Fund Project:Project supported by the State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, China (Grant No. SKLIPR1802Z)
Received Date:23 February 2021
Accepted Date:15 March 2021
Available Online:29 July 2021
Published Online:05 August 2021
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/SiO2 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. Keywords:gate-controlled transistor/ hydrogen/ enhanced low dose rate sensitivity/ interface traps/ oxide trapped charge
图 4 氢气浸泡后与未浸泡条件下辐射感生产物面密度随总剂量的变化 (a)界面陷阱; (b)氧化物陷阱电荷 Figure4. Radiation-induced increases in (a) interface traps and (b) oxide trapped charge with/without soaking in 100% H2 under γ-ray irradiated.
23.2.辐照后氢气氛围中退火实验 -->
3.2.辐照后氢气氛围中退火实验
氢气氛围中退火实验是器件辐照结束后分别在氢气中和空气中退火, 对比退火参数的变化. 图5(a)和图5(b)是两组栅控晶体管辐照前、辐照至100 krad(Si)后分别在空气中和氢气中退火不同时间后的栅扫描曲线. 可以看出, 图5(a)中晶体管辐照后与辐照前相比栅扫描曲线峰值变化很大, 但在空气中退火不同时间几乎没有变化. 而图5(b)中晶体管栅扫描曲线不止在辐照前后变化明显, 而且在氢气中退火过程中栅扫描曲线峰值显著增大, 说明氢气中退火会使栅控晶体管损伤增强. 图 5 辐照前、辐照后、以及不同条件下退火后的晶体管栅扫描曲线 (a) 空气中退火; (b) 氢气中退火 Figure5. Gate sweep results of pre-irradiation, after-irradiation and annealing: (a) In air; (b) in H2.
图6是利用栅扫描曲线和(1)式、(2)式分离出的GLPNP基区Si/SiO2界面附近的界面陷阱和氧化层陷阱电荷面密度随总剂量和退火时间的变化曲线. 可以看出, 空气中退火的器件界面陷阱与氧化物陷阱电荷面密度与刚辐照完相比变化不大, 但氢气中退火的器件与刚辐照完相比, 界面陷阱显著增多, 氧化物陷阱电荷减少. 图 6 辐射感生产物随总剂量和不同条件下退火时间的变化 (a)界面陷阱; (b)氧化物陷阱电荷 Figure6. Radiation-induced increases in (a) interface traps and (b) oxide trapped charge under annealing in air or 100% H2 for 40 hours.
图 1 栅控横向PNP双极晶体管二维结构示意图
图 2 氢气浸泡后与未浸泡条件下归一化的晶体管放大倍数随辐照总剂量的变化
图 3 氢气浸泡后与未浸泡条件下, 不同总剂量时的晶体管栅扫描曲线
图 4 氢气浸泡后与未浸泡条件下辐射感生产物面密度随总剂量的变化 (a)界面陷阱; (b)氧化物陷阱电荷
图 5 辐照前、辐照后、以及不同条件下退火后的晶体管栅扫描曲线 (a) 空气中退火; (b) 氢气中退火
图 6 辐射感生产物随总剂量和不同条件下退火时间的变化 (a)界面陷阱; (b)氧化物陷阱电荷
图 7 氢气氛围中浸泡双极器件损伤增强机理示意图
图 8 仿真得到的不同氢气浓度下辐照感生面密度随总剂量变化 (a)界面陷阱; (b)氧化物陷阱电荷
