Impact of self-heating on the statistical variability in bulk and SOI FinFETs

In this paper for the first time we study the impact of self-heating on the statistical variability of bulk and SOI FinFETs designed to meet the requirements of the 14/16nm technology node. The simulations are performed using the GSS ‘atomistic’ simulator GARAND using an enhanced electro-thermal model that takes into account the impact of the fin geometry on the thermal conductivity. In the simulations we have compared the statistical variability obtained from full-scale electro-thermal simulations with the variability at uniform room temperature and at the maximum or average temperatures obtained in the electro-thermal simulations. The combined effects of line edge roughness and metal gate granularity are taken into account. The distributions and the correlations between key figures of merit including the threshold voltage, on-current, subthreshold slope and leakage current are presented and analysed

Characterisation of thermal and coupling effects in advanced silicon MOSFETs

PhD ThesisNew approaches to metal-oxide-semiconductor field effect transistor (MOSFET) engineering emerge in order to keep up with the electronics market demands. Two main candidates for the next few generations of Moore’s law are planar ultra-thin body and buried oxide (UTBB) devices and three-dimensional FinFETs. Due to miniature dimensions and new materials with low thermal conductivity, performance of advanced MOSFETs is affected by self-heating and substrate effects. Self-heating results in an increase of the device temperature which causes mobility reduction, compromised reliability and signal delays. The substrate effect is a parasitic source and drain coupling which leads to frequency-dependent analogue behaviour. Both effects manifest themselves in the output conductance variation with frequency and impact analogue as well as digital performance. In this thesis self-heating and substrate effects in FinFETs and UTBB devices are characterised, discussed and compared. The results are used to identify trade-offs in device performance, geometry and thermal properties. Methods how to optimise the device geometry or biasing conditions in order to minimise the parasitic effects are suggested. To identify the most suitable technique for self-heating characterisation in advanced semiconductor devices, different methods of thermal characterisation (time and frequency domain) were experimentally compared and evaluated alongside an analytical model. RF and two different pulsed I-V techniques were initially applied to partially depleted silicon-on-insulator (PDSOI) devices. The pulsed I-V hot chuck method showed good agreement with the RF technique in the PDSOI devices. However, subsequent analysis demonstrated that for more advanced technologies the time domain methods can underestimate self-heating. This is due to the reduction of the thermal time constants into the nanosecond range and limitations of the pulsed I-V set-up. The reduction is related to the major increase of the surface to volume ratio in advanced MOSFETs. Consequently the work showed that the thermal properties of advanced semiconductor devices must be characterised within the frequency domain. For UTBB devices with 7-8 nm Si body and 10 nm ultra-thin buried oxide (BOX) the analogue performance degradation caused by the substrate effects can be stronger than the analogue performance degradation caused by self-heating. However, the substrate effects can be effectively reduced if the substrate doping beneath the buried ii oxide is adjusted using a ground plane. In the MHz – GHz frequency range the intrinsic voltage gain variation is reduced ~6 times when a device is biased in saturation if a ground plane is implemented compared with a device without a ground plane. UTBB devices with 25 nm BOX were compared with UTBB devices with 10 nm BOX. It was found that the buried oxide thinning from 25 nm to 10 nm is not critical from the thermal point of view as other heat evacuation paths (e.g. source and drain) start to play a role. Thermal and substrate effects in FinFETs were also analysed. It was experimentally shown that FinFET thermal properties depend on the device geometry. The thermal resistance of FinFETs strongly varies with the fin width and number of parallel fins, whereas the fin spacing is less critical. The results suggest that there are trade-offs between thermal properties and integration density, electrostatic control and design complexity, since these aspects depend on device geometry. The high frequency substrate effects were found to be effectively reduced in devices with sub-100 nm wide fins.Engineering and Physical Sciences Research Council (EPSRC) and EU fundin

5nm 이하 3D Transistors의 Self-Heating 및 전열특성분석 연구

학위논문(박사) -- 서울대학교대학원 : 공과대학 전기·컴퓨터공학부, 2021.8. 신형철.In this thesis, Self-Heating Effect (SHE) is investigated using TCAD simulations in various Sub-10-nm node Field Effect Transistor (FET). As the node decreases, logic devices have evolved into 3D MOSFET structures from Fin-FET to Nanosheet-FET. In the case of 3D MOSFET, there are thermal reliability issues due to the following reasons: ⅰ) The power density of the channel is high, ⅱ) The channel structure surrounded by SiO2, ⅲ) The overall low thermal conductivity characteristics due to scaling down. Many papers introduce the analysis and prediction of temperature rise by SHE in the device, but there are no papers presenting the content of mitigation of temperature rise. Therefore, we have studied the methods of decreasing the maximum lattice temperature (TL,max) such as shallow trench isolation (STI) composition engineering in Fin-FET, thermal analysis according to DC/AC/duty cycle in nanowire-FET, and active region ( e.g., gate metal thickness, channel width, channel number etc..) optimization in nanosheet-FET. In addition, lifetime affected by hot carrier injection (HCI) / bias-temperature instability (BTI) is also analyzed according to various thermal relaxation methods presented.이 논문에서는 다양한 Sub-10nm 노드 전계 효과 트랜지스터 (FET)에서 TCAD 시뮬레이션을 사용하여 자체 발열 효과 (SHE)를 조사합니다. 노드가 감소함에 따라 논리 장치는 Fin-FET에서 Nanosheet-FET로 3D MOSFET 구조로 진화했습니다. 3D MOSFET의 경우 ⅰ) 채널의 전력 밀도가 높음, ⅱ) SiO2로 둘러싸인 채널 구조, ⅲ) 축소로 인해 전체적으로 낮은 열전도 특성 등 다음과 같은 이유로 열 신뢰성 문제가 있습니다. 한편, 많은 논문이 device에서 SHE에 의한 온도 상승의 분석 및 예측을 소개하지만 온도 상승 완화의 내용을 제시하는 논문은 거의 없습니다. 따라서 Fin-FET의 STI (Shallow Trench Isolation) 구성 공학, nanowire-FET의 DC / AC / 듀티 사이클에 따른 열 분석, nanosheet-FET에서 소자의 중요영역(예: 게이트 금속 두께, 채널 폭, 채널 번호 등)의 최적화를 통해서 최대 격자 온도 (TL,max)를 낮추는 방법등을 연구했습니다. 또한 더 나아가서 HCI (Hot Carrier Injection) / BTI (Bias-Temperature Instability)의 영향을 받는 수명도 제시된 다양한 열 완화 방법에 따라 분석하여 소자의 제작에 있어 열적 특성과 수명을 좋게 만드는 지표를 제시합니다 .Chapter 1 Introduction 1 1.1. Development of Semconductor structure 1 1.2. Self-Heating Effect issues in semiconductor devices 3 Chapter 2 Thermal-Aware Shallow Trench Isolation Design Optimization for Minimizing Ioff in Various Sub-10-nm 3-D Transistor 7 2.1. Introduction 7 2.2. Device Structure and Simulation Condition 7 2.3. Results and Discussion 12 2.4. Summary 27 Chapter 3 Analysis of Self Heating Effect in DC/AC Mode in Multi-channel GAA-Field Effect Transistor 32 3.1. Introduction 32 3.2. Multi-Channel Nanowire FET and Back End Of Line 33 3.3. Work Flow and Calibration Process 35 3.4. More Detailed Thermal Simulation of Nanowire-FET 37 3.5. Performance Analysis by Number of Channels 38 3.6. DC Characteristic of SHE in Nanowire-FETs 40 3.7. AC Characteristics of SHE in Nanowire-FETs 43 3.8. Summary 51 Chapter 4 Self-Heating and Electrothermal Properties of Advanced Sub-5-nm node Nanoplate FET 56 4.1. Introduction 56 4.2. Device Structure and Simulation Condition 57 4.3. Thermal characteristics by channel number and width 62 4.4. Thermal characteristics by inter layer-metal thickness (TM) 64 4.5. Life Time Prediction 65 4.6. Summary 67 Chapter 5 Study on Self Heating Effect and life time in Vertical-channel Field Effect Transistor 72 5.1. Introduction 72 5.2. Device Structure and Simulation Condition 72 5.3. Temperature and RTH according to channel width(TW) 76 5.4. Thermal properties according to air spacers and air gap 77 5.5. Ion boosting according to Channel numbers 81 5.6. Temperature imbalance of multi-channel VFETs 82 5.7. Mitigation of the channel temperature imbalance 86 5.8. Life time depending on various analysis conditions 88 5.9. Summary 89 Chapter 6 Conclusions 93 Appendix A. A Simple and Accurate Modeling Method of Channel Thermal Noise Using BSIM4 Noise Models 95 A.1. Introduction 95 A.2. Overall Schematic of the RF MOSFET Model 97 A.3. Verification of the DC Characteristics of the RF MOSFET Model 98 A.4. Verification of the MOSFET Model with Measured Y-parameters 100 A.5. Verification of the MOSFET Model with Measured Noise Parameters 101 A.6. Thermal Noise Extraction and Modeling (TNOIMOD = 0) 103 A.7. Verification of the Enhanced Model with Noise Parameters 112 A.8. Holistic Model (TNOIMOD = 1) 114 A.9. Evaluation the validity of the model for drain bias 115 A.10. Conclusion 117 Abstract in Korean 122박

Benchmarking the screen-grid field effect transistor (SGrFET) for digital applications

Continuous scaling of CMOS technology has now reached a state of evolution, therefore, novel device structures and new materials have been proposed for this purpose. The Screen- Grid field Effect Transistor is introduced as a as a novel device structure that takes advantage of several innovative aspects of the FinFET while introducing new geometrical feature to improve a FET device performance. The idea is to design a FET which is as small as possible without down-scaling issues, at the same time satisfying optimum device performance for both analogue and digital applications. The analogue operation of the SGrFET shows some promising results which make it interesting to continue the investigation on SGrFET for digital applications. The SGrFET addresses some of the concerns of scaled CMOS such as Drain Induce Barrier Lowering and sub-threshold slope, by offering the superior short channel control. In this work in order to evaluate SGrFET performance, the proposed device compared to the classical MOSFET and provides comprehensive benchmarking with finFETs. Both AC and DC simulations are presented using TaurusTM and MediciTM simulators which are commercially available via Synopsis. Initial investigation on the novel device with the single gate structure is carried out. The multi-geometrical characteristic of the proposed device is used to reduce parasitic capacitance and increase ION/IOFF ratio to improve device performance in terms of switching characteristic in different circuit structures. Using TaurusTM AC simulation, a small signal circuit is introduced for SGrFET and evaluated using both extracted small signal elements from TaurusTM and Y-parameter extraction. The SGrFET allows for the unique behavioural characteristics of an independent-gate device. Different configurations of double-gate device are introduced and benchmark against the finFET serving as a double gate device. Five different logic circuits, the complementary and N-inverter, the NOR, NAND and XOR, and controllable Current Mirror circuits are simulated with finFET and SGrFET and their performance compared. Some digital key merits are extracted for both finFET and SGrFET such as power dissipation, noise margin and switching speed to compare the devices under the investigation performance against each other. It is shown that using multi-geometrical feature in SGrFET together with its multi-gate operation can greatly decrease the number of device needed for the logic function without speed degradation and it can be used as a potential candidate in mix-circuit configuration as a multi-gate device. The initial fabrication steps of the novel device explained together with some in-house fabrication process using E-Beam lithography. The fabricated SGrFET is characterised via electrical measurements and used in a circuit configuration

Temperature-dependent thermal capacitance characterization for SOI-MOSFETs

Thermal capacitances are required to describe the fast dynamic thermal behavior in the silicon-on-insulator (SOI) devices. This article presents a physical model based on the ac technique, together with the characteristic thermal frequency determination through the frequency response of the output conductance, for calculating the thermal capacitance of single-finger and multi-finger SOI-MOSFETs. The model accounts for the total gate width and substrate temperature, making evident the augmented thermal coupling when multi-fingers are used. The thermal capacitances and the corresponding time constants, extracted from a variety of gate widths and number of fingers, are correctly predicted up to a substrate temperature of 150 °C.This work was supported by the Spanish MEC under Project GREENSENSE−TEC2015-67883-R and RTI2018-096019-B-C3

Variability analysis of FinFET AC/RF performances through efficient physics-based simulations for the optimization of RF CMOS stages

A nearly insatiable appetite for the latest electronic device enables the electronic technology sector to maintain research momentum. The necessity for advancement with miniaturization of electronic devices is the need of the day. Aggressive downscaling of electronic devices face some fundamental limits and thus, buoy up the change in device geometry. MOSFETs have been the leading contender in the electronics industry for years, but the dire need for miniaturization is forcing MOSFET to be scaled to nano-scale and in sub-50 nm scale. Short channel effects (SCE) become dominant and adversely affect the performance of the MOSFET. So, the need for a novel structure was felt to suppress SCE to an acceptable level. Among the proposed devices, FinFETs (Fin Field Effect Transistors) were found to be most effective to counter-act SCE in electronic devices. Today, many industries are working on electronic circuits with FinFETs as their primary element.One of limitation which FinFET faces is device variability. The purpose of this work was to study the effect that different sources of parameter fluctuations have on the behavior and characteristics of FinFETs. With deep literature review, we have gained insight into key sources of variability. Different sources of variations, like random dopant fluctuation, line edge roughness, fin variations, workfunction variations, oxide thickness variation, and source/drain doping variations, were studied and their impact on the performance of the device was studied as well. The adverse effect of these variations fosters the great amount of research towards variability modeling. A proper modeling of these variations is required to address the device performance metric before the fabrication of any new generation of the device on the commercial scale. The conventional methods to address the characteristics of a device under variability are Monte-Carlo-like techniques. In Monte Carlo analysis, all process parameters can be varied individually or simultaneously in a more realistic approach. The Monte Carlo algorithm takes a random value within the range of each process parameter and performs circuit simulations repeatedly. The statistical characteristics are estimated from the responses. This technique is accurate but requires high computational resources and time. Thus, efforts are being put by different research groups to find alternative tools. If the variations are small, Green’s Function (GF) approach can be seen as a breakthrough methodology. One of the most open research fields regards "Variability of FinFET AC performances". One reason for the limited AC variability investigations is the lack of commercially available efficient simulation tools, especially those based on accurate physics-based analysis: in fact, the only way to perform AC variability analysis through commercial TCAD tools like Synopsys Sentaurus is through the so-called Monte Carlo approach, that when variations are deterministic, is more properly referred to as incremental analysis, i.e., repeated solutions of the device model with varying physical parameters. For each selected parameter, the model must be solved first in DC operating condition (working point, WP) and then linearized around the WP, hence increasing severely the simulation time. In this work, instead, we used GF approach, using our in-house Simulator "POLITO", to perform AC variability analysis, provided that variations are small, alleviating the requirement of double linearization and reducing the simulation time significantly with a slight trade-off in accuracy. Using this tool we have, for the first time addressed the dependency of FinFET AC parameters on the most relevant process variations, opening the way to its application to RF circuits. This work is ultimately dedicated to the successful implementation of RF stages in commercial applications by incorporating variability effects and controlling the degradation of AC parameters due to variability. We exploited the POLITO (in-house simulator) limited to 2D structures, but this work can be extended to the variability analysis of 3D FinFET structure. Also variability analysis of III-V Group structures can be addressed. There is also potentiality to carry out the sensitivity analysis for the other source of variations, e.g., thermal variations

Strain-Engineered MOSFETs

This book brings together new developments in the area of strain-engineered MOSFETs using high-mibility substrates such as SIGe, strained-Si, germanium-on-insulator and III-V semiconductors into a single text which will cover the materials aspects, principles, and design of advanced devices, their fabrication and applications. The book presents a full TCAD methodology for strain-engineering in Si CMOS technology involving data flow from process simulation to systematic process variability simulation and generation of SPICE process compact models for manufacturing for yield optimization

Compact modeling of the rf and noise behavior of multiple-gate mosfets

La reducción de la tecnología MOSFET planar ha sido la opción tecnológica dominante en las últimas décadas. Sin embargo, hemos llegado a un punto en el que los materiales y problemas en los dispositivos surgen, abriendo la puerta para estructuras alternativas de los dispositivos. Entre estas estructuras se encuentran los dispositivos DG, SGT y Triple-Gate. Estas tres estructuras están estudiadas en esta tesis, en el contexto de rducir las dimensiones de los dispositivos a tamaños tales que los mecanismos cuánticos y efectos de calan coro deben tenerse n cuenta. Estos efectos vienen con una seria de desafíos desde el pun to de vista de modelación, unos de los más grandes siendo el tiempo y los recursos comprometidos para ejecutar las simulaciones. para resolver este problema, esta tesis propone modelos comlets analíticos y compactos para cada una de las geometrías, validos desde DC hasta el modo de operación en Rf para los nodos tecnológicos futuros. Dichos modelos se han extendido para analizar el ruido de alta frecuencia en estos diapositivos