Geoffrey K. Reeves

Resistivity measurements of thin film iridium on silicon

The resistivity of thin iridium films deposited on clean silicon substrates was measured by a four point probe technique. A simple electrical model based on parallel current conduction through the Ir film and the silicon substrate is shown to be valid. This allows the Ir contribution to the conduction to be determined. The effect of varying the film thickness from 0.5 to 16 nm caused the measured film resistivity to decrease from 190 to 35×10−6 Ω cm. This variation agrees well with the variation predicted by the Fuchs–Sondheimer and Lucas models for carrier scattering from the film surfaces.

Universal error corrections for finite semiconductor resistivity in cross-Kelvin resistor test structures

The Cross-Kelvin Resistor test structure is commonly used for the extraction of the specific contact resistance of ohmic contacts. Analysis using this structure are generally based on a two-dimensional model that assumes zero voltage drop in the semiconductor layer in the direction normal to the plane of the contact. This paper uses a three-dimensional (3-D) analysis to show the magnitude of the errors introduced by this assumption, and illustrates the conditions under which a 3-D analysis should be used. This paper presents for the first time 3-D universal error correction curves that account for the vertical voltage drop due to the finite depth of the semiconductor layer.

An analytical model for alloyed ohmic contacts using a trilayer transmission line model

This paper describes a Transmission Line Model approach to the modeling and analysis of alloyed planar ohmic contacts. It briefly reviews the standard Transmission Line Model (TLM) commonly used to characterize a planar ohmic contact. It is shown that in the case of a typical Au-Ge-Ni alloyed ohmic contact, a more realistic model based on the TLM should take into account the presence of the alloyed layer at the metal-semiconductor interface. In this paper, such a model is described. It is based on three layers and the two interfaces between them, thus forming a Tri-Layer Transmission Line Model (TLTLM). Analytical expressions are derived for the contact resistance Re and the contact end resistance Rc of this structure, together with a current division factor, S. Values for the contact parameters of this TLTLM model are inferred from experimentally reported values of Re and Re for two types of contact. Using the analytical outcomes of the TLTLM, it is shown that the experimental results obtained using a standard TLM can have considerable discrepancies. >

Pd/Zn/Pd/Au ohmic contacts to p‐type In0.47Ga0.53As/InP

The electrical properties of Pd/Zn/Pd/Au ohmic contacts to p‐type In0.47Ga0.53As/InP have been investigated as a function of the ratio of the interfacial Pd and Zn layers and the annealing treatment. For as‐deposited contacts, the presence of an increasing thickness of interfacial Zn and Pd to ∼300 A in the metallization resulted in a reduction in specific contact resistance, ρc, to a low value of 1.2×10−5 Ω cm2. Annealing of all of the contact configurations except the Zn=0 and 20 A structures produced a reduction in ρc to a minimum value of 7.5×10−6 Ω cm2 at 500 °C. A critical thickness of the Zn≥50 A and Pd≥100 A interfacial layers was required in order to produce a significant reduction in ρc during annealing. These results have been interpreted in terms of the reaction between Pd and In0.47Ga0.53As and an associated doping at the near surface region by Zn atoms. Annealing of the contacts at temperatures of ≥450 °C resulted in significant intermixing of the metal layers and the In0.47Ga0.53As as revea...

Characterization of C54 titanium silicide thin films by spectroscopy, microscopy and diffraction

Titanium silicide (TiSi2) is well known for application as a local interconnect material in complementary metal-oxide semiconductor technology. This paper reports on a comprehensive analysis of titanium silicide thin films by a variety of spectroscopy, diffraction and microscopy techniques. The composition and uniformity of the thin films and the oxygen contamination in the thin films is studied using Auger electron spectroscopy and secondary ion mass spectrometry; these have highlighted the existence of a thin film of uniform and desired composition, with a layer of oxide on the surface. Atomic force microscopy is used to study the surface morphology of the thin films. Microanalysis of the titanium silicide thin films was carried out using cross-sectional transmission electron microscopy; and a silicide–silicon interface which is abrupt and free of amorphous oxide is evident. X-ray diffraction (Bragg-Brentano and glancing angle), reflection high-energy electron diffraction and selected-area electron diffraction have been used to analyse the orientation of the thin films, and verify the presence of the desired C54 phase. The stress of the thin films is qualitatively studied by forming micro-beams of titanium silicide by bulk-micromachining of silicon, and the curvature of the micro-beams formed confirms tensile stress at the silicide–silicon interface. The thin films are also characterized using ellipsometry and thin film resistivity measurements.

Analytical and Finite-Element Modeling of a Two-Contact Circular Test Structure for Specific Contact Resistivity

The specific contact resistivity of a metal-semiconductor ohmic contact can be determined using a number of different test structures, and several of these use the transmission line model approach. In the circular transmission line model test structure, the concentric circular contacts have circular equipotentials in the semiconductor layer, and transmission line model equations can be used to describe their current-voltage behavior. Using test structures with two circular contacts of three different sizes, we present a new technique for determining specific contact resistivity. The analytical expressions are developed and presented, and finite-element modeling results are undertaken to demonstrate the accuracy of the technique. The scaling behavior of this test structure is also discussed. There are no error corrections required for determining contact parameters using the presented test structure.

Analytical and Finite-Element Modeling of a Cross Kelvin Resistor Test Structure for Low Specific Contact Resistivity

Various test structures have been employed to determine the specific contact resistivity (rhoc) of ohmic contacts, and cross Kelvin resistor (CKR) test structures are most suitable for estimating low rhoc values. The value determined by CKRs includes error due to parasitic resistances that have been difficult to account for when rhoc is low (< 10-7 Omega ldr cm2). In this paper, an analytical technique for determining the error in measurements from CKR test structures is presented. The analytical model described for circular contacts is based on Bessel function expressions. Using several contacts of different diameter (d) with d/w les 0.4 (w is the width of the CKR arms), the parasitic resistance can be accurately accounted for by extrapolation of experimental data to d/w rarr 0. Finite-element modeling and experimental results for metal-to-silicide contacts are used to validate the analytical expressions presented.

Refractive indices and thicknesses of optical waveguides fabricated by silicon ion implantation into silica glass

Abstract Planar optical waveguides formed by Si ion implantation into PECVD SiO2 have been characterized by the dark mode spectroscopy method at a wavelength of 0.6328 μm. The measured effective index values of the guided modes have been used to investigate the optical properties of the core layers of the waveguides after different pre-implantation treatments. It was found that annealing the specimens before implantation, affected both the refractive index and thickness of the core layers. In the annealed specimens a thicker core layer and a larger relative refractive index difference between the core and the buffer layer resulted.

Multimode operation of ARROW waveguides

Abstract It is shown that antiresonant reflecting optical waveguides exhibit multimode operation when a refractive index difference of the order of 10 -2 is introduced between the core and the second cladding layer.

Understanding the sheet resistance parameter of alloyed ohmic contacts using a transmission line model

Abstract The electrical characterization of alloyed ohmic contacts is commonly undertaken using a Transmission Line Model (TLM) network to model and experimentally determine two parameters—the specific contact resistance ϱ c and the sheet resistance R sk beneath a planar ohmic contact. This paper describes the use of a recently reported modification to the TLM network [the Tri-Layer Transmission Line Model (TLTLM)] to interpret measurements of the sheet resistance parameter. The TLTLM network models the composite alloyed ohmic contact as three layers (metal layer, alloyed semiconductor layer and the unalloyed semiconductor layer) and two interfaces between the three layers. By assigning appropriate parameters to the TLTLM network, it is possible to calculate a value for the sheet resistance R sk that has been experimentally derived using the standard TLM. The new TLTLM model predicts that values of R sk greater and less than R sh (the unmodified sheet resistance of the epitaxial layer) are possible, in agreement with experimentally reported observations.