Hydrogen Plasma Doping for Polysilicon Thin-Film Transistors
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Solution Overview
Problem
The challenge in fabricating nanometer-scale NAND flash memory devices lies in the interference between cells, particularly in planar NAND cell scaling below 20 nm, where poly-silicon channel material performance is degraded due to defect traps and grain boundaries, requiring effective passivation techniques to improve electrical characteristics.
Innovation Solution
The implementation of hydrogen plasma doping (PLAD) to form doped polycrystalline silicon layers in 3D NAND devices, decoupling hydrogen plasma doping from annealing processes to achieve higher hydrogen concentrations and minimize device reliability issues, with optimized energy and dose levels, and using in-situ deposition or low-temperature metal depositions as diffusion stop layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If annealing process is performed at 350-400°C in forming gas, then hydrogenation occurs to passivate defect traps, but hydrogen ion molecular diffusivity is very low and hydrogen ion gradient is insufficient
Solution Approach 1:
The patent changes the physical state of hydrogen from molecular (H2) to atomic/ionic form through plasma generation, fundamentally altering the hydrogen delivery mechanism. This enables hydrogen to penetrate grain boundaries effectively without relying on slow molecular diffusion at elevated temperatures
Solution Approach 2:
The patent replaces the thermal annealing mechanism with a plasma-based hydrogenation mechanism. Instead of using heat-driven molecular diffusion, the invention uses plasma-generated atomic hydrogen and hydrogen ions to directly passivate defects, achieving faster and more effective hydrogenation
2Productivity
If poly-silicon channel material is used in 3D NAND devices, then device scalability is improved, but electrical characteristics are degraded due to defect traps and grain boundaries
Solution Approach 1:
The patent extracts hydrogen from the processing environment and introduces it directly into the poly-silicon grain boundaries through plasma doping. This targeted delivery of hydrogen removes the harmful effects of grain boundaries while preserving the beneficial scalability of poly-silicon channel material
Solution Approach 2:
The patent uses plasma as an intermediary to deliver hydrogen atoms and ions to the poly-silicon structure. The plasma state acts as a mediator that enables effective hydrogen incorporation without requiring high-temperature annealing, thus passivating grain boundary defects while maintaining device scalability
3Productivity
If hydrogen plasma doping is decoupled from annealing processes, then hydrogen concentration is increased and processing time is reduced, but process complexity increases
Solution Approach 1:
The patent merges the hydrogenation and annealing functions into a single plasma doping process. By generating hydrogen plasma directly during the doping step, the invention eliminates the need for separate annealing equipment and process steps, reducing overall process complexity while achieving both hydrogenation and thermal activation in one operation
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 significantly enhances carrier mobility, reduces off-state leakage current, and effectively passivates defects at the SiO2/Si interface and poly grain boundaries, resulting in improved device performance with higher hydrogen concentrations and faster processing times.
Implementation Method 1
hydrogen plasma doping (PLAD) to form doped polycrystalline silicon layers
Implementation Method 2
hydrogen plasma doping (PLAD) to form doped polycrystalline silicon layers
Implementation Method 3
hydrogen atoms bond with silicon dangling bonds at the grain boundary and gate oxide/Si interface to passivate the defect traps
Implementation Method 4
Annealing in a forming gas (H2+N2), however, suffers from very low hydrogen ion molecular diffusivity
Data Source
AI summary
Methods of forming thin-film transistors and memories are disclosed. In one such method, polycrystalline silicon is hydrogen plasma doped to form doped polycrystalline silicon. The doped polycrystalline silicon is then annealed. The hydrogen plasma doping and the annealing are decoupled.