Multilayers deposited by triode sputtering using a new accurate method of film thicknesses monitoring

Recent progress in thin film deposition techniques has motivated a renewed interest in artifically prepared layered microstructures. These multilayers can be used as Bragg reflectors for X-ray-UV optics in the range 100–1000 eV. Ideal multilayers require optimized thicknesses of low and high absorbing materials with perfect interfaces. The main problems are the control of the layer thicknesses to a high accuracy and the attainment of good quality interfaces between the layers. We have used a low energy (300–500 V) d.c. triode sputtering system which gives very sharp interfaces. We describe a new method of thickness monitoring which is based on the dependence of the deposition rate on the target current. The sequence and timing of the deposition of each layer is controlled using a microprocessor which also regulates the sputtering parameters (pressures, target voltage etc.). Thicknesses can be controlled with an accuracy to better than 0.1 A and a reproducibility of better than 0.1%.