Specific Process Knowledge/Lithography/EBL/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 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.
Contrary to most UV resist it is in general not advisable to use HMDS priming when coating with EBL resists. There can of course be exceptions to this but we do not recommend HMDS priming when using the DTU Nanolab supplied EBL resists.
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 |
|
IPA |
|
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 |
|
DIW |
|
|
Resist thickness as function of spin speed on Lab Spin 2/3 can be estimated from the parameters above as y = axb, 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 | ||
| 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
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.