X-ray reflectometry apparatus and method thereof for measuring three dimensional nanostructures on flat substrate
This disclosure relates to an apparatus and methods for applying X-ray reflectometry (XRR) in characterizing three dimensional nanostructures supported on a flat substrate with a miniscule sampling area and a thickness in nanometers. In particular, this disclosure is targeted for addressing the difficulties encountered when XRR is applied to samples with intricate nanostructures along all three directions, e.g. arrays of nanostructured poles or shafts. Convergent X-ray with long wavelength, greater than that from a copper anode of 0.154 nm and less than twice of the characteristic dimensions along the film thickness direction, is preferably used with appropriate collimations on both incident and detection arms to enable the XRR for measurements of samples with limited sample area and scattering volumes. In one embodiment, the incident angle of the long-wavelength focused X-ray is ≥24°, and the sample area is ≤25 μm×25 μm.
1. An X-ray reflectometry apparatus for measuring a three-dimensional nanostructure on a flat substrate, comprising:
an X-ray source for emitting an X-ray of one wavelength in a multi-wavelength range of 0.154 nm-20 nm;
an X-ray reflector comprising multiple mirrors or a X-ray monochromator;
a six-axis platform configured to control a focus distance of the X-ray reflector such that the focus distance is ≥150 mm, so that the X-ray is point focused on a sample surface from an incident angle ≥24° and a footprint of the focused X-ray is less than or equal to 10 μm×25 μm;
an incident slit disposed between the X-ray reflector and the sample surface, wherein the focused X-ray is controlled by the incident slit to change a divergence angle, and the incident slit is an aperture optical element or a slit element that is controlled in at least one direction;
an X-ray detector configured to collect reflecting and scattering signals from the sample surface, which includes a 2-dimensional X-ray sensor inside a vacuum chamber and an analyzer outside the vacuum chamber; and
a controller configured to control the 2-dimensional X-ray sensor to move along a z-axis with the incident angle of the focused X-ray for collecting the scattering and reflecting signals.
2. The X-ray reflectometry apparatus according to claim 1 , wherein the multiple mirrors are equal to or more than 2.
3. The X-ray reflectometry apparatus according to claim 1 , wherein the multiple mirrors are used as ellipsoidal mirrors, multi-capillary optical mirrors, or multilayer optical mirrors.
4. The X-ray reflectometry apparatus according to claim 1 , wherein a diameter of Rowland circle of the monochromator is equal to or more than 500 mm.
5. The X-ray reflectometry apparatus according to claim 1 , wherein the three-dimensional nanostructure is a two-layer grating nanostructure or a multi-layer nanostructure, and a line width and a line pitch of the three-dimensional nanostructure are measured.
6. The X-ray reflectometry apparatus according to claim 1 , wherein a sensitivity angle is defined as the incident angle at which a reflection signal of an integrated light intensity has a largest change ratio, wherein the largest change ratio occurs when the sample surface has a critical dimension change of several nanometers.
7. The X-ray reflectometry apparatus according to claim 6 , wherein the sensitivity angle has a range equal to or more than 10°.
8. The X-ray reflectometry apparatus according to claim 1 , wherein the divergence angle multiplied by the tangent of the incident angle is changed according to a wavelength dispersion δλ/λ, wherein λ refers to the wavelength of the X-ray and δλ refers to a spread of the wavelength of the X-ray after being reflected by the X-ray reflector.
9. A method for measuring a three-dimensional nanostructure on a flat substrate comprising:
emitting an X-ray of one wavelength in a multi-wavelength range of 0.154 nm-20 nm;
controlling a focus distance of an X-ray reflector including multiple minors or an X-ray monochromator such that the focus distance is ≥150 mm, so that the X-ray is point focused on a sample surface from an incident angle ≥24° and a footprint of the focused X-ray is less than or equal to 10 μm×25 μm;
controlling the focused X-ray by an incident slit to change a divergence angle, and the incident slit is an aperture optical element or a slit element that is controlled in at least one direction;
collecting reflecting and scattering signals from the sample surface by an X-ray detector, which includes a 2-dimensional X-ray sensor inside a vacuum chamber and an analyzer outside the vacuum chamber, and a size of the sensor collects the scattering and reflecting signals completely; and
controlling the 2-dimensional X-ray sensor to move on a z-axis with the incident angle of the focused X-ray for collecting the scattering and reflecting signals.
10. The method according to claim 9 , wherein the multiple mirrors are equal to or more than 2.
11. The method according to claim 9 , wherein the multiple mirrors are used as ellipsoidal mirrors, multi-capillary optical mirrors, or multilayer optical mirrors.
12. The method according to claim 9 , wherein a diameter of Rowland circle of the monochromator is equal to or more than 500 mm.
13. The method according to claim 9 , wherein the three-dimensional nanostructure is a two-layer grating nanostructure, wherein a line width and a line pitch of the three-dimensional nanostructure are measured.
14. The method according to claim 9 , wherein a sensitivity angle is defined as the incident angle at which a reflection signal of an integrated light intensity has a largest change ratio, wherein the largest change ratio occurs when the sample surface has a critical dimension change of several nanometers.
15. The method according to claim 14 , wherein the sensitivity angle has a range equal to or more than 10°.
16. The method according to claim 9 , wherein the divergence angle multiplied by the tangent of the incident angle is changed according to a wavelength dispersion δλ/λ, wherein λ, refers to the wavelength of the X-ray and δλ refers to a spread of the wavelength of the X-ray after being reflected by the X-ray reflector.