! 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|
|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
The AZ 10XT-60 spincurve is shown below, as well as process details for both automatic and manual coating.
Available thicknesses: 5 um / 8 um / 10 um / 15 um / 20 um
Available databases (default: 4inch, check with the staff for 6inch):
- AZ10XT_5to20um_Std_NoDehydrate_x_y (for HMDS-treated wafers)
- AZ10XT_5to20um_HighTopo_Dehydrate_x_y (for wafers with topography, spiral dispense)
- AZ10XT_5to20um_GlassOnly_Dehydrate_x_y (for transparent wafers)
- AZ10XT_5to20um_Quartz_Dehydrate_x_y (for quartz, stacked glass-silicon wafer or SOI wafers. Softbake temperature is 125°C.)
|Recipe name||Spin speed [rpm]||Softbake time [mm:ss]||PR thickness [µm]|
Spin time is 100s, followed by 60 seconds stress relaxation at 0 RPM. Softbake is performed at 300µm proximity. Softbake temperature is 112°C for all options except for “Quartz” (125°C).
- Find the spin-coating speed “XXXX” [RPM] matching your target thickness from the AZ 10XT-60 spincurve.
- When coating on wafers, use the HV_”XXXX” recipe, which includes a 500 RPM spreading step and 100 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: 105°C
- Softbake time: 90” + 20”/um
Important note on rehdratation:
Good result cannot be obtained without a minimum rehydratation delay which allows water molecules to diffuse homogenoueously in the freshly coated layer. Without sufficient water content, chemical reactions induced by photons cannot be completed. Please respect the minimum rehydratation time given in the following table (for normal cleanroom relative humidity conditions (≥40 RH)).
|PR thickness [µm]||Minimum rehydratation time [hour:min]||Remark|
Note: Diffusion time is largely dependant of relative humidity. Dry air with relative humidity smaller by -2.0 RH double the rehydratation time.
The following table lists the recommend dose “to clear” for AZ 10XT-60 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]+++|
* 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
The recommended developer for AZ 10XT is AZ 400K (diluted in water 1:3.5), an organic solution based upon KOH. Development with AZ 400K will result in a sharper edge profile.
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):
Development recipes for AZ 10XT-60 (identical for all are AZ10XT_5to20um_* databases) are listed below:
|Recipe name||PR thickness [µm]||Total contact time [s]|
The development consists in short spray dispense strokes followed by puddle (no rotation) / rinse development cycles. No softbake is applied in order to preserve vertical PR side walls.
Development sequences for AZ 10XT-60 are listed below:
|Sequence Number||Recipe name||PR thickness [µm]||Total contact time [s]|
The development combines spray and puddle methods with intermediates spin-clean steps. No Softbake is applied in order to preserve vertical PR side walls.
- Recommended developer: AZ 400K diluted 1 to 3.5 DI
- Development time: 45″/um
- Rinse: H2O 1min