Design And Research Of Ohmic Contact To P-type 4H-SiC

Compared with the most commonly used semiconductor material Si in the electronics industry today,the new generation of semiconductor material silicon carbide(SiC)has excellent properties such as wide band gap,high breakdown electric field,and high thermal conductivity,making it suitable for high power,high frequency and high temperature devices.However,if there is no contact and interconnection that can work under the same conditions,the operating ability of silicon carbide under these conditions will not be fully exerted.At present,the manufacture of ohmic contacts with low resistance and high stability is a key technical issue in the development of SiC power devices.The ohmic contact of p-type SiC material has the following problems:(1)the temperature of the alloy annealing process for forming ohmic contact is high;(2)the stability and reliability of ohmic contact are poor;(3)the mechanism of ohmic contact formation is not clear.In order to solve the problem of higher alloying annealing temperature,this thesis uses two kinds of Ni/Si/Al and Cu/Ti/Al multilayer system materials as p-type 4H-SiC ohmic contact materials.The addition of Si in the former Ni/Si/Al system reduces the alloying.Annealing temperature,the addition of Cu in the latter Cu/Ti/Al system also plays a certain beneficial role in reducing the specific contact resistance.After several experiments,the best process conditions to meet the requirements of this experiment were explored,and the thickness and annealing temperature of the system materials were discussed and analyzed.The transmission line model(TLM)was used to measure the I-V characteristic curve of the metal/SiC contact and calculate the specific contact resistance ?c.X-ray diffraction analysis(XRD),field emission scanning electron microscope(FE-SEM)and energy dispersive spectrometer(EDS)were used to analyze the changes in the phase and the content of phase components between the contact material and the SiC interface under different parameters.Based on the Al-based system commonly used for p-type ohmic contact,this thesis studies the Ni/Si/Al multilayer system as the contact material.The system can form ohmic contact only after annealing at 650?,it avoids the general ohmic contact system High temperature annealing at 900?1200?.The lowest specific contact resistance value obtained by the system is 1.3×10-4 ?cm2.This thesis also studies the Cu/Ti/Al multilayer metal based on Ti/Al based system as the contact material,adds a new material Cu that has not been used in p-type ohmic contact.The system can be annealed at 800?,and the specific contact resistance is 1.0×10-4 ?cm2.After annealing at 850?,the lowest specific contact resistance is 5.49×10-5 ?cm2,and the system meets the requirements for device use.The new material Cu has certain potential as an ohmic contact material.