CN117317022A - 一种六边屏蔽型井槽sic mosfet结构 - Google Patents

一种六边屏蔽型井槽sic mosfet结构 Download PDF

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CN117317022A
CN117317022A CN202311539450.3A CN202311539450A CN117317022A CN 117317022 A CN117317022 A CN 117317022A CN 202311539450 A CN202311539450 A CN 202311539450A CN 117317022 A CN117317022 A CN 117317022A
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许一力
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Hangzhou Spectro Crystal Semiconductor Technology Co ltd
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Abstract

本发明公开一种六边屏蔽型井槽SIC MOSFET结构，包括多个并联的六边形MOS元胞，在六边形MOS元胞引入井槽，减小单个重复元胞尺寸增大电流密度，六边形MOS元胞中具有JFET区，JFET区的横截面呈柱型轮廓，柱型轮廓至少具有一粗径段和一细径段以形成屏蔽结构，粗径段与所述六边形MOS元胞的栅氧层接触，本发明结构在JFET区底部引入屏蔽结构，可以提高器件的雪崩能力，还可以在高漏源偏压下将细径段JFET电流通道极大程度的耗尽，大幅降低器件发生短路时的饱和电流，从而有效降低器件短路时内部的热产生和热积累，提高器件的短路能力，从而彻底解决现有MOSFET器件时性能单一的问题，采用六边形元胞结构，减少了源区的面积占比，增加了器件的电流密度，进一步降低导通电阻。

Description

一种六边屏蔽型井槽SIC MOSFET结构
技术领域
本发明涉及SiC MOSFET的抗雪崩击穿能力和短路能力的片上结构改进技术领域，具体涉及一种六边屏蔽型井槽SIC MOSFET结构。
背景技术
SiC MOSFET器件具有高频低损耗的显著优势，在电动汽车、光伏逆变器和充电桩等领域有十分广泛的应用。然而，一方面SiC MOSFET极快的开关速度使得器件在关断过程中极易产生漏源电压过冲的问题，尤其在800V的电驱系统等应用中易导致SiC MOSFET器件出现短时的雪崩击穿，在SiC MOS栅氧附近形成极大的电热应力，长期使用过程中易出现器件性能退化甚至损坏的问题；另一方面SiC MOSFET在电驱系统发生负载短路时会出现短路故障，瞬时的高压大电流极易导致器件短路失效。目前针对同时优化SiC MOSFET器件雪崩能力和短路能力的方法极少，大部分仍是基于单种鲁棒性进行优化提升。例如，现有技术通常采用优化P阱掺杂形貌和优化终端电场分布等调整元胞结构参数的方法，或者在器件关断过程中优化驱动防止器件出现漏源电压过冲等方法来提升SiC MOSFET雪崩能力或者抑制器件出现漏源电压过冲，采用缩短JFET区或者在驱动电路中集成短路保护功能等方法来改善SiC MOSFET在实际电源系统中的短路故障穿越能力。这些方法通常只能改善器件的一种鲁棒性，而且会给器件的其他性能引入负面影响。例如，缩短JFET宽度可能造成SiCMOSFET器件比导通电阻增大，导致器件导通损耗增大。如图1所示为提升器件雪崩能力而采用的倒掺杂P阱SiC MOSFET元胞结构，图2所示为提升器件短路能力而采用的窄JFET区SiCMOSFET元胞结构。此外，随着制造工艺的发展，SiC MOSFET器件的元胞尺寸基本已经达到极限，如何进一步缩减器件的元胞尺寸或者提高器件的电流密度，成为制约器件导通电阻的重要因素，因此本发明提供了一种针对SiC MOSFET器件全方位的解决方案。
发明内容
有鉴于此，本发明的目的在于提供一种六边屏蔽型井槽SIC MOSFET结构，通过采用引入井槽的六边形MOS元胞中的JFET区下方引入屏蔽结构，一方面在JFET区底部实现大幅缩短JFET区的宽度，达到屏蔽器件在发生漏源电压过冲时在栅氧下形成的极强电场，提升器件的雪崩能力；另一方面较窄的JFET区出口有利于在JFET区底部通过耗尽效应减小器件短路时的电流路径宽度，大幅降低器件的短路饱和电流，进而提升SiC MOSFET的短路能力。此外，通过引入屏蔽结构，可以对栅氧下方的JFET区形成良好的保护作用，因此可以大幅提高栅氧下方JFET区的掺杂浓度，降低SiC MOSFEET积累层电阻和JFET电阻，突破常规SiC MOSFET结构优化中器件导通电阻和短路能力难以协同提升的难题，第三方面，引入井槽结构使P阱与N阱的欧姆接触需同时与源极的短接由横向转为纵向，减小了单个重复元胞尺寸，增加了器件的电流密度，六边形元胞，减少了源区的面积占比，进一步增加了器件的电流密度。
为解决以上技术问题，本发明提供一种六边屏蔽型井槽SIC MOSFET结构，包括碳化硅外延层，所述碳化硅外延层上通过离子注入等距分布呈井状并为P型半导体的P阱，相邻所述P阱之间形成有JFET区，所述P阱中部通过极高浓度的相同离子注入形成为P型半导体的P+，所述P+的两侧通过极高浓度的离子注入形成为N型半导体的N阱，所述N阱与所述P+接触，所述N阱不靠近所述P阱侧面，所述JFET区上方形成有所述栅氧层，所述栅氧层上淀积有所述多晶硅栅极，所述多晶硅栅极上淀积有介质层，所述栅氧层和所述多晶硅栅极至少延伸位于所述N阱上方，所述碳化硅外延层上淀积有覆盖所述介质层的源极，所述碳化硅外延层下侧具有N衬底，所述N衬底下方具有漏极，为了便于理解，将由多晶硅栅极纵向对应的单位范围内相同的结构定义为所述六边形MOS元胞，包括多个并联的六边形MOS元胞，所述六边形MOS元胞俯视结构呈正六边形，所述六边形MOS元胞六个边相邻位置均分布有所述六边形MOS元胞，相邻所述六边形MOS元胞至少有一边平行，所述N阱上刻蚀开凿有井槽，所述井槽贯穿所述N阱并深入至所述P阱内，所述井槽内淀积有金属的源极，所述源极与所述N阱和P阱的欧姆接触同时短接，使得源极与所述N阱和P阱的欧姆接触同时短接由横向转变为纵向，所述JFET区的横截面呈柱型轮廓，所述柱型轮廓至少具有一粗径段和一细径段以形成屏蔽结构，所述粗径段与所述六边形MOS元胞的栅氧层接触。
在一些实施例中优选地方案，所述粗径段和所述细径段自上而下布置并依次连通。
在一些实施例中优选地方案，所述粗径段与所述细径段的直径呈等差数值，和/或，所述粗径段与所述细径段的直径呈非等差数值。
在一些实施例中优选地方案，所述JFET区的粗径段和细径段对应的离子浓度相同并且为高浓度。
在一些实施例中优选地方案，所述P阱与所述JFET区外侧对应的结构呈榫卯适配的连接。
在一些实施例中优选地方案，所述介质层为SiO2。
在一些实施例中优选地方案，所述P阱上的注入的离子为倒注入，即所述P阱的底部离子浓度高于顶部浓度。
在一些实施例中优选地方案，所述P阱注入的离子为Al离子或B离子，所述P+注入为极高浓度的Al离子或B离子，所述N阱注入的离子为极高浓度的P离子或N离子。
与现有技术相比，本发明的优点如下：
1、本发明引入的屏蔽结构为直接在SiC MOSFET元胞中的JFET区中直接改进形成，结构简单，工艺易于实现。
2、本发明引入的屏蔽结构可以利用底部的细径段的JFET形成良好的夹断效应，有效屏蔽强电场在栅氧下方的分布，从而提高器件的雪崩能力。可以在高漏源偏压下将细径段的JFET电流通道极大程度的耗尽，大幅降低器件发生短路时的饱和电流，从而有效降低器件短路时内部的热产生和热积累，提高器件的短路能力；3、本发明的屏蔽结构的JFET区可以进一步提高栅氧下方粗径段的JFET区的掺杂浓度，进而降低SiC MOSFET积累层电阻和JFET电阻，实现更低比导通电阻的SiC MOSFET。
4、本发明的结构突破了常规SiC MOSFET短路能力和导通电阻难以协同优化的难题，可以大幅提升器件的综合性能
5、本发明的结构通过在六边形MOS元胞中引入井槽结构使P阱与N阱的欧姆接触需同时与源极的短接由横向转为纵向，减小了单个重复元胞尺寸，增加了器件的电流密度，通过采用六边形元胞的SiC MOSFET上的P阱侧面底部JFET区引入屏蔽结构，减少了源区的面积占比，增加了器件的电流密度，进一步降低导通电阻。
附图说明
图1为现有的含倒掺杂P阱注入形貌的SiC MOSFET结构示意图。
图2为现有的窄JFET区的SiC MOSFET结构示意图。
图3为图1和图2两种结构的源区俯视图。
图4为本发明的六边屏蔽型井槽SiC MOSFET俯视和横截面结构示意图。
图5为本发明的六边屏蔽型井槽SiC MOSFET横截面结构示意图。
图6为本发明的六边屏蔽型井槽SiC MOSFET俯视结构示意图。
图7为本发明的屏蔽结构的另一种结构示意图。
图8为本发明的屏蔽结构的另一种结构示意图。
图9为本发明的屏蔽结构的另一种结构示意图。
图10为本发明的屏蔽结构的另一种结构示意图。
图11为本发明的屏蔽结构的另一种结构示意图。
具体实施方式
为了便于理解本发明技术方案，以下结合附图与具体实施例进行详细说明。
参见图4-6，在本实施例中举例说明本发明的一种六边屏蔽型井槽SIC MOSFET结构，首先一般的SiC MOSFET结构，包括碳化硅外延层，碳化硅外延层上通过离子注入等距分布呈井状并为P型半导体的P阱，相邻P阱之间形成有JFET区，P阱中部通过极高浓度的相同离子注入形成为P型半导体的P+，P+的两侧通过极高浓度的离子注入形成为N型半导体的N阱，N阱与P+接触，N阱不靠近P阱侧面，在本发明中，P阱注入的离子为Al离子或B离子，P+注入为极高浓度的Al离子或B离子，N阱注入的离子为极高浓度的P离子或N离子，在本实施例中，P阱注入的离子为Al离子，N阱注入的离子为极高浓度的P离子，并且在本发明中，P阱上的注入的离子为倒注入，即P阱的底部离子浓度高于顶部浓度，JFET区上方形成有栅氧层，栅氧层上淀积有多晶硅栅极，多晶硅栅极上淀积有介质层，栅氧层和多晶硅栅极至少延伸位于N阱上方，碳化硅外延层上淀积有覆盖介质层的源极，在本实施例中，介质层为SiO2，碳化硅外延层下侧具有N衬底，N衬底下方具有漏极，为了便于理解，将由多晶硅栅极纵向对应的单位范围内相同的结构定义为六边形MOS元胞，这些六边形MOS元胞并联连接，在本发明中，六边形MOS元胞俯视结构呈正六边形，六边形MOS元胞六个边相邻位置均分布有六边形MOS元胞，相邻六边形MOS元胞至少有一边平行。
对于现有没有抵抗雪崩击穿能力、较低短路能力以及短路能力和导通电阻难以协同优化的SiC MOSFET结构的JFET区是宽度比较大的竖直井状。而本发明的实施例中提供了一种引入屏蔽结构的JFET区，在本发明中，首先在，N阱上刻蚀开凿有井槽，井槽贯穿所述N阱并深入至P阱内，井槽内淀积有金属的源极，源极与N阱和P阱的欧姆接触同时短接，使得源极与所述N阱和P阱的欧姆接触同时短接由横向转变为纵向，从而单个重复的元胞尺寸得以减小，进而增大电流密度，然后在该SiC MOSFET结构的加入屏蔽结构实现提升雪崩能力、短路能力及降低导通电阻，其具体为，JFET区的横截面呈柱型轮廓，柱型轮廓至少具有一粗径段和一细径段以形成屏蔽结构，粗径段与所述六边形MOS元胞的栅氧层接触，粗径段和所述细径段自上而下布置并依次连通，即无论粗径段和细井段直径之间的连接差值多大，二者之间总是连续连通的，在本发明中，粗径段与细径段的直径呈等差数值，即可以是如梯形状的自上而下均匀变小的形状，也可以是具有台阶状自上而下缩小的多个竖直柱状，如图7和8，当然，本发明还考虑到，粗径段与细径段的直径呈非等差数值，即粗径段是很大的直径突然变化到直径很小的细径段，也可以是，一段是直径连续变小的后又突变差值比较大的，如上面是阶梯状下面是倒锥台或上面是到锥台下面是阶梯状，如图9-11。
具体的，所述JFET区的粗径段和细径段对应的离子浓度相同并且为高浓度。
具体的，所述P阱与所述JFET区外侧对应的结构呈榫卯适配的连接。
工作原理：
SiC MOSFET在发生雪崩击穿时，JFET区域存在极高的电场分布，在强电场的作用下，器件内部将产生强烈的碰撞电离，大量的电子-空穴对在电场作用下可能发生隧穿效应进入栅氧中，进而导致器件出现性能退化甚至因为极强的电热耦合效应损坏器件。本发明的结构在JFET区底部引入屏蔽结构，可以利用底部的细径段的JFET形成良好的夹断效应，有效屏蔽强电场在栅氧下方的分布，从而提高器件的雪崩能力。
SiC MOSFET在发生短路时，较高的漏源偏压导致极大的饱和电流流过器件内部，导致器件内部瞬时形成极高的热积累，进而引发器件性能退化或直接失效。本发明结构在JFET区底部引入的屏蔽结构可以在高漏源偏压下将细径段的JFET电流通道极大程度的耗尽，大幅降低器件发生短路时的饱和电流，从而有效降低器件短路时内部的热产生和热积累，提高器件的短路能力。
此外，由于引入的屏蔽结构可以对栅氧下方的JFET区形成良好的屏蔽保护，因此可以进一步提高栅氧下方JFET区的掺杂浓度，进而降低SiC MOSFET积累层电阻和JFET电阻，实现更低比导通电阻的SiC MOSFET，采用六边形元胞结构，减少了源区的面积占比，增加了器件的电流密度，进一步降低导通电阻。
以上仅是本发明的优选实施方式，本发明的保护范围以权利要求所限定的范围为准，本领域技术人员在不脱离本发明的精神和范围内做出的若干改进和润饰，也应视为本发明的保护范围。

Claims (8)

1.一种六边屏蔽型井槽SIC MOSFET结构，包括碳化硅外延层，所述碳化硅外延层上通过离子注入等距分布呈井状并为P型半导体的P阱，相邻所述P阱之间形成有JFET区，所述P阱中部通过极高浓度的相同离子注入形成为P型半导体的P+，所述P+的两侧通过极高浓度的离子注入形成为N型半导体的N阱，所述N阱与所述P+接触，所述N阱不靠近所述P阱侧面，所述JFET区上方形成有所述栅氧层，所述栅氧层上淀积有所述多晶硅栅极，所述多晶硅栅极上淀积有介质层，所述栅氧层和所述多晶硅栅极至少延伸位于所述N阱上方，所述碳化硅外延层上淀积有覆盖所述介质层的源极，所述碳化硅外延层下侧具有N衬底，所述N衬底下方具有漏极，为了便于理解，将由多晶硅栅极纵向对应的单位范围内相同的结构定义为所述六边形MOS元胞，其特征在于，所述六边形MOS元胞俯视结构呈正六边形，所述六边形MOS元胞六个边相邻位置均分布有所述六边形MOS元胞，相邻所述六边形MOS元胞至少有一边平行，所述N阱上刻蚀开凿有井槽，所述井槽贯穿所述N阱并深入至所述P阱内，所述井槽内淀积有金属的源极，所述源极与所述N阱和P阱的欧姆接触同时短接，使得源极与所述N阱和P阱的欧姆接触同时短接由横向转变为纵向，所述JFET区的横截面呈柱型轮廓，所述柱型轮廓至少具有一粗径段和一细径段以形成屏蔽结构，所述粗径段与所述六边形MOS元胞的栅氧层接触。
2.根据权利要求1所述的一种六边屏蔽型井槽SIC MOSFET结构，其特征在于，所述粗径段和所述细径段自上而下布置并依次连通。
3.根据权利要求1所述的一种六边屏蔽型井槽SIC MOSFET结构，其特征在于，所述粗径段与所述细径段的直径呈等差数值，和/或，所述粗径段与所述细径段的直径呈非等差数值。
4.根据权利要求1所述的一种六边屏蔽型井槽SIC MOSFET结构，其特征在于，所述JFET区的粗径段和细径段对应的离子浓度相同并且为高浓度。
5.根据权利要求1任一项所述的一种六边屏蔽型井槽SIC MOSFET结构，其特征在于，所述P阱与所述JFET区外侧对应的结构呈榫卯适配的连接。
6.根据权利要求1所述的一种六边屏蔽型井槽SIC MOSFET结构，其特征在于，所述介质层为SiO2。
7.根据权利要求1所述的一种六边屏蔽型井槽SIC MOSFET结构，其特征在于，所述P阱上的注入的离子为倒注入，即所述P阱的底部离子浓度高于顶部浓度。
8.根据权利要求1所述的一种六边屏蔽型井槽SIC MOSFET结构，其特征在于，所述P阱注入的离子为Al离子或B离子，所述P+注入为极高浓度的Al离子或B离子，所述N阱注入的离子为极高浓度的P离子或N离子。
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