Chromium Etch Stop Layer for Selective Copper Patterning

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Solution Overview

Problem

The existing methods for patterning metal wiring circuits using nickel as an etch stop layer are hindered by nickel's reactivity with cupric chloride etchants and the porosity of nickel layers, leading to inefficiencies and difficulties in controlling the etching process.

Innovation Solution

A layered metal structure with copper layers flanked by a chromium etch stop layer, which is resistant to cupric chloride and other etchants, allowing for selective patterning and reducing the need for thick nickel layers.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If nickel is used as an etch stop layer between copper layers, then the copper layers can be patterned with different masking layers, but nickel is attacked by cupric chloride etchant requiring more complex etching processes

Engineering Contradiction:

ImproveAbility to pattern copper layers with different masking layersVSAvoidEtching process complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent changes the material parameter of the etch stop layer from nickel to chromium. Chromium is resistant to cupric chloride etchant, allowing the first copper layer to be etched without attacking the etch stop layer. This eliminates the need for dual-etchant processes and simplifies the overall etching procedure while maintaining the ability to pattern both copper layers independently.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces nickel with chromium as the etch stop layer. Chromium serves as a disposable protective layer that can be selectively removed after patterning the first copper layer, simplifying the process by eliminating the need for complex in-situ regeneration or protection mechanisms required with nickel.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

2Reliability

If nickel layer thickness is increased to 5 microns to avoid pinholes, then pinhole emergence is prevented, but etching time and etchant quantity are significantly increased

Engineering Contradiction:

ImproveAbsence of pinholes in etch stop layerVSAvoidEtching time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent changes the material from nickel to chromium, which has fundamentally different etching characteristics. Chromium can be deposited as a thin, non-porous layer that provides adequate pinhole protection without requiring the 5-micron thickness needed for nickel. This dramatically reduces the thickness parameter and consequently the etching time and etchant quantity required.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent addresses the porosity issue by selecting chromium, which forms a non-porous, dense layer when deposited. This eliminates the need to increase thickness to compensate for pinholes, as the material itself provides pinhole-free protection at much thinner dimensions, thereby reducing etching time and resource consumption.

Inventive Principle:

Principle #31Porous materials

3Reliability

If ammoniacal etchant is used to pattern copper layers, then nickel layer is protected from attack, but the etching process becomes more difficult to control

Engineering Contradiction:

ImproveProtection of nickel etch stop layerVSAvoidEtching process control

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent changes the etch stop layer material from nickel to chromium, which is inherently resistant to cupric chloride etchant. This eliminates the need to use ammoniacal etchants for protection, allowing the use of standard cupric chloride etching processes that are easier to control and more commonly used in the industry.

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 chromium etch stop layer enables efficient patterning of copper layers with cupric chloride without attacking the intervening layer, reducing processing time and avoiding pinholes, thus improving the reliability and control of the etching process.

Implementation Method 1

an intervening layer including chromium between the first and second layers of copper which is resistant to an etchant usable to pattern the first and second layers selectively to the intervening layer

Methodology Applied

Scientific EffectChemical resistance:

Implementation Method 2

an etchant such as cupric chloride, ferric chloride (FeCl3), a peroxysulfuric composition, or a persulfate composition may be used

Methodology Applied

Scientific EffectChemical etching:

Data Source

PatentUS7696439B2Layered metal structure for interconnect element

Publication Date: 2010.04.13 ADEIA SEMICONDUCTOR SOLUTIONS LLC

AI summary

A layered metal structure is provided in accordance with an aspect of the invention. The structure can be used, for example, to fabricate a conductive interconnect element for conductively interconnecting one or more microelectronic elements. The layered structure includes first and second metal layers each of which may include one or more of copper or aluminum, for example. An intervening layer, may include for example, chromium between the first and second metal layers, chromium being resistant to an etchant usable to pattern the first and second metal layers selectively to the intervening layer. An etchant such as cupric chloride, ferric chloride (FeCl3), a peroxysulfuric composition, or a persulfate composition may be used to pattern the first and second metal layers in such case.