This paper investigates the subthreshold behavior of Fin Field Effect Transistor (FINFET) by solving 3D Laplace, and Poisson equations. Based on the potential distribution inside the fin, the appropriate band bending and the change in the band bending (∂ψs) were calculated. Three-dimensional analysis of (∂ψs) the change in the band bending indicates that (∂ψs)is less (by ~ 20% for a channel width (Tfin) of 20 nm) in the middle of the channel compared to that at the Si-SiO2 interface. The decrease in (∂ψs) towards the middle of the channel indicates that the control of the gate decreases towards the middle of the channel. Simulation results show that the S-factor of the device increases as Tfin increases. It is observed that the S-factors calculated from the Laplace and the Poisson equations differ by ~7% for a device with a Tfin = 50 nm. However this difference in S-factor gradually decreases and for smaller channel width devices, the S-factors calculated using Laplace and Poisson equations are the same. A comparison of S-factors obtained from Laplace and Poisson equation shows that the S-factor obtained from Poisson equation agrees very well with the reported experimental results. Thus, the systemic study of subthreshold behavior of FinFET shows that it is most appropriate to determine the S-factor of wider channel devices by solving 3D Poisson equation with appropriate doping concentration.
KEYWORDS: Instrument modeling, Data modeling, Transistors, Computer aided design, Solid modeling, Device simulation, Process modeling, System on a chip, Calibration, Measurement devices
In this paper, we present a systematic methodology to extract two-transistor split-gate flash memory cell model for an accurate DC simulation of SoC designs. Since measured device characteristics require re-design of test-structures with FG contacts, we have used a technology CAD (TCAD) based methodology to develop 2T-cell models for sub-0.18 μm split gate flash memory cells.
In this paper systematic simulation-based methodologies for integrated circuit (IC) manufacturing technology development and technology transfer are presented. In technology development, technology computer-aided design (TCAD) tools are used to optimize the device and process parameters to develop a new generation of IC manufacturing technology by reverse engineering from the target product specifications. While in technology transfer to manufacturing co-location, TCAD is used for process centering with respect to high-volume manufacturing equipment of the target manufacturing equipment of the target manufacturing facility. A quantitative model is developed to demonstrate the potential benefits of the simulation-based methodology in reducing the cycle time and cost of typical technology development and technology transfer projects over the traditional practices. The strategy for predictive simulation to improve the effectiveness of a TCAD-based project, is also discussed.
This paper presents a systematic simulation-based study on the design, performance, and scaling issues of sub-20 nm silicon nanotransistors. 3D-process simulation was used to generate silicon FinFET device structures with fin thickness (Tfin) of 10 to 30 nm, fin height (Hfin) of 50 nm, channel length (Lg) of 10 to 50-nm, and gate oxide thickness (Tox(eff)) of 1.5 nm. 3D-device simulation results show that for n-channel FinFETs with Hfin = 50 nm, threshold voltage (Vth) decreases as Lg decreases and Vth roll-of with decreasing Lg is higher for thicker Tfin devices. The simulated drive current (IDSAT) decreases as Tfin decreases for Lg≤ 25 nm while IDSAT increases as Tfin decreases for Lg ≥ 25 nm. It is, also, found that for the devices with Hfin = 50 nm, the simulated subthreshold swing (S) increases as Lg decreases for all devices with 10 nm ≤ Tfin ≤ 30 nm and approaches to 60 mV/decade for Lg≥ 40 nm. Also, S decreases as Tfin decreases for Lg< 40 nm devices. The simulated data for 20 nm nFinFETs with Hfin = 50 nm, Tfin = 10 nm, and TOX(eff) = 1.5 nm show an excellent device performance with Vth ≡ 0.13 V, IDSAT ≡ 775 μA/μm, Ioff ≡ 3 μA/μm, and S ≡ 83 mV/decade. Finally the simulation results for 20 nm nFinFETs and the conventional nMOSFETs were compared. This study, clearly, demonstrates a superior performance and scalability of FinFETs down to near 10 nm regime.
A systematic simulation-based study on scaling gate oxide thickness and the source-drain extension junction dept of r25 nm MOSFET devices is presented. The target 25 nm MOSFETs were obtained from CMOS technologies with gate lengths 40, 50, and 60 nm and the corresponding source-drain extension junction depths of 14, 20, and 26 nm respectively. Each technology was separately optimized for each value of equivalent gate oxide thickness 1, 1.5 and 2 nm to achieve off-state leakage current <EQ 10 nA/micrometers for 25 nm devices. The simulate device characteristics show that for a target value of off-state leakage current, the magnitude of threshold voltage, sub-threshold slope, and the drain-induced barrier lowering increases while the magnitude of drive current decrease with the increase of gate oxide thickness. On the other hand, the variation in the magnitude of threshold voltage, sub-threshold slope, drain-induced barrier lowering, and the drive current for the similar devices is insignificant within the range of source-drain extension junction depth, 14-26 nm, used in this study. It is also found that the gate delay for 25 nm devices increases significantly with the increase of source- drain extension junction depth. This study shows that the requirements for scaling gate oxide thickness and the source- drain extension junction depth for high performance 25 nm MOSFETs are <EQ 1.5 nm and 15 nm respectively.
Control of boron penetration in surface-channel PMOS devices is critical in order to ensure tight threshold voltage (Vt) distribution. Previous work has focused on studying relatively gross boron-penetration effects, which give rise to large shifts in Vt. In practice, low-voltage CMOS technologies are sensitive to small degradation in PMOS Vt scatter due to the onset of boron penetration. Moreover, the use of rapid thermal annealing can give rise to difficult trade-offs between poly depletion and boron penetration. As both of these effects can influence the PMOS Vt we propose a sensitive, systematic, methodology to distinguish between depletion and penetration effects and illustrate its application in a number of advanced CMOS processes, with oxide thickness ranging from 30-50 angstrom.
This paper presents a simple methodology to estimate the impact of inversion layer quantization and polysilicon-gate depletion effects on ultra-thin silicon-dioxide gate dielectric. We have used process and device simulation to determine the physical oxide thickness from the measured capacitance data, and the corresponding effective gate oxide thickness at inversion was computed from the simulation data obtained with an without the quantum mechanical and polysilicon depletion effects. The simulation result indicate that the effective gate oxide thickness is significantly higher than the physically grown oxide thickness due to inversion layer quantization and polysilicon depletion effects. The increase in oxide thickness is strongly dependent on the supply voltage and is more than 0.6 nm at 1 V. We have also measured the gate- leakage current for the same devices with gate oxide thickness less than 3 nm. Our data also show that in order to maintain a leakage current >= 1 A/cm2 for 1 V operation, the effective gate oxide thickness must be >= 2.2 nm.
This paper presents a systematic methodology to optimize the source-drain region of sub-100 nm MOSFET devices to design a high performance CMOS technology. The effect of most critical source-drain parameters such as the lateral and the vertical dimensions of shallow extensions, the junction depth of deep regions, and the strength and confinement of halo profiles on device performance are presented. The simulation results show that the shallower and the longer source=-drain extensions cause a significant degradation in drive current due to an increase in the source-drain series resistance while the deeper and the shorter extensions worsen the short-channel effect due to higher channel charge sharing with the source-drain regions. Similarly, the shallower deep source-drain regions cause performance degradation due to higher source-drain series resistance and deeper junctions cause higher channel charge sharing resulting in a higher short-channel effect. It is shown that the junction depth of shallow source-drain regions must be approximately 30-40 nm to design high performance sub-100 nm MOSFETs, and the short channel effect can be improved by a proper optimization of halo doping profiles around the source-drain extensions. The simulation results also show that the concentration and distribution of halo doping profiles must be optimized to obtain the target off-state leakage current for sub-100 nm CMOS technologies.
An integrated shallow trench isolation process utilizing HDP (High Density Plasma) oxide and a highly manufacturable corner oxidation is described. The choice of trench corner oxidation temperature is shown to be critical in reducing silicon stress, and hence junction leakage, to the levels required by multi-million gate designs. This STI process is shown to be extremely robust and manufacturable. Optimal design of the trench depth and well profiles is shown to provide well-edge isolation adequate for sub-0.18 micrometer technologies.
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