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.
1. An X-ray reflectometry apparatus for measuring three dimensional nanostructures on a flat substrate, 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 with fan-shape onto a surface of a sample;
an incident slit between the X-ray reflector and the sample, a width of the incident slit being greater than an incident slit opening by a factor 10 or above, and the width of the incident slit being aligned perpendicular to a reflection plane of the X-ray; and
an X-ray detector has a fine pixel resolution for collecting the X-ray reflected by the surface of the sample, wherein the X-ray is point focused by the X-ray reflector onto the surface with an incident angle adjustable over a preset range,
an opening angle of the incident X-ray is controlled via the incident slit opening, and a divergence angle of the fan-shape incident X-ray is controlled via the width of the incident slit,
at each azimuthal position of the reflected X-ray collected on the X-ray detector, an off-specular contribution is determined and removed from the reflected X-ray intensity.
2. The X-ray reflectometry apparatus according to claim 1 , wherein the X-ray detector is a 2 dimensional detector.
3. The X-ray reflectometry apparatus according to claim 1 , wherein the wavelength of the X-ray is no more than twice of a characteristic length along a surface normal of a structure of the sample.
4. The X-ray reflectometry apparatus according to claim 3 , wherein the characteristic length is selected from a group consisting of film thicknesses of the surface and heights of a nanostructure of the surface of the sample.
5. The X-ray reflectometry apparatus according to claim 1 , wherein the X-ray reflector is selected from a group consisting of single crystal monochromators and multilayer mirrors, and a wavelength dispersion of multilayer mirrors of the X-ray reflector is less than 0.01.
6. The X-ray reflectometry apparatus according to claim 1 , wherein the incident opening angle is a function of the incident angle.
7. The X-ray reflectometry apparatus according to claim 6 , wherein the incident opening angle is a function of a tangent of the incident angle multiplied by a constant.
8. The X-ray reflectometry apparatus according to claim 1 , wherein the X-ray source comprises a fine focused aluminum anode.
9. The X-ray reflectometry apparatus according to 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.
10. A method for X-ray reflectometry (XRR) to measure three dimensional nanostructures on a flat substrate, comprising:
point focusing a fan-shape X-ray onto a surface of a sample with an incident angle, wherein the incident angle is adjustable over a preset range of angle and a wavelength of the X-ray is larger than 0.154 nanometers (nm);
adjusting an opening angle of the incident X-ray according to an incident slit opening when the incident angle is changed;
adjusting a divergence angle of the fan-shape X-ray via a width of the incident slit;
collecting the fan-shape reflected X-ray by using a X-ray detector, and at each azimuthal position of the reflected X-ray collected on the X-ray detector an off-specular contribution is determined and removed from the reflected X-ray intensity,
wherein a specular component of the remained X-ray intensity at each azimuthal position is integrated to obtain a specular reflection intensity for each incident angle; and
a ratio between the specular reflection intensity and the integrated incident X-ray intensity is collected over the preset range of the incident angle to obtain structure information of the sample.
11. The method according to claim 10 , wherein the X-ray detector is a 2 dimensional detector.
12. The method according to claim 10 , comprising rotating around a surface normal of the sample such that the XRR measurements are conducted at different azimuthal angles between a given axial line assigned on the sample and a reflection plane of the X-ray.
13. The method according to claim 10 , wherein the wavelength of the X-ray is no more than twice of a characteristic length along a surface normal of a structure of the sample.
14. The method according to claim 13 , wherein the characteristic length is selected from a group consisting of film thicknesses of the surface and heights of a nanostructure of the surface of the sample.
15. The method according to claim 10 , wherein the incident opening angle is a function of the incident angle.
16. The method according to claim 15 , wherein the incident opening angle is a function of a tangent of the incident angle multiplied by a constant.
17. The method according to claim 10 , wherein collecting an X-ray photoelectron spectrum (XPS) and an X-ray fluorescence (XRF) signals from the sample during the reflected X-ray is collected by the X-ray detector, and the XPS, XRF signals and XRR results are for analysis of surface structure information of the sample.