Self-Aligned Cut Formation Using Mandrel Spacers
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Solution Overview
Problem
Current methods for forming self-aligned cuts in semiconductor device fabrication are limited by the thickness constraints of optical lithography, which hinder the precise formation of sidewall spacers and subsequent interconnect structures in BEOL interconnects.
Innovation Solution
A method involving the formation of mandrels, cut masks, and selective etching to create mandrel and non-mandrel cuts, followed by the deposition of a spacer layer on vertical sidewalls, allowing for the precise patterning and transfer of these cuts to a dielectric layer and hardmask, enabling the formation of self-aligned trenches and wires with planar sidewalls and projecting tabs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If optical lithography is used to form sidewall spacers, then the current ground rules for optical lithography permit a certain thickness, but the desired thinner sidewall spacers cannot be formed with sufficient precision
Solution Approach 1:
The patent segments the spacer formation process into multiple stages: first forming a mandrel structure, then depositing a conformal spacer layer, and selectively removing portions of the mandrel to create the final spacer pattern. This segmentation allows precise control of spacer thickness independent of lithography limitations.
Solution Approach 2:
The mandrel structure is formed in advance as a sacrificial element that defines the spacer pattern. The conformal spacer layer is deposited on the mandrel before the mandrel is selectively removed, ensuring precise spacer thickness is achieved through deposition control rather than lithography.
2Manufacturing precision
If mandrels are used as sacrificial features to establish feature pitch, then self-aligned patterning can be achieved, but additional dummy removal steps are required
Solution Approach 1:
The patent merges the spacer formation and mandrel removal steps into a single integrated process. The conformal spacer layer is deposited and then selectively etched along with the mandrel in one step, eliminating the need for separate dummy removal steps while maintaining self-alignment.
Solution Approach 2:
The spacer structure itself serves as the etch mask during the selective removal of the mandrel. The spacer protects the regions where mandrels should be retained while allowing removal in cut regions, making the spacer structure serve multiple functions simultaneously.
3Manufacturing precision
If thinner sidewall spacers are formed, then precision in interconnect structures is improved, but the current ground rules for optical lithography prevent formation of such thin spacers
Solution Approach 1:
The patent replaces the lithography-based definition of spacer thickness with a deposition-based approach. The spacer thickness is determined by conformal film deposition on the mandrel, which can achieve much thinner and more precise dimensions than optical lithography allows.
4Manufacturing precision
If self-aligned patterning processes are used, then precise alignment of interconnect structures is achieved, but the process complexity increases due to multiple steps
Solution Approach 1:
The mandrel structure is formed in advance with the exact pattern needed, serving as a self-aligned template for subsequent spacer formation. This preliminary patterning step establishes all alignment references needed for the interconnect structure, eliminating the need for multiple alignment steps.
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 creation of self-aligned cuts and structures with improved precision and spacing, facilitating more efficient electrical isolation and interconnect formation without the need for additional dummy removal steps, thereby enhancing the performance of BEOL interconnects.
Implementation Method 1
a spacer is formed on a vertical sidewall of the mandrel
Implementation Method 2
a spacer is formed on a vertical sidewall of the mandrel
Implementation Method 3
etching in order to section the mandrels and define gaps that subsequently are used to form adjacent wires
Implementation Method 4
the sidewall spacers are used as an etch mask to etch an underlying hardmask, for example, with a directional reactive ion etch (ME) process
Data Source
AI summary
Methods of forming self-aligned cuts and structures formed with self-aligned cuts. A dielectric layer is formed on a metal hardmask layer, and a mandrel is formed on the dielectric layer. A cut is formed that extends through the dielectric layer to the metal hardmask layer. A section of a metal layer is formed on an area of the metal hardmask layer exposed by the cut in the dielectric layer. After the metal layer is formed, a spacer is formed on a vertical sidewall of the mandrel.