the total concentration of bath complexing agent. Based on these analyzes, the concentration of free bath complexing agent may be calculated. The method also provides direct determination of the free bath complexing agent concentration via standard addition of excess bath complexing agent to a sample of the plating bath and titration with the copper ion titrant.