Far-Infrared Interference Technique for Determining Epitaxial Silicon Thickness

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Abstract
Interference technique in the frequency range 30–200 cm−1 has been used for the first time to determine the thickness of low‐conductivity epitaxial films deposited on a highly conducting silicon substrate. It is shown that for thick epitaxial films (d≥4 μm) the frequency at which half‐order minimum occurs is highly sensitive to the epilayer‐substrate interface carrier concentration profile. In general the far ir thickness is close to that obtained by angle‐stain technique. A combination of ir and far‐ir measurements therefore yields valuable information regarding the interface carrier concentration profile. The far‐ir technique can replace the costly and destructive methods presently used, such as angle stain, and capacitance‐voltage measurements made on specially fabricated diodes. The paper also discusses the optical constants of silicon in the far ir. The calculations show that it is necessary to use the energy‐dependent anisotropic scattering time to correctly evaluate the optical constant in the far ir.

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