Performances of interferometric optical transmission diagnostic for in situ and real-time control of magnetron sputtering deposition process

A convenient and simple in situ and real-time method to control PVD processes for transparent thin films deposition on transparent substrate is described in this paper. This method designed for the glass industry and tested today in on-line monitoring, allows to control the thickness and complex indices and then the good running of the treatment. This method consists of a simple measurement of the interferential transmission through the substrate and the deposit. After recalling the principles of this classical method, the optical sensitivity parameters linked with the use of an inverse calculation method are evaluated and commented on. It is shown that, as expected when the refraction index values of the deposited material are close to those of the substrate, the sensitivity of the process control is low. It is often the case for the deposits used in the glass industry. Nevertheless to exploit this very useful method of process control, a solution currently tested on production lines is described here. To boost the sensitivity of the interferential transmission diagnostic it is shown that the measurements can be made through a high refractive index thin film layer, pre-deposited on the substrate with an adequate thickness.