Multiple particle beam microscope and associated method with fast autofocus around an adjustable working distance

Patent metadata

Field	Value
Publication number	US-12494343-B2
Application number	US-202318185324-A
Country	US
Kind code	B2
Filing date	Mar 16, 2023
Priority date	Sep 30, 2020
Publication date	Dec 9, 2025
Grant date	Dec 9, 2025

Abstract

A multiple particle beam microscope and an associated method can provide a fast autofocus around an adjustable working distance. A system can have one or more fast autofocus correction lenses for adapting, in high-frequency fashion, the focusing, the position, the landing angle and the rotation of individual particle beams upon incidence on a wafer surface during the wafer inspection. Fast autofocusing in the secondary path of the particle beam system can be implemented in analogous fashion. An additional increase in precision can be attained via fast aberration correction mechanism in the form of deflectors and/or stigmators.

First claim

What is claimed is:

1 . A multiple particle beam system, comprising:
a multi-beam particle generator configured to generate a first field of a multiplicity of charged first individual particle beams; a first particle optical unit having a first particle optical beam path, the first particle optical unit configured to image the first individual particle beams onto a wafer surface in an object plane of the multiple particle beam system so that the first individual particle beams strike the wafer surface at incidence locations which define a second field; a detection system comprising a multiplicity of detection regions defining a third field; a second particle optical unit having a second particle optical beam path, the second particle optical unit configured to image second individual particle beams emanating from the incidence locations onto the detection regions of the detection system; a magnetic and/or electrostatic objective lens configured to have the first and second individual particle beams pass therethrough; a beam switch in the first particle optical beam path between the multi-beam particle generator and the objective lens, the beam switch in the second particle optical beam path between the objective lens and the detection system; a sample stage configured to hold and/or position a wafer during the wafer inspection; an autofocus determining element configured to generate data to determine actual autofocus data during use of the multiple particle beam system to inspect the wafer; a fast autofocus correction lens; and a controller configured to control particle optical components in the first particle optical beam path and/or in the second particle optical beam path, wherein:
the controller is configured for static or low-frequency adaptation of a focusing to control at least the objective lens and/or an actuator of the sample stage at a first working point with a first working distance so the first individual particle beams are focused on the wafer surface situated at the first working distance;
the controller is configured for high-frequency adaptation of the focusing to generate an autofocus correction lens control signal based on the actual autofocus data at the first working point during use of the multiple particle beam system to inspect the wafer to control the fast autofocus correction lens during use of the multiple particle beam system to inspect the wafer at the first working point;
the first working point is defined by a landing angle of the first individual particle beams in the object plane and by a grid arrangement of the first individual particle beams in the object plane; and
the controller is configured to keep the landing angle and the grid arrangement substantially constant during the high-frequency adaptation at the first working point.

2 . The multiple particle beam system of claim 1 , wherein an adaptation time for the high-frequency adaptation is at least ten times less than the adaptation time TA for the low-frequency adaptation.

3 . The multiple particle beam system of claim 1 , wherein a stroke to set the working distance for the low-frequency or static adaptation is at least five times greater than a stroke for the high-frequency adaptation.

4 . The multiple particle beam system of claim 1 , wherein:
a second working point is defined at least by a second working distance between the objective lens and the wafer surface; the second working distance differs from the first working distance; the controller is configured to perform a low-frequency adaptation when there is a change between the first working point and the second working point; and the controller is configured to control at least the magnetic objective lens and/or an actuator of the sample stage at the second working point so that the first individual particle beams are focused on the wafer surface situated at the second working distance.

5 . The multiple particle beam system of claim 4 , wherein:
the second working point is defined by a landing angle of the first individual particle beams in the object plane and by a grid arrangement of the first individual particle beams in the object plane; and the controller is configured to keep the landing angle and the grid arrangement substantially constant during the high-frequency adaptation at the second working point.

6 . The multiple particle beam system of claim 1 , wherein the fast autofocus correction lens comprises a fast electrostatic lens.

7 . The multiple particle beam system of claim 6 , wherein the fast autofocus correction lens is a first fast autofocus lens between upper and lower pole shoes of the magnetic objective lens.

8 . The multiple particle beam system of claim 7 , wherein the first fast autofocus correction lens is integrated into a beam tube extension which protrudes into the objective lens from a direction of the upper pole shoe.

9 . The multiple particle beam system of claim 8 , wherein the first fast autofocus correction lens comprises at least two parts.

10 . The multiple particle beam system of claim 9 , wherein:
the beam tube extension has two interruptions; and one part of the two-parts is in each of the two interruptions, or each of two parts comprises a tube lens within the beam tube extension.

11 . The multiple particle beam system of claim 10 , wherein the controller is configured to control the two parts with voltages of the same or opposite signs via the autofocus correction lens control signal.

12 . The multiple particle beam system of claim 7 , further comprising:
a beam tube configured to be evacuated, the beam tube substantially enclosing the first particle optical beam path from the multi-beam particle generator to the objective lens; and a field lens system comprising at least one magnetic field lens, the field lens system in the first particle optical beam path between the multi-beam particle generator and the beam switch; and a second fast autofocus correction lens comprising a fast electrostatic lens, wherein:
the second autofocus correction lens is configured to be within a magnetic field of the field lens system during use of the multiple particle beam system; and
the controller is configured to generate a second autofocus correction lens control signal based on the actual autofocus data of the multiple particle beam system to inspect the wafer to control the second fast autofocus correction lens in high-frequency fashion during use of the multiple particle beam system to inspect the wafer at the respective working point.

13 . The multiple particle beam system of claim 7 , further comprising a second fast autofocus correction lens, wherein:
the second fast autofocus correction lens comprises a fast magnetic lens outside and around the beam tube in the first particle optical beam path and in a position that is substantially magnetic field-free; and the controller is configured to generate a third autofocus correction lens control signal based on the actual autofocus data during use of the multiple particle beam system to inspect the wafer to control the third fast autofocus correction lens in high-frequency fashion during use of the multiple particle beam system to inspect the wafer at the respective working point.

14 . The multiple particle beam system of claim 1 , further comprising a second fast autofocus correction lens, which comprises a fast electrostatic lens, wherein the second fast autofocus correction lens is at the multi-beam particle generator, and the controller is configured to generate a second autofocus correction lens control signal based on the actual autofocus data d

Assignees

• Carl Zeiss Multisem Gmbh

Inventors

• Zeidler Dirk
• Schmid Thomas
• Mueller Ingo
• Pauls Walter
• Schubert Stefan

Classifications

• H01J2237/216

  Automatic focusing methods · CPC title

• H01J2237/1534

  Aberrations · CPC title

• H01J37/265

  Controlling the tube; circuit arrangements adapted to a particular application not otherwise provided, e.g. bright-field-dark-field illumination · CPC title

• H01J37/21 Primary

  Means for adjusting the focus · CPC title

• H01J37/153

  Electron-optical or ion-optical arrangements for the correction of image defects, e.g. stigmators · CPC title