CoWB Cap Metal Plating for Copper Interconnect Void Prevention
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Solution Overview
Problem
Conventional electroless plating methods for forming cap metals on copper interconnection lines in semiconductor devices face challenges such as void formation due to hydrogen gas bubbles, leading to poor continuity and increased electro-migration, and difficulties in removing by-products that can cause leakage current and deteriorate the substrate surface.
Innovation Solution
A substrate processing method involving repeated cycles of electroless plating and post-cleaning using a rinsing and chemical liquid process, where the substrate is kept hydrophilic and not dried until after the post-cleaning, to improve the quality of the plated film and enhance electro-migration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electroless plating is performed using a plating liquid containing CoWB or CoWP, then a cap metal film is formed to cover the Cu interconnection line, but hydrogen gas bubbles are generated causing voids in the metal film and damaging continuity
Solution Approach 1:
The substrate surface is pre-treated to enhance wettability before electroless plating, ensuring uniform plating liquid distribution and preventing bubble formation that would cause voids. This preliminary surface preparation eliminates the harmful effect of bubbles on film continuity while maintaining the protective cap metal formation
Solution Approach 2:
The patent employs multiple sequential plating steps with intermediate cleaning processes. By periodically removing by-products and resetting the surface condition between plating cycles, the method prevents cumulative bubble effects and maintains continuous film formation throughout the plating process
2Reliability
If cleaning is performed to remove by-products from the substrate surface, then leakage current is reduced, but the precipitated substances strongly stick to the plated surface making removal difficult with conventional cleaning liquids
Solution Approach 1:
The patent uses cleaning liquids with specific pH ranges (acidic or basic) and controlled surface tension properties. By changing the chemical parameters of the cleaning liquid to match the by-product composition, the method achieves effective removal of strongly adhering precipitated substances without damaging the plated film
Solution Approach 2:
Surfactants are introduced as intermediary substances in the cleaning liquid to reduce the strong adhesion between by-products and the plated surface. These surfactant molecules act as mediators that weaken the bonding force, enabling easy removal of precipitated substances while preserving the underlying metal film
3Ease of operation
If the substrate surface is dried after cleaning, then the surface is prepared for subsequent processes, but re-oxidation of the Cu surface occurs due to deterioration of wettability
Solution Approach 1:
The patent maintains continuous wetting of the substrate surface throughout the processing sequence from cleaning through plating without intermediate drying steps. This continuous liquid environment prevents exposure to oxygen that would cause re-oxidation, while still allowing proper adhesion and uniform coating formation
Solution Approach 2:
The processing is conducted in a controlled atmosphere that excludes oxygen during critical wetting and plating phases. By creating an inert environment through liquid immersion and controlled gas atmospheres, the method prevents Cu surface oxidation while maintaining operational feasibility
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 prevents void formation and improves the coverage and continuity of the plated film, reducing electro-migration and leakage current, while also ensuring effective removal of by-products, resulting in a high-quality plated film with enhanced reliability.
Implementation Method 1
applying electroless plating of a Co (cobalt) alloy onto a Cu (copper) interconnection line formed on a substrate
Implementation Method 2
the plating process is promoted by the electromotive force of electrons generated by decomposition of a reducing agent, such as dimethylamineborane (DMAB), which is a derivative of sodium borohydride (SBH) contained in the plating liquid, and hydrogen gas is generated due to decomposition of the reducing agent
Implementation Method 3
performing a post-cleaning process by use of a cleaning liquid on the substrate, after the electroless plating
Data Source
AI summary
A CoWB film is formed as a cap metal on a Cu interconnection line formed on a substrate or wafer W, by repeating a plating step and a post-cleaning step a plurality of times. The plating step is arranged to apply electroless plating containing CoWB onto the Cu interconnection line. The post-cleaning step is arranged to clean the wafer W by use of a cleaning liquid, after the plating step.