JP4555714B2 - Preparation method of nano-level structural composition observation sample - Google Patents

Description

  The present invention relates to a method for preparing a sample for observing a nano-level structural composition, and in particular, a nano-characteristic technique for completely removing a processing-resistant protective layer provided on the surface of a sample for observing a nano-level structural composition. The present invention relates to a method for producing a sample for level structure composition observation.

In recent years, HDDs (hard disk drives) have been rapidly reduced in size and capacity, and development of heads and media for realizing high-density magnetic recording is required.
In order to convert a magnetic signal generated from recording bits finely arranged on a medium into an electric signal with high efficiency by a reproducing head, miniaturization and thinning of the MR head are required.

In such a miniaturized / thinned MR head, it is necessary to accurately form the thickness of each layer constituting the spin valve film and to maintain a good interface state between the layers.
For example, if the film thickness distribution is not uniform, the interface is curved, or if the constituent atoms are interdiffused at the interface and the interface is unclear, desired characteristics cannot be obtained.
Such a situation also applies to a multilayer thin film structure and an impurity distribution structure in a magnetic recording medium or a semiconductor device.

  Therefore, in the past, the 2θ method using X-ray reflection at the interface was used to evaluate the film thickness and interface state of each layer such as the spin valve film and feed back the results to the manufacturing process. Improvement and production yield were improved.

  However, since the 2θ method is a method that uses the reflection intensity of X-rays at the interface, when the constituent atoms are interdiffused at the interface and the interface is unclear, a highly accurate analysis is difficult. In addition, even when an unexpected layer is present, it is difficult to perform highly accurate analysis.

  Therefore, as a technique for solving such a problem, a three-dimensional atom probe method is known as a technique for directly observing a three-dimensional structure at an atomic level (see, for example, Patent Document 1). A needle-shaped sample with a tip diameter of 1 μm or less formed at an acute angle is irradiated with a pulsed high electric field or laser, and with this energy, surface atoms or clusters are electrolytically evaporated, and a three-dimensional atom of the sample is detected by a two-dimensional position detector. Since the structure of the level is observed, the conventional atom probe method will now be described with reference to FIG.

See FIG.
FIG. 8 is an explanatory diagram of the principle of the atom probe method described above, and is configured from the tip of the needle-like sample 61 by applying a pulse high voltage to the needle-like sample 61 having a tip radius of, for example, 100 nm (= 0.1 μm). The substances 62 and 63 are subjected to field evaporation, and the arrival time (TOF: Time of Flight) of the flying constituent substances 62 and 63 is measured by the measuring device 64, and the ion species of the constituent substances 62 and 63 are identified from the arrival time. is there.

  The sample used for such an atom probe method has been processed using the FIB (focused ion beam) method, but in order to prevent damage to the observation site caused by the gallium ion beam being driven into the sample, Processing was performed after providing a protective layer such as W or C.

  Although a part of such a protective layer remains at the sample tip after processing, as is apparent from FIG. 8, since the atoms are ionized from the tip of the needle in the three-dimensional atom probe analysis, the analysis is desired. The farther the part to be done is from the tip of the needle, the longer it takes to analyze.

  That is, as the thickness of the remaining protective layer increases, the analysis time required for the three-dimensional atom probe analysis becomes longer. For example, when the thickness is about 100 nm, an additional analysis time of 2 to 3 hours is required. .

  This protective layer is necessary at the time of sample processing, but is not necessary at the time of observation, and as an optimum completed sample shape, it is preferable to finish the processing when the protective layer is just gone. Therefore, a technique for reducing the thickness of the protective layer remaining on the surface of the sample as much as possible has been desired.

In addition, when a sample for a transmission electron microscope of silicon single crystal is manufactured by the FIB method, an SiO ₂ film is formed on the outermost surface to prevent damage during FIB processing, and a hydrofluoric acid is used before analysis to form the SiO ₂ film. It has been proposed to solve the problem of remaining protective layers by removing (see, for example, Patent Document 2).
JP 2002-042715 A JP 2001-319954 A

  However, it is difficult to precisely control the remaining film thickness of the protective layer, and it is difficult to determine the optimum stopping conditions, and there are many cases where a large amount of the protective layer remains or excessive processing is performed up to the portion to be viewed. It was.

On the other hand, when SiO ₂ film is used as a protective layer, hydrofluoric acid is used in the removal process, so there is a strong possibility of damaging the observation or analysis location in the sample, and the materials that can be used are limited. Come.

  Therefore, an object of the present invention is to more easily remove the protective layer without damaging the sample.

FIG. 1 is a diagram illustrating the basic configuration of the present invention. Means for solving the problems in the present invention will be described with reference to FIG.
Refer to FIG. 1 In order to solve the above-mentioned problem, the present invention removes from a surface of a needle-like sample 1 a cluster 1 group 1 group consisting of one or more atoms by an external energy or an internal energy to an external space. in the method for manufacturing a nano-level structural composition sample for observation for observing the structural composition of the nano-level needle-shaped sample 1 by the steps of forming a protective layer 2 on the surface of the sample matrix, converges on the protective layer 2 And a step of detecting an end point of the processing by detecting the protective layer component 4 released from the top of the needle-like sample 1 when the sample base is processed into the needle-like sample 1 by the ion beam method. .

Thus, in the processing step of the sample base, the end point of the processing can be accurately detected by detecting the protective layer component 4 released from the top of the needle-like sample 1, and the top of the needle-like sample 1 can be sufficiently pointed. The protective layer 2 can be just removed without damaging the sample, thereby eliminating useless analysis time.
The internal energy in this case is typically a field evaporation by a pulsed high electric field, and the external energy is typically a pulsed electromagnetic wave such as a pulsed laser beam.

  In this case, various detectors 5 can be used to detect the end point of processing. For example, a laser beam for measurement is applied to the vicinity of the tip of the needle-like sample 1 from the top of the needle-like sample 1. The released protective layer component 4 may be detected by atomic absorption spectrometry, or the protective layer component 4 released from the top of the needle-like sample 1 by a mass analyzer installed in the vicinity of the tip of the needle-like sample 1. Further, the protective layer component 4 released from the top of the needle sample 1 may be detected by an emission analyzer installed in the vicinity of the tip of the needle sample 1.

Alternatively, the protective layer 2 is formed on the surface of the sample base via an intervening layer capable of selective wet etching with respect to the sample, and the sample base is formed on the needle-like sample 1 from the protective layer 2 by a focused ion beam method. After processing, the intervening layer may be removed by selective wet etching, in which case the special detector 5 is not required.

  In this case, the intervening layer is preferably a polymer material that can be removed with an organic solvent, in particular, a resist, so that the acicular sample 1 is not damaged when the intervening layer is removed.

  Furthermore, a contamination prevention layer, particularly a contamination prevention layer of 100 nm or less, more preferably 50 nm or less, may be provided between the intervening layer and the sample base material, thereby enabling etching in removing the intervening layer. Contamination can be avoided.

  In the present invention, since the end point detection is used, it is possible to remove just the protective layer, thereby making it possible to produce a sample for an atom probe with a high yield without damaging the sample. Become.

  In the present invention, when a sample base is processed into a needle-like sample by forming a protective layer such as W or C on the surface of the sample base and performing processing from above the protective layer using the FIB method or the like, Detecting the end point by detecting the protective layer component released from the top of the sample by atomic absorption spectrometry, mass spectrometer, or emission analyzer, and the protective layer component released from the top of the needle-like sample is no longer detected The processing is completed at the time.

  Alternatively, the sample base is formed by forming a protective layer on the surface of the sample base via an intervening layer such as a resist that can be selectively wet-etched with respect to the sample, and processing the protective layer using the FIB method or the like. After the sample is processed into a needle-like sample, the protective layer is also removed when the intervening layer is removed by selective wet etching using an organic solvent or the like.

Here, with reference to FIG.2 and FIG.3, the preparation method of the sample for nano level structure composition observation of Example 1 of this invention is demonstrated.
See Figure 2
First, a Cu layer 14 having a thickness of, for example, 1 nm and a Co layer having a thickness of, for example, 1 nm are formed on the silicon substrate 11 through a Ta underlayer 13 having a thickness of, for example, 1 nm. 15 are alternately provided to form the CoCu multilayer film 12, and then a W protective layer 16 having a thickness of, for example, 10 μm is formed as the sample base material 10.

  Next, the sample base material 10 is cut out into a rectangular shape by dicing to obtain a rectangular sample 17.

See Figure 3
Next, the needle-shaped sample 18 is formed by subjecting the rectangular sample 17 to FIB processing.
At this time, a high-resolution quadrupole mass spectrometer 19 is disposed in the vicinity of the tip of the rectangular sample 17, and W atoms 20 that jump out during processing are continuously detected by the quadrupole mass spectrometer 19. Processing is terminated with the point in time when the atoms 20 no longer jump out as the end point of processing.
The distance between the quadrupole mass spectrometer 19 and the tip of the rectangular sample 17 is 3 mm, for example.

  As described above, in the first embodiment of the present invention, since the end point is detected using the mass spectrometer, the protective layer can be surely removed without excessive processing.

Next, with reference to FIG. 4, a method for producing a sample for observing a nano-level structure composition according to Example 2 of the present invention will be described. Therefore, only the end point detection configuration will be described.
See Figure 4
FIG. 4 is an explanatory diagram of the end point detection configuration in the method for producing the nano-level structural composition observation sample of Example 2 of the present invention. In the vicinity of the tip of the rectangular sample 17, for example, a violet laser 21 having a wavelength of 401 nm is shown. The laser beam from the laser beam is branched by a half mirror 22 and a part thereof is used as measurement light 23, and the other is used as reference light 24.

  The measurement light 23 and the reference light 24 are detected by the photodetectors 26 and 27, the detection output is amplified by the comparison amplifier 28, and the output is input to the recorder meter 29. Is detected.

  In this case, when the W protective layer 16 is completely removed, the measurement light 23 is not absorbed by the W atoms 20, so that the output of the comparison amplifier 28 becomes constant at the minimum value, and this point is determined as the processing end point. To finish processing.

Thus, in Example 2 of the present invention, the end point is detected by the two-light absorption analysis, so that it is possible to reliably remove the protective layer without excessive processing.
Further, since the optical means is used, the degree of freedom of arrangement of the measurement system is increased as compared with the case where a mass spectrometer is used.

Next, with reference to FIG. 5, a method for producing a sample for observing a nano-level structure composition according to Example 3 of the present invention will be described. The other configuration is the same as that of Example 1 except that the end point detection means is different. Therefore, only the end point detection configuration will be described.
See Figure 5
FIG. 5 is an explanatory diagram of an end point detection configuration in the method for producing a nano-level structural composition observation sample of Example 3 of the present invention, in which a high-frequency coil 30 is disposed in the vicinity of the tip of the rectangular sample 17 and high-frequency output is performed. Thus, W atoms 20 jumping out during processing are excited to emit light.

  Of the emission line 31 associated with the excitation emission, only the W emission light 33 having a wavelength of 210 nm associated with the excitation emission of the W atom 20 is extracted by the diffraction grating 32, detected by the photomultiplier tube 34, and output from the photomultiplier tube 34. Is no longer obtained, the time is determined as the processing end point, and the processing is terminated.

Thus, in Example 3 of the present invention, since the end point is detected by atomic emission analysis, the protective layer can be reliably removed without excessive processing.
Further, the apparatus configuration can be reduced in size as compared with the case where a mass spectrometer is used, and the detection sensitivity can be increased as compared with the two-light absorption analysis.

Next, a method for preparing a sample for observing a nano-level structure composition according to Example 4 of the present invention will be described. However, since the end point detection method is the same as that of Example 1 described above except for the processing method, illustration is omitted. .
First, a resist is collectively applied to the surface of a 6-inch diameter sample base material formed in the same manner as in Example 1 above, and a circular pattern is exposed and developed to form a resist pattern. Using this resist pattern as a mask A needle-like sample is prepared by dry etching.

  At this time, by incorporating a high-resolution mass spectrometer, for example, a fan-shaped magnetic analyzer mass spectrometer, in the etching chamber, W atoms jumping out during processing are detected, and the time point when the W atoms no longer pop out. The processing is determined to be the processing end point and the processing is terminated.

  Even when the processing method is not the FIB method as in the fourth embodiment of the present invention, the end point detection mechanism is used when processing the sample for the atom probe, so that the protective layer can be securely formed without overprocessing. It becomes possible to remove.

Next, with reference to FIG.6 and FIG.7, the preparation method of the sample for nano level structure composition observation of Example 5 of this invention is demonstrated.
See FIG.
First, a Ru film 42 having a thickness of, for example, 10 nm is formed on the silicon substrate 41 using a sputtering method, and subsequently, a Co contamination prevention layer 43 having a thickness of 100 nm or less, for example, 10 nm. Form.
The Co contamination prevention layer 43 is for preventing contamination of Ru, which becomes an observation portion, in an etching process performed after FIB processing described later.

  Next, a resist is applied to the front surface, and a resist layer 44 having a thickness of, for example, 100 nm is formed by baking at 110 ° C., for example, and then again Au is formed with a thickness of, for example, 100 nm using a sputtering method. A protective layer 45 is formed.

Next, using a dicing process, for example, the FIB processing sample 46 was cut out at a scanning speed of a dicing saw of 1.0 mm / second.
The FIB processing sample 46 cut out in this case was formed into a shape including a protrusion 48 of 0.2 mm × 0.02 mm × 0.02 mm in the center of a base 47 having a size of 0.3 mm × 3 mm × 3 mm.

See FIG.
Next, after cleaning the FIB processing sample 46, it is carried into the FIB apparatus, and a C protective layer 49 having a thickness of, for example, 500 nm is formed on the entire surface. A shaped part 50 is formed.
In this case, the radius of curvature of the tip of the processed needle-like portion 50 is about 50 nm.

  Next, the FIB processed sample 46 is immersed in acetone for 30 minutes to remove the resist layer 44, whereby the observation sample 51 is completed.

  After observing the observation sample 51 using a transmission electron microscope (TEM), the needle-like portion 50 of the observation sample 51 has a Co / Ru / Si structure, and the Au protective layer 45 and It was confirmed that the C protective layer 49 was removed.

  An electric field of atoms on the surface of the observation sample 51 is applied by applying a voltage obtained by superimposing a pulse voltage having a frequency of 1 kHz to a DC voltage of 1.5 kV on the observation sample 51 thus prepared. Atom probe analysis was performed after evaporation.

  As a result, it was possible to obtain a mass spectrum derived from Co in the surface layer immediately after the start of analysis, but this also removed the Au protective layer 45 and the C protective layer 49 at the same time in the step of removing the resist layer 44 as described above. This is because.

  Thus, in Example 5 of the present invention, a resist layer that can be removed with an organic solvent is provided between the protective layer and the analysis layer, so that etching damage is caused to the sample as in the case of using hydrofluoric acid. Never give.

  Further, although the Co contamination prevention layer 43 is provided, since it is about 10 nm, it is possible to perform highly accurate analysis without causing contamination and etching damage without excessively increasing the analysis time.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the conditions and configurations described in the embodiments, and various modifications are possible. For example, the protection described in the embodiments The layer is W, Au, or C. However, the layer is not limited to W, Au, or C, and may be any material that has low reactivity with the sample to be analyzed, depending on the material of the sample. It will be changed.

  In the above embodiment, only a voltage is applied at the time of field evaporation and ionization, but a pulsed electromagnetic wave such as a laser beam may be applied in synchronization with the pulse voltage. Field evaporation at the tip can be easily caused, and is particularly effective when the size of the tip is large.

  Furthermore, evaporation and ionization may be performed only with pulsed electromagnetic waves such as laser light without applying an electric field.

In the first embodiment, a quadrupole mass spectrometer is used as the mass spectrometer. However, although the apparatus configuration is increased in size, the same as in the fourth embodiment in order to enable detection with higher accuracy. Alternatively, a sector magnetic field analyzer mass spectrometer may be used.
Conversely, in Example 4, a quadrupole mass spectrometer may be used instead of the sector magnetic field analyzer mass spectrometer.

  Further, in Example 2 above, atomic absorption spectrometry is used. However, the configuration of the atomic absorption analysis shown is merely an example, and the wavelength of the laser beam used and the configuration of the measurement system are variously changed. Is possible.

  Further, in Example 3 described above, atomic emission analysis is used, but the configuration of the atomic emission analysis shown is merely an example, and the configuration of the measurement system and excitation mechanism used can be variously changed. is there.

  In Example 5 described above, the Co contamination prevention film is provided on the Ru layer serving as the analysis layer. However, this Co contamination prevention film is not always necessary, and is directly on the Ru layer serving as the analysis layer. A resist layer may be provided.

  Further, in Example 5 above, the C protective layer is provided in addition to the Au protective layer. However, this C protective layer is not necessarily required, and the FIB processing is performed using only the Au protective layer as the protective layer. It is good.

The detailed features of the present invention will be described again with reference to FIG. 1 again.
See FIG. 1 again. (Supplementary note 1) From the surface of the needle-shaped sample 1, the cluster-like group consisting of one or more atoms or one element is separated into the external space by external energy or internal energy, and the needle-shaped sample 1 In a method for producing a nano-level structural composition observation sample for observing the nano-level structural composition of the sample 1, a step of forming a protective layer 2 on the surface of the sample base, and a focused ion beam method from above the protective layer 2 in processing the sample matrix to the needle-shaped sample 1, nano-level, characterized by a step of detecting the end point of machining by detecting the protective layer components 4 released from the top of the needle-like sample 1 A method for producing a structural composition observation sample.
(Additional remark 2) In order to detect the end point of the said process, the laser beam for a measurement is irradiated to the front-end | tip part vicinity of the said needle-shaped sample 1, and the protective layer component 4 released from the top part of the said needle-shaped sample 1 is atomic absorption The method for producing a sample for observing a nano-level structure composition according to appendix 1, wherein the sample is detected by an analysis method.
(Additional remark 3) In order to detect the end point of the said process, detecting the protective layer component 4 released from the top part of the said needle-shaped sample 1 with the mass analyzer installed in the vicinity of the front-end | tip part of the said needle-shaped sample 1 is detected. A method for producing a sample for observing a nano-level structure composition according to Supplementary Note 1, wherein the sample is for observation.
(Additional remark 4) In order to detect the end point of the said process, detecting the protective layer component 4 released from the top part of the said needle-shaped sample 1 with the emission analyzer installed in the vicinity of the front-end | tip part of the said needle-shaped sample 1 is detected. A method for producing a sample for observing a nano-level structure composition according to Supplementary Note 1, wherein the sample is for observation.
(Supplementary Note 5) When the cluster 1 group 1 consisting of one or more atoms or one element is separated from the surface of the needle-like sample 1 by external energy or internal energy into the external space, the nano-level of the needle-like sample 1 Forming a protective layer 2 via an intervening layer capable of selective wet etching with respect to the sample on the surface of the sample base in a method for producing a sample for observing a nano-level structural composition for observing the structural composition of the thus the sample matrix on the focused ion beam method from above the protective layer 2 after processed into needle-like sample 1, when removing the intermediate layer by selective wet etching, is removed together the protective layer 2 also nano-level structural composition method for manufacturing a sample for observation, characterized in that a step.
(Additional remark 6) The said intermediate | middle layer consists of a polymeric material which can be removed with an organic solvent, The preparation method of the sample for nano level structural composition observation of Additional remark 5 characterized by the above-mentioned.
(Additional remark 7) The preparation method of the sample for nano-level structure composition observation of Additional remark 5 or 6 characterized by providing the wet-proof etching protection layer between the said intervening layer and sample base material.
(Supplementary note 8) The method for producing a sample for observing a nano-level structure composition according to supplementary note 7, wherein the wet-resistant / etching protective layer has a thickness of 100 nm or less .

  As an example of use of the present invention, a GMR element or a magnetic recording medium constituting a reproducing head is typical, but the present invention is not limited to the reproducing head or the like, and the composition structure near the interface of the gate insulating film in the MISFET It is also applied to the analysis method of the nano-level structure composition of a semiconductor element in which the interface state or the like becomes a problem. Furthermore, it is also applied to the production of a nano-level structure by general FIB processing. .

It is explanatory drawing of the fundamental structure of this invention. It is explanatory drawing of the preparation method to the middle of the sample for nano-level structure composition observation of Example 1 of this invention. It is explanatory drawing of the preparation methods after FIG. 2 of the sample for nano-level structure composition observation of Example 1 of this invention. It is explanatory drawing of the end point detection structure in the preparation methods of the sample for nano-level structure composition observation of Example 2 of this invention. It is explanatory drawing of the end point detection structure in the preparation methods of the sample for nano level structural composition observation of Example 3 of this invention. It is explanatory drawing of the preparation method to the middle of the sample for nano-level structure composition observation of Example 5 of this invention. It is explanatory drawing of the preparation methods after FIG. 6 of the sample for nano-level structure composition observation of Example 5 of this invention. It is explanatory drawing of the principle of an atom probe method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Needle-shaped sample 2 Protective layer 3 Focused ion beam 4 Freed protective layer component 5 Detector 10 Sample base material 11 Silicon substrate 12 CoCu multilayer film 13 Ta underlayer 14 Cu layer 15 Co layer 16 W protective layer 17 Rectangular sample 18 Needle-shaped sample 19 Quadrupole mass spectrometer 20 W atom 21 Purple laser 22 Half mirror 23 Measurement light 24 Reference light 25 Mirror 26 Photo detector 27 Photo detector 28 Comparative amplifier 29 Recorder meter 30 High frequency coil 31 Emission line 32 Diffraction Lattice 33 W emitted light 34 Photomultiplier tube 41 Silicon substrate 42 Ru film 43 Co contamination prevention layer 44 Resist layer 45 Au protective layer 46 FIB processing sample 47 Base 48 Protrusion 49 C protective layer 50 Needle 51 Observation Sample 61 Needle-shaped sample 62 Constituent material 63 Constituent material 64 Measuring instrument

Claims (5)

From the surface of the needle-shaped sample, the cluster-like group of one atom or a plurality of elements is separated from the surface by external energy or internal energy, and the nano-level structural composition of the needle-shaped sample is observed. In order to prepare a nano-level structural composition observation sample for
Forming a protective layer on the surface of the sample matrix,
Wherein said sample matrix from the protective layer by a focused ion beam method in processing a needle-like sample, and detecting the end point of the machining by detecting the released the protective layer components from the top of the needle-like sample < A method for producing a sample for observing a nano-level structural composition, characterized by comprising: In order to detect the end point of the processing, a laser beam for measurement is irradiated to the vicinity of the tip of the needle-shaped sample, and a protective layer component released from the top of the needle-shaped sample is detected by atomic absorption spectrometry. The method for producing a sample for observing a nano-level structural composition according to claim 1. In order to detect the end point of the processing,
Preparation of nano-level structural composition sample for observation of claim 1, wherein the detecting the released protective layer components from the top of the needle-like sample by the mass spectrometer installed in the vicinity of the tip of the needle-like sample Method. In order to detect the end point of the processing,
Preparation of nano-level structural composition sample for observation of claim 1, wherein the detecting the released protective layer components from the top of the needle-like sample by emission analyzer installed in the vicinity of the tip of the needle-like sample Method. From the surface of the needle-shaped sample, the cluster-like group of one atom or a plurality of elements is separated from the surface by external energy or internal energy, and the nano-level structural composition of the needle-shaped sample is observed. In order to prepare a nano-level structural composition observation sample for
Forming a protective layer on the surface of the sample matrix via an intervening layer capable selective wet etching of the sample,
After the sample matrix by focused ion beam method from the protective layer was processed into needle-shaped sample, <br/> the step of also together removing the protective layer when removing the intermediate layer by selective wet etching A method for producing a sample for observing a nano-level structural composition, comprising:

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