Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-10-14
2001-06-19
Nguyen, Vinh P. (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S1540PB
Reexamination Certificate
active
06249137
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to reliability testing of electrical devices, and more particularly the invention relates to current pulse testing of electrical devices such as semiconductor components.
Semiconductor reliability tests require continuous application of electrical stimulus, usually at a controlled temperature ranging from −50° C. to +350° C. based on the specific test parameter (e.g., Hot Carrier, Electromigration). For electromigration test in particular, testing using DC current has always been the preferred approach due to simplicity, built-in conservatism, and relatively low cost. However, recent advances in process miniaturization have rendered DC tests insufficient, thus making similar testing under pulsed conditions a necessity.
An ideal pulsed stimulus should allow flexible control of Pulse-Repetition-Rate, Duty-Cycle, Polarity, and Intensity (Amplitude). These parameters are illustrated in
FIGS. 1A and 1B
where T is the period, frequency (f) is the pulse repetition rate (Hz), duty cycle is 2tp/T; positive amplitude is Ap, and negative amplitude is An (Volt, Amp). Further, while applications such as Hot Carrier (HC) and Time to Dielectric Breakdown (TDDB) require voltage stimulus, Electromigration requires a current pulse-train, which is a more difficult waveform to generate.
Conventional methods require relatively complex circuitry for each current source, as one source is needed for each DUT. While the intended use of the pulsed technique is limited to pulse-repetition-rates of several Mega-Cycle-per-Second (MHz), the required rectangular shape with a minimal overshoot and ringing, as illustrated in
FIG. 2
, is still difficult to meet. This requires that the pulse generating circuitry be very close to the DUT, a requirement difficult to meet especially when DUT temperatures are to be controlled up to 350° C. Thus, reliability tests and electromigration test in particular require complex rectangular pulses, which are capable of driving currents below one milliampere to more than 0.1 ampere under load conditions varying from one Ohm to several kilo-Ohms, all with the above described requirements. Designing such a system based on conventionally available techniques inevitably increases circuit complexity, cost, physical size (footprint) and a compromise on pulse quality to a point where such systems become impractical.
The present invention is directed to achieving a higher quality pulsed reliability test system in which a bipolar pulse waveform is generated close to the DUT by using a dual configuration of high quality DC sources.
SUMMARY OF THE INVENTION
Briefly, the invention is an electrical test system which combines two DC current sources connected to two terminals of a DUT with a fast shunting circuit connected to each terminal, and a timing generator controlling the shunt circuits.
More particularly, the test circuit includes a first DC current source serially connected with a first switch and having a first common terminal, a second DC current source serially connected with a second switch and having a second common terminal, and means for connecting a DUT between the first and second terminals. A timing generator is provided for controlling the conductance of the first switch and the second switch whereby when the first switch is closed current from the second DC current source flows through the DUT and the first switch, and when the second switch is closed current from the first DC current source flows through the DUT and the second switch. Pulse repetition rate and duty cycle of the current pulses are readily controlled by the control voltage pulses from the timing generator. At least one pair of back-to-back diodes can be serially connected with the DUT to limit leakage current through the DUT. Further, at least one resistor can be serially connected with the DUT to limit current pulse overshoot and ringing.
REFERENCES:
patent: 4670877 (1987-06-01), Nishibe
patent: 5257231 (1993-10-01), Masuda
patent: 5463315 (1995-10-01), Grace
patent: 5731700 (1998-03-01), McDonnald
Cuevas Yongbum
Krieger Gedaliahoo
Nguyen Vinh P.
Qualitau, Inc.
Townsend and Townsend / and Crew LLP
Woodward Henry K.
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