Continuous Source Plate Shielding for NAND Flash Reliability

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Solution Overview

Problem

Conventional NAND flash memory devices face issues with electrical shorts and mobile charge damage due to the formation of scratches on interlayer dielectrics during the polishing process, which can lead to conductive bridges and reduced reliability during memory programming operations.

Innovation Solution

A source plate is formed as a continuous metal layer extending over multiple strings of non-volatile memory cells, electrically coupled to source regions and connected via a source line plug, which operates to shield memory cells from voltage fluctuations and prevent electrical shorts by fully removing conductive material from scratches through overetching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a continuous metal source plate layer is formed to provide electromagnetic shielding, then reliability is improved by preventing electrical shorts and mobile charge damage, but device complexity increases due to additional manufacturing steps

Engineering Contradiction:

Improveelectrical isolationVSAvoidmanufacturing process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The source plate is formed as a continuous metal layer before subsequent interlayer dielectric deposition and patterning steps. This preliminary formation ensures electromagnetic shielding is established early, preventing electrical shorts and mobile charge damage before they can occur during later processing or operation.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The source plate serves multiple functions simultaneously: it provides electromagnetic shielding to prevent electrical shorts, acts as a diffusion barrier, and maintains electrical isolation between bit lines and memory cells. This multi-functionality improves reliability without requiring separate dedicated structures for each protective function.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Reliability

If the source plate extends as an uninterrupted metal layer across multiple strings, then electromagnetic shielding effectiveness is improved, but manufacturing precision requirements increase to maintain continuity

Engineering Contradiction:

Improveelectromagnetic shieldingVSAvoidlayer continuity

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The source plate is merged with the common source line structure, extending continuously across multiple memory cell strings without interruption. This merging creates a unified electromagnetic shield that spans the entire array, enhancing shielding effectiveness while using the same metal deposition process for both the source plate and source line connections.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The source plate is formed with different local functions: over the memory cell region it provides electromagnetic shielding, while at the edges it connects to source lines for electrical connection. This local differentiation allows the continuous layer to serve both shielding and electrical connection purposes with appropriate properties in each region.

Inventive Principle:

Principle #3Local quality

3Reliability

If overetching is used to remove conductive material from scratches, then electrical short prevention is improved, but manufacturing complexity increases due to additional etching steps

Engineering Contradiction:

Improvescratch removalVSAvoidetching process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The overetching step is performed immediately after source plate deposition while the metal layer is still fresh and accessible. This preliminary removal of conductive material from scratches prevents potential electrical shorts before subsequent interlayer dielectric deposition, eliminating the need for later corrective steps.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The etching process, which could potentially damage the source plate, is used beneficially to remove harmful conductive material from scratches. By controlling the etch parameters, the harmful effect of etching is converted into the beneficial removal of defect material that would cause electrical shorts.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 source plate effectively prevents electrical shorts and mobile charge damage, enhancing the reliability and stability of memory cell transistors by maintaining electrical isolation and reducing characteristic variations during memory programming.

Implementation Method 1

The source plate is configured as a continuous metal layer that operates to electromagnetically shield the non-volatile memory cells from fluctuations in voltages on the plurality of bit lines during memory programming operations

Methodology Applied

Scientific EffectElectromagnetic shielding: Faraday Cage

Data Source

PatentUS8404578B2Methods of forming nonvolatile memory devices having electromagnetically shielding source plates

Publication Date: 2013.03.26 UNIFICATION TECHNOLOGIES LLC

AI summary

Provided are a semiconductor device and a method of fabricating the same. The semiconductor device includes a semiconductor substrate including a cell array region, memory cell transistors disposed at the cell array region, bitlines disposed on the memory cell transistors, and a source plate disposed between the memory cell transistors and the bitlines to veil the memory cell transistors thereunder.