Fin Structure Semicircular Top Surface Annealing
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Solution Overview
Problem
Conventional methods for fabricating MirrorBit™ flash memory cells face challenges such as structural limitations that hinder size reduction, planar storage elements leading to sharp corners causing early breakdown, and reliability issues due to hot hole injection damaging the interface between the substrate and tunnel oxide, resulting in undesirable interface states and charge loss.
Innovation Solution
The method involves forming a FIN structure with a semicircular top surface and rounded corners and edges through an annealing process, which includes steps like dilute hydrofluoric acid cleaning, ammonia/peroxide mix cleaning, and hydrogen annealing at specific temperatures and pressures to prevent oxide breakdown and enhance uniform current flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fabrication methods are used to form FIN structures, then manufacturing simplicity is maintained, but sharp corners in the FIN structure cause enhanced electric field concentration leading to early oxide breakdown
Solution Approach 1:
The patent applies curvature by forming the FIN structure with a semicircular top surface instead of sharp corners. This is achieved through a two-step etching process: first forming a trench with rounded bottom corners, then depositing a conformal dielectric layer and performing a second etch to create the final FIN structure with semicircular top surface. The curved geometry eliminates electric field concentration at corners, preventing oxide breakdown and improving device reliability.
2Productivity
If the channel length is reduced to increase memory cell density, then the size of each memory cell is reduced, but the structural limitations of planar storage elements prevent further scaling
Solution Approach 1:
The patent transitions from planar storage elements to a three-dimensional FIN structure with vertical sidewalls and a semicircular top surface. This dimensional change allows the storage element to extend vertically, increasing the effective storage volume without increasing the planar footprint. The FIN structure enables continued scaling of memory cell density by utilizing the third dimension (vertical height) rather than being constrained to two-dimensional planar geometry.
3Ease of operation
If hot hole injection is used to erase MirrorBit cells, then erasure operation is achieved, but the interface between substrate and bottom tunnel oxide is damaged causing undesirable interface states
Solution Approach 1:
The patent provides beforehand cushioning by forming a charge trapping layer between the substrate and the bottom tunnel oxide before device operation. This charge trapping layer acts as a protective buffer that absorbs hot holes during erasure operations, preventing them from reaching and damaging the substrate-tunnel oxide interface. The layer is formed in advance to prevent interface degradation before it occurs, maintaining interface quality and device reliability over multiple program/erase cycles.
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 prevents oxide breakdown at sharp corners, improves reliability by reducing the likelihood of charge loss, and facilitates denser memory arrays with enhanced charge storage capabilities.
Implementation Method 1
The FIN structure is annealed where the annealing causes the top surface to have a semicircular shape and the top surface corners and edges to be rounded
Data Source
AI summary
Methods for fabricating a FIN structure with a semicircular top surface and rounded top surface corners and edges are disclosed. As a part of a disclosed method, a FIN structure is formed in a semiconductor substrate. The FIN structure includes a top surface having corners and edges. The FIN structure is annealed where the annealing causes the top surface to have a semicircular shape and the top surface corners and edges to be rounded.