Thickness determination and layer characterization using terahertz scanning reflectometry
A terahertz scanning reflectometer system is described herein for in-situ measurement of polymer coating thickness, semiconductor wafer's surface sub-surface inspection in a non-destructive and non-invasive fashion with very high resolution (e.g., 25 nm or lower) and spectral profiling and imaging of surface and sub-surface of biological tissues (e.g., skin) in a non-invasive fashion.
1. A terahertz scanning reflectometer for layer thickness determination, comprising:
a continuous wave terahertz source configured to generate terahertz radiation toward a reference layer and a target layer, wherein the reference layer and the target layer have a related base structure;
a first detector configured to detect a reference layer reflected beam from the reference layer responsive to the terahertz radiation;
a second detector configured to detect a target layer reflected beam from the target layer responsive to the terahertz radiation; and
a processor configured to determine a difference between the reference layer reflected beam and target layer reflected beam,
wherein the continuous wave terahertz source includes a pump laser in line with a neutral density filter, a mirror, an emitter and aperture and an IR filter, the continuous wave terahertz source feeds parabolic mirrors and beamsplitters to forward the terahertz radiation which includes a terahertz beam directed to the reference layer and another terahertz beam directed to the target layer.
2. The terahertz scanning reflectometer of claim 1 , wherein multiple detectors are deployed for faster scanning of semiconductor wafers.
3. The terahertz scanning reflectometer of claim 1 , wherein scanning resolution for a surface layer is at a resolution of 23.84 nanometer or lower.
4. The terahertz scanning reflectometer of claim 1 , wherein sub-surface layers of a multi-layer substrate are scanned on a layer-by-layer basis.
5. The terahertz scanning reflectometer of claim 1 , wherein a layer structure of a multi-layer substrate is detected and identified.
6. The terahertz scanning reflectometer of claim 1 , wherein defects are detected on a surface and in a sub-surface layer of a multi-layered substrate.
7. The terahertz scanning reflectometer of claim 6 , wherein the defects are inclusion, crack, non-uniformity, dislocation, phase change, and new phase formation.
8. The terahertz scanning reflectometer of claim 1 , wherein the difference is based on measuring material properties including effective density, effective dielectric constant, and effective refractive index.