Uniformity Analysis And Morphology Evolution Of Electrodeposition Height Of Wafer Gold Bump

The popularization of liquid crystal display and portable electronic products with small and light characteristics is increasing rapidly,which promotes the rapid development of highdensity 3D WLP technology.For example,LCD driver chip has thousands of ultra narrow spacing I/O terminals.As the key structure bump of the chip's lead-in interconnection,its ECD molding has become the most economical choice.However,the shape,high consistency and other problems have long plagued the wafer bump forming process.The electrodeposition behavior is controlled by the distribution of flow field and electric field.Therefore,there are great differences in the height and morphology of the wafer bump deposition layer under different processing conditions.In this paper,based on the kinetic law of Butler-Volmer mixed electrochemistry,the inhomogeneous phenomenon of deposition height and morphology evolution caused by concentration polarization and electrochemistry polarization after flow field coupling electric field are analyzed.The process of electrodeposition of flowing bath on wafer was simulated by computer numerical simulation and experiment.The results are as follows:1.In In the process of flow field parameter analysis,it is found that when the diameter D of bath inlet changes from 12 to 20 mm,the uniformity of deposition height presents nonlinear change.When the diameter of the inlet pipe is 18 mm or smaller,the uniformity is better.When the circulation flow rate L is adjusted from 10 to 40 L / min,it is found that when the circulation flow rate is greater than 30 L / min,the height uniformity becomes better and more stable.Changing the height of anode net has little effect on the flow field near the wafer,so it has little effect on the uniformity of electrodeposition height.At the same time,the appropriate density of anode wire mesh is beneficial to the homogeneous deposition of wafer bumps.2.The In the process of electric field analysis,the uniformity of deposition height near and far away from the cathode' routes is analyzed.The current density of anode tends to affect the electrodeposition rate,and there is a good linear relationship.With the increase of deposition rate,the uniformity of deposition height gradually becomes worse.After comprehensive consideration,the anode current density is adjusted to 0.60-0.70 ASD,which is more beneficial to homogeneous deposition.According to the simulation results,when the final plating time is set to 30 min,the height difference of bump can be controlled within 1.4 ?m,the overall deviation is about 0.5 ?m,and the deviation relative to the average height is about 5%.The bump with high uniformity can be obtained,and the overall relative deviation rate is low.The optimized design of electroplating cup,the optimized inlet circulation flow and the proper selection of electroplating conditions can meet the needs of different chips for the height of gold bumps,so as to obtain highly uniform bumps,which can also be used as a reference standard for the future narrow spacing and high-density uniformity electrodeposition of gold bumps.3.It is found that the average thickness of electrodeposition increases with the increase of electrodeposition time,and its morphology gradually evolves from "hat" structure with high middle edge and low edge to "saddle" structure with high middle edge and low middle edge.At the same time,with the evolution of bump shape,the range of deposition thickness increases rapidly with the increase of time,and the uniformity becomes worse,especially obvious in the edge area of photoresist wall.With the increase of the flow rate of the plating solution on the photoresist cavity surface,the range of the electrodeposition thickness decreases sharply at first,and then increases slowly with the increase of the flow rate,that is,the flatness of the gold bump first gets better and then gets worse slowly;with the flow direction,the surface morphology of the bump tends to be flat gradually.When the velocity reaches 0.25m/s,the optimal flatness of single bump is obtained.With the increase of the concentration of the plating solution,the uniformity of the deposition thickness is getting better.When the concentration reaches 0.070mol/l,the deposition thickness range is 0.346?m.Therefore,the higher concentration of the plating solution is more conducive to the uniform deposition of the wafers.From the simulation results,it can be seen that with the increase of electrolyte potential,the high uniformity of bump surface is also rapidly deteriorating.4.In the comparative analysis of the experiment,it is found that the height deviation and range are decreasing with the increase of the circulation flow at the inlet of cup.That is to say,with the increase of the flow rate at the entrance of the cycle,the uniformity of the electrodeposition is improved.In the process of approaching from the center to the edge of the wafer,the deposition height first decreases and then increases rapidly,and a large number of gold deposits appear near the pole of the cathode wafer,which is consistent with the phenomenon of wafer edge in the actual production process.In the investigation of the evolution of wafer single bump morphology,the evolution of deposition morphology obtained in the simulation has also been proved to be a common phenomenon in the existing literature.All of these prove that this simulation has high precision.