發(fā)布時間：2018-06-04 23:31

  本文選題：4H-SiC + PiN功率二極管��； 參考：《西安電子科技大學(xué)》2016年博士論文

【摘要】：碳化硅(SiC)由于具有禁帶寬度大、臨界擊穿電場高、電子飽和漂移速度高、熱導(dǎo)率高以及抗輻射位移能高等優(yōu)點,成為制備高溫、高頻、大功率和抗輻射電力電子器件極具潛力的寬帶隙半導(dǎo)體材料。在功率電力電子系統(tǒng)中,一個良好的整流器應(yīng)具有耐高壓、低漏電、大電流處理能力等特性,因此作為一種雙極載流子器件,4H-SiC PiN二極管就成為了重要的大功率整流器關(guān)鍵部件。近些年來,國外對于4H-SiC PiN功率二極管已有了很多的研究報道,取得了良好的階段性成果,但是在器件制備的關(guān)鍵技術(shù)如Mesa刻蝕、P型歐姆接觸以及實用可靠的終端設(shè)計等方面,還存在較多的問題和難點。而國內(nèi)由于受材料制備和較高的工藝要求等因素限制,相關(guān)的實驗報道還很少。本文主要在以下幾個方面對4H-SiC PiN功率二極管的關(guān)鍵技術(shù)以及器件整體制造做出了針對性的研究:1.理論分析了4H-SiC PiN功率二極管的直流器件物理特性,以及與4H-SiC材料特性相關(guān)的物理機制影響因素和器件設(shè)計要點。建立了合適的數(shù)值分析物理模型,同時給出了可靠的模型材料參數(shù)。2.基于ICP-Bosch刻蝕工藝和F-O基刻蝕氣體,系統(tǒng)研究了4H-SiC Mesa刻蝕中的微溝槽效應(yīng)、形貌缺陷等問題及其解決方法。首先,通過研究鈍化氣體流量對刻蝕速率、形貌的影響,分析了鈍化作用機制和流量優(yōu)化規(guī)律。其次,通過對比不同的刻蝕時間(te)/鈍化時間(tp)以及二者比例所產(chǎn)生的刻蝕效果,建立了刻蝕過程對比模型,結(jié)合鈍化作用分析了微溝槽的形成、擴展以及消除機理,并提出了“高頻刻蝕”概念,由此獲得了無微溝槽的Mesa刻蝕形貌。最后,研究分析了ICP/Bias功率比對刻蝕形貌的影響,研究表明過大或過小的ICP/Bias功率比都會引起物理和化學(xué)刻蝕機制的失衡,從而導(dǎo)致Mesa形貌產(chǎn)生嚴(yán)重的缺陷。3.基于不同的Ti/Al基接觸方案對比,系統(tǒng)研究了在外延特征粗糙表面(Step-bunching)上制備的P型4H-SiC歐姆接觸特性。通過分析表面狀態(tài)變化的內(nèi)因及其對接觸系統(tǒng)內(nèi)在相變的影響,揭示了歐姆接觸形成的“step-bunching有利機制”,即高溫下金半之間的強固相反應(yīng)動力使亞穩(wěn)態(tài)結(jié)構(gòu)的step-bunching分解,過量析出的C、Si原子主導(dǎo)了界面及接觸層中C、Si相的種類,形成了全局分布的非晶SiC以及有利于歐姆接觸特性的Ti3SiC2和石墨態(tài)。電學(xué)特性和微結(jié)構(gòu)表征進(jìn)一步揭示了“液相輔助界面反應(yīng)機制”對Ti/Al P型歐姆接觸的形成和促進(jìn)作用,即高度的合金界面液相有助于有序結(jié)構(gòu)的(0001)Ti3SiC2//(0001)SiC異質(zhì)外延界面的形成�；跉W姆形成和促進(jìn)機制的討論,采用50%低Al組分的Ti(100 nm)/Al(100 nm)接觸,并經(jīng)過1000°C/3 min退火,在具有顯著step-bunching表面的高摻雜P型4H-SiC外延層上制備了達(dá)到國際領(lǐng)先水平的歐姆接觸,測試得到的比接觸電阻值為2.7×10-6Ωcm2。同時實現(xiàn)了接觸退火形貌的改善。4.對4H-SiC PiN功率二極管從材料制備、版圖與工藝流程設(shè)計、器件制造到電學(xué)特性測試分析做了初步系統(tǒng)的研究。通過優(yōu)化外延工藝和加入緩沖層結(jié)構(gòu),生長得到了具有低表面結(jié)構(gòu)缺陷密度的連續(xù)外延P+N結(jié)構(gòu)。其中,N型漂移區(qū)(i區(qū))的摻雜濃度和厚度分別約為5×1015 cm-3和15.5μm。器件采用單一Mesa刻蝕終端,經(jīng)過氧化、歐姆接觸形成、PI固化等工藝步驟,完成流片制造。室溫直流特性測試顯示,大管芯器件(電極面積0.023 cm2)的正向開態(tài)電流可達(dá)30 A,特征導(dǎo)通電阻為0.76mΩcm2;最大擊穿電壓約為1300 V,由此可得器件品質(zhì)因數(shù)為2224 MW/cm2。小管芯器件(Mesa面積0.005 cm2)的最大擊穿電壓約為1565 V。升溫直流特性測試揭示了載流子遷移率在高溫高電流下的退化現(xiàn)象,改變了PiN二極管的開態(tài)負(fù)溫度變化趨勢。分別對Mesa微溝槽、P型歐姆接觸質(zhì)量差異進(jìn)行了量化的電學(xué)特性評估。結(jié)果表明,微溝槽使器件擊穿特性退化,而對器件的漏電及正向特性沒有影響。P型歐姆接觸質(zhì)量直接影響器件的開態(tài)壓降大小以及大電流處理能力。對封裝器件進(jìn)行反向恢復(fù)測試,提取少子壽命約為1μs。最后,通過對比實驗結(jié)果與低場遷移率模型修正的數(shù)值仿真,驗證了所制備的器件在正向開態(tài)下存在遷移率各向異性效應(yīng)的影響。5.基于多區(qū)效應(yīng)原理,設(shè)計了一種單注入形成的多臺階JTE結(jié)構(gòu)(Single implanted multiple steps JTE,SIMS-JTE),并仿真研究了SIMS-JTE摻雜劑量、step電荷梯度等結(jié)構(gòu)參數(shù)對10 kV級4H-SiC PiN功率二極管擊穿特性的影響。根據(jù)電場分布變化,分析了SIMS-JTE結(jié)構(gòu)具有高擊穿效率和寬優(yōu)值劑量窗口的基本物理機制,即多區(qū)step分享電場并逐級發(fā)揮效用,緩解了電場集中且使最大峰值電場位緩慢漂移變化。step電荷梯度大小強烈影響多區(qū)作用效率,根據(jù)優(yōu)值電荷梯度分析,歸納得到了step設(shè)計的一般原則。另外,針對SIMS-JTE所需的階梯注入掩模,提出了一種精確實用的多層Al膜淀積技術(shù)。并通過離子注入仿真和實驗對比,分析了不同厚度Al膜對step注入分布的影響。最后,根據(jù)以上器件仿真設(shè)計和掩膜制備及注入研究,在厚度100μm、摻雜濃度3×1014 cm-3的N型外延片上制備了具有不同JTE結(jié)構(gòu)的10 kV級4H-SiC PiN功率二極管,并通過測試對比,驗證了在高JTE注入劑量條件下(1.72×1013 cm-2),SIMS-JTE(4-steps)結(jié)構(gòu)相比于單區(qū)JTE和SIMS-JTE(2-steps)對于器件擊穿特性的顯著提升,其測試最大擊穿電壓達(dá)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.
【學(xué)位授予單位】：西安電子科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TN313.4
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本文編號：1979337