AZ ECI 3007 ‒ Center of MicroNanoTechnology CMi ‐ EPFL

AZ ECI 3007 is a thin (0.6 to 1.5 um) i-line photoresist designed for high resolution photolithography and accurate pattern transfer. It is the standard resist choice to reach critical dimensions (CD) < 1um with mask-aligners in vaccum contact mode or the VPG200 laser writer.

Coating Tools : ACS 200 ; Sawatec SM-200
Thickness range [µm]: 0.6 … 1.5
Minimum CD / typical aspect ratio: ~ 600nm / AR ~ 1:1
Substrate topography: Planar or very low
Recommended for: Dry etching (depth <5um, high resolution)

Process in CMi

! Cleanroom humidity warning !

Control of the relative humidity (RH) in photolithography zones is extremely critical. Stable and reproducible photolithography is expected within 38% to 48% RH range.

In case of low RH (< 38%), the resist sensitivity and development rate decreases. It is then recommended to increase the recommended exposure doses.
In case of high RH (> 48%), the resist adhesion decreases. It is then recommended to do an additional bake (>10 minutes @ 150°C) before loading the wafers in the HMDS or coating equipment.

Wafer surface preparation

Usually adhesion of photoresist on inorganic materials is poor resulting in losses of fine structures after development. To solve the issue, silicon wafers are generally treated using the HMDS vapor prime treatment before spincoating the photoresist. Details about the HMDS process and control can be found here: link

Assuming wafers with a clean surface free of organic contamination, the best adhesion will be obtained with the surface preparation recommended in the table:

Surface material (larger area)	Vapor HMDS	Plasma O₂	Thermal dehydratation
Si	√√	√	√
SiO₂, fused silica, SiN, Si₃N₄	√√	√	√
Float glass, pyrex	√	√√	√
Metals: Al, Au, Pt, Ti	…	√	√√
Metals: Ag, Cu, Cr, Fe	…	X	√√
III/V semiconductors (GaN, GaAs)	…	X	√√

Legend: √√ Strongly recommended / √ Alternative process / … Not effective / X May affect or destroy underlaying material

Spincoating

The AZ ECI 3007 spincurve is shown below, as well as process details for both automatic and manual coating.

Available thicknesses: 0.6 um / 1 um / 1.5 um

Spin speed [rpm]	Softbake time [mm:ss]	PR thickness [µm]
5800	01:30	0.6
2050	01:30	1
850	02:00	1.5

Spin time is adjusted with the rotation speed. Softbake is performed at minimum proximity. Softbake temperature is 100°C for all options.

Available options:

HMDS / EC (edge clean)
Dehydrate / EC
HMDS / EBR (edge bead removal)
Dehydrate / EBR

Find the spin-coating speed “XXXX” [RPM] matching your target thickness from the AZ ECI 3007 spincurve.
When coating on wafers, use the STD_”XXXX” recipe, which includes a 500 RPM spreading step and 40 seconds of main coating step.
When coating on small chips, use the CHIP_”XXXX” recipe, which includes 40 seconds of main coating step and a short acceleration at the end to reduce edge bead effects.
Softbake temperature: 90°C
Softbake time: 30” + 30”/um

Exposure

The following table lists the recommend dose “to clear” for AZ ECI 3007 coated on silicon wafers. It is recommended to perform a contrast curve / exposure matrix calibration for wafers other than silicon.

Illumination:	Broadband*	i-line (355-365 nm)	h-line (405 nm)
Equipment:	MABA6, MA6 Gen3 (no filter)	VPG 200, MA6 Gen3 (filter), MJB4	MLA 150
PR thickness [µm]	Dose [mJ/cm²]⁺	Dose [mJ/cm²]⁺⁺	Dose [mJ/cm²]⁺⁺⁺
0.6	96	100	Refer to Resist Tables
1	115	120
1.5	145	150

* Mercury Lamp, Mask Aligner with UV400 configuration & no filter / + Based on intensity readings from Süss optometer broadband CCD / ++ Based on intensity readings from Süss optometer i-line CCD / +++ Based on MLA150 internal dose measurements

Development

The recommended developer for AZ ECI 3007 is AZ 726 MIF (or MF CD 26), an organic solution based upon TMAH.

IMPORTANT: AZ ECI 3007 is a chemically amplified resist and requires a post-exposure bake (PEB) before development. On automated development equipment, the PEB is included in the development sequences. For manual development, make sure to perform the PEB as indicated in the section below!

The PEB step is part of the standard development recipes on the ACS 200 system. PEB is performed at 110°C for a minimum of 60 seconds with minimum proximity gap.

Development sequences for AZ ECI 3007 on the ACS200 are listed below:

Recipe name	PR thickness [µm]	Total contact time [s]
D4_PEB_3007_u6_PUD	0.6	27
D4_PEB_3007_1u_PUD	1	37
D4_PEB_3007_1u5_PUD	1.5	47

The developement consists of an initial spray dispense followed by puddle method.

PEB temperature: 100°C
PEB time: 60”
Recommended developer: AZ 726 MIF (no dilution needed)
Development time: 20″-30″/um
Rinse: H₂O 1min

IMPORTANT:
After development, it is mandatory for wafers to go through an additional rinsing step with DI water to avoid backside contamination and damage on equipments (chuck in etcher) in further processing steps. The water baths of the following wet benches can be used free of charge (5 min. billing delay after login):

Z01 – Plade “Solvent” wet bench
Z02 – UFT “Resist” wet bench

Thermal reflow

Thermal reflow of photoresist is used to smooth and reshape photoresist patterns by heating them above their glass transition temperature. This technique allows the photoresist to flow, reducing surface roughness and achieving more rounded features (important for IBE). It is commonly applied to enhance the profile of microstructures, particularly in applications requiring curved or sloped sidewalls. The reflow process must be carefully controlled to avoid excessive deformation or pattern collapse.

The ratio between height and width of the feature to reflow has a great impact on the result. A threshold is found to be at 1:3 to round the structure / lower the sidewalls slope as presented in the image below.