Shape Evolution Of Copper Electrodeposition Onto Surface Modificated Silicon

Among thin film deposition techniques, the economical electroplating process acquires a great deal of attention in the semiconductor industry. Copper is one of the most potential metal and single crystal silicon is widely used due to its good mechanical and electrical properties. But it is critically difficult to obtain the homogeneous copper layer by direct seedless electroplating. Therefore, the behavior of copper which is electrodeposited directly and selectively onto silicon surface is investigated.In order to understand how the electroplating works, theories including the electrical double layer model, nucleation and growth model are studied. Considering the influence of surface defects on nucleation, defects are brought to the silicon surface in the form of mechanical-interlocking, improving the adhesion between copper and silicon. Potassium hydroxide (KOH) wet anisotropic etching is selected to produce the defects. The etching processes of (100) silicon with different shapes in40%KOH at60℃are simulated in the software IntelliSuite.(100) and (111) silicon wafer are chosen as substrates. Oxidation, photolithography and buffered hydrofluoric acid (BHF) etching are used to prepare the patterned silicon cathodes. Pre-treatment approaches, such as BHF or KOH etching and isopropanol immersion, are applied on the silicon cathodes firstly. The plating system is established with a silver/silver chloride (Ag/AgCl) reference electrode. Copper is deposited from the solution of0.01mol GuSO4+0.05mol H2SO4. Experiments are carried out in form of direct current plating or pulse current plating with various parameters.The morphology and topography of plating results are characterized under SEM and AFM. On the BHF treated (100) or (111) silicon surface, majorities of copper clusters are in form of isolated islands. On the KOH treated (100) wafer, copper is deposited successively in larger amount because more preferential nucleation sites are created by defects. It is found that copper is very easy to be deposited on the rough surfaces resulting from the misalignment edges which are etched by KOH. On the KOH treated (111) wafer, copper film with good uniformity is easy to access. The film in the form of islands which grew into agglomerates gradually is consistent with the3D Volmer Weber growth model. This is confirmed by the copper clusters in triangular shape observed under AFM.It is common to find extruded coral structures at edges, which decrease with the increasement of silicon cathode. Dendrites at edges are easy access in direct current plating due to the limitation of ions concentration at the cathode surface near region, if there is a high cathodic potential. The size of humps is reduced in pulse current plating by the replenishment of copper ions during the pulse-off time. Furthermore, a higher plating efficiency is acquired in pulse current plating, which makes the copper film easily to be removed from silicon surface. The ramp voltage applied before the plating holds a high cathodic potential in a short time, resulting in more nuclei growth positions.