Polysilicon Floating Gate Gettering Agents for Oxidation
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Solution Overview
Problem
As memory densities increase, traditional polysilicon floating gate NAND flash structures face challenges with data retention, program saturation, and oxidation, making it impractical for thinner devices, as they lack sufficient room for intergate dielectric and control gate wrapping, and using high-k dielectrics can oxidize polysilicon, reducing its charge storage capability.
Innovation Solution
Incorporating gettering agents, such as metal silicides, into the charge storage structure to mitigate oxidation risks by reacting with SiO2, forming high-k dielectric compounds that reduce equivalent oxide thickness and ensure silicon availability for charge storage, thereby enhancing the functionality of thin polysilicon floating gates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If high-k dielectrics are used to increase memory density, then memory density is improved, but oxidation of polysilicon occurs reducing charge storage capability
Solution Approach 1:
A silicon nitride layer is introduced as an intermediary barrier between the high-k dielectric and the polysilicon floating gate. This intermediate layer prevents direct contact and oxidation reactions between the high-k dielectric materials and the polysilicon charge storage structure, thereby maintaining charge storage capability while enabling the use of high-k dielectrics for increased memory density
Solution Approach 2:
The gate stack is constructed as a composite structure combining multiple materials including silicon nitride, polysilicon, and high-k dielectric materials. This composite approach allows each material to perform its optimal function: silicon nitride provides oxidation protection, polysilicon provides charge storage, and high-k dielectric provides high capacitance for high density, resolving the contradiction between density and reliability
2Quantity of substance
If polysilicon floating gate thickness is reduced to increase memory density, then memory density is improved, but data retention and program saturation worsen
Solution Approach 1:
The gate stack uses a composite structure with silicon nitride and high-k dielectric materials that enables the polysilicon floating gate to be made thinner while maintaining sufficient charge storage capability. The high-k dielectric provides higher capacitance which compensates for the reduced polysilicon thickness, allowing increased memory density without sacrificing data retention
Solution Approach 2:
The invention changes the dielectric constant parameter of the gate insulation layer by using high-k dielectric materials. This parameter change allows the system to achieve the required capacitance with a thinner polysilicon floating gate, thereby increasing memory density while maintaining data retention through the enhanced electric field from the high-k material
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
The use of gettering agents effectively reduces oxidation, maintains silicon's charge storage capability, and lowers the equivalent oxide thickness, improving the programming and erasing efficiency of memory cells, making them suitable for higher memory densities.
Implementation Method 1
Incorporating gettering agents, such as metal silicides, into the charge storage structure to mitigate oxidation risks by reacting with SiO2, forming high-k dielectric compounds
Data Source
AI summary
Memory devices might include an array of memory cells and a control logic to control access of the array of memory cells, where a memory cell of the array of memory cells might include a first dielectric adjacent a semiconductor, a control gate, a second dielectric between the control gate and the first dielectric, and a charge storage structure between the first dielectric and the second dielectric, wherein the charge storage structure comprises a charge-storage material and a gettering agent.