Investigation Of Electrical And Thermal Characteristics Of Three-dimensional Integration

As the feature size of the semiconductor process decreases to the nanometer level,it becomes more and more difficult to further reduce the transistor channel length.In recent years,the semiconductor industry is working in two ways to continue improving the performance of integrated circuits(ICs).On the one hand,new transistor processes such as fin-based field-effect transistors(FinFETs)are being developed to reduce the feature size.On the other hand,new packaging technologies such as three-dimensional(3-D)integration have been proposed to reduce the length of global interconnects and improve the performance of ICs.These two kinds of technology may appear in the same IC products,which can be called 3-D IC for the sake of simplicity.There are interactions among the electrical and thermal behaviors of an IC.The electrical power generation leads to the increase of temperature,which in turn affects the electrical performance via temperature-dependent material parameters.In 3-D ICs,the temperature elevation is usually considerable,and the impact of electrical-thermal coupling effects on the performance should not be neglected.At the transistor level,the electrical-thermal coupling effects cause reliability problems such as the threshold voltage shift of FinFETs through physical mechanisms including hot carrier injection(HCI).At the package level,the coupling effects lead to the variation of the electrical and thermal performances of through silicon vias(TSVs),resulting in problems such as crosstalks and electromagnetic interferences.In order to accurately predict the electrical and thermal performances of a 3-D IC,it is necessary to comprehensively investigate the electrical-thermal coupling mechanism of its key structures.In this paper,electrical-thermal modeling and co-simulations are performed for the TSVs and FinFET devices in 3-D ICs,respectively.And the electrical and thermal performances and reliability are analyzed and discussed.The main contents are as follows.1.A 3-D equivalent thermal circuit(ETC)model is proposed in this paper to quickly obtain the 3-D transient distribution of temperature in TSV arrays.The anisotropy of heat transfer and the temperature dependence of material thermal conductivity are taken into consideration in the model.In order to verify the accuracy and efficiency of the proposed model,transient thermal simulations of TSV arrays are performed under multiple kinds of thermal conditions.Comparisons between the simulation results with those from commercial software show that the proposed model can reduce the simulation time while maintaining a relatively good accuracy if the Biot number is kept small enough in the modeling process.2.The temperature dependence of MOS effects in TSVs and its impact on the electrical-thermal performance of coaxial TSVs(C-TSVs)is investigated.Firstly,the temperature-dependent MOS effects are carefully modeled and investigated,where the simulated MOS capacitance under different temperatures matches well with the measured results in the literature.Then,transient electrical-thermal co-simulations are performed for C-TSVs with the equivalent electrical circuit model(EEC)and the ETC model.A specific method to implement transient electrical-thermal co-simulations by utilizing commonly-used electrical circuit solvers is proposed.The impact of the temperature-dependent MOS effects on the electrical and thermal performances of C-TSVs is demonstrated to be considerable.3.The impact of circuit-level electrothermal effects on the electrothermal reliability of FinFETs is investigated.Firstly,the layout of a nine-stage ring oscillator(RO)is designed and verified,and the oscillating voltage and power generation are obtained through a post-simulation in Cadence.Secondly,a transient heat conduction simulation is performed with the 3-D integrated structure of the RO that is accordingly constructed from the layout.With the obtained AC stress voltages and transient temperature response,the HCI-induced threshold voltage shift of n-type FinFETs is successfully predicted.Moreover,the impact of electrical and thermal parameters of the RO,including the supply voltage and thermal environments,on the results are further studied,and the obtained results can provide guidance for IC designers.