Study On Cumulative Irradiation Effect Of 28nm Process PMOS Device

With the rapid development of semiconductor manufacturing processes,the feature size of devices has reached the nanometer level.The large-scale application of micro-nano devices in the space radiation environment makes the research on radiation effects and reliability of semiconductor devices more and more important.The damage to devices caused by space irradiation is mainly caused by damage to materials through ionization and displacement effects,and the introduction of traps and defects affects device characteristics.In this paper,the proton and heavy ion irradiation experiments are used to study the cumulative irradiation effect of 28 nm process node PMOS devices.At the same time,the principle of the effect of device size on the degradation effect of heavy ion irradiation is discussed.And combined with the strong field experiments,the effect of coupling of heavy ion irradiation and gate stress on the long-term reliability of PMOS devices was explored.First,by analyzing the physical mechanism of cumulative radiation damage in theory,the effects of trap charges and interface states introduced by radiation on device transfer,transconductance,and output characteristics are summarized.Then,28 nm process PMOS devices were subjected to proton and heavy ion cumulative irradiation experiments.The experimental results show that both proton and heavy ion irradiation will cause the threshold voltage of the PMOS device to drift negatively,the maximum transconductance will decrease,and the absolute value of the saturated output current will decrease;the larger the irradiation dose,the more severe the degradation.Theoretical analysis indicates that proton irradiation mainly damages the device through displacement effects,and heavy ion irradiation has a strong ionization effect.For P-type MOS devices,the charges induced by proton and heavy ion irradiation are both positively charged,leading to negative drift in threshold voltage;interface state traps introduced by irradiation reduce the mobility in the channel and reduce the maximum transconductance;saturation output current degradation is closely related to mobility.The size of the device group with the same width and different length is: W = 500 nm,L = 30 nm,60nm,and 100 nm,and the size of the device group with the same length and different width is: L = 30 nm,W = 300 nm,500nm,and 750 nm.Through the comparative analysis of the characteristic parameters,the relationship between the cumulative ionizing effect of heavy ions and the channel length and width of micro-nano PMOS devices was established.The analysis shows that: under the condition of the same channel width,the degradation effect of the shorter channel device is more obvious;under the condition of the same channel length,the degradation effect of the device with narrower channel is more serious.Reflected in that the threshold voltage negative drift is greater,the maximum transconductance is reduced more and the saturation output current degradation is more serious.The analysis points out that at the same width,the short-channel device has a large proportion of the channel source-drain depletion region,which is more seriously damaged by irradiation and has a higher induced charge density.The short-channel effect is main reason for enhancement of degradation effect on short-channel devices after irradiation.At the same length,the induced charges generated by irradiation in the STI regions on both sides of the channel have a stronger effect on narrow channel device,inhibit the formation of the inversion layer,reduce the carrier mobility and aggravate the degradation of narrow trench device characteristics.Finally,based on the 28 nm process PMOS device with W/L = 500nm/50 nm,the effect of heavy ion irradiation damage on the gate stress degradation effect was investigated through a 1000 s strong field experiment,and a model of characteristic parameters degradation with stress time was obtained.The results show that heavy ion irradiation has a negative impact on the long-term reliability of micro-nano PMOS devices.After irradiation,the characteristic parameters of the device degrade with stress time more than the non-irradiated device.The longer the stress time,the more severe the degradation,and eventually it stabilizes.Theoretical analysis indicates that the gate stress introduces positive charges and interface states in the gate oxide layer in the high-field experiment,which leads to the degradation of characteristics;the trap introduced by irradiation has an enhanced effect on stress degradation,which causes more serious degradation of the characteristic parameters.The process of characteristic parameter degradation in semi-logarithmic coordinates can be fitted to a straight line,indicating that the degradation caused by gate stress is a power function of stress time.