Research On Measuring Groove Profile Parameters Of Subwavelength Grating Based On Transmission Spectrum Retrieval Method

The retrieval method with scatterometry is seen as a key technology for measuring the grating groove profile parameters of subwavelength gratings, which is based on the measurement of diffraction features of gratings. The non-contact, scatheless and rapid features of the retrieval method make it prefer to be used in all kinds of online and real time applications. Measurement of transmission spectrum is easy to carry out. The measuring system is simple. The result of measurement is stable and precise. These make it become more outstanding in several retrieval methods with scatterometry. As a kind of fast, accurate algorithm and easy to achieve with computer, the Rigorous Coupled Wave Method (RCWA) is widely used in the scatterometry analysis of gratings. In this paper, it is proved that the direct search algorithm is more suitable for obtaining groove profile parameters of subwavelength grating. The gold-coated grating with high efficiency and broadband spectrum is the core component of chirped pulse amplification system for pulse compression. The aim of our research is to measuring groove profile parameters of photoresist grating which is used for the mask of gold-coated grating and to improve the performance of the gold-coated grating.The main contents of the paper include:Write computer program for calculating the diffraction efficiency of grating based on the RCWA; Analysis the transmission spectrum under different incident conditions; Build the library of the transmission spectrum with different grating groove profile parameters under two groove models(i.e. the quadratic function groove model and SEM extraction model) based on the RCWA.A new evaluation function is put forward in the direct search algorithm. It is proved that this new evaluation function has stronger anti-interference ability and the retrieval result is more accurate.The experimental system for measuring the zeroth-order transmission spectrum and the retrieval program are built. The zeroth-order transmission spectrums within 500nm-700nm of a series of photoresist gratings with period of 574.7nm are measured at TE polarization and then obtain their groove profile parameters from the retrieval program. The retrieval results are compared with the AFM and SEM measurement results. The maxium errors under the quadratic function groove model and SEM extraction model are 17.3nm,0.102 and 10.4nm,0.072 correspondingly. Experiment results show that measuring the grating groove profile parameters based on transmission spectrum retrieval method is feasible.