Scanning Electron Microscopy (SEM)

Transkripsi

1 Electron Mikroskop

2 Scanning Electron Microscopy (SEM) Apa itu SEM? Prinsip Kerja SEM Komponen utama dan fungsinya Electron beam - spesimen interaksi Inteaksi volume dan escape volume Perbesaran, resolusi, depth of field dan kontras bayangan Energy Dispersive X-ray Spectroscopy (EDS) Wavelength Dispersive X-ray Spectroscopy (WDS) Orientation Imaging Microscopy (OIM) X-ray Fluorescence (XRF)

3 Comparison of OM,TEM and SEM Light source Condenser Specimen Objective Source of electrons Magnetic lenses Eyepiece Projector Specimen detector CRT Cathode Ray Tube OM TEM SEM Principal features of an optical microscope, a transmission electron microscope and a scanning electron microscope, drawn to emphasize the similarities of overall design.

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5 Anode Glass Magnetic coils Under vacuum

6 PERBEDAAN MO DAN SEM MO : resolusi/daya pisah lebih rendah SEM: resolusi/daya pisah lebih tinggi Kombinasi perbesaran dan daya pisah yang lebih besar dan kemampuan deteksi unsur pada permukaan material SEM lebih teliti untuk riset dan industri

7 I. Basics of Electron Microscopy Electro-magnetic lenses Scanning Transmission EM (STEM) Mass determination Elemental mapping Scanning EM (SEM) Surface relief Transmission EM (TEM) Structures Imaging or Diffraction 0.03 Å theoretical resolution 1.0 Å practical resolution

8 II. Electron Source Tungsten filament (thermionic) Tungsten crystal (field emission) 100x brighter Electrons Accelerated to defined energy behave as a wave. kv ( kv with 200kV-> Å)

9 Electron beam Source W or LaB 6 Filament Thermionic or Field Emission Gun

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11 ELEKTRON YANG BERHAMBUR DAN DITANGKAP SEM SAAT SAMPEL DITEMBAK ELEKTRON

12 HAMBURAN ELEKTRON DIDETEKSI DAN ENERGINYA DITAMPILKAN DALAM BENTUK GAMBAR DAN GRAFIK Tiap Jenis hamburan elektron ditangkap detektor yang berbeda Tempat Sampel

13 TEMPAT SAMPEL DI SCANNING ELECTRON MICROSCOPE

14 PENGAMATAN DENGAN SCANNING ELECTRON MICROSCOPE OM SEM Aplikasi : Perbesaran 4x 1000x 10x x Mengamati struktur maupun bentuk permukaan yang berskala lebih halus Dilengkapi Dengan EDS (Electron Dispersive X ray Spectroscopy) Dapat mendeteksi unsur2 dalam material. Permukaan yang diamati harus penghantar elektron

15 Keuntungan SEM terhadap OM Perbesaran Depth of Field Resolusi OM 4x 1000x 15.5mm 0.19mm ~ 0.2mm SEM 10x x 4mm 0.4mm 1-10nm SEM mempunyai depth of field yang besar, yang dapat memfokus jumlah sampel yang lebih banyak pada satu waktu dan menghasilkan bayangan yang baik dari sampel tiga dimensi. SEM juga menghasilkan bayangan dengan resolusi tinggi, yang berarti mendekati bayangan yang dapat diuji dengan perbesaran tinggi. Kombinasi perbesaran yang lebih tinggi, dark field, resolusi yang lebih besar, dan komposisi serta informasi kristallografi membuat SEM merupakan satu dari peralatan yang paling banyak digunakan dalam penelitian, R&D industri khususnya industri semikonductor.

16 Topography Aplikasi Utama SEM The surface features of an object and its texture (hardness, reflectivity etc.) Morphology The shape and size of the particles making up the object (strength, defects in IC and chips...etc.) Composition The elements and compounds that the object is composed of and the relative amounts of them (melting point, reactivity, hardness...etc.) Crystallographic Information How the grains are arranged in the object (conductivity, electrical properties, strength...etc.)

17 Electron Gun A More Detaile d Look Inside e - beam Source: L. Reimer, Scanning Electron Microscope, 2 nd Ed., Springer-Verlag, 1998, p.2

18 Preparasi Sampel Hindari semua air, larutan atau material-material lain yang mudah menguap dalam vakum. Permukaan harus rata untuk BSE dan OIM Tentukan jumlah sample. Samples Non-logam, seperti building materials, insulating ceramics, harus di caoting agar konduktivitas listriknya baik. Logam dan samples konduktivitas dapat diletakan langsung kedalam SEM.

19 Image Magnification Example of a series of increasing magnification (spherical lead particles imaged in SE mode)

20 Bagaimana Elektron Beam dihasilkan? Elektron guns digunakan untuk menghasilkan kontrol beam yang halus dari elektron yang kemudian difokuskan pada permukaan spesimen. Eelektron guns bisa dalam bentuk thermionik gun atau field-emission gun

21 Thermionic Emission Gun A tungsten filament heated by DC to approximately 2700K or LaB 6 rod heated to around 2000K A vacuum of 10-3 Pa (10-4 Pa for LaB 6 ) is needed to prevent oxidation of the filament Electrons boil off from the tip of the filament Electrons are accelerated by an acceleration voltage of 1-50kV

22 Field Emission Gun The tip of a tungsten needle is made very sharp (radius < 0.1 mm) The electric field at the tip is very strong (> 10 7 V/cm) due to the sharp point effect Electrons are pulled out from the tip by the strong electric field Ultra-high vacuum (better than 10-6 Pa) is needed to avoid ion bombardment to the tip from the residual gas. Electron probe diameter < 1 nm is possible

23 Source of Electrons Thermionic Gun T: ~1500 o C E: >10MV/cm W Filament (5-50mm) (5nm) W and LaB 6 Cold- and thermal FEG Electron Gun Properties Source Brightness Stability(%) Size Energy spread Vacuum W 3X10 5 ~1 50mm 3.0(eV) 10-5 (t ) LaB 6 3x10 6 ~2 5mm C-FEG 10 9 ~5 5nm T-FEG 10 9 <1 20nm

24 Lensa Magnetik Lensa Condenser focusing determines the beam current which impinges on the sample. Lensa Objective final probe forming determines the final spot size of the electron beam, i.e., the resolution of a SEM.

25 Kenapa perlu Vakum? Bila SEM digunakan, kolum elektron-optik dan sampel chamber harus selalu pada kondisi vakum. 1. Bila kolum ada gas didalamnya maka elektron akan diskaterd oleh molekul gas yang menyebabkan intensitas dan stability beam akan berkurang 2. Molekul-molekul gas lain, yang datang dari sampel atau dari microskop itu sendiri, dapat membentuk persenyawaan dan kondens pada sampel. Ini akan membuatan kontras menjadi lebih rendah dan bayangan menjadi kabur.

26 Electron Detectors and Sample Stage Objective lens Sample stage

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33 Coating Techniques Sputter coater is used to coat insulating samples Au and Al good for SE yield AuPd alloy good for high resolution C used if X-ray microanalysis is required Coating should have low granularity in order not to mask the underlying structure (<20nm thick).

34 OIM-Grain Boundary Maps Grain Boundary Map Orientation Map A Grain boundary Map can be generated by comparing the orientation between each pair of neighboring points in an OIM scan. A line is drawn separating a pair of points if the difference in orientation between the points exceeds a given tolerance angle. An Orientation Map is generated by shading each point in the OIM scan according to some parameter reflecting the orientation at each point. Both of these maps are shown overlaid on the digital micrograph from the SEM.