|Publication number||US4928058 A|
|Application number||US 07/355,514|
|Publication date||May 22, 1990|
|Filing date||May 23, 1989|
|Priority date||May 23, 1989|
|Also published as||DE4001737A1|
|Publication number||07355514, 355514, US 4928058 A, US 4928058A, US-A-4928058, US4928058 A, US4928058A|
|Original Assignee||The University Of Rochester|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (6), Referenced by (74), Classifications (9), Legal Events (6)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present invention relates to electro-optic signal measurement and particularly to probes for making noncontact electro-optical measurements of electrical signals on conductors (by which term is also meant electrodes, lines and other elements) which carry such signals.
The invention is especially suitable for the measurement of electrical signals from submicron devices and structures such as integrated circuits wherein the probe is located in the fringe field from the conductors on the circuits and signal measurements of picosecond or even subpicosecond resolution are desired.
Electro-optic measurements of electro-signals have been made using electro-optic (E-O) elements, such as crystals, the index of refraction of which changes in accordance with the strength of the electrical field being measured. A sampling laser beam of short, picosecond range, pulses is focused on the crystal in the region of the fringing electric (E) field. By electro-optic sampling, the signal can be extracted and displayed with picosecond and even subpicosecond resolution. The spatial resolution is determined by the size of the beam cross section (laser spot) in the electro-optic element. Reference may be had to the following patents as well as to the articles referenced therein for further information with respect to the aforementioned electro-optic measurement approach: Mourou and Valdmanis, U.S. Pat. No. 4,446,426, May, 1984; Mourou and Valdmanis, U.S. Pat. No. 4,618,819, October, 1986 and Mourou and Mayer, U.S. Pat. No. 4,603,293, July, 1986. Another patent issued in July 1987 as U.S. Pat. No. 4,618,449 also describes the techniques and systems of the aforementioned Mourou et al. patents. Improved electro-optic probes for electro-optic sampling are also described in U.S. patent application Ser. No. 218,178 filed July 13, 1988 in the name of Steven L. Williamson, the inventor hereof.
Electro-optic probes, particularly the electro-optic crystals thereof, are very small and very fragile. They are therefore subject to damage. Also in order for performing high spatial resolution signal measurements they must be precisely positioned adjacent the conductor of the device under test so that the region of the crystal which the optical sampling beam traverses is in the fringe field of the electrical signal on the conductor of interest.
Another problem in semiconductor electro-optic probes is that photo conductivity is induced in the electro-optic material of the probe due to the sampling beam thereby causing charge carriers to flow which screen the fringe fields from the material thereby appreciably reducing the modulation of the optical signal in response to the electric field being probed.
It is the principal object of the present invention to provide an improved electro-optic probe having an electro-optic element that is mounted so as to provide a rigid support capable of being precisely positioned and which is protected from physical damage when it contacts the device on the test or even other objects, such as when dropped on a hard surface.
It is another object of the present invention to provide an approved electro-optic probe which enables the position of the probe with respect to a conductor of the device under test to be determined by monitoring the amplitude of the optical beam which traverses the probe.
It is a further object of the present invention to provide an improved electro-optic probe in which the adverse affects of photo-conductivity and charge carriers produced by the sampling optical beam is reduced.
Briefly described, an electro-optic probe in accordance with the invention has an electric-optic element (e.g., a crystal) which is supported by a flexural cantilever at the free end thereof. The cantilever is provided a strip of flexural material, such a metal foil of three to five microns thickness, which is tension loaded so as to provide a rigid support. Contact with the element, causes the cantilever to deflect and thereby absorb impacts and other mechanical forces which could damage the electro-optic material (the crystal). Also the optical sampling beam is focused on the probe in the undeflected position, for example with a high power objective lens with a shallow depth of field. The beam traverses the crystal and may be reflected therefrom and relayed on a photo detector. Since the beam is defocused when the probe position is changed, the illumination of the photo detector and the signal therefrom indicates when the probe has contacted the device under test. The exact moment the probe contacts the device is indicated by the change of signal from the photo detector. The device under test can then be withdrawn slightly and the increase in signal amplitude indicates that the probe lifted off the device under test, thereby enabling the probe to be precisely located with high spatial resolution.
An electro-optic, electrical field probe in accordance with the invention also utilizes a body of electro-optic material. This may be a material which changes polarization of light passing through in accordance with the Pockels effect and is a semiconductor. The material has ions of an element with a lower atomic number (Z), than the atomic number of the elements constituting the electro-optic material implanted therein in sufficient quantity to reduce the conductivity thereof. Then charge carriers are not created during a sampling optical pulse period in sufficient amount to shield the electric field being probed. A sufficient amount of ion implantation may be such that reduces the dielectric relaxation time of the electro-optic material by several orders of magnitude less than the duration of each sampling pulse.
The foregoing and other objects, features and advantages of the invention as well as presently preferred embodiments thereof and the best modes now known for practicing the invention will become apparent from a reading of the following description in connection with the accompanying drawings wherein
FIG. 1 is a plan view showing a portion of an electro-optic probe having a cantilever support in accordance with the invention;
FIG. 2 is a sectional view along the line 2--2 shown in FIG. 1, and in addition showing, schematically, optics for detecting the position of the probe;
FIG. 3 is an enlarged diagrammatic view illustrating the electro-optic crystal used in the probe shown in FIGS. 1 and 2; and
FIG. 4 is a diagrammatic view showing the probe and electro-optic sampling beam in position for measuring the electric signal on a conductor of a device under test (DUT).
Referring to the drawings and, especially to FIGS. 1 and 2, there is shown a microscope slide or cover slip 10 which is made of glass and has an upper surface 12 and an edge 14. A strip 16 of flexural material is disposed on the surface 12. The thickness of the strip is exaggerated in the drawing. In practice it is a few microns (e.g. from 3 to 5 microns) thick and is made from a foil of metal, suitably aluminum. The foil strip is tension loaded by deflecting a rear end 18 thereof above the surface 12 and while deflected holding it in the deflected position by a drop 20 of the epoxy cement. The strip therefore is a tension loaded leaf spring.
The strip 16 may be 3 to 5 millimeters long and extends to a free end 22, which is the end of the cantilever. The end 22 may be approximately 1 millimeter from the edge 14. The strip may be tapered in the forward region 24 thereof as shown in FIG. 1.
Attached to the cantilever end is the electro-optic element 24. The attachment of the element 24 is by way of a drop 26 of conductive material which may be silver paint which is of the type used to make contacts to electrodes. This material is known commercially by the name "Silverprint."
The optical sampling beam is focused by an objective lens 28 so that it has a tight focus on the electro-optic element 24, when the cantilever is in its undeflected state as shown in FIGS. 2 and 4. The beam is then reflected from a reflective metalic layer 30 (see FIG. 3) and through a partially transmitting mirror 32, and is tightly focused on the aperture of a photo detector 34. The photo detector may be a PIN diode with suitable amplification circuits. This diode may be independent of the system which detects the optical pulses which are modulated by fringe fields due to the signal from a conductor of the device under test (DUT). That system may be of the type shown in the above referenced Mourou et al. patents. The photo detector circuit includes filters or integrators so that the optical sampling signal which is in the form of pulses is smoothed. The signal amplitude depends on the illumination of the photo detector. When the electro-optic element 24 moves the focus is blurred, and less light reaches the photo detector. The output of the photo detector as seen on an indicator 25, such as a meter, indicates that it is in the undeflected position.
When it is desired to sample a fringe field, such as the E-field from a conductor 34 of a DUT, as shown in FIG. 4, the position of the probe may be accurately determined. For example, the DUT may be mounted on an X-Y-Z stage which moves in an upward direction, a direction left and right and a direction in and out of the paper as shown by the arrows labeled x, y and z. The stage is moved until deflection of the cantilever occurs. Then the beam, as received by the photo detector, becomes out of focus and the signal as measured on the indicator 35 reduces in amplitude. By backing the stage away slightly, the cantilever "lifts off" from the surface. The movement may be, for example, even less than a micrometer. Then the beam comes back into focus on the photo detector and the signal amplitude increases. Then the probe is just out of contact with the DUT and in the fringe field.
In addition, if the probe impacts a surface, for example if it is dropped on a hard surface, the leaf spring absorbs the shock to the probe instead of breaking, thereby reducing the possibility of physical damage thereto.
In fabricating the probe, an element in the form of a single crystal of electro-optic material, such as gallium arsenide (GaAs), is fabricated which may be approximately 1 millimeter long a few tenths of a millimeter wide and 1 micron in thickness. The element may be made starting with a substrate for example of undoped or semi-insulating GaAs. Then a stop layer, much less than a micron in thickness, of AlGaAs may be epitaxially grown. The GaAs probe layer is then grown to a thickness of one micron (micrometer) to provide the single crystal of electro-optic GaAs (Pockel effect responsive) material.
This GaAs layer is desirably ion implanted with high energy ions of low atomic number than the atomic number of the electro-optic material (in this case GaAs). Suitably high energy (100 to 500 Kev) ions of oxygen or hydrogen from an ion implanter may be used. This provides a few microns of penetration depth resulting in the creation of homogeneously distributed deep lying charge traps through the 1 micron thick probe crystal. The implantation is continued until sufficient traps are created to reduce the photo conductivity of the electro-optic material. Suitably the density of these traps is 1016 to 1018 per cubic centimeter.
Since there are 1023 atoms per cubic centimeter in the GaAs crystal, the damaged sites account for less than 1 part in 105 at most. However, the sites are sufficient in number to reduce the conductivity of the probe say from approximately 105 ohm-centimeter (cm) to greater than 1016 ohm-cm. As a result, the dielectric relaxation time is increased by several orders of magnitude (where the field resulting from photo conductivity reduces to approximately 80% to field in the absence of light and photo conductivity by the reciprocal of the base of Napierian logarithms (1/e)). In other words, the migration of charge carriers of any significance is prevented during the optical sampling pulse, which may be of the order of picoseconds in duration. Therefore, the possibility of neutralizing the electric field within the probe material is essentially eliminated. When the optical-pulse terminates the charge carriers recombine (electrons with holes). Accordingly, the photo conductivity of the electro-optic element 24 does not interfere with electro-optic sampling and the measurement of the signal on the conductor 34 of the DUT.
Returning to the fabrication of the element 24, after the ion implanted GaAs single crystal has been fabricated, the substrate is ground away so that only a small layer thereof remains on the stop layer. Then the remaining GaAs substrate is chemically etched. The etching stops when the etchant reaches the stop layer. A layer of metallic reflective material such as aluminum is then coated, as by sputtering, on the lower side of the crystal. Finally, an anti-reflection (AR) coating such as magnesium fluoride is sputtered on the upper surface of the crystal.
The crystal may now be diced and a segment approximately 1 millimeter long by a few tenths millimeter wide is selected. This segment is, of course, approximately 1 micron thick. In order to adhere and attach the segment to the end of the cantilever, the end is coated with tacky material as by spraying the lower surface with rubber cement. The appropriate size sliver is then attached. The silver print dot 26 is applied and holds the sliver in place. A conductive connection is made from the reflective conductive coating of the element 24 through the silver dot 26 to the conductive strip 16. The strip is connected to ground (or another reference potential). Accordingly, the conductive reflective layer on the underside of the element provides a shield against unwanted fields, safe from a conductor 37 on the DUT (see FIG. 4).
From the foregoing description it will be apparent that there has been provided improved electro-optic signal measurement apparatus and particularly improved electro-optic probes especially suitable for use in a electro-optic sampling signal measurement system. Variations and modifications of the herein described systems and probes, within the scope of the invention, will undoubtedly suggest themselves to those skilled in the art. Accordingly the foregoing description should be taken as a illustrative and not in a limiting sense.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US4446426 *||Nov 4, 1981||May 1, 1984||Westinghouse Electric Corp.||On-line RF arc monitor for large rotating generators|
|US4603293 *||Mar 27, 1984||Jul 29, 1986||University Of Rochester||Measurement of electrical signals with subpicosecond resolution|
|US4618449 *||Apr 19, 1984||Oct 21, 1986||Enichem Polimeri, S.P.A.||Method for the termination of living polymers, and compounds suitable for the purpose|
|US4618819 *||Mar 27, 1984||Oct 21, 1986||The University Of Rochester||Measurement of electrical signals with subpicosecond resolution|
|US4790635 *||Apr 24, 1987||Dec 13, 1988||The Secretary Of State For Defence In Her Brittanic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland||Electro-optical device|
|US4836633 *||Mar 24, 1986||Jun 6, 1989||Plessey Overseas Limited||Optical connecting arrangements|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US5041783 *||Feb 5, 1990||Aug 20, 1991||Olympus Optical Co., Ltd.||Probe unit for an atomic probe microscope|
|US5208531 *||Aug 13, 1990||May 4, 1993||Texas Instruments Incorporated||Apparatus and method for testing integrated circuits|
|US5434698 *||Jul 20, 1993||Jul 18, 1995||Dai Nippon Printing Co., Ltd.||Potential sensor employing electrooptic crystal and potential measuring method|
|US5550370 *||Mar 15, 1995||Aug 27, 1996||Dai Nippon Printing Co., Ltd.||Potential sensor employing electrooptic crystal and potential measuring method|
|US5592101 *||Jul 22, 1993||Jan 7, 1997||Hamamatsu Photonics K.K.||Electro-optic apparatus for measuring an electric field of a sample|
|US5952818 *||Oct 25, 1996||Sep 14, 1999||Rensselaer Polytechnic Institute||Electro-optical sensing apparatus and method for characterizing free-space electromagnetic radiation|
|US6111416 *||Aug 29, 1997||Aug 29, 2000||Rensselaer Polytechnic Institute||Electro-optical and magneto-optical sensing apparatus and method for characterizing free-space electromagnetic radiation|
|US6388454 *||Nov 30, 1999||May 14, 2002||Ando Electric Co., Ltd.||Electro-optic sampling prober|
|US6400165 *||Feb 2, 2000||Jun 4, 2002||Lucent Technologies Inc.||Ultra-fast probe|
|US6414473||Jul 14, 2000||Jul 2, 2002||Rensselaer Polytechnic Institute||Electro-optic/magneto-optic measurement of electromagnetic radiation using chirped optical pulse|
|US6573700||Jun 6, 2002||Jun 3, 2003||Rensselaer Polytechnic Institute||Method of characterizing free-space radiation using a chirped optical pulse|
|US6587258 *||Mar 23, 2001||Jul 1, 2003||Southwest Sciences Incorporated||Electro-optic electric field probe|
|US6677769||Jun 8, 2001||Jan 13, 2004||The Regents Of The University Of Michigan||Scanning electromagnetic-field imager with optical-fiber-based electro-optic field-mapping system|
|US6906506||Mar 6, 2002||Jun 14, 2005||The Regents Of The University Of Michigan||Method and apparatus for simultaneous measurement of electric field and temperature using an electrooptic semiconductor probe|
|US7138295||Dec 18, 2003||Nov 21, 2006||Elm Technology Corporation||Method of information processing using three dimensional integrated circuits|
|US7176545||Jan 27, 2004||Feb 13, 2007||Elm Technology Corporation||Apparatus and methods for maskless pattern generation|
|US7193239||Jul 3, 2003||Mar 20, 2007||Elm Technology Corporation||Three dimensional structure integrated circuit|
|US7223696||Jan 27, 2004||May 29, 2007||Elm Technology Corporation||Methods for maskless lithography|
|US7242012||Mar 7, 2003||Jul 10, 2007||Elm Technology Corporation||Lithography device for semiconductor circuit pattern generator|
|US7307020||Dec 18, 2003||Dec 11, 2007||Elm Technology Corporation||Membrane 3D IC fabrication|
|US7385835||Dec 18, 2003||Jun 10, 2008||Elm Technology Corporation||Membrane 3D IC fabrication|
|US7474004||Dec 18, 2003||Jan 6, 2009||Elm Technology Corporation||Three dimensional structure memory|
|US7479694||Dec 19, 2003||Jan 20, 2009||Elm Technology Corporation||Membrane 3D IC fabrication|
|US7485571||Sep 19, 2003||Feb 3, 2009||Elm Technology Corporation||Method of making an integrated circuit|
|US7504732||Aug 19, 2002||Mar 17, 2009||Elm Technology Corporation||Three dimensional structure memory|
|US7550805||Jun 11, 2003||Jun 23, 2009||Elm Technology Corporation||Stress-controlled dielectric integrated circuit|
|US7615837||Nov 10, 2009||Taiwan Semiconductor Manufacturing Company||Lithography device for semiconductor circuit pattern generation|
|US7670893||Nov 3, 2003||Mar 2, 2010||Taiwan Semiconductor Manufacturing Co., Ltd.||Membrane IC fabrication|
|US7705466||Sep 26, 2003||Apr 27, 2010||Elm Technology Corporation||Three dimensional multi layer memory and control logic integrated circuit structure|
|US7763948||Jul 27, 2010||Taiwan Semiconductor Manufacturing Co., Ltd.||Flexible and elastic dielectric integrated circuit|
|US7820469||Jun 11, 2003||Oct 26, 2010||Taiwan Semiconductor Manufacturing Co., Ltd.||Stress-controlled dielectric integrated circuit|
|US7911012||Mar 22, 2011||Taiwan Semiconductor Manufacturing Co., Ltd.||Flexible and elastic dielectric integrated circuit|
|US8035233||Oct 11, 2011||Elm Technology Corporation||Adjacent substantially flexible substrates having integrated circuits that are bonded together by non-polymeric layer|
|US8080442||Jun 21, 2008||Dec 20, 2011||Elm Technology Corporation||Vertical system integration|
|US8269327||Jun 21, 2008||Sep 18, 2012||Glenn J Leedy||Vertical system integration|
|US8288206||Jul 4, 2009||Oct 16, 2012||Elm Technology Corp||Three dimensional structure memory|
|US8318538||Mar 17, 2009||Nov 27, 2012||Elm Technology Corp.||Three dimensional structure memory|
|US8410617||Apr 2, 2013||Elm Technology||Three dimensional structure memory|
|US8587102||May 9, 2008||Nov 19, 2013||Glenn J Leedy||Vertical system integration|
|US8629542||Mar 17, 2009||Jan 14, 2014||Glenn J. Leedy||Three dimensional structure memory|
|US8791581||Oct 23, 2013||Jul 29, 2014||Glenn J Leedy||Three dimensional structure memory|
|US8796862||Aug 9, 2013||Aug 5, 2014||Glenn J Leedy||Three dimensional memory structure|
|US8824159||Mar 31, 2009||Sep 2, 2014||Glenn J. Leedy||Three dimensional structure memory|
|US8841778||Aug 9, 2013||Sep 23, 2014||Glenn J Leedy||Three dimensional memory structure|
|US8907499||Jan 4, 2013||Dec 9, 2014||Glenn J Leedy||Three dimensional structure memory|
|US8928119||Mar 17, 2009||Jan 6, 2015||Glenn J. Leedy||Three dimensional structure memory|
|US8933570||Mar 17, 2009||Jan 13, 2015||Elm Technology Corp.||Three dimensional structure memory|
|US9087556||Aug 12, 2014||Jul 21, 2015||Glenn J Leedy||Three dimension structure memory|
|US20020132465 *||May 13, 2002||Sep 19, 2002||Elm Technology Corporation||Reconfigurable integrated circuit memory|
|US20030057564 *||Aug 19, 2002||Mar 27, 2003||Elm Technology Corporation||Three dimensional structure memory|
|US20030173608 *||Mar 3, 2003||Sep 18, 2003||Elm Technology Corporation||Three dimensional structure integrated circuit|
|US20030218182 *||Jun 11, 2003||Nov 27, 2003||Leedy Glenn J.||Strees-controlled dielectric integrated circuit|
|US20030223535 *||Mar 7, 2003||Dec 4, 2003||Leedy Glenn Joseph||Lithography device for semiconductor circuit pattern generator|
|US20040070063 *||Sep 26, 2003||Apr 15, 2004||Elm Technology Corporation||Three dimensional structure integrated circuit|
|US20040097008 *||Jul 3, 2003||May 20, 2004||Elm Technology Corporation||Three dimensional structure integrated circuit|
|US20040132231 *||Dec 18, 2003||Jul 8, 2004||Elm Technology Corporation.||Lithography device for semiconductor circuit pattern generator|
|US20040132303 *||Dec 18, 2003||Jul 8, 2004||Elm Technology Corporation||Membrane 3D IC fabrication|
|US20040150068 *||Dec 19, 2003||Aug 5, 2004||Elm Technology Corporation||Membrane 3D IC fabrication|
|US20040151043 *||Dec 18, 2003||Aug 5, 2004||Elm Technology Corporation||Three dimensional structure memory|
|US20040192045 *||Jan 27, 2004||Sep 30, 2004||Elm Technology Corporation.||Apparatus and methods for maskless pattern generation|
|US20040197951 *||Nov 3, 2003||Oct 7, 2004||Leedy Glenn Joseph||Membrane IC fabrication|
|US20050051841 *||Jun 11, 2003||Mar 10, 2005||Leedy Glenn Joseph||Stress-controlled dielectric integrated circuit|
|US20050082626 *||Dec 18, 2003||Apr 21, 2005||Elm Technology Corporation||Membrane 3D IC fabrication|
|US20050082641 *||Oct 22, 2004||Apr 21, 2005||Elm Technology Corporation||Flexible and elastic dielectric integrated circuit|
|US20050130351 *||Jan 27, 2004||Jun 16, 2005||Elm Technology Corporation||Methods for maskless lithography|
|US20050156265 *||Jan 24, 2005||Jul 21, 2005||Elm Technology Corporation||Lithography device for semiconductor circuit pattern generation|
|US20050176174 *||Sep 19, 2003||Aug 11, 2005||Elm Technology Corporation||Methodof making an integrated circuit|
|US20080254572 *||Jun 21, 2008||Oct 16, 2008||Elm Technology Corporation||Vertical system integration|
|US20080302559 *||Jan 18, 2008||Dec 11, 2008||Elm Technology Corporation||Flexible and elastic dielectric integrated circuit|
|US20090219744 *||Mar 17, 2009||Sep 3, 2009||Leedy Glenn J||Three dimensional structure memory|
|US20100173453 *||Jul 8, 2010||Leedy Glenn J||Three dimensional structure memory|
|EP0589593A2 *||Sep 9, 1993||Mar 30, 1994||AT&T Corp.||Electro-optic sampling|
|WO2001094955A2 *||Jun 8, 2001||Dec 13, 2001||The Regents Of The University Of Michigan||Scanning electro-optic near field device and method of scanning|
|WO2001094955A3 *||Jun 8, 2001||Apr 18, 2002||Linda P B Katehi||Scanning electro-optic near field device and method of scanning|
|U.S. Classification||324/96, 359/257|
|International Classification||G01R1/07, G01R15/24, G01R31/302|
|Cooperative Classification||G01R1/071, G01R15/24|
|European Classification||G01R15/24, G01R1/07E|
|May 23, 1989||AS||Assignment|
Owner name: UNIVERSITY OF ROCHESTER, THE, A NOT-FOR-PROFIT COR
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:WILLIAMSON, STEVEN;REEL/FRAME:005085/0285
Effective date: 19890522
|May 24, 1993||FPAY||Fee payment|
Year of fee payment: 4
|Jun 10, 1997||FPAY||Fee payment|
Year of fee payment: 8
|Dec 11, 2001||REMI||Maintenance fee reminder mailed|
|May 22, 2002||LAPS||Lapse for failure to pay maintenance fees|
|Jul 16, 2002||FP||Expired due to failure to pay maintenance fee|
Effective date: 20020522