Floating Gate Nonvolatile Memory Device With Contact Plug Control Gate
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Solution Overview
Problem
Conventional nonvolatile memory devices, such as stack gate EEPROM, dual gate EEPROM, and split gate EEPROM, face limitations in integration due to the need for additional processes to form control gates, while single gate EEPROMs have limited integration due to the coupling of floating gates with impurity regions, restricting the degree of integration in system-on-chip applications.
Innovation Solution
A nonvolatile memory device is fabricated using a floating gate with a contact plug acting as a control gate, where the spacer serves as a dielectric layer, allowing for increased integration without separate processes for forming control gates, and the contact plugs are designed to maximize coupling ratios by adjusting their shapes and distances relative to the floating gate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional processes are used to form control gates (stack gate EEPROM, dual gate EEPROM, split gate EEPROM), then the coupling ratio and operation characteristics are improved, but the fabrication complexity and process steps increase
Solution Approach 1:
The patent merges the control gate function with the contact plug structure. The contact plug is extended to overlap with the floating gate, allowing it to serve dual purposes: providing electrical contact and functioning as the control gate. This eliminates the need for separate control gate formation processes while maintaining the necessary coupling ratio for proper operation.
Solution Approach 2:
The contact plug is designed to perform multiple functions simultaneously: it provides electrical connection to the substrate and acts as the control gate for the floating gate. This multi-functional design reduces the total number of components and process steps required in the fabrication process.
2Ease of manufacture
If single gate EEPROM structure is used with fewer process steps, then the fabrication complexity is reduced, but the degree of integration is limited due to coupling requirements
Solution Approach 1:
The patent transitions from a planar single-gate structure to a three-dimensional configuration where the contact plug extends vertically and laterally to overlap with the floating gate. This dimensional change allows the control gate function to be integrated into the contact structure without increasing the planar footprint, thereby improving the degree of integration while maintaining ease of manufacture.
3Reliability
If contact plug is positioned closer to floating gate to increase overlapping area, then the coupling ratio is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The spacer structure is formed first on the sidewall of the floating gate, establishing a predefined reference structure. The contact plug is then formed to overlap with this spacer, which automatically positions it at the correct distance and orientation relative to the floating gate. This preliminary formation of the spacer eliminates the need for high-precision direct positioning of the contact plug, reducing manufacturing precision requirements while maintaining the necessary overlapping area for adequate coupling ratio.
Data Source
AI summary
A nonvolatile memory device includes a floating gate formed over a substrate; a contact plug formed on a first side of the floating gate and disposed parallel to the floating gate with a gap defined therebetween; and a spacer formed on a sidewall of the floating gate and filling the gap, wherein the contact plug and the floating gate have a sufficiently large overlapping area to enable the contact plug to operate as a control gate for the floating gate.