The Research Of Self-imaging Effect In Lithography

Periodic micro/nano-structures typified by diffraction gratings and the two-dimensional circles or rectangular arrays have always been an attractive research of interest due to their wide applications in various fields.Currently,as an important approach,optical lithography has been widely applied into the fabrication of periodic micro/nano-structures with large-scale and high-precision.Consequently the so-called “self-images” of periodic micro/nano-structures is a key factor that cannot be ignored during the manufacturing by optical lithography.As a classical physical phenomenon of periodic micro/nano-structures,the images of the structure itself and the images of intensity reverse reappear at certain intervals,i.e.self-images and phase-shift images.Hence this effect is typified by non-lens imaging.The recent researches that combine the self-image effect with optical lithography are mainly focusing on the process of capture the self-images and phase-shifted-images with high-resolution on the photoresist-coated substrates.These researched can be summarized as the fixed-position self-image lithography which is derived from proximity lithography.However the short depth-of-focus(DOF)area has blocked the development of the fixed-position self-image lithography.To overcome this problem,the Paul Scherrer Institute(PSI)of Switzerland has promoted a new method called spatial scanning lithography process.However this method is still faced problems of complicated mechanical system and exposure control.In conclusion these researches just pay attention to adopt the self-image effect into high-resolution lithography.The negative factors caused by self-images effect are ignored in the preceding work.Accordingly this thesis discussed the self-image effect in proximity lithography and projection lithography from the aspects of benefit and negative respectively.1.Frist,the thesis studied the DOF problem in the fixed-position self-image lithography.We analytically derived one governing equation for DOF prediction by incorporating the contributions from all diffraction orders,followed by numeric elucidations and a direct lithographic process.Then we fabricated the large-scale freestanding micromeshes on polyimide precursor for further terahertz metal mesh process.2.We introduce the spectrum-integral chromatic self-image effect in ultraviolet(UV)regime into conventional photolithography for sake of DOF extension and thus resolution enhancement as well as the trade-off between the resolution and complexity.The route of spectrum-integral self-image lithography is therefore constructed on basis of conventional proximity lithography and experimentally confirmed free from any moving mechanism using the broad-band incoherent UV illumination.Such spectrum-integral method is highly promising for micro/nanofabrication of periodic patterns with good trade-off among overall size of the patterning area,resolution(down to sub-micron level)and the cost efficiency by directly using the conventional UV lithography,especially in scenarios where low-cost,relatively high resolution and large area patterning is imperative.3.We researched the unwanted phenomenon of frequency-doubling caused by the near-field Talbot effect can still duplicate in the far field,i.e.on the other(wafer)side of the objective during projection lithography.Such far-field behavior of quasi-Talbot propagation at the image side of objective has rarely been touched before.In this case,the self-images and phase-shifted images caused by self-images effect on the mask side of objective are both captured by the objective lens,and transferred onto the photoresist-coated wafer concurrently due to the substantially extended DOF,provided that the feature size is tallied with optical resolution of the objective lens.We explored the anomaly of frequency doubling in an analytical and experimental way.The numerical analysis and simulation results show that both the self-images and ?-phase-shifted images of the one dimensional(1-D)or two dimensional(2-D)features can be recorded to induce the unexpected periodicity doubling.Finally,the proof-of-concept experiments using masks with 1-D and 2-D features are performed to reconfirm the analytical and numerical conclusions.4.Combining the second harmonic nonlinear self-image effect with spatial scanning lithography process,a route for the fabrication of periodic micro/nano-structure with high-precision is promoted in this thesis.The wavelength of the second harmonic wave is a half of the incident one.Hence the resolution of the second harmonic nonlinear self-image shrinks half size of the linear self-image.Meanwhile with the aid of spatial scanning lithography process,both self-image and ?-phase-shifted image could be recorded on the photoresist and realize the frequency-doubling.