Testing of semiconductor devices

• US 5,623,215 A
• Filed: 05/08/1996
• Issued: 04/22/1997
• Est. Priority Date: 12/10/1993
• Status: Expired due to Fees

• Current Assignee: Power Innovations Ltd. (Bourns Incorporated)
• Original Assignee: Texas Instruments, Inc.
• Inventors: Maytum, Michael J.
• Primary Examiner(s): Karlsen, Ernest F.
• Assistant Examiner(s): KOBERT, RUSSELL MARC
• Application Number:
  US08/646,469
• Time in Patent Office: 349 Days
• Field of Search: 324/765, 365/201
• US Class Current: 324/750.03
• CPC Class Codes: G01R 31/1236 of surge arresters monitoring overvoltage diverters or arresters H02H3/048
• CPC Class Codes: G01R 31/2633 for measuring switching properties thereof

Abstract

A method and an apparatus for testing semiconductor devices, especially overvoltage protectors, involves the application to the device to be tested of a standard surge waveform which is truncated by terminating it early. The amount of heating of the device by the truncated surge waveform is ascertained by monitoring or measuring a heat sensitive parameter of the device during and/or shortly after the application of the waveform. Devices which undergo less heating are capable of withstanding higher electrical loads in service than those which become more heated. The early termination is effected by a controllable short circuit operating on the standard waveform. The differential coefficient with respect to time of a heat sensitive parameter may be monitored continually during the truncated waveform and used to operate the short circuit even earlier if the differential coefficient exceeds a threshold value indicating an undue temperature rise in the device.

Claims

1. A method of testing a semiconductor device, comprising the steps of:

during a first period, applying a thermal stress test electrical signal to the semiconductor device tending to heat it towards destruction;

truncating the thermal stress test electrical signal at a predetermined truncation time t_T selected to substantially thermally stress the semiconductor device but avoid permanent damage to it if well made as designed;

during a cooling period beginning at the truncation time t_T, applying a measuring waveform to the semiconductor (i) for inducing a time-changing, temperature-dependent parameter signal indicating the semiconductor'"'"'s instantaneous temperature at successive times (t₁, t₂, t₃, . . . ) shortly after the truncation time t_T, and (ii) for sampling the parameter signal to obtain parameter samples (p(t₁), p(t₂), p(t₃), . . . ) at such successive times;

extrapolating backwards in time from the parameter samples (p(t₁), p(t₂), p(t₃), . . . ) to obtain the value of an estimated parameter signal p(t_T) at the truncation time t_T ;

generating a "passed" signal only if the estimated parameter signal p(t_T) indicates a semiconductor device temperature less than a predetermined no-pass temperature indicating incipient failure of the semiconductor device.

2. A method according to claim 1 wherein the semiconductor device is a two-terminal device and is such that in operation it exhibits breakdown to a low impedance state in response to the test electrical signal.

3. A method according to claim 2 wherein the semiconductor device is an overvoltage protector.

4. A method according to claim 3 wherein the temperature dependent parameter is the zener voltage of the overvoltage protector.

5. A method according to claim 3 wherein the temperature dependent parameter is the leakage current of the overvoltage protector.

6. A method according to claim 2 wherein the test electrical signal comprises a first waveform having a high voltage and a low current followed by a second waveform having a low voltage and a high current, the first waveform causing the semiconductor device to exhibit breakdown to a low impedance state and the second waveform maintaining the device in the low impedance state.

7. A method according to claim 1 wherein the test electrical signal is of such duration and such maximum magnitude that a substandard device having a usable performance below that expected would not be thermally damaged thereby.

8. A method according to claim 7 wherein termination of the test electrical signal is determined by short-circuiting the signal.

9. A method according to claim 1 wherein the semiconductor of the device is silicon and the test electrical signal is such that a device having the performance expected reaches a temperature of between 100°

C. and 300°

C. immediately following the application of the test electrical signal thereto.

10. A method according to claim 9 wherein the test electrical signal is such that a device having the performance expected reaches a temperature of between 190°

-210°

C. following the application of the test electrical signal thereto.

11. A method according to claim 1 wherein the derivation of the performance data includes calculating the value of a temperature dependent parameter for a time instant at the end of the application of the test electrical signal to the device from values of that parameter measured after that instant.

12. A method according to claim 1 including monitoring the value of a temperature dependent parameter of the device during the application of the test electrical signal to the device, and removing the test electrical signal if the value of the parameter indicates that the device is becoming heated excessively.

13. A method according to claim 12 wherein the voltage of the test electrical signal is substantially constant of a period of time, and the monitoring of the value of a temperature dependent parameter is performed during that period.

14. A method according to claim 12 wherein the device is a two-terminal device which exhibits breakdown to a low impedance state and the parameter monitored is the voltage across the device in its low impedance state.

15. A method according to claim 1 wherein the sampling of the temperature-dependent parameter includes deriving the differential coefficient with respect to time of the parameter and detecting the truncation time t_T as when the value of the differential coefficient exceeds a threshold rapid rise value.

16. Apparatus for testing a semiconductor device, comprising:

terminals for connection to a semiconductor device to be tested,

a signal generator,

a parametric tester, and

means for controlling the signal generator and the parametric tester so that in operation the signal generator applies a thermal stress test electrical signal to the terminals, which signal is such as to cause a current flow within the device that is within its operating limits during a predetermined nondestructive heating period, and the parametric tester is connected to the terminals during a cooling period immediately following the heating period so as to sample a value of a temperature-dependent parameter of the device and backwards time extrapolate an indication of the increase in temperature of the device resulting from the application to it of the test electrical signal when the heating period ends.

17. Apparatus according to claim 16 wherein the signal generator includes means for generating a standard waveform for surge testing semiconductor devices, and means truncating that waveform.

18. Apparatus according to claim 17 wherein the means for truncating the waveform comprises a switchable short circuit which is connected in the electrical path from the generating means to the terminals and is operated at a predetermined instant during the generation of the standard waveform to short circuit the output of the generating means and terminate the electrical test signal applied to the device.

19. Apparatus according to claim 17 further including means for deriving from the device during the application of the test electrical signal to the device a signal indicating whether the device is becoming excessively heated, the driving means being connected to the truncating means to terminate the waveform applied to the device if the signal indicates that the device is becoming excessively heated.

20. Apparatus according to claim 19 wherein the means for deriving an indicating signal includes differentiating means for deriving an approximate value of the differential coefficient with respect to time of the temperature dependent parameter and, comparison means for determining whether the differential coefficient exceeds a threshold value, the signal indicating excessive heating if the differential coefficient exceeds the threshold value.