Doped Metal Silicide Source for Flash Memory

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Solution Overview

Problem

Increasing memory density in flash memory devices while maintaining low resistance in the common source, as higher resistance leads to voltage drops that can disrupt memory operations relying on small voltage differences.

Innovation Solution

Forming a doped metal silicide source with a semiconductor material to act as a metal source for vertical strings of memory cells, which reduces sheet resistance and maintains adequate gate-induced drain leakage performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Quantity of substance

If additional groups of strings of memory cells are added to increase memory density, then memory density is improved, but the common source resistance increases causing voltage drops

Engineering Contradiction:

Improvememory densityVSAvoidvoltage stability

Core Design Contradiction:

Quantity of substanceVSReliability

Solution Approach 1:

The patent changes the material parameter of the source from conventional polysilicon to doped metal silicide, which fundamentally alters the resistance characteristic. This material substitution enables the source to maintain low resistance even as its length increases to support additional memory cell strings, thereby resolving the contradiction between increasing memory density and maintaining voltage stability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs a composite structure by doping metal silicide with phosphorus or arsenic to create a material with superior electrical properties. This composite approach combines the low resistance特性 of metal silicide with the benefits of doping, achieving a source that can handle increased current loads from additional memory strings without significant voltage drops.

Inventive Principle:

Principle #40Composite materials

2Reliability

If doped metal silicide source is formed, then sheet resistance is reduced, but manufacturing complexity increases

Engineering Contradiction:

Improvesheet resistanceVSAvoidmanufacturing process

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent applies preliminary doping to the metal silicide source during the fabrication process, incorporating phosphorus or arsenic doping steps into the existing manufacturing flow. By performing the doping action in advance during source formation rather than as a separate subsequent step, the patent reduces overall manufacturing complexity while achieving the desired low resistance properties.

Inventive Principle:

Principle #10Preliminary action

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 doped metal silicide source provides lower sheet resistance and supports efficient memory operations by enabling diffusion from the source to the semiconductor channel, enhancing memory density without significant voltage drops.

Implementation Method 1

enabling diffusion from the source to the semiconductor channel

Methodology Applied

Scientific EffectDiffusion: Diffusion

Data Source

PatentUS11665893B2Methods and apparatuses having strings of memory cells including a metal source

Publication Date: 2023.05.30 MICRON TECHNOLOGY INC

AI summary

Methods for forming a string of memory cells, an apparatus having a string of memory cells, and a system are disclosed. A method for forming the string of memory cells comprises forming a metal silicide source material over a substrate. The metal silicide source material is doped. A vertical string of memory cells is formed over the metal silicide source material. A semiconductor material is formed vertically and adjacent to the vertical string of memory cells and coupled to the metal silicide source material.