g-Line vs i-Line Photoresist: Formulation Basics for DNQ Systems
G-line (436 nm) vs i-line (365 nm) photoresist basics — wavelength, resolution, DNQ-THBP PAC role. Orion P-series grades for both. Request product sheets.
Photoresist formulators and procurement teams regularly conflate g-line and i-line systems because both use DNQ-based positive-tone chemistry on the same spin-coating equipment. The exposure wavelength, resolution capability, and PAC selection differ — and specifying the wrong line costs qualification time.
This guide covers the established formulation principles that separate g-line from i-line DNQ photoresists, then maps where Orion's DNQ-THBP grades fit each wavelength.
G-line and i-line in one paragraph
G-line photoresists expose at 436 nm (mercury g spectral line). I-line photoresists expose at 365 nm (mercury i spectral line). Both are positive-tone systems where DNQ photoactive compounds (PACs) photobleach on exposure, increasing solubility in alkaline developer. Novolak resin provides the base matrix; DNQ-THBP ester functions as the PAC at a standard ratio of 3.0–3.5 parts novolak to 1 part PAC.
G-line dominated semiconductor lithography through the 1980s. I-line extended resolution into the submicron range and remains the workhorse for mature nodes, power devices, MEMS, IoT sensors, and automotive ICs.
Wavelength comparison
Resolution figures are industry-typical ranges for DNQ-THBP systems. Actual resolution depends on process conditions, stepper NA, resist thickness, and bake parameters — not wavelength alone.
| Parameter | G-line | I-line |
|---|---|---|
| Exposure wavelength | 436 nm | 365 nm |
| Spectral source | Mercury g-line (Hg) | Mercury i-line (Hg) |
| Typical resolution | > 0.5 μm | 0.35–0.25 μm |
| DNQ PAC type | DNQ-THBP (standard) | DNQ-THBP (standard) |
| Resin matrix | Novolak (cresol-formaldehyde) | Novolak (cresol-formaldehyde) |
| Developer | Alkaline (aqueous TMAH typical) | Alkaline (aqueous TMAH typical) |
| Mature applications | Power devices, discretes, MEMS, legacy FPD | IoT sensors, analog ICs, automotive, advanced packaging |
How DNQ-THBP behaves at each wavelength
DNQ-THBP (diazonaphthoquinone esterified with tetrahydroxy benzophenone) is the industry-standard PAC for both g-line and i-line positive photoresists. The THBP core provides:
- Strong UV absorption that photobleaches on exposure
- Deep light penetration into the resist film
- Steep dissolution contrast between exposed and unexposed areas
At g-line (436 nm), DNQ-THBP absorption is efficient and the chemistry is well characterised across decades of production. Formulations target thicker resist films and larger feature sizes.
At i-line (365 nm), DNQ-THBP bleaching is faster and contrast is sharper — enabling smaller features. I-line formulations demand tighter control of PAC loading, novolak ADR (acid-dissolution rate), and post-exposure bake conditions.
For the dissolution mechanism, see DNQ Novolak Resist Mechanism.
Formulation variables that differ by wavelength
Novolak resin selection
Novolak resin molecular weight and ADR control developer resistance. I-line formulations typically use novolak grades with higher ADR for sharper sidewalls. G-line formulations may tolerate broader ADR ranges for thicker films.
Orion P-1403 lets you select your own novolak resin. Orion P-1610 includes a matched novolak described as optimised for i-line dominance. [NEEDS VERIFICATION: Exact ADR specification for P-1610 matched novolak.]
PAC loading
Standard blend ratio: 3.0–3.5 parts novolak to 1 part PAC. I-line programmes may push toward the lower end of this range for higher contrast. G-line programmes may use higher PAC loading for faster photospeed in thick-film applications.
Solvent and coating
Both wavelengths use similar spin-coating solvents — ethyl cellosolve, Dowanol-PGMA, or PGMEA depending on grade. Spin speed typically 3500–5000 RPM for uniform wafer coats. Drying at 90–105 °C before exposure.
Development and post-bake
Alkaline developer (typically aqueous TMAH) removes exposed areas. Post-exposure bake at approximately 120 °C stabilises the resist profile. I-line processes are more sensitive to bake temperature and time for submicron features.
Orion DNQ-THBP grades by wavelength
[NEEDS VERIFICATION: Relative g-line vs i-line performance ranking across P-1403, P-3101, and P-1610 on identical process conditions — not in source data. Run parallel trials with product information PDFs.]
For the full four-grade comparison, see DNQ-THBP Grades Compared.
| Grade | G-line suitability | I-line suitability | Notes |
|---|---|---|---|
| P-1403 | Yes (confirmed) | Yes (confirmed) | Dry powder; your novolak choice |
| P-3101 | Yes (confirmed) | Yes (confirmed) | 20% ready liquid; pre-selected resin |
| P-1610 | Yes (confirmed) | Yes — i-line optimised (per product data) | Dry powder with matched novolak |
| P-0711 | Yes (confirmed) | Yes — advanced i-line (confirmed) | CNR PAC; 0.35–0.5 μm nodes published |
When to specify g-line vs i-line
Specify g-line (436 nm) when:
- Your stepper or aligner exposes at 436 nm
- Feature sizes are above 0.5 μm
- Application is power devices, discretes, MEMS, or legacy flat-panel
- Thick-film resist (5–10 μm) is required
Specify i-line (365 nm) when:
- Your stepper exposes at 365 nm
- Feature sizes target 0.35–0.25 μm or below
- Application is IoT sensors, analog ICs, automotive chips, or advanced packaging
- Sidewall steepness and contrast are critical
If your equipment exposes both wavelengths: DNQ-THBP PACs from Orion are stated as g-line/i-line capable across P-1403, P-3101, P-1610, and P-0711. Optimise novolak selection and process parameters per wavelength rather than switching PAC chemistry.
Starting material: DNQ sodium salt
Formulators building DNQ-THBP PACs from upstream chemistry start with Orion Freedom 2-1-4 (CAS 64173-96-2) — the water-soluble sodium salt converted through sulphonyl chloride to esterified PAC. This path is separate from buying finished P-series grades.
Common questions.
What wavelength does g-line photoresist use?
G-line photoresist exposes at 436 nm — the mercury g spectral line. It uses DNQ-THBP PAC blended with novolak resin in positive-tone formulations.
What wavelength does i-line photoresist use?
I-line photoresist exposes at 365 nm — the mercury i spectral line. The same DNQ-THBP PAC chemistry applies, with formulation adjustments for higher contrast and submicron resolution.
Can the same DNQ-THBP grade work on both g-line and i-line?
Orion's P-1403, P-3101, P-1610, and P-0711 grades are stated as g-line/i-line capable. Process parameters — novolak ADR, PAC loading, bake conditions — must be optimised per wavelength. P-1610 is described as i-line optimised; P-0711 targets advanced i-line down to 0.35–0.5 μm nodes.
What is the standard novolak-to-PAC ratio for DNQ photoresists?
3.0–3.5 parts novolak resin to 1 part DNQ-THBP PAC. This ratio applies across g-line and i-line positive-tone formulations using Orion building blocks.