STRAINED FILM DEPOSITION ON THIN SUBSTRATES - RESULTING INTERNAL STRAINS WITH AN APPLICATION TO PRESTRAINED AND PRESHAPED MULTILAYERED MEMBRANES FOR A SOFT-X-RAY WINDOW

When a strained film is deposited on a thin substrate or membrane able to relax laterally, the film induces strains into the substrate. Acco rdingly, the continuing relaxation of the film-substrate system during deposition generates a nonuniform strain field in the film itself. In this study, the substrate shrinkage or expansion and nonuniform strai n distributions within the deposited film are derived. Also, the induc ed strains due to the pressurization of initially strained and buckled multilayered membranes are analyzed. The lateral expansion of a thin membrane by a compressively strained coating is applied to increase th e pressure endurance of the membrane-coating system. An experimental c omparison of pressure endurance is presented for polyimide-based soft- x-ray windows of about a thickness of 200 nm, with thin coatings in va rious stress states. The strains within the window membrane are calcul ated by applying the derived formulae successively to the supporting g rid and to the membrane cells.