Test system for testing semiconductor device

Details Test system for testing semiconductor device Test system for testing semiconductor device

1999-11-04

2001-10-02

Metjahic, Safet (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S760020

Reexamination Certificate

active

06297659

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a test system for testing a semiconductor device, and in particular, to a test system suitable for testing a plurality of samples with one power supply at the same time.
Referring to
FIG. 1
, description will be made about a first related system for testing a semiconductor device (sample).
As illustrated in
FIG. 1
, a system for testing reliability of electromigration (EM) generally includes a sample
61
to be tested, a current source
62
, and a voltmeter
63
.
With such a structure, the current source
62
is provided for the sample
61
. Current flows from the current source
62
, and a voltage applied for the sample
61
is measured by the use of the voltmeter
63
on request.
In this example, although the number of the sample is set to one, a plurality of samples are generally arranged, and the current sources corresponding to the number are provided in the system. In this event, only one voltmeter is provided, and the respective voltages of the samples are sequentially measured by switching terminals.
Referring to
FIG. 2
, description will be made about a second related system for testing a semiconductor device (sample).
The system illustrated in
FIG. 2
is generally used when the number of samples to be tested is increased.
In the system, samples
64
1
~
64
m
(m≧2) are connected for one voltage source (power supply)
65
in parallel. With this structure, a constant voltage is applied to both ends of each sample
64
1
~
64
m
, and thereby, a current, which flows through the total of the samples, is measured by the use of an ammeter (galvanometer)
66
on request.
Under this circumstance, when either one of the samples
64
1
~
64
m
is cut off, a current j, which flows through the ammeter
66
, is reduced.
When the above-mentioned current-carrying test is continued, a relation between elapsed time and current is variable in the step-wise manner as represented in a graph illustrated in FIG.
3
.
In this graph, the elapsed time until the current is changed in the step-wise manner from the current-carrying start time is defined as electromigration (EM) lifetime of the cut-off sample.
In the system illustrated in
FIG. 1
, the current sources corresponding to the sample number are required in the system when the constant current source is provided for each sample to be tested. In consequence, the sample number can not be set to a high value in this system.
On the other hand, in case that a plurality of samples are connected in parallel in the system illustrated in
FIG. 2
, the current is reduced in the step-wise manner when the sample is cut off. Thereby, the time until disconnection is judged as the lifetime of each sample.
However, resistance variation, which is not in a disconnection state, generally occurs in a lamination wiring pattern (for example, TiN/AlCu/TiN/Ti) which is used in the recent LSI (Large Scale Integrated Circuit). Consequently, the sample is also judged as a defective product by the resistance variation.
When the sample is variable in a resistance value, the current continues to flow through the sample, and a current value is changed in dependency upon the resistance value of the sample.
As a result, the current, which flows through the ammeter
66
, is varied with time, and the constant current test can not practically carried out in this system.
In this case, it is difficult to judge the lifetime of each sample because the current value of the ammeter
66
is not changed in the step-wise manner.
From the above-mentioned reason, the system, in which the respective samples are connected in parallel, can not be used for the sample which has variable resistance value.
In general, when the EM reliability of the LSI wiring pattern is evaluated in the test, as the number of the sample is larger, lifetime estimation test can be more accurately performed in the LSI which is fabricated on the basis of the same specification.
In particular, initial faulty is often deviated from the log-normal plot. Therefore, unless the number of the sample is increased, the initial faulty can not be detected.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a test system for testing a semiconductor device which is capable of increasing the number of samples and measuring lifetime of each sample with low cost.
In a test system according to this invention, a plurality of semiconductor devices (samples) to be tested are connected in parallel. Resistors are connected to the respective semiconductor devices in series. Switches are connected to the respective resistors in series.
With this structure, a voltage source (power supply) supplies a constant voltage for the respective semiconductor devices. An ammeter measures current that flows through the respective semiconductor devices from the voltage source. A voltmeter measures the respective voltage drops of the resistors.
A controller is connected to the switches, the voltage source and the ammeter. The controller detects the specific resistor that is changed in a resistance value when the current measured by the ammeter is reduced, and turns off the switch connected to the specific resistor.
In this case, the controller stores first voltage drops of the respective resistors at test starting time, and stores second voltage drops of the respective resistors when the current is reduced. Under this circumstance, the controller detects the specific resistor by comparing the first voltage drops with the second voltage drops.
Further, the controller continues to test the remaining semiconductor devices except the semiconductor device connected to the specific resistor after the detection of the specific resistor.
Herein, elapsed time until the detection of the specific resistor from the test starting time is defined as lifetime of the semiconductor device connected to the specific resistor.
In this event, the current value for the elapsed time is changed in a step-wise manner.
The resistor comprises a variable resistor. The variable resistor serves to correct manufacturing variation of internal resistance with respect to each semiconductor device.
Alternatively, the semiconductor devices and the resistor may be integrated in an integrated circuit. In this event, the integrated circuit has a first electrode pad, a second electrode pad, a third electrode pad, and a fourth electrode pad. The semiconductor device and the resistor are connected between the first electrode pad and the second electrode pad. The first electrode pad is coupled to the ammeter while the second electrode pad is coupled to the switch. The third electrode pad and the fourth electrode pad are coupled to the voltmeter.
More specifically, a plurality of samples are connected in parallel, and the resistor and the switch are directly connected to the respective samples. With this structure, when the current that which flows through the total samples is changed, a voltage drop at both ends of each resistor is monitored by the use of the voltmeter.
When the variation of the voltage drop at the both ends is detected, the elapsed time until the detection of the variation is measured.
Thereafter, the flow of the current through the sample is prevented by turning off the switch. Thereby, the test can be continuously carried out without affect for the other samples.
In the test system, the current flows through a plurality of test samples with one power supply.
Further, the resistor is connected to each sample in series, and the same current simultaneously flows through each sample. Thereby, the changes of the resistance values of the respective samples can be collectively monitored by the changes of the voltage drops at the both ends of the resistors.
Moreover, the switches are connected to the respective resistors in series. Thereby, the sample, which is changed in the resistance value, is cut off from the voltage source (power supply) via the switch, and as a result, the cut-off sample is not tested.
When the switch is turned off, the total current quantity measured by the ammeter (g

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