不同退火温度下Mo/4H-SiC肖特基接触势垒不均匀及XRD分析北大核心

为探究退火温度对Mo/4H-SiC肖特基接触势垒不均匀程度的影响,对在不同退火温度下形成的Mo/4H-SiC肖特基接触进行了不同测试温度下的电流-电压（I-V）及电容-电压（CV）测试,运用Tung理论模型和＂T0反常＂中的T0值评价势垒不均匀程度,X射线衍射（XRD）分析肖特基接触的物相组成。分析结果表明,测试温度升高时I-V测试提取的势垒高度接近于C-V测试提取的势垒高度,退火温度500℃及以上时Mo与4H-SiC发生反应,且导致较低的势垒高度。退火温度为600℃时,肖特基接触具有最低的势垒不均匀程度,且此退火温度下势垒高度相对500℃及700℃时较高,物相组成为Mo2C及Mo4.8Si3C0.6。     

Ni/Ti/Si形成硅化物的特性分析

随着MOSFET的特征尺寸进入20nm技术节点,源漏接触电阻成为源漏寄生电阻的主导部分,后栅工艺对硅化物的高温特性提出了更高的要求。分析了Ni/Ti/Si结构在不同温度退火下形成的硅化物的薄膜特性和方块电阻。分别采用J-V和C-V方法,提取硅化物与n-Si(100)接触的势垒高度。Ni/Ti/Si结构形成的镍硅化物在高温下具有良好的薄膜特性,并且可以得到低势垒的肖特基接触。随着退火温度的升高,势垒高度逐渐降低。研究了界面态的影响,在低于650℃的温度下退火,界面态密度随退火温度升高而逐渐增大,高于750℃后,界面电荷极性翻转。     

不同退火温度下Mo/4H-SiC肖特基接触界面特性分析

为研究退火温度对肖特基接触界面特性的影响,在不同温度下测试了不同退火温度处理的Mo/4H-SiC肖特基接触的I-V及C-V特性.根据金属-绝缘层-半导体(MIS)结构二极管模型理论,认为在金属与半导体间存在薄介质层,通过估算介质层电容值,得到了肖特基接触界面态密度(N88)的能级分布情况,N8s约为1012 eV-1·cm-2量级.退火温度升高,N8s的能级分布靠近导带底;测试温度升高,Ns8增加且其能级分布远离导带底.利用X射线光电子能谱(XPS)分析表征肖特基接触界面态化学组分,分析结果证实接触界面存在SiO.SiO组分随退火温度的升高而减少,在退火温度为500℃及以上时检测到Mo-C成分,说明Mo与4H-SiC发生反应.     

超薄外延CoSi2/n-Si的肖特基势垒接触特性

研究了超薄(～10nm)CoSi2/Si的肖特基势垒接触特性.Co(3-4nm)/Ti(1nm)双层金属通过快速热退火在Si(100)衬底上形成超薄CoSi2薄膜.X射线衍射测试表明该薄膜具有较好的外延特性.用I-V、C-V方法在82-332K温度范围内测试了CoSi2/Sj的肖特基势垒特性.用弹道电子发射显微术直接测量了微区肖特基势垒高度.测试表明,用Co/Ti/Si方法形成的超薄CoSj2/Sj接触在室温时具有优良的肖特基势垒特性,I-V方法测得的势垒高度为0.59eV,其理想因子为1.01;在低温时,I-V方法测得的势垒高度随温度降低而降低,理想因子则升高.采用肖特基势垒不均匀性理论,并假设势垒高度呈高斯分布,实验数据和理论吻合较好.     

采用场板和B+离子注入边缘终端技术的Ti/4H-SiC肖特基势垒二极管

采用自主外延的4H-SiC外延片,利用PECVD生长的SiO2做场板介质,B+离子注入边缘终端技术,制造了Ti/4H-SiC肖特基势垒二极管.测试结果表明,Ti/4H-SiC肖特基势垒二极管的理想因子n=1.08,势垒高度(ψe)=1.05eV,串联电阻为6.77mΩ·cm2,正向电压为4V时,电流密度达到430A/cm2.反向击穿电压大于1.1kV,室温下,反向电压为1.1kV时,反向漏电流为5.96×10-3 A/cm2.     

采用场板和B+离子注入边缘终端技术的Ti/4H-SiC肖特基势垒二极管

采用自主外延的4H-SiC外延片,利用PECVD生长的SiO2做场板介质,B 离子注入边缘终端技术,制造了Ti/4H-SiC肖特基势垒二极管.测试结果表明,Ti/4H-SiC肖特基势垒二极管的理想因子n=1.08,势垒高度(ψe)=1.05eV,串联电阻为6.77mΩ·cm2,正向电压为4V时,电流密度达到430A/cm2.反向击穿电压大于1.1kV,室温下,反向电压为1.1kV时,反向漏电流为5.96×10-3 A/cm2.     

超薄外延CoSi_2/n-Si的肖特基势垒接触特性

研究了超薄(～10nm)CoSi2/Si的肖特基势垒接触特性.Co(3—4nm)/Ti(1nm)双层金属通过快速热退火在Si(100)衬底上形成超薄CoSi2薄膜.X射线衍射测试表明该薄膜具有较好的外延特性.用I-V、C-V方法在82—332K温度范围内测试了CoSi2/Si的肖特基势垒特性.用弹道电子发射显微术直接测量了微区肖特基势垒高度.测试表明,用Co/Ti/Si方法形成的超薄CoSi2/Si接触在室温时具有优良的肖特基势垒特性,I-V方法测得的势垒高度为0.59eV,其理想因子为1.01;在低温时,I-V方法测得的势垒高度随温度降低而降低,理想因子则升高.采用肖特基势垒不均匀性理论,并假设势垒高度呈高斯     

固相反应制备的多晶和外延CoSi2/n-Si(111)接触的肖特基特性

通过硅(111)衬底淀积的单层Co或Co/Ti双金属层在不同退火温度的固相反应,在硅上形成制备了多晶和外延CoSi2薄膜.用电流-电压和电容-电压(I-V/C-V)技术在90K到室温的温度范围内测量了CoSi2/Si肖特基接触特性. 用肖特基势垒不均匀模型分析了所测得的I-V特性,在较高温度下(≥～200K)或较低温度的较大偏压区域,I-V曲线能用热激发和在整个结面积上势垒高度的高斯分布模型描述. 而在较低温度的较小偏压区域,电流由流过一些小势垒高度微区的电流决定,从而在低温I-V曲线上在约10-7A处有一个"曲折”. 在室温下,从I-V曲线得到的多晶CoSi2/Si的势垒高度为约0. 57eV. 对外延CoSi2,势垒高度依赖于最后退火温度,当退火温度从700℃升到900℃,势垒高度从0. 54eV升高到0. 60eV.     

高性能SiC整流二极管研究

在n型4H-SiC单晶导电衬底上制备了具有MPS(merged p-i-n Schottky diode)结构和JTE(junction termination extension)结构的肖特基势垒二极管。通过高温离子注入及相应的退火工艺,进行了区域性p型掺杂,形成了高真空电子束蒸发Ni/Pt/Au复合金属制备肖特基接触,衬底溅射Ti W/Au并合金做欧姆接触,采用场板和JTE技术减小高压电场集边效应。该器件具有良好的正向整流特性和较高的反向击穿电压。反向击穿电压可以达到1300V,开启电压约为0.7V,理想因子为1.15,肖特基势垒高度为0.93eV,正向电压3.0V时,电流密度可以达到700A/cm2。     

AlGaN/AlN/GaN肖特基二极管的电学性能

利用金属有机化学气相淀积(MOCVD)方法生长的AlGaN/AlN/GaN/蓝宝石材料制备了AlGaN肖特基二极管.器件的肖特基接触和欧姆接触分别为Ti/Pt和Ti/Al/Ti/Au,均采用电子束蒸发的方法沉积.AlGaN表面欧姆接触的比接触电阻率为7.48×10-4Ω/cm2,器件的I-V测试表明该AlGaN肖特基二极管具有较好的整流特性.根据器件的正向,I-V特性计算得到器件的势垒高度和理想因子分别为0.57eV和4.83.将器件在300℃中温退火,器件的电学性能有所改善.     

Schottky barrier parameters and structural properties of rapidly annealed Zr Schottky electrode on p-type GaN

The Schottky barrier junction parameters and structural properties of Zr/p-GaN Schottky diode are explored at various annealing temperatures. Experimental analysis showed that the barrier height (BH) of the Zr/pGaN Schottky diode increases with annealing at 400℃ (0.92 eV (I-V)/1.09 eV (C-V)compared to the asdeposited one (0.83 eV (I-V)/0.93 eV (C-V). However, the BH decreases after annealing at 500℃. Also, at different annealing temperatures, the series resistance and BH are assessed by Cheung''s functions and their values compared. Further, the interface state density (N_SS)of the diode decreases after annealing at 400℃ and then somewhat rises upon annealing at 500℃. Analysis reveals that the maximum BH is obtained at 400℃, and thus the optimum annealing temperature is 400℃ for the diode. The XPS and XRD analysis revealed that the increase in BH may be attributed to the creation of Zr-N phases with increasing annealing up to 400℃. The BH reduces for the diode annealed at 500℃, which may be due to the formation of Ga-Zr phases at the junction. The AFM measurements reveal that the overall surface roughness of the Zr film is quite smooth during rapid annealing process.     

Ohmic contact behaviour of Co/C/4H-SiC structures

The electrical contact properties of Co/4H-SiC structures are investigated.A carbon interfacial layer between a Co film and SiC is used to improve the Ohmic contact properties significantly.The C film is deposited prior to Co film deposition on SiC using DC sputtering.The high quality Ohmic contact and specific contact resistivity of 2.30×10^-6Ω·cm² are obtained for Co/C/SiC structures after two-step annealing at 500℃for 10 min and 1050℃for 3 min.The physical properties of the contacts are examined by using XRD.The results indicate that the Co-based metal contacts have better structural stability of silicide phases formed after the high temperature annealing and carbon-enriched layer is produced below the contact,playing a key role in forming an Ohmic contact through the reduction of effective Schottky barrier height for the transport of electrons.The thermal stability of Au/Co/C/SiC Ohmic contacts is investigated.The contacts remain Ohmic on doped n-type(2.8×10¹⁸ cm^-3) 4H-SiC after thermal aging treatment at 500℃for 20 h.     

The ohmic contact formation mechanism of Au/Pt/Pd ohmic contact to p-ZnTe

The ohmic contact formation mechanism and the role of Pt layer of Au(500Å) Pt(500Å)/Pd(100Å) ohmic contact to p-ZnTe were investigated. The specific contact resistance of Au/Pt/Pd contact depended strongly on the annealing temperature. As the annealing temperature increased, the specific contact resistance decreased and reached a minimum value of 6×10^?6 Θcm² at 200°C. From the Hall measurement, the hole concentration increased with the annealing temperature and reached a maximum value of 2.3×10¹⁹ cm^?3 at 300°C. The Schottky barrier height decreased with the increase of annealing temperature and reached a minimum value of 0.34 eV at 200°C and it was due to the interfacial reaction of Pd and ZnTe. Therefore, the decrease of contact resistance was due to the increase of doping concentration as well as the decrease of Schottky barrier height by the interfacial reaction of Pd ZnTe. The specific contact resistances of Au Pd, Au/Pt/Pd and Au/Mo/Pd as a function of annealing time was investigated to clarify the role of Pt layer.     

Schottky barrier heights of contact metals to p-type ZnSe

Schottky barrier heights (SBHs) of a variety of metals (In, Cd, Nb, Ti, W, Cu, Ag, Au, Ni, Pt, and Se) contacting to p-ZnSe grown by a molecular beam epitaxy method were determined by analyzing capacitance-voltage (C-V) and/or current density-voltage (J-V) curves. The SBH values of the Au and Ni contacts were determined from intersections of straight lines of the C⁻²-V curves to be 1.23 and 1.13 eV, respectively. The J-V calculations provided a large SBH value of 1.2 ± 0.1 eV for a variety of metals, indicating that the Fermi-level could be pinned at the contact interface. Reduction of the SBH values to a level lower than 0.4 eV and/or increase of doping concentrations to a level higher than 10²⁰ cm⁻³ are essential to obtain an ohmic contact with contact resistivity of around 10⁻³ Ω·cm².     

Annealing temperature dependence of TiB2 schottky barrier contacts on n-GaN

The annealing temperature (25–700°C) dependence of Schottky contact characteristics on n-GaN using a TiB₂/Ti/Au metallization scheme deposited by sputtering is reported. The Schottky barrier height increased from 0.65 to 0.68 eV as the anneal temperature was varied from 25°C to 350°C and decreased to 0.55 eV after annealing at 700°C. The barrier height showed no measurable dependence on measurement temperature up to 150°C. The elemental profile obtained from samples annealed at 350°C showed limited Ti diffusion from the elemental Ti layer into the gold layer. Annealing at 700°C produced significant out-diffusion of this layer, while the TiB₂ layer retained its stability. These contacts show promise for applications requiring good thermal stability, such as power amplifiers, but much more work is needed to establish their long-term reliability. In addition, TiB₂ has a strong propensity for oxidation, and it is imperative that overlayers such as Au be deposited in the same deposition chamber.     

Annealing temperature effect on electrical and structural properties of Cu/Au Schottky contacts to n-type GaN

Schottky contacts were fabricated on n-type GaN using a Cu/Au metallization scheme, and the electrical and structural properties have been investigated as a function of annealing temperature by current-voltage (I-V), capacitance-voltage (C-V), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) measurements. The extracted Schottky barrier height of the as-deposited contact was found to be 0.69 eV (I-V) and 0.77 eV (C-V), respectively. However, the Schottky barrier height of the Cu/Au contact slightly increases to 0.77 eV (I-V) and 1.18 eV (C-V) when the contact was annealed at 300 °C for 1 min. It is shown that the Schottky barrier height decreases to 0.73 eV (I-V) and 0.99 eV (C-V), 0.56 eV (I-V) and 0.87 eV (C-V) after annealing at 400 °C and 500 °C for 1 min in N₂ atmosphere. Norde method was also used to extract the barrier height of Cu/Au contacts and the values are 0.69 eV for the as-deposited, 0.76 eV at 300 °C, 0.71 eV at 400 °C and 0.56 eV at 500 °C which are in good agreement with those obtained by the I-V method. Based on Auger electron spectroscopy and X-ray diffraction results, the formation of nitride phases at the Cu/Au/n-GaN interface could be the reason for the degradation of Schottky barrier height upon annealing at 500 °C.     

采用场板和边缘终端技术的大电流Ni/4H-SiC SBDs

研究了4H-SiC低缺陷密度外延层的制造和Ni/SiC肖特基势垒二极管的正、反向电学特性。采用了偏8°4H-SiC衬底上台阶控制外延方法进行同质外延,外延温度1580℃,最后得到了低缺陷密度的3英寸外延片。采用了原子力显微镜和扫描电子显微镜进行了测试。在外延片上进行的Ni/4H-SiC肖特基势垒二极管的制造,采用了B+离子注入形成的一个非晶区域作为边缘终端,然后使用经过1000℃下退火10min的PECVD生长的SiO2作为场板介质。最终得到的Ni/4H-SiC肖特基势垒二极管的理想因子为1.03,势垒高度为1.6eV,在反向偏压1102V时,漏电流密度只有1.15×10-3A/cm2。在正向压降3.5V时得到了7.47A的大电流输出,特征导通电阻为6.22Ω.cm2。     

Improved Ni Schottky Contacts on <Emphasis Type="Italic">n</Emphasis>-Type 4H-SiC Using Thermal Processing

High-temperature processing was used to improve the barrier properties of three sets of n-type 4H-SiC Schottky diodes fabricated with Ni Schottky contacts. We obtained an optimum average barrier height of 1.78 eV and an ideality factor of 1.09 using current–voltage measurements on diodes annealed in vacuum at 500°C for 24 h. Nonannealed contacts had an average barrier height of 1.48 eV and an ideality factor of 1.85. The Rutherford backscattering spectra of the Ni/SiC contacts revealed the formation of a nickel silicide at the interface, accompanied by a substantial reduction in oxygen following annealing.