S.-H. Yang

Modeling of ion implantation in single-crystal silicon

Abstract In this paper are described ion implant models that have been developed at the University of Texas at Austin. In this activity the strategy consists of the development of computationally-efficient semi-empirical models and physically-based, more computationally intensive Monte Carlo models. The Dual-Pearson approach has been highly successful in the semi-empirical model development, because of its ability to account so well for the dependence of both the randomly scattered and the channeled parts of the implanted profile on all of the key implant parameters. The physically-based Monte Carlo models provide the theoretical foundation required for technology development and process control, and they serve as the basis for much of the computationally-efficient semi-empirical models. Depth profile models for B, BF 2 , and As implants into single-crystal silicon, and a depth profile model for B implants through oxide layers into single-crystal Si have been developed. An accurate Monte Carlo simulator for boron implants into single-crystal Si or through oxide layers into single-crystal Si has also been developed. This simulator includes dependences on implant beam divergence, wafer temperature, and it has a new local-electron electronic stopping power model with explicit dependence on the local electron density in the Si lattice. In addition, we have developed a cumulative damage model for predicting the dose dependence and the resulting interstitial and vacancy distributions. We have also developed Monte Carlo simulators for BF 2 and As implants into single-crystal Si. The semi-empirical and physically-based models have been applied to develop a 2-dimensional model for boron implants through oxide layers into single-crystal Si. This computationally-efficient model has explicit dependence on energy, oxide thickness, dose, tilt angle, rotation angle, mask thickness, and mask edge orientation.

THE EFFECT OF DOSE RATE ON ION IMPLANTED IMPURITY PROFILES IN SILICON

Abstract In this paper is reported a systematic study of the effect of dose rate (ion beam current) on ion implanted impurity profiles in single-crystal silicon. A close examination of the effect of dose rate on as-implanted profiles reveals that for both boron and arsenic implantation, for beam currents ranging from 0.4 mA to 12 mA, dose rate has a small but clearly observable effect on channeling tails with higher beam currents producing shallower profiles. The effect is greater for on-axis (0° tilt/0° rotation) implants than for off-axis (8–9° tilt/30° rotation) implants. Lower mass (boron) implants have a more significant dose rate effect than do higher mass (arsenic) implants.

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.

Improved efficiency in Monte Carlo simulation of ion implanted impurity profiles in single-crystal materials

Abstract In this paper is reported a new approach with greatly improved efficiency for the Monte Carlo simulation of implanted profiles in single-crystal materials. This approach has been successfully implemented in the UT Monte Carlo code (UT-MARLOWE). A time savings of over 200 × has been observed with a 4-stage simulation yielding a statistically significant distribution over a dynamic range of three orders of magnitude. A simulation of arsenic implants with 15 keV implant energy typically takes approximately 12 minutes on a workstation.

Development and demonstration of a two-dimensional, accurate and computationally-efficient model for boron implantation into single-crystal silicon through overlying oxide layers

A 2-D model for boron implantation into (100) silicon through overlying oxide layers has been developed and implemented into the process simulator FLOOPS. This model is both accurate and computationally efficient and shows explicit dependencies on all of the key implant parameters: energy, dose, tilt and rotation angles, oxide layer thickness, mask height, mask edge orientation, and rotation of the wafer during implantation.

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.

A two-dimensional B implantation model for semiconductor process simulation environments

Abstract A computationally efficient semi-empirical model has been developed for modeling two-dimensional distributions of boron implanted into single-crystal silicon. This model accurately and efficiently models the depth profiles and lateral doping profiles under a masking edge for implantations as a function of dose, tilt angle, rotation angle, orientation of the masking edge, and masking layer thickness, in addition to energy. This new two-dimensional model is based on the dual-Pearson model [A.F. Tasch et al., J. Electrochem. Soc. 136 (1989) 810] for one-dimensional dopant depth distributions, which provides an accurate method of modeling the depth profile based on approximately 1000 SIMS profiles, and the UT-MARLOWE Monte Carlo ion implantation simulation code [K.M. Klein et al., IEEE Trans. Electron Devices ED-39 (1992) 1614], which provides well-modeled lateral dopant profiles. Combining depth profile and lateral profile information from these two models allows this new model to be both accurate and computationally efficient, making it suitable for use in semiconductor process modeling codes.

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.