氮化物MIS-HEMT器件界面工程研究

发布时间：2018-06-27 14:22

本文选题：氮化铝 + 氮化镓　；参考：《西安电子科技大学》2016年博士论文

【摘要】：与传统的肖特基栅HEMT相比,GaN基绝缘栅HEMT器件可以有效减小栅极泄漏电流,在高效微波功率放大器、高压开关等应用中具有广阔的应用前景。然而,栅绝缘层与氮化物之间严重的界面问题会引起器件性能退化和可靠性问题,近年来成为国际研究的热点。本论文创新性地采用AlN栅绝缘层替代常用的栅氧介质,基于高质量AlN绝缘层材料制备工艺和优化的界面预处理工艺,研制了高界面质量的GaN基MIS-HEMT器件,并利用等效电路和解析模型对其界面特性进行了定量表征。论文的主要研究成果包括：(1)采用等离子增强原子层沉积技术在低温下制备了高质量的AlN绝缘层材料。采用TMA和NH3作为反应前驱体源,通过优化前驱体脉冲时间、吹扫时间、RF功率等工艺参数,在100℃-300℃工艺温度范围内实现了AlN薄膜的自限制饱和生长。A1N薄膜沉积速率约为0.081nm/cycle,实现了原子尺度上的膜厚精确控制。通过优化工艺温度,在300℃下得到了光学禁带宽度为5.8eV、表面粗糙度RMS小于0.5nm的AlN薄膜。XPS测试结果显示,PEALD沉积AlN薄膜中氧杂质原子含量处于13%的较低水平,Al/N原子比为1.6。AlN薄膜中不含碳杂质,说明优化的沉积工艺有效避免了TMA前驱体中的碳原子嵌入。快速热退火处理使薄膜结构和电学特性进一步改善,优化的退火温度范围是450℃。(2)开发并优化了GaN基MIS-HEMT器件的低损伤界面预处理技术和表面钝化工艺。HF溶液处理使AlGaN/GaN异质结方阻显著减小,但是导致欧姆接触特性恶化,所以本论文采用对沟道和欧姆接触影响不大的KOH碱溶液化学清洗工艺。Hall测试表明,KOH溶液清洗、N2等离子体处理、02/N2等离子体处理分别使2DEG密度升高10%,迁移率降低10-20%；NH3/N2等离子体处理过程,含氢基团使2DEG密度降低约10%,迁移率提高约10%。基于表面处理结果优化了MIS-HEMT器件的原位界面预处理工艺,确定NH3/N2等离子体预处理可以使器件获得最优的界面和沟道输运特性。研究了10nm表面钝化层对异质结沟道特性的影响,Hall测试显示PEALD沉积、ALD沉积PECVD沉积SiN分别使异质结方阻减小10%以上。拉曼测试表明钝化层对异质结应力作用很小,沟道输运特性变化来源十表而调制作用。A1203钝化层中含有-OH基团,ON使界面态和2DEG面密度增大;A1N和SiN生长过程中有NH3参与反反应,表面施主态减少导致2DEG密度降低20%-50%,迁移率提高至原来的2倍,且AlN饨化层的表面调制作用更强。脉冲测试表明AlN钝化器件的电流崩塌量仅为6%,远远低于常规PECVD沉积SiN钝化器件的26%,从而确定PEALD沉积AlN为最优的表面钝化层材料。(3)基于PEALD沉积AlN栅绝缘层和界面预处理技术,研制了高界面质量和沟道输运特性的AlGaN/GaN MIS-HEMT器件。与肖特基栅HEMT相比,采用20nm厚Al20O栅绝缘层的MOS-HEMT器件Vth负向漂移5.2V,而采用AlN栅绝缘层的MIS-HEMT器件Vth仅负漂了0.8V。AlN栅绝缘层使绝缘栅异质结构的C-V测试Vth回滞电压从0.6V减小至50mV以下,变频C-V表明界面态密度从4.61×1012cm-2减小至2.78×1012cm-2。AlN栅绝缘层使GaN基绝缘栅HEMT器件沟道输运特性和场效应迁移率提高,0.5μm栅长器件的峰值跨导从203mS/mm提高到289mS/mm,甚至超过了肖特基栅器件的270mS/mm。AlN栅绝缘层有效改善了绝缘栅HEMT器件的频率特性和稳定性,与A1203栅绝缘层器件相比fr/fmax水平从10.8GHz/11.6GHz提高到13.4GHz/16.1GHz。研制的5nm-Al2O3/1nm-AlN超薄叠层介质凹槽栅MIS-HEMT饱和输出电流和峰值跨导分别为1.24A/mmm和413mS/mm,开关态电流比达到10-10。100μm凹槽栅MIS-HEMT器件的fr/fmax达到24GHz/102GHz,AB类工作条件下5GHz连续波输出功率超过7W/mm,功率附加效率在40%以上。(4)建立了GaN基绝缘栅HEMT器件的界面电荷定量表征模型,并对AlN/势垒层和A1203/势垒层界面电荷进行了对比分析。建立了GaN基绝缘栅异质结构的界面态等效电路模型,利用变频电导法成功分离了异质结界面和绝缘层/势垒层两个界面处的陷阱,且并联电导谱线拟合方法比常用的C-V测试方法更精确,此方法得到了国际同行的高度评价。PEALD沉积A1N栅绝缘层与势垒层之间界面态密度为0.97-2.2×1013cm-2eV-1,分布在导带底以下0.45-0.67eV能级范围；ALD沉积A1203栅绝缘层与势垒层界面ON缺陷使陷阱能级变深为0.52-0.72eV,态密度增大到1.6-9.0×1013cm-2eV-1。基于异质结能带结构和界面电荷分布,建立了肖特基栅和绝缘栅异质结构的平带电压解析模型,比直接采用阂值电压解析法更加准确。A1203与势垒层界面电荷密度高达8.98x1012cm-2,引起平带电压和阈值电压负漂3.78V；而AlN绝缘层界面电荷密度为-1.18×1012cm-2,界面固定电荷密度极低,而以界面态为主导,界面有效电荷导致平带电压正向漂移0.32V。
[Abstract]:Compared with the traditional Schottky gate HEMT, GaN based insulated gate HEMT devices can effectively reduce gate leakage current, and have broad application prospects in high performance microwave power amplifiers, high voltage switches and other applications. However, the serious interface problems between the gate insulation and nitride will cause the performance degradation and reliability of the devices. This paper innovatively uses the AlN gate insulating layer instead of the common gate oxygen medium. Based on the preparation technology of high quality AlN insulating material and the optimized interface pretreatment process, the GaN based MIS-HEMT device with high interface quality is developed, and the interface characteristics are quantitatively characterized by the equivalent circuit and the analytical model. The main achievements of this paper are as follows: (1) high quality AlN insulating material was prepared by plasma enhanced atomic layer deposition at low temperature. Using TMA and NH3 as the precursor of the reaction, the AlN film was realized by optimizing the process parameters such as the pulse time of the precursor, the blowing time and the RF power, and at the temperature range of -300 C at 100 degrees centigrade. The deposition rate of the self limiting saturated.A1N film is about 0.081nm/cycle, and the membrane thickness is precisely controlled at the atomic scale. By optimizing the process temperature, the.XPS test results of the AlN film with the optical band width of 5.8eV and the surface roughness RMS less than 0.5nm show that the oxygen impurity atom content in the PEALD deposited AlN thin film is at 13%. The lower level of the Al/N atom ratio is carbon free in the 1.6.AlN film. It shows that the optimized deposition process effectively avoids the carbon atom embedded in the precursor of TMA. Rapid thermal annealing can further improve the structure and electrical properties of the film, and the optimized annealing temperature range is 450. (2) the low damage of the GaN based MIS-HEMT device is developed and optimized. .HF solution treatment of interface pretreatment and surface passivation process reduces the square resistance of AlGaN/GaN heterojunction significantly, but leads to the deterioration of ohm contact characteristics. Therefore, the.Hall test of KOH alkali solution, which has little influence on the channel and ohm contact, shows that KOH solution cleaning, N2 plasma treatment, 02/N2 plasma The density of 2DEG increased by 10% and the mobility was reduced by 10-20%, and the NH3/N2 plasma treatment process, the hydrogen containing group reduced the 2DEG density by about 10%, and the mobility increased about 10%. based on the surface treatment results to optimize the in-situ interface pretreatment process of the MIS-HEMT device, and the NH3/N2 plasma pretreatment could make the device get the best interface. The influence of the passivation layer on the 10nm surface on the characteristics of the heterojunction channel is studied. The Hall test shows that the PEALD deposition and the ALD deposition of PECVD deposition SiN reduce the heterojunction square resistance by more than 10% respectively. The Raman test shows that the passivation layer has little effect on the heterojunction stress, the channel transport characteristics change from the ten table and the modulation action in the passive layer of the.A1203 passivation layer. With the -OH group, the density of the interface state and the 2DEG surface is increased by ON, and NH3 is involved in the reaction during the growth of A1N and SiN. The decrease of the surface donor state causes the 2DEG density to decrease 20%-50%, the mobility increases to 2 times that of the original, and the surface modulation of the AlN ton layer is stronger. The pulse test shows that the current collapse of the AlN passivation device is only 6%, far lower than that of the AlN passivation device. Conventional PECVD deposition of SiN passivation device 26%, thus determining PEALD deposition AlN as the best surface passivation material. (3) based on PEALD deposited AlN gate insulating layer and interface pretreatment technology, a AlGaN/GaN MIS-HEMT device with high interfacial mass and channel transport characteristics is developed. Compared with the Schottky gate HEMT, 20nm thick Al20O gate insulating layer The device Vth is negatively drifting 5.2V, while the MIS-HEMT device using the AlN gate insulating layer is only negatively bleaching the 0.8V.AlN gate insulating layer to reduce the C-V test Vth hysteresis voltage of the insulated gate heterostructure from 0.6V to below 50mV. The frequency conversion C-V indicates that the interface state density is reduced from 4.61 x 1012cm-2 to the 2.78 x grid insulation layer. The transmission characteristics and field effect mobility are improved. The peak transconductance of 0.5 mu m gate length device is increased from 203mS/mm to 289mS/mm, and even the 270mS/mm.AlN gate insulation layer of the Schottky gate device improves the frequency characteristics and stability of the insulated gate HEMT device, and the fr/fmax level is improved from the 10.8GHz/11.6GHz to the A1203 gate insulating layer to the 10.8GHz/11.6GHz. The MIS-HEMT saturated output current and peak transconductance of the 5nm-Al2O3/1nm-AlN super thin layer dielectric groove gate are 1.24A/mmm and 413mS/mm respectively. The switching state current ratio reaches fr/fmax to 24GHz/102GHz of 10-10.100 mu m grooves MIS-HEMT device, and the output power of the 5GHz continuous wave exceeds the output power under the AB class working condition, and the power additional is added. The efficiency is above 40%. (4) the quantitative characterization model of the interface charge of the GaN based insulated gate HEMT is established, and the interface charge of the AlN/ barrier layer and the A1203/ barrier layer is contrasted. The equivalent circuit model of the interface state of the GaN based insulated gate heterostructure is established, and the heterojunction interface and insulating layer / potential barrier are successfully separated by the frequency conversion conductance method. The traps at the two interfaces and the parallel conductance spectrum fitting method are more accurate than the common C-V testing methods. This method obtains the high evaluation of the.PEALD deposition A1N gate insulating layer and the barrier layer of 0.97-2.2 x 1013cm-2eV-1, which is distributed at the 0.45-0.67eV level below the bottom of the guide band, and ALD deposition A1203 gate. The ON defects at the boundary layer and the barrier layer make the trap energy level deep to 0.52-0.72eV, the density of States increases to 1.6-9.0 x 1013cm-2eV-1. based on the structure of the heterojunction energy band and the interface charge distribution. The analytical model of the flat band voltage of the Schottky grid and the insulated gate heterostructure is established, which is more accurate than the barrier voltage analytical method for the.A1203 and the barrier layer. The surface charge density is up to 8.98x1012cm-2, which causes the negative drift of the flat band voltage and the threshold voltage 3.78V, while the interface charge density of the AlN insulating layer is -1.18 x 1012cm-2, the fixed charge density at the interface is very low, and the interface state is the dominant factor in the interface state, and the flat band voltage is positive drift 0.32V..
【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】：TN386

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