Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
1999-03-02
2001-08-07
Karlsen, Ernest (Department: 2858)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C451S289000, C279S003000
Reexamination Certificate
active
06271676
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a device for holding a part and a method for making electrical contact with the part. In particular, this invention relates to a chuck for holding a semiconductor wafer using a suction force and a probing method for making electrical contact with a device test pad on the semiconductor wafer.
2. Disclosure of Related Art
Chucks have long been used to fixedly hold semiconductor wafers during testing. Each semiconductor wafer may contain several thousand integrated circuits (“die”) on a wafer surface that must be tested. Probers having a chuck and a probe card are utilized to make electrical contact with the integrated circuits so that electrical test signals can be transmitted from testers to the integrated circuits. The probe cards contain conductive probe needles that make contact (“probe”) with force on conductive test pads disposed on each integrated circuit.
Prior to testing the integrated circuits on a wafer, the prober “profiles ” the wafer which means the prober determines the top surface topology of the wafer. Profiling of the wafer in a plurality of locations is needed because the wafer may not be flat. Generally, integrated circuits have a protective outer passivation layer that may be made from materials that induce a positive or negative surface tension. The positive or negative surface tension may cause a relatively thin wafer to be concave or convex in shape. To compensate for the irregularity in wafer flatness, the prober stores the wafer profile in memory and utilizes the profile during the subsequent probing of all of the integrated circuits on the wafer.
In a first conventional chuck design, an electrostatic force between a chuck and a wafer is used to fixedly hold the wafer against the chuck. The electrostatic force is created by inducing a positive charge on the metal chuck and inducing a negative charge on the wafer. A problem associated with the first conventional chuck is that the metal chuck acts as an antenna and induces electrical noise into the wafers during testing. The induced electrical noise may cause erroneous integrated circuit test failures. Additionally, the metal chuck deflects from the force exerted by the probe needles during probing. Deflection of the chuck may result in a poor electrical contact between the integrated circuit test pads and the probe needles, resulting in erroneous test failures. Additionally, the deflection of the chuck results in the probe needles contacting and fracturing the passivation layer surrounding the test pad which results in scrapped die.
In a second conventional chuck design, a chuck with a top surface containing a plurality of increasingly larger concentric vacuum grooves is utilized to hold a wafer against the chuck utilizing a suction force. Each concentric vacuum groove has one corresponding vacuum hole. A problem associated with the second conventional chuck is that a concave or convex shaped wafer may not be pulled flat during the “profiling ” of the wafer resulting in erroneous integrated circuit test failures. The second conventional chuck has a small number of vacuum holes resulting in a relatively small amount of air flow through the vacuum grooves. The small amount of air flow through the vacuum grooves results in a relatively small suction force being applied to the wafer that may be insufficient to hold the wafer flat against the chuck. During wafer probing, when the probe needles initially contact an integrated circuit in an area of the wafer disposed off of the chuck, the probe needles may move the wafer a sufficient vertical distance so that the small vacuum force applied by the chuck causes the wafer to be sucked flat against the chuck. The shape of the wafer during subsequent testing no longer matches the wafer profile stored in the prober memory. Thereafter, the prober utilizing the profile may move the probe needles an insufficient vertical distance during probing to make electrical contact with the test pads on the integrated circuits resulting in erroneous integrated circuit test failures.
FIG. 1
illustrates a semiconductor die
10
including a substrate
12
, an aluminum test pad
14
, and an oxide layer
16
. Die
10
is disposed on a chuck
18
and a probe needle
20
is contacting test pad
14
on die
10
to remove a portion of oxide layer
16
that forms on test pad
14
. Oxide layer
16
also known as “flash oxide”, automatically forms when aluminum test pad
14
is exposed to oxygen. Oxide layer
16
acts as an insulator and a portion of oxide layer
16
must be removed in order for probe needle
20
to have an electrical conduction path to test pad
14
. In one known test pad scrubbing process, the oxide layer on a test pad is removed by moving a probe needle relative to the test pad a plurality of movements while contacting the test pad. Initially, the probe needle contacts the test pad at a first location. The probe needle is subsequently moved to a plurality of locations on the test pad to approximate a circular scrubbing motion. A problem with the above-described scrubbing process is that in order to move the probe needle in a circular motion relative to the test pad, a large plurality of X and Y axis movements are needed. Using the above-mentioned probing process may result in substantial probing time being required during the testing of wafers.
There is thus a need for a device and method that minimizes or eliminates one or more of the above-mentioned deficiencies.
SUMMARY OF THE INVENTION
The present invention provides a chuck for holding a semiconductor wafer using a suction force and a probing method for making electrical contact with a device test pad on the wafer.
One object of the present invention is to provide a chuck for fixedly holding a semiconductor wafer flat against a side of the chuck.
Another object of the present invention is to provide a method for probing a test pad on a semiconductor die that requires fewer and smaller movements of the probe needle or chuck to remove a portion of an oxide layer on the test pad as compared to conventional probing methods.
A chuck in accordance with a first embodiment of the present invention includes a chuck plate and a seal plate disposed about a first axis. The chuck plate has a first contact region disposed on a first side and a first groove within the first contact region extending from the first side into the chuck plate. The first groove extends generally spirally outwardly from a first location proximate to the first axis to a second location within the first contact region. The chuck plate has a second contact region disposed on the first side of the chuck plate and around the periphery of the first contact region. The chuck plate has a second groove within the second contact region extending from the first side into the chuck plate. The second groove extends generally spirally outwardly from a third location to a fourth location within the second contact region. The chuck plate includes a first chuck plate vacuum reservoir extending from a second side of the chuck plate into the chuck plate. The chuck plate includes a first plurality of vacuum holes extending from the first groove to the first chuck plate vacuum reservoir. The chuck plate includes a second plurality of vacuum holes extending from the second groove to the first chuck plate vacuum reservoir. The seal plate is disposed on a side of the chuck plate to seal against the chuck plate.
A chuck in accordance with a second embodiment of the present invention includes a chuck plate, a manifold plate, and a seal plate disposed about a first axis. The chuck plate in the second embodiment has a substantially similar first contact region, first groove, second contact region, and second groove as the chuck plate in the first embodiment. The chuck plate includes a first plurality of vacuum holes extending from the first groove through the chuck plate and a second plurality of vacuum holes extending from the second groove through the chuck plate. The manifold plate has a fifth side a
Dykema Gossett PLLC
Karlsen Ernest
Kobert Russell M.
TSK America, Inc.
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