Study On High Density Bump Interconnection Of Chip By Directional Growth Of Electroless Cu Deposition

With the development of microelectronic packaging technology,the packaging forms are constantly innovating,and the demand for low-temperature bump interconnection is becoming urgent.Copper has obvious advantages such as superior mechanical properties,electrical and thermal conductivity,and electromigration resistance.However,the conditions of high temperature,high pressure and long-time annealing required by traditional copper bump bonding greatly limit the reliability and practical application of chip bonding.Therefore,there is an urgent need to find a method to realize low-temperature Cu-Cu interconnection.Someone has proposed using electroless deposition interconnection to realize Cu-Cu bonding,which has been proved to be a practical technology,but the gap in the interconnection interface can not be completely eliminated,and the excessive growth around the bump limits the interconnection density.In this paper,the following two aspects are studied:firstly,the electroless deposition layer with special micro cone is obtained by additives,which forms multi-point fusion at the interconnection interface,which is conducive to the formation of higher quality interconnection joints;Second,the selective deposition of chip bump surface and the limited electroless deposition interconnection are realized by self-assembled monolayer method or physical method,which is expected to realize higher density bump interconnection.（1）Through the study of the plating solution process,it is found that under the conditions of temperature 70℃,p H=8.5 and activator Pd Cl₂concentration of 0.2 g/L,standard micro-cone with good o directional with a height of 3-5μm and a bottom diameter of about 2μm can be obtained by using the plating solution containing the additive PEG10,000.The electrochemical analysis shows that adding a small amount of PEG to the plating solution will promote the electroless deposition,rather than the conventional inhibition,and the deposition rate can reach 15μm/h.（2）The microfluidic channel is introduced to assist the electroless deposition interconnection of the chip and promote the contact between the plating solution and the bump.Under the process conditions of temperature80℃,time 90 min,micro-flow-pump speed 150 rpm and p H=8.5,the joints with fewer gaps and higher interface quality can be obtained.It is found that the electroless deposition interconnection process can obtain the joint with higher mechanical strength than the solder interconnection,and the shear force of a single bump can reach 0.99 N.（3）The good selective deposition of chip bumps is realized by self-assembled monolayer method or physical method.Physical method is more stable,low cost and good selectivity than self-assembled monolayer method,which has broad application prospects.The physical method is used to realize limited electroless deposition interconnection,which is expected to realize the low-temperature interconnection of higher density bumps.