Composite High-k DRAM Capacitor Liner for Low Leakage
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Solution Overview
Problem
The challenge in reducing the size of DRAM cells while maintaining sufficient cell capacitance and preventing cell-to-cell shorts is exacerbated by the formation of leaky titanium nitride electrodes during high-κ dielectric deposition, which requires a balance between dielectric thickness and leakage, especially with decreasing dimensions and local critical dimension non-uniformity issues.
Innovation Solution
Introducing a tantalum nitride (TaN) liner that converts to tantalum oxide, allowing for a thinner high-κ layer deposition and reducing leakage, while also optimizing the zirconium oxide film thickness to maintain capacitance and prevent shorts, thereby increasing cell electrode size and reducing cell-to-cell shorts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-κ dielectric layer is deposited on a titanium nitride electrode, then the dielectric constant is improved, but leakage increases due to titanium oxide formation
Solution Approach 1:
A titanium oxide layer is intentionally formed as an intermediary between the titanium nitride electrode and the high-κ dielectric layer. This controlled oxide layer acts as a mediator that prevents direct contact between the high-κ dielectric and titanium nitride, thereby eliminating the harmful leakage effect while preserving the high dielectric constant benefit.
Solution Approach 2:
The naturally occurring titanium oxide, which was previously considered a harmful leakage source, is converted into a beneficial intermediate layer. By controlling its formation and thickness, the oxide layer that caused problems becomes a functional component that protects the high-κ dielectric from the titanium nitride electrode.
2Productivity
If the space between cells is reduced to increase density, then productivity is improved, but the risk of cell-to-cell shorts increases
Solution Approach 1:
The titanium oxide layer serves as a protective intermediary that enables closer cell spacing. By preventing direct contact between adjacent cell structures through this stable oxide barrier, the design allows reduced pitch while maintaining electrical isolation and preventing shorts.
Solution Approach 2:
The approach changes the critical parameter from the physical gap distance to the chemical stability of the oxide layer. Instead of relying solely on physical spacing, the solution uses the electrical properties of the titanium oxide interface to prevent shorts, enabling denser packing.
3Reliability
If aluminum oxide is increased to reduce leakage, then reliability is improved, but capacitance decreases due to thickness loss
Solution Approach 1:
The structure uses a composite approach combining titanium nitride, titanium oxide, and high-κ dielectric materials. This composite stack achieves both low leakage (through the stable titanium oxide interface) and high capacitance (through the high-κ layer), avoiding the trade-off present in single-material solutions.
Solution Approach 2:
The solution changes the material parameter from aluminum oxide to a titanium-based oxide system. The titanium oxide provides comparable or superior leakage blocking properties while allowing for optimized capacitance through the high-κ dielectric layer thickness control.
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 higher cell capacitance with reduced cell-to-cell shorts and improved manufacturing efficiency by allowing larger cell electrodes and thinner high-κ layers, addressing the limitations of existing DRAM cell design.
Implementation Method 1
a metal nitride liner on the bottom electrode... During deposition of the high-κ layer, titanium oxide (TiO) forms on the titanium nitride (TiN) electrode
Implementation Method 2
depositing a high-κ dielectric layer in the plurality of openings on the nitride liner, wherein the deposition forms an oxide layer on the nitride liner
Data Source
AI summary
Provided are methods to reduce the thickness of a high-κ layer needed in a DRAM capacitor and, thus, allow the cell electrodes to be larger, giving higher cell capacitance. A tantalum nitride (TaN) layer is introduced as a liner in the capacitor hole before a titanium nitride (TiN) electrode layer. The TaN layer converts to a thin layer of tantalum oxide (Ta2O5), which permits a reduction in the high-κ layer thickness for the same capacitance versus leakage. Because this Ta2O5 is formed directly on the cell electrode, it ensures a low leakage film exists in the narrowest gaps even before the high-κ layer is deposited.