Thin film thickness measuring method
AssigneeTencor Instruments
InventorArnold Adams
Life of this patent
Estimating the term…
Abstract
A method of measuring thin film thickness, especially on semiconductor substrates, in which the substrate is illuminated with ultraviolet light of a fixed wavelength corresponding to a persistent spectral line and the amount of light reflected from the substrate is detected and measured. The ultraviolet light preferably has a wavelength in the range from 240 nm to 300 nm, and the 253.6 nm spectral line of mercury is considered best. Comparing the measured amount of light from the substrate to a known amount of light detected from a standard calibration substrate with known reflectivity, the reflectivity of the test substrate is computed. The thickness of a thin film on the substrate is determined from the computed reflectivity using Fresnel's equation or a lookup table derived from the same.
Claims7
A method of measuring a thickness of thin film on a reflective substrate comprising the steps of:
- illuminating a portion of a test thin film and substrate with ultraviolet light of a fixed wavelength corresponding to a persistent spectral line;
- measuring the intensity of the ultraviolet light reflected from the test thin film and substrate;
- providing a standard reflectivity calibration of a known thickness of the thin film on a substrate of known reflectivity, at the wavelength .lambda., the standard calibration including an intensity of reflected ultraviolet light;
- determining the light intensity reflectivity R of the test thin film and substrate by multiplying the known reflectivity R.sub.0 by the ratio of the reflected light intensity of the test thin film and substrate divided by the reflected light intensity of the standard reflectivity calibration;
- and
- determining the thickness d of the thin film in the test thin film and substrate by inversion of the relation for reflectivity R, expressed as a function of the thin film thickness d.
A process of using an ultraviolet reflectometer for thin film thickness measurement, the reflectometer having a source of ultraviolet light of fixed wavelength corresponding to a spectral line and an ultraviolet detector communicating with a data processor, the process comprising,
- directing ultraviolet light emitted from said source toward a test substrate so as to illuminate a portion of the test substrate,
- detecting light reflected from said test substrate with said ultraviolet detector, the detector transmitting an electrical signal with a signal strength corresponding to the amount of reflected ultraviolet light detected to a data processor,
- computing with said data processor a reflectivity of said test substrate, said reflectivity being determined to equal the ratio of the signal strength from said detector to the signal strength resulting from measurement of a standard calibration substrate of a known reflectivity times said known reflectivity, and
- determining from said reflectivity of said test substrate a thickness of a thin film on the illuminated portion of said substrate.
Dependencies are inferred from the claim text.