Method for regulating evaporating rate and layer build up in the production of thin layers

A method for regulating the evaporation rate and layer buildup in the production of optically effective thin layer comprising the steps of:

• inserting a substrate of which thin layers are to be produced into a vacuum chamber;
• applying evaporating power for deposition of a layer on said substrate and controlling said evaporation power, said evaporating power corresponding to power applied to an evaporating device for evaporating the material of said layer prior to deposition;
• measuring the optical characteristics of the deposited layer;
• starting the evaporation with a predetermined power;
• forming the time derivative of the measurement resulting from measuring the optical characteristics of the deposited layer after the optical characteristics of the layer start to change;
• generating a predefined sinusoidal signal corresponding to the time rate of change of the optical characteristics of the layer during the layer buildup under predetermined optimum conditions and being independent from the optical characteristics of the layer being deposited;
• comparing continuously the time derivative of said measured result with said generated signal;
• generating a difference signal from said comparison step for regulating said power in accordance with the layer buildup so that the power is increased when layer buildup lags and power is reduced when layer buildup is too rapid;
• said layer being substantially constant as a function of time.