Specific Process Knowledge/Lithography/UVLithography

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UV Lithography uses ultraviolet light to transfer a pattern from a mask to a wafer coated with photoresist. The photoresist film is spin coated on the wafers and the pattern is transferred to the wafer by using a mask aligner. DTU Nanolab houses a number of automatic or semi-automatic coaters and mask aligners.

Getting started

Before you plan your UV processing and request for training on any equipment in UV lithography, please go through the following steps. Include the information in the training request.

If you are new to photolithography, you can visit this wikipedia webpage about photolithography before you start.

• Prepare a process flow which describes all steps in your UV lithography process. You can find docx-templates in this table.

• Substrate pretreatment: In many processes it is recommended to pretreat or prime your wafer before spin-coating. In some spin-coaters, these pretreatment processes are included in the spin coating of resist.

• Spin Coater: Do you wish to use a manual spin coater or a robot spin coater? See a list of spin coaters here.

• Resist Type: Choose the type of resist you wish to use: a list of UV lithography resist types available at DTU Nanolab can be found on this page.
  • Positive tone resist: Resist exposed to UV light will be dissolved in the developer. The mask openings are an exact copy of the resist pattern which is to remain on the wafer.
  • Negative tone resist: Resist exposed to UV light will become polymerized and difficult to dissolve. The mask openings are an inverse copy of the resist pattern which is to remain on the wafer.

• Thickness of resist: In general, it is recommended to work at or below an aspect ratio of ~1, i.e. where the width of the pattern is larger than the thickness of the resist. Furthermore, when you decide for the resist thickness, consider which transfer you need:
  • For lift-off processes, we recommend resist thickness at least 5 times larger than the thickness of the metal to be lifted.
  • For dry etch or wet etch processes, investigate the resist etch rate of your process as this might limit the minimum thickness of your resist.

• Exposure: Choose which aligner you wish to use, and consider the exposure dose.
  • You can find a list of mask aligners here.
  • You can find information on dose here.

• Mask: Design and order a photomask for your UV process. A detailed instruction on how to design and order a photomask can be found here.

• Development: Choose which equipment you wish to use to develop your photoresist from this list. Remember the development process influences the exposure dose.

• Specify whether you wish to strip or lift-off your resist: strip and lift-off.

Resist Overview

Resist	Polarity	Spectral sensitivity	Manufacturer	Comments	Technical reports	Spin Coating	Exposure	Developer	Rinse	Remover	Process flows (in docx-format)
AZ 5214E	Positive but the image can be reversed	310 - 420 nm	Merck KGaA Supplied by MicroChemicals GmbH	Can be used for both positive and reverse processes with resist thickness between 1 and 4 µm.	AZ5214E.pdf‎ Photoresist AZ® 5214 E (TDS)	Spin Coater: Gamma UV, Spin Coater: Gamma e-beam & UV, A manual spin coater or Spin Coater: RCD8	KS Aligner, Aligner: MA6 - 2 or Aligner: 6inch	AZ 351B developer or AZ 726 MIF developer	DI water	Acetone	Process_Flow_AZ5214_pos.docx‎ Process_Flow_AZ5214_rev.docx‎
AZ 4562	Positive	310 - 440 nm	Merck KGaA Supplied by MicroChemicals GmbH	For process with resist thickness between 6 and 25 µm.	AZ4500.pdf‎ Photoresist AZ® 4562 (TDS)	Spin Coater: Gamma e-beam & UV, A manual spin coater or Spin Coater: RCD8	KS Aligner, Aligner: MA6 - 2 or Aligner: 6inch	AZ 351B developer or AZ 726 MIF developer	DI water	Acetone	Process_Flow_thick_AZ4562.docx‎
AZ MiR 701	Positive	310 - 445 nm	Merck KGaA Supplied by MicroChemicals GmbH	High selectivity for dry etch. Resist thickness 1.5 - 4 µm.	AZ_MiR_701.pdf‎ Photoresist AZ® MIR 701 (TDS)	Spin Coater: Gamma UV, Spin Coater: Gamma e-beam & UV, A manual spin coater or Spin Coater: RCD8	KS Aligner, Aligner: MA6 - 2 or Aligner: 6inch	AZ 726 MIF developer	DI water	Remover 1165	Process_Flow_AZ_MiR701.docx‎
AZ nLOF 2020	Negative	310 - 380 nm	Merck KGaA Supplied by MicroChemicals GmbH	Negative sidewalls for lift-off. Resist thickness 1.5 - 4 µm.	AZ_nLOF_2020.pdf‎	Spin Coater: Gamma UV; A manual spin coater or Spin Coater: RCD8	KS Aligner, Aligner: MA6 - 2 or Aligner: 6inch	AZ 726 MIF developer	DI water	Remover 1165	Process_Flow_AZ_nLOF_2020.docx‎
SU-8	Negative	350 - 400 nm	Kayaku Advanced Materials, Inc. Supplied by micro resist technology GmbH	High aspect ratio. Resist thickness 1 µm to several 100 µm.	SU-8_DataSheet_2005.pdf‎, SU-8_DataSheet_2075.pdf‎	Spin Coater: RCD8 or Spin Coater: Manual All Resists	Aligner: 6inch	mr-Dev 600 developer (PGMEA)	IPA	Plasma ashing can remove crosslinked SU-8	Process_Flow_SU8_70um.docx‎

Process information

From our suppliers

Application notes from Microchemicals GmbH, e.g. Lithography Trouble-Shooter