Specific Process Knowledge/Characterization/SEM: Scanning Electron Microscopy

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Scanning electron microscopy in the cleanroom at DTU Nanolab

The number of electron microscopes at DTU Nanolab is large. The five SEMs in building 346 cover a wide range of needs both in the cleanroom and outside: From fast in-process verification of different process parameters such as etch rates, step coverages or lift-off quality to ultra high resolution images on any type of sample intended for publication.

• The SEM Supra 1 is located in the basement outside the cleanroom. It is serving two purposes: Serving the users that have samples from outside the cleanroom and serving as training tool; all new SEM users with no/little SEM experience must be trained on this tool and gain basic knowledge (typically 10 hours of usage) here before being qualified for training on the SEMs in the cleanroom.

• The SEM 2 and 3 are located in the cleanroom where they serve as general imaging tools for samples that have been fabricated in the cleanroom. Like SEM Supra 1, they are VP models from Carl Zeiss and will produce excellent images on any sample. The possibility of operating at higher chamber pressures in the VP mode makes imaging of bulk non-conducting samples possible. The SEM Supra 2 is also equipped with an airlock and an EDX detector.

• The SEM Leo s a very reliable and rugged instrument that provides high quality images of most samples. It is exclusively dedicated to the users of the Raith E-beam lithography system so general imaging of user samples is not allowed.

• The SEM Tabletop 1 is a tabletop SEM that is located in the basement outside the cleanroom. It has a limited resolution, but it is fast and easy to use, also for non-conducting samples. Training in the others SEMs is not required to use this SEM.

SEM Supra 1, 2 and 3 SEM Leo s all manufactured by Carl Zeiss and have the same graphical user interface and very identical electron optics. But there are there are small hardware and software differences, thus a training is needed for each SEM you want to use.

The SEM Tabletop 1 is manufactured by Hitachi.

Common challenges in scanning electron microscopy

• Sample mounting

Comparison of SEM's in building 346

Equipment		SEM LEO	SEM Supra 1	SEM Supra 2	SEM Supra 3	SEM Tabletop 1
Purpose	Imaging and measurement of	Conducting samples Semi-conducting samples Thin (~ 5 µm <) layers of non-conducting materials such as polymers	Conducting samples Semi-conducting samples Thin (~ 5 µm <) layers of non-conducting materials such as polymers Thick polymers, glass or quartz samples	Conducting samples Semi-conducting samples Thin (~ 5 µm <) layers of non-conducting materials such as polymers Thick polymers, glass or quartz samples	Conducting samples Semi-conducting samples Thin (~ 5 µm <) layers of non-conducting materials such as polymers Thick polymers, glass or quartz samples	Conducting samples Semi-conducting samples Thin (~ 5 µm <) layers of non-conducting materials such as polymers Thick polymers, glass or quartz samples
	Other purpose	E-beam lithography using Raith Elphy Quantum system		Surface material analysis using EDX
Instrument Position		Cleanroom of DTU Danchip	Basement of DTU Danchip	Cleanroom of DTU Danchip	Cleanroom of DTU Danchip	Basement of DTU Danchip
Performance	Resolution	The resolution of a SEM is strongly dependent on the type of sample and the skills of the operator. The highest resolution is probably only achieved on special samples
		~ 5 nm (limited by vibrations)	1-2 nm (limited by vibrations)	1-2 nm (limited by vibrations)	1-2 nm (limited by vibrations)	~25 nm (limited by instrument)
Instrument specifics	Detectors	Secondary electron (Se2) Inlens secondary electron (Inlens) Backscatter electron (BSD)	Secondary electron (Se2) Inlens secondary electron (Inlens) 4 Quadrant Backscatter electron (QBSD) Variable pressure secondary electron (VPSE)	Secondary electron (Se2) Inlens secondary electron (Inlens) 4 Quadrant Backscatter electron (QBSD) Variable pressure secondary electron (VPSE)	Secondary electron (Se2) Inlens secondary electron (Inlens) High Definition four quadrant Angular Selective Backscattered electron detector (HDAsB) Variable pressure secondary electron (VPSE)	Secondary electron (SE) Backscatter electron (BSE)
	Stage	X, Y: 125 × 100 mm T: 0 to 90o R: 360o Z: 48 mm	X, Y: 130 × 130 mm T: -4 to 70o R: 360o Z: 50 mm	X, Y: 150 × 150 mm T: -10 to 70o R: 360o Z: 50 mm	X, Y: 130 × 130 mm T: -4 to 70o R: 360o Z: 50 mm	X, Y: 35 mm T: No tilt R: No rotation Z: 0 mm
	Electron source	FEG (Field Emission Gun) source				Thermionic tungsten filament
	Operating pressures	Fixed at High vacuum (2 × 10-5mbar - 10-6mbar)	Fixed at High vacuum (2 × 10-4mbar - 10-6mbar) Variable at Low vacuum (0.1 mbar-2 mbar)	Fixed at High vacuum (2 × 10-4mbar - 10-6mbar) Variable at Low vacuum (0.1 mbar-2 mbar)	Fixed at High vacuum (2 × 10-4mbar - 10-6mbar) Variable at Low vacuum (0.1 mbar-2 mbar)	Conductor vacuum mode: 5 Pa Standard vacuum mode: 30 Pa Charge-up reduction vacuum mode: 50 Pa
	Options	Raith Elphy Quantum E-Beam Litography system	All software options available	Antivibration platform Fjeld M-200 airlock taking up to 8" wafers Oxford Instruments X-MaxN 50 mm2 SDD EDX detector and AZtec software package	High Definition four quadrant Angular Selective Backscattered electron detector (HDAsB)
Substrates	Sample sizes	Wafers up to 6" (only full view up to 4")	Up to 6" wafer with full view	Up to 8" wafer with 6" view	Up to 6" wafer with full view	Up to 70 mm with full wiew
	Allowed materials	Any standard cleanroom materials	Any standard cleanroom material and samples from the Laser Micromachining tool and the Polymer Injection Molding tool	Any standard cleanroom materials	Any standard cleanroom materials	Any standard cleanroom material and samples from the Laser Micromachining tool and the Polymer Injection Molding tool Some biological samples (ask for permission)

Comparison of the SEMs at DTU Nanolab - building 307/314

Equipment	SEM FEI Nova 600 NanoSEM	SEM FEI QFEG 200 Cryo ESEM	Dual Beam FEI Helios Nanolab 600
Purpose	Conductive samples in High Vac Charge reduction in Low Vac X Ray Analysis with EDS Crystallographic analysis using EBSD and both On and Off axis TKD	Conductive samples in High Vac Charge reduction in Low Vac Environmental control using Peltier stage Cryogenic sample fixing/stabilization using cryo stage X Ray Analysis with EDS	Conductive samples in High Vac Micro and Nano milling/fabrication using various gases and FIB X Ray Analysis with EDS Crystallographic analysis using EBSD and Off Axis TKD
Equipment position	CEN Building 314	CEN Building 314	CEN Building 314
Resolution	The resolution of a SEM is strongly dependent on sample type and the operator. Resolution quoted is using sputtered gold on carbon
	B	High vacuum • 0.8 nm at 30 kV (STEM) • 1.0 nm at 30 kV (SE) • 2.5 nm at 30 kV (BSE) - 3.0 nm at 1 kV (SE) High vacuum with beam deceleration option • 3.0 nm at 1 kV (BD mode + BSE) Low vacuum - 1.4 nm at 30 kV (SE) •2.5 nm at 30 kV (BSE) •3.0 nm at 3 kV (SE) Extended vacuum mode (ESEM) •1.4 nm at 30 kV (SE)	Electron Column •0.8nm @15kV •0.9nm @1kV Ion Column •4.5nm @ 30kV
Detectors	ETD/TLD Secondary Electrons BSED Back Scatter Electrons LVD/LFD Low Vac SE Helix Low Vac SE EDS X Ray by energy EBSD Electron Back Scatter Diffraction TKD Transmission Kikuchi Diffraction STEM Scanning Transmission Electron Microscopy GAD Low Vac BSED	ETD Secondary Electrons BSED Back Scatter Electrons LVD/LFD Low Vac SE GSED ESEM SE EDS X Ray by energy STEM Scanning Transmission Electron Microscopy	ETD/TLD Secondary Electrons ABS Annular BSED EDS X Ray by energy EBSD Electron Back Scatter Diffraction CDEM Continuos Dinode Electron Multiplier
Stage specifications	X 150mm Piezo Y 150mm Piezo Z 10mm R 360⁰ Piezo T 70⁰	X 50mm Y 50mm Z 50mm R 360⁰ T 70⁰ Manual	X 150mm Piezo Y 150mm Piezo Z 10mm R 360⁰ Piezo T 70⁰
Options	B	C	E
Max sample size	Consult with DTU Nanolab staff as weight, dimensions, pumping capacity and technique all play a roll in the sample size