Thickness determination and layer characterization using terahertz scanning reflectometry

• US 9,909,986 B2
• Filed: 07/09/2015
• Issued: 03/06/2018
• Est. Priority Date: 10/15/2003
• Status: Active Grant

• Current Assignee: Applied Research And Photonics, Inc.
• Original Assignee: Applied Research And Photonics, Inc.
• Inventors: Rahman, Anis, Rahman, Aunik K.
• Primary Examiner(s): SMITH, CHAD
• Application Number:
  US14/795,663
• Publication Number:
  US 20150316475A1
• Time in Patent Office: 971 Days
• Field of Search: None
• CPC Class Codes: A61B 5/0507 using microwaves or terahertz waves
• CPC Class Codes: A61B 5/444 Evaluating skin marks, e.g. mole, nevi, tumour, scar
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G01B 11/0625 with measurement of absorption or reflection
• CPC Class Codes: G01N 2021/3568 applied to semiconductors, e.g. Silicon
• CPC Class Codes: G01N 21/3563 for analysing solids; Preparation of samples therefor
• CPC Class Codes: G01N 21/3581 using far infrared light; using Terahertz radiation
• CPC Class Codes: G01N 21/3586 by Terahertz time domain spectroscopy [THz-TDS]
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G01N 21/8422 Investigating thin films, e.g. matrix isolation method
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G01N 21/9505 Wafer internal defects, e.g. microcracks
• CPC Class Codes: G01N 2201/101 Scanning measuring head
• CPC Class Codes: G01N 33/4833 of solid biological material, e.g. tissue samples, cell cultures tissue in vivo A61B5/00; cell suspensions G01N33/48735
• CPC Class Codes: G02F 1/353 Frequency conversion, i.e. wherein a light beam is generated with frequency components different from those of the incident light beams
• CPC Class Codes: G02F 1/3558 Poled materials, e.g. with periodic poling; Fabrication of domain inverted structures, e.g. for quasi-phase-matching [QPM]
• CPC Class Codes: G02F 1/361 Organic materials
• CPC Class Codes: G02F 1/365 in an optical waveguide structure G02F1/377, G02F1/395 take precedence
• CPC Class Codes: G02F 2203/13 involving THZ radiation

Abstract

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.

Claims

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.