Study On Physical Model And Key Technology Of SiC CMOS High-Temperature Integrated Circuits

Among wide-band semiconductor materials,silicon carbide（SiC）is one of the most mature materials currently used in semiconductor devices.SiC has excellent physical and chemical stability,high irradiation resistance and mechanical strength,which make SiC capable of operating not only at high temperatures but also under strong irradiation conditions.The research and design of 4H-SiC CMOS high-temperature integrated circuits is of great significance for the current aerospace,oil drilling and other high-temperature fields of work.There are still some problems in the research for 4H-SiC CMOS high-temperature integrated circuits:（1）There is a lack of physical and behavioral models that can accurately represent the temperature-dependent characteristics of 4H-SiC n-MOSFETs and p-MOSFETs.（2）No systematic studies have been developed for key processes in 4H-SiC CMOS ICs,such as ion implantation,gate oxide growth,silicon carbide resistance implanting,interconnection metal deposition,and high-temperature ohmic contact fabrication.In this paper,we explore the main problems related to the research of 4H-SiC CMOS high-temperature integrated circuits,and the main work and results are as follows:（1）Study of physical and behavioral models for temperature-dependent characteristics of4H-SiC n-MOSFETs and p-MOSFETsThe temperature-dependent characteristics of 4H-SiC materials are analyzed in detail,including the intrinsic carrier concentration,the forbidden band width,the variation of impurity dissociation,bulk mobility,and electron-hole complex.The classification of the interfacial charge of MOS devices,the model of interfacial trap distribution of 4H-SiC MOS devices and the method of extracting interfacial traps are presented.The temperature-dependent characteristics of various mobilities and threshold voltages of 4H-SiC MOS devices are analyzed.The structure and parameters of 4H-SiC MOSFET were designed and the devices were fabricated.The output and transfer characteristics and capacitance characteristics of the devices were tested at 25℃ to 500℃.The device parameters such as threshold voltage,field effect mobility,interface fixed charge and interface trap charge at different temperatures were extracted.Based on the previously analyzed temperature-dependent characteristics of SiC materials and SiC MOSFET devices,the extracted parameters are then added to the Sentaurus TCAD software to build a complete physical model of the 4H-SiC MOSFET.At the same time,the Spice static model of the device is built using LTSpice software based on the extracted parameters.Finally,the physical model established by Sentaurus TCAD and the Spice model established by LTSpice are used to simulate the common source amplifier circuit,and the correctness of the Spice model is verified.（2）Study of Key Processes for 4H-SiC MOSFETsThe ohmic contact,interconnection metal and ion implantation resistance in the key process of 4H-SiC MOSFET fabrication were studied.For the characteristics of 4H-SiC ohmic contacts,a Pt/Ta Si₂/Al/Ti/Ni/SiC structure is proposed in this paper,n-type and p-type ohmic contacts are formed simultaneously after annealing at high temperatures of 800℃ for 2 min,and the specific contact resistance values are obtained by I-V measurements as 3.22×10^-4Ω·cm² and 4.41×10^-5Ω·cm²,respectively.The structures exhibited good thermal stability after 100 h of aging at 500℃.In addition,the surface of the formed structures is smooth,which is favorable for interconnection and bonding.For interconnection metal,based on traditional Al-interconnection,Pt/Ta Si₂ layer is added between Al and Si O₂ to form a new interconnection system of Pt/Ta Si₂/Al.After testing the Pt/Ta Si₂/Al interconnection,the quality of the Pt/Ta Si₂/Al interconnection is significantly higher than that of the traditional Al interconnection at high temperature.The 4H-SiC n-type and p-type implanted resistance were also measured at different temperatures.The n-type and p-type block resistance would decrease first and then increase with the increase of temperature.Under certain doping concentration,the block resistance of n-type is 178.7Ω/□,and the block resistance of p-type is 45.7 kΩ/□.For 4H-SiC MOSFET,p-type implanted resistance is more suitable for 4H-SiC integrated circuit design.（3）Fabrication and characteristic analysis of 4H-SiC CMOS high temperature integrated circuitUsing the designed device parameters and the key studied technologies,the complete process flow design of 4H-SiC integrated circuit was carried out,and the experimental layout was designed,including 4H-SiC MOSFETs with different sizes,analog and digital circuits.These devices and circuits have been measured and analyzed at different temperatures.The analog circuit is represented by the common source amplifier and differential amplifier composed of n-MOSFET and p-MOSFET.At room temperature,the gain of the common source amplifier circuit can reach 37 d B,and the bandwidth gain product（GBW）is 125 k Hz.At300℃,its gain decreases to 32 d B,and GBW increases to 600 k Hz.The gain of the differential amplifier circuit can reach 30 d B at room temperature,and the GBW is 25 k Hz.At 300℃,its gain rises to 34.6 d B,and the GBW is 130 k Hz.For digital circuit,the inverter,NAND gate and NOR gate were measured,and the logic output results of the circuit are correct,which shows that the logic gate circuits can be applied to the design of 4H-SiC digital integrated circuit.Compared with the relevant international research,the performance of the common source amplifier circuit has achieved a gain of more than 30 d B in the case of smaller device size.However,due to the limitation of packaging technology,the performance of the circuit above 300℃ has not been measured.In this paper,4H-SiC CMOS high-temperature integrated circuits were researched and fabricated for the first time in China,filling the gap of SiC integrated circuit technology in our country,and the performance of some circuits reached the international advanced level,laying a solid foundation for the subsequent development of 4H-SiC CMOS high-temperature integrated circuits in our country.