Focusing Properties Of Transparent Microsphere And The Study Of Microsphere Array Photolithography

As the further development of integrated circuits and integrated optical,lithography technology, especially low-cost, simple and efficient nanoscale lithography is more important. As the existence of optical diffraction limit, it hinders the development of high-resolution lithography to a large extent. Early years developed electron beam lithography and focused ion beam lithography can achieve a resolution of tens of nanometers, but the efficiency is low and the cost is high. They are not suggested for industrial production. UV laser double / multiple-beam interference lithography is limited by the optical diffraction limit, while deep ultraviolet laser equipments are expensive. In addition, type of the resulting patterns by laser interference lithography is limited. These all make laser interference lithography method in high resolution lithography is not dominant. The resolution of near-field scanning probe lithography is also easy to sub-100 nm lithography resolution, but the way of point by point scanning makes it inefficient. Recent studies show that microspheres with diameter close to wavelength of light have the ability to super-resolution lens focusing. It may converge most of the incident energy, and form a beam waist with sub-half the wavelength width near the back side of the microsphere. The depth of focus can be close to 2λ. One can utilizes the high-energy, ultra-long focal spot forming by a microsphere lens to ablate the surface of material, or expose the photoresist for high resolution lithography.Microspheres assisted lithography has developed into one of the hot areas. This paper suggests an improved microsphere assisted lithography model, that is, adding a tunable transparent spacer layer between the microspheres lens array and photoresist to study the microspheres lithography resolution. The main contents and results of this paper are as follows:First, the microspheres assisted lithography model is studied by computer software,CST Microwave Studio. The results show that the microspheres of 2.06μm diameter illuminated by a linearly polarized light with wavelength of 400 nm, when the gap thickness is fixed, the light intensity and shape of spot at the surface of photoresist varies. Gap value affects the light distribution and effective focal spot size. The effective focal spot size of the data obtained showed: with gap value increases from10 nm to 90 nm gradually, microspheres lithography resolution first declines then increases. The dose of the incident light is reduced within a range such that the overall resolution of photolithography is improved. Comprehensive gap value and the incident dose of lithography resolution affect the trend to give optimum value of a gap: 70 nm.Second, an improved microspheres assisted lithography experiments are carried out to verify the theoretical simulation results. Pore size obtained experimentally(FWHM) close to the theoretical data, the same trend. And the gap is further reduced when the incident 70 nm dose was less than 100 nm feature holes.Finally, when a smaller microsphere(1.25μm in diameter) is chosen, a focal spot with effective focal spot size of 35 nm and effective focus depth of 60 nm is obtained by numerical calculation.