Selective Spacer Double Patterning for Uniform Metal Interconnects
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Solution Overview
Problem
The challenge of fabricating interconnect structures in semiconductor devices at small dimensions is exacerbated by issues such as line wiggling and non-uniformity in metal line heights due to the use of alternative metals like ruthenium, which are difficult to etch and fill without causing irregularities.
Innovation Solution
A method involving selective spacer deposition on metal interconnection patterns, followed by chemical mechanical polishing (CMP) to remove excess material, ensuring uniformity and linearity of metal interconnects, using materials like cobalt, copper, or titanium nitride as spacers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If alternative metals like ruthenium are used for fabricating interconnects, then copper resistivity limits are overcome, but line wiggling and non-uniformity issues occur
Solution Approach 1:
A mandrel structure is introduced as an intermediary element between the first and second metal interconnection patterns. The mandrel serves as a template that guides the formation of the second metal pattern, ensuring uniform spacing and preventing line wiggling. The mandrel is selectively removed after transferring the pattern, leaving precisely spaced second metal lines that maintain geometric uniformity throughout the interconnect structure.
Solution Approach 2:
The first metal interconnection pattern is formed in advance as a preparatory structure that defines the spacing for subsequent second metal patterns. This preliminary pattern serves as a template that pre-establishes the geometric constraints and spacing requirements, allowing the second metal lines to be formed with uniform dimensions and correct positioning before the actual interconnect functionality is completed.
2Manufacturing precision
If subtractive etching is used to pattern metal interconnects, then pattern definition is achieved, but dry etching thick Ru films at tight pitches is very difficult
Solution Approach 1:
The pattern is transferred from the first metal interconnection pattern to the second metal interconnection pattern through a copying process. The first metal pattern serves as a master template that is replicated to create the second metal pattern with identical spacing and geometric characteristics. This copying approach avoids the need for difficult direct etching of thick Ru films at tight pitches, as the pattern information is copied rather than directly etched.
Solution Approach 2:
Instead of directly etching the second metal interconnection pattern through conventional subtractive methods, the approach is inverted by first forming the first metal pattern and using it as a template to define the second pattern. The mandrel structure is formed first, then the second metal is deposited around it, and finally the mandrel is removed. This inversion of the conventional process sequence transforms a difficult etching problem into a more manageable deposition and removal process.
3Ease of manufacture
If Damascene scheme is used for interconnect fabrication, then filling capability is improved, but line wiggling occurs creating high line resistance
Solution Approach 1:
The mandrel structure acts as an intermediary that enforces geometric linearity during the Damascene filling process. By depositing the second metal around the mandrel and then removing the mandrel, the process ensures that the second metal lines maintain straight, uniform geometry throughout the fill operation, preventing the line wiggling that would otherwise occur during conventional Damascene processing of alternative metals.
4Productivity
If conventional etching processes are used, then material removal is achieved, but non-uniform line heights and irregularities are created
Solution Approach 1:
The conventional mechanical etching process is replaced with a deposition-based approach. Instead of removing material through etching to create the second metal pattern, the process uses selective deposition of metal around the mandrel structure. This substitution of the mechanical removal system with a deposition system eliminates the non-uniformities and irregularities inherent in etching, while maintaining high productivity through efficient material deposition.
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 minimizes line wiggling and achieves uniform line heights, improving the fabrication of interconnect structures with critical dimensions of 3 nm or less, reducing non-linearity and irregularities caused by traditional etching processes.
Implementation Method 1
A spacer layer is selectively deposited on the exposed surfaces of the first metal interconnection pattern
Implementation Method 2
A spacer layer is selectively deposited on the exposed surfaces of the first metal interconnection pattern
Implementation Method 3
Subsequently, a metal overburden layer is deposited on the spacer layer. The excess portion of the metal overburden layer is removed, i.e., that portion deposited over a top surface of the metal interconnection pattern and the spacer layer
Data Source
AI summary
A first metal interconnection pattern is formed over a substrate. A spacer layer is selectively deposited on the exposed surfaces of the first metal interconnection pattern. Subsequently, a metal overburden layer is deposited on the spacer layer. The excess portion of the metal overburden layer is removed, i.e., that portion deposited over a top surface of the metal interconnection pattern and the spacer layer. This forms a second metal interconnection pattern. The elements of the second metal interconnection pattern are located between respective elements of the first metal interconnection pattern.