CN112993029A - 一种提高GaN HEMT界面质量的方法 - Google Patents
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Abstract
本发明提供一种提高GaN HEMT界面质量的方法,包括如下步骤:外延生长;Si基GaN外延晶片清洗;光刻及对准标记形成;台面隔离;源、漏欧姆接触;钝化层沉积;栅槽刻蚀;紫外/O2处理;栅金属沉积;保护层沉积;开孔及金属互联。本发明采用有效波长为85%254nm和15%185nm紫外热阴极低压汞蒸汽灯,加上氧气对栅金属沉积前进行预处理生成Ga2O界面介质层,不仅具有低成本无污染的优势而且还有效提高了界面质量,有利于器件的产业化应用。
Description
技术领域
本发明涉及电子元器件制造技术领域,具体涉及一种提高槽栅GaN HEMT(氮化镓高电子迁移率晶体管)器件可靠性的方法。
背景技术
GaN HEMT非常适合高功率开关应用,在击穿电压方面具有突破性的性能优势,并且结合了高速和低损耗开关性能,适合超高带宽的开关电源和蜂窝电话基站的微波功率器件。
但是,现有技术制造的GaN HEMT由于栅极下不可避免的界面缺陷会产生栅电流泄漏、导通电阻增大、电流崩塌、开关损耗增大等问题,并在器件之间引起明显的陷阱辅助隧穿等,是其产业化进程的一大制约因素。因此,有必要对现有技术进行改进,以克服现有技术的不足。
发明内容
本发明的目的是提供一种提高GaN HEMT界面质量的方法,采用有效波长为85%254nm和15%185nm紫外(UV)热阴极低压汞蒸汽灯,加上氧气对栅金属沉积前进行预处理生成Ga2O界面介质层,不仅具有低成本的优势而且还有效提高了界面质量,有利于器件的产业化应用。
为了实现上述目的,本发明采用的技术方案如下:
一种提高GaN HEMT界面质量的方法,包括如下步骤:
1)外延生长:在Si衬底上通过金属有机化学气相沉积(MOCVD)自下而上分别生长AlN成核层、GaN缓冲层、AlN***层、AlGaN势垒层、GaN冒层,形成Si基GaN外延晶片;
2)Si基GaN外延晶片清洗:将外延衬底依次放入MOS级丙酮和MOS级乙醇中超声3min,用流动的去离子水清洗样片2min并用氮***吹干;接着将器件浸入HF:HCl:H2O体积比为1:4:20的溶液1min,去除表面上的天然氧化物,然后用去离子水冲洗2min并用氮***吹干,完成样品清洗;
3)光刻及对准标记形成:对样品甩正胶S9912,转速6000转/min,在100℃的热板上烘5min,通过紫外光刻、显影、定影,形成腐蚀窗口,同时在光刻胶上形成对准标记;
4)台面隔离:采用反应离子刻蚀(RIE)法,利用氯气(Cl2)作为反应刻蚀气体,干法刻蚀GaN冒层、AlGaN势垒层、AlN***层和部分GaN缓冲层;将有源区以外的异质结二维电子气刻蚀掉,形成器件有源区之间的隔离;
5)源、漏欧姆接触:对样品甩正胶AZ6130,转速为6000转/min,95℃的热板上烘2min;与步骤3)的对准标记套刻光刻,显影、定影形成源/漏电极窗口;然后采用电子束蒸发设备完成金属堆栈沉积,形成Ti/Al/Ni/Au金属层;在850℃下快速热退火30s,形成有源极与漏极的欧姆接触电极;
6)钝化层沉积:通过等离子体增强化学气相沉积(PECVD)法,以气体流量为600sccm的SiH4、1960sccm的N2和20sccm的NH3作为化学反应源,温度为250℃,射频功率为60W,等离子体增强化学气相沉积的腔室压力为500Torr的条件下沉积160nm厚的Si3N4钝化层;
7)栅槽刻蚀:对样品甩聚甲基丙烯酸甲酯(PMMA)电子束胶,转速为2000转/min,180℃的热板上烘10min;采用电子束曝光在距离源极3μm,栅源间距为15μm的位置曝光栅槽图形,栅槽图形长度为2μm;经显影25s、定影5s形成栅槽窗口;利用RIE技术,在50W的功率下持续2min,通过CF4等离子体干法刻蚀去除栅极区域的Si3N4层,形成栅槽;
8)UV/O2处理:将经过清洗后的器件置于内置有紫外热阴极和低压汞蒸气灯的真空箱内,将AlGaN势垒层区域暴露于紫外热阴极和低压汞蒸气灯下,通入O2,6min,O2剂量率为7mg/L,形成约1nm的Ga2O介质层;
9)栅金属沉积:对样品甩双层电子束胶,下层为共聚物(Copolymer)胶,转速为3000转/min,150℃的热板上烘15min,上层为PMMA胶,转速为3000转/min,180℃的热板上烘10min;在栅槽位置处,采用电子束曝光套刻栅电极图形,设置栅电极尺寸2μm,曝光后经显影25s、定影5s形成栅电极图形窗口;采用电子束蒸发法在形成栅极图形窗口的介质层上生长Ni/Au金属层,与介质层之间形成肖特基接触,再使用丙酮将光刻胶去除;之后在N2气氛中,400℃下进行快速热退火30s形成肖特基栅电极;
10)保护层沉积:通过等离子体增强化学气相沉积法,以气体流量为1420sccm的N2O、150sccm的SiH4和392sccm的N2作为化学反应源,温度为300℃,射频功率为15W,等离子体增强化学气相沉积的腔室压力为0.9Torr的条件下沉积200nm厚的SiO2保护层;
11)开孔及金属互联:对样品甩正胶S9912,转速6000转/min,在100℃的热板上烘5min,通过紫外光刻、显影、定影形成光刻窗口;最后利用反应离子刻蚀技术将欧姆接触电极和肖特基栅电极表面覆盖的Si3N4保护层材料移除,刻蚀反应气体采用CF4和O2,射频功率为50W完成开孔;互联金属采用粘附性好的Ti/Au金属叠层,利用电子束蒸发和剥离工艺完成。
根据以上方案,所述步骤1)中AlN成核层的厚度为20nm、GaN缓冲层的厚度为2μm、AlN***层的厚度为1nm、AlGaN势垒层的厚度为20nm、GaN冒层的厚度为2nm。
根据以上方案,所述步骤3)、步骤5)与步骤11)中光刻的波长均为435nm,显影液均为质量浓度2.38%的四甲基氢氧化铵(TMAH),定影液均为水。
根据以上方案,所述步骤4)中干刻时在50W的功率下持续2min,刻蚀深度为150nm。
根据以上方案,所述步骤5)中源极与漏极的宽度均为2μm,源极与漏极间距为20μm。
根据以上方案,所述步骤7)与步骤9)中的显影液为甲基异丁基酮与异丙醇(MIBK:IPA)体积比为1:3的混合溶液,定影液为IPA。
本发明在UV/O2处理期间,185nm的紫外线光子首先将分子氧O2分解成三线态氧3O2,然后与分子O2结合生成臭氧O3。接着,254nm紫外线光子解离臭氧O3,形成分子氧O2和单重态氧1O2,其能量比三线态氧高94.29kJ mol-1(0.98eV),导致表面氧化,生成Ga2O。Ga2O层作为界面钝化层抑制了陷阱辅助隧穿,由于在AlGaN和栅金属之间多了一层薄Ga2O层,减小了界面态密度,相当于降低了肖特基势垒高度,HEMT器件阈值电压发生了负移,由于阈值电压的减小,提高了器件的饱和区电流、跨导。
本发明的有益效果是:
本发明采用有效波长为85%254nm和15%185nm紫外热阴极低压汞蒸汽灯,加上氧气对GaN HEMT的栅金属沉积前进行预处理生成Ga2O界面介质层,能有效解决栅电流泄漏、导通电阻增大、电流崩塌、开关损耗增大等问题,且在器件之间不会引起陷阱辅助隧穿等,不仅具有低成本无污染的优势而且还有效提高了界面质量,有利于器件的产业化应用。
附图说明
图1是本发明的衬底清洗时的工件结构示意图;
图2是本发明的台面隔离时的工件结构示意图;
图3是本发明的欧姆接触时的工件结构示意图;
图4是本发明的钝化层生长时的工件结构示意图;
图5是本发明的栅槽刻蚀时的工件结构示意图;
图6是本发明的紫外/O2处理时的工件结构示意图;
图7是本发明的栅金属沉积时的工件结构示意图;
图8是本发明的保护沉积时的工件结构示意图;
图9是本发明的开孔及互联金属沉积时的工件结构示意图。
具体实施方式
下面结合附图与实施例对本发明的技术方案进行说明。
实施例1,见图1至图9:
本发明提供一种提高GaN HEMT界面质量的方法,包括如下步骤(见图1):
1)外延生长:在6英寸(111)Si衬底上通过MOCVD自下而上分别生长20nm厚的AlN成核层、2μm厚的GaN缓冲层、1nm厚的AlN***层、20nm厚的AlGaN势垒层和2nm厚的GaN冒层,形成Si基GaN外延晶片;
2)Si基GaN外延晶片清洗:将外延衬底依次放入MOS级丙酮和MOS级乙醇中超声3min,用流动的去离子水清洗样片2min并用氮***吹干;接着将器件浸入HF:HCl:H2O体积比为1:4:20的溶液1min,去除表面上的天然氧化物,然后用去离子水冲洗2min并用氮***吹干,完成样品清洗(见图1);
3)光刻及对准标记形成:对样品甩正胶S9912,转速6000转/min,在100℃的热板上烘5min,通过紫外光刻(波长435nm)及显影(显影液为质量浓度2.38%的TMAH)/定影(定影液为水)形成腐蚀窗口,同时在光刻胶上形成对准标记;
4)台面隔离:采用RIE法,利用Cl2作为反应刻蚀气体,在50W的功率下持续2min,刻蚀深度为150nm,干法刻蚀GaN冒层、AlGaN势垒层、AlN***层和部分GaN缓冲层;将有源区以外的异质结二维电子气刻蚀掉,形成器件有源区之间的隔离(见图2);
5)源、漏欧姆接触:对样品甩正胶AZ6130,转速为6000转/min,95℃的热板上烘2min;与第一次的对准标记套刻光刻(波长435nm),显影(显影液为质量浓度2.38%的TMAH)、定影(定影液为水)形成源漏电极窗口;然后采用电子束蒸发设备完成金属堆栈沉积,形成Ti/Al/Ni/Au(20nm/50nm/40nm/50nm)金属层;在850℃下快速热退火30s,形成欧姆接触电极,源/漏电极宽度都为2μm,源漏间距为20μm(见图3);
6)钝化层沉积:通过等离子体增强化学气相沉积(PECVD)法,以气体流量为600sccm的SiH4、1960sccm的N2和20sccm的NH3作为化学反应源,温度为250℃,射频功率为60W,PECVD腔室压力为500Torr的条件下沉积160nm厚的Si3N4钝化层(见图4);
7)栅槽刻蚀:对样品甩PMMA胶,转速为2000转/min,180℃的热板上烘10min;采用电子束曝光在距离源极3μm,栅源间距为15μm的位置曝光栅槽图形,栅槽图形长度为2μm;经显影(显影液MIBK:IPA=1:3)25s、定影(定影液为IPA)5s形成栅槽窗口;利用RIE技术,在50W的功率下持续2min,通过CF4等离子体干法刻蚀去除栅极区域的Si3N4层,形成栅槽(见图5);
8)紫外/O2处理:将经过清洗后的器件置于内置有紫外热阴极和低压汞蒸气灯的真空箱内,将AlGaN势垒层区域暴露于紫外热阴极和低压汞蒸气灯下,通入O2,6min,O2剂量率为7mg/L,形成约1nm的Ga2O介质层(见图6);
9)栅金属沉积:对样品甩双层电子束胶,下层为Copolymer胶,转速为3000转/min,150℃的热板上烘15min,上层为PMMA胶,转速为3000转/min,180℃的热板上烘10min;在栅槽位置处,采用电子束曝光套刻栅电极图形,设置栅电极尺寸2μm,曝光后经显影(显影液MIBK:IPA=1:3)25s、定影(定影液为IPA)5s形成栅电极图形窗口;采用电子束蒸发法在形成栅极图形窗口的介质层上生长Ni/Au(50nm/110nm)的金属层,与介质层之间形成肖特基接触,再使用丙酮将光刻胶去除;之后在N2气氛中,400℃下进行快速热退火30s形成肖特基栅电极(见图7);
10)保护层沉积:通过PECVD法,以气体流量为1420sccm的N2O、150sccm的SiH4和392sccm的N2作为化学反应源,温度为300℃,射频功率为15W,PECVD腔室压力为0.9Torr的条件下沉积200nm厚的SiO2保护层(见图8);
11)开孔及金属互联:对样品甩正胶S9912,转速6000转/min,在100℃的热板上烘5min,通过紫外光刻(波长435nm)及显影(显影液为质量浓度2.38%的TMAH)/定影(定影液为水)形成光刻窗口;最后利用RIE刻蚀技术将欧姆接触电极和肖特基栅电极表面覆盖的Si3N4保护层材料移除,刻蚀反应气体采用CF4和O2,射频功率为50W完成开孔;互联金属采用粘附性较好的Ti/Au(20nm/200nm)金属叠层,利用电子束蒸发和剥离工艺完成(见图9)。
以上实施例仅用以说明而非限制本发明的技术方案,尽管上述实施例对本发明进行了详细说明,本领域的相关技术人员应当理解:可以对本发明进行修改或者同等替换,但不脱离本发明精神和范围的任何修改和局部替换均应涵盖在本发明的权利要求范围内。
Claims (6)
1.一种提高GaN HEMT界面质量的方法,其特征在于,包括如下步骤:
1)外延生长:在Si衬底上通过金属有机化学气相沉积自下而上分别生长AlN成核层、GaN缓冲层、AlN***层、AlGaN势垒层、GaN冒层,形成Si基GaN外延晶片;
2)Si基GaN外延晶片清洗:将外延衬底依次放入MOS级丙酮和MOS级乙醇中超声3min,用流动的去离子水清洗样片2min并用氮***吹干;接着将器件浸入HF:HCl:H2O体积比为1:4:20的溶液1min,去除表面上的天然氧化物,然后用去离子水冲洗2min并用氮***吹干,完成样品清洗;
3)光刻及对准标记形成:对样品甩正胶S9912,转速6000转/min,在100℃的热板上烘5min,通过紫外光刻、显影、定影,形成腐蚀窗口,同时在光刻胶上形成对准标记;
4)台面隔离:采用反应离子刻蚀法,利用氯气作为反应刻蚀气体,干法刻蚀GaN冒层、AlGaN势垒层、AlN***层和部分GaN缓冲层;将有源区以外的异质结二维电子气刻蚀掉,形成器件有源区之间的隔离;
5)源、漏欧姆接触:对样品甩正胶AZ6130,转速为6000转/min,95℃的热板上烘2min;与步骤3)的对准标记套刻光刻,显影、定影形成源/漏电极窗口;然后采用电子束蒸发设备完成金属堆栈沉积,形成Ti/Al/Ni/Au金属层;在850℃下快速热退火30s,形成有源极与漏极的欧姆接触电极;
6)钝化层沉积:通过等离子体增强化学气相沉积法,以气体流量为600sccm的SiH4、1960sccm的N2和20sccm的NH3作为化学反应源,温度为250℃,射频功率为60W,等离子体增强化学气相沉积的腔室压力为500Torr的条件下沉积160nm厚的Si3N4钝化层;
7)栅槽刻蚀:对样品甩聚甲基丙烯酸甲酯电子束胶,转速为2000转/min,180℃的热板上烘10min;采用电子束曝光在距离源极3μm,栅源间距为15μm的位置曝光栅槽图形,栅槽图形长度为2μm;经显影25s、定影5s形成栅槽窗口;利用RIE技术,在50W的功率下持续2min,通过CF4等离子体干法刻蚀去除栅极区域的Si3N4层,形成栅槽;
8)UV/O2处理:将经过清洗后的器件置于内置有紫外热阴极和低压汞蒸气灯的真空箱内,将AlGaN势垒层区域暴露于紫外热阴极和低压汞蒸气灯下,通入O2,6min,O2剂量率为7mg/L,形成约1nm的Ga2O介质层;
9)栅金属沉积:对样品甩双层电子束胶,下层为共聚物胶,转速为3000转/min,150℃的热板上烘15min,上层为聚甲基丙烯酸甲酯电子束胶,转速为3000转/min,180℃的热板上烘10min;在栅槽位置处,采用电子束曝光套刻栅电极图形,设置栅电极尺寸2μm,曝光后经显影25s、定影5s形成栅电极图形窗口;采用电子束蒸发法在形成栅极图形窗口的介质层上生长Ni/Au金属层,与介质层之间形成肖特基接触,再使用丙酮将光刻胶去除;之后在N2气氛中,400℃下进行快速热退火30s形成肖特基栅电极;
10)保护层沉积:通过等离子体增强化学气相沉积法,以气体流量为1420sccm的N2O、150sccm的SiH4和392sccm的N2作为化学反应源,温度为300℃,射频功率为15W,等离子体增强化学气相沉积的腔室压力为0.9Torr的条件下沉积200nm厚的SiO2保护层;
11)开孔及金属互联:对样品甩正胶S9912,转速6000转/min,在100℃的热板上烘5min,通过紫外光刻、显影、定影形成光刻窗口;最后利用反应离子刻蚀技术将欧姆接触电极和肖特基栅电极表面覆盖的Si3N4保护层材料移除,刻蚀反应气体采用CF4和O2,射频功率为50W完成开孔;互联金属采用粘附性好的Ti/Au金属叠层,利用电子束蒸发和剥离工艺完成。
2.根据权利要求1所述的提高GaN HEMT界面质量的方法,其特征在于,所述步骤1)中AlN成核层的厚度为20nm、GaN缓冲层的厚度为2μm、AlN***层的厚度为1nm、AlGaN势垒层的厚度为20nm、GaN冒层的厚度为2nm。
3.根据权利要求1所述的提高GaN HEMT界面质量的方法,其特征在于,所述步骤3)、步骤5)与步骤11)中光刻的波长均为435nm,显影液均为质量浓度2.38%的四甲基氢氧化铵,定影液均为水。
4.根据权利要求1所述的提高GaN HEMT界面质量的方法,其特征在于,所述步骤4)中干刻时在50W的功率下持续2min,刻蚀深度为150nm。
5.根据权利要求1所述的提高GaN HEMT界面质量的方法,其特征在于,所述步骤5)中源极与漏极的宽度均为2μm,源极与漏极间距为20μm。
6.根据权利要求1所述的提高GaN HEMT界面质量的方法,其特征在于,所述步骤7)与步骤9)中的显影液为甲基异丁基酮与异丙醇体积比为1:3的混合溶液,定影液为异丙醇。
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