Self-Aligned Via Patterning With Selective Metal Sidewall Growth
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current semiconductor processing techniques, such as 193 nm immersion lithography, are limited in defining vias with critical dimensions (CD) smaller than 50 nm, especially in sub-80 nanometer back end of line (BEOL) dual damascene structures, as they struggle to reduce via CD effectively without increasing the staggered pitch size.
Innovation Solution
The method involves forming a tri-layer mask with a metal layer between insulating layers, selectively growing a metal capping layer on the metal hardmask sidewalls within the trench pattern to decrease the trench width, allowing for the formation of vias with dimensions smaller than the abutting trenches, thereby reducing via CD and pitch size through selective metal growth before etching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If 193 nm immersion lithography is used to define vias, then the manufacturing process is simple and well-established, but the via critical dimension cannot be reduced below 50 nm
Solution Approach 1:
The patterning process is divided into multiple stages: first forming a trench pattern with initial lithography, then selectively growing metal on sidewalls to define the final via pattern. This segmentation allows the via CD to be decoupled from the lithography resolution limit, enabling sub-50 nm via formation.
Solution Approach 2:
A metal layer is deposited and selectively grown on the sidewalls of the trench pattern before the final etching step. This preliminary metal growth establishes the precise via boundaries that will guide the subsequent via etch, ensuring accurate CD control.
2Manufacturing precision
If conventional lithography is used, then the process is straightforward, but the staggered pitch size increases when trying to reduce via CD
Solution Approach 1:
The via pattern and trench pattern are merged into a single self-aligned structure. The metal grown on the trench sidewalls automatically defines the via boundaries, eliminating the need for separate lithography steps and reducing the staggered pitch requirement.
Solution Approach 2:
The trench sidewalls themselves serve as the alignment reference for via formation. The metal growth on the sidewalls creates a self-aligned via pattern that automatically maintains the correct spatial relationship with the trench, eliminating the need for external alignment processes.
3Manufacturing precision
If metal growth is applied to all surfaces, then the process is simple, but the via pattern cannot be precisely controlled
Solution Approach 1:
Metal growth is made selective to specific locations - only on the sidewalls of the trench pattern that face the desired via direction. This local quality control is achieved through directional deposition or selective masking, allowing precise via pattern definition while keeping the process manageable.
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 formation of self-aligned vias with widths less than 50 nm, reducing via-to-adjacent metal short concerns and providing more flexibility in critical dimension manipulation without relying solely on reactive-ion etching, thus overcoming the limitations of existing lithography methods.
Implementation Method 1
growing a metal capping layer on an exposed sidewall of the trench pattern to decrease the first width of the trench pattern to a third width
Data Source
AI summary
A method for fabricating a self-aligned via structure includes forming a tri-layer mask on an ILD layer over a lower metal wiring layer, the tri-layer mask includes first and second insulating layers and a metal layer in between the insulating layers; defining a trench pattern through the first insulating layer and metal layer, the trench pattern having a first width; defining a first via pattern in a lithographic mask over the trench pattern, the first via pattern having a second width that is larger than the first width; growing a metal capping layer on an exposed sidewall of the trench pattern to decrease the first width to a third width that defines a second via pattern; transferring the trench pattern into the ILD layer to form a trench; and transferring the second via pattern through the ILD layer and into the metal wiring layer to form a via.