Fully Aligned Top Via Interconnect Without RIE Damage
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional BEOL interconnect structures face challenges with copper interconnects reaching resistivity limits, and alternative metals like ruthenium face issues such as difficult dry etching at tight pitches and line wiggling, necessitating a fully-aligned via structure that avoids metal fangs and via distortion.
Innovation Solution
A fully-aligned via structure is formed above a bottom conductive line with a dielectric spacer and hard mask wall, using a substrative metal etch to prevent line wiggling and via distortion, and a low-density via opening to avoid damage and distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional subtractive etch scheme is used for ruthenium interconnects, then via formation is possible, but dry etching at tighter pitch becomes very difficult
Solution Approach 1:
The patent inverts the conventional subtractive etch approach by using a additive damascene scheme where metal is deposited over a hard mask pattern and then planarized. This replaces the difficult dry etching step with more manageable deposition and CMP processes, solving the etching difficulty at tight pitches while maintaining via formation precision
Solution Approach 2:
The hard mask pattern is formed first before metal deposition, establishing the via location and dimensions in advance. This preliminary patterning allows subsequent metal filling to proceed without complex etching, enabling precise via formation while avoiding the difficulties of tight-pitch dry etching
2Manufacturing precision
If conventional damascene etch scheme is used for ruthenium interconnects, then via formation is possible, but line wiggling is caused by ruthenium fill
Solution Approach 1:
The patent introduces a hard mask layer as an intermediary between the lithographic pattern and the metal fill process. This hard mask serves as a stable template that prevents direct metal-to-lithography interaction, eliminating the line wiggling effect while maintaining precise via formation through the mediating hard mask structure
Solution Approach 2:
The hard mask is formed and patterned before metal deposition, establishing stable line dimensions in advance. This preliminary structuring prevents the metal fill process from causing line wiggling, as the hard mask maintains critical dimension stability throughout subsequent processing steps
3Measurement precision
If via opening has high density and aspect ratio, then via alignment precision may be improved, but via distortion occurs
Solution Approach 1:
The patent modifies the via opening parameters by optimizing density and aspect ratio to lower values that prevent distortion. This parameter adjustment maintains sufficient alignment precision while avoiding the shape distortion that would result from excessively high density and aspect ratio configurations
4Manufacturing precision
If reactive ion etching is used for via formation, then via shape control is improved, but RIE damage occurs on dielectric surface
Solution Approach 1:
The patent extracts and eliminates the reactive ion etching step from the via formation process. By using alternative methods such as deposition over hard mask followed by planarization, the beneficial via shape control is achieved through different means while removing the harmful RIE damage to the dielectric surface
Data Source
AI summary
An interconnect structure is provided the includes a top electrically conductive via structure that is fully-aligned to a bottom electrically conductive line structure. The interconnect structure has a maximized contact area between the top electrically conductive via structure and the bottom electrically conductive line structure without metal fangs that are caused by over etching. The dielectric surface of the interconnect dielectric material layer that is adjacent to the top electrically conductive via structure is free of reactive ion etch (RIE) damage. Further, there is no line wiggling since the bottom electrically conductive line structure is formed by a substrative metal etch. Further, there is no via distortion since the via opening used to house the top electrically conductive via structure has a density and aspect ratio that are low enough to avoid via distortion.