Database interpolation method for optical measurement of diffractive microstructures

1. A method of evaluating a diffracting structure formed on a semiconductor sample comprising the steps of:

measuring actual optical response characteristics of the sample; and

iteratively interpolating between interpolation points for the sample using an interpolation model, each interpolation point corresponding to a sample parameter set, wherein the interpolation model defines a substantially continuous function which intersects with the interpolation points in order to derive a set of interpolated optical response characteristics that best fit the actual optical response characteristics, in order to evaluate the sample.

2. A method as recited in claim 1 , wherein the actual optical response characteristics are in the form of one or both of complex reflectance coefficients and scattering matrices.

3. A method as recited in claim 1 , wherein the actual optical response characteristics include ellipsometric parameters.

4. A method as recited in claim 1 , wherein said actual optical response characteristics are created and measured as a function of wavelength.

5. A method as recited in claim 1 , wherein said interpolation model utilizes one or more of linear, multi-cubic, and quadratic functions.

6. A method of evaluating parameters of a diffracting structure formed on semiconductor samples comprising the steps of:

calculating optical response characteristics for selected parameter sets, each set of parameters corresponding to an interpolation point;

defining a continuous model of the optical responses as a function of the parameters that equals the optical responses at the interpolation points;

receiving a measurement signal for a sample; and

evaluating the parameters of the sample by iteratively fitting the measurement signal with the interpolation model.

7. A method as recited in claim 6 , wherein the calculating comprises calculating one or both the complex reflectance coefficients and scattering matrices.

8. A method as recited in claim 6 , wherein said measurement signal includes measurement information as a function of wavelength.

9. A method as recited in claim 6 , wherein said measurement signal includes measurement information regarding reflectance of the sample.

10. A method as recited in claim 6 , wherein said interpolation model comprises one or more of linear, multi-cubic, or quadratic functions.

11. A method as recited in claim 6 , wherein fitting comprises calculating a theoretical optical signal from the model.

12. A method as recited in claim 6 , wherein the actual optical response characteristics include ellipsometric parameters.

13. A method of evaluating a diffracting structure formed on a semiconductor sample comprising the steps of:

receiving a measurement signal containing actual optical response characteristics of the sample; and

iteratively interpolating between interpolation points for the sample using an interpolation model, each interpolation point corresponding to a sample parameter set, wherein the interpolation model defines a substantially continuous function which intersects with the interpolation points in order to derive a set of interpolated optical response characteristics that best fit the actual optical response characteristics, in order to evaluate the sample.

14. A method as recited in claim 13 , wherein the actual optical response characteristics are in the form of one or both of complex reflectance coefficients and scattering matrices.

15. A method as recited in claim 13 , wherein said actual optical response characteristics are created and measured as a function of wavelength.

16. A method as recited in claim 13 , wherein said interpolation model utilizes one or more of linear, multi-cubic, and quadratic functions.

17. A method as recited in claim 13 , wherein the actual optical response characteristics include ellipsometric parameters.