Method for film thickness and refractive index determination
US4909631A · kind A · utility
Inventors
Key dates
| Filing date | Dec 18, 1987 |
| Grant date | Mar 20, 1990 |
| Priority date | — |
| Expiry date | Dec 18, 2007 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N2021/4126
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
Two methods for determination of thickness of a film of known material that is mounted on one face of a solid substrate of known material are disclosed, using: (1) inversion of an optical beam reflectivity equation; or (2) determination of the film thickness that minimizes the variance of the optical beam reflectivity, computed at each of a predetermined sequence of optical beam wavelengths. Four methods for determination of the (real) refractive index of a film of known thickness mounted on a face of a solid substrate of known material are disclosed, using: (1) minimization of absolute differences of computed and measured optical beam reflectivity, summed over a sequence of known film thicknesses, for assumed values of the refractive index; (2 and 3) two iterative techniques of promote convergence of an estimate of the index to a final value of the refractive index; or (4) solution of a quadratic equation whose coefficients are slowly varying functions of the solution variable.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.