Zhijie Liao

Photon sieve array X-ray maskless nanolithography

We present the lithography scheme that use high-numerical-aperture photon sieves array as focusing elements in a scanning X-ray maskless nanolithography system. The system operating at wavelength of 0.5~2nm synchrotron light sources radiated, each of a large array of photon sieves focuses incident X-ray into a diffraction-limited on-axis nanoscale spot on the substrate coated photoresist. The X-ray intensity of each spot is modulated by means of a spatial light modulator. Patterns of arbitrary geometry are exposed and written in a dot matrix fashion while the substrate on a stepping stage is precisely driven in two dimensions according to the computer program. The characteristics of synchrotron radiation light, resolution limits and depth of focus of the lithographic system are discussed. The design and fabrication of photon sieve are illustrated with a low-numerical-aperture amplitude-photon sieve fabricated on a chrome-coated quarts plate by means of laser-beam lithographic process, which minimum size of pinhole was 5.6um. The focusing performance of the photon sieve operating at wavelength of 632.8nm was simulated and tested.

Resolution enhancement of photon sieve based on apodization

Photon sieve is a novel diffractive optical element modulating either amplitude or phase which consists of a great number of pinholes distributed appropriately over the Fresnel zones for the focusing and imaging of light. Photon sieve has the advantages of the diameter of pinholes beyond the limitation of the corresponding Fresnel zone width and the minimum background in the focal plane. Furthermore, photon sieve can be fabricated on a single surface without any supporting struts required unlike the Fresnel zone plate. Photon sieve can be used as EUV telescope for solar orbiter, space-based surveillance telescope operating at visible light, or other imaging components. Photon sieve can also be used as one of the promising lithographic tools for nanoscale science and engineering to obtain the lower cost, higher flexibility and better resolution. The approaches to enhancing imaging resolution of photon sieve are presented in detail. According to Fresnel-Kirchhoff diffraction theory, the diffractive field of photon sieve is described by means of the discrete fast Fourier transform algorithm. The related contents include the calculation of point spread function, the suppression of side lobes, the imaging bandwidth, the physical limit of resolution, and the diffraction efficiency. Imaging properties of photon sieve are analyzed on the basis of precise test.

Speckle reduction in laser projection display by modulating illumination light

The use of lasers in a projection display enables the creation of vibrant images with extensive color coverage. By adding a phase modulators in illumination systems and keeping the most part structures of the classic projection, speckle on the screen and retinas of the observers were restrained. The speckles form and restraining were simulated. It was obtained form simulations that the contrasts of residual speckle on screen and on retinas are 0.0107 and 0.0132. The simulation proves that speckle on screen and on retinas can be suppressed by phase modulation of the illumination light in projection. It also indicated that the numerical aperture of projector affect the residual speckle on retinas. Experiments of speckle restraining were performed. It confirmed the results of the simulations.

Wavefront testing of pinhole based on point diffraction interferometer

To overcome the accuracy limitation due to the aberration of reference wavefront in the interferometer testing, the point diffraction interferometer (PDI) uses the pinhole to create an ideal diffraction sphere wavefront as the reference wavefront. Because the perfect pinhole is hard to manufacture, then the imperfect pinhole will cause the wavefront errors which will influence the test accuracy. In this paper we use the absolute testing method to test the wave front of the pinhole. Then the testing accuracy of point diffraction interferometer can be improved by subtracting the error of the pinhole. In this paper a Phase-shifting point diffraction interferometer system is designed to testing the pinhole. We use three pinholes to test each other. According the algorithm of the absolute testing method, we can calculate the wavefront error of the pinhole. Then the testing accuracy of point diffraction interferometer can be improved by subtracting the error of the pinhole.

Error analysis of absolute testing based on even-odd functions method

Recently most of modern absolute measurement rotation the flats or spheres in the interferometer. We review traditional absolute testing of flats methods and emphasize the method of even and odd functions. The rotation of the lens can lead to some errors such as angle rotation error, center excursion error and other coordinate system motion error. We analyze the errors by using Zernike polynomial. The flat or sphere can be expressed as Zernike polynomial which can also be divided into even-odd, odd-even, even-even and odd-odd functions. We can use 36 Zernike polynomials to generate 3 plats A, B, C. Then the six measurements can be generated from the three plats. For the angle rotation error, we can simulate the angle error distribution and substitute in the systems. According the error distribution we can change the arithmetic to improve the measurement accuracy. The results of errors analyzed by means of Matlab are shown that we can change the arithmetic according the coordinate direction motion errors which can be detected to improve the accuracy. The analysis results can also be used in other interferometer systems which have the motion of the coordinate system.

Experiment analysis of absolute flatness testing

Result of the testing contain the reference surface errors and test surface errors in the high-accuracy Phase shifting interferometer which test the relative phase between the two surface. The test accuracy can be achieved by removing the error of reference surface. In this case, one of body of so-called absolute testing must be used which can test the systematic errors, including the reference surface, of the instrument to be used to improve the test accuracy. The accuracy of the interferometer needs different methods to determine in the high accuracy testing. Even-Odd function method and rotation shear method is introduced in this paper. We use the Zygo interferometer Verifire Asphere to do the experiment and analyze the errors caused by data processing and interpolation. The result of the experiment can determine the accuracy of our arithmetic.