CMP Process for MTJ Capping Layer Exposure

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Solution Overview

Problem

Existing methods for manufacturing magnetic tunnel junction (MTJ) devices, particularly in MRAM and magnetic sensors, face challenges in efficiently and effectively exposing the buried capping layer for electrical contact without damaging the structures, often requiring complex via hole formation processes that are costly and prone to errors.

Innovation Solution

A three-stage chemical mechanical polishing (CMP) process using conventional and highly selective slurry systems, followed by dilution with de-ionized water, to planarize and expose the MTJ capping layers without the need for via holes, ensuring minimal damage and precise control over dielectric removal to facilitate direct electrical contact.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If conventional CMP process is used to remove dielectric layer, then planarization is achieved, but the buried capping layer cannot be fully exposed for electrical contact

Engineering Contradiction:

Improveexposure of capping layerVSAvoidvia hole formation process

Core Design Contradiction:

Manufacturing precisionVSDevice complexity

Solution Approach 1:

The invention changes the chemical composition parameters of the CMP slurry by incorporating specific chemicals (HF, nitric acid, acetic acid, and metal salts) to achieve selective removal of the dielectric layer while preserving the capping layer, thereby exposing the capping layer without requiring via hole formation

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The invention extracts and removes only the dielectric layer material through the specialized CMP process, leaving the capping layer intact and exposed, eliminating the need for separate via hole etching and filling operations

Inventive Principle:

Principle #2Taking out (Extraction)

2Manufacturing precision

If highly selective slurry is used to remove dielectric, then capping layer exposure is improved, but removal rate drops with decreasing pressure

Engineering Contradiction:

Improveselective dielectric removalVSAvoidCMP removal rate

Core Design Contradiction:

Manufacturing precisionVSProductivity

Solution Approach 1:

The invention modifies the slurry composition by adding specific chemicals (HF, nitric acid, acetic acid, and metal salts) that enhance the selective removal mechanism, maintaining high selectivity and removal rate even at lower polishing pressures by altering the chemical reactivity rather than relying solely on mechanical pressure

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The CMP slurry is formulated as a composite chemical system containing multiple active ingredients (HF, nitric acid, acetic acid, and metal salts) that work synergistically to achieve both high selectivity and maintained removal rate across varying pressure conditions

Inventive Principle:

Principle #40Composite materials

3Reliability

If via hole formation process is used, then electrical contact is achieved, but process complexity and cost increase

Engineering Contradiction:

Improveelectrical contactVSAvoidnumber of process steps

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention merges the dielectric removal function and the capping layer exposure function into a single CMP process step, eliminating the need for separate via hole etching, filling, and planarization steps that would otherwise be required to achieve electrical contact

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The specialized CMP slurry performs multiple functions simultaneously: it removes the dielectric layer, exposes the capping layer, and prepares the surface for electrical contact, making the process universally applicable without requiring additional specialized steps

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 approach eliminates the need for via hole formation, reduces process complexity and cost, and ensures minimal damage to MTJ devices, allowing for reliable and efficient electrical contact to the metal interconnect layers while maintaining the integrity of the MTJ structures.

Implementation Method 1

CMP is widely used in semiconductor fabrication to planarize a non-planar top surface during the processing of semiconductor wafers. The process uses a slurry of a corrosive chemical along with an abrasive, in conjunction with a polishing pad, to effect the planarization.

Methodology Applied

Scientific EffectChemical Mechanical Polishing:

Implementation Method 2

The process uses a slurry of a corrosive chemical along with an abrasive, in conjunction with a polishing pad, to effect the planarization.

Methodology Applied

Scientific EffectAbrasion: Abrasion

Implementation Method 3

One particular type of CMP involves the use of a highly selective slurry (HSS), which has the ability to remove different materials at significantly different removal rates.

Methodology Applied

Scientific EffectSelective Chemical Etching:

Data Source

PatentUS8105948B2Use of CMP to contact a MTJ structure without forming a via

Publication Date: 2012.01.31 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

A process is described for making contact to the buried capping layers of GMR and MTJ devices without the need to form and fill via holes. CMP is applied to the structure in three steps: (1) conventional CMP (2) a Highly Selective Slurry (HSS) is substituted for the conventional slurry to just expose the capping layer, and (3) the HSS is diluted and used to clean the surface as well as to cause a slight protrusion of the capping layers above the surrounding dielectric surface, making it easier the contact them without damaging the devices below.