Ellipsometer

J.A. WOOLLAM

RC2-XI

Spectroscopy

Ellipsometry measurements are ideal for thin film and multilayer characterization.

It is a dual rotating compensator spectroscopic ellipsometer, which measures the cross-polarization of the light providing the characterization of the most advanced materials.

The light source has low power density: applicable on in vivo tissues.

Ellipsometry can measure:

• film thickness,
• refractive index n as a function of wavelength,
• extinction coefficient k as a function of wavelength,
• surface roughness,
• interfacial mixing and thickness,
• uniformity,
• anisotropy,
• composition, crystallinity,
• graded film (optical constant change with the thickens).

Wavelength range: 210 – 1690 nm.

Nr of wavelengths: 1065.

Incident angles: 45° – 90°.

Measure complete spectrum in 1/3 of a second.

Spot size: 120 μm.

Sample scan: up to 200 mm (8 inch).

 

Obtainable Data

• Film thickness
• Dispersion of complex optical constants:
  • Refractive index n
  • Extinction coefficient k
• Band gap
• Surface roughness
• Interfacial mixing
• Uniformity
• Anisotropy
• Composition
• Crystallinity
• Graded film
• Porous films

Materials

• Thin films starting from ~1 nm
• Thick films up to ~ 10 mm
• Multilayers and bulks
• Any materials (metals, semiconductors, dielectrics), which reflects light in the given wavelength range
• Liquid samples

Application

• Low bandgap semiconductors
• Conductive organics
• Metals, alloys
• Dielectrics
• Mapping: map thin film uniformity (e.g., of wafers or glass panels)
• Anisotropic applications

Display applications: measurements of a-Si, poly-Si, microcrystalline-Si, OLED layers, color filters, ITO, MgO, polyimide, and liquid crystals are beneficial during display R&D and production.

 

PRECISION AND ACCURACY

• Data accuracy: Y = 0.006°, D= 0.015°
• Thickness precision, StdDev down to 0.01 Å
• Optical constant precision, StDev down to 0.0001

 

MEASUREMENT CAPABILITIES

• SE: Y and D over their full wavelength range
• Generalized SE: complete 2×2 Jones matrix for anisotropic samples
• Mueller Matrix SE: all 16 elements of the 4×4 Mueller matrix
• Depolarization: measure and model the non-ideal nature of your sample

Intensity: both reflectance and transmittance, including anisotropic terms such as like and cross-polarized intensities.

Other Applications

• Transmission measurements
• Thermo-optical investigations
• Se measurements on in vivo tissues

WORKING PRINCIPLE

Spectroscopic ellipsometry (SE) measures changes in the reflectance and phase difference between the parallel (R_p) and perpendicular (R_s) components of a polarized light beam upon direct reflection from a surface of liquid or solid sample. 

Reflectance (p, s) is described by the main ellipsometric angles Y and D. Because ellipsometry measures the ratio of two values originated by the same signal, the data collected are highly accurate (e.g., can detected thickness down to Å resolution), and reproducible. Most importantly, no reference specimen is necessary; the measurements are independent from the light source intensity and mechanical vibrations.