Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1998-07-24
2003-11-11
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S1540PB, C451S059000, C451S041000
Reexamination Certificate
active
06646455
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a probe used for testing the operation of semiconductor integrated circuits which are formed on semiconductor wafers, a method of the same, and a member for removing metals, metal oxides, contaminants obstructing electrical contact, etc. which are adhering to the probe.
2. Description of the Related Art
In a conventional probe, as shown in
FIG. 22A
, a testing (probing) is carried out by attaching a probe
202
having a fore end bent into a hook-like shape to a probe card
201
which is vertically movable, and pushing the probe
202
against a test pad of a semiconductor integrated circuit (referred to as a pad hereinafter) in such a condition that an oxide film on the pad surface is broken off to establish true contact (electrical contact) between the probe and a fresh surface of the pad. The condition of a probe tip under the probing is shown in FIG.
22
B. For the sake of explanation,
FIG. 22B
is illustrated in the form of a simplified model with respect to dimensions and so on. A tip
200
of the conventional probe
202
is originally finished to have a flat end face, as shown in FIG.
22
B. Even when the probe tip is machined to have a spherically curved surface intentionally, a sphere approximating the curved surface has a radius R of curvature as large as 20-30 &mgr;m. At the time of probing, therefore, the whole of flat end portion first comes into contact with a pad
203
while an oxide film
204
and contaminants on the surface of the pad
203
are interposed between the probe tip and the pad surface. Then, as the probe
202
is more closely pushed against the pad
203
, the oxide film
204
on the surface of the pad
203
is partly broken off to produce an electrical continuity region
206
in which electrical true contact can be established, thereby enabling a continuity test to be performed. With repetition of the probing, however, the oxide film
204
is accumulated on a heel portion
205
of the probe
202
which is subject to maximum stresses, and an area of the true contact with the pad
203
is so reduced as to make electrical continuity unstable. To reliably establish the electrical contact, vibration is applied to the probe tip in Japanese Unexamined Patent Publication No. 6-18560, for example.
Further, tungsten used as materials of the probe
202
is in the form of a powder sintered compact which has material defects (voids) therein. Accordingly, when the powder sintered compact is machined so as to provide a tip shape of the probe
202
, the material defects appear on the probe surface. Pad materials such as aluminum, for example, enter the material defects appearing in the tip (end) face of the probe
202
to form deposition nuclei and grow into deposits. As a result, contact resistance is increased.
For removing those material defects, heat treatment is applied to tungsten materials in Japanese Unexamined Patent Publication No. 5-140613, for example.
In addition, the card probe
202
, which serves as an interface for electrical signals transferred between a tester for measuring electrical characteristics of a semiconductor integrated circuit formed on a wafer, and the semiconductor integrated circuit, is brought into pressure contact with the pad
203
of the semiconductor integrated circuit in such a manner as to scrape off an aluminum alloy forming the pad
203
. Therefore, scraped-off parts of materials of the pad
203
, such as aluminum and an aluminum oxide, and/or of contaminants remaining on the surface of the pad
203
adhere to the tip of the probe
202
. Unless those adhering substances or deposits are removed from the tip of the probe
202
, the contact resistance between the probe
202
and the pad
203
is so increased that the electrical characteristics of the semiconductor integrated circuit cannot be accurately measured. In other words, if the probe
202
is used for a long period of time with the deposits kept accumulated on the tip of the probe
202
, the contact resistance increases over time.
For those reasons, it is customary to clean out the tip of the probe
202
and remove foreign matter adhering to it whenever the probing is repeated a predetermined number of times.
For example, Japanese Unexamined Patent Publication No. 7-244074 discloses an abrasive sheet formed by mixing fine-grained abrasives for grinding in an elastic matrix and then shaping the matrix into a sheet. The abrasive sheet is attached, instead of a semiconductor wafer, onto a wafer moving table of a probe apparatus which is operated to made a semiconductor integrated circuit and a probe contacted with each other. The wafer moving table is vertically moved to press a tip of the probe against the surface of the abrasive sheet, whereupon contact friction is caused between the tip face of the probe and the fine-grained abrasives dispersed in the abrasive sheet to remove foreign matter adhering to the probe tip.
Thus, in the conventional probe having the above-described construction, as shown in
FIG. 22B
, the true contact area (electrical continuity region
206
) between the tip
200
of the probe
202
and the pad
203
is very small during the test of electrical characteristics. Accordingly, a sufficient degree of electrical continuity is not obtained between the probe
202
and the pad
203
in some cases.
Also, voids produced in tungsten materials of the probe
202
are conceivably eliminated by heat treatment. However, if the tungsten materials are subject to heat treatment at a temperature not lower than the recrystallization temperature, there arises another problem that the probe materials become brittle.
Further, the conventional abrasive sheet for removing foreign matter adhering to the tip
200
of the probe
202
is formed by mixing fine-grained abrasives in an elastic matrix and is deformed upon the tip
200
of the probe
202
being pressed against the surface of the abrasive sheet. As shown in
FIG. 23
, therefore, the tip
200
of the probe
202
is forced to come into a matrix
210
and abraded by fine-grained abrasives
211
over a region indicated by dotted lines. This tip abrasion raises a problem that, with repetition of cleaning, the probe tip is thinned and eventually loses strength to such an extent that it may bend or chip.
SUMMARY OF THE INVENTION
With a view of solving the problems mentioned above, an object of the present invention is to provide a probe which can increase a true contact area between a probe tip and a pad and hence establish reliable electrical contact.
Another object of the present invention is to provide a member for removing foreign matter adhering to the probe tip, which can prevent the probe tip from being thinned with repetition of cleaning and hence has a longer service life.
To this end, according to the present invention, there is provided a test probe for semiconductor devices, the test probe having a tip portion which is pressed against a test pad of a semiconductor device to establish electrical contact between the tip portion and the pad for testing the operation of the semiconductor device, wherein the probe is formed to have a tip shape with an angle of not less than 15 degrees formed at the surface of the pad between a tangential line with respect to a tip face of the probe and the pad surface when the probe is pressed against the pad, the tip shape of said probe having a spherical surface meeting the relationship of:
&thgr;=cos
−1
(1−
t/R
)≧15°
where the radius of curvature of the spherical surface is R, the thickness of the pad is t, and the angle formed at the pad surface between the tangential line with respect to the probe tip face and the pad surface when the probe is pressed against said pad is &thgr;, the probe having a flat portion at an end of the tip portion.
According to another aspect of the present invention, there is provided a method of manufacturing a test probe for semiconductor devices, the test probe having a tip portion which is pressed against a test pad of a semiconductor
Kano Mutsumi
Kashiba Yoshihiro
Maekawa Shigeki
Miki Kazunobu
Nagata Takahiro
Burns Doane , Swecker, Mathis LLP
Cuneo Kamand
Mitsubishi Denki Kabsuhiki Kaisha
Nguyen Jimmy
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