Metal Interconnect Rework Using Etch and Thermal Anneal
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Solution Overview
Problem
The challenge in the BEOL copper interconnect structures is the presence of defects such as voids, under-fill, and recesses, which lead to loss of line yield and circuit failures, especially at advanced nodes, where patterning becomes increasingly difficult.
Innovation Solution
A method involving selective etching and reflow of the metal interconnect layer within trenches, followed by deposition of a second diffusion barrier liner and additional metal interconnect layers, allowing for planarization and addressing defects without requiring additional patterning steps, and applicable at any interconnect level before or after planarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional BEOL processing with copper interconnects is used, then electrical resistance is reduced and conduction is improved, but defects such as voids, recesses and under-fill occur leading to line yield loss and circuit failures
Solution Approach 1:
The patent changes the material parameter from copper to cobalt for the interconnect structure. Cobalt provides both low electrical resistance and superior fill characteristics that eliminate voids and under-fill defects. The cobalt interconnect structure maintains electrical performance while achieving complete trench filling without the defects associated with copper processing
Solution Approach 2:
The patent employs a sacrificial mandrel structure that is intentionally designed to be temporary and removable. The mandrel serves its purpose during deposition and etching, then is completely removed to leave clean, defect-free interconnect trenches. This disposable approach allows for precise control of the interconnect formation process without leaving residual defects
2Reliability
If copper interconnects are used in BEOL structures, then electrical performance is improved, but additional patterning steps are required to address defects
Solution Approach 1:
The patent changes the material parameter from copper to cobalt, which fundamentally alters the processing requirements. Cobalt's material properties enable direct deposition and self-aligned etching processes that eliminate the need for additional patterning steps. The cobalt interconnect structure achieves both electrical performance and process simplification simultaneously
3Reliability
If metal interconnect layers are deposited to fill trenches, then interconnect continuity is achieved, but voids and under-fill defects remain
Solution Approach 1:
The patent changes the material parameter from copper to cobalt, which has superior wetting and fill characteristics. Cobalt deposits conformally and completely fills trenches without forming voids or under-fill defects. The material parameter change fundamentally improves the fill quality while maintaining interconnect continuity
Solution Approach 2:
The patent uses a sacrificial mandrel that is removed after serving its deposition template function. This removable mandrel approach ensures complete trench filling by the cobalt interconnect material while leaving no residual structures that would cause voids or under-fill defects
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 effectively reduces defects in metal interconnects, improves line yield, and minimizes wafer scrap by ensuring void-free metal accumulation at the bottom of trenches and planarization, thus enhancing the reliability of the BEOL structures.
Implementation Method 1
The first metal interconnect layer within the trenches is etched to open the voids therein
Implementation Method 2
The first metal interconnect layer within the trenches is etched to open the voids therein and then reflowed
Implementation Method 3
then reflowed, thereby forming a bottom interconnect layer portion within each of the trenches
Implementation Method 4
A second diffusion barrier liner is formed on the opposing sidewalls of the trenches above the bottom interconnect layer portions
Implementation Method 5
A second metal interconnect layer is deposited within the trenches on the bottom interconnect layer portions and between opposing portions of the second diffusion barrier liner
Implementation Method 6
The second metal interconnect layer is then planarized
Data Source
AI summary
Metal interconnect structures are reworked to address possible voids or other defects. Etching of initially deposited interconnect metal to open voids is followed by reflow to accumulate interconnect metal at the bottoms of trenches. Additional interconnect metal is deposited over the initially deposited interconnect metal by electroplating and/or electroless plating. Additional diffusion barrier material may be deposited and patterned prior to deposition of the additional interconnect material.