US 20070273387 A1
A chuck adapted to test electrical and/or optical components on a device-under-test (DUT).
1. A test assembly comprising:
(a) a chuck for supporting a device under test;
(b) said chuck defining an optical path that is transmissive to an optical signal; and
(c) a conductive member at least partially laterally spaced apart from said chuck connected to a guard potential.
2. The assembly of
3. The assembly of
4. The assembly of
5. The assembly of
6. The assembly of
7. The assembly of
8. The assembly of
9. The assembly of
10. The assembly of
11. The assembly of
12. The assembly of
13. The assembly of
14. The assembly of
15. The assembly of
16. The assembly of
17. The assembly of
18. The assembly of
19. The assembly of
20. A test assembly comprising:
(a) a chuck for supporting a device under test;
(b) said chuck defining an optical path that is transmissive to an optical signal; and
(c) a conductive member positioned at least partially within said optical path wherein said optical signal passes through at least a portion of said conductive member, wherein said conductive member is connected to a guard potential.
21. The assembly of
22. The assembly of
23. The assembly of
24. The assembly of
25. The assembly of
26. The assembly of
27. The assembly of
28. The assembly of
29. The assembly of
30. The assembly of
31. The assembly of
This application is a continuation of U.S. patent application Ser. No. 10/912,789, filed Aug. 6, 2004, which application is a continuation of U.S. patent application Ser. No. 10/214,888, filed Aug. 7, 2002, which claims the benefit of U.S. Prov. App. No. 60/316,644, filed Aug. 31, 2001.
The present invention is directed to a chuck adapted to test electrical and/or optical components on a device-under-test (DUT).
Guarding systems suitable to reduce leakage currents during low current measurements are well known and discussed extensively in the technical literature. See, for example, an article by William Knauer entitled “Fixturing for Low Current/Low Voltage Parametric Testing” appearing in Evaluation Engineering, November, 1990, pages 150-153. Probe stations employing such a guarding system typically route a test signal to selected contact pads on the device-under-test (DUT) and route a guard signal to electrically conductive material surrounding the DUT on several sides, separated from the device-under-test by dielectric material (e.g., air). The guard signal preferably closely approximates the test signal or otherwise follows the test signal, thus reducing electromagnetic leakage currents that might otherwise occur.
Frequently, such probe stations also provide an electrically conductive enclosure around the perimeter of the probe station connected to a shield potential. The shield potential is typically connected to earth ground, instrumentation ground, or some other suitable potential. See, for example, Peters et al., U.S. Pat. No. 6,002,263.
To provide effective guarding and shielding for probe stations, a multi-stage chuck upon which the device-under-test rests during testing may likewise be used. The upper stage of the chuck, which supports the device-under-test, typically includes an electrically conductive metal layer through which the test signal may be routed. A middle stage and a lower stage of the chuck similarly include an electrically conductive metal layer to which a guard signal and a shield signal may be imposed, respectively. In this fashion, a device-under-test resting on such a multistage chuck may be both guarded and shielded from below. Some probe stations also provide for guarding from the sides and from above.
Many electrical devices, in particular semiconductor based devices, include both electrical components and optical components. Some optical components receive an optical signal from an optical source and convert the received optical signal into an electrical signal, e.g., a photo-detector. Other optical components convert an electrical signal into an optical signal, e.g., a light-emitting-diode. Yet other optical components may include multiple optical and/or electrical components. Frequently, a probe station may be used to test the electrical components.
Unfortunately, the aforementioned probe stations are not suitable for testing optical components because there is no optical path through the chuck itself. Accordingly, a different type of chuck, namely an optical chuck, is used for testing devices that include optical components. An optical chuck typically includes an central optically transparent medium over which the device-under-test is supported. For example, an optical signal from a light source may be directed toward the device-under-test from below, above, or to the side of the optical chuck, and a probe or connector used to sense the resulting electrical output from the device-under-test. Similarly for example, a probe or connector may be used to provide an electrical source to the device-under-test, and an optical sensing device located below, above, or to the side of the optical chuck to sense the resulting optical output from the device-under-test. Accordingly, the probe station is used to provide a shielded environment from exterior electromagnetic noise so that the input-output characteristics of an optical device-under-test may be performed. It may be observed that the testing of the optical components on the device-under-test is performed by observing the input and output characteristics of the device which normally have significant voltage and/or current levels (or optical power) making measurements easily performed.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.
The traditional approach to optical testing involves testing the inputs and outputs of a device-under-test with an optical sensor(s), a connector(s), and/or an electrical probe(s). Based upon using the sensor, the connector, and/or electrical probe the overall operational characteristics of the device-under-test may be characterized. The present inventors came to the realization that together with optical testing there is a previously unrealized need to achieve performance levels that were previously not considered needed, namely ultra low noise and low current measurements. In particular, the present inventors determined that unlike measuring the operational inputs and/or outputs of the device-under-test which are sufficiently accurately measured using only a shielded environment because the noise levels are relatively low and the current levels are relatively high, measurements of other electrical characteristics of the device-under-test apart from the operational inputs and/or outputs are desirable. For example, low current measurements with a high degree of accuracy may be desirable of a portion of the electrical aspects of the optical device-under-test, such as the leakage currents of a junction for a light emitting diode.
The support 12 may include one or more connectors 23 to the chuck 10. The connector 23 is preferably a co-axial or tri-axial connector providing a force test signal to the device under test. Also, multiple connectors 23 may be used to provide a Kelvin connection and/or a quasi-Kelvin connection to the device-under-test. In addition, the support 12 may include one or more connectors 25 to provide a sense signal to the conductive member 22. The guard braid on the connector 23 and/or connector 25 may be electrically connected to the conductive member 22.
While the chuck 10 design facilitates improved testing of the device-under-test, at leakage current levels not previously considered obtainable, a tendency for breaking the device-under-test occurs when undergoing pressure as a result of probes. In addition, the device-under-test has a tendency to warp or otherwise become non-uniform as a result of the central region of the device-under-test not being supported. Referring to
The insulating member 18 may include a raised portion 50 and an inset portion 52. The raised portion 50 forms a perimeter having an inner diameter substantially equal to the outer diameter of the chuck 10 which maintains the chuck 10 within the inset portion 52. The inset portion 52 preferably has an inner diameter substantially equal to the inner diameter of the chuck 10 so as to form a substantially continuous boundary for the optical path 34.
In a similar fashion, the conductive member 22 may include a raised portion 60 and an inset portion 62. The raised portion 60 provides a surface having an inner shape, such as a pair of co-planar surfaces, substantially equal to the exterior width of the raised portion 50 of the insulating member 18. In this manner, the insulating member 18 may be positioned within the conductive member 22. The inset portion 62 of the conductive member 22 has an inner diameter substantially equal to the inner diameter of the inset portion 52 and the chuck 10 so as to form a substantially continuous boundary for the optical path 34.
Devices within the optical path 34 may include materials that are optically transparent to the wavelength of the optical signal. A variety of commercially available materials are suitable for use as the optical chuck material 42, such as for example, quartz, sapphire, lithium niobate, and silicon.
After consideration of the support shown in
After consideration of the supports shown in
It is to be understood that the orientation of the device-under-test is shown with the device-under-test on the top with the chuck thereunder. It is to be understood that the testing may be performed with the orientation of the device-under-test and/or chuck (etc.) in an inverted orientation.
The preferred embodiment of the support 12 provides a wafer supporting surface capable of providing a test signal and a guard member 22 that, in conjunction with the lower guard member 70, allows the signal provided to or received from the device-under-test to be electrically guarded. The support 12 also provides an environment suitable for low current low leakage measurements for an optical device so that the device-under test need not be transferred between an optical chuck in an optical probe station and a traditional chuck in an electrical probe station for the testing of optical components and electrical components, respectively, that may be included within the device-under-test.
Generally speaking, chucks used to support a DUT during both electrical and optical testing needs to provide a stable surface where the DUT is held in place while testing is performed. In this regard, a number of chucks, appropriately called vacuum chucks, use vacuum pressure to hold the DUT in place. One problem with existing vacuum chucks is that when testing a DUT on a wafer that has been broken, the vacuum pressure provided by the chuck tends to deform the wafer because the chuck was only designed to hold a full wafer.
After further consideration the present inventors determined that further improvements in the measurement levels may be achieved by incorporating a shield potential within the support. Referring to
The vacuum shafts 108 (or otherwise a passage or chamber) are preferably positioned at 0 degrees, 90 degrees, and 270 degrees around the vacuum chamber 100, respectively. A plug 112 each vacuum shaft, respectively, may be used to selectively isolate portions of the vacuum chamber 100 from the vacuum source. For example, if the vacuum source supplies vacuum pressure through vacuum supply line 104, and the plugs 112 associated with the vacuum shafts 108 at 0 and 90 degrees respectively are activated, then a quarter section of the chuck is providing vacuum pressure to the wafer. Similarly, if the vacuum member is supplying vacuum pressure through either vacuum supply line 102 or vacuum supply line 104, or both, and the plugs 112 at 90 degrees and 270 degrees, respectively, are activated, then a half-section of the chuck is providing vacuum pressure to the wafer. The selective activation of different regions of the vacuum chamber of the chuck in non-concentric rings permits fragments of a semiconductor device to be effectively tested. For example, if a fragment of a semiconductor is available then one or more regions may be interconnected to the vacuum source to maintain the fragment properly positioned on the chuck 10. By disabling the vacuum for the non-used portions of the chuck the vacuum pressure may be more readily controlled and improves the vacuum by reducing leaks. Moreover, if a significant number of small apertures 110 are not covered with a respective device-under-test then the resulting vacuum pressure for the small apertures 110 under the device-under-test may not sufficient vacuum pressure to maintain sufficient pressure. It is to be understood that other patterns of vacuum holes may likewise be used where groups of one or more vacuum holes may be selectively enabled. Also, the different regions may include at least one of the same holes, if desired. The patterns of the vacuum holes preferably include at least one selectable region that is in a non-concentric region. Also, a switching mechanism may be used to select which of the vacuum regions provide a vacuum to the surface of the chuck. In addition, a selectable vacuum source may be provided to each vacuum region.
After further consideration of the planarity of the device-under-test it is preferable to include vacuum holes within the optically transmissive material. Accordingly, a pair of spaced apart transmissive plates with an opening defined therein to which a vacuum is provided may be used with holes in the upper plate to provide a vacuum to the upper surface. However, using sufficiently thick spaced apart glass plates to provide structural integrity to the wafer results in excessive refraction of the optical signal. Also, using sufficiently thin spaced apart glass plates results in deflection of the supporting glass, and thus the wafer, which distorts the measurements. Referring to
All references cited herein are incorporated by reference.
The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.