JP4357347B2 - Sample processing method and sample observation method - Google Patents

Description

  The present invention relates to a sample processing method, a sample processing apparatus, and a sample observation method for processing a sample for cross-sectional observation with a scanning electron microscope and a sample for a transmission electron microscope with a focused ion beam.

  As miniaturization of semiconductor devices progresses year by year, a scanning electron microscope (hereinafter abbreviated as SEM) and a transmission electron microscope (hereinafter abbreviated as TEM) are indispensable for structural analysis of semiconductor devices. In particular, for SEM observation and TEM observation of a specific cross section of a sample, a highly accurate cross-section forming technique and a thin piece sample processing technique are essential. In order to realize this, a processing method using a focused ion beam (hereinafter abbreviated as FIB) has been established.

  FIG. 2 is a diagram for explaining a sample processing method for observing a sample cross-section SEM by a conventional FIB. The outline is that a rectangular recess having a cross section to be observed as one surface is removed by sputtering by FIB irradiation. Specifically, it will be described with reference to the following drawings.

  FIG. 2A: Marks 13 and 13 'are applied to the target sample 11 by sputtering using FIB 14 so that the target cross-sectional position 12 can be identified.

  FIG. 2B shows a step of forming a surface protective film at the cross-sectional processing position. While irradiating the gas 16 from the nozzle 15 toward the region where the protective film is to be formed, the FIB 14 is scanned into a desired protective film shape. The gas 16 is decomposed by the FIB 14 to form a deposition film 17 made of a gas component. The deposition film 17 serves as a protective film when forming a cross section.

  The reason for forming such a protective film is as follows. That is, when the cross-section processing is performed with FIB on a material having unevenness on the sample surface, a striped artificial structure unrelated to the original sample structure is formed from the uneven edge portion in the FIB irradiation direction. For this reason, when the cross section is observed with a TEM or SEM, a shape different from the shape that should be originally observed is observed. An FIB assisted deposition film (hereinafter abbreviated as FIBAD film) is formed to flatten the sample surface so that such an artificial structure is not formed.

  FIG. 2C: A line segment connecting the marks 13 and 13 'is taken as one side, and the FIB 14 is scanned over a region 18 corresponding to a target recess.

  FIG. 2D: When the FIB 14 is scanned for an appropriate time, a recess 19 is formed in the scanning region 18. One of these cross sections is a cross section 20 to be observed by SEM or FIB.

  The TEM sample processing method by FIB is described in Japanese Patent Publication No. 99-05506 “Sample Preparation Apparatus and Method” (Patent Document 1).

To summarize the above prior art, when forming a cross section for observation by FIB, a FIBAD film was always formed for the purpose of flattening the sample surface so that an artificial structure was not formed in the cross section.
Special table 99-05506 Japanese Patent Application Laid-Open No. 5-28950

  High-resolution structural observation and ultrasensitive elemental analysis in a fine region are important for the development of semiconductor devices and magnetic devices. However, in the sample processing method for cross-sectional SEM observation using the current FIB and the TEM sample processing method, the following problems have become apparent.

(1) Problem of outermost surface damage in cross-section formation processing When preparing a cross-section of a mother sample, whether it is a cross-section to be observed by SEM or a thin sample to be observed by TEM, an FIBAD film is used to flatten the surface of the mother sample and protect the surface. Form. During the formation of the FIBAD film, the outermost surface of the sample is always slightly sputtered off, damaged by FIB irradiation, or the original structure of the mother sample surface is not preserved. For this reason, the structure of the outermost surface of the mother sample and the composition analysis may occur with low reliability. Since FIB irradiation damage during the production of the FIBAD film is inevitable, it has become apparent that it is difficult to produce a sample or a TEM sample for observing a cross section without damaging the outermost surface. Even if a cross section is produced without attaching a FIBAD film to the surface, the outermost surface of the sample is damaged by searching for a place to be processed with the FIB.

  Further, as a method of forming a film on the processed surface without using the FIBAD film, a method of forming the FIBAD film after thick deposition is conceivable. In this case, (a) a time loss is large because a vapor deposition apparatus which is a separate apparatus must be used. (B) It is not easy to deposit only in a specific micron region to be observed. (C) There is a problem that the bottom of the deep pore is not uniformly filled.

(2) Problems in TEM sample preparation Problems in the TEM evaluation of the contact hole shape immediately after etching in the semiconductor process will be described with reference to FIG.

  FIG. 3 shows the ideal shape of the cross section immediately after etching (FIGS. 3a and 3b) for the low aspect ratio (the ratio of the depth to the opening of the hole is not large), the mother sample of the high aspect ratio, and the actual shape. FIG. 3 is a diagram schematically showing a cross section (FIG. 3 b and FIG. 3 d) when a FIBAD film is formed and a cross section is formed by FIB.

  3A and 3B show a cross section of the hole 52 formed by etching the mother sample 50, and reference numeral 51 denotes the sample surface. The problem with the sample for forming the FIBAD film 53 is that the FIB is vertically irradiated on the bottom of the sample surface 51 and the hole 52, so that a damaged region 54 is formed on the bottom of the sample surface 51 and the hole 52. The damaged area on the side surface of the hole 52 is smaller than the sample surface 51 and the bottom surface of the hole 52, but is not completely absent. Since it is difficult to determine whether such a damaged region of the sample is caused by the contact hole formation process or the FIB irradiation at the time of sample preparation when evaluating the bottom of the contact hole 52 by TEM, the etching evaluation itself There was a problem that was not possible. Thus, there has been a demand for a TEM sample preparation method capable of accurately evaluating a damaged region generated in a process such as etching.

  Still another problem will be described with reference to FIGS. In recent devices, high aspect ratio (10 to 20) contacts have been used. When the shape of the contact hole 55 having such a high aspect ratio is observed in detail using a TEM or the like, the FIBAD film is formed as in FIG. When the protective film is formed, a void 56 is formed inside the contact hole 55. The cause is that the deposition film is formed early on the upper part of the contact hole, and the upper end is blocked by the film before the lower part is filled, and a void 56 is formed in the center of the hole. If such a void 56 is included in the sample to be cross-sectioned, an artificial structure (vertical stripe) 57 is formed on the downstream side in the FIB irradiation direction of the void when the cross-section is formed by FIB, and a contact hole of interest TEM observation at the bottom of 55 becomes quite difficult.

  From such problems, TEM evaluation of high aspect ratio contact holes can be performed without forming meaningless artificial structures in the original sample structure, and without forming irradiation damage due to FIB processing during sample preparation. Moreover, a method for forming a sample in a short time has been desired.

(3) Problem of TEM sample As the shape of the contact hole formed with the recent miniaturization of the semiconductor process, the depth, the hole entrance diameter on the sample surface, the diameter of the hole bottom, the inclination angle of the inner surface, Strict evaluation is required for a wide variety of areas such as irregularities. However, the conventional TEM sample preparation in which the hole is filled with a deposition film or the like and thinned to evaluate the TEM has the following problems.

  That is, when a contact hole (low aspect ratio) is observed with a conventional method by TEM, the contact hole 61 is filled with a metal FIBAD film made of FIB as shown in FIG. A film 62 is formed. When a TEM sample according to such a conventional method is observed with a TEM, as shown in FIG. 4B, the hole included in the thin piece portion 60 looks black and integrated in the thickness direction. Detailed shape and inner surface state cannot be grasped. In addition, the crystal damage 63 that can be observed on the sample side at the bottom of the contact hole cannot be determined whether it is caused by the etching process or by FIB irradiation during the formation of the FIBAD film, and thus little information is obtained. Further, as shown in FIG. 4C, when the micro sample 60 is further thinned in order to clearly observe the shape of the hole, the outline of the hole becomes clear, but this thin piece 64 is a section including the diameter of the hole, Since it is not possible to judge whether it is included or not, the inclination angle of the inner wall of the hole cannot be accurately evaluated, and the entire bottom surface cannot be obtained.

Summarizing the problems to be solved by the present invention from the above background,
(1) To provide a sample processing method for simply forming a surface protective film without performing a sample surface flattening operation using a FIBAD film, which has been performed prior to cross-section processing and thin piece processing by FIB,
(2) To provide a sample processing method capable of observing a cross-sectional structure even for a sample in which a void is easily formed by deposition, such as an aspect ratio contact hole,
(3) To provide a sample processing method capable of producing a TEM sample in which the shape information inside the contact hole can be obtained nondestructively.

  In order to solve the above-mentioned problems, in the present invention, instead of the FIBAD film that has been produced on the surface of the sample at the time of sample processing, a thin film different from the target sample is moved to the processing position to form a protective film. . The thin film is prepared in advance in the vicinity of the sample in the sample chamber, and the thin film is transferred by fine movement means provided in the sample chamber. The first problem can be solved by simultaneously performing FIB processing on the sample directly under the thin film thus transferred to produce a sample for SEM observation or a sample for TEM observation.

  In addition, in a sample having irregularities on the surface, the thin film is transferred so that the target concave portion is included in the protective thin film, and FIB processing is performed together with the thin film. Using a high-speed scanning electron microscope or a scanning transmission electron microscope The second and third problems can be solved by observing the object.

  According to the present invention, a surface protective film can be easily formed without forming a FIBAD film, which has been conventionally performed prior to the preparation of a cross-sectional observation sample or a TEM sample by FIB. In addition, since the FIB irradiation damage is not given to the outermost surface of the sample, it is possible to evaluate the sample surface with high resolution. TEM samples can also be made for materials that have voids inside by FIBAD, such as high aspect ratio contact holes.

Embodiments of the present invention will be described below with reference to the drawings. First, a configuration example of a sample processing apparatus that realizes the sample processing method of the present invention will be described with reference to FIGS. 10 to 12.
FIG. 10 is a diagram showing a configuration example of a sample processing apparatus according to the present invention. The sample processing apparatus 121 detects secondary particles such as secondary electrons and secondary ions generated from the FIB irradiation optical system 125 that irradiates the FIB 124 to the mother sample 123 placed on the sample moving stage 122 and the irradiation unit of the FIB 124. Secondary particle detector 126 and gas supply means 127 for supplying a gas necessary for forming the FIBAD film in the FIB irradiation region. The gas supply means 127 has a nozzle 128 having a diameter of about 50 μm in the gas irradiation section, and can supply gas only to the FIB irradiation section.

  The thin thin film 130 to be transferred to the surface of the mother sample 123 is installed in the thin film holder 131. This thin film holder 131 is installed in the wafer holder 132 that directly installs the wafer as the mother sample 123, and if necessary, the FIB. Move to the field of view and cut out the thin film 130 of a required size from the large thin film member with the FIB 124 or prepare the thin film 130 of a predetermined size and use the probe 133 to process the processing region of the mother sample 123 Can be transported. The probe 133 can be moved in at least three axes (vertical, parallel to the FIB scanning direction and perpendicular to the FIB scanning direction) in the sample chamber 135 by the probe fine movement mechanism 134. The micro sample fixing tool 136 is a member for fixing a micro sample extracted from the mother sample 123. The micro sample fixing tool 136 can be mounted on the micro sample fixing tool holder 137 and tilted as necessary.

  A specific configuration of the wafer holder 132 will be described later with reference to FIG. The surface and processed cross section of the mother sample 123 can be observed by the SEM optical system 139, and the SEM image can be displayed on the display means 140. Control of each part is performed by the SEM control device 141, the probe control device 142, the FIB control device 143, the gas supply control device 144, the secondary electron detection control device 145, and the stage control device 146 connected to the central control device 147. The central control device 147 has a function of issuing a command such as moving each mechanism system, and a function of accumulating data from each unit and performing calculation and storage.

  Next, a wafer holder 132 on which a thin film holder or the like is mounted will be described with reference to FIG. The mother sample 123 used here is a silicon wafer having a diameter of 300 mm, and is placed on a wafer holder 132 that can be attached to and detached from a sample moving stage 122 that is movable in the sample chamber 135. In addition to the mother sample 123, the wafer holder 132 includes a micro sample fixture holder 137 for installing a micro sample fixture 136, and a thin film holder 131 for holding a transfer thin film or a thin film member 130 capable of excising the micro thin film. Installed. The micro sample fixture holder 137 is mounted on the holder deck 138. In this embodiment, five are mounted, and the holder deck 138 can be tilted by a directly connected small motor or tilting mechanism 139, and a minute sample can be tilted substantially. With this structure, the processed surface of the extracted micro sample can be observed with an FIB or SEM, and the processed surface can be further freely processed.

  One or a plurality of micro sample fixtures 136 can be mounted on the micro sample fixture holder 137, and a plurality of micro samples can be fixed to each micro sample fixture 136. A small sample can be mounted. As specific numerical values, five micro samples are fixed to each micro sample fixing tool 136, and five micro sample fixing tool holders 137 carrying the micro sample fixing tool 136 are installed in the holder deck 138. In addition, 25 minute samples can be extracted and processed by one loading of the holder deck.

  The thin film member 130 is fixed to a thin film member holder 131 detachably installed on the wafer holder 132. The protective thin film can be excised from the thin film member 130 as necessary using a probe and transferred to a desired position on the mother sample 123. A specific example of the thin film member 130 is shown in FIG.

  FIG. 12 (a) shows an example in which a plurality of types of micro thin film members are mounted, and the transfer thin film portions 151a, 151b, 151c, 151d, which are micro thin films to be transferred, are provided in advance so as to be easily separated. And an opening 152 and a cut-out portion 153 that is a cutting edge by FIB. Specific dimensions are about 4 mm in length, 5 mm in width, and about 1 μm in thickness, and a reinforcing rim (not shown) is appropriately disposed on the back surface of the thin film member 130 to prevent bending. The material may be a metal such as copper or platinum, or silicon, and is manufactured using a semiconductor process or the like. If the width of the opening 152 is about 1 to 2 μm and the cutout 153 is about 1 to 2 μm, the excision time by FIB is only tens of seconds, and the probe is fixed to the corner of the transfer thin film unit 151 before the excision. By doing so, the minute thin film can be separated in about 1 minute. The thin film member is formed so that a large number of transfer thin film portions can be mounted, and FIG. 12 (a) is merely an example.

  FIG. 12B shows a state in which the transferred thin film portions 151 a and 151 b are extracted from the thin film member 130. For example, the transfer thin film portion 151a will be described. First, one end 156 of the transfer thin film portion 151a is excised with FIB, and then the probe 154a is brought into contact with the vicinity of the end portion of the transfer thin film portion 151a. Are connected by the FIBAD film 155a. Next, FIB is irradiated to a position 157 corresponding to the desired length of the fine thin film and cut. In the case of the transfer thin film portion 151a, since the width is 3 μm, the cutting by FIB irradiation is completed in about 1 minute. Thereby, the transfer thin film portion 151a can be completely separated from the thin film member 130, and the transfer thin film portion 151a can be transported to a desired place by the movement by the probe 154a. Similarly, the transfer thin film portion 151b can be transported by the above-described procedure, and can be moved to a desired position of the sample.

  FIG. 10 shows a configuration example of the sample processing apparatus according to the present invention including a case where the focused ion beam irradiation optical system is in a vertical relationship with the sample moving stage. However, the apparatus configuration is not limited to this, and the optical axis of the focused ion beam irradiation optical system may always be inclined with respect to the sample moving stage surface.

[Example 1]
As a typical embodiment of the present invention, a method for forming a cross section for observing a specific cross section with SEM or FIB will be described. The feature of the first embodiment is that, in the cross-section processing for forming a rectangular hole for cross-section observation by FIB irradiation, as shown in FIG. While the film was formed, the FIBAD film was not formed, and a thin film different from the target sample was transferred to form a surface protective film, thereby shortening the working time and making the sample surface non-damaged. There is.

Hereinafter, the procedure of the sample processing method will be described with reference to FIG.
FIG. 1 (a): marks 3 and 3 ′ indicating the cross-sectional position 2 to be observed on the surface of the sample 1 are applied by irradiation with the FIB 4. The shapes of the marks 3 and 3 ′ are not unique, but here, two minus signs are provided on the extension line of the cross-sectional position 2. After marking, the sample stage is moved so that the previously prepared thin film member enters the field of view (FIB irradiation range). The thin film member has a plurality of thin film parts to be transferred, and each of the thin film members can be easily removed by FIB. As the thin film component, a thin film having a desired size may be selected from the thin film member, or a thin film component having a desired size and shape may be freely cut out from the large thin film member with an FIB.

  FIG. 1B: The tip of the probe 6 is brought into contact with a thin film prepared in advance, and a FIBAD film is attached so as to be hooked on the tip of the probe, and the thin film and the probe are connected. The stage is moved so that the two marks 3 and 3 ′ installed in the process of FIG. 1A are in the field of view, and the probe 6 is moved and lowered so that the two marks 3 and 3 ′ are not hidden. The thin film component 5 is brought into contact with the sample 1 so as to cover the cross-sectional position 2. After the contact, in order to prevent the displacement of the thin film, the FIBAD film 7 is formed small so as to cover the thin film component 5 and the sample 1, and the thin film component 5 is fixed. Instead of the FIBAD film 7, the sample 1 near the end of the thin film may be irradiated with FIB to attach sputtered particles to the thin film component 5 to connect the sample and the thin film. The thin film component 5 is a substantially uniform thin plate having a thickness of about 1 μm, and has an arbitrary shape having sides of 10 to 20 μm in the plane. It may be of any shape that is large enough not to hide the previous mark in the surface direction. In this embodiment, the material was extracted by dissolving a silicon piece with acid and irradiating the thin film portion with FIB. The material is not limited to silicon, but may be formed from a metal material, and a thin piece whose thickness is controlled by a metallic mold can be formed by, for example, a plating method.

  After the thin film component 5 is fixed to the thin film 1, the tip of the probe 6 is irradiated with FIB to separate the connection between the thin film component 5 and the probe 6. Thereby, the transfer of the thin film component 5 to the sample 1 is completed.

  FIG. 1C: A line segment connecting two marks 3 and 3 ′ is set as a cross-section finishing position, and an area including this line segment (in this embodiment, a quadrangle) is set as a scanning range 8, and the thin piece 5 and the sample 1 are bonded with the FIB 4. Process.

  FIG. 1D: For example, the concave portion 9 is formed by scanning the FIB 4 in a 10 μm × 10 μm square region, and the cross section 10 to be observed last is finished to complete the cross section for SEM observation.

  The cross-section manufacturing method according to the present invention has an effect that the processing time can be shortened as compared with the conventional method of forming the FIBAD film in the cross-section manufacturing portion. Further, since the FIBAD film is not formed on the observation cross section, there is no FIB irradiation damage on the outermost surface portion of the sample 1 in the formed cross section 10, and there is an effect that the fine structure evaluation immediately below the outermost surface and the surface can be performed. .

  Here, known examples similar to the present invention will be shown to clarify differences from the present invention. Japanese Patent Application Laid-Open No. 5-28950 (Patent Document 2) discloses a method of processing a cross section for observation using a movable mask in a vacuum. This will be described with reference to FIG. The purpose of Patent Document 2 is to improve the processing position accuracy of cross-section processing, to form a cross-section at a desired position of a fine device, and to observe the structure of the cross-section. In order to realize this, in Patent Document 2, in the processing method of forming a desired cross section in the sample 502 by using the FIB 501, first, the square hole 503 is processed with the FIB 501 having a large current (FIG. 5A), and then vacuum A movable mask 504 that is movable inside and has a cleavage plane of the crystal as an end face is placed close to a desired cross section by a manipulator 505 (FIG. 5B), and the linear of the movable mask 504 is formed by a fine FIB 501 ′. Finishing is performed by scanning along the end face (FIG. 5C). It is assumed that a clear cross section 506 is obtained by such a method (FIG. 5D).

  On the other hand, the present embodiment is different from Patent Document 2 in the following points. (1) In the present invention, after the thin film material is moved to the sample surface, the cross section is processed by FIB. At that time, the end face of the thin film material (movable mask in Patent Document 2; thin film component in this embodiment) is used. The mother sample is simultaneously FIB processed together with the thin film material. That is, it is completely different that the thin film and the sample under the thin film are processed at the same time, and the thin film material does not necessarily have a linear end surface and does not need to have a rectangular shape. (2) The thin film of the present invention is not always connected to the probe for conveyance, but is connected to the probe when necessary, and is disconnected when it becomes unnecessary or fixed on the surface of the mother sample. (3) The thin film material in the present invention is not used only at the time of cross-section finishing by FIB, but is used from the first roughing. In this respect, it is fundamentally different from Patent Document 2.

[Example 2]
Most of the conventional cross-sectional observations using FIB processing have observed only one cross-section of the recess processing region by FIB. In this case, as shown in FIG. 2B, the FIBAD film is formed on the sample surface corresponding to the cross section to be observed. For example, when it is desired to observe two orthogonal surfaces using this conventional method, a FIBAD film must be formed on the sample surface corresponding to these two cross sections. If the cross-sectional lengths of the two surfaces are substantially the same, the FIBAD film forming time requires approximately twice the FIBAD film forming time by simple calculation as compared to the case of one cross-section. Further, in the case of three cross sections, the FIBAD film formation time is about three times as long. Also, the longer the cross-section length, the longer the FIBAD film must be, and the longer the formation time is. The second embodiment is a sample processing method for significantly reducing the processing time of a sample for evaluating such a large number of cross sections. In Example 2, a thin film component having a size covering a plurality of cross sections is used. This will be described with reference to FIG.

  FIG. 6 is a diagram showing a sample processing procedure for observing the four cross sections by SEM or FIB. Here, the cross section to be observed is four side surfaces with an opening of 10 μm × 10 μm and a depth of 5 μm. Hereinafter, it demonstrates along a figure number.

  FIG. 6A: This figure is a top view for explaining an example of how to apply marks. A mark 72 indicating a cross-sectional position 71 to be formed on the surface of the sample 70 is drawn by FIB irradiation. The cross-sectional position 71 consists of four cross sections. In Example 2, one side of the cross section was set to 10 μm, and a line segment having a length of 3 μm was applied to the mark 72 on the extended line.

  FIG. 6B is a perspective view showing a state in which the thin film component 73 is installed on the surface of the sample 70, and the size of the thin film component 73 is 8 indefinitely in the surface direction of about 12 × 12 × 0.5 μm. Install so that the mark 72 is not hidden. The thin film component 73 is fixed to the sample 70 by applying the FIBAD film 74 to a part of the thin film component 73. There is almost no FIB irradiation to the cross-section formation region, and the damage due to the FIB irradiation on the surface of the cross-sectional position 71 can be ignored.

  FIG. 6C is a perspective view when the concave portion 75 is formed in a rectangular shape on the thin film component 73 and the sample 70 directly below the thin film by FIB irradiation. Since the transferred thin film component 73 is located immediately above the four sample cross sections, the cross section can be formed with almost no sagging at the intersection between the cross section and the sample on all four surfaces. Since the time for installing the thin film can be shortened to about 1/10 of the formation of the FIBAD film having the same shape, the processing time from the laying of the mark to the completion of the formation of the four cross sections can be shortened. When observing the four-section sample with the SEM, the four sections can be easily observed by rotating the sample 70 in an inclined state.

Example 3
A sample processing method for TEM observation of a high aspect ratio contact hole without damage and at a high magnification will be described. The main points to realize this method are: (1) Regardless of the depth of the contact hole, the thin film component is transferred instead of the conventional FIBAD layer for filling the hole and protecting the surface. Process the sample with this thin film part. (2) The contact hole cross-section is held within the sample thickness without being exposed to the processed sample side wall. That is, the entire shape of the contact hole is built in the thin sample, and the shape of the contact hole is grasped three-dimensionally through the TEM or high acceleration SEM.

The procedure of the main point (1) will be described along the figure numbers in FIG.
FIG. 7A: First, a thin film component to be transferred is processed in advance. This may be created in the same environment immediately before creating the TEM sample, or the thin film member 81 created by another method may be brought into the sample chamber. Here, an example is shown in which FIB is created near the sample.

  The thin film component to be transferred has a size of 2 × 10 μm and a thickness of 0.5 μm. First, the FIB 82 is scanned on the thin film member 81 of 200 × 200 μm and thickness 0.5 μm to form a groove in the shape of “U”. By opening 83, a cantilever 84 having a width of 2 μm and a length of 10 μm is prepared. The material of the thin film member 81 used here is silicon. Of course, the size and material are not limited to this example.

  FIG. 7B: The wedge-shaped micro sample 87 including the target position of the sample 85 serving as the mother sample to be observed and supported by a single support portion 86 as shown in FIG. Created by drilling holes. The specific sizes were made of FIBs 88 and 88 ′ that were incident on the mother sample 85 from the vertical and inclined directions so that the width was 4 μm, the length was 15 μm, and the depth (the height of the sample) was 15 μm.

  FIG. 7C: The probe 89 is brought into contact with the tip of the cantilever 84 created earlier, and the FIBAD film 90 is formed so that the tip of the probe 89 is fixed to the tip of the cantilever 84. After fixing the probe 89, the other end 91 of the cantilever 84 is irradiated with FIB to cut out the rectangular fine thin film 92.

  FIG. 7D: By the above operation, the fine rectangular thin film component 92 to be transferred can be separated and transferred to the target position by the movement of the probe 89.

  FIG. 7E: The thin film component 92 is landed by moving the probe 89 to the surface of the wedge-shaped micro sample 87 created earlier. At this time, a FIBAD film 93 is formed on a part of the thin film component 92 and the sample surface, and the thin film component 92 and the micro sample 87 are integrated.

  FIG. 7 (f): FIB is irradiated to the support portion 86 that supports the micro sample 87, the support portion 86 is cut, and the micro sample 94 is separated and extracted from the sample 85 that is the mother sample.

  FIG. 7G: The extracted micro sample 87 is transported to and brought into contact with the upper surface of the micro sample fixture 95 by moving the probe 89 and the sample stage. After the contact, the micro sample 94 and the micro sample fixture 95 are fixed by the FIBAD films 96 and 96 '. Thereafter, the tip of the probe 89 is irradiated with FIB to completely separate the micro sample 87 and the probe 89. By these operations, the micro sample 87 can stand on the micro sample fixture 95.

  FIG. 7 (h): Together with the thin film component 92 moved last, both sides are removed by FIB with reference to a mark laid in advance to make a thin piece. At this time, a single contact hole or a single row of contact holes focusing on the thin piece portion 97 is included. This portion becomes a TEM observation region. A TEM observation sample is completed by the above operation.

  Next, the main point (2) will be described. FIG. 8A is a perspective view showing only the thin piece portion 92 in the TEM sample obtained by the operation described in FIG. In the observation sample 100 of this example, a row of contact holes 102 is included in the thin piece portion 101, and the transferred thin film 103 is in close contact with the upper portion. As described above, the thin film component 103 is made of silicon, the thin piece portion 101 is made of silicon oxide or silicon alone, and the contact hole 102 portion is a space.

  When such a thin piece portion 101 is observed with a TEM or STEM, or a high-acceleration SEM, the observed sample 100 can be seen through as shown in FIG. 8B and attached to the contour 104 and the inner surface of the hollow contact hole 102. It is possible to clearly observe the minute foreign matter 105 and the crystal defect 107 generated under the hole bottom 106. In this observation sample 100, since FIB is not irradiated to the hole bottom 106 during the preparation of the TEM sample, it can be interpreted that the crystal defect 107 measured on the bottom 106 is actually caused by the etching process. In addition, since the hole can be viewed through, the inclination angle of the side surface of the hole 102 and the flatness of the hole bottom 106 can be clearly measured.

  Next, when the sample is tilted in the STEM, the outline of the hole bottom 106 can also be observed. FIG. 8C is a transmission image (model diagram) when the observation sample 100 is slightly tilted around an axis orthogonal to the contact hole axis and the electron beam axis. Unlike FIG. 8B, the contact hole 102 can be observed three-dimensionally, and the contour shape of the hole bottom 106 can be clearly evaluated. Roughness can also be evaluated from the image contrast of the hole bottom 106.

  Thus, by using the sample processing method according to the present invention, the contact hole after etching can be evaluated in a multifaceted manner. As described above, in the TEM evaluation of the contact hole, the method of transferring the thin film component by the sample processing method according to the present invention to the surface of the mother sample compared to the conventional sample processing method by filling the FIBAD film is obtained. It can be seen that there is much more physical property information of the obtained samples.

  In the above description, the TEM observation of the sample obtained by the sample processing method according to the present invention has been described. However, the STEM (scanning transmission electron microscope) observation and the high acceleration SEM observation have similar advantages. In this embodiment, the sample processing method for TEM observation of the contact hole has been described in detail, but the target sample is not limited to the contact hole, and other samples can be processed by the same method.

The points in the third embodiment are summarized as follows.
(1) When evaluating the shape of the contact hole immediately after etching, it is covered with a solid thin film component so as to include the sample surface region of the target portion without using the conventional FIBAD film.
(2) The TEM sample is processed together with the thin film component so that the target portion is included in the TEM sample flake.
(3) The completed sample can be observed three-dimensionally with TEM, STEM or SEM with high acceleration voltage. The contact hole can be evaluated in detail by such a processing method and an observation method.

Example 4
Next, an example in which one noticed contact hole is observed from multiple directions will be described. The sample to be manufactured is not a thin piece shape but a columnar shape, and one contact hole is enclosed substantially coaxially therein. The processing method will be described with reference to FIG.

  FIG. 9A: The sample 110 has a plurality of contact holes 111 formed immediately after etching. Of these, the contact hole denoted by reference numeral 112 is the object of observation, and a mark 113 for discriminating this is formed on the surface of the sample 120 by FIB. Here, four line segment marks 113 are used around the contact hole 112 of interest.

  9B: The thin film component 114 is moved so as to cover the contact hole 112 of interest, the FIBAD film 115 is formed on a part of the thin film component 114, and the thin film component 114 is temporarily fixed to the sample 110. In this state, the sample is fixed to the micro sample fixture by the sample processing method shown in the third embodiment.

  FIG. 9C: The region other than the region 116 is removed using the mark 113 as a reference, and processed into a cylindrical micro sample. In this figure, the contact hole 112 of interest is indicated by a broken line, but it is not actually visible, and the processing is positioned by using the mark 113.

  FIG. 9D: The completed fine cylindrical sample 117 includes the contact hole 112 of interest in a hollow state. Although the thin film 114 is shown in this drawing, the thin piece 114 is only temporarily fixed partially as shown in FIG. 9B, and may be dropped when the fine cylindrical sample 117 is completed. However, there is no problem in observation. There is no problem because the thin film 114 is not removed during the processing.

  The fine cylindrical sample 117 produced by the above sample processing method is mounted on a TEM sample holder, and this TEM holder is loaded on the TEM. By rotating the shaft of the TEM holder, it is possible to rotate about the axis of the fine cylindrical sample 117, so that the contact hole of interest can be observed in detail by TEM from multiple directions and can be stereoscopically observed. By such an observation method, for example, the inclination angle of the inner wall of the hole can be evaluated over the entire circumference of the cylinder, and the delicate inclination of the hole and the opening of the hole can be evaluated.

The figure explaining the example of the cross-section formation processing method by this invention. Explanatory drawing of the conventional cross-section formation processing method. Explanatory drawing of the problem which has become obvious in the conventional TEM evaluation. Explanatory drawing of the problem of the TEM sample created by the conventional sample processing method. The figure explaining the difference with a similar well-known example. Explanatory drawing of the sample processing method suitable for evaluating the several cross section of a sample. Explanatory drawing of the processing method of TEM sample preparation. Explanatory drawing of the TEM sample created by the sample processing method by this invention. Explanatory drawing of the sample processing method for evaluating a contact hole in many aspects without damage. The figure which shows the structural example of the sample processing apparatus by this invention. Explanatory drawing of a wafer holder. Explanatory drawing of a thin film member.

Explanation of symbols

1: mother sample, 2: cross-sectional position, 3, 3 ′: mark, 4: focused ion beam (FIB), 5: thin film component, 6: probe, 7: FIBAD film, 8: processing region, 9: recess, 10 : Cross section, 11: Mother sample, 12: Observation surface position, 13, 13 ': Mark, 14: Focused ion beam (FIB), 15: Nozzle, 16: Gas, 17: FIBAD film, 18: Scanning region, 19: Processing region, 20: observation cross section, 50: sample, 52: contact hole, 53: FIBAD film, 54: damaged region, 56: void, 57: artificial structure, 81, 130: thin film member, 92, 151a, 151b: Thin film parts, 136: Micro sample fixture, 137: Micro sample fixture holder, 138: Holder deck.

Claims (8)

In a sample processing method for processing a sample by irradiating a focused ion beam,
A thin film transfer step of transferring the thin film component prepared in the sample chamber to the surface of the sample;
A processing step of irradiating the thin film component with the focused ion beam to form a cross section of the sample immediately below the thin film component together with the thin film component to produce a cross section of the thin film component and the sample;
A sample processing method comprising:   2. The sample processing method according to claim 1, wherein the thin film transfer step includes an excision step of excising a desired thin film component with the focused ion beam from a thin film member having a thin film component formed in advance. Sample processing method.   3. The sample processing method according to claim 1, wherein the thin film transfer step includes a gas-assisted deposition film by the focused ion beam irradiation or a sputtered film generated from the sample at the end of the thin film transferred to the surface of the sample. A sample processing method comprising a fixing step of fixing the thin film component by forming a thin film.   The sample processing method according to claim 1, wherein the thin film transfer step includes a connection step of connecting the thin film component to a movable probe.   5. The sample processing method according to claim 1, wherein the processing step is processing for forming a cross section of the sample.   5. The sample processing method according to claim 1, wherein an extraction step of extracting a micro sample to which a part of the thin film component is attached from the sample, and transferring the extracted micro sample to a micro sample fixture. A sample processing method, comprising a fixing step of fixing. In the sample observation method for observing the recess provided on the sample surface,
Transferring the prepared thin film parts to the sample surface;
Irradiating the thin film component with a focused ion beam to form a cross-section of the sample directly under the thin film component together with the thin film component, and extracting a micro sample containing the recess;
Slicing the micro sample containing the recess with a focused ion beam; and
A step of observing through the concave portion included in the thinned microsample through a transmission electron microscope or a scanning transmission electron microscope;
The sample observation method characterized by including. 8. The sample observation method according to claim 7 , wherein the recess is a contact hole.

Images