JPH0581175B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an apparatus for testing the characteristics of semiconductor wafers at low temperatures.

<Prior Art> Recently, there has been active development of semiconductor devices that operate at low temperatures, for example, for the purpose of increasing the calculation speed of computers. However, when testing the characteristics of semiconductor devices at the necessary low temperatures,
It goes without saying that cutting out individual chips formed on a semiconductor wafer and immersing each chip in a cryogen such as liquid nitrogen to examine its electrical characteristics requires an enormous amount of time, effort, and expense. In order to eliminate such shortcomings, the special public
36387 is known, which tests a wafer at a low temperature.

This device consists of a metal dewar bottle with a wafer holder inside that holds the wafer to be tested, a bellows surrounding the opening of the dewar bottle on the top surface, and a probe on the top of the bellows.・A means for placing the card, a gap for covering the probe card and keeping the space formed by the inside of the dewar bottle and the bellows airtight from the atmosphere, and a gap for keeping the dewar bottle within a predetermined range. A dewar bottle mounting stand having a positioning mechanism that can be displaced in two dimensions, and a probe card height that allows the above-mentioned bellows card located between the bellows and the cap to be vertically displaced within the extendable range of the bellows. It consists of an adjustment mechanism. In the above overall configuration, the cap located at the top has piping for injecting a cryogen such as liquid nitrogen into the dewar bottle and discharging the cryogen from there, as well as a pipe for discharging the cryogen from there. Correspondingly, a window made of a transparent plate is provided for viewing the interior of the dewar bottle.

In the apparatus having the above configuration, after placing the wafer to be tested on the wafer holder, setting the probe card, and covering the wafer with the cap,
Through a predetermined process (details are omitted), a cryogen such as liquid nitrogen is injected into the dewar bottle to a predetermined height that does not reach the top surface of the wafer holding table. When the wafer reaches a predetermined low temperature through heat conduction on the wafer holder, the top surface of the wafer placed on the wafer holder is observed through the window provided in the cap using a microscope, and the probe card height adjustment mechanism is activated. and a positioning mechanism provided on the dewar bottle mounting stand to electrically contact the probe extending from the probe card to the wafer with a predetermined terminal of a predetermined chip configured on the wafer, and perform the test. Perform the necessary electrical measurements.
According to this method, once the wafer is set in the device, all the chips configured on the wafer can be connected to the predetermined terminals by simply operating the positioning mechanism and probe card height adjustment mechanism. , the tips of the probe card can be brought into contact sequentially. Therefore, compared to the method of putting individual chips in and out of a cryostat for each test measurement,
The time and effort required for a series of circuit tests was significantly improved compared to the device of this Japanese Patent Publication No. 62-36387.

<Problems to be Solved by the Invention> However, in the apparatus according to the prior art described above, it goes without saying that the area of the wafer that can be placed on the wafer holder in the cryostat, and therefore the number of chips, is limited. There are certain limits. Therefore,
It is typically necessary to continue testing on a large number of wafers. Therefore, once all the chips on one wafer have been tested,
Each time the tested wafer must be replaced with a new next wafer. To replace a wafer, first, before taking out the tested wafer, the liquid nitrogen in the dewar bottle is completely transferred to a liquid nitrogen storage container prepared outside, and then the low-temperature nitrogen gas remaining inside the deuwar bottle is removed. While avoiding a rapid temperature rise in the dewar bottle, replace it with room temperature drying gas (usually nitrogen gas) so that the temperature inside the dewar bottle, especially the wafer holder and the tested wafers held on it, is at room temperature. The process of removing the cap and probe car must be carried out after the vehicle has risen to a certain level. Next, the wafer is replaced, the probe card and cap are set in place, the air inside the dewar bottle is evacuated, and liquid nitrogen is gradually reinjected into it. Needless to say, performing more work than is necessary each time a wafer is replaced requires a large amount of labor over a long period of time. In addition to these drawbacks, the probes on the probe card, especially the top, are located very high above the cryogen liquid level.
Moreover, since the surrounding area is only surrounded by bellows and a cap outside the dewar bottle, the temperature is practically close to room temperature. Therefore, there is a large temperature difference between the wafer and the wafer, which is kept at a low temperature, and depending on the degree of shrinkage of the wafer, there may be a shift between the position of the test terminal of each chip formed on the wafer and the array pattern of the tip of the probe. This may result in the probe not being able to properly contact a predetermined terminal of the chip.

<Means for Solving the Problems> In order to eliminate the above-mentioned drawbacks, the main part of the semiconductor wafer low-temperature testing apparatus according to the present invention has a space for accommodating a cryogen and a heater for temperature adjustment, and a test device on the top surface. a wafer low temperature holding table configured to hold a semiconductor wafer to be processed, a wafer stand position adjusting means for three-dimensionally displacing the wafer low temperature holding table within a predetermined range, and a probe card for testing the semiconductor wafer. a probe card low temperature holding plate, which is a means for holding the temperature of the probe card and cooling the probe of the probe card, and has a means to be cooled by a cryogen and a heat transfer means for transmitting the temperature of the cryogen to the probe of the probe card; , a probe card cryostat support means for supporting the probe card cryostat, a wafer precooling table for precooling the semiconductor wafer to be tested, and a means for raising the temperature of the tested semiconductor wafer to substantially room temperature; a wafer heating table for taking in the semiconductor wafer, the wafer pre-cooling table, the wafer low-temperature holding table, a wafer transfer means for sequentially transferring the semiconductor wafer to the wafer heating table and then sending the wafer to the outside; a low temperature holding table, the wafer table position adjustment means, the probe card low temperature holding plate, the probe card low temperature holding plate supporting means,
an insulating chamber for insulating and accommodating the wafer precooling table, the wafer heating table, and the wafer transfer means from the outside environment; and an airtight wafer loading door that accommodates a plurality of semiconductor wafers to be tested and that can be opened and closed. A test wafer storage chamber attached to the above-mentioned heat insulation chamber and a tested semiconductor wafer are stored in the test wafer storage chamber attached to the heat insulation chamber through a door, and airtight wafers that can be opened and closed are delivered to the tested wafer storage chamber attached to the heat insulation chamber. It is configured. With this configuration of the apparatus, while the wafer to be tested remains in the test wafer storage chamber, the insulating container, the test wafer storage chamber, and the tested wafer storage chamber are kept in a vacuum, and the wafer is removed. With the take-in door and the wafer feed-out door open, each time the test of the wafer placed on the wafer support table is completed, the wafer transfer means transfers the tested wafer on the wafer heating table to the tested wafer storage chamber. After sending the wafer out, the wafer immediately after the test on the wafer low temperature holding table is transferred to the wafer heating table 1.
Then, the wafer on the wafer pre-cooling table is transferred to the wafer low-temperature holding table, and then one wafer is taken from the subject wafer storage chamber and placed on the wafer pre-cooling table.

When there are no more wafers in the test object wafer storage chamber, the wafer intake door is closed to isolate the test object wafer storage chamber from the heat insulation chamber, and a new wafer is added by opening the lid of the storage chamber. Next, close the lid, evacuate the inside, and then open the wafer loading door. In addition, when taking out the tested wafers accumulated in the tested wafer storage chamber, the wafer delivery door is used to isolate the tested wafer storage chamber from the residual heat chamber, and then the wafers are taken out, and the inside of the chamber is covered with a lid. Evacuate and open the wafer delivery door.

<Function> As is clear from the above explanation, storage of test wafers, wafer testing, and delivery of tested wafers are all performed in a common vacuum space, and addition of test wafers and removal of tested wafers are Since the residual heat rate is also carried out in a vacuum state, there is no need for wasted time and labor required to return the low-temperature part to room temperature. When testing a large number of wafers over a long period of time, it may be necessary to add cryogen to the wafer holder, but in principle it is now possible to test a large number of wafers virtually indefinitely. There is.

Additionally, the wafer probe has thermal contact with the probe card holder plate, which is kept at a low temperature, in effect
Since the temperature is maintained at the same temperature as the wafer under test, there will be no mismatch between the arrangement of the test terminals on the wafer and the probe arrangement pattern.

<Example> Examples of the present invention will be described below based on the drawings.

FIG. 1 is a sectional view showing a state in which a wafer cryogenic holding table 1 and its peripheral elements are provided inside a heat insulating chamber 8 in an embodiment of the present invention. is shown fixedly held by a presser spring 1c. An exhaust valve 8a is provided on the side wall of the heat insulating chamber 8 to evacuate the inside of the chamber. The wafer cryogenic holding table 1 is provided with a liquid nitrogen reservoir 1a, to which liquid nitrogen is supplied from outside the heat insulating chamber 8 through a pipe 1e. The evaporated nitrogen gas is released to the outside of the heat insulating chamber 8 through the pipe 1f. Wafer cryogenic holding table 1 cooled to low temperature with liquid nitrogen
The temperature control is performed by adjusting the current of the heater 1b. A probe card 11 is located above the wafer low temperature holding table 1 and is held by a probe card low temperature holding plate 3, and the probe 11a is directed from the probe card to the wafer placed on the wafer low temperature holding table 1. It is in contact with W.
The probe card cryogenic plate 3 is provided with a pipe 3a through which liquid nitrogen flows, and the liquid nitrogen is cooled through a heat conductive plate 3b connecting the probe card 11 to the probe card cryogenic plate 3. The signal is transmitted to the probe card 11 and its probe 11a. In this way probe card 1
1 and the probe 11a are kept at virtually the same low temperature as the wafer W to be tested held on the wafer cryogenic stand, so the arrangement of the probe and the arrangement of the test terminals on the wafer are adjusted at room temperature. The correspondence between them remains intact even at low temperatures.
Note that the wafer low temperature holding table 1 and the probe card low temperature holding plate 3 are provided with heaters 1b and 3c for temperature adjustment and temperature sensors 1g and 3d, respectively, so that the wafer can be maintained even at temperatures higher than the liquid nitrogen temperature. It is now possible to test for

Further, the wafer low temperature holding table 1 is fixed on a wafer table position adjustment mechanism 2 via a thermal insulator 1d, and its position is adjusted by the same mechanism. This wafer table position adjustment mechanism 2 consists of a combination of arm and gear, rack and pinion, etc., and motors 2a, 2b, 2
c and 2d to give the wafer cryogenic holding table 1 a rotational axis in a horizontal plane and a linear displacement vertically and horizontally within a predetermined range, but this is a known mechanism and its details will be omitted.

Next, FIG. 2 is a diagram showing a cross section taken along the cross-sectional line AA in FIG. 1. In addition to the wafer low temperature holding table 1, the heat insulating chamber 8 is equipped with a wafer precooling table 5 and a wafer heating table 6 on the same circumference, with a wafer precooling table 5 and a wafer heating table 6 arranged on the same circumference, with a wafer transfer table that is expandable and rotatable at the center. Means 7 are provided. The wafer pre-cooling table 5 is a cooling table for pre-cooling the wafer to be tested before it is placed on the wafer cryo-holding table 1, and may be provided with its own liquid nitrogen reservoir similar to the wafer cryo-holding table 1. Alternatively, the wafer is maintained at a low temperature by a method such as thermally contacting the wafer cryostat 1 via a flexible thermal conductor (such as a bundle of copper wire or copper mesh), but in order to avoid complicating the diagram, Illustration of such cooling means is omitted. Further, the wafer heating table 6 is a heating table for returning the temperature of the tested wafer to room temperature, and is provided with a heater (not shown) as required. Further, the wafer transfer means 7 has a structure in which tongs 7b for grasping the wafer are provided at the tip of a pantograph 7a, but the specific mechanisms for rotation, expansion and contraction, and opening/closing of the tongs belong to the known technical field, and a detailed explanation is not provided. Omitted. Note that the tongs are coated with a soft material so as not to damage the wafer surface. The heat insulating chamber 8 containing the above-mentioned components includes a test wafer storage chamber 9 and a tested wafer storage chamber 10, respectively, via an airtight wafer intake door 9b and a wafer delivery door 10b, which can be opened and closed. There is. Note that the wafer take-in door 9b and the wafer feed-out door 1
All doors 0b are sliding type and electrically operated from the outside (the door opening/closing mechanism is not shown). Multistage racks 12 and 13 capable of accommodating a large number of wafers are housed in the subject wafer storage chamber 9 and the tested wafer storage chamber 10, respectively, so as to be slidable vertically along respective guides 9c and 10c. . Both the subject wafer storage chamber 9 and the tested wafer storage chamber 10 are provided with airtight lids (not shown) on their upper surfaces, and by opening the lids, the respective racks 12 and 13 can be taken out. It's becoming like that.

In FIGS. 1 and 2, the pipes 1e and 1f related to the liquid nitrogen reservoir 1a of the wafer cryostat 1 are shown only in FIG. 1, but the liquid nitrogen flow pipe 3a of the probe card cryostat 3 is shown Piping to and wiring related to the probe card, heaters 3c, 1b, temperature sensors 3d, 1g, motors 2a, 2b, 2c, 2d, and wiring to the various electric mechanisms mentioned above are not shown to avoid complicating the diagram. was omitted. These piping and wiring should be secured in an insulated container 8 using appropriate airtight bushings or hermetic seals.
Alternatively, it passes through the side walls of the subject wafer storage chamber 9 and the tested wafer storage chamber 10 and is guided to the outside.

Next, a method of conducting a series of wafer tests using the apparatus of this embodiment will be explained. First, all stages of the rack 12 for test wafers are filled with wafers to be tested, and the rack is inserted into the test wafer storage chamber 9, and the empty rack 13 for tested wafers is placed in the tested wafer storage chamber 10. Insert it. Close the lids (not shown) of both wafer storage chambers 9 and 10, and fully open the wafer intake door 9b and wafer delivery door 10b that separate both wafer storage chambers 9 and 10 from the thermal insulation rate 8 (both are electrically operated from the outside). (by operation). The insulation chamber 8, the test wafer storage chamber 9 and the tested wafer storage chamber 10 are then insulated through all or part of the respective exhaust valves 8a, 9a and 10a (preferably using all valves). Chamber 8 and both wafer storage chambers 9 and 10 are evacuated simultaneously. When the degree of vacuum reaches a predetermined value, liquid nitrogen is supplied to the liquid nitrogen reservoir 1a of the wafer cryogenic holding table and the liquid nitrogen reflux pipe of the probe card cryogenic holding plate 3. (If the wafer pre-cooling table 5 is a direct cooling type using liquid nitrogen, supply is also supplied there.) While observing the thermometer 1g, the amount of liquid nitrogen supplied and the amount of current supplied to the heater 1b are controlled to cool the wafer. Adjust the temperature of the low temperature holding table to a predetermined value.

When the temperature of the wafer low-temperature holding table stabilizes to a predetermined value, the wafer transfer means 7 is operated (by electric operation from the outside), the wafer is taken out from the rack 12 of the specimen wafer storage chamber 9, and the wafer is transferred to the wafer pre-cooling table 5. I'll put it on. Currently, we are at the stage of starting a series of wafer test processes, so after the time necessary for pre-cooling the wafers, which has been determined from experience, has elapsed, the wafers on the wafer pre-cooling table are transferred to the wafer cryogenic holding table 1, and the wafers to be tested are accommodated. The next wafer is taken out from the rack in chamber 9 and placed on wafer precooling table 5. (Each time a wafer is taken out from the rack 12, the rack is moved up or down one step at a time, so that the wafer can always be taken out by the wafer transfer means 7.) Next, the transparent skylight 8b of the heat insulating container 8 through,
While viewing the wafer surface with a microscope M (Fig. 1), operate the wafer stand position adjustment mechanism 2 (operate the motors 2a, 2b, 2c, and 2d electrically from the outside) to place a predetermined chip on the wafer. The test terminal provided and the probe 11a of the probe card 11
Test the electrical characteristics of the chip by making electrical contact between them. When this operation is completed for all chips on the wafer, the tested wafer is transferred to the wafer heating table 6, and then the chips on the wafer pre-cooling table 5 are immediately transferred to the wafer cryogenic holding table 1 (the chips of the previous wafer are transferred to the wafer pre-cooling table 5). (During the test period, the chips on the wafer pre-cooling table have been pre-cooled completely), the next chip is taken out from the wafer storage chamber 9 and placed on the wafer pre-cooling table 5. Next, a test operation is started on the wafer on the wafer low temperature holding table. When the test is completed, the chips on the wafer heating table are delivered to the rack 13 of the tested chip receiving chamber 10. (Rack 13 is 1 each time a chip is fed.)
Move up and down step by step so that tested chips can always be accepted. ) henceforth,
The above process is repeated every time the wafer test is completed.
This continues until the rack 12 in the subject chip storage chamber is empty.

When the rack 12 in the subject wafer storage chamber 9 is empty, the wafer take-out door 9b is closed, the atmosphere is introduced into the rack through the valve 9a, the rack 12 is taken out, and a new wafer is supplied. Rack 12
After inserting the wafer into the test object wafer storage chamber 9 again, the inside is evacuated again through the valve 9a, and when this is completed, the wafer removal door 9b is opened and the wafer test operation is resumed. Even when the rack 13 of the tested wafer storage chamber 10 is full,
The same series of operations as above are performed regarding the wafer delivery door 10b and the valve 10a.

The present invention can also be modified as follows. In this modified embodiment, the wafer heating table 6
In addition to a heater, cooling means using liquid nitrogen similar to the wafer low temperature holding table 1 is provided, and the tested wafer storage chamber 10 is provided with a wafer heating device using infrared rays or the like. Even in the modified embodiment configured in this way, when liquid nitrogen is not supplied to the cooling means and the infrared wafer heating device is not operated,
Its function is exactly the same as in the previously described embodiment. However, according to this modified embodiment, the number of wafer test items is small, and the time required to hold the wafer on the wafer cryogenic holding table 1 for testing and perform a predetermined test is very long. Even if the next specimen wafer waiting in step 5 is not sufficiently cooled, the heating stage 6
By supplying liquid nitrogen thereto (if a heater is provided, turn off the heater), the wafer can be sufficiently cooled by being diverted to the second pre-cooling table. That is, by transferring the subject wafer to the wafer low-temperature holding table 1 through two pre-cooling tables, the original pre-cooling table 5 and the second pre-cooling table which is a repurposed heating table 6, the wafer inspection time can be shortened. However, the wafer to be tested will be sufficiently pre-cooled. Also, the tested wafers are transferred from the wafer low temperature holding table 1 to the tested wafer storage chamber 10.
and is heated to room temperature in the same room by the infrared heating device mentioned above.

Note that it goes without saying that some or all of the operations in any of the above embodiments can be automated by applying known automation techniques.

<Effects of the Invention> As is clear from the above description, according to the present invention, when testing a large number of wafers, the vacuum in the low temperature region is broken midway through any stage of wafer supply, transfer, or removal. Since there is no need to bring the temperature of the area back to room temperature, wasted waiting time and effort are virtually completely eliminated, as well as cryogen consumption is reduced and therefore significant energy savings are achieved. It will be done.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an embodiment of the present invention. FIG. 2 is an overhead view of a cross section taken along the cross-sectional line AA shown in FIG. DESCRIPTION OF SYMBOLS 1... Wafer low temperature holding table, 2... Wafer stand position adjustment mechanism, 3... Probe card low temperature holding plate, 4... Probe card low temperature holding plate support,
5...Wafer pre-cooling table, 6...Wafer heating table,
7... Wafer transfer means, 8... Heat insulation chamber, 9...
Subject wafer storage chamber, 10...Tested wafer storage chamber.

Claims (1)

[Scope of Claims] 1. A wafer low temperature holding table having a space for accommodating a cryogen and a temperature control heater and configured to hold a semiconductor wafer to be tested on its upper surface; a wafer table position adjusting means for three-dimensionally displacing the wafer within the wafer table; a means for holding a probe card for testing semiconductor wafers and cooling the probe of the probe card; a probe card cryostat having a heat transfer means for transmitting the temperature of the cryogen to the probe of the probe card; a probe card cryostat supporting means for supporting the probe card cryostat; a wafer pre-cooling table having a space for accommodating a cryogen for pre-cooling the semiconductor wafer to be tested; a wafer heating table for raising the temperature of the tested semiconductor wafer to virtually room temperature; and a wafer pre-cooling table for taking in the semiconductor wafer. , the wafer low temperature holding table, a wafer transfer means for sequentially transferring the wafer to the wafer heating table and then sending it outside, the wafer low temperature holding table, the wafer stand position adjustment means, and the probe card low temperature holding plate. , an insulating chamber for insulating and accommodating the probe card low temperature holding plate supporting means, the wafer precooling table, the wafer heating table, and the wafer transfer means from the external environment, and a plurality of semiconductor wafers to be tested. A test wafer storage chamber attached to the heat insulation chamber and a tested semiconductor wafer are accommodated through an airtight wafer intake door that can be opened and closed;
A tested wafer storage chamber is attached to the insulation chamber through an airtight wafer delivery door that can be opened and closed, and the test wafer storage chamber is connected not only to the insulation chamber, but also to the subject wafer storage chamber and the tested wafer storage chamber. A semiconductor wafer low-temperature testing device equipped with vacuum evacuation means. 2. The probe card low temperature holding plate is provided with a heater for temperature adjustment,
A semiconductor wafer low temperature testing apparatus according to claim 1. 3. The semiconductor wafer low temperature testing apparatus according to claim 1 or 2, characterized in that the wafer heating table is provided with a temperature adjusting heater. 4. The wafer heating table is provided with a space for accommodating a heating heater and a cryogen, and the tested wafer storage chamber is provided with heating means for raising the temperature of the tested wafer to room temperature. A semiconductor wafer low-temperature testing apparatus according to claim 1, 2, or 3. 5. Claims 1, 2, and 3, characterized in that the wafer transfer means comprises a rotatable and extendable arm, and tongs provided at the tip of the arm. or 4. The semiconductor wafer low-temperature testing apparatus according to item 4.