Hydrodynamic simulations for advanced SiGe HBTs

Abstract

The latest development of Silicon-Germanium (SiGe) HBTs has clearly demonstrated that the standard driftdiffusion model is not capable to predict the device performance. Thus more advanced simulation approaches are necessary such as simulators with hydrodynamic (HD) transport models. However, for realistic predictions, suitably calibrated models are required. In this paper, new accurate analytical models for the electron energy relaxation time and electron mobility are introduced that are suitable for implementation in HD TCAD simulators. These models are calibrated to simulation results obtained by the Boltzmann transport equation (BTE). Also a comparison with experimental data of an advanced SiGe HBT is given. I. INTRODUCTIONWith shrinking device dimensions and increasing operating frequencies, conventional simulation techniques such as the drift-diffusion (DD) model have started to loose their validity for predicting the electrical behavior of modern HBTs. For an improved description of carrier transport and the device performance, simulators solving the Boltzmann transport equation (BTE) or hydrodynamic (HD) models have been used. Concerning the accuracy, BTE solvers provide more physical insight into carrier transport because they offer a detailed description of band structure effects and scattering. The standard technique for solving the BTE is the MonteCarlo (MC) method, which is attractive due to the relatively small implementation effort. However, the major drawbacks of the MC method are the large simulation times and the noisy results especially for minority carriers.As a compromise HD models have been widely-used, which are derived by moment expansions and simplifications of the BTE. These models are very attractive concerning the simulation time but their accuracy w.r.t. the solution of the BTE strongly depends on the chosen HD formulation and material models, e.g. carrier mobilities. In order to retain the advantages of the HD approach, accurately calibrated HD models are inevitable.In section II of this paper the HD model will be shortly reviewed. In section III an adjustment strategy w.r.t. BTE results is introduced. In addition, a new electron energy relaxation time model and extensions of the Caughey-Thomas [1] mobility model for electrons is given. Section IV contains a comparison of HD simulation results with experimental data.

Characterization and TCAD Modeling of Mixed-Mode Stress Induced by Impact Ionization in Scaled SiGe HBTs

“…The doping profile in the collector/sub-collector and, in general, the overall doping profile is in agreement with that suggested by a TCAD-based roadmap for SiGe HBT devices developed in the DOTSEVEN project [1]. Hydrodynamic simulations were carried out to correctly reproduce the currents in all regimes of operation [12]. The lattice, electron, and hole temperatures are self-consistently calculated in TCAD, which accounts for the effects of self-heating.…”

“…The lattice, electron, and hole temperatures are self-consistently calculated in TCAD, which accounts for the effects of self-heating. Models for carriers' recombination (and doping-dependent Shockley-Read-Hall), II (Okuto model), and field-, material-, and doping-dependent mobility [12]- [14] were also included. Calibrating such models for SiGe required only a slight tuning of few parameters in agreement with earlier literature reports [8], [14].…”

TCAD Calibration of High-Speed Si/SiGe HBTs in 55-nm BiCMOS

“…-Hydro Dynamic (HD) parameters [6] -Bandgap (BG) of SiGe structure [12] and bandgap narrowing (BGN) [13] -Energy and relaxation time, mobility [8] -Intrinsic carrier saturation velocity [7] -Default Shockley-Read-Hall (SRH), surface SRH and Auger recombination models from Synopsys TCAD [14] These physical models are fed into Sdevice simulation to investigate the possibility of TCAD calibration in 55-nm Si/SiGe BiCMOS. The limitation of current models is thoroughly discussed as well.…”

“…The critical fabrication process steps including the SiGe:C epitaxy growth and in-situ As doped emitter are calibrated in TCAD simulation to match vertical profiles with those obtained from secondary ion mass spectrometry (SIMS) (for As, Ge and B) and energy-dispersive X-ray spectroscopy (EDX) (for As and Ge) measurements. Moreover, the feasibility of capturing accurately electrical performance by physical models calibrated in previous studies [6][7][8] is systematically evaluated in the paper. The first part of the paper presents the calibration of the fabrication process with focus on both the 1D-doping vertical profiles and polysilicon / silicon base link.…”