Nanocrystal Memory Device Manufacturing via Precursor Self-Assembly
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Solution Overview
Problem
The existing methods for forming metal nanocrystals in memory devices result in a random size distribution, making it difficult to control the threshold voltage across semiconductor wafers, and are costly and complex, with the control oxide layer degrading the charge storage capacity and failing to fill spaces between small dimension nanocrystals effectively.
Innovation Solution
A method involving the formation of a substrate with a dielectric layer, followed by the deposition of precursor molecules with specific ligands that govern the spacing of nucleation centers, allowing for controlled metal island formation and subsequent annealing to create uniform nanocrystals, which are then embedded in a dielectric material for charge storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the agglomeration process is used to form nanocrystals, then nanocrystals can be formed in the charge storage region, but the size distribution of nanocrystals becomes random and difficult to control
Solution Approach 1:
The patent applies preliminary action by forming a self-assembled monolayer of precursor molecules on the tunnel oxide surface before nanocrystal formation. The ligands on these precursor molecules pre-determine the spacing and positioning of nucleation centers, ensuring uniform nanocrystal size and distribution from the outset rather than relying on random agglomeration processes.
Solution Approach 2:
The patent uses precursor molecules with sacrificial ligands as intermediaries between the tunnel oxide and the metal nanocrystals. These precursor molecules serve as templates that guide metal atom deposition and control nanocrystal nucleation, enabling precise size and spacing control while simplifying the overall process.
2Manufacturing precision
If high temperatures are used for metal agglomeration, then nanocrystals form, but the mean size becomes sensitive to local temperature variations
Solution Approach 1:
The patent performs preliminary self-assembly of precursor molecules on the tunnel oxide surface before metal deposition. This pre-organization of nucleation centers at controlled spacing ensures that subsequent low-temperature metal deposition produces uniform nanocrystals, eliminating sensitivity to local temperature variations during the formation process.
Solution Approach 2:
The patent changes the temperature parameter from high-temperature agglomeration (typically >400°C) to low-temperature deposition (below 200°C). This parameter change, combined with the use of precursor molecules, enables precise control of nanocrystal size and reduces sensitivity to temperature variations across the wafer.
3Ease of manufacture
If control oxide layer is deposited on nanocrystals, then gate structure is completed, but the nanocrystals are oxidized degrading charge storage capacity
Solution Approach 1:
The patent uses a dielectric material as an intermediary barrier between the control oxide and the metal nanocrystals. This intermediate layer prevents direct contact and oxidation of the nanocrystals while still allowing the control oxide to be deposited and the gate structure to be completed, thereby preserving charge storage capacity.
Solution Approach 2:
The patent employs sacrificial ligands on precursor molecules that are removed during processing, and uses a thin dielectric barrier that serves its protective function and can be integrated into the existing dielectric stack. These disposable or temporary elements enable the protection of nanocrystals without adding permanent complexity to the device structure.
4Manufacturing precision
If traditional metal layers (gold, platinum silicide, silver, nickel) are used for nanocrystal formation, then nanocrystals can be formed, but the process becomes costly and complex
Solution Approach 1:
The patent replaces expensive traditional metal layers (gold, platinum silicide, silver, nickel) with inexpensive precursor molecules that self-assemble on the tunnel oxide. These cheap organic precursors serve as templates for nanocrystal formation, dramatically reducing material costs while maintaining or improving nanocrystal uniformity.
Solution Approach 2:
The patent substitutes the mechanical/thermal agglomeration process with a chemical self-assembly process. Instead of relying on high-temperature heating to drive metal atom diffusion and agglomeration, the patent uses chemical reactions of precursor molecules with metal sources to deposit metal atoms at controlled positions, simplifying the process and reducing costs.
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 well-controlled size and distribution of nanocrystals, resulting in consistent threshold voltages and allowing the use of a variety of metals, including those with higher melting temperatures, while avoiding the drawbacks of traditional agglomeration processes.
Implementation Method 1
A plurality of nucleation centers are formed on the first layer of dielectric material
Implementation Method 2
An absorption layer comprising a first atom having a sacrificial ligand and a second atom having a sacrificial ligand are formed on the first layer of dielectric material
Implementation Method 3
A metal island is formed from at least one nucleation center of the plurality of nucleation centers
Implementation Method 4
subsequent annealing to create uniform nanocrystals
Data Source
AI summary
A method for manufacturing a memory device having a metal nanocrystal charge storage structure. A substrate is provided and a first layer of dielectric material is grown on the substrate. An absorption layer is formed on the first layer of dielectric material. The absorption layer includes a plurality of titanium atoms bonded to the first layer of dielectric material, a nitrogen atom bonded to each titanium atom, and at least one ligand bonded to the nitrogen atom. The at least one ligand is removed from the nitrogen atoms to form nucleation centers. A metal such as tungsten is bonded to the nucleation centers to form metallic islands. A dielectric material is formed on the nucleation centers and annealed to form a nanocrystal layer. A control oxide is formed over the nanocrystal layer and a gate electrode is formed on the control oxide.