Radiation mechanism of gate-controlled lateral PNP bipolar transistors in the hydrogen environment

Abstract

Hydrogen plays a crucial role in realizing modern silicon devices. Molecular hydrogen may be found in processes of integrated circuit fabrication and packaging, such as wafer cleaning procedure, film depositions, high- and low-temperature anneal and die attachment by forming gas. It has been shown that hydrogen has strong effects on the total dose and dose rate response to bipolar devices. In order to study the relationship between hydrogen and radiation-induced products, we preform two experiments by using gate-lateral PNP transistors. In the first experiment, one set of devices is soaked in 100% hydrogen gas for 60 h and another set is not soaked, they are together irradiated at 5 rad(Si)/s to a total dose of 50 krad(Si). In the second experiment, devices are irradiated at 50 rad(Si)/s to 100 krad(Si), and then one group is annealed in 100% hydrogen gas and the other is annealed in the air for 40 h at the same temperature. The results show that the damage to devices which are soaked in hydrogen before irradiation is stronger than the devices that are not soaked, the anneal characteristics of devices in hydrogen gas are also changed more greatly than in the air. So the hydrogen can enhance the radiation and anneal damage to bipolar transistors. Using the gate-sweep technique, the radiation-induced products are separated and show that the hydrogen that enters into the transistor will cause the interface traps to increase and oxide trapped charge to decrease. The main reason is that the hydrogen can react with the oxide trapped charge to produce protons which can transport to the Si/SiO<sub>2</sub> interface, and then react with H-passivized bond to create interface trap. Based on the reaction mechanism presented in our work, a numerical model of enhanced low dose rate sensitivity including molecular hydrogen reaction and proton generation mechanism is established. The simulation results for the density of interface traps and oxide trapped charge show a trend consistent with the experimental data, which verifies the correctness of the damage mechanism. This research provides not only the basis of the study of damage mechanism of bipolar devices, but also the powerful support for hydrogen soaking irradiation acceleration method.