- Email: [email protected]
Detection efficiency and spatial resolution of the SIRAD ion electron emission microscope
Nuclear Instruments and Methods in Physics Research B 267 (2009) 2269–2272
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Detection efficiency and spatial resolution of the SIRAD ion electron emission microscope D. Bisello a, P. Giubilato a, A. Kaminsky a, S. Mattiazzo a,*, M. Nigro a, D. Pantano a, L. Silvestrin a, M. Tessaro a, J. Wyss b, S. Bertazzoni c, L. Mongiardo c, M. Salmeri c, A. Salsano c a
University of Padova, Dept. of Physics, and INFN Padova, Via Marzolo 8, 35131 Padova, Italy University of Cassino, DiMSAT, and INFN Padova, Italy c University of Rome ‘‘Tor Vergata”, Dept. of Electronics Engineering, Italy b
a r t i c l e
i n f o
Available online 13 March 2009 PACS: 61.80.Jh 85.60.Gz Keywords: Ion electron emission microscopy Single event effects
a b s t r a c t An axial ion electron emission microscope (IEEM) has been built at the SIRAD irradiation facility at the 15 MV Tandem accelerator of INFN Legnaro National Laboratory (Padova, Italy) to obtain a micrometric sensitivity map to single event effects (SEE) of electronic devices. In this contribution we report on two experiments performed with the IEEM. Si3N4 ultra-thin membranes with a gold deposition were placed on the device under test (DUT) to ensure a uniform and abundant secondary electron emission In the first experiment we measured an IEEM ion detection efficiency of 83% with a 58Ni (220 MeV) beam, in good agreement with the expected value. The second experiment allowed us to estimate the lateral resolution of the IEEM. The positions of ion induced single event upsets (SEU) in a synchronous dynamic random access memory (SDRAM), used as a reference target, were compared with the corresponding ion impact points reconstructed by the IEEM. The result (FWHM 4.4 lm with a 79Br beam of 214 MeV) is encouraging because of the residual presence of distortions of the image and mechanical vibrations. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction An ion electron emission microscope (IEEM) is working at the SIRAD [1] irradiation facility at the 15 MV Tandem accelerator of the INFN National Laboratory of Legnaro (Italy). The IEEM furnishes the precise space and time coordinates of individual random ion impacts in an area of hundreds of square microns. This information is used to study the effects induced by single ions impacting microelectronic devices to be used in radiation hostile environments. SEE studies are typically performed with high atomic number energetic ions beams able to produce the high levels of ionization required to induce SEE. The ions must also be energetic enough to traverse the electronically active layers of the DUT and probe for deeper sensitivity. In addition there may also be many microns of metallization layers on the DUT surface. It is hence necessary that the heavy ions for SEE studies have a range in silicon at least of many tens of microns.
each ion impact are collected and focused by the electron emission microscope onto an annular micro-channel plate detector (MCP). In our system [3] the MCP is coupled to a phosphor layer (P47) that converts the electron signal into a luminous one. The photons are then extracted outside the vacuum chamber, enter a beamsplitter and are imaged by both a conventional CCD camera and by a special high-rate position detector that records the spatial and temporal coordinates of the light spots due to individual ion impacts [4]. The intrinsic resolution of the electron emission microscope is set by the contrast diaphragm that cuts the secondary electrons that do not follow ideal trajectories through the microscope and would otherwise be not properly focused. In our case the small aperture (diameter 200 lm) in the diaphragm guarantees a good theoretical lateral resolution (400 nm), but the fraction of secondary electrons transported to the MCP (transmission efficiency) is low (3%) [2].
2. The SIRAD axial IEEM
3. Target preparation
In the IEEM technique [2] a broad beam is sent onto the DUT and the secondary electrons emitted from the target surface by
The surface of a typical DUT is usually a bad secondary electron emitter. For this reason we place on the top of the DUT a selfstanding Si3N4 membrane window in a silicon support-frame with a gold layer on the side facing the IEEM to ensure copious secondary electron emission [5]. Moreover, in this case the DUT needs no
* Corresponding author. E-mail address: [email protected] (S. Mattiazzo). 0168-583X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2009.03.048
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specific preparation and it is separated from the electric field of the immersion lens of the IEEM. The membrane window we use [6] is 5 mm wide, 100 nm thick with a 40 nm gold layer deposition. Ions lose a negligible amount of energy in traversing it. The window presents a flat side, where the membrane is flush with the support-frame (525 lm thick), and a deep concave side. However, these membranes are very delicate and cannot be placed directly in contact with the DUT. As a consequence the lateral resolution of the IEEM is degraded. For typical heavy ions available at SIRAD and for a large membrane distance of 1 mm, the FWHM of the distribution of the lateral displacements at the surface of the DUT is a few microns. To limit the FWMH to 1 lm, one must ensure a distance of 200 lm, a very challenging task.
As we know the correspondence between the logical addresses of the cells and their physical locations, we can reconstruct the spatial map of detected SEUs. A common clock (master clock) is used to time-stamp both IEEM events and SDRAM operations. A shutter system is used to inhibit ion impacts while read-out operations are performed. The SEU events in each exposure are then compared with the database of the events detected by the IEEM during the same time interval. The SDRAM was surmounted by the standard Au/Si3N4 membrane and was irradiated with 214 MeV 79Br ions. The microbonds of the SDRAM were made as flat as possible to permit a distance of its surface from the membrane better than 300 lm (Fig. 1); the
4. Ion detection efficiency measurement The ion impact detection efficiency of the IEEM depends both on the secondary electron emission and on the detection efficiency (transmission and amplification) of the IEEM column and detector ensemble. We performed an experiment using a 220 MeV 58Ni beam impinging on a PIN diode surmounted by the standard Au/Si3N4 membrane. In these experiments the CCD camera was replaced by a photomultiplier tube (PMT) to detect the luminous signals from the phosphor layer of the MCP. The ion detection efficiency of the IEEM is the ratio between the number of PMT signals in coincidence with the ion signals in the diode and the total number of diode signals. We used standard NIM1 discriminators, coincidence and counter modules. The discriminator threshold was set low enough to accept all ion induced signals. We measured an ion detection efficiency of 83%. For each 220 MeV 58Ni ion impact, 90 secondary electrons are emitted by the Au layer [5]. With a diaphragm aperture diameter of 200 lm, and assuming the MCP to be 55% efficient (a conservative estimate), we calculated an ion impact detection efficiency of 93%. Several factors account for the 10% efficiency loss. About 6% of the ion impacts are lost, because of some dead regions of the annular MCP (e.g. the central hole). In addition, the voltage step between the MCP output and the phosphor screen is 2.5 kV, while the optimal voltage step should be 3–5 kV, because a higher voltage power supply was unavailable during this experiment. We estimate this to account for 2% of the deficit. The residual 2% deficit is due to distortions and incompleteness of the image caused by the bulge of the wide membrane we used. The later two causes of the deficit will soon be removed. Using these membranes we expect the efficiency of the SIRAD IEEM to be better than 50% for heavy ions with Z > 10.
Fig. 1. Sketch of the setup. The membrane surmounts the SDRAM and faces the IEEM head.
5. Spatial resolution measurement An ion detector system, based on SEU detection in a SDRAM, was developed to measure the effective lateral resolution of the IEEM system. The SDRAM was chosen because of the sensitivity to ion induced SEU, the high regularity and small feature size of the memory cells [7]. Two identical memory arrays are available in the SDRAM system: only one device is exposed to ions, while the other one is used as reference. A common pattern is written in both the SDRAMs before irradiation; after irradiation, the content of each cell of the exposed SDRAM is compared with the corresponding content of the reference SDRAM. If a difference, i.e. a SEU, is detected, the logical address of the cell is registered.
1
Nuclear instrumentation module.
Fig. 2. A single exposure. Circles are ion impacts in the IEEM, squares are SEUs in the SDRAM; dashed lines are the boundaries of the sensitive areas (darker background).
D. Bisello et al. / Nuclear Instruments and Methods in Physics Research B 267 (2009) 2269–2272
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Fig. 4. (a) Membrane with the concave side towards the IEEM head and (b) membrane with the flat side towards the IEEM head.
Fig. 3. Distribution of the lateral distance along the Y-axis between each IEEM event and the barycenter of nearby SEU-clusters (closer than 35 lm) in a low distortion area.
FWHM of the lateral displacements of the ions on the SDRAM was estimated to be better than 1.5 lm by SRIM simulations [8]. In the experiment the ion flux was adjusted to 105 ion/cm2 s and the duration of the exposures to ions (shutter open) was set to 500 ms. On average 20 ions impacted the SDRAM in each exposure. Events from both the SDRAM and IEEM systems for a typical exposure are shown in Fig. 2. It is worth noting that a single ion may induce a cluster of upsets in the memory array (multiple errors) [7]. In the following analysis the barycenter of the clusters will be considered. Both systems have regions that are not sensitive as shown in Fig. 2. Here, the large and the small circle correspond respectively to the aperture of the contrast diaphragm and to the hole in the annular MCP; the lines are the boundaries of the arrays of SEU sensitive SDRAM memory cells. By considering only events common to both active areas, we estimate that the fraction of SEU events that are reconstructed by the IEEM sensor (ion impact reconstruction efficiency) is 90%. We studied the distribution in the difference in the Y-coordinates (lateral distance) of the ion impact points reconstructed by the IEEM and the barycenter of the clusters of SEU detected by the SDRAM (Fig. 3). The most distorted regions, characterized by systematic shifts between IEEM events and SDRAM clusters, were not included in the analysis. The distribution shows a Gaussian peak due to correlated hits over a background (uncorrelated hits). The measured FWHM 4.4 lm is an upper estimate of the lateral resolution of the IEEM using the membrane.
field that collects the secondary electrons. Thin (100–200 lm) support-frames will make possible to mount the membrane windows with the flat side towards the IEEM head (Fig. 4(b)). Presently, the membrane is mounted on top of the DUT. The magnification and focus of the electron emission microscope must be adjusted each time and to do this we use calibration grids mounted on the sample holder with the DUT. By mounting the membrane in a fixed position in front of the IEEM the magnification and focus can be set once and for all, independently of the DUT; moreover a fixed membrane may be made very narrow (0.5 mm) and this will reduce the amplitude of the bulge. The fixed membrane approach will allow us to use the SDRAM as a standard calibration device: the resolution of the IEEM can be measured as a function of the distance from the membrane and the image distortions mapped and corrected for once and for all. Finally, the SDRAM system will be used to align the true DUT in the field of view of the IEEM. The SDRAM, mounted on the sample holder along with the true DUT, is first exposed to ions and located by detecting a recognizable SEU pattern in the memory array, or by imaging just a few SEU-IEEM event pairs. The true DUT is then precisely moved into position into the field of view of the IEEM.
7. Conclusions The SIRAD IEEM shows interesting performances for SEE studies. High detection efficiency can be achieved for many ion species. The lateral spatial resolution of the IEEM is still low but we are confident that it can be improved to reach 1–2 lm, possibly better. This is a factor 2–4 worse than the very best longstanding SEE microbeam facilities, but can be considered a competitive solution. An IEEM system is compact, relatively inexpensive and straightforward to install and operate at pre-existing beam lines at any suitable ion accelerator.
6. Immediate plans The use of membranes is problematic for two other important reasons. The membranes we presently use are very wide and they bulge significantly in the electric field of the IEEM. As a consequence, the trajectories of the electrons are perturbed and the final image is distorted. In addition, the membranes we use have thick support-frames and to minimize the degradation of the effective lateral resolution on the DUT we mount the membrane with the concave side towards the IEEM (Fig. 4(a)). However, the concave shape of the support-frame of the membrane distorts the electrical
References [1] J. Wyss, D. Bisello, D. Pantano, SIRAD: an irradiation facility at the LNL Tandem accelerator for radiation damage studies on semiconductor detectors and electronic devices and systems, Nucl. Instr. and Meth. A 462 (2001) 426. [2] B.L. Doyle, G. Vizkelethy, D.S. Walsh, B. Senftinger, M. Mellon, A new approach to nuclear microscopy: the ion electron emission microscope, Nucl. Instr. and Meth. B 158 (1999) 6. [3] D. Bisello, A. Candelori, P. Giubilato, A. Kaminsky, S. Mattiazzo, M. Nigro, D. Pantano, R. Rando, M. Tessaro, J. Wyss, S. Bertazzoni, D. Di Giovenale, Ion electron emission microscopy at SIRAD, Nucl. Instr. and Meth. B 231 (2005) 65.
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D. Bisello et al. / Nuclear Instruments and Methods in Physics Research B 267 (2009) 2269–2272
[4] P. Giubilato, S. Mattiazzo, Novel imaging sensor for high-rate and high resolution applications, in: Proceedings of the SNIC 2006 (International Symposium on Detector Development), Stanford, California, April 3–6, 2006. [5] D. Bisello, A. Candelori, P. Giubilato, A. Kaminsky, S. Mattiazzo, M. Nigro, D. Pantano, R. Rando, L. Silestrin, M. Tessaro, J. Wyss, Secondary electron yield of Au and Al2O3 surfaces from swift heavy ion impact in the 2.5–7.9 MeV/amu energy range, Nucl. Instr. and Meth. B 266 (2008) 173.
[6]. [7] D. Bisello, P. Giubilato, S. Bertazzoni, A. Kaminsky, S. Mattiazzo, L. Mongiardo, D. Pantano, R. Rando, M. Salmeri, A. Salsano, L.Silvestrin, M. Tessaro, J. Wyss, Ion impact detection and micromapping with a SDRAM for IEEM diagnostics and applications, in: Proceedings of the SORMA 2008 (Symposium on Radiation Measurement and Applications), Berkeley, California, June 2–5, 2008. [8] SRIM, 2008. .
Contents lists available at ScienceDirect
Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb
Detection efficiency and spatial resolution of the SIRAD ion electron emission microscope D. Bisello a, P. Giubilato a, A. Kaminsky a, S. Mattiazzo a,*, M. Nigro a, D. Pantano a, L. Silvestrin a, M. Tessaro a, J. Wyss b, S. Bertazzoni c, L. Mongiardo c, M. Salmeri c, A. Salsano c a
University of Padova, Dept. of Physics, and INFN Padova, Via Marzolo 8, 35131 Padova, Italy University of Cassino, DiMSAT, and INFN Padova, Italy c University of Rome ‘‘Tor Vergata”, Dept. of Electronics Engineering, Italy b
a r t i c l e
i n f o
Available online 13 March 2009 PACS: 61.80.Jh 85.60.Gz Keywords: Ion electron emission microscopy Single event effects
a b s t r a c t An axial ion electron emission microscope (IEEM) has been built at the SIRAD irradiation facility at the 15 MV Tandem accelerator of INFN Legnaro National Laboratory (Padova, Italy) to obtain a micrometric sensitivity map to single event effects (SEE) of electronic devices. In this contribution we report on two experiments performed with the IEEM. Si3N4 ultra-thin membranes with a gold deposition were placed on the device under test (DUT) to ensure a uniform and abundant secondary electron emission In the first experiment we measured an IEEM ion detection efficiency of 83% with a 58Ni (220 MeV) beam, in good agreement with the expected value. The second experiment allowed us to estimate the lateral resolution of the IEEM. The positions of ion induced single event upsets (SEU) in a synchronous dynamic random access memory (SDRAM), used as a reference target, were compared with the corresponding ion impact points reconstructed by the IEEM. The result (FWHM 4.4 lm with a 79Br beam of 214 MeV) is encouraging because of the residual presence of distortions of the image and mechanical vibrations. Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction An ion electron emission microscope (IEEM) is working at the SIRAD [1] irradiation facility at the 15 MV Tandem accelerator of the INFN National Laboratory of Legnaro (Italy). The IEEM furnishes the precise space and time coordinates of individual random ion impacts in an area of hundreds of square microns. This information is used to study the effects induced by single ions impacting microelectronic devices to be used in radiation hostile environments. SEE studies are typically performed with high atomic number energetic ions beams able to produce the high levels of ionization required to induce SEE. The ions must also be energetic enough to traverse the electronically active layers of the DUT and probe for deeper sensitivity. In addition there may also be many microns of metallization layers on the DUT surface. It is hence necessary that the heavy ions for SEE studies have a range in silicon at least of many tens of microns.
each ion impact are collected and focused by the electron emission microscope onto an annular micro-channel plate detector (MCP). In our system [3] the MCP is coupled to a phosphor layer (P47) that converts the electron signal into a luminous one. The photons are then extracted outside the vacuum chamber, enter a beamsplitter and are imaged by both a conventional CCD camera and by a special high-rate position detector that records the spatial and temporal coordinates of the light spots due to individual ion impacts [4]. The intrinsic resolution of the electron emission microscope is set by the contrast diaphragm that cuts the secondary electrons that do not follow ideal trajectories through the microscope and would otherwise be not properly focused. In our case the small aperture (diameter 200 lm) in the diaphragm guarantees a good theoretical lateral resolution (400 nm), but the fraction of secondary electrons transported to the MCP (transmission efficiency) is low (3%) [2].
2. The SIRAD axial IEEM
3. Target preparation
In the IEEM technique [2] a broad beam is sent onto the DUT and the secondary electrons emitted from the target surface by
The surface of a typical DUT is usually a bad secondary electron emitter. For this reason we place on the top of the DUT a selfstanding Si3N4 membrane window in a silicon support-frame with a gold layer on the side facing the IEEM to ensure copious secondary electron emission [5]. Moreover, in this case the DUT needs no
* Corresponding author. E-mail address: [email protected] (S. Mattiazzo). 0168-583X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2009.03.048
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D. Bisello et al. / Nuclear Instruments and Methods in Physics Research B 267 (2009) 2269–2272
specific preparation and it is separated from the electric field of the immersion lens of the IEEM. The membrane window we use [6] is 5 mm wide, 100 nm thick with a 40 nm gold layer deposition. Ions lose a negligible amount of energy in traversing it. The window presents a flat side, where the membrane is flush with the support-frame (525 lm thick), and a deep concave side. However, these membranes are very delicate and cannot be placed directly in contact with the DUT. As a consequence the lateral resolution of the IEEM is degraded. For typical heavy ions available at SIRAD and for a large membrane distance of 1 mm, the FWHM of the distribution of the lateral displacements at the surface of the DUT is a few microns. To limit the FWMH to 1 lm, one must ensure a distance of 200 lm, a very challenging task.
As we know the correspondence between the logical addresses of the cells and their physical locations, we can reconstruct the spatial map of detected SEUs. A common clock (master clock) is used to time-stamp both IEEM events and SDRAM operations. A shutter system is used to inhibit ion impacts while read-out operations are performed. The SEU events in each exposure are then compared with the database of the events detected by the IEEM during the same time interval. The SDRAM was surmounted by the standard Au/Si3N4 membrane and was irradiated with 214 MeV 79Br ions. The microbonds of the SDRAM were made as flat as possible to permit a distance of its surface from the membrane better than 300 lm (Fig. 1); the
4. Ion detection efficiency measurement The ion impact detection efficiency of the IEEM depends both on the secondary electron emission and on the detection efficiency (transmission and amplification) of the IEEM column and detector ensemble. We performed an experiment using a 220 MeV 58Ni beam impinging on a PIN diode surmounted by the standard Au/Si3N4 membrane. In these experiments the CCD camera was replaced by a photomultiplier tube (PMT) to detect the luminous signals from the phosphor layer of the MCP. The ion detection efficiency of the IEEM is the ratio between the number of PMT signals in coincidence with the ion signals in the diode and the total number of diode signals. We used standard NIM1 discriminators, coincidence and counter modules. The discriminator threshold was set low enough to accept all ion induced signals. We measured an ion detection efficiency of 83%. For each 220 MeV 58Ni ion impact, 90 secondary electrons are emitted by the Au layer [5]. With a diaphragm aperture diameter of 200 lm, and assuming the MCP to be 55% efficient (a conservative estimate), we calculated an ion impact detection efficiency of 93%. Several factors account for the 10% efficiency loss. About 6% of the ion impacts are lost, because of some dead regions of the annular MCP (e.g. the central hole). In addition, the voltage step between the MCP output and the phosphor screen is 2.5 kV, while the optimal voltage step should be 3–5 kV, because a higher voltage power supply was unavailable during this experiment. We estimate this to account for 2% of the deficit. The residual 2% deficit is due to distortions and incompleteness of the image caused by the bulge of the wide membrane we used. The later two causes of the deficit will soon be removed. Using these membranes we expect the efficiency of the SIRAD IEEM to be better than 50% for heavy ions with Z > 10.
Fig. 1. Sketch of the setup. The membrane surmounts the SDRAM and faces the IEEM head.
5. Spatial resolution measurement An ion detector system, based on SEU detection in a SDRAM, was developed to measure the effective lateral resolution of the IEEM system. The SDRAM was chosen because of the sensitivity to ion induced SEU, the high regularity and small feature size of the memory cells [7]. Two identical memory arrays are available in the SDRAM system: only one device is exposed to ions, while the other one is used as reference. A common pattern is written in both the SDRAMs before irradiation; after irradiation, the content of each cell of the exposed SDRAM is compared with the corresponding content of the reference SDRAM. If a difference, i.e. a SEU, is detected, the logical address of the cell is registered.
1
Nuclear instrumentation module.
Fig. 2. A single exposure. Circles are ion impacts in the IEEM, squares are SEUs in the SDRAM; dashed lines are the boundaries of the sensitive areas (darker background).
D. Bisello et al. / Nuclear Instruments and Methods in Physics Research B 267 (2009) 2269–2272
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Fig. 4. (a) Membrane with the concave side towards the IEEM head and (b) membrane with the flat side towards the IEEM head.
Fig. 3. Distribution of the lateral distance along the Y-axis between each IEEM event and the barycenter of nearby SEU-clusters (closer than 35 lm) in a low distortion area.
FWHM of the lateral displacements of the ions on the SDRAM was estimated to be better than 1.5 lm by SRIM simulations [8]. In the experiment the ion flux was adjusted to 105 ion/cm2 s and the duration of the exposures to ions (shutter open) was set to 500 ms. On average 20 ions impacted the SDRAM in each exposure. Events from both the SDRAM and IEEM systems for a typical exposure are shown in Fig. 2. It is worth noting that a single ion may induce a cluster of upsets in the memory array (multiple errors) [7]. In the following analysis the barycenter of the clusters will be considered. Both systems have regions that are not sensitive as shown in Fig. 2. Here, the large and the small circle correspond respectively to the aperture of the contrast diaphragm and to the hole in the annular MCP; the lines are the boundaries of the arrays of SEU sensitive SDRAM memory cells. By considering only events common to both active areas, we estimate that the fraction of SEU events that are reconstructed by the IEEM sensor (ion impact reconstruction efficiency) is 90%. We studied the distribution in the difference in the Y-coordinates (lateral distance) of the ion impact points reconstructed by the IEEM and the barycenter of the clusters of SEU detected by the SDRAM (Fig. 3). The most distorted regions, characterized by systematic shifts between IEEM events and SDRAM clusters, were not included in the analysis. The distribution shows a Gaussian peak due to correlated hits over a background (uncorrelated hits). The measured FWHM 4.4 lm is an upper estimate of the lateral resolution of the IEEM using the membrane.
field that collects the secondary electrons. Thin (100–200 lm) support-frames will make possible to mount the membrane windows with the flat side towards the IEEM head (Fig. 4(b)). Presently, the membrane is mounted on top of the DUT. The magnification and focus of the electron emission microscope must be adjusted each time and to do this we use calibration grids mounted on the sample holder with the DUT. By mounting the membrane in a fixed position in front of the IEEM the magnification and focus can be set once and for all, independently of the DUT; moreover a fixed membrane may be made very narrow (0.5 mm) and this will reduce the amplitude of the bulge. The fixed membrane approach will allow us to use the SDRAM as a standard calibration device: the resolution of the IEEM can be measured as a function of the distance from the membrane and the image distortions mapped and corrected for once and for all. Finally, the SDRAM system will be used to align the true DUT in the field of view of the IEEM. The SDRAM, mounted on the sample holder along with the true DUT, is first exposed to ions and located by detecting a recognizable SEU pattern in the memory array, or by imaging just a few SEU-IEEM event pairs. The true DUT is then precisely moved into position into the field of view of the IEEM.
7. Conclusions The SIRAD IEEM shows interesting performances for SEE studies. High detection efficiency can be achieved for many ion species. The lateral spatial resolution of the IEEM is still low but we are confident that it can be improved to reach 1–2 lm, possibly better. This is a factor 2–4 worse than the very best longstanding SEE microbeam facilities, but can be considered a competitive solution. An IEEM system is compact, relatively inexpensive and straightforward to install and operate at pre-existing beam lines at any suitable ion accelerator.
6. Immediate plans The use of membranes is problematic for two other important reasons. The membranes we presently use are very wide and they bulge significantly in the electric field of the IEEM. As a consequence, the trajectories of the electrons are perturbed and the final image is distorted. In addition, the membranes we use have thick support-frames and to minimize the degradation of the effective lateral resolution on the DUT we mount the membrane with the concave side towards the IEEM (Fig. 4(a)). However, the concave shape of the support-frame of the membrane distorts the electrical
References [1] J. Wyss, D. Bisello, D. Pantano, SIRAD: an irradiation facility at the LNL Tandem accelerator for radiation damage studies on semiconductor detectors and electronic devices and systems, Nucl. Instr. and Meth. A 462 (2001) 426. [2] B.L. Doyle, G. Vizkelethy, D.S. Walsh, B. Senftinger, M. Mellon, A new approach to nuclear microscopy: the ion electron emission microscope, Nucl. Instr. and Meth. B 158 (1999) 6. [3] D. Bisello, A. Candelori, P. Giubilato, A. Kaminsky, S. Mattiazzo, M. Nigro, D. Pantano, R. Rando, M. Tessaro, J. Wyss, S. Bertazzoni, D. Di Giovenale, Ion electron emission microscopy at SIRAD, Nucl. Instr. and Meth. B 231 (2005) 65.
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D. Bisello et al. / Nuclear Instruments and Methods in Physics Research B 267 (2009) 2269–2272
[4] P. Giubilato, S. Mattiazzo, Novel imaging sensor for high-rate and high resolution applications, in: Proceedings of the SNIC 2006 (International Symposium on Detector Development), Stanford, California, April 3–6, 2006. [5] D. Bisello, A. Candelori, P. Giubilato, A. Kaminsky, S. Mattiazzo, M. Nigro, D. Pantano, R. Rando, L. Silestrin, M. Tessaro, J. Wyss, Secondary electron yield of Au and Al2O3 surfaces from swift heavy ion impact in the 2.5–7.9 MeV/amu energy range, Nucl. Instr. and Meth. B 266 (2008) 173.
[6]