4H-SiC结型势垒肖特基二极管的制作与特性研究

本文设计制作了两种具有不同结构参数的4H-SiC结型势垒肖特基二极管,在制作过程中采用了两种制作方法：一种是对正电极上的P型欧姆接触进行单独制作,然后制作肖特基接触的工艺过程;另一种是通用的通过一次肖特基接触制作就完成正电极制作的工艺过程。器件制作完成后,通过测试结果比较了采用场限环作为边界终端与未采用边界终端的器件的反向特性,结果显示采用场限环有效地提高了该器件的击穿电压,减小了其反向电流。另外,测试结果还显示采用独立制作P型欧姆接触的工艺过程有效提高了4H-SiC结型势垒肖特基二极管的反向特性,其中P型欧姆接触的制作过程和结果也在本文中做出了详细叙述。     

Si基JBS整流二极管的设计与制备

基于JBS整流二极管理论,详细介绍了一种Si基JBS整流二极管设计方法、制备工艺及测试结果。在传统肖特基二极管(SBD)有源区,利用光刻和固态源扩散工艺形成掺硼的蜂窝状结构,与n型衬底形成pn结,反向偏置时抑制了因电压增加引起的金属-半导体势垒高度降低,减小了漏电流;采用离子注入形成两道场限环的终端结构,有效防止了边缘击穿,提高了反向击穿电压。对制备的器件使用Tektronix 370B可编程特性曲线图示仪进行了I-V特性测试,结果表明本文设计的Si基JBS整流二极管正向压降VF=0.78 V(正向电流IF=5 A时),反向击穿电压可达340 V。     

Analytical Modeling of High-Voltage 4H-SiC Junction Barrier Schottky (JBS) Rectifiers

We develop a new analytical model for the junction barrier Schottky (JBS) rectifier and apply it to high-voltage 4H-SiC JBS rectifiers. This model uses a novel method to approximate the electric field at the Schottky contact, which is together with the Fowler–Nordheim tunneling equation to accurately calculate the reverse leakage current of a high-voltage 4H-SiC JBS rectifier. The forward on-resistance of a high-voltage 4H-SiC JBS rectifier consists of several components, which are dominated by the spreading resistances in the drift layer. Moreover, this model has been verified by comparing the simulation and experimental results, and they are shown to be in good agreement.      

Fabrication and characteristics of a 4H-SiC junction barrier Schottky diode

4H-SiC junction barrier Schottky(JBS)diodes with four kinds of design have been fabricated and characterized using two different processes in which one is fabricated by making the P-type ohmic contact of the anode independently,and the other is processed by depositing a Schottky metal multi-layer on the whole anode.The reverse performances are compared to find the influences of these factors.The results show that JBS diodes with field guard rings have a lower reverse current density and a higher breakdown voltage,and with independent P-type ohmic contact manufacturing,the reverse performance of 4H-SiC JBS diodes can be improved effectively. Furthermore,the P-type ohmic contact is studied in this work.     

Study of 4H-SiC JBS Diodes Fabricated with Tungsten Schottky Barrier

Tungsten is a suitable metal contact for high-temperature applications. We fabricated 1.7-kV and 6-kV 4H-SiC junction barrier Schottky (JBS) diodes with a tungsten Schottky contact with different geometries, and their forward characteristics were measured up to 300°C. The 1.7-kV diodes exhibited unipolar conduction up to 6 V at 275°C, whereas 6-kV diodes showed ideal on-resistance, R _on. An optimized JBS design permits a higher breakdown voltage to be obtained than for the pure Schottky diode, with a reasonable increase (10%) of the on-resistance. Results demonstrate the feasibility of tungsten JBS diodes for fast-switching, high-voltage, and high-temperature applications.     

Inversion layer at the interface of Schottky diodes

An inversion layer can be present at the metal-semiconductor inteface of Schottky diodes with a high barrier and a lightly doped semiconductor. Its influence on the potential distribution and on the electric field distribution (especially on its maximum) is quite important and may be analyzed by means of an analytical model. The current characteristics calculated by the usual models are modified if one takes the inversion layer into account. In particular, the theoretical n of the Schottky diode is smaller than the value obtained from the usual depletion hypothesis, while the barrier height deduced from the experimental saturation current becomes larger. Excellent agreement between the experimental current characteristics of an PtSiSi diode and the combined model of thermionic emission-diffusion is obtained if the inversion layer is considered.     

Influence of inhomogeneous contact in electrical properties of 4H–SiC based Schottky diode

Schottky diodes realized on 4H–SiC n-type wafers with an epitaxial layer and a metal-oxide overlap for electric field termination were studied. The oxide was grown by plasma enhanced chemical vapor deposition (PECVD) and the Schottky barriers were formed by thermal evaporation of titanium or nickel. Diodes, with voltage breakdown as high as 700 V and ideality factor as low as 1.05, were obtained and characterized after packaging in standard commercial package (TO220).The electrical properties such as ideality factor, hight barrier, the series resistance R_s were deduced by current/voltage (I–V) analysis using the least mean square (LMS) method. The temperature effect on break voltage, R_s and saturation current was studied. A model based on two parallel Schottky diodes with two barrier heights is presented for some devices having an inhomogeneous contact. It is shown that the excess current at low voltage can be explained by a lowering of the Schottky barrier in localized regions. We use the two series RC components electrical model in order to study the dynamic behaviour of the Schottky diode in low frequency and to improve the effect of barrier inhomogeneities in electrical properties.     

The influence of high-temperature annealing on SiC schottky diode characteristics

The influence of high temperature (up to 800C) annealing on the current-voltage characteristics of n-type 6H-SiC Schottky diodes is presented. Our experimental results indicate that high-temperature annealing can result in the improvement of the forw ard and reverse electrical characteristics of SiC Schottky diodes by repairing any leaky low barrier secondary diode parallel to the primary diode that may be present due to the barrier inhomogeneities at the Schottky contact interface.     

300V以上硅基新型JBS肖特基二极管的制备

为了在保留传统肖特基二极管正向压降低、电流密度大优点的基础上,使其反向击穿电压提高到了300 v以上,我们采用硅材料做为衬底,肖特基结区采用蜂房结构,终端采用两道场限环结构加一道切断环结构,所制备的肖特基二极管在正向电流10A时,正向压降仅为0.79 V;同时在施加300 V反向电压时,反向漏电流在5μA以下.     

Experimental 4<Emphasis Type="Italic">H</Emphasis>-SiC junction-barrier Schottky (JBS) diodes

4H-SiC junction-barrier Schottky (JBS) diodes have been fabricated with local p–n junctions under the Schottky contact formed by nonequilibrium diffusion of boron. Static and dynamic characteristics of the JBS diodes are compared with those of similar 4H-SiC Schottky diodes. It is shown that, compared with ordinary Schottky diodes, the JBS diodes have leakage currents that are, on average, a factor of 200 lower at the same reverse bias. The reverse recovery charge is the same for both types of diodes and equal to the charge of majority carriers removed from the n-type base region in switching.     

标准CMOS工艺集成肖特基二极管设计与实现

提出了一种在标准CMOS工艺上集成肖特基二极管的方法,并通过MPW在charted 0.35μm工艺中实现.为了减小串连电阻,肖特基的版图采用了交织方法.对所设计的肖特基二极管进行了实测得到I-V,C-V和S参数,并计算得出所测试肖特基二极管的饱和电流、势垒电压及反向击穿电压.最后给出了可用于SPICE仿真的模型.     

1200V/100A高温大电流4H-SiC JBS器件的研制

基于SiC结势垒肖特基(JBS)二极管工作原理及其电流/电场均衡分布理论,采用高温大电流单芯片设计技术及大尺寸芯片加工技术,研制了1 200 V/100 A高温大电流4H-SiCJBS二极管.该器件采用优化的材料结构、有源区结构和终端结构,有效提高了器件的载流子输运能力.测试结果表明,当正向导通压降为1.60 V时,其正向电流密度达247 A/cm2(以芯片面积计算).在测试温度25和200℃时,当正向电流为100 A时,正向导通压降分别为1.64和2.50 V;当反向电压为1 200 V时,反向漏电流分别小于50和200μA.动态特性测试结果表明,器件的反向恢复特性良好.器件均通过100次温度循环、168 h的高温高湿高反偏(H3TRB)和高温反偏可靠性试验,显示出优良的鲁棒性.器件的成品率达70％以上.     

Ni，Ti/4H-SiC肖特基势垒二极管

采用本实验室生长的4H-SiC外延片,分别用高真空电子束蒸Ni和Ti做肖特基接触金属,Ni合金作欧姆接触,SiO_2绝缘环隔离减小高压电场集边效应等技术,制作出4H-SiC肖特基势垒二极管(SBD)。该器件在室温下反向击穿电压大于600 V,对应的漏电流为2.00×10~(-6)A。对实验结果分析显示,采用Ni和Ti作肖特基势垒的器件的理想因子分别为1.18和1.52,肖特基势垒高度为1.54 eV和1.00 eV。实验表明,该器件具有较好的正向整流特性。     

Bipolar Conduction Impact on Electrical Characteristics and Reliability of 1.2- and 3.5-kV 4H-SiC JBS Diodes

4H-SiC Junction Barrier Schottky (JBS) diodes (1.2 and 3.5 kV) have been processed using the same technology with two different layouts. From 4 A and for the whole temperature range, the 3.5-kV diodes exhibit a bipolar conduction independent of the layout. However, the behavior of the 1.2-kV diodes depends on the design. At 500 V–300 $^{circ}hbox{C}$, the leakage current is only 100 nA and 10 $muhbox{A}$ for the 3.5- and 1.2-kV diodes, respectively. The switch-off performances show a reverse peak current of only 50% of the nominal current at 300 $^{circ}hbox{C}$ for all JBS diodes. The JBS diodes have a surge current capability of around 80 A, two times higher than the Schottky diodes. DC electrical stresses are performed during 50 h, and all the 1.2-kV diodes exhibit no bipolar degradation. Nevertheless, some slight bipolar degradation is observed in 3.5-kV JBS diodes. Electroluminescence measurements exhibit the expansion of stacking faults in 3.5-kV diodes unlike in 1.2-kV diodes.      

Characterization of shallow silicided junctions for sub-quartermicron ULSI technology. Extraction of silicidation induced Schottkycontact area

The current-voltage (I-V) characteristics of shallow silicided p ⁺-n and n⁺-p junctions are presented. In the former the diode behavior was same as in nonsilicided junction, while drastic change in diode I-V was observed in the latter. The formation of Schottky contact was conclusively shown to be the root cause of the modified I-V behavior of n⁺-p junction in the forward bias region. Poole-Frenkel barrier lowering predominantly influenced the reverse leakage current, masking thereby the effect of Schottky contact. The leakage current in n⁺-p diodes was higher than in nonsilicided diodes by two orders of magnitude and this is consistent with the formation of Schottky contact via titanium or titanium-silicide penetrating into the p-substrate and generating trap sites. There is no increase in the leakage current and no formation of Schottky contact in case of the p⁺-n junction. The Schottky contact amounting to less than 0.01% of the total junction area and not amenable for SEM or TEM observation was extracted for the first time by simultaneous characterization of forward and reverse characteristics of silicided n ⁺-p diode     

Small-signal conductance vs temperature: A rapid means of determining the nature of current transport in high-doped n-GaAs Schottky barrier diodes

Measurements of small-signal forward conductance vs temperature at a constant bias current, and the reverse conductance vs temperature at a constant bias voltage have been carried out on ion-implanted n-GaAs Schottky barrier diodes fabricated on semi-insulated substrates, for the temperature range of 97–340 K. The results obtained have been interpreted in terms of diode ideality factors and compared with those calculated using the thermionic field emission model for the forward bias case and the pure field emission model for the reverse bias case.     

Effect of crystallographic defects on the reverse performance of 4H-SiC JBS diodes

A quantitative analysis of the effect of crystallographic defects on the performance of 4H-SiC junction barrier Schottky (JBS) diodes was performed. It has been shown that higher leakage current in diodes is associated with a greater number of elementary screw dislocations. Further, threading dislocation pair arrays were observed in some of the fabricated devices and, for the first time, the role of such defects on JBS reverse leakage currents is investigated.     

Barrier height diminution in Schottky diodes due to electrostatic screening

Electrostatic screening in the metal contact of a Schottky (metal-semiconductor) diode is shown to influence the calculated electrical characteristics of the diode. A thin space-charge layer is formed at the surface of the metal contact by capacitively induced free charges, This results in a voltage dependent diminution of the barrier height of the diode that increases in magnitude with increasing semiconductor dielectric constant and carrier concentration. Predicted values of the barrier height diminution exceed those attributed to image forces or tunneling effects for materials with dielectric constants greater than about 20. In diodes using semiconducting ferroelectric or piezoelectric materials, an additional diminution of the barrier height results from free charges induced in the metal contact by a remanent polarization field or an externally applied mechanical stress. Current-voltage characteristics of a metal-semiconductor diode are shown to be significantly influenced by the electrostatic screening effect. A soft breakdown current as opposed to saturation current is predicted for reverse biases while an exponential forward current with an η coefficient exceeding unity is predicted for forward biases. Photoemission characteristics are also affected. A voltage-dependent diminution of the threshold energy for photoresponse is predicted. Capacitance-voltage characteristics, on the other hand, differ only slightly from those of an ideal Schottky diode except in the case of a ferroelectric diode where excessively large screening effects are possible.     

Micro-Raman spectroscopy applied in crystal structure analysis on the ESD failure mechanism of SiC JBS diodes

This paper propose a novel reliability analysis approach for electrostatic discharge (ESD) stress on 4H-SiC junction barrier Schottky (JBS) diodes using the technology of Micro-Raman spectroscopy. Several conventional analysis are firstly used to determine the failure site after the JBS diodes are destructed by ESD stress, including optical microscope (OM), Photoemission microscopy (PEM) and scanning electron microscopy (SEM). Then, the Micro-Raman spectroscopy is applied to analyze element identification and crystal structure of micro failure site. The analysis reveals that high electric field and high temperature concentrate in the high-voltage termination, resulting in diode burnout and changing the physical microstructure of base SiC. Furthermore, in the micro failure site, 4H-SiC with different Raman spectrum from base 4H-SiC are clearly found, and carbon escapes out from base SiC by combustion, leaving a mixture of amorphous silicon and polysilicon, which is decomposed from the base SiC on the failure surface.