Bit Line Metal Smoothing via Titanium Barrier Annealing
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Solution Overview
Problem
Modern integrated circuits face issues with surface roughness and increased resistance due to high temperature deposition processes affecting bit line metals, leading to operational integrity damage and contamination risks in silicon nitride hardmask deposition.
Innovation Solution
A method involving the deposition of a titanium layer, followed by titanium nitride layers, annealing, and the formation of a ruthenium bit line metal layer, along with a cap layer and hardmask, using low-pressure chemical vapor deposition and atomic layer deposition processes at controlled temperatures to minimize surface roughness and resistivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high temperature deposition processes are used for bit line metal formation, then deposition speed and film quality improve, but surface roughness increases and resistance increases
Solution Approach 1:
A titanium layer is deposited on the polysilicon layer before the bit line metal deposition. This preliminary titanium layer serves as a foundation that prevents surface roughness development during subsequent high-temperature deposition processes, while still allowing fast deposition speeds and maintaining low resistance.
2Stability of the object's composition
If high temperature annealing is performed, then grain growth and metal density improve, but surface roughness increases
Solution Approach 1:
A titanium nitride layer is deposited over the titanium layer to act as an intermediary barrier. This layer allows the bit line metal to undergo grain growth and densification during high-temperature annealing while preventing the formation of surface roughness, effectively mediating between the competing requirements of grain growth and surface smoothness.
3Device complexity
If conventional deposition processes are used, then process simplicity is maintained, but contamination occurs between metal and silicon nitride hardmask
Solution Approach 1:
The titanium and titanium nitride layers serve as diffusion barrier intermediaries between the bit line metal and the silicon nitride hardmask. These layers prevent inter-diffusion of metal atoms into the silicon nitride and silicon into the metal, eliminating contamination without requiring complex process changes.
4Manufacturing precision
If titanium layer and titanium nitride layers are added, then surface roughness and resistance are reduced, but manufacturing complexity increases
Solution Approach 1:
The titanium layer thickness is optimized to approximately 30-50 angstroms and the titanium nitride layer to approximately 15-40 angstroms. These specific parameter ranges provide the optimal balance between preventing surface roughness, maintaining low resistance, and minimizing the number of additional process steps required.
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 bit line resistance and surface roughness, provides cleaner interfaces, and minimizes contamination, ensuring lower resistivity and flexibility in bit line metal choices while maintaining the thermal budget of the device.
Implementation Method 1
depositing a titanium layer of approximately 30 angstroms to approximately 50 angstroms on a polysilicon layer on a substrate, depositing a first titanium nitride layer of approximately 15 angstroms to approximately 40 angstroms on the titanium layer
Implementation Method 2
annealing the substrate at a temperature of approximately 700 degrees Celsius to approximately 850 degrees Celsius
Implementation Method 3
depositing a bit line metal layer of ruthenium on the second titanium nitride layer
Implementation Method 4
depositing a cap layer on the bit line metal layer at a deposition temperature of approximately 350 degrees Celsius to approximately 400 degrees Celsius and depositing a hardmask layer on the cap layer
Data Source
AI summary
A process of smoothing a top surface of a bit line metal of a memory structure decreases resistance of a bit line stack. The process includes depositing a titanium layer of approximately 30 angstroms to 50 angstroms on a polysilicon layer on a substrate, depositing a first titanium nitride layer of approximately 15 angstroms to approximately 40 angstroms on the titanium layer, annealing the substrate at a temperature of approximately 700 degrees Celsius to approximately 850 degrees Celsius, depositing a second titanium nitride layer of approximately 15 angstroms to approximately 40 angstroms on the first titanium nitride layer after annealing, and depositing a bit line metal layer of ruthenium on the second titanium nitride layer.