Open-loop for waveform acquisition

A charged-particle-beam probe system for measuring voltage at a location of interest on a device under test, the system comprising:

• a voltage source to supply a filter voltage, the filter voltage having been pre-calibrated to a linear region in acquired S-curve data of a device under test so that a change in a voltage at a probe point of the charged-particle-beam probe system is directly proportional in a 1-to-1 ratio to a change in voltage at an output of an integrator;
• a filter mesh charged by the filter voltage, and situated between a device under test and a detector;
• a beam source to apply to the location of interest a charged-particle-beam pulse at a selected delay ti;
• a detector to detect secondary charged-particles passing through the filter mesh producing a detector current (ISEC);
• a current-combining circuit to combine the detector current with a reference current to produce an error signal (VERROR);
• and
• the integrator to integrate the error signal over a time period to produce an integrator voltage (VINT), wherein the integrator voltage (VINT) is representative of the voltage at the location of interest due to the filter mesh being charged at the pre-calibrated filter voltage.

An electron-beam probe system, comprising:

• a beam source to direct electrons at a probe point on a device under test;
• a filter mesh having been pre-calibrated to a voltage within a linear region in acquired S-curve data of a device under test so that a change in a voltage at a probe point of the electron-beam probe system is directly proportional in a 1-to-1 ratio to a change in voltage at an output of an integrator;
• a detector to detect a number of electrons that have sufficient energy to overcome a voltage difference between a voltage at the filter mesh and the probe point, the detector producing an output that is proportional to the number of electrons that the detector detects;
• a subtractor to receive the output of the detector and a reference input, the subtractor to produce an output that is proportional to the difference between the output of the detector and the reference input;
• the integrator to receive the output of the subtractor and produce an output that is linearly proportional to the voltage difference, wherein a measured voltage swing of the output of the integrator reflects a measured voltage swing of the voltage at the probe point due to the filter mesh having been pre-calibrated.

A computer program product, tangibly stored on machine-readable medium, for driving a voltage of a filter mesh of an electron-beam probe system, the product including instructions to cause a processor to:

• receive an output of an open acquisition loop of a an electron-beam probe system;
• retrieve S-curve data that describes changes in output of the acquisition loop in response to changes of a voltage difference between a filter mesh and a probe point on a device under test, the filter mesh being part of the acquisition loop;
• and
• drive the voltage of the filter mesh to a fixed working point (VW) within a linear region of the S-curve data so that a change in a voltage at a probe point of the electron-beam system is directly proportional in a 1-to-1 ratio to a change in voltage at an output of the acquisition loop.

A method for open-loop waveform acquisition using an electron-beam probe system, the method comprising:

• acquiring an S-curve of an acquisition loop of an electron-beam probe system, the S-curve representing a response of the acquisition loop to changes of potential differences between a filter mesh and a device under test, the filter mesh being part of the acquisition loop;
• calibrating the acquisition loop including adjusting a voltage of the filter mesh to a fixed working point (VW) within a linear region in the acquired S-curve;
• and
• performing a voltage measurement at a location of interest on a device under test including probing a probe point of the electron-beam probe system to the location of interest;
• and
• determining a voltage swing at the location of interest while maintaining the voltage of the filter mesh at the fixed working point (VW).