Kevin M. Klein

Monte Carlo simulation of boron implantation into single-crystal silicon

An improved Monte Carlo simulation model has been developed for boron implantation into single-crystal silicon. This model is based on the Marlowe Monte Carlo code and contains significant improvements for the modeling of ion implantation, including a newly developed local electron concentration-dependent electronic stopping model and a newly developed cumulative damage model. These improvements allow the model to reliably predict boron implant profiles not only as a function of energy, but also as a function of other important implant parameters such as tilt angle, rotation angle, and dose. In addition, profiles of implant generated point defects (silicon interstitials and vacancies) can be calculated. >

Local electron concentration‐dependent electronic stopping power model for Monte Carlo simulation of low‐energy ion implantation in silicon

We have developed a new electronic (inelastic) stopping model for low‐energy implanted ions which explicitly accounts for the effect of the local variation of the electron density between the lattice atoms in the silicon crystal target material on the amount and rate of energy loss due to electronic processes. Designed for incorporation into Monte Carlo simulation codes, this model more accurately predicts the energy loss of ions due to electronic processes, and it provides significantly better agreement with experimental profiles of boron implanted into single‐crystal silicon over a wide range of energies and incident angles compared with the agreement obtained with other electronic stopping models.

Modeling of cumulative damage effects on ion-implantation profiles

Abstract Ion-implantation-induced damage in crystalline material can cause the shape of implanted impurity distributions to vary strongly with dose. We have developed a model which directly simulates the accumulation of this damage and the effect it has on the trajectories of subsequently implanted ions. Comparison with experimental profiles of boron implantation into single-crystal silicon indicates that this model accurately predicts the onset and effects of this cumulative damage. Additionally, distributions of the point defects formed during implantation which reflect the expected influence of varying implant energies, tilt and rotation angles, and doses are given by this model.

Efficient modeling parameter extraction for dual pearson approach to simulation of implanted impurity profiles in silicon

Abstract A semi-empirical approach for modeling of ion-implanted impurity distributions has an inherent advantage of high computational efficiency which is a vital issue for the simulation of a large number of processing steps required in the fabrication of high density integrated circuits with submicrometer feature sizes. The accuracy of this modeling technique has been substantially improved with the introduction of the dual Pearson modeling approach for simulation of implanted impurity distributions in single-crystal silicon so that the entire profile, including the broad channeling tail, is accurately predicted[1]. The dual Pearson modeling approach is based on the use of two Pearson functions describing two scattering mechanisms encountered in ion implantation into single-crystal silicon. Since semi-empirical approaches are based on experimental data, it is crucial to maintain a sizable data base of modeling parameters extracted from measured profiles in order to fully exploit the advantages of semi-empirical approaches. In this paper, a computer program which extracts all nine parameters for the dual Pearson modeling approach will be introduced. This program provides an easy and efficient way of extracting very accurate parameters in a two-step extraction process. The first step obtains a preliminary set of nine parameters which is then used as the initial condition for the second step in which the Levenberg-Marquardt algorithm is used to find the final set of accurate parameters. The incorporation of the first step for self-generation of the initial conditions makes the program easy to use, even for those with no previous experience with Pearson functions or the curve-fitting processes.

An accurate and efficient model for boron implants through thin oxide layers into single-crystal silicon

This paper presents a computationally efficient and accurate depth profile model for boron implants through a thin (0-50 nm) oxide layer into single-crystal silicon. This is the first reported model with explicit dependence on all of the key implant parameters, which include oxide thickness, implant energy, dose, tilt angle, and rotation angle. The detailed effects of thin oxide layers on the tilt and rotation angle, as well as the dose and energy dependencies of boron profiles, have been studied as the basis of the model. It is shown that this model is able to predict the profile dependencies very well, including subtle, unexpected behavior of the implanted profiles for certain implant conditions. The model has been implemented into SUPREM 3, SUPREM 4, and FLOOPS in order to demonstrate its capabilities. >

Channeling control for large tilt angle implantation in Si 〈100〉

Abstract This investigation will present measurements of silicon 〈100〉 wafers, implanted with tilt angles in the range 7–60°, which identify combinations of tilt and azimuthal (twist) angles that avoid major channeling zones. The orientations identified in this study minimize channeling effects even for very low dose implantation. A stereographic projection demonstrates that all major variations in observed channeling behavior are explained by channeling in the six major (low Miller index) crystallographic axes and planes. The implanted wafers were characterized using modulated reflectance and SIMS measurements. We investigated the relative severity of ion channeling in major poles and planes and the effect of energy and species variations on channeling behavior. The physical basis for the observed variations is explained by employing the concepts of critical channeling angles and average distance traveled within a channel.

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.

Boron implant profile variation across a single wafer due to electrostatic scanning

Abstract The implanted impurity profile variation across a wafer due to an electrostatic scanning system has been studied for boron implants into (100) silicon wafers. The variation of the actual tilt and rotation angles across a wafer has been precisely determined for the implanter used in this study. The sensitivity of the impurity profiles to this angular variation has been studied through both a theoretical prediction based on an improved calculation of critical angles for channeling, and a qualitative analysis using the thermal wave measurement technique. A quantitative study of the profile variation across a wafer has also been performed using extensive secondary ion mass spectrometry (SIMS) profile measurements. For the energy range (15–80 keV) and angle range (0–10° tilt angle, 0–360° rotation angle) used in this study, we have identified the ranges of tilt and rotation angles that should be used for minimum channeling and minimum profile variation.

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.