CN102881717B - 一种高压器件的保护环结构及其制造方法 - Google Patents

一种高压器件的保护环结构及其制造方法 Download PDF

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CN102881717B
CN102881717B CN201210404971.3A CN201210404971A CN102881717B CN 102881717 B CN102881717 B CN 102881717B CN 201210404971 A CN201210404971 A CN 201210404971A CN 102881717 B CN102881717 B CN 102881717B
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孙德明
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Shanghai IC R&D Center Co Ltd
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Abstract

本发明提供一种半导体高压器件的保护环结构及其制造方法,其保护环结构包括第一N型单晶硅衬底、第二N型单晶硅衬底、间断的氧化层、金属场板、器件区、多个P+型注入扩散环和等位环;其中,第二N型单晶硅衬底为从第一N型单晶硅衬底上外延一层的N型单晶层;且其掺杂浓度低于第一N型单晶硅衬底。并且,在P+型注入扩散环的内侧,还嵌有零偏压下完全耗尽的N型注入扩散环。因此,在相同的耐压值的情况下,本发明的场板加场限环结构,不仅优化每一个环间距缩,减少了环的数目,节省面积,同时也缩短保护环设计时间。

Description

一种高压器件的保护环结构及其制造方法
技术领域
本发明涉及半导体领域,尤其涉及一种高压半导体功率器件中的保护环结构及其制造方法。
背景技术
随着石油煤炭储备不停地减少,而人类的能源消耗却不断增加,节能成为二十一世纪人类的共识。据美国能源部估计,有三分之二的电力被用在马达驱动上。而主要应用于开关电源、PWM脉宽调制器、变频器等电子电路中,作为高频整流二极管、续流二极管或阻尼二极管使用等功率器件,绝缘栅双极型晶体管(Insulated Gate Bipolar Transistor,简称IGBT)和与之配套的快恢复二极管(简称FRD),可以使马达驱动节能20%~30%。可以预计,功率器件会在未来快速增长。
半导体功率器件的结构离不开PN结(PN junction)。采用不同的掺杂工艺,通过扩散作用,将P型半导体与N型半导体制作在同一块半导体(通常是硅或锗)基片上,在它们的交界面就形成空间电荷区称PN结。
然而,扩散形成的PN结结深一般为几个微米,其曲率会导致电场集中,使击穿电压远比平面结的低。如平面结耐压超过1200V的器件,如使用5微米深的结,其曲率会导致电场集中使击穿电压低于400V,远低于平面结的击穿电压,因此在器件的需的外围需要保护环。场板场限环结构是其中发展较早的,工艺比较简单,同时不增加光刻层次的方法,至今被广泛应用。
请参阅图1,图1为现有技术中的场板场限环结构的截面示意图。如图所示,中间区域是器件区9,保护环由一系列嵌在N型单晶硅区3中的P+型注入扩散区的扩散环5、以及最外围的N+注入扩散层区的等位环4(工作时接高压或悬浮)组成。从保护环的截面来看,保护环是以器件区9为对称结构,器件区9外的两个P+型注入扩散区的扩散环5之间的区域为主要的耐压区。紧邻器件区9的P+型注入扩散区的扩散环5为零环,该扩散环5在器件区9工作时接零,再外一圈的P+型注入扩散区的扩散环5为第一环,工作时悬浮,依次类推,即图1的P+型注入扩散区的扩散环5(场限环部分)不停重复,可得到第二、三、四环以至更多的环,以满足耐压的需求。保护环的制作过程大致如此,在衬底上,光刻P+型注入扩散区的扩散环5,注入,然后,光刻等位环区4,注入并推阱。
请参阅图2,图2为应用于现有技术中的场限环结构的截面的细节图;其中,细虚线是耗尽区边界,点划线是电场切割线。图2中的现有技术的场限环结构形成三角形的横向电场分布。
请参阅图5,图5为应用于现有技术中的场限环和本发明两种结构的氧化层下电场分布的比较示意图;其中的三角形电场分布为应用于现有技术中的场限环结构一个环间距内的电场分布示意图。从图5中可以看出,现有技术中的场限环结构形成三角形的横向电场分布,其三角形左侧斜率大的由P+型注入扩散区的扩散环5区的P型硅耗尽引入,右侧斜率小的区域由两个P+型注入扩散区的扩散环5区之间的N型硅耗尽引入。
然而,斜率的大小只与掺杂浓度有关,掺杂高的斜率也大。由于P+型注入扩散区的扩散环5区的P+型掺杂总比两个P+型注入扩散区的扩散环5区之间的N型掺杂高,因此,左侧的斜率也总比右侧的大,三角形的顶点处的电场就是击穿电场,三角形所构成的三角形面积就是耐压值。
本领域技术人员知道,如果随着耐压的增加,则所需要的环的数目也相应增加(例如,1200V的场限环结构通常需要使用4个环,3300V的耐压通常需要22个环)。因此,保护环面积随之增大,保护环的设计时间也大大增加。
因此,现有技术中的场限环结构形成三角形的横向电场分布,使环间距没有得到充分利用。如何环间距得到更充分的利用,可以在相同耐压下使环间距更小,或每一环间距上耐压更高,减少环的数目是目前业界急需解决的问题。
发明内容
本发明的主要目的在于提供一种半导体功率器件中的高压保护环结构,通过改变现有技术中的环结构,在相同的耐压值下,通过缩短环间距,从而缩小了保护环面积,或优化每一个环间距,使每一环间距的耐压增加,以减少环的数目,缩小保护环面积同时缩短保护环设计时间。
为达成上述目的,本发明提供一种半导体高压器件的保护环结构,其包括:第一N型单晶硅衬底、第二N型单晶硅衬底、间断的氧化层、金属场板、器件区、多个P+型注入扩散环和等位环;其中,第二N型单晶硅衬底为位于第一N型单晶硅衬底上的一层N型单晶层;且其掺杂浓度低于第一N型单晶硅衬底;间断的氧化层位于第二N型单晶硅衬底的表面上;金属场板部分覆盖在露出的第二N型单晶硅衬底的表面和部分嵌于氧化层中;器件区嵌于第二N型单晶硅衬底中;多个P+型注入扩散环嵌于所述第二N型单晶硅衬底中,其中,紧邻所述器件区的P+型注入扩散环为零环,且以器件区为中间区域环绕分布,在所述器件区工作时接零;其他P+型注入扩散环在所述器件区工作时悬浮,且以零环为中间区域,一环环绕于另一个环的外圈;等位环嵌于第二N型单晶硅衬底中,且环绕于多个P+型注入扩散环的外围。
优选地,所述第二N型单晶硅衬底的深度大于P+型注入扩散环的结深,且小于10微米。
优选地,还包括零偏压下完全耗尽的N型注入扩散环,嵌于P+型注入扩散环的环内。
优选地,所述N型注入扩散环靠近位于所述P+型注入扩散环的内环边界。
优选地,所述N型注入扩散环位于所述P+型注入扩散环的内环边界和耗尽区边界之间。
优选地,所述N型注入扩散环的底边小于或与P+型注入扩散环内的耗尽区边界底边平齐。
优选地,所述N型注入扩散环的掺杂浓度高于第二N型单晶硅衬底的掺杂浓度,且小于等于1e15/cm3
优选地,所述氧化层的厚度为50nm。
为达成上述目的,本发明还提供一种半导体高压器件保护环结构的制造方法,包括如下步骤:
步骤S01:采用区熔法形成在第一N型单晶硅衬底上外延轻掺的第二N型单晶硅衬底;其中,第二N型单晶硅衬底的掺杂浓度低于第一N型单晶硅衬底;
步骤S02:在第二N型单晶硅衬底表面上生长一薄层氧化层,光刻生成等位环区,注入N型杂质,去胶后推阱;
步骤S03:在第二N型单晶硅衬底表面上和间断的氧化层上生长场氧化;光刻P+型注入扩散环区,刻蚀氧化层,在扩散环区注入P+型杂质,生成P+型注入扩散环,并推阱;光刻器件区,刻蚀场氧化层;
步骤S04:金属沉积刻蚀,钝化层沉淀刻蚀,背面注入减薄,注入杂质激活,背面金属沉积。
优选地,所述的步骤S02还包括:光刻N型注入扩散环区,并注入N型杂质,生成N型注入扩散环。
从上述技术方案可以看出,本发明的半导体功率器件中的高压保护环结构引入了N型外延和P型环内侧的N型环,使现有技术中的高压保护环结构所形成的三角形电场分布变成梯形分布。因此,在相同的耐压值的情况下,本发明的场板加场限环结构,不仅优化每一个环间距缩,减少了环的数目,节省面积,同时也缩短保护环设计时间。
附图说明
图1为应用于现有技术中的场限环结构的截面示意图;
图2为应用于现有技术中的场限环结构的截面的细节图;其中,细虚线是耗尽区边界,点划线是电场切割线;
图3为本发明一具体实施例的场限环结构截面图示意图;
图4为本发明图3中本发明结构的细节图,细虚线是耗尽区边界,点划线是电场切割线;
图5为应用于现有技术中的场限环和本发明两种结构的氧化层下电场分布的比较示意图;其中,现有技术场限环结构所形成三角形电场分布,本发明的场限环结构所形成的梯形电场分布。
具体实施方式
体现本发明特征与优点的一些典型实施例将在后段的说明中详细叙述。应理解的是本发明能够在不同的示例上具有各种的变化,其皆不脱离本发明的范围,且其中的说明及图示在本质上当作说明之用,而非用以限制本发明。
上述及其它技术特征和有益效果,将结合实施例及附图3-5对本发明的场板加场限环的保护环结构进行详细说明。
请参阅图3,图3为本发明一具体实施例场板加场限环的保护环结构截面示意图。为叙述方便起见,在本发明的实施例中,器件区9外的保护环仅包括两个P+型注入扩散环5和一个等位环4,在其它的实施例中,P+型注入扩散环5可以根据耐压的需要设置3、4、5个或更多,在此不再赘述。
本发明与现有技术所应用结构不相同的是:从第一N型单晶硅衬底3上增加了一层轻掺N型外延层(即第二N型单晶硅衬底8)和在P+型注入扩散环5内嵌了零偏压下完全耗尽的N型注入扩散环6。
我们知道,第一N型单晶硅衬底3区的掺杂成数量级的提高,可以有限地提高击穿电场,但时耗尽区宽度变小,会在器件区早早击穿。请再参阅图5,如果想把图5所示的三角形电场分布中的斜率做小,需要第一N型单晶硅衬底3区的低浓度N型的掺杂。由于N掺杂浓度(第一N型单晶硅衬底3区)决定漂移区的电学特性,不能随意选择,因此,本发明采用了在第一N型单晶硅衬底3上外延一层比第一N型单晶硅衬底3掺杂更低的第二N型单晶硅衬底8。
如图3所示,在本发明的一个实施例中,该保护环结构包括第一N型单晶硅衬底3、第二N型单晶硅衬底8、嵌于第二N型单晶硅衬底8中的器件区9、在第二N型单晶硅衬底8表面上具有间断的氧化层2以及金属场板1;金属场板1是部分覆盖在露出的第二N型单晶硅衬底8的表面和氧化层2上。优选地,氧化层2的厚度为50nm。
每个器件区9的保护环结构由2个嵌于N型单晶硅衬底3中的P+型注入扩散环5和一个等位环4,且以器件区9为中间区域环绕分布。其中,第二N型单晶硅衬底8为从第一N型单晶硅衬底3上外延一层的N型单晶层;且其掺杂浓度低于第一N型单晶硅衬底3。
紧邻器件区9的P+型注入扩散环5为零环,在器件区9工作时接零;另一个P+型注入扩散环5,以零环为中间区域,且环绕于零环的外圈,在器件区9工作时悬浮;N+注入扩散等位环4环绕于P+型注入扩散环5的外圈,在器件区9工作时,等位环4接高压或悬浮。
更进一步地,第二N型单晶硅衬底8的深度大于P+型注入扩散环5的结深,且小于10微米。
请参阅图4,图4为本发明图3中本发明保护环结构的细节图,其中,细虚线是耗尽区边界,点划线是电场切割线。如图所示,在本发明的一些实施例中包括的零偏压下完全耗尽的N型注入扩散环6,嵌于P+型注入扩散环5的环内,提供了正电荷,使电场迅速上升,从而形成梯形电场。优选地,每个P+型注入扩散环5中均包含N型注入扩散环6,且N型注入扩散环6须完全耗尽才能提供正电荷。
更进一步地,N型注入扩散环6靠近位于P+型注入扩散环5的外环边界。较优地,N型注入扩散环6靠近位于所述P+型注入扩散环5的内环边界,即N型注入扩散环6位于P+型注入扩散环5的内环边界和耗尽区边界之间。
众所周知,P+型环区引入的N区的电荷数目越多,P+型环区之间的N型单晶硅内的P型区的电荷数目越多,附加电场越强。因此,在设计中尽量增加这N型注入扩散环6区域的面积,在实际的设计中,一般将N型注入扩散环6的底边尽量设计成与P+型注入扩散环5内的耗尽区边界底边平齐。
而且,因需要完全耗尽,掺杂不能非常高,因此,N型注入扩散环6的掺杂浓度高于第一N型单晶硅衬底3,而一般情况下,对于1200V的第一N型单晶硅衬底3掺杂为6.5e13/cm3。N型注入扩散环6区的掺杂可以比第二N型单晶硅衬底8区域的高接近两个数量级,但小于等于1e15/cm3。且在P+型注入扩散环5内的内侧的N型注入扩散环6必须完全覆盖P+型注入扩散环5的内侧。
请参阅图5,图5为应用于现有技术中的场限环和本发明两种结构的氧化层下电场分布的比较示意图;其中,梯形电场分布为应用于本发明实施例中的场限环结构一个环间距内的电场分布示意图。
如图5所示,本发明保护环结构使一个环间距内的电场分布从三角形电场变为梯形电场,其梯形电场的面积即代表耐压值,可以看出,梯形电场的面积大于三角型电场的面积。可以看出,梯形电场比三角形电场更有效地利用面积。在实际应用中,可以根据需要从两种情况下考虑使用梯形电场的方式:第一种是在相同的耐压下,所设计的结构要求两个P+型注入扩散环5之间的距离更小。第二种是要求优化每一个环间距,使梯形电场的效率最大,即每个环的耐压达到最大。不论怎样,在相同的耐压要求的情况下,均可以减少使用的环的数目,从而减少了面积。例如,对于商用的3300V的耐压环的数目一般需要22个,在器件模拟阶段都需要大量时间,需要逐个加环优化,每增加一环,需要增加时间,因此,如果减少了环的数量,可以大大缩短保护环设计时间。
在本发明的一个实施例中,上述半导体高压器件保护环结构的制造方法可以包括如下步骤:
步骤S01:采用区熔形成在第一N型单晶硅衬底上外延轻掺的第二N型单晶硅衬底;其中,第二N型单晶硅衬底的掺杂浓度低于第一N型单晶硅衬底;
步骤S02:在第二N型单晶硅衬底表面上生长一薄层氧化层,光刻生成等位环区,注入N型杂质,去胶后推阱;
步骤S03:在第二N型单晶硅衬底表面上和间断的氧化层上生长场氧化;光刻P+型注入扩散环区,刻蚀氧化层,在扩散环区注入P+型杂质,生成P+型注入扩散环,并推阱;光刻器件区,刻蚀场氧化层;
步骤S04:金属沉积刻蚀,钝化层沉淀刻蚀,背面注入减薄,注入杂质激活,背面金属沉积。
在本发明的较佳的实施例中,在步骤S02后,还包括光刻N型注入扩散环区,并注入N型杂质,生成N型注入扩散环。如果N型注入扩散环形成后,当然,在步骤S03中生成的P+型注入扩散环一定是要包含N型注入扩散环,且较优地,N型注入扩散环6靠近位于所述P+型注入扩散环5的内环边界,即N型注入扩散环6位于P+型注入扩散环5的内环边界和耗尽区边界之间。
综上所述,本发明的结构引入了轻掺外延第二N型单晶硅衬底和在P+型注入扩散区的扩散环环内侧的N型注入扩散环,使传统结构的三角形电场分布变成梯形分布。在相同的耐压值下可以缩短环间距,从而缩小了保护环面积;或优化每一个环间距,使每一环间距的耐压增加,以减少环的数目,缩小保护环面积同时缩短保护环设计时间。
以上所述的仅为本发明的实施例,所述实施例并非用以限制本发明的专利保护范围,因此凡是运用本发明的说明书及附图内容所作的等同结构变化,同理均应包含在本发明的保护范围内。

Claims (7)

1.一种半导体高压器件的保护环结构,其特征在于,包括:
第一N型单晶硅衬底(3);
第二N型单晶硅衬底(8),其为位于所述第一N型单晶硅衬底(3)上的一层N型单晶层;且其掺杂浓度低于所述第一N型单晶硅衬底(3);
间断的氧化层(2),位于第二N型单晶硅衬底(8)的表面上;
金属场板(1),其部分覆盖在露出的第二N型单晶硅衬底(8)的表面和部分嵌于氧化层(2)中;
器件区(9),嵌于所述第二N型单晶硅衬底(8)中;
多个P+型注入扩散环(5),嵌于所述第二N型单晶硅衬底(8)中,其中,紧邻所述器件区(9)的P+型注入扩散环(5)为零环,且以所述器件区(9)为中间区域环绕分布,在所述器件区(9)工作时接零;其他P+型注入扩散环(5),在所述器件区(9)工作时悬浮,且以零环为中间区域,一环环绕于另一个环的外圈;
等位环(4),嵌于所述第二N型单晶硅衬底(8)中,且环绕于所述多个P+型注入扩散环(5)的外围;
零偏压下完全耗尽的N型注入扩散环(6),嵌于所述P+型注入扩散环(5)的环内。
2.根据权利要求1所述的保护环结构,其特征在于,所述第二N型单晶硅衬底(8)的深度大于所述P+型注入扩散环(5)的结深,且小于10微米。
3.根据权利要求1或2所述的保护环结构,其特征在于,所述N型注入扩散环(6)靠近位于所述P+型注入扩散环(5)的内环边界。
4.根据权利要求3所述的保护环结构,其特征在于,所述N型注入扩散环(6)位于所述P+型注入扩散环(5)的内环边界和耗尽区边界之间。
5.根据权利要求4所述的保护环结构,其特征在于,所述N型注入扩散环(6)的底边小于或与所述P+型注入扩散环(5)内的耗尽区边界底边平齐。
6.根据权利要求1或2所述的保护环结构,其特征在于,所述N型注入扩散环(6)的掺杂浓度高于第二N型单晶硅衬底(8)的掺杂浓度,且小于等于1e15/cm3
7.根据权利要求1所述的保护环结构,其特征在于,所述氧化层的厚度为50nm。
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