JP2010230518A - Thin sample preparing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin sample preparing method which prevents an FIB (focused ion beam) processing from forming any hole and allowing any redeposition to originate in holes when forming a protection film in preparing a thin sample, in order to obtain a good image by using an electron microscope. <P>SOLUTION: The thin sample preparing method which prepares a thin sample from a test piece by using a focused ion beam apparatus, in order, includes: a step of applying ink to a thin-sample preparation part of the test piece, thereby forming a coating film; a step of introducing the test piece into the focused ion beam apparatus and operating an ion beam to form the protection film on the thin-sample preparation part by using a metal material; and a step of preparing the thin sample by applying an ion beam etching process to the thin-sample preparation part having the protection film formed thereon. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for preparing a thin piece sample for observation using a microscope such as a transmission electron microscope (TEM) or a scanning electron microscope (SEM). More specifically, the present invention relates to a method for preparing a slice sample for cross-sectional observation using a focused ion beam apparatus (FIB).

  Conventionally, in an electron microscope, particularly a transmission electron microscope (TEM), it is necessary to slice a sample to a thickness that allows an electron beam to pass therethrough, and various methods have been used. As a method for slicing, a pulverization method for pulverizing a sample with a mortar, an ion polishing method using polishing and ion milling, a microtome method using an ultramicrotome cross-section cutting device, or a focused ion beam (FIB) apparatus was used. Thin slice processing methods, an electrolytic polishing method in which a sample is dissolved in an electrolytic solution, a chemical etching method in which etching is performed with acid or alkali, and the like are performed as main thinning methods.

  A focused ion beam (FIB) apparatus is an apparatus that performs material processing with Ga ions. Although it is used for cross-sectional observation in the semiconductor field, it may be used not only for the semiconductor field but also for the production of thin-section samples for TEM because of its processing performance. Since it can be observed with a scanning ion microscope image (SIM image) by an ion beam, it is possible to observe a minute portion, and it is possible to aim and process a minute specific region in units of microns as an observation point. It is also possible to form a deposition film (hereinafter referred to as a deposition film) as a protective film at a specific position by depositing a gas and decomposing it with an ion beam (hereinafter referred to as a deposition). .

  In addition to the apparatus equipped with only the ion gun, the FIB apparatus structure is further equipped with an electron gun and has two types of observations: a scanning ion microscope image (SIM image) and a scanning electron microscope image (SEM image). There are also FIB devices that make it possible.

  In the FIB apparatus, the sample surface is damaged when the sample surface is irradiated with an ion beam or an electron beam. In particular, the ion beam is more likely to damage the sample. Therefore, it is desirable to form a protective film when observing in the FIB apparatus. The deposition film is formed as a protective film that protects the sample surface from damage at locations where FIB processing is performed by specifying the position.

  For the purpose of preventing damage to the processing site from the ion beam, a method in which the current is set to a strong value only during FIB processing and the current value is reduced during observation is used for a structure having only an ion gun. It is done. If the FIB apparatus has a structure in which an ion gun and an electron gun are mounted, a method of confirming with an SEM image at the time of observation is used.

JP-A-11-258130 International Publication No. 99/005506 JP 2002-150990 A JP 2004-071486 A

  When a thin sample is prepared with a focused ion beam apparatus (FIB apparatus), it is possible to prevent the surface structure from being destroyed due to damage from the ion beam by forming a deposition film. In addition, when the unevenness of the surface of the sample perpendicular to the direction in which the ion beam is incident is severe, the processed beam trace may occur along the direction perpendicular to the ion beam, resulting in uneven thickness. The effect of reducing this phenomenon is also recognized.

  However, in the case of a sample having a fine concavo-convex shape of nanometer order on the surface, such as a pattern sample in the semiconductor field, the deposition film may not be uniformly formed on the concave portion of the surface. When a deposit film cannot be formed in a concave portion with a fine irregular shape on the sample surface, a minute hole is formed in the concave portion, and when the minute hole is formed, processing that is presumed to originate from a protective film around the formed hole There is a case where debris (hereinafter sometimes referred to as redepot) adheres and the interface becomes unclear. Moreover, it is difficult to fill a fine hole once generated with FIB, and the state in which the hole is generated often continues.

  In the thin sample preparation using the FIB apparatus, in the state where a minute hole is formed on the sample surface, the processed residue adheres to the opposite side surface from the gap between the holes, and the image of the residue is mixed around the hole and the observation site. In some cases, the microscopic image obtained becomes unclear. In particular, when the protective film is a heavy element, the transmitted image has a dark contrast, and a minute part such as an interface may not be observed.

  Accordingly, the present invention provides a thin piece sample preparation method that prevents a hole from being formed when forming a protective film and prevents redeposition from the hole when a thin piece sample is formed by FIB processing, and a good image can be obtained with an electron microscope. It is an issue to provide.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a thin sample preparation method for preparing a thin sample from a sample using a focused ion beam apparatus, wherein an ink is applied to a thin sample preparation portion of the sample and a coating film is formed. A step of introducing a sample into the focused ion beam apparatus, forming a protective film by ion beam on a thin piece sample preparation portion using a metal-based material, and a thin piece sample preparation portion on which the protective film is formed And a step of preparing a thin piece sample by etching using an ion beam in order.

  The invention according to claim 2 is the thin piece sample preparation method according to claim 1, wherein the step of applying the ink to the thin piece sample preparation portion of the sample is performed with a pen.

  The invention according to claim 3 further comprises a step of forming a conductive film on the surface of the sample after the step of applying the ink to the thin sample preparation portion of the sample and forming the coating film. The sample flake preparation method according to claim 2 was used.

  According to a fourth aspect of the present invention, the surface of the thin sample preparation site of the sample is provided with an uneven shape, the interval between the recessed portions of the uneven shape is in the range of 1 nm to 100 nm, and the height of the recessed portions is high. The thin-film sample preparation method according to any one of claims 1 to 3, wherein the thickness is in a range of 1 nm to 1 µm.

  A thin piece that can be observed well in cross section without redepo when a sample having a fine concavo-convex structure on the surface is produced as a thin piece sample for electron microscope observation with a focused ion beam apparatus by the thin piece sample preparation method of the present invention. A sample could be made.

FIG. 1 is an explanatory cross-sectional view up to the formation of a protective film in the thin piece sample preparation method of the present invention. FIG. 2 is an explanatory view ((a) top view, (b) side view) of thin sample preparation by an ion beam of the present invention. FIG. 3 is an explanatory view (perspective view) for producing a thin sample by an ion beam according to the present invention. FIG. 4 is an explanatory view of a conventional method for preparing a thin piece sample. FIG. 5 is an explanatory cross-sectional view of another embodiment up to the formation of a protective film in the thin sample preparation method of the present invention. FIG. 6 is a cross-sectional explanatory view of a thin piece sample of the present invention.

  The method for preparing a thin piece sample of the present invention will be described below.

  In the thin sample preparation method of the present invention, a focused ion beam apparatus is used. A focused ion beam (FIB) apparatus is an apparatus that focuses an ion beam taken out from an ion source to 5 to 10 nm using an aperture and a lens, and irradiates the sample surface. It is an apparatus that can perform observation (etching (removal processing)) and deposition (deposition / addition processing) of fine regions by interaction. Ga ions are used as the ion source. Further, as the FIB apparatus, in addition to an apparatus including only an ion gun that irradiates an ion beam, an electron gun that can irradiate an electron beam may be mounted.

The thin sample preparation method of the present invention is characterized by comprising the following (Step 1) to (Step 3) in order.
(Step 1) A step of forming a coating film by applying ink to a thin sample preparation place of a sample.
(Step 2) A step of introducing a sample into the focused ion beam apparatus and forming a protective film at a thin sample preparation site using a metal material.
(Step 3) A step of producing a thin piece sample by performing an etching process with an ion beam on a thin piece sample production place where a protective film is formed.

  The thin piece sample preparation method of the present invention is characterized by including a step (step 1) of applying ink to a thin piece preparation portion of the sample to form a coating film. The coating film made of ink formed at the thin sample preparation site of the sample can provide a smooth surface at the thin sample preparation site by filling the uneven shape of the sample surface by the capillary action of the ink. The coating film made of ink gives a smooth surface without fine holes. Therefore, the protective film formed on the coating film does not have minute holes. Therefore, it is possible to provide a thin piece sample that can be observed favorably without redeposition in the step of producing a thin piece sample by the ion beam to be formed (step 3).

  The ink applied to the thin sample preparation site is preferably an ink that is easy to dry and does not react with the sample. Further, it is preferable that the ink has a certain degree of resistance to heat and does not deform due to heat generated by electron beam or Ga ion beam irradiation. The ink application means is preferably a pen such as a stationery fountain pen or felt pen.

  Since pens such as fountain pens and felt pens for stationery are writing instruments, they are easy to handle, and since the ink is colored, there are also advantages in that it is easy to visually check the marking location. An organic solvent is used for the ink, but most of it is ethanol, which is quick-drying and can be used without changing the quality of various materials such as glass and metal. Inks are divided into oil-based and water-based inks, and dye-based and pigment-based inks, but since the subsequent processes are for processing under dry conditions under vacuum, they can be applied without repelling the sample surface. As long as it does not cause a chemical reaction with the sample, the type is not limited. When observing with a transmission electron microscope image, the contrast becomes dark when there are many inorganic components. Therefore, if the material that forms the sample surface is mainly composed of inorganic components, the organic ink has a contrast difference and is easier to see during observation. It can be preferably used. In addition, if the material forming the sample surface is mainly composed of an organic component, it can be suitably used because it makes it easy to see the contrast difference due to the use of inorganic ink. In addition, since the method of forming a coating film with ink can be easily applied at atmospheric pressure and at room temperature, it has an advantage that it is less time-consuming than a vapor deposition method which is generally performed in a low vacuum state.

  The thickness of the coating film formed with the ink is preferably within the range of 5 μm or less from the position of the concavo-convex convex surface of the sample surface to the depth of the concavo-convex concave portion. When the thickness of the coating film is less than the depth of the concave and convex portions, a smooth surface may not be obtained by the coating film, and a hole may be formed in the concave portion in the protective film (deposition film) forming step in the next step. is there. On the other hand, when the thickness of the coating film exceeds 5 μm from the convex surface position of the micro unevenness, the thickness of the flakes increases, so the processing time until the observation site is thinned to a thickness sufficient for observation may be long. .

  FIG. 1 shows a cross-sectional explanatory diagram up to the formation of a protective film in the thin piece sample manufacturing method of the present invention. In FIG. 1, ink is applied to the surface of a sample 1 having a concavo-convex structure on the surface to form a coating film 2 (FIGS. 1A and 1B), and the sample 1 is placed in a focused ion beam apparatus (FIB). The deposited film 3 as a protective film is formed using a metal material or a carbon material (FIG. 1D).

  By forming a deposition film as a protective film in the focused ion beam apparatus (FIB), the sample can be protected from damage caused by the ion beam.

  In forming a deposition film as a protective film in the focused ion beam apparatus, a deposition film is formed at a thin piece production site by introducing a source gas to the sample surface and irradiating with an ion beam. At this time, a metal-based material can be used as the source gas, and specifically, a tungsten-based material or a carbon-based material can be used as the source gas.

  The thickness of the deposition film, which is a protective film formed in the focused ion beam apparatus, is preferably in the range of 0.10 μm to 5 μm. When the thickness of the deposition film is less than 0.10 μm, the formed deposition film does not function as a protective film, and the surface portion of the thin sample may be damaged and good observation may not be performed. On the other hand, when the thickness of the deposition film exceeds 5 μm, the processing time for thinning the observation site to a thickness sufficient for observation may be prolonged.

  After a protective film is formed on a thin piece production site on the sample surface, a thin piece sample is produced by etching using an ion beam. FIG. 2 shows an explanatory view ((a) top view, (b) side view) of thin sample preparation by the ion beam of the present invention. FIG. 3 shows an explanatory view (perspective view) of thin sample preparation using the ion beam of the present invention.

  2 and 3, the sample 1 is processed into a thin piece sample 1a by etching the processed portion 1b with an ion beam.

  In the production of the thin piece sample of the present invention, the thin piece sample can be produced by performing ion beam processing from both sides of the thin piece production site. As shown in FIG. 2A, the protective deposition film 3 is formed in a rectangular shape that is long in the width direction of the surface of the sample 1. Then, as shown in FIG. 2 (b), etching is performed so as to narrow the long side of the rectangle, and deeper processing is performed toward the thin sample 1a side. In the ion beam processing, it is preferable to perform roughing using a high-energy ion beam having a high etching rate and finish using a low-energy ion beam as the thickness is reduced. Finally, the bottom (bottom) and both ends (sides) of the thin sample are separated from the sample 1 by the ion beam. Then, the separated thin piece sample is collected and subjected to cross-sectional observation with a transmission electron microscope (TEM) and a scanning electron microscope (SEM).

  At this time, the sample is finally thinned to a thickness that allows transmission of the electron beam to form a thin piece sample, and then the thin piece sample is collected and placed on a mesh grid with a supporting film, which is a TEM observation sample stage, and observed with a transmission electron microscope. be able to. In addition, a sample may be collected in the form of a thin piece having a thickness of 1 μm to 2 μm, moved to a grid that is a TEM observation sample stage, and then processed to a thickness that allows transmission of an electron beam to obtain a thin piece sample, which may be observed with a transmission electron microscope. it can. That is, in the preparation of the thin piece sample, the finishing process can be performed after the thin piece sample is separated from the sample.

  FIG. 4 is an explanatory view of a conventional method for preparing a thin piece sample. When a deposition film as a protective film is formed in the FIB apparatus without forming a coating film with ink on a sample having a fine concavo-convex structure on the surface, the deposition film 3 may be buried in a recess on the sample surface. The minute hole 9 is formed without being able to be performed (FIG. 4A). When etching with an ion beam is performed from above the protective film having fine holes, a processing residue 10 called redepo adheres to the vicinity of the bottom of the hole 9 (FIG. 4B), and the sample It becomes impossible to perform good cross-sectional observation in the vicinity of the surface.

  In the present invention, by forming a coating film with ink on the surface of the sample before forming the protective film, it is possible to form a flat coating film so as to fill the uneven structure on the surface at the thin piece preparation site of the sample. it can. And by forming the deposition film which is a protective film on a flat coating film, generation | occurrence | production of the fine hole in a deposition film can be prevented. Therefore, it is possible to obtain a thin piece sample capable of satisfactorily observing a cross section having no redepot in the thin piece sample cross section.

  FIG. 5 shows an explanatory cross-sectional view of another embodiment up to the formation of the protective film of the thin piece sample manufacturing method of the present invention. In the thin sample preparation method of FIG. 5, ink is applied to the surface of the sample 1 having a concavo-convex structure on the surface to form a coating film 2 (FIGS. 5A and 5B). A conductive film 4 is formed on the conductive film 4 (FIG. 5C). After the conductive film 4 is formed, the sample is introduced into a focused ion beam device (FIB) to form a deposition film 3 that is a protective film using a metal material or a carbon material. (FIG. 5D).

  By forming a conductive film on the coating film as shown in FIG. 5, it is possible to prevent charge-up when the sample surface does not have conductivity and to enable easy observation in the FIB apparatus. it can. At the same time, it functions as a protective film for the coating film. As the conductive film forming material, a metal material such as Pt, Ag, Au, C, W, Al, or Cr can be used. As the conductive film formation method, a vacuum film formation method such as an evaporation method, a sputtering method, a plasma CVD method, an ion plating method, or an ion beam assist method can be used.

  The conductive film is preferably formed on the entire sample surface for the purpose of preventing charge-up. In addition, the thickness of the conductive film is preferably in the range of 0.05 μm or more and 1.0 μm or less. If the thickness of the conductive film is less than 0.05 μm, the conductive film disappears in a short observation with an ion beam, the coating film is damaged, the coating film is deformed, and observation is difficult. It may become. In addition, sufficient conductivity may not be imparted to the sample surface, and charging may occur when the insulating sample surface is observed in the FIB apparatus. Note that the thickness of the conductive film is preferably as large as possible. However, if the thickness of the conductive film formed by the vacuum film formation method exceeds 1.0 μm, the film formation time becomes long, resulting in inefficiency. It is.

  FIG. 6 is a cross-sectional explanatory view of the thin piece sample of the present invention. In the thin sample of the present invention, the surface of the sample 1 is provided with an uneven shape at the thin sample preparation location, and the interval (S) between the concave portions of the uneven shape is in the range of 1 nm to 100 nm, and the concave portion The height (H) is preferably in the range of 1 nm to 1 μm.

  The thin sample preparation method of the present invention can be suitably used for a sample having a fine concavo-convex structure on the surface. In particular, in a sample in which the interval (S) between the concave and convex portions in the concave-convex shape is in the range of 1 nm to 100 nm and the height (H) of the concave portion is in the range of 1 nm to 1 μm, When a deposition film as a protective film is formed, the protective film cannot be filled in the recesses on the sample surface, and fine holes are easily formed. The thin sample preparation method of the present invention for a sample in which the interval (S) between the concaves and convexes in the concavo-convex shape is in the range of 1 nm to 100 nm and the height (H) of the concaves is in the range of 1 nm to 1 μm. To form a smooth coating film in a form that fills the uneven structure of the surface at the location where the thin piece sample is prepared, and prevents the formation of holes in the protective film formed on the coating film, allowing good observation Can be done.

  In a sample whose surface is made of a metal material made of Cr and whose concave and convex shape has an average width and height of 50 nm, the processing location is determined with an optical microscope and the processing location is planned with an ultra-fine felt pen I drew a point with a pen pressure that lightly touched. After drawing the dots, a photograph was obtained with an optical microscope, and allowed to stand at room temperature and atmospheric pressure for about 1 minute, and dried to form a coating film. Next, Pt was deposited by magnetron sputtering at a setting of 0.10 μm to form a conductive film. After forming the conductive film, the sample was fixed to the FIB processing jig with a conductive tape and introduced into a focused ion beam apparatus (FIB apparatus). The FIB apparatus is a type equipped with an electron gun and an ion gun. After identifying the processing position marked with a felt pen by SEM observation in the FIB apparatus based on the photo of the optical microscope, a protective film with a width of 20 μm, a length of 2 μm, and a thickness of about 2 μm is formed at the W deposit. did. Etching was performed from both ends so as to sandwich the elongated W deposition film. After etching to a thickness of 2 μm, the sample inclination angle was changed, and a bottom portion as a bottom portion and side portions at both ends of the sample were cut. A part of the side is left, the tip of the probe is brought close to the sample piece, a W deposition film is formed at the contacted position, and the probe and the sample are bonded. After bonding, a part of the remaining side was cut off with an ion beam, and the thin sample adhered to the probe was separated from the sample. The thin sample was adhered to a TEM observation grid with a W deposition film, and after the grid and the sample were adhered, the probe and the sample were separated by an ion beam. The flake sample adhering to the grid had a thickness of about 2 μm, but was further thinned to a thickness of about 50 to 100 nm with a weak current beam from both sides. When the obtained thin piece sample was observed using a transmission electron microscope, three layers of a coating film formed with a felt pen, a Pt conductive film, and a W deposition film were formed, and a hole was also formed between the irregularities of the sample. It was intrusive. Further, since the sample was a metal, the contrast of the protective film of the felt pen mainly composed of the organic component was bright, the contrast difference of the interface was added, and the concavo-convex cross-sectional shape of the thin sample and the cross-sectional state near the sample surface became easy to see. In addition, as the thin sample was processed, the W deposition film located on the surface was cut and the film thickness was reduced. As a result of final cross-sectional observation, the thickness of the W deposition film was 0.4 μm, the thickness of the conductive film was 0.08 μm, and the thickness of the coating film by felt pen was 0.2 μm. .

1 Sample 1a Thin Sample 1b Etching location 2 Coating 3 Protective film
4 Conductive film 9 hole (small hole)
10 Redepo
H Recess height S Recess width

Claims (4)

A thin sample preparation method for producing a thin sample from a sample using a focused ion beam device,
A step of applying ink to a thin sample preparation part of the sample to form a coating film;
Introducing a sample into the focused ion beam apparatus, and forming a protective film with an ion beam at a thin sample preparation site using a metal-based material;
And a step of producing a thin piece sample by etching using an ion beam at a thin piece sample production place on which the protective film is formed.   The method for preparing a thin piece sample according to claim 1, wherein the step of applying ink to the thin piece sample preparation portion of the sample is performed with a pen.   The method for producing a sample flake according to claim 1 or 2, further comprising a step of forming a conductive film on the surface of the sample after the step of applying ink to a thin piece sample preparation location of the sample to form a coating film.   The surface of the thin sample preparation site of the sample has an uneven shape, the interval between the recesses of the uneven shape is in the range of 1 nm to 100 nm, and the height of the recesses is in the range of 1 nm to 1 μm. The method for preparing a thin sample according to any one of claims 1 to 3.

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