Study Of Time-Dependent Dielectric Breakdown Based On 65nm Commercial CMOS Process

The 65 nm CMOS process has been widely used in the civilian field as an advanced CMOS process,but the industry has reported a little about its TDDB characteristics and lifetime assessment,especially in complex and harsh environments.Based on a foundry's65 nm CMOS process line,this paper studies the following aspects of TDDB.Firstly,a test system is designed for TDDB testing;According to the relevant standards for the TDDB testing at home or abroad and the design requirements of TDDB test structures,a test structure design plan is made combining with the test objectives;Based on the 65 nm 1P9M technology library provided by a foundry,the layout design of the test structure is completed and delivered to a foundry to tape out.Secondly,the characteristics of TDDB including the influence of gate voltage polarity,gate voltage,temperature,gate oxide area,gate oxide thickness and radiation environment on TDDB is studied based on test structures fabricated by a foundry.In the study of influence of gate voltage polarity on TDDB,a special experiment is designed to verify the existing explanation of the difference in breakdown phenomenon under different polarity gate voltage,and another factor is proposed which will also cause the difference:due to the thermal conductivity of the electrons,the different gate currents under two polarities gate voltages also lead to differences in the internal heat dissipation of the gate oxide layer,which in turn will cause a difference in the breakdown phenomenon.In the study of influence of gate voltage and temperature on time-to-breakdown it is found that time-to-breakdown is exponential with the gate voltage and temperature.In the study of the relationship between gate oxide area and time-to-breakdown,it is found the Weibull slopes of the time-to-breakdown of the test samples with different gate oxide areas are almost the same,which is consistent with the statistical properties of Poisson area.In the study of the relationship between gate oxide thickness and time-to-breakdown,the T_BD-V_G data of test samples with different gate oxide thickness are processed in V model.It is found time-to-breakdowns of test samples with different gate oxide thicknesses have different voltage accelerating coefficients in V model.There may be two reasons.First,the applicable range of V model is limited because V model is not compatible with the FN tunneling mechanism and DT tunneling mechanism at the same time.Second,the defect generation rate is likely to relate to the gate current tunneling mechanism.Besides,it is found when NMOSFET is in the unbias state Cobalt source radiation has little or no effect on TDDB of NMOSFET.Thirdly,the main voltage acceleration models in the reliability evaluation of TDDB are compared.The reliability evaluation of 1.2V NMOS capacitors based on 65 nm CMOS process is carried out with Power-law model and temperature acceleration model.And the problem of extrapolating the test data under negative gate voltage to positive gate voltage is solved.The result shows that the quality of gate oxide of 1.2V NMOS can meet the requirement of industrial standard.