CN112635544A - 具有偶极子层的增强型AlGaN-GaN垂直型超结HEMT及其制备方法 - Google Patents

具有偶极子层的增强型AlGaN-GaN垂直型超结HEMT及其制备方法 Download PDF

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CN112635544A
CN112635544A CN202011502471.4A CN202011502471A CN112635544A CN 112635544 A CN112635544 A CN 112635544A CN 202011502471 A CN202011502471 A CN 202011502471A CN 112635544 A CN112635544 A CN 112635544A
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郭志友
马建铖
李渊
谭秀洋
夏晓宇
夏凡
张淼
孙慧卿
黄志辉
王鹏霖
丁霄
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Abstract

本发明涉及具有偶极子层的增强型AlGaN/GaN垂直型超结HEMT及其制备方法,该器件中通过在AlGaN势垒层上设置无意掺杂的AlGaN形成偶极子层,且该偶极子层位于栅电极和漏电极之间的钝化层中,偶极子层沿着与AlGaN势垒层的界面形成负电荷。因此通过部分耗尽通道层中的2DEG,偶极子层可以调制沿通道的电场分布,从而大大提高了击穿电压。另一方面,该器件中通过对超结进行梯度掺杂更有效的实现了调制电场,相对于传统的超结结构,这种渐变梯度的掺杂超结能在不牺牲击穿电压的情况下降低导通电阻。本发明的制备方法降低了工业难度,减少了器件制造工艺过程中的损伤,能够提高器件的可靠性,满足实际应用的要求。

Description

具有偶极子层的增强型AlGaN-GaN垂直型超结HEMT及其制备 方法
技术领域
本发明涉及微电子技术领域,具体涉及具有偶极子层的增强型AlGaN-GaN垂直型超结HEMT及其制备方法。
背景技术
氮化镓作为第三代宽禁带半导体的代表,具有宽禁带,高饱和电子速度和高击穿电场的特性,其器件功率密度是硅、砷化镓功率密度的10倍以上,已被广泛用于射频设备和高功率开关设备中。
垂直型氮化镓基HEMT器件中P埋层和超结等结构的引入,提高了垂直器件电学性能。然而,现有技术中器件击穿电压和导通电阻之间的矛盾较难解决,因此如何进一步提升功率器件性能,是当前学者关注的焦点。
发明内容
针对现有技术中存在的技术问题,本发明的首要目的是提供具有偶极子层的增强型AlGaN-GaN垂直型超结HEMT及其制备方法,其在提高击穿电压的同时保持较低的导通电阻和频率特性,并提高饱和电流以及更有效的高温传导,器件可靠性高。且本发明通过对制备方法的优化,降低了工业难度,减少了器件制造工艺过程中的损伤,能够提高器件的可靠性,满足实际应用的要求。
该HEMT器件中在AlGaN势垒层上设置无意掺杂的AlGaN形成偶极子层,并且该偶极子层位于栅电极和漏电极之间的钝化层中,偶极子层沿着与AlGaN势垒层的界面形成负电荷。因此,通过部分耗尽通道层中的2DEG,偶极子层可以调制沿通道的电场分布,从而大大提高了击穿电压。另一方面,该器件中通过对超结进行梯度掺杂更有效的实现了调制电场,相对于传统的超结结构,这种渐变梯度的掺杂超结能在不牺牲击穿电压的情况下降低导通电阻。
为了达到上述目的,本发明至少提供如下技术方案:
1、具有偶极子层的增强型AlGaN/GaN垂直型超结HEMT,其特征在于,包括第一导电类型的GaN基底,其包括第一表面及与该第一表面相对的第二表面;
设置于该第一表面的超结结构,其中超结结构包括在平行于该第一表面的第一方向中依次交替排列设置的第二导电类型的GaN梯度柱和第一导电类型的GaN梯度柱;以及
第二导电类型的GaN电流阻挡层,设置于第二导电类型的GaN柱表面;
第二导电类型的源极区域,设置于部分第二导电类型的GaN电流阻挡层表面;
第一导电类型的GaN沟道层,设置于部分所述GaN电流阻挡层和所述第一导电类型的GaN柱的表面,位于所述源极区域之间;
第一导电类型的AlGaN势垒层,设置于所述GaN沟道层表面;
第一、第二钝化层和第二导电类型的GaN帽层,设置于所述AlGaN势垒层表面,其中所述第一、第二钝化层分别隔离所述源极区域和所述GaN帽层,第一、第二钝化层中设置有AlGaN偶极子层,所述AlGaN偶极子层与所述AlGaN势垒层接触;
栅电极设置于所述GaN帽层的表面,其两侧端面分别与所述第一、第二钝化层接触;
漏极,设置于所述GaN基底的第二表面。
进一步地,所述AlGaN偶极子层中的Al组分小于所述AlGaN势垒层中的Al组分。
进一步地,所述AlGaN偶极子层的厚度小于所述钝化层的厚度。
进一步地,所述第一导电类型的GaN梯度柱和所述第二导电类型的GaN梯度柱构成至少四层不同掺杂浓度的PN结。
进一步地,所述第二导电类型的GaN梯度柱的掺杂浓度沿远离所述GaN基底的方向依次减小,所述第一导电类型的GaN梯度柱的掺杂浓度沿远离所述GaN基底的方向依次增大。
进一步地,所述AlGaN偶极子层中的Al组分优选0.1。
进一步地,所述第一导电类型为N型,所述第二导电类型为P型。
进一步地,所述钝化层优选氮化硅。
本发明还提供具有偶极子层的增强型AlGaN/GaN垂直型超结HEMT的制备方法,包括以下步骤:
在第一导电类型的GaN基底表面外延生长第二导电类型的GaN柱,刻蚀该第二导电类型GaN柱形成沟槽,在该沟槽之外的第二导电类型GaN柱表面沉积第一掩膜层,外延生长第一导电类型的GaN柱填充该沟槽,去除该第一掩膜层,形成第二导电类型的GaN柱、第一导电类型的GaN柱和第二导电类型的GaN柱的PN结结构;
重复上述步骤至少三次,其中调整所述GaN柱的掺杂浓度,形成至少四层不同掺杂浓度的PN结;
在所述第二导电类型的GaN柱表面外延生长第二导电类型的GaN电流阻挡层,刻蚀所述GaN电流阻挡层暴露所述第一导电类型的GaN柱的表面;
在所述GaN电流阻挡层表面沉积第二掩膜层,在所述第一导电类型的GaN柱的表面外延生长第一导电类型的GaN层,与所述GaN电流阻挡层平齐;
去除所述第二掩膜层,在所述GaN电流阻挡层表面形成源极窗口,沉积源极金属层,形成源极;
在所述源极表面沉积第三掩膜层暴露所述第一导电类型的GaN层和部分所述GaN电流阻挡层;
在所述第一导电类型的GaN层和所述部分GaN电流阻挡层表面依次外延生长第一导电类型的GaN层、第一导电类型的AlGaN势垒层和第二导电类型的GaN帽层;
刻蚀所述GaN帽层,在所述源极和预定栅极区域的端面之间形成凹槽暴露所述AlGaN势垒层的表面;
在所述凹槽内的边缘区域以及凹槽外的源极和GaN帽层区域沉积第四掩膜层,暴露该凹槽的中心区域;
在该凹槽的中心区域外延生长AlGaN偶极子层;
去除所述凹槽外的第四掩膜层,在所述源极区域沉积第五掩膜层;
沉积钝化层,包裹所述AlGaN偶极子层,之后刻蚀GaN帽层区域的钝化层至GaN帽层表面露出;
在GaN帽层表面沉积栅极金属层,在所述GaN基底的背面制备漏极。
附图说明
图1是本发明一实施例的具有偶极子层的增强型AlGaN/GaN垂直型超结HEMT器件结构剖面示意图。
具体实施方式
接下来将结合本发明的附图对本发明实施例中的技术方案进行清楚、完整地描述,所描述的实施例仅仅是本发明一部分实施例,而不是全部的实施例。基于本发明中的实施例,本领域普通技术人员在没有做出创造性劳动的前提下所获得的其它实施例,均属于本发明保护的范围。
下面来对本发明做进一步详细的说明。参照图1,本发明的一实施例提供一种具有偶极子层的增强型AlGaN/GaN垂直型超结HEMT器件,属于垂直型结构,如图1,该器件整体左右对称。
该器件包括第一导电类型的GaN基底2,具有第一表面和与该第一表面相对的第二表面。该实施例中,第一导电类型为N型,第二导电类型为P型。超结结构设置于GaN基底的第一表面,其中超结结构包括在平行于该第一表面的第一方向中依次交替排列设置的第二导电类型的GaN梯度柱和第一导电类型的GaN梯度柱。第一导电类型的GaN梯度柱和第二导电类型的GaN梯度柱的厚度分别为8μm~12μm,分别由至少4层的GaN柱组成。该实施例中,如图1,第二导电类型的GaN梯度柱的掺杂浓度由P型GaN柱31至34逐渐减小,及P型GaN柱35至38逐渐减小。第一导电类型的GaN梯度柱的掺杂浓度由N型GaN柱41至44逐渐增大。其中同一层的P型GaN柱的掺杂浓度相同,如P型GaN柱31的掺杂浓度等于P型GaN柱35的掺杂浓度。
第二导电类型的GaN电流阻挡层51和52分别设置于第二导电类型的GaN柱34和38的表面。GaN电流阻挡层厚度为0.8μm~1.2μm。
第二导电类型的源极区域71和72分别设置于第二导电类型的GaN电流阻挡层51和52的表面,与部分GaN电流阻挡层的表面接触。第一导电类型的GaN沟道层6的截面呈T型,由上下两部分构成,上部分GaN沟道层设置于部分GaN电流阻挡层的表面,位于源极区域71和72之间,其厚度为80nm~120nm。下部分GaN沟道层设置于第一导电类型的GaN柱的表面,位于电流阻挡层51和52之间,其厚度与电流阻挡层相同。
第一导电类型的AlGaN势垒层8设置于GaN沟道层6的表面,位于源极区域71和72之间,其厚度为20nm~30nm,其中Al组分为10%~15%。
第一钝化层101、第二导电类型的GaN帽层9和第二钝化层102依次排列设置于AlGaN势垒层表面。GaN帽层9的厚度为180nm~250nm。第一钝化层101隔离源极区域71和GaN帽层9,第二钝化层102隔离源极区域72和GaN帽层9。
第一钝化层101和第二钝化层102优选SiN。其中,第一钝化层101中设置有AlGaN偶极子层121,AlGaN偶极子层121与AlGaN势垒层8接触。第二钝化层102中设置有AlGaN偶极子层122,AlGaN偶极子层122与AlGaN势垒层8接触。AlGaN偶极子层121和122中的Al组分小于AlGaN势垒层中的Al组分,此时,偶极子层与势垒层界面处产生负电荷,通过部分耗尽通道层中的2DEG,偶极子层可以调制沿通道的电场分布,从而大大提高了击穿电压。在一优选实施例中,AlGaN偶极子层的Al组分为0.1,AlGaN势垒层中的Al组分为0.15,其形状为矩形。在其它实施例中,偶极子层的个数、宽度与厚度可根据具体器件的要求进行参数调整,其形状并不局限于矩形。
栅电极11设置于GaN帽层9的表面,其两侧端面分别与第一、第二钝化层接触。漏极1设置于GaN基底2的第二表面。
基于该器件结构,接下来提供该垂直型超结HEMT器件的制备方法,包括以下步骤:
步骤1,选用金属有机物化学气相沉积(MOCVD)工艺,设定生长温度为920℃,压强为40Torr,氢气流量为5000sccm,氨气流量为5000sccm,镓源流量为220sccm,在N型GaN衬底上淀积厚度为2μm的P型GaN柱。
步骤2,接着,使用氯基电感耦合等离子体(ICP)刻蚀工艺刻蚀上述P型GaN柱,上刻蚀出宽度为16μm,厚度为2μm的沟槽。ICP系统的线圈功率和压板功率分别设置为50W和15W。
步骤3,在上述沟槽两侧沉积掩膜层遮盖沟槽两侧的P型GaN柱,掩膜层例如选用二氧化硅,使用基于GaN的选择性区域生长技术(SAG),调整掺杂类型,设定生长温度为920℃,压强为40Torr,氢气流量为5000sccm,氨气流量为5000sccm,镓源流量为220sccm,在该沟槽内外延生长一个厚度为2μm的N型GaN柱,以填充沟槽。之后去除二氧化硅掩膜层。
步骤4,步骤1至3重复3次,累计生长4层PN结,且P型GaN柱中浓度自上向下依次增加构成P型GaN梯度柱,N型GaN柱中浓度自上向下依次减少构成N型GaN梯度柱。P型GaN梯度柱与N型GaN梯度柱沿平行于GaN基底表面的方向形成交替排列单元。
步骤5,继续使用MOCVD工艺,调整掺杂类型,设定生长温度为920℃,压强为40Torr,氢气流量为5000sccm,氨气流量为5000sccm,镓源流量为220sccm,在P型GaN柱上淀积厚度为1μm的P型GaN电流阻挡层(CBL)。并选用ICP刻蚀工艺刻蚀N型GaN柱区域的电流阻挡层,形成16μm宽度和1μm厚度的沟槽。
步骤6,在上述沟槽两侧沉积掩膜层,掩膜层例如选用二氧化硅。掩膜层遮盖沟槽两侧的GaN电流阻挡层。继续使用MOCVD工艺,调整掺杂类型,生长工艺参数保持不变,在沟槽中外延生长约1μm厚度的N型GaN。之后去除二氧化硅掩膜层。
步骤7,通过旋涂光刻胶、软烘、曝光以及显影工艺,在电流阻挡层的部分表面形成源极窗口区域,接着选用电子束蒸发法,设定真空度小于1.8×10-3Pa,功率范围为200~1000W,蒸发速率为
Figure BDA0002844002370000071
淀积Ti/Al/Ni/Au欧姆接触复合金属层,使得源极在器件的两端,优选地,每层金属的厚度分别为0.05μm/0.15μm/0.75μm/0.75μm。
将蒸发完欧姆接触复合金属的外延片在丙酮溶液中浸泡20min,然后进行超声清洗,再用超纯水冲洗和氮气吹干,实现金属剥离。随后,在氮气气氛中,加热温度为850℃下进行30s的欧姆接触退火,形成源极。
步骤8,在源极区域的表面沉积掩膜层,掩膜层例如选用二氧化硅。继续使用MOCVD外延工艺,调整掺杂类型,设定生长温度为920℃,压强为40Torr,氢气流量为5000sccm,氨气流量为5000sccm,镓源流量为220sccm,外延生长100nm厚度的N型GaN沟道层。
接着设定生长温度为1070℃,压强为40Torr,氨气流量为1500sccm,镓源流量为90sccm,铝源流量为8sccm,氢气流量为2500sccm,在N型GaN沟道层上生长厚度为25nm的N型Al0.15Ga0.85N势垒层。继续调整生长温度为920℃,压强为40Torr,氢气流量为5000sccm,氨气流量为5000sccm,镓源流量为220sccm,在N型Al0.15Ga0.85N层上生长厚度为200nm的P型GaN帽层。
步骤9,刻蚀P型GaN帽层,在源极和预定栅极区域的端面之间形成宽度为2μm和厚度为200nm的凹槽,该凹槽暴露N型Al0.15Ga0.85N势垒层的表面。
步骤10,在凹槽内靠近该凹槽边缘的区域以及该凹槽外的GaN帽层和源极区域沉积掩膜层,例如是氮化硅。暴露该凹槽的中心区域。该实施例中,暴露的该中心区域为矩形。
接着在该凹槽的中心区域外延生长厚度为20nm的Al0.10Ga0.90N层偶极子层,生长工艺条件为:生长温度1070℃,压强为40Torr,氨气流量为1500sccm,镓源流量为90sccm,铝源流量为8sccm,氢气流量为2500sccm。在偶极子层AlGaN生长过程中,偶极子层的个数,宽度与厚度可根据具体器件的要求进行参数调整,且形状并不局限于矩形。继续去除该凹槽之外的氮化硅掩膜层。
步骤11,在源极区域沉积掩膜层,例如选用二氧化硅。在300℃下通过等离子体增强化学气相沉积法(PECVD)沉积225nm的SiN作为钝化层。接着选用高温ICP蚀刻掩模,将P型GaN表面的钝化层刻蚀掉。
步骤12,通过旋涂光刻胶、软烘、曝光以及显影,形成栅极窗口,随后利用电子束蒸发法淀积Ti/Al/Ni/Au复合欧姆接触金属层,设定真空度小于1.8×10-3Pa,功率范围为200~1000W,蒸发速率为
Figure BDA0002844002370000091
金属层的淀积厚度Ti/Al/Ni/Au分别为0.003μm/0.01μm/0.005μm/0.005μm。
将蒸发完欧姆接触金属的外延片在丙酮溶液中浸泡20min,然后进行超声清洗,再用超纯水冲洗和氮气吹干,最终获得栅极。
步骤13,倒转此外延片,在衬底的背面光刻出漏区域,刻蚀出漏窗口,随后利用电子束蒸发法淀积Ti/Al/Ni/Au复合金属层,金属层的厚度依次为0.03μm/0.1μm/0.05μm/0.05μm,并通过剥离、退火后形成漏极。
最后对已经成源、漏、栅极的外延片表面进行光刻,获得加厚电极图形,并采用电子束蒸发对电极进行加厚,完成如图1所示的器件制造。
上述实施例为本发明较佳的实施方式,但本发明的实施方式并不受上述实施例的限制,其他的任何未背离本发明的精神实质与原理下所作的改变、修饰、替代、组合、简化,均应为等效的置换方式,都包含在本发明的保护范围之内。

Claims (10)

1.具有偶极子层的增强型AlGaN/GaN垂直型超结HEMT,其特征在于,包括第一导电类型的GaN基底,其包括第一表面及与该第一表面相对的第二表面;
设置于该第一表面的超结结构,其中超结结构包括在平行于该第一表面的第一方向中依次交替排列设置的第二导电类型的GaN梯度柱和第一导电类型的GaN梯度柱;以及
第二导电类型的GaN电流阻挡层,设置于第二导电类型的GaN柱表面;
第二导电类型的源极区域,设置于部分第二导电类型的GaN电流阻挡层表面;
第一导电类型的GaN沟道层,设置于部分所述GaN电流阻挡层和所述第一导电类型的GaN柱的表面,位于所述源极区域之间;
第一导电类型的AlGaN势垒层,设置于所述GaN沟道层表面;
第一、第二钝化层和第二导电类型的GaN帽层,设置于所述AlGaN势垒层表面,其中所述第一、第二钝化层分别隔离所述源极区域和所述GaN帽层,第一、第二钝化层中设置有AlGaN偶极子层,所述AlGaN偶极子层与所述AlGaN势垒层接触;
栅电极设置于所述GaN帽层的表面,其两侧端面分别与所述第一、第二钝化层接触;
漏极,设置于所述GaN基底的第二表面。
2.根据权利要求1的所述垂直超结HEMT,其特征在于,所述AlGaN偶极子层中的Al组分小于所述AlGaN势垒层中的Al组分。
3.根据权利要求1或2的所述垂直超结HEMT,其特征在于,所述AlGaN偶极子层的厚度小于所述钝化层的厚度。
4.根据权利要求1或2的所述垂直超结HEMT,其特征在于,所述第一导电类型的GaN梯度柱和所述第二导电类型的GaN梯度柱构成至少四层不同掺杂浓度的PN结。
5.根据权利要求4的所述垂直超结HEMT,其特征在于,所述第二导电类型的GaN梯度柱的掺杂浓度沿远离所述GaN基底的方向依次减小,所述第一导电类型的GaN梯度柱的掺杂浓度沿远离所述GaN基底的方向依次增大。
6.根据权利要求2的所述垂直超结HEMT,其特征在于,所述AlGaN偶极子层中的Al组分优选0.1。
7.根据权利要求1、2、5或6的所述垂直超结HEMT,其特征在于,所述第一导电类型为N型,所述第二导电类型为P型。
8.根据权利要求7的所述垂直超结HEMT,其特征在于,所述钝化层优选氮化硅。
9.具有偶极子层的增强型AlGaN/GaN垂直型超结HEMT的制备方法,其特征在于,包括以下步骤:
在第一导电类型的GaN基底表面外延生长第二导电类型的GaN柱,刻蚀该第二导电类型GaN柱形成沟槽,在该沟槽之外的第二导电类型GaN柱表面沉积第一掩膜层,外延生长第一导电类型的GaN柱填充该沟槽,去除该第一掩膜层,形成第二导电类型的GaN柱、第一导电类型的GaN柱和第二导电类型的GaN柱的PN结结构;
重复上述步骤至少三次,其中调整所述GaN柱的掺杂浓度,形成至少四层不同掺杂浓度的PN结;
在所述第二导电类型的GaN柱表面外延生长第二导电类型的GaN电流阻挡层,刻蚀所述GaN电流阻挡层暴露所述第一导电类型的GaN柱的表面;
在所述GaN电流阻挡层表面沉积第二掩膜层,在所述第一导电类型的GaN柱的表面外延生长第一导电类型的GaN层,与所述GaN电流阻挡层平齐;
去除所述第二掩膜层,在所述GaN电流阻挡层表面形成源极窗口,沉积源极金属层,形成源极;
在所述源极表面沉积第三掩膜层暴露所述第一导电类型的GaN层和部分所述GaN电流阻挡层;
在所述第一导电类型的GaN层和所述部分GaN电流阻挡层表面依次外延生长第一导电类型的GaN层、第一导电类型的AlGaN势垒层和第二导电类型的GaN帽层;
刻蚀所述GaN帽层,在所述源极和预定栅极区域的端面之间形成凹槽暴露所述AlGaN势垒层的表面;
在所述凹槽内的边缘区域以及凹槽外的源极和GaN帽层区域沉积第四掩膜层,暴露该凹槽的中心区域;
在该凹槽的中心区域外延生长AlGaN偶极子层;
去除所述凹槽外的第四掩膜层,在所述源极区域沉积第五掩膜层;
沉积钝化层,包裹所述AlGaN偶极子层,之后刻蚀GaN帽层区域的钝化层至GaN帽层表面露出;
在GaN帽层表面沉积栅极金属层,在所述GaN基底的背面制备漏极。
10.根据权利要求9的所述制备方法,其特征在于,所述AlGaN偶极子层的Al组分小于所述AlGaN势垒层。
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