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 [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.