- Email: [email protected]
Ion electron emission microscopy at SIRAD
Nuclear Instruments and Methods in Physics Research B 231 (2005) 65–69 www.elsevier.com/locate/nimb
Ion electron emission microscopy at SIRAD D. Bisello a, A. Candelori a, P. Giubilato a,*, A. Kaminsky a, S. Mattiazzo a, M. Nigro a, D. Pantano a, R. Rando a, M. Tessaro a, J. Wyss b, S. Bertazzoni c, D. Di Giovenale c a
c
Department of Physics, University of Padova, and INFN Padova, via Marzolo 8, 35131 Padova, Italy b University of Cassino and INFN Pisa, Via F. Buonarroti 2, 56127 Pisa, Italy University of Tor Vergata, Roma, and INFN Roma, Via della ricerca scientifica 1, 00133 Roma, Italy Available online 7 April 2005
Abstract In this contribution we describe how single event effect (SEE) studies will be performed with the ion electron emission microscope (IEEM) of the SIRAD irradiation facility located at the INFN Legnaro Laboratory. The IEEM will be used to locate with micrometric precision the impact points of impinging ions that give rise to SEE in an electronic device under test (DUT). In the IEEM technique the ion beam is not microfocused: the position of single ion impact is reconstructed by locating the secondary electron emission points on the DUT surface. We briefly review the original solutions under implementation at SIRAD, such as the opto-electronic approach used to reconstruct the secondary electron emission points by means of a fast, high-resolution imaging of point-like light sources, and a new IEEM test system under development based on a commercial memory array sensitive to single event upsets. 2005 Elsevier B.V. All rights reserved. PACS: 61.82.Fk; 61.80.Jh; 29.40.Wk Keywords: Ion electron emission microscopy; Single event effect
1. Introduction: SIRAD, single event effects and IEEM applications The study of the effects of natural and artificial radiation on semiconductor devices is an impor*
Corresponding author. Tel.: +39 49 827 7215; fax: +39 49 827 7237. E-mail address: [email protected] (P. Giubilato).
tant and lively field in scientific and technological research. In particular radiation tolerance is a fundamental issue for electronic devices and systems in many applications such as nuclear plants, space research, telecommunications, avionics, and highenergy physics. The SIRAD irradiation facility, located at the 15 MV Tandem accelerator of the INFN Laboratory in Legnaro (Italy), is actively dedicated to bulk damage and to single event effect
0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.01.036
66
D. Bisello et al. / Nucl. Instr. and Meth. in Phys. Res. B 231 (2005) 65–69
(SEE) studies in semiconductor devices and electronic systems for high energy physics and space applications [1]. An impinging ion will deposit energy in the semiconductor material (silicon) of an electronic device by generating electron–hole pairs. High electron–hole pair densities along a single ion track can influence the device functionality if the charge is generated in a high electric field region and/or it is collected at a sensitive node of the circuit. Single ionizing ions are able to induce device failures, such as single event upsets (SEU) and single event functionality interrupts (SEFI) in digital electronics, and also lead to permanent device damage, such as single event burn-out (SEB) in power diodes, single event gate rupture (SEGR) in power MOSFET and single event latch-up (SEL) in CMOS technologies [2]. Typically SEE studies require a broad selection of energetic ion species to determine both the threshold and the saturation (plateau) values of the linear energy transfer (LET) needed to induce functionality failures in the device under test (DUT). For SEE studies the SIRAD facility can deliver beams ranging from 7Li+3 (60 MeV) to 197Au+25 (300 MeV) with a limit in magnetic rigidity of about 1.4 T m. Global device SEE characterizations are routinely performed at SIRAD using broad beams to uniformly irradiate areas up to several cm2 of a DUT. To improve this capability the group is now developing IEEM capabilities that will allow the location of SEE sensitive points of a DUT with micrometric resolution. Ion electron emission microscopy [3] is somewhat complementary to the consolidated nuclear microprobe technique that builds up sensitivity maps with lateral resolutions of the order of 0.5–1.0 lm by moving a microfocused beam spot systematically across the DUT with micrometric precision. In the IEEM technique a broad (not microfocused) ion beam irradiates the portion of the DUT that is inside the field of view of a commercial photon electron emission microscope. The ion impact positions are reconstructed by collecting the secondary electrons emitted from the DUT surface during ion impact and focusing them onto a two-dimensional electron detector placed at the
focal plane. The IEEM lens system suffers from aberrations that are limited by means of a contrast diaphragm: our standard maximum aperture of 300 lm ensures an intrinsic resolution of about 0.6 lm over a field of view of 250 lm; using a 200 lm diaphragm the resolution improves to 0.4 lm. Moreover, diaphragm aperture size sets the lens transmission efficiency, about 15% with a size of 200 lm and reaching 30% with maximum aperture. As a focal plane electron detector one may use a microchannel plate (MCP) detector: the intrinsic resolution, set by the physical size of microchannels (some tens of microns), fits the resolution of the image produced by the IEEM with a FOV of 250 lm, and it is fast and hence can be used to resolve in time individual ion impacts. For SEE studies the X, Y transverse coordinates and the time T of reconstructed random ion impacts are to be correlated with any interesting events, in particular SEE, induced in the DUT. The technique may be also used for time resolved ion beam induced charge collection (IBICC) studies.
2. Opto-electronic IEEM of SIRAD In the SIRAD IEEM (Fig. 1) the secondary electron MCP detector is annular to allow for the ion beam to pass axially through the microscope and impact normally the DUT surface. The large electronic MCP signal (gain 107) is used to excite a fast phosphor screen to create a light spot. The photons are then extracted from the irradiation chamber by means of a mirror and a quartz window. The optical image is focused by a system of lenses onto a fast photon position sensitive detector, for the determination of the position of the luminous spots corresponding to the secondary electron signals. By depositing a thin gold layer (20–40 nm) on the DUT surface, to ensure good secondary electron emission, we expect, at the level of the phosphor screen, an ion impact detection efficiency of 45% for 100 MeV C ions, reaching full efficiency for ions with Z > 25. The opto-electronic approach, original to the SIRAD IEEM, allows the use of complex sensing devices for greater sensing performance, flexibility
D. Bisello et al. / Nucl. Instr. and Meth. in Phys. Res. B 231 (2005) 65–69
67
Fig. 1. Schematic of the SIRAD IEEM setup. Wireframes parts show beamline and vacuum chamber boundaries, while shaded cones show electrons and photons path through the system: electrons inside the microscope column to the MCP and photons from the MCP phosphor to the CCDs.
and ease of use. The main drawback is the low optical efficiency of the system, not better than 1%, that requires high sensitivity sensors [4–6]. Commercial CCD two-dimensional arrays, used for photon electron emission microscopy (PEEM) surface analysis techniques, have intrinsically long readout times (low frame rates; e.g. about 30 frames per second for a one-output 1024 · 1024 array), which would severely limit the ion fluxes for time-resolved single ion impact effect studies (such as SEE or IBICC studies) to levels of about 10 ion impacts/s in the field of view (corresponding to an ion flux of about 2 · 103 ions/cm2 s). Such low rates are also comparable to the noise level of the large MCP inside the IEEM. To avoid any IEEM detector limitations for SEE applications (in general the maximum ion flux will be limited by the DUT and the SEE detection system) we have developed two fast high resolu-
tion opto-electronic photon detection systems that can handle event (single ion impact) rates of a few 104 Hz in the field of view of the microscope. The first system is based on a commercial 2 · 2 cm2 semiconductor position sensitive device (PSD) wherein the orthogonal coordinates of a light spot signal are obtained analogically by charge division using two pairs of electrodes [5]. A second system uses an optical system based on a beam splitter and two orthogonal linear 1024 pixel CCD sensors, one for each coordinate: the optical system splits the image and squeezes each copy onto one of the two CCDs. This way we read out just 1024 pixels (both linear CCDs are read simultaneously) instead of 1 million, and consequently we have reduced data throughput by a factor 1000, increasing the speed by the same factor. This novel system ensures, in terms of data processing capabilities, an even greater flexibility for time-resolved IEEM applications. The system
68
D. Bisello et al. / Nucl. Instr. and Meth. in Phys. Res. B 231 (2005) 65–69
is intrinsically digital: each pixel is an independent detector and the minimum sensitivity is set by the noise level of each pixel, hence the spatial resolution for a given pixel size is independent of the intensity of the luminous spot, unlike the PSD analogue system [6]. All the raw data elaboration is performed by a dedicated home made solid state DSP system, based on a Virtex-II FPGA plus support electronics. Analysis starts by cleaning signals from bias levels and then filtering them to optimize the S/N ratio. Dedicated algorithms work in parallel to reconstruct the spatial coordinates by combining the signals coming from the two CCDs. Data are sent to a computer through a simple USB connection, already arranged as X, Y, T coordinates. While the first system has been used to take preliminary data with the microscope, the second one has been successfully tested as a prototype, and we are now working to install it as the final IEEM sensor. First data with new system are scheduled to be taken in spring 2005.
3. Optical alignment at SIRAD Unlike common PEEM based instruments, the SIRAD IEEM sensing system is off the beam axis and outside the vacuum chamber (Fig. 1). The light spots generated by the phosphor layer at the MCP output are imaged by means of a 45 mirror that reflects the image to the light sensor, placed orthogonal to the main axis of the microscope outside the irradiation chamber. The mirror is tiltable for fine adjustments. To properly align the DUT, we look into the microscope field of view (FOV) with a lateral oblique optical microscope. To deal with parallax errors, a laser-pointer was added to the system. Using the same optical system that carries photons from the phosphor to the external sensor, the laser beam is injected in the reverse direction into the microscope through the hole of the MCP and down the microscope axis. The observation of the laser spot on the target through the lateral oblique optical microscope allows us to know where the target is located within the field of view of the IEEM.
4. SEE testing with the IEEM; the SDRAM IEEM test system During irradiation of a DUT, the ion impact information furnished by the IEEM (position and time coordinates) is stored into a temporary internal data buffer while waiting for control calls generated by the control electronics of the DUT. If the device control setup recognizes that something interesting has happened (SEU, SEL, SEFI, . . .), it sends a trigger signal to the IEEM control unit, that retrieves the coordinates of the time-corresponding ion impact point from the internal data buffer. This procedure permits the identification of SEE sensitive areas by precisely locating the corresponding ion entry points on the DUT surface. At present we are developing a global triggering (time-stamp) system to allow an easy synchronization between the microscope control unit and the control setup of the DUT. The SIRAD IEEM will be tested in a practical situation with a real microelectronic device to demonstrate its capabilities and define general methodological procedures for SEE testing. For this purpose we will use a commercial 256 MB SDRAM and a single event upset (SEU) test system. The SDRAM system will also be used as a twodimensional ion detector. Indeed the SDRAM is a large array of small unit memory cells (512 · 4096) words · 8 bits · 4 banks, and it is extremely regular (except for a few sparse cells), and each unit memory cell is subject to SEU: about 104 cells will be in the field of view of the IEEM and the measured SEU cross-section for heavy ions (Z > 13) is rbit 10 9 cm2 [7]. Hence about 2% of the heavy ions impacting inside the field of view will give rise to a SEU. With an access clock of 100 MHz the cells in the array that undergo upsets will be identified and located [8]. Such a system will be used to measure the effective spatial resolution that an IEEM can achieve in locating the lateral position of a SEE sensitive volume as compared to the resolution one may measure using a target with regular surface features such a metal grid (TEM grid). Indeed in stateof-the-art CMOS devices the electronically sensitive volumes are a typically a few microns in depth below the metallization and passivation layers, and
D. Bisello et al. / Nucl. Instr. and Meth. in Phys. Res. B 231 (2005) 65–69
any additional coatings applied to ensure adequate secondary electron emission from the top surface during ion impact. The SDRAM array offers an ensemble of single ion detectors that are distributed with a precision that is about 100 times greater than the resolution of the IEEM and, using statistical methods, the effective resolution of the IEEM can determined by comparing the coordinates of ion entry points given by the IEEM with the SDRAM coordinates of the SEU cells. Tests with commercial off the shelf SDRAM devices represent a typical application of the SIRAD IEEM facility. For this reason the requirements of the SDRAM test equipment are driving the development of the facility. As a relevant part of the data acquisition electronics is going to be shared with future users of the facility, its implementation is designed to anticipate future requirements and standard interfaces (electrical and software) are provided. In particular we are testing WLAN (wireless local area network) connections to avoid cabling to the DUT inside the vacuum chamber.
5. Conclusions The SIRAD group is developing an advanced implementation of an ion electron emission microscope to map the sensitivity to single event effect of
69
electronic devices and systems. The first applications will use a SEU detection system based on a commercial SDRAM.
References [1] J. Wyss, D. Bisello, D. Pantano, Nucl. Instr. and Meth. A 462 (2001) 426. [2] A. Holmes-Siedle, L. Adams, Handbook of Radiaion Effect, Oxford Science, 1993. [3] B.L. Doyle, G. Vizkelethy, D.S. Walsh, B. Senftinger, M. Mellon, Nucl. Instr. and Meth. B 158 (1999) 6. [4] D. Bisello, A. Kaminsky, A. Magalini, M. Nigro, D. Pantano, S. Sedykh, J. Wyss, Nucl. Instr. and Meth. B 181 (2001) 254. [5] D. Bisello, A. Candelori, M. Dal Maschio, P. Giubilato, A. Kaminski, M. Nigro, D. Pantano, R. Rando, S. Sedykh, M. Tessaro, J. Wyss, Nucl. Instr. and Meth. B 210 (2003) 146. [6] D. Bisello, M.D. Maschio, P. Giubilato, A. Kaminsky, M. Nigro, D. Pantano, R. Rando, M. Tessaro, J. Wyss, Nucl. Instr. and Meth. B 219–220 (2004) 1000. [7] S. Bertazzoni, G. Cardarilli, D. Piergentili, M. Salmeri, A. Salsano, D. Di Giovenale, G. Grande, P. Marinucci, S. Sperandei, S. Bartalucci, G. Massenga, M. Ricci, V. Bidoli, D. De Francesco, P. Picozza, A. Rovelli, IEEE International Symposium on Defect and Fault Tolerance in VLSI Systems, DFT 99, Albuquerque, New Mexico, USA, November 1999, 158. [8] S. Bertazzoni, D. Di Giovenale, M. Salmeri, A. Salsano, J. Wyss, Workshop on Radiation Effects on Components and Systems, Radecs 2002, Padova, Italy, September 2002.
Ion electron emission microscopy at SIRAD D. Bisello a, A. Candelori a, P. Giubilato a,*, A. Kaminsky a, S. Mattiazzo a, M. Nigro a, D. Pantano a, R. Rando a, M. Tessaro a, J. Wyss b, S. Bertazzoni c, D. Di Giovenale c a
c
Department of Physics, University of Padova, and INFN Padova, via Marzolo 8, 35131 Padova, Italy b University of Cassino and INFN Pisa, Via F. Buonarroti 2, 56127 Pisa, Italy University of Tor Vergata, Roma, and INFN Roma, Via della ricerca scientifica 1, 00133 Roma, Italy Available online 7 April 2005
Abstract In this contribution we describe how single event effect (SEE) studies will be performed with the ion electron emission microscope (IEEM) of the SIRAD irradiation facility located at the INFN Legnaro Laboratory. The IEEM will be used to locate with micrometric precision the impact points of impinging ions that give rise to SEE in an electronic device under test (DUT). In the IEEM technique the ion beam is not microfocused: the position of single ion impact is reconstructed by locating the secondary electron emission points on the DUT surface. We briefly review the original solutions under implementation at SIRAD, such as the opto-electronic approach used to reconstruct the secondary electron emission points by means of a fast, high-resolution imaging of point-like light sources, and a new IEEM test system under development based on a commercial memory array sensitive to single event upsets. 2005 Elsevier B.V. All rights reserved. PACS: 61.82.Fk; 61.80.Jh; 29.40.Wk Keywords: Ion electron emission microscopy; Single event effect
1. Introduction: SIRAD, single event effects and IEEM applications The study of the effects of natural and artificial radiation on semiconductor devices is an impor*
Corresponding author. Tel.: +39 49 827 7215; fax: +39 49 827 7237. E-mail address: [email protected] (P. Giubilato).
tant and lively field in scientific and technological research. In particular radiation tolerance is a fundamental issue for electronic devices and systems in many applications such as nuclear plants, space research, telecommunications, avionics, and highenergy physics. The SIRAD irradiation facility, located at the 15 MV Tandem accelerator of the INFN Laboratory in Legnaro (Italy), is actively dedicated to bulk damage and to single event effect
0168-583X/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.01.036
66
D. Bisello et al. / Nucl. Instr. and Meth. in Phys. Res. B 231 (2005) 65–69
(SEE) studies in semiconductor devices and electronic systems for high energy physics and space applications [1]. An impinging ion will deposit energy in the semiconductor material (silicon) of an electronic device by generating electron–hole pairs. High electron–hole pair densities along a single ion track can influence the device functionality if the charge is generated in a high electric field region and/or it is collected at a sensitive node of the circuit. Single ionizing ions are able to induce device failures, such as single event upsets (SEU) and single event functionality interrupts (SEFI) in digital electronics, and also lead to permanent device damage, such as single event burn-out (SEB) in power diodes, single event gate rupture (SEGR) in power MOSFET and single event latch-up (SEL) in CMOS technologies [2]. Typically SEE studies require a broad selection of energetic ion species to determine both the threshold and the saturation (plateau) values of the linear energy transfer (LET) needed to induce functionality failures in the device under test (DUT). For SEE studies the SIRAD facility can deliver beams ranging from 7Li+3 (60 MeV) to 197Au+25 (300 MeV) with a limit in magnetic rigidity of about 1.4 T m. Global device SEE characterizations are routinely performed at SIRAD using broad beams to uniformly irradiate areas up to several cm2 of a DUT. To improve this capability the group is now developing IEEM capabilities that will allow the location of SEE sensitive points of a DUT with micrometric resolution. Ion electron emission microscopy [3] is somewhat complementary to the consolidated nuclear microprobe technique that builds up sensitivity maps with lateral resolutions of the order of 0.5–1.0 lm by moving a microfocused beam spot systematically across the DUT with micrometric precision. In the IEEM technique a broad (not microfocused) ion beam irradiates the portion of the DUT that is inside the field of view of a commercial photon electron emission microscope. The ion impact positions are reconstructed by collecting the secondary electrons emitted from the DUT surface during ion impact and focusing them onto a two-dimensional electron detector placed at the
focal plane. The IEEM lens system suffers from aberrations that are limited by means of a contrast diaphragm: our standard maximum aperture of 300 lm ensures an intrinsic resolution of about 0.6 lm over a field of view of 250 lm; using a 200 lm diaphragm the resolution improves to 0.4 lm. Moreover, diaphragm aperture size sets the lens transmission efficiency, about 15% with a size of 200 lm and reaching 30% with maximum aperture. As a focal plane electron detector one may use a microchannel plate (MCP) detector: the intrinsic resolution, set by the physical size of microchannels (some tens of microns), fits the resolution of the image produced by the IEEM with a FOV of 250 lm, and it is fast and hence can be used to resolve in time individual ion impacts. For SEE studies the X, Y transverse coordinates and the time T of reconstructed random ion impacts are to be correlated with any interesting events, in particular SEE, induced in the DUT. The technique may be also used for time resolved ion beam induced charge collection (IBICC) studies.
2. Opto-electronic IEEM of SIRAD In the SIRAD IEEM (Fig. 1) the secondary electron MCP detector is annular to allow for the ion beam to pass axially through the microscope and impact normally the DUT surface. The large electronic MCP signal (gain 107) is used to excite a fast phosphor screen to create a light spot. The photons are then extracted from the irradiation chamber by means of a mirror and a quartz window. The optical image is focused by a system of lenses onto a fast photon position sensitive detector, for the determination of the position of the luminous spots corresponding to the secondary electron signals. By depositing a thin gold layer (20–40 nm) on the DUT surface, to ensure good secondary electron emission, we expect, at the level of the phosphor screen, an ion impact detection efficiency of 45% for 100 MeV C ions, reaching full efficiency for ions with Z > 25. The opto-electronic approach, original to the SIRAD IEEM, allows the use of complex sensing devices for greater sensing performance, flexibility
D. Bisello et al. / Nucl. Instr. and Meth. in Phys. Res. B 231 (2005) 65–69
67
Fig. 1. Schematic of the SIRAD IEEM setup. Wireframes parts show beamline and vacuum chamber boundaries, while shaded cones show electrons and photons path through the system: electrons inside the microscope column to the MCP and photons from the MCP phosphor to the CCDs.
and ease of use. The main drawback is the low optical efficiency of the system, not better than 1%, that requires high sensitivity sensors [4–6]. Commercial CCD two-dimensional arrays, used for photon electron emission microscopy (PEEM) surface analysis techniques, have intrinsically long readout times (low frame rates; e.g. about 30 frames per second for a one-output 1024 · 1024 array), which would severely limit the ion fluxes for time-resolved single ion impact effect studies (such as SEE or IBICC studies) to levels of about 10 ion impacts/s in the field of view (corresponding to an ion flux of about 2 · 103 ions/cm2 s). Such low rates are also comparable to the noise level of the large MCP inside the IEEM. To avoid any IEEM detector limitations for SEE applications (in general the maximum ion flux will be limited by the DUT and the SEE detection system) we have developed two fast high resolu-
tion opto-electronic photon detection systems that can handle event (single ion impact) rates of a few 104 Hz in the field of view of the microscope. The first system is based on a commercial 2 · 2 cm2 semiconductor position sensitive device (PSD) wherein the orthogonal coordinates of a light spot signal are obtained analogically by charge division using two pairs of electrodes [5]. A second system uses an optical system based on a beam splitter and two orthogonal linear 1024 pixel CCD sensors, one for each coordinate: the optical system splits the image and squeezes each copy onto one of the two CCDs. This way we read out just 1024 pixels (both linear CCDs are read simultaneously) instead of 1 million, and consequently we have reduced data throughput by a factor 1000, increasing the speed by the same factor. This novel system ensures, in terms of data processing capabilities, an even greater flexibility for time-resolved IEEM applications. The system
68
D. Bisello et al. / Nucl. Instr. and Meth. in Phys. Res. B 231 (2005) 65–69
is intrinsically digital: each pixel is an independent detector and the minimum sensitivity is set by the noise level of each pixel, hence the spatial resolution for a given pixel size is independent of the intensity of the luminous spot, unlike the PSD analogue system [6]. All the raw data elaboration is performed by a dedicated home made solid state DSP system, based on a Virtex-II FPGA plus support electronics. Analysis starts by cleaning signals from bias levels and then filtering them to optimize the S/N ratio. Dedicated algorithms work in parallel to reconstruct the spatial coordinates by combining the signals coming from the two CCDs. Data are sent to a computer through a simple USB connection, already arranged as X, Y, T coordinates. While the first system has been used to take preliminary data with the microscope, the second one has been successfully tested as a prototype, and we are now working to install it as the final IEEM sensor. First data with new system are scheduled to be taken in spring 2005.
3. Optical alignment at SIRAD Unlike common PEEM based instruments, the SIRAD IEEM sensing system is off the beam axis and outside the vacuum chamber (Fig. 1). The light spots generated by the phosphor layer at the MCP output are imaged by means of a 45 mirror that reflects the image to the light sensor, placed orthogonal to the main axis of the microscope outside the irradiation chamber. The mirror is tiltable for fine adjustments. To properly align the DUT, we look into the microscope field of view (FOV) with a lateral oblique optical microscope. To deal with parallax errors, a laser-pointer was added to the system. Using the same optical system that carries photons from the phosphor to the external sensor, the laser beam is injected in the reverse direction into the microscope through the hole of the MCP and down the microscope axis. The observation of the laser spot on the target through the lateral oblique optical microscope allows us to know where the target is located within the field of view of the IEEM.
4. SEE testing with the IEEM; the SDRAM IEEM test system During irradiation of a DUT, the ion impact information furnished by the IEEM (position and time coordinates) is stored into a temporary internal data buffer while waiting for control calls generated by the control electronics of the DUT. If the device control setup recognizes that something interesting has happened (SEU, SEL, SEFI, . . .), it sends a trigger signal to the IEEM control unit, that retrieves the coordinates of the time-corresponding ion impact point from the internal data buffer. This procedure permits the identification of SEE sensitive areas by precisely locating the corresponding ion entry points on the DUT surface. At present we are developing a global triggering (time-stamp) system to allow an easy synchronization between the microscope control unit and the control setup of the DUT. The SIRAD IEEM will be tested in a practical situation with a real microelectronic device to demonstrate its capabilities and define general methodological procedures for SEE testing. For this purpose we will use a commercial 256 MB SDRAM and a single event upset (SEU) test system. The SDRAM system will also be used as a twodimensional ion detector. Indeed the SDRAM is a large array of small unit memory cells (512 · 4096) words · 8 bits · 4 banks, and it is extremely regular (except for a few sparse cells), and each unit memory cell is subject to SEU: about 104 cells will be in the field of view of the IEEM and the measured SEU cross-section for heavy ions (Z > 13) is rbit 10 9 cm2 [7]. Hence about 2% of the heavy ions impacting inside the field of view will give rise to a SEU. With an access clock of 100 MHz the cells in the array that undergo upsets will be identified and located [8]. Such a system will be used to measure the effective spatial resolution that an IEEM can achieve in locating the lateral position of a SEE sensitive volume as compared to the resolution one may measure using a target with regular surface features such a metal grid (TEM grid). Indeed in stateof-the-art CMOS devices the electronically sensitive volumes are a typically a few microns in depth below the metallization and passivation layers, and
D. Bisello et al. / Nucl. Instr. and Meth. in Phys. Res. B 231 (2005) 65–69
any additional coatings applied to ensure adequate secondary electron emission from the top surface during ion impact. The SDRAM array offers an ensemble of single ion detectors that are distributed with a precision that is about 100 times greater than the resolution of the IEEM and, using statistical methods, the effective resolution of the IEEM can determined by comparing the coordinates of ion entry points given by the IEEM with the SDRAM coordinates of the SEU cells. Tests with commercial off the shelf SDRAM devices represent a typical application of the SIRAD IEEM facility. For this reason the requirements of the SDRAM test equipment are driving the development of the facility. As a relevant part of the data acquisition electronics is going to be shared with future users of the facility, its implementation is designed to anticipate future requirements and standard interfaces (electrical and software) are provided. In particular we are testing WLAN (wireless local area network) connections to avoid cabling to the DUT inside the vacuum chamber.
5. Conclusions The SIRAD group is developing an advanced implementation of an ion electron emission microscope to map the sensitivity to single event effect of
69
electronic devices and systems. The first applications will use a SEU detection system based on a commercial SDRAM.
References [1] J. Wyss, D. Bisello, D. Pantano, Nucl. Instr. and Meth. A 462 (2001) 426. [2] A. Holmes-Siedle, L. Adams, Handbook of Radiaion Effect, Oxford Science, 1993. [3] B.L. Doyle, G. Vizkelethy, D.S. Walsh, B. Senftinger, M. Mellon, Nucl. Instr. and Meth. B 158 (1999) 6. [4] D. Bisello, A. Kaminsky, A. Magalini, M. Nigro, D. Pantano, S. Sedykh, J. Wyss, Nucl. Instr. and Meth. B 181 (2001) 254. [5] D. Bisello, A. Candelori, M. Dal Maschio, P. Giubilato, A. Kaminski, M. Nigro, D. Pantano, R. Rando, S. Sedykh, M. Tessaro, J. Wyss, Nucl. Instr. and Meth. B 210 (2003) 146. [6] D. Bisello, M.D. Maschio, P. Giubilato, A. Kaminsky, M. Nigro, D. Pantano, R. Rando, M. Tessaro, J. Wyss, Nucl. Instr. and Meth. B 219–220 (2004) 1000. [7] S. Bertazzoni, G. Cardarilli, D. Piergentili, M. Salmeri, A. Salsano, D. Di Giovenale, G. Grande, P. Marinucci, S. Sperandei, S. Bartalucci, G. Massenga, M. Ricci, V. Bidoli, D. De Francesco, P. Picozza, A. Rovelli, IEEE International Symposium on Defect and Fault Tolerance in VLSI Systems, DFT 99, Albuquerque, New Mexico, USA, November 1999, 158. [8] S. Bertazzoni, D. Di Giovenale, M. Salmeri, A. Salsano, J. Wyss, Workshop on Radiation Effects on Components and Systems, Radecs 2002, Padova, Italy, September 2002.