Floating Potential Electroless Plating for Copper Interconnects
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Solution Overview
Problem
Conventional electroless plating methods for forming diffusion layers on copper interconnects in semiconductor processing often result in pinhole defects and excessive surface roughness, leading to inefficient bonding operations that exceed thermal budgets and risk device damage.
Innovation Solution
Applying a floating potential to the plating bath during electroless plating, combined with the use of a grain refining compound like glyoxylic acid or ethylene diamine tetraacetic acid, to facilitate the formation of a thin, smooth diffusion layer of metals such as silver on copper interconnects, reducing pinhole defects and enabling bonding at lower temperatures and pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional electroless plating is performed without a floating potential, then the plating process is simple, but pinhole defects and excessive surface roughness occur
Solution Approach 1:
The patent applies a floating potential (electrical parameter change) to the plating bath during electroless plating. This parameter modification controls the deposition process to produce a smooth, pinhole-free diffusion layer by regulating metal ion reduction and surface deposition characteristics.
2Manufacturing precision
If conventional electroless plating is performed without a grain refining compound, then the plating process is simple, but the diffusion layer exhibits excessive surface roughness
Solution Approach 1:
The patent introduces a grain refining compound as an intermediary substance in the plating bath. This compound mediates the deposition process by controlling crystal grain growth and morphology, resulting in a smooth diffusion layer surface without requiring complex equipment modifications.
3Strength
If high temperature bonding is used to join interconnects, then bonding strength is achieved, but thermal budget is exceeded and device damage risk increases
Solution Approach 1:
The patent performs preliminary electroless plating to deposit a diffusion layer on the interconnect surfaces before bonding. This preliminary action creates a metallurgical diffusion barrier that enables subsequent low-temperature bonding by facilitating atomic diffusion at reduced temperatures, thereby achieving strong bonds without exceeding thermal budgets.
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 achieves a diffusion layer with reduced defects and enhanced copper diffusion across contact surfaces, allowing for efficient metal-to-metal bonding at lower temperatures and pressures, thereby improving the quality and reliability of semiconductor interconnects.
Implementation Method 1
Metal ions in the plating bath plate out on exposed metal surfaces that include a metal that has a lower reduction potential that the metal ions in the plating bath, creating a plated metal layer on the underlying metal surfaces
Implementation Method 2
a grain refining compound that reduces the formation of pinhole defects in the diffusion layer
Implementation Method 3
The diffusion layers increase the diffusion of copper across the contact surface during a bonding operation that joins opposite-facing portions of the interconnect into a single metal-to-metal interconnect
Data Source
AI summary
Exemplary methods of plating are described. The methods may include applying a floating potential to a plating bath in a plating chamber. The methods further include contacting a patterned substrate with the plating bath in the plating chamber. The patterned substrate includes at least one metal interconnect with a contact surface that is exposed to the plating bath. The metal interconnect is made of a first metal characterized by a first reduction potential. The methods further include plating a diffusion layer on the contact surface of the metal interconnect. The diffusion layer is made of a second metal characterized by a second reduction potential that is larger than the first reduction potential of the first metal in the metal interconnects. The plating bath also includes one or more ions of the second metal and a grain refining compound that reduces the formation of pinhole defects in the diffusion layer.