Michael P. Masquelier

Ab initio modeling of boron clustering in silicon

We present results of ab initio calculations for the structure and energetics of boron-interstitial clusters in Si and a respective continuum model for the nucleation, growth, and dissolution of such clusters. The structure of the clusters and their possible relationship to boron precipitates and interstitial-cluster formation are discussed. We find that neither the local-density approximation nor the generalized-gradient approximation to the density-functional theory result in energetics that predict annealing and activation experiments perfectly well. However, gentle refitting of the numbers results in a model with good predictive qualities.

First-principles study of phosphorus diffusion in silicon: Interstitial- and vacancy-mediated diffusion mechanisms

A vacancy-mediated diffusion mechanism has been assumed in traditional models of P diffusion in Si. However, recent experiments have suggested that for intrinsic P diffusion in Si, the interstitial-assisted diffusion mechanism dominates. Here, we describe first-principles calculations of P diffusion in Si performed to study interstitial- and vacancy-mediated diffusion mechanisms. Special care is taken with regard to structural minimization, charge state effects and corrections. We calculated the defect formation energies and migration barriers for the various competing P–interstitial diffusion mechanisms, as well as P–vacancy diffusion energetics in different charge states. For P–interstitial diffusion, we find overall diffusion activation energies of 3.1–3.5 eV for neutral and +1 charge states, in close agreement with experiments at intrinsic conditions. For P–vacancy diffusion, our calculation is in agreement with previous calculations in the neutral case, but suggests that only P+V= plays a role in the...

Multiscale modeling of stress-mediated diffusion in silicon: Ab initio to continuum

In this letter, we present the development of a complete methodology to simulate the effects of general anisotropic nonuniform stress on dopant diffusion in silicon. The macroscopic diffusion equation is derived from microscopic transition-state theory; the microscopic parameters are calculated from first principles; a feature-scale stress-prediction methodology based on stress measurements in the relevant materials as a function of temperature has been developed. The developed methodology, implemented in a continuum solver, is used to investigate a TiN metal gate system. A compressive stress field is predicted in the substrate, resulting in an enhancement in lateral boron diffusion. This enhancement, which our model attributes mostly to solubility effects, is in good agreement with experiment.

Ab initio modeling study of boron diffusion in silicon

Abstract We present investigations of boron diffusion in crystalline silicon using ab initio calculations (W. Windl et al., Phys. Rev. Lett. 83 (1999) 4345). Based on these results, a new mechanism for B diffusion mediated by Si self-interstitials was proposed. Rather than kick-out of B into a mobile channel-interstitial, one- or two-step diffusion mechanisms have been found for the different charge states. The predicted activation energy of 3.5–3.8 eV, migration barrier of 0.4–0.7 eV, and diffusion-length exponent of −0.6 to −0.2 eV are in excellent agreement with experiment. We also present results of ab initio calculations for the structure and energetics of boron-interstitial clusters in Si. We show how these first-principles results can be used to create a physical B diffusion model within a continuum simulator which has strongly enhanced predictive power in comparison to traditional diffusion models.

First-principles modeling of boron clustering in silicon

We present results of ab initio calculations for the structure and energetics of boron–interstitial clusters in Si and a respective continuum model for the nucleation, growth, and dissolution of such clusters. The structure of the clusters and their possible relationship to boron precipitates and interstitial-cluster formation are discussed. Our continuum model suggests that inclusion of the fractional activation of charged clusters into the overall carrier count can make a substantial differ

Ab-Initio Pseudopotential Calculations of Boron Diffusion in Silicon

In this work we investigate boron diffusion as a function of the Fermi-level position in crystalline silicon using ab-initio calculations and the nudged elastic band method to optimize diffusion paths. Based on our results, a new mechanism for B diffusion mediated by Si self-interstitials is proposed. We find a two-step diffusion process for all Fermi-level positions, which suggests a kick-out with a directly following kick-in process without extensive B diffusion on interstitial sites in-between. Our activation energy of 3.47 – 3.75 eV and diffusion-length exponent of -0.55 to -0.18 eV are in excellent agreement with experiment.

Method of internal overvoltage protection and current limit for a lateral PNP transistor formed by polysilicon self-aligned emitter and base, with extended collector

An internal overvoltage protection and current limiting function has been integrated into a self-aligned lateral PNP output device of a high-voltage BiCMOS process. The PNP is formed utilizing existing diffusions. Self-protection is achieved by integrating a JFET junction field effect transistor mechanism into the lateral PNP which interrupts base current at a predetermined collector-base voltage. The P field diffusion forms the extended collector, which acts as the gate of a JFET. The channel of the JFET, which is formed in the N-epitaxial layer, electrically connects the intrinsic base to the external base contact. This internal protection mechanism eliminates the need for external devices which provide the same function, but would add cost and unnecessary power dissipation. Devices which electrically exhibited the internal protection mechanism were simulated and fabricated.<<ETX>>