JP2017150840A - Preparation method of sample for transmission electron microscope and confirmation method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of removing a damaged layer of a sample piece as a sample for a transmission electron microscope (TEM) while a removal state of the damaged layer is accurately grasped, before TEM observation is performed.SOLUTION: A preparation method and a confirmation method of a sample for TEM include: a removal step of removing a portion containing predetermined ions X in a sample piece which is extracted from a sample by a focused ion beam device using the ions X; and a confirmation step of detecting Auger electrons generated when an electron beam is applied to the sample piece in the removal step, so as to confirm the presence or absence or the content of the ions X in the sample piece.SELECTED DRAWING: Figure 2

Description

  The present invention belongs to a preparation method and a confirmation method of a sample for a transmission electron microscope.

  A TEM sample used for observation with a transmission electron microscope (TEM, hereinafter also referred to as a TEM apparatus) needs to be thinned to a thickness that allows transmission of an electron beam. General sample thinning methods include pulverization method in which a sample is crushed with a mortar, microtome method in which the sample is cut with a diamond knife, chemical polishing method in which etching is performed with an acid or alkali solution, and electropolishing method in which an electrolytic solution is used for electrolysis. An ion polishing method in which ion etching using Ar ions or Ga ions is performed. Among these thinning methods, recently, a focused ion beam (FIB) apparatus belonging to the ion polishing method has been widely used (see, for example, Patent Document 1).

  The FIB apparatus irradiates a sample surface while scanning with a Ga ion beam focused to a diameter of several nanometers to several hundred nanometers, and has functions of “see”, “shave”, and “attach” to the sample surface. Specifically, secondary ions or secondary ions generated from the sample surface are captured by a detector to observe (see) a scanning ion microscope (SIM) image, and the Ga ion sputtering phenomenon is observed. It is possible to ion-etch (shave) a specific area by using it, or to spray a gas containing carbon, tungsten, platinum, etc. on the specific area, and to decompose (reduce) and deposit (attach) it. .

  The FIB apparatus has the great advantage that a sample piece can be collected from an arbitrary minute part of a sample and can be thinned using the function as described above. However, since sample etching or thinning usually involves ion etching with Ga ions, Ga ions can penetrate into the surface of the sample piece to form a damage layer (mainly an amorphous layer). It has been known. This damaged layer causes a decrease in image quality in TEM observation, and Ga may become a contaminating element in elemental analysis in TEM observation.

  As a method of avoiding such a problem, a method of soft ion etching with a low acceleration Ga ion beam, a method of ion etching with Ar ions without using Ga ions in the first place (ion thinning method), etc. are adopted. . In particular, the latter method is widely used because it can be applied to many materials without using Ga ions (see Non-Patent Document 1).

On the other hand, the FIB apparatus has a function capable of producing a sample piece that is a TEM sample, and in addition to the FIB column, a scanning electron microscope (SEM) column and Ar ions There is a triple beam type FIB apparatus that also has a beam. With this apparatus, even if Ga ions enter the surface of the sample piece by performing ion etching with Ga ions and the damaged layer is formed, the damaged layer can be removed by the Ar ion beam. Can observe the sample piece from the cross-sectional direction without damaging it by the SEM function, and can confirm the presence or absence of a damaged layer in the sample piece (see Non-Patent Document 2).
After this confirmation, the sample piece is taken out from the FIB apparatus, set in the TEM apparatus, and TEM observation is performed on the sample piece.

Japanese Unexamined Patent Publication No. 2000-214056

Hirokazu Sasaki, Takeharu Kato, Takeyoshi Matsuda, Tsukasa Hirayama. TEM sample preparation technology using FIB. microscope. 2011, vol 46, No. 3, p. 188-194. Haruo Takahashi. TEM sample preparation using a triple beam device. microscope. 2008.vol 43, No. 2, p. 130-132.

In the removal method of the damaged layer by the ion thinning method of Non-Patent Document 1, since the removal conditions differ depending on the material of the sample, it is necessary to find an optimum condition for each material of the sample, which is troublesome.
On the other hand, if the damage layer removal method by the triple beam type FIB apparatus of Non-Patent Document 2 is adopted, the damage layer is removed by an Ar ion beam anyway, unlike the ion thinning method of Non-Patent Document 1. There is no need to find an optimum condition for each material of the sample, and a TEM sample can be produced more efficiently than Non-Patent Document 1 in view of time and effort alone.

  However, regarding the production of the sample piece (TEM sample) of Non-Patent Document 2, the following great knowledge was obtained by the present inventor. That is, it has been found that there is a big problem in the confirmation method after removing the damaged layer with an Ar ion beam in actually producing a sample piece as a TEM sample.

  For example, consider a case where a sample piece is manufactured by a triple beam type FIB apparatus as in Non-Patent Document 2. Using the FIB apparatus, the damaged layer in the sample is removed with an Ar ion beam to obtain a sample piece. Subsequently, an SEM image of the sample piece is obtained by the SEM function in the FIB apparatus. And the removal state of a damage layer is confirmed from the contrast of the said SEM image.

  In this case, the damaged layer (for example, the presence or absence of Ga ions) in the sample piece had to be confirmed based only on the contrast of the SEM image, that is, the visual information. For example, as a result of TEM observation after setting a sample piece judged to have no damaged layer from the contrast of the SEM image in the TEM apparatus, Ga ions actually remain in the sample piece, It can also have an adverse effect.

  In addition, when an abnormal TEM observation result is generated due to Ga ions, it is certainly considered that the damaged layer is removed again by resetting the sample piece to the above-described ion thinning apparatus or FIB apparatus. It is done. However, in any case, in any case, the ion thinning device, FIB device, and TEM device require that the sample piece be in a vacuum state in order to introduce the sample piece into the device, and conversely, in order to remove the sample piece from the device, The piece must be at atmospheric pressure. That is, when the damaged layer needs to be removed again, it is inevitably necessary to perform an operation for bringing the sample piece into a vacuum state and an atmospheric pressure state, which is not efficient.

  The above inefficient situation occurs even when SEM observation is performed on a sample piece using a triple beam FIB apparatus as in Non-Patent Document 2. With the technique described in Non-Patent Document 1 that does not assume SEM observation, the presence or absence of a damaged layer must be confirmed by TEM observation. It is also envisaged that the combination “perform” must be performed twice or three times. In addition, when anaerobic sample pieces are handled, it is not preferable because the sample may be altered by an operation in which a vacuum state and an atmospheric pressure state are repeated.

  An object of the present invention is to provide a technique capable of removing a damaged layer while accurately grasping a removed state of a damaged layer of a sample piece that is a TEM sample before performing TEM observation.

In order to solve the above problems, the present inventor has intensively studied. As a result, the present inventor, in the stage before performing TEM observation,
-Step of removing Ga ions that became the basis of the damaged layer from the sample piece-We sought a method capable of executing a step of accurately confirming the presence or absence of Ga ions that became the basis of the damaged layer on the surface of the sample piece.

  As a result of trial and error by the present inventors, the sample piece after the step of removing the damaged layer is irradiated with an electron beam, and the presence of Ga ions in the sample piece is detected by detecting Auger electrons generated at that time. Or the method of confirming content was invented. With this technique, it is possible to remove the damaged layer while qualitatively or quantitatively grasping the Ga ions in the sample piece after performing the step of removing the damaged layer as an elemental analysis. It was found that the damaged layer can be removed while accurately grasping the removed state of the damaged layer of the sample piece.

The embodiments of the present invention made based on the above findings are as follows.
The first aspect of the present invention is:
A method for preparing a sample for a transmission electron microscope,
A removing step of removing a portion containing the ion X in the sample piece extracted from the sample by the focused ion beam apparatus using the predetermined ion X;
A confirmation step of confirming the presence or content of the ions X in the sample piece by detecting Auger electrons generated when the sample piece is irradiated with an electron beam during the removing step;
This is a method for manufacturing a sample for a transmission electron microscope.

According to a second aspect of the present invention, in the invention according to the first aspect,
The removal step and the confirmation step are performed while being arranged in one Auger electron spectrometer having an ion etching function using ions Y different from the ions X.

According to a third aspect of the present invention, in the invention according to the first or second aspect,
The ions X are Ga ions, and the ions Y are rare gas ions.

The fourth aspect of the present invention is:
A method for confirming a sample for a transmission electron microscope,
Before the sample piece from which the part containing the ion X is removed from the sample piece extracted from the sample by the focused ion beam apparatus using the predetermined ion X is placed on the sample piece, A confirmation step of confirming the presence or content of the ions X in the sample piece by detecting Auger electrons generated when the electron beam is irradiated;
This is a method for confirming a sample for a transmission electron microscope.

  According to the present invention, it is possible to remove the damaged layer while accurately grasping the removed state of the damaged layer of the sample piece, which is a TEM sample, before performing TEM observation.

It is a schematic sectional drawing which shows a mode that a sample piece is extracted from a sample using a FIB apparatus. It is a schematic sectional drawing which shows the Auger spectroscopy apparatus in this embodiment.

Hereinafter, embodiments of the present invention will be described in the following order.
1. 1. Preparation method of TEM sample 1-1. Preparation process 1-2. Removal step 1-3. Confirmation process (confirmation method)
2. Effects in the Embodiments The TEM apparatus in the present specification includes an apparatus related to a transmission electron microscope, as well as an apparatus that employs a technique that employs a transmission type (for example, a scanning transmission electron microscope (STEM)). including.

<1. Preparation method of TEM sample>
In the present embodiment, the following steps are mainly performed. Hereinafter, each step will be described.

1-1. Preparatory process In this process, a stage until the above-described removal process and confirmation process are performed. Specifically, a sample piece is extracted from a sample by a focused ion beam apparatus using predetermined ions X (for example, Ga ions). Then, the step of thinning is performed until the electron beam is transmitted through the sample piece. In addition, what is necessary is just to use the apparatus as described in the above-mentioned patent document 1 or the item of the below-mentioned Example for the process which concerns on this thinning, and abbreviate | omits for details.

As a precaution, the steps related to thinning are listed as follows.
(1) A step of fixing the sample to the FIB sample holder (2) A step of introducing the FIB sample holder into the FIB (3) A step of forming a protective film by deposition at an arbitrary position of the sample (4) High energy ( (5) Process of roughing the periphery of the protective film using a Ga ion beam with a high etching rate (5) Process of tilting the rough sample by 60 ° and etching the lower part of the sample from the cross-sectional direction (6) A step of lifting the sample piece with the micro-sampling device after returning the inclination to 0 ° (7) A step of bonding the lifted sample piece to a sample fixing base for TEM observation (hereinafter simply referred to as a TEM sample fixing base) (8) Bonding The thinned sample piece until the electron beam is transmitted

  Incidentally, FIG. 1A is a schematic cross-sectional view of steps (3) to (4), and FIG. 1 (b) is a schematic cross-sectional view of step (5). In the step (4), the sample piece s that is being formed from the sample S on which the protective film p is formed has a taper shape with the ion beam X (that is, Ga ion beam) downward. This is because the beam width becomes wider and the intensity becomes weaker as it goes, so that it becomes harder to etch as it goes down. Further, in the step (5), the lower part of the sample is etched by tilting 60 °, so that a sample piece s having a shape as shown in FIG. However, the surface of the sample piece s is damaged by the Ga ion beam, and a damaged layer d derived from Ga ions is formed.

  Moreover, although Ga ion was mentioned as said predetermined | prescribed ion X in said example, you may employ | adopt the ion (for example, I ion, Cs ion, etc.) concerning other elements.

1-2. Removal Step In this step, the portion containing the ion X is removed from the sample piece extracted from the sample by the focused ion beam apparatus using the predetermined ion X. By doing so, it is possible to remove the damaged layer d accompanying the collection of the sample piece s by the FIB apparatus, and it is not necessary to deteriorate the image quality in the TEM observation.

  In addition, there is no limitation in particular as a removal method of the part containing the ion X. FIG. For example, a method of etching the damaged layer d in the sample piece s by an apparatus having an ion etching function using ions Y different from the ions X may be employed. If an ion Y different from the ion X is used, the degree of removal of the damaged layer d formed by the ion X can be confirmed without any problem. The ion Y is not particularly limited, and examples thereof include rare gas (Ar, Xe, etc.) ions.

However, a very suitable example in this embodiment is that the removal step, which is this step, and the confirmation described later in an apparatus having an ion etching function using an ion Y different from the ion X and an element analysis function. The process is performed while the sample piece s is set in the apparatus.
As a specific example, the above-described removal process and the confirmation described later are performed while the sample piece s is placed in one Auger Electron Spectroscopy (AES) apparatus 1 having an ion etching function using Ar or Xe. It is highly preferred to carry out the process.

1-3. Confirmation process (confirmation method)
One of the features of the present embodiment is to perform the confirmation process, which is the present process, following the above-described removal process. In this step, the presence or content of ions X in the sample piece s is confirmed by detecting Auger electrons generated when the sample piece s is irradiated with an electron beam in the previous removal step.

As the timing of this confirmation process, it may be performed after the removal process is completed as scheduled.
A confirmation process is performed at this timing, and if the damaged layer d is removed as expected in the sample piece s, the sample piece s is installed in the TEM apparatus together with the TEM sample fixing base.
If it is not removed as expected and the damaged layer d remains, the above removal process is performed again. However, even if the removal step is performed again, according to the present embodiment, these operations can be performed in the Auger electron spectrometer. For this reason, the work of checking each time with the TEM device (and the work of evacuating the sample pieces one by one) becomes unnecessary, and the labor can be saved considerably.

Moreover, as a confirmation method of the damage layer d (ion X), confirming from the Auger electron spectroscopy spectrum obtained by irradiating the sample piece s with an electron beam is mentioned. For example, the presence or absence of the damage layer d may be determined based on the presence or absence of a peak derived from the ion X (for example, Ga) in the Auger electron spectroscopy spectrum. Even if the peak derived from the ion X can be confirmed, the ion X is determined from the peak area. If the amount of ions X is equal to or less than a predetermined value, the sample piece s may be moved to the work for installing the sample piece s together with the TEM sample fixing base in the TEM apparatus. Conversely, the removal step and the confirmation step which is the main step may be alternately performed finely, and the degree of removal of the damaged layer d may be confirmed each time. For example, as the timing of the confirmation process, the removal process may be interrupted frequently, the confirmation process which is the main process is performed each time, and the amount of damage layer d (that is, the amount of Ga) may be grasped quantitatively.
Furthermore, as a method for confirming the damaged layer d (Ga ions), of course, it may be confirmed qualitatively from the viewpoint of elemental analysis. For example, an element distribution photograph can be obtained from a qualitative analysis function in an AES detector (reference numeral 4 in FIG. 2) to be described later or an energy dispersive X-ray spectroscopy (EDS) detector (not shown) in the same manner to be described later. The presence or absence of Ga ions may be confirmed based on this.
In addition to the above confirmation methods, a sample piece s may be imaged with a secondary electron detector (reference numeral 3 in FIG. 2) described later, and the removal status of the damaged layer d may be confirmed from the result. .

  In any case, in the present embodiment, the damaged layer d in the sample piece s is removed by a single process regardless of the material of the sample S, and the removed state of the damaged layer d is grasped qualitatively or quantitatively. Removal is possible. Of course, the removal state may be grasped qualitatively and quantitatively, and it is preferable to improve the accuracy.

Note that a known device may be used as the Auger electron spectroscopy apparatus 1 mentioned in the present embodiment, but the outline will be described with reference to FIG. As shown in FIG. 2, an electron gun 2 that emits an electron beam E to a sample piece s, and a secondary electron detector that enables imaging of the sample piece s by detecting secondary electrons generated from the sample piece s. 3. An AES detector 4 for detecting Auger electrons generated from the sample piece s, an Ar ion beam gun 5 capable of irradiating an Ar ion beam Y having an ion etching function, and a table for fixing the sample piece s, and in the future TEM The TEM sample fixing base 6 and the like are arranged in the apparatus together with the sample pieces s. Hereinafter, the reference numerals are omitted.
An ion source used for ion etching is preferable from the viewpoint of elemental analysis because Ar is frequently used and easily available, and is not usually contained in the material.

The damage layer removal step and the confirmation step by the apparatus include the following steps.
(9) The step of fixing the sliced sample together with the TEM sample fixing base to the sample holder for an analyzer equipped with an ion etching function (10) The step of introducing the sample holder into an Auger electron spectrometer equipped with an ion etching function (11) The surface of the sample piece is ion-etched with Ar ions to remove the damaged layer, and the elemental analysis is performed on Ga from the spectrum of Auger electron spectroscopy generated by irradiating the sample piece with an electron beam. Determining whether the removal of the layer is complete

  In addition, as long as it is an apparatus which can perform said removal process and the confirmation process which is this process, you may use things other than an Auger electron spectrometer. Moreover, you may perform both said processes with a separate apparatus (For example, a removal process is performed with a FIB apparatus, and a confirmation process is performed with the EDS detector which is another apparatus). However, an Auger electron spectrometer is very preferable in that both of the above steps can be performed in the apparatus and it is easy to use.

  The thin film sample from which the damaged layer has been removed by performing the above steps is placed in the TEM apparatus and the cross section is observed. There is no particular limitation on the TEM apparatus used for observation, and a known TEM apparatus may be adopted.

<2. Effect in Embodiment>
According to this embodiment, there are mainly the following effects.
According to the present invention using the above means, the damaged layer can be removed by the ion etching function, and ions X (for example, Ga ions) derived from the damaged layer can be traced by the elemental analysis function.
In addition, it is possible to grasp the removal state of the damaged layer over time, to confirm the state of the sample by observing an image with a secondary electron detector, and to determine the removal of the damaged layer quantitatively. There is no need to examine conditions and reprocess each time, and a significant improvement in time efficiency can be expected.
Furthermore, the repetition of the vacuum state and the atmospheric pressure state accompanying the removal of the remaining damaged layer can be avoided. For example, in the case where the sample piece is anaerobic, an effect of suppressing deterioration of the sample is also obtained.

  As a result, according to the present embodiment, it is possible to remove the damaged layer while accurately grasping the removed state of the damaged layer of the sample piece, which is a TEM sample, before performing TEM observation.

  In the sense that the above effects are achieved, the present invention is also technically significant in terms of a method for confirming a TEM sample. In other words, the invention using the above confirmation process as a confirmation method is also technically significant.

  Hereinafter, this embodiment will be described. The technical scope of the present invention is not limited to the following examples.

Example 1
A Si wafer was used as a sample for TEM observation, and a Hitachi FIB apparatus (FB-2000A) was used for the thinning process. Moreover, a carbon-based material was used as a deposition source of the apparatus.
The sample piece was extracted by the apparatus, and the sample piece was thinned to a thickness (thickness of 100 nm or less) enough to transmit the electron beam. The sample piece was attached to an AES dedicated holder and introduced into an AES apparatus (JAMP / 9500 manufactured by JEOL).
Next, the surface of the sample piece was etched with an Ar ion gun, and Ga was tracked and detected by qualitative analysis of AES (presence or absence of Ga-derived peak by Auger electron spectroscopy spectrum).
As a result, the amount of Ga was below the lower limit of detection after an etching time of about several tens to several minutes. Moreover, when the sample piece after removing the damage layer by this method was observed with a TEM (Hitachi HF-2200), a high quality TEM image was obtained because the contrast derived from the damage layer disappeared.
In addition, when the elemental analysis was implemented with respect to the said sample piece with the EDS detector attached to the TEM apparatus after TEM observation, Ga was a detection minimum.

(Comparative Example 1)
The same operation as in the example was performed on the sample piece thinned by the FIB apparatus in a state where Ar ion etching by the AES apparatus was not performed. As a result, the TEM image became unclear due to the contrast derived from the damaged layer, and Ga was remarkably detected in the EDS analysis.

(Summary)
As a result, in this example, it was found that the removal state of the damaged layer of the sample piece, which is a sample for TEM, could be accurately grasped before TEM observation.

The details of the present invention have been described above. However, the present invention is not limited to the embodiments, and various improvements, changes, and combinations are made to the contents described above without departing from the gist of the present invention. Of course it is also good. Further, the present invention is not limited to the preparation of a TEM sample, and can be used for removing a damaged layer in the field of electron microscopes, for example.
In addition, unlike the conventional case, the present invention has technical significance in that the state of removal of the damaged layer is confirmed by using a device other than the TEM device, instead of placing the sample piece in the TEM device suddenly. .
The configuration in view of the above contents is as follows.
"This is a method for preparing a sample (for an electron microscope)
A removing step of removing a portion containing the ion X in the sample piece extracted from the sample by the focused ion beam apparatus using the predetermined ion X;
A confirmation step of confirming the presence or content of the ions X in the sample piece before installing the sample piece in the analyzer;
A method for preparing a sample (for an electron microscope). "
With the above configuration, for example, before performing observation with an electron microscope or the like, it is possible to remove the damaged layer while accurately grasping the removed state of the damaged layer of the sample piece that is the sample for the electron microscope. In addition, the repetition of the vacuum state and the atmospheric pressure state accompanying the removal of the remaining damaged layer can be avoided, and as a result, there is an effect of suppressing the deterioration of the sample. In other words, there is a problem related to the deterioration of the sample related to the reciprocation. It can be solved.

DESCRIPTION OF SYMBOLS 1 ... Auger electron spectrometer 2 ... Electron gun 3 ... Secondary electron detector 4 ... AES detector 5 ... Ar ion beam gun 6 ... TEM sample fixing stand S ... Sample s ... Sample piece d ... Damaged layer p ... Protective film X ... (Ga) Ion beam Y ... (Ar) Ion beam E ... Electron beam

Claims (4)

A method for preparing a sample for a transmission electron microscope,
A removing step of removing a portion containing the ion X in the sample piece extracted from the sample by the focused ion beam apparatus using the predetermined ion X;
A confirmation step of confirming the presence or content of the ions X in the sample piece by detecting Auger electrons generated when the sample piece is irradiated with an electron beam during the removing step;
A method for producing a sample for a transmission electron microscope having:   2. The transmission electron microscope according to claim 1, wherein the removing step and the confirmation step are performed while being arranged in one Auger electron spectrometer having an ion etching function using an ion Y different from the ion X. Sample preparation method.   The method for manufacturing a sample for a transmission electron microscope according to claim 1, wherein the ions X are Ga ions, and the ions Y are rare gas ions. A method for confirming a sample for a transmission electron microscope,
Before the sample piece from which the part containing the ion X is removed from the sample piece extracted from the sample by the focused ion beam apparatus using the predetermined ion X is placed on the sample piece, A confirmation step of confirming the presence or content of the ions X in the sample piece by detecting Auger electrons generated when the electron beam is irradiated;
A method for confirming a sample for a transmission electron microscope.