Self-Aligned Programmable Resistive RAM Cell Formation

Solution Overview

Problem

The challenge in manufacturing small programmable resistive RAM cells lies in the reliance on aggressive photolithography masks for precise alignment, which is costly and prone to errors in integrating them with existing planar integrated circuit layers.

Innovation Solution

A self-aligned process is developed for forming nonvolatile memory cells, where programmable resistive elements with a smaller cross-section are formed by removing upper portions of interlayer contacts and filling the resulting openings, reducing the need for precise photolithographic masks and enhancing product yield.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If photolithographic masks are used to define small programmable resistive RAM cells, then manufacturing precision is improved, but device complexity and cost increase

Engineering Contradiction:

Improvealignment precisionVSAvoidmask alignment complexity

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The interlayer contact structures serve as self-aligned masks for defining the programmable resistive RAM cells. The contact openings automatically provide the precise alignment references needed, eliminating the need for separate photolithographic masks and their associated alignment procedures.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The interlayer contact structures act as an intermediary element that bridges the function of both electrical contacts and alignment masks. By forming contacts first, they become the reference structures for subsequent cell definition, combining two functions into one structure.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Manufacturing precision

If photolithographic masks are used to define small programmable resistive RAM cells, then manufacturing precision is improved, but production cost increases

Engineering Contradiction:

Improvecell size precisionVSAvoidmanufacturing cost

Core Design Contradiction:

Manufacturing precisionVSEase of manufacture

Solution Approach 1:

The interlayer contact structures serve as self-aligned masks for defining the programmable resistive RAM cells. The contact openings automatically provide the precise alignment references needed, eliminating the need for separate photolithographic masks and their associated alignment procedures.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The upper portions of the interlayer contacts are removed to create the cell-defining openings. The lower portions of the contacts remain to provide electrical connectivity, effectively discarding the unnecessary upper portions while recovering and utilizing the lower portions for their primary electrical function.

Inventive Principle:

Principle #34Discarding and recovering

3Use of energy by moving object

If smaller programmable resistive RAM cells are manufactured, then power consumption decreases, but manufacturing precision requirements increase

Engineering Contradiction:

Improvepower consumptionVSAvoidalignment precision

Core Design Contradiction:

Use of energy by moving objectVSManufacturing precision

Solution Approach 1:

The interlayer contact structures serve as self-aligned masks for defining the programmable resistive RAM cells. The contact openings automatically provide the precise alignment references needed, eliminating the need for separate photolithographic masks and their associated alignment procedures.

Inventive Principle:

Principle #25Self-service

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

This method allows for the cost-effective and precise formation of small programmable resistive RAM cells with improved alignment, reducing the complexity and cost of photolithography while maintaining high precision and yield in integrated circuit manufacturing.

Implementation Method 1

Two dielectric layers have an etching selectivity difference. The step of removing a dielectric layer until exposing at least part of another dielectric layer, thereby exposing at least part of the upper portions of the interlayer contacts.

Methodology Applied

Scientific EffectEtching selectivity:

Implementation Method 2

A high current reset electrical pulse melts and quenches the programmable resistive element into an amorphous state, raising the resistance of the programmable resistive element. A low current set electrical pulse crystallizes and lowers the resistance of the programmable resistive element.

Methodology Applied

Scientific EffectPhase change: Phase Change

Data Source

PatentUS7595218B2Programmable resistive RAM and manufacturing method

Publication Date: 2009.09.29 MACRONIX INTERNATIONAL CO LTD

AI summary

Programmable resistive RAM cells have a resistance that depends on the size of the programmable resistive elements. Manufacturing methods and integrated circuits for programmable resistive elements with uniform resistance are disclosed that have a cross-section of reduced size compared to the cross-section of the interlayer contacts.