NOVELTY - A multilayer body thermal treatment apparatus comprises semi-transparent bodies (5, 12) located between electromagnetic radiation energy sources (7, 11) and the body layers (2, 4).    USE - For thermally treating a multilayer body, e.g. to form a thin film solar cell functional layer of copper-indium-gallium sulfide-selenide (CIGSSe) from copper, indium, gallium, sulfur and selenium layers on a molybdenum-coated glass substrate, optionally in the presence of a process gas.    ADVANTAGE - The transparent bodies allow individual and controlled heating of the layers to permit rapid heating rates of e.g. 1 degrees C/sec. while minimizing mechanical stresses and consequent distortion.    DETAILED DESCRIPTION - A multilayer body thermal treatment apparatus comprises first and second energy sources (7, 11) which are arranged such that a first layer (2) is positioned between the first energy source (7) and a second layer (4) and the second layer (4) is positioned between the second energy source (11) and the first layer (2), and which exhibit a certain emission of electromagnetic radiation (8, 13) with a radiation field (9, 15). The layers (2, 4) exhibit a certain absorption for the electromagnetic radiation (8, 13) and are positioned in the radiation field (9, 15). Transparent bodies (5, 12), which exhibit a certain transmission and a certain absorption for the electromagnetic radiation, are located in the radiation fields (9, 15) between the energy sources (7, 11) and the layers (2, 4).    INDEPENDENT CLAIMS are also included for the following: (i) a process for thermally treating a multilayer body using the above apparatus; and    (ii) a multilayer body thermally treated by the above process.    Preferred Features: At least one of the layers consists of glass, glass-ceramic, ceramic, plastic and/or metal, and the transparent body consists of glass and/or glass-ceramic.    DESCRIPTION OF DRAWING(S) - The drawing shows a cross-sectional view of a thermal treatment apparatus according to the invention.    Thin film solar cell module (1)    Glass substrate (2)    Molybdenum layer (3)    Copper-indium-gallium sulfide-selenide semiconductor layer (4)    Transparent bodies (5, 12)    Energy sources (7, 11)    Radiation fields (8, 13)    Electromagnetic radiation (9, 15)    Heat conduction (10)    Heat radiation (14)