4H-SiC MESFET肖特基栅接触的界面参数提取

研究了界面态对4H-SiC MESFET的肖特基栅接触的影响.栅接触工艺主要采用Ti/Pt/Au蒸发,经过剥离后形成.基于热电子理论提出了一种参数提取方法,得到界面态密度和界面电容分别为4.386×1013cm-2·eV-1和8.394×10-6F/cm2,这与测量得到的器件端特性一致.     

反应离子刻蚀氮化硅过程的损伤研究

针对反应离子刻蚀氮化硅过程中无图形60 nm栅氧的等离子体损伤问题进行了研究.采用接触电势差技术研究了反应刻蚀中电荷在硅片表面上的沉积,利用非接触式CV测试技术研究了Si/SiO2界面态的变化.研究表明,电荷沉积与Si/SiO2界面态密度增加有较好的对应关系,电荷沉积较多的区域具有更高的界面态密度.然而,电荷沉积量与界面态密度不成正比例.     

退火气氛对Ge MOS电容电特性的影响

采用反应磁控溅射法在Ge衬底上制备了HfTiO高介电常数k栅介质薄膜,研究了不同气体(N2、NO、N2O)淀积后退火对Ge金属-氧化物-半导体(MOS)电容性能的影响.透射电子显微镜和电特性测量表明,湿N2退火能有效抑制界面层的生长,提高界面质量,改善栅极漏电流特性,从而得到最优的器件性能,即Al/HfTiO/n-Ge MOS电容的栅介质等效氧化物厚0.81 nm,k=34.5,带隙中央界面态密度为2.4×1011cm-2·eV-1,1 V栅偏压下的栅极漏电流为2.71×10-4A·cm-2.     

PDSOI nMOSFETs关态击穿特性

分别采用不同的背栅沟道注入剂量制成了部分耗尽绝缘体上硅浮体和H型栅体接触n型沟道器件.对这些器件的关态击穿特性进行了研究.当背栅沟道注入剂量从1.0×1013增加到1.3×1013cm-2,浮体n型沟道器件关态击穿电压由5.2升高到6.7V,而H型栅体接触n型沟道器件关态击穿电压从11.9降低到9V.通过测量寄生双极晶体管静态增益和漏体pn结击穿电压,对部分耗尽绝缘体上硅浮体和H型栅体接触n型沟道器件的击穿特性进行了定性解释和分析.     

PDSOI nMOSFETs关态击穿特性

分别采用不同的背栅沟道注入剂量制成了部分耗尽绝缘体上硅浮体和H型栅体接触n型沟道器件.对这些器件的关态击穿特性进行了研究.当背栅沟道注入剂量从1.0×1013增加到1.3×1013cm-2,浮体n型沟道器件关态击穿电压由5.2升高到6.7V,而H型栅体接触n型沟道器件关态击穿电压从11.9降低到9V.通过测量寄生双极晶体管静态增益和漏体pn结击穿电压,对部分耗尽绝缘体上硅浮体和H型栅体接触n型沟道器件的击穿特性进行了定性解释和分析.     

中波碲镉汞/钝化层界面电学特性研究

HgCdTe表面/界面特性对器件性能具有重要的影响,表面/界面的状态主要依赖于表面处理和钝化工艺。采用Br2/CH3OH腐蚀液对液相外延(LPE)生长的中波HgCdTe薄膜进行表面处理后,使用Cd Te/Zn S复合钝化技术进行表面钝化,制备了相应的MIS器件并进行器件C-V测试。结果表明,HgCdTe/钝化层界面固定电荷极性为正,面密度为2.1×1011 cm-2,最低快界面态密度为1.43×1011 cm-2·e V-1,在10 V栅压极值下慢界面态密度为4.75×1011 cm-2,较低的快界面态密度体现出了CdTe/ZnS复合钝化技术的优越性。     

埋氧离子注入对P型部分耗尽SOI电学与低频噪声的影响

针对抗辐照SOI PMOS器件的直流特性与低频噪声特性展开试验与理论研究,分析离子注入工艺对PMOS器件电学性能的影响,并预测其稳定性的变化。首先,对离子注入前后PMOS器件的阈值电压、迁移率和亚阈摆幅进行提取。测量结果表明:埋氧化层离子注入后,器件背栅阈值电压由-43.39 V变为-39.2 V,空穴有效迁移率由127.37 cm2/Vs降低为80.45 cm2/Vs,亚阈摆幅由1.35 V/dec增长为1.69 V/dec;结合背栅阈值电压与亚阈摆幅的变化,提取得到埋氧化层内电子陷阱与背栅界面态数量的变化。随后,分析器件沟道电流噪声功率谱密度随频率、沟道电流的变化,提取γ因子与平带电压噪声功率谱密度,由此计算得到背栅界面附近的缺陷态密度。基于电荷隧穿机制,提取离子注入前后埋氧化层内陷阱态随空间分布的变化。最后,基于迁移率随机涨落机制,提取得到离子注入前后PMOS器件的平均霍格因子由6.19×10-5增长为2.07×10-2,这表明离子注入后器件背栅界面本征电性能与应力稳定性将变差。     

金属/p-GaAs界面态对接触电阻作用机理的研究

本文针对大功率垂直腔面发射激光器(vertical cavity surface emitting laser, VCSEL)阵列热阻大、出光不均匀的问题,研究p-GaAs层欧姆接触电阻值的作用机理,降低欧姆接触串联电阻的方法,以提高VCSEL阵列出射光功率的均匀性。基于3种常用欧姆接触金属Ti/Au、Ni/Au、Ti/Al/Ti/Au,研究各层金属厚度和金属组合对与p型欧姆接触电阻的作用规律;结合等离子体表面处理工艺,改变金属/p-GaAs界面态,研究界面态对欧姆接触电阻的影响规律。实验对比分析得到金属Ti/Au结构电极欧姆接触的比接触电阻率最低,为3.25×10^-4 Ω·cm²;基于金半接触势垒模型,通过表面等离子体处理,界面势垒可降低12.6%(0.269 2 eV降至0.235 3 eV),等离子体轰击功率可调控金半界面的势垒和态密度。     

p-Si TFT栅绝缘层用SiNx薄膜界面特性的研究

以NH3和SiH4为反应源气体,在低温下采用射频等离子体增强化学气相沉积(RF-PECVD)法在多晶硅(p-Si)衬底上沉积了SiNx薄膜.系统地分析讨论了沉积温度、射频功率、反应源气体流量比对SiNx薄膜界面特性的影响.分析表明,沉积温度和射频功率主要是通过影响SiNx薄膜中的si/N比和H含量影响薄膜的界面特性,而NH3/SiH4流量比则主要通过影响薄膜中的H含量影响薄膜界面特性.实验制备的SiNx薄膜层中的固定电荷密度、可动离子密度、SiNx与p-si之间的界面态密度分别达到了1.7×1012/cm2、1.4×1012/cm2、3.5×1012/(eV·cm2),其界面特性达到了制备高质量p-si TFT栅绝缘层的性能要求.     

高阈值电压低界面态增强型Al2O3/GaN MIS-HEMT

采用高温热氧化栅极凹槽刻蚀工艺并结合高温氮气氛围退火技术,制备出了高阈值电压的硅基GaN增强型Al_2O_3/GaN金属-绝缘体-半导体高电子迁移率晶体管(MIS-HEMT)。采用高温热氧化栅极凹槽刻蚀工艺刻蚀AlGaN层,并在AlGaN/GaN界面处自动终止刻蚀,可有效控制刻蚀的精度并降低栅槽表面的粗糙度。同时,利用高温氮气退火技术能够修复Al_2O_3/GaN界面的界面陷阱,并降低Al_2O_3栅介质体缺陷,因此能够减少Al_2O_3/GaN界面的界面态密度并提升栅极击穿电压。采用这两项技术制备的硅基GaN增强型Al_2O_3/GaN MIS-HEMT具有较低的栅槽表面平均粗糙度(0.24 nm)、较高的阈值电压(4.9 V)和栅极击穿电压(14.5 V)以及较低的界面态密度(8.49×10¹¹ cm^-2)。     

Neutron radiation effect on 4H-SiC MESFETs and SBDs

4H-SiC metal Schottky field effect transistors (MESFETs) and Schottky barrier diodes (SBDs) were irra-diated at room temperature with 1 MeV neutrons. The highest neutron flux and gamma-ray total dose were 1×1015n/cm2 and 3.3 Mrad(Si), respectively. After a neutron flux of 1×1013 n/cm2, the current characteristics of the MES-FET had only slightly changed, and the Schottky contacts of the gate contacts and the Ni, Ti/4H-SiC SBDs showed no obvious degradation. To further increase the neutron flux, the drain current of the SiC MESFET decreased and the threshold voltage increased. φB of the Schottky gate contact decreased when the neutron flux was more than or equal to 2.5×1014n/cm2. SiC Schottky interface damage and radiation defects in the bulk material are mainly mechanisms for performance degradation of the experiment devices, and a high doping concentration of the active region will improve the neutron radiation tolerance.     

SiC表面氢化研究

该文提出6H-SiC ( 0001)/SiO2间过渡层的概念和过渡层结构,通过分析过渡层与HF溶液的反应机理,建立湿化学处理中的SiC表面氢化模型。模型以氢钝化SiC表面悬挂键,降低SiC表面的界面态密度,消除了费米能级钉扎,获得理想的SiC表面。将此模型用于SiC/金属接触的SiC表面处理,在100℃以下制备了理想因子n=1.2~1.25的肖特基结和比接触电阻＝510-3 cm2~710-3 cm2的SiC欧姆接触,其优点在于不仅避免了欧姆接触800~1200℃的高温合金,而且改善了肖特基接触的电学特性。SiC表面模型与实验结果吻合较好。     

6H-SiC Schottky二极管的正向特性

提出了一种考虑Schottky结势垒不均匀性和界面层作用的Si C Schottky二极管( SBD)正向特性模型,势垒的不均匀性来自于Si C外延层上的各种缺陷,而界面层上的压降会使正向Schottky结的有效势垒增高.该模型能够对不同温度下Si C Schottky结正向特性很好地进行模拟,模拟结果和测量数据相符.它更适用于考虑器件温度变化的场合,从机理上说明了理想因子、有效势垒和温度的关系.     

Nanometer-scale investigation of metal-SiC interfaces using ballistic electron emission microscopy

We report ballistic-electron emission microscopy (BEEM) investigation of Pd, Pt Schottky contacts on 6H-, 4H-SiC, and Pd/15R-SiC. Measured Schottky barrier heights of 6H- and 4H-SiC samples appear spatially uniform up to the fitting error due to noise (0.03–0.04 eV and 0.1–0.2 eV for 6H- and 4H-SiC, respectively). In 4H-SiC, we observed an additional conduction band minimum (CBM) ∼0.14 eV above the lowest CBM, which provide direct experimental verification of band theoretical calculation results. Additionally, we sometimes observed enhancement in ballistic transmittance over regions intentionally stressed by hot electron injection using BEEM. We also report recent results on Pd/15R-SiC sample indicating a higher CBM ∼0.5 eV above the lowest CBM. In Pd/15R-SiC, interesting large variations in BEEM spectra at different locations were observed, possibly suggesting an inhomogeneous metal/semiconductor interface.     

Effect of surface inhomogeneities on the electrical characteristicsof SiC Schottky contacts

This paper reports analysis of the role of defects on the electrical characteristics of high-voltage 6H-SiC Schottky rectifiers. The measured reverse leakage current of high-voltage Ti and Pt rectifiers was found to be much higher than that predicted by thermionic emission theory and using a barrier height extracted from the C-V measurements. In this paper, a model based upon the presence of defects at the 6H-SiC/metal interface is used to explains this behavior. It is proposed that these defects result in lowering of the barrier height in the localized regions and thus, significantly affect the reverse I-V characteristics of the Schottky contacts. The presence of electrically active defects in the Schottky barrier area has been verified by EBIC studies     

Barrier height determination for n-type 4H-SiC schottky contacts made using various metals

We have studied Schottky barrier contacts to n-type 4H-SiC with Cr, Mo, Ta, W, Au, and Ni. We have focused on effects of the metal work function, measurement technique and interface behavior on the Schottky barrier heights (SBHs). The contacts were prepared by metal deposition via high frequency cathodic sputtering on chemical vapor epitaxially grown epitaxial layers with low residual doping (2 × 10¹⁵ cm⁻³). Prior to deposition on Si-terminated surfaces, they were in-situ cleaned by Ar-ion sputtering for 5 and 10 min, respectively. The contacts have been characterized by means of current-voltage, capacitance-voltage (C-V), and internal photoemission (IPE) methods at room temperature. With deep level transient spectroscopy, interface deep electron traps have been detected with thermal ionization energies of 0.68, 0.77, and 1.04 eV, respectively. These traps have been attributed to structural defects formed during epitaxial growth termination. The diodes have relatively low reverse leakage current, but the ideality factor is larger than one. The SBHs have been determined from C-V and IPE measurements. It has been shown that the C-V data may contain errors resulting in a low SBH if electron deep traps are present in the interface region. In general, the SBH of various metals are influenced by the metal work function and also by the semiconductor surface preparation. The interface homogeneity is an important characteristic of the Schottky contacts, which may be improved by an optimized ion sputtering prior to metal deposition. We have considered the SBHs determined by IPE measurements as most reliable.     

Schottky barrier height modification in Au/n-type 6H-SiC structures by PbS interfacial layer

We have prepared the Au/PbS/n-6H-SiC Schottky diodes with interface layer and the reference Au/n-6H-SiC/Ni Schottky diodes without interface layer to realize Schottky barrier height (SBH) modification in the Au/SiC Schottky diodes. The BH reduction has been succeeded by the PbS interlayer to modify the effective BH by influencing the space charge region of the SiC. The PbS thin layer on the SiC was formed by the vacuum evaporation. The SBH values of 0.97 and 0.89 eV for the samples with and without the interfacial PbS layer were obtained from the forward bias current-voltage (I-V) characteristics. X-ray diffraction (XRD) study was carried out to determine the structural formation of the PbS on SiC. The reduction of the BH in the Au/PbS/n-6H-SiC Schottky diodes has been attributed to the fact that the interface states have a net positive interface charge in metal/n-type semiconductor contact, and thus the positive space charge Q_sc in the Au/PbS/n-6H-SiC Schottky diodes becomes smaller than if the interface state charges Q_ss were absent. The experimental carrier concentration value of 4.73 × 10¹⁷ cm⁻³ obtained from the forward and reverse bias capacitance-voltage characteristics for the Au/PbS/n-6H-SiC contacts is lower than the value of 5.52 × 10¹⁷ cm⁻³ obtained for the reference diode, and this is an evidence of the reduction of the BH by the modification of the space charge density of the SiC.     

不同退火温度下金属/4H-SiC Schottky势垒高度的研究

采用磁控溅射的方法在4H-SiC样品上分别沉积四种金属薄膜(Ag,Cu,Ni,Cr)形成Schottky接触,研究了不同温度退火对Schottky势垒高度的影响.通过对样品的I-V测试结果的拟合,得到各金属/4H-SiC Schottky接触的势垒高度以及理想因子.在反向偏压100V下,样品的反向漏电流小于10-10A,说明样品的反向特性良好.样品经过不同温度的退火后,发现Cu、Ni与4H-SiC的势垒高度(SBH)随退火温度的升高而提高,超过某一温度,其整流特性变差;Ag、Cr的SBH在退火后降低.SBH与金属功函数呈线性关系(Cr金属除外),斜率为0.11.     

High-quality schottky and ohmic contacts in planar 4H-SiC metal semiconductor field-effect transistors and device performance

We have fabricated planar 4H-SiC, metal-semiconductor field-effect transistors (MESFETs) with high-quality metal/SiC contacts. To eliminate potential damage to the gate region caused by etching and simplify the device fabrication process, gate Schottky contacts were formed without any recess gate etching, and an ideality factor of 1.03 was obtained for these gate contacts. The interface state density between the contact metal and SiC was 5.7×10¹² cm⁻²eV⁻¹, which was found from the relationship between the barrier height and the metal work function. These results indicate that the interface was well controlled. Thus, a transconductance of 30 mS/mm was achieved with a 3-μm gate length as the performance figure of these MESFETs with high-quality metal/SiC contacts. Also, a low ohmic contact resistance of 1.2×10⁻⁶ Θcm² was obtained for the source and drain ohmic contacts by using ion implantation.     

基于结终端扩展的4H-SiC肖特基势垒二极管研制

采用高真空电子束热蒸发金属Ni分别作肖特基接触和欧姆接触,离子注入形成结终端扩展表面保护,研制出Ni/4H-SiC肖特基势垒二极管(SBD)。I-V特性测量说明,Ni/4H-SiCSBD有较好的整流特性,热电子发射是其主要的运输机理。实验测量其反向击穿电压达1800V,且反向恢复特性为32ns。