Method for operating a multiple particle beam system, calibration method for a multiple particle beam system, computer program product and multiple particle beam system with increased performance

A calibration method for a multiple particle beam system operating with a plurality of first individual charged particle beams arranged in a first raster arrangement and imaged on an object at incidence locations defining a second raster arrangement, the first individual particle beams being guided over the object using a collective scan deflector in a crossover region of the first individual particle beams, with second individual particle beams emanating from the incidence locations of the object being detected in each case by a detection system comprising a particle multi-detector and with the multiple particle beam system comprising a data capture and data processing unit, the calibration method comprising:

• setting a first operating point of the multiple particle beam system with a first beam current;
• at the first operating point, recording a focus series of a reference object using the plurality of first individual particle beams and creating and storing digital images of the focus series using the detection system and the data capture and data processing unit;
• analysing the digital images and ascertaining a first best global focus location using a first algorithm;
• analysing the digital images and ascertaining a second best global focus location using a second algorithm;
• determining an offset between the first and second best global focus locations;
• and
• storing the offset in the data capture and processing unit in relation to the first beam current.

A multiple particle beam system, comprising:

• a multi-beam particle generator configured to generate a first field of a plurality of first individual charged particle beams;
• a first particle-optical unit with a first particle-optical beam path, the first particle-optical unit configured to image the first individual particle beams on a wafer surface in an object plane so that the first individual particle beams are incident on the wafer surface at incidence locations which define a second field;
• a detection system comprising a plurality of detection regions defining a third field;
• a second particle-optical unit with a second particle-optical beam path, the second particle-optical unit configured to image second individual particle beams emanating from the incidence locations in the second field on the third field of the detection regions of the detection system;
• a magnetic and/or electrostatic objective lens configured to have both the first and the second individual particle beams pass therethrough;
• a beam splitter in the first particle-optical beam path between the multi-beam particle generator and the objective lens, the beam splitter in the second particle-optical beam path between the objective lens and the detection system;
• a collective first scan deflector configured to collectively scan the first individual charged particle beams over the object, the object in a crossover region a crossover region of the first individual charged particle beams in the first particle-optical beam path;
• a sample stage configured to hold and/or position a wafer during a wafer inspection;
• an autofocus measuring element configured to create measurement data for ascertaining actual autofocus data during the wafer inspection;
• a fast autofocus correction lens;
• a controller having a data processing and storage unit;
• and
• an autofocus correction mode selection device configured to select:
• i) a first autofocus correction mode which is beam current-independent in view of an autofocus correction;
• and ii) a second autofocus correction mode which is beam current-dependent in view of the autofocus correction,
• wherein:
• the controller is configured to control particle-optical components in the first and/or in the second particle-optical beam path;
• the controller is configured for static or low-frequency adaptation of a focusing to control the objective lens and/or an actuator of the sample stage at an operating point with a beam current and a working distance so that the first individual particle beams are focused on the wafer surface situated at the working distance;
• the controller is configured for high-frequency adaptation of the focusing in the first autofocus correction mode to create an autofocus correction lens control signal based on the actual autofocus data at the operating point during the wafer inspection to control the fast autofocus correction lens during the wafer inspection at the operating point;
• the controller is configured for high-frequency adaptation of the focusing in the second autofocus correction mode to create an autofocus correction lens control signal based on the actual autofocus data and based on the beam current at the operating point during the wafer inspection to control the fast autofocus correction lens in high-frequency fashion during the wafer inspection at the operating point and/or to control the objective lens in static or low-frequency fashion during the wafer inspection at the operating point so that the first individual particle beams are focused in detuned fashion on the wafer surface situated at the working distance.