Lumen Intellectual Property Services
Method and apparatus for optically determining physical parameters of underlayers
 A method and apparatus for optically determining a physical parameter of an underlayer such as the underlayer refractive index N.sub.u, extinction coefficient k.sub.u and/or thickness t.sub.u through a top layer having a first top layer thickness t.sub.1 and an assigned refractive index index n.sub.t and coefficient of extinction k.sub.t. The values of index n.sub.t and extinction coefficient k.sub.t can be estimated, optically determined or assigned based on prior knowledge. In a subsequent step a first reflectance R.sub.1 is measured over a wavelength range .DELTA..lambda. by using a test beam spanning that wavelength range. Then, a second reflectance R.sub.2 of the top layer and underlayer is measured using the test beam spanning wavelength range .DELTA..lambda. at a second top layer thickness t.sub.2. In a calculation step the physical parameter of the underlayer is determined from the first reflectance measurement R.sub.1, the second reflectance measurement R.sub.2, and the assigned or predetermined thickness values t.sub.1, t.sub.2, and the refractive index n.sub.t. and coefficient of extinction k.sub.t of the top layer. A dispersion model can be used in this calculation step. Alternatively, with transmissive samples, a first and second transmittance T.sub.1, T.sub.2 can be used. 
N & K Technology, Inc.
G G G
G01N G01N G01N
inventional inventional inventional
Dale A. Weilu Hongwei Guoguang Abdul Rahim
Harrison Xu Zhu Li Forouhi