Galen L. Pfeiffer

Variable angle spectroscopic ellipsometry in the vacuum ultraviolet

Optical properties of thin films and bulk materials at short wavelengths, including 157 nm and shorter, are needed for development of new lithographic processes, new fundamental science, and new metrology in the semiconductor, optical and data storage industries. Variable angle spectroscopic ellipsometry offers non-destructive and precise measurement of thin film thickness and refractive index in the wavelength range from 140 nm to 1700 nm (0.73 eV to 8.9 eV). The addition of short wavelengths allows analysis of multilayer dielectric stacks, often difficult to do using visible spectroscopy alone. Another major application is in study of wide bandgap materials such as SiC and GaN related compound semiconductors for blue lasers and detectors. This paper reviews the present status of spectroscopic ellipsometry applications in the vacuum ultraviolet.

Infrared and visible ellipsometric studies of cholera toxin in ELISA structures

Ellipsometry is well known for its extreme sensitivity to the presence and properties of ultra-thin films. In the infrared, resonance response to chemical bonds allows chemical identification in monolayer-thick biological films. In this paper we show results of attachment repeatability for successive layers of monosialoganglioside, cholera toxin, and related antibodies using in situ visible spectroscopic ellipsometry. Several factors contributing to difficulty in obtaining reproducible results are discussed. Soecifically, these include freshness of reagents; surface type, cleaning, and preparation; temperature; birefringence of liquid cell windows; and cell design. Sensitivity and signal noise considerations for infrared spectra of molecular monolayers are discussed.