33 terms, grouped from coating through defects. Manufacturer-agnostic — see the process recipe library for values cited to a specific datasheet — filterable by application, thickness and tone if you don’t yet know which resist you need.
Coating & surface prep
Adhesion promotion / HMDS
Adhesion promotion is a surface treatment applied before resist coating so the film sticks through development and later processing — almost always vapor-primed hexamethyldisilazane (HMDS). HMDS reacts with hydroxyl (silanol) groups on native oxide or another hydrophilic surface, replacing them with a hydrophobic layer so aqueous developer cannot creep under the resist edge and lift fine features. It is standard on oxide for DNQ-novolak resists, and is usually unnecessary for epoxy resists such as SU-8, which adhere well without it.
Spin curve
A spin curve plots the final, post-bake film thickness a resist reaches against the spin speed used to coat it, for a fixed spread/dry recipe. Because centrifugal thinning follows roughly an inverse-square-root relationship with angular velocity, thickness falls steeply at low speed and levels off at high speed — read a target thickness from an actually plotted point rather than interpolating between two, since the curve is only as accurate as the points that were measured. AZ 5214E's process recipe shows a worked example.
Dry-film lamination
Dry-film lamination applies photoresist as a preformed solid sheet — rolled onto the substrate under heat and pressure — instead of spin-coating a liquid resist. It gives a film thickness that is largely independent of substrate topography, size or shape, which makes it common for thick, coarse-feature and panel-scale (e.g. PCB-style) processes, though it generally cannot match the finest resolution of a spin-coated resist.
Softbake / prebake
Softbake (also called prebake) is the bake performed immediately after spin-coating and before exposure, driving off the casting solvent so the film is dry, dimensionally stable and adherent. Underbaking leaves residual solvent that causes scumming and poor adhesion; overbaking can drive off photoactive compound or otherwise reduce sensitivity, so a recipe specifies both a temperature and a time.
Edge bead removal (EBR)
Edge bead removal strips the thickened rim of resist that builds up at the wafer's outer edge during spin coating, either with a solvent rinse on an EBR module or a peripheral expose-and-develop step. Left in place, that bead flakes during handling and contaminates the tool and later process steps, so it is removed immediately after coat.
DNQ rehydration
DNQ rehydration is the gradual re-absorption of atmospheric moisture by a DNQ-novolak resist film after softbake has driven solvent — and some water — out of it. Because the exposure reaction that makes DNQ soluble consumes water, a freshly baked, very dry film can show reduced apparent sensitivity until it rehydrates, which is why some datasheets specify a minimum delay between softbake and exposure.
Exposure & dose
Dose-to-clear (E0)
Dose-to-clear (E0) is the minimum exposure dose, in mJ/cm², at which a positive resist fully clears — down to bare substrate — after development. It is read off a dose-array test and serves as the practical zero point for setting a working exposure dose, which is normally specified as some multiple of E0.
Sizing energy / E-size
Sizing energy (E-size) is the exposure dose that reproduces a mask or pattern's intended critical dimension after development, rather than merely clearing the resist. E-size is generally higher than dose-to-clear for a positive resist, and the choice between them trades CD accuracy against process latitude.
Contrast (γ)
Contrast (γ) is a single number describing how sharply a resist's remaining-film-thickness-after-develop transitions between fully retained and fully cleared as exposure dose increases, plotted against log(dose). A higher-contrast resist gives steeper sidewalls and tighter CD control; γ is read from the slope of that contrast curve at its steepest point.
Exposure latitude
Exposure latitude is the percentage range of exposure dose over which a printed feature stays within a specified critical-dimension tolerance — commonly ±10%. A wider exposure latitude means the process tolerates more dose variation across a wafer, or from run to run, without features drifting out of spec.
Depth of focus (DOF)
Depth of focus (DOF) is the range of focus offset — above and below best focus, in micrometers — over which a pattern still prints within specification. DOF shrinks both as the target feature size shrinks and as the exposure optics' numerical aperture increases, which is why finer features demand tighter focus control.
Swing curve
The swing curve is a periodic ripple in linewidth (or dose-to-clear) as resist film thickness varies, caused by thin-film interference between light reflected off the resist's top surface and light reflected back up from the substrate underneath it. Coating at a thickness near a swing-curve minimum — or adding a bottom anti-reflective coating — reduces how sensitive the printed CD is to small thickness variations.
Standing waves
Standing waves are vertical intensity ripples formed inside the resist film by interference between the incoming exposure light and light reflecting back up from the substrate, which print as fine horizontal ridges on an otherwise smooth sidewall. In resists that use one, a post-exposure bake diffuses the exposed species enough to smooth the sidewall back out.
Grayscale lithography
Grayscale lithography uses multiple, or continuously varying, exposure-dose levels within a single exposure — via a graytone photomask, several exposures, or a spatial light modulator such as a DMD — to leave a resist surface with continuously varying thickness after development, rather than a simple open/closed binary pattern. It is how 3D microstructures such as microlenses, blazed gratings and continuous-relief profiles are made directly in resist; see how maskless lithography works for how a DMD implements it.
Aspect ratio
Aspect ratio is the ratio of a resist feature's height (film thickness) to its lateral critical dimension — width or hole diameter. High-aspect-ratio work (thick resist, narrow openings) is harder both to expose, since light must reach the full film depth, and to develop, since developer must penetrate and rinse fully out of a narrow, deep opening — AZ 9260 is a shipped high-aspect-ratio recipe.
Post-exposure & develop
Post-exposure bake (PEB)
Post-exposure bake (PEB) is a bake performed after exposure and before development. In chemically amplified resists it drives the acid-catalyzed reaction that actually defines solubility, so PEB temperature and time are among the most dose-sensitive parameters in the whole process; in DNQ-novolak resists that use one, PEB instead diffuses out standing-wave ripple to smooth the sidewall.
Developer normality / dilution
Developer normality / dilution describes the strength of an aqueous-base developer — almost always TMAH-based — either as a molar normality (e.g. 0.26 N) for ready-to-use developers, or as a dilution ratio of a metal-ion-free concentrate (e.g. AZ 400K) in water. Development rate, contrast and dark loss all depend strongly on this concentration, so a recipe specifies it alongside develop time and method.
TMAH
TMAH (tetramethylammonium hydroxide) is the aqueous base used in nearly all metal-ion-free photoresist developers, and it is what actually dissolves the exposed (or deprotected) resist regions. The most common ready-to-use strength, across both DNQ-novolak and chemically amplified resists, is 0.26 N, sold as a 2.38% w/w solution.
Puddle vs immersion development
Puddle and immersion are the two ways a track applies developer. Puddle development dispenses a static pool of developer onto a stationary (or slow-spinning) wafer and holds it for a fixed time before a high-speed spin rinse; immersion (dip) development submerges the wafer in a developer bath, often with agitation, typically as a batch process. Puddle development gives more repeatable single-wafer CD control; immersion favors batch throughput.
Hardbake
Hardbake is a high-temperature bake performed after development, used to further cross-link or dry the final resist film so it survives the etch, implant or electroplating step that follows. It increases the film's thermal and chemical resistance, but can round sharp corners or, in some resists, cause reflow if pushed too far.
Resist chemistry
DNQ (diazonaphthoquinone)
DNQ (diazonaphthoquinone) is the photoactive compound in most conventional positive g/h/i-line resists. Unexposed DNQ inhibits dissolution of the underlying novolak resin in aqueous-base developer; UV exposure converts it, via a ketene intermediate and water, into an alkali-soluble carboxylic acid — which is what makes the exposed area dissolve away. AZ 10XT is a shipped example of this chemistry.
Novolak
Novolak is the phenol-formaldehyde resin that forms the base polymer of conventional DNQ resists. It is inherently somewhat soluble in aqueous-base developer on its own; the unexposed DNQ photoactive compound suppresses that dissolution, and UV exposure removes the suppression, which is what gives the resist its positive-tone behavior.
Chemically amplified resist (CAR)
A chemically amplified resist (CAR) generates a small amount of photoacid on exposure, and its post-exposure bake uses that acid to catalytically deprotect — or crosslink — many polymer sites per absorbed photon, amplifying sensitivity well beyond a DNQ-novolak resist. That sensitivity comes with a cost: CARs are markedly more sensitive to PEB temperature and time, delay between steps, and airborne amine contamination. AZ nLOF 2020 is a shipped, negative-tone CAR.
Epoxy (SU-8-type) resist
An epoxy (SU-8-type) resist is a negative, chemically amplified resist built on an epoxy-based polymer — most commonly EPON SU-8 — instead of the phenol-formaldehyde novolak resin used in conventional DNQ resists. Exposure generates acid that catalyzes ring-opening crosslinking of the epoxy groups during PEB, giving a highly crosslinked film that is unusually thick-coatable and chemically and thermally robust, which is why it is favored for permanent structural, microfluidic and high-aspect-ratio layers.
Profile, defects & process outcomes
Image reversal
Image reversal converts a nominally positive DNQ-novolak resist into a negative-acting one: after a first exposure, a reversal bake — often with amine vapor or a crosslinking additive — makes the exposed regions insoluble, and a blanket flood exposure then renders the remaining, still-unexposed area soluble for development. The result combines a positive resist's resolution with the undercut sidewall profile lift-off needs. AZ 5214E is the shipped example.
Lift-off
Lift-off patterns a film by coating and developing resist first, depositing a film (commonly a metal) over the whole wafer, and then dissolving the resist in solvent — carrying away, or lifting off, the film sitting on top of it and leaving film only where the resist had an opening. It requires a negative or undercut sidewall profile so the deposited film is physically discontinuous at the resist edge; see library recipes suited to lift-off.
Undercut / re-entrant profile
An undercut, or re-entrant, profile is a resist sidewall that slopes inward at its base, so the opening is wider at the top than at the bottom — the opposite of a typical sloped positive-resist wall. That break in film continuity at the resist edge is what makes lift-off possible; it comes from image-reversal resists, dedicated lift-off resists, or a bilayer with a faster-dissolving underlayer such as LOR or PMGI beneath an ordinary positive resist.
Dark erosion / dark loss
Dark erosion (or dark loss) is unwanted removal of resist thickness in the nominally unexposed (dark) field during development, most often seen in negative-tone or thick-film processes. It reduces the retained film thickness and can round or thin features that were meant to stay fully intact through develop.
T-topping
T-topping is a defect in which the top of a resist feature is wider than its body, giving the sidewall profile a T-shaped cross-section. It is most commonly caused, in chemically amplified resists, by airborne amine contamination neutralizing the photoacid near the resist surface during the delay before, or during, post-exposure bake.
Footing
Footing is a defect in which a thin flare of unwanted resist remains at the base of a feature. Common causes are substrate reflectivity and standing waves, insufficient exposure dose reaching the resist-substrate interface, or substrate surface chemistry that locally inhibits development right at that interface.
Scumming
Scumming is residual resist left across a field that should have cleared completely — usually from underexposure, an underbaked film retaining solvent, a spent or under-agitated developer, or debris redeposited from an unremoved edge bead. It interferes with etch masking and can block lift-off entirely.
Striations
Striations are fine, roughly radial thickness ripples in a spin-coated resist film, visible as faint interference-color bands, caused by uneven solvent evaporation during spin. They are usually cosmetic at typical linewidths, but can affect CD uniformity in very thin or unusually dose-sensitive films.
Comets
Comets are streak-shaped resist-thickness defects trailing outward from a particle on the wafer during spin coating, named for their comet-like tail shape. They originate from particulate contamination on the wafer or chuck rather than from the resist chemistry itself.
Expose it at 365 and 405 nm
NANYTE BEAM is a desktop maskless lithography system with software-selectable dual-wavelength exposure and 16-bit grayscale — no photomask, no mask cost, same-day iteration.
Book a demo →General photolithography reference material, not a specification of any particular NANYTE BEAM configuration. Product names and trademarks belong to their respective owners; NANYTE is not affiliated with the manufacturers mentioned. Still stuck on a specific process? Talk to an engineer.