OPTICAL THICKNESS MONITORING FOR THE A-SI PRODUCTION LINE

To produce efficient a-Si:H solar modules it is essential to control the deposition processes and thus the thickness of each sub-layer. An optical thickness monitoring system was developed to measure the growth of these thin films. Thereby the change of the spectra of the reflected white light between 350nm and 1000nm is analyzed. By means of this nondestructive monitoring method the production processes itself is not influenced. The thickness of the thin films is calculated by the matrix method according to the well established theory of the optical behavior of stacked planar multilayer. The optical properties of the deposited layer materials are the fundament input of the calculation. Amorphous silicon layers with a thickness in the range between 30 - 1000 nm have been analyzed successfully.