Back End of Line Metallization Using Ruthenium and Etch Stop
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional metals like copper and tungsten in semiconductor interconnects face increased resistivity and electromigration issues at scaled dimensions below 30 nm, making it difficult to form reliable tall metal interconnect structures without causing shorts or opens, especially at pitches less than 26 nm.
Innovation Solution
The use of alternative metals such as ruthenium and a subtractive etching method to form fully aligned top vias and metal lines, where a conductive etch stop layer and sacrificial fill material are employed to control etching and ensure precise alignment and height, overcoming the challenges of conventional metals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional metals like copper and tungsten are used in interconnects at scaled dimensions below 30 nm, then the interconnect structure can be formed, but resistivity increases and electromigration issues occur
Solution Approach 1:
The patent changes the material parameter by substituting conventional metals (copper, tungsten) with alternative metals ( ruthenium, cobalt, tungsten alloys) that have different electrical and mechanical properties. This material substitution resolves the resistivity and electromigration issues by selecting metals with superior performance characteristics at scaled dimensions below 30 nm
Solution Approach 2:
The patent employs composite material structures including multi-layer metal stacks with conductive liners, etch stop layers, and barrier layers. These composite structures address the reliability issues by combining materials with complementary properties - the alternative metal provides low resistivity while the conductive liner and barrier layers prevent diffusion and reduce electromigration
2Reliability
If tall metal interconnect structures are formed without a conductive etch stop layer, then the structure can be built, but shorts or opens occur especially at pitches less than 26 nm
Solution Approach 1:
The patent introduces a conductive etch stop layer as an intermediary element within the metal stack. This layer serves as a mediator that provides a reliable etch termination point during via formation, preventing both shorts (by stopping etching before penetrating through) and opens (by ensuring complete via formation when needed). The conductive nature of this layer maintains electrical continuity while the etch stop function adds necessary process control
Solution Approach 2:
The patent segments the metal interconnect structure into multiple functional layers including the alternative metal layer, conductive liner layer, etch stop layer, and barrier layer. This segmentation allows each layer to perform its specific function - the etch stop layer provides etch termination while the other layers provide conductivity and structural integrity, resolving the reliability issue without excessive complexity
3Reliability
If alternative metals like ruthenium are used at pitches less than 26 nm, then lower line resistance and increased reliability are achieved, but precise alignment and height control become challenging
Solution Approach 1:
The patent performs preliminary patterning actions by forming mandrel lines and sidewall spacers before the final via etching process. The sidewall spacers are deposited conformally on the mandrels, and gaps between adjacent spacers are filled with non-mandrel material. This preliminary structuring establishes precise geometric relationships that guide subsequent etching, ensuring accurate via placement and alignment with metal lines at pitches less than 26 nm
Solution Approach 2:
The patent replaces direct mechanical alignment methods with a self-aligned chemical etching system. The conductive etch stop layer provides a chemical etch termination point that automatically defines via depth, eliminating the need for complex mechanical depth control. The etch process itself becomes the alignment mechanism, with the etch stop layer serving as a chemical reference that ensures precise via-to-line alignment
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 allows for the fabrication of reliable tall metal interconnect structures with alternative metals like ruthenium at pitches less than 26 nm, providing lower line resistance and increased reliability by ensuring precise alignment and control over via and line heights.
Implementation Method 1
The exposed portions of the second alternative metal layer are etched to the conductive etch stop layer
Implementation Method 2
The fill material is then removed
Data Source
AI summary
Interconnect structures and methods for forming the interconnect structures generally include a subtractive etching process to form a fully aligned top via and metal line interconnect structure. The interconnect structure includes a top via and a metal line formed of an alternative metal other than copper or tungsten. A conductive etch stop layer is intermediate the top via and the metal line. The top via is fully aligned to the metal line.