Thermochemical Copper Cap Formation for Electromigration Resistance

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Solution Overview

Problem

In the fabrication of advanced integrated circuits, copper interconnects face challenges such as electromigration-induced material transport and diffusion issues at the interface with dielectric cap layers, leading to premature device failure and signal propagation delays, particularly due to the complexity of filling high aspect ratio vias and the sensitivity of low-k dielectric materials to reactive plasma ambients.

Innovation Solution

A thermochemical treatment process is employed, using oxide-reducing gases like ammonia and nitrogen to form a conductive cap layer on copper surfaces, followed by a silicon-containing treatment to enhance surface characteristics and reduce carbon depletion, thereby improving electromigration performance and dielectric material stability without compromising conductivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conductive cap layer is formed on copper surface to improve electromigration resistance, then electromigration performance is enhanced, but carbon depletion and deterioration of low-k dielectric materials occurs

Engineering Contradiction:

Improveelectromigration resistanceVSAvoidcarbon depletion and dielectric deterioration

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent changes the fundamental parameter of the cleaning process by replacing plasma with thermal/chemical treatment. Specifically, it uses a multi-step thermal process involving oxide-reducing gases (ammonia, nitrogen) at controlled temperatures (200-400°C) to modify the copper surface and form the conductive cap layer without causing carbon depletion in the low-k dielectric material.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs an inert thermal atmosphere using oxide-reducing gases (ammonia NH3 and nitrogen N2) during the conductive cap layer formation process. This inert chemical environment prevents unwanted reactions with the low-k dielectric material while allowing controlled surface modification of the copper, thereby avoiding carbon depletion and dielectric deterioration.

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

2Manufacturing precision

If reactive plasma treatment is used to clean dielectric surfaces, then surface cleanliness is improved, but low-k dielectric materials suffer from carbon depletion and etch damage

Engineering Contradiction:

Improvesurface cleanlinessVSAvoidcarbon depletion and etch damage

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent substitutes the plasma-based cleaning mechanism with a thermal/chemical cleaning mechanism. Instead of using reactive plasma species to clean the dielectric surface, it employs controlled thermal treatment in an oxide-reducing atmosphere (ammonia and nitrogen gases) to achieve surface cleaning and conductive cap layer formation without the harsh effects of plasma on low-k dielectric materials.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Productivity

If copper interconnect dimensions are reduced to increase circuit density, then functionality and speed are improved, but electromigration and diffusion problems increase

Engineering Contradiction:

Improvecircuit density and switching speedVSAvoidelectromigration and diffusion resistance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent creates a composite structure on the copper surface by forming a conductive cap layer through thermal treatment in oxide-reducing atmosphere. This composite surface structure combines the high conductivity of copper with the protective and electromigration-resistant properties of the thermally-formed surface layer, enabling reduced dimensions while maintaining reliability.

Inventive Principle:

Principle #40Composite materials

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 enhances electromigration resistance and dielectric strength, reducing carbon depletion and etch-related damage, resulting in superior reliability and stability of metallization systems with improved signal propagation and reduced parasitic capacitance.

Implementation Method 1

performing a first thermo chemical treatment on an exposed surface of the low-k dielectric material on the basis of a copper oxide reducing process gas

Methodology Applied

Scientific EffectOxide-reducing process: Reduction

Implementation Method 2

performing a second thermo chemical treatment on the exposed surface on the basis of a silicon-containing process ambient after performing the first thermo chemical treatment

Methodology Applied

Scientific EffectThermochemical treatment: Heat Treatment

Data Source

PatentUS8153524B2Providing superior electromigration performance and reducing deterioration of sensitive low-k dielectrics in metallization systems of semiconductor devices

Publication Date: 2012.04.10 ADVANCED MICRO DEVICES INC

AI summary

During the formation of complex metallization systems, a conductive cap layer may be formed on a copper-containing metal region in order to enhance the electromigration behavior without negatively affecting the overall conductivity. At the same time, a thermo chemical treatment may be performed to provide superior surface conditions of the sensitive dielectric material and also to suppress carbon depletion, which may conventionally result in a significant variability of material characteristics of sensitive ULK materials.