Bhola N. De

Thin‐film hermeticity: A quantitative analysis of diamondlike carbon using variable angle spectroscopic ellipsometry

The purpose of this paper is twofold. First, we report on the successful application of variable angle spectroscopic ellipsometry to quantitative thin‐film hermeticity evaluation. Secondly, it is shown that under a variety of film preparations and moisture introduction conditions water penetrates only a very thin diamondlike carbon (DLC) top surface‐roughness region. Thus DLC is an excellent candidate for use as protective coatings in adverse chemical and aqueous environments.

Measurement of superlattice optical properties by variable angle spectroscopic ellipsometry

Abstract Variable angle of incidence spectroscopic ellipsometry is a sensitive, nondestructive technique for determining optical constants, layer thicknesses, microstructure, and other parameters. We have applied this technique to the study of AlAs-GaAs and Al (x)Ga(1−x)AsGaAs superlattices. For a sample with Al (0.5)Ga(0.5)As barrier layers and 20 periods, sharp spectroscopic features were observed at the first electron to heavy hole, e-hh(1), first electron to light hole, e-lh(1), and second electron to heavy hole, e-hh(2) transition energies. Cross sectional transmission electron microscopy (XTEM) showed this superlattice to be of good quality. Ellipsometric data for two other samples, with AlAs barriers, did not contain any sharp features due to quantized level transitions, and XTEM of these samples revealed poor quality superlattice structure. An advantage of ellipsometry is that the complex refractive index can be obtained without Kramers-Kronig analysis. The effective refractive index for a 20 period superlattice was solved using ellipsometric data at three angles of incidence, near 74°. The real part is increased by about 2% at the e-hh(1) peak, and the imaginary part (extinction coefficient) is increased by 0.05.

Ellipsometric study of Al2O3/Ag/Si and SiO2/Ag/quartz ashed in an oxygen plasma

Using monolayer‐sensitive variable angle of incidence spectroscopic ellipsometry, the silver oxide growth on a silver mirror, coated with an Al2 O3 or SiO2 protective layer, was investigated. The oxidation was done in a pure oxygen plasma asher. The resulting silver oxide growth was monitored accurately as a function of exposure time in the plasma asher. It was found that silver was converted to silver oxide under the protective coating, during ashing of a sample. The optical constants of a dense silver oxide thin film, created by oxidizing in the asher, were also measured.

Ellipsometric Studies of the Diffusion of Automic Oxygen Through Silicon Dioxide Thin Films

In this paper we describe the application of variable angle spectroscopic ellipsometry to the study of diffusion of atomic oxygen through SiO 2 . Data are found to be well fit to the universal growth parabola, and the diffusion coefficient is estimated to be 10 −5 cm 2 /min

Superlattice Optical Properties Measured by Variable Angle Spectroscopic Ellipsometry

Variable Angle of incidence Spectroscopic Ellipsometry (VASE) is a sensitive, nondestructive method of determining optical constants, layer thicknesses, alloy compositions and other parameters. We model the VASE data for a sample containing a 20 period Al 0 5 Ga 0 5 As-GaAs superlattice, to obtain the effective index of refraction (n) and e tinction coefficient (k) of the superlattice layer. The room temperature VASE spectra contain strong, sharp features at the e-hh(1), e-lh(1) and e-hh(2) excitonic tran-sition energies. In addition, VASE was used to characterize more compli-cated layered structures, which also contained superlattices.

Study of temperature-dependent ultrathin oxide growth on Si(111) using variable-angle spectroscopic ellipsometry

Abstract Using the monolayer-sensitive variable-angle spectroscopic ellipsometry technique,we have studied the temperature-dependent growth mechanisms of an ultrathin oxide layer on top of silicon. The oxidation was done in atomic oxygen produced in a pure oxygen plasma and driven by an r.f. power source. The results have been compared with the recently proposed model of Murali and Murarka for ultrathin oxide growth on top of silicon. The activation energies of different growth parameters associated with the oxide growth have also been determined.

Coloration of glass exposed to atomic oxygen

The atomic oxygen in low earth orbit is harmful to spacecraft materials. Simulation of this space environment is often done with a plasma asher. We observed a browning effect of common glass placed in a plasma asher. After a detailed analysis, we conclude that this browning effect was not due to deposition of a film on the material surface; rather, it was the effect of optical color centers generated by the plasma. Thus ashing experiments can be safely carried out on space materials, without fears of spurious film deposition.

Ellipsometric analysis of computer disk structures

We have used variable angle spectroscopic ellipsometry (VASE) to analyze the materials surfaces and interfaces in multilayer sputtered media computer disks. Specifically, the system C/CoNiCr/Cr/NiP/Al has been investigated for layer thicknesses, interfacial and surface roughness, and radial and circumferential uniformity. By first characterizing the Cr/NiP/Al then CoNiCr/Cr/NiP/Al structures, we were able to fully characterize the complete disk structure. The interface width between the carbon layer and CoNiCr magnetic layer was determined to be approximately 260 A. This is reasonable considering typical surface roughness present on magnetic disks, and that the carbon ‘‘fills’’ in this surface roughness. VASE is a nondestructive technique and used at atmospheric pressure, and is thus suitable for use in a production environment.

Study Of Indium Tin Oxide Films Exposed To Atomic Oxygen

Indium tin oxide thin films (650 Å) were prepared by dc sputtering onto room temperature substrates. The films were exposed to an rf excited oxygen plasma, to qualitatively simulate the effects of atomic oxygen. Changes in optical, electrical, and structural properties were characterized as a function of exposure time.