Ionic Current Collimator for Electroplating Uniformity

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Solution Overview

Problem

The semiconductor industry faces challenges in achieving uniform electroplating thickness across large wafers due to the terminal effect, where highly resistive seed layers result in non-uniform current distribution, leading to thicker plating at the wafer edge, especially as the industry transitions to larger 450 mm wafers.

Innovation Solution

The introduction of an ionic current collimator and a flexibly biased auxiliary electrode in the electroplating apparatus, which directs ionic current from the periphery to the center of the wafer and adjusts its biasing from cathodic to anodic during the process to compensate for the terminal effect, ensuring uniform plating.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If electrical contact is made only at the edge region of the wafer, then the plating tool can effectively plate large surface area, but the potential at the edge is significantly greater than at the central region, leading to non-uniform plating thickness

Engineering Contradiction:

Improveplating surface areaVSAvoidplating thickness uniformity

Core Design Contradiction:

Area of stationary objectVSManufacturing precision

Solution Approach 1:

An ionic current collimator is introduced as an intermediary component between the anode and the wafer. This collimator directs the ionic current flow to compensate for the voltage drop across the resistive seed layer, ensuring more uniform current distribution and thus uniform plating thickness across the entire wafer surface while maintaining edge contact configuration.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The system dynamically changes the ionic current distribution parameters by using the collimator to redirect current paths. This parameter adjustment compensates for the resistive voltage drop in the seed layer, transforming the non-uniform current distribution into a more uniform one without changing the electrical contact configuration.

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If the seed layer is made thinner to reduce resistance, then the terminal effect is reduced, but the seed layer becomes too thin to provide adequate electrical conduction

Engineering Contradiction:

Improveterminal effectVSAvoidelectrical conduction

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The ionic current collimator serves as a mediator that compensates for the high resistance of thin seed layers by redirecting ionic current flow. This allows the system to use thin seed layers (reducing terminal effect) while maintaining adequate electrical conduction through the collimator's current redistribution function.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Productivity

If the wafer size is increased from 300 mm to 450 mm, then the productivity is improved, but the terminal effect becomes even more pronounced

Engineering Contradiction:

Improvewafer processing capacityVSAvoidplating thickness uniformity

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The ionic current collimator is specifically designed to address the amplified terminal effect in large 450 mm wafers. By intercepting and redirecting the ionic current flow, the collimator compensates for the increased voltage drop across larger wafer areas, enabling uniform plating on large-diameter wafers that would otherwise exhibit severe non-uniformity.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 solution effectively mitigates the terminal effect by redistributing ionic current, achieving center-to-edge uniformity and maintaining uniform current distribution throughout the electroplating process, even with highly resistive seed layers and large wafers, thereby ensuring consistent metal layer deposition.

Implementation Method 1

an ionic current collimator proximate the anode, wherein the ionic current collimator is a non-conductive member configured to direct the ionic current from the anode generally from the periphery to the center of the plating vessel

Methodology Applied

Scientific EffectIonic current direction control: Electrical Resistance

Implementation Method 2

an auxiliary electrode configured to be both cathodically and anodically biased during electroplating

Methodology Applied

Scientific EffectElectrical bias adjustment: Electrical Resistance

Implementation Method 3

electroplating metal on a wafer substrate

Methodology Applied

Scientific EffectElectroplating: Electroplating

Implementation Method 4

the apparatus is configured for cathodically biasing the wafer substrate during electroplating

Methodology Applied

Scientific EffectElectrochemical reduction: Electrodeposition

Data Source

PatentUS9909228B2Method and apparatus for dynamic current distribution control during electroplating

Publication Date: 2018.03.06 LAM RES CORP

AI summary

An apparatus for electroplating a layer of metal onto the surface of a wafer includes an auxiliary electrode that is configured to function both as an auxiliary cathode and an auxiliary anode during the course of electroplating. The apparatus further includes an ionic current collimator (e.g., a focus ring) configured to direct ionic current from the main anode to central portions of the wafer. The provided configuration effectively redistributes ionic current in the plating system allowing plating of uniform metal layers and mitigating the terminal effect. In one example, the auxiliary electrode functions as an auxiliary cathode in the beginning of electroplating when the terminal effect is pronounced, and subsequently is anodically biased.