Reliability Study of Oxidized Deposited Polysilicon (ODP) Gate Oxide for Silicon Carbide Power Transistors

碳化硅（SiC）是一种宽带隙半导体，在高功率和高温应用中非常受欢迎。特别是，SiC金属氧化物半导体场效应晶体管（MOSFET）由于MOSFET固有的温度稳定性和高质量的氧化物（SiO2）而具有高功率，高温应用的前景。在各种MOSFET设计中，u型槽MOSFET （U-MOSFET）由于其高电流能力而特别适合于高功率应用。U-MOSFET可以通过外延和离子注入在SiC中制备，然后进行各向异性刻蚀形成u型槽，然后热氧化形成栅氧化物。这种方法虽然在Si技术中是标准的，但在SiC中存在问题，因为热氧化的各向异性很强。最近的研究表明，这个问题可以通过沉积多晶硅，然后进行热氧化来解决。这两步工艺可以在u型槽结构上得到厚度均匀的栅极质量的氧化物。此外，氧化沉积多晶硅（ODP）栅极氧化物的使用为栅极氧化物的氮化提供了很大的灵活性。初步研究表明，SiC MOSFET栅极氧化物氮化可以减少热载流子注入，提高可靠性。然而，迄今为止，关于SiC MOSFET中栅氧化物在高温、高场条件下的可靠性的研究很少，而对于ODP栅氧化物的研究则没有这样的研究。PI提出在高应力条件下研究SiC上ODP栅氧化物的可靠性。在本研究中，多晶硅将在{0001}4H SiC晶圆上的化学气相沉积系统中沉积。多晶硅沉积将在700℃下使用超高压氢稀释的硅烷进行。大约100nm厚的多晶硅将在1100℃的干燥O2中氧化足够的时间以消耗所有多晶硅。然后通过铝的蒸发或掺杂多晶硅的沉积沉积金属栅极。PI将研究在高应力条件下产生的MOS电容器的可靠性。MOS电容器将保持在高场（106-107 V/cm）和高温（100-300℃）。PI将在整个应力过程中定期检查平带电压以评估退化。PI还将使用光电cv测量来确定应力前后的氧化物界面态密度

9906543AyersSilicon carbide (SiC) is a wide-bandgap semiconductor of great interest for high-power and high-temperature applications. In particular, SiC metal oxide semiconductor field effect transistors (MOSFET's) are promising for high-power, high-temperature applications because of the inherent temperature stability of MOSFET's and because of the high quality of the oxide, which is SiO2. Of the various MOSFET designs, the U-groove MOSFET (U-MOSFET) is particularly well suited for high-power applications due to its high current capability. U-MOSFET's may be fabricated in SiC using epitaxy and ion implantation, followed by anisotropic etching to form the U-groove, and then thermal oxidation to form the gate oxide. This approach, although standard in Si technology, is problematic in SiC because of the strong anisotropy of the thermal oxidation. It has been shown recently that this problem can be solved by the deposition of polycrystalline silicon, followed by thermal oxidation. This two-step process results in gate-quality oxide with uniform thickness over U-groove structures. In addition, the use of oxidized deposited polysilicon (ODP) gate oxide provides great flexibility in nitridation of the gate oxide. Initial studies indicate that nitridation of the gate oxide in SiC MOSFET's can reduce hot carrier injection and improve reliability. To date however, there have been few studies of the reliability of gate oxides in SiC MOSFET's under high-temperature, high-field conditions, and there have been no such studies in the case of ODP gate oxide. The PI's propose to study the reliability of ODP gate oxide on SiC under high-stress conditions.For this study, polysilicon will be deposited in a chemical vapor deposition system on {0001} 4H SiC wafers. Polysilicon deposition will be carried out using silane diluted in UHP hydrogen, at 700oC. The polysilicon, approximately 100 nm thick, will be oxidized in dry O2 at 1100oC for a time sufficient to consume all of the polysilicon. Metal gates will then be deposited by the evaporation of aluminum or the deposition of doped polysilicon. The PI's will study the reliability of the resulting MOS capacitors under high-stress conditions. The MOS capacitors will be held at high field (106-107 V/cm) and high temperature (100-300oC). The PI's will periodicallycheck the flat band voltage throughout the course of the stressing to assess the degradation. The PI's will also use photo-CV measurements to determine the oxide interface state density before and after stressing.***