New Method and Tool for TEM Samples Preparation

А new tool for TEM sample preparation, which allows preparing a thin lamella with thickness less than 20 nm surrounded by and embedded in bulk material, is presented. The main advantages of this system are low ion milling induced damage (less than 2 nm in depth), low process time (1—2 hours), in sit...

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Дата:	2013
Автори:	Boguslavsky, D., Cherepin, V., Polubotko, Y., Smith, C.
Формат:	Стаття
Мова:	English
Опубліковано:	Інститут металофізики ім. Г.В. Курдюмова НАН України 2013
Назва видання:	Металлофизика и новейшие технологии
Теми:	Металлические поверхности и плёнки
Онлайн доступ:	http://dspace.nbuv.gov.ua/handle/123456789/104073
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Назва журналу:	Digital Library of Periodicals of National Academy of Sciences of Ukraine
Цитувати:	New Method and Tool for TEM Samples Preparation / D. Boguslavsky, V. Cherepin, Y. Polubotko, C. Smith // Металлофизика и новейшие технологии. — 2013. — Т. 35, № 2. — С. 163-173. — Бібліогр.: 8 назв. — англ.

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Digital Library of Periodicals of National Academy of Sciences of Ukraine

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spelling	irk-123456789-1040732016-07-02T03:01:34Z New Method and Tool for TEM Samples Preparation Boguslavsky, D. Cherepin, V. Polubotko, Y. Smith, C. Металлические поверхности и плёнки А new tool for TEM sample preparation, which allows preparing a thin lamella with thickness less than 20 nm surrounded by and embedded in bulk material, is presented. The main advantages of this system are low ion milling induced damage (less than 2 nm in depth), low process time (1—2 hours), in situ sample monitoring during ion milling (topography and sample thickness), and large treated area (5—30 μm along the area of interest). Comparison of few kinds of working substance of ion sources as well as schemes or drawings of key components of the tool are presented. Представлено нову методику і технологію виготовлення зразків для ПЕМ, яка уможливлює підготувати зразок завтовшки до 20 нм, оточений об’ємним матеріалом і втілений у нього. Головна перевага системи полягає в малій товщині шару пошкоджень, спричинених йонним обробленням (менше 2 нм), в малому часі оброблення (1—2 години), в моніторинґу зразка під час йонного фрезерування (топографія і товщина зразка) і у великій площі, що обробляється (5—30 мкм вздовж області, яка являє інтерес). Виконано порівняння декількох типів робочої речовини для йонних джерел, наведено схеми або креслення ключових вузлів пристрою. Представлена новая методика и технология приготовления образцов для ПЭМ, позволяющая подготовить образец толщиной до 20 нм, окружённый объёмным материалом и вмурованный в него. Главным преимуществом системы является малая толщина слоя повреждений, индуцированных ионной обработкой (меньше 2 нм), малое время обработки (1—2 часа), мониторинг образца во время ионного фрезерования (топография и толщина образца) и большая обрабатываемая площадь (5—30 мкм вдоль интересующей области). Проведено сравнение нескольких рабочих веществ для ионных источников, приведены схемы или чертежи ключевых узлов устройства. The authors would like to thank the staff of SELA and PETRC of Ukraine for taking part in the development and fabrication of Xact. In particular, D. Viazovsky and T. Krasovsky for electronics development, V. Kontorov and V. Isyanov for technical documentation development, D. Farhana, L. Berner for software development, A. Berner, A. Bekkerman, A. Eizner, V. Kuchik, S. Yakovlev, G. Aharonov, all who made this achievement real by their hard work and talent. 2013 Article New Method and Tool for TEM Samples Preparation / D. Boguslavsky, V. Cherepin, Y. Polubotko, C. Smith // Металлофизика и новейшие технологии. — 2013. — Т. 35, № 2. — С. 163-173. — Бібліогр.: 8 назв. — англ. 1024-1809 PACS numbers: 06.60.Ei, 06.60.Mr, 41.85.Ja, 68.37.Ma, 68.37.Og, 81.20.Wk http://dspace.nbuv.gov.ua/handle/123456789/104073 en Металлофизика и новейшие технологии Інститут металофізики ім. Г.В. Курдюмова НАН України
institution	Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection	DSpace DC
language	English
topic	Металлические поверхности и плёнки Металлические поверхности и плёнки
spellingShingle	Металлические поверхности и плёнки Металлические поверхности и плёнки Boguslavsky, D. Cherepin, V. Polubotko, Y. Smith, C. New Method and Tool for TEM Samples Preparation Металлофизика и новейшие технологии
description	А new tool for TEM sample preparation, which allows preparing a thin lamella with thickness less than 20 nm surrounded by and embedded in bulk material, is presented. The main advantages of this system are low ion milling induced damage (less than 2 nm in depth), low process time (1—2 hours), in situ sample monitoring during ion milling (topography and sample thickness), and large treated area (5—30 μm along the area of interest). Comparison of few kinds of working substance of ion sources as well as schemes or drawings of key components of the tool are presented.
format	Article
author	Boguslavsky, D. Cherepin, V. Polubotko, Y. Smith, C.
author_facet	Boguslavsky, D. Cherepin, V. Polubotko, Y. Smith, C.
author_sort	Boguslavsky, D.
title	New Method and Tool for TEM Samples Preparation
title_short	New Method and Tool for TEM Samples Preparation
title_full	New Method and Tool for TEM Samples Preparation
title_fullStr	New Method and Tool for TEM Samples Preparation
title_full_unstemmed	New Method and Tool for TEM Samples Preparation
title_sort	new method and tool for tem samples preparation
publisher	Інститут металофізики ім. Г.В. Курдюмова НАН України
publishDate	2013
topic_facet	Металлические поверхности и плёнки
url	http://dspace.nbuv.gov.ua/handle/123456789/104073
citation_txt	New Method and Tool for TEM Samples Preparation / D. Boguslavsky, V. Cherepin, Y. Polubotko, C. Smith // Металлофизика и новейшие технологии. — 2013. — Т. 35, № 2. — С. 163-173. — Бібліогр.: 8 назв. — англ.
series	Металлофизика и новейшие технологии
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last_indexed	2025-07-07T14:48:50Z
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fulltext	163 МЕТАЛЛИЧЕСКИЕ ПОВЕРХНОСТИ И ПЛЁНКИ PACS numbers: 06.60.Ei, 06.60.Mr, 41.85.Ja, 68.37.Ma, 68.37.Og, 81.20.Wk New Method and Tool for TEM Samples Preparation D. Boguslavsky, V. Cherepin, Y. Polubotko, and C. Smith Camtek Ltd., P.O. Box 544, Migdal Ha’emek, 23150 Israel Physical Engineering Teaching and Research Centre, Academician Vernadsky Blvd. 36, 03680 Kyiv-142, Ukraine А new tool for TEM sample preparation, which allows preparing a thin lamel- la with thickness less than 20 nm surrounded by and embedded in bulk mate- rial, is presented. The main advantages of this system are low ion milling in- duced damage (less than 2 nm in depth), low process time (1—2 hours), in situ sample monitoring during ion milling (topography and sample thickness), and large treated area (5—30 μm along the area of interest). Comparison of few kinds of working substance of ion sources as well as schemes or drawings of key components of the tool are presented. Представлено нову методику і технологію виготовлення зразків для ПЕМ, яка уможливлює підготувати зразок завтовшки до 20 нм, оточений об’ємним матеріалом і втілений у нього. Головна перевага системи поля- гає в малій товщині шару пошкоджень, спричинених йонним оброблен- ням (менше 2 нм), в малому часі оброблення (1—2 години), в моніторинґу зразка під час йонного фрезерування (топографія і товщина зразка) і у ве- ликій площі, що обробляється (5—30 мкм вздовж області, яка являє інте- рес). Виконано порівняння декількох типів робочої речовини для йонних джерел, наведено схеми або креслення ключових вузлів пристрою. Представлена новая методика и технология приготовления образцов для ПЭМ, позволяющая подготовить образец толщиной до 20 нм, окружён- ный объёмным материалом и вмурованный в него. Главным преимуще- ством системы является малая толщина слоя повреждений, индуциро- ванных ионной обработкой (меньше 2 нм), малое время обработки (1—2 часа), мониторинг образца во время ионного фрезерования (топография и толщина образца) и большая обрабатываемая площадь (5—30 мкм вдоль интересующей области). Проведено сравнение нескольких рабочих ве- ществ для ионных источников, приведены схемы или чертежи ключевых Металлофиз. новейшие технол. / Metallofiz. Noveishie Tekhnol. 2013, т. 35, № 2, сс. 163—173 Оттиски доступны непосредственно от издателя Фотокопирование разрешено только в соответствии с лицензией © 2013 ИМФ (Институт металлофизики им. Г. В. Курдюмова НАН Украины) Напечатано в Украине. 164 D. BOGUSLAVSKY, V. CHEREPIN, Y. POLUBOTKO, and C. SMITH узлов устройства. Key words: ion milling, thin lamella, radiation damage. (Received January 18, 2013; in a final version, February 21, 2013) 1. INTRODUCTION Preparing of thin coplanar high quality samples for TEM with minimal preparation induced damage is a key problem on transmitted electron microscopy as a method of analysis in electronics. Currently, the CMOS (Complementary Metal—Oxide—Semiconductor technology) manufacturing is based on the 32 nm technological process. Now, the 20 nm thick samples seem reasonable and the damage induced by prep- aration procedure of a work piece must not exceed 1—2 nm. The easiest way is to etch a work piece by a beam of accelerated ions. Etching by Ar + ion beams (PIPS1) or focused Ga + ion beams (FIB2) are most prevalent. These technologies failed to solve this issue [1]. In 2004, the necessity to develop a new system for TEM samples prepara- tion was realized. Listed below are the following conditions to be met: — ion etching process must occur when using stationary sample with the ability to control the quality and the thickness of the specimen in real time, using scanning electron microscope with resolution of 50—100 Å; — at least 5-degrees of freedom manipulator is required for specimen handling; — availability of ion source with resources up to 2000 hours (up to 6 months in operation) and the possibility to focus the ion beam to sever- al tens of micrometres in diameter; — ion beam management should be purely electrostatic with the possibil- ity to alter its focus, angle of incidence and energy of ions in a wide range; — sample preparation procedure should be fully automated and pro- cess time must not exceed of 2 hours. In a given article, the conditions mentioned above and the intense and innovative efforts responsible for the success of the new method will be discussed. 2. INSTRUMENTATION Commercial designation of the system is Xact3. This system utilizes AIMTM (Adaptive Ion Milling) technology. Xact equipped (Fig. 1) with commercial scanning electron micro- 1 http://www.gatan.com/specimenprep/691_pips.php 2 http://www.fei.com/products/focused-ion-beams/ 3 http://www.camtek.co.il/php/index.php?option=com_content&task=view&id=313&Itemid=249 NEW METHOD AND TOOL FOR TEM SAMPLES PREPARATION 165 scope. The resolution of the microscope is 6 nm on the distance of 18 mm. The SEM image is generating via detectors of secondary electrons (SED), back scattered electrons (BSED) and primary transmitted elec- trons (TED). The BSED is a multidetector (A, B) that allows receiving two types of images: topographic (difference of A and B signals) and composition (sum of A and B signals). The TED is composed of three concentric detectors allowing receiving of bright field and dark field images and measuring (control) thickness of a work piece beginning from 6 nm (Fig. 2). Vacuum in the system is supported by the turbomolecular pump with 400 l/s (N2) efficiency at the level of (2.53—3)⋅10 −6 torr. Vacuum in the area of tungsten filament of the microscope is supported by the ion pump at the level of 2⋅10 −7 torr. The process of mounting the sample on the manipulator and loading it into the chamber takes approximately 1 minute. 5-degrees of free- dom manipulator (X, Y, Z, R, T, where R–rotation around X-axis, T–rotation around Z-axis) is designed for accurate positioning of the sample for milling and observation. The FIB has been developed utilizing LMIS (Liquid Metal Iron Source)–high brightness ion source. The FIB small beam size is achieved due to low ion current and high accelerating voltage (30—50 kV). Low ion current does not allow removing bulk of sample’s material (to open wide area of interest). Increased ion energy leads to the development of exten- sive damaged layer on sample’s surface. The ion source used in the sys- tem has several important characteristics: high brightness (≅ 300 A⋅m−2⋅sr−1⋅V−1), high ion current (up to 30 μA) and low vacuum load (working pressure is ≅ 3⋅10 −6 torr). The only adjustable parameter of the Fig. 1. Xact general view. 166 D. BOGUSLAVSKY, V. CHEREPIN, Y. POLUBOTKO, and C. SMITH ion source is discharge voltage, which is stabilized by automated manag- ing of the leak valve flow rate. Thermomechanical leak valve appeared to be the easiest and most reliable. The flow rate of the leak valve was man- aged by controlled thermal expansion (CTE) of high-CTE body relative to invar (CTE = 0.6 μm/m⋅°C) closing pin. The time constant of the feedback circuit (few seconds) correlated well with the working gas pressure varia- tion time in the discharge area. The leak valve and ion-beam-accelerating electrode are of the same potential (up to 10 kV). Therefore, to prevent breakouts, HV isolation is provided from the high-pressure side (usually 110 kPa) of the working gas line (Fig. 3). An ion source of this kind allows the generation of an ion current of 30 μA at accelerating voltage of 8 kV and 0.5 μA at accelerating voltage Fig. 2. Xact scheme. Fig. 3. Leak valve. NEW METHOD AND TOOL FOR TEM SAMPLES PREPARATION 167 of 1 kV. The generating and accelerating of ions are separated. This sig- nificantly simplifies the adjustment and managing of the ion source, thereby allowing working in a wide range of energies. Ion source time to service depends on the time needed for sidewall of hollow cathode to be sputtered through and it is more than 6 months of continuous work. 3. WORKING SUBSTANCE AND OPTICAL SYSTEM Ions of Ar + or Ga + are usually used for etching, particularly, in TEM sample preparation. Analysis of amorphous and damaged layers caused by ion etching revealed reduction of ion beam induced damage while increasing the ion’s mass. Simulation of this effect was made utilizing TRIM (Transport of Ions in Matter) SW for Ga + , Ar + , and Xe + ions (Fig. 4, Tables 1 and 2). Range – depth the primary ion penetrates to; Yield Fig. 4. Maximum vacancy depth for different kinds of ions. TABLE 1. Ar, 8 kV, 7° Ga, 8 kV, 7° Xe, 8 kV, 7° a.m.u. Range Yield Vac. depth Range Yield Vac. depth Range Yield Vac. depth Si 14 50 12.20 255 35 16.10 173 31 20.20 210 Ti 22 42 7.60 225 30 10.00 203 24 12.30 120 Cu 29 29 17.30 135 19 21.20 113 15 25.60 83 Ga 31 49 13.90 218 30 16.20 173 23 20.30 128 Mo 42 33 7.30 143 24 9.30 105 17 11.10 98 Ag 47 41 14.00 195 26 18.20 150 17 20.70 105 In 49 62 13.70 270 40 17.30 188 26 21.10 173 W 74 39 5.80 180 25 7.80 128 15 9.40 75 168 D. BOGUSLAVSKY, V. CHEREPIN, Y. POLUBOTKO, and C. SMITH – number of sputtered atoms per incident ion; Vac. depth – depth of structure distortions. It appears that usage of Xe as a working gas reduces the depth of damaged layer by 20—40%. In addition, noble gases do not interact chemically with target material. Another advantage is the low poten- tial of ionization of Xe (12.13 eV) relative to Ar (15.8 eV) which en- sures a more stable ion source discharge. The most innovative Xact component solved the initial issue–the multideflecting system for the ion beam. The final scheme of ion optics is shown in Fig. 5. The ion beam extracted from anode by the extractor (1) is focused by first condenser lens (2) to 1.5—2 mm dia. Beam tails are cut by the dia- phragm (3). The position of the beam is corrected according to system’s axis by first deflecting unit (4). Then second long-focus low spherical TABLE 2. Ar, 2 kV, 7° Ga, 2 kV, 7° Xe, 2 kV, 7° a.m.u. Range Yield Vac. depth Range Yield Vac. depth Range Yield Vac. depth Si 14 21 5.80 100 18 7.10 95 17 8.60 75 Ti 22 18 3.70 75 15 4.50 75 12 5.40 60 Cu 29 12 7.30 65 9 8.20 50 9 9.30 45 Ga 31 20 6.30 95 15 7.30 75 13 8.50 55 Mo 42 16 3.30 60 11 3.80 50 9 4.20 45 Ag 47 18 6.40 80 13 7.20 60 10 7.90 50 In 49 27 6.60 120 19 7.40 95 14 8.40 80 W 74 17 2.60 65 12 3.20 45 9 3.50 40 Fig. 5. Scheme of ion optics of Xact. NEW METHOD AND TOOL FOR TEM SAMPLES PREPARATION 169 aberrations lens (5) forms a paraxial slightly convergent I-beam. Sec- ond deflecting unit (6) is capable of deflecting the I-beam 7 degrees from system’s axis without distortions. Computer simulation (Simion) and experiment have confirmed that conical dodecapole (12 poles de- flector) [2] can handle this. Deflected beam reaches the key unit of the system–spherical deflectron (7). It is a slice of spherical condenser (Figs. 6, 7) where θ2 is the maxi- Fig. 6. Spherical deflectron. Fig. 7. Initial sample. 170 D. BOGUSLAVSKY, V. CHEREPIN, Y. POLUBOTKO, and C. SMITH mum angle of incidence into horizontal sample. It is known that spher- ical condenser is the deflecting, stigmating and focusing element. The point object, centre of the sphere, and point image of the object are located on the same line. This characteristic made it possible to po- sition all of the ion-optical elements and an area of interest of the sam- ple into the same axis. The area of interest of the sample coincide with the intersection of ion gun and SEM axes, so it is possible to examine the sample during preparation. Actual dimensions of spherical deflectron are defined by the work- ing distance of SEM and maximum angle of incidence of ion beam into the sample. With a maximum angle of incidence of 60 degrees (from the normal to surface) that corresponds to the angle close to maximum sputtering rate [3], the distance between the centre of sphere and elec- tron beam equals to diameter of sphere. Angle of incidence of the ion beam to the sample varies by polar angle variation according to the formula: Fig. 8. Ion beam visualization. NEW METHOD AND TOOL FOR TEM SAMPLES PREPARATION 171 2sin (incidence) = sin (polar angle), i.e. a thin static sample could be treated from both sides with an ion beam with angles of 0−30 degrees (Fig. 6). The main purpose of the system is the preparation of thin lamellas of the IC cross-section. Prior to Xact treatment, samples are cryogen cut from a wafer by EM34 [1]. Configuration of a sample is shown on the Fig. 7. The target area is masked by the substrate silicon, which in any case (utilizing of any sample preparation tool) could be a contaminant. After EM3 cutting, the sample is located in a relatively big clamp, so, it is safe and easy to manipulate. Further work is a piece thinning resulting ideally–in thin lamella (20−50 nm) supported by bulk sili- con, usually–low angle wedge. Xact has an ion beam visualization system. Possible beam shapes are shown on Fig. 8: horizontal ellipsis, circle, and vertical ellipsis. The Table 3 lists the typical sequence of TEM (HRTEM) sample preparation. Xe + ion beam induced damage was measured for the Xact and com- pared to damage caused by other systems utilizing Ar + and Ga + [1]. De- pendence is as follows: ≈ 1nm of damaged layer for 1 keV of ion energy (for 3−7 degrees incidence). For the first time, direct measurement of amorphous layer thickness of Si caused by Xe + ions bombardment was performed [4]. It was shown that as low as 1−1.8 nm of amorphous lay- er thickness is feasible. In Figure 9, HRTEM image shows the depth of damaged layer on crystalline silicon. Preparation of the sample is described in detail in the article [4]. However, the protective Cu layer has not been applied. It had no influ- ence on the result. The Table 4 shows the comparison of popular methods of TEM sam- ple preparation. 4 http://www.camtek.co.il/php/index.php?option=com_content&task=view&id=314&Itemid=250 TABLE 3. Automatic sub-process Incident angle of ion beam, degrees Thickness of a sample after each sub-process, nm Trenching milling, 8 kV 30 3500 Glancing milling, 8 kV 4 500 Glancing milling, 4 kV 4 350 Glancing milling, 3 kV 4−5 200 Glancing milling, 2 kV 5−6 100 Glancing milling, 1.5 kV 5−7 50 and below 172 D. BOGUSLAVSKY, V. CHEREPIN, Y. POLUBOTKO, and C. SMITH Fig. 9. Cross-section of crystal silicon exposed by 7°, 1.5 keV Xe + beam. Top- down: c-Si, damaged Si layer, glue (bright). TABLE 4. FIB BIB AIM Pre-processing yes/no required required Sample handling difficult difficult easy Process control good poor good Target localization good poor good Auto endpoint detection no no yes In situ imaging yes no yes Treated area small large large Minimum accelerating voltage, V 500 100 500 Sample quality fair good very good Ga/Ar/Xe contamination heavy Ga low Ar low Xe Artefacts removing Ar milling not required not required Time consumption 1—4 hours not relevant* 1—2 hours * depends on FIB process; no further milling possible for some processes; * manual handling dependent. NEW METHOD AND TOOL FOR TEM SAMPLES PREPARATION 173 4. CONCLUSION The new method and tool for TEM samples preparation has been devel- oped and successfully introduced in laboratory practice for examina- tion of electronic components with the lowest level of radiation damage currently achieved at global level (1 nm). Further reduction of this im- portant value may be obtained by lowering the energy of bombarding ions but a source with a higher brightness is needed for this purpose. ACKNOWLEDGEMENTS The authors would like to thank the staff of SELA and PETRC of Ukraine for taking part in the development and fabrication of Xact. In particular, D. Viazovsky and T. Krasovsky for electronics develop- ment, V. Kontorov and V. Isyanov for technical documentation devel- opment, D. Farhana, L. Berner for software development, A. Berner, A. Bekkerman, A. Eizner, V. Kuchik, S. Yakovlev, G. Aharonov, all who made this achievement real by their hard work and talent. REFERENCES 1. D. Horvitz, M. Baram et al., 42nd Annual Meeting of ISM (Israel: Technion: 2008). 2. В. Т. Черепин, В. Н. Василенко, Т. А. Красовский, Е. А. Полуботько, ПТЭ, № 5: 138 (2007). 3. В. Т. Черепин, Ионный микрозондовый анализ (Киев: Наукова думка: 1990). 4. Е. А. Полуботько, В. Т. Черепин, Металлофиз. новейшие технол., 31, № 6: 805 (2009). 5. Introduction to Focused Ion Beams. Instrumentation, Theory, Techniques and Practice (Eds. L. A. Giannuzzi and F. A. Stevie) (New York: Springer Sci- ence+Business Media: 2005). 6. V. T. Cherepin, S. P. Chenakin, Ya. Ya. Dyadkin, W. Heichler, and W. Zwan- sig, Experimentelle Technik der Physik, 33, No. 3 (1985). 7. D. Boguslavsky, C. Smith, D. Viazovsky et al., Sample Preparation for Microa- nalysis, International Patent Application No. PCT/IL2006/000141 (Published August 10, 2006). 8. D. Boguslavsky, V. Cherepin, and C. Smith, Directed Multi-Deflected Ion Beam Milling of a Work Piece and Determining and Controlling Extent Thereof, Sin- gapore Patent No. 130320 (March 31, 2009).

New Method and Tool for TEM Samples Preparation

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