Infrared reflectance spectra of thin epitaxial silicon layers

IR reflectance spectra of thin (0.5–3.0 μm) epitaxial layers on substrates containing n-type buried layers are investigated in the 5–50-μm wavelength range. From measurements on uniformly doped wafers it is found that the Drude model should be used to compute the optical constants of the buried layers. The reflectance spectra can then be used to determine epitaxial layer thickness, peak concentration of the buried layer, and the thickness of the buried layer. For our process conditions the optically measured epitaxial thickness and peak concentration are in close agreement to measurements performed with a secondary ion microprobe.