Effect Of CMP On Low K Material And Research On Its Optimization Methods

With the continuous development of IC industry,the circuit feature size is becoming smaller and the layers of copper interconnection are increasing. As a result, RC delay becomes a huge obstacle of the development of IC. New materials, such as Cu, Ta and low k are introduced in IC to reduce RC delay. With the introduction of the new materials, traditional etching process was replaced by dual damascene process.In dual damascene process, chemical mechanical polishing(CMP) is adopted to achieve material planarization. Barrier CMP can finally determine the result of planarization and the circuit yield. In barrier CMP, the relative permittivity of low k materials are easily to be raised because of its sponginess and porosity, which will finally affect the property and reliability of IC. Therefore, barrier CMP must aim not only for high removal rates and high dishing correction, but also for lowering the effect to k value of low k material.Firstly, we studied barrier CMP in depth. The effect of slurry components on CMP was found through some single factor experiments. A new kind of alkaline slurry was developed as a preliminary one. By applying this slurry to 12 inch M1 copper pattern wafer, alkaline slurry was proved feasible in barrier CMP.Low k material was studied in this paper. Theoretical basis of getting the value of relative permittivity from capacitance measurement was stated after the concept of relative permittivity was introduced. By observing the Fourier transform infrared spectra before and after CMP, it was found that CMP made changes to the inside of low k material. Then, we studied the influence of concentration of SiO2 and pH of slurry on relative permittivity. It was found out that alkaline slurries of low concentration of SiO2 and low pH showed lower affect on the value of relative permittivity. In addition, annealing after CMP could repair the relative permittivity partly. We finally improved the preliminary alkaline slurry by lowering its pH. The improved slurry could not only achieve an acceptable dishing and erosion, but also make the resistance of 12 inch M1 copper pattern wafer range from 1.19 kohm to 1.46 kohm, as well as the capacitance from 2.24 to 2.43 pF. We achieved a nice result as all the data can meet the requirements of industry.After a series of studies, the effect of CMP with alkaline slurries on low k materials could be reduced. The effect even could be lower than CMP with acidic slurries. Moreover, the result of CMP with alkaline slurries could achieve a high standard. The composition of this alkaline slurry is so simple that it is easy to be clean after CMP. In addition, the alkaline slurries has higher selectivity on removal rates than acidic slurries. The slurries have lower corrosivity to CMP equipment and it is more environmental-friendly.