Development of an Automatic Null Ellipsometer for Sputtering Rate Monitoring of EUV Multilayer Fabrication

Instrumentation To overcome current difficulty of absolute period control in the EUV multilayer fabrication by sputtering, we have developed an automatic null ellipsometer as a sputtering rate monitor having high enough picometer thickness sensitivity enabling accurate monitoring of the nm period multilayer fabrication [1]. Figure 1 shows schematic drawing of the ellipsometer installed as the sputtering rate monitor of our ion beam sputtering multilayer fabrication system. By the ellipsometer, the complex relative amplitude attenuations are measured and plotted on a complex plane at an every 200 msec time intervals during a periodic multilayer fabrication. A growth curve displayed on the complex plane gives information of the film properties such as the complex refractive indices and thicknesses. The ellipsometric data obtained in a series are used to determine the thicknesses of each layer in every 100 msec [2].