CoSi2 Formation via Amorphous MSix Interlayer and Silicon Nitride Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for forming CoSi2 in integrated circuit fabrication often require multiple annealing steps and struggle to prevent void formation, with high-temperature annealing leading to cobalt oxide formation that is difficult to remove.
Innovation Solution
A method involving the deposition of a substantially amorphous metal silicide layer and a cobalt layer over a silicon-containing substrate, followed by annealing to form CoSi2 beneath the amorphous layer, which prevents void formation and allows for single-step cobalt silicide conversion without unreacted cobalt stripping.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature annealing is used to form CoSi2, then conductivity is improved, but cobalt oxide formation occurs which is difficult to remove
Solution Approach 1:
A thin layer of silicon nitride is deposited over the cobalt layer before annealing. This preliminary protective layer prevents cobalt from reacting with oxygen during high-temperature annealing, eliminating cobalt oxide formation while allowing the annealing process to proceed at temperatures sufficient to form CoSi2 with good conductivity
Solution Approach 2:
Silicon nitride serves as an intermediary protective layer between the cobalt and the oxygen-containing environment. This intermediate layer blocks oxygen from reaching the cobalt during annealing, preventing harmful oxidation while permitting the desired silicide formation reaction to occur
2Reliability
If multiple annealing steps are used to form CoSi2, then conversion completeness is improved, but process complexity increases
Solution Approach 1:
The protective silicon nitride layer enables combining multiple annealing functions into a single annealing step. The layer protects against oxidation while permitting silicide formation, allowing one annealing process to simultaneously achieve complete CoSi2 conversion without requiring separate protective and conversion annealing steps
Solution Approach 2:
The presence of the silicon nitride layer changes the effective annealing parameters, allowing the process to be conducted at temperatures and for durations that would normally cause oxidation. This parameter change enables complete conversion in a single step by preventing the harmful side reaction that would otherwise require process compromises
3Speed
If cobalt layer is deposited directly on silicon, then diffusion efficiency is improved, but void formation occurs during annealing
Solution Approach 1:
A thin layer of silicon nitride is introduced as an intermediary between the cobalt and silicon layers. This intermediate layer controls the diffusion process and prevents direct cobalt-silicon contact that leads to void formation, while still allowing sufficient diffusion to form CoSi2 efficiently
Solution Approach 2:
The silicon nitride layer is applied with specific local properties - it is thin enough to permit diffusion but structured to prevent the direct cobalt-silicon interface that causes voiding. The local quality of this intermediate layer modifies the diffusion characteristics to eliminate the harmful void formation while maintaining efficiency
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 enables efficient formation of CoSi2 with reduced void formation and eliminates the need for multiple annealing steps, ensuring effective cobalt silicide conversion and preventing cobalt oxide formation at high temperatures.
Implementation Method 1
The substrate is annealed effective to diffuse cobalt of the cobalt-comprising layer through the substantially amorphous MSix-comprising layer and combine with silicon of the silicon-containing substrate to form CoSi2 beneath the substantially amorphous MSix-comprising layer
Implementation Method 2
The substrate is annealed effective to diffuse cobalt of the cobalt-comprising layer through the substantially amorphous MSix-comprising layer
Data Source
AI summary
The invention included to methods of forming CoSi2, methods of forming field effect transistors, and methods of forming conductive contacts. In one implementation, a method of forming CoSi2 includes forming a substantially amorphous layer comprising MSix over a silicon-containing substrate, where “M” comprises at least some metal other than cobalt. A layer comprising cobalt is deposited over the substantially amorphous MSix-comprising layer. The substrate is annealed effective to diffuse cobalt of the cobalt-comprising layer through the substantially amorphous MSix-comprising layer and combine with silicon of the silicon-containing substrate to form CoSi2 beneath the substantially amorphous MSix-comprising layer. Other aspects and implementations are contemplated.