Research On The Machining Of Copper Surface Based On Confined Etchant Layer Technique

Copper has been widely employed as integrated circuits’interconnect material in the semiconductor industry due to its low electric resistance and high electro-migration resistance. In order to solve the problems like RC delay and interlayer crosstalk, the low-k materials have been widely used as the inter-level dielectric for interconnects in the manufacturing of integrated circuits. Chemical Mechanical Polishing (CMP) is the traditional method for planarization of copper interconnects. As an effective method for high precision planarization, it integrates the chemical effects from the polishing slurry and the mechanical effects from the polishing pad. However, because of low-k materials’ low hardness and high porosity, the low-k/Cu structure has a low mechanical strength. The abrasives in the polishing slurry, the polishing pressure and related polishing friction will deform the structure of low-k/Cu and even cause the separation between the copper wire and the low-k material.In order to achieve stress-free and high precision machining of copper, a new method was proposed based on Confined Etchant Layer Technique (CELT). As a distance sensitive method, it can realize micro/nano precision material removal by chemical etching, which has no mechanical damage and heat effect. The core issue of this method is the development of the working solution for copper. In this paper, Fe(bpy)3(ClO4)2and Ru(bpy)3Cl2are selected as the precursors of the working solution. Cyclic voltammetry method was used to investigate the effects of Oxalic acid, Tri amphetamine and Aminoacetic acid. According to the results, Oxalic acid has a better effect. Moreover, the pH of the working solution and the concentration of oxalic acid were optimized.In order to verify the effect of the optimized working solution, systematic etching experiments were carried out for both the [Fe(bpy)3]2+and the [Ru(bpy)3]2+optimized working solution with oxalic acid as the scavenger. The experiment table for copper etching has three parts, a3-D motion platform, an electrochemical working center and a data processing center. Also, the fixture of the working electrode and the electrolytic cell were designed according to related requirements. The experiments showed that, the scavenger, oxalic acid, can greatly hinder the radial diffusion of the etchant for both the [Fe(bpy)3]2+and the [Ru(bpy)3]2+working solutions. Compared with the etching results from working solutions without scavenger, the working solution with scavenger can result in clearer etched pits and improved etching resolution. Moreover, besides the traditional single point cylinder electrode, a novel band electrode was designed. With the new electrode, a2-D band area can be machined, which laid foundation of large area machining of copper.At last, in order to realize large area material removing of copper using the developed working solutions, two different strategies were presented, that is, static etching with a large working electrode and dynamic etching with a small electrode. For the first method, the strategy for the control of the distance between the working electrode and the workpiece was studied. Based on the squeeze film theory and related experiments, the distance will fall into a relative constant stage after first few minutes’rapid falling, and the the ultra-thin liquid film will deter the decrease of the distance between the large area electrode and the workpiece. For the dynamic etching of copper, dynamic etching experiments showed that the motion between the electrode and the workpiece will change the style of mass transfer, which has an effect on the etching result.