CN113078050B - 一种C面SiC外延结构及外延沟槽的填充方法 - Google Patents

一种C面SiC外延结构及外延沟槽的填充方法 Download PDF

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CN113078050B
CN113078050B CN202110339323.3A CN202110339323A CN113078050B CN 113078050 B CN113078050 B CN 113078050B CN 202110339323 A CN202110339323 A CN 202110339323A CN 113078050 B CN113078050 B CN 113078050B
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左万胜
钮应喜
单卫平
朱明兰
张晓洪
胡新星
仇成功
袁松
史田超
史文华
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Anhui Changfei Advanced Semiconductor Co ltd
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Abstract

本发明公开了一种C面SiC外延结构及外延沟槽的填充方法，包括以下步骤：对正轴C面4H‑SiC衬底进行刻蚀、在正轴C面4H‑SiC衬底上生长N型4H‑SiC缓冲层、在4H‑SiC缓冲层上生长N型4H‑SiC外延层、由N型4H‑SiC外延层的表面向下刻蚀沟槽、通入含氯的硅源气体、碳源、HCl和B2H6、H2，于1700～1800℃温度和10～50mbar压力下填满沟槽、抛光，抛去N型4H‑SiC外延层表面过生长的4H‑SiC，得到上表面光滑的交替排列的p型和n形区域；本发明提供的C面SiC外延沟槽的填充方法降低了BPD密度和台阶聚集缺陷的发生。

Description

一种C面SiC外延结构及外延沟槽的填充方法
技术领域
本发明属于半导体材料技术领域，具体涉及一种C面SiC外延结构及外延沟槽的填充方法。
背景技术
SiC作为第三代宽禁带半导体材料的典型代表，具有宽禁带宽度、高临界击穿场强、高热导率及高载流子饱和速率等特性。
SiC器件优化进步的重要方向之一是不断降低器件的比导通电阻。而超级结技术毫无疑问是降低漂移区比导通电阻的最有效手段。超级结技术是一种通过采用交替的P型掺杂区域和N型掺杂区域结构来实现电荷补偿并作为耐压层，以同时得到低比导通电阻和高耐压能力的技术。理论上已经证明超级结器件可以将半导体材料导通电阻与器件耐压能力理论极限的Ron,sp∝BV2.3～2.5降低到Ron,sp∝BV1.32。
SiC外延材料是器件制备的基础，基于Si面SiC外延生长通过竞位原理可实现低的背景掺杂，Si面衬底得到广泛使用，目前SiC沟槽填充都在Si面进行。在Si面外延生长过程中，由于Si面低的表面扩散长度，导致Si面容易出现3C-SiC杂晶问题，为解决该问题，1987年Matsunami等人提出在具有偏角衬底进行上进行同质外延生长。衬底偏角的意义在于在衬底表面引入台阶，吸附的原子在衬底表面扩散，最终在能量较低的台阶或扭折处并入晶格，晶体会沿着台阶向前推进，使得外延的材料能够有效的继承衬底的堆垛序列，偏角越大引入的台阶密度便越高，就越有利于外延生长在台阶流的生长方法中。
目前SiC外延生长普遍采用的是偏[11-20]晶向4°或者8°Si面衬底，偏角越大，台阶密度越高，外延层表面形貌越好，然而BPD的burgers矢量为1/3[11-20]，偏角越大，衬底上的BPD越容易贯穿到外延层中，同时也带来成本的上升。BPD对器件有着严重的危害，当少数载流子到达BPD扩展为高电阻的堆垛层错，增大器件的导通电阻，使SiC器件性能劣化。此外，Si面的表面自由能较高为2220J/cm2，根据吉布斯自由能原理，体系总是自发的向自由能减小的方向运动，在外延生长时容易以形成突起和凹坑的方式释放表面自由能，Si面较容易出现台阶聚集。
发明内容
为解决上述技术问题，本发明提供了一种C面SiC外延结构及外延沟槽的填充方法。C面较Si面有着显著的优点，C面上表面扩散长度值比Si面长一个数量级以上，在C面可以在几乎正轴衬底上生长得到无3C-夹杂的SiC表面。其次，C面的表面自由能为300J/cm2，较S面的表面自由能较高为2220J/cm2低很多，C面生长外延表面较光滑，不易出现台阶聚集。
本发明采取的技术方案为：
一种C面SiC外延沟槽的填充方法，所述方法包括以下步骤：
(1)对正轴C面4H-SiC衬底进行刻蚀；
(2)在正轴C面4H-SiC衬底上生长N型4H-SiC缓冲层；
(3)在4H-SiC缓冲层上生长N型4H-SiC外延层；
(4)由N型4H-SiC外延层的表面向下刻蚀沟槽；
(5)通入含氯的硅源气体、碳源、HCl和B2H6、H2，于1700～1800℃温度和10～50mbar压力下填满沟槽；
(6)抛光，抛去N型4H-SiC外延层表面过生长的4H-SiC，得到上表面光滑的交替排列的p型和n形区域。
进一步地，步骤(5)中，所述含氯的硅源气体、碳源、HCl、B2H6、H2的流量为100～200sccm、30～80sccm、1000～5000sccm、5～10sccm、100～800slm。
步骤(5)中，HCl与含氯的硅源气体的流量之比为15～40：1；碳源与含氯的硅源气体的流量之比0.6～1：1。
步骤(1)中，所述刻蚀的方法为：以100～800slm流量通入H2，于5-50mbar压力和1600-1700℃温度下刻蚀3～10min。
步骤(2)中，所述4H-SiC缓冲层的厚度为10～200nm，掺杂浓度为2×1018～1×1019cm-3。超级结比导通电阻和耐压能力关系为：Ron,sp∝BV1.32，而导通电阻与掺杂浓度和厚度的关系为：Ron,sp＝WN/(qμND),其中WN为外延层厚度，μ为电子迁移率，ND为掺杂浓度。因此，缓冲层厚度小于10nm难以有效缓冲晶格失配，厚度大于200nm，降低器件耐压性能。掺杂浓度高于1×1019cm-3降低导通电阻从而降低器件耐压性能，浓度低于2×1018cm-3与衬底浓度差异较大，较大的失配应力在界面处会形成堆垛层错缺陷。
进一步地，所述4H-SiC缓冲层的生长方法为：分别以100～800slm、80～150sccm、80～150sccm和10～20sccm的流量通入载气H2、含氯的硅源气体、碳源和N2，且碳源与含氯的硅源气体的流量之比为0.6～1：1；于1700～1800℃温度和10～50mbar压力下进行生长。
步骤(3)中，所述N型4H-SiC外延层的厚度为5～20μm；掺杂浓度为2×1014～8×1016cm-3。外延层厚度和掺杂浓度决定器件的耐压能力，厚度越厚，耐压能力越强；掺杂浓度越低，耐压能力越强，但导通电阻越高。
进一步地，所述N型4H-SiC外延层的生长方法为：分别以100～800slm、100～200sccm、30～80sccm和5～20sccm的流量通入载气H2、含氯的硅源气体、碳源和N2，且碳源与含氯的硅源气体的流量之比为0.6～1，于1700～1800℃温度和10～50mbar压力下进行生长。
步骤(4)中，所述沟槽的深度5-15μm，沟槽侧壁倾角86～90°，底部宽度与台面顶部宽度一致，均为2～2.5μm。
本发明还提供了根据上述所述的C面SiC外延沟槽的填充方法填充得到的含超级结的C面SiC外延结构。
本发明提供的C面SiC外延沟槽的填充方法中，在外延沟槽中填充P型SiC的过程中使用不含C原子的B2H6作为P型掺杂剂，这样填充之后的沟槽表面较为光滑，如果在填充P型SiC的过程中使用TMAl作为掺杂剂，当TMAl供应量较大时，TMAl在反应室释放出CH3，使得生长条件变得更加富C，多余的C原子在C面上的生长会受二维或三维成核，最终导致表面石墨化，形成粗糙的表面。
C面4H-SiC衬底的表面自由能为300×10-7J/cm2，Si面4H-SiC衬底的表面自由能为2220×10-7J/cm2，由于C面较Si面表面自由能较低，能显著抑制台阶聚集的发生，但由于表面自由能较低C面形核发生频率要高于Si面，而富Si气氛中表面迁移长度要比富C气氛中高；为弥补C面容易成核的问题，本发明在4H-SiC缓冲层、N型4H-SiC外延层生长及向外延沟槽中填充P型SiC的过程中设定碳源与含氯的硅源气体的流量之比0.6～1：1，如果C/Si>1，则在富C气氛中，C-C原子容易成键，C原子容易覆盖在表面，导致三角型缺陷密度上升，如果C/Si<0.6，在富Si的气氛中，容易形成硅滴。
同时，本发明为了抑制4H-SiC缓冲层、N型4H-SiC外延层生长及向外延沟槽中填充P型SiC的过程中硅滴缺陷的发生，设定生长温度较Si面高100～200℃，本发明中各步骤中的生长温度均设定为1700～1800℃。由于C面4H-SiC衬底与Si面4H-SiC衬底的极性和密排方式不同，在常压条件下，原位刻蚀反应弱，产生的空位少，而在低压条件下，原位刻蚀反应加剧，产生的空位上升，掺杂效率上升，因此，在C面缓冲层、外延层生长及沟槽填充工艺使用低压条件，压力为10～50mbar。
与现有技术相比，本发明采用正轴C面4H-SiC衬底生长外延，然后对外延进行沟槽刻蚀并填充沟槽，在过程中控制各步骤的生长温度和压力均为1700～1800℃、10～50mbar，碳源与含氯的硅源气体的流量比值均为0.6～1.0抑制C面成核和出现硅滴缺陷；同时在外延沟槽填充的过程中，通过控制掺杂气体的使用，经抛光后得到上表面光滑的交替排列的p型和n形区域。本发明提供的C面SiC外延沟槽的填充方法降低了BPD密度和台阶聚集缺陷的发生。
附图说明
图1为C面SiC外延沟槽的填充过程图。
具体实施方式
下面结合实施例对本发明进行详细说明。
实施例1
一种C面SiC外延沟槽的填充方法，包括以下步骤：
1)原位刻蚀衬底：选取正轴C面4H-SiC衬底，对其进行标准清洗；将正轴C面4H-SiC衬底放置到充抽过的SiC化学气相沉积设备的反应室中，再将反应室抽成真空，以100～800slm流量通入H2，于5-50mbar压力和1600-1700℃温度下刻蚀3～10min；
2)4H-SiC缓冲层生长：分别以100～800slm、80～150sccm、80～150sccm和10～20sccm的流量通入载气H2、含氯的硅源气体(SiCl4，SiHCl3，SiH2C12或SiH3Cl)、碳源和N2，其中，碳源与含氯的硅源气体的流量之比为0.6～1：1，于1700～1800℃温度和10～50mbar压力，生长厚度10～200nm，掺杂浓度2×1018～1×1019cm-3的缓冲层；
3)N型4H-SiC外延层生长：分别以100～800slm、100～200sccm、30～80sccm和5～20sccm的流量通入载气H2、含氯的硅源气体(SiCl4，SiHCl3，SiH2C12或SiH3Cl)、碳源和N2，其中，碳源与含氯的硅源气体的流量之比为0.6～1：1，于1700～1800℃温度和10～50mbar压力，在外延炉生长5～20μm，掺杂浓度2×1014～8×1016cm-3N型4H-SiC外延层，取出，清洗；
4)沟槽刻蚀：刻蚀深度5-15μm，沟槽侧壁倾角86～90°，底部宽度与台面顶部宽度一致，均为2～2.5μm；再一次清洗，烘干，送入外延炉中；
5)填满沟槽：分别以100～200sccm、30～80sccm、1000～5000sccm和5～10sccm的流量通入含氯的硅源气体(SiCl4，SiHCl3，SiH2C12或SiH3Cl)、碳源、HCl和B2H6，以100～800slm通入载气H2，控制HCl与含氯的硅源气体的流量之比为15～40：1；碳源与含氯的硅源气体的流量之比0.6～1：1，于1700～1800℃温度和10～50mbar压力下，填满沟槽；
6)CMP抛光：使用标准工艺进行化学机械抛光，抛去台面顶部过生长的4H-SiC，得到上表面光滑的交替排列的p型和n形区域。
KOH腐蚀观察BPD密度：使用马弗炉加热熔融KOH颗粒，待KOH完全熔融，放入SiC外延片。腐蚀温度设定450～500℃，腐蚀时间设定10～20min。腐蚀结束后，依次用去离子水、稀盐酸、去离子水清洗SiC样品。使用光学显微镜对SiC腐蚀坑进行观察确认BPD密度。结果如表1所示。
比较例1
采用标准工艺在标准晶面Si面偏4°SiC衬底上填充的超级结结构，包括以下步骤：
1)原位刻蚀衬底：选取偏向<11-20>方向4°的Si面4H-SiC衬底，对其进行标准清洗；将4H-SiC衬底放置到充抽过的SiC化学气相沉积设备的反应室中，再将反应室抽成真空。以100～800slm流量通入H2，于5-50mbar压力和1400-1500℃温度下刻蚀3～10min；
2)4H-SiC缓冲层生长：停止通入HCl，分别以10～100slm、50～100sccm、50～100sccm和10～20sccm的流量通入载气H2、含氯的硅源气体、碳源和N2，于1600～1640℃温度和50～100mbar压力，生长0.1～0.2μm厚的4H-SiC缓冲层，掺杂浓度1×1017～1×1018cm-3；
3)N型4H-SiC外延层的生长:分别以100～800slm、100～200sccm、30～80sccm和5～20sccm的流量通入载气H2、含氯的硅源气体(SiCl4，SiHCl3，SiH2C12或SiH3Cl)、碳源和N2，于1600～1700℃温度和50～100mbar压力，在外延炉生长5～20μm，掺杂浓度2×1014～8×1016cm-3N型4H-SiC外延层，取出，清洗；
4)沟槽刻蚀：刻蚀深度5-15μm，沟槽侧壁倾角86～90°，底部宽度与台面顶部宽度一致，均为2～2.5μm；再一次清洗，烘干，送入外延炉中；
5)填满沟槽：分别以100～200sccm、30～80sccm、1000～5000sccm和5～10sccm的流量通入含氯的硅源气体(SiCl4，SiHCl3，SiH2C12或SiH3Cl)、碳源、HCl和TMAl，以100～800slm通入载气H2，控制HCl与含氯的硅源气体的流量之比为15～40：1，于1600～1700℃温度和500～600mbar压力下，填满沟槽；
6)CMP抛光：使用标准工艺进行化学机械抛光，抛去台面顶部过生长的4H-SiC，得到上表面光滑的交替排列的p型和n形区域。
7)KOH腐蚀观察BPD密度：使用马弗炉加热熔融KOH颗粒，待KOH完全熔融，放入SiC外延片腐蚀。使用光学显微镜对SiC腐蚀坑进行观察确认BPD密度。
表1
Figure BDA0002998901370000081
上述参照实施例对一种C面SiC外延结构及外延沟槽的填充方法进行的详细描述，是说明性的而不是限定性的，可按照所限定范围列举出若干个实施例，因此在不脱离本发明总体构思下的变化和修改，应属本发明的保护范围之内。

Claims (8)

1.一种C面SiC外延沟槽的填充方法，其特征在于，所述方法包括以下步骤：
（1）对正轴C面4H-SiC衬底进行刻蚀；
（2）在正轴C面4H-SiC衬底上生长N型4H-SiC缓冲层；
（3）在4H-SiC缓冲层上生长N型4H-SiC外延层；
（4）由N型4H-SiC外延层的表面向下刻蚀沟槽；
（5）通入含氯的硅源气体、碳源、HCl和B2H6、H2，于1700～1800℃温度和10～50mbar压力下填满沟槽；
（6）抛光，抛去N型4H-SiC外延层表面过生长的4H-SiC，得到上表面光滑的交替排列的p型和n形区域；
步骤（2）中，所述4H-SiC缓冲层的厚度为10～200 nm，掺杂浓度为2×1018～1×1019cm-3；
步骤（2）中，4H-SiC缓冲层生长时，碳源与含氯的硅源气体的流量之比为0.6～1：1；于1700～1800℃温度和10～50mbar压力下进行生长；
步骤（3）中，N型4H-SiC外延层生长时，碳源与含氯的硅源气体的流量之比为0.6～1，于1700～1800℃温度和10～50mbar压力下进行生长；
步骤（4）中，沟槽侧壁倾角86～90°；
步骤（5）中，HCl与含氯的硅源气体的流量之比为15～40：1；碳源与含氯的硅源气体的流量之比0.6～1：1。
2.根据权利要求1所述的C面SiC外延沟槽的填充方法，其特征在于，步骤（5）中，所述含氯的硅源气体、碳源、HCl 、B2H6、H2的流量为100～200sccm、30～80sccm、1000～5000sccm、5～10sccm、100～800slm。
3.根据权利要求1或2所述的C面SiC外延沟槽的填充方法，其特征在于，步骤（1）中，所述刻蚀的方法为：以100～800slm流量通入H2，于5-50mbar压力和1600-1700℃温度下刻蚀3～10min。
4.根据权利要求1所述的C面SiC外延沟槽的填充方法，其特征在于，所述4H-SiC缓冲层的生长方法为：分别以100～800slm、80～150sccm、80～150sccm和10～20sccm的流量通入载气H2、含氯的硅源气体、碳源和N2。
5.根据权利要求1或2所述的C面SiC外延沟槽的填充方法，其特征在于，步骤（3）中，所述N型4H-SiC外延层的厚度为5～20μm；掺杂浓度为2×1014～8×1016cm-3。
6.根据权利要求5所述的C面SiC外延沟槽的填充方法，其特征在于，所述N型4H-SiC外延层的生长方法为：分别以100～800slm、100～200sccm、30～80sccm和5～20sccm的流量通入载气H2、含氯的硅源气体、碳源和N2。
7.根据权利要求1或2所述的C面SiC外延沟槽的填充方法，其特征在于，步骤（4）中，所述沟槽的深度5-15μm，底部宽度与台面顶部宽度一致，均为2～2.5μm。
8.如权利要求1-7任意一项所述的C面SiC外延沟槽的填充方法填充得到的含超级结的C面SiC外延结构。
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