Apparatus of plural charged-particle beams

A multi-beam apparatus for observing a surface of a sample, comprising:

• an electron source;
• a condenser lens below said electron source;
• a source-conversion unit below said condenser lens;
• an objective lens below said a source-conversion unit;
• a deflection scanning unit below said source-conversion unit;
• a sample stage below said objective lens;
• a beam separator below said a source-conversion unit;
• and
• a detection unit above said beam separator and comprising a secondary projection imaging system and an electron detection device with a plurality of detection elements,
• wherein said electron source, said condenser lens, said source-conversion unit, said objective lens, said deflection scanning unit and said beam separator are aligned with a primary optical axis of said apparatus, said sample stage is configured to sustain said sample so that said surface faces to said objective lens, said detection unit is aligned with a secondary optical axis of said apparatus, and said secondary optical axis is not parallel to said primary optical axis,
• wherein said plurality of detection elements is placed on a detection plane, said secondary projection imaging system comprises a zoom lens, an anti-scanning deflection unit, projection lens, a first field lens at a first transfer plane and a second field lens at a second transfer plane, said first and second field lens are between said zoom lens and said projection lens, and said first field lens is between said second field lens and said projection lens,
• wherein said electron source is configured to generate a primary electron beam along said primary optical axis, said condenser lens is configured to focus said primary electron beam, said source-conversion unit is configured to change said primary electron beam into a plurality of beamlets and make said plurality of beamlets form a plurality of first image of said electron source, said objective lens is configured to focus said plurality of beamlets to image said plurality of first images onto said surface and therefore form a plurality of probe spots thereon respectively, and said deflection scanning unit is configured to deflect said plurality of beamlets to scan said plurality of probe spots respectively over a plurality of scanned regions within an observed area on said surface,
• wherein a plurality of slow secondary electron beams and a plurality of backscattered electron beams are generated by said plurality of probe spots respectively from said plurality of scanned regions and then incident to said objective lens, said objective lens is configured to in passing focus said plurality of slow secondary electron beams and said plurality of backscattered electron beams,
• wherein said detection unit is configured to separately operate on a SSE mode and a BSE mode when said beam separator respectively deflects said plurality of slow secondary electron beams and said plurality of backscattered electron beams to enter said secondary projection imaging system along said secondary optical axis,
• wherein in said SSE mode, said second field lens is turned off, said zoom lens is configured to focus said plurality of slow secondary electron beams onto said first transfer plane, said first field lens is configured to bend said plurality of slow secondary electron beams towards said secondary optical axis, said projection lens is configured to focus said plurality of slow secondary electron beams onto said detection plane, said plurality of slow secondary electron beams is configured to then form a SSE crossover between said projection lens and said detection plane and a plurality of slow-secondary-electron spots on said detection plane, said plurality of slow-secondary-electron spots is inside said plurality of detection elements respectively, consequently a SSE corresponding relationship between said plurality of probe spots and said plurality of detection elements is established, and accordingly each detection element is configured to generate a SSE image signal of one corresponding scanned region,
• wherein in said BSE mode, said first field lens is turned off, said zoom lens is configured to focus said plurality of backscattered electron beams onto said second transfer plane, said second field lens is configured to bend said plurality of backscattered electron beams towards said secondary optical axis, said projection lens is configured to focus said plurality of backscattered electron beams onto said detection plane, said plurality of backscattered electron beams is configured to then form a BSE crossover between said projection lens and said detection plane and a plurality of backscattered-electron spots on said detection plane, said plurality of backscattered-electron spots is inside said plurality of detection elements respectively, consequently a BSE corresponding relationship between said plurality of probe spots and said plurality of detection elements is established, and accordingly each detection element is configured to generate a BSE image signal of one corresponding scanned region,
• wherein in said SSE mode, said anti-scanning deflection unit is configured to deflect said plurality of slow secondary electron beams in step with said plurality of probe spots scanning over said plurality of scanned regions to remain positions of said plurality of slow-secondary-electron spots and thereby keeping said SSE corresponding relationship all the time,
• wherein in said BSE mode, said anti-scanning deflection unit is configured to deflect said plurality of backscattered electron beams in step with said plurality of probe spots scanning over said plurality of scanned regions to remain positions of said plurality of backscattered-electron spots and thereby keeping said BSE corresponding relationship all the time,
• wherein when observing said surface in different conditions, an imaging magnification of said zoom lens is configured to be adjusted to keep said SSE and BSE corresponding relationships in said SSE and BSE modes respectively.

A method to configure a detection system of a multi-beam apparatus for observing a surface of a sample, comprising steps of:

• deflecting, by a beam separator, a plurality of secondary electron beams generated by a plurality of probe spots on said surface to travel along a secondary optical axis of said apparatus;
• focusing, by a zoom lens, said plurality of secondary electron beams onto a transfer plane, wherein said zoom lens is aligned with said secondary optical axis;
• focusing, by a projection lens, said plurality of secondary electron beams from said transfer plane onto a detection plane to form a plurality of secondary-electron spots thereon, wherein said projection lens is aligned with said secondary optical axis;
• detecting, by an electron detection device with a plurality of detection elements, said plurality of secondary-electron spots respectively, wherein said plurality of detection elements is placed on said detection plane;
• deflecting, by an anti-scanning deflection unit, said plurality of secondary electron beams in step with said plurality of probe spots scanning over a plurality of scanned regions on said surface to keep positions of said plurality of secondary-electron spots all the time;
• and
• adjusting said zoom lens and said projection lens to cancel radial and rotational variations of positions of said plurality of secondary-electron spots when observing said surface in different conditions.

A method to configure a detection system of a multi-beam apparatus for observing a surface of a sample, comprising steps of:

• operating the detection system in a SSE mode, which comprises sub-steps of:
• deflecting, by a beam separator, a plurality of slow secondary electron beams generated by a plurality of probe spots on said surface to travel along a secondary optical axis of said apparatus;
• focusing, by a zoom lens aligned with said secondary optical axis, said plurality of slow secondary electron beams onto a first transfer plane;
• bending, by a first field lens aligned with said secondary optical axis and placed at said first transfer plane, said plurality of slow secondary electron beams;
• focusing, by a projection lens aligned with said secondary optical axis, said plurality of secondary electron beams onto a detection plane to form a SSE crossover therebetween and a plurality of slow-secondary-electron spots thereon;
• detecting, by an electron detection device with a plurality of detection elements, said plurality of slow-secondary-electron spots respectively, wherein said plurality of detection elements is placed on said detection plane;
• deflecting, by an anti-scanning deflection unit, said plurality of slow secondary electron beams in step with said plurality of probe spots scanning over a plurality of scanned regions on said surface to keep positions of said plurality of slow-secondary-electron spots all the time;
• and
• adjusting said zoom lens and said projection lens to cancel radial and rotational variations of positions of said plurality of slow-secondary-electron spots respectively when observing said surface in different conditions;
• and
• operating the detection system in a BSE mode, which comprises sub-steps of:
• deflecting, by said beam separator, a plurality of backscattered electron beams generated by said plurality of probe spots on said surface to travel along said secondary optical axis of said apparatus;
• focusing, by said zoom lens, said plurality of backscattered electron beams onto a second transfer plane;
• bending, by a second field lens aligned with said secondary optical axis and placed at said second transfer plane, said plurality of backscattered electron beams;
• focusing, by said projection lens, said plurality of backscattered electron beams onto said detection plane to form a BSE crossover therebetween and a plurality of backscattered-electron spots thereon;
• detecting, by said plurality of detection elements, said plurality of backscattered-electron spots respectively;
• deflecting, by said anti-scanning deflection unit, said plurality of backscattered electron beams in step with said plurality of probe spots scanning over said plurality of scanned regions to keep positions of said plurality of backscattered-electron spots all the time;
• and
• adjusting said zoom lens and said projection lens to cancel radial and rotational variations of positions of said plurality of backscattered-electron spots respectively when observing said surface in different conditions.