4H-SiC PiN功率二极管研制及其关键技术研究

发布时间：2018-06-04 23:31

  本文选题：4H-SiC + PiN功率二极管　； 参考：《西安电子科技大学》2016年博士论文

【摘要】：碳化硅(SiC)由于具有禁带宽度大、临界击穿电场高、电子饱和漂移速度高、热导率高以及抗辐射位移能高等优点,成为制备高温、高频、大功率和抗辐射电力电子器件极具潜力的宽带隙半导体材料。在功率电力电子系统中,一个良好的整流器应具有耐高压、低漏电、大电流处理能力等特性,因此作为一种双极载流子器件,4H-SiC PiN二极管就成为了重要的大功率整流器关键部件。近些年来,国外对于4H-SiC PiN功率二极管已有了很多的研究报道,取得了良好的阶段性成果,但是在器件制备的关键技术如Mesa刻蚀、P型欧姆接触以及实用可靠的终端设计等方面,还存在较多的问题和难点。而国内由于受材料制备和较高的工艺要求等因素限制,相关的实验报道还很少。本文主要在以下几个方面对4H-SiC PiN功率二极管的关键技术以及器件整体制造做出了针对性的研究:1.理论分析了4H-SiC PiN功率二极管的直流器件物理特性,以及与4H-SiC材料特性相关的物理机制影响因素和器件设计要点。建立了合适的数值分析物理模型,同时给出了可靠的模型材料参数。2.基于ICP-Bosch刻蚀工艺和F-O基刻蚀气体,系统研究了4H-SiC Mesa刻蚀中的微沟槽效应、形貌缺陷等问题及其解决方法。首先,通过研究钝化气体流量对刻蚀速率、形貌的影响,分析了钝化作用机制和流量优化规律。其次,通过对比不同的刻蚀时间(te)/钝化时间(tp)以及二者比例所产生的刻蚀效果,建立了刻蚀过程对比模型,结合钝化作用分析了微沟槽的形成、扩展以及消除机理,并提出了“高频刻蚀”概念,由此获得了无微沟槽的Mesa刻蚀形貌。最后,研究分析了ICP/Bias功率比对刻蚀形貌的影响,研究表明过大或过小的ICP/Bias功率比都会引起物理和化学刻蚀机制的失衡,从而导致Mesa形貌产生严重的缺陷。3.基于不同的Ti/Al基接触方案对比,系统研究了在外延特征粗糙表面(Step-bunching)上制备的P型4H-SiC欧姆接触特性。通过分析表面状态变化的内因及其对接触系统内在相变的影响,揭示了欧姆接触形成的“step-bunching有利机制”,即高温下金半之间的强固相反应动力使亚稳态结构的step-bunching分解,过量析出的C、Si原子主导了界面及接触层中C、Si相的种类,形成了全局分布的非晶SiC以及有利于欧姆接触特性的Ti3SiC2和石墨态。电学特性和微结构表征进一步揭示了“液相辅助界面反应机制”对Ti/Al P型欧姆接触的形成和促进作用,即高度的合金界面液相有助于有序结构的(0001)Ti3SiC2//(0001)SiC异质外延界面的形成。基于欧姆形成和促进机制的讨论,采用50%低Al组分的Ti(100 nm)/Al(100 nm)接触,并经过1000°C/3 min退火,在具有显著step-bunching表面的高掺杂P型4H-SiC外延层上制备了达到国际领先水平的欧姆接触,测试得到的比接触电阻值为2.7×10-6Ωcm2。同时实现了接触退火形貌的改善。4.对4H-SiC PiN功率二极管从材料制备、版图与工艺流程设计、器件制造到电学特性测试分析做了初步系统的研究。通过优化外延工艺和加入缓冲层结构,生长得到了具有低表面结构缺陷密度的连续外延P+N结构。其中,N型漂移区(i区)的掺杂浓度和厚度分别约为5×1015 cm-3和15.5μm。器件采用单一Mesa刻蚀终端,经过氧化、欧姆接触形成、PI固化等工艺步骤,完成流片制造。室温直流特性测试显示,大管芯器件(电极面积0.023 cm2)的正向开态电流可达30 A,特征导通电阻为0.76mΩcm2;最大击穿电压约为1300 V,由此可得器件品质因数为2224 MW/cm2。小管芯器件(Mesa面积0.005 cm2)的最大击穿电压约为1565 V。升温直流特性测试揭示了载流子迁移率在高温高电流下的退化现象,改变了PiN二极管的开态负温度变化趋势。分别对Mesa微沟槽、P型欧姆接触质量差异进行了量化的电学特性评估。结果表明,微沟槽使器件击穿特性退化,而对器件的漏电及正向特性没有影响。P型欧姆接触质量直接影响器件的开态压降大小以及大电流处理能力。对封装器件进行反向恢复测试,提取少子寿命约为1μs。最后,通过对比实验结果与低场迁移率模型修正的数值仿真,验证了所制备的器件在正向开态下存在迁移率各向异性效应的影响。5.基于多区效应原理,设计了一种单注入形成的多台阶JTE结构(Single implanted multiple steps JTE,SIMS-JTE),并仿真研究了SIMS-JTE掺杂剂量、step电荷梯度等结构参数对10 kV级4H-SiC PiN功率二极管击穿特性的影响。根据电场分布变化,分析了SIMS-JTE结构具有高击穿效率和宽优值剂量窗口的基本物理机制,即多区step分享电场并逐级发挥效用,缓解了电场集中且使最大峰值电场位缓慢漂移变化。step电荷梯度大小强烈影响多区作用效率,根据优值电荷梯度分析,归纳得到了step设计的一般原则。另外,针对SIMS-JTE所需的阶梯注入掩模,提出了一种精确实用的多层Al膜淀积技术。并通过离子注入仿真和实验对比,分析了不同厚度Al膜对step注入分布的影响。最后,根据以上器件仿真设计和掩膜制备及注入研究,在厚度100μm、掺杂浓度3×1014 cm-3的N型外延片上制备了具有不同JTE结构的10 kV级4H-SiC PiN功率二极管,并通过测试对比,验证了在高JTE注入剂量条件下(1.72×1013 cm-2),SIMS-JTE(4-steps)结构相比于单区JTE和SIMS-JTE(2-steps)对于器件击穿特性的显著提升,其测试最大击穿电压达到11.1 kV。
[Abstract]:Silicon carbide (SiC) has the advantages of high band gap, high critical breakdown electric field, high electron saturation drift speed, high thermal conductivity and high radiation resistance. It has become a potential wide band gap semiconductor material for the preparation of high temperature, high frequency, high power and anti radiation power electronic devices. A good rectification in power electronic system is a good rectification. The device should have the characteristics of high voltage resistance, low leakage and high current processing capability. So as a bipolar carrier device, 4H-SiC PiN diode has become the key component of the important power rectifier. In recent years, there have been a lot of research reports on 4H-SiC PiN power diodes in recent years. The key technology of device preparation, such as Mesa etching, P type ohm contact and practical and reliable terminal design, has many problems and difficulties. However, there are few related experimental reports due to the limitation of material preparation and high technical requirements in China. This paper mainly deals with the 4H-SiC PiN power diode in the following aspects. The key technology and the overall fabrication of the device have been studied. 1. the physical characteristics of the DC device of 4H-SiC PiN power diode are analyzed theoretically, the physical mechanism influencing factors related to the properties of the 4H-SiC material and the key point of the device design are analyzed. A suitable numerical model is established, and a reliable model material reference is given. .2. based on ICP-Bosch etching process and F-O based etching gas, the micro groove effect, morphologies and other problems in 4H-SiC Mesa etching are systematically studied. First, the effect of passivation gas flow on the etching rate and morphology is studied, and the mechanism of passivation and the optimization of flow rate are analyzed. Secondly, the comparison of different engraving is made by comparing different engraving. The etching effect of etching time (TE) / passivation time (TP) and the ratio of two is established, and the contrast model of etching process is established. The formation, expansion and elimination mechanism of micro groove are analyzed by the effect of passivation, and the concept of "high frequency etching" is put forward, thus the Mesa etching morphology of no microgroove is obtained. Finally, the power of ICP/Bias is studied and analyzed. Compared to the influence of the etching morphology, it is shown that the excessive or too small ICP/Bias power ratio causes the imbalance of the physical and chemical etching mechanism, which leads to the serious defect of the Mesa morphology,.3. based on the comparison of the different Ti/Al based contact schemes, the P type 4H-SiC ohm prepared on the epitaxial rough surface (Step-bunching) is systematically studied. By analyzing the internal causes of the change of the surface state and its influence on the internal phase transition of the contact system, the "step-bunching favorable mechanism" formed by ohmic contact is revealed, that is, the strong solid phase reaction force between the gold half of the high temperature makes the step-bunching decomposition of the metastable structure, the over the precipitated C, and the Si atom dominates the interface and contact layer. The type of C and Si phase formed the global distribution of amorphous SiC and the Ti3SiC2 and graphite states which are beneficial to the ohmic contact characteristics. The electrical properties and microstructural characterization further reveal the formation and promotion of the "liquid phase assisted interface reaction mechanism" for the Ti/Al P type ohm contact, that is, the high alloy interface liquid phase is helpful to the ordered structure (0 001) formation of the heteroepitaxial interface of Ti3SiC2// (0001) SiC. Based on the discussion of the ohm formation and promotion mechanism, the Ti (100 nm) /Al (100 nm) contact of 50% low Al components and 1000 degree C/3 min annealing have been used to prepare the ohm contact on the highly doped P type 4H-SiC epitaxial layer with a significant step-bunching surface, and the test results are obtained. The contact resistance value is 2.7 x 10-6 Omega cm2. simultaneously to achieve the improvement of the contact annealing morphology..4. to the 4H-SiC PiN power diode from material preparation, layout and process design, device manufacturing to electrical characteristics test analysis made preliminary systematic research. By optimizing the epitaxial process and adding buffer layer structure, the growth has been low. The continuous epitaxial P+N structure of the surface structure defect density, in which the doping concentration and thickness of the N type drift region (I zone) are about 5 x 1015 cm-3 and 15.5 mu m. respectively using a single Mesa etching terminal, through oxidation, ohm contact formation and PI curing process, complete flow sheet making. The positive open state current of the area of 0.023 cm2 is up to 30 A, the characteristic resistance is 0.76M Omega cm2, and the maximum breakdown voltage is about 1300 V. Thus the maximum breakdown voltage of the device's quality factor of 2224 MW/cm2. small tube core device (Mesa area 0.005 cm2) is about 1565 V. heating direct current test reveals the carrier mobility under high temperature and high current. The negative temperature change of PiN diode is changed. The electrical characteristics of Mesa micro groove and P type ohm contact quality are evaluated respectively. The results show that the micro groove makes the breakdown characteristics of the device degenerate, but the leakage and positive characteristics of the device have no effect on the.P type ohm contact quality directly affecting the device. The size of open state pressure drop and the ability of large current processing. The reverse recovery test of the package device is carried out. The lifetime of the minority carrier is about 1 s.. The effect of the anisotropy on the mobility of the device in the forward open state is verified by the comparison of the experimental results and the numerical simulation of the low field mobility model. The effect of.5. is based on the multi zone effect. According to the principle, a single injection multi step JTE structure (Single implanted multiple steps JTE, SIMS-JTE) is designed. The influence of structure parameters such as SIMS-JTE doping dose, step charge gradient and other structural parameters on the breakdown characteristics of 10 kV 4H-SiC PiN power diode is simulated. The structure has high breakdown based on the variation of the electric field distribution. The basic physical mechanism of the efficiency and the wide optimal value of the dose window, that is, the multi zone step sharing the electric field and giving full play to the utility, relieves the concentration of the electric field and makes the maximum peak electric field shift change slowly and changes the size of the.Step charge gradient. The general principle of the step design is summed up according to the gradient analysis of the optimal charge. An accurate and practical multilayer Al membrane deposition technology is proposed for the stepped injection mask required by SIMS-JTE. The influence of different thickness of Al film on the step injection distribution is analyzed by ion implantation simulation and experimental comparison. Finally, the thickness of the above device is designed and the mask preparation and injection research, at the thickness of 100 mu m, and the doping concentration of 3 x 1014 C The 10 kV 4H-SiC PiN power diodes with different JTE structures are prepared on the N epitaxial slice of m-3. The test comparison shows that the SIMS-JTE (4-steps) structure is significantly higher than the single region JTE and SIMS-JTE (1.72 * 1013 cm-2), and the maximum breakdown voltage is measured. To 11.1 kV.
【学位授予单位】：西安电子科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN313.4
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本文编号：1979337