Chromatic confocal device and method for 2D/3D inspection of an object such as a wafer with variable spatial resolution
A confocal chromatic device is provided for inspecting the surface of an object such as a wafer, including a plurality of optical measurement channels with collection apertures arranged for collecting the light reflected by the object through a chromatic lens at a plurality of measurement points, and a magnifying lens arranged for introducing a variable or changeable scaling factor between the spatial repartition of the collection apertures and the measurement points. A method is also provided for inspecting the surface of an object such as a wafer including tridimensional structures.
1. A confocal chromatic device for inspecting the surface of an object such as a wafer, comprising:
a chromatic lens with an extended axial chromatism;
a light source for illuminating the object through the chromatic lens with a plurality of optical wavelengths being focused at different axial distances;
a plurality of optical measurement channels with collection apertures arranged for collecting the light reflected by the object through the chromatic lens at a plurality of measurement points; and
a magnifying lens arranged for introducing a variable or changeable scaling factor between the spatial repartition of the collection apertures and the measurement points.
2. The device of claim 1 , wherein the plurality of optical measurement channels comprises optical measurement channels with an intensity detector for measuring a total intensity of the collected light.
3. The device of claim 1 , wherein the plurality of optical measurement channels comprises at least one optical measurement channel with a spectral detector for measuring a spectral information of the collected light and deducing an axial distance information.
4. The device of claim 1 , which comprises a magnifying lens positioned between the collection apertures and the chromatic lens.
5. The device of claim 1 , which comprises a magnifying lens and a chromatic lens arranged so that to provide an intermediate conjugate focal plane which is simultaneously:
a conjugate focal plane of the plane with the collection apertures for a lens assembly comprising the magnifying lens; and
a conjugate focal plane of the plane with the measurement points for a lens assembly comprising the chromatic lens.
6. The device of claim 5 , wherein the intermediate conjugate focal plane is:
at a finite distance; or
at a finite distance and positioned between the magnifying lens and the chromatic lens.
7. The device of claim 6 , wherein the intermediate conjugate focal plane is at infinite distance, corresponding to collimated beams.
8. The device of claim 1 , further including a collimating lens positioned between the collection apertures and the magnifying lens.
9. The device of claim 7 , further including a magnifying lens with an afocal lens arrangement.
10. The device of claim 1 , which comprises a magnifying lens of a zoom type allowing introducing a variable magnification.
11. The device of claim 10 , wherein the magnifying lens comprises:
at least one lens movable and allowing varying a magnification;
a lens arrangement allowing varying the magnification between the plane of the collection apertures and an intermediate conjugate focal plane at finite distance; and
an afocal zoom arrangement allowing modifying the width of collimated beams, for operating with an intermediate conjugate focal plane at infinite distance.
12. The device of claim 1 , which further comprises a mechanical mount allowing changing a magnifying lens.
13. The device of claim 12 , wherein the mechanical mount comprises a turret or a linear stage.
14. The device of claim 1 , further including collection apertures arranged along a line.
15. A method for inspecting the surface of an object such as a wafer comprising tridimensional structures, comprising:
providing a chromatic lens with an extended axial chromatism;
illuminating the object through the chromatic lens with a plurality of optical wavelengths being focused at different axial distances;
collecting the light reflected by the object through the chromatic lens at a plurality of measurement points using a plurality of optical measurement channels with collection apertures; and
changing optically a scaling factor between a spatial repartition of the collection apertures and a spatial repartition of the measurement points.
16. The method of claim 15 , further comprising at least one of the following steps:
measuring a total intensity of the light collected by at least one of the optical measurement channels for obtaining an intensity information; and
measuring a spectral information of the light collected by at least one of the optical measurements channels for obtaining an axial distance information.
17. The method of claim 15 , further comprising at least one of the following steps:
adjusting a spatial repartition of the measurement points taking into account a spatial repartition of structures on the object; and
adjusting a spacing of measurements points as to substantially match a spacing of structures on the object.
18. The method of claim 15 , which is implemented for inspecting bump structures on a wafer.