Systems and method for laser voltage imaging state mapping

Abstract

An apparatus and method for laser probing of a DUT is disclosed. The system enables laser voltage imaging state mapping of devices within the DUT. A selected area of the DUT is illuminating a while the DUT is receiving test signals causing certain of the active devices to modulate. Light reflected from the DUT is collected and is converted into an electrical signal. Phase information is extracting from the electrical signal and a two-dimensional image is generated from the phase information, wherein the two-dimensional image spatially correlates to the selected area.

What is claimed is: 
     
         1 . A system for testing an IC device under test (DUT), comprising:
 a laser source generating a laser beam;   optical elements for conditioning and scanning the optical beam onto a selected area of the DUT and for collecting reflected beam from the DUT;   a sensor for converting the reflected beam into an electrical signal;   a data acquisition module configured for extracting phase information from the electrical signal and generating a two-dimensional image from the phase information to thereby provide a phase map of the selected area of the DUT; and,   electrical components for introducing an interference signal into the data acquisition module to be mixed with the electrical signal.   
     
     
         2 . The system of  claim 1 , wherein the data acquisition module comprise a spectrum analyzer. 
     
     
         3 . The system of  claim 2 , wherein the electrical components comprise:
 an interference signal generator; and,   a combiner combining the electrical signal and the interference signal to generate a combined signal and deliver the combined signal to the spectrum analyzer.   
     
     
         4 . The system of  claim 3 , wherein the combiner comprises one of: a summing amplifier, a voltage adder, a radiating antenna, or a T-connector. 
     
     
         5 . The system of  claim 4 , further comprising apparatus for conditioning the interference signal prior to mixing, the apparatus comprising at least one of: amplifier, attenuator, and phase shifter. 
     
     
         6 . The system of  claim 5 , further comprising a collector for collecting the interference signal from one of the DUT, a tester, a test board, a DUT board, or cables. 
     
     
         7 . The system of  claim 6 , further comprising a frame grabber having one input receiving a DC component of the electrical signal and generating therefrom an image of the selected area, and having a second input receiving the phase information from the spectrum analyzer and generating therefrom a grey scale image. 
     
     
         8 . The system of  claim 7 , wherein the frame grabber is configured to assign one grey level to pixels wherein the interference signal interferes constructively with the electrical signal, assign another grey level to pixels wherein no electrical activity is sensed within the corresponding spot on the DUT, and a third grey level to pixels wherein the interference signal interferes destructively with the electrical signal. 
     
     
         9 . The system of  claim 1 , wherein the data acquisition module comprises:
 a trans-impedance amplifier receiving and amplifying the electrical signal from the sensor;   a signal separator receiving an output of the trans-impedance amplifier and separating the output into a DC component and an RF component;   an RF amplifier receiving and amplifying the RF component and providing an amplified RF component;   a spectrum analyzer receiving the amplified RF component and extracting therefrom the phase information.   
     
     
         10 . The system of  claim 9 , further comprising a frame grabber having one channel receiving the DC component and a second channel receiving the phase information. 
     
     
         11 . The system of  claim 10 , further comprising a video amplifier interposed between the spectrum analyzer and the frame grabber. 
     
     
         12 . The system of  claim 10 , wherein the electrical components comprise a phase shifter and an amplifier or an attenuator. 
     
     
         13 . The system of  claim 12 , wherein the electrical components further comprises a combiner combining the electrical signal and the interference signal. 
     
     
         14 . The system of  claim 13 , wherein the combiner comprises one of a summing amplifier and a voltage adder. 
     
     
         15 . The system of  claim 12 , wherein the combiner is interposed between the signal separator and the RF amplifier. 
     
     
         16 . The system of  claim 12 , wherein the combiner is interposed between the RF amplifier and the spectrum analyzer. 
     
     
         17 . The system of  claim 12 , wherein the combiner comprises an antenna configured to radiate the interference signal into a path of the electrical signal. 
     
     
         18 . The system of  claim 9 , wherein the electrical components comprise:
 an interference signal a collector configured for collecting the interference signal from one of the DUT, a tester, a test board, a DUT board, or cables; and,   a combiner combining the electrical signal and the interference signal to generate a combined signal and deliver the combined signal to the spectrum analyzer.   
     
     
         19 . The system of  claim 18 , wherein the combiner comprises an antenna configured to radiate the interference signal into a path of the electrical signal. 
     
     
         20 . The system of  claim 18 , wherein the combiner comprises one of a summing amplifier and a voltage adder.