JP4185604B2 - Sample analysis method, sample preparation method and apparatus therefor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention provides a sample preparation method for observing a cross section of a target portion in a thin piece sample observed with a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), and sample analysis for analyzing the target portion The present invention also relates to a method and an apparatus for realizing the sample preparation or analysis method.
[0002]
[Prior art]
The TEM is a microscope that observes a TEM image formed by magnifying the transmitted electron beam by irradiating the electron beam to a thin sample that can transmit electrons, for example, about 0.05 to 0.4 μm. It is a microscope which scans the electron beam focused on the above-mentioned thin piece sample, introduce | transduces the transmitted electron beam into a detector, and acquires a STEM image. In any case, shape information accumulated in the thickness direction of the thin sample can be obtained because the electron beam is transmitted through the thin sample, but since it can be observed with high resolution, it is used for material evaluation in many fields including semiconductors. .
[0003]
In the manufacture of semiconductor devices, defective parts such as foreign matters, shape defects, disconnections, and short circuits detected in a certain manufacturing process are analyzed immediately to find out the cause of the occurrence, and there are many defective elements unless countermeasures are taken. Produced and has a significant impact on profits for manufacturing companies. For this reason, in order to improve the manufacturing yield of the semiconductor device, the defective portion analysis is essential. Of the defect analysis methods, TEM and STEM play a major role in shape observation. In addition, TEM and STEM are equipped with analysis functions, enabling high-resolution elemental analysis and indispensable for semiconductor analysis. It has become.
[0004]
In analysis by TEM or STEM (hereinafter abbreviated as analysis, representative of observation, elemental analysis, and measurement), a sample (hereinafter abbreviated as a planar sample) and a cross section in a horizontal direction with respect to the surface of the sample such as a semiconductor wafer or chip Observation is performed on a sample in a direction (hereinafter abbreviated as a cross-sectional sample).
[0005]
For cross-sectional samples, a method has been performed in which a cross-section is mechanically exposed and thin sections are processed in the cross-sectional direction by polishing and ion thinning. Recently, a method of accurately processing a desired region into a cross-sectional slice sample using a focused ion beam (hereinafter abbreviated as FIB) has come to be performed.
[0006]
First, a sample preparation method using polishing will be described with reference to FIG. As shown in Fig. A, a mark is made on an area to be observed with respect to the sample 20 such as a wafer, and the sample is scratched with a diamond pen or cleaved or cut into strip-shaped pellets 21 with a dicing saw, for example, along a cutting line (Fig. b). Next, in order for the central part of the TEM sample to be prepared to be an observation region, the surface 22 of the two strip-shaped pellets 21 is pasted with an adhesive 23 so as to face each other, thereby creating a laminated sample 24 (see FIG. c). The bonded sample 24 is sliced with a dicing saw or the like, and the slice sample 25 is cut out (FIG. D). The size of the slice sample 25 is about 3 × 3 × 0.5 mm. Furthermore, the cross section of the slice sample 25 is thinly polished on a polishing board to produce a polished sample 25 ′ having a thickness of about 20 μm, and this is attached to a single-hole mesh 26 mounted on the TEM sample stage (FIG. E), Ion thinning is performed by irradiating an ion beam 27 such as argon on both surfaces of the polished sample 25 '(FIG. F) to thin the central portion (FIG. G). When the hole becomes thin enough to open or not open in the center, the irradiation of the ion beam 27 is stopped, and the thin piece 28 (in the circle in Fig. H) thinned to about 100 nm or less is used as the TEM observation area. Yes.
[0007]
In addition, a method for producing a cross-sectional TEM sample by FIB is described in, for example, ECG Kirk et al., In the collection of papers Microscopy of Semiconducting Materials 1989, Institute of Physics Series No. 100., p. 501-506 (Prior Art 1). Yes.
[0008]
Hereinafter, an example of manufacturing a cross-sectional TEM sample by FIB will be described with reference to FIG. Mark the area of the sample 20 to be observed, such as a wafer, with a laser or FIB, dice the wafer as shown in Fig. A (the broken line is the cutting line), cut out the strip-shaped pellet 21, and pay attention to further observation Cut into pellets 21 ′ containing the part (FIG. B). The size of this pellet is approximately 2 × 0.1 × 0.5 mm. The pellet 21 ′ is attached to a TEM sample holder 29 made of a circular thin metal piece having a notch 29 ′ in part with an adhesive (FIG. C).
[0009]
The TEM sample holder 29 to which the pellet 21 'is fixed is introduced into the FIB apparatus, and processing is performed so that the thin piece portion 28' remains by irradiating a part of the surface 22 with the FIB 18. Processing is performed so that the concave portion 22 ′ is formed so that the thickness of the thin piece portion 28 ′, which is the observation region, becomes a wall of about 100 nm (this processing method is hereinafter referred to as thin wall processing) to become a TEM sample ( Figure e). In the TEM, the electron beam 65 is perpendicularly incident on the thin piece portion 28 '.
[0010]
Examples of the shape of the FIB-processed TEM sample are shown in FIGS. 4a and 4b. The cross-sectional shape is variously deformed, such as the convex shape in Fig. A and the L shape in Fig. B, but the basic point is to machine as thinly as possible to reduce the lower 30A and FIB machining area with some mechanical strength In the strip-shaped test pieces 21A and 21B having the upper portion 30B subjected to the above, a desired part of the strip-shaped test pieces 21A and 21B is processed into a thin piece portion 28 ′ by FIB so that electrons can pass therethrough. Finally, the thin-walled sample is placed on the TEM stage together with the sample holder, and introduced into the TEM device, so that the sample can be observed with a cross-sectional TEM. Such strip-shaped test pieces 21A and 21B can be mounted on the TEM sample stage 6 shown in FIG. 4c to perform FIB processing and TEM observation.
[0011]
The sample stage 6 includes a cylindrical portion 83, a grip 84 for holding or operating the sample stage 6, fixtures 32 and 32 ′ for holding the strip-shaped test piece 21A, and the most advanced of the sample stage 6 It is composed of small protrusions 87 for supporting a load, reducing vibrations, and preventing rotation of the rotating shaft. Further, since it has the notch 31 and can rotate the shaft, the thin piece portion 28 ′ can be rotated 90 ° after the thin piece portion 28 ′ is processed by FIB and can be observed by TEM. Although the supporting portion for supporting the small protrusions 87 is in the sample chamber substantially coaxially with the axis of the sample stage 6, the illustration is omitted, and since the cylindrical portion 83 of the sample stage 6 is long, the middle is omitted in the figure. The electron beam is incident on the flake portion 28 'almost perpendicularly. By this method, it becomes possible to position at the μm level, and a cross section from a certain direction of the specific region can be observed by TEM.
[0012]
As for the FIB apparatus, for example, LRHarriott describes in detail a paper entitled “The technology of finely focused ion beams” in the paper “Nuclear Instruments and Methods in Physics Research B55 (1991) p.802-p.810 (known example 2)”. It is stated. FIB is an ion beam in which ions emitted from a liquid metal ion source are focused to a diameter of several tens of nanometers by an aperture and an electrostatic lens, and this FIB is irradiated by deflecting and scanning a predetermined area of the sample surface with a deflection electrode. The surface can be sputtered according to the scanning shape to form a recess. Furthermore, by installing a gas supply unit in the FIB device and performing FIB scanning while introducing deposition gas and reactive gas, a deposition film of gas components can be formed in the scanning area, or at high speed Etching can be performed.
[0013]
On the other hand, a typical conventional method relating to a method for producing a planar sample will be described with reference to FIG. The sample is a wafer-like sample, and the analysis region is a specific region of the wafer and a 0.5 μm square region at a depth of about 1 μm from the surface. First, as shown in FIG. A, the wafer 20 is cut into a test piece 21 having a size of, for example, about 10 mm × 10 mm including a desired analysis portion using a diamond cutter or a die-thin saw (FIG. B). The broken line in FIG. A is a cutting line.
[0014]
The polishing jig (not shown) is bonded and fixed with the cut surface 21B (FIG. C) of about 1 mm square including the desired observation area of the cut piece 21 having its surface as an adhesive surface. There are various types of polishing jigs. Basically, using a polishing jig equipped with a micrometer head and other equipment capable of measuring dimensions on the order of μm, it is pushed onto the polishing board while adjusting the flatness of the sample. Apply and polish. The cut specimen 21B is polished from the backside of the wafer while adjusting the abrasive and the rotational speed of the polishing machine, and a polished sample 21C having a thickness of about 10 μm can be obtained (FIG. D).
[0015]
In order to make this polished sample 21C thinner, it is fixed to the single-hole mesh 26A (Fig. E), and further, the single-hole mesh 26A is rotated and obliquely irradiated with argon ions 27 from the front and rear surfaces as shown in Fig. F. . Finally, as shown in FIG. G, the thin film portion 28 thinned to about 100 nm or less around the center is used as a TEM sample.
[0016]
The thin sample 28 is mounted on a TEM stage together with the mesh 26A, and TEM analysis is executed. Observation of a planar TEM sample is very effective in, for example, investigating the distribution of crystal defects scattered in a material because a wide area of several hundred μm square can be observed at a time.
[0017]
Regarding the method of preparing a flat sample, for example, H. Cerva et al. In “Ultramicroscopy”, Vol. 52, (1993) 127-140 (Ultramicroscopy, 52 (1993) 127-140) “Specific preparation procedures”. Forn failure analysis of (sub) micron areas in silicon devices "(known example 3) is described in detail.
[0018]
There is a method for producing a TEM sample without cleaving the wafer. In the cross-sectional sample preparation method according to the above-described known example 2, the wafer must be cut, strip-shaped pellets including a desired analysis region must be prepared, and FIB processing must be performed. On the other hand, regarding a method of separating a part of the above sample into a TEM sample without cleaving the original sample such as a wafer, Japanese Patent Application Laid-Open No. 5-52721 “Sample separation method and separation obtained by this separation method” It is disclosed in “Analysis Method of Sample” (Known Example 4). This method is a method of separating a micro sample piece including a desired analysis region from a sample such as a wafer by using FIB processing and a micro sample transport means. By introducing the micro sample separated by this method into various analysis apparatuses, it is possible to analyze the defective portion without cleaving the original sample such as a wafer.
[0019]
This will be described with reference to FIG. First, by making the FIB 16 perpendicularly incident on the surface of the sample 20 and performing rectangular scanning, a square hole 33A having a required depth is formed on the surface of the sample 20 (FIG. A). Next, the sample 20 is inclined so that the axis of the FIB 16 with respect to the surface of the sample 20 is inclined at about 70 °, thereby forming the bottom hole 33B. The inclination angle of the sample 20 is changed by a sample stage (not shown) (FIG. B). The posture of the sample 20 is set so that the FIB 16 can be made perpendicularly incident again, and a notch groove 33C is formed (FIG. C).
[0020]
A manipulator (not shown) is driven, and the tip of the probe 34 at the tip of the manipulator is brought into contact with a portion where the sample 20 is separated (FIG. D). The deposition gas 36 is supplied from the deposition gas nozzle 35, and the FIB 16 is locally irradiated to the region including the tip of the probe 34 to form the deposition film 37. The separation part of the sample 20 in contact with the tip of the probe 34 is connected by a deposition film 37 (FIG. E). The remaining part is cut and processed with FIB 16 (Fig. F), and a hexahedral separation sample 38 can be cut out from sample 30. The separated sample 38 cut out is supported by the probe 34 (FIG. G). In this way, a minute sample can be extracted without cleaving the wafer.
[0021]
Furthermore, as another method for producing a TEM sample without cleaving the wafer, there is a method of extracting a micro sample using FIB and a probe. LA Giannuzzi, JLDrown, SRBrown, RBIrwin, and FAStevie in “Materials Research Society, Symposium Proceedings, vol.480 Specimen Preparation for Transmission Electron Microscopy 4”, “Focused Ion Beam Milling and Micromanipulation Lift Out for Site Specific Cross Section TEM Specimen This is shown in a paper entitled “Preparation” (Prior Art 5). In this state, the desired observation part is processed into a thin piece by FIB and separated from the sample substrate with respect to the sample substrate, the sample substrate is taken out into the atmosphere, and the needle-like probe is placed under the optical sample under the optical sample. In this method, a thin sample is adsorbed by electrostatic force and transferred to a mesh for TEM observation.
[0022]
In addition, F. Shaapur, T. Stark, T. Woodward., And RJGraham have also described “Evaluation of a new strategy for transverse TEM specimen preparation by focused Ion Beam Thinning” (p.173-180 of the same document as in known example 5) ( It shows a paper entitled Known Example 6). Also in this method, the same method as in known example 5 is used.
[0023]
[Problems to be solved by the invention]
Normally, images obtained by TEM or STEM are images that have passed through a thin sample, so that information in the thickness direction of the thin sample appears to overlap. For this reason, it is difficult to accurately analyze the shape of the thin sample in the thickness direction. In particular, the structure of recent semiconductor devices is so fine that it enters a thin sample of about 0.2 μm. For example, the smallest plug will enter a thin sample having a diameter of about 0.1 μm and a thickness of 0.2 μm. In addition, once a thin piece sample is prepared, the shape in the thickness direction cannot be grasped because the viewing angle cannot be changed from a right angle, and the plug shape cannot be accurately interpreted from the TEM image. It ends in. Furthermore, even if the two-dimensional distribution of the flakes is clarified using elemental analysis means such as EDX, the three-dimensional element distribution of the previous plug cannot be grasped.
[0024]
Therefore, if a method capable of observing from the cross-sectional direction of the thin sample for the same observation spot observed in plan for the thin sample for TEM observation is realized, the structure in the thin sample as described above is three-dimensionally formed. It is very effective in grasping. Therefore, it is very important to realize a simple and reliable method for producing a cross-sectional sample of a thin piece sample, an apparatus therefor, and a sample analysis method using such a flat and cross-sectional sample.
[0025]
When a cross-sectional sample is produced from a thin sample or a thin piece produced by polishing or the like with the current technology, a curable material 42A such as epoxy is provided on both sides of the thin piece sample 40 including the target portion 41 as shown in FIG. Cover (embed) with 42B and solidify to form an embedded sample 43 (Fig. B). Thereafter, as shown in FIG.c, the embedded sample 43 is cut in a direction perpendicular to the original thin sample 40, and both sides of the slice sample 44 are polished to obtain a cross-sectional thin sample 44 ′ having a thickness of about 0.1 to 0.2 μm. Is made. After further ion thinning, the cross section of the target portion 41 can be observed by making the electron beam 65 substantially perpendicularly incident on the cross-sectional thin sample 44 ′ as shown in FIG.
[0026]
In this method, the cross-sectional thin sample 44 'must also be processed to a thickness of about 0.1 to 0.2 μm, and the desired attention area 41 detected by the thin piece TEM observation as shown in FIG. In this case, it is almost impossible to fit the attention portion 41 in the thin-section sample 44 ′. That is, there is no position controllability. In addition, labor and time such as embedding, flake processing, polishing and ion thinning are required. Therefore, even if polishing is performed for a long time, the desired target part is not included in the cross-sectional slice, and the initial purpose of observing and analyzing the target part by changing the viewpoint by 90 ° cannot be achieved at all. In most cases, the success rate is very low.
[0027]
The known example 2 has an advantage that the cross-section flakes can be manufactured in a short time with higher processing accuracy than the conventional polishing method. However, once a conventional TEM sample as shown in FIG. 4a is produced, in order to process the cross-section of the thin piece portion 28 'so that it can be observed by TEM, TEM observation cannot be performed unless both sides (upper portion 30B) of the thin piece portion are deleted. . In particular, it takes an enormous amount of time to process the sample 21A, which is 2 mm to 3 mm in the longitudinal direction, to thin the both sides of the thin piece portion 28 ′ to several hundred μm, and when taking a method of adding machining such as dicing, This also causes a fatal problem of damaging the precious flake 28 ', and the application of these conventional methods has not been practical.
[0028]
In the known example 4, once the sample is set on the sample stage, it is not necessary for a human to directly perform manual work until separation of a minute sample, and it is not necessary to cut the wafer unnecessarily. However, in this method, since the separated sample piece is supported by the probe, in order to form a cross section of the thin piece portion, the position of the probe must be controlled in a complicated manner. In addition, it is not easy to introduce a probe into a TEM in order to observe the formed cross section because of limitations on the positional relationship and angle relationship between the observation surface and the probe. Furthermore, when the bottom hole 33B is formed, the sample stage must be tilted as much as 70 °, and a sample stage on which a large-diameter wafer is placed is not practical in terms of structure and accuracy.
[0029]
In addition, in the known examples 5 and 6, the thin piece of the target portion can be taken out of the sample substrate by electrostatic force, but since the extracted thin piece sample is attached to the mesh with an adhesive, it cannot be reprocessed. ing. That is, the processing for observing the cross section of the thin sample observed by TEM cannot be performed. In addition, these methods have a problem that the observation part of the thin sample is unfortunately overlapped with the mesh because it is an operation of attaching the extracted sample to the mesh under an optical microscope. Further, as described in the known examples 5 and 6, the sample is adsorbed by the electrostatic force with the probe, so that there is a defect that the adsorption is not reliable.
[0030]
As described above, in spite of many conventional techniques, there is no simple and reliable sample preparation method for observing the cross section of the thin sample, and it is difficult to observe the cross section easily.
[0031]
Therefore, in view of the above-mentioned problems of the prior art, a first object of the present invention is to perform a sample analysis method for observing and analyzing a target portion of a thin sample with a TEM or STEM from a horizontal direction and a cross-sectional direction. The second purpose is to provide a sample preparation method for observing a cross section of a target portion in a thin piece sample to be observed by TEM or STEM. Further, as a third purpose, An object of the present invention is to provide a sample preparation apparatus for realizing the first object or the second object.
[0032]
[Means for Solving the Problems]
The first object is realized by a sample analysis method having the following configuration.
[0033]
(1) Planar observation process for observing a thin piece sample with a transmission electron microscope (hereinafter referred to as TEM) or a scanning transmission electron microscope (hereinafter referred to as STEM), and extracting a thin thin piece sample including a desired portion of interest from the thin piece sample By a method including at least a cross-sectional thin piece processing step of processing the micro thin sample into a cross-sectional sample perpendicular to the surface of the thin sample, and a cross-sectional observation step of observing the micro cross-sectional sample by TEM or STEM, A sample analysis method for analyzing the target portion from a plane direction and a cross-sectional direction.
[0034]
(2) A thin piece processing step for processing a sample into a thin piece sample, a planar observation step for observing the thin piece sample by TEM or STEM, an extraction step for taking out a fine thin piece sample including a desired target portion from the thin piece sample, and the above An adhering step for adhering a micro thin sample to a sample holder, a cross-sectional thin piece processing step for processing into a cross-sectional sample perpendicular to the surface of the thin sample, and a cross-sectional observation step for observing the micro cross-sectional sample by TEM or STEM The sample analysis method which analyzes the said attention part from a plane direction and a cross-sectional direction by the method of including.
[0035]
(3) Planar observation process for observing a thin piece sample mounted on a side entry type sample stage by TEM or STEM, and a microscopic part including a desired target portion from the thin piece sample mounted on a sample preparation device for processing the thin piece sample Extraction step for taking out the thin sample, fixing step for fixing the micro thin sample on the sample holder previously mounted on the sample stage, and production of a cross-sectional thin sample perpendicular to the surface of the thin sample on the sample holder A sample analysis method comprising: a cross-sectional slice processing step to perform; and a cross-section observation step of observing the cross-sectional slice sample by introducing the sample stage into the TEM or STEM.
[0036]
(4) In particular, whether the cross-section slice processing step of the sample analysis method of any one of (1) to (3) above is performed by focused ion beam irradiation,
(5) The extraction process and the fixing process in the sample analysis method of (2) or (3) are performed by irradiation with a focused ion beam.
[0037]
(6) In the above method, the above attention is obtained by the image information by TEM observation or STEM observation in the planar direction of the target portion of the thin sample and the image information by TEM observation or STEM observation of the cross section of the target portion of the thin sample. Sample analysis method to grasp the pseudo three-dimensional shape of the part.
[0038]
(7) In the above method, the information on the target portion of the flake sample is simulated by the TEM analysis or STEM analysis, and the information on the cross section of the target portion of the flake sample is analyzed by the TEM analysis or STEM analysis. A sample analysis method to grasp the three-dimensional element composition.
[0039]
The sample preparation as the second object is realized by a method having the following configuration.
[0040]
(8) Extracting the minute thin piece sample including the attention part from the thin piece sample to be observed or analyzed by TEM or STEM, and observing the attention part from a direction parallel to the surface of the thin piece sample. A sample preparation method in which processing is performed so that electrons can be transmitted in the direction of a thin sample surface.
[0041]
(9) An extraction step of taking out a minute thin piece sample including a target portion from a thin piece sample through which electrons can pass, a fixing step of fixing the extracted minute thin piece sample to another member, and a part of the thin piece sample A sample preparation method in which a cross-sectional thin sample having a thickness that allows electrons to pass through is processed.
[0042]
(10) A thin piece processing step for processing the target sample into a thin piece sample through which electrons can permeate, a flat TEM observation step for observing the thin piece sample by TEM or STEM, and a desired target portion from the thin piece sample An extraction step of taking out a minute thin piece sample containing, an adhering step of adhering the minute thin piece sample to a sample holder, an electron permeation that is substantially perpendicular to the surface of the minute thin piece sample including a target portion of the minute thin piece sample A sample preparation method including a cross-section processing step of processing into a thin-section sample having a thin cross-section.
[0043]
(11) An extraction process for extracting a part of the thin TEM sample including the target portion from the thin sample for TEM observation mounted on the side entry type sample stage, and the fine thin piece on the sample holder previously mounted on the sample stage. A fixing step for fixing the sample, and a cross-section processing step for processing into a cross-sectional thin sample of a thickness that is perpendicular to the surface of the micro thin sample and includes a target portion of the micro thin sample, and is thin enough to transmit electrons. Including a sample preparation method.
[0044]
(12) The sample preparation method, wherein the processing of the thin sample and the fine thin sample in (9) or (11) includes at least processing with a focused ion beam.
[0045]
(13) The sample preparation method in which the thin piece sample and the cross-sectional thin piece sample in any one of (9) to (12) are thin piece samples for observation or analysis by TEM or STEM.
[0046]
(14) The extraction process according to any one of (9) to (13) described above is a process in which a protective film is formed in a region including the target portion, and a focused ion beam is irradiated around the region including the protective film. The process of processing into a cantilever sample held by a part of the thin sample, the process of fixing the conveying means to the cantilever sample, and the process of separating the cantilever sample from the thin sample A sample preparation method including at least.
[0047]
(15) The fixing process in any one of (9) to (13) above, or the process of fixing the transport means to the cantilever sample in (14) is based on a local deposition film using a focused ion beam and a deposition gas. A sample preparation method that is adhesion.
[0048]
(16) The extraction process in any one of (9) to (13) above is performed by using a TEM or STEM image of the thin sample obtained by TEM or STEM observation and a secondary of the thin sample obtained by irradiation with a focused ion beam. A sample preparation method including a process of superimposing an electronic image and specifying a position of the target portion.
[0049]
(17) The extraction step in any one of (9) to (13) described above is a process of storing a TEM or STEM image of the thin sample including the target portion and a characteristic pattern of the TEM image or STEM image. A calculation process for forming a line, and a process for identifying the position of the desired target portion by superimposing the secondary electron image of the surface of the thin sample obtained by irradiation of the focused ion beam and the contour line. Including a sample preparation method.
[0050]
The third object is realized by an apparatus having the following configuration.
[0051]
(18) A focused ion beam irradiation unit that irradiates a desired region of a thin sample with a focused ion beam, a secondary particle detector that detects secondary particles generated from the sample by irradiation with the focused ion beam, and the focusing A deposition gas supply source for forming a deposition film in the ion beam irradiation region, a sample stage on which the thin sample is placed, and a minute thin sample obtained by separating a part of the thin sample are transferred to another member. A sample preparation device having a transfer unit and a sample holder holding unit for holding a sample holder on which the micro thin sample is placed.
[0052]
(19) The sample stage of (18) is a sample preparation device having a structure having a mesh holder fixing portion for attaching a mesh holder for fixing a TEM mesh, or (20) the sample stage of (18) is a mesh A sample preparation device which is a side entry type sample stage having a holder fixing portion and the sample holder holding portion.
[0053]
(21) The sample preparation device according to (20), wherein the sample fixing unit is a fixing unit for attaching a mesh holder for fixing a TEM mesh on which a thin sample is mounted.
[0054]
(22) In any one of the above (18) to (21), in particular, the sample preparation device in which the surface on which the micro sample is placed in the sample holder and the surface of the mesh are in a parallel positional relationship.
[0055]
(23) The sample preparation device in which the side entry type sample stage in (20) is a structure that can be inserted and removed in common with at least one of TEM or STEM and the sample preparation device.
[0056]
(24) In the above (18), it has a calculation processing unit for receiving TEM image information by TEM or STEM, or
(25) In the above (18), it has a calculation processing unit for receiving image information by TEM or STEM stored in a computer via a network, or
(26) In (18), at least the TEM image information and the secondary particle image information by irradiation with the focused ion beam are stored, and at least a composite image obtained by superimposing the TEM image information and the secondary particle image information is formed. A sample preparation apparatus comprising: a calculation processing unit to be created; and an image display unit that displays at least one of the TEM image information, the secondary particle image information, or a composite image of both.
[0057]
The sample preparation apparatus as the third object is as follows.
(27) The sample preparation system may include a sample preparation device, a TEM or STEM, a computer, the sample preparation device, and a network connecting the TEM or STEM and the computer.
[0058]
Furthermore, as a sample holder for realizing the sample preparation apparatus which is the third object,
(28) A sample holder for a TEM or STEM for fixing a micro thin sample obtained by separating a desired part of a thin sample, in particular, a prismatic shape or a shape having an arc portion, or
(29) The prismatic cross section in (28) above is particularly convex, L-shaped or rectangular, or
(30) The location for fixing the microlamellar sample in (28) or (29) above is a recess provided in a substantially central portion in the longitudinal direction of the sample holder, or
(31) In the above (30), in particular, a sample holder in which a support base lower than the depth of the recess and thinner than the width of the sample holder is installed at the bottom of the recess to fix the micro thin sample is preferable. It is.
[0059]
Moreover, as a form of the sample for achieving the third object,
(32) It is preferable that the sample to be observed or analyzed from at least two perpendicular directions by TEM or STEM is a sample processed into a shape including a square column having a height of 0.4 μm or less, a width of 0.4 μm or less, and a length of 1 μm or more. It is.
[0060]
DETAILED DESCRIPTION OF THE INVENTION
In the embodiment of the sample analysis method according to the present invention, after observing or analyzing a desired region of a thin sample that can transmit electrons by TEM or STEM, the desired portion of the thin sample is further converted into a cross-sectional thin piece. It is a method of processing and observing or analyzing with TEM or STEM.
[0061]
Specific examples of the present invention will be described below, and further, examples of the sample preparation method and sample preparation apparatus according to the present invention will be described with reference to FIGS. 9 to 16. Here, the terms are first unified. This will be described with reference to FIG.
[0062]
As shown in FIG. 8a, a sample having a thin piece portion 45 at least partially capable of TEM observation, or a thin plate-like sample over the entire surface as shown in FIG. Called. The thin sample 46 refers to a flat TEM sample parallel to the reference plane of the original sample or a vertical cross-sectional TEM sample. In order to observe the cross section of the thin piece part 45 or the thin piece sample 46, extracting a part of the thin piece part 45 as shown in FIG.
[0063]
Here, the symbol D is the incident direction of the electron beam when the thin sample 46 is observed on a plane, and the thickness E of the thin sample is preferably about 0.05 μm to 0.4 μm. Also. The extracted sample is referred to as a micro thin sample 47 (FIG. 8d). Here, the cross-sectional observation direction indicates F or F ′, but the processing time is shorter as the width parallel to the observation cross-section is thinner. A sample obtained by processing at least a part of the width of the minute thin piece sample 47 so as to pass through an electron beam is referred to as a cross-sectional thin piece sample 48. Reference symbol D ′ represents the incident direction of the electron beam when observing the cross-section of the cross-sectional thin sample 46, and the width E ′ of the sample at this time is preferably about 0.05 μm to 0.4 μm.
[0064]
<Example 1>
The sample analysis method of the present invention will be described with reference to FIGS. 9 and 10 with examples. In this example, as a result of performing electrical inspection on the semiconductor device for which the manufacturing process has been completed, a malfunctioning portion is detected, planar TEM observation is performed on the defective portion, and defects found by observation are further observed in the cross-sectional direction (planar TEM). An example of observation from the side direction of the sample will be described. Hereinafter, in order to clarify the procedure of the sample analysis method, it is divided into several steps and explained.
[0065]
(1) Thin section processing for planar TEM
First, with respect to a semiconductor device, coordinate information of a malfunctioning portion (hereinafter collectively referred to as a target portion) is stored by an electrical inspection device such as a prober. The storage of the coordinate information is stored in the calculation processing device as the coordinate information of the defective portion with reference to the chip mark previously set on the chip. Based on this coordinate information, out of the chip (about 8mm x 15mm), a small piece of about 1mm square including the target part is mechanically cut out from the back of the chip using the conventional technique as shown in Fig. 4 By flattening and ion thinning, the flattened TEM sample is made into thin pieces until the thickness of the target portion becomes about 0.1 μm. This thin sample is attached to a mesh and mounted on a TEM stage. Since the structure of the TEM stage is an important part of the present invention, it will be described in detail in a later embodiment.
[0066]
(2) Planar TEM observation
A TEM stage is introduced into a TEM or STEM for observation. The TEM observation method is known and will not be described in detail here. As a result of observing the same coordinate area with the TEM based on the coordinate information of the defective part previously stored by observation, it is assumed that a minute linear defect having a length of about 3 nm is found in the visual field. TEM image information obtained by planar TEM observation is stored in the TEM calculation processing unit from low magnification to high magnification. The calculation processing unit can process the TEM image information as necessary to display the target portion and other characteristic structures and forms in outlines. Furthermore, the acquired TEM image can be subjected to processing such as enlargement / reduction, front / back reversal and left / right reversal, and can be stored.
[0067]
(3) Extraction of small thin sample
This step is an operation of setting a sample stage in a sample preparation apparatus and extracting a minute thin piece sample including a target portion from the above thin piece sample. This process will be described with reference to FIG.
[0068]
FIG. 9a shows a flake sample 50 secured to a mesh or the like. However, the mesh is not shown. The thickness is about 0.1 μm and the size is about 1 mm square, but is not particularly limited. First, when a minute thin piece sample including a target portion is extracted from the thin piece sample 50, the target portion must be accurately grasped. In particular, it is very difficult to locate the target area from the SIM image (secondary electron image obtained by FIB scanning, Secondary Ion Microscopy) It becomes. Although the surface shape of the sample can be observed with a SIM image, internal defects that can be observed with a TEM cannot be observed, so even if you try to pick out the part of interest that contains internal defects, the exact processing position cannot be determined from the SIM image. It is. Therefore, the following method for determining the processing position based on the TEM image was adopted.
[0069]
Here, a method for determining the machining position will be described with reference to FIG. FIG. 16a is a TEM image. In the observation visual field 110, it is possible to confirm the presence of the internal defect 111, the surface foreign matter 112, 112 ′, and the point defect 113 or the line defect 114 of interest. This TEM image information is temporarily stored in a computer.
[0070]
FIG. 16b is a SIM image. The SIM image field 115 is wider than the TEM image field 110. Since the SIM image can observe the morphology of the sample surface, the surface foreign matter 112, 112 ', and other surface foreign matters 116, 117, 118, and 119 that can be observed by the TEM image can be observed. This SIM image information is also stored in the computer. The above computer processor does not have to be the same as the computer processor that stores the previous TEM image information, and it is sufficient if the image information can be called to a specific computer processor and edited and analyzed as necessary. Here, the previously stored TEM image information is called to another computer via the network, and the observation magnification, field of view, removal of unnecessary background signals, emphasis on internal defects of interest, emphasis processing of surface foreign matter, etc. Is carried out by a computer, and the SIM image field 115 is superimposed on the surface foreign matter 112, 112 'in both the TEM field and the SIM field.
[0071]
FIG. 16c is a composite image 120 in which the SIM image and the processed TEM image are superimposed. In this composite image 120, the TEM image processed by reference numeral 110 'can confirm the positional relationship between the internal defect 111, the point defect 113, and the line defect 114 of interest that could not be recognized from the composite image by the SIM image. The extraction region 121 necessary for TEM observation of the internal defect 111 from its side surface can be determined.
[0072]
In the above image processing, in order to distinguish the sample or image from the TEM image or SIM image, for example, identification numbers 122a, 122b, 122c and symbols are entered as image information, and further extracted in the subsequent steps. By entering the identification numbers and symbols corresponding to the micro-thin specimens in the FIB, the management of SIM images, TEM processed images, and specimens is ensured.
[0073]
Based on the composite image 120 obtained in this way, marking is performed so that the position of the target portion can be recognized.
[0074]
FIG. 9b shows an example of how to attach the mark 51. For example, the mark 51 is applied to both ends forming the observation cross section by FIB 52 or laser processing. The mark 51 'is a mark with a narrow line width in order to realize more precise alignment. In this example, four line segment marks 51 are applied by irradiation with FIB 52 at intervals of 10 μm and 1 μm across the observation region.
[0075]
Next, as shown in FIG. 9c, a protective film 53 for protecting the sample is formed so as to cover the line segment connecting the two marks 51. The protective film 53 can form a metal film in the scanning region by scanning the FIB 52 in a rectangular shape while supplying a deposition gas. In this example, a tungsten film having a width of about 2 μm, a length of 14 μm, and a height of about 1 μm was formed. However, the protective film 53 is not limited to tungsten, and may be another material such as a carbon film or a platinum film.
[0076]
Next, a sample separation step is entered. As shown in FIG. 9d, a cantilever-like structure 55 can be formed by making a notch 54 with FIB so as to surround the protective film 53. As an example, the dimensions are approximately 4 μm width, 18 μm length, and 0.1 μm sample thickness.
[0077]
Next, the probe 56 is brought into contact with the tip of the cantilever-like structure 55 as shown in FIG. 9e. The probe is fixed to the tip of the transfer means (not shown) of the micro sample, and the cantilever-like structure 55 and the probe 56 are not damaged by the careless pressing of the probe on the drive part (not shown) of the transfer means. In order to avoid this, the probe 56 has a function of stopping driving when it contacts the sample. In order to fix the probe 56 to the cantilever-like structure 55, a deposition film 57 is formed in an area of about 2 μm square including the tip of the probe 56. The deposition film 57 is formed by the same method as the protective film 53 and has the same components. In this way, the probe 56 and the cantilever-like structure (sample to be extracted) 55 can be connected (FIG. 9f).
[0078]
Thereafter, as shown in FIG. 9g, the support 58 of the cantilever-like structure 55 is irradiated with FIB 52 and sputtered to cut the cantilever-like structure 55. When the probe 56 is gradually raised after cutting, it can be separated and extracted from the original thin sample 50 as a fine thin sample 59 as shown in FIG. 9h.
[0079]
(4) Fixing of small thin sample
This step is an operation of fixing the extracted minute thin piece sample 59 to the sample holder. This will be described with reference to FIG. The movement of the micro thin sample 59 from the thin sample to the sample holder 60 is performed by moving the sample stage by stopping the probe 56 in a state where the probe 56 is raised from the thin sample and moving the micro thin sample relatively. Thus, the sample stage is stopped when the sample holder 60 comes directly under the minute thin sample 59. Next, the probe 56 is lowered and bonded to the sample holder 60 as shown in FIG. When the micro thin sample 59 comes into contact with the sample holder 60, the descent of the probe 56 can be automatically stopped.
[0080]
Next, while introducing a deposition gas to fix the micro thin sample 59 to the sample holder 60, the FIB 52 is partly deposited on the surface of the micro thin sample 59 and part of the sample as shown in FIG. Scanning was performed to adhere to the holder 60. The deposition film 61 in this example was formed to have a length of about 2 μm square on the edge in the longitudinal direction of the minute thin piece sample 59. Thereafter, in order to separate the probe 56 and the minute thin piece sample 59, the deposition film 57 is irradiated with FIB 52 ′.
[0081]
After the deposition film 57 is removed, the probe 56 is avoided from the sample holder 60. Therefore, as shown in FIG. 10 l, a deposition film 61 ′ of about 2 μm square is formed on the other end side in the longitudinal direction of the micro thin sample 59 in order to securely fix the micro thin sample to the sample holder.
[0082]
(5) Cross-section processing
By the operation so far, the micro thin sample including the target portion can be fixed to the sample holder. Next, FIB 52 is irradiated to the minute thin piece sample 59 fixed as shown in FIG. 10m, and the side surface is deleted together with the sample holder 60 to form the recess 62. In this example, the opening of the recess 62 is about 10 μm, the depth is about 2 μm, and the depth is about 3 μm. Further, the opposite side surface is also deleted and processed into a concave shape 62 ′ so that a thin wall having a thickness of about 0.1 μm is formed at the center (FIG. 10n).
[0083]
FIG. 10o is a cross-sectional sample of the completed thin sample, and the upper part of the central thin wall portion 63 is the cross-sectional sample 64 of the micro thin sample 59, which is actually observed by TEM or STEM at a height of about 0.1 μm. It is a thin wire with a width of about 0.1 μm and a length of about 10 μm. For reference, the incident electron beam 65 at the time of TEM observation is incident substantially parallel to the surface of the minute thin piece sample 59 as indicated by the arrow.
[0084]
In this way, a sample for observing the cross section of the thin sample can be prepared by the procedure shown in FIGS. According to this method, since all these steps are performed in a vacuum atmosphere, unnecessary fine powder is hardly attached and positioning can be performed with high accuracy.
[0085]
(6) Cross-sectional TEM observation
The sample stage is inserted into the TEM without removing the cross-sectional thin sample prepared in the sample preparation apparatus from the sample stage. At this time, TEM observation can be performed by rotating the TEM stage so that the electron beam path and the cross section intersect perpendicularly. Since the subsequent TEM observation technique is well known, it is omitted here.
[0086]
The sample preparation procedure described above is not limited to a TEM sample, and can be used for elemental analysis and observation techniques using EDX (electron beam X-ray diffraction analysis).
[0087]
(7) Grasping three-dimensional shape
The planar structure obtained in the step (2) and the cross-sectional TEM image obtained in the step (6) can be interpreted in a complex manner to estimate the three-dimensional structure of the target portion. In this way, even for a sample that is difficult to interpret by TEM observation of only a plane or a cross-section, it is now possible to accurately interpret the sample structure by observing the same part from 90 ° different directions. .
[0088]
<Example 2>
This example relates to a sample preparation apparatus according to the present invention and will be described with reference to the schematic configuration diagram of FIG.
[0089]
The sample preparation device 1 includes a FIB irradiation system 3 for processing and observing a sample 2 such as a semiconductor chip, a thin piece sample, and a cross-sectional sample, and a secondary electron and secondary ion for detecting secondary electrons and secondary ions emitted from the irradiated portion by the FIB irradiation. Particle detector 4, Deposition gas source 5 that supplies a material gas for forming a deposition film in the FIB irradiation area, Sample stage 6 on which the sample 2 is placed, and a small thin piece sample from which a part of the sample has been extracted is fixed A sample holder 7, a fixture 8 for holding the sample holder 7, a transfer unit 9 for transferring a minute thin piece sample to the sample holder, and the like.
[0090]
Furthermore, a stage control unit 10 for controlling the position of the sample stage 6, a transfer means control unit 11 for driving the transfer unit 9 independently of the sample stage 6, a calculation processing unit 15, a sample holder 7 and the sample 2 and transfer An image display unit 16 for displaying the unit 9 and the like, an FIB control unit 13 for the FIB irradiation system 2, and the like are also included.
[0091]
The calculation processing unit 15 controls the stage control unit 10, the transfer means control unit 11, the secondary particle detector control unit 12, the deposition gas source control unit 13, the FIB control unit 14, and the like, and further SIM image information It can also store and process image information from TEMs. In addition to the SIM image, the image display unit 16 can also display a TEM image or an image obtained by processing the TEM image, and can further display the SIM image and the TEM image by being processed by the calculation processing unit 15. . The TEM image information can be transferred from the calculation processing unit 19 provided in the TEM via the network 19 ′, or may be introduced into the calculation processing unit 15 by a storage medium.
[0092]
Furthermore, it is networked around the main computer, and has a function of registering the shape of the sample and the element information data obtained by the sample preparation device and the TEM via the network in the database of the main computer. This makes it possible to centrally manage SIM images, TEM images, and processed images that have been processed, and also allows sample preparation devices, TEMs, and other calculation processing units to capture images from the main computer database via a network. Information can be called. For this reason, it is not necessary to perform image synthesis or processing at a location adjacent to the sample preparation device or TEM, and calculation processing can be performed by incorporating different information at different locations in the work environment.
[0093]
The FIB irradiation system 3 includes a liquid metal ion source, a beam limiting aperture, a focusing lens, an objective lens, and the like. The ions emitted from the ion source are FIB 17 having a diameter of several tens nm to several μm. The FIB 17 is scanned on the sample 2 using a deflector, and processing from the μm to sub-μm level corresponding to the scanning shape is performed. Processing here refers to the formation of a concave portion by sputtering, the formation of a convex portion by FIB assist deposition, or an operation of combining them to deform the sample shape. The deposition film formed by FIB irradiation is used to connect the probe 56 at the tip of the transfer means 9 and the sample 2 or to fix the minute thin piece sample to the sample holder 7. The sample holder used here is an important component in the sample preparation apparatus of the present invention, and will be described in detail in Example 3.
[0094]
The sample stage 6 is a side entry method. The side entry type sample stage 6 can be inserted and installed in the sample chamber 17 without releasing the vacuum in the sample chamber 17. Further, when it is desired to extract the sample chamber 17, the sample chamber 17 can be extracted without breaking the vacuum. This sample stage 6 is characterized in that it has a structure in which a thin sample 2 and a minute thin sample extracted from the thin sample 2 can be mounted.
[0095]
Note that the principle of holding the vacuum when the sample stage 6 is inserted and removed is the same as the principle of the side entry type stage and its insertion port conventionally used in a scanning electron microscope and a transmission electron microscope. However, since both the thin sample and the micro thin sample are processed, the axial direction of the sample stage can be stopped at least two places, and the sample can be processed and observed at each stop position. Different from the entry type stage. Since the sample stage 6 used here is an important component in the sample preparation apparatus according to the present invention, the detailed structure will be described in detail in Example 3.
[0096]
The micro sample transfer unit 9 includes a coarse movement mechanism that moves in three axes of XYZ and a fine movement mechanism that finely moves in the Z direction, both of which are operated by the transfer mechanism control unit 11. A probe 56 for extracting a small thin piece is installed at the tip.
[0097]
FIG. 11 is a diagram for explaining the transfer unit 9 in more detail, and is an example composed of a coarse moving unit 70 and a fine moving unit 71. The coarse moving part 70 can be moved in the XYZ directions by means of three encoders 74X, 74Y (not shown) and 74Z with the support 73 as a fulcrum. The coarse stroke and moving resolution depend on the encoder performance, but there are 10mm stroke and 1μm resolution. The force against the force by the encoder is due to the spring 75a and the like, but details are omitted here. The drive system of the coarse movement unit 70 is on the atmosphere side through the lateral port of the sample chamber wall 76, and the vacuum is blocked by the bellows 77 and the O-ring 78.
[0098]
The fine movement portion 71 uses only the Z axis and employs a bimorph piezoelectric element 79, and a submicron moving resolution can be obtained. The tip of the bimorph piezoelectric element 79 had a diameter of about 30 μm, and a needle-like tungsten probe 56 sharpened to a tip curvature radius of about 0.1 μm was fixed. The bimorph piezoelectric element 79 can be finely moved in the Z direction by gradually applying a voltage up to about several tens of volts. Conduction with the probe 56 and voltage applied to the bimorph piezoelectric element 79 are performed through a terminal 80.
[0099]
By the transfer unit 9 having such a probe 56 and FIB processing, it is possible to contact the desired location of the thin sample 50 with sub-μm level accuracy and extract the micro thin sample 59 as shown in FIG. Further, the extracted minute thin piece sample 59 can be accurately fixed to the sample holder 60.
[0100]
With the sample preparation device 1 having the above-described configuration, it is possible to manufacture a minute thin piece sample in the cross-sectional direction from the thin piece sample 50 for TEM observation. In addition, the realization of the thin-section sample from such a thin-section sample enables detailed observation from two directions of the target sub-μm level of the sample, enabling pseudo three-dimensional evaluation. .
[0101]
A configuration example of the FIB irradiation unit 3 is described in the known example 2 and the like. Further, a deposition gas supply unit 5 is mounted, and a gas component deposition film can be formed in the scanning region by performing FIB scanning while introducing gas into the sample from the nozzle 5 ′ at the tip. This deposition film plays the role of protecting the surface of the sample.
[0102]
<Example 3>
The present embodiment relates to an example of the sample stage 6 in the sample preparation apparatus according to the present invention, and is a side entry type sample stage that can be inserted and removed from the wall surface of the vacuum vessel without deteriorating the degree of vacuum of the sample chamber. It is characterized by a sample stage that is also used as an apparatus.
[0103]
The major difference between the sample stage 6 according to the present invention and the conventional side entry type TEM stage or FIB stage is that a mesh or mesh holder to which a thin sample for TEM observation is fixed and a sample holder 7 to which a fine thin sample can be fixed are mounted. This is a possible structure. When the TEM observation is completed, the sample stage 6 is pulled out of the TEM and transferred to the sample preparation device. When the sample preparation is completed by the sample preparation device, the sample stage 6 can be introduced into the TEM again and observed.
[0104]
Hereinafter, a description will be given with reference to FIG. 12a is a view of the sample stage 6 viewed from a direction perpendicular to the FIB optical axis, and FIG. 12b is a view of the sample stage 6 as viewed from the ion source side (a state in which FIG. 12 (a) is rotated by 90 ° axis). The passing direction of the electron beam at that time is parallel to the paper surface.
[0105]
Although the schematic configuration of the sample stage 6 has been described with reference to FIG. 4c, a characteristic point of the sample stage 6 used in this embodiment is that a mesh holder 82 to which a mesh 26 on which a thin sample 25 'is installed is fixed is mounted. And a sample holder installation portion 86 for installing a sample holder 60 for fixing a micro sample obtained by extracting a target portion detected by TEM observation at the tip thereof. Note that the support for supporting the small protrusions 87 is substantially coaxial with the axis of the sample stage 6, but is not shown.
[0106]
The mesh holder 82 and the sample holder 60 are fixed to the installation portions 85 and 86, respectively. The installation surface of the micro thin sample 59 in the sample holder 60 is in a parallel relationship with the mesh 19 surface. The sample stage 6 can be controlled to move and rotate in three dimensions (X, Y, Z) by a stage controller 10 (see FIG. 1). As described above, the sample stage 6 has a side entry structure in which the mesh holder 82 on which the thin sample 25 ′ is placed and the sample holder 7 on which the extracted minute thin sample 21 is fixed can be mounted on the same sample stage 6. It is the biggest feature. In addition, the upper part 88 of the sample holder 7 is in an open state so that the incidence of the FIB 52 on the micro thin sample 59 is not hindered on the sample stage 6, and this sample stage 6 can be mounted on both the TEM and the sample preparation device. is there.
[0107]
FIG. 12b shows a state where the shaft is rotated 90 ° from the state shown in FIG. 12a and introduced into the TEM, and the incident direction of the electron beam is indicated by arrows 89 and 89 ′. Therefore, TEM observation can be performed immediately by simply removing and inserting the observation sample processed in the sample preparation device from the insertion port of the sample stage, and the thin sample 25 ′ before extraction and the minute thin sample 21 after processing are also included. Another major feature is the ability to observe TEM. With such a structure, a micro thin sample extracted from a thin sample for TEM observation is processed into a sample shape suitable for analysis and observation without any special sample processing equipment or manual work requiring tension and skill. As a result, it is now possible to immediately move to analysis and observation work by simply inserting and removing the sample stage.
[0108]
Furthermore, although not shown in FIG. 12, the sample stage 6 has a rotating mechanism of the mesh holder 82, and the thin sample 25 ′ can be rotated in-plane while TEM observation is performed. With this structure, it is possible to set the direction of the desired target portion of the thin sample 25 ′ parallel to the axis of the sample stage 6, and it is easy without causing the transfer means (see FIG. 1) to perform complicated movement such as rotation. In addition, the minute thin piece sample 21 extracted from the thin piece sample 25 ′ can be transferred to the sample holder 60.
[0109]
The sample stage 6 has a structure capable of temporarily stopping at approximately the center of each of the mesh holder fixing portion and the sample holder when being introduced from the sample stage insertion port. In order to perform the operation of stopping from the sample holder (extracted sample) to the mesh holder (thin sample) or vice versa, the sample stage may be slightly pushed in or pulled out. Thus, when the sample stage is set, either the mesh holder or the sample holder always enters the field of view. In this way, the target area such as FIB irradiation or TEM observation can be quickly moved to the center of the visual field at each stop position. Further, when the position is deviated from the central portion, it can be searched by moving the X and Y by the sample stage control device.
[0110]
A mechanism for stopping the sample stage with the mesh holder or the sample holder can be easily achieved by a known technique. For example, the sample stage can be stopped at a desired position by installing a means for measuring the distance between the reference surface provided on the wall surface side of the sample chamber and the reference portion of the sample stage.
[0111]
In this method, since the observation sample can be extracted from the original thin sample in the sample preparation device, mechanical polishing like the preparation of the conventional thin sample is unnecessary, and the sample to be extracted is at the μm level. A plurality of micro samples can be extracted from the thin sample, and a sample for TEM observation of each cross section can be made.
[0112]
The sample holder 60 is a member for fixing a minute thin piece sample 59 extracted from the thin piece sample 50 of FIG. 9 and performing FIB processing so that an electron beam easily passes during TEM observation. It corresponds to a mesh in conventional TEM observation.
[0113]
An example of the sample holder used in this example will be described with reference to FIG. FIG. 13a shows an embodiment of the sample holder 60, which is a strip-shaped member having a convex cross section and formed of silicon. The length is about 2 mm, the width of the lower portion 90 is 400 μm, and the width of the convex portion 91 is about 40 μm. The feature is that a sunk portion 92 is provided in the vicinity of the center of the convex portion 91 in the longitudinal direction, and the micro thin piece sample 59 extracted from the bottom surface 93 of the sunk portion 92 is fixed. The sinking portion 92 is provided so that the fixed thin slice sample 59 or the thin slice section sample subjected to the thinning process is not damaged when the sample holder 60 is handled. In addition, even if the probe is operated on the bottom surface 93 of the sinking portion 92 for fixing, the probe does not come into contact with the surroundings. The dimensions of the sinking portion 92 are, for example, a width of about 200 μm and a depth of about 50 μm.
[0114]
FIG. 13 b shows a state in which a thin thin piece sample 59 is placed in the approximate center of the bottom surface 93 of the sinking portion 92 and thin wall processing is performed. FIG. 13c is an enlarged view of the sinking portion 92. Both side surfaces of the minute thin piece sample 59 are deleted by FIB to form the recesses 62 and 62 ', and a part of the minute thin piece sample 59 is thin-walled in the cross-sectional direction. The direction of electron beam irradiation during TEM observation is as shown by arrow 65 in the figure. Although the dimensions shown here are merely examples, it is desirable that the width is as narrow as possible so that the probe does not touch, and the depth is as deep as possible so that the minute thin sample 59 can be securely fixed to the bottom surface 93.
[0115]
The cross section of the sample holder 60 itself is not limited to the convex shape of FIG. 13a, and may be a shape in which the thin piece base 94 is installed in the sinking portion 92 in the L-shaped cross section of FIG. The thin piece base 94 has a width of 4 μm, a length of 20 μm, and a height of about 15 μm, and can be installed using conveyance by a probe and adhesion by an FIB assist deposition film. A micro thin piece sample 59 extracted from the upper surface of the thin piece base 94 is fixed. With this structure, the electron beam 65 can irradiate and pass a minute thin piece sample without being affected by the unevenness of the bottom surface 93 of the sinking portion 92 during TEM observation.
[0116]
Furthermore, the same effect can be obtained with a structure in which a sinking portion 92 and a thin piece base 94 are provided on the side surface in the diameter direction of a semicircular sample holder 60 as shown in FIG. 13f. The point of these structures is to prevent damage due to contact with other members when handling the sample holder, such as attaching a minute sample, observing and analyzing, and storing the sample holder or performing observation again The fixed part of the minute thin piece sample is slightly sunk (provided with a recess). Moreover, it is also a structure in which an obstacle does not protrude into the passage to the observation unit so as not to obstruct the passage of the electron beam. The material is not limited to silicon, but may be a conductive ceramic such as silicon carbide, or a metal such as molybdenum, tantalum, or niobium.
[0117]
Next, another embodiment of the sample stage 6 ′ will be described with reference to FIG. In FIG. 14, only the characteristic tip portion of the sample stage 6 ′ is shown, and descriptions of grips and the like are omitted. This sample stage 6 'is a new side entry type sample stage configuration that realizes TEM observation of the cross section of the TEM observation region which is a thin piece portion of the TEM sample 40 of FIG. 7 processed by the conventional dicing apparatus and FIB processing. It is.
[0118]
Structurally, the first sample holder 95 and the second sample holder 60 are provided with respective fixing portions so that the first sample holder 95 and the second sample holder 60 can be mounted at the same time, and the first sample holder 95 can rotate in the plane. . The first sample holder 95 is a jig for installing the cross-sectional TEM observation sample 40 formed by using the dicing and FIB processing described in the above-mentioned known example 2, and is a ring with a part cut off. The second sample holder 60 is a jig for fixing the minute thin piece sample 59 extracted from the cross-sectional TEM observation region 41 in the cross-sectional TEM observation sample 40, and is fixed by a fixture 86 or the like. Second shown here
Reference numeral 60 denotes the shape shown in FIG.
[0119]
The sample placement surface of the sample holder 60 (perpendicular to the paper surface) is in a substantially vertical positional relationship with the surface of the cross-sectional TEM observation region 41 (parallel to the paper surface). In order to facilitate the incidence of FIB 52 ′ for processing a thin slice of a diced strip-shaped sample, and when a micro thin sample 59 extracted from the cross-sectional TEM observation region 41 is transferred to the second sample holder 60, it interferes with the transfer probe. Notches 88 and 88 ′ were provided on the side surfaces of the respective sample holders so as not to be formed. When the sample stage 6 ′ is introduced into either the TEM or the sample preparation device, the structure can be temporarily stopped at the approximate center of either the cross-sectional TEM observation sample 40 or the second sample holder 60. When installed, either the cross-sectional TEM observation region 41 or the minute thin sample 59 always enters the visual field. In this way, the target area such as FIB irradiation or TEM observation can be quickly moved to the center of the visual field at each stop position. Further, when the position is deviated from the central portion, it can be searched for by moving X and Y by the sample stage control device (reference numeral 10 in FIG. 1).
[0120]
After processing the slice of the cross-sectional TEM observation sample 40 with the sample preparation device, the sample stage 6 ′ is pulled out and introduced into the TEM to observe the observation region 41. As a result of TEM observation, an abnormal form is observed. In order to prepare a sample for observing the cross-sectional shape of the abnormal form from the direction parallel to the surface of the observation region 41, the sample stage 6 ′ is inserted again into the sample preparation apparatus and the following operation is performed.
[0121]
The first sample holder 95 is rotated by 90 ° to set the positional relationship as shown in FIG. 14 b, and the thin piece including the target portion 41 ′ is extracted from the observation region 41. A method for extracting a micro sample from a thin piece of a cross-sectional TEM sample and a method for fixing it to a sample holder will be described later. With the extracted minute thin piece sample fixed to the probe tip (not shown), the sample is once withdrawn from the sample stage, and the sample holder is rotated 90 ° about the axis. At this time, the sample mounting surface of the second sample holder 60 is in a relationship perpendicular to the FIB optical axis. Therefore, the probe is brought close to the second sample holder 60 and fixed to the sample installation surface. The method for fixing the micro sample is the same as described above. After the probe is cut, a thin slice sample is sliced perpendicular to the slice surface. The same applies to the vertical flake processing. In thinning, the sample holder or the height adjustment table may be processed at the same time. After the processing is completed, the sample stage can be pulled out and introduced into the TEM to observe the cross section.
[0122]
By the sample stage as described above, a cross-sectional thin piece sample of a portion of interest in the thin piece TEM sample can be produced. In addition, this series of sample preparation operations enables easy TEM observation of the cross-section of a flat TEM sample or the side of a cross-sectional sample in a certain direction. Since the same sample can be observed from 90 ° different directions with respect to the microstructure, shape, and defects for which information has been obtained, the above microstructure, shape, and defects can be simulated in three dimensions, and the sample structure can be observed from one direction. New knowledge that was not clarified by observation alone can be obtained.
[0123]
<Example 4>
This example is an example of a sample preparation method according to the present invention, in which a cross section TEM observation sample prepared by FIB is observed by TEM observation and the target portion detected by changing the observation direction by 90 ° is further observed in a cross section of a thin piece This will be described with reference to FIG. Note that the sample stage is as shown in FIG. 14, and the procedure after the cross-section flake processing by the FIB 52 ′ in the sample preparation apparatus will be described.
[0124]
(1) Cross-sectional TEM observation
As shown in FIG. 15a, the orientation of the TEM observation region 41 is adjusted so that the electron beam 89 can easily pass through the TEM observation region 41 of the cross-sectional TEM sample 40 formed by the conventional method. The thickness of the TEM observation region 41 is a thin piece of about 0.1 μm. An enlarged view of portion A in the figure is shown in FIG. 15b. As a result of the cross-sectional TEM observation, in order to observe the attention part 100 in more detail, the target part 100 is sandwiched below, and the TEM observation is performed from the cross-section by cutting at the planes 101 and 101 ′ located at an interval of about 0.1 μm. Sample preparation is performed.
[0125]
The sample stage is transferred from the TEM to the sample preparation device. As described above, the movement of the sample stage is a side entry type stage, so that it can be easily performed without taking time by evacuation or the like. First, the sample stage introduced into the sample preparation device is rotated approximately 90 ° so that the minute thin piece sample can be easily extracted, and the surfaces 101 and 101 ′ are parallel to the sample holder for fixing the extracted minute sample. Set to. (See Figure 15c)
(2) Extraction of small thin sample
Next, as shown in FIG. 15d, a protective film 53 is formed on a part of the TEM observation surface 41 in order to protect the target portion 100. In addition, a part of the periphery of the thin piece to be extracted is cut by FIB 52 ′, and the tip of the probe 56 as a transfer means is connected to a part on the TEM observation surface 41 by a deposition film 57. Thereafter, the minute thin piece sample 59 can be separated from the TEM sample 40 by further cutting 54 by scanning FIB 52 ′. FIG. 15 e shows a state in which the minute thin piece sample 59 is extracted by the probe 56.
[0126]
(3) Fixing of small thin sample
By moving the sample stage together with the movement of the probe 56, the minute thin piece sample 59 is positioned directly below the sample holder 60. Thereafter, the probe is gradually lowered to contact the sample holder 60. Since the specific shape of the sample holder 60 has already been described, only a part of the fixed portion of the minute thin sample 59 is shown in FIG. 15f. Next, as shown in FIG. 15g, the sample holder 60 and the minute thin sample 59 are fixed by the deposition film. After both are fixed, the deposition film 57 fixing the probe is sputtered away by FIB to separate the micro thin sample 59 and the probe 56 from each other.
[0127]
(4) Micro thin section processing
Next, both sides are removed by FIB irradiation so that the target portion 100 remains. Finally, the micro thin sample 59 is processed so as to include the target portion 100 and have a thin piece width of about 0.1 μm. In this way, the minute thin piece sample 59 fixed to the sample holder 60 becomes a thin piece 103 for cross-sectional observation, and has a thin line shape with a height of about 0.1 μm, a width of about 0.1 μm, and a length of about 10 μm. Further, the sample holder 60 is formed with concave portions 104 and 104 ′ by FIB scanning, and the electron beam 105 is not affected by the surrounding shape by the concave portions 104 and 104 ′ when TEM observation is performed. Can be observed.
[0128]
(6) Cross-sectional TEM observation
Through the above operation, the thin piece 103 for observing the cross section of the thin piece sample 59 is completed, and this sample stage can be mounted on a TEM to observe the target portion 100.
[0129]
(7) Grasping three-dimensional shape
According to the present invention, the cross-sectional TEM image obtained in the above (1) and the cross-sectional TEM image obtained in (6) with different 90 ° observation directions are interpreted in a complex manner, and the structure of the target portion 100 is pseudo-stereoscopic. Can be interpreted. In this way, even a sample that is difficult to interpret by TEM observation of only a flat surface or only a cross section of one surface can now be observed by TEM from the same location at a different angle of 90 °. It is now possible to make accurate interpretations based on spread, structure, and shape. Furthermore, the sample preparation procedure described above can be used not only for TEM samples but also for elemental analysis such as other EDX analysis.
[0130]
【The invention's effect】
According to the present invention, a target portion of a thin sample can be analyzed by a TEM or STEM from a plane direction and a cross-sectional direction, and a sample can be prepared for analysis by a TEM or STEM from a plane direction and a cross-sectional direction. Furthermore, it is possible to provide a sample preparation apparatus for realizing the above analysis and sample preparation for performing the analysis.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of a sample preparation apparatus according to the present invention.
FIG. 2 is an explanatory view of a cross-sectional sample manufacturing method using conventional polishing and ion thinning.
FIG. 3 is an explanatory diagram of a sample preparation method using conventional dicing and focused ion beam processing.
FIG. 4 is an explanatory view of the shape and sample stage of a TEM sample by conventional dicing and FIB processing.
FIG. 5 is an explanatory diagram of a method for manufacturing a planar sample using conventional polishing and ion thinning.
FIG. 6 is an explanatory diagram of a conventional method for separating a micro sample.
FIG. 7 is an explanatory view of a sample preparation method for performing cross-sectional TEM observation of a conventional thin piece sample.
FIG. 8 is an explanatory diagram for explaining a sample preparation method according to an embodiment of the present invention.
FIG. 9 is an explanatory view of a process for extracting a minute thin piece sample in one embodiment of the present invention.
FIG. 10 is an explanatory diagram of a process for extracting a minute thin piece sample continued from FIG. 9;
FIG. 11 is a longitudinal cross-sectional view of a sample preparation apparatus of an embodiment of the present invention, particularly a transfer section.
FIGS. 12A and 12B are a plan view and a partial cross-sectional view of a sample stage portion of a sample preparation apparatus according to an embodiment of the present invention. FIGS.
FIG. 13 is an explanatory diagram of an example of a sample holder used in the sample preparation device of one example of the present invention.
FIG. 14 is an explanatory view showing another example of the sample stage of the sample preparation device according to the embodiment of the present invention.
FIG. 15 is an explanatory diagram of a TEM sample manufacturing method for observing a cross section of an example of the present invention.
FIG. 16 is an explanatory diagram of a method for determining the extraction position in the sample preparation method of the present invention.
[Explanation of symbols]
1 ... Sample preparation device, 2 ... Sample, 3 ... FIB irradiation unit, 4 ... Secondary particle detector, 5 ... Deposition gas source, 6,6 '... Sample stage, 7,7' ... Sample holder, 8 ... Fixed 9 ... Transport means, 10 ... Stage control device, 11 ... Transport means control device, 12 ... Secondary electron detector control device, 13 ... Deposition gas source control device, 14 ... FIB control device, 15 ... Calculation processing unit , 16 ... Image display unit, 19 ... Computer, 19 '... Network, 45 ... Thin piece part, 46 ... Thin piece sample, 47 ... Fine thin piece sample, 48 ... Cross-section fine thin piece sample, 50 ... Thin piece sample, 51 ... Mark, 52 ... FIB, 56 ... Probe, 59 ... Small flake sample, 60 ... Sample holder, 64 ... Cross-section sample, 65 ... Electron beam, 82 ... Mesh holder, 89,89 '... Electron beam, 92 ... Sink part, 94 ... Small Table, 95 ... Second sample holder, 110 ... TEM image, 111 ... Internal defect, 112, 112 '... Surface foreign matter, 115 ... SIM image, 120 ... Composite image, 121 ... Extraction area, 122a, 122b, 122c ... Sample Recognition Identification number.

Claims (9)

And the vacuum sample chamber,
A sample stage on which a thin sample that can be observed with a transmission electron microscope or a scanning transmission electron microscope can be placed;
An irradiation optical system for irradiating the thin sample in the vacuum sample chamber with a focused ion beam;
And a transfer means to remove the micro-thin sample from the slice sample is irradiated with the focused ion beam to the thin sample in the vacuum sample chamber,
The sample stage is further provided with a can be placed sample holder in the vacuum sample chamber the micro flakes specimen that is removed by the transfer means,
The sample stage allows the thin sample and the sample holder to be inserted into and removed from the vacuum sample chamber without breaking the vacuum in the vacuum sample chamber , and is installed in a vacuum sample chamber of a transmission electron microscope or a scanning transmission electron microscope. A sample preparation apparatus, which is a side entry type sample stage that can be inserted and removed . The sample preparation apparatus according to claim 1,
The sample preparation apparatus, wherein the transfer means includes at least a probe and a drive means for driving the probe . The sample preparation apparatus according to claim 1,
The sample stage has an installation part of a mesh holder that fixes the thin sample and a mesh to be placed, and observes the thin sample before extraction of the fine thin sample with a transmission electron microscope or a scanning transmission electron microscope. A sample preparation apparatus characterized by being capable of performing. In the sample preparation device according to claim 3,
The sample preparation apparatus, wherein the sample stage has a stop position that can be temporarily stopped at substantially the center of the mesh holder installation portion and the sample holder when inserted into the sample preparation apparatus. The sample preparation apparatus according to claim 1,
Further, at least the transmission image information of the transmission electron microscope or the scanning transmission electron microscope and the secondary particle image by irradiation of the focused ion beam are stored, and at least the transmission image information and the secondary particle image information are superimposed. A calculation processing unit for forming a composite image;
An image display unit that displays at least one of the transmission image information, the secondary particle image information, and the composite image . The sample preparation apparatus according to claim 1,
The sample preparation apparatus , wherein the sample holder for fixing the minute thin piece sample has a prismatic shape or a shape having an arc portion . In the sample preparation device according to claim 6,
The sample holder having a prismatic shape has a convex, L-shaped or rectangular cross-sectional shape . In the sample preparation device according to claim 6 or 7,
The sample preparation apparatus , wherein the portion for fixing the micro thin sample is a recess provided in a substantially central portion in the longitudinal direction of the sample holder . A sample preparation method for observing a cross section of a thin film sample observable with a transmission electron microscope or a scanning transmission electron microscope with a transmission electron microscope or a scanning transmission electron microscope,
A step of observing a thin sample with a transmission electron microscope or a scanning electron microscope;
A step of storing image information by a transmission electron microscope or a scanning electron microscope, in which a target portion and a surface foreign substance have entered the observation field;
A step of applying a mark with which a position of the target portion can be confirmed based on the image information to the thin sample with a focused ion beam;
Separating the minute thin piece sample including the target portion on the basis of the mark;
Fixing the separated microflame sample to a sample holder in a vacuum sample chamber;
A step of irradiating a micro-thin sample fixed to the sample holder with an ion beam and a focused ion beam to process a cross-section of the thin film sample including the portion of interest into a sample that can be observed with a transmission electron microscope or a scanning transmission electron microscope A sample preparation method comprising:

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