Bi-layer Mandrel Self-aligned Double Patterning for BEOL Interconnects
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Solution Overview
Problem
Conventional self-aligned double patterning techniques for BEOL interconnect structures are limited by the width of sidewall spacers, leading to incomplete filling of mandrel cuts and potential shorts between wires due to metal asperities, restricting design flexibility and causing distortion in metallization lines.
Innovation Solution
The method involves forming bi-layer mandrel lines with cuts defined after non-mandrel lines have been patterned and cut, allowing for a single etch step that avoids spacer thickness limitations and reduces distortion, enabling greater design flexibility and preventing shorts by maintaining adequate spacing between metallization lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional sidewall spacers are used to define mandrel cuts, then the patterning process is simpler, but the tip-to-tip spacing is limited to twice the spacer thickness, causing incomplete filling and potential shorts
Solution Approach 1:
The patent divides the mandrel structure into two separate layers: a lower mandrel layer that defines the mandrel cut and an upper mandrel layer that is removed later. This segmentation allows the mandrel cut to be defined independently of the sidewall spacer thickness, enabling complete filling of the cut while maintaining design flexibility for various tip-to-tip spacings.
Solution Approach 2:
The patent transitions from a single-layer mandrel structure to a bi-layer mandrel structure, adding a vertical dimension to the mandrel design. By stacking two mandrel layers, the invention decouples the mandrel cut definition from the spacer thickness constraint, allowing independent optimization of both parameters.
2Reliability
If smaller tip-to-tip spacing is used to prevent shorts, then wire separation is improved, but design flexibility and routing options are restricted
Solution Approach 1:
By segmenting the mandrel into two layers, the patent enables independent control of the mandrel cut geometry and the sidewall spacer dimensions. This allows optimization of tip-to-tip spacing for reliability while maintaining adequate spacing for routing flexibility, as the two parameters are no longer coupled.
3Adaptability or versatility
If bi-layer mandrel structure with delayed cut definition is used, then design flexibility and complete filling are achieved, but process complexity increases
Solution Approach 1:
The patent performs preliminary actions by forming both the lower and upper mandrel layers before defining the mandrel cuts. The lower mandrel layer is prepared in advance with the understanding that it will define the cut, while the upper layer is added and then removed to enable clean cut definition without interfering with the spacer formation process.
Data Source
AI summary
Methods of self-aligned double patterning and improved interconnect structures formed by self-aligned double patterning. A mandrel line including an upper layer and a lower layer is formed over a hardmask. A non-mandrel cut block is formed over a portion of a non-mandrel line, after which the upper layer of the mandrel line is removed. An etch mask is formed over a first section of the lower layer of the mandrel line defining a mandrel cut block over a first portion of the hardmask. The first section of the lower layer is arranged between adjacent second sections of the lower layer. The second sections of the lower layer of the mandrel line are removed to expose respective second portions of the hardmask, and the second portions of the hardmask are removed to form a trench. The mandrel cut block masks the first portion of the hardmask during the etching process.