5  EP 2 000 008 B1 6  ible substrates, such as on plastic substrates for organic light emitting diode (OLED) displays, and the deposition of conformal coatingson verylarge substrates. Manyad- ditional advantages and uses of the systems and meth- odswill become apparent fromthe following detailed de- scription, which proceeds with reference to the accom- panying drawings. [0020] FIG. 1 illustrates a schematic cross- section view of a system 10 according to a first embodiment for the deposition of a thin-film coating onto a flexible sub- strate 12 (shown in profile in FIG. 1), such as a web of plastic film or metal foil, for example. With reference to FIG. 1, system 10 includes first and second precursor zones 14 and 16, respectively, separated by an interme- diate isolation zone 20 in which an inert fluid is present. The inert fluid may comprise an inert liquid, but more preferably consists essentially of an inert gas, such as nitrogen (N$_{2}$).Wheninuse,reactive firstandsecondpre- cursor gases (Precursor 1 and Precursor 2) are intro- duced into the respective first and second precurso zones14,16fromfirst andsecond precursor deliverysys- tems 24, 26. Precursor delivery systems 24, 26 may in- clude precursor source containers (not shown) located outside or within precursor zones 14, 16. Additionally or alternatively, precursor delivery systems 24, 26 may in- cludepiping, pumps, valves, tanks,and other associated equipment for supplying precursor gases into precursor zones14, 16. An inert gasdelivery system 28is similarly included for injecting inert gas into isolation zone 20. [0021] In the embodiment shown, precursor zo nes 14,16 andisolation zone 20aredefined and borderedby an outer reaction chamber housing or vessel 30, divided by first and second dividers 34, 36 into three sub-cham- bers, namely, a first precursor chamber 44, a second precursor chamber 46and aninertgaschamber 50. Ves- sel30maycompriseapressurevesselorvacuumvessel substantially isolating the process space from the exter- nal environment. In other embodiments, the vessel 30 may have entranceand exitpassageways for interfacing with other process modules or equipment, as described below with reference to FIG. 4. A series of first passage- ways 54 through first divider 34 are spaced apart along a general direction of travel of substrate 12, and a cor- responding series of second passageways 56 are pro- vided through second divider 36. The passageways 54, 56 are arranged and configured for substrate 12 to be threaded therethrough back and forth between first and second precursor zones 14,16 multiple times, and each time through isolation zone 20. For aweb substrate,pas- sageways54, 56 preferablycompriseslits having a width (exaggerated in FIG. 1) that is slightly greater than the thickness of substrate 12 and a length (not shown) ex- tending into the plane of FIG.1 (i.e., normal to the page) and that is slightly greater than a width of the substrate. Isolation zone 20 is, thus, preferably separated (albeit imperfectly) from the first precursor zone 14 by first di- vider 34 and from second precursor zone 16 by second divider 36. [0022] To substantially prevent non- ALD reactions caused by mixing of nonadsorbed quantities of the first and second precursor gases in one of the chambers 44, 46, 50, it is necessary for the system 10 to inhibit the migrationofPrecursor 1 from first precursor zone 14 into isolation zone 20 and the migration of Precursor 2 from second precursor zone 16 into isolation zone 20. Pas- sageways54,56 are preferablyconfigured torestrict the flow of gases between the zones 14,16, 20, to avoid or limit diffusion of precursor gases into a common zone. Passageways 54, 56 may include slits sized only slightly thicker and wider than the thickness and width of the substratepassing throughthem, leavingonlyaverysmall amount of headroom and margins to allow substrate 12 to pass therethrough without scraping against the sides of the passageways. For example, headroom and mar- gins may range between microns and millimeters in cer- tain embodiments. The passageways 54, 56 may also include elongate tunnels through which the substrate 12 passes, as depicted in FIGS. 1, 2, and 4. Such slits and tunnels are sometimes referred toasslit valves, although no actual moving valve gate is utilized. In some embod- iments, the passageways 54, 56 include a wiper for fur- ther restricting flow. In one such embodiment, the sub- strate is threaded through opposing leaves of resilient material, such as a synthetic rubber, which wipe against opposing surfaces of the substrate. [0023] In an alternate embodiment (not shown), the inert gas chamber 50 of isolation zone 20 and dividers 34,36 are eliminated, sothatisolation zone20essentially consistsofa seriesoflong narrowpassagewaysextend- ing completely between precursor zones 14,16. In such an embodiment, no common inert gas chamber 50 con- nects the passageways, so inert gas is injected directly into the passageways medially of the first and second precursor zones 14,16 to help prevent precursor migra- tion and mixing. Isolation zone 20 of this embodiment would include a manifold, or a number of manifolds, for routing inert gas lines to nozzles along the sides of the passageways. The manifold or manifolds would formedin the materialof the reactionchamber bordering the passageways, and may be connected toan inert gas deliverysystemalong the sidesof the system, ratherthan at an end of the system as shown in FIG. 1. [0024] To help isolate the first precursor gas from the second precursor gas, pressure differentials are prefer- ably established between the isolation zone 20 and the first precursor zone 14 and between the isolation zone 20 and the second precursor zone 16. In one embodi- ment, the pressure differentials may be generated by in- jecting inert gasinto isolation zone 20 at a pressure great- er than the operating pressure of the precursor zones 14, 16, and then passively exhausting gases from the precursor zones 14, 16. In another embodiment, the ex- haust from precursor zones 14, 16 could be controlled relative to a passive exhaust from isolation zone 20 or bythrottling an exhaust flowfrom isolation zone20. Pres- sure differentialsmayalsobegenerated bypumpingfrom 4