Sample processing method and charged particle beam device
View Patent ↗The present invention provides, in the preparation of a TEM or STEM sample using FIB-SEM, a technique for obtaining a processing end point on the back surface side of the sample. The state of the sample back surface being processed by the FIB is detected using a Kikuchi pattern formed when electrons that have been injected by the SEM are emitted from the sample back surface. Since this Kikuchi pattern is caused by the crystal structure of the sample back surface, the crystal orientation relative to the injected electron beam, and the crystal lattice constants, detecting the pattern allows the processing end point on the back surface side to be obtained during the FIB processing.
1. A sample processing method of processing a sample including at least two phases, at least one of the at least two phases including a structure serving as an observation target, the sample processing method comprising:
a step of performing, by using an ion beam, ion milling on a phase on a back surface of the sample facing a front surface of the sample serving as an electron beam irradiation surface of the sample, the phase being different from the phase including the structure serving as the observation target; and
a step of determining a processing end point on the back surface of the sample on the basis of a strength of an interference image of an electron diffraction wave generated from the back surface of the sample by, after performing ion milling on the back surface of the sample, irradiating the front surface of the sample with an electron beam and transmitting the electron beam through the sample;
wherein at least two or more parameters of a peak height, a signal/noise ratio, and a half-value width of a line profile of the strength of the interference image of the electron diffraction wave emitted from the back surface of the sample are selected, and the processing end point on the back surface of the sample is determined on the basis of a change in the selected parameters.
2. The sample processing method according to claim 1 , wherein
a depth of ion milling in the phase different from the phase including the structure serving as the observation target is determined on the basis of an entering depth of the electron beam obtained when, before ion milling, the sample is irradiated with the electron beam and an image of the structure is obtained.
3. The sample processing method according to claim 1 , wherein
an irradiation direction of the ion beam and an injection direction of the electron beam intersect with each other, and an angle between the irradiation direction of the ion beam and the injection direction of the electron beam is 20 to 60°.
4. The sample processing method according to claim 3 , wherein
the angle between the irradiation direction of the ion beam and the injection direction of the electron beam is 40°.
5. The sample processing method according to claim 1 , wherein
a point of time at which it is determined that the strength of the interference image of the electron diffraction wave emitted from the back surface of the sample has been saturated is determined as the processing end point on the back surface.
6. The sample processing method according to claim 1 , wherein:
the sample is a sample in which a crystalline phase includes a non-crystalline structure; and
a point of time at which the interference image of the electron diffraction wave emitted from the back surface of the sample disappears is determined as the processing end point on the back surface of the sample.
7. The sample processing method according to claim 1 , wherein:
the sample is a sample in which a phase having a first crystallinity includes a structure having a second crystallinity different from the first crystallinity; and
a point of time at which the interference image of the electron diffraction wave emitted from the back surface of the sample is confirmed to be an interference image of a planned material is determined as the processing end point on the back surface of the sample.
8. The sample processing method according to claim 1 , wherein
interference images of electron diffraction waves emitted from the back surface of the sample, the interference images being interference images of the electron diffraction waves in a plurality of thicknesses of the sample, are acquired in advance and the interference images acquired in advance in the plurality of thicknesses are compared with an interference image of an electron diffraction wave emitted from the back surface of the sample, the interference image being obtained when the sample is actually processed, and a point of time at which the interference images are matched is determined as the processing end point on the back surface of the sample.
9. The sample processing method according to claim 1 , wherein
interference images of electron diffraction waves emitted from the back surface of the sample, the interference images being interference images of the electron diffraction waves in a plurality of thicknesses of the sample, are obtained by calculation using Monte Carlo simulation and the interference images obtained by calculation in advance in the plurality of thicknesses are compared with an interference image of an electron diffraction wave emitted from the back surface of the sample, the interference image being obtained when the sample is actually processed, and a point of time at which the interference images are matched is determined as the processing end point on the back surface of the sample.
10. A charged particle beam device for processing a sample including at least two phases, at least one of the at least two phases including a structure serving as an observation target, the charged particle beam device comprising:
a SEM housing configured to scan the sample with an electron beam, the SEM housing including an electron source, an electron acceleration unit, an electron focusing lens, and an electron beam scanning mechanism;
a FIB housing configured to irradiate, with an ion beam, a back surface of the sample facing a front surface of the sample serving as an electron beam irradiation surface of the sample and perform ion milling on a phase different from the phase including the structure, the FIB housing including an ion source, an ion acceleration unit, an ion focusing lens, and an ion beam scanning mechanism;
a transmission back-scattered electron diffraction wave detector configured to detect an electron diffraction wave generated from the back surface of the sample by transmitting the electron beam through the sample, the transmission back-scattered electron diffraction wave detector being placed below the back surface of the sample; and
a computer configured to generate an interference image of the electron diffraction wave on the basis of the electron diffraction wave detected by the transmission back-scattered electron diffraction wave detector, wherein
the computer determines a processing end point on the back surface of the sample on the basis of a strength of the interference image of the electron diffraction wave, and
at least two or more parameters of a peak height, a signal/noise ratio, and a half-value width of a line profile of the strength of the interference image of the electron diffraction wave emitted from the back surface of the sample are selected, and the processing end point on the back surface of the sample is determined on the basis of a change in the selected parameters.
11. The charged particle beam device according to claim 10 , wherein
the SEM housing and the FIB housing are placed so that an axis of the electron beam and an axis of the ion beam intersect with each other in the vicinity of the sample.
12. The charged particle beam device according to claim 10 , further comprising
at least one or more of a detector configured to detect back-scattered electrons emitted from the front surface of the sample, a detector configured to detect a characteristic X-ray emitted from the front surface of the sample, a detector configured to detect a back-scattered electron diffraction wave emitted from the front surface of the sample, and a detector configured to detect transmission electrons transmitted through the sample.
13. The charged particle beam device according to claim 10 , wherein
the computer measures the strength of the interference image of the electron diffraction wave emitted from the back surface of the sample and specifies a sample film thickness associated in advance with the strength of the interference image of the electron diffraction wave.