Multilayer BEOL Metal Lines for Tight Pitch and Low Resistance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current technologies face challenges in forming BEOL interconnects with tight pitches and low resistance, as copper-based methods struggle with tight pitch patterns, and alternative metals like Ru and W exhibit high resistivity, especially at certain aspect ratios.
Innovation Solution
The development of multilayer metal lines with a metal core sandwiched by layers of aluminum and other metals like tungsten, ruthenium, and a stress layer to minimize defects and oxidation, fabricated through subtractive etch with a hard mask and oxygen-free passivation to achieve tight pitches and low resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper-based methods are used for BEOL interconnects, then low resistance is achieved, but tight pitch patterns cannot be formed
Solution Approach 1:
The metal interconnect line is divided into multiple layers (first metal layer, second metal layer, third metal layer) with different materials. The first layer provides low resistance (copper), while the second and third layers enable tight pitch patterning (tungsten, ruthenium, or rhodium), allowing both low resistance and tight pitch requirements to be satisfied simultaneously.
2Manufacturing precision
If alternative metals like Ru and W are used to achieve tight pitches, then tight pitch patterns are formed, but high resistivity occurs
Solution Approach 1:
The interconnect structure is segmented into multiple metal layers with different materials. The second and third layers (tungsten, ruthenium, or rhodium) provide tight pitch patterning capability, while the first layer (copper) provides low electrical resistance, resolving the contradiction between pitch precision and electrical conductivity.
3Ease of manufacture
If metal layers are exposed to oxygen during fabrication, then standard fabrication processes are used, but oxidation and defects occur in the metal core
Solution Approach 1:
The second metal layer is deposited over the first metal layer before any oxygen exposure occurs during subsequent fabrication steps. This preliminary protective action prevents oxidation of the copper core in the first layer, allowing standard fabrication processes to be used while maintaining metal quality.
Solution Approach 2:
The second metal layer acts as an intermediary protective barrier between the first metal layer (copper core) and the oxygen-containing environment during fabrication. This intermediary layer prevents direct contact between oxygen and the copper, avoiding oxidation and defects while allowing standard fabrication processes to proceed.
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 enables the fabrication of BEOL interconnects with pitches under 20 nm and significantly lower resistance than current methods, with the metal core protected from oxidation and defects by the surrounding layers.
Implementation Method 1
a first layer, a second layer, and a third layer are formed over the support structure. The first layer is between the second layer and the third layer. The first layer includes a first metal, and the second layer or the third layer includes a second metal that is different from the first metal
Data Source
AI summary
An IC device includes a multilayer metal line that is at least partially surrounded by one or more electrical insulators. The multilayer metal line may be formed by stacking four layers on top of one another. The four layers may include a first layer between a second layer and a third layer. The first layer may include Al. The second or third layer may include W. The fourth layer may be a conductive or dielectric layer. The second layer, third layer, and fourth layer can protect the first layer from defects in Al core layer during fabrication or operation of the multilayer metal line. Substrative etch may be performed on the stack of the four layers to form openings. An electrical insulator may be deposited into to the openings to form multiple metal lines that are separated by the electrical insulator. A via may be formed over the third layer.