Charged particle beam apparatus including aberration corrector
View Patent ↗A focused charged particle beam apparatus including an aberration corrector, capable of finding the absolute value of the aberration coefficient at high speed, and capable of making high-accuracy adjustments at high speed. A deflection coil tilts the input beam relative to the object point, and measures the defocus data and aberration quantity at high speed while the beam is tilted from one image, and perform least squares fitting on these results to find the absolute value of the aberration coefficient prior to tilting the beam, and to adjust the aberration corrector.
1. A charged particle beam apparatus comprising:
a charged particle optical system to scan a primary charged particle beam on a specimen, detect secondary charged particles emitted from the specimen due to the scanning and output the detection results as a secondary charged particle signal;
a control unit for controlling the charged particle optical system;
a data processing device to process the secondary charged particle signal that was output and acquire two-dimensional distribution information on pixels matching the area scanned by the primary charged particle beam,
wherein the charged particle optical system includes:
an aberration corrector to reduce the aberration generated by the charged particle optical system; and
a unit to guide the charged particle beam from the optical axis of the charged particle beam in a tilted state onto the specimen, and
wherein the data processing device:
calculates an out-of-focus amount and astigmatic difference in the charged particle optical system from multiple two-dimensional distribution information acquired by scanning the specimen with the primary charged particle beam in a tilted state and also while changing a degree of focus and,
calculates an optical order aberration coefficient to use in the charged particle optical system, by utilizing the two-dimensional distribution information obtained from scanning the specimen in a state where the primary charged particle beam is not tilted, and the calculated out-of-focus amount and astigmatic difference.
2. The charged particle beam apparatus according to claim 1 , wherein the data processing device calculates a correction quantity of the aberration corrector by utilizing the calculated optical order aberration coefficient.
3. The charged particle beam apparatus according to claim 1 , comprising:
a standard specimen utilized to acquire the two-dimensional distribution information for adjusting the aberration corrector,
wherein the standard specimen contains multiple charged particle beam irradiation surfaces formed in a pattern or a structure for acquiring the two-dimensional distribution information, and
wherein the multiple irradiation surfaces include a structure positioned continuously in a lateral direction and arrayed via steps in a height direction.
4. The charged particle beam apparatus according to claim 3 , wherein the charged particle beam apparatus acquires the two-dimensional distribution information in a state where the scanning range of the primary charged particle beam was adjusted so as to include all the multiple irradiation surfaces positioned consecutively in the lateral direction.
5. The charged particle beam apparatus according to claim 4 , wherein the data processing device extracts the two-dimensional distribution information corresponding to one of the multiple irradiation surfaces among all the multiple irradiation surfaces from the acquired two-dimensional distribution information, and calculates the out-of-focus amount and astigmatic difference based on the extracted two-dimensional distribution information.
6. The charged particle beam apparatus according to claim 3 , wherein the data processing device includes a storage unit that stores a size of the steps, and calculates the out-of-focus amount by using the applicable stored step size information.
7. The charged particle beam apparatus according to claim 1 ,
wherein the charged particle optical system contains a magnetic field objective lens including an electrostatic lens, and
wherein the control unit for the charged particle optical system changes the degree of focus by adjusting the applicable electrostatic lens.
8. The charged particle beam apparatus according to claim 7 , comprising a storage unit to store information relating to the range width of the focus adjustment.
9. The charged particle beam apparatus according to claim 1 , comprising:
a specimen stage to hold the specimen,
wherein the specimen stage contains a drive mechanism utilizing a piezoelement for moving the specimen in the height direction, and
wherein the applicable drive mechanism changes the degree of focus.
10. The charged particle beam apparatus according to claim 9 , wherein the data processing device calculates the specimen position in the height direction based on the feed amount for the piezoelement, and calculates the out-of-focus amount by using the applicable position in the height direction.
11. The charged particle beam apparatus according to claim 9 , comprising a storage unit to store information relating to a piezoelectric feed range.
12. The charged particle beam apparatus according to claim 1 ,
wherein the data processing device calculates the out-of-focus amount and dual symmetrical aberration from the two-dimensional distribution information and, calculates the aberration coefficient by using the applicable calculated out-of-focus amount and dual symmetrical aberration.