Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-05-17
2002-03-19
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S765010, C324S755090
Reexamination Certificate
active
06359457
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention lies in the field of semiconductor manufacture. Specifically, the invention relates to a holding device for a wafer and to a test method for integrated circuits on a wafer.
European patent application EP 0 465 017 A1 describes a holding device for a wafer, which includes a so-called wafer chuck (a wafer suction plate). The disk-shaped wafer, made of a semiconductor material, for example silicon, is placed on a support surface on the suction plate and is held firmly there by producing a vacuum. The vacuum is produced in annular structures in the support surface. Furthermore, a description is provided in that document of how the suction plate has further annular structures to which helium is supplied as a coolant. This is used to dissipate the high thermal energy which is produced during the testing of integrated circuits on the wafer, in order to prevent the destruction of the circuits. For the same purpose, the integrated circuits to be tested in each case, with which contact is made via test points, are supplied locally, from the side facing away from the chuck, with a further coolant. The supply is provided via the test probe having test points.
It is desirable to test all the integrated circuits on a wafer at different temperatures, for example at a minimum and a maximum temperature, since the circuits generally have to be serviceable over a specific temperature range in accordance with their specification. A typical maximum temperature is 90° C., a typical minimum temperature is −10° C. This therefore results in a relatively large temperature range of 100° C. In order to be able to test a wafer at these different temperatures in accordance with the European specification EP 0 465 017 A1, it is possible to set the temperature of the wafer as desired by selecting the temperature or the quantity of the helium supplied as coolant for each measuring operation, and then to test the integrated circuits on the wafer one after another. However, in order to set the wafer to the respective new temperature between the measurement passes (that is to say to cool down or heat up through 100° C.), a time interval which depends on the material of the wafer and on the material of the suction plate is needed. One restriction in that case is the heat storage capacity of the materials used, and a further restriction consists in the fact that in the event of excessively rapid temperature changes the circuits on the wafer could be damaged. A typical time for changing the temperature of a wafer of 200 mm diameter within the above-mentioned temperature range is 20 minutes. Since the total test time for all the integrated circuits on the wafer is 2.5 hours, for example, for one test pass, the time to change the temperature, during which the testing has to be interrupted, since the circuits are not then at the desired temperature, is quite crucial.
International PCT publication WO 96/11495 describes a wafer chuck having a heating device which is divided into two. The task of the heating device is to achieve a uniform temperature distribution over the entire wafer surface.
German patent DE 32 13 239 C2 describes a holding device for a wafer which has a large number of heating or cooling elements. These are used to compensate for a relative offset, brought about by a parameter change, between a mask which is held by a mask holder and a wafer which is arranged on the wafer support, by means of appropriate activation of the heating and/or cooling elements.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a testing method and holding device for testing a wafer with integrated circuits, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which shortens or entirely eliminates the time for the above-mentioned temperature changes of the wafer between two test passes at different temperatures.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of testing integrated circuits on a wafer, which comprises:
placing a wafer with integrated circuits in thermal contact with a support surface of a wafer holding device, the support surface being divided into at least a first segment and a second segment;
testing respective integrated circuits in thermal contact with the first segment, maintaining a temperature of the first segment at a substantially constant first temperature, and simultaneously varying a temperature of the second segment; and
after the second segment reaches a predetermined second temperature, testing the respective integrated circuits in thermal contact with the second segment.
The holding device has a support surface for the wafer, and the support surface is divided into at least two segments, each of which is assigned a temperature influencing device, which is used to independently set the temperature of the respective segment. The term “thermal contact” means that the wafer rests on the support surface. Those integrated circuits which are in thermal contact with the first segment are tested first, the segment is kept at an essentially constant temperature, while at the same time the temperature of the second segment is varied. After the changed temperature of the second segment has been reached, those integrated circuits which are in thermal contact with the second segment are tested.
The invention makes it possible to set at least two segments of the support surface or of the wafer to two different temperatures at the same time, so that the time needed for changing the temperature of a segment can run in parallel with the test time of another segment. The test time and the time to change the temperature are therefore contemporaneous rather than additive. In the most favorable case, the second segment has already reached the desired new temperature before the testing of the first segment has been completed. Testing at the new temperature can then be continued immediately. In turn, the first segment can then likewise be brought to the new temperature, in parallel with the testing of the second segment, and can thus be prepared for renewed testing.
The temperature influencing device may be a heating and/or a cooling device. A heating device may be implemented, for example, electrically by means of an appropriate heating winding, while a cooling device may be implemented by supplying a suitable cooling liquid or a suitable cooling gas.
As noted, the segmented support surface is a component part of a wafer suction plate, i.e., a wafer chuck. The wafer is held on the latter by means of a vacuum, so that simple handling is ensured and thermal contact is produced.
The thermal division of the support surface is best obtained in that a thermal insulation is provided between the segments of the support surface. This permits the setting of temperature differences, even at the segment boundaries. The support surface may be formed from a metal, and its thermal insulation from a ceramic material, so that good thermal isolation is achieved.
The support surface may be subdivided into the segments both horizontally and vertically, that is to say it may have segmentation in each of its two dimensions. This permits the presence of a large number of thermally isolated, controllable segments. A large number of segments permits the setting of smaller temperature differences between adjacent segments, so that the mutual temperature influence is only slight. For instance, the temperature may increase in intervals from segment to segment, when considered in one direction over the support surface. In this case, it is necessary only for the segments which are located furthest from each other to exhibit the actually required, maximum temperature difference.
In accordance with another feature of the invention, the method further comprises:
isolating the first segment and the second segment from one another with at least a third segment; and
during a period in which the first segment is at the first temp
Greenberg Laurence A.
Lerner Herbert L.
Metjahic Safet
Siemens Aktiengesellschaft
Stemer Werner H.
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