Copper Interconnect Diffusion Layers With Pinhole-Free Electroless Plating
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Solution Overview
Problem
Conventional electroless plating methods for metal diffusion layers on copper-containing interconnects in semiconductor structures often result in pinhole defects and excessive surface roughness due to variations in metal deposition, leading to inefficient bonding operations and potential device damage.
Innovation Solution
The method involves electroless plating a diffusion layer of a metal with a higher reduction potential, such as silver, gold, platinum, or palladium, on copper interconnects, using a plating bath with a grain refining compound like glyoxylic acid or ethylene diamine tetraacetic acid, at a temperature below 25°C, to create a thin, smooth, and defect-free layer that facilitates copper diffusion across contact surfaces at lower temperatures and pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional electroless plating is performed on copper interconnects, then metal diffusion layers are formed, but pinhole defects and excessive surface roughness occur due to variations in metal deposition
Solution Approach 1:
The patent changes multiple parameters of the plating bath including temperature (maintained at 25°C or lower), pH (adjusted to 2-7), and chemical composition (adding grain refining compounds like glyoxylic acid or EDTA at specific concentrations). These parameter changes control the deposition rate and crystal growth to eliminate pinholes and reduce surface roughness, achieving smooth, defect-free diffusion layers suitable for reliable bonding.
2Productivity
If higher plating temperatures are used to increase deposition rate, then productivity improves, but surface roughness and pinhole defects increase
Solution Approach 1:
The patent maintains the plating bath temperature at 25°C or lower to control the deposition rate. This lower temperature slows crystal growth, allowing for more uniform metal deposition that fills interstitial areas between nucleation sites, thereby achieving smooth surfaces without pinhole defects while maintaining acceptable productivity through optimized chemical composition.
Solution Approach 2:
The patent introduces grain refining compounds (glyoxylic acid or ethylene diamine tetraacetic acid) as intermediaries in the plating bath. These compounds act as mediators that control crystal growth kinetics, promoting uniform deposition and reducing surface roughness. They refine the grain structure of the deposited metal layer, enabling smooth surfaces even at controlled deposition rates.
3Manufacturing precision
If conventional plating methods are used, then diffusion layers are formed, but time-consuming patterning and deposition operations are required
Solution Approach 1:
The patent employs electroless plating, a self-service process where the copper interconnect itself serves as the reducing agent for metal ion deposition. The copper metal spontaneously reduces the metal ions in the plating bath without requiring external energy input or complex patterning steps. This self-service mechanism directly forms the diffusion layer on the interconnect surface, eliminating time-consuming patterning and separate deposition operations.
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 enables the formation of high-quality diffusion layers that enhance copper diffusion across contact surfaces, reducing bonding temperatures, pressures, and times, while eliminating the need for time-consuming patterning and deposition operations, resulting in improved interconnect bonding and reduced thermal budgets.
Implementation Method 1
Electroless plating may be performed in a plating chamber with the target side of the wafer in contact with a liquid plating bath. 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
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.
Data Source
AI summary
Exemplary methods of plating are described. The methods may include contacting a patterned substrate with a plating bath in a 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.