XiaoCong Yuan

Synthesis of multiple collinear helical modes generated by a phase-only element

Phase-only elements are generally more desirable than complex-amplitude-modulated elements not only because of the higher diffraction efficiency but the readier implementation and fabrication. A novel iterative algorithm is proposed for generating multiple helical modes by a single phase-only element. A superposition of four helical modes is demonstrated experimentally by using a spatial light modulator.

X-ray holography for VLSI using synthetic bilevel holograms

The gains are pointed out of the potential replacement of the usual patterned transmission x-ray mask, in consideration of high-resolution proximity lithography for VLSI, by a diffraction element, or bilevel in-line hologram, to be projected under near-field conditions using synchrotron radiation. The hologram can be configured to correct for diffraction blurring due to projection, and be designed for pre-determined gaps between mask and wafer. The adjustment of experimental parameters can account for the waveguide effects that arise from mask elements with small features which are several hundred x-ray wavelengths thick.It is shown that the hologram, for projection printing at the 50nm feature size, at mask to wafer gaps of 10micrometers or greater, can be fabricated in a similar fashion to a high-resolution mask. The calculation of the hologram is computationally intensive, but a database of calculated features is envisaged.

Polarization dependence of the electromagnetic field distribution across wavelength-sized relief grating surfaces

The complex values of the surface electromagnetic fields of relief gratings for both TE and TM polarization are rigorously evaluated with use of the boundary-matching technique. The amplitude and phase of the surface field can be significantly modified by the edges and walls. The degree of modulation is strongly dependent on various factors, including the incident polarization. As the incident angle varies, the behavior of the surface-field amplitude is considered to be connected to the Brewster-angle effect. The complex refractive index of the grating material also influences the shape of the surface field but not in a proportional way. The oscillating surface fields with depth for both TE and TM polarization are explained as being due to secondary backward diffraction. In particular, as the edge and wall effects influence the TE and TM components differently, the oscillation peaks occur at different positions when TE and TM curves are compared.

Analysis of surface electromagnetic fields of wavelength-sized surface relief gratings

Abstract The complex values of the electromagnetic fields along surface relief gratings for TE polarization are rigorously evaluated. The amplitude and phase of the surface field show the dependence upon various factors including the incident angle, complex refractive index of the material and the depth of the slots. The results are analyzed and given physical explanations. It is found that for wavelength-sized slots the edges and walls have significant effects on the surface electromagnetic field distributions.

Analysis of Far-field Diffraction Characteristics of Wavelength-sized Surface Relief Gratings

The rigorous boundary matching technique was used to analyse the far-field diffraction from wavelength-sized surface relief gratings for TE polarization. Diffraction characteristics of such surface relief gratings were studied as functions of complex refractive index, groove depth and the angle of incidence. The surface field at the bottom of the grooves is more severely influenced by the edges and walls for metallic material than dielectric ones. The reflectivities of gold gratings show significant fluctuation for different incident wavelengths. This can be clearly seen from the fact that the zeroth-order diffraction efficiency DE 0 of gold is lower than that of aluminium at u = 0·4 wm but higher at u = 1·0 wm. It is also shown that the depth of the grooves has significant influences on the diffraction efficiencies, an optimum depth can be chosen to minimize the specular component. However, this optimum depth value is found to be different for the gratings of different materials, e.g. aluminium and gold,...

Diffractive properties of surface-relief microstructures

By analyzing the complex values of the electromagnetic fields along surface relief gratings for TE polarization, the diffractive properties of surface relief micro-structures are discussed. The edges and walls of the grooves are found to have significant effects on the surface fields for wavelength-size grooves. The dependence of these effects upon several factors, including the complex refractive index of the material, incident angle and the depth of the grooves, is examined. An oscillating property of the surface field amplitude at the bottom of the grooves against the depth is discovered and discussed. The far field intensity is also found to be closely related to the depth of the grooves.

Mixed-proximity holographic mask technology for 50-nm VLSI by x-ray lithography

The development of mixed proximity and binary phase holographic x-ray masks for feature sizes of 50nm is continued for mask to wafer gaps of 50micrometers for printing into photoresist with 1nm x-rays. The maximum gap for binary holographic correction for image blurring on reconstruction is shown to be limited by the symmetry impressed by the binary phase encoding. The computation of the holograms is described. A hologram is calculated in patches limited in size by computational restrictions and procedures are described for superposition at the wafer of structures reconstructed from adjacent patches. The fabrication of binary masks is well suited to electron beam writing.

Soft x-ray imaging and vector diffraction theory

A comprehensive computational analysis of soft x-ray imaging has been undertaken for both thin transmitting objects and lossy dielectric, potentially binary, objects and some representative results are given here. Both near-field and far-field computations are considered. The theoretical treatment derives from Maxwells vector electromagnetic equations rather than scalar diffraction theory. A range of computational approaches is used in the computations ranging from the integral method, to the coupled wave method, and the finite element methods. The relationships between these methods are considered. The results bear upon a range of imaging protocols from contact x-ray images and images taken with high resolution zone plate optics with feature dimensions of a few wavelengths to x-ray masks with sub-micron feature sizes interpreted as lossy waveguides several hundreds of x-ray wavelengths thick. Consideration is also given to the use of vector theory in the investigation of the focal plan intensity profile of a circular Fresnel zone plate when the widths of the outermost zones approach wavelength dimensions.