Electro-optic sampling prober

• US 6,388,454 B1
• Filed: 11/30/1999
• Issued: 05/14/2002
• Est. Priority Date: 11/30/1998
• Status: Expired due to Fees

• Current Assignee: Nippon Telegraph and Telephone Corporation, Ando Electric Co., Ltd. (Yokogawa Electric Corporation)
• Original Assignee: Nippon Telegraph and Telephone Corporation, Ando Electric Co., Ltd. (Yokogawa Electric Corporation)
• Inventors: Shinagawa, Mitsuru, Ohta, Katsushi, Nagatsuma, Tadao, Akikuni, Fumio, Yamada, Junzo
• Primary Examiner(s): Sherry, Michael J.
• Assistant Examiner(s): Nguyen, Jimmy
• Application Number:
  US09/452,297
• Time in Patent Office: 896 Days
• Field of Search: 324/158.1, 324/751, 324/752, 324/753, 324/96, 356/382, 422/82.08, 250/310, 250/311
• US Class Current: 324/754.06
• CPC Class Codes: G01R 13/347 using electro-optic elements

Abstract

An electro-optic sampling prober is used to measure a waveform of a measured signal applied to wiring of an IC wafer. Herein, a laser radiates laser beams, which are supplied to an optical module containing an optical isolator and photodiodes by way of an optical fiber. Then, the laser beams pass through an optical wavelength filter to propagate through a prober unit. The laser beams are incident on an electro-optical element, which is changed in polarization state in response to an electric field being caused by the measured signal. The laser beams are reflected by a surface mirror of the electro-optical element, so that reflected beams propagate back through the prober unit and are returned to the optical module by way of the optical wavelength filter. During the measurement, a human operator watches an image of a selected portion of the IC wafer presently placed beneath the prober unit to adjust a positional relationship between the prober unit and IC wafer. The image is produced by an infrared camera equipped with a halogen lamp and a monitor. Incidentally, the optical wavelength filter has an optical characteristic such that a center wavelength in transmission of light coincides with a wavelength of the laser beams whose intensities are maximal, so it is possible to prevent components of light, which are not required for measurement, from being unnecessarily returned to the optical module, and it is possible to improve a S/N ratio in measurement.

Claims

1. An electro-optic sampling prober comprising:

a laser for radiating laser beams based on a control signal;

an electro-optical element which is placed in contact with wiring of an IC wafer which is a measured subject, wherein an electric field caused by a measured signal applied to the wiring of the IC wafer is applied to the electro-optical element to be changed in optical characteristic;

an optical module which is configured using polarization beam splitters, wavelength plates and photodiodes, wherein the optical module isolates reflected beams, which are produced by reflection of the laser beams transmitting through the electro-optical element by a surface of the electro-optical element placed opposite to the wiring of the IC wafer, so that the optical module converts the reflected beams to electric signals;

a lamp for illuminating the IC wafer with illumination light;

a prober unit for enclosing an optical path along which the laser beams propagate and an optical path along which the illumination light propagate;

an infrared camera for producing an image of the IC wafer which is illuminated by the lamp;

a dichroic mirror for separating the laser beams from the illumination light;

an optical wavelength filter which is arranged on an optical path connected between the dichroic mirror and the photodiode; and

wherein the optical wavelength filter is attached to installation/removal members, by which the optical module is fixed to the prober unit.