LOR 3A process recipe

Spin coating

LOR 3A is spin-coated to 0.3–0.6 µm. The curve below is redrawn from the manufacturer's published data — read your target thickness off the vertical axis and take the matching spin speed as a starting point.

Recommended baseline coating parameters (Table 1, applies across the LOR/PMGI line, not LOR 3A-specific): dispense 5 mL for a 150 mm wafer, dynamic dispense 3-5 s at 300-500 rpm, acceleration 10,000 rpm/s, terminal spin speed 3,000 rpm held for 45 s, edge-bead removal with EBR PG. Spin speeds of 2,500-4,500 rpm give maximum coating uniformity (higher speeds for smaller substrates, lower for larger/topographic ones). Acetone and conventional resist edge-bead removers are explicitly NOT recommended with LOR (causes precipitation) — use EBR PG.

Soft bake

Soft bake

180 °C · 3 min · hotplate

Notes

180°C for 3 min is the specific bake condition the manufacturer states was used to generate its own published spin-curve/optical-constant data ('Products were soft-baked at 180°C for 3 min', Technical Data section). It is not published as 'the' single recommended production bake. The datasheet's general recommended prebake range is 150-200°C (hotplate preferred, oven-compatible; some PMGI grades up to 250°C) — no single fixed time is prescribed for LOR 3A, because prebake temperature is the dominant control lever for undercut rate and is meant to be tuned experimentally (a temperature/time matrix) against the target undercut, developer choice, and develop time. An earlier (2002) MicroChem flyer for the LOR-A series quotes a narrower 150-190°C recommended range.Show more

SOURCE: Technical Data section note (p.5) and 'Soft-bake/Prebake Process' section (p.3), Kayaku/MicroChem 'LOR and PMGI Resists' datasheet Rev. A

Exposure

LOR 3A is not photoimageable. It is not exposed at all — it is coated beneath an imaged top resist and undercut laterally during development. See the development step below.

Development

Developer

0.26N (2.38%) TMAH metal-ion-free developer — e.g. Shipley/Rohm and Haas CD-26 or TOK NMD-3 — is the developer class the LOR-A series (including LOR 3A) is optimized for; the LOR-B series is instead optimized for lower-normality/metal-ion-bearing developers such as AZ 400K 1:4 or Shipley MF-319.Show more

Dilution

ready-to-use (as supplied)

Time

Not published — characterize on-tool

Method

immersion (spray development is recommended instead for thick, >2 µm LOR/PMGI stacks, for straighter sidewalls)

Rinse

DI water

Developer family

TMAH-based

SOURCE: 'Development Process' section (p.4) and Product Selection Guide (p.6), Kayaku/MicroChem 'LOR and PMGI Resists' datasheet Rev. A. Develop time is explicitly not published as a single fixed number — the datasheet states it depends on the combined thickness of the LOR/PMGI layer and the patterning resist layer, and on the desired undercut (see undercut-rate figures); it must be set experimentally, not read off a table.

Hard bake, etch & strip

Descum

Not required. The datasheet states no intermixing occurs between LOR and the imaging resist above it, so the bilayer stack does not need a plasma descum step between coating the LOR layer and the patterning resist.Show more

Stripper

MicroChem/Kayaku Remover-PG is the recommended stripper; baseline two-tank process at 60°C for 30 min per tank, optionally ultrasonic-assisted to improve strip efficiency (actual time varies with prebake temperature, step coverage, and resist profile). Acetone will NOT dissolve or remove LOR — keep acetone (and PGMEA, ethyl-lactate) waste streams separate, as LOR precipitates in these solvents and can clog lines.Show more

Storage

Store upright in original sealed containers in a dry area between 4-27°C (40-80°F), away from ignition sources, light, heat, oxidants, acids, and reducers. Do not use past the expiration date (1 year from date of manufacture). Recommended processing environment: 20-25°C ± 1°C, 35-45% ± 2% relative humidity.Show more

Not published for this resist: Hard bake, Etch resistance — characterize on-tool.

Where it's used

LOR 3A is not a photoresist in the imaging sense — it is a non-photoimageable PMGI underlayer that is coated and soft-baked beneath a conventional imaging resist, which alone is exposed and developed. During development the LOR layer dissolves isotropically (laterally undercutting beneath the imaged top resist), producing the re-entrant sidewall profile a clean bilayer lift-off requires. Undercut amount is set primarily by LOR soft-bake temperature — higher bake temperature lowers the dissolution rate and reduces undercut for a given develop time; the manufacturer's own bar-chart data (0.26N TMAH/CD-26 developer) give LOR-A-class undercut rates of 42 Å/s at 190°C, 67 Å/s at 170°C, and 111 Å/s at 150°C (recommended bake range 150-200°C). This rate is published for the 'LOR A' class as a whole (which LOR 3A belongs to), not broken out for the 3A sub-grade specifically. Secondary levers are prebake time, developer choice/normality, develop mode, and develop time (increasing develop time increases undercut for otherwise fixed bake conditions). HMDS priming is explicitly not required. For clean lift-off, LOR film thickness should exceed the deposited metal thickness, by roughly 25-33% per the two primary datasheets (guidance differs slightly: 'typically 1.2 to 1.3 times' the metal thickness in the 2002 flyer vs. 'typically by 25%' in the later Rev. A datasheet).

Sources & disclaimer

• Kayaku Advanced Materials — LOR 3A datasheet (Kayaku/MicroChem 'LOR and PMGI Resists', Rev. A (undated on the document itself); cross-checked against the earlier MicroChem 'LOR™ Lift-Off Resists' flyer, © MicroChem Corp. 2002, mirrored at https://amolf.nl/wp-content/uploads/2016/09/datasheets_LOR_datasheet.pdf. The current kayakuam.com-hosted PDF (https://kayakuam.com/wp-content/uploads/2023/06/KAM-LOR-PMGI-Datasheet-4.30.24-final-1.pdf, dated 4/30/24 per its filename) returned HTTP 403 and could not be fetched directly; the two documents actually read are university-hosted mirrors of the same manufacturer-authored content.) · accessed 2026-07-10
• https://bionium.miami.edu/_assets/pdf/lor-3a-photoresist-process.pdf — University of Miami cleanroom process recipe for LOR 3A — used only to corroborate typical practical parameters (180°C/5min softbake, 3000rpm/35s spin, CD-26 60-90s or MF-319 45-60s develop), not as a primary numeric source
• https://cns1.rc.fas.harvard.edu/facilities/docs/SOP112_r1_1_%20LOR.pdf — Harvard CNS SOP112 lift-off processing procedure — used only to corroborate typical bake (180°C/4min) and CD-26 develop (75s) practice, and to confirm HMDS is not used with LOR; not a primary numeric source

1. Chen. A lift-off process for high resolution patterns using PMMA/LOR resist stack. Microelectronic Engineering (2004). doi:10.1016/j.mee.2004.02.053
   Sub-100 nm lift-off geometry demonstrated with a PMMA/LOR resist bilayer.

Manufacturer datasheet values are starting points; optimal parameters depend on your substrate, equipment and environment. Product names and trademarks belong to their respective owners. NANYTE is not affiliated with the manufacturers listed. Last updated 2026-07-12.

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