BEOL Interconnect Air Gap Structure for RC Delay Reduction
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Solution Overview
Problem
Conventional methods struggle to form large air gaps in tight pitch semiconductor interconnect structures, leading to significant RC delay, which hinders the scaling of interconnects in semiconductor devices.
Innovation Solution
A method involving the formation of sacrificial materials, conformal dielectric deposition, and selective dielectric growth to create large air gaps between metal lines, using techniques like damascene and subtractive etching to achieve consistent air gap formation and reduce capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional methods are used to form air gaps in tight pitch interconnect structures, then manufacturing simplicity is maintained, but air gap size is insufficient leading to significant RC delay
Solution Approach 1:
The air gap formation process is segmented into multiple distinct stages: (1) forming sacrificial material around metal lines, (2) depositing conformal dielectric layer, (3) performing selective etchback to expose sacrificial material, (4) removing sacrificial material to create air gap, and (5) depositing additional dielectric to fill remaining spaces. This segmentation enables precise control of air gap dimensions while managing process complexity through systematic breakdown of steps.
Solution Approach 2:
Sacrificial material is deposited around metal lines before the air gap is actually formed. This preliminary action creates a template structure that defines the future air gap geometry. The conformal dielectric is then deposited over this sacrificial structure, and selective removal of the sacrificial material subsequently creates the air gap with precisely controlled dimensions, enabling large air gaps in tight pitch structures.
2Manufacturing precision
If interconnect scaling is pursued to reduce capacitance, then RC delay reduction is achieved, but resistance increases significantly
Solution Approach 1:
The air gap structure provides localized dielectric modification around metal signal lines, creating regions of different electrical properties. The air gap (lower dielectric constant) is positioned specifically between adjacent signal lines to reduce capacitive coupling, while the conformal dielectric layers maintain proper insulation and mechanical support. This local quality change reduces capacitance without requiring overall interconnect dimension changes that would increase resistance.
Solution Approach 2:
The effective dielectric constant parameter is changed by introducing air gaps between metal lines. Since air has a dielectric constant of approximately 1.0 compared to typical dielectric materials (3.0-4.0), this parameter change directly reduces capacitance between adjacent lines. The conformal dielectric layers ensure that this parameter change is achieved while maintaining proper electrical isolation and mechanical integrity of the interconnect structure.
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 method allows for the consistent formation of large air gaps in tight pitch structures, enhancing thermal isolation and reducing signal line capacitance, thereby reducing RC delay and enabling interconnect scaling without significant increases in resistance.
Implementation Method 1
forming a conformal dielectric surrounding vertical sidewalls of each of the first signal line and the second signal line
Implementation Method 2
growing a dielectric selectively from an upper portion of the conformal dielectric
Data Source
AI summary
A first BEOL layer, including a first and a second signal line, a conformal dielectric surrounding an upper portion of a vertical sidewall of each of the first signal line and the second signal line, an air gap between the first and the second signal line, a vertical side boundary of the air gap is a vertical side surface of the first signal line. Forming a first and a second metal line in a sacrificial material in a first BEOL layer, removing the sacrificial material, forming a conformal dielectric surrounding vertical side surfaces of the first and the second metal line, an air gap between the first and the second metal line exposes an upper horizontal surface of a dielectric layer below the first BEOL layer, growing a dielectric selectively from an upper portion of the conformal dielectric, the air gap remains between the first and the second metal line.