The present invention relates to a reference voltage setting method and apparatus for a semiconductor IC tester, which sets a reference voltage used as the standard voltage level for supplied signals and measurement signals when inspecting the electrical properties of semiconductor IC devices.
Before shipping semiconductor IC devices as the final product, in which the performance and the quality are guaranteed, it is necessary to sample all or a part of the semiconductor IC devices at each process of manufacturing and inspection, and to inspect the electrical properties of them. A semiconductor IC tester inspects such electrical properties. The semiconductor IC tester supplies the predetermined test pattern data to a semiconductor IC device under test, reads the output data from the device under test, analyzes defect information based on the output data from the device under test to check whether there are any problems in the fundamental operation or the function of the device under test, and inspects the electrical properties.
Tests executed by the semiconductor IC tester are divided roughly into a direct current test and a function test. The direct current test is to inspect whether there are any defects in the fundamental operation of the semiconductor IC device under test by supplying a predetermined voltage or a predetermined current to input/output terminals of the device under test from a DC measurement circuit. On the other hand, the function test is to inspect whether there are any problems in the fundamental operation or the function of the semiconductor IC device under test by supplying the predetermined test pattern data to input terminals of the device under test from a pattern generator and by reading the output data from the device under test. That is, the function test changes input conditions, such as input timing, amplitude, etc., of incoming signals, such as an address, data, a write enable signal, and a tip selection signal, to the semiconductor IC devices under test, and examines the output timing, the output amplitude, etc. from the device under test.
Since pin electronics substrates, which are equipped with drivers for supplying signals, comparators for measuring signals, etc., and a back board of a test head, on which the substrates are mounted, are small, a conventional reference voltage setting apparatus for a semiconductor IC tester prepares only one ground level, which is used as the standard for supplied signals and measurement signals, in the test head, and sets a reference voltage based on it.
When the back board of the test head is comparatively small, the conventional reference voltage setting apparatus for a semiconductor IC tester has the simple structure, and has an advantage that assembly and adjustment is easy. However, when the number of the semiconductor IC devices under test, which can be inspected simultaneously, is increased and the whole equipment becomes large, the structure of the substrates itself also becomes large. In that case, variations of the substrates or variations of the test head turn into variations of the whole equipment, and variations come to arise in reference voltages among each substrate when making the reference voltage based on one place. When the reference voltages vary among each substrate, there is a disadvantage that variations arise also in levels of signals, which are supplied to the semiconductor IC devices under test.
The present invention is made in view of the problem mentioned above. The purpose of the present invention is to offer a reference voltage setting method and apparatus for a semiconductor IC tester, which is able to set a reference voltage having no variation among each substrate, even if the number of the semiconductor IC devices under test is increased and the whole equipment becomes large.
A feature of the present invention is inputting reference voltages of a certain number of semiconductor IC devices under test respectively to each substrate having drivers for supplying signals to semiconductor IC devices under test and comparators for measuring signals from said semiconductor IC devices under test, outputting a mean voltage of input reference voltages from each substrate, and setting a compound voltage of voltages, which are output from a plurality of substrates, as a reference voltage for the semiconductor IC tester.
In this invention, for example, when three (the 1st to 3rd) substrates supply and measure various signals for eight (the 1st to 8th) semiconductor IC devices under test, reference voltages of three (the 1st to 3rd) devices under test are input to the 1st substrate, reference voltages of three (the 4th to 6th) devices under test are input to the 2nd substrate, and reference voltages of two (the 7th and 8th) devices under test are input to the 3rd substrate. The reference voltages of the 1st to 3rd semiconductor IC devices under test input to the 1st substrate are added and averaged by the 1st level generating circuit prepared on the 1st substrate. The reference voltages of the 4th to 6th semiconductor IC devices under test input to the 2nd substrate are added and averaged by the 2nd level generating circuit prepared on the 2nd substrate. The reference voltages of the 7th and 8th semiconductor IC devices under test input to the 3rd substrate are added and averaged by the 3rd level generating circuit prepared on the 3rd substrate. Mean voltages made in the 1st to 3rd substrates are connected to each other among the 1st to 3rd substrates, and a compound voltage comes out at a connecting point. This compound voltage is set as a reference voltage for the semiconductor IC tester. By this, variations of the reference voltages among the substrates, which are used in the test head, and variations of the reference voltages within each substrate are minimized even if the number of the semiconductor IC devices under test is increased and the whole equipment becomes large. Moreover, in order to raise the test level accuracy of the semiconductor IC devices under test, it becomes possible to always make the reference voltages of the semiconductor IC devices under test into the standard for the semiconductor IC tester.
Another feature of the present invention is setting the compound voltage as a reference voltage for a voltage/current measurement circuit of the semiconductor IC device under test. By this, the voltage/current measurement is performed correctly since the same voltage or the same current is supplied to all semiconductor devices under test.
Another feature of the present invention is connecting lines, which input the reference voltages of a certain number of semiconductor IC devices under test to each substrate, to the ground through resistors respectively, and setting a compound voltage of voltages, which are detected through said resistors, when there is no semiconductor IC device under test, as a reference voltage for a self-diagnostic mode of the semiconductor IC tester. By this, a self-diagnosis is performed correctly even if the semiconductor IC device under test does not exist during the self-diagnostic mode since voltages of the nearest portions to the output parts of the substrates are made into the reference voltage.
Another feature of the present invention, when there are n semiconductor IC devices under test and m substrates, is that the number of semiconductor IC devices under test, of which the reference voltages are input to each substrate, corresponds to a whole number obtained by rounding up a fraction of n divided by m, and a mean voltage of input reference voltages is output from each substrate respectively. For example, when m=3 substrates supply and measure various signals for n=8 semiconductor IC devices under test, a whole number obtained by rounding up a fraction of n divided by m (8/3=2.66 . . . is three. Therefore, reference voltages of three (the 1st to 3rd) devices under test are input to the 1st substrate, reference voltages of three (the 4th to 6th) devices under test are input to the 2nd substrate, and reference voltages of the rest (the 7th and 8th) devices under test are input to the 3rd substrate. By equalizing the number of the reference voltages input to each substrate, variations of the reference voltages among the substrates, which are used in the test head, and variations of the reference voltages within each substrate are minimized.