Introduction DualBeam Application Training Presentation: DB basic functions and cross-sections Essential DualBeam Functionality & Cross Sections Hand on/demo/training: DB concepts: working distance, eucentric height and co-incident point; Making cross-sections: normal cross-section, corner-cross section; cross-section for XEDS, cross-section before Slice and View; Imaging the cross-section: SEM cross-section image and Ion beam cross-section image; Curtains: how to minimise the curtains; SPI mode: SPI and manual SEM Snapshot during patterning; Slice and Views. Chengge Jiao 2 Introduction FEI Confidential Copyright © 2006 DualBeam Concept: DualBeam point DualBeam Concepts • Eucentric Height • Co-incident point 3 FEI Confidential Copyright © 2006 4 FEI Confidential Copyright © 2006 1 DualBeam Concept: Co-incident point Stage Positioning, Working Distance (WD) Eucentric height: The reference height of the microscope i W D Ion Be am Electron Beam WD on tati Ro Sample im ec Sp Y X en ge Sta Z Tilt STEM detector FEI Confidential Copyright © 2006 5 6 DualBeam Concept: Eucentric Height FEI Confidential Copyright © 2006 Cross-Section Overview: FIB/DB SEM The eucentric height is a stage Zheight, which means that the height of the specimen at which its image does not moved laterally (side movement of the imaging) as a function of stage tilting. FIB All aligned: • Gas injectors • SEM coincident • Tilt axis • Beams pre-focused • Optical microscope • Charge neutralizer 7 High Beam currents for milling Staircase pattern is used in making a FIB cross section for bulk remove of material FEI Confidential Copyright © 2006 8 Low beam currents for imaging. Stage tilted 45 degree to allow view the face FEI Confidential Copyright © 2006 2 Cross-Section Overview Well known Cross-section Procedures The Feature Bulk Mill • Removes material in front of feature for viewing 3. Cleaning Cross-section 2. Box pattern or cleaning xs <0.5 m 1-2 m Intermediate Mill • make face more perpendicular Cleaning Mill • Finely removes material to reveal feature 7-15 m 1. Regular Cross-section Low kV cleaning before Ebeam in-situ decoration Imaging 10-20 m Making a cross-section FEI Confidential Copyright © 2006 9 10 Why IBID before CS: General purposes Planarize with FIB Deposition Evens out the surface topography Deposit Platinum bar • x = 1-2 8m wider than crosssection • y = ~2 microns • z = height of step of 1 8m • I = x * y * 6 pA / 8m* 8m • application file: pt E-beam Pt deposition for planarization to protect surface features, curtains, and TEM. 11 FEI Confidential Copyright © 2006 FEI Confidential Copyright © 2006 The Ion beam deposited metal serves a few purposes for DualBeam sample preparations 1. To locate the area of interested; 2. To prevent the outer surface of the sample from being damaged during subsequent ion milling operations; 3. To minimize the cross-section surface curtaining. Always put IBID before making a cross-section 12 FEI Confidential Copyright © 2006 3 Bulk Mill Intermediate Mill Draw cross-section pattern • Align top edge ~ 1-2 7m from front of feature • For X: Allow 3-4 microns on each side • For Y: 1 - 2 times the depth • For Z: The desired depth of the deepest part Set beam current upto 20 nA FEI Confidential Copyright © 2006 13 Select 1/4 - 1/2 the beam current Remove previous pattern Draw box pattern or cleaning cross section pattern • Set X to be about 1 7m smaller than previous mill • Set Z to about 1/4 to 1/2 of desired depth 14 FEI Confidential Copyright © 2006 Cross-section geometry: FIB and DB Final Polish Select 150 - 1000 pA Draw Cleaning Cross-Section • Adjust leading edge to go through feature • Adjust trailing edge just beyond previous mill • Set X to be about 1 8m smaller than previous mill • Set Z to about 1/4 to 1/2 of desired depth Start milling Grab frames periodically to check progress Single Ion Beam 15 FEI Confidential Copyright © 2006 16 DB FEI Confidential Copyright © 2006 4 Imaging cross-section by FIB Corner cross-section Corner cross-section: 2D/3D images • • • • Set aperture to 1-10 pA Tilt stage to 0°; rotate 180° Critical focus/stigmate Use beam shift and, mag. to frame picture perfectly • Use a slow single scan ~40s to generate a nice photo FEI Confidential Copyright © 2006 17 18 Corner Cross-section Procedure FEI Confidential Copyright © 2006 Preparing cross-sections for EDS analysis Procedure Want a clear x-ray signal that is only derived from the cross-section face The back of a typical cross-section will reflect rays These rays obscure the real signal • Make cross-section pattern bigger than face to expose, and use two cross-section patterns in parallel mode; • Use large beam current to reduce the milling time; • Using two boxes patterns in parallel mode; • Use ion beam in low current to scan the cross-section face for final cleaning. 19 FEI Confidential Copyright © 2006 20 FEI Confidential Copyright © 2006 5 Preparing cross-sections for EDS analysis Q3D EDS below the sample surface: Geometry Extra materials need to remove by FIB to have shadow free to CEDS detector So make a big box, also deeper than before X-ray signal just from cross-section Typical size would be 20 7m by 20 7m by 20 7m Use largest beam current available for bulk mill FIB XEDS detector To limit the interaction volume, remove material behind cross-section first. Thin the back side like for TEM samples, then fill with Pt as a beam dump. Pt not used in IC process and does not have any overlap peaks. SEM Galvanized Steel 21 FEI Confidential Copyright © 2006 Q3D EDS analysis below the sample surface 22 FEI Confidential Copyright © 2006 Cross-section for EBSD in a SDB: Summary a) a cross-section image of the Zn-coating on steel acquired by Q3D SSBSE detector, b) a XEDS map mixed with Mg-Al-Zn elements of the cross-section Galvanized Steel 23 FEI Confidential Copyright © 2006 24 FEI Confidential Copyright © 2006 6 Curtains: Causes and Solutions Minimizing curtaining from the beginning Causes • Surface topography - top-level metal lines • Below the surface inside the materials: Sputter rate differences – i.e., Tungsten. The Feature Solutions • Planarize with FIB deposition • Reduce beam current • Change OL and Dwell • Large tilt angle, for example: up to 8 degrees, depending materials. • Angled cut. • For large patterns, using box for cleaning instead of CSCLs. FEI Confidential Copyright © 2006 25 7-15 m 10-20 m FEI Confidential Copyright © 2006 26 Angled Cut: To change the curtain directions Angled Cut to change curtain direction Reduces cumulative effects of stacked tungsten plugs. Voids and edges transfer to lower levels • • • • • • • 1. Bulk mill as usual (an extra 3 7m wider) 2. Save stage location at 52° and 0°, respectively 3. Stage rotate 90° (at 52° tilted) 4. Tilt stage to 15° to 25° away from 52° 5. Scan rotate -90° 6. Save position -“angled” 7. Polish as usual 1. Regular Cross-section Tilt Axis 1. 4. 4. 7. 15° to 25° degree away from 52° 27 FEI Confidential Copyright © 2006 28 FEI Confidential Copyright © 2006 7 Angled Cut: To change the curtain directions Cross-section: No Gas/Gas as Preferential Etch No Gas • Can give nice results for SEM without changing features too much. • Reduces SEM charging and enhances edges. • Enhances by • implanting some Ga, making surface more conductive. The modification of nitride layer is often seen within cross section. Before modification, the nitride is insulating and appear dark in images, while afterwards it appears bright indicating that ti is at least slight conductive. • some preferential milling. Gas • Can use to enhance for FIB or SEM. • Increases the number of edges; major contrast mechanism, SE. • Gas “prefers” some material and it is removed more. SEM cross-section images of sample V 29 FEI Confidential Copyright © 2006 Iodine as Preferential Etch 30 FEI Confidential Copyright © 2006 Example: Cross-section of car paint Iodine (I2) = Enhanced Etch = EE • Metal selective • Enhances barriers • Cleans redeposition, if any • Metal selective etch ~5-10:1 • Mills Al about 15x than sputtering • Mills Oxides about 1-3x than sputtering 31 FEI Confidential Copyright © 2006 32 FEI Confidential Copyright © 2006 8 XeF2 and Delineation Etch as Preferential Etch Electron beam in-situ etching with XeF2 XeF2 : Insulator Enhanced Etch (IEE) • • • • Oxide, insulator selective Spontaneously etches poly-Si and silicon Oxide selective etch ~5:1 Mills thermal oxide, TEOS ~ 8x than sputtering Delineation • Oxide selective • No Spontaneous etching of silicon • Mills oxides at different rates GaAs transistors with and without Ebeam XeF2 in-situ etching Ebeam 2 kV, spot 5, selected area imaging with XeF2 gas valve open 33 FEI Confidential Copyright © 2006 Preferential Etch Example 34 FEI Confidential Copyright © 2006 Preferential Etch Procedure Gas Procedure • 1. Tilt cross-section face at eucentric height • 2. Insert gas needle • 3. Image at 10-50 pA, fast scan, med. resolution • 4. Open valve • For IEE, a few seconds ok • For EE, 10-30 seconds may be needed using medium scan, medium resolution • For Delineation Etch, use milling pattern for 2-5 minutes • 5. Close valve No Gas procedure • 1. Tilt cross-section face to ion beam • 2. Set beam current to 5 - 10 pA • 3. Take two 10 second photo scans SEM Image of DRAM after XeF2 Preferential Etch 35 FEI Confidential Copyright © 2006 36 FEI Confidential Copyright © 2006 9 Grounding a Floating Line SPI, iSPI and Slice and View • SPI: Simultaneous Patterning and Imaging mode: Direct TV rate real time SEM imaging of FIB milling and deposition. There are contribution of ISEs. A few holes milled on the back of the cross-section used ion beam in spot mode. A very thin layer of Pt is deposited around the hole and the cross-section before the last step of cleaning. This can minimise the surface and cross-section charging. 37 FEI Confidential Copyright © 2006 Electron is doing raster imaging and ion beam is doing patterning live image update, pure image quality, no UHR) 38 SPI, iSPI and Slice and View • SPI: Simultaneous Patterning and Imaging mode: Direct TV rate real time SEM imaging of FIB milling and deposition. There are contribution of ISEs. • iSPI: Intermittent Switching Patterning and Imaging mode: FEI Confidential Copyright © 2006 SPI, iSPI and Slice and View iSPI: Intermittent Switching Patterning and Imaging mode: Highest resolution, unattended and automated SEM imaging of FIB patterning. There no contribution of ISEs. Highest resolution, unattended and automated SEM imaging of FIB patterning. There no contribution of ISEs. • SV: Slice and View: Highest resolution, unattended and automated SEM imaging of FIB slices for 2D and 3D reconstruction. No contribution of SE’s from the FIB. 39 FEI Confidential Copyright © 2006 Automated snaphots=slow, good image quality, HR & UHR 40 FEI Confidential Copyright © 2006 10 SPI Mode operation iSPI mode = clean image • • • • • • - A superposition of SE’s from FIB milling + SEM imaging - To Image in SPI Mode: • iSEM >> iFIB • Use fast SEM acquisition scanning • Use SEM frame averaging - Alternatively: use BSE SEM imaging - An inherently “low resolution” method - OK for end-pointing – fast High resolution: Snapshot SEM imaging while Patterning. 41 FEI Confidential Copyright © 2006 Fast way to make a cross-section: Multiscan CS Snapshots in time intervals (fastest 0.5 sec) According actual UI imaging settings HR and UHR After complete pattern cycles Or after defined CCS lines Optionally to pause the patterning • Compatible with the RTM 42 FEI Confidential Copyright © 2006 Patterning – Multipass cleaning cross section The Multiscan CS is about 3x faster than stair step pattern The fast way to do the rough milling is to apply two or three cleaning cross-section patterns over the patterning area. This is call Multiscan cross-section. Each line milled contains the number of passes needed to reach a fraction of the specified depth where this fraction is equal to the depth to the depth divided by the number of multi passes. Ion Beam current: 1 nA Pattern time: 120 seconds each Two parameters are used in the UI: (a) Scan passes: number of passes (b) scan ratio: enables a dose ramp (i.e. low at start and high at final face). 43 FEI Confidential Copyright © 2006 44 FEI Confidential Copyright © 2006 11 Patterning – Multipass cleaning cross section 45 FEI Confidential Copyright © 2006 Using Pre-tilted holder for side milling Using pre-tilted Stage for 0º to 90° view FEI Confidential Copyright © 2006 46 AutoSlice and View G2: Red Blood Cells Input parameters: > Ion beam milling and deposition parameters. > Total number and dimension of slices. > Electron beam scan parameters. >Imaging match for milling (G2 version) The total milling volume is about: 24 um x 23 um x10 um = 5520 um3 47 FEI Confidential Copyright © 2006 48 FEI Confidential Copyright © 2006 12 AutoSlice and View G2: Red Blood Cells AutoSlice and View G2: Red Blood Cells ASV G2 Automatically run about 16 hours • • SEM image Horizontal field Width (HFW): 9.95 um • Image( ResolutionX),(ResolutionY): 2048 Pixel x 1768 Pixel • PixelWidth and PixelHeight: X-Pixels = Y-Pixels: 6.07nm/Pixel (with out tilt correction) • Setup for 220 slices – 100 nm thick per slice • Ebeam at 5 keV and SSBSE detector with the Zcontrast. 49 FEI Confidential Copyright © 2006 50 FEI Confidential Copyright © 2006 AutoSlice and View G2: Red Blood Cells The END Thanks 51 FEI Confidential Copyright © 2006 52 FEI Confidential Copyright © 2006 13
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