the coating area b this flow is selected within the knudsen or viscous range there is valid wherein p stands for the total pressure in slit 3 and u03c6 stands for the width of slit 3 preferably this gas flow is selected in the knudsen range further there is preferably valid wherein f stands for the flow of working gas per surface area of the slit opening peferably there is thereby valid width of the slit u03c6 i e mutual distance of the targets 1 a 1 b depth of the slit target extent h s in direction g of fig1 if similar to a magnetron tunnel shaped magnetic fields h are realized over the sputtering surfaces of the targets 1 a and 1 b then preferably so that measured parallel to the sputtering surfaces of the targets 1 a and 1 b and in the middle of the slit 3 there is valid with the help of a heating and or cooling arrangement which is adjustable in an open loop controlled or in a negative feedback controlled manner by means of an adjusting member 19 a the substrate temperature t in the area b is set a coating apparatus as schematically shown in fig1 was dimensioned and operated as follows target material 1 a 1 b mg 3 n 5 purity 99 95 target discharge voltage with respect to anode 5 on ground potential 310v power density per sputtering surface unit and at planar yet unsputtered sputtering surfaces 15w cm 2 dynamic deposition rate 30 50 nm m min which results from multiplying nm as deposited thickness and speed of the substrate in meters per minute this produces a static deposition rate.