JP2009216478A - Method of manufacturing thin-film sample for observing transmission electron microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a thin-film sample for transmission electron microscopes can set a sample having not less than one observation place located at a deep region of not less than 10 μm from the surface to be an appropriate thin-film sample for TEM observation by an inexpensive and simple process. <P>SOLUTION: The manufacturing method of a thin-film sample for TEM observation includes: an extraction/fixation process of a minute sample piece 1 for extracting the minute sample piece from a sample 1 including an observation place inside at a depth of not less than 10 μm from the surface for adhering to a sample stand for TEM observation; and a thinning process for machining as a thin-film sample for TEM observation by focused ion beam irradiation machining in a direction vertical to the surface of the minute sample piece. In the manufacturing method of a thin-film sample for TEM observation, before the extraction process, an oblique cutting process is inserted to cut an upper-layer section 2 at the observation place of the sample 1 to not more than 10 μm from an oblique upper surface by the focused ion beam irradiation machining 7. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for preparing an observation sample for a transmission electron microscope (hereinafter referred to as TEM) using a focused ion beam (hereinafter referred to as FIB: Focused Ion Beam), and in particular, in the case of thinning a sample by FIB. This relates to a pre-processing method.

Transmission electron microscope (TEM) observation is effective for high-magnification observation for defect analysis and defect analysis of a fine portion of a sample such as a semiconductor wafer or semiconductor chip. In TEM observation, it is necessary to thin the sample to an extremely thin thickness of 0.1 μm or less so that the electron beam can pass through the sample. In recent years, it has become common to use FIB as a means for thinning a sample so as to enable such TEM observation. However, this FIB can be processed to a depth of several tens of μm or more over time, but in the sense of processing to obtain a good thin film sample having a thickness and surface state suitable for TEM observation, Processing at a depth of about 10 μm is the limit.
Two methods are known for producing a thin film sample for observation with a transmission electron microscope (TEM) by FIB. One of them is a method in which a semiconductor wafer, a semiconductor chip, or the like is cut into a sample block 14 of a size that can be mounted on a TEM apparatus by dicing using a diamond saw or the like, and then thinned by FIB only in the vicinity of the observation location. In this method, when there is an observation place in a deep region of 10 μm or more from the surface of the sample, as shown in the perspective view of FIG. For the cut sample block 1 (FIG. 4 (a)) consisting of the observation location 4 and the lower layer portion 6, the upper layer portion 2 having a thickness of 10 μm or more is removed by planar polishing or etching before processing by FIB. As shown in FIG. 4B, the observation point 4 indicated by hatching is positioned within 10 μm from the sample surface 1-1, and then processed by irradiation with FIB 7 as shown in FIG. It is necessary to. Or when removal of the upper layer part 2 is difficult, as shown to Fig.5 (a), (b), once the cross section of observation location 4 vicinity is produced, and the cross section is made into the surface, and it shows with a dotted line by FIB7 irradiation processing Thus, it is necessary to prepare the thin film sample 15 for TEM observation as shown in FIG. 5C (Non-patent Document 1).

Second, after extracting a micro sample piece of several μm to several tens of μm in size from a semiconductor wafer or semiconductor chip and bringing the micro probe (metal micro needle) equipped on the FIB into contact with the surface of the micro sample piece. While injecting a compound forming gas containing a conductive element such as platinum or tungsten as a component, a conductive film is deposited on the micro sample piece by a chemical reaction with an ion beam, and the micro probe and the micro sample piece are bonded. Next, the microprobe and the micro sample piece are moved and fixed to the mesh on which the TEM sample is placed by the same adhesion method as described above, and then the micro probe is separated from the micro sample piece. Furthermore, it is a method for producing an ultrathin thin film sample for TEM observation by FIB irradiation processing (this method is referred to as a method for producing a thin film sample for TEM observation by a microsampling method) (Patent Document 1).
In any case, the FIB can be processed so that the thickness and surface state are appropriate as a thin film sample for TEM observation. As described above, the depth is usually about 10 μm, and an observation region deeper than that is excellent with the FIB. Thinning is difficult.
According to the above-described microsampling method, according to the following Patent Document 1, a portion including an observation portion is cut out from a surface of a semiconductor wafer or the like by using an ion beam, for example, as a micro sample piece of 5 μm × 20 μm and a depth of 15 μm. Since the probe can be moved minutely as a micromanipulator and used like tweezers to directly extract the minute sample piece, it is also easy to specify a minute observation location in the sample. As described above, according to the microsampling method described in Patent Document 1 in which a target observation location is extracted with a size of several tens of microns without applying mechanical force, there is a risk of destruction of the observation location due to machining or the like. A TEM observation sample can be produced without concern.
Masao Hirasaka, Kentaro Asakura “FIB / Ion Milling Techniques for Electron Microscope Researchers Q & A” Agne Jofusha 2002 P59 JP-A-5-52721

However, according to the one method described in Non-Patent Document 1, the upper layer portion is thinned by FIB after removing the upper layer portion by planar polishing or etching on a sample having an observation portion in a deep region. There is a concern about the adverse effect of the removal process on the observation site. Furthermore, with this thinning method, it is difficult to cope with a sample having a plurality of observation locations having different depths. Also, in the case of a method in which a cross section in the vicinity of an observation point is once prepared and thinned by FIB irradiation processing using the cross section as a surface, there is a concern about the influence of machining during the cross section preparation. In some cases, it may be difficult to produce a cross-section. In addition, in either of the methods described above, the sample must be destroyed by cutting or polishing, and the sample preparation time increases considerably.
On the other hand, the second method described in Patent Document 1 is suitable when the observation location is at a shallow position within 10 μm from the sample surface, but when it is deeper than 10 μm, it is also observed in advance by some method. Since it is necessary to process the part within 10 μm from the surface, there is a problem that the process takes time or there is a concern that the processing may have an adverse effect on the observation part.
The present invention has been made in view of the above-described problems, and an object of the present invention is to perform a transmission electron microscope on a sample having one or more observation sites in a region deeper than 10 μm from the surface by a simple and inexpensive process. An object of the present invention is to provide a method for producing a thin film sample for observation with a transmission electron microscope, which can be a good thin film sample for observation.

According to the first aspect of the present invention, in order to achieve the object of the present invention, a micro sample piece is extracted from a sample including an observation site within a depth of 10 μm or more from the surface and transmitted. A step of extracting and fixing a micro sample piece to be adhered to a sample stage for observation with a scanning electron microscope, and a thinning step of processing as a thin film sample for transmission electron microscope observation by focused ion beam irradiation processing perpendicular to the surface of the micro sample piece In the manufacturing method of a thin film sample for transmission electron microscope observation, before the extraction step, the upper layer portion of the observation portion of the sample is cut to a thickness of 10 μm or less by focused ion beam irradiation processing from an oblique upper surface. A method for producing a thin film sample for observation with a transmission electron microscope into which a process is inserted is used.
According to the second aspect of the present invention, the extraction and fixing step of the micro sample piece includes a first step of cutting out a micro sample piece including an observation portion by focused ion beam irradiation processing, a metal micro A second step in which a needle is brought into contact with the surface of the micro sample piece; a conductive film is deposited on the micro sample piece by a chemical reaction while injecting a compound forming gas containing a conductive element as a component; The third step of bonding the sample piece, the metal microneedle is moved, the fine sample piece is brought into contact with the transmission electron microscope observation sample stage and bonded in the same manner as in the third step, and then the metal microneedle The thin film sample for observation with a transmission electron microscope according to claim 1, which has a fourth step of separating the sample from the minute sample piece.

According to the third aspect of the present invention, before the step of extracting and fixing the micro sample piece, the upper layer portion of the observation portion having a plurality of different depths of the sample is respectively inclined from the upper surface. The method for producing a thin film sample for observing a transmission electron microscope according to claim 2, wherein an oblique cutting step of cutting to a thickness of 10 μm or less is inserted by the focused ion beam irradiation processing.
According to the invention described in claim 4, the oblique cutting process is a process of cutting to a thickness of several μm or less by focused ion beam irradiation processing. It is preferable to use the method for producing a thin film sample for observation with a transmission electron microscope according to any one of the above items.
According to the invention of claim 5, the angle of the focused ion beam irradiation processing from the oblique upper surface is 30 ° to 60 ° with respect to the sample surface. It is more preferable to use the method for producing a thin film sample for observation with a transmission electron microscope according to any one of items 1 to 4.

  According to the present invention, for a sample having one or more observation points in a region deeper than 10 μm from the surface, the transmission electron microscope can be obtained as an excellent thin film sample for transmission electron microscope observation by a simple and inexpensive process. A method for manufacturing a thin film sample can be provided.

Hereinafter, a method for producing a thin film sample for observation with a transmission electron microscope of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the description of the examples described below unless it exceeds the gist.
As a method for producing a thin film sample for TEM observation of the present invention, a method for producing a thin film sample for TEM observation by cutting out the sample by dicing as described above and thinning by FIB irradiation processing, or a thin film for TEM observation by the micro sampling method described above. As a pretreatment such as a sample preparation method, details of adding a step of removing an upper layer portion of an observation portion deep inside 10 μm or more from the surface by FIB irradiation processing from the oblique upper surface will be described in detail.
FIG. 1 shows an oblique cutting process by FIB irradiation processing of a characteristic portion in the method for producing a thin film sample for TEM observation of the present invention, by oblique FIB irradiation and vertical FIB irradiation along the arrow direction from the oblique upper surface to the sample 1. It is a schematic perspective view which shows having formed the notch recessed part. A notch having an inclined surface above the target observation location by applying oblique FIB irradiation processing 7 and vertical irradiation to the sample surface 1-1 of the sample 1 composed of a stack of the lower layer portion 6, the observation layer 3, and the upper layer portion 2. A recess 12 is formed. When changing the FIB irradiation angle with respect to the sample surface 1-1, in practice, the FIB irradiation direction is fixed, and the angle is controlled by tilting a stage (stage) on which the irradiated sample (not shown) is placed. The irradiation angle is preferably 30 to 60 ° with respect to the sample surface 1-1. If the angle with the sample surface 1-1 is less than 30 °, the distance to be processed becomes longer with respect to the thickness of the upper layer portion to be removed, which is not preferable. If it exceeds 60 ° and is close to 90 °, it becomes close to cross-section processing, and it becomes difficult to aim at a target depth region when thinning the film.

An example of a method for producing a thin film sample for TEM observation according to the present invention in the case where the target observation location is one location is shown in FIG. 2, FIG. 6-1, and FIG. An example of a method for producing a thin film sample for TEM observation according to the present invention in the case where there are two observation locations is shown in FIGS. 2 and 3, (a), (c), and (e) are plan views of the position of the sample surface and the vicinity of the notch recess viewed from the sample surface side, respectively (b), (d), (F) is sectional drawing of a sample, and sectional drawing of the inclination surface vicinity in the notch recessed part formed by diagonal FIB irradiation processing, respectively. 6-1, FIG. 6-2, FIG. 7-1, and FIG. 7-2 each add a FIB irradiation process from a diagonally upper surface to a sample such as a semiconductor chip, so that the target observation location is the sample. It is a perspective view which shows the main processes of the method which can produce the thin film sample for TEM observation easily even when it exists in the place deeper than 10 micrometers from the surface. FIGS. 2G and 3G are cross-sectional views of the thin film sample for TEM observation when FIGS. 2E and 3E are viewed from the TEM observation direction, respectively.
According to the present invention, a sample composed of an upper layer portion 2 having a thickness of 10 μm or more, an observation layer 3 and a lower layer portion 6, and an observation at a certain depth in a part of the observation layer 3 as shown in FIG. It is a feature that a thin film sample for TEM observation can be produced by oblique FIB irradiation processing even for a sample having the location 4. According to the conventional microsampling method, for a sample having such a thick upper layer portion 2, the upper layer portion is processed in advance to a thickness of 10 μm or less by a method or means different from FIB irradiation processing. Otherwise, it was difficult to produce a thin film sample for TEM observation by FIB irradiation processing. However, the excision of the upper layer by a method or means different from that of the FIB has a concern about an adverse effect on the observation site. Furthermore, according to the present invention, as shown in FIG. 3, even when the observation layer 3 of the sample has the first observation location 4 and the second observation location 5 having different depths, the thin film sample for TEM observation is satisfactory. Can be manufactured. However, the maximum number of observation points is not limited to two in the method for producing a thin film sample for TEM observation according to the present invention.

A method for producing a thin film sample for TEM observation according to the present invention will be sequentially described below. As shown in the perspective view of FIG. 1 and the perspective cross-sectional view of FIG. 6-1 (b) for the sample 1 consisting of the upper layer part 2 having a thickness of 10 μm or more, the observation layer 3 and the lower layer part 6, the arrow A notch recess 12 having an inclined surface 11 formed by oblique FIB irradiation processing reaching the lower layer portion 6 from the surface of the upper layer portion 2 is formed by FIB irradiation 7 parallel to 7a. This inclined surface 11 is also shown in the plan view of FIG. 2C and the cross-sectional view of FIG. 2 (c) and 2 (d), when a thin film sample for TEM observation is used with reference to the distance from the boundary between each layer (2, 3, 6) of the sample block 1 and the sample surface 1-1. The center line 13 of the thin film sample for TEM observation indicated by the dotted line in FIGS. 2C and 2D is determined so that the observation location 4 is at least 10 μm or less, preferably several μm deep from the inclined surface 11. That is, in other words, when forming a thin film sample for TEM observation by irradiating and cutting in the vertical direction 7b by FIB from the inclined surface 11 having a distance of 0.05 μm or less on both sides across the center line 13, it is good. The center line 13 is determined so that the thickness of the upper layer portion 2 is at least 10 μm or less, preferably several μm, so as to be a thin film sample for TEM observation.
When there are two observation places, the first oblique FIB irradiation processing shown in FIG. 3C and the second oblique FIB irradiation processing shown in FIG. At this time, as shown in FIGS. 3C and 3D, on the center line 13 of the TEM observation thin film sample corresponding to the first observation location 4 determined from the oblique slope of the first oblique FIB irradiation processing. The second oblique FIB irradiation processing is performed so that the second observation location 5 is at least 10 μm or less, preferably several μm deep from the surface.

  Next, a protective film was formed on the surface of the sample portion to be thinned by ion beam assisted deposition such as platinum or tungsten according to the steps in the microsampling method, which is a well-known method described in Patent Document 1. After (not shown), as shown in FIGS. 2C, 2D, 3C, and 3D, a distance of about 0.5 μm to 1.5 μm on both sides across the center line 13 Is cut by FIB irradiation processing from the direction 7b perpendicular to the surface, as shown in FIGS. 6 (c), (d), (e), FIGS. 7 (d), (e), and (f). Cut out a piece. As shown in FIGS. 6-2 (e) and 7-2 (f), after attaching a microprobe (metal microneedle) 8 to the surface of the micro sample piece, the bottom surface of the micro sample piece is subjected to oblique FIB irradiation processing. Then, as shown in FIGS. 6-2 (f) and 7-2 (g), the micro sample piece 10 is completely separated from the sample 1, and moved to the fixed surface of the mesh sample stage and bonded (FIG. Not shown). Adhesion between the microprobe and the minute sample piece, and the fixed surface between the minute sample piece and the sample table can be performed using ion beam assisted deposition such as platinum or tungsten. Thereafter, the microprobe and the small sample piece are separated by FIB irradiation processing (not shown), and finally 0.1 μm as shown in FIGS. 2 (e), (f), 3 (e), and (f). FIB processing in the vertical direction is performed so that the thickness is as follows, and TEM observation is performed.

  When viewed from the direction of TEM observation, this thin film sample for TEM observation has two parts with different depths as shown in FIG. It is a thin film sample for TEM observation from which the upper layer portion is removed at the observation location. Although the above description is applied to the microsampling method, it can also be applied to the case where the sample is cut out by dicing or the like and then processed into a thin film sample for TEM observation by FIB. In that case, before or after dicing, The upper layer portion may be removed by FIB irradiation processing from the upper surface.

EXAMPLE 1 Hereinafter, Example 1 concerning the preparation method of the thin film sample for transmission electron microscope observation concerning this invention is demonstrated, referring FIG. 3, FIG. 7-1, FIG. 7-2.
(Sample block overview)
A sample block 1 was formed by laminating two layers of plating films on a copper frame. As shown in FIG. 3, the plating film on the surface with a thickness of 20 μm is the upper layer part 2, the second plating film with a thickness of 30 μm is the observation layer 3, and the copper frame is the lower layer part 6. A region having a depth of 10 μm from the interface with the upper layer portion 2 of the observation layer 3 is a first observation location 4, and a region having a depth of 20 μm is a second observation location 5.
(Removal of upper layer by oblique FIB irradiation processing)
As shown in FIGS. 7-1 (b) and (c) and FIGS. 3 (c) and (d), the first FIB irradiation processing 7 is performed at an angle of 45 ° with respect to the surface. The inclined surface 11 is observed from the surface, and the dotted line of 27 μm to the right in the drawing from the point A (FIG. 3C) where the sample surface 1-1 and the inclined surface 11 intersect is the center line 13 for thinning. At this dotted line 13, the first observation point 4 is 3 μm deep from the surface. Next, as shown in FIG. 7-1 (c), the second FIB irradiation processing 7-1 was performed. As shown in FIG. 3C, the second FIB irradiation processing 7-1 is performed at an angle of 45 ° with respect to the surface from the point A to 10 μm left in the drawing. As a result, the second observation spot 5 is also 3 μm deep from the surface.
(Micro sampling)
A protective film with a thickness of 1 μm is formed on the surface of the thinned portion by ion beam-assisted deposition of platinum so that the short side is in the thickness direction of the thin film to be produced with an area of 3 μm × 15 μm (not shown). As shown in FIGS. 7-2 (d) and (e), the periphery of the portion to be thinned by the FIB irradiation processing 7 from the direction 7b perpendicular to the surface was scraped to the edge of the platinum protective film to form a micro sample piece. As shown in FIG. 7-2 (f), after the microprobe 8 is bonded to the surface of the minute sample piece 9 by platinum ion beam assisted deposition, the bottom surface of the minute sample piece is cut by oblique FIB irradiation processing. As shown in FIG. 2 (g), the micro sample piece 10 was completely separated from the sample 1, moved to the sample fixing surface of the mesh, and adhered by ion beam assisted deposition of platinum (not shown). Thereafter, the microprobe 8 and the micro sample piece 10 were separated by FIB irradiation processing. (Not shown).
(Thinning by FIB irradiation processing)
As shown in FIGS. 3 (e) and 3 (f), the film was thinned with an ion beam until the thickness became 0.1 μm or less at which the electron beam was transmitted by the FIB irradiation processing 7 in the direction 7 b perpendicular to the surface. When viewed from the direction of TEM observation, as shown in FIG. 3G, the first observation point 4 and the second observation point 5 are at a depth of 3 μm from the surface.
(TEM observation)
When the TEM observation was performed on the thin film sample for TEM observation that had been thinned, the plating structure could be clearly observed at both the first observation location 4 and the second observation location 5 (the TEM observation figure is a figure). Not shown).

It is a schematic perspective view of the sample which shows having formed the notch recessed part by FIB irradiation processing from the diagonally upper surface in this invention. It is the top view and sectional drawing of the position of the notch recessed part seen from the sample surface and the sample surface side in case the observation location in this invention is one location. It is the top view and sectional drawing of the position of the notch recessed part vicinity seen from the sample surface and the sample surface side in case the observation location in this invention is two places. It is a perspective view which shows the method of producing the thin film sample for TEM observation in the conventional sample block. It is a perspective view which shows the different method for producing the thin film sample for TEM observation in the conventional sample block. It is a perspective view (the 1) which shows the main processes which produce the thin film sample for TEM observation in case the observation location in this invention is one location. It is a perspective view (the 2) which shows the main processes which produce the thin film sample for TEM observation in case the observation location in this invention is one location. It is a perspective view (the 1) which shows the main processes which produce the thin film sample for TEM observation in case the observation location in this invention is two places. It is a perspective view (the 2) which shows the main processes which produce the thin film sample for TEM observation in case the observation location in this invention is two locations.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sample 1-1 Sample surface 2 Upper layer part 3 Observation layer 4 1st observation location 5 2nd observation location 6 Lower layer 7 Focused ion beam, FIB, 1st FIB irradiation processing 7-1 2nd FIB irradiation processing 8 Microprobe, metal microneedle 9 Micro sample piece surface 10 Micro sample piece 11 Inclined surface 12 Notch recess 13 Center line 14 Sample block 15 Thin film sample for TEM observation

Claims (5)

Extracting a micro sample piece from a sample including an observation location within a depth of 10 μm or more from the surface, extracting the micro sample piece to be adhered to a transmission electron microscope observation sample stage, fixing step and perpendicular to the surface of the micro sample piece A thin film sample for transmission electron microscope observation having a thin film processing step for processing as a thin film sample for transmission electron microscope observation by a focused ion beam irradiation processing, before the extraction step, A method for producing a thin film sample for transmission electron microscope observation, wherein an oblique cutting step is performed in which an upper layer portion is cut to a thickness of 10 μm or less by focused ion beam irradiation processing from an oblique upper surface. Extracting and fixing the micro sample piece is a first step of cutting out a micro sample piece including an observation location inside by focused ion beam irradiation processing, a second step of bringing a metal micro needle into contact with the surface of the micro sample piece, A third step of depositing a conductive film on a small sample piece by chemical reaction while injecting a compound-forming gas containing a conductive element as a component, and bonding the metal microneedle and the fine sample piece, moving the metal microneedle And a fourth step of bringing the micro sample piece into contact with a sample stage for transmission electron microscope observation and adhering it in the same manner as in the third step, and then separating the metal micro needle from the micro sample piece. The method for producing a thin film sample for transmission electron microscope observation according to claim 1. Before the step of extracting and fixing the micro sample piece, the upper layer portion of the observation portion having a plurality of different depths of the sample is cut obliquely to a thickness of 10 μm or less by focused ion beam irradiation processing from the oblique upper surface. 3. The method for producing a thin film sample for transmission electron microscope observation according to claim 2, wherein a cutting step is inserted. The thin film sample for transmission electron microscope observation according to any one of claims 1 to 3, wherein the oblique cutting step is a step of cutting to a thickness of several μm or less by focused ion beam irradiation processing. Manufacturing method. The transmission electron microscope observation according to any one of claims 1 to 4, wherein an angle of the focused ion beam irradiation processing from the oblique upper surface is 30 ° to 60 ° with respect to the sample surface. Method for manufacturing thin film samples.

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