CN113517335B - 一种可调节的复合凹槽栅e-hemt器件及制备方法 - Google Patents

一种可调节的复合凹槽栅e-hemt器件及制备方法 Download PDF

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CN113517335B
CN113517335B CN202110657623.6A CN202110657623A CN113517335B CN 113517335 B CN113517335 B CN 113517335B CN 202110657623 A CN202110657623 A CN 202110657623A CN 113517335 B CN113517335 B CN 113517335B
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尹以安
李佳霖
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Abstract

本发明属于HEMT器件的技术领域,具体涉及一种可调节的复合凹槽栅E‑HEMT器件及其制备方法。所述E‑HEMT器件包括如下依次设置的组件:衬底、AlN缓冲层、AlGaN/GaN应力释放层、高阻GaN缓冲层、GaN沟道层、AlN插入层以及AlxInyGa1‑x‑yN势垒层,还包括设置于势垒层上的复合凹槽栅极、源极、漏极以及钝化层,复合凹槽栅极包括P‑GaN层、栅介质层以及栅金属层组成,其位于势垒层的凹槽中,凹槽的一侧生长P‑GaN层,另一侧与P‑GaN层上方之间依次外延生长栅介质层以及栅金属层填满凹槽,形成复合凹槽栅极,形成高阈值电压,较高饱和电流、低栅极漏电流、大栅压摆幅的E‑HEMT器件。

Description

一种可调节的复合凹槽栅E-HEMT器件及制备方法
技术领域
本发明属于HEMT器件的技术领域,具体涉及一种可调节的复合凹槽栅E-HEMT器件及其制备方法。
背景技术
目前,GaN基电子电力应用中最常见的器件是GaN基高电子迁移率晶体管(HEMT)。GaN基HEMT具有高浓度和高电子迁移率的二维电子气(2DEG),在物联网与基站通信,电源、光伏逆变器、电机驱动等领域有着广阔的应用前景。虽然耗尽型HEMT用于低压和高频应用,但对于电源开关应用,需要增强型的HEMT(E-HEMT)来保证电路安全操作和简单的栅极驱动配置。如今,高性能GaN HEMT正朝着增强型工作模式的方向发展,因此,实现增强型的HEMT器件对其应用发展具有重要的意义。
另外,生长外延结构的质量也对器件的性能具有很大的影响,它很大程度上决定了HEMT在实际工作的特性,如散热性,击穿电压,缓冲层泄漏电流等。众所周知,非掺杂的GaN通常显示n型导电性,原因是在生长过程中由外界或衬底引入了硅(Si)、氧(O)等施主杂质,这些施主杂质的存在,会造成严重的缓冲层泄漏,器件的性能变差。此外,AlGaN与GaN的晶格常数不同,在外延生长中会产生失配位错和裂纹,严重影响器件的性能。因此,生长具有高质量的外延结构对器件实际应用也十分重要。
发明内容
针对上述问题,本发明的目的在于提供一种可调节的复合凹槽栅E-HEMT器件及制备方法,形成一种可调节的高阈值电压、高饱和电流、低栅极漏电流、大栅极摆幅的高质量E-HEMT器件。
本发明的技术内容如下:
本发明提供了一种可调节的复合凹槽栅E-HEMT器件,所述E-HEMT器件包括如下依次设置的组件:衬底、AlN缓冲层、AlGaN/GaN应力释放层、高阻GaN缓冲层、GaN沟道层、AlN插入层以及AlxInyGa1-x-yN势垒层;
还包括设置于势垒层上的复合凹槽栅极、源极、漏极以及钝化层;
所述复合凹槽栅极包括P-GaN层、栅介质层以及栅金属层组成;
所述AlxInyGa1-x-yN势垒层上设置有凹槽,复合凹槽栅极位于所述凹槽中,凹槽的一侧生长P-GaN层,另一侧与P-GaN层上方之间依次外延生长栅介质层以及栅金属层填满凹槽,形成复合凹槽栅极。
所述衬底包括蓝宝石、Si或SiC;
所述AlN缓冲层的厚度为10~50 nm,其为通过磁控溅射沉积到衬底上;
所述AlGaN/GaN应力释放层其为AlGaN和GaN薄层叠加而成,成长厚度分别为15~30nm;
所述高阻GaN缓冲层的厚度为2~5 μm;
所述GaN沟道层的厚度为0.3~0.5 μm;
所述AlN插入层的厚度为1~2 nm;
所述AlxInyGa1-x-yN势垒层中Al、In、Ga选用与GaN晶格匹配的任一组分的组合,所述AlxInyGa1-x-yN势垒层中0<x<0.83,0<y<0.17,其厚度为15~30 nm,优选厚度为25 nm;
所述钝化层包括SiNx、SiO2、Al2O3或HfO2,其厚度为30~50nm;
所述栅介质层包括SiO2、SiNx、HfO2、Al2O3或TiO2,其厚度为10~20 nm。
本发明还提供了一种可调节的复合凹槽栅E-HEMT器件的制备方法,包括如下步骤:
清洁衬底表面,在衬底上溅射AlN缓冲层,之后在AlN缓冲层上依次外延生长AlGaN/GaN应力释放层、高阻GaN缓冲层、GaN沟道层、AlN插入层和AlxInyGa1-x-yN势垒层;
在AlxInyGa1-x-yN势垒层上沉积钝化层;
刻蚀AlxInyGa1-x-yN势垒层表面的钝化层,形成源极、漏极和复合凹槽栅极开孔;
在复合凹槽栅极开孔处刻蚀AlxInyGa1-x-yN势垒层形成一凹槽;
在源极、漏极开孔处沉积金属层形成源极、漏极;
在上述外延片上沉积SiO2掩膜层,光刻露出凹槽的一侧,在该侧外延生长P-GaN层;
对SiO2掩膜层进行腐蚀,露出凹槽的另一侧,在P-GaN层外延和凹槽上依次生长栅介质层和栅金属层至填满凹槽,形成复合凹槽栅极;
所述AlN缓冲层为采用磁控溅射技术形成,在衬底上生长致密的AlN缓冲层,AlN缓冲层能够有效的抑制外界或衬底中的施主杂质进入缓冲层中,减小缓冲层的背景载流子浓度,从而得到高晶体质量的高阻GaN缓冲层;
所述AlGaN/GaN应力释放层、高阻GaN缓冲层、GaN沟道层、AlN插入层和AlxInyGa1-x-yN势垒层均为通过金属氧化物化学气相沉积法(MOCVD)外延生长得到;
所述金属层的结构由下而上依次为Ti/Al/Ni/Au金属;
所述衬底为采用丙酮、乙醇、去离子水进行清洗,并用N2吹干;
所述刻蚀为采用感应耦合等离子体刻蚀技术。
上述中,在AlxInyGa1-x-yN势垒层刻蚀一定深度的凹槽,可减少部分二维电子气,同时提高栅极的控制能力。凹槽左侧的P-GaN层,其高浓度的空穴会向沟道层扩散,与电子发生复合,从而耗尽栅极下方大量二维电子气(2DEG),可显著提高阈值电压;同时P-GaN层上的栅介质的引入,不仅能够减小栅极泄漏电流和提高击穿电压,还能够减小P-GaN层的压降,使得2DEG缓慢的补充,进一步提高阈值电压。在凹槽右侧形成的凹槽MIS结构(栅介质层和栅金属层)能够有效提高器件表面势垒高度,降低器件的栅极漏电流,提高击穿电压;同时还能够提高栅极控制能力和提高饱和电流。
本发明的有益效果如下:
本发明的可调节的复合凹槽栅E-HEMT器件,采用P-GaN栅、栅介质层与栅金属层组成复合凹槽栅的结构,获得高阈值电压,较高饱和电流、低栅极漏电流、大栅压摆幅的E-HEMT器件,以及采用四元化合物AlxInyGa1-x-yN代替传统的AlGaN势垒层,可通过调节Al组分和In组分生长与GaN晶格匹配的AlxInyGa1-x-yN,能够与GaN沟道层形成高质量的异质结和高电子迁移率的2DEG,也能够形成高质量的P-GaN层。同时根据不同Al组分和In组分,所形成的AlxInyGa1-x-yN的能带与自发极化不同,可根据实际应用场景,选择合适的AlxInyGa1-x-yN,实现不同的增强型器件性能,形成可调节的增强型HEMT(E-HEMT)器件;
本发明的E-HEMT器件的制备方法,在衬底上采用磁控溅射生长致密的AlN缓冲层,AlN缓冲层能够有效的抑制外界或衬底中的施主杂质(如氧原子)进入缓冲层中,从而减小缓冲层的背景载流子浓度,得到高晶体质量的高阻GaN缓冲层,还在AlN缓冲层上引入了AlGaN/GaN应力释放层,由于AlN缓冲层与衬底存在晶格失配而产生压缩应变,利用生长AlGaN/GaN应力释放层来减小AlN缓冲层的残余应力,进一步提高高阻GaN缓冲层的晶体质量,提高器件的电学性能;本发明的制备方法简单,可行性高,制备的器件稳定性良好。
附图说明
图1为实施例1的E-HEMT器件的制备工艺示意图;
图2为本发明E-HEMT器件的结构示意图;
图3为本发明E-HEMT器件采用的AlxInyGa1-x-yN材料的禁带宽度与晶格常数关系图;
图4为本发明E-HEMT器件与凹槽MIS-HEMT和凹槽P-GaN栅HEMT的转移特性的对比图。
具体实施方式
以下通过具体的实施案例以及附图说明对本发明作进一步详细的描述,应理解这些实施例仅用于说明本发明而不用于限制本发明的保护范围,在阅读了本发明之后,本领域技术人员对本发明的各种等价形式的修改均落于本申请所附权利要求所限定。
若无特殊说明,本发明的所有原料和试剂均为常规市场的原料、试剂。
实施例1
一种可调节的复合凹槽栅E-HEMT器件的制备:
1)清洗SiC衬底1:用丙酮、乙醇、去离子水将SiC衬底超声10分钟,取出后SiC衬底后用去离子水进行冲洗,然后用N2吹干,去除衬底表面的污染物;
2)生长AIN层2:将清洗干净的SiC衬底放入反应炉后抽真空,直到真空度为5.5×10-3Pa。通入Ar气,对Al靶进行预溅射10min,去除靶材表面氧化层。然后通入高纯(99.999%)N2气,气压为5×10-2Pa,溅射电压为350V,将衬底对准Al靶后,开始沉积AlN缓冲层,厚度为15nm;
3)生长AlGaN/GaN应力释放层3:利用MOCVD技术生长,采用三甲基铝(TMAl)、三甲基镓(TMGa)、氨气(NH3)作为铝源、镓源、氮源,在温度为500℃下生长AlGaN/GaN薄叠层,作为位于AIN层之上的AlGaN/GaN应力释放层3,其总厚度为16nm;
4)生长高阻GaN缓冲层4:之后采用三甲基镓(TMGa)、氨气(NH3)作为镓源、氮源在温度为950℃下生长厚度为2.6 μm的高阻GaN缓冲层4;
5)生长GaN沟道层5:采用三甲基镓(TMGa)、氨气(NH3)作为镓源、氮源在温度为1050℃下生长厚度为0.4μm的GaN沟道层5;
6)生长AlN插入层6:在GaN沟道层5上利用MOCVD技术生长1nm的AlN插入层6;
7)生长AlxInyGa1-x-yN势垒层7:采用三甲基铝(TMAl)、三甲基稼(TMGa)、三甲基铟(TMIn)、氨气(NH3)作为铝源、镓源、铟源、氮源,通过控制不同生长源流量与生长温度,获得不同组分的AlxInyGa1-x-yN势垒层7,其生长厚度为25nm;
8)选用离子增强型化学气相沉积(PECVD)工艺,在AlxInyGa1-x-yN势垒层7表面沉积SiN4钝化层13;
刻蚀钝化层,选用反应离子刻蚀(RIE),在钝化层上进行复合凹槽栅极、源极和漏极的开孔;
利用感应耦合等离子体刻蚀(ICP)刻蚀技术在AlxInyGa1-x-yN势垒层7继续刻蚀出一凹槽,势垒层的刻蚀深度15 nm,如图1(8)所示;
9)源极、漏极:选用电子束蒸发工艺,分别在源/漏极开孔位置沉积Ti/Al/Ni/Au(25nm/110nm/45nm/25nm)金属电极,之后在850℃的氮气气氛中快速退火45s,形成欧姆接触的源极、漏极;
在上述外延片上沉积一层80 nm的SiO2掩膜层,之后采用光刻工艺,只露出凹槽左半边,操作如下:
10.1)清洗:将SiO2掩膜层用丙酮超声清洗5min,异丙醇超声3min,再用去离子水清洗,交替超声清洗3遍;
10.2)烘干:将清洗干净的基底用N2吹干,并用热台120℃加热5min;
10.3)涂胶:用台式匀胶机涂上反型光刻胶;
10.4)前烘:把涂胶后的基片放在150℃的热台加热2min;
10.5)曝光:在凹槽以外地方采用G-25型光刻机进行曝光操作,紫外供灯功9 mW,时间5s;
10.6)后烘:热台100℃加热30s;
10.7)显影:用反胶显影液显影1min;
10.8)坚膜:把显影完的基片用N2吹干,并用热台150℃加热1min;
10.9)去胶:配置BOE溶液对SiO2掩膜层进行刻蚀,刻蚀1min,然后用丙酮超声5min,同时露出栅极开孔左侧
10.10)生长P-GaN层8:采用三甲基镓(TMGa),Cp2Mg和氨气(NH3)作为镓源,镁源和氮源,在温度为950℃条件下,控制镁源流量为150sccm,氮源与镓源摩尔比(Ⅴ/Ⅲ比)为3060,在栅极开孔左侧生长厚度为40nm P-GaN层,生长后置于含Mg的N2气氛中,在750℃下退火30min;
11)栅介质层:采用氢氟酸将SiO2腐蚀,露出栅极开孔右半边,接着选用原子层淀积(ALD)工艺在P-GaN层上方和右凹槽内壁上生长15 nm的Al2O3作为栅介质层;
栅金属层:采用电子束蒸发工艺在Al2O3栅介质层上继续沉积Ni/Au金属,并在氮气气氛下,温度为45℃的条件下退火8min,形成肖特基接触的栅金属层。
以上制备步骤如图1所示,每个步骤分别与图相对应。
实施例2
一种可调节的复合凹槽栅E-HEMT器件:
该E-HEMT器件的制备步骤同实施例1所示,制得的E-HEMT器件的结构由下至上依次包括蓝宝石衬底1、10nm的AlN缓冲层2、15 nm的AlGaN/GaN应力释放层3、2 μm的高阻GaN缓冲层4、0.3 μm的GaN沟道层5、1.5 nm的AlN插入层6、15 nm的AlxInyGa1-x-yN势垒层7、P-GaN层8、介质层9、栅极10、源极11、漏极12、Al2O3钝化层13;
所述P-GaN层8空穴浓度约为5×1017 cm-3,长度为1 μm,厚度为40 nm;
所述势垒层凹槽的深度为8 nm;
所述栅介质层9材料为HfO2,厚度为10 nm;
所述源极11和漏极12通过电子束沉积法沉积欧姆接触金属Ti/Al/Ni/Au(20nm/130nm/50nm/150nm),并在850℃的氮气氛围下快速退火30s,形成欧姆接触。
实施例3
一种可调节的复合凹槽栅E-HEMT器件:
该E-HEMT器件的制备步骤同实施例1所示,制得的E-HEMT器件的结构由下至上依次包括Si衬底1、35 nm的AlN缓冲层2、20 nm的AlGaN/GaN应力释放层3、3 μm的高阻GaN缓冲层4、0.4 μm的GaN沟道层5、1.8 nm的AlN插入层6、20 nm的AlxInyGa1-x-yN势垒层7、P-GaN层8、介质层9、栅极10、源极11、漏极12、SiO2钝化层13;
所述P-GaN层8空穴浓度约为3×1017cm-3,长度为1μm,厚度为40nm;
所述凹槽的深度为10 nm;
所述栅介质层9材料为TiO2,厚度为16 nm;
所述源极11和漏极12通过电子束沉积法沉积欧姆接触金属Ti/Al/Ni/Au(20nm/130nm/50nm/150nm),并在900℃的氮气氛围下快速退火40s,形成欧姆接触。
实施例4
一种可调节的复合凹槽栅E-HEMT器件:
该E-HEMT器件的制备步骤同实施例1所示,制得的E-HEMT器件的结构由下至上依次包括SiC衬底1、50 nm的AlN缓冲层2、30 nm的AlGaN/GaN应力释放层3、5 μm的高阻GaN缓冲层4、0.5 μm的GaN沟道层5、2 nm的AlN插入层6、30 nm的AlxInyGa1-x-yN势垒层7、P-GaN层8、介质层9、栅极10、源极11、漏极12、HfO2钝化层13;
所述P-GaN层8空穴浓度约为1×1017cm-3,长度为1μm,厚度为40nm;
所述凹槽的深度为15 nm;
所述栅介质层9材料为Al2O3,厚度为20 nm;
所述源极11和漏极12通过电子束沉积法沉积欧姆接触金属Ti/Al/Ni/Au(20nm/130nm/50nm/150nm),并在900℃的氮气氛围下快速退火40s,形成欧姆接触。
如图2所述,为本发明的可调节的复合凹槽栅E-HEMT器件的结构示意图。
如图3所示,本发明的AlxInyGa1-x-yN材料的禁带宽度与晶格常数关系图。从图中可以看出,与GaN晶格匹配的AlxInyGa1-x-yN的禁带宽度可由3.4-4.9eV之间,越大的禁带宽度可与GaN形成更大的带阶,相当于形成更高的电子势垒,电子隧穿几率降低,从而对2DEG的空间限制作用更为显著。同时,不同Al组分的AlxInyGa1-x-yN自发极化也不同,越大的Al组分自发极化效应,在没有压电极化效应情况下也能在异质结界面形成高浓度的2DEG。但2DEG浓度越大的同时也会使阈值电压降低。因此,本发明的增强型HEMT器件,可根据具体应用场景,选择合适的AlxInyGa1-x-yN,其中,0<x<0.83,0<y<0.17。
本发明采用复合凹槽栅结构,将凹槽、P-GaN层与MIS结构(栅金属层、栅介质层和势垒层组成MIS结构)三者优势结合在一起。采用凹槽使栅极下方的势垒层变薄,2DEG浓度降低,有助于实现增强型器件,并且只减薄了栅极下方的势垒层厚度,其他区域的势垒层厚度不变,因此器件导通性能变化相对较小。之后,利用P-GaN层显著耗尽栅极下方大量二维电子气(2DEG),进一步提高阈值电压。栅介质的引入,一方面可降低器件的栅极漏电流,提高击穿电压,另一方面,在凹槽右侧形成MIS栅,能够提高器件的饱和电流。特别的,栅介质还能够减小P-GaN层的压降,使得2DEG缓慢的补充,阈值电压进一步提高。
如图4所示,为本发明实施例可调节的复合凹槽栅E-HEMT与凹槽MIS-HEMT、凹槽P-GaN栅HEMT的转移特性的对比图。在漏极电压为10V时,复合凹槽栅HEMT、凹槽P-GaN栅HEMT与凹槽MIS-HEMT的阈值电压分别为4.45V、3.5V和1.3V。相比于凹槽MIS-HEMT(1.3V),表明P-GaN层可显著提高阈值电压(3.5V)。特别的,复合凹槽栅极因为在P-GaN层上引入栅介质层,使得阈值电压进一步增大到4.45V。
同时,从图4也可得到,在源漏电压=10V,栅极电压=10V时,凹槽MIS-HEMT、凹槽P-GaN栅HEMT和复合凹槽栅HEMT的源漏电流分别为862 mA/mm、621 mA/mm和601 mA/mm。凹槽MIS-HEMT其饱和电流最大,表明凹槽MIS-HEMT可使器件具有饱和电流,因此复合凹栅HEMT的MIS结构能够使阈值电压提高的同时,保持高的饱和电流。与凹槽P-GaN栅相比,复合凹栅HEMT阈值电压提高了约27%,而饱和电流仅下降约3.2%。
因此,本发明的E-HEMT器件,结合了P-GaN栅HEMT和凹槽MIS-HEMT二者优势;优化了制备工艺和采用了AlInGaN势垒层,获得了可调节的高阈值电压、高饱和电流、低栅极漏电流、大栅极摆幅的高质量E-HEMT器件。

Claims (9)

1.一种可调节的复合凹槽栅E-HEMT器件,其特征在于,所述E-HEMT器件包括如下依次设置的组件:衬底、AlN缓冲层、AlGaN/GaN应力释放层、高阻GaN缓冲层、GaN沟道层、AlN插入层以及AlxInyGa1-x-yN势垒层;
还包括设置于势垒层上的复合凹槽栅极、源极、漏极以及钝化层;
所述复合凹槽栅极包括P-GaN层、栅介质层以及栅金属层组成;所述AlxInyGa1-x-yN势垒层中Al、In、Ga选用与GaN晶格匹配的任一组分的组合,所述AlxInyGa1-x-yN势垒层中0<x<0.83,0<y<0.17;所述AlxInyGa1-x-yN势垒层上设置有凹槽,复合凹槽栅极位于所述凹槽中,凹槽的一侧生长P-GaN层,另一侧与P-GaN层上方依次外延生长栅介质层以及栅金属层填满凹槽,形成复合凹槽栅极;
所述钝化层包括SiNx、SiO2、Al2O3或HfO2
所述栅介质层包括SiO2、SiNx、HfO2、Al2O3或TiO2
2.由权利要求1所述的复合凹槽栅E-HEMT器件,其特征在于,所述AlN缓冲层的厚度为10~50nm。
3.由权利要求1所述的复合凹槽栅E-HEMT器件,其特征在于,所述AlGaN/GaN应力释放层其为AlGaN和GaN薄层叠加而成,成长厚度分别为15~30nm。
4.由权利要求1所述的复合凹槽栅E-HEMT器件,其特征在于,所述AlxInyGa1-x-yN势垒层的厚度为15~30nm。
5.由权利要求1所述的复合凹槽栅E-HEMT器件,其特征在于,所述钝化层的厚度为30~50nm。
6.由权利要求1所述的复合凹槽栅E-HEMT器件,其特征在于,所述栅介质层的厚度为10~20nm。
7.一种权利要求1~6任一项所述的可调节的复合凹槽栅E-HEMT器件的制备方法,其特征在于,包括如下步骤:
清洁衬底表面,在衬底上溅射AlN缓冲层,之后在AlN缓冲层上依次外延生长AlGaN/GaN应力释放层、高阻GaN缓冲层、GaN沟道层、AlN插入层和AlxInyGa1-x-yN势垒层;
在AlxInyGa1-x-yN势垒层上沉积钝化层;
刻蚀AlxInyGa1-x-yN势垒层表面的钝化层,形成源极、漏极和复合凹槽栅极开孔;
在复合凹槽栅极开孔处刻蚀AlxInyGa1-x-yN势垒层形成一凹槽;
在源极、漏极开孔处沉积金属层形成源极、漏极;
在形成的钝化层、凹槽、源极、漏极上沉积一掩膜层,光刻露出凹槽的一侧,在该侧外延生长P-GaN层;
对掩膜层进行腐蚀,露出凹槽的另一侧,在P-GaN层外延和凹槽上依次生长栅介质层和栅金属层至填满凹槽,形成复合凹槽栅极。
8.由权利要求7所述的复合凹槽栅E-HEMT器件的制备方法,其特征在于,所述AlN缓冲层为采用磁控溅射技术形成。
9.由权利要求7所述的复合凹槽栅E-HEMT器件的制备方法,其特征在于,所述掩膜层包括SiO2掩膜层。
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