Specific Process Knowledge/Characterization/SEM: Scanning Electron Microscopy

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The Leo SEM

Scanning electron microscopy at Danchip

At Danchip there a four SEMs (scanning electron microscopes) that all cover a wide range of needs both in the cleanroom and outside: From the fast in-process verification of different process parameters such as etch rates, step coverages or lift-off quality to the ultra high resolution images on any type of sample intended for publication.

All four SEMs all manufactured by Carl Zeiss and have the same graphical user interface and very identical electron optics.

Three SEMs are located in the cleanroom (SEM Supra 2, SEM Supra 3 and SEM LEO), and one SEM is located in the basement (SEM Supra 1).

At the turn of the year 2015-2016 we made a reorganisation of the SEM's at Danchip. The old workhorse SEM's (the LEO and Supra 1) that have excellently served the users of the cleanroom for many years will be given new roles:

• The Leo SEM is 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 no longer allowed.
• The SEM Supra 1 (formerly known as SEM Zeiss) has been relocated to the basement with 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 other SEM's.

The two remaining SEM's at Danchip (called SEM Supra 2 and SEM Supra 3) serve as general imaging tools in the cleanroom. Like 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 user manuals, quality control procedures and results, user APVs, technical information and contact information can be found in LabManager:
SEM's at DTU Danchip:

• The SEM Leo page in LabManager,
• The SEM Supra 1 page in LabManager,
• The SEM Supra 2 page in LabManager,
• The SEM Supra 3 page in LabManager,

SEM's at DTU-Cen:

• The Dual beam FEI Helios Nanolab 600 page in LabManager,
• The SEM FEI Nova NanoSEM 600 page in LabManager,

Common challenges in scanning electron microscopy

• Sample mounting
• Image optimisation
• Problems related to sample charging

Equipment performance and process related parameters

Equipment		SEM Leo	SEM Supra 1	SEM Supra 2	SEM Supra 3
Purpose	Imaging and measurement of	Any (semi)conducting sample that may have thin (> ~ 5 µm) layers of non-conducting materials on top	Any sample except bulk insulators such as polymers, glass or quartz wafers	Any sample except bulk insulators such as polymers, glass or quartz wafers	Samples from the 'real' world outside the lab
Instrument Position		Cleanroom of DTU Danchip	Basement of DTU Danchip	Cleanroom of DTU Danchip	Cleanroom 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 nanometers (limited by vibrations)	1-2 nm (limited by vibrations)	1-2 nm (limited by vibrations)	20 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) (out of order) Variable pressure secondary electron (VPSE)	Secondary electron (Se2) Inlens secondary electron (Inlens) 4 Quadrant Backscatter electron (QBSD) Variable pressure secondary electron (VPSE)	Secondary electron (SEI) Backscatter electron (BEI)
	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: XXX mm	X, Y: 73 × 40 mm T: -10 to 90o R: 360o Z: 38 mm
	Electron source	FEG (Field Emission Gun) source	FEG (Field Emission Gun) source	FEG (Field Emission Gun) source	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
	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
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 4" wafer
	Allowed materials	Any standard cleanroom material except graphene or CNT samples	Any standard cleanroom material except graphene or CNT samples	Any standard cleanroom material except graphene or CNT samples	Any standard cleanroom material including graphene or CNT samples Biological samples