Specific Process Knowledge/Lithography/EBeamLithography/EBLsubstratePrep

Resist coating

An appropriate EBL resist must naturally be applied to the substrate. DTU Nanolab supplies a number of standard resists, please consult the table below. The default positive EBL resist is AR-P 6200.09 (CSAR). CSAR is installed on Spin Coater: Gamma E-beam and UV for spin coating of 2", 4" and 6" substrates. For other substrate sizes (i.e. chips) or other resists Spin Coater: LabSpin 02/03 have to be used instead. The standard resist bottles are stored in the chemical cupboard in E-4.

We recommend all groups or users to have their own bottle of e-beam resist inside the cleanroom. Please follow the user resist bottles in the cleanroom guide.

DTU Nanolab supplied standard EBL resists and process guides
Resist	Polarity	Manufacturer	Technical reports	Spin Coater	Polynomial	Thinner	Developer	Rinse	Remover	Process flows (in docx-format)
CSAR AR-P 6200	Positive	AllResist	AR-P 6200 info	Spin Coater: Gamma E-beam and UV or Spin Coater: LabSpin 02/03	a = 7252.2, b = -0.454	Anisole	AR-600-546 AR-600-548 N50 MIBK:IPA	IPA	AR-600-71 Remover 1165	CSAR CSAR with Al LOR5A with CSAR
Medusa AR-N 8200	Negative	AllResist	AR-N 8200 info	Spin Coater: LabSpin 02/03	a = ?, b = ?	AR 600-07	AR 300-47:DIW (1:1)	DIW	BOE
AR-N 7500	Negative	AllResist	AR-N 7500 info	Spin Coater: LabSpin 02/03	a = 17126, b = -0.435	PGMEA	AR 300-47:DIW (4:1) MIF726:DIW (8:5)	DIW	AR 300-73 O2 plasma

Resist thickness as function of spin speed on Lab Spin 2/3 can be estimated from the parameters above as y = ax^b, where y is resist thickness in nm and x is spin speed in RPM.

It is possible to obtain permission to user other resists at DTU Nanolab, users must however provide these resists and possibly developers themselves. A non-exhaustive list of user supplied EBL resist used at DTU Nanolab and some process guidelines can be found in the table below.

Non standard, user supplied EBL resists and process guides
Resist	Polarity	Manufacturer	Comments	Technical reports	Spin Coater	Thinner	Developer	Rinse	Remover	Process flows (in docx-format)
ZEP520A	Positive resist, contact Lithography if you plan to use this resist	ZEON	Positive resist	ZEP520A.pdf, ZEP520A spin curves on SSE Spinner	See table here	Anisole	ZED-N50/Hexyl Acetate,n-amyl acetate, oxylene. JJAP-51-06FC05‎, JVB001037	IPA	acetone/1165	Process Flow ZEP
Copolymer AR-P 617	Positive	AllResist	Approved, not tested yet. Used for trilayer (PE-free) resist-stack or double-layer lift-off resist stack. Please contact Lithography for information.	AR_P617	See table here	PGME	AR 600-55, MIBK:IPA		acetone/1165	Trilayer stack: Process Flow
mr EBL 6000.1	Negative	MicroResist	Standard negative resist	mrEBL6000 processing Guidelines‎	See table here	Anisole	mr DEV	IPA	mr REM	Process Flow‎
HSQ (XR-1541)	Negative	DOW Corning	Approved. Standard negative resist	HSQ Dow Corning, MSDS HSQ	See table here		TMAH, AZ400K:H2O	H2O		process flow HSQ High resolution patterning with HSQ
AR-N 7520	Negative	AllResist	Both e-beam, DUV and UV-sensitive resist. Currently being tested, contact Peixiong Shi for information.	AR-N7500-7520	See table here	PGMEA	AR 300-47, TMAH	H2O
PMMA	Positive	AllResist			See table here	Anisole	MIBK:IPA (1:3), IPA:H2O	IPA	acetone/1165/Pirahna
ZEP7000	Positive	ZEON	Not approved. Low dose to clear, can be used for trilayer (PEC-free) resist-stack. Please contact Lithography for information.	ZEP7000.pdf	See table here	Anisole	ZED-500/Hexyl Acetate,n-amyl acetate, oxylene.	IPA	acetone/1165	Trilayer stack: Process Flow‎

Discharge layer application

As exposure is done with an electron beam, insulating substrates will cause a build up of charge that will deflect the incoming beam and disturb pattern definition. It is therefore necesarry when working with insulating substrates or substrates with thick (> 200 nm) dielectric films to apply a discharge layer. This is typically applied on top of the EBL resist layer and must be removed in between exposure and development. The most common discharge layer is 20 nm thermally evaporated Al. Bear in mind that it should be thermally evaporated and not e-beam evaporated. Thermal evaporation of Al can be done in Thermal evaporator and Wordentec. The Al layer can be removed with MIF726 after exposure. MIF726 etch rate in Al is about 0.5 nm/s, although only about 1 nm/min in oxidized aluminium.

For samples with 2D materials such as graphene, HBN, etc., it is mandatory to apply a 20 nm Al layer on top of the resist in order to expose the substrate in the JEOL 9500 system. The Raith eLine system does not have this requirement.

Another possibility is to use a spin-on conductive layer such as AR-PC 5090. It can be removed with water after exposure. At the moment we do not have much experience with this, contact the EBL team if you are interested in this option.

Inspection

Example of rejected samples with visible bubbles in resist/Al coating and (a lot) of resist residue on the backside.

Post exposure pattern dimensions are dependent on resist thickness. Thus, it is advisable to verify resist thickness after spin coating. This can be done by ellipsometry in the VASE Ellipsometer.

As the cleanliness requirement of the JEOL is very high, substrates that does not visually appear to be in a good condition will be rejected by the JEOL 9500 cassette loading team. It is therefore a good idea to perform your own visual inspection. The loading team will inspect your samples for any types of flakes or bubbles in the surface layers of the sample. Samples with flakes or bubbles will be rejected.

Samples with resist residues on the backside will also be rejected. If you have resist residues on the backside of your wafer you should wipe it off with an appropriate solvent.

Example of rejected samples with visible bubbles in resist/Al coating and (a lot) of resist residue on the backside.. Photo: Thomas Pedersen.