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Test System Requirements For Wafer Level MRAM Test

Raphael RobertazziIBM/Infineon MRAM Development Alliance

With Acknowledgement ToCascade Microtech Inc.

AndTemptronics Inc.

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Outline Brief Introduction To MRAM Technology. MRAM Specific Test Challenges For Analytical Test. Brief Review Of Magnetism. YKT Analytical MRAM Test System. Experiments: Magnetic Characterization Of Summit

12K Probe Station With Thermal Chuck. Ambient Field, With And Without Temperature Control. Field With Applied Magnet. AC Field Characterization. Degaussing Experiments. Conclusions.

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What Is MRAM?

Tunneling Barrier

SL m-1

SLm+1SL m

WLn-1

WLn+1

WL n

Magnetic Tunnel

Junction

Free Layer

Pinned Layer

Characteristics

High Density.

SRAM Read Speed. (2ns)

SRAM Write Speed. (5ns)

Non-volatile

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Data Storage

Pinned Layer

Tunneling Oxide

Free Layer

Low Resistance, "0"

High Resistance, "1"

Magnetization

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FET Cell Architecture

MTJ

Read, Row Select

Read, Column SelectWrite, Column Select

Write, Row Select

Hard Axis WriteCurrent

Easy Axis WriteCurrent Or Read Bias

Sense Amp

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Write Selection

S NEasy Axis

Hard Axis

Storage ElementBit Line Magnetic Select

Word Line Magnetic Select

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Analytical Test System Requirements

Digital Tester With Highly Flexible Test Pattern Capability.

High Bandwidth Connections To The DUT. Low Level Of Electrical Noise. Mixed Signal Capability. Temperature Control. Magnetics Package (Experiments)

Ability To Apply Arbitrary Magnetic Fields In The Plane Of The Wafer.

Magnetically Characterized Chuck, BA < 1 G.

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Magnetism Basics

B = H (Paramagnetism ~1) (Diamagnetism

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Permeable Materials Disturb Applied Fields

>>1

H

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MRAM YKT Test System

Magnet Control

HP82000

S12K

SMUs

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MRAM Probe Card

Magnet

High Performance ATECable, 20/80 < 400 ps

ThermometerH

X

Z

Y

Magnetic Sensors

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*Magnet

Iron Core

Current

B=0B>0

Flux

One Set Of Windings

Two Sets Of Windings In Opposition

Current

* IBM Almaden Research Center

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Chuck Characterization1. Remnant Field Experiments (H = 0).

Focus On Variation Of In Plane Fields.[Static (DC) Measurements.]

Thermal Chuck Off. Thermal Chuck On.

T = 25 C, Scalar And Vector Measurements. T = 40 C.

2. Field Measurements With Applied In Plane (H > 0).Focus On Search For Highly Permeable Magnetic Materials In The Chuck. [Static (DC) Measurements.]

Thermal Chuck Off.3. AC Field Measurements (HA = 0) For Different

Temperature Set Points. Focus On Current Induced Fields.

Thermal Chuck Off. TSet Point = 25 C. TSet Point = 200 C.

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Chuck Characterization

4. Remnant Fields Revisited.Focus On Absolute Remnant Field Measurements, Remnant Fields After Application Of Large Magnetizing Force.[Static (DC) Measurements.]

Absolute Field Away From The Chuck. Absolute Field Near Center Of Chuck And Aux Stage. Degaussing Experiments.

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Chuck Magnetic Characterization Set Up

Probe Hall Sensors Positioned Where Wafer Surface Would Be. Chuck Is Scanned In X &Y, Scan Step 2.5 mm.

Y

Chuck Aux Stage

B

MagnetX

Y Scan

X Scan

Probe

Top View Side View

1kHz Bandwidth

Applied FieldHA

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2 4 6 8 10

2

4

6

8

10|B| (G)

Ambient Field, (Hx = Hy = 0), Thermal Unit Off

X Position

Y P

ositi

on0.1500.2000.2500.3000.3500.4000.4500.5000.5500.6000.650

Ambient Magnetic Field Of Chuck

B < 0.05 OeIn Central Contour

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2 4 6 8 10

2

4

6

8

10|B| (G)

Applied Field, (Hx = 0, Hy = 19.9 Oe), Thermal Unit Off

X Position

Y P

ositi

on

16.0016.2516.5016.7517.0017.2517.5017.7518.0018.2518.5018.7519.0019.2519.5019.7520.0020.2520.50

Response To Applied Field

B < 1.3%In Orange Contour

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2 4 6 8 10

2

4

6

8

10|B| (G)

Ambient Field, (Hx = Hy = 0), Thermal Unit On, T = 25C

X Position

Y P

ositi

on0.4000.4250.4500.4750.5000.5250.5500.5750.6000.6250.6500.6750.7000.7250.7500.7750.8000.8250.8500.8750.900

Ambient Magnetic Field Of Chuck

Variation < 0.3 G Away From Aux Chucks

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Thermal Module And Screw Locations*(Thermal Unit On, T = 25 C)

* Courtesy Of Temptronics Inc.

# 5-40 Screw

ThermoelectricModule

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Ambient Magnetic Field Of Chuck

Variation < 0.3 G Away From Aux Chucks 2 4 6 8 10

2

4

6

8

10 |B| (G)Ambient Field, (Hx = Hy = 0), Thermal Unit On, T = 40C

X Position

Y P

ositi

on0.2000.2250.2500.2750.3000.3250.3500.3750.4000.4250.4500.4750.5000.5250.5500.5750.6000.6250.6500.6750.700

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Vector Field PlotAmbient Magnetic Field Of Chuck

(Thermal Unit On, Ts = 25C)

0.65 G

Ambient Field Very Constant Both In Magnitude And Direction

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Vector Field PlotApplied Field (Hx = 0, Hy = 19.9 Oe)

(Thermal Unit Off)

19.9 G

Almost No Distortion Of Applied Field Magnitude Or Direction Near Studs

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AC Magnetic Field Characterization(Center Of Chuck)

0.05 Oe

4 ms

Thermal Chuck Off Thermal Unit On,TSet Point = 25 CTChuck = 25 C

Thermal Unit On,TSet Point = 200 C

TChuck = 40 C

B(t)

t

No Differences Observed

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Degaussing Procedure

B

H

0 20 40 60 80 100 120 140 160 180 200-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

Mag

net C

urre

ntTime (ms)

250 Oe Degaussing Curve

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Degaussing Experiments

1. Zero Probe In Zero Gauss Chamber.2. Read Field In Lab Far From Probe Station: |B| = 0.34 G. 3. Read Field At Center Of Chuck: |B| = 0.35 G.4. Read Field Near Aux Chuck: |B| = 0.35 G.

Apply Hy = 250 Oe And Measure Remnant Fields

Measure Baseline Fields

1. Read Field At Center of Chuck: |B| = 0.45 G. (Remnant Magnet?)2. Degauss And Read Field At Center Of Chuck: |B| = 0.44 G. 3. Read Field Near Aux Chuck: |B| = 0.85 G.4. Degauss And Read Field Near Aux Chuck: |B| = 0.5 G.

Application Of Large Fields Produced Some Remnant Offsets,Which Can Be Reduced By Degaussing.

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Conclusions

Summit 12K Demonstrated Excellent Magnetic Performance For Demanding Analytical Studies Of MRAM Devices.

Best Magnetic Performance Observed Near The Center Of The Chuck.

Aux Stages Perturbed Applied Fields And Had Remnant Offsets, But The Stages Can Be Easily Removed Or Replaced With Parts Made From Non-magnetic Materials.

Turning Thermal Unit On Did Not Significantly Degrade Magnetic Performance.

Negligible AC Fields Detected.