TEM sample slicing process

#The present invention relates to a technique for processing a slice sample for a transmission electron microscope (TEM) using a focused ion beam device.

#A sample for a transmission electron microscope is to be observed as an image of an object through which electrons have passed, which means that there is a need to process that sample to an extent that it becomes extremely thin. Production of a cross sectional sample such as a wafer by a slicing process using a focused ion beam device as shown in FIG. 6 is well known, and the following two processes are well known.

#1) Mechanically cutting away a small piece form a wafer-shaped sample as shown in FIGS. 5A—5C and processing this piece.

#FIG. 1 is a drawing for describing ion bean irradiation region setting for slice finishing processing, with A showing ion beam irradiation region setting in the related art and B showing ion beam irradiation region setting of the present invention.

#FIG. 2 is a drawing showing beam density distribution of the focused ion beam.

#FIG. 3 is a drawing showing an etching rate/angle of incidence characteristic for the focused ion beam.

#Basically, the present invention makes effective use of an etching rate/angle of incidence characteristic for a focused ion beam shown graphically in FIG. 3. The fact that etching rate of a focused ion beam is higher for a large angle of incidence than for a small angle of incidence is well known. As shown in this graph, a beam parallel to the process surface can not contribute to etching, but etching rate varies with angle and suddenly rises to a peak close to an angle of incidence of 80 degrees, and from there decreases quite rapidly up to 60 degrees, decreases more gradually to 30 degrees, and decreases very gradually from 30 degrees to 0 degrees. Specifically, with respect to the sample surface, considering that etching rate of an ion beam from directly above is obviously not high, in etching the top surface 21 of a slice processing section 2 using ion beam irradiation close to an angle of incidence of 80 degrees, the present invention confidently assumes irradiation of a focused ion beam from immediately above towards the top surface 21 of the slice process section 2 without absolute conditions to be avoided as in the related art. However, the etching rate with ion beam irradiation close to this angle of incidence of 0 degrees is much lower compared to the etching rate with ion beam irradiation with a peak value close to an angle of incidence of 80 degrees, but there is no guarantee that there will be no damage to the sample if the amount of accumulation during processing is considered. With the present invention, a thick protective film DG is formed in advance on a top surface 21 of the slice process section 2, thus avoiding damage to the top surface of the slice process region by the ion beam irradiation close to an incident angle of 0 degrees.

#A setting state of an irradiation region SA of the present invention is shown in FIG. 1B. A region to be irradiated of the entire slice processing section 2 is set without worrying about irradiation of a beam to the top surface 21 of the slice processing section 2 as in the related art. In this case also, if irradiation is carried out with a low acceleration voltage, beam sag of about 0.4 um arises in the ion beam, similarly to the related art, and there is positional slippage in positional control for scanning by deflection means of an ion optical system 11 by that sag amount. However, the beam in the case of the present invention uses a central part where ion beam density is extremely high as shown in FIG. 2, which means that beam energy becomes extremely high. An etching rate of a beam from above then becomes an extremely high value because the two process surfaces having the condition of the sloping surface 22 are close to an angle of incidence of 80 degrees, as opposed to the low value for the top surface 21 of the slice processing section 2 close to an incident angle of 0 degrees, as shown in FIG. 3. Accordingly, at the time of processing, processing of both processing surfaces can be carried out at the same time, and processing with good efficiency is performed taking advantage of the angle of incidence characteristic of the ion beam etching rate. With respect to the top surface 21, the etching rate of items irradiated with an ion beam is always low during processing, and it is possible to adequately prevent damage by the simple measure of depositing a thick protection film. This means that adoption of the processing method of the present invention can be expected to reduce processing time compared to the inefficient processing time of the related art. This processing time is also different depending on the type and structure of the sample to be processed, which means that at the time of actual processing basic data is extracted for the sample and processing time etc. is set.

#[Embodiment 1]