JP4350425B2 - Pickup sample vertical positioning method and sample with vertical marking - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for processing a fine observation portion from a large sample such as a TEM sample, picking it up, fixing the observation portion to a table, and preparing an observation sample, and a sample form created by the method.
[0002]
[Prior art]
In order to observe the internal structure of a semiconductor device, etc., or to analyze the internal composition and state, the cross section of the target portion is exposed from a large sample by focused ion beam (FIB) processing, etc. The sample is cut out and picked up and fixed on a table to make a sample for a microscope or an analytical instrument. For example, a conventional method for manufacturing a transmission electron microscope (TEM) sample disclosed in Patent Document 1 will be described with reference to FIGS. As shown in FIG. 7 (a), the processing part is first irradiated with an ion beam while injecting a raw material gas with a gas gun to form a protective deposition film, and then, as shown in FIG. A focused ion beam is irradiated from above the surface, and the rear side of the observation cross section is dug by etching, and then the front side of the observation cross section is dug by etching as shown in FIG. Square front and rear holes 4 are formed on both sides of the observation cross-section slice with a focused ion beam device. Since the observation surface is damaged by drilling, finishing is performed with the beam current suppressed, and the surface is polished. As shown in (d), the sample surface is tilted and the peripheral part of the sample processed into a thin section as an observation cross section is irradiated with a focused ion beam as shown by the arrow to perform cutting (bottom cut). Both sides of the observation cross section are side cut with FIB from above. When the sample processed to this state is operated with a manipulator (not shown) as shown in FIG. 8A to bring the glass probe 5 having a tip diameter of 10 μm or less closer to the sample section 2, the sample section 2 It adheres to the tip of the glass probe 5 so as to be sucked by an electrostatic force, and as shown in B, the sample section 2 is held by the glass probe 5 and separated from the thinning portion. The sample section 2 held by the glass probe 5 is carried and placed on a fixed base 3 such as a mesh as shown in FIG. This sample stage is made of a material that does not affect observation or analysis such as a collodion membrane-clad mesh or a microgrid, and the sample section 2 is indicated by D by the adhesive force or electrostatic force of the membrane. It was fixed.
[0003]
However, when actually trying to observe the TEM sample produced in this way, the thickness is too large and the electron transmission is still insufficient. In such a case, even if thinning is performed by reworking, the specimen section is laid down and fixed to a film such as a mesh, so that the second FIB processing is extremely difficult. There is. In such a case, in general, a similar specimen must be processed again from the beginning, and if it is a substitute sample, everything will be frustrating. Further, when the sample is a ferromagnetic material, there is a problem that the sample is lost due to the influence of a magnetic field during TEM observation. The discovery is hopeless because it is a very fine sample. Under such circumstances, Non-Patent Document 1 presents a form of a sample that can be additionally processed with respect to the cut sample section as “FIB lift-out method that can be additionally processed”. This is not schematically shown in FIG. 6A and fixed in a state in which the sample section 2 is laid on an organic thin film such as a collodion film as in the conventional method shown in FIG. As shown in Fig. 2, the sample section 2 is fixed on the block-shaped sample fixing base 3 in a standing state. FIB deposition using an epoxy-based adhesive or gas is used for fixing to the fixed base 3. As shown in FIG. 5A, this sample is transported to the fixing base 3 with the sample section 2 having a width of several tens of μm upright, and fixed with an adhesive, so that the entire fixing base 3 is mounted on the stage of the FIB apparatus. It is possible to perform additional machining with FIB in a stable state on both sides of the sample section 2. In addition, since it is fixed to the block-shaped fixing base 3 instead of a thin film, it has a certain weight and does not fly under the influence of a magnetic field during TEM observation.
[0004]
However, when the sample is manufactured in such a form, for example, a sample such as a semiconductor device having a structure in the vertical direction of a narrow region, it is necessary to mount the sample perpendicular to the FIB. . If the observation surface of the sample section 2 picked up is fixed perpendicularly to the upper surface of the fixed base 3, the FIB is mounted by placing this block base on the stage of the FIB apparatus set in a horizontal state. Although irradiation can be performed in parallel to the observation surface, when the observation surface of the sample section 2 is not fixed vertically to the fixed base 3, this block shape is placed on the stage of the FIB apparatus set in a horizontal state. When the fixed base 3 is placed and the FIB is irradiated, the beam direction is inclined with respect to the observation surface, and the cross section cannot be clearly obtained. FIG. 4 shows this, and as shown in the perspective view on the left side of the figure, the block-shaped fixing base 3 is placed on the stage of the FIB apparatus set in a horizontal state, and the FIB is irradiated from above. In this case, if the sample section 2 is vertically set on the fixing base 3, the FIB is irradiated vertically from above as shown in the upper stage on the right side in the figure, but the sample section 2 is perpendicular to the fixing base 3. If not, the FIB is irradiated with an inclination from above as shown in the middle section on the right side of the figure. This is clearly shown in a cross-sectional view in the lower part of the right side of the figure.
[0005]
[Patent Document 1]
Japanese Laid-Open Patent Publication No. 2002-148162 “Method for Fixing Thin Sample and Sample Using This Method” published on May 22, 2002 [Non-Patent Document 1]
Daisuke Sakata "FIB lift-out method that can be additionally processed" The 58th Annual Meeting of the Electron Microscopy Society of Japan Vol.37, P247 2002 [0006]
[Problems to be solved by the invention]
The subject of the present invention is that when the picked-up sample is fixed to a block-like table, the original sample surface direction is not perpendicular to the FIB irradiation direction without any deviation of several degrees. It is to present a technique that can be set and processed as described above.
[0007]
[Means for Solving the Problems]
The vertical positioning method of the pickup sample of the present invention is as follows.
(1) Before cutting a section from a large sample by FIB processing, a mark indicating a direction perpendicular to the sample surface is provided.
(2) At the time of additional processing, the vertical direction of the sample piece picked up is confirmed based on this mark, and the sample section picked up so that the sample surface is perpendicular to the FIB by the stage tilt control of the FIB apparatus. Make out.
The mark is provided by forming a pillar or a cut groove in a direction perpendicular to the sample surface or by forming a two-dimensional pattern such as a three-point mark.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
As described above, if the sample section picked up can be fixed upright on the surface of the block table, the subsequent processing can be performed very conveniently. However, it is extremely difficult to operate the manipulator to drive the glass probe and to accurately fix the minute sample section on the block-shaped table without causing any deviation in the original sample surface direction. Therefore, it was conceived that a mark indicating the original sample surface direction was provided on the sample, and based on this, the posture of the sample slice picked up with respect to the FIB irradiation direction was adjusted by additional processing. This means that even if the picked-up sample section is not fixed upright with respect to the surface of the block table, if the angle at which it is fixed with respect to the original sample surface direction is known, the tilt mechanism of the FIB apparatus is used. This is based on the knowledge that the FIB irradiation direction can be determined in the vertical direction with respect to the sample by correcting the inclination. Since the picked-up sample is separated from the original sample body, it is advantageous to mark the surface of the portion serving as the section on the surface of the section while confirming the sample surface direction before separation. When the sample section is picked up, the sample section is fixed to the fixing table. This fixing base is placed and fixed on the stage of the FIB apparatus. At the time of additional machining, this mark is first observed with the microscope function of the FIB apparatus to confirm the direction of the sample observation surface. Control is performed based on the direction in which the sample slice, which is a workpiece to be processed, is confirmed, and the additional processing is executed so that FIB irradiation is performed on the sample from a desired direction. A further advantage of the present invention is that the yield is improved. This is because the additional processing after the sample section is fixed to the table can be performed, so that it can be processed to an optimum thickness while being processed slightly thicker and actually observed. In addition, there is an advantage that the material which is reattached at the time of bottom cut or side cut is removed at the stage of finishing and the surface can be finished cleanly.
The present invention is not limited to a TEM sample, but is a pickup sample such as a scanning electron microscope (SEM), a scanning transmission electron microscope (STEM), an Auger electron analyzer (AES), and a secondary ion mass spectrometer (SIMS). It can be applied as it is.
[0009]
[Example 1]
One embodiment of the method for vertically picking up a pickup sample according to the present invention will be described with reference to FIGS. In this embodiment, pillars (columns) perpendicular to the sample surface are built as marks indicating the sample surface direction. First, the large sample is set on the stage so that the surface is perpendicular to the FIB irradiation direction. A target observation cross section is identified from the sample, and protective deposition is applied to the surface portion and the vicinity thereof. In this method, FIB is irradiated while jetting a material gas to cause deposition in the irradiated portion. This method is referred to herein as “CVD by FIB” (chemical vapor deposition). Next, as shown in FIG. 1A, holes 4 are formed by etching using FIB on both sides of the observation cross-section portion specified in the large sample 1. This etching may be simple sputter etching or gas assist etching. In this figure, the protective deposition is omitted. At the stage where the thickness of the observation cross section is processed to 5 to 10 μm, as shown in the figure, a vertical pillar P is formed by CVD using FIB on the upper surface (original sample surface) portion of the sample processed into a thin piece. Will do. The process before the pillar P is formed is not particularly different from the conventional sample preparation method. However, since it is a sample form that can be additionally processed, it is not always necessary to process to the optimum thin piece thickness as a sample at this stage. Future mark formation is a feature of the present invention. At this time, the upper surface of the sliced sample is not a horizontal plane as shown in the figure, and is actually non-planar due to the previous protective deposition. However, since the direction of the sample surface can be grasped as the FIB apparatus, the FIB irradiation direction can be set perpendicular to the sample surface, and the vertical pillar P can be formed accurately. When the pillar P, which is a direction indicating mark, is formed, the preparation for separating the observation cross section from the sample body 1 is completed. The formation of the pillars P is not limited to the above-described timing, and may be performed at any time before the separation from the sample body 1 such as the first protection deposition.
[0010]
The sample stage is tilted to perform FIB irradiation, and bottom cut is performed by sputter etching as shown in FIG. 1B. The sample stage is returned to the horizontal position and side cut is performed by FIB from above. At this stage, the observation sample portion is separated from the sample body. The manipulator is operated to pick up the sample section 2 with the glass probe 5 and carry it on the sample fixing table 3. As shown in FIG. 2A, an adhesive such as an epoxy resin is dropped on the surface of the sample fixing base 3, and the sample section 2 is placed thereon. The sample section 2 is fixed on the surface of the sample fixing base 3 by the force of the adhesive. In this case, since the adhesion surface of the sample piece 2 is a bottom cut portion by sputter etching, it is not a clean horizontal surface, and it is difficult to determine the direction with the glass probe 5 and fix it. is there. Therefore, it should be unlikely that the observation surface of the sample piece 2 is fixed to the surface of the sample fixing base 3 accurately in the vertical direction, and will be slightly inclined. However, the advantage of the present invention is that the direction of the observation surface is accurately displayed by the pillar P even if the fixing is inclined, so that this inclination does not hinder any additional processing. In order to further secure the adhesive by the adhesive, the peripheral portion may be fixed by CVD using FIB.
[0011]
When this pick-up sample is observed with the microscope function of the FIB apparatus, if the side surface of the pillar P is observed as shown in the lower side of FIG. 2B, it indicates that the observation cross section of the sample is not parallel to the FIB irradiation direction. ing. Therefore, at that time, as shown in the upper part of the drawing, the stage is controlled so that the side surface of the pillar P is not visible in the microscope image and only the upper surface shape is visible. This state is an arrangement relationship in which the observation cross section of the sample and the FIB irradiation direction are parallel, and additional processing of the cross section with high accuracy can be executed based on this posture. As mentioned earlier, optimal thinning and finishing can be performed at this stage as needed. Further, in the case of this sample, since TEM observation can be performed and additional processing can be performed as necessary, optimal processing can be executed, so that optimization and solidification of processing can be achieved.
[0012]
[Example 2]
Next, another embodiment of the pick-up sample vertical alignment method of the present invention will be described with reference to FIG. In this embodiment, a groove is formed in a direction perpendicular to the sample surface as a mark indicating the sample surface direction. As in the previous embodiment, first, the large sample 1 is set so that the surface is perpendicular to the FIB irradiation direction while being placed on the stage. An observation cross-sectional portion of interest is identified from the sample 1, and deposition for CVD protection by FIB is performed in the vicinity of the surface portion. Next, a hole is made by etching using FIB on both sides of the identified observation cross section. The sliced sample is cut out from the sample body 1 at the stage where the thickness of the observation cross section is processed to 5 to 10 μm. The sample slice 2 cut out before that is the surface direction of the original sample. The mark which shows is put. The mark in this embodiment is the groove C perpendicular to the sample surface as described above, and this groove processing is performed at this point. Since the location for grooving cannot be the observation cross-section location, it is either one of both sides. Considering the convenience and efficiency of processing, it is better to first perform side-cut processing on the side surface on which this processing is performed. This is because simply digging a hole with a high aspect ratio is a troublesome operation that takes time and effort, and the operation with the cut side surface is easy to process by grooving. Further, the state in which the bottom cut and the other side cut are not performed is a state in which the observation cross section is firmly integrated with the sample body, and the accuracy in the surface direction is maintained. At this time, the top surface of the sliced sample is not a horizontal plane as shown in the figure, and is actually non-planar due to the previous protective deposition. Since it is grasped, the irradiation direction of the FIB can be set perpendicular to the sample surface, and the vertical groove C can be accurately formed. When the groove C, which is a direction indicating mark, is formed, the observation cross section can be separated from the sample body 1.
[0013]
When this pick-up sample is observed with the microscope function of the FIB apparatus, if the side surface and the opening of the groove C are observed as shown in the lower side of FIG. 3, the observation cross section of the sample is not parallel to the FIB irradiation direction. Is shown. Therefore, at that time, as shown in the upper part of the figure, the stage is controlled so that the side surface of the groove C is not visible in the microscopic image and only the groove cross-sectional shape is visible. This state is an arrangement relationship in which the observation cross section of the sample section 2 and the FIB irradiation direction are parallel, and additional processing of the cross section with high accuracy can be executed based on this posture. However, in the case of this embodiment, the side surface and the opening of the groove C may not be visible even when the groove opening side is inclined low. In order to avoid erroneous confirmation, it is safe to make adjustment after making the side surface and opening of the groove C visible once as shown in the figure.
[0014]
[Example 3]
A further different embodiment of the method for vertically picking up a pickup sample of the present invention will be described with reference to FIG. In this embodiment, a predetermined pattern is written on the surface of the sample as a mark indicating the direction of the surface of the sample. In this example, a three-point mark (p1, p2, p3) is added. This predetermined pattern written on the sample surface is recognized as the same two-dimensional pattern when the sample 2 after being picked up is set in the same posture as the original sample 1 surface. In other words, if the sample piece 2 is set in an inclined state, the triangular shape indicated by the three points p1, p2, and p3 is observed distorted, so that the posture can be confirmed. The work until writing the mark indicating the sample surface direction is the same as in the previous embodiment. At the stage where the thickness of the observation cross section is thinned to 5 to 10 μm, the three points p1, p2, and p3 indicating the sample surface direction are written by etching using FIB or CVD, but no writing is performed. However, if there are three points that can be specified at appropriate places on the surface, they may be registered as a pattern. After the registration information is stored, the sliced sample is cut out from the sample body. The marks of this embodiment are the three points p1, p2, and p3 on the surface of the sample as described above. The sample after picking up is observed and takes a posture with respect to the FIB irradiation direction by matching with the registered pattern. . In order to perform accurate posture adjustment by this method, the three points p1, p2, and p3 need to be separated by a certain distance in both the X direction and the Y direction. Therefore, in the case of this embodiment, it is better not to perform the thinning process at this stage. Further, since the observation cross section is thinned by later processing, it is considered that this mark may be removed, so it is convenient to write it on both sides of the observation cross section. However, if the information is stored when the orientation of the sample section 2 is detected at the time of the first observation before cutting, there is no problem in subsequent processing and observation.
[0015]
When this pickup sample 2 is observed with the microscope function of the FIB apparatus, as shown in the lower side of FIG. 3B, if the observation cross section of the sample is not parallel to the FIB irradiation direction, a triangular shape connecting the three points p1, p2, and p3. The pattern does not match exactly when compared with the previously registered pattern and is distorted. Therefore, at that time, as shown in the upper part of the figure, the sample stage is adjusted so that the triangle connecting the three points in the microscope image matches the previously registered pattern. The state when they match is an arrangement relationship in which the observation cross section of the sample and the FIB irradiation direction are parallel to each other, and additional machining of the cross section with high accuracy can be executed based on this posture.
[0016]
【The invention's effect】
In the method for vertical positioning of a sample according to the present invention, before a sample section is cut out from a large sample by FIB processing, a pillar or a cut groove is formed in a direction perpendicular to the sample surface, or a two-dimensional pattern is marked. In this way, a mark indicating the vertical direction is attached, and observation is performed with an ion microscope at the time of additional processing, the posture of the sample piece picked up based on this mark is confirmed, and the original sample surface is controlled by the stage tilt control of the FIB apparatus. Since the sample section picked up so as to be perpendicular to the FIB direction is leveled, it is possible to perform additional processing by controlling the posture of the picked-up sample in a desired direction. Furthermore, in TEM sample processing before pick-up, it can be processed slightly thicker than the appropriate flake thickness, and can be made to an appropriate thickness by additional machining after actual TEM observation, so that proper and solid processing is possible. Yes.
[0017]
The sample having a mark indicating the vertical direction of the present invention is fixed in a form that stands on the surface of the sample stage so that the cut surface of the sample section can be observed, and the sample surface is attached to the upper surface of the sample section. Since pillars or grooves are formed in the direction perpendicular to the surface, when this sample is additionally processed, the surface direction in the original sample can be easily detected by observing the pillars or grooves with a microscope. The sample can be set in a desired posture by stage control. Therefore, machining with high accuracy is required.
The picked-up sample section is fixed in a standing state on the surface of the sample table so that the cut-out surface of the sample section can be observed, and a two-dimensional pattern is formed on the sample surface on the upper surface of the sample section. The sample having a mark indicating the vertical direction of the present invention is the original sample by performing stage control so that the two-dimensional pattern observed with a microscope matches the pattern written on the sample when the sample is additionally processed. Can be easily set in the surface direction. Therefore, the additional machining with high accuracy in the desired posture is processed.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram illustrating a production procedure of one embodiment of the present invention.
FIG. 2 is a diagram for explaining how to take a vertical direction in a sample according to the present invention.
FIG. 3 is a diagram for explaining how to take a vertical direction in another embodiment of the present invention;
FIG. 4 is a diagram illustrating a problem of the present invention.
FIG. 5 is a diagram illustrating a conventional technique that enables additional machining.
FIG. 6 is a diagram illustrating a conventional TEM sample and a TEM sample that can be additionally processed.
FIG. 7 is a diagram for explaining a conventional thinning process of a TEM sample.
FIG. 8 is a diagram for explaining a conventional method for producing a TEM sample.
[Explanation of symbols]
1 Sample body P Pillar 2 Sample section C Groove 3 Fixing base p1, p2, p3 Points to be registered 4 Hole 5 Glass probe

Claims (3)

  Before the step of cutting a sample section from a large sample in FIB processing, a mark indicating the direction perpendicular to the sample surface is attached to the surface of the sample section by using the FIB CVD or etching means in the FIB apparatus, At the time of additional processing, the mark is observed by the ion microscope function of the FIB apparatus, the posture of the sample section picked up based on the mark is confirmed on the sample fixing table, and the stage tilt control of the FIB apparatus is used to control the sample. A method for vertically positioning a pickup sample, characterized in that the surface of the section is perpendicular to the FIB direction.   The sample vertical positioning method according to claim 1, wherein the method for producing the mark is selected from any one of pillar production, cut groove processing, and two-dimensional pattern marking in a direction perpendicular to the sample surface. Using a charged particle beam to mark the sample in a direction perpendicular to the sample surface;
  Cutting a sample section together with the landmark using the charged particle beam;
  Fixing the cut-out sample section on a fixing table with the sample surface facing up;
  A step of observing the sample section fixed to a fixing table together with the mark with a microscope using the charged particle beam;
  Adjusting the inclination of the sample based on the observed mark so that the surface of the sample section is perpendicular to the charged particle beam;
  Processing the side surface of the sample section adjusted so as to be perpendicular to the charged particle beam using the charged particle beam to make a thin piece;
  A method for preparing a sliced sample comprising:

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