Molecular Simulation Study Of Gold Bump Electrodeposition And UBM Layer Thin Film Sputtering Deposition

With the rapid development of semiconductor technology,semiconductor process has gradually approached the atomic size level.Advanced packaging technologies such as wafer-level packaging,micro-nano structure interconnects,and 3D packaging have become important ways to continue Moore's Law and the hotspot research directions.As a key link in the advanced packaging technology,the bump interconnect structure plays an essential role in electrical connection,heat dissipation and mechanical connection.The surface morphology of the bump and the structure of the UBM layer film directly affect the quality of the bump and determine the performance and reliability of subsequent packaging structures.Many research turn out that in the process of bumps electro-deposition and UBM film sputter deposition,different process parameters seriously affect the quality and surface morphology of the coating.However,due to the limitation of the experimental conditions,it is difficult to observe the growth process of the coating directly,which limits the study on the mechanism of its morphological structure.The molecular simulation method reveals the growth rule and structure formation mechanism of the coating at the atomic level and remedies for the deficiencies in experimental research.Therefore,molecular dynamics and kinetic Monte Carlo method are used in this paper to simulate the process of making Au bump with electro-deposition method and Pt/Au UBM film with sputtering method.From the micro-scale perspective,the effect of different deposition parameters on the micro-morphology and structure of the coating are revealed through the research on the micro-mechanism of the growth process of the coating.The main conclusions are as follows:1.In the molecular dynamics study of the effect of deposition parameters on the surface roughness of sputtered films,it is found that:(1)Increasing the deposition energy can help to reduce the surface roughness of the film.When the deposition energy of Au atom increases from 0.1e V to 20 e V,the RMS roughness and Average roughness of the film surface decreased from 4.343? and 3.743? to 2.487? and 1.934?,and the number of vacancies and defects decreased,the surface quality significantly improved.(2)At higher substrate temperatures,the height of the film surface atom is more uniform and the surface roughness is lower.When the substrate temperature is 300 K,the RMS roughness and Average roughness of the film surface are 3.868? and 3.195?.When the temperature rises to 700 K,the RMS roughness and Average roughness significantly decrease to 2.161? and 1.887?.(3)Due to the shadow effect,the increase of the incident angle will make the deposited atoms easily captured by the top of the isolated island and cannot reach the gap between the atomic islands and result in an increase in the height difference of the surface atom.When the incident angle is increases from 0 ° to 60 °,the RMS roughness and Average roughness of the film increased from 3.363? and 2.854? to 4.526? and 3.821?,the surface roughness of the film is significantly increased.2.The effect of deposition parameters on the hybrid of the interface between the Au film and the Pt substrate were studied.The results show that:(1)The increase in deposition energy will increase the damage to the substrate surface by deposition atoms,and a large number of Au atoms can diffuse into the substrate surface.When the deposition energy is 20 e V,the proportion of Au atoms in the surface layer of the substrate reaches 0.343,and the Au atoms can diffuse to the third atomic layer below the substrate surface.(2)The higher substrate temperature accelerates the frequency of interaction between the substrate atoms and the deposited atoms,and thus increase the mixing of the substrate atoms and the film atoms.When the substrate temperature is 700 K,the proportion of Au atom in the substrate surface layer is 0.311,and obviously hybrid occurs at the interface.(3)The change of the incident angle has less effect on the interface hybrid.As the incident angle increases,the interface hybrid gradually decreases,because the velocity component of the deposited atoms in the direction perpendicular to the substrate decreases,making it difficult for the atoms to enter the substrate.3.Kinetic Monte Carlo simulation results of Au bumps made by electro-deposition show that:(1)Under lower deposition voltage,lower ion concentration,and higher bath temperature,the size of atom islands formed on the coating surface is larger.The increase of the deposition voltage,the increase of the ion concentration,and the decrease of the solution temperature will lead to the formation of vacancies and defects on the surface and rough surface morphology.(2)The deposition voltage and the solution temperature have a greater effect on the morphology compared with the ion concentration.In the coupling effect of the deposition voltage and the ion concentration,the RMS roughness of the coating surface reaches the minimum at 2.3631 ? when the voltage is-0.8V and the concentration is 0.025 mol/L.In the coupling effect of the solution temperature and the deposition voltage,when the temperature is 358 K and the voltage is-0.8V,the RMS roughness is 2.2179?.In the coupling effect of the ion concentration and the solution temperature,when the concentration is 0.025mol/L and the temperature is 358 K,the surface RMS roughness reaches the minimum,which is 2.3571?.Therefore,the optimal process parameters are a deposition voltage of-0.8V,a solution temperature of 358 K,and an ion concentration of 0.025 mol/L.(3)Comparing the migration events under different deposition parameters,it can be found that the deposition voltage and the solution temperature have a greater impact on the migration events.An increase in temperature will significantly increase the number of atomic migrations,and an increase in voltage will decrease the number of atomic migration events.At the same time,ion concentration have less effect in migration events.When the number of migration events increases,the morphology of the bump surface tends to be flat and smooth and the roughness is significantly reduced.