Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1998-07-02
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
C324S1540PB, C324S760020
Reexamination Certificate
active
06297656
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a probe-test method and also to a prober.
More particularly, the present invention relates to a probe-test method for determining certain electric characteristics of an object of examination and also to a prober to be used for such a test. While a prober for determining certain electric characteristics of integrated circuits (hereinafter referred to as IC chips) that are arranged on a semiconductor wafer (hereinafter referred to simply as wafer) may represent a typical and specific application of the present invention, the present invention is not limited thereto and a prober according to the invention may find applications in examining various electronic elements and devices for certain electric characteristics by means of a probe.
FIG. 6
of the accompanying drawings schematically illustrates known prober to be used for examining IC chips.
The prober
10
comprises a loader chamber
11
from which wafers contained in respective cassettes are taken out one by one and transferred, a prober chamber
12
for examining the wafers W transferred from the loader chamber
11
, a controller
13
for controlling the prober chamber
12
and the loader chamber
11
and a display unit
14
that also operates as a control panel for driving the controller
13
.
In the loader chamber
11
, a fork
15
is rotatably fitted to a rotary shaft for transferring a wafer W from the inside of a cassette C. The fork
15
is horizontally extensible/retractable and also rotatable to face oppositely in order to take out wafers W in the cassette C on a one by one basis and transfer them to the prober chamber
12
. A sub-chuck
16
is arranged near the fork
15
for pre-aligning wafers W. More specifically, the sub-chuck receives a wafer W from the fork
15
, rotates it in the sense of &thgr; in order to make it face oppositely and then pre-align the wafer W by referring to its orientation flat.
In the prober chamber
12
, there are provided a main chuck
17
for carrying a wafer w therein, an aligning means
20
and a probe card. The main chuck
17
is adapted to be driven in the X- and Y-directions of the prober by means of X- and Y-stages
18
and
19
and also in the Z- and &thgr;-directions by means of a built-in drive mechanism.
The aligning means
20
comprises an alignment bridge having a first image pick-up means (e.g., a CCD camera)
21
for shooting the wafer W in position to pick up an image thereof, a pair of guide rails
23
,
23
for reciprocating the alignment bridge
22
along the Y-direction and a second image pick-up means (not shown, e.g, a CCD camera) fitted to the main chuck
17
.
A tester head (not shown) is arranged on the upper surface of the probe card and connected thereto by means of a connection ring (not shown). A test signal transmitted from the tester that comprises the prober is sent to electrodes of the IC chip being examined by way of the tester head, the connection ring and the probes of the probe card and the output signal of the IC chip representing the test result is sent back to the tester by way of the same signal route. The tester is adapted to determine certain electric characteristics of the IC chip on the basis of the signal representing the test result.
For testing a wafer W, the fork
15
takes a wafer W out of the cassette C in the loader chamber
11
. The wafer W is then pre-aligned by the sub-chuck
16
on its way of being transferred to the prober chamber
12
and moved onto the main chuck
17
in the prober chamber
12
. Then, the alignment bridge
22
moves over the main chuck
17
until the wafer W is placed to a position right below the first image pick-up means
21
of the alignment bridge
22
, where the first image pick-up means
21
and the second image pick-up means of the main chuck
17
cooperate for the alignment of the wafer W on the main chuck
17
. The main chuck
17
is adapted to move in the X- and Y-directions for indexing the wafer W for each test and then move upward in the Z-direction until the wafer W comes into physical contact with the probes. Then, the main chuck
17
is driven upward excessively further in the Z-direction to make the electrode pads of the IC chip on the wafer W electrically contact with the probes in order to determine certain electric characteristics of the IC chip. Note that, if the wafer W has a size not greater than 8 inches, the wafer W is held substantially horizontal as shown in
FIG. 7A
when the main chuck
17
is driven upward excessively and the wafer W on the main chuck
17
is raised to the position indicated by a solid line from the position indicated by a broken line in FIG.
7
A. Consequently, each of the probes
24
A of the probe card
24
is resiliently moved up from the position indicated by a broken line to the position indicated by a solid line in
FIG. 7A
so that the tip of each of the probes moves from the starting point S to the terminal point E on the thick line in FIG.
7
A.
FIG. 7B
shows the apparent horizontal movement of the tip from the starting point S to the terminal point E on the surface of the wafer W. However, since the tip of the probe is located within an electrode pad P of the IC chip, the probe
24
A is held in electric contact with the electrode pad P. If, on the other hand, the wafer W has a larger size of, for example, 12 inches, the IC chip will have to be ultra-micro-machined and the electrode pads will probably be arranged at a smaller pitch. Then, the probe card will be provided with a correspondingly increased number of probes, which may be as many as 2,000. So, the load of all the probes
24
A to be borne by the main chuck
17
will be very heavy and found somewhere between 10 kg and 20 kg. Then, as the wafer W is excessively raised from the position indicated by a broken line to the position indicated by a solid line in
FIG. 8A
, the shaft of the support (not shown) of the main chuck
17
will be bent and the wafer W will be tilted by, e.g., 20 to 30 &mgr;m and moved outwardly to the position shown by solid lines in FIG.
8
A. Consequently, each of the probes
24
A of the probe card
24
is resiliently moved up from the position indicated by a broken line to the position indicated by a solid line in
FIG. 8A
so that the tip of each of the probes travels from the starting point S to the terminal point E on the thick line in
FIG. 8A
by a distance greater than its counterpart in
FIG. 7A
(as indicated by the arrow in FIG.
8
B). Therefore, if the starting point S of the tip of the probe in
FIG. 8A
is identical with that of the probe in
FIG. 7A
, the terminal point E can be located out of the electrode pad P as shown in FIG.
8
B. Then, no test signal will be transmitted from the probe
24
A to the electrode pad P to damage the reliability of the test.
BRIEF SUMMARY OF THE INVENTION
It is therefore the object of the invention to solve the above identified technical problem.
More specifically, an object of the present invention is to provide a probe-test method and a prober with which each probe can reliably contact with the corresponding one of the electrodes of the object of examination to ensure a test to be performed highly reliably.
As pointed out above, as the main chuck carrying thereon an object of examination is raised toward probes to bring the object into contact with the probes, the main chuck can be tilted under the pressure applied by the probes, which by turn displaces the contact point of each of the probes and the corresponding one of the electrodes of the object of examination. Thus, another object of the present invention is to provide a probe-test method and a prober that can predict and correct the displacement on the basis of various data so that each of the probes can reliably contact with the corresponding one of the electrodes of the object of examination to ensure a test to be performed highly reliably.
Still another object of the present invention is to provide a probe-test method and a prober that can reliably and excessively drive the main chuck in the X-, Y- and Z-directions
Ishii Kazunari
Kobayashi Masahito
Metjahic Safet
Nguyen Jimmy
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tokyo Electron Limited
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