A Review on Dielectric Breakdown in Thin Dielectrics: Silicon Dioxide,High‐k,and Layered Dielectrics

Thin dielectric films are essential components of most micro‐ and nanoelectronic devices, and they have played a key role in the huge development that the semiconductor industry has experienced during the last 50 years. Guaranteeing the reliability of thin dielectric films has become more challenging, in light of strong demand from the market for improved performance in electronic devices. The degradation and breakdown of thin dielectrics under normal device operation has an enormous technological importance and thus it is widely investigated in traditional dielectrics (e.g., SiO₂, HfO₂, and Al₂O₃), and it should be further investigated in novel dielectric materials that might be used in future devices (e.g., layered dielectrics). Understanding not only the physical phenomena behind dielectric breakdown but also its statistics is crucial to ensure the reliability of modern and future electronic devices, and it can also be cleverly used for other applications, such as the fabrication of new‐concept resistive switching devices (e.g., nonvolatile memories and electronic synapses). Here, the fundamentals of the dielectric breakdown phenomenon in traditional and future thin dielectrics are revised. The physical phenomena that trigger the onset, structural damage, breakdown statistics, device reliability, technological implications, and perspectives are described.     

薄栅介质TDDB效应

在恒压和恒流应力条件下测试了超薄栅氧化层的击穿特性 ,研究了 TDDB(Tim e Dependent DielectricBreakdown)的可靠性表征方法 .对相关击穿电荷量 QBD进行了实验测试和分析 .结果表明 :相关击穿电荷量 QBD除了与氧化层质量有关外 ,还与应力电压和应力电流密度以及栅氧化层面积有关 .对相关系数进行了拟合 ,给出了 QBD的解析表达式 .按照上述表达式外推的结果和实验值取得了很好的一致 .提出了薄栅介质 TDDB效应的表征新方法     

Thin film dielectric materials for microelectronics

Important applications of dielectric films used in modern integrated circuit technology include dielectric insulation, surface passivation, diffusion masking, radiation resistance, and hermetic seal. These many functional applications pose stringent requirements on the various properties of the insulating films and the methods used for their preparation. To date silicon dioxide (SiO2) has been used almost exclusively because of 1) its ease of preparation, 2) its well-understood properties, and 3) its generally good compatibility and satisfactory interface with silicon. There are, however, drawbacks to the use of SiO2and other materials have been sought for better performance, greater versatility, higher reliability, and lower cost. These include binary metal oxides and silicon nitride. The state of the art of thin film dielectric materials for microelectronics is reviewed in this paper. The role of thin film dielectrics for devices is presented, and new and known materials are discussed for potential applications.     

ULSI低介电常数材料制备中的CVD技术

综述了制备ULSI低介电常数材料的各种CVD技术。详细介绍了PCVD技术淀积含氟氧化硅薄膜、含氟无定型碳膜与聚酰亚胺类薄膜的工艺,简要介绍了APCVD技术淀积聚对二甲苯类有机薄膜及RTCVD技术淀积SiOF薄膜的工艺。     

High-field breakdown in thin oxides grown in N2O ambient

A detailed study of time-dependent dielectric breakdown (TDDB) in N₂O-grown thin (47-120 Å) silicon oxides is reported. A significant degradation in breakdown properties was observed with increasing oxide growth temperatures. A physical model based on undulations at the Si/SiO₂ interface is proposed to account for the degradation. Accelerated breakdown for higher operating temperatures and higher oxide fields as well as thickness dependence of TDDB are studied under both polarities of injection. Breakdown under unipolar and bipolar stress in N₂O oxides is compared with DC breakdown. An asymmetric improvement in time-to-breakdown under positive versus negative gate unipolar stress is observed and attributed to charge detrapping behavior in N₂O oxides. A large reduction in time-to-breakdown is observed under bipolar stress when the thickness is scaled below 60 Å. A physical model is suggested to explain this behavior. Overall, N₂O oxides show improved breakdown properties compared with pure SiO₂     

薄栅介质层可靠性与陷阱统计分析

本文以高电场(＞11.8MV/cm)恒电流TDDB为手段研究了厚度为7.6、10.3、12.5、14.5nm薄氧化层的击穿统计特性.实验分析表明在加速失效实验中测量击穿电量Q_bd的同时,还可以测量击穿时的栅电压增量ΔV_bd.因为ΔV_bd的统计分布反映了栅介质层中带电陷阱的数量及其位置分布,可以表征栅介质层的质量和均匀性.此外由Q_bd和ΔV_bd能够较合理地计算临界陷阱密度N_bd.实验结果表明本征击穿时N_bd与测试条件无关而随工艺和介质层厚度变化.同样厚度时N_bd反映不同工艺生成的介质质量.陷阱生成的随机性使N_bd随栅介质厚度减小而下降.氧化层厚度约10nm时N_bd达到氧化层分子密度的1%发生击穿(10²⁰cm^-3).N_bd的物理意义清楚,不象Q_bd随测试应力条件变化,是薄栅介质层可靠性的较好的定量指标.     

Charge to breakdown mechanism of thin ONO films

Effects of charge trapping in the thin ONO (oxide silicon nitride oxide) film caused by the voltage stress on the time-dependent dielectric breakdown (TDDB) mechanism are studied. The purpose is to report the TDDB data of the films after various treatments of charge injection and thermal annealing together with analysis of the experimental data to enhance the understanding of the dielectric breakdown mechanisms of the ONO film. It is observed that the trapped charges injected from one electrode have very little effect on the TDDB mechanism during stress to the other electrode. This suggests that the position of trapped charges may be quite different for the two injecting electrodes and that breakdown mechanisms may be initiated from the different charge positions and sources     

Evaluation of thin oxides grown by the atomic oxygen afterglow method

This paper discusses the basic electrical properties of thin, less than 200 Å, films of silicon dioxide grown on silicon by a microwave plasma atomic oxygen afterglow method. This method of remote plasma oxidation of silicon allows gate oxides to be grown at temperatures as low as 400° C, and hence, is possibly attractive in VLSI/ULSI applications. Electrical properties of studied oxides depend strongly upon the composition of the discharge gas. The use of nitrogen as an oxygen diluent has an adverse impact on the fixed oxide charge density and dielectric strength. Superior oxide characteristics were obtained by adding hydrogen to the discharge gas particularly in the area of oxide breakdown statistics. Values of the intrinsic breakdown field in the range from 8 MV/ cm to 14 MV/cm were recorded in this case.     

Ultrathin gate oxide reliability: physical models, statistics, andcharacterization

The present understanding of wear-out and breakdown in ultrathin (t_ox < 5.0 nm) SiO₂ gate dielectric films and issues relating to reliability projection are reviewed in this article. Recent evidence supporting a voltage-driven model for defect generation and breakdown, where energetic tunneling electrons induce defect generation and breakdown will be discussed. The concept of a critical number of defects required to cause breakdown and percolation theory will be used to describe the observed statistical failure distributions for ultrathin gate dielectric breakdown. Recent observations of a voltage dependent voltage acceleration parameter and non-Arrhenius temperature dependence will be presented. The current understanding of soft breakdown will be discussed and proposed techniques for detecting breakdown presented. Finally, the implications of soft breakdown on circuit functionality and the applicability of applying current reliability characterization and analysis techniques to project the reliability of future alternative gate dielectrics will be discussed     

Thermal Nitridation of Si and SiO/sub 2/ for VLSI

This paper presents an extensive review of our work on thermal nitridation of Si and SiO/sub 2/. High-quality ultrathin films of silicon nitride and nitrided-oxide (nitroxide) have been thermally grown in ammonia atmosphere in a cold-wall RF-heated reactor and in a lamp-heated system. The growth kinetics and their dependence on processing time and temperature have been studied from very short to long nitridation times. The kinetics of thermal nitridation of SiO/sub 2/ in ammonia ambient have also been studied. In nitroxide, nitrogen-rich layers are formed at the surface and interface at a very early stage of the nitridation. Then the nitridation reaction mainly goes on in the bulk region with the surface and near interface nitrogen content remaining fairly constant. Our results also indicate the formation of an oxygen-rich layer at the interface underneath the nitrogen-rich layer whose thickness increases slowly with nitridation time. The nitride and nitroxide films were analyzed using Auger electron spectroscopy, grazing angle Rutherford backscattering, and etch rate measurements. MIS devices were fabricated using these films as gate insulators and were electrically characterized using I-V, C-V, time-dependent breakdown, trapping, and dielectric breakdown techniques. Breakdown, conduction, and C -V measurements on metal-insulator semiconductor (MIS) structures fabricated with these films show that very thin thermal silicon nitride and nitroxide films can be used as gate dielectrics for future highly scaled-dowm VLSI devices. The electrical characterization results also indicate extremely low trapping in the nitride films. The reliability of ultrathin nitride was observed to be far superior to SiO/sub 2/ and nitroxide due to its much less trapping. Studies show that the interface transition from nitride to silicon is almost abrupt and the morphology and roughness of the interface are comparable to the SiO/sub 2/-Si interfaces.     

Thermal nitridation of Si and SiO2for VLSI

This paper presents an extensive review of our work on thermal nitridation of Si and SiO2. High-quality ultrathin films of silicon nitride and nitrided-oxide (nitroxide) have been thermally grown in ammonia atmosphere in a cold-wall RF-heated reactor and in a lamp-heated system. The growth kinetics and their dependence on processing time and temperature have been studied from very short to long nitridation times. The kinetics of thermal nitridation of SiO2in ammonia ambient have also been studied. In nitroxide, nitrogen-rich layers are formed at the surface and interface at a very early stage of the nitridation. Then the nitridation reaction mainly goes on in the bulk region with the surface and near interface nitrogen content remaining fairly constant. Our results also indicate the formation of an oxygen-rich layer at the interface underneath the nitrogen-rich layer whose thickness increases slowly with nitridation time. The nitride and nitroxide films were analyzed using Auger electron spectroscopy, grazing angle Rutherford backscattering, and etch rate measurements. MIS devices were fabricated using these films as gate insulators and were electrically characterized usingI - V, C - V, time-dependent breakdown, trapping, and dielectric breakdown techniques. Breakdown, conduction, andC-Vmeasurements on metal-insulator semiconductor (MIS) structures fabricated with these films show that very thin thermal silicon nitride and nitroxide films can be used as gate dielectrics for future highly scaled-down VLSI devices. The electrical characterization results also indicate extremely low trapping in the nitride films. The reliability of ultrathin nitride was observed to be far superior to SiO2and nitroxide due to its much less trapping. Studies show that the interface transition from nitride to silicon is almost abrupt and the morphology and roughness of the interface are comparable to the SiO2-Si interfaces.     

Projecting gate oxide reliability and optimizing reliabilityscreens

The effect of time-dependent stress voltage and temperature on the reliability of thin SiO₂ films is incorporated in a quantitative defect-induced breakdown model. Based on this model, design curves which can be used along with a breakdown voltage distribution for an oxide technology to determine optimal burn-in conditions are presented. The tradeoff between improved reliability and lower burn-in yield for different gate oxide technologies can also be examined quantitatively using the model     

Effect of deposition methods on dielectric breakdown strength of PECVD low-k carbon doped silicon dioxide dielectric thin films

The effect of deposition methods on dielectric breakdown strength of PECVD low-k dielectric carbon doped silicon dioxide films is investigated. I-V measurements were performed using metal-insulator semiconductor structures for carbon doped silicon dioxide thin films with various thicknesses by single deposition station and six sequential deposition systems. I-t measurements are also performed for films with the thickness of 32 nm prepared using both deposition methods. Comparison studies have been carried out for the thickness dependence, temperature dependence, conduction mechanism and time dependence of dielectric breakdown for carbon doped silicon dioxide with single layer and six sub-layers. Results demonstrated that both films follow the newly obtained relationship between dielectric strength E_B and thickness d, i.e. E_B∝(d−d_c)⁻ⁿ, but with a lower exponential factor n and a larger thickness limit d_c for films with six sub-layers. It is also demonstrated that films with six sub-layers have a higher dielectric strength in all the thickness and temperature ranges, a thickness independent thermal behavior and a longer lifetime under constant voltage stressing. This indicates that by tuning the deposition methods smaller thickness with desired dielectric properties can be achieved.     

TDDB击穿特性评估薄介质层质量

与时间相关电介质击穿(TDDB)测量是评估厚度小于20nm薄栅介质层质量的重要方法.氧化层击穿前,隧穿电子和空穴在氧化层中或界面附近产生陷阱、界面态,当陷阱密度超过临界平均值 _bd时,发生击穿.击穿电量Q_bd值表征了介质层的质量.Q_bd值及其失效统计分布与测试电流密度、电场强度、温度及氧化层面积等有定量关系.TDDB的早期失效分布可以反映工艺引入的缺陷.TDDB可以直接评估氧化、氮化、清洗、刻蚀等工艺对厚度小于10nm的栅介质质量的影响.它是硅片级评估可靠性和预测EEPROM擦写次数的重要方法.     

Critical reliability challenges in scaling SiO2-based dielectric to its limit

The limitations of silicon dioxide dielectric reliability for future CMOS scaling are investigated. Several critical aspects are examined, and new experimental results are used to form an empirical approach to a theoretical framework upon which the data is then interpreted. Experimental data over a wide range of oxide thickness, voltage, and temperature were gathered using structures with a wide range of gate-oxide areas, and over very long stress times. Resolution of seemingly contradictory observations regarding the temperature dependence of oxide breakdown is provided by this work. On the basis of these results, a unified, global picture of oxide breakdown is constructed and the resulting model is applied to project reliability limits for the wear-out of silicon dioxide. It is concluded that silicon dioxide-based dielectrics can provide reliable gate dielectric, even to a thickness of 1 nm, and that CMOS scaling may well be viable to the 50 nm technology node using silicon-dioxide-based gate insulators.     

固态介质薄膜的电击穿场强

对于微电子和光电子元器件及其集成电路来讲,固态介质薄膜是一类重要的基础材料。它们的电击穿场强是一个特殊的特性参数。本文从理论上论述了这类薄膜的电击穿场强,并概述了现在所用的测试方法和多位研究者得出的测试结果。此外, 文中还分类提出了这类薄膜内的弱点类型。     

Large-scale atomistic modeling of nanoelectronic structures

Large-scale molecular-dynamics simulations are performed on parallel computers to study critical issues on ultrathin dielectric films and device reliability in next-decade semiconductor devices. New interatomic-potential models based on many-body, reactive, and quantum-mechanical schemes are used to study various atomic-scale effects: growth of oxide layers; dielectric properties of high-permittivity oxides; dislocation activities at semiconductor/dielectric interfaces; effects of amorphous layers and pixellation on atomic-level stresses in lattice-mismatched nanopixels; and nanoindentation testing of thin films. Enabling technologies for 10 to 100 million-atom simulations of nanoelectronic structures are discussed, which include multiresolution algorithms for molecular dynamics, load balancing, and data management. In ten years, this scalable software infrastructure will enable trillion-atom simulations of realistic device structures with sizes well beyond μm on petaflop computers     

Preparation and properties of plasma-anodized silicon dioxide films

The preparation and properties of thin films of silicon dioxide formed at ～ 200°C by anodization in an RF plasma are described. A suitable procedure for obtaining good quality films is given along with information on the effects of film sputtering and internal stress build-up during anodization. Measurements on MOS capacitors utilising the plasma-grown oxide yielded information on oxide charges, Si/SiO₂ interface state density, oxide permittivity, leakage resistance and film breakdown strength. Additional measurements determined the physical properties of stochiometry, impurity content, refractive index and etching behaviour. The plasma-anodized films can be routinely grown to a quality comparable with the best thermally-grown oxides.     

A new soft breakdown model for thin thermal SiO2 filmsunder constant current stress

Soft breakdown properties of thin gate oxide films are investigated using a constant current stress measurement. The soft breakdown can be classified into two different modes from the current conduction characteristics of post breakdown oxides: one of the modes shows a telegraph switching pattern and the other random noise. The generation probabilities of two soft breakdown modes and hard breakdown strongly depend on the stress current. Time-to-breakdown is well characterized by a universal function of stress conditions regardless of the breakdown modes. These experimental findings imply that all types of breakdown originate from the same precursor and the magnitude of the following local heating due to the transient current in a conductive micro spot determines the charge conduction properties after a breakdown event     

Dependence of gate oxide breakdown on initial charge trapping under Fowler-Nordheim injection

This work demonstrates that for constant oxide reliability stresses in the Fowler-Nordheim regime a low initial rate of charge trapping/detrapping results in long times to breakdown. It was found for MOS gate oxides that when the initial trapping has been completed at low fields times to breakdown enhance. Depending on the stress sequence measurement results can vary significantly which is of great relevance for correct oxide lifetime predictions.