JP4037023B2 - Incision processing method and preparation method of transmission electron microscope sample - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technique for processing a sample for a transmission electron microscope (TEM) using a focused ion beam apparatus.
[0002]
[Prior art]
It is well known that a cross-sectional sample for TEM observation is made by thinning using a focused ion beam apparatus. A method of cutting a small piece mechanically from a wafer-like sample and processing it, and etching the wafer as it is Then, a method of taking out a thinned sample is known. As shown in FIG. 4-A, the former processing method requires a machining process in which a small block 11 having a width of 500 μm to 2 mm and a length of 3 mm is first cut from a wafer as a sample, and the upper portion is further cut to 50 μm or less. As shown in FIG. 4B, the protective film 6 is formed on the small block by spraying W (CO) 6 onto the processed portion by the gas gun 5. Thereafter, the focused ion beam is irradiated as shown in FIG. 4-C to perform slicing processing, and the electron beam is transmitted as shown in FIG. 4-D to be used as a cross-sectional sample for TEM observation. The latter processing method executes focused ion beam processing directly from the wafer without machining. The present invention relates to the latter method. In this method, as shown in FIG. 3, first, a protective film is formed on a processed portion by a gas gun, and a focused ion beam is irradiated from above the surface of the sample 1 to illuminate both sides of the observation cross section. Scraping is performed by etching, and square holes 3 and 4 are formed on both sides of the observation cross-section thin piece 2 with a focused ion beam device. The size of the hole is such that the front hole 3 tilts the sample stage and the observation cross section can be observed with a scanning ion microscope. The rear hole 4 has the same width as the front hole 3 and the depth is about 2/3. Drilled. In FIG. 3, A is a view of the processed portion observed from above, B is a cross-sectional observation view, and C is a microscope observation image from obliquely above. As shown in Fig. B, the sample surface is tilted to scan the focused ion beam as shown by an arrow on the periphery of the sample that has been processed into a thin section as an observation cross section. Since the sample surface is damaged by the processing, the sample cross section must be polished again. In order to prevent the positional deviation of the thinned sample at the time of the finishing process, it is necessary to leave an unprocessed part (left shoulder part in the drawing) in the peripheral part as shown in FIG. Then, after the cutting process, the sample surface is returned to the original state, the beam is irradiated from above the sample surface to finish the thinning process, and finally the thin sample is held by a glass probe operated by a manipulator, The sample is moved and adhered onto the mesh to complete the TEM observation sample. However, since the thinned sample has a connection part that is not partly cut, the glass probe is broken into pieces. You will carry a sample. The probe holds the sample piece mainly by electrostatic force. However, when the section sample is folded, the section sample repels and is lost from the probe. Once lost, it is an extremely small piece that cannot be discovered, and a series of operations will be attributed to water bubbles.
[0003]
[Problems to be solved by the invention]
An object of the present invention is to provide a processing method that solves the above-described problems, that is, a processing method that can be securely transported and placed on a mesh using a glass probe after thinning finish processing to prepare a sample for TEM observation. It is.
[0004]
[Means for Solving the Problems]
A wafer-like sample is irradiated with a focused ion beam from above the sample surface to etch both sides of the observation cross section, and the sample surface is tilted in a state where the thinning has progressed moderately, and the focused ion beam is applied to the thinned sample. Scanning is performed to cut at least the bottom of the sample, and the sample surface is returned to its original position, and a focused ion beam is irradiated from above to perform a thinning finish. When the finishing process is completed, the focused ion beam is irradiated from above the sample surface to both sides where the cutting process is not performed, and the cutting process is executed.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, a protective film is first formed on a processed portion by a gas gun, a focused ion beam is irradiated from above the sample surface, both sides of the observation cross section are etched away, and a square hole that allows a cross section to be observed with a scanning ion microscope The process is the same as in the conventional processing up to the point where the clearance is made. Next, the sample stage is tilted and the focused ion beam is scanned around the periphery of the sample 2 that has been processed into a thin slice as an observation cross section, and the cut processing is performed. Because of this deep beam irradiation, the sample surface is deeply damaged. Accordingly, it is the same as before that the cross section of the sample has to be polished again. However, the present invention starts with an arrow on the bottom of the sample 2 that has been cut into pieces as shown in FIG. 1A. It is characterized in that the beam is scanned and executed as in a. This is because the cutting process at least on the bottom side cannot be performed unless the sample surface is tilted. Even after this cutting process, the thinned sample 2 remains connected to the wafer body 1 at both sides. Therefore, the sample 2 thinned at the time of the next finishing process is secured in a stable fixed state and does not cause a positional shift. Then, after the cutting process, the sample table is returned to the original angle, and the beam is irradiated from above the sample surface to finish the thinning process, and the thinning process is completed. However, the thinned sample 2 is still connected to the wafer body at both sides. In the present invention, a beam from above the sample surface, that is, from the direction of the thin piece surface is irradiated to the connecting portion of both side portions that are not cut in the sample surface without tilting the sample surface. As shown by c, cutting is performed on both sides of the thinned sample. Since this part is thin enough after thinning, it can be easily cut by irradiation with the beam from the surface extension direction, and the material scattered by etching is very small. Since the incident angle is shallow, the damage caused by this cutting process is negligible. Finally, the sliced sample is held by a glass probe 7 operated by a manipulator (not shown) as shown in FIGS. 1C and 1D, and as shown in FIGS. The TEM observation sample is completed by moving and adhering to the mesh 8, but the glass probe 7 carries the section sample 21 cut from the sample body 1 by the cutting process, and is folded from the sample body as in the conventional case. Since it is not necessary to carry the sample piece, even if the sample piece is held by an electrostatic force, the sample will not fly off and be lost from the probe.
[0006]
The point of the present invention is that the beam irradiation from a deep angle causes great damage to the sample. Therefore, the incision processing on both sides can be performed by the beam irradiation from the direction of the thin slice surface. It is the point that the base is first processed first by turning the sample to tilt and processing the sample at a deep incident angle. As a result, the finishing process can be executed in a form in which both sides are held, so that the position holding stability is higher than that of the conventional one-point holding, which contributes to increasing the machining accuracy. And since the sample piece is picked up in a state of complete separation, the conventional problem that the sample repels and is lost can be solved. In other words, if the connecting portion is made large in the cutting process, the position holding function in the finishing process is ensured, but the reluctance force becomes large at the last sample piece pick-up, and the probability of losing the thinned sample increases. However, the present invention has been able to solve the problem at a stretch, although it has been difficult in the past.
Note that the cutting process from a deep angle with respect to the observation cross section is not limited to the bottom side part, and part of both side parts may be processed. The point is that it is only necessary to ensure holding stability when the flake is connected to the sample body, and even after beam irradiation from the flake surface direction with minimal damage, beam processing after the flake finish processing is minimized. If you want to do this, it is better to leave only the part necessary for stable maintenance.
[0007]
[Example 1]
An embodiment in which a sample for TEM observation is prepared from a wafer-like 64M DRAM sample according to the present invention will be described. A wafer-like 64M DRAM is placed on the sample stage of the focused ion beam apparatus, and positioning is performed so that a specific portion to be a sample for TEM observation comes to the irradiation position when the beam is irradiated from above the wafer surface. Then, after forming a protective film 6 by spraying W (CO) 6 or phenanthrene or the like from the gas gun 5 onto the processed portion, both sides of the observation cross section identified by ion beam irradiation from above the wafer surface are shown in FIG. Etching is performed in the form (front hole 3 is 20 μm wide × 20 μm deep × 10 μm deep, and rear hole 4 is about 20 μm wide × 10 μm deep × 10 μm deep). When this processing is finished, the thickness of the sliced portion 2 of the observation cross section is about 0.5 μm. In this state, the sample stage is tilted by 60 degrees, and a focused ion beam is scanned from the front of the observation section, and a cut a is made at the bottom of the observation section as shown in FIG. 1A. Since this cutting process is a beam irradiation from a deep angle of 60 degrees with respect to the observation cross section, damage to the sample cannot be ignored. Therefore, when the cutting process is completed, the sample stage is returned to the original position, and the finishing process for thinning the observation cross section is executed again by the focused ion beam from above the wafer surface. This finishing process not only grinds and removes the material scattered and adhered during the previous cutting process, but also performs further thinning. The finishing process has a thickness of 0.1 μm for the sliced section 2 of the observation cross section. It is executed until it becomes. When the slicing process is completed, the irradiation position of the focused ion beam is fixed in the vicinity of both ends of the thin sample, and the beam is irradiated from the thin film surface extending direction. In this processing, the beam is irradiated from a shallow angle of 0 degrees with respect to the observation cross section, and since the thickness of the thin piece is 0.1 μm, the amount of material that is easily cut and scattered is very small. Damage to can be ignored. As shown in FIG. 1B, incisions of b and c are made in the depth direction on both side portions of the thin sample, and reach the incision position of the previous bottom portion. It is completely separated from the sample body 1. The work time so far can be executed in about 60 minutes.
[0008]
The manipulator (not shown) is operated to bring the glass probe 7 into contact with the section sample 21 as shown in FIG. Since the section sample 21 is completely separated from the wafer-like sample body 1, it is held by the probe 7 by electrostatic force without being bounced and is surely picked up. Subsequently, the manipulator is operated to move the section sample 21 onto the collodion membrane tension mesh (150 mesh) 8 and place it. The section sample 21 cut out on the mesh 8 adheres to complete the preparation of the sample for TEM observation. The section sample 21 can be picked up and attached to the mesh 8 in about 10 minutes.
[0009]
【The invention's effect】
In the present invention, as in the conventional processing method, a wafer-like sample is subjected to a thinning process using a focused ion beam from above the sample surface. In the next step, the sample stage is tilted to obtain a beam from a deep angle. The bottom part of the thin piece is cut by irradiation, and at least a part of both side parts is not cut at this point. And after putting the sample table back and finishing the sample surface, the irradiation position of the beam in the direction of the thin piece is positioned in the vicinity of both ends of the thin piece, and the remaining both sides are cut. When the section sample is picked up, the section sample is completely separated from the wafer, and there is no need to fold the connection portion to pick up. Therefore, there is no problem that the slice sample repels and loses as in the prior art, and the transmission electron microscope sample can be stably and reliably manufactured without wasting the previous work.
[0010]
In addition, the finishing process can be performed in a state in which the thinned portion is fixed and held on both sides, so that it is possible to perform highly accurate processing. If the connecting portion is made large as in the conventional case, the position holding function at the time of finishing will be ensured, but the repelling force at the time of the final sample piece pick-up will increase, and the probability that the thinned sample will be lost increases. There is no need to struggle with the trade-off between the spaces.
[Brief description of the drawings]
FIG. 1 is a diagram showing a cut-out form of a thinned sample of the present invention.
FIG. 2 is a diagram showing a form of picking up a section sample of the present invention.
FIG. 3 is a diagram showing a mode in which a thinning process is directly performed from a wafer.
FIG. 4 is a diagram showing a form in which a thinning process is performed after machining.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Wafer-like sample a Bottom part cut 11 Sample small block b, c Both sides cut 2 Thin piece 21 Section sample 3 Front hole 4 Back hole 5 Gas gun 6 Glass probe 8 Mesh

Claims (2)

Thinning the wafer-shaped sample with a focused ion beam from above the sample surface, tilting the sample stage and cutting at least the bottom of the thin piece by beam irradiation, and returning the sample stage to its original position a step of performing a finishing polished sample surface damages received by said rebated, the irradiation position of the thin one side direction of the beam is positioned adjacent thin end portions by executing a thinning process again Te, the both end portions A method for cutting a sample for a transmission electron microscope, comprising the step of performing the cutting process. Attaching a thin sample embodying the rebated how according to claim 1, comprising the steps of: picking up by a glass probe to be operated by a manipulator, a step of transferring on the mesh by the operation of the manipulator, a thin sample sections on the mesh A method for preparing a sample for observation with a transmission electron microscope.

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