14:15 〜 14:30
▼ [15p-A201-6] Mechanical-stress-induced anomalous change of electrical characteristics of 4H-SiC (0001) NMOSFET fabricated on Al-implanted p-type well
キーワード：Silicon Carbide, Strain Engineering, MOSFET
In this research, we investigate on the impact of mechanical stress on the electrical characteristics of 4H-SiC (0001) MOSFET fabricated on Al-implanted p-type well.
For uniaxial stress applied along channel direction <11-20>, μFE increased monotonically while tensile stress increased, and decreased monotonically while compressive stress increased. On the other hand, for biaxial stress, μFE tended to increase when compressive stress was applied. Note that we applied only a small mechanical stress, in the order of tens of MPa. Compared to previous researches on p-type epitaxial layer (p-epi layer) channel, the observed change of mobility in this study seems multiple times higher. Moreover, the uniaxial stress-induced effect on μFE seems opposite to the previous report on p-epi layer channel. Though the origin of such anomalous phenomenon and the discrepancy from the previous report is still not clear, we assume that it is related to the ion-implantation-induced significant strain in the channel region, which exists even without applying mechanical stress.
In addition to the mobility change, it should be noted that significant change in threshold voltage (Vth) was observed while applying mechanical stress. Both compressive and tensile stress can induce change in Vth, though tensile stress leads to larger shift in Vth. Considering that such anomalous change of Vth has not been reported in classical study of mechanical stress effect on Si MOSFETs, this result may indicate a possibility that the band alignment at SiC/SiO2 interface should be quite sensitive to the mechanical stress, or the amount of trapped charges at the interface should be quite sensitive to a small change of electric structure of SiC.
For uniaxial stress applied along channel direction <11-20>, μFE increased monotonically while tensile stress increased, and decreased monotonically while compressive stress increased. On the other hand, for biaxial stress, μFE tended to increase when compressive stress was applied. Note that we applied only a small mechanical stress, in the order of tens of MPa. Compared to previous researches on p-type epitaxial layer (p-epi layer) channel, the observed change of mobility in this study seems multiple times higher. Moreover, the uniaxial stress-induced effect on μFE seems opposite to the previous report on p-epi layer channel. Though the origin of such anomalous phenomenon and the discrepancy from the previous report is still not clear, we assume that it is related to the ion-implantation-induced significant strain in the channel region, which exists even without applying mechanical stress.
In addition to the mobility change, it should be noted that significant change in threshold voltage (Vth) was observed while applying mechanical stress. Both compressive and tensile stress can induce change in Vth, though tensile stress leads to larger shift in Vth. Considering that such anomalous change of Vth has not been reported in classical study of mechanical stress effect on Si MOSFETs, this result may indicate a possibility that the band alignment at SiC/SiO2 interface should be quite sensitive to the mechanical stress, or the amount of trapped charges at the interface should be quite sensitive to a small change of electric structure of SiC.