Microelectronics & Solid-state Electronics

Photolithography has been a key technique in semiconductor nano-facture and micro-fabrication for several decades, with the development of Super Large Scale Integration (SLSI) and integrated optics; high resolution photolithography has become more and more important. However the traditional photolithography is limited by the illuminating wavelength due to the optical diffraction limit. Many nano-scale lithography techniques like the electron beam lithography and deep ultraviolet (UV) lithography have been applied to achieve high resolution, but these techniques require quite expensive equipment and cannot meet the industrial mass fabrication needs. The recent discovery of extraordinary transmission through perforated metal films shows that the surface plasmon polaritons (SPPs) on the metal surface can greatly enhance the light transmission and redistribute the electromagnetic field in nanometer scale. These give us a novel method of photolithography beyond the diffraction limit.In this paper first from the principle of Kretschmann prism, the mechanism is discussed to excite surface plasmon polaritons in dielectric-metal-dielectric three layers system. And then the experimental technique to enhance transmission is analyzed from four perspectives of incident light frequency, dielectric constant of photoresist, depth of Ag film, angle of incident light.Finite Difference Time Doman (FDTD) method is employed to simulate the electromagnetic field distribution in the process of lithography based on surface plasmon polaritons. The numerical simulation indicates that this SPPs method can achieve the feature size of 32nm. In this paper first it is simulated by FDTD method that the electromagnetic field of a one-dimension periodical gratings with triangular ridges and planar grooves covered by a silver membrane. And then the analysis of transmission and resolution is given as the base-angle of ridges changes. When the base-angle varies from 57 to 64 degree, the enhanced transmission is found at the area under the ridges and the maximum of amplitude reaches 4.2 times compared with the incident light. The resolution size changes within 30±5nm. At the same time the transmission from grooves of the mask is quite little. Therefore a good contrast is achieved. The comparison between the non-periodical and periodical boundary conditions suggests that the enhanced transmission is the result of the shape of ridges instead of the periodical conditions At last the experiment result is discussed. The pattern of 1500nm periodical gratings is perfectly transferred on the photoresist and the resolution is 500nm.