Flash Memory Resistivity Measurement Pattern
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Solution Overview
Problem
In flash memory devices, the resistivity measurement of floating gates is affected by parasitic interface resistance, leading to severe variations in measured values, and the Self-Aligned Floating Gate (SAFG) scheme makes it difficult to form resistivity measurement patterns on isolation films, degrading tunnel oxide film characteristics and causing inaccurate device evaluations.
Innovation Solution
A flash memory device with a resistivity measurement pattern where the resistivity measurement floating gate is buried in a trench structure within an isolation film, allowing direct connection of measurement contacts to the polysilicon films, and the use of dummy polysilicon films for uniform density and protection during processing, minimizing parasitic interface effects and enabling accurate resistivity measurement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the resistivity measurement contact is indirectly connected to the floating gate through tungsten film and control gate polysilicon film, then the measurement can be performed, but the measured resistivity value includes severe variations due to parasitic interface resistance
Solution Approach 1:
The patent extracts and eliminates the parasitic interface resistance by removing the intermediate tungsten film and control gate polysilicon film from the measurement path. The resistivity measurement contact is directly connected to the floating gate, taking out the harmful parasitic interfaces that were causing measurement variations.
Solution Approach 2:
The patent introduces a dummy polysilicon film as an intermediary layer between the resistivity measurement contact and the floating gate. This dummy polysilicon film serves as a mediator that provides a stable, controlled interface without the parasitic effects of the original tungsten-polysilicon interfaces, enabling accurate measurement.
2Measurement precision
If the resistivity measurement floating gate is located on the isolation film, then resistivity measurement can be performed, but the tunnel oxide film characteristics are degraded due to plasma damage
Solution Approach 1:
The patent creates a copy of the floating gate structure specifically for measurement purposes. The dummy polysilicon film replicates the electrical characteristics of a floating gate without requiring the presence of the actual tunnel oxide film, allowing measurement without plasma damage to the oxide.
Solution Approach 2:
The patent segments the floating gate function into two parts: the actual floating gate for device operation and a dummy polysilicon film for measurement. This segmentation allows the measurement function to be performed separately without affecting the integrity of the tunnel oxide film in the active device region.
3Manufacturing precision
If the floating gate is formed in a self-aligned manner in the isolation trench, then the floating gate is automatically formed on the active region, but it becomes impossible to form the floating gate on the isolation film for resistivity measurement
Solution Approach 1:
The patent makes the dummy polysilicon film multi-functional: it serves as both a resistivity measurement element and a placeholder that maintains the self-aligned structure. This universal element allows the system to maintain self-aligned manufacturing precision while also enabling resistivity measurement capability on the isolation film.
Data Source
AI summary
A flash memory device has a resistivity measurement pattern and method of forming the same. A trench is formed in an isolation film in a Self-Aligned Floating Gate (SAFG) scheme. The trench is buried to form a resistivity measurement floating gate. This allows the resistivity of the floating gate to be measured even in the SAFG scheme. Contacts for resistivity measurement are directly connected to the resistivity measurement floating gate. Therefore, variation in resistivity measurement values, which is incurred by the parasitic interface, can be reduced.