X-ray reflectometry apparatus for samples with a miniscule measurement area and a thickness in nanometers and method thereof
This application relates to an apparatus and methods for enhancing the performance of X-ray reflectometry (XRR) when used in characterizing thin films and nanostructures supported on a flat substrate. In particular, this application is targeted for addressing the difficulties encountered when XRR is applied to samples with very limited sampling volume, i.e. a combination of small sampling area and miniscule sample thickness or structure height. Point focused X-ray with long wavelength, greater than that from a copper anode or 0.154 nm, is preferably used with appropriately controlled collimations on both incident and detection arms to enable the XRR measurements of samples with limited volumes.
1. An X-ray reflectometry (XRR) apparatus, comprising:
an X-ray source for emitting an X-ray with a wavelength larger than 0.154 nanometers (nm);
an X-ray reflector for point focusing the X-ray onto a surface of a sample;
a set of incident slits between the X-ray reflector and the sample, for adjusting an incident angle opening of the X-ray;
an X-ray detector for collecting the X-ray reflected by the surface of the sample; and
a set of detector slits between the X-ray detector and the sample, for controlling a detecting angle opening;
wherein the X-ray is point focused by the X-ray reflector onto the surface with an incident angle adjustable over a preset range.
2. The XRR apparatus in claim 1 , wherein the wavelength is no more than twice of a characteristic length of a structure of the surface.
3. The XRR apparatus in claim 2 , wherein the characteristic length is selected from the group consisting of film-thicknesses of the surface and heights of a nanostructure of the surface.
4. The XRR apparatus in claim 1 , wherein the X-ray reflector is selected from the group consisting of single crystal monochromators and multilayer mirrors.
5. The XRR apparatus in claim 4 , wherein the X-ray reflector is a multilayer mirror type and a wavelength dispersion of the X-ray reflector is less than 0.01.
6. The XRR apparatus in claim 4 , wherein the incident angle opening is a function of the incident angle.
7. The XRR apparatus in claim 6 , wherein the incident angle opening is a function of a tangent of the incident angle.
8. The XRR apparatus in claim 7 , wherein the X-ray source comprises a fine focused Aluminum anode.
9. The XRR apparatus in claim 1 , wherein the incident angle opening is a function of the incident angle.
10. The XRR apparatus in claim 9 , wherein the incident angle opening is a function of a tangent of the incident angle.
11. The XRR apparatus in claim 1 , wherein the X-ray source comprises a fine focused Aluminum anode.
12. The XRR apparatus in claim 1 , further comprising at least one analyzer for collecting an X-ray photoelectron spectrum (XPS) and/or an X-ray fluorescence (XRF) signals from the sample during the reflected X-ray is collected by the X-ray detector.
13. A method for X-ray reflectometry (XRR), comprising:
point focusing an X-ray onto a sample surface with an incident angle, wherein the incident angle is adjustable over a preset range of angles and a wavelength of the X-ray is larger than 0.154 nanometers (nm);
adjusting an incident angle opening of an incident X-ray according to the incident angle when the incident angle is changed to enhance an incident X-ray flux while keeping a resolution in a desirable range;
adjusting a detecting angle opening of a reflected X-ray seen by a detector according to a reflection angle when the reflection angle is changed; and
collecting the X-ray reflected by the sample surface to obtain nanostructure information of the sample surface.
14. The method in claim 13 , wherein the wavelength is no more than twice of a characteristic length of a nanostructure on the sample surface.
15. The method in claim 14 , wherein the characteristic length is selected from the group consisting of film-thicknesses of the surface and heights of a nanostructure of the surface.
16. The method in claim 13 , wherein the incident angle opening is a function of the incident angle.
17. The method in claim 16 , wherein the incident angle opening is a function of a tangent of the incident angle.
18. The method in claim 13 , further comprising:
collecting an X-ray photoelectron spectrum (XPS) from the sample during the X-ray reflected by the sample surface is collected; and
collecting an X-ray fluorescence (XRF) signal corresponding to the sample during the X-ray reflected by the sample surface is collected;
wherein the nanostructure information of the sample surface is deduced further from the combination of the XPS, the XRF and the XRR signals.