Seamless High Aspect Ratio Contact Metallization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current metallization techniques for advanced CMOS devices face challenges in reducing contact resistance due to the increasing contribution of middle-of-line (MOL) contact resistance, particularly with the use of titanium nitride and tungsten layers, which lead to seam formation and voids in high aspect ratio contact holes, affecting the performance of scaled-down tungsten contacts.
Innovation Solution
A method involving a patterned mandrel with columns, conformal deposition of a contact metal layer, isotropic etching to form discrete vertical metal contact portions, and subsequent removal of the mandrel, ensuring seamless interconnect structures by maintaining gaps between metal contact portions, which are then filled with a dielectric layer to eliminate seams and reduce resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conformal deposition processes are used to fill high aspect ratio contact holes, then the contact holes can be filled with metal conductor, but vertical seams are formed within the metal contacts which displace metal conductor volume and lead to higher resistance
Solution Approach 1:
The patent segments the continuous conformal metal layer into discrete vertical metal contact portions by introducing a mandrel structure. The mandrel divides the contact hole into multiple regions, causing the conformally deposited metal to form separate vertical segments along the sidewalls rather than a continuous layer, thereby eliminating seam formation at the convergence point
Solution Approach 2:
The mandrel acts as an intermediary structure that mediates the deposition process. By introducing this temporary physical barrier, the patent enables the conformal deposition to proceed without seam formation, as the mandrel prevents metal accumulation at the center where seams would otherwise form. The mandrel is later removed, leaving the desired seam-free metal contact structure
2Reliability
If thick TiN liners are used to prevent fluorine diffusion during tungsten deposition, then diffusion protection is improved, but contact hole diameter is reduced and metal conductor volume is displaced leading to higher resistance
Solution Approach 1:
The patent applies preliminary action by forming the metal contact structure before the tungsten deposition step. The conformal metal layer is deposited and patterned into vertical contact portions prior to introducing the tungsten layer, ensuring that the metal conductor volume is established before any fluorine diffusion risk arises. This sequence allows for optimized metal volume while maintaining diffusion protection through process sequencing rather than relying on thick liners
3Productivity
If dimensional scaling is applied to reduce transistor size, then performance and power consumption are improved, but contact resistance increases due to the increasing contribution of middle-of-line contact resistance
Solution Approach 1:
The patent transitions from traditional planar contact structures to a three-dimensional vertical architecture. By forming high aspect ratio vertical metal contact portions along the sidewalls of mandrel structures, the invention exploits the vertical dimension to increase effective contact area and conductor volume without increasing lateral footprint, thereby maintaining low contact resistance despite dimensional scaling
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 results in low-resistance interconnect structures with high aspect ratios, compatible with existing metal deposition processes, and eliminates seams within metal contact structures, facilitating the adoption of scaled-down technology nodes.
Implementation Method 1
A contact metal layer is conformally deposited on the structure such that vertically extending gaps are formed between portions of the contact metal layer lining the sidewalls of the columns
Implementation Method 2
The contact metal layer is isotropically etched to form discrete vertical metal contact portions lining the sidewalls of the columns
Data Source
AI summary
A low resistance middle-of-line interconnect structure is formed without liner layers. A contact metal layer is deposited on source/drain regions of field-effect transistors and directly on the surfaces of trenches within a dielectric layer using plasma enhancement. Contact metal fill is subsequently provided by thermal chemical vapor deposition. The use of low-resistivity metal contact materials such as ruthenium is facilitated by the process. The process further facilitates the formation of metal silicide regions on the source/drain regions.