Method and device for measuring heights of patterns

1. A method for measuring the heights of patterns of an object, comprising:

a light emission, said light comprising a propagation mode of interest for at least one wavelength of interest,

an illumination of the surface of said object by the light,

a reflection of the light by the surface of the object,

a collection of the reflected light,

a division of the wavefront of the reflected light into division components, by at least one pattern of the illuminated surface,

a filtering of the collected light, comprising a modal filtering removing all modes other than the propagation mode of interest, for the wavelengths of interest, and

from the filtered light, and for the wavelengths of interest, an extraction of information about phase differences between the division components.

2. The measurement method according to claim 1 , wherein the propagation mode of interest consists of a fundamental transverse mode TEM 00 .

3. The measurement method according to claim 1 , wherein said illumination by the light is normally incident with respect to the surface of the object.

4. The measurement method according to claim 1 , further comprising a displacement of the illumination over the surface of the object.

5. The measurement method according to claim 1 , wherein the light emission comprises:

an emission of a plurality of propagation modes for a plurality of wavelengths, and

a modal filtering removing all modes other than the propagation mode of interest, for the wavelengths of interest.

6. The measurement method according to claim 1 , in which said method is carried out during an operation of etching patterns on the object.

7. The measurement method according to claim 6 , further comprising a determination of an etching end time.

8. A device for measuring the heights of patterns of an object, using the method according to claim 1 , and comprising:

light emission means, said light comprising a propagation mode of interest for at least one wavelength of interest,

means for outward guidance of the light,

means of illumination, by the light, of the surface of said object reflecting the light,

means for collecting the reflected light,

means for return guidance of the collected light,

means for filtering the collected light, comprising modal filtering means of the collected light, removing all modes other than the propagation mode of interest, for the wavelengths of interest, and

means for extracting from the filtered light, and for the wavelengths of interest, information about phase differences between components of a wavefront division of the reflected light.

9. The measuring device according to claim 8 , further comprising means for displacing the illumination over the surface of the object.

10. The measuring device according to claim 8 , wherein said outward and return guidance means comprise monomode optical fibres.

11. The measuring device according claim 8 , wherein said illumination means and the collection means are merged, and in further comprising a coupler, Y-junction or circulator separating the emitted light and the collected light.

12. The measuring device according claim 8 , wherein said extraction means include a Michelson interferometer.

13. The measuring device according to claim 8 , comprising:

a camera focused on the object,

means of lighting the object with white light, and

means for emitting a laser beam pointing a measurement area, emitting in the visible range.

14. The measuring device according to claim 8 , in which it is coupled to means for etching patterns.

15. The measuring device according to claim 14 , further comprising means for determining an etching end time.

16. The measuring device according to claim 14 , wherein said etching means comprises a plasma etching device.

17. The device according to claim 8 , in which it is applied to a measurement of the heights of steps between mirrors of a segmented mirror.