Specific Process Knowledge/Lithography/Resist

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UV Resist

Specific Process Knowledge/Lithography/DUVStepperLithography#Process_information_2

UV resist comparison table

Comparison of specifications and feature space of UV photoresists.

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 coaters: Spin coater: Gamma UV lithography Spin coater: Gamma ebeam & UV Manual coaters: Spin coater: Labspin 2 Spin coater: Labspin 3 Spin coater: RCD8 Spray coater	Automatic coaters: Spin coater: Gamma UV lithography Spin coater: Gamma ebeam & UV Manual coaters: Spin coater: Labspin 2 Spin coater: Labspin 3 Spin coater: RCD8 Spray coater	Automatic coaters: Spin coater: Gamma UV lithography Manual coaters: Spin coater: Labspin 2 Spin coater: Labspin 3 Spin coater: RCD8 Spray coater	Automatic coaters: Spin coater: Gamma ebeam & UV Manual coaters: Spin coater: Labspin 2 Spin coater: Labspin 3 Spin coater: RCD8	Manual coaters: Spin coater: RCD8 or Spin coater: Labspin 2 Spin coater: Labspin 3	Spray coater
Spectral sensitivity	310 - 420 nm	310 - 445 nm	310 - 380 nm	310 - 445 nm	300 - 375 nm	310 - 440 nm
Exposure tool	Mask aligner or Maskless aligner
Developer	AZ 351B AZ 726 MIF	AZ 351B AZ 726 MIF	AZ 726 MIF	AZ 726 MIF	mr-DEV 600 (PGMEA)	AZ 726 MIF
Rinse	DIW	DIW	DIW	DIW	IPA	DIW
Remover	Acetone Remover 1165	Acetone Remover 1165	Acetone Remover 1165	Remover 1165	Cured SU-8 is practically insoluble Plasma ashing can remove crosslinked SU-8	Acetone Remover 1165
Comments	Can be used for both positive and image reversed (negative) processes with resist thickness between 1 and 4 µm. 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 several 100 µm Available in cleanroom: 2005, 2035, and 2075	Spray coater specific resist
Process flow examples	Mask aligner: Process flow AZ 5214E positive‎ MA6 Process flow AZ 5214E image reversal MA6 Maskless aligner: Process flow AZ 5214E positive‎ MLA Process flow AZ 5214E image reversal MLA	Mask aligner: Process flow AZ MiR 701‎ MA6 Maskless aligner: Process flow AZ MiR 701‎ MLA	Mask aligner: Process flow AZ nLOF 2020‎ MA6‎ Maskless aligner: Process flow AZ nLOF 2020‎ MLA‎	Mask aligner: Process flow AZ 4562 MA6‎ Maskless aligner: Process flow AZ 4562 MLA	Mask aligner: Process flow SU-8 MA6‎ Maskless aligner: Process flow SU-8 MLA‎ NB! Most of the process knowledge on SU-8 is based in research groups	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.

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

The exposure doses listed below are for generic good exposure results, and can be a compromise between getting good lines, as well as good dots, in both clear field and dark field exposures. The optimal dose for any given specific project, could be different from the listed values.

All doses are for standard silicon wafers, unless otherwise stated. Development is done using 2.38% TMAH (AZ 726 MIF).

Aligner: MA6-1

The Aligner: MA6-1 has an i-line notch filter installed. This results in an exposure light peak around 365 nm with a FWHM of 7 nm.

	Date	Thickness	Dose	Development	Comments
AZ 5214E Data from discontinued German version	Long ago	1.5 µm	72 mJ/cm2	Single puddle, 60 s	Positive process
	Long ago	2.2 µm	80 mJ/cm2
	Long ago	4.2 µm	160 mJ/cm2
AZ 4562 Data from discontinued German version	Long ago	10 µm	510 mJ/cm2	Multiple puddle, 4 x 60 s	Multiple exposure with 10-15 s pauses is recommended.
AZ MiR 701 Data from discontinued PFOA containing version	Long ago	1 µm	180 mJ/cm2	Single puddle, 60 s	PEB: 60 s at 110°C
	Long ago	2 µm	200 mJ/cm2	Single puddle, 60 s
	Long ago	4 µm	400 mJ/cm2	Single puddle, 60 s	PEB: 90 s at 110°C
AZ nLOF 2020	Long ago	2 µm	110 mJ/cm2	Single puddle, 60 s	PEB: 60 s at 110°C Side wall angle ~15° For smaller angle (~5°), develop 30 seconds instead

Aligner: MA6-2

The Aligner: MA6-2 has an i-line notch filter installed. This results in an exposure light peak around 365 nm with a FWHM of 7 nm.

New resists
As of 2023-03-21 we no longer have any of the old versions of the resists: AZ 5214E, AZ 4562, AZ MiR 701. The following table contains only information about the new resist versions.

	Date	Thickness	Dose	Development	Comments
AZ MiR 701	2023-09-26 taran	1.5 µm	150 mJ/cm2 (13.5s @ 11mW/cm2)	Single puddle, 60 s	PEB: 60 s @ 110°C
AZ nLOF 2020	2023-09-26 taran	2 µm	121 mJ/cm2 (11 s @ 11 mW/cm2)	Single puddle, 60 s	PEB: 60 s @ 110°C 60 s development for lift-off
AZ 5214E	2023-01-11 jehem	1.5 µm	70 mJ/cm2	Single puddle, 60 s
AZ 5214E Image Reversal	2023-01-11 jehem	2.2 µm	22 mJ/cm2	Single puddle, 60 s	Reversal bake: 60 s at 110°C Flood exposure: 500 mJ/cm2
AZ 4562	2021-12-08 jehem	10 µm	550 mJ/cm2	Multiple puddles, 5 x 60 s	Priming: HMDS Rehydration after SB: 1 hour (may not be necessary) Exposure: Multiple exposures with pauses, 5 x (10 s exposure + 10 s pause) Degassing after exposure: 1 hour (may not be necessary)

Exposure dose for maskless aligners

The exposure doses listed below are for generic good exposure results, and can be a compromise between getting good lines, as well as good dots, in both clear field and dark field exposures. The optimal dose and achievable resolution for any given specific project, could be different from the listed values.

All doses are for standard silicon wafers, unless otherwise stated. Development is done using 2.38% TMAH (AZ 726 MIF).

Aligner: Maskless 01

The Aligner: Maskless 01 has a 365 nm LED light source with a FWHM of 8 nm.

New resists
As of 2023-03-21 we no longer have any of the old versions of the resists: AZ 5214E, AZ 4562, AZ MiR 701. The following table contains only information about the new resist versions.

	Date	Thickness	Exposure mode	Dose	Defoc	Resolution	Comments
AZ MiR 701	2023-07-06 jehem	1.5 µm	Fast	275 mJ/cm2	1	1 µm Tested using dehydration reducing measures	PEB: 60s@110°C Dev: SP60s
AZ nLOF 2020	2023-07-06 jehem	2.0 µm	Fast	180 mJ/cm2	0	1.5 µm	PEB: 60s@110°C Dev: SP60s
AZ 5214E	2023-07-06 jehem	1.5 µm	Fast	110 mJ/cm2	0	1.75 µm	Dev: SP60s
AZ 5214E image reversal	2023-04-05 jehem	2.2 µm	Fast	possibly obsolete data 20 mJ/cm2	possibly obsolete data -2	2.0 µm	Reversal bake: 60s@110°C, Flood exposure: 500mJ/cm2 Dev: SP60s
AZ 4562	2023-04-05 jehem	10 µm	Fast	possibly obsolete data 1050 mJ/cm2	possibly obsolete data -1	≤5 µm	Priming: HMDS Rehydration after SB: 1 hour (may not be necessary) Exposure: Single exposure Degassing after exposure: 1 hour (may not be necessary) Development: Multiple puddles, 5 x 60 s

Dehydration reducing measures used for testing AZ MiR 701:
The CDA used for the pneumatic autofocus will dehydrate the resist. To reduce this effect, the writehead is parked far away from the write area while setting up the job for at least a few minutes, before starting the exposure.

Aligner: Maskless 02

The Aligner: Maskless 02 has a 375 nm laser light source with a FWHM of ~1 nm.

New resists
As of 2023-03-21 we no longer have any of the old versions of the resists: AZ 5214E, AZ 4562, AZ MiR 701. The following table contains only information about the new resist versions.

New writehead
As of 2023-03-21 the MLA2 has a new writehead installed, converting it from a write mode 1 tool to a write mode 2 tool. This makes all previous dose/defocus settings obsolete. The following table contains only the dose/defocus values for the new writehead.

	Date	Thickness	Laser	Autofocus	Exposure mode	Dose	Defoc	Resolution	Comments
AZ MiR 701	2023-08-21 taran	1.5 µm	375	Optical	Quality	325 mJ/cm2	1	1 µm Tested using dehydration reducing measures (design elongated +40mm in y).	PEB: 60s @ 110°C Dev: SP60s
				Pneumatic			?
AZ nLOF 2020	2023-08-21 taran	2.0 µm	375	Optical	Quality	450 mJ/cm2	0	1.5 µm	PEB: 60s @ 110°C Dev: SP60s
				Pneumatic			?
AZ 5214E	2024-08-16 taran	1.5 µm	375	Optical	Quality	95 mJ/cm2	2	1.5 µm	Dev: SP60s
				Pneumatic			-2
AZ 5214E image reversal	2023-04-17 jehem	2.2 µm	375	Optical	Quality	35 mJ/cm2	0	1.5 µm	Reversal bake: 60s @ 110°C Flood exposure: 500 mJ/cm2 Dev: SP60s
				Pneumatic			?
AZ 4562	2023-04-19 jehem	10 µm	375	Optical	Quality	1150 mJ/cm2	0	≤5 µm	Priming: HMDS Rehydration after softbake: 1 hour (may not be necessary) Exposure: Single exposure Degassing after exposure: 1 hour (may not be necessary) Development: Multiple puddles, 5 x 60 s
				Pneumatic			?

Dehydration reducing measures used for testing AZ MiR 701:
The CDA used for the pneumatic autofocus will dehydrate the resist. To reduce this effect, the writehead is parked far away from the write area while setting up the job for at least a few minutes, before starting the exposure.

Aligner: Maskless 03

The Aligner: Maskless 03 has a 405 nm laser light source with a FWHM of ~1 nm.

New resists
As of 2023-03-21 we no longer have any of the old versions of the resists: AZ 5214E, AZ 4562, AZ MiR 701. The following table contains only information about the new resist versions.

	Date	Thickness	Laser	Autofocus	Exposure mode	Dose	Defoc	Resolution	Comments
AZ MiR 701	2023-06-30 jehem	1.5 µm	405	Pneumatic	Quality	175 mJ/cm2	0	1 µm Tested using dehydration reducing measures	PEB: 60s@110°C Dev: SP60s
AZ nLOF 2020	2023-06-30 jehem	2.0 µm	405	Pneumatic	Quality	9000 mJ/cm2	2	1 µm	PEB: 60s @ 100°C Dev: SP60s Due to the high dose required on this tool, it is recommended to process nLOF on tools with a more appropriate exposure light source
AZ 5214E	2023-06-30 jehem	1.5 µm	405	Pneumatic	Quality	75 mJ/cm2	0	1 µm	Dev: SP60s
AZ 5214E Image reversal	2023-06-30 jehem	2.2 µm	405	Pneumatic	Quality	50 mJ/cm2	0	1 µm	Reversal bake: 60s@110°C Flood exposure: 500mJ/cm2 Dev: SP60s
AZ 4562	2023-06-30 jehem	10 µm	405	Pneumatic	Quality	550 mJ/cm2	3	≤5 µm	Priming: HMDS Rehydration after SB: 1 hour (may not be necessary) Exposure: Single exposure Degassing after exposure: 1 hour (may not be necessary) Development: Multiple puddles, 5 x 60 s

Dehydration reducing measures used for testing AZ MiR 701:
The CDA used for the pneumatic autofocus will dehydrate the resist. To reduce this effect, the writehead is parked far away from the write area while setting up the job for at least a few minutes, before starting the exposure.

Exposure dose when using AZ 351B developer (NaOH)

The exposure doses listed below are for generic good exposure results, and can be a compromise between getting good lines, as well as good dots, in both clear field and dark field exposures. The optimal dose for any given specific project, could be different from the listed values.

All doses are for standard silicon wafers, unless otherwise stated. Development is done using AZ 351B developer (NaOH) diluted 1:5.

KS Aligner (351B)

The KS Aligner has an i-line notch filter installed. This results in an exposure light peak around 365 nm with a FWHM of 7 nm.

	Date	Thickness	Dose	Development]	Comments
AZ 5214E Data from discontinued German version	Long ago	1.5 µm	70mJ/cm2	60 s	Positive process
	Long ago	2.2 µm	72 mJ/cm2	70 s
	Long ago	4.2 µm	160 mJ/cm2	180 s
AZ 5214E Data from discontinued German version	Long ago	1.5 µm	30 mJ/cm2	60 s	Image reversal process. Reversal bake: 100s at 110°C. Flood exposure after reversal bake: 210 mJ/cm2
	Long ago	2.2 µm	35 mJ/cm2	70 s
AZ 4562 Data from discontinued German version	Long ago	10 µm	320 mJ/cm2	5 minutes	Multiple exposure with 10-15 s pauses is recommended.

DUV Resist

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