AlN Cap for Self-Aligned Contact on Non-Recessed Metal Gate
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Solution Overview
Problem
The existing self-aligned contact (SAC) formation processes face challenges in forming contacts on non-recessed metal gates, leading to contact-to-gate short circuit failures due to the erosion of insulating cap layers during CMP and etching processes, particularly at smaller technology nodes like 14 nm and beyond, where lateral scaling and material interactions complicate the formation of uniform metal recesses.
Innovation Solution
The use of an aluminum nitride (AlN) cap formed over a non-recessed metal gate, with a recess depth of 3 nm to 10 nm and a uniform thickness of 1 nm to 10 nm, achieved through a dry or wet etch process and nitrogen plasma treatment, providing a superior insulating layer that withstands subsequent processing steps without degrading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional SAC process with insulating cap layer (e.g., silicon nitride) is used to insulate gate metal from contact metal, then electrical isolation between gate and contact is achieved, but the cap layer is eroded during subsequent CMP and etching processes, leading to contact-to-gate short circuit failures
Solution Approach 1:
The patent changes the material parameter of the cap layer from conventional silicon nitride to aluminum nitride (AlN). AlN possesses superior chemical inertness and etch resistance compared to silicon nitride, allowing it to withstand subsequent CMP and etching processes without erosion. This material substitution maintains electrical isolation reliability while eliminating the erosion problem that causes short circuit failures.
Solution Approach 2:
The patent employs a composite structure consisting of multiple metal layers in the gate (including tungsten and cobalt) combined with an AlN cap layer. The AlN cap serves as a protective composite material that combines electrical insulation with high etch resistance, creating a multi-functional layer that protects the underlying metal gate structure during processing while maintaining electrical isolation.
2Reliability
If a taller dummy gate is used to achieve sufficient SAC cap thickness (at least 30 nm), then effective insulation is obtained, but integration difficulties arise
Solution Approach 1:
The patent changes the material composition parameter to AlN, which has superior etch resistance compared to silicon nitride. This allows the formation of a sufficiently thick cap layer (30 nm or more) without requiring an increased dummy gate height. The AlN material inherently provides both the necessary thickness for effective insulation and the chemical stability to withstand processing, thereby avoiding integration difficulties associated with taller dummy gates.
3Manufacturing precision
If uniform metal recess is formed for SAC on multi-layer metal gate, then proper contact alignment is achieved, but the process becomes complicated due to multiple metal layers of different materials
Solution Approach 1:
The patent extracts the recess formation step from the overall SAC process by forming the AlN cap over a non-recessed metal gate. The AlN cap is deposited conformally over the complete multi-layer metal gate structure without requiring selective recessing of individual metal layers. This extraction of the recess step simplifies the process while the AlN cap maintains proper contact alignment by providing a uniform protective layer over the entire gate structure.
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 reduces the likelihood of contact-to-gate short circuit failures, simplifies the SAC process, and maintains device performance by using a robust AlN cap that is chemically inert and resistant to etching, allowing for effective integration without the need for taller dummy gates.
Implementation Method 1
converting the Al to AlN by a nitrogen plasma treatment or a nitrogen plasma doping process
Implementation Method 2
converting the Al to AlN by a nitrogen plasma treatment or a nitrogen plasma doping process
Data Source
AI summary
A methodology for forming a self-aligned contact (SAC) that exhibits reduced likelihood of a contact-to-gate short circuit failure and the resulting device are disclosed. Embodiments may include forming a replacement metal gate, with spacers at opposite sides thereof, on a substrate, forming a recess in an upper surface of the spacers along outer edges of the replacement metal gate, and forming an aluminum nitride (AlN) cap over the metal gate and in the recess.