Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2002-06-10
2003-09-09
Cuneo, Kamand (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C324S762010, C324S1540PB
Reexamination Certificate
active
06617865
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a compliant probe apparatus. In particular, this invention relates to the burn-in and testing of microelectronic devices, and specifically to contact assemblies used for connecting electrical signals to integrated circuits during burning-in and testing of individual chips and of full wafers.
BACKGROUND OF THE INVENTION
Microelectronic devices are subjected to a series of test procedures during the manufacturing process in order to verify functionality and reliability. Prior art testing procedures conventionally include wafer probe testing, in which microelectronic device chips are tested to determine operation of each chip before it is diced from the wafer and packaged. Prior art probe cards are built of long cantilever wires that are used to test one or several chips at a time at the wafer level.
Typically, not all chips on a wafer are found to be operable in the wafer probe test, resulting in a yield of less than 100% good devices. The wafer is diced into individual chips and the good chips are assembled into packages. The packaged devices are dynamically burned-in by loading into sockets on burn-in boards and electrically operating at a temperature of from 125° C. to 150° C. for a burn-in period of 8 to 72 hours in order to induce any defective devices to fail. Burn-in accelerates failure mechanisms that cause infant mortality or early failure of the devices, and allows these defective devices to be screened out by a functional electrical test before they are used commercially.
A full functional test is done on packaged devices, which are operated at various speeds in order to categorize each by maximum speed of operation. Testing discrete packaged devices also permits elimination of any devices that failed during the burn-in process. Burn-in and test of packaged devices is accomplished by means of sockets specially suited to the burn-in reconditions and to high speed testing respectively. As a result, conventional manufacturing processes are expensive and time consuming because of repeated handling and testing of individual discrete devices through a lengthy set of steps that adds weeks to the total manufacturing time for the device.
A considerable advantage in cost and in process time can be obtained by burn-in and test of the wafer before it is diced into discrete devices. Additional savings can be obtained by fabricating chip size packages on each device on a wafer before the wafer is diced into discrete devices. A considerable effort has been expended by the semiconductor industry to develop effective methods for wafer level packaging, burn-in and test in order to gain benefits of a greatly simplified and shortened process for manufacturing microelectronic devices. In order to reap these benefits, it is necessary to provide means to burn-in and speed test chips before they are diced from the wafer into individual discrete devices.
Conventional cantilever wire probes, however, are not suited to burn-in and speed testing of devices on the wafer. Cantilever wire probes are too long and bulky to allow simultaneous contact to all of the devices on a wafer, as required for simultaneous burn-in of all of the devices on the wafer. In addition, long cantilever wire probes are not suitable for functional testing of high-speed devices, among other things, because of a high self and mutual inductance of the long, parallel wires comprising the probes.
A small, high-performance probe that can be made at low cost is required for practical application of wafer burn-in and test procedures. To be useful for wafer burn-in and test, the desired probes must reliably contact all of the pads on the devices under test while they are on the undiced wafer. Probes for contacting the wafer must also provide electrical contact to pads on devices even, and especially, where the pads vary in height on the surface of the wafer. In addition, the probes must break through any oxide layers on the surface of the contact pads in order to make a reliable electrical contact to each pad. Many approaches have been tried to provide a cost-effective and reliable means to probe wafers for burn-in and test, without complete success.
The prior art reveals a number of attempts that have been tried to provide small, vertically compliant probes for reliably contacting the pads on devices on a wafer. According to the invention represented by U.S. Pat. No. 4,189,825, a cantilever probe is provided for testing integrated circuit devices. In
FIG. 1
, cantilever
22
supports sharp tips
26
above aluminum contact pads
24
on a chip
23
. A compliant member
25
is urged downward to move tips
26
into contact with pads
24
. An aluminum oxide layer on pad
24
is broken by sharp tip
26
in order to make electrical contact between tip
24
and the aluminum metal of pad
24
. The rigidity of small cantilever beams, however is generally insufficient to apply the force to a tip that is necessary to cause it to break through an aluminum oxide layer on a contact pad, without an external means of applying force to the cantilever. Cantilever beams of glass, silicon, ceramic material, and tungsten have also been tried in various configurations, without success in providing burn-in probes of sufficient force and flexibility.
A flexible membrane probe is described in Flexible Contact Probe, IBM Technical Disclosure Bulletin, October 1972, page 1513 as shown in
FIG. 2A. A
flexible dielectric film
32
includes terminals
33
that are suited to making electrical contact with pads on integrated circuits. Terminals
33
are connected to test electronics by means of flexible wires
34
attached to contact pads
35
on terminals
33
. Probes fabricated on a flexible polyimide sheet were described in the Proceedings of the IEEE International Test Conference (1988) by Leslie et al. The flexible sheet allows a limited amount of vertical motion to accommodate variations in height of bond pads on integrated circuits on a wafer under test. Membrane probes such as that described by Leslie et al provide connections to integrated circuit chips for high performance testing. However, dimensional stability of the membrane is not sufficient to allow contacts to pads on a full wafer during a burn-in temperature cycle.
Fabrication of the contacts on a thin silicon dioxide membrane as described in U.S. Pat. No. 5,225,771 is shown in
FIG. 2B. A
silicon dioxide membrane
40
has better dimensional stability than polyimide, thereby somewhat ameliorating the dimensional stability problem of mating to contact pads on a wafer under burn-in test. Probe tips
41
are connected by vias
44
through membrane
40
to circuit traces
45
that are linked to an additional layer of circuitry
42
above a dielectric film
43
. However, limited vertical compliance of the test probes on silicon dioxide membrane
40
renders use of such probe arrays unreliable for use in burn-in of devices on a semiconductor wafer.
Fabrication of an array of burn-in probes on a semiconductor wafer is described in U.S. Pat. No. 4,585,991, especially as illustrated in
FIGS. 3A and 3B
showing a top plan view and a sectional view respectively. Probe
51
is a pyramid attached to semiconductor wafer substrate
52
by arms
54
. Material
53
is removed from the semiconductor wafer
52
in order to mechanically isolate the probe
51
. A probe as in
FIG. 3A
provides a limited vertical movement but it does not allow space on the substrate for wiring needed to connect an array of probes to test electronics required for dynamic burn-in.
Another marginally successful approach to providing flexible probes to device contact pads involves the use of flexible wires or posts to connect the test circuitry to the pads. A flexible probe is described in U.S. Pat. No. 5,977,787 as shown in FIG.
4
A. There, probe
60
is a buckling beam probe, earlier generally described in U.S. Pat. No. 3,806,801. The buckling beam probe
60
is adapted for use in burn-in of devices on a wafer. The buckling beam probe
60
is held by guides
61
and
62
that have
Allen Kenneth R.
Cuneo Kamand
Decision Track LLC
Patel Paresh
Townsend and Townsend / and Crew LLP
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