Method of using automated test equipment to screen for leakage inducing defects after calibration to intrinsic leakage
The present invention is directed to a method of identifying test devices having excessive leakage current and also includes computer program products that enable the same. The method obtaining background test data using a test routine to measure the leakage current for a set of test devices as a function of a parameter associated with device speed for the device under test. From the test data, a leakage threshold function is defined that correlates leakage current with the parameter associated with device speed. The test routine and the leakage threshold function are then input into an automated testing apparatus configured to execute the test on production or other devices. Devices are tested to determine leakage current over a range of parameter values associated with device speed. The devices are then screened using the leakage threshold function to determine the status of the device.
1. A method for identifying test devices having excessive leakage current, the method comprising:
a) obtaining background test data by using a test routine to measure leakage current as a function of test operating frequency for a set of test devices such that the testing is performed on a test set of device lots having a known range of device speeds, the testing being performed at a range of test operating frequencies to define a relationship between leakage current and the test operating frequency;
b) determining, from the test data, a leakage threshold function that correlates with test operating frequency wherein leakage defines a measured leakage cunent and the leakage threshold function defines a leakage current value above which the device under test is determined to have failed the test wherein said process of determining the leakage threshold function comprises statistically evaluating the results of the testing performing on the test set of device lots to define a leakage threshold function that defines an acceptable leakage current over a range of test operating frequencies;
c) inputting the test routine and the leakage threshold function into an automated testing apparatus configured to execute testing on devices;
d) testing a device to determine its leakage current over a range of parameter values associated with device speed; and
e) screening the device using the leakage threshold function to determine the status of the device.
2. The method of claim 1 wherein the leakage threshold function comprises a curve that characterizes acceptable leakage current as a function of test operating frequency.
3. The method of claim 1 wherein the leakage threshold function comprises a plurality of test operating frequency regimes and a curve for each regime that characterizes acceptable leakage current as a function of test operating frequency for each regime.
4. The method of claim 1 wherein the leakage threshold function comprises a step function comprising a plurality of test operating frequency regimes and a leakage current cut-off value for each regime.
5. The method of claim 1 wherein the leakage threshold function is adjustable enabling the threshold to filter out a greater or fewer number of devices at the election of a user.
6. The method of claim 1 wherein the leakage threshold function comprises a means for screening out devices having to high a leakage current for a given test operating frequency.
7. A method for identifying test devices having excessive leakage current, the method comprising:
a) obtaining background test data by measuring a leakage current for a set of test devices as a function of test operating frequency for the device under test;
b) determining, from the test data, a leakage threshold function that correlates with the test operating frequency wherein leakage defines a measured leakage current and the leakage threshold function defines a leakage current value above which the device under test is determined to have failed the test;
c) inputting the test routine and the leakage threshold function into an automated testing apparatus configured to execute testing on devices;
wherein the operations of: a) obtaining background test data ; b) determining a leakage threshold function that correlates with the test operating frequency; and c) inputting the test routine and the leakage threshold function into the automated testing apparatus can all be conducted off-line prior to any testing of production devices;
d) testing a device to determine its leakage current over a range of test operating frequencies wherein said testing is not performed on a dedicated test structure;
e) screening the device using the leakage threshold function to determine the status of the device; and
wherein d) testing devices to determine leakage current over a range of test operating frequencies is performed on production devices after steps a)-c) have been previously performed such that e) screening the production devices can be used to determine the status of the production devices substantially contemporaneous with said d) testing.
8. A computer program product embodied on a computer readable media including computer program code for identifying defective devices having excessive leakage current, the computer program product including:
a) computer program code instructions for executing a test routine capable of measuring leakage current of a device under test as a function of test operating frequency for a set of test devices such that the testing is performed on a test set of device lots having a known range of device speeds, the testing being performed at a range of test operating frequencies to define a relationship between leakage current and the test operating frequency;
b) computer program code instructions for determining, from the test data, a leakage threshold function that correlates with test operating frequency wherein leakage defines a measured leakage current and the leakage threshold function defines a leakage current value above which the device under test is determined to have failed the test wherein said code instructions for determining the leakage threshold function include statistically evaluating the results of the testing performing on the test set of device lots to define a leakage threshold function that defines an acceptable leakage current over a range of test operating frequencies;
c) computer program code instructions for inputting the test routine and the leakage threshold function into an automated testing apparatus configured to execute testing on devices;
d) computer program code instructions for testing a device to determine its leakage current over a range of parameter values associated with device speed; and
e) computer program code instructions for screening the device using the leakage threshold function to determine the status of the device.
9. The computer program product of claim 8 wherein the determined leakage threshold function comprises a curve that characterizes acceptable leakage current as a function of test operating frequency.
10. The computer program product of claim 8 wherein the leakage threshold function comprises a plurality of test operating frequency regimes and a curve for each regime that characterizes acceptable leakage current as a function of test operating frequency for each regime.
11. The computer program product of claim 8 wherein the leakage threshold function comprises a step function comprising a plurality of test operating frequency regimes and a leakage current cut-off value for each regime.
12. The computer program product of claim 8 wherein the leakage threshold function is adjustable enabling the threshold to filter out a greater or fewer number of devices at the election of a user.
13. The computer program product of claim 8 wherein the leakage threshold function comprises a means for screening out devices having to high a leakage current for a given test operating frequency.