CN104037235B - 一种快速软恢复功率开关二极管及其制备方法 - Google Patents

一种快速软恢复功率开关二极管及其制备方法 Download PDF

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CN104037235B
CN104037235B CN201410261023.8A CN201410261023A CN104037235B CN 104037235 B CN104037235 B CN 104037235B CN 201410261023 A CN201410261023 A CN 201410261023A CN 104037235 B CN104037235 B CN 104037235B
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马丽
谢加强
高勇
王秀慜
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Xi'an Guochuang Electronics Co.,Ltd.
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Abstract

本发明公开了一种快速软恢复功率开关二极管,从上到下依次设置有P+阳极区、超结部分、N-层和N+P+N+阴极区;所述的超结部分为对半设置的N柱和P柱组成,N柱和P柱沿横向排列,超结部分的N柱和P柱至少设置一对。本发明还公开了该种快速软恢复功率开关二极管的制备方法。本发明的快速软恢复功率开关二极管及制备方法,使得二极管的反向恢复峰值电流较常规的PiN二极管大大减小,反向阻断特性和正向导通特性有了很大提升,能够更好的适用于高频电路应用中。

Description

一种快速软恢复功率开关二极管及其制备方法
技术领域
本发明属于电力半导体器件技术领域,涉及一种快速软恢复功率开关二极管,本发明还涉及该种快速软恢复功率开关二极管的制备方法。
背景技术
电力半导体器件的发展,特别是新型器件的出现和应用,都会以自己独有的特性占有不同的相关领域,使应用范围不断的拓展。同时,电力电子技术的发展对器件提出更高的要求,又会促进器件性能的提高和新器件的研究与发展。
在许多工作条件下,很多器件需要一个与之反并联的二极管以提供续流通道,减少电容的充放电时间,同时抑制因负载电流瞬时反向而感应的高电压。其中续流二极管的反向特性对施加于有源元件的尖峰电压及电路的效率产生很大影响,要求具有良好的快速和软恢复特性。
二极管和一般开关的不同在于,“开”与“关”由所加电压的极性决定,而且“开”态有微小的压降Vf,“关”态有微小的电流I0。如图1所示,当电压由正向变为反向时,电流并不立刻成为(-I0),而是在一段时间ts内,反向电流始终很大,二极管并不关断。经过ts后,反向电流才逐渐变小,再经过tf时间,二极管的电流才成为(-I0),ts称为储存时间,tf称为下降时间。trr=ts+tf称为反向恢复时间,以上过程称为反向恢复过程。软度因子S定义为S=tf/ts,S越大,说明反向恢复电流曲线越平缓,即曲线的软度越好。Ifm为正向通态电流,Irm为反向恢复峰值电流。
传统的Si功率PiN开关二极管虽然具有较低的正向压降、较好的阻断能力、造价低廉、制作简单,然而它的反向恢复性能较差。为减少开态时的贮存电荷量获得较快的开关速度,常利用金和铂的扩散以及通过高能电子辐照等引入复合中心的方法减少少子寿命,这样又会造成二极管的硬恢复特性差及漏电流较大,同时也不易于集成。因此需要采用新材料和新结构解决这样的矛盾。
发明内容
本发明的目的是提供一种快速软恢复功率开关二极管,解决了现有技术中存在的传统PiN二极管的反向恢复峰值电流过大,反向恢复时间长的问题。
本发明的另一个目的是提供该种快速软恢复功率开关二极管的制备方法。
本发明所采用的第一种技术方案是,一种快速软恢复功率开关二极管,从上到下依次设置有P+阳极区、超结部分、N-层和N+P+N+阴极区。
本发明所采用的第二种技术方案是,一种快速软恢复功率开关二极管的制备方法,按照如下步骤实施:
步骤1、选取掺杂浓度均为2×1014cm-3-3×1015cm-3数量级的轻掺杂衬底晶片,厚度为20μm-400μm;
步骤2、采用外延方法,使用氢气作为还原剂,在1100℃-1300℃高温下四氯化硅被氢还原析出硅,外延时间为20-120min,形成厚度为10μm-200μm的本征硅片;
步骤3、采用干-湿-干氧化法在本征硅片表面生长一层SiO2薄膜,厚度为2-4μm;
步骤4、涂抹并刻蚀光刻胶,使得右半部分SiO2表面裸露出来;
步骤5、刻蚀SiO2露出需要进行离子注入的右半边硅片表面区域;
步骤6、进行硼离子注入;
步骤7、刻蚀掉剩余光刻胶和SiO2掩蔽层;
步骤8、采用干-湿-干氧化法在硅片表面生长一层薄膜SiO2,厚度为2-4μm,并涂抹刻蚀光刻胶;
步骤9、刻蚀SiO2露出需要进行离子注入的左半边硅片表面区域;
步骤10、进行磷离子注入;
步骤11、刻蚀掉剩余光刻胶和SiO2掩蔽层;没有区别这个步骤是重复的,只不过刻蚀部位不同;
步骤12、进行硼离子注入形成阳极区;
步骤13、翻转器件;
步骤14、采用干-湿-干氧化法在硅片表面生长一层薄膜SiO2,厚度为2-4μm;
步骤15、涂抹并刻蚀光刻胶,使得与阴极P+柱宽度相等部分SiO2表面裸露出来;
步骤16、刻蚀未被掩蔽的SiO2区域,露出需要进行离子注入的硅片表面区域;
步骤17、进行硼离子注入;
步骤18、刻蚀掉剩余光刻胶和SiO2掩蔽层;
步骤19、氧化形成SiO2并涂抹刻蚀光刻胶,采用干-湿-干氧化法在硅片表面生长一层薄膜SiO2,厚度为2-4μm;
步骤20、涂抹并刻蚀光刻胶,使得剩余光刻胶覆盖对应阳极P+柱的上方部位;
步骤21、刻蚀未被光刻胶覆盖的SiO2,露出需要进行离子注入的硅片表面区域;
步骤22、进行磷离子注入;
步骤23、刻蚀掉剩余光刻胶和SiO2掩蔽层;
步骤24、蒸铝:双面蒸铝形成阴极和阳极欧姆接触,并做SiO2钝化保护,最终形成具有阴极P+柱结构和超结结构的功率开关二极管。
本发明的有益效果是:在阴极区和耐压层中分别引入P+柱掺杂结构和超结结构以后,经实验,二极管的反向恢复峰值电流较常规的PiN二极管减小了将近一半;反向恢复时间缩短到原来的1/3左右;较低的反向恢复时间使得该结构的快速软恢复功率开关二极管能够更好的适用于高频电路应用中,并减小了在高频振荡中由于反向恢复峰值电流过大而引起电路烧毁的可能性。同时,在同等掺杂浓度下,该结构的反向阻断特性较现有PiN二极管提升了1/3左右,且具有更小的正向导通压降Vf,使得器件在动态电路中工作时能够获得更小的功率损耗,极大的节约了能源和提升了电能的利用率。
附图说明
图1是现有的功率开关二极管的反向恢复电流图;
图2是现有的功率开关二极管(PiN二极管)的器件纵向剖面图;
图3是本发明快速软恢复功率开关二极管的器件纵向剖面图;
图4是本发明快速软恢复功率开关二极管与普通二极管和PiN二极管的反向恢复特性对比曲线;
图5是本发明快速软恢复功率开关二极管和现有PiN二极管的反向阻断特性对比曲线;
图6是本发明快速软恢复功率开关二极管和现有PiN二极管的正向导通特性对比曲线;
图7是本发明快速软恢复功率开关二极管在外压为0V时的空间电荷图;
图8是本发明快速软恢复功率开关二极管的制作工艺流程示意图。
图中,1.P+阳极区,2.超结部分,3.N-层,4.N+P+N+阴极区。
具体实施方式
下面结合附图和具体实施方式对本发明进行详细说明。
如图2所示,现有的功率开关二极管(PiN二极管)的结构是,从上到下依次设置有P+阳极区、N-耐压层和N+阴极区。
如图3所示,本发明快速软恢复功率开关二极管,从上到下依次设置有P+阳极区1、超结部分2、N-层3(超结部分2、N-层3一起合称为耐压层)和N+P+N+阴极区4,全部是硅材料构成;其中,超结部分2为对半设置的N柱和P柱组成,N柱和P柱沿横向排列,超结部分2的N柱和P柱至少设置一对。
其中的P+阳极区1的掺杂浓度为1×1019cm-3-5×1022cm-3,掺杂剂为硼离子,厚度为3μm-6μm;
超结部分2的掺杂浓度为8×1014cm-3-6×1015cm-3,厚度为10μm-80μm,P柱和N柱厚度均为10μm-80μm,掺杂剂为磷离子和硼离子;
N-层3的掺杂浓度为2×1014cm-3-3×1015cm-3,厚度为10μm-320μm,掺杂剂为磷离子;
N+P+N+阴极区4的掺杂浓度为1×1019cm-3-5×1022cm-3,其中N+部分掺杂剂为磷离子,厚度为3μm-6μm,P+部分掺杂剂为硼离子,P+柱高度为3μm-10μm;器件总宽度为20-200μm。
由上可见,本发明与现有结构的区别特征主要在于,引入超结部分2结构;N+P+N+阴极区4为在原有的N+阴极区中间位置贯通设置有P+阴极区(以下文本中简称P+柱),P+阴极区两边均为N+阴极区,或者说,由现有的单一N+阴极区结构改变为并列的N+P+N+阴极区4的创新结构。
本发明器件与现有结构器件的性能对比:
为了直观对比方便,在具有相同的工艺参数和结构尺寸的情况下,本发明结构的器件与现有PiN二极管i区的掺杂浓度均为2×1014cm-3-6×1015cm-3范围内,两者的阴极和阳极的掺杂浓度均为1×1019cm-3-5×1022cm-3
如图4可以看出,本发明具有阴极P+柱和超结结构的快恢复二极管的反向恢复峰值电流明显较普通结构和PiN二极管的小了很多,经计算,反向恢复电流降低至普通PiN二极管的一半左右,反向恢复时间缩减至PiN二极管的1/3左右;
如图5可以看出,本发明快恢复功率二极管的反向阻断电压较现有PiN二极管有了明显的提升,经计算,在同等掺杂浓度下,本发明器件的反向阻断特性较现有PiN二极管提升了三分之一,这是因为在相同的掺杂浓度下,超结部分2的加入后由于PN结之间载流子的相互扩散补偿,使得超结部分载流子有了较大的耗尽层(参照图7中的空间电荷分布图),这一现象很好的解释了为什么会因为超结的介入而提升了器件的反向阻断电压;
如图6可以看出,本发明快恢复功率二极管的正向导通电压较现有PiN二极管低,这是因为超结部分2掺杂浓度高于N-层3的掺杂浓度,这样在外加正向电压时其具有较小的导通压降;
图7为本发明器件在外加电压为0V时的空间电荷分布图,其中阴极处的P+柱在N-层3中产生的内建电场,使得存在于耐压层中的载流子在器件的反向恢复过程中很快就会被抽取并复合掉,因此极大的降低了反向恢复峰值电流,减小了反向恢复电荷的存储时间。
本发明是在常规的PiN二极管的基础上,将普通N+阴极区结构用N+P+N+结构代替,其结构与PiN二极管的工艺具有很好的兼容性,很好地提升了器件的动态特性;同时在耐压层中加入超结结构,提升了器件的反向阻断电压;该器件的N+P+N+阴极区4和P+阳极区1均采用重掺杂和电极部分形成欧姆接触。
本发明器件结构有效地改善了器件的反向恢复时间、反向恢复峰值电流,反向阻断特性及正向导通压降,从而使得器件更好的应用于高频动态电路。虽然引入超结结构所带来的不足是反向恢复硬度大,但总体上来看,其带来的优点是现有PiN二极管无法比拟的。
如图8所示,本发明快速软恢复功率开关二极管的制备方法,具体按照以下步骤实施:
步骤1、选取掺杂浓度均为2×1014cm-3-3×1015cm-3数量级的轻掺杂衬底晶片,厚度为20μm-400μm;
步骤2、采用外延方法,使用氢气作为还原剂,在1100℃-1300℃高温下四氯化硅被氢还原析出硅,外延时间为20-120min,形成厚度为10μm-200μm的本征硅片;
步骤3、采用干-湿-干氧化法在本征硅片表面生长一层SiO2薄膜,厚度为2-4μm;
步骤4、涂抹并刻蚀光刻胶,使得右半部分SiO2表面(图8中的右半部分)裸露出来;
步骤5、刻蚀SiO2露出需要进行离子注入的右半边硅片表面区域;
步骤6、进行硼离子注入,剂量为2.95×1011cm-2-3.06×1012cm-2,注入能量为30-500Kev;
步骤7、刻蚀掉剩余光刻胶和SiO2掩蔽层;
步骤8、采用干-湿-干氧化法在硅片表面生长一层薄膜SiO2,厚度为2-4μm,并涂抹刻蚀光刻胶;
步骤9、刻蚀SiO2露出需要进行离子注入的左半边硅片表面区域;(本步骤与步骤5位置左右对应)
步骤10、进行磷离子注入,剂量为2.95×1011cm-2-3.06×1012cm-2,注入能量为30-500Kev;
步骤11、刻蚀掉剩余光刻胶和SiO2掩蔽层;没有区别这个步骤是重复的,只不过刻蚀部位不同(与步骤7位置左右对应)
步骤12、进行硼离子注入形成阳极区,剂量为2.95×1015cm-2-3.06×1015cm-2,注入能量为30-500Kev;
步骤13、翻转器件;
步骤14、采用干-湿-干氧化法在硅片表面生长一层薄膜SiO2,厚度为2-4μm;
步骤15、涂抹并刻蚀光刻胶,使得与阴极P+柱宽度相等部分SiO2表面裸露出来;
步骤16、刻蚀未被掩蔽的SiO2区域,露出需要进行离子注入的硅片表面区域;
步骤17、进行硼离子注入,剂量为2.95×1015cm-2-3.06×1015cm-2,注入能量为300-500Kev;
步骤18、刻蚀掉剩余光刻胶和SiO2掩蔽层;
步骤19、氧化形成SiO2并涂抹刻蚀光刻胶,采用干-湿-干氧化法在硅片表面生长一层薄膜SiO2,厚度为2-4μm;
步骤20、涂抹并刻蚀光刻胶,使得剩余光刻胶覆盖对应阳极P+柱的上方部位;
步骤21、刻蚀未被光刻胶覆盖的SiO2,露出需要进行离子注入的硅片表面区域;
步骤22、进行磷离子注入,剂量为2.95×1015cm-2-3.06×1015cm-2,注入能量为300-500Kev;
步骤23、刻蚀掉剩余光刻胶和SiO2掩蔽层;
步骤24、蒸铝:双面蒸铝形成阴极和阳极欧姆接触,并做SiO2钝化保护,最终形成具有阴极P+柱结构和超结结构的功率开关二极管。
本发明以N+P+N+阴极结构替换了传统PiN二极管的N+阴极,且用超结结构替代了部分耐压层结构。阴极处的P+柱在耐压层中产生的电场使得存在于耐压层中的载流子在器件的反向恢复过程中很快就会被抽取并复合掉,因此极大的降低了反向恢复峰值电流,减小了反向恢复时间,同时由于超结的引入使得器件的反向阻断特性和正向压降均有较大的改善。
本发明的关键参数是新结构中P+柱的掺杂浓度、柱区厚度和宽度超结部分的宽度厚度及掺杂浓度。众所周知,一个二极管的动态特性和静态特性的好坏很大程度上依赖于耐压层的结构尺寸和工艺参数。而静态特性主要包括正向导通压降、正向导通电阻、反向阻断电压等,动态特性主要包括反向恢复时间、反向恢复电荷量、反向恢复峰值电流等参数。
反向恢复时间指开关电流过零到开关过程结束的时间。由于反向电流逐渐下降,想要准确估算它的值总是很困难的。因此,关断时刻通常定义为穿过Irr和0.25Irr的一条直线与时间轴的交点。
反向恢复电荷Qrr,Qrr可由公式(2-2)求出:
Q rr = Q 1 + Q 2 = ∫ t 0 t 2 i rr dt
其中导通电阻Ron和击穿电压的关系式为:
R on = C p - V B / 2 q μ n E c Q = C p - V B / 2 μ n ϵ s i E ϵ 2
式中,VB表示击穿电压,Cp表示原胞宽度,μn为电子的迁移率,Ec表示临界场强,Q表示电荷量,εSi是硅的电介质常数。
可以看出,正向导通电阻Ron与电荷量Q成反比,所以为了降低导通电阻,必须保持尽量高的电荷。
在工艺制作过程中,离子注入是必不可少的步骤之一。而注入离子的浓度分布从本质上取决于入射离子能量损失机构,与之相关的参数有:入射离子的能量、质量和原子序数;离子注入剂量和速度以及硅片温度等;同时还应当注意晶体的晶向和离子束的入射方向。

Claims (1)

1.一种快速软恢复功率开关二极管的制备方法,基于一种快速软恢复功率开关二极管,其结构是:从上到下依次设置有P+阳极区(1)、超结部分(2)、N-层(3)和N+P+N+阴极区(4);
所述的P+阳极区(1)的掺杂浓度为1×1019cm-3-5×1022cm-3,掺杂剂为硼离子,厚度为3μm-6μm;
所述的超结部分(2)为对半设置的N柱和P柱组成,N柱和P柱沿横向排列,超结部分(2)的N柱和P柱至少设置一对;所述的超结部分(2)的掺杂浓度为8×1014cm-3-6×1015cm-3,厚度为10μm-80μm,P柱和N柱厚度均为10μm-80μm,掺杂剂为磷离子和硼离子;
所述的N-层(3)的掺杂浓度为2×1014cm-3-3×1015cm-3,厚度为10μm-320μm,掺杂剂为磷离子;
所述的N+P+N+阴极区(4)的掺杂浓度为1×1019cm-3-5×1022cm-3,其中N+部分掺杂剂为磷离子,厚度为3μm-6μm,P+部分掺杂剂为硼离子,P+柱高度为3μm-10μm;器件总宽度为20-200μm,
依赖于上述的快速软恢复功率开关二极管,其特征在于,该方法按照如下步骤实施:
步骤1、选取掺杂浓度均为2×1014cm-3-3×1015cm-3数量级的轻掺杂衬底晶片,厚度为20μm-400μm;
步骤2、采用外延方法,使用氢气作为还原剂,在1100℃-1300℃高温下四氯化硅被氢还原析出硅,外延时间为20-120min,形成厚度为10μm-200μm的本征硅片;
步骤3、采用干-湿-干氧化法在本征硅片表面生长一层SiO2薄膜,厚度为2-4μm;
步骤4、涂抹并刻蚀光刻胶,使得右半部分SiO2表面裸露出来;
步骤5、刻蚀SiO2露出需要进行离子注入的右半边硅片表面区域;
步骤6、进行硼离子注入,剂量为2.95×1011cm-2-3.06×1012cm-2,注入能量为30-500Kev;
步骤7、刻蚀掉剩余光刻胶和SiO2掩蔽层;
步骤8、采用干-湿-干氧化法在硅片表面生长一层薄膜SiO2,厚度为2-4μm,并涂抹刻蚀光刻胶;
步骤9、刻蚀SiO2露出需要进行离子注入的左半边硅片表面区域;
步骤10、进行磷离子注入,剂量为2.95×1011cm-2-3.06×1012cm-2,注入能量为30-500Kev;
步骤11、刻蚀掉剩余光刻胶和SiO2掩蔽层;
步骤12、进行硼离子注入形成阳极区,硼离子注入的剂量为2.95×1015cm-2-3.06×1015cm-2,注入能量为30-500Kev;
步骤13、翻转器件;
步骤14、采用干-湿-干氧化法在硅片表面生长一层薄膜SiO2,厚度为2-4μm;
步骤15、涂抹并刻蚀光刻胶,使得与阴极P+柱宽度相等部分SiO2表面裸露出来;
步骤16、刻蚀未被掩蔽的SiO2区域,露出需要进行离子注入的硅片表面区域;
步骤17、进行硼离子注入,剂量为2.95×1015cm-2-3.06×1015cm-2,注入能量为300-500Kev;
步骤18、刻蚀掉剩余光刻胶和SiO2掩蔽层;
步骤19、氧化形成SiO2并涂抹刻蚀光刻胶,采用干-湿-干氧化法在硅片表面生长一层薄膜SiO2,厚度为2-4μm;
步骤20、涂抹并刻蚀光刻胶,使得剩余光刻胶覆盖对应阳极P+柱的上方部位;
步骤21、刻蚀未被光刻胶覆盖的SiO2,露出需要进行离子注入的硅片表面区域;
步骤22、进行磷离子注入,剂量为2.95×1015cm-2-3.06×1015cm-2,注入能量为300-500Kev;
步骤23、刻蚀掉剩余光刻胶和SiO2掩蔽层;
步骤24、蒸铝:双面蒸铝形成阴极和阳极欧姆接触,并做SiO2钝化保护,最终形成具有阴极P+柱结构和超结结构的功率开关二极管。
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