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Sensor Testing at University of New Mexico. C. H ägemann, M. Hoeferkamp, D. Fields, A. Zimmerman, M. Malik VTX Meeting 03 June 2005. Sensor QA Testing. Sensor QA Testing – Visual Sensor QA Testing – Electrical Sensor QA Testing – Mechanical. Sensor QA Testing.
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Sensor Testingat University of New Mexico C. Hägemann, M. Hoeferkamp, D. Fields, A. Zimmerman, M. Malik VTX Meeting 03 June 2005
Sensor QA Testing Sensor QA Testing – Visual Sensor QA Testing – Electrical Sensor QA Testing – Mechanical
Sensor QA Testing Sensor QA Testing – Visual Sensor QA Testing – Electrical Sensor QA Testing – Mechanical
Production Test Stand • Semiautomatic probestation, 2 Keithley 706 scanners with 10 and 3 Keithley7058 low current scanner cards respectively
Production Test Stand • Cleanroom
Visual Testing As seen before: Equipment is functional, Visual Testing can be easily performed Sintef Wafers: A1 and A3 are scratched; Not seen on the other wafers
Sensor QA Testing-Electrical • Test stand using scanner and probecard is fully operational • Tests that will be performed on the wafer: • Current Scan (Measure ILeak at each strip; VBias = const) • Capacitance Scan (Measure C at each strip; VBias = const) • IV Measurement (on 10% of the strips) • CV Measurement (on 10% of the strips)
Current Scan VBias = 100 V • 6 measurements total, each with 64 needles (melted needles on probe card) • Strip #3, 67, 131,…: either bad needle or bad cable
Current Scan • What is the difference between the 3rd measurement and the last three ?
Current Scan • Only 61 needles are actually touching pads • Change of the magnitude of the current by 100 → indicates bad strip?
IV • Characteristic IV curve of a p-n-junction • Def VBreak: Point where IV curve starts rising exponentially
IV VBreak ~ 320 V Def VBreak where I > 2.5*Inominal ~ 2.5nA
Capacitance Scan • OPEN correction accounts for test fixture on LCR meter • Measure Capacitance of each channel when needles are above the wafer No VBias • Plot Ccorr. = Cuncorr. – Ccorrection vs Channel Number
Capacitance Scan VBias = 150V • Same shape as data seen from BNL (~1pF; we don’t get any peaks in the middle) -> due to wafer / probecard?
Capacitance Scan • Same shape as data seen from BNL (~1pF; we don’t get any peaks in the middle) -> due to wafer / probecard?
CV • On each sensor, measure 10% of the strips • Substract Ccorrection for each particular strip measured • Inquire about AC frequency dependence of measured C first (LCR meter)
CV • Other wafers/channels look about the same
CV • Other wafers/channels look the same → Should use AC frequency of at least 10kHz
CV VDepletion ~ 70 V • Plot 1/C2 to find VDepletion • This defines VBias: 150 V or VDepletion + 50V
Sensor QA Testing-Mechanical • We have made wafer thickness and flatness measurements on the eight Pre Production wafers. • Use our E+H MX203 Contactless Wafer Geometry Gauge • Performs contactless measurements with capacitive sensors on both sides of wafer, there are no moving parts during measurement • Resolution 0.1 mm
Summary / Next Steps • Probestation is fully functional with all the VI’s working and tested • Compare VBreak and VDepletion for all the wafers • Investigate further into the effect of the guard ring on current scan • Once we get Hamamatsu wafers & new probe card - Compare measurements BNL – UNM - Remember: Need to normalize I to 20°C - Define what we mean with “bad sensor” - Start some thickness/flatness measurements