Fritting Experiences with non-ohmic contact resistance C RES while wafer test probing

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1 Fritting Experiences with non-ohmic contact resistance C RES while wafer test probing Jan Martens Philips Semiconductors Hamburg Awarded Best Overall Presentation at SWTW-2006

2 Overview Fritting What s that? Fritting How to measure? C RES measurements within production environment Definition of the Fritting ratio Φ Why measuring Fritting and not only C RES? Measurement results Summary and Outlook 06/12/2006 SWTW2006 Jan Martens 2

3 Fritting What s that? The vertical Probe tip touches the contact pad. Depending on the contact pressure the oxide film is broken partly and electrical bridges arise. The number and size of the bridges is equivalent to the C RES quality Probe Tip Contact Pad 06/12/2006 SWTW2006 Jan Martens 3

4 Fritting What s that? What happens, if bridges are only few and small? Probe tip Oxide film Contact pad Small bridge through oxide film. Before high current flow. 06/12/2006 SWTW2006 Jan Martens 4

5 Fritting What s that? Current must flow through small bridge. Bridge and neighbourhood are heated up Contact Pad material migrates to the bridge. Probe tip Oxide film Contact pad High current flow situation: Black Lines of current flow. White Lines of equipotential surface. 06/12/2006 SWTW2006 Jan Martens 5

6 Fritting What s that? Bridge is widened C RES decreased Contact pad material migrated to the bridge and tip surface Probe tip Oxide film Contact pad Wide bridge through oxide film. After high current flow. Tip surface is contaminated. 06/12/2006 SWTW2006 Jan Martens 6

7 Fritting What s that? Fritting is a kind of electrical breakdown at the contact surface between the probe tip and the contact pad of the IC. It improves the electrical contact by building or stabilizing bridges through the oxide film, if the film was not mechanically broken completely. After Fritting the probe tip is welded with the contact pad. After removing the contact residuals of the welding remain at the probe tip and will oxidize. Probe Tip Contact Pad 06/12/2006 SWTW2006 Jan Martens 7

8 Fritting How to measure? Needs: A C RES measurement is needed before and after fritting. The change of C RES is the indicator of occurence. Implementation: C RES Monitor is installed twice within the production test program flow of a smart card measuring C RES on the power supply pin for every IC. First monitor at test program start, last monitor at the end. Hardware used is Teradyne J750, Accretech (TSK) prober UF200A and 32-multisite vertical probe card Viprobe from Feinmetall. Data of first and last C RES per touchdown is collected and analyzed. 06/12/2006 SWTW2006 Jan Martens 8

9 Fritting How to measure? 10 C RES Scatter Plot 8 Last CRES / Ω First C RES = Last C RES Stable contact! First C RES > Last C RES Fritting contact! First C RES / Ω 06/12/2006 SWTW2006 Jan Martens 9

10 Fritting First data review 5000 C RES Distribution 4000 Number of TDs C RES Improvement First Cres First Cres Last Cres C RES / Ω 06/12/2006 SWTW2006 Jan Martens 10

11 Definition of Fritting ratio Φ C RES Distribution Fritting Ratio Φ = N NFrit + N Frit Stab Number of TDs First Cres First Cres First First Cres Cres / Stable First Cres Stable First Cres / Fritting C RES / Ω 06/12/2006 SWTW2006 Jan Martens 11

12 Fritting ratio Φ. Typical examples 100% Change of Fritting ratio Φ per time 90% 80% Fritting ratio Φ 70% 60% 50% 40% 30% 20% Within 2k TDs Φ<10% Φ>80% example 1 example 2 10% 0% Touchdowns 06/12/2006 SWTW2006 Jan Martens 12

13 Why measuring Fritting and not only C RES? C RES measurement only indicates a problem in the signal path but doesn t answer where. Fritting measurement verifies a probe tip contamination. In cases where an absolut C RES measurement is impossible, a relative C RES decrease can still be measured. The fritting analysis is more convenient and simpler to analyze. 06/12/2006 SWTW2006 Jan Martens 13

14 How influencing the fritting ratio? Changing overdrive Probing on gold bumps instead of aluminum Using refurbishment methods Probe Polish (online cleaning) T.I.P.S. (offline cleaning) 06/12/2006 SWTW2006 Jan Martens 14

15 Changing overdrive 100% Fritting ratio Φ 90% 80% 70% 60% 50% 40% 30% 20% Fritting ratio Φ Overdrive improves Φ (nonlinear probing force only small improvement) 10% 0% 2 Mil 3 Mil 4 Mil 5 Mil Overdrive 06/12/2006 SWTW2006 Jan Martens 15

16 Probing on gold bumps (instead of aluminum) Searched in many production lots Fritting ratio always Φ=0% Gold is not oxidized. No Fritting! 06/12/2006 SWTW2006 Jan Martens 16

17 Probe tip refurbishment How does it work? Probe Tip Flattened tip Highly cross-linked polymeric material with spatially distributed abrasive particles. (Probe Polish ) Semiround tip Pictures from T.I.P.S. Messtechnik GmbH 06/12/2006 SWTW2006 Jan Martens 17

18 Online cleaning method: Probe Polish (ITS) 90% Fritting ratio Φ Online using Probe Polish 80% (1000 touchdowns) 70% Probe tip Refurbishment Fritting prevention and Yield win 1% 60% 50% 40% Fritting ratio Φ 30% 20% 10% 0% Touchdowns 06/12/2006 SWTW2006 Jan Martens 18

19 Fritting measurement and Probe Polish C RES Distribution First Cres / before cleaning with Probe Polish First Cres before cleaning with Probe Polish Last Cres / before cleaning with Probe Polish First Cres / after cleaning with Probe Polish Last Cres before cleaning with Probe Polish Last Cres / after cleaning with Probe Polish Number of TDs Fritting prevention with Probe Polish C RES / Ω 06/12/2006 SWTW2006 Jan Martens 19

20 Offline cleaning method: T.I.P.S. 100% Fritting ratio Φ Offline using T.I.P.S. 90% 80% (24k touchdowns) Probe tip Refurbishment Fritting prevention and Yield win 3% 70% 60% 50% 40% Fritting ratio Φ 30% 20% 10% 0% Touchdowns 06/12/2006 SWTW2006 Jan Martens 20

21 Fritting measurement with T.I.P.S. Number of TDs C RES Distribution First Cres w/o T.I.P.S. First Cres w/o T.I.P.S. Last Cres w/o T.I.P.S. First Cres w/ T.I.P.S. Last Cres w/o T.I.P.S. Last Cres w/ T.I.P.S. Fritting prevention with T.I.P.S C RES / Ω 06/12/2006 SWTW2006 Jan Martens 21

22 Summary Fritting was detected by comparing C RES values during one touchdown. Fritting ratio Φ was defined and used as C RES quality indicator. Fritting contaminates probe tips. Fritting was prevented and yield was increased by using probe tip refurbishment techniques: Probe Polish T.I.P.S. 06/12/2006 SWTW2006 Jan Martens 22

23 Outlook Fritting ratio Φ can indicate preventive maintenance of probe cards. Fritting ratio Φ can help to optimize cleaning setups. Fritting can help to identify and engineer (too) high current tests. Fritting could be an explanation for a fast abrasion of probe tip material. 06/12/2006 SWTW2006 Jan Martens 23

24 Thank You! Questions? 06/12/2006 SWTW2006 Jan Martens 24