Specific Process Knowledge/Lithography/Resist/UVresist

UV resist comparison table

Comparison of specifications and feature space of the standard UV photoresists available at DTU Nanolab.

Resist	AZ 5214E	AZ MiR 701	AZ nLOF 2020	AZ 4562	SU-8	TI Spray
Resist tone	Positive Negative (image reversal)	Positive	Negative	Positive	Negative	Positive Negative (image reversal)
Thickness range	1.5 - 4.2 µm	1.5 - 4 µm	1.5 - 4 µm	5 - 10 µm	1 - 200 µm	0.5 - 5 µm
Coating tool	Automatic spin coaters: Spin coater: Gamma UV lithography Spin coater: Gamma E-beam & UV Manual spin coaters: Spin coater: Labspin 02 Spin coater: Labspin 03 Spin coater: RCD8 Spray coater	Automatic spin coaters: Spin coater: Gamma UV lithography Spin coater: Gamma E-beam & UV Manual spin coaters: Spin coater: Labspin 02 Spin coater: Labspin 03 Spin coater: RCD8 Spray coater	Automatic spin coaters: Spin coater: Gamma UV lithography Manual spin coaters: Spin coater: Labspin 02 Spin coater: Labspin 03 Spin coater: RCD8 Spray coater	Automatic spin coaters: Spin coater: Gamma E-beam & UV Manual spin coaters: Spin coater: Labspin 02 Spin coater: Labspin 03 Spin coater: RCD8	Manual spin coaters: Spin coater: Labspin 02 Spin coater: Labspin 03 Spin coater: RCD8	Spray coater
Spectral sensitivity	310 - 420 nm	310 - 445 nm	310 - 380 nm	310 - 445 nm	300 - 375 nm	310 - 440 nm
Exposure tool	Maskless aligners Mask aligners	Maskless aligners Mask aligners	Maskless aligners Mask aligners	Maskless aligners Mask aligners	Maskless aligners Mask aligners	Maskless aligners Mask aligners
Developer	AZ 726 MIF (2.38% TMAH) AZ 351 B (NaOH)	AZ 726 MIF (2.38% TMAH) AZ 351 B (NaOH)	AZ 726 MIF (2.38% TMAH) Solvent development possible	AZ 726 MIF (2.38% TMAH)	mr-DEV 600 (PGMEA)	AZ 726 MIF (2.38% TMAH)
Development rinse agent	DIW	DIW	DIW	DIW	IPA	DIW
Remover	Acetone Remover 1165 (NMP)	Acetone Remover 1165 (NMP)	Acetone Remover 1165 (NMP)	Remover 1165 (NMP)	Cross-linked SU-8 is practically insoluble Oxygen plasma ashing can remove cross-linked SU-8	Acetone Remover 1165 (NMP)
Comments	Good adhesion for wet etch	High selectivity for dry etch	Negative sidewalls for lift-off	For processes with resist thickness between 6 µm and 25 µm	High aspect ratio Resist thickness 1 µm to hundreds of µm Available in cleanroom: 2005, 2035, and 2075. Considering discontinuation of the SU-8 2000 series we need to move to another product SU8 3000 and SU8 XTF series. New formulation will be available in cleanroom and tested: 3005 instead of 2005, 3035 instead of 2035, XTF75 instead of 2075 and new 3025.	TI spray resist is an image reversal resist, similar to AZ 5214E. The process flow will be similar to the process flows for 5214, except for the coating step. The exposure dose and development will depend on the specific process.

Process flow examples

Comparison of specifications and feature space of the standard UV photoresists available at DTU Nanolab. These are just examples and may contain obsolete information regarding exposure dose, etc.

Resist	AZ 5214E	AZ MIR 701	AZ nLOF 2020	AZ 4562	SU-8	Ti Spray
Maskless aligner	Process flow AZ 5214E positive‎ MLA Process flow AZ 5214E image reversal MLA	Process flow AZ MiR 701‎ MLA	Process flow AZ nLOF 2020‎ MLA‎	Process flow AZ 4562 MLA	Process flow SU-8 MLA‎ NB! Most of the process knowledge about SU-8 is based in research groups
Mask aligner	Process flow AZ 5214E positive‎ MA6 Process flow AZ 5214E image reversal MA6	Process flow AZ MiR 701‎ MA6	Process flow AZ nLOF 2020‎ MA6‎	Process flow AZ 4562 MA6‎	Process flow SU-8 MA6‎ NB! Most of the process knowledge about SU-8 is based in research groups

Other process flows: Chip on carrier: A procedure for UV lithography on a chip using automatic coater and developer.

Exposure dose

Spectral sensitivity of AZ resists represented as optical absorption coefficient.

During exposure of the resist, the photoinitiator, or photo-active component, reacts with the exposure light, and starts the reaction which makes the resist develop in the developer.

In a positive resist, it makes the resist become soluble in the developer. In a negative resist, usually assisted by thermal energy in the post-exposure bake (PEB), it makes the resist insoluble in the developer. The amount of light required to fully develop the resist in the development process, is the exposure dose.

The optimal exposure dose is a function of many parameters, including the type of resist, the resist thickness, and the sensitivity of the resist.

Resist sensitivity
The resist sensitivity is a measure of how efficiently it reacts to the exposure light. Spectral sensitivity is the sensitivity of the resist as a function of wavelength. It is usually given simply as the range from the wavelength below which absorption in the resist material makes lithography impractical to the wavelength at which the photoinitiator is no longer efficiently activated.

Within the sensitivity range, the optical absorption is commonly used as a measure of sensitivity. A high absorption coefficient signifies a high sensitivity, as the light is absorbed by the photoinitiator. Because of spectral sensitivity, the optimal dose of a given resist type and thickness is also a function of the spectral distribution of the exposure light, i.e. the equipment used for the exposure. Using a combination of experience, calculation and assumptions, it may be possible to estimate the dose for an exposure equipment, if the exposure dose is already known on another equipment.

Due to reflection and refraction at the interface between the resist and the substrate, the optimal dose may also be a function of the type of substrate used. Unless otherwise stated, the exposure doses given below are for standard silicon wafers.

Apart from the already mentioned factors, the optimal dose also depends on the developer chemistry and the parameters used in the development process. Finally, the requirements to the lithographic process in terms of resolution, bias (line broadening), etch selectivity, side wall angle, etc. may narrow down, or widen, the process window. The exposure doses given in the sections below should be used as a starting point for individual fabrication process development.

Due to the process of bleaching, where the absorption of the resist changes during exposure, the exposure dose is unfortunately not always constant at different intensities of the exposure light. The exposure time is thus not always a linear function of the exposure intensity.

Calculate exposure time

In the maskless aligners, the dose is set directly as a process parameter in the job. In mask aligners, on the other hand, the parameter that is set is the exposure time, i.e. how long the shutter is open during the exposure.

The exposure dose, D [J/m²], in terms if exposure light intensity I [W/m²] and exposure time t [s], is given by:

$D=I\cdot t$

Since the intensity is specific to the spectral sensitivity of the sensor used to measure the exposure light, and the exposure time is specific to the spectral distribution of the exposure light (cf. spectral sensitivity), this dose is specific to the combination of exposure source and optical sensor.

Given an exposure dose, the exposure time, t, is calculated as:

$t=D\cdot I^{-1}$

It is important to keep in mind that this exposure time is valid only for a specific combination of exposure source and optical sensor, as well as for a specific development process.

Exposure dose for mask aligners

Information about the exposure dose for mask aligners can be found here.

Exposure dose for maskless aligners

Information about the exposure dose for maskless aligners can be found here.

Exposure dose when using AZ 351B developer (NaOH)

Information about the exposure dose when using AZ 351B developer can be found here.