! 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
When used as recommended, primers such as HMDS are typically NOT required to promote the adhesion of XRHiC BARC layers.
Assuming wafers with clean surface without organic contamination, good adhesion of the XHRiC-16 polymer are observed with the following surface treatments:
| 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
While the XHRiC BARC layer can be spin-coated at different speed, it is meant to be used at a single thickness of ~ 160nm corresponding to a λ/4 optical path length at 365nm (i-line).
XHRiC target thickness: 0.16 um
Coating:
| XHRiC thickness [μm] | Grade | Dispense method | Spin speed [RPM] | Spin duration [sec] | Notes |
|---|---|---|---|---|---|
| 0.16 | XHRiC-16 | dynamic, 1500RPM | 5900 | 30 |
Softbake:
| XHRiC thickness [μm] | Bake method | Temperature [°C] | Bake duration [sec] |
|---|---|---|---|
| 0.16 | proximity – 150um | 180 | 60 |
Available sequence options:
- Dehydrate / EC
XHRiC cleaning options are EC only. An EBR step can be added when coating the top imaging resist.
- To reach a target thickness of 160nm using a manual coater with a static dispense of the polymer, the spin speed should e ~3500 RPM.
- When coating on wafers, use the STD_”3500″ recipe, which includes a 500 RPM spreading step and 40 seconds of main coating step.
- When coating on small chips, use the CHIP_”3500″ recipe, which includes 60 seconds of main coating step and a short acceleration at the end to reduce edge bead effects.
- XHRiC-16 cure temperature: 180°C
- XHRiC-16 cure time: 60”
Imaging Resist
While using a BARC layer will have a positive impact on the photolithography process with any imaging resist, it makes sense to use XHRiC with high-resolution, high transfer accuracy resists such as AZ ECI 3007 or AZ ECI 3027, which are available on the EVG 150 automatic coater and the Sawatec SM-200 manual coater. The spincurves are shown below.
We recommend the following combinations:
| XHRiC thickness [μm] | Grade | PR thickness [μm] | Photoresist | Notes | |
|---|---|---|---|---|---|
| 0.16 | XHRiC-16 | + | 0.6 | AZ ECI 3007 | |
| 0.16 | XHRiC-16 | + | 2.6 | AZ ECI 3027 |
The imaging resist is applied by spincoating directly after the XHRiC softbake, without any additional surface preparation.
On the EVG 150, make sure to select sequence without preparation, i.e. “C4.N.”…
On the Sawatec SM-200, make sure to use the correct spin-coating parameters for each photoresist.
Details are available here: AZ ECI 30XX
Exposure
Since XHRiC will absorb all reflected light, the exposure doses should be increased by ~35% compared to exposure without the BARC layer. The following table lists the recommended dose “to clear” for some combinations of XHRiC and AZ ECI double layers, 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 combination | Dose [mJ/cm2]+ | Dose [mJ/cm2]++ | Dose [mJ/cm2]+++ |
| XHRiC 160nm + AZECI 3007 0.6um | 135 | 140 | Refer to Resist Tables |
| XHRiC 160nm + AZECI 3027 2.6um | 240 | 250 |
* 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
XHRiC is a dry-etchable BARC that will not be developped together with the photoresist. For the development step, you should use the standard recommendations and sequences of the imagine top photoresist. For the AZ ECI family, please find the details here: AZ ECI 30XX
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
Etching
Since XHRiC is a dry-etchable BARC, it will need to be etched down in a plasma ICP/RIE equipment, prior to etching of the substrate material.
Here is the breakdown of the available equipment options. Please note that specific equipment have material & wafer restrictions. Make sure that you are allowed to process your wafer in these equipment.
| Equipment Name | Process Name | Plasma Chemistry | Etch Rate [nm/min] | Etch Duration [sec] | Notes |
|---|---|---|---|---|---|
| SPTS Rapier DSE | BARC | C4F8/Ar | ~78nm/min | ~125″ | |
| SPTS APS | BARC_Slow | CHF3/O2 | ~130nm/min | ~72″ | |
| SPTS Synapse | 00_CMi_BARC | CHF3/O2 | TBD | TBD | |
| TEL Unity Me | CMI.BARC | CF4 | TBD | TBD |
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