6/07/04 SWTW-2004 Page [1]

Test System Requirements For Wafer Level MRAM Test

Raphael RobertazziIBM/Infineon MRAM Development Alliance

With Acknowledgement ToCascade Microtech Inc.

AndTemptronics Inc.

6/07/04 Robertazzi / SWTW-2004 Page [2]

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.

6/07/04 Robertazzi / SWTW-2004 Page [3]

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

6/07/04 Robertazzi / SWTW-2004 Page [4]

Data Storage

Pinned Layer

Tunneling Oxide

Free Layer

Low Resistance, "0"

High Resistance, "1"

Magnetization

6/07/04 Robertazzi / SWTW-2004 Page [5]

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

6/07/04 Robertazzi / SWTW-2004 Page [6]

Write Selection

S NEasy Axis

Hard Axis

Storage ElementBit Line Magnetic Select

Word Line Magnetic Select

6/07/04 Robertazzi / SWTW-2004 Page [7]

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.

6/07/04 Robertazzi / SWTW-2004 Page [8]

Magnetism Basics

B = µ H (Paramagnetism µ~1) (Diamagnetism µ<1)

B = F (H) (Ferromagnetism)

B: Magnetic Field

H: Magnetizing ForceB

H

FerromagneticMaterial

Current

6/07/04 Robertazzi / SWTW-2004 Page [9]

Permeable Materials Disturb Applied Fields

µ>>1

H

6/07/04 Robertazzi / SWTW-2004 Page [10]

MRAM YKT Test System

Magnet Control

HP82000

S12K

SMUs

6/07/04 Robertazzi / SWTW-2004 Page [11]

MRAM Probe Card

Magnet

High Performance ATECable, τ20/80 < 400 ps

ThermometerH

X

Z

Y

Magnetic Sensors

6/07/04 Robertazzi / SWTW-2004 Page [12]

*Magnet

Iron Core

Current

B=0B>0

Flux

One Set Of Windings

Two Sets Of Windings In Opposition

Current

* IBM Almaden Research Center

6/07/04 Robertazzi / SWTW-2004 Page [13]

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.

6/07/04 Robertazzi / SWTW-2004 Page [14]

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.

6/07/04 Robertazzi / SWTW-2004 Page [15]

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

Bφ

MagnetX

Y Scan

X Scan

Probe

Top View Side View

1kHz Bandwidth

Applied FieldHA

6/07/04 Robertazzi / SWTW-2004 Page [16]

2 4 6 8 10

2

4

6

8

10|Bφ| (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

6/07/04 Robertazzi / SWTW-2004 Page [17]

2 4 6 8 10

2

4

6

8

10|Bφ| (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

6/07/04 Robertazzi / SWTW-2004 Page [18]

2 4 6 8 10

2

4

6

8

10|Bφ| (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

6/07/04 Robertazzi / SWTW-2004 Page [19]

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

* Courtesy Of Temptronics Inc.

# 5-40 Screw

ThermoelectricModule

6/07/04 Robertazzi / SWTW-2004 Page [20]

Ambient Magnetic Field Of Chuck

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

2

4

6

8

10 |Bφ| (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

6/07/04 Robertazzi / SWTW-2004 Page [21]

Vector Field PlotAmbient Magnetic Field Of Chuck

(Thermal Unit On, Ts = 25C)

0.65 G

Ambient Field Very Constant Both In Magnitude And Direction

6/07/04 Robertazzi / SWTW-2004 Page [22]

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

6/07/04 Robertazzi / SWTW-2004 Page [23]

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

6/07/04 Robertazzi / SWTW-2004 Page [24]

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

6/07/04 Robertazzi / SWTW-2004 Page [25]

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.

6/07/04 Robertazzi / SWTW-2004 Page [26]

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.