CN213750181U

CN213750181U - Testing machine

Info

Publication number: CN213750181U
Application number: CN202022932401.4U
Authority: CN
Inventors: 杨浩; 王山平; 向雪燕; 杨富可; 张嘉修
Original assignee: Chongqing Kangjia Photoelectric Technology Research Institute Co Ltd
Current assignee: Chongqing Kangjia Photoelectric Technology Research Institute Co Ltd
Priority date: 2020-12-08
Filing date: 2020-12-08
Publication date: 2021-07-20
Anticipated expiration: 2030-12-08

Abstract

The utility model relates to a test machine. The testing machine comprises: the testing mechanism is provided with a testing area, and the wafer to be tested is placed at the testing area; the distance measuring device is positioned on one side of the testing mechanism and used for measuring the distance between the distance measuring device and the wafer to be tested; the light receiving structure is positioned on one side of the testing mechanism and used for collecting light emitted by the wafer to be tested; and the distance adjusting device adjusts the distance between the testing mechanism and the light receiving structure according to the distance measured by the distance measuring device so that the distance between the wafer to be tested and the light receiving structure is always the same. The utility model provides an among the prior art test machine have the big problem of testing error.

Description

Testing machine

Technical Field

The utility model relates to a semiconductor test equipment technical field especially relates to a test machine.

Background

The principle of the electroluminescence photoelectric test is that a probe is used for contacting a chip electrode to carry out electric injection on the chip, and under the action of an electric field, electron transition and holes are subjected to radiation combination to emit photons. The electrical characteristics of the LED are recorded by the source meter, the light emitted by the LED is received by the integrating sphere, and the optical characteristics of the LED such as the luminous wavelength, the luminous intensity and the like are analyzed by the spectrometer.

Because of the requirement of testing efficiency, the LED testing machine generally adopts a mode of receiving light outside the integrating sphere, and then calibrates the LED testing machine with a standard value of a standard Integrating Sphere (IS) to obtain a relatively accurate numerical value, and because of the characteristics (external light receiving) of the testing machine, the light receiving amount of the integrating sphere IS greatly influenced by the distance between the integrating sphere and a chip; and because the Wafer is subjected to the action Of processes (epitaxy, etching, coating and annealing) in the production process, stress is always generated, the Wafer is usually in a warping state due to the stress action, the warping (Bend Of Wafer, BOW) value can usually reach 150 micrometers, the influence on the brightness is as high as 2.6%, and a test error is caused.

That is to say, the testing machine in the prior art has the problem that the testing error is large.

SUMMERY OF THE UTILITY MODEL

In view of the above deficiencies of the prior art, the present application aims to provide a testing machine, which aims to solve the problem of large testing error of the testing machine in the prior art.

A testing machine, comprising: the testing mechanism is provided with a testing area, and the wafer to be tested is placed at the testing area; the distance measuring device is positioned on one side of the testing mechanism and used for measuring the distance between the distance measuring device and the wafer to be tested; the light receiving structure is positioned on one side of the testing mechanism and used for collecting light emitted by the wafer to be tested; and the distance adjusting device adjusts the distance between the testing mechanism and the light receiving structure according to the distance measured by the distance measuring device so as to keep the distance between the wafer to be tested and the light receiving structure consistent.

The distance measuring device is arranged to enable the position between the wafer to be tested and the distance measuring device to be controllable, the distance measuring device is electrically connected with the distance adjusting device, the distance measuring device feeds back the measured distance between the distance measuring device and the wafer to be tested to the distance adjusting device, the distance adjusting device adjusts the distance between the light receiving structure and the testing mechanism according to the measured distance, and therefore the distance between the wafer to be tested and the light receiving structure is always the same, the light receiving angle of the light receiving structure is always the same, the testing stability of the testing machine is guaranteed, the testing precision of the testing machine is improved, testing errors caused by warping of the wafer to be tested in the testing process of the wafer are reduced, and the testing accuracy of the testing machine is improved.

Optionally, the testing machine further includes an image acquisition device, the image acquisition device is located on a side of the testing mechanism away from the light receiving structure, and the image acquisition device is configured to scan the wafer to be tested to obtain the position coordinates of the chips on the wafer to be tested and the quantity information of the chips.

Optionally, the distance measuring device and the image collecting device are located on the same side of the testing mechanism, the testing machine further comprises a switching device, the distance measuring device and the image collecting device are arranged on the switching device, and the switching device is used for adjusting the position relation between the distance measuring device and the testing area, and the position relation between the image collecting device and the testing area.

Optionally, the distance measuring device and the light receiving structure are located on the same side of the testing mechanism, the testing machine further includes a switching device, the distance measuring device and the light receiving structure are disposed on the switching device, and the switching device is configured to adjust a positional relationship between the distance measuring device and the light receiving structure, and the testing area.

Optionally, the testing machine further includes a moving device, the testing mechanism is disposed on the moving device, and the moving device is configured to adjust a positional relationship between the testing mechanism and the distance measuring device and the light receiving structure.

Optionally, the switching device is moved in translation or in rotation.

Optionally, the distance adjusting device comprises: the guide rods extend along the direction of a connecting line of the testing mechanism and the light receiving structure; the testing mechanism or the light receiving structure is arranged on the base, the base is provided with a plurality of through holes, and the guide rods correspondingly extend into the through holes one by one; and the driving structure drives the base to move along the guide rod so as to adjust the distance between the testing mechanism and the light receiving structure.

Optionally, the driving structure further comprises: the screw rod is connected with the base; a motor; the worm wheel is arranged on an output shaft of the motor and meshed with the screw rod, the motor rotates, and the worm wheel drives the screw rod to move.

Optionally, the testing mechanism comprises: a stage having a test area; and the test structure is arranged on the surface of one side of the carrying platform, which is far away from the light receiving structure, and is used for testing the wafer to be tested.

Optionally, the test structure comprises: the probe base is arranged on the carrying platform and provided with a testing hole, and the testing hole and the testing area are coaxially arranged; the probe base is arranged on the probe base and is provided with a central hole which is coaxial with the test hole; the probe extends out from the hole wall of the central hole to the center of the central hole and extends into the wafer to be tested through the testing hole; and the edge finder extends out of the hole wall of the central hole, clamps the probe, and is triggered after the probe is contacted with the wafer to be tested.

Drawings

Fig. 1 is a schematic structural diagram of a testing machine according to an embodiment of the present invention;

fig. 2 is a schematic structural diagram of a distance adjusting device according to an embodiment of the present invention.

Description of reference numerals:

10-a testing mechanism; 11-a stage; 12-a test structure; 121-a probe base; 122-test wells; 123-a probe seat; 124-center hole; 125-probe; 126-edge finder; 20-a wafer to be tested; 30-a distance measuring device; 40-a light-receiving structure; 41-integrating sphere; 42-an optical fiber; 43-spectrometer; 50-distance adjusting means; 51-a guide rod; 52-a base; 53-a drive configuration; 531-screw rod; 532-electric machine; 60-an image acquisition device; 70-switching means.

Detailed Description

To facilitate an understanding of the present application, the present application will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present application are given in the accompanying drawings. This application may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

As described in the background section, the testing machine in the prior art has a problem of large testing error.

Based on this, the present application intends to provide a solution to the above technical problem, the details of which will be explained in the following embodiments.

As shown in fig. 1 to 2, the testing machine includes a testing mechanism 10, a distance measuring device 30, a light receiving structure 40 and a distance adjusting device 50, wherein the testing mechanism 10 has a testing area, and the wafer 20 to be tested is placed at the testing area; the distance measuring device 30 is located at one side of the testing mechanism 10, and the distance measuring device 30 is used for measuring the distance between the distance measuring device 30 and the wafer 20 to be tested; the light receiving structure 40 is located at one side of the testing mechanism 10, and the light receiving structure 40 is used for collecting light emitted by the wafer 20 to be tested; the testing mechanism 10 or the light receiving structure 40 is disposed on the distance adjusting device 50, and the distance adjusting device 50 adjusts the distance between the testing mechanism 10 and the light receiving structure 40 according to the distance measured by the distance measuring device 30, so that the distance between the wafer 20 to be tested and the light receiving structure 40 is always the same.

The position between the wafer 20 to be tested and the ranging device 30 is controllable by arranging the ranging device 30, the ranging device 30 is electrically connected with the distance adjusting device 50, the ranging device 30 feeds the measured distance between the ranging device 30 and the wafer 20 to be tested back to the distance adjusting device 50, the distance adjusting device 50 adjusts the distance between the light receiving structure 40 and the testing mechanism 10 according to the measured distance, and therefore the distance between the wafer 20 to be tested and the light receiving structure 40 is always the same, the light receiving angle of the light receiving structure 40 is always the same, the testing stability of the testing machine is guaranteed, the testing precision of the testing machine is improved, the testing error of the wafer caused by the warping of the wafer 20 to be tested in the testing process is reduced, and the testing accuracy of the testing machine is improved.

It should be noted that, since the wafer 20 to be tested is usually in a warped state under the action of the stress, when different positions of the wafer 20 to be tested are tested, distances from different testing positions to the light receiving structure 40 are different, which further causes a difference in light receiving range of the light receiving structure 40, thereby affecting a testing error of the testing machine. In the present application, the distance adjusting device 50 adjusts the distance between the mechanism to be tested 10 and the light receiving structure 40 according to the measured distance from the distance measuring device 30 to the testing position of the wafer 20 to be tested by setting the distance measuring device 30 and the distance adjusting device 50 to be matched with each other, so that the distance between the testing position of the wafer 20 to be tested and the light receiving structure 40 is always the same.

In the embodiment shown in fig. 1, the testing machine further includes an image capturing device 60, the image capturing device 60 is located on a side of the testing mechanism 10 away from the light receiving structure 40, and the image capturing device 60 is used for scanning the wafer 20 to obtain the position coordinates of the chips on the wafer 20 and the number information of the chips. The image acquisition device 60 is arranged to acquire the position coordinates of each chip on the wafer 20 to be tested and the number of the chips, the image acquisition device 60 is electrically connected with the test structure 12 on the test mechanism 10, the image acquisition device 60 feeds back the position coordinate information of each chip and the number information of the chips to the test structure 12, and then the test structure 12 tests each chip on the wafer 20 to be tested according to the position coordinate information of the chip and the number information of the chips.

In the embodiment shown in fig. 1, the distance measuring device 30 and the image capturing device 60 are located on the same side of the testing mechanism 10, the testing machine further includes a switching device 70, the distance measuring device 30 and the image capturing device 60 are disposed on the switching device 70, and the switching device 70 is used for adjusting the positional relationship between the distance measuring device 30 and the image capturing device 60 and the testing area. Because the distance measuring device 30 and the image capturing device 60 are located on the same side of the testing mechanism 10, the distance measuring device 30 and the image capturing device 60 need to be arranged opposite to the testing area during operation to enable the distance measuring device 30 and the image capturing device 60 to work. The switching device 70 is configured to switch the positions of the distance measuring device 30 and the image capturing device 60, so that the distance measuring device 30 and the image capturing device 60 are just opposite to the test area during operation. The provision of the switching device 70 enables the ranging device 30 and the image pickup device 60 to operate stably.

It should be noted that, in the working process of the image capturing device 60, it is not necessary to frequently capture the chip positions and the number of chips of the wafer 20 to be tested, so the distance measuring device 30 and the image capturing device 60 are switched and are not frequently switched, and thus the testing efficiency of the testing machine can be effectively increased.

Because the distance measuring device 30 and the light receiving structure 40 are located at two opposite sides of the testing mechanism 10, the distance adjusting device 50 adjusts the distance between the testing mechanism 10 and the light receiving structure 40 while the distance measuring device 30 measures the distance from the distance measuring device 30 to the testing chip of the wafer 20 to be tested, so that the distance between the testing position of the wafer 20 to be tested and the light receiving structure 40 is always the same. The distance measuring device 30 and the light receiving structure 40 are arranged on two opposite sides of the testing mechanism 10, so that after the distance measuring device 30 measures the distance, the distance adjusting device 50 is synchronously adjusted without waiting, and the testing efficiency of the testing machine is improved.

In the embodiment shown in fig. 1, the switching device 70 is moved in translation. The distance measuring device 30 and the image acquisition device 60 perform a translational motion under the action of the switching device 70. The requirement of the translational motion on the switching device 70 is low, the space occupied by the switching device 70 is low, and meanwhile, the translational motion is stable, so that the phenomenon of blocking is not easy to occur, and the distance measuring device 30 and the image acquisition device 60 can be stably switched.

Of course, the switching device 70 may also be rotated. The distance measuring device 30 and the image capture device 60 are at different angular positions of the switching device 70, and the switching device 70 is rotated by a preset angle to change the positions of the distance measuring device 30 and the image capture device 60 to align the desired structure with the test area. The rotation movement requires a large space, so that the tester occupies a large space, which is not favorable for the miniaturization of the tester.

When the testing mechanism 10 tests the wafer to be tested for the first time, the distance measured by the distance measuring device 30 is the preset distance.

In this embodiment, when the light receiving structure 40 is disposed on the distance adjusting device 50, the distance adjusting device 50 adjusts the position of the light receiving structure 40, that is, directly adjusts the distance between the testing position of the wafer 20 to be tested and the light receiving structure 40, so that the distance between the light receiving structure 40 and the testing position of the wafer 20 to be tested is always the same.

As shown in fig. 2, the distance adjusting device 50 includes a plurality of guide rods 51, a base 52 and a driving structure 53, wherein the plurality of guide rods 51 extend along a direction of a connection line between the testing mechanism 10 and the light receiving structure 40; the testing mechanism 10 or the light receiving structure 40 is arranged on the base 52, the base 52 is provided with a plurality of through holes, and the guide rods 51 correspondingly extend into the through holes one by one; the driving structure 53 drives the base 52 to move along the guide rod 51 to adjust the distance between the testing mechanism 10 and the light receiving structure 40. The base 52 has a plurality of through holes, and a plurality of guide rods 51 extend into the plurality of through holes in a one-to-one correspondence manner, so that the base 52 can slide along the extending direction of the guide rods 51 under the action of the driving structure 53, the rotation of the base 52 can be effectively avoided, the base 52 only moves along the direction of the guide rods 51, the stability of the movement of the base 52 is ensured, and the base 52 only moves along a single direction, and then the base 52 drives the testing mechanism 10 or the light receiving structure 40 to move, so as to adjust the distance between the wafer 20 to be tested and the light receiving structure 40.

As shown in fig. 2, the driving structure 53 further includes a screw 531, a motor 532, and a worm gear provided on an output shaft of the motor, the screw 531 being connected to the base 52; the worm gear is meshed with the screw 531, the motor 532 rotates, and the worm gear drives the screw 531 to move. The screw 531 is connected to the base 52 to drive the base 52 to move in the extending direction of the guide bar 51. The turbine is arranged to change the rotary motion of the motor 532 into the linear motion of the screw 531, so that the unicity of the moving direction of the base 52 is ensured.

As shown in fig. 1, testing mechanism 10 includes a stage 11 and a test structure 12, stage 11 having a test area; the test structure 12 is disposed on a surface of the stage 11 away from the light receiving structure 40, and tests the wafer 20 to be tested. The arrangement of stage 11 provides a placement location for a wafer to be tested, which is placed at a test area. The test structure 12 is disposed on the carrier 11, so that the position between the test structure 12 and the wafer to be tested is fixed, the accuracy of the test structure 12 on the wafer 20 to be tested is ensured, and the test error is reduced.

Optionally, the test structure 12 includes a probe base 121, a probe seat 123, a probe 125 and an edge finder 126, the probe base 121 is disposed on the carrier 11, and the probe base 121 has a test hole 122, and the test hole 122 is disposed coaxially with the test area; the probe seat 123 is arranged on the probe base 121, and the probe seat 123 is provided with a central hole 124 which is coaxially arranged with the test hole 122; the probe 125 extends from the wall of the central hole 124 to the center of the central hole 124, and the probe 125 extends into the wafer 20 to be tested through the testing hole 122; the edge finder 126 extends from the sidewall of the central hole 124, the edge finder 126 extends from the wall of the central hole 124, and holds the probe 125, and the edge finder 126 is triggered after the probe 125 contacts with the wafer 20 to be tested. The probe base 121 is disposed on the stage 11, and the probe base 121 supports the probe base 123. The probe base 123 is disposed on the probe base, and the probe 125 extends from the hole wall of the central hole 124 and the probe 125 is connected to the electrode of the chip of the wafer 20 to be tested, so as to perform the optoelectronic test on the chip. The aperture of the central hole 124 is larger than that of the test hole 122, and the edge finder 126 extends from the wall of the central hole 124 but does not extend into the range of the test hole 122. The edge finder 126 is triggered to indicate that the probes 125 are in good contact with the wafer 20, and if the probes 125 are not in good contact with the wafer 20, the edge finder 126 is not triggered.

The working flow of the testing machine in this application is as follows, the stage 11 moves, the probe seat 123 presses the probe 125 down to contact with the wafer 20 to be tested, the edge finder 126 confirms whether the probe 125 is in good contact with the electrode of the chip, if so, the distance measuring device 30 starts to measure the distance, the distance adjusting device 50 adjusts the position of the light receiving structure 40, the testing mechanism 10 is powered on to light the chip, and the light receiving structure 40 receives the light to test the optical performance. The probe base 123 raises the probes 125 out of contact with the wafer 20 to be tested and the stage 11 moves to the position of the next chip.

As shown in fig. 2, the light receiving structure 40 includes an integrating sphere 41, an optical fiber 42 and a spectrometer 43, the integrating sphere 41 is electrically connected to the spectrometer 43 through the optical fiber 42, the integrating sphere 41 is used for receiving light emitted from the chip, the integrating sphere 41 is disposed on a base 52, and a distance adjusting device 50 is used for adjusting a distance between the integrating sphere 41 and the chip. The integrating sphere 41 transmits the collected light information to the spectrometer 43 through the optical fiber 42, and the spectrometer 43 analyzes the light information to obtain the photoelectric property of the chip.

Because the distance measuring device 30 and the distance adjusting device 50 are matched with each other, the distance between the light receiving structure 40 and the wafer 20 to be measured is always the same in the measuring process, the influence of the warping of the wafer 20 to be measured on the measuring precision caused by stress is eliminated, and the error caused by the stress warping phenomenon can be eliminated.

In some embodiments, rather than the light collecting structure 40 being disposed on the distance adjustment device 50, the testing mechanism 10 is disposed on the distance adjustment device 50. When the testing mechanism 10 is disposed on the distance adjusting device 50, since the distance adjusting device 50 adjusts the position of the testing mechanism 10, the distance between the testing position of the wafer 20 to be tested on the testing mechanism 10 and the ranging device 30 is adjusted to be the predetermined distance, so that the testing position of the wafer 20 to be tested and the light receiving structure 40 are always the same.

In some embodiments, the distance measuring device 30 and the light receiving structure 40 have different positional relationships. The distance measuring device 30 and the light receiving structure 40 are located on the same side of the testing mechanism 10, the testing machine further includes a switching device 70, the distance measuring device 30 and the light receiving structure 40 are disposed on the switching device 70, and the switching device 70 is used for adjusting the position relationship between the distance measuring device 30 and the light receiving structure 40 and the testing area. Since the distance measuring device 30 and the light receiving structure 40 need to be arranged opposite to the test area during operation, and the distance measuring device 30 and the light receiving structure 40 are located on the same side of the testing mechanism 10, the switching device 70 needs to be arranged to change the positions of the distance measuring device 30 and the light receiving structure 40. When the testing mechanism 10 tests each chip of the wafer 20 to be tested, the distance measuring device 30 and the light receiving structure 40 both need to detect the position and the light emitting condition of each chip, and the switching device 70 needs to frequently switch the positions of the distance measuring device 30 and the light receiving structure 40, so that the efficiency of the testing machine is low.

In some embodiments, ranging device 30 and image capture device 60 are stationary, while testing mechanism 10 is moving. The testing machine further comprises a moving device, wherein the testing mechanism 10 is arranged on the moving device, and the moving device is used for adjusting the position relation of the testing mechanism 10, the distance measuring device 30 and the image acquisition device 60. In this embodiment, the light receiving structure 40 and the image capturing device 60 are located on two opposite sides of the testing mechanism 10, the image capturing device 60 and the distance measuring device 30 are located on the same side of the testing mechanism 10, and the moving device drives the testing mechanism 10 to move to change the position of the testing area, thereby adjusting the position relationship between the testing area and the image capturing device 60, the distance measuring device 30 and the light receiving structure 40, so as to make the testing area directly face the image capturing device 60, or make the distance measuring device 30 directly face the testing area.

Optionally, when the distance measuring device 30 is aligned with the test area, the light receiving structure 40 is also aligned with the test area. This may increase the testing efficiency of the tester.

In some embodiments, the light receiving structure 40 is located on the same side of the testing mechanism as the ranging device 30. The light receiving structure 40 and the distance measuring device 30 are located on the same side of the testing mechanism 10, and the moving device drives the testing mechanism 10 to move so as to change the position of the testing area, thereby adjusting the position relationship between the testing area and the light receiving structure 40 as well as the distance measuring device 30.

In some embodiments, light receiving structure 40, distance measuring device 30, and image capture device 60 are all located on the same side of testing mechanism 10. The moving device drives the testing mechanism 10 to move so as to change the position of the testing area, and further adjust the position relationship between the testing area and the light receiving structure 40, the distance measuring device 30 and the image acquisition device 60.

It is to be understood that the invention is not limited to the above-described embodiments, and that modifications and variations may be made by those skilled in the art in light of the above teachings, and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.

Claims

1. A testing machine, comprising:

the testing mechanism is provided with a testing area, and a wafer to be tested is placed at the testing area;

the distance measuring device is positioned on one side of the testing mechanism and used for measuring the distance between the distance measuring device and the wafer to be tested;

the light receiving structure is positioned on one side of the testing mechanism and used for collecting light rays radiated by the wafer to be tested;

the distance adjusting device adjusts the distance between the testing mechanism and the light receiving structure according to the distance measured by the distance measuring device, so that the distance between the wafer to be tested and the light receiving structure is kept consistent.

2. The testing machine of claim 1, further comprising an image capture device located on a side of the testing mechanism away from the light receiving structure, the image capture device being configured to scan the wafer to obtain information on the position coordinates and the number of chips on the wafer.

3. The testing machine of claim 2, wherein the distance measuring device and the image acquisition device are located on the same side of the testing mechanism, the testing machine further comprising a switching device, the distance measuring device and the image acquisition device being disposed on the switching device, the switching device being configured to adjust a positional relationship between the distance measuring device and the image acquisition device and the test area.

4. The testing machine of claim 1, wherein the distance measuring device and the light receiving structure are located on the same side of the testing mechanism, the testing machine further comprising a switching device, the distance measuring device and the light receiving structure being disposed on the switching device, the switching device being configured to adjust a positional relationship between the distance measuring device and the light receiving structure and the testing area.

5. The testing machine of claim 1, further comprising a moving device on which the testing mechanism is disposed, the moving device being configured to adjust a positional relationship of the testing mechanism with the distance measuring device and the light collecting structure.

6. The testing machine of claim 3 or 4, wherein the switching device moves in translation or in rotation.

7. The testing machine of any one of claims 1-5, wherein the distance adjustment device comprises:

the guide rods extend along the direction of a connecting line of the testing mechanism and the light receiving structure;

the testing mechanism or the light receiving structure is arranged on the base, the base is provided with a plurality of through holes, and the guide rods correspondingly extend into the through holes one by one;

the driving structure drives the base to move along the guide rod so as to adjust the distance between the testing mechanism and the light receiving structure.

8. The testing machine of claim 7, wherein the drive structure further comprises:

the screw rod is connected with the base;

a motor;

the worm wheel is arranged on an output shaft of the motor, the worm wheel is meshed with the screw rod, the motor rotates, and the worm wheel drives the screw rod to move.

9. The testing machine of any one of claims 1-5, wherein the testing mechanism comprises:

a stage having the test area;

and the test structure is arranged on the surface of one side of the carrying platform, which is far away from the light receiving structure, and is used for testing the wafer to be tested.

10. The testing machine of claim 9, wherein the test structure comprises:

the probe base is arranged on the carrying platform and provided with a testing hole, and the testing hole and the testing area are coaxially arranged;

the probe base is arranged on the probe base and is provided with a central hole which is coaxial with the test hole;

the probe extends into the wafer to be tested through the test hole;

and the edge finder extends out of the hole wall of the central hole and clamps the probe, and the edge finder is triggered after the probe is contacted with the wafer to be tested.