# US 6,853,941 B2 · Open-loop for waveform acquisition > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 6,853,941 B2 - Document ID: US6853941B2 - Status: Granted - Kind: B2 - Application number: 10/136,710 - Filed: 2002-04-30 - Published: 2003-01-23 - Granted: 2005-02-08 - Earliest claimed: 2002-04-30 - Assignees: NPTest, LLC - Inventors: Hui Wang; Kenichi Kanai; Hiroyasu Koike - Web page: https://patentgrep.com/patent/US6853941B2 ## CPC - G01R 31/305: using electron beams {(investigating or analysing materials by measuring photoelectric effect G01N23/227)} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract Methods and apparatus, including computer program products, implementing and using techniques for open-loop waveform acquisition. In general, in one aspect, the invention provides a method for open-loop waveform acquisition. The method includes acquiring an S-curve of an acquisition loop of an electron-beam probe system. The S-curve represents a response of the acquisition loop to changes of potential differences between the acquisition loop and a device under test. The method includes calibrating the acquisition loop to obtain a linear region in the acquired S-curve and using the linear portion of the acquired S-curve to calculate voltage at a probe point of the device under test. ## Claims ### Claim 1 A method for open-loop waveform acquisition, 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 the acquisition loop and a probe point; and using the acquired S-curve to calibrate the acquisition loop so that a change in voltage at an output of the acquisition loop is directly proportional in a 1-to-1 ratio to a change in a voltage at the probe point. ### Claim 2 (depends on 1) The method of claim 1, wherein acquiring the S-curve includes: varying a voltage difference between the acquisition loop and the probe point; and measuring an output of the acquisition loop. ### Claim 3 (depends on 2) The method of claim 2, wherein varying the voltage difference between the acquisition loop and the probe point includes: varying a voltage at the probe point of while keeping constant a voltage of a filter mesh that is part of the acquisition loop. ### Claim 4 (depends on 2) The method of claim 2, wherein varying the voltage difference between the acquisition loop and the probe point includes: varying a voltage of a filter mesh while keeping constant a voltage of the probe point, the filter mesh being part of the acquisition loop. ### Claim 5 (depends on 1) The method of claim 1, wherein calibrating the acquisition loop includes: adjusting a filter mesh voltage to a linear portion of the acquired S-curve, the filter mesh being part of the acquisition loop; and adjusting a gain of the acquisition loop so that a change in voltage at an output of the acquisition loop is directly proportional in a 1to-1 ratio to a change in a voltage at the probe point. ### Claim 6 (depends on 1) The method of claim 1, wherein calibrating the acquisition loop includes: performing a linear regression to determine a slope and offset of the acquired S-curve such that a change in a voltage at the probe point is directly proportional in a 1 to 1 ratio to a change in voltage at an output of the acquisition loop. ### Claim 7 (depends on 1) The method of claim 1, further comprising performing a voltage measurement at a location of interest on a device under test including probing the probe point to the location of interest, wherein a measured voltage swing of the output of the acquisition loop reflects in a 1-to-1 ratio a measured voltage swing of the voltage at the location of interest due to the calibrated acquisition loop. ### Claim 8 (depends on 7) The method of claim 7, wherein the steps of calibrating and performing a voltage measurement at a location of interest on a device under test are combined. ### Claim 9 (depends on 1) The method of claim 1, further comprising: re-calibrating the acquisition loop to reduce errors. ### Claim 10 (depends on 1) The method of claim 1, wherein using the acquired S-curve to calibrate the acquisition loop includes: adjusting a voltage of a filter mesh to a linear region in the acquired S-curve, the filter mesh being part of the acquisition loop; and adjusting a gain of the acquisition loop so that a change in a voltage at the probe point of is directly proportional in a 1-to-1 ratio to a change in voltage at the output of the acquisition loop. ### Claim 11 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. ### Claim 12 (depends on 11) The system of claim 11, wherein the voltage source comprises a digital-to-analog converter connected to receive the acquired S-curve data from the computing device for supplying the filter voltage. ### Claim 13 (depends on 12) The system of claim 12, wherein the computing device further selects a working point (VW) so that the working point is within the linear portion of the S-curve data, and drives the filter mesh to the working point. ### Claim 14 (depends on 11) The system of claim 11, wherein the integrator comprises a capacitor, and a controllable switch for discharging the capacitor to reset the integrator voltage. ### Claim 15 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. ### Claim 16 (depends on 15) The system of claim 15, wherein the computing device further selects a working point (VW) so that the working point is within the linear portion of the S-curve, and drives the filter mesh to the working point. ### Claim 17 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. ### Claim 18 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). ### Claim 19 (depends on 18) The method of claim 18, wherein calibrating the acquisition loop further includes adjusting a gain of the acquisition loop 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.