Reseach On Ionizing Irradiation Induced Total Dose Effects In NMOS Transistors

With the development of the aerospace industry and the nuclear industry, the radiation effects on electronic equipment during operation are also growing. As the core part of these devices, integrated circuit chips are to bear the brunt. In order to ensure the chip performance and reliability, research on anti-radiation theory is becoming increasingly important.Total dose effect in dielectric is studied, focusing mainly on the total dose radiation theory under 0 bias and total dose irradiation charge modeling.Based on the fundamental physical processes of the total dose irradiation, the results of different bias on the basic process are discussed. This paper finds that fixed oxide charge and trapped charge at Si-SiO2 interface under the 0 bias are less than positive and negative bias case, and the ratio of the two charges is different. This is because initial composite rate and recombination rate in the capturing and annealing process of carriers are lower under 0 bias due to the low electric field.Anti-radiation measures such as improved gate structures and material is simulated with Sentaurus TCAD, with which the total dose irradiation experiments under 0 bias are designed. Considering both the simulation results of various measures and the actual process conditions, this paper uses the enclosed-gate MOSFETs and conventional MOSFETs with different width to length ratios under different total dose of radiation for comparison to study total dose effects under 0 bias.Then MOSFETs are fabricated using standard CMOS process and then irradiated. After irradiation, the electrical curves of each transistor under different doses are measured. The effects of different voltage, total dose, and width to length ratios of each transistor on device parameters are analysised.Based on test data, this paper extracted irradiation induced fixed oxide charge and trapped charge at Si-SiO2 interface. Finally, the fixed oxide charge model is proposed, considering the influence of the 0 bias condition during the irradiation process. The one-dimensional continuity equations are proposed to describe the generation, the initial compound, transportation, and the annealing process of holes in oxide with certain thickness. Equivalent charge model is proposed to calculate the fixed charge in oxide with varied thickness. The model is solved in MATLAB, and simulation results of both enclosed-gate MOSFETs and conventional MOSFETs after radiation agree well with experimental data.This article has made some achievements on NMOS total dose radiation under 0 bias. The fixed oxide charge model is proposed, providing a foundation for subthreshold current modeling.