US20080042675A1 - Probe station - Google Patents

Abstract

A probe station.                

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation of U.S. patent application Ser. No. 10/759,481, filed Jan. 16, 2004, which is a continuation of U.S. patent application Ser. No. 10/285,135, filed Oct. 30, 2002, now U.S. Pat. No. 6,777,964, which claims the benefit of U.S. Provisional App. No. 60/351,844, filed Jan. 25, 2000.
BACKGROUND OF THE INVENTION
• The present invention relates to a probe station.
BRIEF SUMMARY OF THE INVENTION
• Probe stations are designed to measure the characteristics of electrical devices such as silicon wafers. Probe stations typically include a chuck that supports the electrical device while it is being probed by needles or contacts on a membrane situated above the chuck. In order to provide a controlled environment to probe the electrical device, many of today's probe stations surround the chuck with an environmental enclosure so that temperature, humidity, etc. may be held within predetermined limits during testing. Environmental enclosures protect the device from spurious air currents that would otherwise affect measurements, and also facilitate thermal testing of electrical devices at other-than-ambient environmental conditions. Environmental conditions within the enclosure are principally controlled by a dry air ventilation system as well as a temperature element, usually located below the chuck, that heats or cools the electrical device being tested through thermal conduction.
• Many probe stations also incorporate guarding and electromagnetic interference (EMI) shielding structures within or around the environmental enclosures in order to provide an electrically quiet environment, often essential during high frequency testing where electrical noise from external electromagnetic sources can hinder accurate measurement of the electrical device's characteristics. Guarding and EMI shielding structures are well known and discussed extensively in 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 incorporating EMI shielding structures will usually at least partially surround the test signal with a guard signal that closely approximates the test signal, thus inhibiting electromagnetic current leakage from the test signal path to its immediately surrounding environment. Similarly, EMI shielding structures may provide a shield signal to the environmental enclosure surrounding much of the perimeter of the probe station. The environmental enclosure is typically connected to earth ground, instrumentation ground, or some other desired potential.
• To provide guarding and shielding for systems of the type just described, existing probe stations may include a multistage chuck upon which the electrical device rests when being tested. The top stage of the chuck, which supports the electrical device, typically comprises a solid, electrically conductive metal plate through which the test signal may be routed. A middle stage and a bottom stage of the chuck similarly comprise solid electrically conductive plates through which a guard signal and a shield signal may be routed, respectively. In this fashion, an electrical device resting on such a multistage chuck may be both guarded and shielded from below.
• FIG. 1 shows a generalized schematic of aprobe station10. Theprobe station10 includes thechuck12 that supports theelectrical device14 to be probed by theprobe apparatus16 that extends through an opening in theplaten18. Anouter shield box24 provides sufficient space for thechuck12 to be moved laterally by apositioner22. Because thechuck12 may freely move within theouter shield box24, a suspendedmember26 electrically interconnected to a guard potential may be readily positioned above thechuck12. The suspendedguard member26 defines an opening that is aligned with the opening defined by theplaten18 so that theprobe apparatus16 may extend through theguard member26 to probe theelectrical device14. When connected to a guard signal substantially identical to the test signal provided to theprobe apparatus16, the suspendedguard member26 provides additional guarding for low noise tests. Such a design is exemplified byEP 0 505 981 B1, incorporated by reference herein.
• To provide a substantially closed environment, theouter shield box24 includes asliding plate assembly28 that defines a portion of the lower perimeter of theshield box24. Thesliding plate assembly28 comprises a number of overlapping plate members. Each plate member defines acentral opening30 through which thepositioner22 may extend. Each successively higher plate member is smaller in size and also defines asmaller opening30 through which thepositioner22 extends. Thesliding plate assembly28 is included to permit lateral movement of thepositioner22, and hence thechuck12, while maintaining a substantially closed lower perimeter for theshield box24.
• Referring toFIG. 2, in many cases the semiconductor wafers that are tested within such a probe station are edge coupled photonics devices. Edge coupled photonics devices are normally arranged within each semiconductor wafer in orthogonal arrays of devices. Typically, the wafers are sliced in thin strips of a plurality individual optical devices, as illustrated inFIG. 3. Edge coupled photonics devices may include, for example, lasers, semiconductor optical amplifiers, optical modulators (e.g., Machzhender, electro-absorption), edge coupled photo-diodes, and passive devices. Referring toFIG. 4, many such photonics devices provide light output through one side of the device. Normally, the photonics devices receive light through the opposing side of the device from the light output. On another side of the device one or more electrical contacts are provided. In typical operation, the light provided by the device may be modulated or otherwise modified by changing the input light and/or the electrical signal to the device, or the electrical output may be modulated or otherwise modified by changing the input light. Similarly, other photonics devices are surface coupled where the electrical contact and the light output (or light input) are both on the same face of the device, as illustrated inFIG. 5. On such surface coupled photonics device is a VCSEL laser.
• Referring toFIG. 6, a typical arrangement to test such photonics devices within a probe station is shown. A set ofelectrical probe positioners50 are arranged on the platen to provide electrical signals to and from the device under test, as needed. In addition, one or moreoptical probe positioners60 are positioned on the platen to sense the light output from the device under test or provide light to the device under test. As it may be observed, when testing devices that include both optical and electrical attributes the number of positioners may be significant thereby potentially resulting in insufficient space on the platen to effectively accommodate all the necessary positioners. In addition, the opening provided by the platen is normally relatively small so that the space available for extending the probes through the platen is limited. This limited space significantly increases the difficulty in positioning the electrical and optical probes. Similarly, the end of the optical probes typically need to be positioned within 0.10 microns in x/y/z directions which is somewhat awkward from a position on the platen above the chuck. Moreover, the angular orientation of the end portion of the optical probe likewise needs to be very accurate to couple light between the optical probe and the device under test which is similarly difficult. In many applications extreme positional and angular accuracy is needed to couple the optical waveguide or free space optical path (i.e., optical probe) to a photonics device or another optical waveguide. Moreover, during the testing of wafers the optical probes frequently tend to be out of alignment requiring manual alignment for each photonics device while probing each of the devices.
• What is desired, then, is a probe station that facilitates accurate alignment of electrical and optical probes.
• 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.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
• FIG. 1 shows a cross sectional view of an existing probe station.
• FIG. 2 illustrates a wafer with photonics devices thereon.
• FIG. 3 illustrates a strip of photonics devices.
• FIG. 4 illustrates an edge coupled photonics device.
• FIG. 5 illustrates an upper surface coupled photonics device.
• FIG. 6 shows a cross sectional view of the probe station ofFIG. 1 with electrical and optical probes.
• FIG. 7 shows a pictorial view of a modified probe station.
• FIG. 8 shows a pictorial view of another modified probe station.
• FIG. 9 shows a pictorial view of yet another modified probe station.
• FIG. 10 shows a pictorial view of the support assembly for the probe station ofFIG. 7.
• FIG. 11 shows a pictorial view of a further modified probe station.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
• During testing, the end of the optical probes are typically aligned with the edge of the device under test while the electrical probes are typically aligned with the contacts on the upper surface of the device under test, with both the electrical probes and the optical probes being supported by the platen. In many cases, the entire platen is moved in the z-axis direction for selectively contacting the electrical probes on the device under test. Alternatively, the chuck is moved in a z-axis direction. The z-axis movement of the platen permits consistent simultaneous relative movement of all the electrical and optical probes. Each component of the device under test is successively moved in x and/or y lateral directions relative to the electrical probes using a chuck or other support to a location under the electrical probes.
• The present inventors considered the z-axis movement of the platen or chuck to perform simultaneous probing and came to the realization that normal z-axis movement of the platen typically brings the probes into contact with the device under test with sufficient additional z-axis movement to result in lateral scrubbing of the contact surfaces to provide a good contact. This additional z-axis movement for the electrical probes, which may vary depending on the particular circuit being probed, different electronic components, the planarity of the devices, and differences in the height of the different contacts between devices, may result in inaccurate alignment of the optical probes which are likewise being moved in the z-axis direction together with the platen or chuck. The alignment of the optical inputs and outputs of the devices tends not to vary in the same manner as the contacts, if they vary significantly at all. In summary, the appropriate z-axis movement of the electrical probes varies depending on the particular device being tested; while the appropriate z-axis movement of the optical probes tends to be at a substantially fixed location with respect to the device under test, which may not be consistent with the z-axis movement provided for the electrical probes. Moreover, the relatively long optical device tends to expand and contract with temperature variations of the environment resulting in additional difficulty properly positioning the optical probe.
• In light of the foregoing realizations the present inventors determined that the traditional probe station should be modified in some manner to facilitate at least partial independent movement or otherwise separation of the optical probes and electrical probes. Referring toFIG. 7, a modifiedprobe station100 includes achuck102 that supports a device undertest104. The device undertest104 in many instances is one or more photonics devices. Anupper platen106 defines anopening108 therein and is positioned above thechuck102. Theopening108 may be, for example, completely encircled by theupper platen106 or a cutout of a portion of theupper platen106.Electrical probes110 are supported by theupper platen106. Theplaten106 is supported by a plurality of supports112a,112b,112c, and112d. Positioned below the supports112a-112dis alower platen114. Theoptical probes116 are supported by thelower platen114. A microscope, not shown, may be used to position the device undertest104 relative to theprobes110 and116. During probing theupper platen106 is moved in a z-axis direction to make contact between theelectrical probes110 and the device undertest104. The x and/or y position of the chuck102 (hence the device under test104) relative to theelectrical probes110 is modified, and thereafter theupper platen106 is moved in a z-direction to make contact between theelectrical probes110 and the device undertest104. During testing theoptical probes116 are aligned with the edge of the device undertest104.
• In the case that the device under test is moved in a direction perpendicular to the edge of the device undertest104 being tested, it may be observed that theoptical probes116 may not need to be repositioned for each device being tested. If realignment of theoptical probes116 are necessary, there is a good likelihood that minimal adjustment is necessary. In particular, there is a high likelihood that the elevation of theoptical probe116 is accurate (or nearly so) because thechuck102 is moving within a horizontal plane for testing the device undertest104. It may be observed thatoptical probes116 are effectively decoupled from the z-axis motion of theupper platen106. Moreover movement of theupper platen106 for bringing theelectrical probes110 into contact with the device undertest104 does not result in movement of theoptical probe116 with respect to the device undertest104. Similarly, it may be observed that movement of theoptical probes116 does not result in movement of theelectrical probes110.
• As illustrated inFIG. 7, it may be observed that there is substantial open space on thelower platen114 to position the optical probes116. Further, the open space permits operators to access theoptical probes116 to make adjustments, as necessary. For example, thelower platen114 may include at least 70% of its surface area free of other components and structures, such as the chuck and supports, available for the positioning of optical components thereon. More preferably, at least 80%, 85%, 90%, and 95% of the surface area of thelower platen114 is free of other components and structures. Moreover, from a region defined by the perimeter of the supports, thelower platen114 has preferably 70%, 80%, 85%, 90%, or 95% of the surface area of the upper platen free from other components and structures thereon in any outward direction, such as +x, −x, +y, or −y directions. This free space more readily permits the attachment of free space optics thereon, which frequently require substantial space and flexibility to set up. The size of theupper platen106 may have less surface area, the same surface area, or greater surface area than thelower platen114. For example, the lower platen114 (e.g., optical platen) may have a surface area that is 25%, 35%, or 50% or more greater than the upper platen106 (e.g., non-optical platen). This increased surface area of thelower platen114 relative to theupper platen106 permits more open access to thelower platen114 to locate optical components thereon without limitations resulting from the proximityupper platen106. Preferably thelower platen114 is a single integral member or otherwise a rigidly interconnected set of members. It is of course to be understood that the system may include more than two platens, as desired. In addition, the electrical components may be located on the lower platen, as desired. Also, the optical components may be located on the upper platen, as desired, which may include holes therein for an optical breadboard if desired. Furthermore, with the upper platen being maintained in position principally by gravity, such that it would become detached from the supports if the probe station were turned up side down, a set of different upper platens may be provided, each of which is designed to be particularly suitable for a particular test. For example, some upper platens may be small, large, oval, rectangular, thin, thick, etc.
• Another feature that may be included is the capability of removing or otherwise moving the upper platen out of the way for in a controlled manner. The movement of the upper platen facilitates the adjustment and installation of the optical components thereunder. For example, a mechanical support mechanism may be included that supports the upper platen while the platen is moved with respect to the remainder of the probe station, and in particular the lower platen. For example, the upper platen may be displaced such that at least 20% (or at least 30% or at least 40% or at least 50%) of its surface area is laterally displaced beyond its original position on the supports. Alternatively, the upper platen may be tilted upwardly. For example, the upper platen may be tilted such that it is at least 5 degrees (or at least 10 degrees or at least 20 degrees or at least 45 degrees or at least 75 degrees) of its surface area is tiled with respect to its position when probing, such as horizontal.
• Referring toFIG. 8, a modifiedprobe station200 includes anupper platen206 supported by a set of upper supports212a-212d. The upper supports212a-212dextend through respective openings220a-220din alower platen214 and are supported by abase222. Thelower platen214 is supported by a set of supports224a-224dwhich is supported by thebase222. The supports224a-224dand the supports212a-212dare preferably adjustable in height. Thechuck202 extends through anopening226 in thelower platen214 and is supported by thebase222. With this structure, one or moreoptical probes216 supported by thelower platen214 may be simultaneously moved in the z-axis direction with respect to a device undertest204 supported by thechuck202. Also, one or moreelectrical probes210 may be simultaneously moved in the z-axis direction with respect to a device undertest204 supported by thechuck202. Furthermore, one or moreelectrical probes210 may be simultaneously moved in the z-axis direction with respect to theoptical probes216, or vise versa, both of which may be moved relative to the device undertest204. This permits effective realignment of one or moreoptical probes216 with respect to the edge of the device undertest204. In this manner, at least a portion of the alignment of theoptical probes216 may be performed by the probe station, as opposed to the individual positioners attached to the optical probes116. It is to be understood that thelower platen214 is preferably positioned at a location below the device undertest204 while theupper platen206 is positioned above the device undertest204. Also, it is to be understood that thelower platen214 may be positioned at a location above the device undertest204 while theupper platen206 is likewise positioned above the device undertest204. Also, it is to be understood that thelower platen214 may be positioned at a location below the device undertest204 while theupper platen206 is likewise positioned below the device undertest204. Moreover, the range of movement of the supports may permit theupper platen206 and/or thelower platen214 to be moved from a position above the device undertest214 to a position below the device undertest214, or from a position below the device undertest214 to a position above the device undertest214.
• Referring toFIG. 9, a modifiedprobe station300 includes thechuck202 being supported by thelower platen214. In this manner, thechuck202 and thelower platen214 will move together in the z-axis. This is beneficial, at least in part, to assist in maintaining the relative alignment between the optical probes and the device under test.
• Referring toFIGS. 7-9, the lower platen (or the upper platen) may include a set ofopenings170 defined therein suitable for engaging an optical device. Typically theopenings170 are arranged in an orthogonal array. Theopenings170 provide a convenient mechanism for interconnection between the lower platen and the optical probes.
• The probe station facilitates the testing of a photonics device that includes an optical test path, which is optimized based upon optical characteristics. In addition, the probe station facilitates the testing of a photonics device that includes an electrical test path, which is similarly optimized based upon electrical characteristics. Typically multiple electrical probes are supported and simultaneously brought into contact with the device under test. In this manner, the probe station includes a structure that brings together optimized electrical test paths and optimized optical test paths together on the device under test.
• Referring toFIG. 10, the upper platen106 (or other platens) is supported by a plurality of supports350a-350d. Preferably theplaten106 is supported by a set of contacts352a-352d. The contacts352a-352dare preferably not fixedly interconnected with theupper platen106, but rather maintained in contact by the force of gravity free from a fixed interconnection, such as a screw or bolt. Accordingly, theupper platen106 may be removed from the supports350a-350dby merely lifting theupper platen106. A set of interconnectingmembers354,356, and358 may be included to provide increased rigidity to the supports350a-350d. In addition, the length of the interconnectingmembers354,356,358 may be adjustable, such as extending through the supports350a-350dor otherwise including a length adjustment mechanism for the interconnecting members themselves. In this manner theupper platen106 may be lifted from the supports350a-350d, the position of the supports350a-350dand relative spacing thereof modified, and theupper platen106 repositioned on the supports350a-350d. In addition, amechanical lift mechanism358 may be included to raise and lower theupper platen106. Also, the supports350a-350dmay include internal height adjustment for z-axis movement. Further, computer controlled lift control mechanisms may likewise be used. Moreover, it may be observed that theupper platen106 may be moved in the z-axis direction, and in the x and/or y direction by simply moving theupper platen106. In an alternative embodiment, the supports350a-350dmay include horizontal movement structures to move theupper platen106 in the x and/or y directions. As one example, the horizontal movement structures may be a set of rollers that permit the selective lateral movement of theupper platen106.
• Referring toFIG. 11, a substantiallyenclosed environment400 may be provided around the device under test. The environment may be electrically connected to an earth ground potential, an instrument ground potential, a guard potential, a shield potential, or otherwise remains floating. Anoptical box402 may be provided within the lower region of the probe station to provide a substantially light tight environment around the device under test, which may be useful for many applications. Theoptical box402 preferably includes a plurality of sealable openings to permit access to the optical probes. Anelectrical box404 may be provided within the upper region of the probe station to provide a substantially noise controlled environment around the electrical probes, which may be useful for many applications. Theelectrical box404 may be electrically connected to an earth ground potential, an instrument ground potential, a guard potential, a shield potential, or otherwise remains floating.
• 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.

Claims (25)

1. A method of probing a device under test comprising:

(a) supporting said device under test on a first support;

(b) supporting an electrical probe on a second support;

(c) supporting an optical probe on a third support; and

(d) moving said electrical probe relative to said device under test in a first direction relative to the surface of said device under test to sense electrical characteristics of said device under test while said optical probe remains substantially aligned with the edge of said device under test to sense optical characteristics of said device under test.

2. The method ofclaim 1 wherein said first support is a chuck.

3. The method ofclaim 2 wherein said chuck includes a substantially planar upper surface.

4. The method ofclaim 1 wherein said second support is a platen positioned above said device under test.

5. The method ofclaim 4 wherein said platen defines an opening therein though which a portion of said electrical probe extends.

6. The method ofclaim 1 wherein said first support is located between said second support and said third support.

7. The method ofclaim 1 wherein said second support and said third support remain stationary with respect to each other while said first support moves relative to said device under test while said moving.

8. The method ofclaim 1 wherein said first direction is a z-axis direction.

9. The method ofclaim 1 wherein said electrical probe may be moved independently of said optical probe.

10. A probe station for testing a device under test comprising:

(a) a first platen supporting an electrical probe;

(b) a chuck supporting said device under test;

(c) a second platen supporting an optical probe;

(d) said first platen and said second platen positioned at different elevations from one another and different elevations from said chuck;

(e) said second platen movable relative to said chuck in a perpendicular direction, said first platen movable relative to said chuck in a perpendicular direction;

(e) at least 70% of the top surface of said second platen terminating in free space when said optical probe is not supported thereon.

11. The probe station ofclaim 10 wherein said first platen and said second platen are movable in a perpendicular direction relative to one another.

12. The probe station ofclaim 10 wherein at least 80% of the top surface of said second platen terminating in free space when said optical probe is not supported thereon.

13. The probe station ofclaim 10 wherein at least 90% of the top surface of said second platen terminating in free space when said optical probe is not supported thereon.

14. The probe station ofclaim 10 wherein at least 95% of the top surface of said second platen terminating in free space when said optical probe is not supported thereon.

15. The probe station ofclaim 10 wherein said second platen has a greater top surface area than said first platen.

16. The probe station ofclaim 10 wherein said second platen has a smaller top surface area than said first platen.

17. The probe station ofclaim 10 wherein said first platen is maintained in position with respect to said second platen by gravity such that if said probe station were turned upside down said first platen would freely fall away from said second platen.

18. A probe station for testing a device under test comprising:

(a) a first platen supporting an electrical probe;

(b) a chuck supporting said device under test;

(c) said first platen is positioned at a different elevation than said device under test;

(d) a movement mechanism laterally displacing said first platen in a controlled manner such that at least 20% of the surface area of said first platen is laterally displaced to a spatial region not previously occupied by said first platen prior to said lateral displacement.

19. The probe station ofclaim 18 wherein said controlled manner is at least 30% of said surface area.

20. The probe station ofclaim 18 wherein said controlled manner is at least 40% of said surface area.

21. The probe station ofclaim 18 wherein said controlled manner is at least 50% of said surface area.

22. A probe station for testing a device under test comprising:

(a) a first platen supporting an electrical probe;

(b) a chuck supporting said device under test;

(c) said first platen is positioned at a different elevation than said device under test;

(d) a movement mechanism angularly displacing said first platen in a controlled manner such that said first platen is tilted at an angle of at least 5 degrees with respect to the angle of said first platen when probing said device under test.

23. The probe station ofclaim 22 wherein said controlled manner is at least 10 degrees.

24. The probe station ofclaim 22 wherein said controlled manner is at least 45 degrees.

25. The probe station ofclaim 22 wherein said controlled manner is at least 75 degrees.

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