Test System Requirements For Wafer Level MRAM Test Raphael Robertazzi IBM/Infineon MRAM Development Alliance With Acknowledgement To Cascade Microtech Inc. And Temptronics Inc. 6/07/04 SWTW-2004 Page [1]
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 [2]
What Is MRAM? SL m-1 WL n-1 Free Layer Tunneling Barrier SL m WL n SL m+1 WL n+1 Characteristics High Density. SRAM Read Speed. (2ns) SRAM Write Speed. Magnetic (5ns) Tunnel Non-volatile Junction Pinned Layer 6/07/04 Robertazzi / SWTW-2004 Page [3]
Free Layer Data Storage Tunneling Oxide Pinned Layer Magnetization Low Resistance, "0" High Resistance, "1" 6/07/04 Robertazzi / SWTW-2004 Page [4]
FET Cell Architecture Read, Column Select Write, Column Select Hard Axis Write Current MTJ Sense Amp Write, Row Select Read, Row Select Easy Axis Write Current Or Read Bias 6/07/04 Robertazzi / SWTW-2004 Page [5]
Write Selection Word Line Magnetic Select Hard Axis S N Easy Axis Storage Element Bit Line Magnetic Select 6/07/04 Robertazzi / SWTW-2004 Page [6]
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, B A < 1 G. 6/07/04 Robertazzi / SWTW-2004 Page [7]
Magnetism Basics B: Magnetic Field H: Magnetizing Force Current Ferromagnetic Material B B = µ H (Paramagnetism µ~1) (Diamagnetism µ<1) H B = F (H) (Ferromagnetism) 6/07/04 Robertazzi / SWTW-2004 Page [8]
Permeable Materials Disturb Applied Fields µ>>1 H 6/07/04 Robertazzi / SWTW-2004 Page [9]
MRAM YKT Test System HP82000 S12K SMUs Magnet Control 6/07/04 Robertazzi / SWTW-2004 Page [10]
MRAM Probe Card Magnetic Sensors Thermometer Magnet X Z H Y High Performance ATE Cable, τ 20/80 < 400 ps 6/07/04 Robertazzi / SWTW-2004 Page [11]
*Magnet Flux Iron Core B=0 Current Current B>0 One Set Of Windings Two Sets Of Windings In Opposition * IBM Almaden Research Center 6/07/04 Robertazzi / SWTW-2004 Page [12]
Chuck Characterization 1. 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 (H A = 0) For Different Temperature Set Points. Focus On Current Induced Fields. Thermal Chuck Off. T Set Point = 25 C. T Set Point = 200 C. 6/07/04 Robertazzi / SWTW-2004 Page [13]
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 [14]
Chuck Magnetic Characterization Set Up Chuck Aux Stage Y Bφ Probe 1kHz Bandwidth Y Scan X Scan Top View X Magnet Applied Field H A Side View Probe Hall Sensors Positioned Where Wafer Surface Would Be. Chuck Is Scanned In X &Y, Scan Step 2.5 mm. 6/07/04 Robertazzi / SWTW-2004 Page [15]
Ambient Magnetic Field Of Chuck Ambient Field, (Hx = Hy = 0), Thermal Unit Off 10 B φ (G) Y Position 8 6 4 2 0.150 0.200 0.250 0.300 0.350 0.400 0.450 0.500 0.550 0.600 0.650 B < 0.05 Oe In Central Contour 2 4 6 8 10 X Position 6/07/04 Robertazzi / SWTW-2004 Page [16]
Response To Applied Field Applied Field, (Hx = 0, Hy = 19.9 Oe), Thermal Unit Off 10 B φ (G) Y Position 8 6 4 2 B < 1.3% In Orange Contour 2 4 6 8 10 X Position 16.00 16.25 16.50 16.75 17.00 17.25 17.50 17.75 18.00 18.25 18.50 18.75 19.00 19.25 19.50 19.75 20.00 20.25 20.50 6/07/04 Robertazzi / SWTW-2004 Page [17]
Ambient Magnetic Field Of Chuck Ambient Field, (Hx = Hy = 0), Thermal Unit On, T = 25C 10 B φ (G) Y Position Variation < 0.3 G Away From Aux Chucks 8 6 4 2 2 4 6 8 10 X Position 0.400 0.425 0.450 0.475 0.500 0.525 0.550 0.575 0.600 0.625 0.650 0.675 0.700 0.725 0.750 0.775 0.800 0.825 0.850 0.875 0.900 6/07/04 Robertazzi / SWTW-2004 Page [18]
Thermal Module And Screw Locations* (Thermal Unit On, T = 25 C) # 5-40 Screw Thermoelectric Module * Courtesy Of Temptronics Inc. 6/07/04 Robertazzi / SWTW-2004 Page [19]
Ambient Magnetic Field Of Chuck Ambient Field, (Hx = Hy = 0), Thermal Unit On, T = 40C 10 B φ (G) Y Position 8 6 4 Variation < 0.3 2 G Away From Aux Chucks 2 4 6 8 10 X Position 0.200 0.225 0.250 0.275 0.300 0.325 0.350 0.375 0.400 0.425 0.450 0.475 0.500 0.525 0.550 0.575 0.600 0.625 0.650 0.675 0.700 6/07/04 Robertazzi / SWTW-2004 Page [20]
Vector Field Plot Ambient 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 [21]
Vector Field Plot Applied 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 [22]
AC Magnetic Field Characterization (Center Of Chuck) 0.05 Oe B(t) 4 ms t Thermal Chuck Off Thermal Unit On, T Set Point = 25 C T Chuck = 25 C No Differences Observed Thermal Unit On, T Set Point = 200 C T Chuck = 40 C 6/07/04 Robertazzi / SWTW-2004 Page [23]
Degaussing Procedure B H Magnet Current 1.0 0.8 0.6 0.4 0.2 0.0-0.2-0.4-0.6-0.8-1.0 250 Oe Degaussing Curve 0 20 40 60 80 100 120 140 160 180 200 Time (ms) 6/07/04 Robertazzi / SWTW-2004 Page [24]
Degaussing Experiments Measure Baseline Fields 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 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 [25]
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. 6/07/04 Robertazzi / SWTW-2004 Page [26]