Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2003-06-11
2004-10-12
Nguyen, Vinh P. (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S073100
Reexamination Certificate
active
06803779
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a system for high-frequency evaluation of probe measurement networks and, in particular, to a system for accurately evaluating the signal conditions existing in such networks even in those ones of such networks, for example, that are of a multichannel type in which each channel communicates through a separate device-probing end and even in those ones of such multichannel networks, for example, that have their device-probing ends crowded together in a high-density coplanar probing array as suitable for the measurement of integrated circuits or other microelectronic devices.
FIG. 1
shows a probe station
20
that includes a multichannel measurement network
21
of a type suitable for measuring high-frequency microelectronic devices at the wafer level. A probe station of this type is manufactured, for example, by Cascade Microtech, Inc. of Beaverton, Oreg. and sold under the trade name SUMMIT 10000. The various devices
24
, the characteristics of which are to be measured by the network, are formed on the surface of a wafer
22
in isolation from each other. An enlarged schematic plan view of an individual device
24
is shown in FIG.
2
. The surface of each device includes a predetermined pattern of bonding pads
26
that provide points of connection to the respective electrical components (not shown) formed on the central area of each device. The size of each bonding pad is exaggerated for ease of illustration in
FIG. 2
, but it will be recognized by one of ordinary skill in the art that there will typically be hundreds of bonding pads in the rectangular arrangement shown, each of a size that is barely visible to the eye without magnification. If a hybrid device instead of a flat wafer is being tested, then the individual devices can rise to different heights above the plane of the hybrid device's upper surface.
As depicted in
FIG. 1
, to facilitate high-frequency measurement of each device
24
, a typical probe station
20
includes a wafer-receiving table or chuck
28
for supporting the wafer
22
. The probe measurement network
21
of the station includes a probing assembly
30
which, as shown, can take the form of a probe card with a multiconductor probe tip array for delivering signals to, and receiving signals from, the respective bonding pads of each individual device. One common type of probe card structure, as depicted, includes an open-centered rectangular-shaped frame
32
with numerous needle-like probe tips
34
that downwardly converge toward the open center of the frame. The end portion of each tip is bent at a predetermined angle so that the lower extremities or device-probing ends of the tips, which typically have been blunted by lapping to form a coplanar array, are suitably arranged for one-to-one contact with the bonding pads
26
provided on each respective microelectronic device. The measurement signals provided by the network are generated within and monitored by a multichannel test instrument
36
, which is connected to the probe card via a suitable multiconductor cable
38
. The probe station also includes an X-Y-Z positioner (e.g., controlled by three separate micrometer knobs
40
a, b, c
) for permitting fine adjustments in the relative positions of the probe card
30
and the selected device-under-test.
The individual elements that make up a probe measurement network can take forms other than those shown in FIG.
1
. For example, depending on the particular requirements of the devices to be measured, the probing assembly can take the form of a multiconductor coplanar waveguide as shown in Strid et al. U.S. Pat. No. 4,827,211 or Eddison et al. UK Patent No. 2,197,081. Alternatively, the assembly can take-the form of an encapsulated-tip probe card as shown in Higgins et al. U.S. Pat. No. 4,566,184, or a multiplane probe card as shown in Sorna et al. U.S. Pat. No. 5,144,228, or a dual-function probe card in which the probe card not only probes but also supports the downturned wafer, as shown in Kwon et al. U.S. Pat. No. 5,070,297. Use of this last card structure, however, is limited to the probing of flat wafers or other device configurations in which all devices are of the same height.
Before using a probing station or other probing system to measure the high-frequency performance of individual devices, such as those formed on a wafer, it is desirable to first accurately evaluate the signal conditions that are actually present in the measurement network of the system with reference, in particular, to the device-probing ends of the network.
For example, with respect to a probing system of the type shown in
FIG. 1
, in order to accurately calibrate the source or incoming channels of the system's measurement network, preferably measurements are made of the respective signals that are generated by the various sourcing units of the test instrument
36
in order to reveal how these signals actually appear in relation to each other when they arrive at the device-probing ends that correspond to the respective source channels, since the signals that actually enter the input pads of each device come directly from these ends. Conversely, in order to accurately calibrate the sense or outgoing channels of the probing network, preferably the respective signal conditions that are indicated by the various sensing units of the test instrument
36
are observed when reference signals of identical or otherwise relatively known condition are conveyed to the device-probing ends that correspond to the respective sense channels, since the signals that actually exit the output pads of each device go directly to these ends. Should any channel-to-channel differences be found to exist in the network, these differences can be compensated for so that the test instrument will only respond to those differences which actually arise from the different input/output characteristics of the device-under-test.
Typically it is difficult, however, to make comparatively accurate high-frequency measurements in reference to the extreme ends of a probing assembly where the ends have been arranged for the measurement of planar microelectronic devices because of the reduced size and the closely crowded arrangement of such ends. This is particularly so when the probing assembly is of the card-like type
30
shown in
FIG. 1
, due to the inherent fragility of the needle-like tips
34
that are part of such an assembly.
The reason for this difficulty can be better understood in reference to
FIG. 3
, which shows one common type of interconnect assembly that has been used to evaluate probe measurement systems of the type shown in FIG.
1
. This assembly includes a signal probe
42
having a single pointed transmission end
44
, which probe is connected, via a cable, to the sensing unit, for example, of a test instrument. This instrument can either be the same as that instrument
36
which provides the sourcing units for the probe measurement network or, as shown, can be an entirely separate instrument
46
. Viewing
FIGS. 1 and 3
together, when the pointed end of the signal probe is being repositioned from one tip
34
to another, normally it is necessary to move the relatively stiff end of the probe slowly and deliberately in order to avoid damaging the delicate needle-like tips, so that a relatively long period of time is needed in order to complete evaluation in relation to all the tips. Additionally, this type of probe has poor high-frequency measurement stability in moderately noisy test environments. Even more significantly, because the extreme ends of the needle-like tips
34
on the probe card are too thin and delicate to be probed directly, probe-to-probe contact between the pointed transmission end
44
of the signal probe and each needle-like tip of the probe card must occur further up nearer to the base of each tip. This introduces, for example, a phase offset of indeterminate amount between the signal that is being measured by the signal probe and the signal as it will actually appear in relation to the bondin
Carlton Dale E.
Gleason K. Reed
Schappacher Jerry B.
Strid Eric W.
Cascade Microtech, Inc.
Chernoff Vilhauer McClung & Stenzel LLP
Nguyen Vinh P.
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