In-situ measurement of Cu film thickness during the CMP process by using eddy current method alone

摘要

A fast, accurate and in situ method for determination of interconnect Cu film thickness in the range from 200 to 500 nm is a crucial requirement in the stress free polishing (SFP) process which is a novel semiconductor manufacture technique. This paper presents an in situ Cu film thickness measurement system with an optimized eddy current transducer for this purpose. The fabricated transducer has been integrated into a chemical mechanical polishing (CMP) platform for the purpose of testing. Measurement tests for both the Cu film with uniform thickness and the Cu film with interconnects are conducted. The CMP experiment results show that the resolution of the transducer can achieve a few nanometers under 3 mm lift-off distance. With the increase in the density of the underlying Cu interconnects, the measured thickness value of the overlaid Cu film is also increased. By using an on-line differential signal processing method, the drift of the measurement system is removed. The repeatability and instability errors are less than 1.6%. The system can meet the technical requirements for advanced CMP processes.