Electroless Copper Seed Layer Deposition on Barrier Substrates

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Solution Overview

Problem

Existing methods for depositing copper seed layers onto barrier layers, such as ruthenium and cobalt, result in copper seed layers with high surface roughness, which is unsuitable for microchip manufacturing due to the need for homogeneous thickness and smoothness in nanometer-scale recessed structures.

Innovation Solution

A method involving an aqueous electroless copper plating bath with a water-soluble Cu(II) source, a reducing agent, a complexing agent, and hydroxide ions from RbOH, CsOH, or their mixtures is used, eliminating the need for noble metal activation and achieving improved adhesion and surface smoothness.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If standard electroless copper plating bath composition with NaOH or KOH is used, then the copper seed layer can be deposited onto the barrier layer, but the outer surface roughness is too high

Engineering Contradiction:

Improvesurface smoothnessVSAvoidprocess complexity

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The patent changes the chemical parameters of the electroless plating bath by replacing conventional NaOH/KOH hydroxide sources with organic hydroxide sources (RbOH, CsOH, or their ammonium salts). This parameter substitution fundamentally alters the deposition mechanism to produce a smooth surface while maintaining processability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs temporary organic hydroxide sources (RbOH, CsOH, ammonium salts) that are consumed during the plating process and can be easily removed in subsequent rinsing steps. These disposable-like reagents enable smooth surface formation without requiring complex surface preparation or activation steps

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If noble metal activator is used to activate the barrier layer, then copper deposition can proceed, but the process complexity and cost increase

Engineering Contradiction:

Improveadhesion qualityVSAvoidprocess steps

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts and eliminates the noble metal activator step from the conventional process sequence. By using organic hydroxide sources in the electroless plating bath, the invention achieves direct copper deposition onto the barrier layer without requiring intermediate activation steps, thereby simplifying the process while maintaining adhesion

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The organic hydroxide sources enable the barrier layer to self-activate during the electroless plating process itself. The deposition mechanism inherently provides the necessary surface activation and adhesion promotion in a single step, eliminating the need for separate noble metal activation steps

Inventive Principle:

Principle #25Self-service

3Manufacturing precision

If conventional electroless plating is used, then copper can be deposited on the barrier layer, but the thickness distribution is non-homogeneous

Engineering Contradiction:

Improvethickness uniformityVSAvoiddeposition rate

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The patent modifies the chemical environment of the electroless plating bath by introducing organic hydroxide sources (RbOH, CsOH, ammonium salts) which change the deposition kinetics and mass transport characteristics. This parameter change results in more uniform copper distribution and homogeneous thickness across the barrier layer surface

Inventive Principle:

Principle #35Parameter changes

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 provides a copper seed layer with homogeneous thickness distribution and a smooth outer surface, enhancing the electrical conductivity and adhesion properties necessary for microchip manufacturing.

Implementation Method 1

a reducing agent for Cu(II) ions

Methodology Applied

Scientific EffectReduction: Reduction

Implementation Method 2

at least one complexing agent for Cu(II) ions

Methodology Applied

Scientific EffectComplexation:

Implementation Method 3

at least one source for hydroxide ions selected from the group consisting of RbOH, CsOH and mixtures thereof

Methodology Applied

Scientific EffectDissociation:

Data Source

PatentUS10077498B2Method for depositing a copper seed layer onto a barrier layer and copper plating bath

Publication Date: 2018.09.18 ATOTECH DEUT GMBH & CO KG

AI summary

The present invention relates to a method for providing a copper seed layer on top of a barrier layer wherein said seed layer is deposited onto said barrier layer from an aqueous electroless copper plating bath comprising a water-soluble source for Cu(II) ions, a reducing agent for Cu(II) ions, at least one complexing agent for Cu(II) ions and at least one source for hydroxide ions selected from the group consisting of RbOH, CsOH and mixtures thereof. The resulting copper seed layer has a homogeneous thickness distribution and a smooth outer surface which are both desired properties.