| As the device dimensions are continuously scaling down, negative biastemperature instability (NBTI) has become a critical reliability issue that threatens thedevice performance in the sub-micron CMOS technology, which inspiring manyattempts for the study on NBTI effect in terms of experimental, modeling andmechanism to obtain an deep understanding of this failure mode physics and apowerful reliability engineering capability. For this purpose, this dissertation is mainlyconcerned with the simulation and experiment analysis of the NBTI effect, and theestablishment of the NBTI degradation model. The main results of the study arediscussed as follows:1. With the reaction-diffusion (R-D) theory, the generation of NBTI inducedinterface trap (ΔNit) is investigated by simulations with varying stress and deviceconditions. For DC stress simulations: the exponent n of the power-law degradationand its time evolution is performed with varied Vgand T stress. It is found that theexponent n of ΔNitdegradation in the diffusion-limited phase is irrelevant to both Vgand T, while the time evolution of the exponent n is affected by the stress conditions.The diffusion profiles of the degradation-produced hydrogen species show the buildupof Nitis strongly correlated with Vgand T, whereas the diffusion of the hydrogenspecies shows Vg-unaffected but T-affected relations. Besides, for larger initial densityof interface trap (Nit0), the degradation of Nitweakens. And it can be deduced that Nit0is governing the generation of resultant Nit, but not controlling the diffusion process ofthe resultant hydrogen species through the diffusion profiles. For alternative stresssimulations: the dual negative stress VgLow&VgHighmixed mode has an significanteffect both on ΔNitand n. ΔNitcan be recovered under VgLowphase, leading to thedecrease of the absolute amount of ΔNitin the next VgHighphase. The results of thedelay setting and AC stress simulations show the significant value of R-D model instudy on NBTI effect.2. Based on the R-D framework, an improved NBTI model is proposed whichencapsulates the stress condition and key process parameters dependencies of theNBTI degradation. This new model is developed with the consideration of the timedependent diffusion front moving in oxide and poly-Si layer, especially thedependence of degradation on channel length (L) and width (W) is taken into account simultaneously and a2D geometry scaling method is provided for the first time. Themodel is implemented with Verilog-A to be compatible with commercial simulators,and has been validated with silicon data showing good accuracy.3. The effect of static NBT stress on p-channel power MOSFETs is investigatedby experiment and simulation. The threshold voltage (Vth) shift as a function of timeobeys the power-law relationship originated from the R-D theory. However, thedegradation behaves the similar trend but with the exaggerated time scale compared tothat of nano-scale MOSFETs. Peculiarly, the phenomena of the flat-roof section areobserved under various stress condition, which can be considered as the dynamicequilibrium phase in the R-D process. And the time duration of the flat-roof section iseffected by the stressed Vgand T, which has been verified by the simulation results.4. For the reason that both the interface traps (Nit) and oxide traps (Not) aregenerated during the NBTI degradation process, the mechanism of hole trapped byoxide defect and the two-stage model (TSM) which describes the coupling generationof Nitand Notare discussed, and the simulations based on TSM model are conductedwith the varied heights of barriers, which are employed in TSM mechanism to presentthe trap states’ transition. The trap state occupation probability and the Vthshift areobserved and explained according to the simulated results. |
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