A Study On Indium Column Forming And Flip Bonding Based On Ⅲ-Ⅴ Laser And Silicon Wafer

Flip chip bonding（FCB）is one of the main chip interconnection technologies to realize the laser integration in silicon photonics.In contrast with the direct growth of III-V materials on silicon substrates,the mismatch of lattice constants and thermal expansion coefficients between III-V and IV family will be reduced due to the use of indium solder bump as intermediate bonding layers.In addition,the use of indium bump provides better stability and reliability than the use of DVS-BCB polymeric materials or conductive adhesives.In this thesis,based on the finite element（FE）numerical simulation and experimental verification,FCB processing recipe and bonding sample reliability are thoroughly investigated.The following researches are carried out:（1）The FE model of indium bump in FCB is established by ANSYS LS-DYNA,and hence the stress and strain distribution of it is analyzed to demonstrate that the larger plastic deformation is located on the edge of the bump,and the smaller one is at the center.Such modeling is in good accordance with the measurement result of the residual indium distribution on gold electrode obtained by the shear force test.（2）The influence of muti-parameters on the geometric parameters of indium bump is analyzed.The diameter and height of the bump change obviously with the bonding pressure:when a force of 2.5gf is applied,the diameter of the indium bump only expands by 0.25μm and the height decreases by 0.062μm within 0.75ms;when the bonding pressure increases to14.17gf,the height decreases by 0.18μm and the diameter increases by 4.3μm.Moreover,the above changes occur within a short period of time and stabilize soon,which is consistent with stress and strain changes.（3）Bumps with different shape,size and layout are designed.At the same time,evaporation deposition is utilized to fabricate indium bumps considering the material and size of the bumps.For AZ4620 photoresist with the thickness of 10μm,the spin coating speed is experimentally validated.FCB is implemented using different process parameters after the above steps are completed.（4）The shear force test procedure is designed to explore the effect of different bumps,pressure,temperature and duration on the bonding strength.When the bump is a cylinder with30μm diameter and 6μm height,the shear strength ascends to the peak of 173.5g with the bonding temperature of 200°C,pressure of 90gf,and duration of 120s.Then the bonding interface is observed by EDX.Based on the bonding mechanism of Au-In,the formation process is depicted to show that for the external factors the gold and indium atoms undergo solid-liquid diffusion.Subsequently,the generated Au In₂ continues to undergo solid-solid diffusion to generate Au₇In₃.The electro-optic characteristics of the laser before and after the bonding are compared,showing that the V-I curve remains unchanged and meanwhile the output power decreases slightly.The thesis focuses on the FCB of lasers and silicon wafers,implementing not only the stress-strain simulations but also the bonding experiments.The optimal bonding recipe proposed herein could enable efficient and reliable heterogeneous integration for optoelectronics devices.