Research On Alignment Method Based On Spectral Analysis Of Wide-spectrum Self-reference Interference

With the development of information society,integrated circuits have been more and more widely used.Lithography machine is the core device of manufacturing integrated circuit.Whether the performance of lithography machine can be improved determines whether the integrated circuit can develop towards the next node.Because the integrated circuit is a layered three-dimensional structure,the alignment accuracy between the mask and the silicon wafer is very critical,and the importance of lithography alignment technology is reflected.In order to deploy the development of advanced lithography machine,the research of high-precision alignment method is of great significance.Among many lithography alignment methods,the SMASH alignment method applied by ASML in the advanced extreme ultraviolet lithography machine has important reference value for the research of lithography alignment system.The essence of SMASH alignment method is an alignment method based on selfreference interference.This alignment method can achieve high alignment accuracy.However,it has high requirements for the stability of light source and the response frequency of detector.In this thesis,the principle of self-reference interference alignment method is analyzed,and the self-reference interference alignment theory is verified by simulation and experiment.Then,combined with the white-light spectral interference theory,an alignment method based on spectral analysis of wide-spectrum self-reference interference is proposed.In this method,a wide-spectrum light source is used to replace the coherent light source,a spectrometer is used to receive the white-light spectral interference signal,and the alignment information is obtained by dephasing the spectral signal.In addition,this paper also proposes a method of white-light spectrum interference phase extraction using S-transform.Compared with the methods of whitelight spectrum interference phase extraction using Fourier transform and wavelet transform,this method shows better performance in simulation and distance measurement experiments.Finally,according to the principle of the proposed alignment method,an experimental system is built to collect the spectral signal,and the phase of the spectrum is extracted by S-transform.The experimental results show that the contrast accuracy of alignment system is better than 18.8 nm,the standard deviation of repeated measurement is better than 1.46 nm within the 50 μm displacement range of linear piezo positioning table.