Interfacial Capping Layers for Copper Interconnects
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Solution Overview
Problem
Electromigration failure in copper interconnects due to poor adhesion between copper and dielectric diffusion barrier layers, exacerbated by copper oxide formation and weak bonding energy, becomes a significant reliability issue as device dimensions shrink and current densities increase.
Innovation Solution
Forming a thin adhesion layer with atomic thickness using metal precursors like aluminum, titanium, or magnesium on copper surfaces, which improves bonding with dielectric diffusion barrier layers without significantly increasing interconnect resistance, by depositing a precursor layer and modifying it to form metal-oxygen, metal-nitrogen, or metal-carbon bonds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thin adhesion layer is formed on copper interconnects, then adhesion between copper and dielectric diffusion barrier layers is improved, but interconnect resistance increases
Solution Approach 1:
The adhesion layer is applied locally only at the interface between copper interconnects and dielectric diffusion barrier layers, rather than throughout the entire interconnect structure. This localized application provides adhesion improvement precisely where needed while minimizing the total volume of resistive material in the conductive path
Solution Approach 2:
An extremely thin adhesion layer (thin film) is used to provide the necessary adhesive function at the copper-dielectric interface. The thin film approach ensures that the layer is sufficient for adhesion improvement but thin enough to minimize its impact on overall interconnect resistance
2Productivity
If copper interconnect dimensions are decreased, then device miniaturization is achieved, but electromigration failure probability increases
Solution Approach 1:
The adhesion layer acts as an intermediary between copper atoms and the dielectric diffusion barrier layer. This intermediate layer prevents direct copper-dielectric contact that would facilitate electromigration, thereby protecting the copper interconnect from electromigration failure even as dimensions are reduced
Solution Approach 2:
The adhesion layer is applied in advance to prevent electromigration before it can occur. By establishing a protective interface layer prior to interconnect operation, the structure is preemptively protected against the harmful effects of electromigration that would otherwise accelerate with miniaturization
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
Enhances the adhesion between copper and dielectric layers, improving electromigration performance and extending the time to failure of copper interconnects while maintaining low resistance.
Implementation Method 1
contacting a substrate having an exposed layer of a first metal (e.g., copper or copper alloy) and an exposed layer of dielectric with a precursor compound comprising a second metal to deposit a precursor layer over both the dielectric and the first metal
Implementation Method 2
modifying the precursor layer to form a passivated layer having metal-oxygen, metal-nitrogen, metal-carbon bonds and essentially no free metal on the copper surface
Implementation Method 3
A thin layer of a dielectric diffusion barrier material, such as silicon carbide or silicon nitride, is deposited between adjacent metallization layers to prevent diffusion of metal into bulk layers of dielectric
Data Source
Figure 1A~1C
Figure 1D~1E
Figure 2
AI summary
Adhesive layers residing at an interface between metal lines and dielectric diffusion barrier (or etch stop) layers are used to improve electromigration performance of interconnects. Adhesion layers are formed by depositing a precursor layer of metal-containing material (e.g., material containing A1, Ti, Ca, Mg, etc.) over an exposed copper line, and converting the precursor layer to a passivated layer (e.g., nitridized layer). For example, a substrate containing exposed copper line having exposed Cu-O bonds is contacted with trimethylaluminum to form a precursor layer having A1-O bonds and A1-C bonds on copper surface. The precursor layer is then treated to remove residual organic substituents and to form A1-N, A1-H bonds or both. The treatment can include direct plasma treatment, remote plasma treatment, UV-treatment, and thermal treatment with a gas such as NH3, H2, N2, and mixtures thereof. A dielectric diffusion barrier layer is then deposited.