Charged particle optical device, objective lens assembly, detector, detector array, and methods
The embodiments of the present disclosure provide various techniques for detecting backscatter charged particles, including accelerating charged particle sub-beams along sub-beam paths to a sample, repelling secondary charged particles from detector arrays, and providing devices and detectors which can switch between modes for primarily detecting charged particles and modes for primarily detecting secondary particles.
1. A charged particle-optical device configured to project a multi-beam of charged particles along sub-beam paths towards a sample, the multi-beam comprising sub-beams, the charged particle-optical device comprising:
an objective lens array configured to project an array of charged-particle sub-beams onto the sample; and
a detector array configured to capture charged particles emitted from the sample,
wherein the charged particle-optical device is configured to switch between two operation states,
wherein in a first operation state, the detector array is configured to detect more secondary charged particles than backscattered charged particles, and in a second operation state, the detector array is configured to detect more backscattered charged particles than secondary charged particles.
2. The charged particle-optical device of claim 1 , the objective lens array comprising an array of objective lenses configured to project a respective sub-beam onto the sample, wherein in the first operation state, the objective lenses are configured to decelerate the respective charged-particle sub-beams onto the sample, and in the second operation state, the objective lenses are configured to accelerate the charged-particle sub-beam onto the sample.
3. The charged particle-optical device of claim 1 , wherein the objective lens array is configured to maintain a focus of the charged-particle sub-beams on the sample in the first and second operation states.
4. The charged particle-optical device of claim 1 , wherein the objective lens array comprises a first electrode configured to have a first electrode potential and a second electrode configured to have a second electrode potential, the first electrode being up-beam of the second electrode.
5. The charged particle-optical device of claim 4 , wherein in the first operation state, the first electrode potential is more positive than the second electrode potential.
6. The charged particle-optical device of claim 4 , wherein in the second operation state, the second electrode potential is more positive than the first electrode potential.
7. The charged particle-optical device of claim 4 , wherein at least the first electrode potential is adjusted between the first and second operation states to maintain a focus of a primary sub-beam on the sample in the first and second operation states.
8. The charged particle-optical device of claim 4 , wherein adjacent electrodes are separated by an insulating structure which is configured for use in the first operation state and the second operation state, preferably wherein the objective lens array comprises the insulating structure.
9. The charged particle-optical device of claim 8 , wherein the insulating structure is formed of a main body and a protrusion radially inwards of the main body, the main body featuring a first and second side, the first side opposing the second side, wherein: on the first side of the insulating structure the main body contacts one of the electrodes and a first gap is formed between the protrusion and the one of the electrodes, and on the second side of the insulating structure, the main body contacts another one of the electrodes and a second gap is formed between the protrusion and the other of the electrodes.
10. The charged particle-optical device of claim 4 , further comprising an electric power source which is configured to apply the first electrode potential to the first electrode and/or the second electrode potential to the second electrode.
11. The charged particle-optical device of claim 1 , wherein the detector array is configured to be proximate the sample.
12. The charged particle-optical device of claim 1 , wherein the charged particle-optical device is configured to maintain a distance between the detector array and the sample between the first and second operation states and vice versa.
13. The charged particle-optical device of claim 1 , wherein the charged particle-optical device is configured to alter a distance between the detector array and the sample so that the secondary charged particles are focused on the detector array when in the first operation state and the backscattered charged particles are focused on the detector array when in the second operation state.
14. The charged particle-optical device of claim 1 , wherein the charged particle-optical device is configured in use to alter a distance between the objective lens array and the sample when switching between the first and second operation states and vice versa.
15. The charged particle-optical device of claim 1 , wherein the charged particle-optical device is configured to switch the device between the first and second operation state continuously.
16. A charged particle-optical device configured to project an array of beams of charged particles towards a sample, the charged particle-optical device comprising:
an objective lens array configured to project the array of beams onto the sample; and
an array of detectors configured to detect backscattered particles from the sample,
wherein the charged particle-optical device is configured to switch between two operation states,
wherein in a first operation state, the detector array is configured to detect more secondary charged particles than backscattered charged particles, and in a second operation state, the detector array is configured to detect more backscattered charged particles than secondary charged particles.
17. The charged particle-optical device of claim 16 , the objective lens array comprising an array of objective lenses configured to project a respective sub-beam onto the sample, wherein in the first operation state, the objective lenses are configured to decelerate the beam onto the sample, and in the second operation state, the objective lenses are configured to accelerate the beam onto the sample.
18. The charged particle-optical device of claim 16 , wherein the objective lens array is configured to maintain a focus of the array of beams on the sample in the first and second operation states.
19. A method of selectively detecting secondary charged particles and backscatter charged particles emitted from a sample, the method comprising:
a) selecting a mode of operation of a detector between:
a backscatter mode for detecting more backscatter charged particles than secondary charged particles; and
a secondary mode for detecting more secondary charged particles than backscatter charged particles;
b) projecting a plurality of charged particle beams onto a surface of the sample; and
c) detecting charged particles emitted from the sample in the selected mode of operation.
20. The method of claim 19 , further comprising accelerating the plurality of charged particle beams in an objective lens array in the backscatter mode and/or decelerating the plurality of charged particle beams in an objective lens array in the secondary mode.