Three-dimensional Topography And Its Super-resolution Measurement Of Micro/Nano Structures Based On White-light Microscopy Interferometry

With the rapid development of information era and super-precision fabrication technology,micro/nano technology,which is a mark of high technology,has already become one of the most important modern scientific directions.Micro/nano devices have significant influences on the applications of varieties of domains,including extreme fabrication,biomedicine,aerospace and quantum communication.The developing level of micro/nano technology has absolutely become an indicator to judge the technology ab ility all over the nations.As is one of the methods for fabrication,measurement is also a basement to confirm the fabricating accuracy.A satisfying measurement method is a must for higher precision fabrication.Recently,in order to store more data thro ugh micro/nano devices,the structures of them have been revolutionized for higher precision.The requirements of the measurement have been changed from micrometer to nanometer and from two dimensions to three dimensions.The existing methods for 3-dimensional reconstructions of micro/nano structures can be classified into two varieties,which contain optical and non-optical ways.Usually,although the non-optical methods have high precision,it will be easy to hurt the samples and the speed of measurement is quite low.O n the other hand,optical methods have the advantages of non-contact,high resolution and high speed.Among the optical methods,white-light interferometry method uses the low-coherence light to achieve the 3D topography measurement with the advantages of high accuracy,large measurement range and non-contact.White-light interferometry method is deemed as a very potential technology for super-precision devices,obtaining numerous foci through researchers all around the world.White-light interferometry technology has been developed rapidly,nonetheless there are still some challenges waiting to be overcome.For example,(1)The measurement stability and accuracy are negatively influenced by light fluctuations,external disturbances and system vibrations;(2)The measurement precision is limited to the scanning resolution and the measurement range is short enough due to the limited distance of piezoelectric ceramics devices,so the applications are limited in some extent;(3)Although the vertical resolution is improved,the lateral resolution is still larger than 200 nm due to the optics diffraction limit.The lateral resolution is no longer satisfactory for the discerning of micro/nano world,hence how to break though the diffraction limit and how to level up the imaging resolution have become the key problems.In this paper,we first analyze the theories of broadband light interferometry and the corresponding 3D reconstruction algorithms.We propose a spatial modulation-based method to connect the information between the pixels in one interferogram.The method can effectively improve the system stability and measurement precision.Then we propose a phase stitching technology,which utilizes the threshold of spatial modulation to judge the effectiveness of the sample points and calculates the phase distribution though stitching process along scanning direction.In the system,the piezoelectric ceramics device is replaced by step electric motor,the interferograms can be simultaneously captured though camera with external triggering mode.The experimental results can verify that the phase stitching method can eliminate the scanning errors and improve the measuring efficiency.Next,in order to improve the lateral resolution,we utilize a dielectric microsphere-assisted system to achieve super-resolution imaging in white-light illumination.We analyze how some parameters have influences on super-resolution imaging qualities,such as the sizes and reflective indices of microspheres,illuminating modes,and immersion methods.Then we experimentally verify that the imaging quality can be significantly improved though dark-field illumination and partly immersing.Lastly,we can experimentally achieve 3D super-resolution topography reconstruction through combing white-light interferometry and microsphere-assisted system.The paper mainly points out some challenges and problems in white-light interferometry method,and then proposes corresponding technologies to solve the problems.The proposed techno logies,which aim at improving the system stability,measurement efficiency,measurement precision and lateral resolution,can provide novel ways and basements for the further applications in 3D topography measurement.