Gayle Lux

SIMS characterization of HgCdTe and related II–VI compounds

The production of consistent high purity materials is critical for improvement in performance and sensitivity of II-VI photovoltaic and photoconductive devices. Information regarding the energy band structure and impurity or defect levels present in the material is essential to understand and enhance the performance of current detectors along with the development of future novel devices. Secondary ion mass spectrometry (SIMS) is capable of providing information of purity, junction depths, dopant distribution, and stoichiometry in the material. SIMS techniques can achieve high detection sensitivities in very small analytical volumes and for a wide range of elements (almost the entire periodic table). SIMS analysis also provides unique capabilities for localizing atomic distribution in two and three dimensions. Ion images can be obtained by registering the positions of mass selected ions formed in the sputtering process. The combination of excellent detection sensitivity, high mass resolution, depth profiling capability, and high resolution image acquisition on a wide spectrum of elements by a SIMS instrument is not matched by any other instrumentation technique.

An accurate and computationally efficient semi-empirical model for arsenic implants into single-crystal (100) silicon

In this paper is reported an accurate and computationally efficient semiempirical model based on an extensive set of experimental data for arsenic implants into (100) single-crystal silicon. Experimental and model development details are given, and issues of the measurements are discussed. The newly developed model has explicit dependence on tilt angle, rotation angle, and dose, in addition to energy. Comparisons between the model predictions and experimental data are made in order to demonstrate the accuracy of this model.

Ultra-shallow junctions in silicon using amorphous and polycrystalline silicon solid diffusion sources

The inter-dependence of diffusion behavior and grain microstructure in amorphous silicon/polysilicon-on-single crystal silicon systems has been studied for rapid thermal and furnace annealing for P and BF2 implants. It is found that the changes of microstructure during annealing play a major role in determining the diffusion profiles in the substrate as well as in the polysilicon layer. For P doping, a drive-in diffusion results in a much larger grain microstructure for as-deposited amorphous silicon than for as-deposited polysilicon, which leads to the formation of shallower junctions in the substrate for the first case. For B doping, there is little difference in the final microstructure and junction depth between the two cases. The P and B junctions formed in the substrate are found to be laterally very uniform in spite of expected doping inhomogeneities due to polysilicon grain boundaries both for as-deposited amorphous silicon diffusion sources and for as-deposited polysilicon diffusion sources.

The Detailed Variation of Boron and Fluorine Profiles with Tilt and Rotation Angles for BF 2 + ION Implantation in (100) Silicon

Over 250 boron and over 250 fluorine profiles have been obtained from BF 2 + implants over a wide range of implant energies, doses, tilt angles, and rotation angles. A detailed study has been conducted on the boron and fluorine profile variations with the tilt and rotation angles over the available range of energies and doses. Channeling through a few low index axial and planar channels in (100) silicon has been found to account for the observed profile variations with implant angle. Tilt and rotation angle combinations which minimize channeling and ensure process uniformity have been deduced.

Modeling of boron diffusion in polysilicon-on-silicon structures using a rapid thermal anneal step for ultra-shallow junction formation

The diffusion of boron in polysilicon-on-silicon structures subjected to a rapid thermal anneal (RTA) step in investigated. The high temperature step (> 1000 °C) causes a breakdown of the interfacial oxide leading to increased dopant flux across the polysilicon-silicon interface. The effect of the break-up of the interfacial oxide is modeled as a temperature-dependent interface transport coefficient across the polysilicon-silicon interface. The enhanced boron diffusion is attributed to the interfacial oxide breakdown and the dissociation of boron defect complexes at the polysilicon-silicon interface. The enhanced concentration-dependent effective boron diffusivities in the single crystal silicon for polysilicon-on-silicon structures are extracted using Boltzmann-Matano analysis. A phenomenological model is implemented in SUPREM-III to accurately model the boron diffusion profiles in polysilicon-on-silicon structures subjected to a RTA step.

Comparison of Amorphous and Polycrystalline Silicon Films as a Solid Diffusion Source for Advanced VLSI Processes

This paper discusses the diffusion behavior of P, B and As from as-deposited amorphous/ polycrystalline silicon into the underlying Si substrate as a function of RTA/ furnace annealing conditions. The evolution of grain microstructure has been studied in as-deposited amorphous/ polycrystalline silicon to determine the inter-dependency of diffusion behavior and grain microstructure. After 60 s RTA at 1100° C for P doping, the microstructure of asdeposited amorphous silicon is drastically changed by rapid grain growth, whereas it is only slightly changed for asdeposited polysilicon. This leads to formation of deeper junctions for as-deposited polysilicon than for as-deposited amorphous Si. For B doping, there is little difference in the final microstructure between as-deposited polysilicon and as-deposited amorphous silicon after anneal. For low annealing temperatures, the junctions for both amorphous and polysilicon diffusion sources are laterally uniform in spite of local inhomogeneities due to grain boundaries. This is believed to be due to the rapid lateral spread of dopants along the interface prior to indiffusion into the substrate. At high annealing temperatures, a number of dark fringes are observed in the substrate along the interface from Crosssectional Transmission Electron Microscopy (XTEM) micrographs, which are more conspicuous for as-deposited amorphous Si. We believe that these fringes arise from local doping inhomogeneities or lattice strain in the substrate. For 30 s RTA at 1150° C, the native interfacial oxide appears to break up, causing epitaxial alignment of the polysilicon layer with respect to the underlying substrate.

Analysis of ion scattering by thin SiO2 layers in boron implants through SiO2 into silicon

The effects of ion scattering by a silicon dioxide layer on boron distribution profiles implanted through the oxide layer into single‐crystal silicon have been studied. The intensity of ion scattering and the degree of randomization of the directions of the implanted ions have been investigated through observations of a series of boron profiles measured by secondary ion mass spectroscopy (SIMS) analysis. The effectiveness of the oxide layer in randomizing the directions of implanted ions is found to be strongly dependent on the correlation between the ion energy and the oxide thickness. It is also shown by SIMS anaysis that even the total randomization of the direction of the ions does not completely eliminate ion channeling. This study reveals an unexpected effect of ion scattering by screen oxide layers on implant profiles: ion scattering by the oxide layer can cause enhanced channeling and deeper profile depth.