Spectral Ellipsometry for In Situ Real-Time Measurement and Control

*Described is a spectral ellipsometer capable of precisely measuring thicknesses and compositions of multilayer structures, in situ and in real time. This spectral ellipsometer has been applied to wafer property monitoring during remote microwave plasma etching. Thicknesses, etch rates and compositions are fed back to a process host computer in real-time for single layer or multilayer film stacks of Si3N4, Si02, SiqN4 and Si02 mixtures, polycrystalline Si. It is noteworthy that unlike many other sensing techniques, interfaces can be anticipated using ellipsometry, allowing end pointing at any desired film thickness. Standard deviations for repeat thickness measurement are better than 0.04 nm for single layer films and about 0.2 nm for individual films within multilayer stacks. Spectral ellipsometry allows over determination of variables in multilayer stacks, hence, structure models and layer ,parameters can be verified using statistical methods. Spectral information also allows self calibration of incident angles.