Low and Stable Contact Resistance With Reduced Cleaning......A Paradigm Shift

Transcription

1 Low and Stable Contact Resistance With Reduced Cleaning......A Paradigm Shift Jerry J. Broz, Ph.D. Research and Development Boulder, Colorado Reynaldo M. Rincon Probe Coordinator, Inc. Dallas, Texas 1

2 Overview Participants Introduction, Constraints, and Objectives Experimental Design Alpha-Testing Results Contact Theory and Tip Oxidation Probe Card Metrology Beta-Testing Results Summary 2

3 Participants End User -! Rey Rincon Probe Material Development -! Jerry Broz, Ph.D. Probe Card Construction - Micro-Probe, Inc.! Carol Whann! Paul Elizondo! Steve Beaver Testing Facilities Applied Precision - Probe card analyzer! Scott Lindblat! John Strom Sandia National Laboratories - Prober and tester! David Monroe, Ph.D.! Scot Swanson 3

4 Introduction & Objectives 4

5 Introduction Factors Affecting Probe Card Life Probe wear Cleaning frequency Factors Affecting Probe Card Performance Low and stable contact resistance Test temperature range - 25 o C to 150 o C Approach Develop and characterize a new probe material Understand mechanisms and phenomena of contact 5

6 Research Constraints Identify and Develop a New Probe Material Stiffness, strength, and wear characteristics! Elastic modulus sufficient force to make good electrical contact! Yield strength no plastic deformation during touchdown! Microhardness resistance to mechanical wear Consistent scrub on aluminum wafer! Balanced contact force! Planarity and alignment Low and stable C RES! Test temperature range 30 o C to 85 o C! Reduced cleaning frequency target 75% reduction! Good electrical properties bulk resistivity within 10X Reasonable cost and availability! Consistent with existing technologies 6

7 Research Objectives Benchmark Existing Technologies vs. New Material Common probe materials! Tungsten (W)! Tungsten-rhenium (WRe) Low contact resistance probe materials! Beryllium-copper (BeCu)! Paliney-7 (high palladium alloy) Solve Real World Production Floor Issues Contact resistance instability during testing! Temperature range 25 o C to 85 o C (and above)! High current testing Cost of ownership! Probe card service life! Cleaning frequency! Through-put 7

8 Experimental Design 8

9 Experimental Design Pseudo Production Test Environment Test temperatures - 30 o C and 85 o C Forcing current - 50 ma Probing on blank aluminum wafer with 3-mil overtravel No overlapping scrub marks Primary Probe Needle Properties Failure mode observations during wafer test Contact resistance magnitude and stability Probe needle life and post-test properties! Tip diameter changes! Balanced contact force! Planarity and alignment Consistent Variables Identical probe card builds - probe material variations 9

10 Probe Card Layout Y - Position (mils) Probe Card Design I Tungsten Tungsten-rhenium Contact Material NewTek Probe Probe Card Design II Beryllium-copper Paliney-7 Contact Material NewTek Probe X - Position (mils) 10

11 Alpha - Testing Results 11

12 100 α -Test Results: Contact Resistance (W and WRe Probes) C RES values were "filtered" using a maximum allowable value of 60-Ω Ω) Log Contact Resistance (log 10 1 W-Probes at 85 o C WRe-Probes at 85 o C W-Probes at 30 o C WRe-Probes at 30 o C Abrasive cleaning on 3-µm grit pad performed after 100K touchdowns 0.1 0K 50K 100K 150K 200K Touchdowns on Aluminum Wafer 12

13 100 α -Test Results: Contact Resistance (All Probe Material at 85 o C) C RES values were "filtered" using a maximum allowable value of 60-Ω Log Contact Resistance (log Ω) Abrasive cleaning on 3-µm grit pad performed after 100K touchdowns on Card Design I W and WRe-Probes NewTek TM Probes Paliney7-Probes BeCu-Probes 0K 100K 200K 300K 400K 500K Touchdowns on Aluminum Wafer 13

14 Probe Tip Contact Surface Heel After 500K touchdowns on Al-wafer at 85 o C Heel S c r u b NewTek Probe S c r u b Tungsten S c r u b Tungsten-Rhenium Heel 14

15 Probe Tip Contact Surface Heel After 500K touchdowns on Al-wafer at 85 o C Heel S c r u b NewTek Probe S c r u b Beryllium-Copper S c r u b Paliney-7 Heel 15

16 Contact Theory and Probe Tip Oxidation 16

17 Contact Theory and Wafer Test FULL OVERTRAVEL HEEL Contact 60-70% of Tip Diameter Probe Tip Diameter TOE Estimated Contact Area During Scrub S Non-Conducting Regions c r u b HEEL FIRST CONTACT TOE Contact 25-30% of Tip Diameter Conducting Metal-to-Metal a-spots Semi-Conducting Regions PRVX 2 images courtesy of Applied Precision, Inc. 17

18 a-spot Temperature Joule Heating at Conductive a-spot during Wafer Test Dramatic increase in localized temperature Function of voltage drop and material properties ONLY First approximation of temperature at the a-spot (Carbonéro et al., 1995): T a Spot = T Bulk + U αρλ α 1 α T Bulk = ambient temperature U = voltage drop across the interface α = temperature coefficient of resistivity ρ = bulk resistivity λ = thermal conductivity 18

19 Approximate a-spot Temperature (W and WRe-Probes) o C) Log Temperature (log Abrasive cleaning on 3-µm grit pad performed after 100K touchdowns 1200 o C = onset of "catastrophic" oxidation in air 700 o C = onset of rapid oxidation (WO 3 forms on surface of "lower" tungstate layer) 500 o C = oxide allotropic transformation (oxide cracks and becomes unprotective) 300 o C = W-oxidation threshold (formation of "higher" tungstenates) W-Probes at 85 o C WRe-Probes at 85 o C W-Probes at 30 o C WRe-Probes at 30 o C 0K 50K 100K 150K 200K Touchdowns on Aluminum Wafer 19

20 Approximate a-spot Temperature (All Probe Materials at 85 o C) o C) Log Temperature (log W and WRe-Probes Onset of BeCu-oxidation at o C NewTek TM Probes Paliney 7-Probes BeCu-Probes Abrasive cleaning on 3-µm grit pad performed after 100K touchdowns 0K 100K 200K 300K 400K 500K Touchdowns on Aluminum Wafer 20

21 Probe Card Metrology 21

22 Metrology after 500K Touchdowns Probe Alignment All materials within the test floor tolerance of ±0.30-mils No significant differences between materials Probe Planarity Overall NewTek-Probes maintained better planarity Probe Tip Diameter W and WRe demonstrated the smallest diameter change BeCu exhibited the largest diameter change of all materials NewTek changes was not significantly different than Paliney-7 Balanced Contact Force (BCF) No significant changes between initial and final values Design-I significantly lower BCF than Design-II BCF differences were not reflected in C RES response 22

23 Card Design-I Alignment Card Design I W and WRe Card Design I NewTek-Probe VYErr (mil) VYErr (mil) VXErr (mil) VXErr (mil) 23

24 Card Design-II Alignment Card Design II BeCu and Paliney-7 Card Design II NewTek-Probe VYErr (mil) VYErr (mil) VXErr (mil) VXErr (mil) 24

25 Probe Card Planarity Card Design I Card Design II Planarity (mil) Tungsten Tungsten-Rhenium NewTek Probe Beryllium-Copper Paliney-7 NewTek Probe Probe Material Probe Material 25

26 Probe Tip Diameter One abrasive cleaning at 100K: 30-hits on 3-µm grit abrasive pad Time = 0K Touchdowns Time = 500K Touchdowns Tip Diameter (mils) Final Average Initial Average Tungsten Tungsten Rhenium NewTek Design-I Beryllium Copper Paliney-7 NewTek Design-II Probe Material 26

27 Balanced Contact Force Card Design I Card Design II Probe Force (gram-force) Tungsten Tungsten-Rhenium NewTek Probe Beryllium-Copper Paliney-7 NewTek Probe Probe Material Probe Material 27

28 4.0 Probe Contact Resistance (3-mil overtravel at 85 o C) NewTek Avg BCF = 5.2 grams NewTek Avg BCF = 3.7 grams Contact Resistance (Ω) NewTek Avg C RES = 560 mω NewTek Avg C RES = 670 mω 0.0 0K 100K 200K 300K 400K 500K Touchdowns on Aluminum Wafer 28

29 Beta-Testing Results 29

30 Preliminary Beta - Test Results Probe Cards Built with NewTek Probes 5-mil and 8-mil diameter needles Room temperature wafer test Elevated temperature and high current testing - IN PROGRESS Testing Performed on Actual Product Fewer continuity failures Drastically reduced cleaning frequency Significantly less operator intervention required Some Operational Modifications Are Necessary NewTek Probes are not as robust as W and WRe-probes Handling, tweaking, and abrasive cleaning procedures 30

31 Summary 31

32 Paradigm Shifts.. Adherent aluminum NOT SOLEY responsible for C RES variations Al and Al 2 O 3 particles visible on ALL materials at 85 o C W and WRe probes demonstrated increasing and unstable C RES C RES of other materials remained relatively low and stable Tungstenate film resistance contributes to high and unstable C RES Formation of tenacious tungstenates on W and WRe probe tips occurs with elevated ambient and high localized temperatures Cyclic C RES variations related to a-spot melting/solidification phenomena Low bulk resistivity does not imply low C RES Contact properties are a function of the size and number of a-spots Film resistance dominates over the bulk resistance contribution 32

33 Summary NewTek Probe Material Advantages Non-oxidizing probe material Higher modulus, strength, and hardness than BeCu and Paliney-7 Lower and more stable C RES than W and WRe at elevated temperature Alpha-Test Results at 30 o C and 85 o C Low and stable C RES Lower contact force achieved stable electrical contact BCF, planarity, and alignment maintained over time Reasonable wear behavior 33

34 Summary Preliminary Beta-Test Results Infrastructure Modifications Required! Production floor handling procedures! Probe needle tweaking practices! Abrasive cleaning protocols! Overtravel to make reliable contact! Required probe card BCF! Etc... 34

35 Summary Preliminary Beta-Test Results Decreased continuity failures Reduced cleaning frequency Less operator intervention 3-6% increase in throughput is predicted Additional Beta-Testing Recommended 35