""UnderUnder PressurePressure" " -- fromfrom High High VoltageVoltage to MEMS to MEMS PressurePressure

Sensors Sensors WaferWafer ProbingProbing

Rainer Gaggl, Rainer Gaggl, Ph.DPh.D..T.I.P.S.MesstechnikT.I.P.S.Messtechnik GmbHGmbH

June 8June 8--11, 200811, 2008San Diego, CA USASan Diego, CA USA

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

OverviewOverview

• High Voltage Devices vs. MEMS Pressure Sensors – the D.U.T.

• HV Wafer Test - overview• MEMS Pressure Sensors• Probe Card Concept• Features• Summary

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

TheThe D.U.T. D.U.T. ……. .

• High Voltage Devices vs. MEMS Pressure Sensors

Gate

Emitter

High Voltage IGBT (Wafer)

≈

13 mm

MEMS Pressure Sensor

Pressure Sensing

Membrane Structure

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

High High VoltageVoltage DevicesDevices

• Test of breakthrough voltage for high voltage IGBTs, Diodes, MOSFETSChallenge: flashovers ….

GND

Probe(s)

+HV Wafer Chuck, Prober

Source-Pad, GNDPad 2,High Voltage

Wafer

d… when field strength

E=U/dexceeds breakthrough

limit of atmosphere

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

AvoidingAvoiding FlashoversFlashovers……. .

• Physics of Gas Discharges: – breakthrough voltage increases with atmospheric pressure -

"Paschen Curves" – breakthrough voltage vs. pressure

600 V

10 kVarea of

wafer test ……..byby applicationapplication of of

pressurepressure !!Paschen Diagram for Air

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

High High VoltageVoltage Probe Card Probe Card

• Concept of "Luftpolster" probe card *)– device is tested under increased atmospheric pressure

(compressed air)

*) presented at SWTW 2002

gas inlet

prober chuck

probe needle(s) wafer

"Luftpolster" pressure chamber

chamber sealto wafer

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

MEMS MEMS PressurePressure Sensors Sensors

• Technology: surface micro machined sensor cell

Bond pad

CMOS circuitry

Sensor cell area

Array of cells to

increase sensitivity

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

barometric air pressure sensors – e.g. used in engine control unit (ECU)

ApplicationsApplications forfor MEMS MEMS PressurePressure Sensors (Sensors (exampleexample) )

side crash detection for air bag release

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

ProbingProbing MEMS MEMS PressurePressure SensorsSensors……• signal capture through electrical probes• + mechanical excitation of sensor cells…..

….by application of pressure !

Same concept (though refined) as for High Voltage Wafer Test can be employed:

"LuPo-ABS" Probe Card

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

""LuPoLuPo--ABSABS" Probe Card" Probe Card

compressed air

prober chuck

probe needles

wafer

pressure chamber

gap seal≈

80 µm

PCBmovable side wall

principle setup of "No Touch" – gap seal probe card

•"LuPo-ABS": Luftpolster – Air Bearing Seal

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

""LuPoLuPo--ABSABS" Probe Card" Probe Card

Probe card top view with chip- scale pressure chamber

Probe card bottom view

"LuPo- ABS"

gap seal

pressure chamber

air connectors

Load board with electro-pneumatical components

magnetic valve

reference sensor

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

""LuPoLuPo--ABSABS" Probe Card " Probe Card -- detailsdetails

"LuPo-ABS" movable side wall with gap

sealpressure chamber

air piping

probes(2x2 array)

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

""LuPoLuPo--ABSABS" " -- Features (1)Features (1)

LuPo - pressure profile

-30

0

30

60

90

120

0 2 4 6 8 10 12 14

LuPo dimension / mm

pres

sure

/ kP

a

pressure chamberinner diameter

gap seal region

outside of chamber

Pressure profile of LuPo pressure chamber (diameter 8 mm)

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

""LuPoLuPo--ABSABS" " -- Features (2)Features (2)

Rise time, fall time of chamber pressure at switching from atmospheric pressure to approx. 1 bar overpressure

550 ms 80 ms

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

""LuPoLuPo--ABSABS" " -- SummarySummary• Based on a chip-scale pressure chamber with

a movable side wall that rests hovering about 80µm above the wafer surface - without touching it

• Application in wafer test of pressure sensors and high voltage devices

• Very homogenious pressure profile due to static pressure generation (compared to dynamic pressure generation with nozzles blowing on wafer)

• Fast change of pressure levels: wafer-level sensor calibration feasible

• Suitable for multi-site testing (up to 16x demonstrated)• Suitable for integration in modern prober environment

(probe card changer, automatic docking of air supplies)

June 8 to 11, 2008June 8 to 11, 2008June 8 to 11, 2008

AcknowledgementsAcknowledgements

• A. Reithofer, F. Reinwald, Infineon Technologies• customers that remain anonymous…