Microscopy, 2014, Vol. 63, No. S1 SPM system for semiconductor device applications Hiroshi Itoh, Takahiro Odaka, and Junichi Niitsuma National Institute of Advanced Industrial Science and Technology AIST Tsukuba Central 2, 1-1-1 Umezono,Tsukuba-shi, Ibaraki-ken, 305-8568, Japan
Acknowledgment I would like to thanks Ms. Ito and Dr. C.M. Wang in AIST for discussions. This study was partially supported from MEXT.
Fig. 1. Conductive probe microscopy, which is compatible to the pulse signals ranging to 50nS.
References 1. 2. 3. 4.
Tominaga J., et al., Jpn. J. Appl. Phys. 47, 5763, (2008). Wang C.M., Itoh H., JJAP Conf. Proc. 1, 011005, (2013). Itoh H., et al., Rev. Sci. Instrum. 77, 103704, (2006). Itoh Hiroshi, Takagi Hideki, Chunmei Wang, Proc. of SPIE Vol. 7971, 79711A, (2011). doi: 10.1093/jmicro/dfu091
Atomic resolution holography Kouichi Hayashi Institute for Materials Research, Tohoku University, Katahira, Sendai 980-8577, Japan
*Email: [email protected] Atomic resolution holography, such as X-ray fluorescence holography (XFH)[1] and photoelectron holography (PH), has the attention of researcher as an informative local structure analysis, because it provides three dimensional atomic images around specific elements within a range of a few nanometers. It can determine atomic arrangements around a specific element without any prior knowledge of structures. It is considered that the atomic resolution holographic is a third method of structural analysis at the atomic level after X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). As known by many researchers, XRD and XAFS are established methods that are widespread use in various fields. XRD and XAFS provide information on long-range translational periodicities and very local environments, respectively, whereas the atomic resolution holography gives 3D information on the local order and can visualize surrounding atoms with a large range of coordination shells. We call this feature “3D medium-range local structure observation”. In addition to this feature, the atomic resolution holography is very sensitive to the displacement of atoms from their ideal positions, and one can obtain quantitative information about local lattice distortions by analyzing reconstructed atomic images[2] When dopants with different atomic radii from the matrix elements are present, the lattices around the dopants are distorted. However, using the conventional methods of structural analysis, one cannot determine the extent to which the local lattice distortions are preserved from the dopants. XFH is a good tool for solving this problem. Figure 1 shows a recent achievement on a relaxor ferroelectric of Pb(Mg1/3Nb2/3)O3 (PMN) using XFH. The structural studies of relaxor ferroelectrics have been carried out by X-ray or neutron diffractions, which suggested rhombohedral distortions of their lattices. However, their true pictures have not been obtained, yet. The Nb Kα holograms showed four separate Pb images, as shown in Fig.1. Using
Fig. 1. 3D images of the nearest Pb and O atoms around Nb in Pb(Mg1/ The cube represents 1/8 of the unit cell.
3Nb2/3)O3.
Downloaded from http://jmicro.oxfordjournals.org/ at Florida Atlantic University on November 24, 2014
Recently, scanning probe microscopy (SPM) is widely used for development of semiconductor devices. One of the important functions of SPM is high resolution topography, such as shape of the nanoscale devices and surface roughness of the films. Additionally, SPM can measure the electronic structure of the nanoscale-devices. SPM system for thin films was developed to characterize the thin films for device applications. First, SPM system which can be apply short pulses to the sample holder is constructed to evaluate the electronic response of the thin film without using complex patterning on the Si wafer as shown in Fig. 1. Current design rule of the semiconductor devices is around 20 nm. The dimension of the devices are close to the probe radius of conductive SPM probes. The instrument was designed to characterize not only the static properties of nanoscale devices, but also the dynamic electronic properties. Shortest pulses which can be applied to the sample without destroying waveform were less than 50 nS. Time response of the current amplifier is ranging from 50 nS to 200 nS depending on the trans-impedance gains. The conditions (time and dimension) are similar to the active devices on the chip in the circuit. Thus, dynamic electronic properties of the thin films can be tested on a film without fabricating to the nanoscale devices. It is very helpful to optimizing the depositing conditions, such as sputtering parameters, of the thin film for semiconductor devices. For example, the system is used to optimize the film qualities for resistive memories [1]. The second function of the SPM system is the reproducible roughness measurement. Roughness of the film is also important for optimizing the depositing conditions of the thin film. Virtual reference probe method was developed for removing the variations of the SPM probes [2]. One of the biggest problems of SPM roughness measurement is the huge variations of the SPM probe apexes. The method is to normalizing the probe to the largest probe used in the measurements, after characterizing the probe shape with suitable reference artefact [3,4]. Image reconstruction, such as erosion and dilation process is used for the analysis. In this presentation, we will introduce the SPM system developed for semiconductor device applications. The SPM system also includes function to characterize the nanoscale contaminants on the Si wafer.
i13
Microscopy, 2014, Vol. 63, No. S1
i14 these images, we could obtain acute and obtuse rhombohedral structures of the crystal unit cells. Moreover, the Pb-Pb correlated images reconstructed from Pb Lα holograms showed a local structure of body center-like 2a0 ×2a0 × 2a0 superlattice, proving a rigid 3D network structural model combining the two kinds of rhombohedrons. This superstructure are believed to play an important role in the relaxor behaviour of PMN at atomic level[3].
References 1. Hayashi K., et al. J. Phys.: Condens. Matter 24, 093201 (2012). 2. Hosokawa S., et al. Phys. Rev. B 87, 094104 (2013). 3. Hu W., et al. Phys. Rev. B 89, 140103(R) (2014). doi: 10.1093/jmicro/dfu047
Motohiro Suzuki* Japan Synchrotron Radiation Research Institute/SPirng-8, Kouto, Sayo, Hyogo 679-5198, Japan
*Email: [email protected] X-ray measurement offers several useful features that are unavailable from other microscopic means including electron-based techniques. By using X-rays, one can observe the internal parts of a thick sample. This technique basically requires no high vacuum environment such that measurements are feasible for wet specimens as well as under strong electric and magnetic fields and even at a high pressure. X-ray spectroscopy using core excitation provides element-selectivity with significant sensitivities to the chemical states and atomic magnetic moments in the matter. Synchrotron radiation sources produce a small and low-divergent X-ray beam, which can be converged to a spot with the size of a micrometer or less using X-ray focusing optics. The recent development in the focusing optics has been driving X-ray microscopy, which has already gone into the era of X-ray nanoscopy. With the use of the most sophisticated focusing devices, an X-ray beam of 7-nm size has successfully been achieved [1]. X-ray microscopy maintains above-mentioned unique features of X-ray technique, being a perfect complement to electron microscopy. In this paper, we present recent studies on magnetic microscopy and local magnetic analysis using hard X-rays. The relevant instrumentation developments are also described. The X-ray nanospectroscopy station of BL39XU at SPring-8 is equipped with a focusing optics consisting of two elliptic mirrors, and a focused X-ray beam with the size of 100 × 100 nm2 is available [2]. Researchers can perform X-ray absorption spectroscopy: nano-XAFS (X-ray absorption fine structure) using the X-ray beam as small as 100 nm. The available X-ray energy is from 5 to 16 keV, which allows nano-XAFS study at the K edges of 3d transition metals, L edges of rare-earth elements and 5d noble metals. Another useful capability of the nanoprobe is X-ray polarization tunability, enabling magnetic circular dichroism (XMCD) spectroscopy with a sub-micrometer resolution. Scanning XMCD imaging, XMCD measurement in local areas, and element-specific magnetometry for magnetic particles/magnetic devices as small as 100 nm can be performed. Nano-XAFS application includes visualization of the chemical state in a particle catalyst [3] and phase-change memory devices [4]. For magnetic microscopic study, magnetization reversal processes of an individual magnetic CoPt dot in bit-patterned media have directly been observed [2]. Imaging of the chemical distribution and magnetic domain evolution in a Nd-Fe-B sintered magnet in demagnetization processes is presented. References 1. Mimura H., Handa S., Kimura T., Yumoto H., Yamakawa D., Yokoyama H., Matsuyama S., Inagaki K., Yamamura K.,
doi: 10.1093/jmicro/dfu041
X-ray STM: Nanoscale elemental analysis & Observation of atomic track Akira Saito1,2, Y. Furudate1,2, Y. Kusui1,2, T. Saito1,2, M. Akai-Kasaya1, Y. Tanaka2, K. Tamasaku2, Y. Kohmura2, T. Ishikawa2, Y. Kuwahara1,2, and M. Aono3 1 Dept. Precision Sci.& Technol.,Graduate School of Engineering, Osaka Univ.,Osaka, Japan, 2RIKEN SPring-8 Center, Sayo-cho, Hyogo, Japan, and 3National Inst. for Materials Science, Tsukuba, Ibaraki, Japan Scanning tunneling microscopy (STM) combined with brilliant X-rays from synchrotron radiation (SR) can provide various possibilities of original and important applications, such as the elemental analysis on solid surfaces at an atomic scale. The principle of the elemental analysis is based on the inner-shell excitation of an elementspecific energy level “under STM observation”. A key to obtain an atomic locality is to extract the element-specific modulation of the local tunneling current (not emission that can damage the spatial resolution), which is derived from the inner-shell excitation [1]. On this purpose, we developed a special SR-STM system and smart tip. To surmount a tiny core-excitation efficiency by hard X-rays, we focused two-dimensionally an incident beam having the highest photon density at the SPring-8. After successes in the elemental analyses by SR-STM [1,2] on a semiconductor hetero-interface (Ge on Si) and metal-semiconductor interface (Cu on Ge), we succeeded in obtaining the elemental contrast between Co nano-islands and Au substrate. The results on the metallic substrate suggest the generality of the method and give some important implications on the principle of contrast. For all cases of three samples, the spatial resolution of the analysis was estimated to be ∼1 nm or less, and it is worth noting that the measured surface domains had a deposition thickness of less than one atomic layer (Fig. 1, left and center). On the other hand, we found that the “X-ray induced atomic motion” can be observed directly with atomic scale using the SR-STM system effectively under the incident photon density of ∼2 x1015 photon/sec/mm2 [3]. SR-STM visualized successfully the track of the atomic motion (Fig. 1, right), which enabled the further analysis on the mechanism of the atomic motion. It is worth comparing our results with past conventional thermal STM observations on the same surface [4], where the atomic motion was found to occur in the 2-dimensional domain. However, our results show the atomic track having a local chain distribution [3]. The above mentioned results will allow us to investigate the chemical analysis and control of the local reaction with the spatial resolution of STM, giving hope of wide applications.
Downloaded from http://jmicro.oxfordjournals.org/ at Florida Atlantic University on November 24, 2014
Hard-X-ray magnetic microscopy and local magnetization analysis using synchrotron radiation
Sano Y., Tamasaku K., Nishino Y., Yabashi M., Ishikawa T., Yamauchi K., Nat. Phys. 6, 122 (2010). 2. Suzuki M., Kawamura N., Mizumaki M., Terada Y., Uruga T., Fujiwara A., Yamazaki H., Yumoto H., Koyama T., Senba Y., Takeuchi T., Ohashi H., Nariyama N., Takeshita K., Kimura H., Matsushita T., Furukawa Y., Ohata T., Kondo Y., Ariake J., Richter J., Fons P., Sekizawa O., Ishiguro N., Tada M., Goto S., Yamamoto M., Takata M., Ishikawa T., Phys J..: Conf. Ser. 430, 012017 (2013). 3. Ishiguro N., Uruga T., Sekizawa O., Tsuji T., Suzuki M., Kawamura N., Mizumaki M., Nitta K., Yokoyama T., Tada M., ChemPhysChem 15, 1563 (2014). 4. Richter J.H., Kolobov A.V., Fons P., Wang X., Mitrofanov K.V., Tominaga J., Osawa H., Suzuki M., MRS Proc. 1563, mrss13 (2013).
Acknowledgment I would like to thanks Ms. Ito and Dr. C.M. Wang in AIST for discussions. This study was partially supported from MEXT.
Fig. 1. Conductive probe microscopy, which is compatible to the pulse signals ranging to 50nS.
References 1. 2. 3. 4.
Tominaga J., et al., Jpn. J. Appl. Phys. 47, 5763, (2008). Wang C.M., Itoh H., JJAP Conf. Proc. 1, 011005, (2013). Itoh H., et al., Rev. Sci. Instrum. 77, 103704, (2006). Itoh Hiroshi, Takagi Hideki, Chunmei Wang, Proc. of SPIE Vol. 7971, 79711A, (2011). doi: 10.1093/jmicro/dfu091
Atomic resolution holography Kouichi Hayashi Institute for Materials Research, Tohoku University, Katahira, Sendai 980-8577, Japan
*Email: [email protected] Atomic resolution holography, such as X-ray fluorescence holography (XFH)[1] and photoelectron holography (PH), has the attention of researcher as an informative local structure analysis, because it provides three dimensional atomic images around specific elements within a range of a few nanometers. It can determine atomic arrangements around a specific element without any prior knowledge of structures. It is considered that the atomic resolution holographic is a third method of structural analysis at the atomic level after X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). As known by many researchers, XRD and XAFS are established methods that are widespread use in various fields. XRD and XAFS provide information on long-range translational periodicities and very local environments, respectively, whereas the atomic resolution holography gives 3D information on the local order and can visualize surrounding atoms with a large range of coordination shells. We call this feature “3D medium-range local structure observation”. In addition to this feature, the atomic resolution holography is very sensitive to the displacement of atoms from their ideal positions, and one can obtain quantitative information about local lattice distortions by analyzing reconstructed atomic images[2] When dopants with different atomic radii from the matrix elements are present, the lattices around the dopants are distorted. However, using the conventional methods of structural analysis, one cannot determine the extent to which the local lattice distortions are preserved from the dopants. XFH is a good tool for solving this problem. Figure 1 shows a recent achievement on a relaxor ferroelectric of Pb(Mg1/3Nb2/3)O3 (PMN) using XFH. The structural studies of relaxor ferroelectrics have been carried out by X-ray or neutron diffractions, which suggested rhombohedral distortions of their lattices. However, their true pictures have not been obtained, yet. The Nb Kα holograms showed four separate Pb images, as shown in Fig.1. Using
Fig. 1. 3D images of the nearest Pb and O atoms around Nb in Pb(Mg1/ The cube represents 1/8 of the unit cell.
3Nb2/3)O3.
Downloaded from http://jmicro.oxfordjournals.org/ at Florida Atlantic University on November 24, 2014
Recently, scanning probe microscopy (SPM) is widely used for development of semiconductor devices. One of the important functions of SPM is high resolution topography, such as shape of the nanoscale devices and surface roughness of the films. Additionally, SPM can measure the electronic structure of the nanoscale-devices. SPM system for thin films was developed to characterize the thin films for device applications. First, SPM system which can be apply short pulses to the sample holder is constructed to evaluate the electronic response of the thin film without using complex patterning on the Si wafer as shown in Fig. 1. Current design rule of the semiconductor devices is around 20 nm. The dimension of the devices are close to the probe radius of conductive SPM probes. The instrument was designed to characterize not only the static properties of nanoscale devices, but also the dynamic electronic properties. Shortest pulses which can be applied to the sample without destroying waveform were less than 50 nS. Time response of the current amplifier is ranging from 50 nS to 200 nS depending on the trans-impedance gains. The conditions (time and dimension) are similar to the active devices on the chip in the circuit. Thus, dynamic electronic properties of the thin films can be tested on a film without fabricating to the nanoscale devices. It is very helpful to optimizing the depositing conditions, such as sputtering parameters, of the thin film for semiconductor devices. For example, the system is used to optimize the film qualities for resistive memories [1]. The second function of the SPM system is the reproducible roughness measurement. Roughness of the film is also important for optimizing the depositing conditions of the thin film. Virtual reference probe method was developed for removing the variations of the SPM probes [2]. One of the biggest problems of SPM roughness measurement is the huge variations of the SPM probe apexes. The method is to normalizing the probe to the largest probe used in the measurements, after characterizing the probe shape with suitable reference artefact [3,4]. Image reconstruction, such as erosion and dilation process is used for the analysis. In this presentation, we will introduce the SPM system developed for semiconductor device applications. The SPM system also includes function to characterize the nanoscale contaminants on the Si wafer.
i13
Microscopy, 2014, Vol. 63, No. S1
i14 these images, we could obtain acute and obtuse rhombohedral structures of the crystal unit cells. Moreover, the Pb-Pb correlated images reconstructed from Pb Lα holograms showed a local structure of body center-like 2a0 ×2a0 × 2a0 superlattice, proving a rigid 3D network structural model combining the two kinds of rhombohedrons. This superstructure are believed to play an important role in the relaxor behaviour of PMN at atomic level[3].
References 1. Hayashi K., et al. J. Phys.: Condens. Matter 24, 093201 (2012). 2. Hosokawa S., et al. Phys. Rev. B 87, 094104 (2013). 3. Hu W., et al. Phys. Rev. B 89, 140103(R) (2014). doi: 10.1093/jmicro/dfu047
Motohiro Suzuki* Japan Synchrotron Radiation Research Institute/SPirng-8, Kouto, Sayo, Hyogo 679-5198, Japan
*Email: [email protected] X-ray measurement offers several useful features that are unavailable from other microscopic means including electron-based techniques. By using X-rays, one can observe the internal parts of a thick sample. This technique basically requires no high vacuum environment such that measurements are feasible for wet specimens as well as under strong electric and magnetic fields and even at a high pressure. X-ray spectroscopy using core excitation provides element-selectivity with significant sensitivities to the chemical states and atomic magnetic moments in the matter. Synchrotron radiation sources produce a small and low-divergent X-ray beam, which can be converged to a spot with the size of a micrometer or less using X-ray focusing optics. The recent development in the focusing optics has been driving X-ray microscopy, which has already gone into the era of X-ray nanoscopy. With the use of the most sophisticated focusing devices, an X-ray beam of 7-nm size has successfully been achieved [1]. X-ray microscopy maintains above-mentioned unique features of X-ray technique, being a perfect complement to electron microscopy. In this paper, we present recent studies on magnetic microscopy and local magnetic analysis using hard X-rays. The relevant instrumentation developments are also described. The X-ray nanospectroscopy station of BL39XU at SPring-8 is equipped with a focusing optics consisting of two elliptic mirrors, and a focused X-ray beam with the size of 100 × 100 nm2 is available [2]. Researchers can perform X-ray absorption spectroscopy: nano-XAFS (X-ray absorption fine structure) using the X-ray beam as small as 100 nm. The available X-ray energy is from 5 to 16 keV, which allows nano-XAFS study at the K edges of 3d transition metals, L edges of rare-earth elements and 5d noble metals. Another useful capability of the nanoprobe is X-ray polarization tunability, enabling magnetic circular dichroism (XMCD) spectroscopy with a sub-micrometer resolution. Scanning XMCD imaging, XMCD measurement in local areas, and element-specific magnetometry for magnetic particles/magnetic devices as small as 100 nm can be performed. Nano-XAFS application includes visualization of the chemical state in a particle catalyst [3] and phase-change memory devices [4]. For magnetic microscopic study, magnetization reversal processes of an individual magnetic CoPt dot in bit-patterned media have directly been observed [2]. Imaging of the chemical distribution and magnetic domain evolution in a Nd-Fe-B sintered magnet in demagnetization processes is presented. References 1. Mimura H., Handa S., Kimura T., Yumoto H., Yamakawa D., Yokoyama H., Matsuyama S., Inagaki K., Yamamura K.,
doi: 10.1093/jmicro/dfu041
X-ray STM: Nanoscale elemental analysis & Observation of atomic track Akira Saito1,2, Y. Furudate1,2, Y. Kusui1,2, T. Saito1,2, M. Akai-Kasaya1, Y. Tanaka2, K. Tamasaku2, Y. Kohmura2, T. Ishikawa2, Y. Kuwahara1,2, and M. Aono3 1 Dept. Precision Sci.& Technol.,Graduate School of Engineering, Osaka Univ.,Osaka, Japan, 2RIKEN SPring-8 Center, Sayo-cho, Hyogo, Japan, and 3National Inst. for Materials Science, Tsukuba, Ibaraki, Japan Scanning tunneling microscopy (STM) combined with brilliant X-rays from synchrotron radiation (SR) can provide various possibilities of original and important applications, such as the elemental analysis on solid surfaces at an atomic scale. The principle of the elemental analysis is based on the inner-shell excitation of an elementspecific energy level “under STM observation”. A key to obtain an atomic locality is to extract the element-specific modulation of the local tunneling current (not emission that can damage the spatial resolution), which is derived from the inner-shell excitation [1]. On this purpose, we developed a special SR-STM system and smart tip. To surmount a tiny core-excitation efficiency by hard X-rays, we focused two-dimensionally an incident beam having the highest photon density at the SPring-8. After successes in the elemental analyses by SR-STM [1,2] on a semiconductor hetero-interface (Ge on Si) and metal-semiconductor interface (Cu on Ge), we succeeded in obtaining the elemental contrast between Co nano-islands and Au substrate. The results on the metallic substrate suggest the generality of the method and give some important implications on the principle of contrast. For all cases of three samples, the spatial resolution of the analysis was estimated to be ∼1 nm or less, and it is worth noting that the measured surface domains had a deposition thickness of less than one atomic layer (Fig. 1, left and center). On the other hand, we found that the “X-ray induced atomic motion” can be observed directly with atomic scale using the SR-STM system effectively under the incident photon density of ∼2 x1015 photon/sec/mm2 [3]. SR-STM visualized successfully the track of the atomic motion (Fig. 1, right), which enabled the further analysis on the mechanism of the atomic motion. It is worth comparing our results with past conventional thermal STM observations on the same surface [4], where the atomic motion was found to occur in the 2-dimensional domain. However, our results show the atomic track having a local chain distribution [3]. The above mentioned results will allow us to investigate the chemical analysis and control of the local reaction with the spatial resolution of STM, giving hope of wide applications.
Downloaded from http://jmicro.oxfordjournals.org/ at Florida Atlantic University on November 24, 2014
Hard-X-ray magnetic microscopy and local magnetization analysis using synchrotron radiation
Sano Y., Tamasaku K., Nishino Y., Yabashi M., Ishikawa T., Yamauchi K., Nat. Phys. 6, 122 (2010). 2. Suzuki M., Kawamura N., Mizumaki M., Terada Y., Uruga T., Fujiwara A., Yamazaki H., Yumoto H., Koyama T., Senba Y., Takeuchi T., Ohashi H., Nariyama N., Takeshita K., Kimura H., Matsushita T., Furukawa Y., Ohata T., Kondo Y., Ariake J., Richter J., Fons P., Sekizawa O., Ishiguro N., Tada M., Goto S., Yamamoto M., Takata M., Ishikawa T., Phys J..: Conf. Ser. 430, 012017 (2013). 3. Ishiguro N., Uruga T., Sekizawa O., Tsuji T., Suzuki M., Kawamura N., Mizumaki M., Nitta K., Yokoyama T., Tada M., ChemPhysChem 15, 1563 (2014). 4. Richter J.H., Kolobov A.V., Fons P., Wang X., Mitrofanov K.V., Tominaga J., Osawa H., Suzuki M., MRS Proc. 1563, mrss13 (2013).
