SiN钝化前的NF3等离子体处理对AlGaN/GaN HEMT性能的影响

研究了SiN钝化前利用感应耦合等离子体（ICP）对AlGaN/GaN HEMT表面进行NF3等离子体处理对器件性能的影响. 结果表明,运用低能量的NF3等离子体处理钝化前的AlGaN/GaN HEMT表面能有效抑制器件电流崩塌,而器件直流及微波小信号特性则未受影响. 微波功率测试表明,经过6min NF3等离子体处理的AlGaN/GaN HEMT在2GHz, 30V工作电压下达到6.15W/mm的输出功率密度,而未经过处理的器件只达到1.82W/mm的输出功率密度.     

SiN钝化前的NF3等离子体处理对AlGaN/GaN HEMT性能的影响

研究了SiN钝化前利用感应耦合等离子体(ICP)对AlGaN/GaN HEMT表面进行NF3等离子体处理对器件性能的影响.结果表明,运用低能量的NF3等离子体处理钝化前的AlGaN/GaN HEMT表面能有效抑制器件电流崩塌,而器件直流及微波小信号特性则未受影响.微波功率测试表明,经过6min NF3等离子体处理的AIGaN/GaN HEMT在2GHz,30V工作电压下达到6.15W/mm的输出功率密度,而未经过处理的器件只达到1.82W/mm的输出功率密度.     

具有低欧姆接触电阻的高性能AlGaN/GaN HEMT器件研制

研究了AlGaN/GaN HEMT器件Ti/Al/Ti/Au四层金属结构欧姆接触的形成过程.通过系统研究退火条件获得了较低的欧姆接触电阻,实现了10-7Ω·cm2的欧姆接触率,并在此基础上对AlGaN/GaN HEMT欧姆接触形成机理进行了深入讨论.通过器件工艺的优化,研制了高性能的AlGaN/GaN HEMT器件.栅宽40μm的器件跨导达到250mS/mm,fT达到70GHz;栅宽0.8mm的功率器件电流密度达到1.07A/mm(Vg=0.5V),Vds=30V时,8GHz工作频率下(在片测试)器件的输出功率为32.5dBm(1.6W),输出功率密度达到2.14W/mm,功率增益为12.7dB.     

具有低欧姆接触电阻的高性能AlGaN/GaN HEMT器件研制

研究了AlGaN/GaN HEMT器件Ti/Al/Ti/Au四层金属结构欧姆接触的形成过程.通过系统研究退火条件获得了较低的欧姆接触电阻,实现了10-7Ω·cm2的欧姆接触率,并在此基础上对AlGaN/GaN HEMT欧姆接触形成机理进行了深入讨论.通过器件工艺的优化,研制了高性能的AlGaN/GaN HEMT器件.栅宽40μm的器件跨导达到250mS/mm,fT达到70GHz;栅宽0.8mm的功率器件电流密度达到1.07A/mm(Vg=0.5V),Vds=30V时,8GHz工作频率下(在片测试)器件的输出功率为32.5dBm(1.6W),输出功率密度达到2.14W/mm,功率增益为12.7dB.     

具有低欧姆接触电阻的高性能AlGaN/GaN HEMT器件研制

研究了AlGaN/GaN HEMT器件Ti/Al/Ti/Au四层金属结构欧姆接触的形成过程. 通过系统研究退火条件获得了较低的欧姆接触电阻，实现了1E-7Ω·cm2的欧姆接触率，并在此基础上对AlGaN/GaN HEMT欧姆接触形成机理进行了深入讨论. 通过器件工艺的优化，研制了高性能的AlGaN/GaN HEMT器件. 栅宽40μm的器件跨导达到250mS/mm, fT达到70GHz; 栅宽0.8mm的功率器件电流密度达到1.07A/mm(Vg=0.5V),Vds=30V时，8GHz工作频率下（在片测试）器件的输出功率为32.5dBm(1.6W)，输出功率密度达到2.14W/mm，功率增益为12.7dB.     

UV/Ozone 表面处理对AlGaN/GaN HEMTs 性能的影响

工艺过程中对晶圆表面处理对制作出高性能的AlGaN/GaN HEMT起到至关重要的作用,洁净的表面能够有效提高器件性能以及器件可靠性。本文发现通过UV/Ozone表面处理,AlGaN/GaN HEMT器件的欧姆接触以及肖特基接触的电学特性均发生明显变化,根据实验中现象以及相关实验数据,并且采用X射线光电子能谱对实验样品进行表面分析测试,着重阐述了UV/Ozone处理对晶圆表面的作用,以及其影响AlGaN/GaN HEMT器件欧姆接触特性以及肖特基接触特性的原因。     

氧等离子体处理对薄势垒增强型AlGaN/GaN HEMT的影响

提出了一种利用薄势垒结构制造增强型AlGaN/GaN HEMT的方法。研究了SiN钝化对薄势垒AlGaN/GaN异质结的影响,并利用其控制沟道中的二维电子气密度。具有10nm SiN介质插入层欧姆接触在800℃下退火可以得到较好的接触性能。栅极区域中的SiN被刻蚀,以耗尽下面的二维电子气,从而使薄势垒AlGaN/GaN HEMT实现增强特性,其阈值电压为50 mV。对介质刻蚀后暴露的AlGaN表面进行氧等离子体处理,与未经处理的器件作对比,发现阈值电压提升到0.5V,栅漏电降低了一个数量级,击穿特性得到改善,但是最大饱和电流密度降低了。     

非掺杂AlGaN/GaN微波功率HEMT

报道了研制的AlGaN/GaN微波功率HEMT,该器件采用以蓝宝石为衬底的非掺杂AlGaN/GaN异质结构,器件工艺采用了Ti/Al/Ni/Au欧姆接触和Ni/Au肖特基势垒接触以及SiN介质进行器件的钝化.研制的200μm栅宽T型布局AlGaN/GaN HEMT在1.8GHz,Vds=30V时输出功率为28.93dBm,输出功率密度达到3.9W/mm,功率增益为15.59dB,功率附加效率(PAE)为48.3%.在6.2GHz,Vds=25V时该器件输出功率为27.06dBm,输出功率密度为2.5W/mm,功率增益为10.24dB,PAE为35.2%.     

非故意掺杂GaN上Ti/Al/Ni/Au欧姆接触研究

基于圆形传输线模型,研究了背景载流子浓度为71016cm3的非故意掺杂GaN与Ti/Al/Ni/Au多层金属之间欧姆接触的形成。样品在N2气氛中,分别经过温度450,550,700,800,900℃的1 min快速热退火处理后发现,当退火温度高于700℃欧姆接触开始形成,随着温度升高欧姆接触电阻持续下降,在900℃时获得了最低比接触电阻6.6106O·cm2。研究表明,要获得低的欧姆接触电阻,需要Al与Ti发生充分固相反应,并穿透Ti层到达GaN表面;同时,GaN中N外扩散到金属中,在GaN表面产生N空位起施主作用,可提高界面掺杂浓度,从而有助于电子隧穿界面而形成良好欧姆接触。     

氧等离子体对GaNHEMT器件的影响

研究了不同条件下氧等离子体对GaN器件表面的影响。在合适的条件下,氧等离子体可以使AlGaN表面发生氧化,形成Al2O3薄氧化膜,提高肖特基势垒,从而降低GaN器件的阈值电压,提高器件导通电流。该结果可望用于更高性能AlGaN/GaN HEMT器件制备的应用中。     

Structural properties of alloyed Ti/Al/Ti/Au and Ti/Al/Mo/Au ohmic contacts to AlGaN/GaN

Two alloyed ohmic contact structures for AlGaN/GaN–Ti/Al/Ti/Au and Ti/Al/Mo/Au were studied. Both structures were optimized for minimum ohmic contact resistance. Structures grown on sapphire and SiC substrates were used to investigate structural properties of ohmic contacts to AlGaN/GaN. Ohmic contacts to AlGaN/GaN on SiC showed higher contact resistance values compared to contacts to AlGaN/GaN on sapphire. Ohmic contact metals were etched on samples after annealing. The alloyed interface was studied with backside illumination under an optical microscope. Alloyed inclusions associated with threading dislocations were observed on the surface. For the AlGaN/GaN on SiC sample the inclusion density was an order of magnitude lower than for the sample on sapphire. Conductive atomic force microscopy with carbon nanotube tip was used to investigate topography and conductivity profile of the surface after ohmic contact metal removal by etching.     

Ti/Al/Ni/Au在GaN N面上的欧姆接触

以Ti/Al/Ni/Au作为欧姆接触金属体系,通过电感耦合等离子体(ICP)刻蚀的预处理,在氢化物气相外延法生长的单晶氮化镓(GaN)材料的N面实现了良好的欧姆接触,其比接触电阻率为3.7×10-4 Ω·cm2.通过扫描电子显微镜、原子力显微镜、阴极荧光和光致发光谱对GaN N面的表面、光学特性进行了对比表征.结果表明:未刻蚀GaN衬底的N面表面存在一定的损伤层,导致近表面处含有大量缺陷,不利于欧姆接触的形成;而ICP刻蚀处理有效地去除了损伤层.X射线光电子能谱(XPS)分析显示刻蚀后样品的Ga 3d结合能比未刻蚀样品向高能方向移动了约0.3 eV,其肖特基势垒则相应降低,有利于欧姆接触的形成.同时对Fe掺杂半绝缘GaN的N面也进行了刻蚀处理,同样实现了良好的Ti/Al/Ni/Au欧姆接触,其比接触电阻率为0.12 Ω·cm2.     

表面处理对AlGaN欧姆接触的影响及机理

研究了溶液表面处理对AlGaN欧姆接触的影响及机理。用氟硝酸(HNO3+HF)、稀盐酸(HCl)和硫代乙酰胺(CS3CSNH2)溶液处理AlGaN表面后,Ti/Al/Ti/Au电极的比接触电阻率有显著的降低。样品表面Ga3d与O1s的X射线光电子能谱(XPS)测试结果显示:氧元素含量明显降低,表明这三种溶液可以有效地去除AlGaN表面氧化层,其中CS3CSNH2效果最佳;Ga3d峰位在表面处理后发生蓝移现象,相当于AlGaN表面处的费米能级向导带一侧移动,使电子在隧穿过程中的有效势垒高度降低。以上两个因素均对优化AlGaN/GaN欧姆接触有十分重要的意义。     

Systematic characterization of Cl2 reactive ion etchingfor improved ohmics in AlGaN/GaN HEMTs

Pre-metal-deposition reactive ion etching (RIE) was performed on an Al_0.3Ga_0.7N/AlN/GaN heterostructure in order to improve the metal-to-semiconductor contact resistance. An optimum AlGaN thickness for minimizing contact resistance was determined. An initial decrease in contact resistance with etching time was explained in terms of removal of an oxide surface layer and/or by an increase in tunnelling current with the decrease of the AlGaN thickness. The presence of a dissimilar surface layer was confirmed by an initial nonuniform etch depth rate. An increase in contact resistance for deeper etches was experienced. The increase was related to depletion of the two-dimensional (2-D) electron gas (2-DEG) under the ohmics. Etch depths were measured by atomic force microscopy (AFM). The contact resistance decreased from about 0.45 Ωmm for unetched ohmics to a minimum of 0.27 Ωmm for 70 Å etched ohmics. The initial thickness of the AlGaN layer was 250 Å. The decrease in contact resistance, without excessive complications on device processing, supports RIE etching as a viable solution to improve ohmic contact resistance in AlGaN/GaN HEMTs     

基于AlGaN/GaN HEMT的源漏整体刻蚀欧姆接触结构

研究了源漏整体刻蚀欧姆接触结构对AlGaN/GaN高电子迁移率晶体管(HEMT)的欧姆接触电阻和金属电极表面形貌的影响.利用传输线模型(TLM)对样品的电学性能进行测试,使用原子力显微镜(AFM)对样品的表面形貌进行表征,通过透射电子显微镜(TEM)和X射线能谱仪(EDS)对样品的剖面微结构和界面反应进行表征与分析.实验结果显示,采用Ti/Al/Ni/Au(20 nm/120 nm/45 nm/55 nm)金属和源漏整体刻蚀欧姆接触结构,在合金温度870 c℃,升温20 s,退火50 s条件下,欧姆接触电阻最低为0.13 Ω·mm,方块电阻为363.14 Ω/□,比接触电阻率为4.54×10-7Ω·cm2,形成了良好的欧姆接触,降低了器件的导通电阻.     

Nonalloyed ohmic contacts in AlGaN/GaN HEMTs by ion implantation with reduced activation annealing temperature

This letter reports AlGaN/GaN high-electron mobility transistors with capless activation annealing of implanted Si for nonalloyed ohmic contacts. Source and drain areas were implanted with an Si dose of 1/spl times/10/sup 16/ cm/sup -2/ and were activated at /spl sim/1260/spl deg/C in a metal-organic chemical vapor deposition system in ammonia and nitrogen at atmospheric pressure. Nonalloyed ohmic contacts to ion-implanted devices showed a contact resistance of 0.96 /spl Omega//spl middot/mm to the channel. An output power density of 5 W/mm was measured at 4 GHz, with 58% power-added efficiency and a gain of 11.7 dB at a drain bias of 30 V.     

等离子体刻蚀凹栅槽影响AlGaN/GaN HEMT栅电流的机理

对等离子体干法刻蚀形成的凹栅槽结构AlGaN/GaN HEMTs肖特基电流增加的机理进行了研究.实验表明,凹栅槽结构AIGaN/GaN HEMTs肖特基栅电流增加一个数量级以上,击穿电压有一定程度的下降.利用AFM和XPS的方法分析AlGaN表面,等离子体干法刻蚀增加了AlGaN表面粗糙度,甚至出现部分尖峰状突起,增大了栅金属与AlGaN的接触面积;另一方面,等离子体轰击使AlGaN表面出现一定量的N空位,相当于栅金属与AlGaN接触界面处出现n型掺杂层,使肖特基结的隧道效应加强,降低了肖特基势垒.由此表明,AlGaN表面粗糙度的增加以及一定量的N空位出现是引起栅电流急剧增大的根本原因.     

High resolution physical analysis of ohmic contact formation at GaN-HEMT devices

A low ohmic contact resistance is a key request on AlGaN/GaN HEMT devices especially when dealing with higher frequency applications. In such a GaN material system very high annealing temperatures of up to 900 °C are frequently necessary to achieve low ohmic resistance. It is known that high annealing temperatures could reduce electrical performance and reliability of the devices. Therefore, low contact resistances at reduced annealing temperatures are beneficial. In the present work a special SiCl₄ plasma treatment was applied prior to the ohm metallisation resulting in sufficiently low ohmic resistances at a significantly reduced anneal temperature of 750 °C. High resolution physical analysis by transmission electron microscopy (TEM) and time of flight secondary mass spectroscopy (TOFSIMS) have been performed to understand the structural and chemical differences between the treated ohmic contacts compared to contacts processed under standard conditions. An advanced preparation technique was developed to get access to the reaction interfaces for TOFSIMS analysis from backside. It could be shown that the SiCl₄ treated samples reveal less impurities/contaminants on the ohmic metal–GaN/AlGaN interface and a different metal semiconductor alloying. The diffusion of metals like Al and Au into the semiconductor substrate was detected at the front of the TiN forming reaction.