CN112614887B - 增强型AlGaN-GaN垂直超结HEMT及其制备方法 - Google Patents
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Abstract
本发明涉及增强型AlGaN/GaN垂直超结HEMT及其制备方法，包括沿GaN基底表面边缘设置的P型GaN柱，设置于GaN基底表面中间区域的N型GaN梯度柱，其掺杂浓度自远离GaN基底的方向依次递减，设置于所述P型GaN柱表面的P型GaN电流阻挡层，依次设置于所述P型GaN电流阻挡层和所述N型GaN梯度柱表面的N型沟道层和N型势垒层，间隔分布的钝化层和P型GaN帽层，以及截面呈π型的栅极；其有效调解了导通电阻和击穿电压不可兼顾的限制，并提高了饱和电流，以及更有效的高温传导。该制备方法中的工艺步骤使用的均是目前比较成熟的技术，能够减少器件制造工艺过程中的损伤，提高器件的可靠性。
Description
技术领域
本发明涉及微电子技术领域，具体涉及增强型AlGaN-GaN垂直超结HEMT及其制备方法。
背景技术
GaN具有禁带宽度大、热导率高、耐高温、抗辐射、耐酸碱、高强度和高硬度等优异的性能特点，在高亮度蓝、绿、紫和白光二极管，蓝、紫色激光器以及抗辐射、高温大功率微波器件等领域有着广泛的应用潜力和良好的市场前景。
近年来，垂直型GaN基HEMT器件以其优异的性能，在大功率电力电子领域备受关注，研究改善垂直器件的击穿和导通特性之间的矛盾已成为该领域一大热点。如何更好地解决该问题，进一步提升功率器件性能，是本发明要解决的问题之一。
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一种增强型AlGaN-GaN垂直超结HEMT及其制备方法，其提高了器件的性能，尤其是有效调解了导通电阻和击穿电压改善其一必将恶化另一的矛盾限制，并提高了饱和电流，以及更有效的高温传导。该制备方法中的工艺步骤使用的均是目前比较成熟的技术，能够减少器件制造工艺过程中的损伤，提高器件的可靠性，满足实际应用的要求。
另一方面，该垂直超结HEMT器件中选用对超结进行梯度掺杂的调制电场方式，实现了在不牺牲击穿电压的情况下降低导通电阻，同时采用特殊形状的P型栅极缩小了被截断的2DEG长度，在不影响击穿电压的情况下减少导通电阻并实现了饱和区电流的提高。另外本发明的制备方法采用选择性区域生长工艺(SAG)和GaN的刻蚀工艺相结合，改善了P/N型GaN柱的外延生长，提高了器件的生长质量，保障了器件具有低的导通电阻和高饱和区电流。
基于此，本发明至少提供如下技术方案：
增强型AlGaN/GaN垂直超结HEMT，包括：N型GaN基底，包含第一表面及与该第一表面相对的第二表面；第一、第二P型GaN柱，设置于所述GaN基底第一表面；
N型GaN梯度柱，邻接设置于所述第一、第二P型GaN柱之间，其掺杂浓度自远离所述GaN基底的方向依次递减，其厚度与所述P型GaN柱相等；
第一、第二P型GaN电流阻挡层，分别设置于所述P型GaN柱的表面；
第一、第二源极，分别设置于所述P型GaN电流阻挡层的部分表面；
N型GaN沟道层，设置于所述P型GaN电流阻挡层和所述N型GaN梯度柱的表面；
N型AlGaN势垒层，设置于所述GaN沟道层的表面；
钝化层和P型GaN帽层，自所述钝化层开始，所述钝化层与所述GaN帽层沿所述P型GaN柱指向所述N型GaN梯度柱的方向上交替分布于所述AlGaN势垒层的表面，所述钝化层的一侧端面与所述源极邻接；
栅极，自所述GaN帽层开始，设置于所述GaN帽层和所述钝化层的表面，其中所述栅极下方的GaN帽层的厚度大于其下方所述钝化层的厚度；
漏极，设置于所述GaN基底第二表面。
进一步地，所述栅极的截面呈“π”型。
进一步地，所述N型GaN梯度柱包含奇数个掺杂浓度沿远离所述GaN基底的方向依次递减的N型GaN柱。
进一步地，所述N型GaN梯度柱包含5个掺杂浓度沿远离所述GaN基底的方向依次递减的N型GaN柱。
进一步地，所述N型GaN梯度柱中，第三个所述N型GaN柱的掺杂浓度与所述P型GaN柱相同。
进一步地，所述P型GaN电流阻挡层的厚度为0.8μm～1.2μm。
进一步地，所述N型GaN沟道层呈T型，其中，位于所述GaN电流阻挡层之间的沟道层厚度为0.8μm～1.2μm，位于所述源极之间的沟道层厚度为80nm～120nm；所述N型AlGaN势垒层的厚度为20nm～30nm，其Al组分为10％～15％。
本发明还提供增强型AlGaN/GaN垂直超结HEMT的制备方法，包括以下步骤：
在N型GaN基底上外延生长厚度为8μm～12μm的P型GaN柱；
刻蚀所述P型GaN柱的中间区域，形成15μm～17μm宽度和8μm～12μm厚度的沟槽；
在所述P型GaN柱的表面沉积第一掩膜层，选用选择性区域外延生长工艺在所述沟槽内生长N型GaN梯度柱至所述沟槽填满；
去除所述第一掩膜层，在所述P型GaN柱和所述GaN梯度柱表面外延生长P型GaN电流阻挡层；
刻蚀所述P型GaN电流阻挡层暴露所述GaN梯度柱表面；
在所述P型GaN电流阻挡层表面沉积第二掩膜层，在所述GaN梯度柱表面外延生长厚度等于所述P型GaN电流阻挡层的N型GaN层；
在所述P型GaN电流阻挡层的部分表面形成源极窗口层，沉积欧姆接触金属，剥离退火后形成源极；
在所述源极上沉积第三掩膜层，在所述源极之间外延生长N型GaN沟道层、N型AlGaN势垒层以及P型GaN帽层；
刻蚀所述P型GaN帽层，在所述源极与预定区域的栅极之间形成暴露所述N型AlGaN势垒层的第一凹槽，在栅极预定区域的中部两边各形成一个暴露所述N型AlGaN势垒层的第二凹槽；
沉积钝化层以填充所述第一凹槽和所述第二凹槽；
刻蚀栅极预定区域的钝化层，暴露所述P型GaN帽层，并确保所述第二凹槽区域的钝化层厚度小于所述P型GaN帽层的厚度；
在栅极预定区域沉积欧姆接触金属形成栅极；
在所述N型GaN基底的背面光刻形成漏极区域，在该漏极区域沉积欧姆接触的金属形成漏极。
进一步地，所述N型GaN梯度柱包含五个掺杂浓度不同的N型GaN柱，所述掺杂浓度沿远离所述基底的方向依次减小。
进一步地，所述N型GaN梯度柱中，第三个N型GaN柱的掺杂浓度等于所述P型GaN柱。
附图说明
图1是本发明一实施例的增强型AlGaN-GaN垂直超结HEMT器件的剖面结构示意图。
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。本发明的一实施例提供一种增强型lGaN-GaN垂直超结HEMT器件，属于垂直型结构，参照图1，该器件整体左右对称。
该器件包括N型GaN基底2，GaN基底2的一表面设置有漏极1，与该表面相对的表面设置有第一P型GaN柱31和第二P型GaN柱32，P型GaN柱31和32的厚度为8μm～12μm。N型GaN梯度柱邻接设置于第一P型GaN柱31和第二P型GaN柱32之间，其掺杂浓度自远离GaN基底的方向依次递减。在一具体实施例中，N型GaN梯度柱包含5个N型GaN柱41～45，其掺杂浓度沿远离GaN基底2的方向依次递减，即其掺杂浓度从N型GaN柱41至N型GaN柱45依次递减，其中第三个N型GaN柱43的掺杂浓度等于P型GaN柱3。此处对超结进行梯度掺杂是更为有效的调制电场方式，相对于传统的超结结构，梯度掺杂的超结可以在不牺牲击穿电压的情况下降低导通电阻。
P型GaN电流阻挡层51和52分别设置于P型GaN柱31和32的表面，厚度为0.8μm～1.2μm。源极71和72分别设置于P型GaN电流阻挡层51和52的部分表面，在一具体实施例中，源极优选Ti/Al/Ni/Au复合金属层，其厚度分别为0.05μm/0.15μm/0.75μm/0.75μm。
N型GaN沟道层6设置于P型GaN电流阻挡层51、52和N型GaN梯度柱4的表面。如图1，N型GaN沟道层6的截面呈T型，具体的，其由位于P型GaN电流阻挡层51和52之间的厚度为0.8μm～1.2μm的N型GaN层和位于源极71和72之间的厚度为80nm～120nm的N型GaN层叠而成，位于源极之间的N型GaN的两侧端与源极7邻接。
N型AlGaN势垒层8设置于GaN沟道层6的表面，其两侧端与源极7邻接，其厚度为20nm～30nm。其中，Al组分为10％～15％。
参照图1，该器件的剖面图中，钝化层101～104和P型GaN帽层91～93交替设置于N型AlGaN势垒层8的表面，其中P型GaN帽层91～93和钝化层102～103的表面设置有栅极11。钝化层101隔离源极71和栅极11，钝化层104隔离源极72和栅极11。其中钝化层101和104的宽度为1.5μm～2.5μm。
P型GaN帽层91和93的宽度为1μm～5μm，厚度为200nm～300nm。P型GaN帽层92的宽度为和2μm～10μm，厚度为200nm～300nm。
栅极下方的GaN帽层91～93的厚度大于其下方钝化层102～103的厚度。P型GaN帽层91～93之间的钝化层102和103的宽度为1μm～5μm，其厚度为180nm～250nm。栅极11的截面呈“π”型。特殊形状的P型栅极缩小了被截断的2DEG长度，在不影响击穿电压的情况下减少导通电阻并提高饱和区电流。
基于该垂直超结HEMT器件，接下来详细介绍该器件的制备方法，包括如下的步骤：
选用N型GaN基底，在该基底上使用金属有机物化学气相沉积(MOCVD)工艺淀积厚度为8μm～12μm的P型GaN柱。优选地，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基底上生长厚度为10μm的P型GaN柱。
刻蚀P型GaN柱，形成15μm～17μm宽度和8μm～12μm厚度的沟槽。在一优选实施例中，选用氯基电感耦合等离子体(ICP)刻蚀工艺在P型GaN基底上刻蚀出宽度为16μm，厚度为10μm的沟槽。ICP系统的线圈功率和压板功率分别设置为50W和15W。
在P型GaN柱的表面沉积第一掩膜层，第一掩膜层例如选用二氧化硅。选用选择性区域外延生长工艺，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，在上一步形成的沟槽内生长五个掺杂浓度依次递减的N型GaN柱至沟槽填满，每个N型GaN柱的厚度为2μm。其中第三个N型GaN梯度柱的掺杂浓度等于P型GaN柱。
去除第一掩膜层，在P型GaN柱和N型GaN梯度柱表面外延生长P型GaN电流阻挡层。P型GaN电流阻挡层的厚度为0.8μm～1.2μm。优选地，P型GaN电流阻挡层的厚度为1μm。
选用ICP刻蚀工艺刻蚀N型GaN梯度柱区域的P型GaN电流阻挡层，至GaN梯度柱表面暴露，以在P型GaN电流阻挡层上形成16μm宽度和1μm厚度的沟槽。在一优选实施例中，ICP系统的线圈功率和压板功率分别设置为50W和15W。
在P型GaN电流阻挡层表面沉积第二掩膜层，第二掩膜层例如选用二氧化硅。在GaN梯度柱表面选用MOCVD工艺外延生长厚度等于P型GaN电流阻挡层的N型GaN层。该实施例中，N型GaN层的厚度为1μm。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。
接着，通过甩光刻胶、软烘、曝光以及显影，在P型GaN电流阻挡层的部分表面形成源极窗口，随后选用电子束蒸发工艺，设定真空度小于1.8×10-3Pa，功率范围为200～1000W，蒸发速率为
淀积Ti/Al/Ni/Au金属组合，使源极在器件两端，其金属层的厚度分别为0.05μm/0.15μm/0.75μm/0.75μm。
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，以实现金属剥离。随后，在氮气气氛中且温度为850℃下进行30s的欧姆接触退火，形成源极。
在上述源极上沉积第三掩膜层，第三掩膜层例如选用二氧化硅，选用MOCVD工艺，在源极之间依次外延生长N型GaN沟道层、N型AlGaN势垒层以及P型GaN帽层。该实施例中，GaN的生长工艺条件为：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。AlGaN的生长时工艺条件为，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。
选用ICP刻蚀工艺刻蚀P型GaN帽层，在源极与预定区域的栅极之间形成暴露N型AlGaN势垒层的第一凹槽，在栅极预定区域的中部两边各形成一个暴露N型AlGaN势垒层的第二凹槽。在一优选实施例中，第一凹槽的宽度为2μm，厚度为200nm。第二凹槽的宽度为2μm，厚度为200nm。
接着选用等离子体增强化学气相沉积(PECVD)工艺沉积钝化层，具体地，在300℃下沉积的SiN作为钝化层填充第一凹槽和第二凹槽。
随后选用高温ICP蚀刻钝化层，暴露P型GaN帽层，并确保第二凹槽区域的钝化层厚度小于P型GaN帽层的厚度。
接着，通过甩光刻胶、软烘、曝光以及显影，在预定区域形成栅极窗口，随后选用电子束蒸发工艺淀积Ti/Al/Ni/Au金属组合，设定真空度小于1.8×10-3Pa，功率范围为200～1000W，蒸发速率为
其金属层厚度分别为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。
接着倒转此外延片，在基底的背面光刻出漏极区域，刻蚀出漏极窗口，随后选用电子束蒸发工艺淀积Ti/Al/Ni/Au金属组合，其金属层的厚度分别为0.03μm/0.1μm/0.05μm/0.05μm，之后通过剥离、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 (8)
1.增强型AlGaN/GaN垂直超结HEMT，其特征在于，包括：N型GaN基底，包含第一表面及与该第一表面相对的第二表面；第一、第二P型GaN柱，设置于所述GaN基底第一表面；
N型GaN梯度柱，邻接设置于所述第一、第二P型GaN柱之间，其掺杂浓度沿远离所述GaN基底的方向依次递减，其厚度与所述P型GaN柱相等，所述N型GaN梯度柱包含奇数个掺杂浓度沿远离所述GaN基底的方向依次递减的N型GaN柱；
第一、第二P型GaN电流阻挡层，分别设置于所述P型GaN柱的表面；
第一、第二源极，分别设置于所述P型GaN电流阻挡层的部分表面；
N型GaN沟道层，设置于所述P型GaN电流阻挡层和所述N型GaN梯度柱的表面；
N型AlGaN势垒层，设置于所述GaN沟道层的表面；
钝化层和P型GaN帽层，自所述钝化层开始，所述钝化层与所述GaN帽层沿所述P型GaN柱指向所述N型GaN梯度柱的方向上交替分布于所述AlGaN势垒层的表面，所述钝化层的一侧端面与所述源极邻接；
栅极，自所述GaN帽层开始，设置于所述GaN帽层和所述钝化层的表面，其中所述栅极下方的GaN帽层的厚度大于其下方所述钝化层的厚度，所述栅极的截面呈“π”型；
漏极，设置于所述GaN基底第二表面。
2.根据权利要求1的所述垂直超结HEMT，其特征在于，所述N型GaN梯度柱包含5个掺杂浓度沿远离所述GaN基底的方向依次递减的N型GaN柱。
3.根据权利要求2的所述垂直超结HEMT，其特征在于，所述N型GaN梯度柱中，第三个所述N型GaN柱的掺杂浓度与所述P型GaN柱相同。
4.根据权利要求1至3之一的所述垂直超结HEMT，其特征在于，所述P型GaN电流阻挡层的厚度为0.8μm～1.2μm。
5.根据权利要求1至3之一的所述垂直超结HEMT，其特征在于，所述N型GaN沟道层呈T型，其中，位于所述GaN电流阻挡层之间的沟道层厚度为0.8μm~1.2μm，位于所述源极之间的沟道层厚度为80nm～120nm；所述N型AlGaN势垒层的厚度为20nm～30nm，其Al组分为10%～15%。
6.增强型AlGaN/GaN垂直超结HEMT的制备方法，其特征在于，包括以下步骤：
在N型GaN基底上外延生长厚度为8μm~12μm的P型GaN柱；
刻蚀所述P型GaN柱的中间区域，形成15μm～17μm宽度和8μm～12μm厚度的沟槽；
在所述P型GaN柱的表面沉积第一掩膜层，选用选择性区域外延生长工艺在所述沟槽内生长N型GaN梯度柱至所述沟槽填满，所述N型GaN梯度柱的掺杂浓度沿远离所述基底的方向依次减小；
去除所述第一掩膜层，在所述P型GaN柱和所述GaN梯度柱表面外延生长P型GaN电流阻挡层；
刻蚀所述P型GaN电流阻挡层暴露所述GaN梯度柱表面；
在所述P型GaN电流阻挡层表面沉积第二掩膜层，在所述GaN梯度柱表面外延生长厚度等于所述P型GaN电流阻挡层的N型GaN层；
在所述P型GaN电流阻挡层的部分表面形成源极窗口层，沉积欧姆接触金属，剥离退火后形成源极；
在所述源极上沉积第三掩膜层，在所述源极之间外延生长N型GaN沟道层、N型AlGaN势垒层以及P型GaN帽层；
刻蚀所述P型GaN帽层，在所述源极与预定区域的栅极之间形成暴露所述N型AlGaN势垒层的第一凹槽，在栅极预定区域的中部两边各形成一个暴露所述N型AlGaN势垒层的第二凹槽；
沉积钝化层以填充所述第一凹槽和所述第二凹槽；
刻蚀栅极预定区域的钝化层，暴露所述P型GaN帽层，并确保所述第二凹槽区域的钝化层厚度小于所述P型GaN帽层的厚度；
在栅极预定区域沉积欧姆接触金属形成栅极；
在所述N型GaN基底的背面光刻形成漏极区域，在该漏极区域沉积欧姆接触的金属形成漏极。
7.根据权利要求6的所述制备方法，其特征在于，所述N型GaN梯度柱包含五个掺杂浓度不同的N型GaN柱，所述掺杂浓度沿远离所述基底的方向依次减小。
8.根据权利要求7的所述制备方法，其特征在于，所述N型GaN梯度柱中，第三个N型GaN柱的掺杂浓度等于所述P型GaN柱。
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