Si_3N_4钝化层对横向PNP双极晶体管电离辐射损伤的影响机理

航天器中电子器件在轨服役期间,会遭受到空间带电粒子及各种射线的辐射环境的显著影响,易于造成电离辐射损伤.本文采用60Coγ射线辐照源,针对有/无Si_3N_4钝化层结构的横向PNP型(LPNP)双极晶体管,开展了电离辐射损伤效应及机理研究.利用KEITHLEY 4200-SCS半导体参数测试仪测试了LPNP晶体管电性能参数(包括Gummel特性曲线和电流增益等).采用深能级瞬态谱分析仪(DLTS),对辐照前后有/无Si_3N_4钝化层结构的LPNP晶体管的电离缺陷进行测试.研究结果表明,在相同吸收剂量条件下,与无Si_3N_4钝化层的晶体管相比,具有Si_3N_4钝化层的LPNP晶体管基极电流退化程度大,并且随吸收剂量的增加,电流增益退化更为显著.通过DLTS分析表明,与无Si_3N_4钝化层的晶体管相比,有Si_3N_4钝化层的晶体管辐射诱导的界面态能级位置更接近于禁带中心.这是由于制备Si_3N_4钝化层时引入了大量的氢所导致,而氢的存在会促使辐射诱导的界面态能级位置更接近于禁带中心,复合率增大,从而加剧了晶体管性能的退化.

Impact of nitride passivation layer on ionizing irradiation damage on LPNP bipolar transistors

Bipolar junction transistors (BJTs) are generally employed in spacecraft, due to their current drive capability, linearity and excellent matching characteristics. High-energy particles and cosmic rays in space environment remarkably affect electronic devices, especially in BJTs producing total ionizing dose, displacement damage or single event effect. Among them, ionizing irradiation effects on BJTs dominates. For BJTs, ionization damage can induce the oxide trapped charges in SiO₂ layer and interface traps in Si/SiO₂, resulting in more recombination base current and the degradation of current gain. Consequently, the accumulation of both oxide charges and interface traps causes an increase in the base current.#br#Passivation layer is also an important factor of the irradiation effects of BJTs. Previous works only studied the degradation of electrical properties of the devices with/without passivation layer induced by irradiation, and did not give an influence mechanisms of passivation layer on the irradiation respond of devices. Therefore, the irradiation damage mechanisms of the BJTs with or without nitride passivation layer are not clear so far.#br#In this paper, the impact of Si₃N₄ passivation layer on ionizing irradiation damage on lateral PNP bipolar transistors (LPNP) was studied by using ⁶⁰Co gamma irradiation source. The KEITHLEY 4200-SCS semiconductor parameter analyzer was used to measure the relationship between the electrical properties of LPNP transistors and ionization dose, including the Gummel characteristics, the degradation of current gain, etc. The irradiation defects of the LPNP transistors with/without passivation layer structure were analyzed by the deep level transient spectroscopy (DLTS). The experimental results show that the electrical properties of the LPNP transistors with and without passivation layer exhibit similar characteristics. For all samples, the base current increases with increasing the total dose, while the collector current does not almost change. Compared with the LPNP transistors without Si₃N₄ passivation layer, the degradation of LPNP transistor with Si₃N₄ passivation layer is severe.#br#Based on the excess base current as a function of base-emitter voltage for the LPNP transistors with/without nitride passivation layer, the degradation of bipolar transistors with nitride passivation layer is severe under the same irradiation conditions. The DLTS analyses show that compared with the bipolar transistors without nitride passivation layer, the signal peak located at about 300 K is shifted to low temperature for the bipolar transistors with nitride passivation layer. The above results show that the LPNP transistors with nitride passivation could produce a large number of interface states with the energy level is closer to the middle of the forbidden band during the irradiation, which is attributed to a large number of hydrogen presence during the processing of fabricated passivation layer.