CN110797402A - PNP型肖特基集电区AlGaN/GaN HBT器件及其制备方法 - Google Patents
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Abstract
本发明公开了PNP型肖特基集电区AlGaN/GaN HBT器件,从下往上依次包括:衬底、埋氧层、集电区、基区以及发射区,所述集电区包括下层的P型单晶硅层以及上层的金属硅化物层,所述基区包括N型AlGaN层,所述发射区包括P型GaN层;所述P型单晶硅层上设有集电极,所述N型AlGaN层上设有基极,所述P型GaN层上设有发射极。本发明接触界面特性好,可提高器件开关速度和截止频率,工艺简单且兼容现有硅基工艺。
Description
技术领域
本发明属于半导体技术领域,具体涉及PNP型肖特基集电区AlGaN/GaN HBT器件及其制备方法。
背景技术
以硅(Si)和砷化镓(GaAs)为代表的传统半导体材料,其器件在抗辐射、高温、高压和高功率的要求下已逐渐不能满足现代电子技术的发展。宽禁带半导体GaN电子器件,可以应用在高温、高压、高频和恶劣的环境中,如雷达和无线通信的基站及卫星通信。
由于GaN的禁带宽度大、击穿电压高、电子饱和漂移速度高,具有优良的电学和光学特性以及良好的化学稳定性,使其在高频大功率、高温电子器件等方面倍受青睐。GaN异质结双极晶体管(HBT)具有高的电流增益。目前,据报道用于大功率通信和雷达的功率放大器的AlGaN/GaN NPN型HBT器件,其高温工作的温度可达到300℃,从而得到了国防、通信领域的广泛重视。
随着GaN器件技术的日渐成熟,越来越多的通信系统设备中会更多的使用GaNHBT,使系统的工作能力与可靠性都得到最大限度的提升:在军事方面,美国雷声公司正在研发基于GaN HBT的收发组件,以用于未来的军事雷达升级;在民用方面,GaN HBT对高频率和大功率的处理能力对于发展高级通信网络中的放大器和调制器以及其它关键器件都很重要。
然而现有技术中的GaN HBT器件,一方面受限于以蓝宝石和碳化硅(SiC)作为衬底的异质外延技术生长出的GaN单晶的位错密度较高,性能还不太令人满意,GaN HBT的直流电流增益仍比较小,工艺过程并不十分稳定;另一方面现有的HBT器件要进一步提高开关性能,需要在原有的基础上引入额外的工艺流程,不仅工艺流程变得更加复杂,生产成本也会随之上升,生产效率降低。
发明内容
针对现有技术中所存在的不足,本发明提供了一种接触界面特性好、可提高器件开关速度和截止频率、工艺简单、兼容现有硅基工艺的PNP型肖特基集电区AlGaN/GaN HBT器件及其制备方法。
本发明的一个方面,PNP型肖特基集电区AlGaN/GaN HBT器件,从下往上依次包括:衬底、埋氧层、集电区、基区以及发射区,所述集电区包括下层的P型单晶硅层以及上层的金属硅化物层,所述基区包括N型AlGaN层,所述发射区包括P型GaN层;所述P型单晶硅层上设有集电极,所述N型AlGaN层上设有基极,所述P型GaN层上设有发射极;所述金属硅化物层中的金属硅化物是TiSi2、CoSi2、MoSi2中的其中一种。
进一步地,所述N型AlGaN层与所述金属硅化物层之间设有第一本征GaN阻挡层,所述N型AlGaN层与所述P型GaN层之间设有第二本征GaN阻挡层。
特别地,所述第一本征GaN阻挡层和第二本征GaN阻挡层的厚度为5~10nm。
进一步地,所述N型AlGaN层包括N型掺杂AlxGa1-xN层以及其下的N型掺杂AlrGa1-rN组分渐变层,所述N型掺杂AlrGa1-rN组分渐变层中自上而下Al的摩尔组分r从x渐变至0。
特别地,所述N型掺杂AlxGa1-xN层的厚度为20nm;所述N型掺杂AlrGa1-rN组分渐变层的厚度可为50nm。
本发明的另一方面,PNP型肖特基集电区AlGaN/GaN HBT器件制备方法,包括如下步骤:
S1:准备SOI衬底,其顶层为P型单晶硅层;对所述P型单晶硅层表面进行清洗和化学机械抛光(CMP)处理;
S2:淀积生长一层金属Ti或Co或Mo,然后进行快速热退火处理,使金属Ti或Co或Mo与其下的P型单晶硅层表面氧化为TiSi2或CoSi2或MoSi2,形成金属硅化物层以作为集电区;
S3:在金属硅化物层上生长第一本征GaN阻挡层;
S4:在所述第一本征GaN阻挡层上生长N型AlGaN层;
S5:继续生长第二本征GaN阻挡层;在所述第二本征GaN阻挡层上生长P型GaN层;
S6:制备发射极、基极和集电极。
进一步地,所述步骤S4中生长N型AlGaN层的方法包括:先利用MOCVD在所述第一本征GaN阻挡层上生长N型掺杂AlrGa1-rN组分渐变层,再在所述N型掺杂AlrGa1-rN组分渐变层上生长N型掺杂AlxGa1-xN层;所述N型掺杂AlrGa1-rN组分渐变层的Al组分r自上而下从x渐变至0。
特别地,所述Al组分r自上而下从x渐变至0中的渐变方式是线性渐变或指数渐变。
相比于现有技术,本发明具有如下有益效果:
1、通过在单晶硅上生长一层极薄的、界面形貌和界面态良好的金属硅化物层,与单晶硅形成硅/金属硅化物的肖特基接触,既保证了优良的接触界面特性,又可以提高器件开关速度和截止频率,同时制备工艺相对简单,可与常规的硅基工艺相兼容,降低生产成本,提高生产效率;
2、通过在AlGaN/GaN HBT器件制备中引入SOI衬底技术,进一步起到减小寄生电容效应、降低器件功耗、避免闩锁效应等作用,可提升器件的整体性能,便于与目前的小尺寸低功耗SOI CMOS器件进行工艺集成;
3、通过在金属硅化物层之上设置一层第一本征GaN阻挡层,可有效防止重掺杂N型AlGaN基区的杂质原子向金属硅化物层扩散所导致的寄生势垒效应;通过在P型GaN层之下设置一层第二本征GaN阻挡层,能够有效抑制P型重掺杂的GaN发射区中的掺杂原子向基区扩散所导致的寄生势垒效应;
4、通过采用包括组分渐变的多层基区结构,在发射结正向偏置条件下,在渐变层内引入加速正向注入的少子(空穴)输运的电场,进一步提高基区渡越时间,有利于提高器件的频率特性。
附图说明
图1为本发明中PNP型肖特基集电区AlGaN/GaN HBT器件的结构示意图;
图2为本发明中N型掺杂AlrGa1-rN组分渐变层的渐变示意图;
图3为本发明中PNP型肖特基集电区AlGaN/GaN HBT器件制备方法步骤S1后的器件结构示意图;
图4为本发明中PNP型肖特基集电区AlGaN/GaN HBT器件制备方法步骤S2后的器件结构示意图;
图5为本发明中PNP型肖特基集电区AlGaN/GaN HBT器件制备方法步骤S4后的器件结构示意图;
图6为本发明中PNP型肖特基集电区AlGaN/GaN HBT器件制备方法步骤S5后的器件结构示意图;
图7~8为本发明中PNP型肖特基集电区AlGaN/GaN HBT器件制备方法步骤S6中的器件结构示意图;
其中,1衬底,2埋氧层,3集电区,31P型单晶硅层,32金属硅化物层,33集电极,4基区,41N型掺杂AlxGa1-xN层,42N型掺杂AlrGa1-rN组分渐变层,43第一本征GaN阻挡层,44基极,5发射区,51P型GaN层,52第二本征GaN阻挡层,53发射极。
具体实施方式
为了使发明实现的技术手段、创作特征、达成目的与功效易于明白了解,下面结合具体图示,进一步阐述本发明。可以理解,本文中采用的如“上”、“下”之类的方位用语并非特指某个具体方位,不构成对方案本身的限定,而仅仅是根据具体说明书附图图示采取的便于理解的描述方式。
本发明的一个方面,PNP型肖特基集电区AlGaN/GaN HBT器件,从下往上依次包括:衬底1、埋氧层2、集电区3、基区4以及发射区5,所述集电区3包括下层的P型单晶硅层31以及上层的金属硅化物层32,所述基4区包括N型AlGaN层,所述发射区5包括P型GaN层51;所述P型单晶硅层31上设有集电极33,所述N型AlGaN层上设有基极44,所述P型GaN层51上设有发射极53。特别地,所述金属硅化物层32中的金属硅化物可以是TiSi2、CoSi2、MoSi2中的其中一种。
所述衬底可以是N型掺杂单晶硅衬底。所述P型单晶硅层两侧是集电极接触区域。在实践中发现,所述金属硅化物层和其下的单晶硅接触的界面处的界面形貌和界面态对器件特性的影响较大,金属硅化物层与其下的N型单晶硅层形成了“组合集电极”的结构。所述P型GaN层厚度可为100nm,与发射极形成良好的肖特基接触。
首先,本方案在AlGaN/GaN HBT器件制备中采用SOI衬底,进一步起到减小寄生电容效应、降低器件功耗、避免闩锁效应等作用,可提升器件的整体性能,便于与目前的小尺寸低功耗SOI CMOS器件进行工艺集成。
其次,本方案将常规HBT的集电结换为肖特基结,除了可以避免基于蓝宝石或碳化硅衬底的单晶GaN集电极所产生的较大位错和界面态,还可以进一步提高器件的工作速度,这是因为肖特基接触具有如下两个明显的主要优势:(1)集电极电阻为0;(2)因为没有集电结空间电荷区,集电结的渡越时间可为0,同样电荷存贮时间也为零,可以进一步提高截止频率,同时也兼顾了与常规硅基CMOS工艺的兼容性,便于大规模商业制造。考虑到硅化钛(TiSi2)具有非常理想的材料物理特性:高导电性、高选择性、优良的热稳定性以及更好的硅吸附性,好的工艺适应性以及很低的信号干扰性,本方案中通过在单晶硅材料之上生长一层极薄的界面形貌和界面态良好的金属硅化物,与单晶硅形成硅/金属硅化物的肖特基接触,既保证了优良的接触界面特性,又可以提高器件开关速度和截止频率,同时制备工艺相对简单,可与常规的硅基工艺相兼容。所述TiSi2也可以替换为性质相似的CoSi2和MoSi2等,就目前的工艺来说,TiSi2是优选方案。
作为进一步优化,所述N型AlGaN层与所述金属硅化物层32之间设有第一本征GaN阻挡层43,所述N型AlGaN层与所述P型GaN层51之间设有第二本征GaN阻挡层52。特别地,所述第一本征GaN阻挡层43和第二本征GaN阻挡层52的厚度可为5~10nm。阻挡层若太薄起不到阻挡作用,增大串联电阻;若太厚会增加载流子的输运时间,影响频率性能。
本方案在金属硅化物层之上设置一层第一本征GaN阻挡层,可以防止重掺杂的N型AlGaN基区的杂质原子向金属硅化物层扩散,形成寄生势垒效应,恶化肖特基界面的电学特性;在P型GaN层之下设置一层第二本征GaN阻挡层,能够有效抑制P型重掺杂的GaN发射区中的掺杂原子向基区扩散所导致的寄生势垒效应。
作为进一步优化,所述N型AlGaN层包括N型掺杂AlxGa1-xN层41以及其下的N型掺杂AlrGa1-rN组分渐变层42,所述N型掺杂AlrGa1-rN组分渐变层42中自上而下Al的摩尔组分r从x渐变至0。
所述N型掺杂AlxGa1-xN层中0<x<1,x的取值可根据实际需要进行调整;该层厚度可为20nm,掺杂浓度可为1×1018cm-3。所述N型掺杂AlrGa1-rN组分渐变层中0<r<x,该层厚度可为50nm,砷的掺杂浓度可为2×1019cm-3。在N型掺杂AlxGa1-xN层之下设置N型掺砷(As)的AlrGa1-rN组分渐变层作为基区,能够避免基区陷落效应以及加速基区少子空穴的输运过程。如图2所示,所述渐变方式可以是线性渐变,也可以是指数渐变。
本方案采用多层基区结构,在发射结正向偏置条件下,N型掺杂AlrGa1-rN组分渐变层的导带几乎不发生倾斜,禁带宽度的变化主要体现在价带,因此在渐变层内会引入一个加速正向注入的少子(空穴)输运的电场,进一步提高基区渡越时间,有利于提高器件的频率特性。
本发明的另一方面,PNP型肖特基集电区AlGaN/GaN HBT器件制备方法,包括如下步骤:
S1:准备SOI衬底,其顶层P型单晶硅层31为重掺杂,掺杂浓度可以是2×1019cm-3;对所述P型单晶硅层31表面进行清洗和化学机械抛光(CMP)处理;如图3所示;
S2:制备金属硅化物层32:淀积生长一层金属钛(Ti)或钴(Co)或钼(Mo),然后进行快速热退火(RTA)处理,使Ti与其下的P型单晶硅层31表面氧化为TiSi2或CoSi2或MoSi2,形成金属硅化物层32以作为集电区;如图4所示;
S3:在金属硅化物层32上生长第一本征GaN阻挡层43,其厚度可为5nm;
S4:在所述第一本征GaN阻挡层43上生长N型AlGaN层;如图5所示;
S5:继续生长第二本征GaN阻挡层52,其厚度可为5nm;在所述第二本征GaN阻挡层52上生长P型GaN层51,其厚度可以是100nm;如图6所示;
S6:制备发射极53、基极44和集电极33:根据预设的发射极、基极、集电极宽度依次刻蚀出发射极区域、基极区域和集电极区域,形成台面结构;在整个刻蚀完成的台面结构之上,通过干氧氧化形成覆盖整个台面的SiO2氧化层,如图7所示;该氧化层的上表面与GaN发射区层的上表面之间的距离可为20nm,之后利用干法等离子刻蚀工艺去掉台面两侧多余的平面SiO2氧化层,使得两侧各保留20nm厚的氧化层,如图8所示;之后刻蚀掉发射区、基区和集电区窗口的氧化层以形成发射区、基区和集电区窗口,最后在发射区、基区和集电区窗口之上淀积金属或金属硅化物(如CoSi2)分别与重掺杂的发射区、基区和集电区形成良好的欧姆接触,并作为发射极、基极和集电极。如图1所示。
所述步骤S2中生长金属钛可采用物理气相淀积(PVD)的方法。所述步骤S3和S4中生长本征GaN阻挡层以及生长N型AlGaN层可采用金属有机化学气相淀积(MOCVD)的方法。所述SOI衬底的埋氧层厚度不应太厚,其典型值可为0.5μm。所述金属钛的厚度可以是5nm,氧化而成的所述金属硅化物层的厚度通常小于10nm。所述步骤S6中制备发射极、基极和集电极的方法属于现有技术。
所述P型单晶硅层,掺杂浓度可为2×1019cm-3。为了减小集电区的电容,P型单晶硅层厚度不应过薄;又因为耗尽区的电阻很大,为了保证集电区的电阻不至于受耗尽区宽度的影响而变得过大,其厚度应远大于衬底偏置所导致的该层耗尽厚度t。在衬底电压作用下,此时SOI衬底形成了一个背向的MOS电容结构,根据半导体器件物理,耗尽厚度t可以由一个一元二次方程解出:
式中,q为电子电量,NSi为氧化层之上的P+单晶硅层掺杂浓度,εSi和εOX分别为单晶硅和氧化层的介电常数,tOX为氧化层的厚度,VS、VC和VMS分别为衬底电压、集电极电压和氧化层两侧单晶硅区域的功函数差值。
作为进一步优化,如图5所示,所述步骤S4中生长N型AlGaN层的方法包括:
先利用MOCVD在所述第一本征GaN阻挡层43上生长N型掺杂AlrGa1-rN组分渐变层42,再在所述N型掺杂AlrGa1-rN组分渐变层42上生长N型掺杂AlxGa1-xN层41;所述N型掺杂AlxGa1-xN层41中0<x<1,x的取值可根据实际需要进行调整,所述N型掺杂AlrGa1-rN组分渐变层42的Al组分r自上而下从x渐变至0。
所述N型掺杂AlrGa1-rN组分渐变层可采用砷掺杂,其厚度可为50nm,砷掺杂浓度可为2×1019cm-3;所述N型掺杂AlxGa1-xN层的厚度可为20nm,其掺杂浓度可为1×1018cm-3。所述渐变方式可以是线性方式渐变,也可以是指数方式渐变,如图2所示。
以上所述仅为本发明的优选实施方式,本发明的保护范围并不仅限于上述实施方式,凡是属于本发明原理的技术方案均属于本发明的保护范围。对于本领域的技术人员而言,在不脱离本发明的原理的前提下进行的若干改进,这些改进也应视为本发明的保护范围。
Claims (8)
1.PNP型肖特基集电区AlGaN/GaN HBT器件,其特征在于,从下往上依次包括:衬底、埋氧层、集电区、基区以及发射区,所述集电区包括下层的P型单晶硅层以及上层的金属硅化物层,所述基区包括N型AlGaN层,所述发射区包括P型GaN层;所述P型单晶硅层上设有集电极,所述N型AlGaN层上设有基极,所述P型GaN层上设有发射极;所述金属硅化物层中的金属硅化物是TiSi2、CoSi2、MoSi2中的其中一种。
2.根据权利要求1所述的PNP型肖特基集电区AlGaN/GaN HBT器件,其特征在于:
所述N型AlGaN层与所述金属硅化物层之间设有第一本征GaN阻挡层,所述N型AlGaN层与所述P型GaN层之间设有第二本征GaN阻挡层。
3.根据权利要求2所述的PNP型肖特基集电区AlGaN/GaN HBT器件,其特征在于:
所述第一本征GaN阻挡层和第二本征GaN阻挡层的厚度为5~10nm。
4.根据权利要求1-3任一项所述的PNP型肖特基集电区AlGaN/GaN HBT器件,其特征在于:
所述N型AlGaN层包括N型掺杂AlxGa1-xN层以及其下的N型掺杂AlrGa1-rN组分渐变层,所述N型掺杂AlrGa1-rN组分渐变层中自上而下Al的摩尔组分r从x渐变至0。
5.根据权利要求4所述的PNP型肖特基集电区AlGaN/GaN HBT器件,其特征在于:
所述N型掺杂AlxGa1-xN层的厚度为20nm;所述N型掺杂AlrGa1-rN组分渐变层的厚度可为50nm。
6.PNP型肖特基集电区AlGaN/GaN HBT器件制备方法,其特征在于,包括如下步骤:
S1:准备SOI衬底,其顶层为P型单晶硅层;对所述P型单晶硅层表面进行清洗和化学机械抛光(CMP)处理;
S2:淀积生长一层金属Ti或Co或Mo,然后进行快速热退火处理,使金属Ti或Co或Mo与其下的P型单晶硅层表面氧化为TiSi2或CoSi2或MoSi2,形成金属硅化物层以作为集电区;
S3:在金属硅化物层上生长第一本征GaN阻挡层;
S4:在所述第一本征GaN阻挡层上生长N型AlGaN层;
S5:继续生长第二本征GaN阻挡层;在所述第二本征GaN阻挡层上生长P型GaN层;
S6:制备发射极、基极和集电极。
7.根据权利要求6所述的PNP型肖特基集电区AlGaN/GaN HBT器件制备方法,其特征在于:
所述步骤S4中生长N型AlGaN层的方法包括:先利用MOCVD在所述第一本征GaN阻挡层上生长N型掺杂AlrGa1-rN组分渐变层,再在所述N型掺杂AlrGa1-rN组分渐变层上生长N型掺杂AlxGa1-xN层;所述N型掺杂AlrGa1-rN组分渐变层的Al组分r自上而下从x渐变至0。
8.根据权利要求7所述的PNP型肖特基集电区AlGaN/GaN HBT器件制备方法,其特征在于:
所述Al组分r自上而下从x渐变至0中的渐变方式是线性渐变或指数渐变。
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