Study On Low Temperature And Low Pressure Sintering Properties Of Micro-nano Composite Copper Powders

The third generation semiconductor materials have high power density,high thermal conductivity and large band gap.The interconnection materials of their devices need to meet the working requirements of"low temperature interconnection and high temperature service".Traditional interconnection materials,such as tin based alloy solder,have some problems,such as poor high temperature resistance(>300?)and easy to produce brittle intermetallic compounds,which are not suitable for the interconnection of the third generation semiconductor devices.Nano metal materials such as nano copper can be used as interconnection materials of the third generation semiconductor devices because of their low-temperature sintering characteristics,but nano copper is prone to oxidation in air.How to improve the oxidation resistance of nano copper powders and take into account its sintering performance has become an important research topic.To solve this problem,a method of adding micron copper particles to nano copper particles was proposed to improve the oxidation resistance and sintering performance of copper powders.Combined with the characteristics of low surface activity of micron copper and large specific surface area of nano copper,composite copper powders with higher density and better oxidation resistance can be obtained for the interconnection of third generation semiconductor devices.In order to verify this research idea,the difference of sintering properties of 250 nm-1?m composite copper powder with different ratios was explored,and the preparation process of copper paste was improved in this thesis.It was found that micro-nano copper powders can obtain good sintering properties.The shear strength of the best proportioned micro-nano copper powders can reach 81.4 MPa under the sintering conditions of 260?,2 MPa and 30min,the resistivity after sintering was 6×10^-7?·m,and the thermal conductivity was 186.74W/m·K.The shear strength of micro-nano copper powders was 42 MPa at 220?,2 MPa and30 min.The micro-nano copper powders can obtain good interconnection performance at low temperature and low pressure.In order to explain the sintering mechanism of micro-nano copper particles at low temperature(<300?),a micro flow sintering mechanism was proposed in this thesis.Copper particles with particle size of about 40 nm?1.8?m were used for pressureless sintering,and the particle size and sintering neck length were measured.It was found that there is a quantitative relationship between sintering neck radius(x)and particle radius(a).Considering that the mass transfer between adjacent particles was a material micro flow process driven by surface tension,a quantitative model was proposed to describe the relationship between sintering neck length and particle radius in the sintering process.In order to reveal the control mechanism of micro-nano copper powders on sintering properties,the structure property relationship of micro-nano particle sinter was discussed from the perspective of agglomerates.Through dilution,hot pressing sintering and characterization analysis of micro-nano copper paste prepared in different solvents,it was found that there is a linear relationship between the pore size(L_C)of copper sintered body and the size(La)of copper particle agglomerates.On the basis of experiments,a quantitative model was proposed to predict the overall strength of the sintered body.The results showed that the larger the solvent contact angle,the smaller the agglomerates size after copper paste dilution,the smaller the defect size of the sintered body,and the sintering performance was better.In conclusion,this thesis puts forward a new theoretical explanation for the sintering mechanism and performance regulation mechanism of micro-nano particles.