A device for thermally treating semiconductor wafers having at least one
silicon layer to be oxidized and a metal layer, preferably a tungsten
layer, which is not to be oxidized. The inventive device comprises the
following: at least one radiation source; a treatment chamber receiving
the substrate, with at least one wall part located adjacent to the
radiation sources and which is substantially transparent for the
radiation of said radiation source; and at least one cover plate between
the substrate and the wall part of the treatment chamber located adjacent
to the radiation sources, the dimensions of said cover plate being
selected such that it fully covers the transparent wall part of the
treatment chamber in relation to the substrate in order to prevent
material, comprising a metal, metal oxide or metal hydroxide such as
tungsten, tungsten oxide or tungsten hydroxide, from said substrate from
becoming deposited on or evaporating onto the transparent wall part of
the treatment chamber.