NOVELTY - Thin insoluble ceramic, oxide, other chalcogenide or metallic coating production, by contacting a dried precursor layer (PL) with a humid reactant gas (RG) and heat treating, is new.    USE - For production of thin difficultly soluble coatings, especially ceramic or oxide layers or possibly metallic or other chalcogenide layers, on substrates of any morphology, e.g. for producing solar cell components, doped layers, multilayers, surface protection layers or conductive, reflective, absorbent, catalytic or chemisorbent layers.    ADVANTAGE - The process extends the ILGAR (ionic layer gas reaction) process, described in DE19831214.8, to further surface layers of other material compositions and allows simple, ecological and economical production of higher quality coatings with higher yields using a wider range of precursors.    DETAILED DESCRIPTION - Thin difficultly soluble coatings are produced on substrates (S) by the following ceramic or oxide layer (CL/OL) production steps carried out cyclically in dependence on the desired layer thickness: (a) application of one or more layer-forming precursors (P) onto the substrate surface; (b) drying of the precursor layer (PL) in an inert gas stream (GS) or by evaporation; (c) contacting of the dried layer (PLD) with a humid reactant gas (RG) for conversion into a corresponding hydroxide or complex layer (HL); (d) thermal treatment of the layer (HL) to form the respective final layer (CL/OL); and, if unreacted starting components or undesired by-products occur, (e) rinsing and drying. INDEPENDENT CLAIMS are also included for the following: (i) a similar process for metallic coating production in which step (c) uses a humid reducing reactant gas and step (d) removes unreacted starting components or undesired by-products; and (ii) a similar process for other chalcogenide coating production in which step (d) is followed by (d') contacting of the layer with an additional reactant gas containing chalcogen-hydrogen compounds to form the final chalcogenide layer.    DESCRIPTION OF DRAWING(S) - The drawing shows equipment for ceramic coating production by a process according to the invention.    Precursor application step (I)    Drying step (II)    Reactant gas contact step (III)    Heat treatment step (IV)    Wash bottle (B)    Cover (C)    Gas stream (GS)    Furnace (H)    Hydroxide layer (HL)    Solution bath (LB)    Oxide or ceramic layer (OL/CL)    Precursor (P)    Precursor layer (PL)    Dried precursor layer (PLD)    Humid reactant gas (RG)    Substrate (S)    Substrate holder (SH)    Vessel (V)