Changhae Park

An improved approach to accurately model shallow B and BF2 implants in silicon

In this paper, an improved modeling approach is described for simulating as-implanted boron impurity profiles for B + and BF2 ~ implants into single*crystal silicon. This method uses the sum of two Pearson distribution functions to account for the nonchanneling and channeling components of the implant distribution. The ratio of the two Pearson functions varies with dose, which accounts for the change in the degree of channeling with dose. This modeling approach has been compared with experimentally measured SIMS profiles for a wide range of energies and doses for shallow B § and BF2 § implants. The excellent agreement indicates that this method offers a large improvement in simulation capability for B § and BF2 § implants. In addition, this method should be applicable to accurately model other impurities which have channeling tendencies.

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.

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.

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.

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.

Accurate profile simulation parameters in BF/sub 2/ implants in pre-amorphized silicon

For the formation of shallow p/sup +/-n source-drain junctions for submicrometer CMOS technologies without the undesired channeling effects associated with B/sup +/ or BF/sub 2//sup +/ ion implantation, the surface region of the silicon wafer is preamorphized by a silicon or germanium implant. The parameters that allow accurate simulation of as-implanted boron profiles in the preamorphized silicon obtained by BF/sub 2//sup +/ implants are given. Parameters which allow simulation using either a Gaussian distribution function or a Pearson distribution function, the latter giving a slight improvement in accuracy, are provided. The energy range covered by these parameters is 15-80 keV, which results in as-implanted junction depths of 800-1800 AA. >